Fluid fractionation of tungsten during granite-pegmatite differentiation and the metal source of peribatholitic W quartz veins: Evidence from the Karagwe-Ankole Belt (Rwanda)

NASA Astrophysics Data System (ADS)

Hulsbosch, Niels; Boiron, Marie-Christine; Dewaele, Stijn; Muchez, Philippe

2016-02-01

The identification of a magmatic source for granite-associated rare metal (W, Nb, Ta and Sn) mineralisation in metasediment-hosted quartz veins is often obscured by intense fluid-rock interactions which metamorphically overprinted most source signatures in the vein system. In order to address this recurrent metal sourcing problem, we have studied the metasediment-hosted tungsten-bearing quartz veins of the Nyakabingo deposit of the Karagwe-Ankole belt in Central Rwanda. The vein system (992 ± 2 Ma) is spatiotemporal related to the well-characterised B-rich, F-poor G4 leucogranite-pegmatite suite (986 ± 10 Ma to 975 ± 8 Ma) of the Gatumba-Gitarama area which culminated in Nb-Ta-Sn mineralisation. Muscovite in the Nyakabingo veins is significantly enriched in granitophile elements (Rb, Cs, W and Sn) and show alkali metal signatures equivalent to muscovite of less-differentiated pegmatite zones of the Gatumba-Gitarama area. Pegmatitic muscovite records a decrease in W content with increasing differentiation proxies (Rb and Cs), in contrast to the continuous enrichment of other high field strength elements (Nb and Ta) and Sn. This is an indication of a selective redistribution for W by fluid exsolution and fluid fractionation. Primary fluid inclusions in tourmaline of these less-differentiated pegmatites demonstrate the presence of medium to low saline, H2O-NaCl-KCl-MgCl2-complex salt (e.g. Rb, Cs) fluids which started to exsolve at the G4 granite-pegmatite transition stage. Laser ablation inductively coupled plasma mass-spectrometry shows significant tungsten enrichment in these fluid phases (∼5-500 ppm). Fractional crystallisation has been identified previously as the driving mechanism for the transition from G4 granites, less-differentiated biotite, biotite-muscovite towards muscovite pegmatites and eventually columbite-tantalite mineralised pegmatites. The general absence of tungsten mineralisation in this magmatic suite, including the most differentiated columbite-tantalite mineralised pegmatites of the Gatumba-Gitarama area, emphasises the efficiency of fluid saturation to extract crystal-melt incompatible tungsten from the differentiating melt phase. Fluid-melt-crystal partitioning calculations support the concept of a magmatic-hydrothermal fluid source for tungsten and constrain the range of permissible crystal-melt and fluid-melt partition coefficients together with realistic values for water solubility in the parental G4 granitic melt. Consequently, we propose that for highly-differentiated B-rich, F-poor granite systems fluid saturation started prior to or at the granite-pegmatite transition stage resulting in apical to peribatholitic tungsten veins systems that are paragenetically older than the final pegmatite stage.

Origin of pegmatites and fluids at Ponta Negra (RJ, Brazil) during late- to post-collisional stages of the Gondwana Assembly

NASA Astrophysics Data System (ADS)

Bongiolo, Everton Marques; Renac, Christophe; Piza, Patricia d'Almeida de Toledo; Schmitt, Renata da Silva; Mexias, André Sampaio

2016-01-01

The Ponta Negra Pegmatites (PNP), part of a pegmatitic province in Rio de Janeiro State, Brazil, crop out along an intensely deformed, medium- to high-grade metamorphic area that is proximal to a crustal-scale thrust zone developed during the Brasiliano/Pan-African Orogeny. Fieldwork shows that the pegmatites formed in two distinct stages: (i) syn-collisional leucosome veins (Group I) conformable with the tectonic foliation of the gneissic host rocks and (ii) late- to post-collisional dykes (Group II) that cross-cut the same tectonic foliation at a high angle. In this paper, we use geochemistry of whole-rock and mineral separates (alkali-feldspar and biotite), fluid inclusion microthermometry and stable isotopic (δ18O, δD, δ13C) determinations on minerals (quartz, alkali-feldspar, biotite and magnetite) and fluid inclusions to provide insights into the composition of the pegmatite-forming melts, associated fluids, and their geotectonic significance. U-Pb SHRIMP dating of the Cajú syenogranite was performed to evaluate and compare the timing of magmatic events along the Cabo Frio Tectonic Domain as this is the closest post-collisional pluton to the studied pegmatites. The calculated temperature for the Group I syn-collisional veins (740 °C) is similar to previous estimates for the peak metamorphic conditions in the study area. Variations in the temperature of the Group II pegmatite dykes obtained from stable isotopes (380 to 720 °C), and microthermometric data from primary fluid inclusions with traces of N2 (Th = 280 to 360 °C), may reflect the thermodynamics of the pegmatite crystallization, exsolution textures and isotopic exchange. The composition of fluids in equilibrium within the pegmatite dykes consists of magmatic and metamorphic components. The minimum pressures calculated for the emplacement of the pegmatites are equivalent to a shallow crustal depth between 1.7 and 3.5 km, which corresponds to the exhumation of the orogen since the emplacement of the pegmatites. A linear trend of decreasing CO2 content and δ13CCO2 is consistent with mixtures between (i) carbon derived from organic matter or volatilization of skarns and (ii) inorganic carbon (carbonate). Based on the data obtained, we propose that the pegmatites of Ponta Negra are close to an LCT-type geochemical signature (highly peraluminous magmas with normative corundum), and originated by partial melting of the metasedimentary Palmital succession at depth, during the waning stages of the Búzios Orogeny. The primary melts of the PNP cross-cut both the Neoproterozoic supracrustals and the Paleoproterozoic orthogneissic basement during its ascent and emplacement at higher crustal levels. Variable melt sources explain the slight differences in geochemical compositions among the studied rocks within the metasedimentary succession, which probably include Mn-bearing exhalites, as well as differentiation processes. The 454 ± 5 Ma U-Pb (zircon) age of the Cajú syenogranite overlaps previous geochronological data of 440 ± 11 Ma obtained on a pegmatite dyke at Ponta Negra, bracketing and extending the time interval for the Gondwana assembly collapse magmatism in the region. The heat that triggered this magmatic event could still be a consequence of the collisional orogeny, increasing contents of heat-producing elements, or, a large intraplate extension that followed the Gondwana amalgamation and initiated the formation of Paleozoic basins.

Emerald mineralization and metasomatism of amphibolite, khaltaro granitic pegmatite - Hydrothermal vein system, Haramosh Mountains, Northern Pakistan

USGS Publications Warehouse

Laurs, B.M.; Dilles, J.H.; Snee, L.W.

1996-01-01

Emerald mineralization is found within 0.1- to 1-m-thick hydrothermal veins and granitic pegmatites cutting amphibolite within the Nanga Parbat - Haramosh massif, in northern Pakistan. The amphibolite forms a sill-like body within garnet-mica schist, and both are part of a regional layered gneiss unit of Proterozoic (?) age. The 40Ar/39Ar data for muscovite from a pegmatite yield a plateau age of 9.13 ?? 0.04 Ma. Muscovite from mica schist and hornblende from amphibolite yield disturbed spectra with interpreted ages of 9 to 10 Ma and more than 225 Ma, respectively, which indicate that peak Tertiary metamorphism reached 325 to 550??C prior to 10 Ma. Pegmatites were emplaced after peak metamorphism during this interval and are older than pegmatites farther south in the massif. At Khaltaro, simply zoned albite-rich miarolitic pegmatites and hydrothermal veins containing various proportions of quartz, albite, tourmaline, muscovite, and beryl are associated with a 1- to 3-m-thick heterogeneous leucogranite sill, that is locally albitized. The pegmatites likely crystallized at 650 to 600??C at pressures of less than 2 kbar. Crystals of emerald form within thin (0.20, 0.54-0.89 wt%), to pale blue beryl (<0.07, 0.10-0.63%), to colorless beryl (<0.07, 0.07-0.28%). The amphibolite is metasomatized in less than 20-cm-wide selvages that are symmetrically zoned around veins or pegmatites. A sporadic inner zone containing F-rich biotite, tourmaline, and fluorite, with local albite, muscovite, quartz, and rare beryl, gives way to an intermediate zone containing biotite and fluorite with local plagioclase and quartz, and to an outer zone of amphibolite containing sparse biotite and local quartz. The inner and intermediate zones experienced gains of K, H, F, B, Li, Rb, Cs, Be, Ta, Nb, As, Y and Sr, and losses of Si, Mg, Ca, Fe, Cr, V and Sc. The outer alteration zone has gained F, Li, Rb, Cs, and As. Oxygen isotope analyses of igneous and hydrothermal minerals indicate that a single fluid of magmatic origin with ??18OH2O = 8??? produced the pegmatite-vein system and hydrothermal alteration at temperatures between 550 and 400??C. The formation of emerald results from introduction of HF-rich magmatic-hydrothermal fluids into the amphibolite, which caused hydrogen ion metasomatism and released Cr and Fe into the pegmatite-vein system.

Isotope age of the rare metal pegmatite formation in the Kolmozero-Voron'ya greenstone belt (Kola region of the Fennoscandian shield): U-Pb (TIMS) microlite and tourmaline dating

NASA Astrophysics Data System (ADS)

Kudryashov, Nikolay; Lyalina, Ludmila; Mokrushin, Artem; Zozulya, Dmitry; Groshev, Nikolay; Steshenko, Ekaterina; Kunakkuzin, Evgeniy

2016-04-01

The Kolmozero-Voron'ya greenstone belt is located in the central suture zone, which separates the Murmansk block from the Central-Kola and the Keivy blocks. The belt is represented by volcano-sedimentary rocks of Archaean age of 2.9-2.5 Ga. Rare metal pegmatites (Li, Cs with accessory Nb, Ta, and Be) occur among amphibolite and gabbroid intrusions in the northwestern and southeastern parts of the belt. According to the Rb-Sr data, the age of pegmatites was considered to be 2.7 Ga. Until recently there was no generally accepted point of view on the origin of pegmatites. Now we have isotopic data for a range of rock complexes that could pretend to be parental granites for the rare metal pegmatites. These are granodiorites with the zircon age of 2733±Ma, and microcline and tourmaline granites, which Pb-Pb isochronal age on tourmaline from the tourmaline granite located near the deposit is estimated to be 2520±70 Ma. The pegmatite field of the Vasin Myl'k deposit with the lepidolite--albite--microcline--spodumene--pollucite association is located among amphibolites in the northwestern part of the belt. The deposit is represented by subparallel low-angle zoned veins up to 220 m long and 5 m thick dipping in the southeastern direction at an angle of 10° too 30°. The minerals of the columbite--tonalite group from Vasin Myl'k deposit include microlite, simpsonite, and torolite, and are the oldest among different minerals represented by several generations in pegmatites under consideration. Zircons from the pegmatites are mostly represented by crystals with the structure affected by the action of fluids that put certain restrictions on its use as a geochronometer of the crystallization process. Microlite from the pegmatite taken from the dump of a prospecting drill hole was used for U--Pb (TIMS). The mineral is represented by 0.5--1.0 mm long euhedral octahedral crystals. It is brown in color, and transparent. The microlite crystals were preliminarily cleaned from surface contamination being placed the ultrasonic bath with the 7N HNO3 solution. The discordia constructed for seven measured microlite weights is characterized by upper intercepts with concordia at 2454±8 Ma, which probably reflects the time of rare metal pegmatite crystallization, coeval with the age of tourmaline granites. Taking into consideration the obtained U--Pb age of microlite, it may be assumed that the tourmaline granites dated back to 2520±70 Ma served as the most probable parental rocks for rare metal pegmatites of the Vasin-Myl'k deposit. The work is supported by RFBR No 16-05-00367, No 16-05-00427 and project No 0231-2015-0005

Characterization of fluid inclusions from mineralized pegmatites of the Damara Belt, Namibia: insight into late-stage fluid evolution and implications for mineralization

NASA Astrophysics Data System (ADS)

Ashworth, Luisa; Kinnaird, Judith Ann; Nex, Paul Andrew Martin; Erasmus, Rudolph Marthinus; Przybyłowicz, Wojciech Józef

2018-05-01

Mineralized NYF and LCT pegmatites occur throughout the northeast-trending Neoproterozoic Damara Belt, Namibia. Mineralization in the pegmatites varies geographically, from the northeast, where they are enriched in Li-Be, to the southwest, where they also contain notable Sn and U. Similar fluid inclusion populations occur throughout the pegmatites, regardless of their respective metal enrichments, and primary fluid inclusion textures were destroyed by continued fluid activity. Pseudosecondary to secondary inclusions are aqueo-carbonic, carbonic, and aqueous in composition, and have been divided into five types. The earliest populations are saline (>26.3 eq. wt.% NaCl), homogenizing at temperatures in excess of 300 °C. Their carbonic phase is composed of CO2, with minor CH4, and micro-elemental mapping indicates they contain trace metals, including Ca, Fe, Zn, Cu, and K. Type 3 inclusions formed later, homogenize at 325 °C, and are less saline, with a carbonic phase composed of CO2. Type 4 carbonic inclusions are composed of pure CO2, and represent the latest stages of fluid evolution, while Type 5 aqueous inclusions are believed to be unrelated to the crystallization of the pegmatites, and rather the result of regional Cretaceous magmatism, or the ingress of meteoric water. The similarities in fluid inclusion populations observed in the pegmatites suggest that differences in mineralization were driven by magma composition rather than fluid activity alone, however saline fluids facilitated the enrichment and deposition of metals during the late stages of crystallization. Furthermore, the similarities between fluid inclusion populations in different pegmatites suggests they share a similar fluid evolution.

Mineralogy and geochemical evolution of the Little Three pegmatite-aplite layered intrusive, Ramona, California.

USGS Publications Warehouse

Stern, L.A.; Brown, Gordon E.; Bird, D.K.; Jahns, R.H.; Foord, E.E.; Shigley, J.E.; Spaulding, L.B.

1986-01-01

Several layered pegmatite-aplite intrusives exposed at the Little Three mine, Ramona, display closely associated fine-grained to giant-textured mineral assemblages which are believed to have co-evolved from a hydrous aluminosilicate residual melt with an exsolved supercritical vapour phase. Calculations of phase relations between the major pegmatite-aplite mineral assemblages and supercritical aqueous fluid were made, assuming equilibrium and closed-system behaviour as a first-order model.-J.A.Z.

Relation between Fabric Anisotropy of Host-Rock vis-à-vis Far-Field Stress, and the Emplacement Of Pegmatite Dikes - an example from the Dharwar Craton (South India)

NASA Astrophysics Data System (ADS)

Bhatt, S.; Rana, V.; Mamtani, M. A.

2017-12-01

Dikes are known to control magma transport within the lithosphere. They (dikes) usually form by the fracturing of host rock and propagate orthogonal to the minimum principal stress direction and/or may follow the pre-existing anisotropy depending on the magnitude of fluid pressure and the tensile strength of the host rock. Pegmatite veins/dikes are often associated with hydraulic fracturing and high magmatic fluid pressure, which is attributed to volatile rich hydrous melt. The Koppal Pluton (KP) is a syenite body that lies to the East of the Chitradurga Shear Zone, which separates the Dharwar Craton into East and West Dharwar Craton. The KP is visually isotropic and profusely permeated by pegmatite dikes. Orientation data of the pegmatite dikes (n=357) were collected for geometric and paleostress analysis. The orientation of anisotropy with respect to the maximum principal stress and fluid pressure dictates whether a new fracture will form or a pre-existing anisotropy will be reactivated/dilated. To understand the relationship between the pre-existing anisotropy and orientation of pegmatite dikes, anisotropy of magnetic susceptibility (AMS) analysis was performed on the samples of KP. AMS analysis reveals NNE-SSW oriented magnetic fabric ascribed to regional D3 deformational event (NW-SE compression). Mean orientation of the magnetic fabric (NNE-SSW) is oblique to the mean orientation of the pegmatite dikes (NNW-SSE). It is envisaged that pegmatite dikes emplaced syntectonically as mode-I crack during regional D3 deformation event (pure shear dominated transpression) and developed oblique to the magnetic fabric of the pluton. The present study leads to a better understanding about the influence and interaction of principle stress, magmatic fluid pressure, and host-rock anisotropy on the ascent and emplacement of pegmatite dikes that intrude the visually isotropic KP. Acknowledgments: SB acknowledges INSPIRE Fellowship Programme (Award no: IF131138) of DST (New Delhi). VR and MAM thank Ministry of Earth Sciences (project no: MoES/P.O.(Geosci)/1/2013).

New data on the substantial composition of Kalba rare metal deposits

NASA Astrophysics Data System (ADS)

Oitseva, T. A.; Dyachkov, B. A.; Vladimirov, A. G.; Kuzmina, O. N.; Ageeva, O. V.

2017-12-01

Geotectonic position, features of the geological structure and rare metal specialization of the Kalba-Narym granitoid belt formed in the Hercynian cycle in the postcollision (orogenic) geodynamic situation are considered. A geological-genetic model for the formation of the leading type of rare-metal pegmatite deposits (Ta, Nb, Be, Li, etc.) is presented. They are spatially and genetically related mainly to the granitoids of the 1st phase of the Kalba complex, P1 (Bakennoye, Jubilee, Belaya Gora, etc.). The rhythmically pulsating orientation of the process of pegmatite formation with the introduction of ore-bearing fluids (H2O, F, B, Cl, Ta, Nb, Be, etc.) is emphasized from the intracamera focus of a semi-closed magmatic system. The preferred location of ore pegmatite veins in granitoids of moderate basicity occupying an intermediate position in the petrochemical composition between normal granites and granodiorites geochemically specialized in Li, Rb, Cs, Sn, Nb, Ta. The leading ore-controlling role of the latitudinal deep faults of the ancient site in the distribution of rare-metal ore fields and deposits (Ognevsk-Bakennoye, Asubulak, Belogorsk, etc.) is determined. There is a zonal structure of pegmatite veins, a gradual development of mineral complexes from the graphic and oligoclase-microcline (non-ore) to microcline-albite and color albite-spodumene (ore). The mineralization of pegmatite veins is determined by the degree of intensity of the manifestation in them of metasomatic processes (microclinization, alibitization, greisenization, spodumenization, tourmalinization, etc.) and the identification of the main ore minerals (tantalite-columbite, cassiterite, spodumene and beryl). The diversity of the material composition of rare-metal pegmatites containing many unique minerals (cleavelandite, lepidolite, ambligonite, color tourmaline, spodumene, pollucite, etc.) is reflected, which brings them closer to the pegmatite deposits of foreign countries (Koktogai, Bernik Lake, etc.). New results of the investigation of the material composition of ore-bearing granites, pegmatites and typomorphic minerals using electron microscopy reflecting the distribution of rare-earth, rare-metal, chalcophile and other elements in them are presented. Indicators of rare metal ore formation are rock-forming minerals of granites (quartz, microcline, biotite, muscovite), ore and associated minerals (cleavelandite, lepidolite, cassiterite, etc.). The most informative minerals include mica (muscovite, giltbertite, lepidolite), colored tourmalines and beryls of different composition and color. Identified typomorphic minerals and geochemical elements-indicators of rare metal pegmatite formation are considered as a leading search criterion in assessing the prospects of the territory of East Kazakhstan.

The mineralogy of Ba- and Zr-rich alkaline pegmatites from Gordon Butte, Crazy Mountains (Montana, USA): comparisons between potassic and sodic agpaitic pegmatites

NASA Astrophysics Data System (ADS)

Chakhmouradian, Anton; Mitchell, Roger

2002-01-01

At Gordon Butte (Crazy Mountains, Montana), agpaitic nepheline-syenite pegmatites intrude potassic alkaline rocks (principally, malignites and nepheline microsyenites). All pegmatite veins are composed predominantly of potassium feldspar, nepheline, prismatic aegirine, barytolamprophyllite, wadeite, eudialyte, loparite-(Ce) and altered rinkite ("vudyavrite") embedded in spherulitic and fibrous aegirine. Well-differentiated veins contain "pockets" filled with calcite, fluorapatite, mangan-neptunite, Mn-Ti-enriched prismatic aegirine, calcium catapleiite, and an unidentified Ca-Ti silicate. The potassium feldspar corresponds to Ba-rich sanidine with relatively low Na contents. The nepheline contains low levels of SiO2 and elevated Fe contents. The compositions of nepheline cluster in the lower portion of the Morozewicz-Buerger convergence field, indicating low-temperature crystallization and/or chemical re-equilibration of this mineral. The association of sanidine with nearly stoichiometric nepheline is unusual for agpaitic rocks and probably reflects inhibition of Al/Si ordering in the feldspar by Ba. At least four types of clinopyroxene can be distinguished on the basis of their morphology and composition. All these types correspond to Al- and Ca-poor aegirine (typically <0.6 and 2.6 wt% Al2O3 and CaO, respectively). The overall evolutionary trend of clinopyroxene in the Gordon Butte rocks is from Fe-poor diopside to aegirine-augite in the malignites and nepheline microsyenites, and culminates with the pegmatitic aegirine. This trend is characteristic for potassic alkaline complexes and results from preferential partitioning of Fe2+ into biotite during the magmatic crystallization. Barytolamprophyllite in the pegmatites is primary (as opposed to deuteric); only a few crystals contain a core composed of lamprophyllite. The evolutionary history of the Gordon Butte pegmatites can be subdivided into primary, agpaitic, and deuteric stages. The earliest paragenesis to crystallize included accessory zircon and thorite. Sr-rich loparite also precipitated relatively early serving as a major repository for Sr, REE, and Nb. During the agpaitic stage, diverse titano- and zircono-silicates (barytolamprophyllite, eudialyte, wadeite, and rinkite, among others) consumed most of the Ba, Sr, Ti, Zr, and Nb still remaining in the melt. The final stage in the evolution of the pegmatites involved interaction of the earlier-formed mineral assemblages with deuteric fluids. In common with the Rocky Boy pegmatites, Sr-REE-Na-rich fluorapatite, Ba-Fe titanates and REE-bearing carbonates (ancylite, calcio-ancylite, and bastnäsite-parisite series) are chief products of the deuteric stage. The alteration of the primary mineral assemblages by deuteric fluids also produced muscovite-zeolite pseudomorphs after nepheline, replacement of wadeite and eudialyte by catapleiite-group minerals, re-deposition of Ba in the form of hyalophane, baotite, and benitoite, and cation leaching from rinkite, eudialyte, and loparite. The mineralogy of the pegmatites from Gordon Butte, other potassic complexes, and sodic agpaitic occurrences is compared in detail.

Episodic growth of a Late Cretaceous and Paleogene intrusive complex of pegmatitic leucogranite, Ruby Mountains core complex, Nevada, USA

USGS Publications Warehouse

Howard, Keith A.; Wooden, J.L.; Barnes, C.G.; Premo, W.R.; Snoke, A.W.; Lee, S.-Y.

2011-01-01

Gneissic pegmatitic leucogranite forms a dominant component (>600 km3) of the midcrustal infrastructure of the Ruby Mountains–East Humboldt Range core complex (Nevada, USA), and was assembled and modified episodically into a batholithic volume by myriad small intrusions from ca. 92 to 29 Ma. This injection complex consists of deformed sheets and other bodies emplaced syntectonically into a stratigraphic framework of marble, calc-silicate rocks, quartzite, schist, and other granitoids. Bodies of pegmatitic granite coalesce around host-rock remnants, which preserve relict or ghost stratigraphy, thrusts, and fold nappes. Intrusion inflated but did not disrupt the host-rock structure. The pegmatitic granite increases proportionally downward from structurally high positions to the bottoms of 1-km-deep canyons where it constitutes 95%–100% of the rock. Zircon and monazite dated by U-Pb (sensitive high-resolution ion microprobe, SHRIMP) for this rock type cluster diffusely at ages near 92, 82(?), 69, 38, and 29 Ma, and indicate successive or rejuvenated igneous crystallization multiple times over long periods of the Late Cretaceous and the Paleogene. Initial partial melting of unexposed pelites may have generated granite forerunners, which were remobilized several times in partial melting events. Sources for the pegmatitic granite differed isotopically from sources of similar-aged interleaved equigranular granites. Dominant Late Cretaceous and fewer Paleogene ages recorded from some pegmatitic granite samples, and Paleogene-only ages from the two structurally deepest samples, together with varying zircon trace element contents, suggest several disparate ages of final emplacement or remobilization of various small bodies. Folded sills that merge with dikes that cut the same folds suggest that there may have been in situ partial remobilization. The pegmatitic granite intrusions represent prolonged and recurrent generation, assembly, and partial melting modification of a batholithic volume even while the regional tectonic environment varied dramatically from contractile thickening to extension and mafic underplating.

Petrography, geochemistry, and U-Pb geochronology of pegmatites and aplites associated with the Alvand intrusive complex in the Hamedan region, Sanandaj-Sirjan zone, Zagros orogen (Iran)

NASA Astrophysics Data System (ADS)

Sepahi, Ali Asghar; Salami, Sedigheh; Lentz, David; McFarlane, Christopher; Maanijou, Mohammad

2018-04-01

The Alvand intrusive complex in the Hamedan area in Iran is in the Sanandaj-Sirjan zone of the Zagros orogen. It consists of a wide range of plutonic rocks, mainly gabbro, diorite, granodiorite, granite, and leucogranites that were intruded by aplitic and pegmatitic dykes. At least three successive magmatic episodes generated an older gabbro-diorite-tonalite assemblage, followed by a voluminous granodiorite-granite association, which was then followed by minor leucocratic granitoids. Aplitic and pegmatitic dykes and bodies have truncated both plutonic rocks of the Alvand intrusive complex and its metamorphic aureole. Chemically they belong to peraluminous LCT (Li-, Cs-, and Ta-bearing) family of pegmatites. Mineralogically, they resemble Muscovite (MS) and Muscovite Rare Element (MSREL) classes of pegmatites. High amounts of some elements, such as Sn (up to 10,000 ppm), Rb (up to 936 ppm), Ba (up to 706 ppm), and LREE (up to 404 ppm) indicate the highly fractionated nature of some of these aplites and pegmatites. U-Pb dating of monazite, zircon, and allanite by LA-ICPMS indicate the following ages: monazite-bearing aplites of Heydareh-e-Poshteshahr and Barfejin areas, southwest of Hamedan, give an age range of 162-172 Ma; zircon in Heydareh-e-Poshteshar gives an average age of 165 Ma and for allanite-bearing pegmatites of Artiman area, north of Tuyserkan, an age of 154.1 ± 3.7 Ma was determined. These overlap with previously reported ages (ca. 167-153 Ma) for the plutonic rocks of the Alvand complex. Therefore, these data reveal that the Jurassic was a period of magmatism in the Hamedan region and adjacent areas in the Sanandaj-Sirjan zone, which was situated at the southern edge of the central Iranian micro-plate (southern Eurasian plate) at this time. Our results also suggest that advective heating in a continental arc setting has caused melting of fertile supracrustal lithologies, such as meta-pelites. These partial melts were then emplaced at much higher crustal levels, but within a thermally anomalous environment, which, therefore, leads to formation of evolved felsic rocks, such as the studied LCT aplite-pegmatite suite and their parental granitic rocks. This is a new result that indicates the role of syn-subduction crustal partial melting in the region as part of Zagros orogeny.

The role of pegmatites and acid fluids for REE/HFSE mobilization in the Strange Lake peralkaline granitic pluton, Canada

NASA Astrophysics Data System (ADS)

Gysi, A. P.; Williams-Jones, A.

2012-12-01

The Strange Lake pluton in Canada is a mid-Proterozoic peralkaline granitic intrusion that is host to a world-class rare earth element (REE), yttrium (Y) and high-field strength element (HFSE) deposit containing more than 50 Mt ore at >1.5 wt.% REE and >3 wt.% Zr. The highest REE/HFSE concentrations are found in pegmatite-rich zones characterized by intense alteration. Previous studies of Strange Lake and other peralkaline and alkaline intrusions, such as Khan Bogd (Mongolia) and Tamazeght (Morocco) plutons have shown that hydrothermal alteration may play an important role in the mobility of the REE/HFSE. However, the fluid chemistry and conditions of alteration (i.e., P, T, pH, fO2, ligand activity) in these systems still need to be constrained to evaluate the importance and scale of such hydrothermal mobilization. We present new data from the B-zone, a pegmatite-rich zone located in NW Strange Lake. The pegmatites are generally zoned and form two main types. The border-type pegmatites consist of quartz, K-feldspar and hematized aegirine, whereas volatile-rich pegmatites consist of hydrothermal quartz and fluorite. Transitions between both types were also observed, with the K-feldspar being partly altered and replaced by Al-Si-rich phyllosilicates. The heavy (H)REE and Zr were primarily concentrated in zirconosilicates such as elpidite, now pseudomorphed by zircon or gittinsite, whereas light (L)REE and Y were concentrated in REE-F-(CO2)-minerals such as fluocerite and bastnäsite. Textural and mineralogical observations indicate that these minerals are primary and were partly to completely leached upon fluid-rock interaction in the pegmatites. Secondary phases include Ca-F-Y-rich minerals, mainly hydrothermal fluorite, that fill vugs and replaced primary REEHFSE minerals. The presence of hydrothermal fluorite veins, micro-veins, vugs and micro-breccia in the most altered parts of the B-zone are interpreted to reflect interaction of the rocks with a F-rich fluid. We modeled the interaction of HF-NaCl and HF-HCl-NaCl fluids with a Strange Lake pegmatite at 400-250 °C to test different alteration scenarios. The simulations indicated that a stronger acid than HF is needed to shift the system towards fluid buffered pH values, which are required to remobilize the REE and Zr. Comparison of the field study with numerical simulation indicates that for the effective hydrothermal remobilization of REE/HFSE, the system needs a source of elevated acidity and high fluid/rock ratios. We propose a model in which the Strange Lake pegmatites were a source of acidic fluids and upon cooling were affected by autometasomatic alteration due to increased acidity of the fluids, creating pathways for REE/HFSE mobilization.

Cooling rates and crystallization dynamics of shallow level pegmatite-aplite dikes, San Diego County, California

USGS Publications Warehouse

Webber, Karen L.; Simmons, William B.; Falster, Alexander U.; Foord, Eugene E.

1999-01-01

Pegmatites of the Pala and Mesa Grande Pegmatite Districts, San Diego County, California are typically thin, sheet-like composite pegmatite-aplite dikes. Aplitic portions of many dikes display pronounced mineralogical layering referred to as "line rock," characterized by fine-grained, garnet-rich bands alternating with albite- and quartz-rich bands. Thermal modeling was performed for four dikes in San Diego County including the 1 m thick Himalaya dike, the 2 m thick Mission dike, the 8 m thick George Ashley dike, and the 25 m thick Stewart dike. Calculations were based on conductive cooling equations accounting for latent heat of crystallization, a melt emplacement temperature of 650 °C into 150 °C fractured, gabbroic country rock at a depth of 5 km, and an estimated 3 wt% initial H2O content in the melt. Cooling to -5 cm/s. Crystal size distribution (CSD) studies of garnet from layered aplites suggest growth rates of about 10-6 cm/s. These results indicate that the dikes cooled and crystallized rapidly, with variable nucleation rates but high overall crystal-growth rates. Initial high nucleation rates coincident with emplacement and strong undercooling can account for the millimeter-size aplite grains. Lower nucleation rates coupled with high growth rates can explain the decimeter-size minerals in the hanging walls, cores, and miarolitic cavities of the pegmatites. The presence of tourmaline and/or lepidolite throughout these dikes suggests that although the melts were initially H2O-undersaturated, high melt concentrations of incompatible (or fluxing) components such as B, F, and Li (±H2O), aided in the development of large pegmatitic crystals that grew rapidly in the short times suggested by the conductive cooling models.

Fracture mechanics and geochemical factors influencing the emplacement mechanisms of the Stewart Lithia gem bearing granitic pegmatite, Pala District, San Diego County, California

NASA Astrophysics Data System (ADS)

Patterson, Jeffrey E.

The emplacement mechanisms and cooling characteristics of pegmatites are not well understood, yet little work has been done on this subject. Historically, it is the pegmatite mineralogy and zonation that has been the focus of attention because of fascination with giant sized crystals, diversity of mineralization, and abundance of minerals containing important strategic elements, (Li, Be, Ta, Nb, and others). In this thesis the subject of the emplacement mechanisms is a synergistic approach from geophysical and engineering viewpoints, using the principals of fracture mechanics to determine the properties related to emplacement. From this, the cooling characteristics are considered to explain the zonation of a pegmatite based upon the temperature of crystallization of each mineral. This provides a model to image the position of each mineral according to the temperature profiles over time. Finally, the mineral growth characteristics are considered in light of the boundary conditions placed upon them by the cooling period. To test these hypothetical conditions in the real world, the Stewart Lithia Pegmatite, Pala, California, has been evaluated both physically and geochemically. The structure of the pegmatite was examined along strike and along dip, as exposed in underground workings. The analyses of these data show that there are 5 discreet divisions along strike. The analyses of the geochemical data for precisely located tourmalines shows that these divisions are composed of approximately 10 discreet pulses, with the economically important "Chimney Division" containing all 10. The importance of this work is that it demonstrates the following. A complex pegmatite is more likely to consist of multiple pulses of different melt composition than a single pulse with un-explainable mineralogy and zonation; Giant crystals are more likely due to rapid polymerization of a few mineral species where the cooling rate and crystallization rate are nearly equal; The range of mineral sizes to eleven orders of magnitude is due to the minimal rate of cooling, with the smallest crystals nucleating and not growing because there is no thermal differential driving force; and gem crystals generally only occur in fluid filled miarolitic cavities.

Comparative Fluid Inclusion Chemistry of Miarolitic Pegmatites from San Diego County, California, USA

NASA Astrophysics Data System (ADS)

Nymberg, D.; Sirbescu, M. L. C.

2014-12-01

Miarolitic Li-Cs-Ta pegmatites are an important source of gemstones such as tourmaline var. elbaite and spodumene var. kunzite, but the distribution of gem-bearing pegmatites within a pegmatite field is not understood. This microthermometry, LA-ICP-MS, Raman spectroscopy, and crush-leach study of fluid inclusions in pegmatite quartz aims to discern the chemical variations of late-stage pegmatite fluids in relation to gem mineralization. We studied five mines from three San Diego Co. districts: Chihuahua Valley (C), Jacumba (J), and Pala (P). The ~100 Ma old, 1-10 m thick, subparallel magma sheets intruded plutons of the Peninsular Ranges Batholith or prebatholitic metasediments at an estimated pressure of 200-300 MPa. The pegmatites formed sequentially, from outer zones with comb, layered, and graphic quartz-feldspar textures at the magmatic stage to massive cores and miarolitic pockets at a late, fluid-saturated stage. Pocket quartz was analyzed from pegmatites of variable host rock, magmatic mineral assemblages, and known gem production. The inclusions contained two-phase aqueous fluids and no CO2 or other gases. Fluid salinity ranged from 0.5 to 8.6 wt.% NaCl eq. and correlated positively with inclusion homogenization temperature. Isochoric T at 250 MPa calculated for primary and pseudosecondary inclusions in pocket quartz ranged from 280 to 500 °C in district P, 310-420°C in J, and 230-290°C in C. We attribute the higher T of pocket formation in districts P and J to higher surrounding T at emplacement caused by proximity to other dikes. This preliminary study suggests that gem elbaite and/or kunzite occurrence correlates to Li and B contents in the pocket fluid, which, in turn, are a function of consumption by early, magmatic minerals. The P district has a simple leucogranite mineralogy at the magmatic stage; has as much as 5760 ppm B and 4950 ppm Li in the pocket fluid; and produced both elbaite and kunzite. The J district has abundant magmatic tourmaline; has only 3800 ppm B but up to 4700 ppm Li in the fluid; and produced only kunzite. The C district has no tourmaline in the outer zones; widely variable B and Li; and produced sporadic elbaite but no kunzite. In addition, variations in fluid chemistry and productivity along dike strike in district J is attributed to a change from gabbroic to metasedimentary host rocks.

Raman spectroscopic study of the mineral qingheiite Na2(Mn2+,Mg,Fe2+)2(Al,Fe3+)(PO4)3, a pegmatite phosphate mineral from Santa Ana pegmatite, Argentina.

PubMed

Frost, Ray L; Xi, Yunfei; Scholz, Ricardo; López, Andrés; Moreira, Caio; de Lena, Jorge Carvalho

2013-10-01

The pegmatite mineral qingheiite Na2(Mn(2+),Mg,Fe(2+))2(Al,Fe(3+))(PO4)3 has been studied by a combination of SEM and EMP, Raman and infrared spectroscopy. The studied sample was collected from the Santa Ana pegmatite, Argentina. The mineral occurs as a primary mineral in lithium bearing pegmatite, in association with beausite and lithiophilite. The Raman spectrum is characterized by a very sharp intense Raman band at 980 cm(-1) assigned to the PO4(3-) symmetric stretching mode. Multiple Raman bands are observed in the PO4(3-) antisymmetric stretching region, providing evidence for the existence of more than one phosphate unit in the structure of qingheiite and evidence for the reduction in symmetry of the phosphate units. This concept is affirmed by the number of bands in the ν4 and ν2 bending regions. No intensity was observed in the OH stretching region in the Raman spectrum but significant intensity is found in the infrared spectrum. Infrared bands are observed at 2917, 3195, 3414 and 3498 cm(-1) are assigned to water stretching vibrations. It is suggested that some water is coordinating the metal cations in the structure of qingheiite. Copyright © 2013 Elsevier B.V. All rights reserved.

Geological setting and petrogenesis of symmetrically zoned, miarolitic granitic pegmatites at Stak Nala, Nanga Parbat - Haramosh Massif, northern Pakistan

USGS Publications Warehouse

Laurs, B.M.; Dilles, J.H.; Wairrach, Y.; Kausar, A.B.; Snee, L.W.

1998-01-01

Miarolitic granitic pegmatites in the Stak valley in the northeast part of the Nanga Parbat - Haramosh Massif, in northern Pakistan, locally contain economic quantities of bi- and tricolored tourmaline. The pegmatites form flat-lying sills that range from less than 1 m to more than 3 m thick and show symmetrical internal zonation. A narrow outer or border zone of medium-to coarse-grained oligoclase - K-feldspar - quartz grades inward to a very coarse-grained wall zone characterized by K-feldspar - oligoclase - quartz - schorl tourmaline. Radiating sprays of schorl and flaring megacrysts of K-feldspar (intermediate microcline) point inward, indicating progressive crystallization toward the core. The core zone consists of variable mixtures of blocky K-feldspar (intermediate microcline), oligoclase, quartz, and sparse schorl or elbaite, with local bodies of sodic aplite and miarolitic cavities or "pockets". Minor spessartine-almandine garnet and lo??llingite are disseminated throughout the pegmatite, but were not observed in the pockets. The pockets contain well-formed crystals of albite, quartz, K-feldspar (maximum microcline ?? orthoclase overgrowths), schorl-elbaite tourmaline, muscovite or lepidolite, topaz, and small amounts of other minerals. Elbaite is color-zoned from core to rim: green (Fe2+- and Mn2+-bearing), colorless (Mn2+-bearing), and light pink (trace Mn3+). Within ???10 cm of the pegmatites, the granitic gneiss wallrock is bleached owing to conversion of biotite to muscovite, with local quartz and albite added. Schorl is disseminated through the altered gneiss, and veins of schorl with bleached selvages locally traverse the wallrock up to 1 m from the pegmatite contact. The schorl veins can be traced into the outer part of the wall zone, which suggests that they formed from aqueous fluids derived during early saturation of the pegmatite-forming leucogranitic magma rich in H2O, F, B, and Li. Progressive crystallization resulted in a late-stage sodic magma and abundant aqueous fluids. Two late stages of volatile escape are recognized: the first stage caused pressure-quenching of the last magma, which produced aplite and caused albitization (An3 to An8) of earlier crystallized K-feldspar and oligoclase. The second stage, released during the rupture of miarolitic cavities, produced platy albite ("cleavelandite," An1) locally associated with F-rich moscovite and elbaite. Albitization is likely due to cooling of alkali-fluoride-dominated fluids at less than 2 kbar pressure. The pegmatites are derived from Himalayan leucogranitic magma emplaced prior to 5 Ma into granulitic gneiss that was at 300?? to 550??C and 1.5 to 2 kbar. The pegmatites were emplaced during uplift of the Haramosh Massif, since they cross-cut ductile normal faults but are cut by brittle normal faults. Economically important pink tourmaline mineralization formed in pockets concentrated near the crest of a broad antiform, as a result of trapping of late magmatic aqueous fluids that had become Fe-poor owing to the prior crystallization of schorl.

Partial melting of amphibolite to trondhjemite near Ykutat, Alaska

NASA Technical Reports Server (NTRS)

Barker, F.

1986-01-01

At Nunatak Fiord, 55 km NE of Yakutat, Alaska, a uniform layer of Cretaceous metabasalt approximately 3 km thick was metamorphosed to amphibolite facies and locally partially melted to trondhjemite pegmatite. Results of the rare earth element analysis performed on the amphibolite and the trondhjemite pegmatite are discussed.

A synthesis of mineralization styles and geodynamic settings of the Paleozoic and Mesozoic metallic ore deposits in the Altay Mountains, NW China

NASA Astrophysics Data System (ADS)

Yang, Fuquan; Geng, Xinxia; Wang, Rui; Zhang, Zhixin; Guo, Xuji

2018-06-01

The Altay Mountains within the Xinjiang region of northwestern China hosts major metallic ore deposits. Here we review the geological characteristics, metallogenic features and tectonic settings of these deposits. The metallic ore deposits in the Altay Mountains occur mainly within four regions: North Altay, Central Altay, South Altay and Erqis. We recognize seven types of metallic ore deposits in the Altay Mountains: VMS, submarine volcanogenic iron, magmatic, skarn, pegmatite, hydrothermal vein (Cu-Zn, Fe) and orogenic gold. Among these types, the VMS, pegmatite, orogenic gold and skarn deposits are the most common. Most of the rare metal pegmatite deposits are distributed in Central Altay, with only a few in South Altay. The VMS, submarine volcanogenic type iron and skarn-type deposits are distributed in South Altay, whereas the orogenic-type gold deposits are distributed in the Erqis Fault belt. The hydrothermal vein-type deposits occur in the Erqis Fault belt and Chonghu'er Basin in South Altay. Magmatic-type deposits are mostly in the Erqis Fault belt and Central Altay. Based on isotopic age data, the VMS, submarine volcanogenic-type Fe and skarn-type Cu, Pb, Zn, Fe mineralization occurred during Early-Middle Devonian (∼410-377 Ma), orogenic-type Au, magmatic-type Cu-Ni, and a small number of skarn-type Fe, hydrothermal vein-type Cu-Zn, pegmatite-type rare-metal deposits in Early-Middle Permian (293-261 Ma), pegmatite-type rare-metal deposits, few skarn-type Fe deposit in Early-Middle Triassic (248-232 Ma), and dominantly represented by pegmatite-type rare-metal deposits in Late Triassic-Early Jurassic (223-180 Ma). The metallic ore deposits in the Altay Mountains formed in various tectonic settings, such as the Early-Middle Devonian continental arc and oceanic island arc, Early-Middle Permian post-collisional extensional setting, and Triassic-Early Jurassic intracontinental setting.

Mineralized aplite—pegmatite at Jabal Sa'id, Hijaz region, Kingdom of Saudi Arabia

NASA Astrophysics Data System (ADS)

Hackett, Damien

The Jabal Sa'id aplite—pegmatite, located at 23°49'03″N, 40°56'30″E, is part of the Jabal Hadb ash Sharar granite complex and resulted from emplacement of a residual volatile-rich fraction of alkali granite magma dominantly above a chilled carapace. Mineralization is layered, with four peak grades in layers 20-25 m wide, one of which may represent a mineral resource with greater potential than the aplite—pegmatite as a whole. The grades of all elements, except Zr, increase towards the upper part of the body. Chemical composition is extremely variable. Major-oxide data confirm previously determined geochemical characteristics and genetic relationships that suggested this body is an apogranite. However, the abundant new data also show that differences between the aplite—pegmatite and cognate alkali microgranite are not as great as previously reported, except for Na 2O which is extremely depleted in the apogranite. REE data support suggested genetic relationships and indicate that feldspar fractionation was important during crystallization. They also show that the content of HREE is comparatively constant throughout the aplite—pegmatite, and that variations in total REE content are caused by variations in the content of LREE. Bastnaesite and synchysite-(Y) are the principal rare-earth-element minerals, and are accompanied by monazite and synchesite; pyrochlore and thorite are also important ore minerals. Other elements concentrated in the aplite—pegmatite, such as Ta, Sn and U, occur only in solid solution in these minerals. The grain size of the ore minerals is commonly in the range 0.02-0.2 mm, and the grain size of gangue minerals, quartz, microcline and lesser amounts of aegirine and arfvedsonite, is typically in the range 1.0-4.0 mm. The ore minerals occur typically along gangue mineral boundaries. Zoning within the body permits calculation of high- and low-grade reserves which correspond to the upper and lower part of the apogranite.

Zircon trace element and isotopic (Sr, Nd, Hf, Pb) effects of assimilation-fractional crystallization of pegmatite magma: A case study of the Guangshigou biotite pegmatites from the North Qinling Orogen, central China

NASA Astrophysics Data System (ADS)

Yuan, Feng; Liu, Jia-Jun; Carranza, Emmanuel John M.; Zhang, Shuai; Zhai, De-Gao; Liu, Gang; Wang, Gong-Wen; Zhang, Hong-Yuan; Sha, Ya-Zhou; Yang, Shang-Song

2018-03-01

Evidence for open-system magmatic processes related to wallrock assimilation accompanied by fractional crystallization (AFC) is present in the Guangshigou biotite pegmatites, North Qinling Orogen. The biotite pegmatite-gneiss contacts generally coincide with the greatest enrichment of U and Th. Zircon Usbnd Pb dating constrains the crystallization ages of the biotite pegmatite (rim zone-415 ± 2.6 Ma; internal zone-413.5 ± 2.5 Ma), in line with a pyrite Pbsbnd Pb isochron age (413 ± 22 Ma). Metamict areas in zircon show generally elevated concentrations of trace elements and expulsion of radioactive Pb. Internal zone samples, representing uncontaminated magma, have negative to positive zircon ( 413 Ma) εHf(t) (- 1.53 - + 3.24), low εNd(t) values (- 2.4), and old Hf and Nd model ages (tDM2 = 1.5-1.19 Ga, T2DM = 1.35 Ga, respectively), indicating a dominantly recycled Mesoproterozoic lower crustal material with involvement of some juvenile materials in the source region. The magmatic oxygen fugacity (fO2) and crystallization temperatures ranges from - 24.81 to - 13.34 of log fO2 and 570 °C to 793 °C, respectively. Compared to the internal zone, pegmatite rim samples display a variable and lower εNd(t) values (- 3.9 to - 2.8) and T2DM (1.47-1.37 Ga), but similar Hf isotopic compositions, favouring a three-component isotopic mixing model (recycled Mesoproterozoic lower crust materials, juvenile materials, and host gneiss). Pronounced variations of Ti, Y, U, Th, Hf, and REE concentrations in zircon from grain to grain in individual samples and from area to area within individual grains suggest a fluctuating crystallization environment in hybridized magma from which the rim-hosted zircons crystallized. Variable and high radiogenic Pb ratios of pyrites forming in the hybridized magma were inherited from the matrix. Zircons from both zones exhibit similar Hf isotope patterns, indicating the rim-hosted zircons crystallized during the early stage of hybridization of magma. However, the heterogeneous Nd isotopic composition in individual pegmatites imply an incorporation of wallrock-derived melt with less radiogenic Nd.

The Zapot pegmatite mineral county

USGS Publications Warehouse

Foord, E.E.; Soregaroli, A.E.; Gordon, H.M.

1999-01-01

The Zapot pegmatite is currently being mined for mineral specimens (chiefly amazonite, topaz and smoky quartz in miarolitic cavities), for gemstones (topaz and smoky quartz) and for decorative rock (amazonite). The deposit is owned and operated by Harvey Gordon Minerals of Reno, Nevada, and is the only amazonite-topaz mining operation in the state. Thousands of specimens from this operation have reached the collector market.

The transition from granite to banded aplite-pegmatite sheet complexes: An example from Megiliggar Rocks, Tregonning topaz granite, Cornwall

NASA Astrophysics Data System (ADS)

Breiter, K.; Ďurišová, J.; Hrstka, T.; Korbelová, Z.; Vašinová Galiová, M.; Müller, A.; Simons, B.; Shail, R. K.; Williamson, B. J.; Davies, J. A.

2018-03-01

The genetic relationship between a granite pluton and adjacent complex of rare-metal pegmatite-aplite-banded sheets (Megiliggar Sheet Complex - MSC) has been studied at the border of the Tregonning topaz granite at Megiliggar Rocks, Cornwall, SW England. Similarities in whole-rock chemical and mineralogical compositions, together with a gradual change in textures away from the granite margin, provide strong evidence for a genetic link between the Tregonning Granite and MSC. The sheets are likely to represent apophyses of residual melt which escaped from the largely crystallized roof of the granite pluton. The escaping melt was peraluminous, had a composition near the F, B, Li slightly enriched granite minimum, and, in comparison with other Cornish granites, was enriched in F, Li, Rb, Cs, Sn, W, Nb, Ta, and U, and depleted in Fe, Mg, Ca, Sr, Th, Zr, and REE. With increasing distance from the Tregonning Granite, the silicate melt crystallized as homogeneous leucogranite sheets and banded complex sheets (i.e. combinations of bands with granitic, aplitic and pegmatitic textures), then layered aplite-pegmatites; this sequence becoming progressively more depleted in the fluxing and volatile elements F, Li, Rb, and Cs, but showing no change in Zr/Hf ratios. The fixed Zr/Hf ratio is interpreted as indicating a direct genetic link (parental melt) between all rock types, however the melt progressively lost fluxing and volatile elements with distance from the granite pluton, probably due to wall-rock reaction or fluid exsolution and migration via fractures. Differentiation of the primary melt into Na-Li-F-rich and separate K-B-rich domains was the dominant chemical process responsible for the textural and mineral diversity of the MSC. On a large (cliff-section) scale, the proximal Na-Li-F-rich leucogranite passes through complex sheets into K-B-rich aplite-pegmatites, whilst at a smaller (<1 m) scale, the K-B-rich bands are interspersed (largely overlain) by Na-Li-F-rich segregations. The grain size differences between the aplite and pegmatite could be related to pressure fluctuations and/or undercooling.

Geology of the Spruce Pine District, Avery, Mitchell, and Yancy Counties, North Carolina

USGS Publications Warehouse

Brobst, Donald Albert

1962-01-01

The Spruce Pine pegmatite district, a northeastward-trending belt 25 miles long and 10 miles wide, lies in parts of Avery, Mitchell, and Yancey Counties in the Blue Ridge Province of western North Carolina. The most abundant rocks in the district are interlayered mica and amphibole gneisses and schists, all of which are believed to be of Precambrian age. These rocks are cut by small bodies of dunite and associated rocks of Precambrian (?) age, large bodies of alaskite and associated pegmatite of early Paleozoic age, and basaltic and diabasic dikes and sills of Triassic (?) age. The rocks of the district have been weathered to saprolite that is locally 50 feet thick. The major structure in the area is a southwestward-plunging asymmetrical synclinorium that has its steeper limb on the northwest side. Feldspar, muscovite as sheet and scrap (ground) mica, and kaolin from the alaskite and associated pegmatite account for over 90 percent of the total mineral production of the district. Amounts of other pegmatite minerals, including quartz, beryl, columbite-tantalite, rare-earth and uranium minerals are an extremely small part of the mineral resources. Actual or potential products from other rocks are olivine, vermiculite, asbestos, talc, chromium and nickel, soapstone, mica schist, garnet, kyanite, dolomite marble, and construction materials.

High-fluorine rhyolite: An eruptive pegmatite magma at the Honeycomb Hills, Utah

NASA Astrophysics Data System (ADS)

Congdon, Roger D.; Nash, W. P.

1988-11-01

The Honeycomb Hills rhyolite dome in western Utah displays chemical and mineralogical features characteristic of a rare-element pegmatite magma. The lavas show extreme enrichments in such trace elements as Rb (≤1960 ppm), Cs (≤78), Li (≤344), Sn (≤33), Be (≤270), and Y (≤156). Phenocrysts (10%-50% by volume) include sanidine (Or66-70), plagioclase (Ab83-92), quartz, biotite approaching fluorsiderophyllite, and fluortopaz, as well as accessory phases common to highly differentiated granites and pegmatites, including zircon, thorite, fluocerite, columbite, fergusonite, and samarskite. Low temperatures (600 to 640 °C), coupled with high phenocryst and silica content, might normally preclude eruption due to the extremely high viscosity of the melt. However, high concentrations of fluorine (2%-3%) could domal lavas significantly reduce viscosity and allow eruption of domal lavas even after dewatering of the mama during the initial pyroclastic phase of the eruptive cycle. Fractionation of phenocrysts and accessory phases, for which partition coefficients have been measured, is sufficient to account for most compositional gradients inferred in the preeruptive magma body, although transport by a fluid phase formed a may have caused upward enrichments in Li, Be, and Cs. If the Honeycomb Hills magma had crystallized at depth, it would have formed a rare-element pegmatite.

The Black Pearl mine, Arizona - Wolframite veins and stockscheider pegmatite related to an albitic stock

NASA Technical Reports Server (NTRS)

Schmitz, Christopher; Burt, Donald M.

1990-01-01

Wolframite-bearing quartz veins flanked by greisen alteration occur at and near the Black Pearl mine, Yavapai County, Arizona. The veins are genetically related to a small albitite stock, and cut a series of Proterozoic metasedimentary and intrusive rocks. The largest vein, the only one mined, is located at the apex of the stock. Field relations imply that this stock is a late-stage differentiate of time 1.4-Ga anorogenic Lawler Peak batholith, which crops out about 3 km to the south. The albitites are of igneous origin and have suffered only minor deuteric alteration. A thin (1 to 2 m) pegmatite unit ('stockscheider') occurs at the contact of the Black Pearl Albitite stock with the country rocks. Directional indicators and other evidence suggest that the pegmatite was formed in the presence of a volatile-rich fluid phase close to the time of magma emplacement. The sudden change from coarse-grained microcline-rich pegmatite to fine-grained, albite-rich albitite suggests pressure quenching, possibly due to escape of fluids up the Black Pearl vein. Stockscheider-like textures typically occur near the apical contacts of productive plutons. The presence or absence of this texture is a useful guide in prospecting for lithophile metal deposits.

Genesis of rare-metal pegmatites and alkaline apatite-fluorite rocks of Burpala massi, Northern Baikal folded zone

NASA Astrophysics Data System (ADS)

Sotnikova, Irina; Vladykin, Nikolai

2015-04-01

Burpalinsky rare metal alkaline massif in the Northern Baikal folded zone in southern margin of Siberian Platform, is a of intrusion central type, created 287 Ma covering area of about 250 km2. It is composed of nepheline syenites and pulaskites grading to quartz syenites in the contacts. Veines and dykes are represented by shonkinites, sodalite syenite, leucocratic granophyres, alkali granites and numerous rare metal alkaline syenite pegmatites and two dykes of carbonatites. All rocks except for granites are cut by a large apatite-fluorite dyke rocks with mica and magnetite, which in turn is cut by alaskite granites dyke. The massif has been studied by A.M. Portnov, A.A. Ganzeev et al. (1992) Burpalinsky massif is highly enriched with trace elements, which are concentrated in pegmatite dykes. About 70 rare-metal minerals we found in massif. Zr-silicates: zircon, eudialyte, lovenite, Ti-lovenite, velerite, burpalite, seidozerite, Ca- seidozerite, Rosenbuschite, vlasovite, katapleite, Ca-katapleite, elpidite. Ti- minerals:- sphene, astrophyllite, ramsaite, Mn-neptunite bafertisite, chevkinite, Mn-ilmenite, pirofanite, Sr-perrerit, landauite, rutile, anatase, brookite; TR- minerals - loparite, metaloparite, britolite, rinkolite, melanocerite, bastnesite, parisite, ankilite, monazite, fluocerite, TR-apatite; Nb- minerals - pyrochlore, loparite. Other rare minerals leucophanite, hambergite, pyrochlore, betafite, torite, thorianite, tayniolite, brewsterite, cryolite and others. We have proposed a new scheme massif: shonkinites - nepheline syenites - alkaline syenite - quartz syenites - veined rocks: mariupolites, rare-metal pegmatites, apatite, fluorite rock alyaskite and alkaline granites and carbonatites (Sotnikova, 2009). Apatite-fluorite rocks are found in the central part of massif. This is a large vein body of 2 km length and a 20 m width cutting prevailing pulaskites. Previously, these rocks were regarded as hydrothermal low-temperature phase. New geological and thermobarometric evidence suggests that apatite-fluorite rocks were formed from the residual fluid-melt, separated after crystallization of rare-metal pegmatites. Petrochemical and geochemical data Burpalinsky are in accord of general trend of crystal differentiation of alkaline magma containing small concentrations of CO2 and higher P2O5 and F, which accumulated significantly separated from the pegmatite melts. In some pegmatites fluorite with rare-metal minerals (flyuocerit etc) are separating in schlieren. Apatite-fluorite rocks are cut by leucogranite dyke, having genetic connection with rare-metal pegmatites. Late granitic phases has its own association of rare-metal minerals described by A.A. Ganzeev (1972). Thermobarometric geochemical study of apatite-fluorite rocks Burpala massif found a large number of primary fluid inclusions (15-50 micrometers). Thermal and cryometric research of 60 individual fluid inclusions in fluorite showed the domination of Na, Ca, Mg chlorides and high temperatures salt inclusions in fluorites (above 550C) and melt inclusions in apatites (800C). Apatite-fluorite rocks in massif are similar to foskorites in carbonatite complexes, with similar high Ca content, but instead fluorite, together with other "foskoritovymi" minerals - apatite, magnetite, mica, and pyroxene were formed instead for calcite. Isotopic studies (Sr-Nd) indicate the mantle source of primary magma Burpala massif close to EM-2, which is characteristic of alkaline intrusions in the folded belts (Vladykin 2009). RBRF grant 14-45-04057

Pegmatite/wallrock interactions, Black Hills, South Dakota: Progressive boron metasomatism adjacent to the Tip Top pegmatite

NASA Astrophysics Data System (ADS)

Shearer, C. K.; Papike, J. J.; Simon, S. B.; Laul, J. C.; Christian, R. P.

1984-12-01

Interaction between country rock and fluids derived from the Tip Top pegmatite has resulted in a series of boron enriched assemblages. Between unaltered quartz-mica schist to the pegmatite contact is a succession of four mineral assemblages: (1) Quartz-Biotite-Potassium Feldspar assemblage (Q-B-K), which consists essentially of the original metamorphic silicate assemblage plus anomalously high amounts of modal tourmaline (2) Quartz-Biotite-Tourmaline assemblage (Q-B-T) (3) Tourmaline-Quartz-Muscovite assemblage (T-Q-M) (4) Tourmaline-Quartz assemblage (T-Q). Alkali elements (Cs, Rb, K, Li), SiO 2, and Ba show a decrease from the Q-B-K assemblage to the T-Q assemblage. A1 2O 3, Ga, B, total Fe and Zn increase moderately from the Q-B-K assemblage to the T-Q assemblage. The mineral chemistries also change considerably. The Mg/(Mg + Fe 2+) ratios in biotites range from 0.54 to 0.50 in samples from the Q-B-K assemblage to 0.39 in the (Q-B-T) assemblage. The range in tourmaline end-member components from the Q-B-K assemblage to the T-Q assemblage is as follows: Q-B-K: Dravite .63 Schorl .23 Elbaite .05 Buergerite .09 T-Q: Dravite .23 Schorl .37 Elbaite .17 Buergerite .23. Observed variations in mineral assemblage and whole rock chemistry within the alteration zone appear to a first approximation to be a function of μB2O3 (boron metasomatism) and μK2O (alkali leaching). The breakdown of feldspar and biotite may be approximated by reactions: 2HCl + 2(K, Na)AlSi 3O 8 /ai 2(K, Na)Cl + Al 2SiO 5 + 5SiO 2 + H 2O and 2 Annite + SiO 2 + 5Al 2SiO 5 + 2NaCl + 6H 3BO 3 /ai 2 Tourmaline + 2KCl + 7H 2O. The alteration zone may represent either a single episode (B-, Cs-, Li-, Rb-enriched fluid) or multiple episodes (B, Zn, Mn fluid and Cs, Li, Rb fluid) of pegmatite fluid-schist interactions. In both situations, B in the aqueous fluid from the pegmatite reacts with the schist breaking down sheet silicate "traps" for Cs, Rb, Li, and K and forming tourmaline-rich assemblages.

Pegmatite/wallrock interactions, Black Hills, South Dakota: Progressive boron metasomatism adjacent to the Tip Top pegmatite

USGS Publications Warehouse

Shearer, C.K.; Papike, J.J.; Simon, S.B.; Laul, J.C.; Christian, R.P.

1984-01-01

Interaction between country rock and fluids derived from the Tip Top pegmatite has resulted in a series of boron enriched assemblages. Between unaltered quartz-mica schist to the pegmatite contact is a succession of four mineral assemblages: 1. (1) Quartz-Biotite-Potassium Feldspar assemblage (Q-B-K), which consists essentially of the original metamorphic silicate assemblage plus anomalously high amounts of modal tourmaline 2. (2) Quartz-Biotite-Tourmaline assemblage (Q-B-T) 3. (3) Tourmaline-Quartz-Muscovite assemblage (T-Q-M) 4. (4) Tourmaline-Quartz assemblage (T-Q). Alkali elements (Cs, Rb, K, Li), SiO2, and Ba show a decrease from the Q-B-K assemblage to the T-Q assemblage. A12O3, Ga, B, total Fe and Zn increase moderately from the Q-B-K assemblage to the T-Q assemblage. The mineral chemistries also change considerably. The Mg/(Mg + Fe2+) ratios in biotites range from 0.54 to 0.50 in samples from the Q-B-K assemblage to 0.39 in the (Q-B-T) assemblage. The range in tourmaline end-member components from the Q-B-K assemblage to the T-Q assemblage is as follows: Q-B-K: Dravite.63 Schorl.23 Elbaite.05 Buergerite.09 T-Q: Dravite.23 Schorl.37 Elbaite.17 Buergerite.23. Observed variations in mineral assemblage and whole rock chemistry within the alteration zone appear to a first approximation to be a function of ??B2O3 (boron metasomatism) and ??K2O (alkali leaching). The breakdown of feldspar and biotite may be approximated by reactions: 2HCl + 2(K, Na)AlSi3O8 /ai 2(K, Na)Cl + Al2SiO5 + 5SiO2 + H2O and 2 Annite + SiO2 + 5Al2SiO5 + 2NaCl + 6H3BO3 /ai 2 Tourmaline + 2KCl + 7H2O. The alteration zone may represent either a single episode (B-, Cs-, Li-, Rb-enriched fluid) or multiple episodes (B, Zn, Mn fluid and Cs, Li, Rb fluid) of pegmatite fluid-schist interactions. In both situations, B in the aqueous fluid from the pegmatite reacts with the schist breaking down sheet silicate "traps" for Cs, Rb, Li, and K and forming tourmaline-rich assemblages. ?? 1984.

Hydrothermal mobilization of pegmatite-hosted REE and Zr at Strange Lake, Canada: A reaction path model

NASA Astrophysics Data System (ADS)

Gysi, Alexander P.; Williams-Jones, Anthony E.

2013-12-01

Petrological and geochemical observations of pegmatites in the Strange Lake pluton, Canada, have been combined with numerical simulations to improve our understanding of fluid-rock interaction in peralkaline granitic systems. In particular, they have made it possible to evaluate reaction paths responsible for hydrothermal mobilization and mineralization of rare earth elements (REE) and Zr. The focus of the study was the B-Zone in the northwest of the pluton, which contains a pegmatite swarm and is the target of exploration for an economically exploitable REE deposit. Many of the pegmatites are mineralogically zoned into a border consisting of variably altered primary K-feldspar, arfvedsonite, quartz, and zirconosilicates, and a core rich in quartz, fluorite and exotic REE minerals. Textural relationships indicate that the primary silicate minerals in the pegmatites were leached and/or replaced during acidic alteration by K-, Fe- and Al-phyllosilicates, aegirine, hematite, fluorite and/or quartz, and that primary zirconosilicates (e.g., elpidite) were replaced by gittinsite and/or zircon. Reaction textures recording coupled dissolution of silicate minerals and crystallization of secondary REE-silicates indicate hydrothermal mobilization of the REE. The mobility of the light (L)REE was limited by the stability of REE-F-(CO2)-minerals (basnäsite-(Ce) and fluocerite-(Ce)), whereas zirconosilicates and secondary gadolinite-group minerals controlled the mobility of Zr and the heavy (H)REE. Hydrothermal fluorite and fluorite-fluocerite-(Ce) solid solutions are interpreted to indicate the former presence of F-bearing saline fluids in the pegmatites. Numerical simulations show that the mobilization of REE and Zr in saline HCl-HF-bearing fluids is controlled by pH, ligand activity and temperature. Mobilization of Zr is significant in both saline HF- and HCl-HF-bearing fluids at low temperature (250 °C). In contrast, the REE are mobilized by saline HCl-bearing fluids, particularly at high temperature (400 °C). The LREE are more mobile than the HREE in saline HCl-bearing fluids due to the greater stability of LREE-chloride complexes. The simulated mineralogy is consistent with the zonation observed in the pegmatites and with fluid-rock interaction at conditions that were rock-buffered in the pegmatite borders (low fluid/rock ratio; and pH > 4) and fluid-buffered in the cores (high fluid/rock ratio; pH ⩽ 2). We propose a model in which saline HCl-HF-bearing fluids created pathways during acidic alteration from the pegmatite cores outward. This led to the mobilization of REE and Zr due to progressive alteration of primary silicate minerals and increased acidity upon cooling. The key requirement for REE and Zr mobilization in peralkaline igneous intrusions is the formation of an acidic subsystem with high fluid/rock ratios that increases the overall permeability of the rocks. In these zones, the extent of late stage hydrothermal redistribution and concentration of REE and Zr depends on the buffering capacity of the rocks and the availability of fluids that may produce autometasomatic rock alteration, interact with external rock units and/or mix with fluids from other sources. b The detection limits of Yb were 1043 ppm for zircon, 380 ppm for gadolinite-group minerals and 380 ppm for REE-F-(CO2)-minerals. bAja et al. (1995). cMigdisov et al. (2011). dTagirov et al. (1997). eTagirov and Schott (2001). fMigdisov et al. (2009) with REE (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). b Calculated using the methods of the Chermak and Rimstidt (1989), Berman and Brown (1985) and Holland (1989) with molar volume of arfvedsonite from Hawthorne (1976). cZotov et al. (1998). d GEM-Selektor v.3 database (http://gems.web.psi.ch). eMigdisov et al. (2009).

Composition of coarse-grained magnetite from pegmatite dikes related to plutons of quartz monzonite in the Jabal Lababa area, Kingdom of Saudi Arabia

USGS Publications Warehouse

Overstreet, William C.; Mousa, Hassan; Matzko, John J.

1985-01-01

Crystals of magnetite as large as 30 mm long and 7 mm thick are locally present in quartz-rich zones of interior and exterior pegmatite dikes related to plutons of quartz monzonite in the Jabal Lababa area. Niobium, tin, and yttrium are strongly enriched in six specimens of magnetite from interior pegmatite dikes in a small pluton where these elements form geochemical anomalies in nonmagnetic heavy-mineral concentrates from wadi sediment. Less abundant anomalous elements in the magnetite are molybdenum, lead, and zirconium, which also tend to be present in anomalous amounts in the nonmagnetic concentrates from the niobium-bearing pluton. The most anomalous trace element in the magnetite is zinc, which is at least 10 times as abundant as it is in the quartz monzonite plutons or in the nonmagnetic concentrates. The capacity of magnetite to scavenge molybdenum, zinc, niobium, lead, tin, yttrium, and zirconium suggests the possible utility of magnetite as a geochemical sample medium.

U-Pb zircon geochronology of Mesoproterozoic postorogenic rocks and implications for post-Ottawan magmatism and metallogenesis, New Jersey Highlands and contiguous areas, USA

USGS Publications Warehouse

Volkert, R.A.; Zartman, R.E.; Moore, P.B.

2005-01-01

Postorogenic rocks are widespread in Grenville terranes of the north-central Appalachians where they form small, discordant, largely pegmatitic felsic intrusive bodies, veins, and dikes, and also metasomatic calcic skarns that are unfoliated and postdate the regional 1090 to 1030 Ma upper amphibolite- to granulite-facies metamorphism related to the Grenville (Ottawan) Orogeny. Zircons from magmatic and nonmagmatic rocks from northern New Jersey and southern New York were dated to provide information on the regional tectonomagmatic and metallogenic history following Ottawan orogenesis. We obtained U-Th-Pb zircon ages of 1004 ?? 3 Ma for pegmatite associated with the 1020 ?? 4 Ma Mount Eve Granite near Big Island, New York, 986 ?? 4 Ma for unfoliated, discordant pegmatite that intrudes supracrustal marble at the Buckwheat open cut, Franklin, New Jersey, ???990 Ma for a silicate-borate skarn layer in the Franklin Marble at Rudeville, New Jersey, and 940 ?? 2 Ma for a calc-silicate skarn layer at Lower Twin Lake, New York. This new data, together with previously published ages of 1020 ?? 4 to 965 ?? 10 Ma for postorogenic rocks from New Jersey and southern New York, provide evidence of magmatic activity that lasted for up to 60 Ma past the peak of high-grade metamorphism. Postorogenic magmatism was almost exclusively felsic and involved relatively small volumes of metaluminous to mildly peraluminous melt that fractionated from an A-type granite parent source. Field relationships suggest the melts were emplaced along lithosphere-scale fault zones in the Highlands that were undergoing extension and that emplacement followed orogenic collapse by least 30 Ma. Postorogenic felsic intrusions correspond to the niobium-yttrium-fluorine (NYF) class of pegmatites of C??erny?? (1992a). Geochronologic data provide a temporal constraint on late-stage hydrothermal activity and a metallogenic event in New Jersey at ???990 to 940 Ma that mineralized pegmatites with subeconomic to economic deposits of magnetite ?? U ?? Th ?? rare earth element (REE) and formed metasomatic calcic skarn bodies in marble and reactive carbonate rocks. Mineralization associated with this event overlaps the timing of pegmatite emplacement, suggesting a petrogenetic relationship. Coeval metallogeny at 975 to 950 Ma in the New York Hudson Highlands and 980 to 937 Ma in the Canadian Grenville Province implies that this event was widespread following the Ottawan phase of the Grenville Orogeny. ?? 2005 Elsevier B.V. All rights reserved.

Y,REE,Nb,Ta,Ti-oxide (AB 2O 6) minerals from REL-REE euxenite-subtype pegmatites of the Třebíč Pluton, Czech Republic; substitutions and fractionation trends

NASA Astrophysics Data System (ADS)

Škoda, Radek; Novák, Milan

2007-04-01

Aeschynite-group minerals (AGM) and euxenite-group minerals (EGM) occur in REL-REE euxenite-subtype pegmatites from the Třebíč Pluton, Czech Republic. They form strongly metamictized, light brown to black, equigranular to needle-like, subhedral to anhedral grains enclosed in blocky K-feldspar and less commonly in albite, and blocky quartz, and in the graphic unit (quartz and K-feldspar). Both AGM and EGM are homogeneous to slightly heterogeneous in BSE images. They are not commonly associated with the other primary Y,REE,Ti,Nb-bearing minerals, i.e. allanite-(Ce), monazite-(Ce), titanite, and ilmenite, which occur within the same textural-paragenetic unit. Aeschynite-(Y), aeschynite-(Ce), aeschynite-(Nd), nioboaeschynite-(Ce), tantalaeschynite-(Ce), vigezzite and polycrase-(Y) were identified using EMP and canonical discrimination analysis [Ercit, T.S., 2005a. Identification and alteration trends of granitic-pegmatite-hosted (Y,REE,U,Th)-(Nb,Ta,Ti) oxide minerals: a statistical approach. Can. Mineral. 43, 4 1291-1303.]. The exchange vector ACa B(Nb,Ta) A(Y,REE) - 1 BTi - 1 or its combination with the exchange vector ACa 2B(Nb,Ta) 3A(U,Th) - 1 A(Y,REE) - 1 BTi - 3 have been elucidated for the AGM. The exchange vector ACa A(U,Th) A(Y,REE) - 2 is predominant in the EGM. The AGM are enriched in HREE, whereas LREE are concentrated in the EGM. Weak to none-existent geochemical fractionations, as expressed by the U/(U + Th), Y/(Y + REE), Ta/(Ta + Nb) and (Nb + Ta)/(Ti + Nb + Ta) ratios, were noted for single grains from both the AGM and EGM, as well as in grains of polycrase-(Y) from four different textural-paragenetic units located in the Vladislav pegmatite. Simultaneous increase of U/(U + Th) and Y/(Y + REE) in the AGM during fractionation is typical. The Ta/(Ta + Nb) fractionation is usually weak and contradicts the Y/(Y + REE) and U/(U + Th) fractionation trends. This unusual behavior of Nb and Ta may be controlled by associated Ti-rich minerals (titanite, ilmenite, rutile), the composition of parental melt and/or by elevated F activity. The AGM and EGM from pegmatites of the Třebíč Pluton are quite similar in composition to those from REL-REE euxenite-subtype pegmatites in the Trout Creek Pass, Chaffee County, Colorado, USA, which are generally Ca,U,Th-depleted, show lower Ta/(Ta+Nb), and lower variation in HREE/LREE.

The behaviour of boron in a peraluminous granite-pegmatite system and associated hydrothermal solutions: a melt and fluid-inclusion study

NASA Astrophysics Data System (ADS)

Thomas, Rainer; Förster, Hans-Jürgen; Heinrich, Wilhelm

2002-09-01

Detailed analyses of melt and fluid inclusions combined with an electron-microprobe survey of boron-bearing minerals reveal the evolution of boron in a highly evolved peraluminous granite-pegmatite complex and the associated high- and medium-temperature ore-forming hydrothermal fluids (Ehrenfriedersdorf, Erzgebirge, Germany). Melt inclusions in granite represent embryonic pegmatite-forming melts containing about 10 wt% H2O and 1.8 wt% B2O3. These melts are also enriched in F, P, and other incompatible elements such as Be, Sn, Rb, and Cs. Ongoing differentiation and volatile enrichment drove the system into a solvus, where two pegmatite-forming melts coexisted. The critical point is at about 712 °C, 100 MPa, 20 wt% H2O and 4.1 wt% B2O3. Cooling and concomitant fractional crystallisation from 700 to 500 °C induced development of two conjugate melts, an H2O-poor (A-melt) and an H2O-rich melt (B-melt) along the opening solvus. Boron is a major element in both melts and is preferentially partitioned into the H2O-rich melt. Temperature-dependent distribution coefficients $ D{boron}{{B - melt/A - melt}} $ are 1.3 at 650 °C, 1.5 at 600 °C, and 1.8 at 500 °C. In both melts, boron concentrations decreased during cooling because of exsolution of a boron-rich hypersaline brine throughout the pegmatitic stage. Boromuscovite containing up to 8.5 wt% was another sink for boron at this stage. The end of the melt-dominated pegmatitic stage was attained at a solidus temperature of around 490 °C. Fluid inclusions of the hydrothermal stage reveal trapping temperatures of 480 to 370 °C, along with varying densities and highly variable B2O3 contents ranging from 0.20 to 2.94 wt%. A boiling system evolved, indicating a complex interplay between closed- and open-system behaviour. Pressure switched from lithostatic to hydrostatic and back, generating hydrothermal convection cells where meteoric waters were introduced and mixed with magmatic fluids. Boron-rich solutions originated from magmatic fluids, whereas boron-depleted fluids were mainly of meteoric origin. This highlights the potential of boron for discriminating fluids of different origin. Tin is continuously enriched during the evolution because tin and boron are cross-linked by formation of boron-, fluorine- and tin-fluorine-bearing complexes and is finally deposited within quartz-cassiterite veins during the transition from closed- to open-system behaviour. Boron does not only trace the complex evolution of the Ehrenfriedersdorf complex but exerts, together with H2O, F and P, an important control on the physical and chemical properties of pegmatite-forming melts, and particularly on the formation of a two-melt solvus at low pressure. We discuss this with respect to experimental results on H2O solubility and the critical behaviour of the haplogranite-water system which contained variable concentrations of volatiles.

The behaviour of boron in a peraluminous granite-pegmatite system and associated hydrothermal solutions: a melt and fluid-inclusion study

NASA Astrophysics Data System (ADS)

Thomas, Rainer; Förster, Hans-Jürgen; Heinrich, Wilhelm

Detailed analyses of melt and fluid inclusions combined with an electron-microprobe survey of boron-bearing minerals reveal the evolution of boron in a highly evolved peraluminous granite-pegmatite complex and the associated high- and medium-temperature ore-forming hydrothermal fluids (Ehrenfriedersdorf, Erzgebirge, Germany). Melt inclusions in granite represent embryonic pegmatite-forming melts containing about 10 wt% H2O and 1.8 wt% B2O3. These melts are also enriched in F, P, and other incompatible elements such as Be, Sn, Rb, and Cs. Ongoing differentiation and volatile enrichment drove the system into a solvus, where two pegmatite-forming melts coexisted. The critical point is at about 712 °C, 100 MPa, 20 wt% H2O and 4.1 wt% B2O3. Cooling and concomitant fractional crystallisation from 700 to 500 °C induced development of two conjugate melts, an H2O-poor (A-melt) and an H2O-rich melt (B-melt) along the opening solvus. Boron is a major element in both melts and is preferentially partitioned into the H2O-rich melt. Temperature-dependent distribution coefficients $ D{boron}{{B - melt/A - melt}} $ are 1.3 at 650 °C, 1.5 at 600 °C, and 1.8 at 500 °C. In both melts, boron concentrations decreased during cooling because of exsolution of a boron-rich hypersaline brine throughout the pegmatitic stage. Boromuscovite containing up to 8.5 wt% was another sink for boron at this stage. The end of the melt-dominated pegmatitic stage was attained at a solidus temperature of around 490 °C. Fluid inclusions of the hydrothermal stage reveal trapping temperatures of 480 to 370 °C, along with varying densities and highly variable B2O3 contents ranging from 0.20 to 2.94 wt%. A boiling system evolved, indicating a complex interplay between closed- and open-system behaviour. Pressure switched from lithostatic to hydrostatic and back, generating hydrothermal convection cells where meteoric waters were introduced and mixed with magmatic fluids. Boron-rich solutions originated from magmatic fluids, whereas boron-depleted fluids were mainly of meteoric origin. This highlights the potential of boron for discriminating fluids of different origin. Tin is continuously enriched during the evolution because tin and boron are cross-linked by formation of boron-, fluorine- and tin-fluorine-bearing complexes and is finally deposited within quartz-cassiterite veins during the transition from closed- to open-system behaviour. Boron does not only trace the complex evolution of the Ehrenfriedersdorf complex but exerts, together with H2O, F and P, an important control on the physical and chemical properties of pegmatite-forming melts, and particularly on the formation of a two-melt solvus at low pressure. We discuss this with respect to experimental results on H2O solubility and the critical behaviour of the haplogranite-water system which contained variable concentrations of volatiles.

Lead isotopic evidence for mixed sources of Proterozoic granites and pegmatites, Black Hills, South Dakota, USA

NASA Astrophysics Data System (ADS)

Krogstad, Eirik J.; Walker, Richard J.; Nabelek, Peter I.; Russ-Nabelek, Carol

1993-10-01

The lead isotopic compositions of K-feldspars separated from the ca. 1700 Ma Harney Peak Granite complex and spatially associated granitic pegmatites indicate that these rocks were derived from at least two sources. It has been reported previously that the core of the Harney Peak Granite complex is dominated by relatively lower/ gd18O (avg. 11.5 %.) granites, whereas higher / gd18O (avg. 13.2%.) granites occur around the periphery of the complex. The higher δ 18O granites and one simple pegmatite have low values of 207Pb /204Pb for their 206Pb /204Pb Thus, they likely were derived from a source with a short crustal residence time. This source may have been the pelitic schists into which the Harney Peak Granite complex and pegmatites were intruded. Feldspars from granites with lower / gd18O values have significantly higher 207Pb /204Pb for their 206Pb /204Pb . The data define a linear array with a slope equivalent to an age of ca. 2.6 Ga with t 2 defined to be 1.7 Ga. Such a slope could represent a mixing array or a secondary isochron for the source. These low δ18O granites could have been derived from a source with a high U/ Pb and with a crustal residence beginning before the Proterozoic. The source (s) of these granites may have been a sediment derived from late Archean continental crust. The highly evolved Tin Mountain pegmatite has lead isotopic systematics intermediate between those of the two granite groups, suggesting either a mixed source or contamination. Two late Archean granites, the Little Elk Granite and the Bear Mountain Granite, had precursors with high U/Pb and low Th/U histories. The Th/U history of the Bear Mountain Granite is too low for this rock to have been an important component of the source of the Proterozoic granites. However, crustal rocks with lead isotopic compositions similar to those of the Little Elk Granite were an important source of lead for some of the Proterozoic granitic rocks.

Complex pegmatite - apelitic of Cabecinha - strategies appreciation of geological heritage and economic development of the region

NASA Astrophysics Data System (ADS)

Nobre, José; Cabral, Tiago; Cabral, João; Gomes, Ana

2014-05-01

The Complex pegmatite - apelitic of Cabecinha corresponds to an isolated ridge that reaches 933 meters, located in the middle zone of transition between the Hesperian massif and the Cova da Beira being located in the NE central part of Portugal, more specifically in the Mountainous region of the province of Beira Alta, council of Sabugal. This complex lies embedded in porphyritic granites with terms of switching to a medium-grained granite rich in sodium feldspars in which they are muscovite granite intrusions. The lodes have pegmatites with NE-SW orientation, presenting phases of predominantly quartz crystallization with multiple parageneses. The inclusions observed are veins filonianian secondary. Some veins have structural discontinuity due to further their training tectonics. The apelitico material is basic in nature engaging in descontinuiddes of pegmatite material, showing no preferred orientation. The petrological characteristics of the area in question provide the appearance of motivating exotic landforms of scientific interest. These landforms, over time, have motivated the popular level the emergence of various myths, thus contributing to the enrichment of the local cultural heritage. This study proceeded to the geological and geomorphological mapping an area of about 6945,350 m2 with a maximum length of 182 m. The huge patent mineralogical, petrological and geomorphological level geodiversity, allied to the structural complexity and associated cultural heritage, allow geoconservation strategies and recovery, using new multimedia technologies including use of QR codes and 3D. All this geological framework and environment becomes an asset for the scientific, educational and economic development of the region. On the other hand, it has the vital Importance in the context of the strategy of forming a geological park, in the point of view of tourism, research and interpretation.

Contrasting accessory mineral behavior in minimum-temperature melts: Empirical constraints from the Himalayan metamorphic core

NASA Astrophysics Data System (ADS)

Cottle, John M.; Larson, Kyle P.; Yakymchuk, Chris

2018-07-01

Medium-grained leucogranite in the Tama Kosi region of the Nepalese Himalayan Metamorphic Core yields a relatively narrow range of monazite 208Pb/232Th dates with a dominant population at 21.0 Ma inferred to represent crystallization of an early plutonic phase. In contrast, the pegmatitic portion of the same intrusive complex, that cross-cuts the medium-grained leucogranite, contains zircon, monazite and xenotime that each display near-identical age spectra, recording semi-continuous (re-)crystallization from 27.5 Ma to 21.0 Ma, followed by a 2 m.y. hiatus then further (re-)crystallization between 19.4 and 18.6 Ma. The "gap" in pegmatite dates corresponds well to the crystallization age of the older leucogranite, whereas the end of accessory phase growth in the pegmatite coincides with the onset of regional-scale cooling. Detailed textural, trace element and thermochronologic data indicate that the range of zircon, monazite and xenotime dates recorded in the pegmatite reflect inherited components that underwent semi-continuous (re-)crystallization during metamorphism and/or anatexis in the source region(s), whereas dates younger than the hiatus indicate accessory phase recrystallization, related to both fluid influx and a concomitant increase in temperature. In contrast, the lack of an inherited component(s) in the medium-grained leucogranite phase is inferred to be a result of complete dissolution during partial melting. A model is proposed in which influx of heat and H2O-rich fluids associated with early leucogranite emplacement temporarily delayed zircon and monazite and xenotime crystallization, respectively. These data highlight the importance of measuring spatially resolved dates, trace elements and textural patterns from multiple accessory minerals combined with model constraints to better understand the often-complex crystallization history of anatectic melts in collisional orogens.

Hogtuvaite, a new beryllian member of the aenigmatite group from Norway, with new X-ray data on aenigmatite

USGS Publications Warehouse

Grauch, R.I.

1994-01-01

Hogtuvaite is a new beryllian member of the aenigmatite group that was discovered in Nordland County, Norway. It is a metamorphic mineral, hosted by Proterozoic granitic gneisses and mafic pegmatites of metamorphic origin. Compositional variations within and between gneiss-hosted samples of hogtuvaite are minimal; however, pegmatite-hosted samples of hogtuvaite are significantly different, containing less Al and Sn, and more Ti and Mn, than those from the gneisses. The mineralogical, optical and crystallographic properties of hogtuvaite are described. A new and uniquely indexed set of X-ray powder diffraction data for aenigmatite is presented. -from Authors

Crisp clustering of airborne geophysical data from the Alto Ligonha pegmatite field, northeastern Mozambique, to predict zones of increased rare earth element potential

NASA Astrophysics Data System (ADS)

Eberle, Detlef G.; Daudi, Elias X. F.; Muiuane, Elônio A.; Nyabeze, Peter; Pontavida, Alfredo M.

2012-01-01

The National Geology Directorate of Mozambique (DNG) and Maputo-based Eduardo-Mondlane University (UEM) entered a joint venture with the South African Council for Geoscience (CGS) to conduct a case study over the meso-Proterozoic Alto Ligonha pegmatite field in the Zambézia Province of northeastern Mozambique to support the local exploration and mining sectors. Rare-metal minerals, i.e. tantalum and niobium, as well as rare-earth minerals have been mined in the Alto Ligonha pegmatite field since decades, but due to the civil war (1977-1992) production nearly ceased. The Government now strives to promote mining in the region as contribution to poverty alleviation. This study was undertaken to facilitate the extraction of geological information from the high resolution airborne magnetic and radiometric data sets recently acquired through a World Bank funded survey and mapping project. The aim was to generate a value-added map from the airborne geophysical data that is easier to read and use by the exploration and mining industries than mere airborne geophysical grid data or maps. As a first step towards clustering, thorium (Th) and potassium (K) concentrations were determined from the airborne geophysical data as well as apparent magnetic susceptibility and first vertical magnetic gradient data. These four datasets were projected onto a 100 m spaced regular grid to assemble 850,000 four-element (multivariate) sample vectors over the study area. Classification of the sample vectors using crisp clustering based upon the Euclidian distance between sample and class centre provided a (pseudo-) geology map or value-added map, respectively, displaying the spatial distribution of six different classes in the study area. To learn the quality of sample allocation, the degree of membership of each sample vector was determined using a-posterior discriminant analysis. Geophysical ground truth control was essential to allocate geology/geophysical attributes to the six classes. The highest probability to meet pegmatite bodies is in close vicinity to (magnetic) amphibole schist occurring in areas where depletion of potassium as indication of metasomatic processes is evident from the airborne radiometric data. Clustering has proven to be a fast and effective method to compile value-added maps from multivariate geophysical datasets. Experience made in the Alto Ligonha pegmatite field encourages adopting this new methodology for mapping other parts of the Mozambique Fold Belt.

In Situ Observations of Crystallization in Water-Undersaturated Pegmatite Liquids

NASA Astrophysics Data System (ADS)

Sirbescu, M. L. C.; Wilke, M.; Gehrmann, S.; Schmidt, C.

2014-12-01

Crystallization behavior of water-undersaturated haplogranite-Li-B-H2O melts was observed and recorded in diamond anvil cell (DAC) experiments. We have generated salient pegmatitic features such as coarse and zoned crystals; comb and radiating textures; and graphic intergrowths from moderately-fluxed granitic melts in the absence of a hydrous phase. The experimental conditions placed the hydrous melt under variable degrees of undercooling between their liquidus and glass transition. Undercooling of ~100-150°C below the liquidus produced crystals that reached 0.4 of cell diameter in less than one day. The starting material was a homogeneous glass with 2% Li2O, 4.6% B2O3, and 3.0 or 6.5% H2O synthesized in an internally heated pressure vessel at 1200°C and 400 MPa. The composition was selected to approximate bulk cores of Li-rich pegmatites. The crystallization temperature was dropped in 50°C intervals from 600°C to 400°C to simulate pegmatite cooling. Run duration was < 3.2 days. The pressure of ~150 to 450 MPa was generated isochorically, based on a preconfigured ratio of glass to void space (created by femtosecond laser drilling) included in the cell. The shift in the wavenumber of the ν3-SiO4Raman band of a chemically inert zircon crystal was used to determine pressure as a function of temperature. Reproducible phase assemblages were documented using Raman spectroscopy and EPMA. Virgilite (solid solution between SiO2 and LiAlSi2O6) nucleated at T≤600°C. Alkali-feldspar and muscovite nucleated at T≤550°C. Virgilite and alkali-feldspar nucleated heterogeneously on surfaces of zircon, gasket, and diamond windows (see attached figure), whereas muscovite nucleated homogeneously. Development of pegmatite texture was facilitated by the relatively low nucleation density at P of ~300 to 400 MPa. Radically higher nucleation density at an estimated P of <2.5 GPa led to an equigranular, fine-grained texture. Time-lapse photography allowed for accurate growth-rate measurements and demonstrated constant volumetric growth rate of unobstructed crystals at low to moderate fraction of crystallization. The DAC experiments complement prior kinetic studies conducted in 3 to 60 day-long time series runs in cold-seal vessels. This technique has a great potential for further applications in physical petrology.

Constraints on the timing of multiple thermal events and re-equilibration recorded by high-U zircon and xenotime: Case study of pegmatite from Piława Górna (Góry Sowie Block, SW Poland)

NASA Astrophysics Data System (ADS)

Budzyń, Bartosz; Sláma, Jiří; Kozub-Budzyń, Gabriela A.; Konečný, Patrik; Holický, Ivan; Rzepa, Grzegorz; Jastrzębski, Mirosław

2018-06-01

The application of zircon and xenotime geochronometers requires knowledge of their potential and limitations related to possible disturbance of the age record. The alteration of the intergrown zircon and xenotime in pegmatite from the Góry Sowie Block (SW Poland) was studied using the electron microprobe analysis, X-ray WDS compositional mapping, micro-Raman analysis, and LA-ICP-MS U-Pb dating of zircon and xenotime, as well as the U-Th-total Pb dating of uraninite. These microanalytical techniques were applied to understand the formation mechanisms of the secondary textures related to post-magmatic processes in the zircon and xenotime intergrowth, and to constrain their timing. Textural and compositional features combined with U-Pb data indicate that the pegmatite-related crystallization of the zircon and xenotime intergrowth occurred ca. 2.09 Ga (2086 ± 35 Ma for zircon and 2093 ± 52 Ma for xenotime), followed by the re-equilibration of zircon and xenotime ca. 370 Ma (373 ± 18 Ma and 368 ± 6 Ma, respectively) during the formation of the younger pegmatite. The zircon and xenotime were most likely derived from Precambrian basement rocks and emplaced in the pegmatite as a restite. The zircon preserved textures related to diffusion-reaction processes that affected its high-U core (up to ca. 9.6 wt% UO2), which underwent further metamictization and amorphization due to self-radiation damage. The zircon rim and xenotime were affected by coupled dissolution-reprecipitation processes that resulted in patchy zoning, age disturbance and sponge-like textures. Xenotime was also partially replaced by fluorapatite or hingganite-(Y) and Y-enriched allanite-(Ce). The termination of the low-temperature alteration was constrained by the U-Th-total Pb age of the uraninite inclusions that crystallized in zircon at 281 ± 2 Ma, which is consistent with the age of 278 ± 15 Ma obtained from the youngest cluster of U-Pb ages in the re-equilibrated high-U zircon domains. This study demonstrates the importance of the careful examination of compositional, microtextural and geochronological data obtained using microanalytical techniques to reconstruct the complex thermal histories recorded by accessory minerals.

Gamma-rays and heat-treatment conversions of point defects in massive rose quartz from the Borborema Pegmatite Province, Northeast Brazil

NASA Astrophysics Data System (ADS)

Guzzo, Pedro L.; Barreto, Sandra B.; Miranda, Milena R.; Gonzaga, Raysa S. G.; Casals, Sandra A.

2017-11-01

An extensive characterization of trace elements and point defects in rose quartz from the Borborema Pegmatite Province (BPP) in the northeast of Brazil was carried out by complementary spectroscopic methods. The aim here was to document the change in the configuration of point defects into the quartz lattice induced by heat-treatment and ionizing radiation. The samples were extracted from the core of two granitic rare element (REL) pegmatites, Taboa (Carnaúba dos Dantas, RN) and Alto do Feio (Pedra Lavrada, PB). The contents of Al, P, Ti, Ni, Fe, Ge, Li, Be, B and K were measured by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Polished plates were heat-treated at 500 and 1000 °C and then irradiated with 50 kGy of γ rays. Point defects were characterized by optical (UV-Vis), infrared (IR), and electron paramagnetic resonance (EPR) spectroscopies. In the as-received condition, [AlO4/H]0 centers, Li- and B-dependent OH defects were observed. Point defects related to Al and Li species were significantly affected by heat-treatment at 1000 °C and/or γ radiation. Paramagnetic centers such as [AlO4]0, [GeO4/Li]0, [TiO4/Li]0 and [O2 3-/Li]0 were created by the diffusion of Li+ ions from their original diamagnetic centers related to substitutional Al3+ and OH-species. The smoky color developed after irradiation and the signal intensities of the paramagnetic centers were independent from the original rose color grade. The samples from the Taboa (TB) pegmatite showed the highest concentration of Al, Ti, Fe and Li elements as well as the highest signal intensities for [AlO4]0, [AlO4/H]0, [GeO4/Li]0 and [TiO4/Li]0 centers. Although TB also showed the higher concentration of B element, the intensity of the 3597 cm-1 IR band related to [BO4/H]0 centers was higher for Alto do Feio (AF) samples. This result suggests that the uptake of B into the quartz core of each pegmatite took place through different mechanisms. It was concluded that the change in the point defect configuration was essentially governed by the motion of Li species whose incorporation into the quartz lattice is closely related to Al concentration.

Mineralogical and geochemical evolution of micas from miarolitic pegmatites of the anorogenic pikes peak batholith, Colorado

USGS Publications Warehouse

Foord, E.E.; Cerny, P.; Jackson, L.L.; Sherman, David M.; Eby, R.K.

1995-01-01

A suite of 29 micas from miarolitic pegmatites associated with granitic units of the anorogenic Pikes Peak batholith (1.08-1.02 Ga), Colorado range in composition, and follow in paragenetic sequence, from 1M siderophyllite (N = 1), and 3T or 2M1 lithian biotite (N = 5) to 1M zinnwaldite (N = 20) and 1M ferroan lepidolite (N = 1). Locally, 1M (?) phlogopite (N = 1) and ferroan 2M1 muscovite (N = 1) are also present. Pervasive, late-stage hydrothermal alteration along with possible supergene weathering of many of these micas produced vermiculite. Additionally, some vugs and cavities were filled with chlorite and/or smectite. Early crystallized micas form tapered columnar crystals in graphic pegmatite, growing toward, and adjacent to the miarolitic cavity zone which contains the later crystallized micas. Principal associated minerals are quartz, microcline perthite (mostly amazonite), and albite, with local topaz or fluorite, and rarely tourmaline (schorl-elbaite). Progressively younger micas of the main crystallization sequence display increasing Si, Li, F, and Al/Ga, and decreasing total Fe, Mg, and octahedral occupancy. The zinc content of all micas is considerably elevated, whereas Mn, Rb, Cs, and Sc are moderate and T1 is very low. Early siderophyllite and lithian biotite show a narrow range of FeO/Fe2O3 (5.6-8.0), whereas later zinnwaldite is much more variable (2.4-40.3). Annite of the host granite and early graphic pegmatite is compositionally homogeneous, but most mica crystals from cavities show remarkable compositional and abrupt, sharp and distinct color zoning. Most cavity-grown zinnwaldite crystals show a decrease, from core to rim, in total Fe and Mg, whereas Si, Li and F increase and Mn, Rb, Cs and Na are essentially constant. A few to more than 100 color zones have been identified in some mica crystals. The zones are well correlated with the Ti content (<0.2 wt. % TiO2 colorless, 0.4-0.6 wt.% TiO2 red-brown). The total Fe content may or may not correlate with color zoning, whereas Zn variations (up to 1.1 wt. %) are entirely independent. The dark color zones probably reflect Fe-Ti charge transfer. The mica composition sequence described here is typical of the extreme fractionation observed in pegmatites of the NYF family, associated with anorogenec granites. Elevated Fe, Zn, and enhanced Sc contents are characteristic of this family. Strong enrichment in Li, Rb, and F is present, particularly in the micas of the miarolitic cavities. Sharp color zonation and compositional variation in cavity-grown zinnwaldite and ferroan lepidolite crystals suggest rapid changes in the intensive parameters, particularly the f(O2), of the parent fluid during the final stages of pegmatite consolidation ?? 1995 Springer-Verlag.

Application of Data-Driven Evidential Belief Functions to Prospectivity Mapping for Aquamarine-Bearing Pegmatites, Lundazi District, Zambia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carranza, E. J. M., E-mail: carranza@itc.nl; Woldai, T.; Chikambwe, E. M.

A case application of data-driven estimation of evidential belief functions (EBFs) is demonstrated to prospectivity mapping in Lundazi district (eastern Zambia). Spatial data used to represent recognition criteria of prospectivity for aquamarine-bearing pegmatites include mapped granites, mapped faults/fractures, mapped shear zones, and radioelement concentration ratios derived from gridded airborne radiometric data. Data-driven estimates EBFs take into account not only (a) spatial association between an evidential map layer and target deposits but also (b) spatial relationships between classes of evidences in an evidential map layer. Data-driven estimates of EBFs can indicate which spatial data provide positive or negative evidence of prospectivity.more » Data-driven estimates of EBFs of only spatial data providing positive evidence of prospectivity were integrated according to Dempster's rule of combination. Map of integrated degrees of belief was used to delineate zones of relative degress of prospectivity for aquamarine-bearing pegmatites. The predictive map has at least 85% prediction rate and at least 79% success rate of delineating training and validation deposits, respectively. The results illustrate usefulness of data-driven estimation of EBFs in GIS-based predictive mapping of mineral prospectivity. The results also show usefulness of EBFs in managing uncertainties associated with evidential maps.« less

Exploring the U-Pb systematics of titanite from the Archean Stillwater Complex

NASA Astrophysics Data System (ADS)

Friedman, R. M.; Wall, C. J.; Scoates, J. S.; Weis, D. A.; Meurer, W. P.

2011-12-01

The Stillwater Complex is a large mafic-ultramafic layered intrusion in the Beartooth Mountains of Montana (USA) and host to the world-class J-M Reef platinum group element deposit. The size and geologic/economic importance of this igneous complex make it an important target for high-precision U-Pb dating. As a part of a comprehensive U-Pb study of the Stillwater Complex, we present ID-TIMS U-Pb titanite data, including new single grain results produced using the EARTHTIME ET535 spike, for very low-volume, relatively felsic granophyric and pegmatitic rocks associated with Stillwater layered rocks. Four samples studied include a pegmatitic ksp-qtz core to a gabbroic pegmatoid in the Lower Banded Series (N1), an alaskite (quartz diorite) and an amphibole-rich reaction zone between the alaskite and anorthosite (AN1) in the Middle Banded Series, and an amphibole-bearing granophyre from the Upper Banded Series (GN3). CA-TIMS U-Pb dating of zircon from these samples yielded concordant results only for the pegmatitic rock (weighted 207Pb/206Pb: 2709.65 ± 0.80 Ma, n = 5), which agrees with new zircon ages from Stillwater layered rocks. Results for high-U (up to 1438 ppm) metamict zircon that occurs in the other three rocks were highly discordant and did not yield precise ages. Titanite U-Pb results for the pegmatite are about -1% to +1% discordant with two groupings of 207Pb/206Pb dates: one with a weighted average of 2708.1 ± 2.0 Ma (n = 2), which overlaps in age with zircon from the same sample and the crystallization age of the Stillwater Complex, and a second, younger grouping of 2701.1 ± 1.3 Ma (n = 5). Younger dates record an early Pb-loss event, possibly related to intrusion of cross-cutting quartz monzonites. The alaskite data also shows two groupings of 207Pb/206Pb dates, although more subtle: a weighted average of 2709.3 ± 1.8 Ma (n = 3) and a single result of 2706.5 ± 1.7 Ma. Titanite from the other two samples has undergone significant Pb-loss. Results for four analyses from the reaction zone sample are 1.74-54.3% discordant and lie in a quasi-linear array with intercepts at ca. 2700 Ma and 325 Ma. Data for the granophyre in the Upper Banded Series also have a wide range of discordance (1.5-3.4%, 21.4% and 61.3%). Titanites from these samples appear to have undergone a two stage Pb-loss history: an early, relatively minor event as suggested for the pegmatite, and a subsequent episode, which for some grains resulted in significant discordance. Concordant U-Pb titanite data from two of the Stillwater Complex granophyres confirms nearly synchronous crystallization with that of the layered rocks in the intrusion. For the pegmatite, the ages and overlap of zircon and titanite suggest a direct relationship between the granophyres and the layered rock and relatively rapid cooling of the complex through titanite closure temperature. Titanite from the alaskite yields useful age information, whereas coexisting zircon are highly discordant and not age diagnostic.

Geology of the Plumtree area, Spruce Pine district, North Carolina

USGS Publications Warehouse

Brobst, Donald Albert

1953-01-01

This report describes the results of study and geologic mapping (1:12,000) in the 70-square-mile Plumtree area in the northeastern part of the Spruce Pine pegmatite district, on the Blue Ridge upland in western North Carolina. The district has been the chief domestic source of feldspar and sheet mica. The mining belt just west of the Blue Ridge Front trends northeast and is 25 miles long and 10 miles wide. The center of the Plumtree area lies 10 miles northeast of Spruce Pine pegmatite district, on the Blue Ridge upland in western North Carolina. The district has been the chief domestic source of feldspar and sheet mica. The mining belt just west of the Blue Ridge Front trends northeast and is 25 miles long and 10 miles wide. The center of the Plumtree area lies 10 miles northeast of Spruce Pine and includes parts of Mitchell and Avery Counties shown on the portions of the 7.5-minute Spruce Pine, Linville Falls, Newland, North Carolina, and Carvers Gap, North Carolina and Tennessee quadrangle. The topography varies from rugged mountains to rounded or flat topped hills near the entrenched, meandering master streams. Old erosion surfaces are approximately 600,1,100, 1,500, and 2,500 feet above the present master stream level. The area is in late youth or early maturity after rejuvenation.. The regionally metamorphosed rocks of the amophibolite facies form three mappable units: mica gneiss, mica schist, and hornblende rock. These rocks, perhaps of Precambrian age, are intimately interlayered with thicknesses of the individual layers ranging from less than one inch to several tons of feet. Field relationships and chemical data suggest that the mica (Carolina-type) rocks were derived from sandstones, graywackes, and shales and that the hornblende-rich (Roan-type) layers were derived from impure carbonate rocks. The igneous rocks include alaskite and associated pegmatite of early Paleozoic age (?), dunite and associated soapstone of a prepegmatite age, and a few diabasic dikes of post-pegmatite age (Triassic?). The alaskite and pegmatite have similar bulk compositions, notably low in iron (0.3 percent). The major constituents in order of decreasing abundance are plagioclase, perthitic microcline, quartz, and muncovite. All of these minerals, as well as clay deposits derived from the weathering of alaskite under old terraces, have economic value. The zoned pegmatites contain fewer zones which are less complex mineralogically than those in the pegmatites of many other areas. These essentially unmetamorphosed bodies were intruded approximately at the peak of the regional metamorphism. Their emplacement was controlled by local structure and rock type. The source of this igneous material may have been the mobilized portions of the Cranberry gneiss which underlies the area. The dunite bodies were intruded early in the metamorphic cycle. The bodies are commonly zoned: from the wall rock inwards (1) talc-antrophyllite-serpentine fringe, (3) serpentinized dunite, (3) granular olivine core. Dunite, chromite, vermiculite, and anthophyllite are the major economic commodities. Extensive hydrothermal alteration of dunite bodies produced soapstone. The area is the northeast end of a southwest plunging synclinorium about 20 miles wide with the steeper limb on the northwest side. There are three structural zones: zone I on the northwest is characterized by the northeast-trending isoclinal folds with steep southeast dips; zone II on the southwest includes an area of rocks with low and variable dip; zone III is the complex central core. In the extreme northeast zones I and II have an indistinct boundary where they coalesce along the rim of the synclinorium. Six stratigraphic units are exposed totaling approximately 10,500 feet of metamorphic rocks. Small scale structural features include a foliation, and a lineation in the planes of the foliation. Minor folding reflects the trends of the major structures. There are randomly orient

Boromuscovite, a new member of the mica group, from the Little Three mine pegmatite, Ramona district, San Diego County, California

USGS Publications Warehouse

Foord, E.E.; Martin, R.F.; Fitzpatrick, J.J.; Taggart, J.E.; Crock, J.G.

1991-01-01

Boromuscovite, ideally KAl2(Si3B)O10(OH,F)2, in which [4]Al is replaced by B relative to muscovite, occurs as a late-stage, postpocket rupture mineral within the New Spaulding Pocket, main Little Three pegmatite dike. The mineral is white to cream colored and occurs as a porcelaneous veneer and coating on primary minerals. The average grain size is less than 3-4 ??m, but the coatings may be as much as 1 cm or more thick. Fragments of topaz, albite, elbaite, and other pocket minerals are included in the coating. The boromuscovite precipitated from a late-stage hydothermal fluid; it occurs only as a snowlike coating. Chemical composition, unit-cell parameters, Mohs hardness, cleavage, fracture, and optical properties are reported. -from Authors

Lithium

USGS Publications Warehouse

Bradley, Dwight C.; Stillings, Lisa L.; Jaskula, Brian W.; Munk, LeeAnn; McCauley, Andrew D.; Schulz, Klaus J.; DeYoung,, John H.; Seal, Robert R.; Bradley, Dwight C.

2017-12-19

Lithium, the lightest of all metals, is used in air treatment, batteries, ceramics, glass, metallurgy, pharmaceuticals, and polymers. Rechargeable lithium-ion batteries are particularly important in efforts to reduce global warming because they make it possible to power cars and trucks from renewable sources of energy (for example, hydroelectric, solar, or wind) instead of by burning fossil fuels. Today, lithium is extracted from brines that are pumped from beneath arid sedimentary basins and extracted from granitic pegmatite ores. The leading producer of lithium from brine is Chile, and the leading producer of lithium from pegmatites is Australia. Other potential sources of lithium include clays, geothermal brines, oilfield brines, and zeolites. Worldwide resources of lithium are estimated to be more than 39 million metric tons, which is enough to meet projected demand to the year 2100. The United States is not a major producer at present but has significant lithium resources.

Additional studies on mixed uranyl oxide-hydroxide hydrate alteration products of uraninite from the palermo and ruggles granitic pegmatites, grafton county, New Hampshire

USGS Publications Warehouse

Foord, E.E.; Korzeb, S.L.; Lichte, F.E.; Fitzpatrick, J.J.

1997-01-01

Additional studies on an incompletely characterized secondary uranium "mineral" from the Ruggles and Palermo granitic pegmatites, New Hampshire, referred to as mineral "A" by Frondel (1956), reveal a mixture of schoepite-group minerals and related uranyl oxide-hydroxide hydrated compounds. A composite chemical analysis yielded (in wt.%): PbO 4.85 (EMP), UO3 83.5 (EMP), BaO 0.675 (av. of EMP and ICP), CaO 0.167 (av. of EMP and ICP), K2O 2.455 (av. of EMP and ICP), SrO 0.21 (ICP), ThO2 0.85 (ICP), H2O 6.9, ??99.61. Powder-diffraction X-ray studies indicate a close resemblance in patterns between mineral "A" and several uranyl oxide-hydroxide hydrated minerals, including the schoepite family of minerals and UO2(OH)2. The powder-diffraction data for mineral "A" are most similar to those for synthetic UO2.86??1.5H2O and UO2(OH)2, but other phases are likely present as well. TGA analysis of both mineral "A" and metaschoepite show similar weight-loss and first derivative curves. The dominant losses are at 100??C, with secondary events at 400?? and 600??C. IR spectra show the presence of (OH) and H2O. Uraninite from both pegmatites, analyzed by LAM-ICP-MS, shows the presence of Th, Pb, K and Ca.

Mesoproterozoic graphite deposits, New Jersey Highlands: Geologic and stable isotopic evidence for possible algal origins

USGS Publications Warehouse

Volkert, R.A.

2000-01-01

Graphite deposits of Mesoproterozoic age are locally abundant in the eastern New Jersey Highlands, where they are hosted by sulphidic biotite-quartz-feldspar gneiss, metaquartzite, and anatectic pegmatite. Gneiss and metaquartzite represent a shallow marine shelf sequence of locally organic-rich sand and mud. Graphite from massive deposits within metaquartzite yielded ??13C values of -26 ?? 2??? (1??), and graphite from massive deposits within biotite-quartz-feldspar gneiss yielded ??13C values of -23 ??4???. Disseminated graphite from biotite-quartz-feldspar gneiss country rock was -22 ??3???, indistinguishable from the massive deposits hosted by the same lithology. Anatectic pegmatite is graphitic only where generated from graphite-bearing host rocks; one sample gave a ??13C value of -15???. The ??34S values of trace pyrrhotite are uniform within individual deposits, but vary from 0 to 9??? from one deposit to another. Apart from pegmatitic occurrences, evidence is lacking for long-range mobilization of carbon during Grenvillian orogenesis or post-Grenvillian tectonism. The field, petrographic, and isotope data suggest that massive graphite was formed by granulite-facies metamorphism of Proterozoic accumulations of sedimentary organic matter, possibly algal mats. Preservation of these accumulations in the sedimentary environment requires anoxic basin waters or rapid burial. Anoxia would also favour the accumulation of dissolved ferrous iron in basin waters, which may explain some of the metasediment-hosted massive magnetite deposits in the New Jersey Highlands. ?? 2000 NRC.

Radioactive deposits in California

USGS Publications Warehouse

Walker, George W.; Lovering, Tom G.

1954-01-01

Reconnaissance examination by Government geologists of many areas, mine properties, and prospects in California during the period between 1948 and 1953 has confirmed the presence of radioactive materials in place at more than 40 localities. Abnormal radioactivity at these localities is due to concentrations of primary and secondary uranium minerals, to radon gas, radium (?), and to thorium minerals. Of the known occurrences only three were thought to contain uranium oxide (uranitite or pitchblende), 4 contained uranium-bearing columbate, tantalate, or titanate minerals, 12 contained secondary uranium minerals, such as autunite, carnotite, and torbernite, one contained radon gas, 7 contained thorium minerals, and, at the remaining 16 localities, the source of the anomalous radiation was not positively determined. The occurrences in which uranium oxide has been tentatively identified include the Rathgeb mine (Calaveras County), the Yerih group of claims (San Bernardino County), and the Rainbow claim (Madera County). Occurrences of secondary uranium minerals are largely confined to the arid desert regions of south-eastern California including deposits in San Bernardino, Kern, Inyo, and Imperial Counties. Uranium-bearing columbate, tantalate, or titanate minerals have been reported from pegmatite and granitic rock in southeastern and eastern California. Thorium minerals have been found in vein deposits in eastern San Bernardino County and from pegmatites and granitic rocks in various parts of southeastern California; placer concentrations of thorium minerals are known from nearly all areas in the State that are underlain, in part, by plutonic crystalline rocks. The primary uranium minerals occur principally as minute accessory crystals in pegmatite or granitic rock, or with base-metal sulfide minerals in veins. Thorium minerals also occur as accessory crystals in pegmatite or granitic rock, in placer deposits derived from such rock, and, at Mountain Pass, in veins containing rare earths. Secondary uranium minerals have been found as fracture coatings and as disseminations in various types of wall rock, although they are largely confined to areas of Tertiary volcanic rocks. Probably the uranium in the uraniferous deposits in California is related genetically to felsic crystalline rocks and felsic volcanic rocks; the present distribution of the secondary uranium minerals has been controlled, in part, by circulating ground waters and probably, in part, by magmatic waters related to the Tertiary volcanic activity. The thorium minerals are genetically related to the intrusion of pegmatite and plutonic crystalline rocks. None of the known deposits of radioactive minerals in California contain marketable reserves of uranium or thorium ore under economic conditions existing in 1952. With a favorable local market small lots of uranium ore may be available in the following places: the Rosamund prospect, the Rafferty and Chilson properties, the Lucky Star claim, and the Yerih group. The commercial production of thorium minerals will be possible, in the near future, only if these minerals can be recovered cheaply as a byproduct either from the mining of rare earths minerals at Mountain Pass or as a byproduct of placer mining for gold.

Partial melting of amphibolite to trondhjemite at Nunatak Fiord, St. Elias Mountains, Alaska

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barker, F.; McLellan, E.L.; Plafker, G.

1985-01-01

At Nunatak Fiord, 55km NE of Yakutat, Alaska, a uniform layer of Cretaceous basalt ca. 3km thick was metamorphosed ca. 67 million years ago to amphibolite and locally partially melted to pegmatitic trondhjemite. Segregations of plagioclase-quartz+/-biotite rock, leucosomes in amphibolite matrix, range from stringers 5-10mm thick to blunt pods as thick as 6m. They tend to be parallel to foliation of the amphibolite, but crosscutting is common. The assemblage aluminous hornblende-plagioclase-epidote-sphene-quartz gave a hydrous melt that crystallized to plagioclase-quartz+/-biotite pegmatitic trondhjemite. 5-10% of the rock melted. Eu at 2x chondrites is positively anomalous. REE partitioning in melt/residum was controlled largelymore » by hornblende and sphene. Though the mineralogical variability precludes quantitative modeling, partial melting of garnet-free amphibolite to heavy-REE-depleted trondhjemitic melt is a viable process.« less

Minor elements in Keweenawan lavas, Michigan

USGS Publications Warehouse

Cornwall, H.R.; Rose, H.J.

1957-01-01

The distribution of minor elements in three basaltic flows of the Keweenawan series, of Michigan, is related to differentiation in the flows. Thus, nickel is most abundant in the early differentiates; nickel, chromium, and barium are generally deficient in the pegmatites, which formed late; whereas copper, vanadium, yttrium, and other minor elements are concentrated in the pegmatites. The minor-element content of individual minerals in the Greenstone flow varies markedly from one mineral to another and seems to depend primarily on the presence or absence in the minerals of major elements for which the minor elements can substitute. Minor elements have substituted most readily for those major elements with similar ionic radii. Valence and electronegativity also seem to influence the ease of substitution. The distribution of other minor elements in copper-bearing lodes of the Michigan copper district shows no apparent relation to copper mineralization. ?? 1957.

Multi-stage evolution of xenotime-(Y) from Písek pegmatites, Czech Republic: an electron probe micro-analysis and Raman spectroscopy study

NASA Astrophysics Data System (ADS)

Švecová, E.; Čopjaková, R.; Losos, Z.; Škoda, R.; Nasdala, L.; Cícha, J.

2016-12-01

The chemical variability, degree of radiation damage, and alteration of xenotime from the Písek granitic pegmatites (Czech Republic) were investigated by micro-chemical analysis and Raman spectroscopy. Dominant large xenotime-(Y) grains enriched in U, Th and Zr crystallized from a melt almost simultaneously with zircon, monazite and tourmaline. Xenotime is well to poorly crystalline depending on its U and Th contents. It shows complex secondary textures cutting magmatic growth zones as a result of its interaction with F,Ca,alkali-rich fluids during the hydrothermal stage of the pegmatite evolution. The magmatic xenotime underwent intense secondary alteration, from rims inwards, resulting in the formation of inclusion-rich well crystalline xenotime domains of near end-member composition. Two types of recrystallization were distinguished in relation to the type of inclusions: i) xenotime with coffinite-thorite, cheralite and monazite inclusions and ii) xenotime with zirconcheralite and zircon inclusions. Additionally, inner poorly crystalline U,Th-rich xenotime domains were locally altered, hydrated, depleted in P, Y, HREE, U, Si and radiogenic Pb, and enriched in fluid-borne cations (mainly Ca, F, Th, Zr, Fe). Interaction of radiation-damaged xenotime with hydrothermal fluids resulted in the disturbance of the U-Th-Pb system. Alteration of radiation-damaged xenotime was followed by intensive recrystallization indicating the presence of fluids >200 °C. Subsequently other types of xenotime formed as a consequence of fluid-driven alteration of magmatic monazite, and Y,REE,Ti,Nb-oxides or crystallized from hydrothermal fluids along cracks in magmatic monazite and xenotime.

Geology and ore deposits of the Chicago Creek area, Clear Creek County, Colorado

USGS Publications Warehouse

Harrison, J.E.; Wells, J.D.

1956-01-01

The Chicago Creek area, Clear Creek County, Colo., forms part of the Front Range mineral belt, which is a northeast-trending belt of coextensive porphyry intrusive rocks and hydrothermal veins of Tertiary age. More than $4.5 million worth of gold, silver, copper, lead, zinc, and uranium was produced from the mines in the area between 1859 and 1954. This investigation was made by the Geological survey on behalf of the Division of Raw Materials of the U.S. Atomic Energy Commission. The bedrock in the area is Precambrian and consists of igneous rocks, some of which have been metamorphosed , and metasedimentary rocks. The metasedimentary rocks include biotite-quartz-plagioclase gneiss that is locally garnetiferous, sillimanitic biotite-quartz gneiss, amphibolite, and lime-silicate gneiss. Rocks that may be metasedimentary or meta-igneous are quartz monzonite gneiss and granite gneiss and pegmatite. The granite gneiss and pegmatite locally form a migmatite with the biotitic metasedimentary rocks. These older rocks have been intruded by granodiorite, quartz, and granite pegmatite. During Tertiary time the Precambrian rocks were invaded by dikes and plugs of quartz monzonite porphyry, alaskite porphyry, granite porphyry, monzonite porphyry, bostonite and garnetiferous bostonite porphyry, quartz bostonite porphyry, trachytic granite porphyry, and biotite-quartz latite-porphyry. Solifluction debris of Wisconsin age forms sheets filling some of the high basins, covering some of the steep slopes, and filling parts of some of the valleys; talus and talus slides of Wisconsin age rest of or are mixed with solifluction debris in some of the high basins. Recent and/or Pleistocene alluvium is present along valley flats of the larger streams and gulches. Two periods of Precambrian folding can be recognized in the area. The older folding crumpled the metasedimentary rocks into a series of upright and overturned north-northeast plunging anticlines and synclines. Quartz monzonite gneiss, granite gneiss and pegmatite, granodiorite, and quartz diorite and associated hornblendite are metamorphosed during this period. The second period of folding appears to have been the reflection at depth of faulting nearer the surface; it resulted in crushing as well as some folding of the already folded rocks into terrace and monoclinal folds that plunge gently east-northeast. The biotite-muscovite granite, which is the youngest major Precambrian rock unit, is both concordant (phacolithic) and crosscutting along the older fold system and has been fractured by the younger fold system.

The role of diffusion-controlled oscillatory nucleation in the formation of line rock in pegmatite-aplite dikes

USGS Publications Warehouse

Webber, K.L.; Falster, A.U.; Simmons, W.B.; Foord, E.E.

1997-01-01

The George Ashley Block (GAB), located in the Pala Pegmatite District, San Diego County, California, is a composite pegmatite-aplite dike of 8 m thickness displaying striking mineralogical layering in the aphte portion of the dike, referred to as line rock. Rhythmic layering is characterized by garnet-rich bands alternating with albite-quartz-muscovite-rich bands. Cumulus textures are notably absent from the layered portion of the dike. Elongated quartz, megacrysts are oriented perpendicular to the garnet-rich layers and poikilitically include garnet, albite, and muscovite. Calculated crystal-free magma viscosity with 3% H2O is 106.2 Pa s and the calculated settling velocity for garnet is 0??51 cm/year. Conductive cooling calculations based on emplacement of a 650??C dike into 150?? C fractured gabbroic country rock at 1??5 kbar, and accounting for latent heat of crystallization, demonstrate that the line rock portion of the dike cools to 550?? C in about 1 year. Crystal size distribution studies also suggest very rapid nucleation and crystallization. Diffusion-controlled gel crystallization experiments yield textures virtually identical to those observed in the layered aplite, including rhythmic banding, colloform layering, and band discontinuities. Thus, observed textures and calculated magmatic parameters suggest that mineralogical layering in the GAB results from an in situ diffusion-controlled process of oscillatory nucleation and crystallization. We propose that any event that promotes strong undercooling has the potential to initiate rapid heterogeneous nucleation and oscillatory crystal growth, leading to the development of a layer of excluded components in front of the crystallization front, and the formation of line rock.

Kosnarite, KZr2(PO4)3, a new mineral from Mount Mica and Black Mountain, Oxford County, Maine

USGS Publications Warehouse

Brownfield, M.E.; Foord, E.E.; Sutley, S.J.; Botinelly, T.

1993-01-01

Kosnarite, ideally KZr2(PO4)3, has been identified as part of a late-stage, secondary phosphate mineral assemblage from the Mount Mica pegmatite at Paris, and from the Black Mountain pegmatite, Rumford, Oxford County, Maine. Kosnarite from Mount Mica occurs as pseudocubic rhombohedral crystals, as much as 0.9 mm in maximum dimension, that display the dominant {102} form. Color ranges from pale blue to blue-green to nearly colorless. The mineral has a white streak, is transparent, has a vitreous luster, and is nonfluorescent in ultraviolet light. It has a hardness of 4.5, is brittle with a conchoidal fracture, and has perfect {102} cleavage. Kosnarite from Black Mountain is almost pure KZr2(PO4)3 with only trace amounts of Hf, Mn, Na, and Rb. The mineral is one of three known alkali zirconium phosphates; the others are gainesite and the Cs analogue of gainesite. -from Author

Mines, prospects, and occurrences of metallic (excluding gold), pegmatite, and rare-earth mineral commodities in the Greenville 1 degree by 2 degrees Quadrangle, South Carolina, Georgia, and North Carolina

USGS Publications Warehouse

D'Agostino, John P.; Zupan, Alan Jon; Maybin, Arthur H.; Abrams, Charlotte E.; German, Jerry M.

1994-01-01

All of the known mines, prospects, and occurrences of metallic (excluding gold, pegmatite, and rare-earth mineral commodities for the Greenville 1° x 2° quadrangle are tabulated in this report. The table lists, in consecutive order for each county (fig. 1), the map number of each item, which correlates and locates the item on the accompanying Greenville 1° x 2° quadrangle map. The known name of the feature; the 7.5' topographic map on the which the commodity site is located; the Universal Transverse Mercator (UTM) northing and easting grid coordinates from the appropriate 7.5' topographic map; the commodity; remarks; and references are also listed. Some locations are known, but many sites are not verified and their locations are only approximate. References are listed in References Cited and referred to by number to save space.

Geological setting and timing of the cassiterite vein type mineralization of the Kalima area (Maniema, Democratic Republic of Congo)

NASA Astrophysics Data System (ADS)

Dewaele, S.; Muchez, Ph; Burgess, R.; Boyce, A.

2015-12-01

The Central African Mesoproterozoic Karagwe-Ankole belt in the Great Lakes area (DRCongo, Rwanda, Burundi, Uganda and Tanzania) forms a metallogenic province that hosts a variety of granite-related mineralization, which contains cassiterite, columbite-tantalite, wolframite/ferberite, spodumene and beryl. The Kalima area in the Maniema province of the DRCongo forms one of the most important areas for cassiterite mineralization in the eastern part of the DRCongo, even after many decades of exploitation. The mineralization dominantly consists of quartz veins that are hosted in Mesoproterozoic metasediments at the contact with granitic rocks of the Kalima granite (Avuanga and Yubuli) or directly crosscutting these granitic rocks (Atondo). Only limited - and mainly unmineralized pegmatites - have been described in the Lutshurukuru area. Mineralized quartz veins - and some granite bodies - intruded following the regional tectonic foliation or existing fracture zones, confirming the late-to post-tectonic origin of the fertile granite system. The emplacement of the quartz veins resulted in an alteration of the metasedimentary and granitic host-rocks, mainly resulting in muscovitization, tourmalinization and silicification. Cassiterite itself formed relatively late during vein formation and is associated with muscovite in fractures in or along the margins of the quartz veins. 40Ar-39Ar age dating of muscovite of an unmineralized pegmatite from the Lutshurukuru area gave an excellent plateau age of 1024 ± 5.5 Ma, while the muscovite associated with mineralization gave plateau ages of 986 ± 5.3 Ma for the Atondo deposit and 992.4 ± 5.4 Ma for the Yubuli deposit. The rather large spread in ages between the supposed parental granite/pegmatite and quartz veins is interpreted to reflect different magmatic events in the evolution of a composite granite system, starting at ∼1020 Ma and ending with mineralized quartz vein formation at ∼990 Ma. The latter age corresponds with the U-Pb age reported for columbite-tantalite in the area (993 ± 1 Ma at Kamisuku), which could be interpreted as the primary formation age of a new generation of mineralized pegmatites in the Kalima area, or as the resetting age of the U-Pb system during the ∼990 Ma mineralizing event. Muscovite of a mineralized greisen sample of Avuanga gave a plateau age with relaxed constraints of 1010.3 ± 5.9 Ma, which has been interpreted as a partially resetting of muscovite formed at ∼1020 Ma age, during the ∼990 Ma event.

International strategic minerals inventory summary report; lithium

USGS Publications Warehouse

Anstett, T.F.; Krauss, U.H.; Ober, J.A.; Schmidt, H.W.

1990-01-01

Major world resources of lithium are described in this summary report of information in the International Strategic Minerals Inventory (ISMI). ISMI is a cooperative data-collection effort of earth-science and mineral-resource agencies in Australia, Canada, the Federal Republic of Germany, the Republic of South Africa, the United Kingdom, and the United States of America. Part I of this report presents an overview of the resources and potential supply of lithium on the basis of inventory information; Part II contains tables of some of the geologic information and mineral-resource information and production data collected by ISMI participants. In terms of lithium-resource availability, present economically viable resources are more than sufficient to meet likely demand in the foreseeable future. In times of excess capacity such as currently exist, some pegmatite operations cannot compete with brine operations, which are less costly. A further production shift from pegmatites to brines will result in the concentration of supply in a few countries such as Chile and the United States. This shift would lead to the dependence of industrialized countries on deliveries from these sources.

Li- and F-bearing alkali amphibole from granitic pegmatite at Hurricane Mountain, Carroll County, New Hampshire

USGS Publications Warehouse

Foord, E.E.; Erd, Richard C.; Robie, S.B.; Lichte, F.E.; King, V.T.

1996-01-01

At Hurricane Mountain, Carroll County, New Hampshire, bodies of granitic pegmatite in riebeckite granite contain large (up to 10 cm long and 2 cm across) primary crystals of Li-bearing fluor-arfvedsonite in miarolitic cavities, grading to euhedral Li- and F-poor arfvedsonite. Fine-grained, fibrous, light blue-gray riebeckite occurs as a late-stage hydrothermal filling in the miarolitic cavities. The early, Li-rich, fluor-arfvedsonite has: a 9.836(5), b 17.997(7), c 5.316(4) A??, ?? 103.735(4)??, V 914.20(6) A??3; Z = 2, Dmeas. 3.34 g/cm3, Dcalc. 3.353 g/cm3; biaxial (-), 2Vmeas. 44(1)??, 2Vcalc. 46??; ?? 1.681(2), ?? 1.692(2), ?? 1.694(2), inclined dispersion, r > v; X ??? c -7??, Y = b, Z ??? a +7??; X dark blue, Y lavender gray, Z pale yellowish brown; X > Y > Z; X is opaque at 0.03 mm thickness. A structural formula, on the basis of 24 (O,OH,F) atoms is: (Na0.86K0.25)Na2(Fe2+2.54Fe3+1.485Mn0.10Zn 0.02Li0.49Ti0.07)(Si7.71Al 0.07)O22(F1.34OH0.63). Arfvedsonite within the miarolitic cavities contains less Li and F than that of the earlier generation, and the still later riebeckite contains only 0.09 wt.% Li2O and 0.3 wt.% F. The Fe3+:Fe2+ ratio of the early Li-bearing fluor-arfvedsonite and that of the euhedral arfvedsonite crystals within miarolitic cavities is 0.58. The late, fibrous, cavity-filling riebeckite has an Fe3+:Fe2+ ratio of 0.99. The total iron content of the three amphiboles increases with continued crystallization. These amphiboles are products of peralkaline pegmatites locally derived from peralkaline granite.

Petrology, geochemistry and LA-ICP-MS U-Pb geochronology of Paleoproterozoic basement rocks in Bangladesh: An evaluation of calc-alkaline magmatism and implication for Columbia supercontinent amalgamation

NASA Astrophysics Data System (ADS)

Hossain, Ismail; Tsunogae, Toshiaki; Tsutsumi, Yukiyasu; Takahashi, Kazuki

2018-05-01

The Paleoproterozoic (1.7 Ga) basement rocks from Maddhapara, Bangladesh show a large range of chemical variations (e.g. SiO2 = 50.7-74.7%) and include diorite, quartz diorite, monzodiorite, quartz monzonite and granite. The pluton overall displays metaluminous, calc-alkaline orogenic suite; mostly I-type suites formed within subduction-related magmatism. The observed major elements show general trends for fractional crystallization. Trace element contents also indicate the possibility of a fractionation or assimilation; explain the entire variation from diorite to monzonite, even granite. The pluton may have evolved the unique chemical features by a process that included partial melting of calc-alkaline lithologies and mixing of mantle-derived magmas, followed by fractional crystallization, and by assimilation of country rocks. The pluton shows evidence of crystal fractionation involving largely plagioclase, amphibole and possibly biotite. Some of the fractionated magmas may have mixed with more potassic melts from distinct parts of the continental lithosphere to produce granites and/or pegmatites. New geochronological results of granitic pegmatite (1722 ± 10 Ma) are indisputably consistent with diorite and tonalite and those data showing credible geochronological sequence (i.e., diorite - tonalite - granitic pegmatite). Identical Paleoproterozoic age (1.7 Ga) with distinctive magmatism of the Maddhapara basement rocks have agreeable relationship with the CITZ, India. The consistent magmatism is also common in the Transamazonian of South America, Trans-Hudson orogeny in North America, Bohemian Massif and the Svecofennian, Poland, have identified the sequential growth of the continent through the amalgamation of juvenile terrains, succeeded by a major collisional orogeny. Such Paleoproterozoic subduction-related orogens in Australia have similar counterparts in Antarctica and other part of the world. These types of Paleoproterozoic magmatism dominantly contributed to assemble, amalgamation and breakup of the enormous Columbia supercontinent.

Simmonsite, Na2LiAlF6, a new mineral from the Zapot amazonite-topazzinnwaldite pegmatite, Hawthorne, Nevada, U.S.A

USGS Publications Warehouse

Foord, E.E.; O'Connor, J. T.; Hughes, J.M.; Sutley, S.J.; Falster, A.U.; Soregaroli, A.E.; Lichte, F.E.; Kile, D.E.

1999-01-01

Simmonsite, Na2LiAlF6, a new mineral of pegmatitic-hydrothermal origin, occurs in a late-stage breccia pipe structure that cuts the Zapot amazonite-topaz-zinnvvaldite pegmatite located in the Gillis Range, Mineral Co., Nevada, U.S.A. The mineral is intimately intergrown with cryolite, cryolithionite and trace elpasolite. A secondary assemblage of other alumino-fluoride minerals and a second generation of cryolithionite has formed from the primary assemblage. The mineral is monoclinic, P21 or P21/m, a = 7.5006(6) A??, b = 7.474(1) A??, c = 7.503(1) A??, ??= 90.847(9) ??, V=420.6(1) A??3, Z = 4. The four strongest diffraction maxima [d(A??), likl, I/I100] are (4.33, 111 and 111, 100); (1.877, 400 and 004, 90); (2.25, 13T, 113, 131 and 311, 70); and (2.65, 220, 202, 022, 60). Simmonsite is pale buff cream with white streak, somewhat greasy, translucent to transparent, Mohs hardness of 2.5-3, no distinct cleavage, subconchoidal fracture, no parting, not extremely brittle, Dm is 3.05(2) g/cm3, and Dc is 3.06(1) g/cm3. The mineral is biaxial, very nearly Isotropie, N is 1.359(1) for ?? = 589 nm, and birefringence is 0.0009. Electron microprobe analyses gave (wt%) Na = 23.4, Al = 13.9, F = 58.6, Li = 3.56 (calculated), with a total of 99.46. The empirical formula (based on 6 F atoms) is Na1.98Li1.00 ooAl|ooF6. The crystal structure was not solved, presumably because of unit-cell scale twinning, but similarities to the perovskite-type structure exist. The mineral is named for William B. Simmons, Professor of Mineralogy and Petrology, University of New Orleans, New Orleans.

Reconnaissance geology of the Qufar Quadrangle, sheet 27/41 D, Kingdom of Saudi Arabia

USGS Publications Warehouse

Kellogg, K.S.

1984-01-01

The last major plutonic event in the area is the intrusion of the alkalic granite complexes at Jabal Aja and Jabal Sal ma about 580 Ma ago. Of particular note is a per alkalic border facies of the Jabal Aja complex that is associated with pegmatites enriched in thorium, niobium, and rare-earth elements. 

Crystal Structure of Cl-Deficient Analogue of Taseqite from Odikhincha Massif

NASA Astrophysics Data System (ADS)

Rastsvetaeva, R. K.; Chukanov, N. V.; Zaitsev, V. A.; Aksenov, S. M.; Viktorova, K. A.

2018-05-01

An eudialyte group mineral, found in pegmatites of the Odikhincha massif (the northern part of the Siberian platform), has been investigated using X-ray diffraction, IR spectroscopy, and Raman spectroscopy. The mineral is characterized by a high strontium content and a low chlorine content. It has a trigonal unit cell with the following parameters: a = 14.2700(6) Å and c = 30.057(1) Å; V = 5300.6(1) Å3; sp. gr. R3 m. The structure has been refined to R = 0.047 in the anisotropic approximation of atomic displacements using 1697 F > 4σ( F). The idealized formula ( Z = 3) was found to be Na12Sr2Ca6Fe 3 2+ Zr3NbSi25O72(OH,O)4Cl(H2O)0.2. The chemical composition and structure of this mineral are close to those of taseqite; however, it differs from the holotype sample by a low chlorine content and peculiarities of cation distribution over basic structure sites. A comparative analysis of strontium-rich eudialytes has revealed their important crystallochemical feature: selective concentration of strontium in the N4 site. Thus, taseqite, along with heterophyllosilicates, may play a role of strontium concentrator in agpaitic pegmatites.

Crystal growth mechanisms in miarolitic cavities in the Lake George ring complex and vicinity, Colorado

USGS Publications Warehouse

Kile, D.E.; Eberl, D.D.

1999-01-01

The Crystal Peak area of the Pikes Peak batholith, near Lake George in central Colorado, is world-renowned for its crystals of amazonite (the blue-green variety of microcline) and smoky quartz. Such crystals, collected from individual miarolitic pegmatites, have a remakably small variation in crystal size within each pegmatite, and the shapes of plots of their crystal size distributions (CSDs) are invariably lognormal or close to lognormal in all cases. These observations are explained by a crystal growth mechanism that was governed initially by surface-controlled kinetics, during which crystals tended to grow larger in proportion to their size, thereby establishing lognormal CSDs. Surface-controlled growth was followed by longer periods of supply controlled growth, during which growth rate was predominantly size-independent, consequently preserving the lognormal shapes of the CSDs and the small size variation. The change from surface- to supply controlled growth kinetics may have resulted from an increasing demand for nutrients that exceeded diffusion limitations of the system. The proposed model for crystal growth in this locality appears to be common in the geologic record, and can be used with other information, such as isotopic data, to deduce physico-chemical conditions during crystal formation.

Geochemistry of zircons from basic rocks of the Korosten anorthosite-mangerite-charnockite-granite complex, north-western region of the Ukrainian Shield

NASA Astrophysics Data System (ADS)

Shumlyanskyy, Leonid; Belousova, Elena; Petrenko, Oksana

2017-09-01

The concentrations of 26 trace elements have been determined by laser ablation ICP-MS in zircons from four samples of basic rocks of the Korosten anorthosite-mangerite-charnockite-granite plutonic complex, the Ukrainian Shield. Zircons from the Fedorivka and Torchyn gabbroic intrusions and Volynsky anorthosite massif have distinctive abundances of many trace elements (REE, Sr, Y, Mn, Th). Zircons from the gabbroic massifs are unusually enriched in trace elements, while zircons from pegmatites in anorthosite are relatively depleted in trace elements. High concentrations of trace elements in zircons from gabbroic intrusions can be explained by their crystallization from residual interstitial melts enriched in incompatible elements. The zircons studied demonstrate a wide range of Ti concentrations, which reflects their temperature of crystallization: the zircons most enriched in Ti, from mafic pegmatites of the Horbuliv quarry (20-40 ppm), have the highest temperature of crystallization (845 ± 40 °C). Lower (720-770 °C) temperatures of zircon crystallization in gabbroic rocks are explained by its crystallization from the latest portions of the interstitial melt or by simultaneous crystallization of ilmenite. The Ce anomaly in zircons correlates with the degree of oxidation of the coexisting ilmenite.

Liandratite from Karkonosze pegmatites, Sudetes, Southwestern Poland

NASA Astrophysics Data System (ADS)

Matyszczak, Witold

2018-06-01

The chemical composition of liandratite, U6+(Nb,Ta)2O8, was determined from material collected in Niobium, Yttrium, Fluorine type (NYF) pegmatites of the Karkonosze intrusion (Sudetes, SW Poland). Liandratite occurs mainly as rims, up to 40 µm thick, and fracture infillings in fergusonite-(Y) and other Nb-Ta-Ti minerals. Its formation was related to the fluid-driven alteration of primary minerals by three potential mechanisms: (i) direct replacement of a primary mineral by liandratite; (ii) breakdown of the primary mineral to liandratite and a product with the composition of minerals of the pyrochlore group; (iii) multistage alteration, which involved: removal of A-site cations (mostly Y + REE with the exception of U4+) and formation of phases with the composition of pyrochlore group minerals; then crystallization of U-, Bi-, Pb-rich pyrochlores and their replacement by liandratite. The chemical compositions of liandratite formed by the breakdown of different primary minerals are also different, mainly in their U, Ti and Nb contents. Excess Ti, relative to the U6+Nb2O8 end-member, is incorporated into the structure together with additional U. The Ti content of liandratite, and partially through this the U content, are dependent on the nature of the precursor mineral.

Mineral resources of the Mount Tipton Wilderness Study Area, Mohave County, Arizona

USGS Publications Warehouse

Greene, Robert C.; Turner, Robert L.; Jachens, Robert C.; Lawson, William A.; Almquist, Carl L.

1989-01-01

The Mount Tipton Wilderness Study Area (AZ-020-012/ 042) comprises 33,950 acres in Mohave County, Ariz. At the request of the U.S. Bureau of Land Management, this area was evaluated for identified mineral resources (known) and mineral resource potential (undiscovered). This work was carried out by the U.S. Bureau of Mines and the U.S. Geological Survey in 1984-87. In this report, the area studied is referred to as the "wilderness study area" or simply "the study area." There are no identified mineral resources in the study area. The southernmost part of the study area is adjacent to the Wallapai (Chloride) mining district and has low mineral resource potential for gold, silver, copper, lead, zinc, and molybdenum in hydrothermal veins. This area also has a low mineral resource potential for tungsten in vein deposits and for uranium in vein deposits or pegmatites. In the central part of the wilderness study area, one small area has low mineral resource potential for uranium in vein deposits or pegmatites and another small area has low resource potential for thorium in vein deposits. The entire study area has low resource potential for geothermal energy but no potential for oil or gas resources.

H 2OCH 4NaClCO 2 inclusions from the footwall contact of the Tanco granitic pegmatite: Estimates of internal pressure and composition from microthermometry, laser Raman spectroscopy, and gas chromatography

NASA Astrophysics Data System (ADS)

Thomas, A. V.; Pasteris, J. D.; Bray, C. J.; Spooner, E. T. C.

1990-03-01

Fluid inclusions in tourmaline and quartz from the footwall contact of the Tanco granitic pegmatite, S.E. Manitoba were studied using microthermometry (MT), laser Raman spectroscopy (LRS) and gas chromatography (GC). CH 4-bearing, aqueous inclusions occur in metasomatic tourmaline of the footwall amphibolite contact. The internal pressures estimated from MT are lower than those obtained from LRS (mean difference = 54 ± 19 bars). The difference is probably due to errors in the measurement of Th CH 4 (V) and to the presence of clathrate at Th CH 4 (V) into which CO 2 had been preferentially partitioned. LRS estimates of pressure (125-184 bars) are believed to be more accurate. Aqueous phase salinities based on LRS estimates of pressure are higher than those derived using the data from MT: 10-20 eq. wt% NaCl. The composition of the inclusions determined by GC bulk analysis is 97.3 mol% H 2O, 2.2 mol% CH 4, 0.4 mol% CO 2, 250 ppm C 2H 6, 130 ppm N 2, 33 ppm C 3H 8, 11 ppm C 2H 4, and 3 ppm C 3H 6, plus trace amounts of C 4 hydrocarbons. The composition is broadly similar to that calculated from MT (92% H 2O and 8% CH 4, with 7 eq. wt% NaCl dissolved in the aqueous phase and 2 mol% CO 2 dissolved in the CH 4 phase), as expected due to the dominance of a single generation of inclusions in the tourmaline. However, two important differences in composition are: (i) the CH 4 to CO 2 ratio of this fluid determined by GC is 5.33, which is significantly lower than that indicated by MT (49.0); and (ii) the H 2O content estimated from MT is 92 mol% compared to 98 mol% from GC. GC analyses may have been contaminated by the presence of secondary inclusions in the tourmaline. However, the rarity of the latter suggests that they cannot be completely responsible for the discrepancy. The differences may be accounted for by the presence of clathrate during measurement of Th CH 4 (critical), which would reduce CO 2 relative to CH 4 in the residual fluid, and by errors in visually estimating vol% H 2O. The compositions of the primary inclusions in tourmaline are unlike any of those found within the pegmatite and indicate that the fluid was externally derived, probably of metamorphic origin. Inclusions in quartz of the border unit of the pegmatite are secondary and are either aqueous (18 to 30 eq. wt% CaCl 2; Th total = 184 ± 14° C) or carbonic. Tm CO 2 for the carbonic inclusions ranges from -57.5 to -65.4°C and is positively correlated with Th CO 2. Analyses of X CH 4 based on LRS agree within 5 mol% of those derived from MT and together indicate a range of compositions from 5 to 50 mol% CH 4 in the CO 2 phase. Bulk analysis by GC gives 99.0 mol% H 2O, 0.6 mol% CO 2, 0.4 mol% CH 4, 160 ppm N 2, 7 ppm C 2H 6, 4 ppm C 3H 8, and 2 ppm C 2H 4, with trace amounts of COS (carbonyl sulphide) and C 3H 6. The level of H 2O in the analysis is consistent with the dominance of the aqueous inclusions in these samples, and the CH4: CO2 ratios are consistent with estimates from MT and LRS. The preservation of variable ratios of CH 4:CO 2 in inclusions < 50 μm apart indicates that neither H 2 diffusion out of the inclusions nor reduction of fluids leaving the pegmatite were responsible for the more oxidized chemistries of the border unit inclusions relative to those in the tourmaline of the metasomatised amphibolite. The compositions of the inclusions in the quartz lie between those of the fluid trapped by the tourmaline (externally derived) and the measured composition of a CO 2-bearing pegmatitic fluid, which indicates that the secondary fluids trapped in the border unit quartz were produced by late mixing.

A Ta-rich low-P peraluminous granite: the Rechla cupola (Hoggar, Algeria) and associated pegmatites, the result of extreme fractionation of a A2-type magma.

NASA Astrophysics Data System (ADS)

Kesraoui, M.; Marignac, C.; Hamis, A.; Cuney, M.

2012-04-01

In the c. 525 Ma RMG province of the Laouni terrane of the Pan-African Tuareg Shield (Hoggar), the small N20°E elliptic Rechla cupola (200x100 m) is particularized by a rim of Qtz-Kfs-Znw pegmatite. It is a medium-grained Na-Li-F granite, with quartz, albite (An01), rare microcline, topaz, Mn-lepidolite (≤ 8% MnO) and Hf-zircon, and: 71.4 % SiO2, 0.93% FeO+MgO+MnO (Mg # 0.19, Mg/Mg+Fe+Mn 0.09), 9.22% Na2O+K2O (Na # 0.7), Al-Na-K-2Ca from 55 to 85, and low P2O5 (0.05%) and ∑ REE (23 ppm) contents, with a pronounced tetrad effect and <0 Eu anomaly in the REE pattern. Such a composition is typical of a low-P peraluminous RMG deriving from highly potassic calcalkaline suites (A2 type) (Linnen & Cuney 2005), enriched in F (1.6%), Li (1,600 ppm), Zn (300 ppm), Be (7 ppm), Sn (740 ppm), W (40 ppm) and specially Ta (165 ppm, Ta/Nb between 2.4 and 2.6), the latter as columbo-tantalite and Mn-wodginite (Ta # 0.8). The pegmatite rim comprises, towards the intrusion (i) thick Kfs lenses (palissadic crystals ≥ 50 cm), (ii) a laminated quartz-zinnwaldite-(beryl) sequence , and (iii) a discontinuous band of fine-grained granite, with quartz, albite, topaz, Mn-lepidolite and beryl, equally fractionated: 69.4% SiO2, 0.85% FeO+MgO+MnO (Mg# 0.06, Mg/Mg+Fe+Mn 0.02), Al-Na-K-2Ca = 32, F 0.4%, Li 610 ppm, Ta 240 ppm (Ta/Nb = 2.4), Be 500 ppm. The laminated sequence overprints the Kfs lenses. It comprises thick (≤ 20 m) quartz lenses cross-cut by 10 cm-sized alternating bands of euhedral quartz and Mn-zinnwaldite (≤ 6.5% MnO). REE-patterns of the Mn-Znw display a clear inverse tetrad effect, symmetrical of the granite pattern. At the boundary with the fine-grained internal band, euhedral quartz crystals are projecting toward the inner wall. The Rechla body and its surrounding pegmatites are intrusive into a porphyritic biotite-granite representative of the evolved magmas of the A2-type Taourirt suite (Azzouni-Sekkal & Boissonnas 1993), with a classical "seagull" pattern and a pronounced <0 Eu anomaly. Geochemical modelling shows that the main Rechla magma is likely the fractionated product of this already differentiated magma, mainly involving quartz and Kfs. The pegmatite rim is interpreted as the result of the sequential crystallization of a Rechla-type melt, with late individualisation of a Fe-rich magmatic-hydrothermal phase responsible for the quartz-zinnwaldite assemblage, leaving a strongly Be-enriched residual liquid (the fine-grained granite). As demonstrated by the Rechla occurrence, Ta concentration at levels similar to those in Beauvoir-type high-P peraluminous granites may be reached in the low-P low-Ta A2 suites, provided that extreme fractionation processes are established. Azzouni-Sekkal, A., Boissonnas, J. (1993). Une province magmatique de transition du calco-alcalin à l'alcalin : les granitoïdes pan-africains à structure annulaire de la chaîne pharusienne du Hoggar (Algérie). Bulletin Société Géologique France 164, 597-608. Linnen, R.L., Cuney, M. (2005). Granite-related rare-element deposits and experimental constraints on Ta-Nb-W-Sn-Zr-Hf mineralization. In: RL Linnen, IM Samson (eds), Rare-element geochemistry and mineral deposits, Geological Association of Canada (GAC) Short Course Notes 17, pp. 45-67.

Intrusive rocks northeast of Steamboat Springs, Park Range, Colorado, with a section on geochronology

USGS Publications Warehouse

Snyder, George L.; Hedge, Carl E.

1978-01-01

Major Precambrian and minor Tertiary intrusive rocks northeast of Steamboat Springs in the Park Range between 40?30' and 40?45' N. lat. are described and compared with related rocks elsewhere in Colorado and Wyoming. The Precambrian intrusives were emplaced in a sequence of high-grade interlayered felsic gneisses, amphibolites, and pelitic schists of sedimentary and volcanic origin. These rocks are cut by a major northeast-trending Precambrian shear zone where mainly left lateral movement of 1/ 2 to 1 mile is certain. Cumulative movement of many miles is possible. The Precambrian intrusives consist of a batholith, the Mount Ethel pluton, a smaller Buffalo Pass pluton, and small dikes or lenses of fine-grained porphyry, pegmatites, and ultramafics. The Mount Ethel pluton is an oval shaped body 7 miles wide by about 40 miles long (shown by geophysical data to extend beneath younger sediments in North Park). Outer batholithic contacts are sharp and dip steeply outward at about 85?. Five mappable internal variants consist, in order of decreasing age, of granodiorite, quartz monzonite porphyry of Rocky Peak, quartz monzonite of Roxy Ann Lake, granite and quartz monzonite, and. leucogranite. Internal contacts between these plutonic variants are sharp, and evidence of liquid-solid relationships abounds; despite this, all rocks except the granodiorite contribute to an Rb-Sr whole-rock isochron indicating emplacement about 1.4 b.y. (billion years) ago. The most important variants volumetrically are: the quartz monzonite porphyry of Rocky Peak, which forms an irregular 2-mile-thick carapace or mapped band around the west edge of the pluton and is lithologically similar to nearby Sherman Granite, and the quartz monzonite of Roxy Ann Lake, which forms most of the rest of the pluton and is lithologically similar to Silver Plume Granite. An apparent Sherman -Silver Plume dichotomy with similar rock types and similar relative ages is noted throughout Colorado plutons of that age. The Buffalo Pass pluton consists of the quartz monzonite and gra- nodiorite augen gneiss of Buffalo Mountain and equigranular quartz monzonite gneiss. Internal contacts are not exposed. These rocks contribute to an Rb-Sr whole-rock isochron indicating syntectonic emplacement 1.7-1.8 b.y. ago, essentially the same as the metamorphism of the felsic gneiss wallrocks in the area of this report, and of rocks of Boulder Creek age elsewhere in Colorado. The fine-grained porphyry dikes cut the Buffalo Pass pluton, the ultramafics, and some pegmatites. The dikes are within the age range of the Mount Ethel pluton and are older than the mylonite and shear zones. They occur in both an older northwest-trending and a somewhat younger northeast-trending set but do not appear to change compositionally from one set to the other. Regional considerations indicate that they were emplaced between about 1.1 and 1.5 b.y. ago, a time when intermediate to mafic dikes were commonly emplaced throughout Colorado, Wyoming, and southwestern Montana. The pegmatite and ultramafic bodies are not dated directly, but clustering of many pegmatites outside the contacts of the Mount Ethel pluton may indicate a genetic relation of the pegmatites to the Mount Ethel rocks. Fluorite is a common accessory mineral in the rocks of the Mount Ethel pluton; it has not been observed in this area in the petrographically similar rocks of the Buffalo Pass pluton. Fluorite was precipitated most abundantly from the Precambrian magma that formed the quartz monzonite of Roxy Ann Lake. In 70 percent of these rocks fluorite is observed in amounts as great as 2 percent and is successively less abundant in both older and younger plutonic phases. Textural evidence indicates that, although most fluorite is intergrown with and contemporaneous with other magmatic minerals, some fluorite is associated with alteration minerals in a manner demonstrating its mobility since its initial deposition. Five areas of ec

The geological processes time scale of the Ingozersky block TTG complex (Kola Peninsula)

NASA Astrophysics Data System (ADS)

Nitkina, Elena

2013-04-01

Ingozersky block located in the Tersky Terrane of the Kola Peninsula is composed of Archean gneisses and granitoids [1; 5; 8]. The Archaean basement complexes on the regional geological maps have called tonalite-trondemit-gneisses (TTG) complexes [6]. In the previous studies [1; 3; 4; 5; 7] within Ingozersky block the following types of rocks were established: biotite, biotite-amphibole, amphibole-biotite gneisses, granites, granodiorites and pegmatites [2]. In the rocks of the complex following corresponding sequence of endogenous processes observed (based on [5]): stage 1 - the biotitic gneisses formation; 2 - the introduction of dikes of basic rocks; 3 phase - deformation and foliation; 4 stage - implementation bodies of granite and migmatization; 5 stage - implementation of large pegmatite bodies; stage 6 - the formation of differently pegmatite and granite veins of low power, with and without garnet; stage 7 - quartz veins. Previous U-Pb isotopic dating of the samples was done for biotite gneisses, amphibole-biotite gneisses and biotite-amphibole gneisses. Thus, some Sm-Nd TDM ages are 3613 Ma - biotite gnesses, 2596 Ma - amphibole-biotite gnesses and 3493 Ma biotite-amphibole gneisses.. U-Pb ages of the metamorphism processes in the TTG complex are obtained: 2697±9 Ma - for the biotite gneiss, 2725±2 and 2667±7 Ma - for the amphibole-biotite gneisses, and 2727±5 Ma for the biotite-amphibole gneisses. The age defined for the biotite gneisses by using single zircon dating to be about 3149±46 Ma corresponds to the time of the gneisses protolith formation. The purpose of these studies is the age establishing of granite and pegmatite bodies emplacement and finding a geological processes time scale of the Ingozerskom block. Preliminary U-Pb isotopic dating of zircon and other accessory minerals were held for granites - 2615±8 Ma, migmatites - 2549±30 Ma and veined granites - 1644±7 Ma. As a result of the isotope U-Pb dating of the different Ingozerskogo TTG complex rocks, the following age-formation stages are determined: protolith of the biotite gneisses - 3149±46 Ma; metamorphism, deformation of rocks, foliation - 2727±5 - 2725±2 - 2697±9 - 2667±7 Ma, granite bodies formation - 2615±8 Ma and biotite gneisses migmatization - 2549±30 Ma, formation of different pegmatite and granite veins -1644±7 Ma. Author are grateful to Akad. Mitrofanov F.P. and Bayanova T.B. for the consultations. The work is supported by RFBR 12-05-31063, 11-05-00570. 1.Batieva I.D., Belkov I.V. Granitoidnie formacii Kolskogo poluostrova. // Ocgerki po petrologiy, mineralogiy i metallogeniy Kolskogo poluostrova. L.: Nauka. 1968. p. 5-143. (in russian) 2. Belkov I.V., Zagorodny V.G., Predovsky A.A. et al. Stratigraficheskoe raschlenenie i korrelyacia dokembria severo-vostochoi chasty Baltiyskogo shita. L.: Nauka. 1971. p. 141-150. (in russian) 3. Docembriskaya tektonica severo-vostochoi chasty Baltiyskogo shita (Ob'asnitelnaya zapiska k tektonicheskoi karte severo-vostochoi chasty Baltiyskogo shita 1:500000) / ed.: F.P.Mitrofanov. Apatity: KFAN SSSR. 1992. 112 P. (in russian) 4. Zagorodny V.G., Radchenko A.T. Tectonika i glubinnoe stroenie severo-vostochoi chasty Baltiyskogo shita. Apatity: KFA SSSR. 1978. p. 3-12. (in russian) 5. Kozlov N.E., Sorohtin N.O., Glaznev V.N. et al. Geologia Arhea Baltiskogo shita. S.Pb.: Nauka. 2006. 329 p. (in russian) 6. Mitrofanov F.P. Sovremennie problemy i nekotorie resheniya dokembriskoy geologii kratonov. (2001) Litosphera.2001. V 1. P. 5-14. (in russian) 7. Ob'asnitelnaya zapiska k geologicheskoy karte severo-vostochoi chasty Baltiyskogo shita 1:500000 / ed.: F.P.Mitrofanov. Apatity: KFAN SSSR. 1994. 95 P. (in russian) 8. Haritonov L.Y. Structura i stratigraphia karelid vostoka Baltiskogo shita. M.: Nedra. 1966. 354 P. (in russian)

Sources and controls of Arsenic contamination in groundwater of Rajnandgaon and Kanker District, Chattisgarh Central India

NASA Astrophysics Data System (ADS)

Shukla, Dericks Praise; Dubey, C. S.; Singh, Ningthoujam P.; Tajbakhsh, M.; Chaudhry, M.

2010-12-01

SummaryA high concentration of Arsenic (As) contamination in ground water has been reported in the village of Kaudikasa in Rajnandgaon district, wherein around 10% of the population is suffering from As-borne diseases. The region does not share any demographic or geological similarity with the sedimentary aquifers of the Bengal Delta Plain in Eastern India, but represents an igneous terrain with elevated As concentrations in groundwater. There is limited information about the source of As in groundwater and its mobility constraints. In this area, almost all the wells are located in the granitic terrain with pegmatitic intrusions. Most of these wells are characterized by As concentration above the World Health Organization ( WHO, 1999) and the BIS (Bureau of Indian Standards) standards, with the highest being found in a well with more than 250 μg/L of As. Here we report petrographic studies of the granitic host rock and X-ray diffraction results that indicate that altered realgar (α-As 4S 4), para realgar (AsS), and/or tennantite (Cu 12As 4S 13), are the main mineral that contain As. This element is leached during the weathering and water-rock interactions. Microprobe analysis of the altered realgar grains of in pegmatitic intrusions of the host granite indicate 23-27 wt.% As. Remote sensing is useful to delineate the source of this contaminant, which appears to lie at the intersection of a mineralized NW-SE and N-S lineaments associated with the Kotri rift zone. These lineaments are structurally controlled as rifting followed by thrusting and other types of faulting caused left-lateral displacement of N-S Kotri lineament along a NW-SE fault plane showing sinistral shearing. This process caused water drainage in the areas to flow along these highly mineralized weak zones. Thus, the water becomes highly contaminated due to leaching of minerals at the intersection of these lineaments, clearly visible at two areas of high contamination that lie very near to this intersection over granitic rock. The source of As affecting the Rajnandgaon district is located in granites that have pegmatitic intrusions likely generated by hydrothermal activity.

Late Cretaceous to Paleocene metamorphism and magmatism in the Funeral Mountains metamorphic core complex, Death Valley, California

USGS Publications Warehouse

Mattinson, C.G.; Colgan, J.P.; Metcalf, J.R.; Miller, E.L.; Wooden, J.L.

2007-01-01

Amphibolite-facies Proterozoic metasedimentary rocks below the low-angle Ceno-zoic Boundary Canyon Detachment record deep crustal processes related to Meso-zoic crustal thickening and subsequent extension. A 91.5 ?? 1.4 Ma Th-Pb SHRIMP-RG (sensitive high-resolution ion microprobe-reverse geometry) monazite age from garnet-kyanite-staurolite schist constrains the age of prograde metamorphism in the lower plate. Between the Boundary Canyon Detachment and the structurally deeper, subparallel Monarch Spring fault, prograde metamorphic fabrics are overprinted by a pervasive greenschist-facies retrogression, high-strain subhorizontal mylonitic foliation, and a prominent WNW-ESE stretching lineation parallel to corrugations on the Boundary Canyon Detachment. Granitic pegmatite dikes are deformed, rotated into parallelism, and boudinaged within the mylonitic foliation. High-U zircons from one muscovite granite dike yield an 85.8 ?? 1.4 Ma age. Below the Monarch Spring fault, retrogression is minor, and amphibolite-facies mineral elongation lineations plunge gently north to northeast. Multiple generations of variably deformed dikes, sills, and leucosomal segregations indicate a more complex history of partial melting and intrusion compared to that above the Monarch Spring fault, but thermobarometry on garnet amphibolites above and below the Monarch Spring fault record similar peak conditions of 620-680 ??C and 7-9 kbar, indicating minor (<3-5 km) structural omission across the Monarch Spring fault. Discordant SHRIMP-RG U-Pb zircon ages and 75-88 Ma Th-Pb monazite ages from leucosomal segregations in paragneisses suggest that partial melting of Proterozoic sedimentary protoliths was a source for the structurally higher 86 Ma pegmatites. Two weakly deformed two-mica leucogranite dikes that cut the high-grademetamorphic fabrics below the Monarch Spring fault yield 62.3 ?? 2.6 and 61.7 ?? 4.7 Ma U-Pb zircon ages, and contain 1.5-1.7 Ga cores. The similarity of metamorphic, leuco-some, and pegmatite ages to the period of Sevier belt thrusting and the period of most voluminous Sierran arc magmatism suggests that both burial by thrusting and regional magmatic heating contributed to metamorphism and subsequent partial melting. ??2007 Geological Society of America. All rights reserved.

Linking precious metal enrichment and halogen cycling in mafic magmatic systems: insights from the Rum layered intrusion, NW Scotland

NASA Astrophysics Data System (ADS)

Kelly, A. P.; O'Driscoll, B.; Clay, P. L.; Burgess, R.

2017-12-01

Layered intrusions host the world's largest known concentrations of the platinum-group elements (PGE). Emphasis has been attached to the role of halogen-bearing fluids in concentrating the precious metals, but whether this occurs at the magmatic stage, or via subsequent metasomatism, is actively debated. One obstacle to progress has been the analytical difficulty of measuring low abundances of the halogens in the cumulate products of layered intrusions. To elucidate the importance of the halogens in facilitating PGE-mineralisation, as well as fingerprint halogen provenance and assess the importance of halogen cycling in mafic magma systems more generally, a suite of samples encompassing different stages of activity of the Palaeogene Rum layered intrusion was investigated. Halogen abundances were measured by neutron irradiation noble gas mass spectrometric analysis, permitting the detection of relatively low (ppm-ppb) abundances of Cl, Br and I in mg-sized samples. The samples include PGE-enriched chromite seams, various cumulates (e.g., peridotites), picrites (approximating the Rum parental magma), and pegmatites representing volatile-rich melts that circulated the intrusion at a late-stage in its solidification history. The new data reveal that PGE-bearing chromite seams contain relatively low Cl concentrations (2-3 ppm), with high molar ratios of Br/Cl and I/Cl (0.005 and 0.009, respectively). The picrites and cumulates have Br/Cl and I/Cl ratios close to sub-continental lithospheric mantle values of approximately 0.0013 and 0.00002, respectively, and thus likely reflect the Rum magma source region. A positive correlation between Cl and Br signifies comparable partitioning behaviour in all samples. However, I is more variable, displaying a positive correlation with Cl for more primitive samples (e.g. picrite and peridotite), and seemingly decoupling from Br and Cl in chromite seams and pegmatites. The relative enrichment of I over Cl in the chromite seams points to the local involvement of an organic-rich sedimentary assimilant and potentially represents an important trigger for PGE-mineralisation. Similarly high I/Cl signatures in some of the late-stage pegmatites suggest that fluids with this distinctive composition circulated the cooling Rum intrusion for a protracted period of time.

Chevkinite-group minerals from granulite-facies metamorphic rocks and associated pegmatites of East Antarctica and South India

USGS Publications Warehouse

Belkin, H.E.; Macdonald, R.; Grew, E.S.

2009-01-01

Electron microprobe data are presented for chevkinite-group minerals from granulite-facies rocks and associated pegmatites of the Napier Complex and Mawson Station charnockite in East Antarctica and from the Eastern Ghats, South India. Their compositions conform to the general formula for this group, viz. A4BC2D2Si4O22 where, in the analysed specimens A = (rare-earth elements (REE), Ca, Y, Th), B = Fe2+, Mg, C = (Al, Mg, Ti, Fe2+, Fe3+, Zr) and D = Ti and plot within the perrierite field of the total Fe (as FeO) (wt.%) vs. CaO (wt.%) discriminator diagram of Macdonald and Belkin (2002). In contrast to most chevkinite-group minerals, the A site shows unusual enrichment in the MREE and HREE relative to the LREE and Ca. In one sample from the Napier Complex, Y is the dominant cation among the total REE + Y in the A site, the first reported case of Y-dominance in the chevkinite group. The minerals include the most Al-rich yet reported in the chevkinite group (49.15 wt.% Al2O3), sufficient to fill the C site in two samples. Conversely, the amount of Ti in these samples does not fill the D site, and, thus, some of the Al could be making up the deficiency at D, a situation not previously reported in the chevkinite group. Fe abundances are low, requiring Mg to occupy up to 45% of the B site. The chevkinite-group minerals analysed originated from three distinct parageneses: (1) pegmatites containing hornblende and orthopyroxene or garnet; (2) orthopyroxene-bearing gneiss and granulite; (3) highly aluminous paragneisses in which the associated minerals are relatively magnesian or aluminous. Chevkinite-group minerals from the first two parageneses have relatively high FeO content and low MgO and Al2O3 contents; their compositions plot in the field for mafic and intermediate igneous rocks. In contrast, chevkinite-group minerals from the third paragenesis are notably more aluminous and have greater Mg/Fe ratios. ?? 2009 The Mineralogical Society.

Chevkinite-group minerals from granulite-facies metamorphic rocks and associated pegmatites of East Antarctica and South India

USGS Publications Warehouse

Belkin, Harvey E.; Macdonald, R.; Grew, E.S.

2009-01-01

Electron microprobe data are presented for chevkinite-group minerals from granulite-facies rocks and associated pegmatites of the Napier Complex and Mawson Station charnockite in East Antarctica and from the Eastern Ghats, South India. Their compositions conform to the general formula for this group, viz. A4BC2D2Si4O22 where, in the analysed specimens A = (rare-earth elements (REE), Ca, Y, Th), B = Fe2+, Mg, C = (Al, Mg, Ti, Fe2+, Fe3+, Zr) and D = Ti and plot within the perrierite field of the total Fe (as FeO) (wt.%) vs. CaO (wt.%) discriminator diagram of Macdonald and Belkin (2002). In contrast to most chevkinite-group minerals, the A site shows unusual enrichment in the MREE and HREE relative to the LREE and Ca. In one sample from the Napier Complex, Y is the dominant cation among the total REE + Y in the A site, the first reported case of Y-dominance in the chevkinite group. The minerals include the most Al-rich yet reported in the chevkinite group (≤9.15 wt.% Al2O3), sufficient to fill the C site in two samples. Conversely, the amount of Ti in these samples does not fill the D site, and, thus, some of the Al could be making up the deficiency at D, a situation not previously reported in the chevkinite group. Fe abundances are low, requiring Mg to occupy up to 45% of the B site. The chevkinite-group minerals analysed originated from three distinct parageneses: (1) pegmatites containing hornblende and orthopyroxene or garnet; (2) orthopyroxene-bearing gneiss and granulite; (3) highly aluminous paragneisses in which the associated minerals are relatively magnesian or aluminous. Chevkinite-group minerals from the first two parageneses have relatively high FeO content and low MgO and Al2O3 contents; their compositions plot in the field for mafic and intermediate igneous rocks. In contrast, chevkinite-group minerals from the third paragenesis are notably more aluminous and have greater Mg/Fe ratios

Geology and preliminary hydrogeologic characterization of the cell-house site, Berlin, New Hampshire, 2003-04

USGS Publications Warehouse

Degnan, James R.; Clark, Stewart F.; Harte, Philip T.; Mack, Thomas J.

2005-01-01

At the cell-house site, thin, generally less than 20-foot thick overburden, consisting of till and demolition materials, overlies fractured crystalline bedrock. Bedrock at the site consists of gneiss with thin discontinuous lenses of chlorite schist and discontinuous tabular pegmatite. Two distinct fracture domains, with principal trends to the west and northwest, and to the north, overlap near the site. The cell-house site shows principal trends common to both domains. Gneiss is the most abundant rock at the site. Steeply dipping fractures within the gneiss terminate on subhorizontal contacts with pegmatite and on moderately dipping contacts with chlorite schist. Steeply northwest-dipping en Echelon fracture zones, parallel joint zones, and silicified brittle faults show consistent strikes to the northeast. Gently east-dipping to subhorizontal fractures, sub-parallel to gneissosity, strike northeast. The impermeable cap, barrier wall, and bedrock surface topography affect ground-water flow in the overburden. There is relatively little ground-water flow in the overburden in the capped area and a poor hydraulic connection between the overburden and the underlying bedrock over most of the site. The overburden beneath the cap may receive inflow through or beneath the barrier wall, or by flow through vertical fractures in the underlying bedrock beneath the barrier wall. The bedrock aquifer near the river is well connected to the river and head difference in the bedrock across the site are large (greater than 13 ft). Horizontal hydraulic conductivities of 0.2 to 20 ft/d were estimated for the bedrock. Individual fractures or fracture zones likely have hydraulic conductivities greater than the bulk rock. Subhorizontal fractures occur at pegmatite contacts or along chlorite schist lenses and may serve as ground-water conduits to the steeply dipping fractures in gneiss. The effective hydraulic conductivity across the site is likely to be in the low range of the estimated values (0.2 ft/d). Ground water discharges to the river from the bedrock aquifer and is greatest during periods of large river stage fluctuations.

Late magmatic controls on the origin of schorlitic and foititic tourmalines from late-Variscan peraluminous granites of the Arbus pluton (SW Sardinia, Italy): Crystal-chemical study and petrological constraints

NASA Astrophysics Data System (ADS)

Bosi, Ferdinando; Naitza, Stefano; Skogby, Henrik; Secchi, Francesco; Conte, Aida M.; Cuccuru, Stefano; Hålenius, Ulf; De La Rosa, Nathaly; Kristiansson, Per; Charlotta Nilsson, E. J.; Ros, Linus; Andreozzi, Giovanni B.

2018-05-01

Tourmalines from the late-Variscan Arbus pluton (SW Sardinia) and its metamorphic aureole were structurally and chemically characterized by single-crystal X-ray diffraction, electron and nuclear microprobe analysis, Mössbauer, infrared and optical absorption spectroscopy, to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages. The Arbus pluton represents a peculiar shallow magmatic system, characterized by sekaninaite (Fe-cordierite)-bearing peraluminous granitoids, linked via AFC processes to gabbroic mantle-derived magmas. The Fe2+-Al-dominant tourmalines occur in: a) pegmatitic layers and pods, as prismatic crystals; b) greisenized rocks and spotted granophyric dikes, as clots or nests of fine-grained crystals in small miaroles locally forming orbicules; c) pegmatitic veins and pods close to the contacts within the metamorphic aureole. Structural formulae indicate that tourmaline in pegmatitic layers is schorl, whereas in greisenized rocks it ranges from schorl to fluor-schorl. Tourmalines in thermometamorphosed contact aureole are schorl, foitite and Mg-rich oxy-schorl. The main substitution is Na + Fe2+ ↔ □ + Al, which relates schorl to foitite. The homovalent substitution (OH) ↔ F at the O1 crystallographic site relates schorl to fluor-schorl, while the heterovalent substitution Fe2+ + (OH, F) ↔ Al + O relates schorl/fluor-schorl to oxy-schorl. Tourmaline crystallization in the Arbus pluton was promoted by volatile (B, F and H2O) enrichment, low oxygen fugacity and Fe2+ activity. The mineralogical evolutive trend is driven by decreasing temperature, as follows: sekaninaite + quartz → schorl + quartz → fluor-schorl + quartz → foitite + quartz. The schorl → foitite evolution represents a distinct trend towards (Al + □) increase and unit-cell volume decrease. These trends are typical of granitic magmas and consistent with Li-poor granitic melts, as supported by the absence of elbaite and other Li-minerals in the Arbus pluton. Tourmaline-bearing rocks reflect the petrogenetic significance of contribution from a metapelitic crustal component during the evolution of magmas in the middle-upper crust.

Courtright intrusive zone: Sierra National Forest, Fresno County, California.

USGS Publications Warehouse

Bateman, P.C.; Kistler, R.W.; DeGraff, J.V.

1984-01-01

This is a field guide to a well-exposed area of plutonic and metamorphic rocks in the Sierra National Forest, Fresno County, California. The plutonic rocks, of which three major bodies are recognized, besides aplite and pegmatite dykes, range 103 to approx 90 m.y. in age. Points emphasized include cataclastic features within the plutonic rocks, schlieren and mafic inclusions. (M.A. 83M/0035).-A.P.

THE AGES OF BOMA MIGMATITES AND OF THE WEST CONGOLIAN OROGENY. PRELIMINARY DATA ON THE AGES OF THE MAYUMBIAN AND AN EARLIER FORMATION (in French)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cahen, L.; Delhal, J.; Ledent, D.

1963-08-01

The oldest, (2760 plus or minus 500) million years or older, is interpreted as representing an episode of an orogenic cycle, older than the Mayumbian orogeny. The next event, also only approximately dated between 1480 and 1800 million years is the Mayumbian orogeny. The last major event, of which a late tectonic phase is circa 615 million years old, is the West-Congolian orogeny which is followed by posttectonic pegmatites and veins spanning the interval between 520 (pegmatites) to circa 445 (last veins) million years. Numerous biotites have, by both the Rb--Sr and the K--Ar method, yielded apparent ages similar tomore » those of the last post-tectonic veins, though their true age be certainly older. This is also the case for-a K--Ar age on microcline. These results indicate that these apparent ages on biotite and microcline are probably caused by a post-tectonic hydrothermal event and/or by the uplift which took place at the same time, after the West Congolian folding. It therefore follows that low Rb-- Sr apparent ages on biotites are not necessarily caused by superimposed tectonics or by an important metamorphism. (auth)« less

Main types of rare-metal mineralization in Karelia

NASA Astrophysics Data System (ADS)

Ivashchenko, V. I.

2016-03-01

Rare-metal mineralization in Karelia is represented by V, Be, U deposits and In, Re, Nb, Ta, Li, Ce, La, and Y occurrences, which are combined into 17 types of magmatic, pegmatite, albitite-greisen, hydrothermal-metasomatic, sedimentary, and epigenetic groups. The main vanadium resources are localized in the Onega ore district. These are deposits of the Padma group (556 kt) and the Pudozhgorsky complex (1.5 Mt). The REE occurrences are primarily characterized by Ce-La specialization. The perspective of HREE is related to the Eletozero-Tiksheozero alkaline and Salmi anorthosite-rapakivi granite complexes. Rare-metal pegmatites bear complex mineralization with insignificant low-grade resources. The Lobash and Jalonvaara porphyry Cu-Mo deposits are potential sources of rhenium: Re contents in molybdenite are 20-70 and 50-246 ppm and hypothetical resources are 12 and 7.5 t, respectively. The high-grade (˜100 ppm) and metallogenic potential of indium (˜2400 t) make the deposits of the Pitkäranta ore district leading in the category of Russian ore objects most prospective for indium. Despite the diverse rare-metal mineralization known in Karelia, the current state of this kind of mineral commodities at the world market leaves real metallogenic perspective only for V, U, Re, In, and Nb.

Application of pinch-and-swell structure rheology gauge to determine rock paleo-rheological parameters in Taili, western Liaoning, NE China

NASA Astrophysics Data System (ADS)

Sun, Zhengquan; Zeng, Zuoxun; Wu, Linbo; Xu, Shaopeng; Yang, Shuang; Chen, Deli; Wang, Jianxiu

2017-05-01

New results, in combination with previously published ones, reveal that when the Stress Exponent of the Competent layer (SEC) ranges from 1 to 10 (1 < n < 10), Pinch-and-Swell structure Rheology Gauge (PSRG) can only be available under the condition that the Viscosity ratio between the Competent layer and its corresponding Matrix layer (VCM) is larger than 10. Therefore, we made the attempt to calculate the viscosity ratio of pinch-and-swell structure of competent layer to the related matrix and stress exponent. Based on this knowledge, we applied this gauge to calculate SECs and VCMs of eight types of pinch-and-swell structures, which are widely developed in the Taili area of the west Liaoning Province in China. Statistical analysis of the SEC resulted in intervals of four types of competent layers, that is, Medium-scale Granitic coarse-to-pegmatitic Veins, Small-scale Augen Granite aplite Veins, Small-scale Granite aplite Veins, and Small-scale Augen Quartz-K-feldspar veins, with intervals of [3.50, 4.63], [2.64, 4.29], [2.70, 3.51], and [2.50, 3.36] respectively. The preferred intervals of VCM of the five types of pinch-and-swell structures, Small-scale Augen Granite aplite Veins + Fine-grained Biotite-Hornblende-plagioclase Gneiss, Medium-scale Granitic coarse-to-pegmatitic Veins + Fine-grained Biotite-Hornblende-plagioclase Gneiss, Small-scale Augen Granite aplite Veins + medium-to-fine-grained granitic gneiss, Medium-scale Granitic coarse-to-pegmatitic Veins + medium-to-fine-grained granitic gneiss, and Small-scale Augen Granite aplite Veins + fine-grained biotite-plagioclase gneiss, are [19.98, 62.51], [15.90, 61.17], [26.72, 93.27], [22.21, 107.26], and [76.33, 309.39] respectively. The similarities between these calculated SEC statistical preferred intervals and the physical experimental results verify the validity of the PSRG. The competent layers of the pinch-and-swell structures were presented in this study as power-law flow with SEC values that increased with the thickness of the layer. Grain-size plays an important role in the rheology of pinch-and-swell structures. The results offer a case for the application of PSRG and determine the key rock rheological parameters of North China Craton for future related studies.

Timing of metamorphism and exhumation in the Nordøyane ultra-high-pressure domain, Western Gneiss Region, Norway: New constraints from complementary CA-ID-TIMS and LA-MC-ICP-MS geochronology

NASA Astrophysics Data System (ADS)

Butler, J. P.; Jamieson, R. A.; Dunning, G. R.; Pecha, M. E.; Robinson, P.; Steenkamp, H. M.

2018-06-01

We present the results of a combined CA-ID-TIMS and LA-MC-ICP-MS U-Pb geochronology study of zircon and associated rutile and titanite from the Nordøyane ultra-high-pressure (UHP) domain in the Western Gneiss Region (WGR) of Norway. The dated samples include 4 eclogite bodies, 2 host-rock migmatites, and 2 cross-cutting pegmatites and leucosomes, all from the island of Harøya. Zircon from a coesite eclogite yielded an age of ca. 413 Ma, interpreted as the time of UHP metamorphism in this sample. Zircon data from the other eclogite bodies yielded metamorphic ages of ca. 413 Ma, 407 Ma, and 406 Ma; zircon trace-element data associated with 413 Ma and 407 Ma ages are consistent with eclogite-facies crystallization. In all of the eclogites, U-Pb dates from zircon cores, interpreted as the times of protolith crystallization, range from ca. 1680-1586 Ma, consistent with Gothian ages from orthogneisses in Nordøyane and elsewhere in the WGR. A zircon core age of ca. 943 Ma from one sample agrees with Sveconorwegian ages of felsic gneisses and pegmatites in the western part of the area. Migmatites hosting the eclogite bodies yielded zircon core ages of ca. 1657-1591 Ma and rim ages of ca. 395-392 Ma, interpreted as the times of Gothian protolith formation and Scandian partial melt crystallization, respectively. Pegmatite in an eclogite boudin neck yielded a crystallization age of ca. 388 Ma, interpreted as the time of melt crystallization. Rutile and titanite from 3 samples (an eclogite and two migmatites) yielded concordant ID-TIMS ages of 378-376 Ma. The results are similar to existing U-Pb data from other Nordøyane eclogites (415-405 Ma). In combination with previous pressure-temperature data from the coesite eclogite, these ages indicate that peak metamorphic conditions of 3 GPa/760 °C were reached ca. 413 Ma, followed by decompression to 1 GPa/810 °C by ca. 397 Ma and cooling below ca. 600 °C by ca. 375 Ma. The results are compatible with protracted UHP metamorphism followed by relatively slow exhumation. The question of whether partial melting began at UHP conditions is not resolved by this study.

Vibrational spectroscopic characterization of the phosphate mineral ludlamite (Fe,Mn,Mg)₃(PO₄)₂⋅4H₂O - a mineral found in lithium bearing pegmatites.

PubMed

Frost, Ray L; Xi, Yunfei; Scholz, Ricardo; Belotti, Fernanda M

2013-02-15

The objective of this work is to analyze ludlamite (Fe,Mn,Mg)(3)(PO(4))(2)⋅4H(2)O from Boa Vista mine, Galiléia, Brazil and to assess the molecular structure of the mineral. The phosphate mineral ludlamite has been characterized by EMP-WDS, Raman and infrared spectroscopic measurements. The mineral is shown to be a ferrous phosphate with some minor substitution of Mg and Mn. Raman bands at 917 and 950 cm(-1) are assigned to the symmetric stretching mode of HOPO(3)(2-) and PO(4)(3-) units. Raman bands at 548, 564, 599 and 634 cm(-1) are assigned to the ν(4)PO(4)(3-) bending modes. Raman bands at 2605, 2730, 2896 and 3190 cm(-1) and infrared bands at 2623, 2838, 3136 and 3185 cm(-1) are attributed to water stretching vibrations. By using a Libowitzky empirical function, hydrogen bond distances are calculated from the OH stretching wavenumbers. Strong hydrogen bonds in the structure of ludlamite are observed as determined by their hydrogen bond distances. The application of infrared and Raman spectroscopy to the study of ludlamite enables the molecular structure of the pegmatite mineral ludlamite to be assessed. Copyright © 2012 Elsevier B.V. All rights reserved.

Spectrochemical determination of thorium in monazite by the powder-d.c. arc technique

USGS Publications Warehouse

Dutra, C.V.; Murata, K.J.

1954-01-01

Thorium in monazite is determined by a d.c. carbon-arc technique using zirconium as the internal standard. The analytical curve for Th II 2870.413 A??/Zr II 2844-579 A?? is established by means of synthetic standards containing graduated amounts of thoria and 0.500 per cent zirconia in pegmatite base (60 parts quartz, 40 parts microchne, and 1 part ferric oxide). Monazite samples are diluted 14-fold with pegmatite base that contains 0.538 per cent ZrO2, so that the zirconia content of the resulting mixture is also 0.500 per cent. In addition, both the standards and the diluted monazites are mixed with one-half their weight of powdered graphite. Approximately 25 mg of the prepared samples are arced to completion at 15.5 to 17.5 amperes. With the 14-fold dilution employed, the accurate range of the method is 3 to 20 per cent thoria in the original monazite. The coefficient of variation for a single determination is 4 per cent at the 7 per cent thoria level. Tests with synthetic unknowns and chemically analyzed monazites show a maximum error of ??10 per cent of the thoria content. If niobium is substituted for zirconium as the internal standard, there is a loss of precision. Platinum as the internal standard gives results of good precision but introduces a marked sensitivity to matrix effects. ?? 1954.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delhal, J.; Lay, C.; Ledent, D.

Ten Sr/Rb apparent ages obtained on minerals separated from rocks of the Kasai (South Congo) basement are interpreted as giving the age of three major events of the geological history of this basement. From North to South the area studied can be subdivised into three major portions: the Dibaya-type basement, the intermediate region, and the Luiza-type basement. A first metamorphism in the Luiza basement appears to be at least 3,300 m.y. old. It is followed by a charnockitization and a migmatitization. The latter phenomenon appears to be identical with the granitization of the Dibaya basement which occurred at circa 2,700more » m.y. Later, an important cataclasis with pegmatitic intrusions affected the Dibaya basement. The pegmatites are dated at circa 2,100 m.y. This is also the age of the metamorphism and orogeny of the Luiza metasedimentary series which forms part of the intermediate region. This orogeny is therefore considered responsible for the above mentioned widespread cataclasis and activity. Three dated orogenic cycles are therefore superposed in this part of the Kasai basement; at least one younger, undated, cycle (the Lulua cycle) is recognized in the same general area. These preliminary results will be used as a foundation for a more complete dating program based not only on further Sr/Rb ages but also on ages obtained by other methods. An adequate nomenclature will be adopted as a result of the planned detailed studies. (auth)« less

Petrologic Applications of Tourmaline

NASA Astrophysics Data System (ADS)

London, D.; Morgan, G. B., VI; Wolf, M. B.; Guttery, B. M.

2011-12-01

Compositions of tourmaline reflect its chemical environment of formation. Schorl-dravite is an accessory in metapelites and persists up to the onset of anatexis. Amphibolites and marbles contain uvite, and magnesiofoitite-povandraite is distinctive of base-metal porphyries. In granitic pegmatites, schorl-dravite at the contacts evolves toward foitite and olenite (aluminous) components as Fe is depleted from the melt. Fractionation may bring residual melts to saturation in elbaite, an Li-rich component of tourmaline. Common tourmaline (schorl-dravite-olenite-foitite solid solution) possesses a wide P-T field of stability. Synthesis experiments put the upper thermal limit of common tourmaline at ~ 750°-850°C from 50 MPa to 10 GPa, and dravite has been synthesized as low as 350°C. The boron content of granitic melt or aqueous fluid in equilibrium with common tourmaline alone and with equivalent silicate mineral assemblages varies sharply with temperature according to a relationship of CB2O3melt,vapor ~ 0.0032e0.0087T(C). Common tourmaline is stable over an aSiO2 at and below saturation in Qtz; besides FeMg, its stability hinges principally on the solubility product [aAl2O3]3*[aB2O3]1.5 in vapor or melt. Surprisingly, increasing activities of H2O or fluoride components (both are present in tourmaline) destabilize common tourmaline in granitic melt, as both components form complexes with Al that reduce aAl2O3 in the melt. As a result, common tourmaline may survive anatexis when the aH2O attending melting is low. In contrast to common tourmaline, most attempts to synthesize elbaite have failed. Aluminous tourmaline containing 37 mol% Elb component has been synthesized recently, which is significant for understanding occurrences in pegmatites as well as for the potential appearance of synthetic elbaite on the gem market. Experimental calibration of δ11B between aqueous fluid and dravite at 50-500 MPa and 350°-750°C varies by only 6.1 % over this range of conditions (tourmaline is isotopically light with respect to the fluid), but it is pressure-dependent at least up to 200 MPa. This isotopic range is narrow in relation to vast tourmaline-producing magmatic-hydrothermal systems, such as the granites of Cornwall, UK. Preliminary experiments by Hervig et. al. (2002) report a large variation of Δ11B between aqueous fluid and granitic melt over small ranges of T, such that the isotopic composition of tourmaline should shift dramatically to higher (vapor) or lower (melt) values when crystallization occurs from a two-phase fluid system. Existing studies of consanguineous granite-pegmatite systems show nearly no variation of δ11B from common tourmaline in source granites to elbaite in the most fractionated pegmatites; the values correspond to those of tourmaline-melt, with little evidence for crystallization from vapor. Tourmaline may prove useful as a geothermometer in the same way as other AFM minerals, but the complexities of coupled substitutions in relation to the multitude of site occupancies in tourmaline will make experimental calibration a difficult, if not futile effort. Elemental fractionation between the polar ends of tourmaline, and its tendency for unidirectional growth, further complicate any quantitative treatment of its chemical composition.

The vernon supersuite: Mesoproterozoic A-type granitoid rocks in the New Jersey highlands

USGS Publications Warehouse

Volkert, R.A.; Drake, Avery A.

1998-01-01

Abundant Mesoproterozoic A-type granitoid rocks of two intrusive suites underlie approximately 50 percent of the New Jersey Highlands. These rocks, the Byram Intrusive and Lake Hopatcong Intrusive Suites, consist of granite, alaskite, quartz monzonite, monzonite, and minor pegmatite. Byram and Lake Hopatcong rocks, although different mineralogically, are similar geochemically and contain overlapping abundances of most major and trace elements. Petrographic relationships, geochronology, field relationships, and geochemical similarities support a comagmatic origin for both suites. They constitute the here named Vernon Supersuite.

Mineral potential for incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites in the Islamic Republic of Mauritania (phase V, deliverable 87): Chapter Q in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Taylor, Cliff D.; Giles, Stuart A.

2015-01-01

USGS review of PRISM-I data suggests that there is abundant documentation of the Bou Naga alkaline complex and to a lesser degree, the Guelb er Richat carbonatite complex, but that all other occurrences of U, Th, REE, and associated elements are poorly described, and poorly understood (Taylor, 2007)

CHRONOLOGY OF MAJOR METAMORPHIC EVENTS IN THE SOUTHEASTERN UNITED STATES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, L.E.; Kulp, J.L.; Eckelmann, F.D.

1959-10-01

Potassium-argon and rubidium-strontium age measurements have been made on a variety of granites, pegmatites, gneiases and schists which comprise the plutonicmetamorphic complex of the Piedmont and Blue Ridge of the southeastern United States. Large portions of the area appear to have been metamorphosed initially approximately at the same time as the Grenville Province, i.e., about 900 to 1100 m.y. ago. Superimposed on this older metamorphic province was a major orogenic event culminating at about 350 m.y. with widespread recrystallization of existing rocks and intrusion of pegmatites in the Spruce Pine, Franklin-Sylva and Bryson City Districts, and granites in the Virginiamore » and North Carolina Piedmont. There is strong evidence of an additional metamorphic epoch between 350 and 1000 m.y., but its effects have been largely obliterated by the 350 m.y. event. In western North Carolina a transition of apparent ages from 355 to 890 m.y. occurs in the same rock unit. (Cranberry gneiss) over a distance of about 10 miles across the strike of the border- of the 350 m.y. event. In the southeastern Piedmont of Georgia and South Carolina a younger metamorphic event or events can be detected producing rocks of apparent age ranging from 230 to 310 m.y. The time of these orogenies is compared with those in the Central and Northern Appalachians. Evidence is accumulating that the Holmes' time scale will have to be considerably lengthened. (auth)« less

Natural occurrence and significance of fluids indicating high pressure and temperature

USGS Publications Warehouse

Roedder, E.

1981-01-01

Most natural minerals have formed from a fluid phase such as a silicate melt or a saline aqueous solution. Fluid inclusions are tiny volumes of such fluids that were trapped within the growing crystals. These inclusions can provide valuable but sometimes ambiguous data on the temperature, pressure, and composition of these fluids, many of which are not available from any other source. They also provide "visual autoclaves" in which it is possible to watch, through the microscope, the actual phase changes take place as the inclusions are heated. This paper reviews the methods of study and the results obtained, mainly on inclusions formed from highly concentrated solutions, at temperatures ???500??C. Many such fluids have formed as a result of immiscibility with silicate melt in igneous or high-temperature metamorphic rocks. These include fluids consisting of CO2, H2O, or hydrosaline melts that were <50% H2O. From the fluid inclusion evidence it is clear that a boiling, very hot, very saline fluid was present during the formation of most of the porphyry copper deposits in the world. Similarly, from the inclusion evidence it is clear that early (common) pegmatites formed from essentially silicate melts and that the late, rare-element-bearing and chamber-type pegmatites formed from a hydrosaline melt or a more dilute water solution. The evidence on whether this change in composition from early to late solutions was generally continuous or involved immiscibility is not as clear. ?? 1981.

Zinc- and Y-group-bearing senaite from St Peters Dome, and new data on senaite from Dattas, Minas Gerais, Brazil.

USGS Publications Warehouse

Foord, E.E.; Sharp, W.N.; Adams, J.W.

1984-01-01

'Mineral Y', an unidentified phase described in association with murataite from a pegmatite in the Pikes Peak granite, El Paso County, Colorado (A.M. 59-172) is now found to be a senaite containing ZnO 7.05% and RE2O3 + Y2O3 5.24%, with the Zn and Y-group REE entering the (Ti,Fe,Mn) position. A Zn-bearing senaite from Dattas, Diamantina, Minas Gerais, has ZnO 7.7%.-R.A.H.

Electric-field-ratio profiling at the Silsilah tin-bearing greisen deposit, Kingdom of Saudi Arabia

USGS Publications Warehouse

Kamilli, R.J.; Zablocki, C.J.

1993-01-01

Buried, possibly mineralized granite cupolas at the Silsilah tin deposit in Saudi Arabia have been successfully located using a closely spaced electric-field-ratio profiling technique. In this study electrical fields at 27 and 270 Hz across grounded electrodes spaced 50m apart were measured along six traverses. The technique allowed the authors to identify and distinguish among unroofed granite cupolas, cupolas with their aplite-pegmatite apical contact zones intact, strong and weak greisens, dikes, faults, and pervasively argillized rocks. -from Authors

Thermochronologic constraints on mylonite and detachment fault development, Kettle Highlands, northeastern Washington and southern British Columbia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berger, B.R.; Snee, L.W.

1992-01-01

The Kettle dome, northeastern Washington and southern British Columbia, is one of several large metamorphic core complexes in the region. New Ar-40/Ar-39 cooling dates from the mylonite immediately beneath the Kettle River detachment fault at Barney's Junction, a cross-cutting mafic dike, and the youngest Eocene lavas in the Republic graben set constraints on kinematic models of the tectonic evolution of the dome and related grabens: Amphibolite--hornblende (59.0 [+-] 0.2); Pegmatite--muscovite (49.3 [+-] 0.2); Pegmatite--K-feldspar (49.2 [+-] 1); Augen gneiss--K-feldspar (48.0 [+-] 1); Mafic dike--hornblende (54.5 [+-] 0.1) and biotite (49.6 [+-] 0.1); Klondike Mt. Formation lava--feeder dike (48.8 [+-] 1).more » The authors interpret the dates to indicate that the tectonized amphibolite, part of a Cretaceous and older metamorphosed terrane, had formed and cooled to [approx] 500 C by Late Paleocene, the mylonite zone was being domed above the ductile zone by Early Eocene at the time of emplacement of the dike--temporally equivalent to the Keller Butte suite, Eocene Colville batholith--which crosscuts the mylonite, and incipient rifting was occurring in the Republic graben as evidenced by dike swarms. The mylonite complex reached 300 C by 49Ma coincident with the termination of Sanpoil volcanism, and then cooled rapidly to near or below 150 C by 48 Ma. At about this time, mafic Klondike Mt. lavas mark the termination of Republic graben rifting and possibly detachment faulting along the Kettle River fault.« less

Genesis of kasolite associated with aplite-pegmatite at Jabal Sayid, Hijaz region, Kingdom of Saudi Arabia

NASA Astrophysics Data System (ADS)

Dawood, Yehia H.; Harbi, Hesham M.; Abd El-Naby, Hamdy H.

2010-01-01

In this study, we report kasolite Pb(UO 2)SiO 4·(H 2O) for the first time as a main uranyl mineral in the mineralized aplite-pegmatite of Jabal Sayid, Hijaz region. It commonly forms clusters of yellow acicular crystals in the voids and fractures. The mineral chemistry and mineralogical characteristics of kasolite were investigated using different techniques. Calcium, iron and phosphorus are detected in kasolite in addition to its major constituents; uranium, lead and silicon. Lead does not exist as a radiogenic product and not even as a substitute for uranium in the mineral structure. Alternatively, galena mineralization could be considered as a source for lead. The fluoride and carbonate complexes played a significant role in the formation of kasolite. High temperature hydrothermal solutions reacted with pre-existing uranium-bearing metamictized accessory minerals such as pyrochlore, U-rich thorite and zircon to form uranous fluoride complexes. These complexes are predominant in reducing environment and at pH 4. When the fluids approached the surface passing through fracture system, the oxygen fugacity ( fO 2) and the pH increased because of the loss of volatile components. At these conditions, uranous fluorides would convert to uranyl fluoride complexes UO 2F 3-. Further decrease in temperature was associated with the decay of the activity of fluorine ion by the dilution of hydrothermal solutions and precipitation of fluorite. At this condition, uranyl-carbonate complexes are favoured. These complexes were combined later with silica and lead to form kasolite.

Quantitative kinematic analysis within the Khlong Marui shear zone, southern Thailand

NASA Astrophysics Data System (ADS)

Kanjanapayont, Pitsanupong; Grasemann, Bernhard; Edwards, Michael A.; Fritz, Harald

2012-02-01

The NNE trending Khlong Marui shear zone has a strong geomorphic signal with marked fault-strike parallel topographic ridges. The lithologies within the strike-slip zone mainly consist of vertical layers of mylonitic meta-sedimentary rocks associated with orthogneisses, mylonitic granites, and pegmatitic veins. The pegmatitic veins concordantly intrude the mylonitic foliation but were sheared at the rims indicating syn-kinematic emplacement. Microstructures and mineral assemblages suggest that the rocks in the area have been metamorphosed at amphibolite facies and low to medium greenschist facies by the first deformation. The Khlong Marui shear zone was deformed under dextral simple shear flow with a small finite strain. The ductile-to-brittle deformation involves a period of exhumation of lenses of higher grade rocks together with low grade fault rocks probably associated with positive flower structures. The final stage brittle deformation is reflected by normal faulting and formation of proto-cataclasites to cataclasites of the original mylonitic meta-sedimentary host rock. Although clear age-constraints are still missing, we use regional relationships to speculate that earlier dextral strike-slip displacement of the Khlong Marui shear zone was related to the West Burma and Shan-Thai collision and subduction along the Sunda Trench in the Late Cretaceous, while the major exhumation period of the ductile lens was tectonically influenced by the early India-Asia collision. The changing stress field has responded by switching from dextral strike-slip to normal faulting in the Khlong Marui shear zone, and is associated with "escape tectonics" arising from the overall India-Asia collision.

Plume-related mantle source of super-large rare metal deposits from the Lovozero and Khibina massifs on the Kola Peninsula, Eastern part of Baltic Shield: Sr, Nd and Hf isotope systematics

NASA Astrophysics Data System (ADS)

Kogarko, L. N.; Lahaye, Y.; Brey, G. P.

2010-03-01

The two world’s largest complexes of highly alkaline nepheline syenites and related rare metal loparite and eudialyte deposits, the Khibina and Lovozero massifs, occur in the central part of the Kola Peninsula. We measured for the first time in situ the trace element concentrations and the Sr, Nd and Hf isotope ratios by LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometer) in loparite, eudialyte an in some other pegmatitic minerals. The results are in aggreement with the whole rock Sr and Nd isotope which suggests the formation of these superlarge rare metal deposits in a magmatic closed system. The initial Hf, Sr, Nd isotope ratios are similar to the isotopic signatures of OIB indicating depleted mantle as a source. This leads to the suggestion that the origin of these gigantic alkaline intrusions is connected to a deep seated mantle source—possibly to a lower mantle plume. The required combination of a depleted mantle and high rare metal enrichment in the source can be explained by the input of incompatible elements by metasomatising melts/fluids into the zones of alkaline magma generation shortly before the partial melting event (to avoid ingrowth of radiogenic isotopes). The minerals belovite and pyrochlore from the pegmatites are abnormally high in 87Sr /86Sr ratios. This may be explained by closed system isotope evolution as a result of a significant increase in Rb/Sr during the evolution of the peralkaline magma.

Mercury contamination in agricultural soils from abandoned metal mines classified by geology and mineralization.

PubMed

Kim, Han Sik; Jung, Myung Chae

2012-01-01

This survey aimed to compare mercury concentrations in soils related to geology and mineralization types of mines. A total of 16,386 surface soils (0~15 cm in depth) were taken from agricultural lands near 343 abandoned mines (within 2 km from each mine) and analyzed for Hg by AAS with a hydride-generation device. To meaningfully compare mercury levels in soils with geology and mineralization types, three subclassification criteria were adapted: (1) five mineralization types, (2) four valuable ore mineral types, and (3) four parent rock types. The average concentration of Hg in all soils was 0.204 mg kg(-1) with a range of 0.002-24.07 mg kg(-1). Based on the mineralization types, average Hg concentrations (mg kg(-1)) in the soils decreased in the order of pegmatite (0.250) > hydrothermal vein (0.208) > hydrothermal replacement (0.166) > skarn (0.121) > sedimentary deposits (0.045). In terms of the valuable ore mineral types, the concentrations decreased in the order of Au-Ag-base metal mines ≈ base metal mines > Au-Ag mines > Sn-W-Mo-Fe-Mn mines. For parent rock types, similar concentrations were found in the soils derived from sedimentary rocks and metamorphic rocks followed by heterogeneous rocks with igneous and metamorphic processes. Furthermore, farmland soils contained relatively higher Hg levels than paddy soils. Therefore, it can be concluded that soils in Au, Ag, and base metal mines derived from a hydrothermal vein type of metamorphic rocks and pegmatite deposits contained relatively higher concentrations of mercury in the surface environment.

SHRIMP-RG U-Pb ages of provenance and metamorphism from detrital zircon populations and Pb-Sr-Nd signatures of prebatholithic metasedimentary rocks at Searl Ridge, northern Peninsular Ranges batholith, southern California: Implications for their age, origin, and tectonic setting

USGS Publications Warehouse

Premo, Wayne R.; Morton, Douglas M.

2014-01-01

Twenty-four samples were collected from prebatholithic metasedimentary rocks along Searl Ridge, the north rim of the Diamond Valley Reservoir, Domenigoni Valley, centrally located in the northern Peninsular Ranges of southern California. These rocks exhibit progressive metamorphism from west to east across fundamental structural discontinuities now referred to as a “transition zone.” Documented structural and mineralogical changes occur across this metamorphic gradient. Sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) U-Pb ages were obtained from detrital zircons from metasedimentary rocks through the transition zone. To the west, metapelitic and minor metasandstone units yielded numerous concordant 206Pb/238U ages between 210 and 240 Ma, and concordant 207Pb/206Pb ages at 1075–1125 Ma, 1375–1430 Ma, and 1615–1735 Ma, although distinct differences in provenance were noted between units. A few older 207Pb/206Pb ages obtained were ca. 2250 Ma and ca. 2800 Ma. Rocks of the eastern part of the transition zone include high-grade paragneisses that yielded numerous concordant 206Pb/238U ages between 103 and 123 Ma and between 200 and 255 Ma, and concordant 207Pb/206Pb ages at 1060–1150 Ma, 1375–1435 Ma, and 1595–1710 Ma. Some zircon results from these high-grade gneisses are marked by distinct Pb-loss discordia with lower-intercept ages of ca. 215 Ma and Paleoproterozoic upper-intercept ages. Younger ages between 100 and 105 Ma are mainly obtained from rims of some zircon grains that are characterized by low Th/U values (<0.1) and high U contents (>1000 ppm), indicating the likelihood of metamorphic zircon growth at that time. The similarity of zircon age populations between western and eastern units through the transition zone indicates that this fundamental structure probably dissects sediments of the same basin. This supposition is further supported by initial whole-rock Pb-Sr-Nd isotopic data that show similar average initial 206Pb/204Pb (18.65 to 18.9), 87Sr/86Sr (0.713 to 0.718), and εNd (−7 to −12) values for both the western and eastern units—values that also indicate the presence of significantly older crustal material in their provenance.Magmatic zircons from a diorite dike that crosscuts the foliation, but is itself subsequently metamorphosed, yielded a SHRIMP-RG concordia age of 103.3 ± 0.73 Ma, which is within agreement of an isotope dilution–thermal ionization mass spectrometry (ID-TIMS) U-Pb age of 103.37 ± 0.25 Ma. A postmetamorphic, cross-cutting pegmatite yielded discordant U-Pb zircon age data, but euhedral, glassy monazite from the pegmatite yielded a slightly discordant 207Pb/235U age of 101.85 ± 0.35 Ma and a Th-Pb age of 97.53 ± 0.18 Ma, suggesting that this pegmatite was injected during or just after deformation ceased. The age and initial Pb-Sr-Nd signature for the dioritic dike indicate it was produced during the transition zone plutonism elsewhere in the northern Peninsular Ranges batholith, whereas the pegmatitic dike was derived from crustal anatexis.Collectively, these results indicate that this sequence of metasedimentary rocks was derived from mainly a Late Permian to Early Triassic igneous provenance that probably intruded Proterozoic crust. The sequence was subsequently metamorphosed during deformation of the Cretaceous continental margin at ca. 105 to 97 Ma.

Batievaite-(Y), Y2Ca2Ti[Si2O7]2(OH)2(H2O)4, a new mineral from nepheline syenite pegmatite in the Sakharjok massif, Kola Peninsula, Russia

NASA Astrophysics Data System (ADS)

Lyalina, L. M.; Zolotarev, A. A.; Selivanova, E. A.; Savchenko, Ye. E.; Krivovichev, S. V.; Mikhailova, Yu. A.; Kadyrova, G. I.; Zozulya, D. R.

2016-12-01

Batievaite-(Y), Y2Ca2Ti[Si2O7]2(OH)2(H2O)4, is a new mineral found in nepheline syenite pegmatite in the Sakharjok alkaline massif, Western Keivy, Kola Peninsula, Russia. The pegmatite mainly consists of nepheline, albite, alkali pyroxenes, amphiboles, biotite and zeolites. Batievaite-(Y) is a late-pegmatitic or hydrothermal mineral associated with meliphanite, fluorite, calcite, zircon, britholite-group minerals, leucophanite, gadolinite-subgroup minerals, titanite, smectites, pyrochlore-group minerals, zirkelite, cerianite-(Ce), rutile, behoite, ilmenite, apatite-group minerals, mimetite, molybdenite, and nickeline. Batievaite-(Y) is pale-cream coloured with white streak and dull, greasy or pearly luster. Its Mohs hardness is 5-5.5. No cleavage or parting was observed. The measured density is 3.45(5) g/cm3. Batievaite-(Y) is optically biaxial positive, α 1.745(5), β 1.747(5), γ 1.752(5) (λ 589 nm), 2 V meas. = 60(5)°, 2 V calc. = 65°. Batievaite-(Y) is triclinic, space group P-1, a 9.4024(8), b 5.5623(5), c 7.3784(6) Å, α 89.919(2), β 101.408(2), γ 96.621(2)°, V 375.65(6) Å3 and Z = 1. The eight strongest lines of the X-ray powder diffraction pattern [ d(Å)(I)( hkl)] are: 2.991(100)(11-2), 7.238(36)(00-1), 3.061(30)(300), 4.350(23)(0-1-1), 9.145(17)(100), 4.042(16)(11-1), 2.819(16)(3-10), 3.745(13)(2-10). The chemical composition determined by electron probe microanalysis (EPMA) is (wt.%): Nb2O5 2.25, TiO2 8.01, ZrO2 2.72, SiO2 29.96, Al2O3 0.56, Fe2O3 0.43, Y2O3 11.45, La2O3 0.22, Ce2O3 0.33, Nd2O3 0.02, Gd2O3 0.07, Dy2O3 0.47, Er2O3 1.07, Tm2O3 0.25, Yb2O3 2.81, Lu2O3 0.45, CaO 24.98, MnO 1.31, MgO 0.01, Na2O 1.13, K2O 0.02, F 2.88, Cl 0.19, H2O 6.75 (determined on the basis of crystal structure data), O = (F,Cl) -1.25, total 97.09 wt.%. The empirical formula based on the EPMA and single-crystal structure analyses is (Y0.81Ca0.65Mn0.15Zr0.12Yb0.11Er0.04Fe3+ 0.04Ce0.02Dy0.02Lu0.02La0.01Tm0.01)Σ2.00((H2O)0.75Ca0.70□0.55)Σ2.00Ca2.00(□0.61Na0.25( H2O)0.14)Σ1.00(Ti0.76Nb0.15Zr0.09)Σ1.00[(Si3.91Al0.09)Σ4.00O14]((OH)1.56F0.44)Σ2.00((H2O)1.27F0.73)Σ2.00. The infrared spectrum of the mineral contains the following bands (cm-1): 483, 584, 649, 800, 877, 985, 1630, 1646, 1732, 3426. Batievaite-(Y) belongs to the rosenbuschite group minerals and is the Na-deficient Y-analogue of hainite. The mineral is named in honour of the Russian geologist Iya Dmitrievna Batieva (1922-2007) in recognition of her remarkable contribution into the geology and petrology of metamorphic and alkaline complexes of the Kola Peninsula.

Mineral resources and resource potential map of the Pyramid Peak Roadless Area, Riverside County, California

USGS Publications Warehouse

Calzia, J.P.

1988-01-01

Geologic and geochemical data indicate that the study area has high resource potential for marble, and moderate resource potential for epithermal gold deposits and tungsten skarns. The Desert Divide Group and the Palm Canyon Complex contain large resources of marble quarried for Portland cement and for construction applications. Gold occurs in quartz veins and pegmatites in the Desert Divide Group and the Penrod Quartz Monzonite. Skarns in the Desert Divide Group contain scheelite and anomalous concentrations of arsenic and beryllium. Thin layers of tremolite asbestos along low-angle thrust faults occur outside of the study area.

A discussion of 'Anomalous quartz from the Roter Kamm impact crater, Namibia - Evidence for post-impact hydrothermal activity?'

NASA Astrophysics Data System (ADS)

Roedder, Edwin

1990-11-01

This paper presents arguments against the statement made by Koeberl et al. (1989) to the effect that various differences between the quartz of the three quartz pebbles from the Roter Kamm impact crater (Namibia) and the quartz of the pegmatites present in the basement rocks of this crater can be best interpreted as evidence that the pebbles were formed (or 'recrystallized') by a post-impact hydrothermal system. Arguments are presented that suggest that the three quartz pebbles are, most likely, fragments of a preimpact vein quartz of hydrothermal origin.

Geology of the Quartz Creek Pegmatite District, Gunnison County Colorado

USGS Publications Warehouse

Staatz, Mortimer H.; Trites, A.F.

1952-01-01

Inferred reserves of the district are estimated for beryl, scrap mica, both hand-cobbing and milling feldspar, lepidolite, columbite-tantalite, topaz, monazite, and microlite. No sheet mica was found. Reserves are small and transportation costs are high so substantial production of low-priced feldspar and scrap mica will depend on the adoption of economica milling techniques for recovering the large quantities of feldspar available.  Beryl is irregularly distributed and its recovery as a byproduct will depend on the establishment of a stable market for feldspar and scrap mica.  Lepidolite reserves are small low grade.

McCrillisite, NaCs(Be,Li)Zr2(PO4)4.1-2H2O, a new mineral species from Mount Mica, Oxford County, Maine, and new data for gainesite

USGS Publications Warehouse

Foord, E.E.; Brownfield, M.E.; Lichte, F.E.; Davis, A.M.; Sutley, S.J.

1994-01-01

McCrillisite, a member of the gainesite group, occurs in the Mount Mica granitic pegmatite, South Paris, Oxford County, Maine. The mineral is a product of late-stage hydrothermal alteration and is associated with approximately 20 other silicate, oxide, carbonate, arsenite and phosphate minerals. Crystals occur in mm- to cm-sized cavities, and individuals are up to 1.2 mm in maximum dimension. The crystallography and mineral chemistry of McCrillisite are described. -from Authors

Formation and Cross-Cumulus Migration of Silica-Rich Liquids in the Skaergaard Intrusion, East Greenland

NASA Astrophysics Data System (ADS)

Larsen, R. B.; Sorensen, B. E.; Muller, A.

2008-12-01

In a recent publication on the Skaergaard intrusion evidence for the formation of silica-rich melts by silicate- silicate liquid immiscibility was proposed (Jakobsen et al., Geology 33, 2005). Coexisting iron-rich and silica- rich microscopic melt inclusions were trapped in apatite during crystallisation of the Skaergaard melts. Given this evidence for liquid immiscibility it is possible to explain the formation of macroscopic accumulations of silica rich entities throughout the magmatic stratigraphy. Previously, the formation and emplacement of these granophyric entities were challenging to explain. Examples include decimetre to metre size granophyric /melano-granophyric aggregates in either gabbroic pegmatite, in chimney shaped columns intersecting the layering or in isolated pods. Particularly, the presence of numerous granophyric pods a few metres above large gabbroic pegmatite were enigmatic. Moving the granophyric melts from the pegmatite where they formed (Larsen and Brooks, Journal of Petrology 35, 1994) and several metres across the magmatic stratigraphy would require unconsolidated cumulates i.e. a crystal mush. Geothermobarometric estimates from fluid inclusions, amphibole and feldspars show that the silica-rich aggregations solidified between 900 and 660 C at P from 1.8 to 2.9 kb. However, to be true products of liquid immiscibility they should form at T > 1050 C. With an average of 960 ppm Zr, the silica-rich aggregates are extremely Zr rich. Zr saturation thermometry imply minimum T's of 1070 (c. 2000 ppm Zr) to 900 C (c. 700 ppm Zr). Ti in Zr thermometry is progressing and may further constrain the T of formation. Although large uncertainties apply, a T of 1070 C or higher, would agree with a formation by liquid immiscibility. Assuming T > 1070 C the cumulus stratigraphy was unconsolidated with > 30 vol% intercumulus melts in the lower part of the magmachamber. With a density of 2.4-2.6 g/cm3, the silica-rich melts were much lighter than the ambient mush (c. 3.2 g/cm3) and may have migrated diapirically and/or along syn-magmatic semi-ductile fault systems (as observed in Lower Zone c and the Middle Zone). With an onset of silica-rich melt migration at T > 1070 C in the Lower Zone, large proportions of the magma chamber was molten and, at least theoretically, it was possible to reintroduce the silica-rich melts in the convecting magma. 19 chimney shaped structures of granophyric and melano-granophyric rocks in MZ with diameters of 2-5 metres, imply that the transfer of silica-rich melts was not only a trivial matter but substantially may have interacted with the cumulates they transgressed or the ambient convecting melt if they migrated this far.

Deformation behaviour of feldspar in greenschist facies granitoide shear zones from the Austroalpine basement to the south of the western Tauern window, Eastern Alps

NASA Astrophysics Data System (ADS)

Hentschel, Felix; Trepmann, Claudia

2015-04-01

Objective of this study is to elucidate the feldspar deformation behaviour at greenschist facies conditions relevant for the long-term rheological properties of continental crust. Uncertainties in models for the rheological properties are partly due to a poor knowledge of the deformation mechanisms taking place in granitoid rocks at inaccessible depth. The deformation behaviour of feldspar, the most abundant mineral in the continental crust, is characterized by an interaction of brittle, dissolution-precipitation and crystal-plastic processes, which is difficult to evaluate in experiments given the problematic extrapolation of experimental conditions to reasonable natural conditions. However, microfabrics of metamorphic granitoid rocks record the grain-scale deformation mechanisms and involved chemical reactions proceeding during their geological history. This usually includes deformation and modification through several stages in space (depth, i.e., P, T conditions) and/or time. For deciphering the rock's record this implies both, challenge and chance to resolve these different stages. Here, we use the deformation record of mylonitic pegmatites from the Austroalpine basement south to the western Tauern window. The structural, crystallographic and chemical characteristics of the feldspar microfabrics are determined via micro-analytical techniques (polarized light microscopy, scanning electron microscopy, SEM, electron back scatter diffraction, EBSD) to identify the relevant deformation mechanisms and deformation conditions. The pegmatites represent a relatively simple Ca-poor granitoid system, mineralogically dominated by albite-rich plagioclase, K-feldspar and quartz. The matrix of the mylonitic pegmatites is composed of alternating monomineralic albite and quartz ribbons defining the foliation. Fragmented tourmaline and K-feldspar porphyroclasts occur isolated within the matrix. At sites of dilation along the stretching lineation K-feldspar porphyroclasts show serrated boundaries to matrix albite grains. In intragranular zones within K-feldspar porphyroclasts, small albite but also K-feldspar grains and "subgrains" (K-feldspar domains with a small misorientation angle to the host K-feldspar porphyroclast) occur. Strain shadows around porphyroclasts are composed of polymineralic aggregates of albite, K-feldspar and quartz. The albite grains in ribbons show a shape preferred orientation (SPO) with a long axis of about 50-100 µm in the foliation plane and EBSD data reveal an absent to very weak crystallographic orientation (CPO). These microfabrics show indication of a sequence of brittle behaviour, localized dislocation glide-controlled deformation and dissolution-precipitation creep of feldspar. Monomineralic quartz ribbons and shear bands show evidence of dislocation glide by a pronounced CPO, implying dislocation creep. The microfabric is interpreted to have evolved during different stages of episodic deformation at transient high stresses with subsequent viscous flow at decreasing stresses.

Origin of the Lyme Dome and implications for the timing of multiple Alleghanian deformational and intrusive events in southern Connecticut

USGS Publications Warehouse

Walsh, G.J.; Aleinikoff, J.N.; Wintsch, R.P.

2007-01-01

Geologic mapping, structural analysis, and geochronology in the area of the Lyme dome, southern Connecticut provides constraints on the origin of the rocks in the core of the dome, the absolute timing of the principal deformational and thermal events attributed to Alleghanian orogenesis, and the processes that generated the dome. Detrital zircon geochronology in combination with ages on intrusive rocks brackets the deposition of quartzite in the core of the dome sometime between ca. 925 and 620 Ma. Granite and granodiorite intruded the Neoproteorozic metasedimentary rocks in the core of the dome at ca. 620 to 610 Ma. Four major early Permian events associated with the Alleghanian orogeny affected the rocks in the Lyme dome area. Syn-tectonic migmatization and widespread penetrative deformation (D1, ca. 300 - 290 Ma) included emplacement of alaskite at 290 ?? 4 Ma during regional foliation development and aluminosilicate-orthoclase metamorphic conditions. Rocks of the Avalon terrane may have wedged between Gander cover rocks and Gander basement in the core of the Lyme during D1. Limited structural evidence for diapiric uplift of the Lyme dome indicates that diapirism started late in D1 and was completed by D2 (ca. 290 - 280 Ma) when horizontal WNW contractional stresses dominated over vertical stresses. Second sillimanite metamorphism continued and syn-tectonic D2 granite pegmatite (288 ?? 4 Ma) and the Joshua Rock Granite Gniess (284 ?? 3 Ma) intruded at this time. North-northwest extension during D3 (ca. 280 - 275 Ma) led to granitic pegmatite intrusion along S3 cleavage planes and in extensional zones in boudin necks during hydraulic failure and decompression melting. Intrusion of a Westerly Granite dike at 275 ?? 4 Ma suggests that D3 extension was active, and perhaps concluding, by ca. 275 Ma. Late randomly oriented but gently dipping pegmatite dikes record a final stage of intrusion during D4 (ca. 275 - 260 Ma), and a switch from NNW extension to vertical unloading and exhumation. Monazite and metamorphic zircon rim ages record this event at ca. 259 Ma. The evolution of the Lyme dome involved D1 mylonitization, intrusion, and migmatization during north-directed contraction, limited late D1 diapirism, D2 migmatization during WNW contraction with associated flexural flow and fold interference, D3 NNW horizontal extension and decompression melting, and final D4 vertical extension and rapid exhumation. Late regional uplift, extension, and normal faulting at higher crustal levels may have been caused by diapiric rise of the lower crust, below the structural level of the Lyme dome. The rocks record no evidence of Acadian metamorphism or deformation, suggesting that the Gander zone here was not tectonically juxtaposed with Avalon until the Alleghanian orogeny.

Nature and time of emplacement of a pegmatoidal granite within the Delhi Fold Belt near Bayalan, Rajasthan, India

NASA Astrophysics Data System (ADS)

Dasgupta, N.; Sen, J.; Pal, T.; Ghosh, T.

2009-04-01

The study area is situated about 70 km south east of Ajmer, in Rajasthan, India around the village Bayala (26o 02' 19 N''; 74o 21' 01'') within the Ajmer district of Central Rajasthan. The area is along the eastern flank of the central portion of the Precambrian South Delhi Fold Belt (SDFB) and it stratigraphically belongs to the Bhim Group of rocks. Basement rocks of Archaean age, commonly known as the Banded gneissic Complex (BGC), is exposed to the east, where the rocks of the Bhim Group rests unconformably over BGC. To the west gneissic basement rocks of mid-Proterozoic times underlie the Bhim Group and have been referred to as the Beawar gneiss (BG). The Bhim Group of rocks comprises of metamorphosed marls and calc-silicate gneisses with minor amounts of quartzites and pelitic schists, indicative of its shallow marine origin. Within the Bhim Group, a pegmatoidal granite has intruded the calc silicate gneisses of the area. The pegmatoidal granite body is elliptical in outline with the long dimension(20 km) trending N-S and covers an area of 300 sq. km. approximately. This granite have so far been mapped as basement rocks (BG) surrounding the Beawar town (26o 06' 05'' N; 74o 19' 03'' E), 50 km south east of Ajmer. Rafts of calc-silicate gneisses, belonging to the Bhim Group, are seen to be entrapped within granite. Fragments of BG and its equivalents have also been found as caught up blocks within this pegmatoidal granite body near Andheri Devari, a small hamlet east of Beawar. The objective of the study was to map this pegmatoidal body, and decipher the mechanism and time of emplacement of this granite. A detailed structural mapping of the area in a 1:20000 scale spread over a 30 sq. km area in the vicinity of Bayala was carried out to analyse the geometry and the time of emplacement of the pegmatitic granite. The ridges of calc silicates and marbles adjoining the area were studied for the structural analyses of the Delhi fold belt rocks of the area. The calc silicate gneisses of the Bhim Group have been deformed by three major phases of folding, namely D1, D2 and D3. Of these the D1 folds defined by transposed compositional layering are intrafolial and isoclinal in nature. The D2 folds are asymmetric with alternate steeply and gently easterly dipping limbs and are defined by compositional banding and schistosity (S1). A good compositional layering parallel to the S2 fabric has been observed within the calc silicate gneisses. The D2 folds are close to tight, gently plunging with a modal plunge of 20o towards 40o; and has an inclined axial plane which has an easterly vergence. This is the most dominant phase of deformation. The D3 folds have developed on the gentle limbs of the D2 folds with a horizontal axis on a vertical axial plane. Interference of the D1 with D2 and D1 with D3 has produced Type III type of interference pattern. The pegmatitic granite body is a coarse grained rock composed of quartz feldspar (dominantly K-feldspar), muscovite, biotite, and tourmaline. A weak foliation has developed within this rock which is parallel to the D3 axial planar structure found within the calc silicate gneisses. Thus from the structural study it is proposed that the pegmatitic granite was emplaced post-D2 and possibly syn D3. The presence of narrow planar zones of hornfelsic rocks parallel to the D3 axial plane within the calc silicate rocks also attests to the above fact. Therefore the D3 axial planes provided the necessary conduits of the granite fluid movement within the calcsilicate rocks. The intrusions have scaled off the calc silicate gneisses into large continuous pieces along the gneissosity plane and got emplaced along the hinges of the D2 and D3 folds. Though disturbed, it has been seen that the orientation of the structural elements within these ripped off blocks of the calc silicate gneisses were quite similar to those found within the ridges, unaffected by the granite. The granites were thus emplaced lit-par-lit in the country rocks and on their contact with the calc gneisses shows hornfelsic textures within the calcsilicates (Tremolite-actinolite schists). It is thought of that this pegmatoidal granite has a bearing in age with the wide scale granite activity seen within this region. The structural study shows that this pegmatitic granite was emplaced synchronous to the D3 deformation episode which is the last major recognizable deformation within the Delhi Orogeny. Therefore this pegmatitic granite marks the closing stages of the Delhi Orogeny. Combined with the 1 Ga age of the formation of crust, in the western segment of the Delhi basin, a proper dating of this granite could give us the exact time span of the delhi orogenic cycle.

Deformation ages within the Klong Marui continental wrench fault, southern Thailand

NASA Astrophysics Data System (ADS)

Kanjanapayont, P.; Grasemann, B.; Edwards, M. A.

2009-04-01

The Klong Marui Fault is a ductile to brittle dextral strike-slip shear zone characterized by strong NNE-SSW geomorphic ridges trending up to 150 km. from Thai Gulf to Andaman Sea. At it southern part in the Phung Nga region, the ductile core forms a 40km long ridge. The geology within this wrench zone consisted of steep strongly deformed layers of migmatitic gneisses, mylonitic granites/pegmatites and phyllonitic metapelites. Brittle cataclasitc zones were localized in the eastern and western margin of this ductile core zone. The first deformation stage was dextral ductile strike-slip movement at mid to upper crustal levels and formed the main mylonitic foliation (c), secondary synthetic foliations (c'), and lineation in the migmatitic gneisses, mylonitic granites and metapelites. Locally sillimanite-clasts in high-temperature recrystallization quartz fabric fabric suggest deformation at amphibolite facies condition. More typically, quartz dynamically recrystallize by subgrain rotation and grain boundary migration under greenschist facies conditions. Microstructure of myrmekite and "V"-pull-apart clearly indicates dextral sense of shear. Pegmatites cross-cut the main mylonitic foliation but were sheared at the rims indicating syn-kinematic emplacement. Dynamically recrystallizing quartz mainly by basal gliding, bulging and low-temperature subgrain rotation record the latest stage of ductile dextral strike-slip deformation during decreasing temperature conditions. The NNE-SSW trending dextral strike-slip deformation accommodated the E-W transpression as a result of the differential movement of the northward drifting Indian craton and Asia. The brittle/ductile deformation produced cataclasites and minor faults which overprint the higher temperature fabric causing exhumation and juxtaposition of fault rocks developed under different metamorphic conditions in a positive flower structure.

Temporal evolution of mineralization events in the Bohemian Massif inferred from the Re-Os geochronology of molybdenite

NASA Astrophysics Data System (ADS)

Ackerman, Lukáš; Haluzová, Eva; Creaser, Robert A.; Pašava, Jan; Veselovský, František; Breiter, Karel; Erban, Vojtěch; Drábek, Milan

2017-06-01

Molybdenite is a common mineral accompanying Sn-W, Au, and base metal mineralizations located in different geotectonic units of the Bohemian Massif, but it is also widespread in granitoids and/or related quartz veins/pegmatites forming disseminated Mo mineralization. Thirty Re-Os ages were obtained for molybdenite samples from the Bohemian Massif to provide constraints on the timing and duration of mineralization event(s) within the framework of previously published geochronological data for the host and/or associated rocks. The obtained data for Sn-W-(Li) deposits in the Erzgebirge metallogenetic province indicate the predominance of one and/or multiple short-time mineralization events taking place between ˜319 and 323 Ma, with the exception of the Krupka deposit associated with the Altenberg-Teplice caldera where the data may suggest prolonged activity until ˜315 Ma. The ages of the Pb-Zn-(Au-Mo) Hůrky u Rakovníka and Fe-Cu-As Obří důl mineralizations from the exocontacts of the Čistá pluton and Krkonoše-Jizera Plutonic Complex, respectively, provide evidence for synchronous emplacement of the ore and the associated granitic rocks. In contrast, the Padrť Fe-As-Mo mineralization postdates the age of the associated Padrť granite. Disseminated Mo mineralization in Cadomian and Variscan granitoids and/or related to quartz veins/pegmatites provides Re-Os ages that overlap with the previously published geochronological data for the host rocks, suggesting coeval evolution. Molybdenite samples from the Sázava suite granites of the Central Bohemian Plutonic Complex (CBPC) have resolvable younger ages than their host granites, but similar to the age of spatially related Au mineralization which is associated with the latest evolution of the CBPC.

Lithium-bearing fluor-arfvedsonite from Hurricane Mountain, New Hampshire: A crystal-chemical study

USGS Publications Warehouse

Hawthorne, F.C.; Oberti, R.; Ottolini, L.; Foord, E.E.

1996-01-01

The structures of two crystals of Li-bearing fluor-arfvedsonite (1) (K0.32Na0.68)Na2(Li0.48Fe 2+2.83Mn2+0.10Zn 0.06Fe3+1.46Ti0.07) (Si7.88Al0.12)O22[Fu1.15(OH) 0.85] and (2) (K0.25Na0.75)Na2(Li0.48Fe 2+2.84Mn2+0.11Zn 0.05Fe3+1.45Ti0.07)(Si 7.89Al0.11)O22[F1.35(OH) 0.65] from a granitic pegmatite, Hurricane Mountain, New Hampshire, have been refined to R indices of 1.5(1.6)% based on 1380(1387) reflections measured with MoK?? X-radiation. The unit cell parameters are (1) a 9.838(4), b 17.991(6), c 5.315(2) A??, 103.78(3)??, V 913.7 A??3 and (2) a 9.832(3), b 17.990(7), c 5.316(3) A??, ?? 103.79(3)??, V 913.2 A??3. Site-scattering refinement shows Li to be completely ordered at the M(3) site in these crystals. The amphibole composition is intermediate between fluor-arfvedsonite and fluor-ferro-leakeite with a small component (???10%) of fluor-ferro-ferri-nybo??ite. These amphibole crystals project into miarolitic cavities in a pegmatitic phase of a riebeckite granite. The early-crystallizing amphibole is close to fluor-ferro-leakeite in composition, but becomes progressively depleted in Li and F as crystals project out into miarolitic cavities; the final amphibole to crystallize is a fibrous Li-poor riebeckite. Li plays a significant role in late-stage fractionation involving the crystallization of alkali amphibole in peralkaline granitic environments.

Post-magmatic solid solutions of CaCeAl2(Fe3+ 2/3□1/3)[Si2O7][SiO4]O(OH), allanite-(Ce) and REE-bearing epidote in miarolitic pegmatites of Permian Baveno granite (Verbania, central-southern alps, Italy)

NASA Astrophysics Data System (ADS)

Guastoni, Alessandro; Nestola, Fabrizio; Schiazza, Mariangela

2017-06-01

CaCeAl2(Fe3+ 2/3□1/3)[Si2O7][SiO4]O(OH), allanite-(Ce) and rare earth element (REE)-bearing epidote occur as globular aggregates and platy prismatic crystals in miarolitic cavities in a niobium, yttrium, fluorine (NYF) granitic pegmatite at Baveno, Verbania, Southern Alps, Italy. These samples were investigated by means of an electron probe micro-analyser (EPMA) and single-crystal X-ray diffraction. Our EPMA results show that the globular aggregates have the highest REE content in the core portion and decreases to REE-bearing epidote towards the rim whereas the prismatic crystals are characterized by marked oscillatory zoning that have the highest REE contents at the rim of the crystal. The unit-cell parameters of "allanites" have an intermediate unit-cell between CaCeAl2(Fe3+ 2/3□1/3)[Si2O7][SiO4]O(OH), allanite-(Ce) and REE-free epidote, because reflect the strong chemical heterogeneity of the samples which form complete solid solutions. Hydrothermal fluids control the activity and precipitation of incompatible elements like high field strength elements (HFSE), Sc and REE by hydrous F-rich fluids below the critical temperature which allow to deposit accessory minerals in the cavities with decreasing temperature. The source of REE and Y are the sheet and REE-silicates like siderophyllite-annite, and gadolinite-(Y) which underwent partial to complete decomposition by the activity of aggressive F-rich hydrothermal fluids.

Crystal structure of hydrogen-bearing vuonnemite from the Lovozero alkaline massif

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rastsvetaeva, R. K., E-mail: rast@ns.crys.ras.ru; Aksenov, S. M.; Verin, I. A.

2011-05-15

Hydrogen-bearing vuonnemite from the Shkatulka hyperagpaitic pegmatite (the Lovozero alkaline massif, Kola Peninsula) was studied by single-crystal X-ray diffraction. The triclinic unit-cell parameters are as follows: a = 5.4712(1) Angstrom-Sign , b = 7.1626(1) Angstrom-Sign , c = 14.3702(3) Angstrom-Sign , {alpha} = 92.623(2) Degree-Sign , {beta} = 95.135(1) Degree-Sign , {gamma} = 90.440(1) Degree-Sign , sp. gr. P1, R = 3.4%. The Na{sup +} cations and H{sub 2}O molecules are ordered in sites between the packets. The water molecules are hydrogen bonded to the PO{sub 4} tetrahedra.

Colorado quartz: occurrence and discovery

USGS Publications Warehouse

Kile, D.E.; Modreski, P.J.; Kile, D.L.

1991-01-01

The many varieties and associations of quartz found throughout the state rank it as one of the premier worldwide localities for that species. This paper briefly outlines the historical importance of the mineral, the mining history and the geological setting before discussing the varieties of quartz present, its crystallography and the geological enviroments in which it is found. The latter include volcanic rocks and near surface igneous rocks; pegmatites; metamorphic and plutonic rocks; hydrothermal veins; skarns and sedimentary deposits. Details of the localities and mode of occurrence of smoky quartz, amethyst, milky quartz, rock crystal, rose quartz, citrine, agate and jasper are then given. -S.J.Stone

Loparite-(Ce) from the Khibiny Alkaline Pluton, Kola Peninsula, Russia

NASA Astrophysics Data System (ADS)

Konopleva, N. G.; Ivanyuk, G. Yu.; Pakhomovsky, Ya. A.; Yakovenchuk, V. N.; Mikhailova, Yu. A.

2017-12-01

Data on the occurrence, morphology, anatomy, composition, and formation conditions of loparite-(Ce) in the Khibiny alkaline pluton are given. Loparite-(Ce), (Na,Ce,Sr)(Ce,Th)(Ti,Nb)2O6, resulted from metasomatic alteration and assimilation of metamorphic host rocks at the contact with foyaite as well as foyaite on the contact with foidolite. This alteration was the highest in pegmatite, and albitite developed there. A decrease in temperature resulted in enrichment of the perovskite and tausonite endmembers in loparite-(Ce) owing to a decrease in the loparite and lueshite endmembers. La and Ce sharply predominate among rare earth elements in the composition of loparite-(Ce).

Strain localization in the lower crust: brittle precursors versus lithological heterogeneities (Musgrave Ranges, Central Australia)

NASA Astrophysics Data System (ADS)

Hawemann, Friedrich; Mancktelow, Neil; Wex, Sebastian; Pennacchioni, Giorgio; Camacho, Alfredo

2016-04-01

The Davenport shear zone in Central Australia is a strike-slip ductile shear zone developed during the Petermann Orogeny (~ 550 Ma). The conditions of shearing are estimated to be amphibolite-eclogite facies (650 °C, 1.2 GPa). The up to seven kilometre thick mylonite zone encloses several large low strain domains with excellent exposure, thus allowing a thorough study of the initiation of shear zones. Quartzo-feldspathic gneisses and granitoids inherit a suite of lithological heterogeneities such as quartz-rich pegmatites, mafic layers and dykes. When in a favourable orientation to the shortening direction, these rheologically different pre-existing layers might be expected to localize deformation. However, with the singular exception of long, continuous and fine-grained dolerite dykes, this is not observed. Quartz-rich pegmatites are mostly unsheared, even if in a favourable orientation, and sometimes boudinaged or folded. There are instead many shear zones only a few mm to cm in width, extending up to tens of metres, which are in fact oriented at a very high angle to the shortening direction. Parallel to these, a network of little to moderately overprinted brittle fractures are observed, commonly marked by pseudotachylyte (pst) and sometimes new biotite. Shear reactivation of these precursor fractures is generally limited to the length of the initial fracture and typically re-uses and shears the pst. The recrystallized mineral assemblage in the sheared pst consists of Cpx+Grt+Fsp±Ky and is the same to that in the adjacent sheared gneiss, with the same PT estimates (650 °C, 1.2 GPa). In some cases, multiple generations of cross-cutting and sheared pst demonstrate alternating fracture and flow during progressive shear zone development and a clear tendency for subsequent pst formation to also localize in the existing shear zone. The latest pst may be both unsheared and unrecrystallized (no grt) and is probably related to a late stage, still localized within the same shear zone. The observation that pst is preferentially sheared indicates that it is weaker than the host rock, although their bulk compositions are about the same, suggesting that the governing factors for localization are the finer grain size and the elongate, nearly planar geometry of the original pst generation zone. The same may be true of the sheared dolerite dykes, which are long, narrow and generally finer grained than the surrounding gneiss or granite. Although quartz-rich pegmatites are not preferred sites of localization, quartzo-feldspathic mylonites are fully recrystallized with a relatively coarse grain size (typically > 50 microns) typical of rather low long-term flow stress. We therefore propose that localization in the lower crust only occurs on long planar layers with a finer grain size that can promote weakening by grain-size sensitive creep. Coarser-grained lithological layers and boundaries are not exploited during the initiation of a shear zone and, in particular, quartz-rich layers are not preferentially sheared.

U-Pb systematics in coexisting zircon, rutile and titanite from granophyres in the Archean Stillwater Complex: metamictization and the fate of radiogenic Pb

NASA Astrophysics Data System (ADS)

Friedman, R. M.; Wall, C. J.; Scoates, J. S.; Meurer, W. P.

2009-12-01

Self-irradiation of zircon causes structural damage (metamictization) that can result in the loss of radiogenic Pb during interaction with aqueous solutions. To evaluate this behavior in metamict zircon, and in other U-bearing accessory phases like titanite and rutile, we are examining the U-Pb systematics of granophyric rocks from the ca. 2.7 Ga Stillwater layered intrusion, Montana. Four samples were studied in detail, including a pegmatitic ksp-qtz core to a gabbroic pegmatoid in the Lower Banded Series (N1), an alaskite and an amphibole-rich reaction zone between the alaskite and anorthosite (AN1) in the Middle Banded Series, and an amphibole-bearing granophyre from the Upper Banded Series (GN3). Except in the pegmatite, zircon is variably metamict with amorphous zones characterized by distinctive Ca-enrichment. Single zircon grains were analyzed by ID-TIMS following annealing and chemical abrasion, and multi-grain (n=4-5) fractions of titanite and rutile were analyzed by conventional ID-TIMS; the UBC 233-235U-205Pb isotopic tracer is calibrated against mixed U-Pb gravimetric reference solutions made available through the EarthTime initiative. The U-Pb systematics are coherent only for the pegmatite yielding both a Concordia age of 2709.60 ± 0.80 Ma (2σ, including tracer calibration, decay-constant errors not included) for low-U zircon (76-237 ppm) and concordant titanite results with 207Pb/206Pb ages from 2701-2710 Ma. The results for high-U zircon (up to 1438 ppm) for the other three samples are strongly discordant (9-43%, 85-89%, 28-71%, respectively) with a wide range of 207Pb/206Pb ages (2583-2647 Ma, 2210-2357 Ma, 2345-2499 Ma). Given the extreme incompatibility of Pb2+ in zircon and the highly metamict state of zircon in these granophyres, we are investigating the extent to which radiogenic lead is selectively removed during the chemical abrasion and annealing process from step-wise leaching experiments and image analysis (CL, SEM). In contrast, titanite and rutile analyses yield highly variable results that are grouped based on degree of discordance: (1) minor to moderate discordance (0-20%) with titanite ages at ca. 2.7 Ga and rutile ages from 2.6-2.7 Ga, (2) strong discordance (34-78%) with variable and young ages defined by fractions with relatively high-U contents (60-774 ppm), and (3) strong reverse discordance (3-21%), especially titanite from the reaction zone, which nonetheless gives 207Pb/206Pb ages of ca. 2705 Ma. We speculate that reverse discordance may be related to elemental redistribution in the granophyres during hydrothermal alteration of the co-existing highly metamict zircon, and other U-bearing phases, and subsequent incorporation of Pb into co-existing titanite and rutile.

OVERFLOW ROADLESS AREA, GEORGIA AND NORTH CAROLINA.

USGS Publications Warehouse

Koeppen, Robert P.; Davis, Michael P.

1984-01-01

The Overflow Roadless Area in the Blue Ridge Mountains of Georgia and North Carolina is underlain by complexly folded schist and gneiss of Proterozoic age. A mineral-resource survey found little likelihood for the occurrence of mineral or energy resources in the area. Minor isolated localities of mica pegmatite and amethyst gemstone occur in the area. Gneiss and schist suitable for rock aggregate are present in large quantities, but similar rocks abound outside the area. Natural gas may possibly be present at great depth beneath the overthrust of the Blue Ridge. Further seismic studies and exploratory drilling are needed to evaluate the natural gas potential of this part of the Eastern Overthrust Belt.

Germanium geochemistry and mineralogy

USGS Publications Warehouse

Bernstein, L.R.

1985-01-01

Germanium is enriched in the following geologic environments: 1. (1) iron meteorites and terrestrial iron-nickel; 2. (2) sulfide ore deposits, particularly those hosted by sedimentary rocks; 3. (3) iron oxide deposits; 4. (4) oxidized zones of Ge-bearing sulfide deposits; 5. (5) pegmatites, greisens, and skarns; and 6. (6) coal and lignitized wood. In silicate melts, Ge is highly siderophile in the presence of native iron-nickel; otherwise, it is highly lithophile. Among silicate minerals, Ge is concentrated in those having less polymerized silicate tetrahedra such as olivine and topaz. In deposits formed from hydrothermal solutions, Ge tends to be enriched mostly in either sulfides or in fluorine-bearing phases; it is thus concentrated both in some hydrothermal sulfide deposits and in pegmatites, greisens, and skarns. In sulfide deposits that formed from solutions having low to moderate sulfur activity, Ge is concentrated in sphalerite in amounts up to 3000 ppm. Sulfide deposits that formed from solutions having higher sulfur activity allowed Ge to either form its own sulfides, particularly with Cu, or to substitute for As, Sn, or other metals in sulfosalts. The Ge in hydrothermal fluids probably derives from enrichment during the fractional crystallization of igneous fluids, or is due to the incorporation of Ge from the country rocks, particularly from those containing organic material. Germanium bonds to lignin-derivative organic compounds that are found in peat and lignite, accounting for its common concentration in coals and related organic material. Germanium is precipitated from water together with iron hydroxide, accounting for its concentration in some sedimentary and supergene iron oxide deposits. It also is able to substitute for Fe in magnetite in a variety of geologic environments. In the oxidized zone of Ge-bearing sulfide deposits, Ge is concentrated in oxides, hydroxides, and hydroxy-sulfates, sometimes forming its own minerals. It is particularly enriched in some iron- and manganese-bearing oxides and hydroxides, including goethite (up to 5300 ppm) and hematite (up to 7000 ppm). ?? 1985.

Alteration and chemical U-Th-total Pb dating of heterogeneous high-uranium zircon from a pegmatite from the Aduiskii massif, middle Urals, Russia

NASA Astrophysics Data System (ADS)

Zamyatin, Dmitry A.; Shchapova, Yuliya V.; Votyakov, Sergey L.; Nasdala, Lutz; Lenz, Christoph

2017-09-01

The U-Th-Pb isotope system in the accessory mineral zircon may be disturbed, as for instance by the secondary loss of radiogenic lead. The recognition of such alteration is crucial for the sound interpretation of geochronology results, in particular for chemical dating by means of an electron probe micro-analyser (EPMA). Here we present the example of high-U zircon samples from a granite pegmatite from the Aduiskii Massif, Middle Urals, Russia. The structural and chemical heterogeneity of samples was characterised by EPMA, including joint probability distribution (JPD) analysis of back-scattered electrons (BSE), cathodoluminescence (CL) and U M β images, and by Raman and photoluminescence (PL) spectroscopy. We found a high-U interior region (U up to 11.4 wt%) without any obvious indication of alteration. This domain has stoichiometric composition, and its Raman spectrum is similar to that of amorphous ZrSiO4. In addition, altered lower-U regions are present that are non-stoichiometric and contain non-formula elements such as Ca, Al, Fe, and water up to several wt%. Their Raman spectra yielded a band near 760-810 cm-1 which is not related to any ZrSiO4 vibration; we assign it tentatively to the symmetric stretching of (UO2)2+ groups. This assignment is supported by the observation of a fairly intense PL phenomenon whose spectral position and vibrational-coupling structure strongly indicates a uranyl-related emission. Altered zones were formed by both fluid-driven diffusion reaction and coupled dissolution-reprecipitation processes. The variation of BSE and CL intensities in amorphous high-U zircon is controlled by its chemical composition and the presence of water and uranyl groups. We have determined a weighted mean EPMA age of 246 ± 2 Ma, which agrees reasonably well with previous dating results for the Aduiskii Massif.

International strategic minerals inventory summary report; niobium (columbium) and tantalum

USGS Publications Warehouse

Crockett, R.N.; Sutphin, D.M.

1993-01-01

Major world resources of niobium and tantalum are described in this summary report of information in the International Strategic Minerals Inventory (ISMI). ISMI is a cooperative data-collection effort of earth-science and mineral-resource agencies in Australia, Canada, the Federal Republic of Germany, the Republic of South Africa, the United Kingdom, and the United States of America. Part I of this report presents an overview of the resources and potential supply of niobium and tantalum based on inventory information; Part II contains tables of both geologic and mineral-resource information and includes production data collected by ISMI participants. Niobium is used principally as an alloying element in special steels and superalloys, and tantalum is used mainly in electronics. Minerals in the columbite-tantalite series are principal ore minerals of niobium and tantalum. Pyrochlore is a principal source of niobium. These minerals are found in carbonatite, certain rocks in alkaline igneous complexes, pegmatite, and placer deposits. ISMI estimates show that there are over 7 million metric tons of niobium and almost 0.5 million metric tons of tantalum in known deposits, outside of China and the former Soviet Union, for which reliable estimates have been made. Brazilian deposits, followed by Canadian deposits, contain by far the largest source of niobium. Tantalum production is spread widely among several countries, and Brazil and Canada are the most significant of these producers. Brazil's position is further strengthened by potential byproduct columbite from tin mining. Present economically exploitable resources of niobium appear to be sufficient for the near future, but Brazil will continue to be the predominant world supplier of ferrocolumbium. Tantalum, a byproduct of tin production, has been captive to the fluctuations of that market, but resources in pegmatite in Canada and Australia make it likely that future increases in the present modest demand will be met.

Citizen-Scientist Led Quartz Vein Investigation in the McDowell Sonoran Preserve, Scottsdale, Arizona, Resulting in Significant Geologic Discoveries and a Peer-Reviewed Report Coauthored and with Maps by Citizen-Scientists.

NASA Astrophysics Data System (ADS)

Gruber, D.; Gootee, B.

2016-12-01

Citizen-scientists of the McDowell Sonoran Conservancy Field Institute originated and led this project to study milky quartz deposits. Milky quartz veins of all sizes are visible throughout the McDowell Sonoran Preserve (Scottsdale, Arizona) and are commonly found in Arizona Proterozoic rocks. No research on milky quartz has been done locally and little is known about its formation and emplacement history. Working with Brian Gootee, research geologist with the Arizona Geological Survey (AZGS), a citizen science team identified candidate study sites with large quartz veins and then conducted aerial balloon photography followed by geologic mapping, basic data collection, photo-documentation, and sampling from two sites. Samples were analyzed with a UV lamp, Geiger counter, and x-ray fluorescence spectrometer. Petroscopic analysis and interpretation of the samples were done by Gootee. Daniel Gruber, the citizen-science project leader, and Gootee summarized methodology, sample analyses, and interpretation in a report including detailed geologic maps. Analysis of samples from one site provided evidence of several events of Proterozoic quartz formation. The other site hosted pegmatite, cumulates, graphic granite and orbicular granite in association with milky quartz, all discovered by citizen scientists. The milky quartz and surrounding pegmatites in granite at this site trace the progression of late-stage crystallization at the margin of a fractionated granite batholith, providing an exemplary opportunity for further research into batholith geochemistry and evolution. The project required 1000 hours of citizen-science time for training, field work, data organization and entry, mapping, and writing. The report by Gootee and Gruber was reviewed and published by AZGS as an Open File Report in its online document repository. The citizen scientist team leveraged the time of professional geologists to expand knowledge of an important geologic feature of the McDowell Mountains.

Crystal structure and genesis of the hydrated analog of rastsvetaevite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rastsvetaeva, R. K., E-mail: ras@ns.crys.ras.ru; Aksenov, S. M.; Rozenberg, K. A.

2015-11-15

The crystal structure of the hydrated analog of the mineral rastsvetaevite (tentatively called “hydrorastsvetaevite”), which was found by A.P. Khomyakov in ultraagpaitic pegmatites at the Rasvumchorr Mountain of the Khibiny alkaline massif (Kola Peninsula), has been determined by single crystal X-ray diffraction. The trigonal unit-cell parameters are as follows: a = 14.2812(2) Å, c = 60.533(5) Å, V = 10691.54(3) Å{sup 3}, sp. gr. R3m. The structure was refined to R = 5.9% in the isotropic and anisotropic approximation of atomic displacement parameters based on 2068 ref lections with |F| > 3σ(F). “Hydrorastsvetaevite” is on the whole analogous to othermore » 24-layer representatives of the eudialyte group (called “megaeudialytes”), but is characterized by a high potassium content and is distinguished from other potassium-rich minerals (rastsvetaevite, davinciite, and andrianovite) by low sodium and alkaline-earth metal content, as well as by a high degree of hydration accompanied by the insertion of H{sub 3}O groups, which partially or completely replace large cations. The idealized formula of “hydrorastsvetaevite” (Z = 3) is (Na{sub 11}(H{sub 3}O){sub 11}K{sub 6}(H{sub 2}O){sub 1.5}Sr)Ca{sub 12}Fe{sub 3}Na{sub 2}MnZr{sub 6}Si{sub 52}O{sub 144}(OH){sub 4.5}C{sub l3.5}(H{sub 2}O){sub 0.5}. In alkaline pegmatites, “hydrorastsvetaevite” occurs as a secondary mineral developed from the original rastsvetaevite through decationation and hydration. The characteristic features of the genesis of eudialyte-group minerals containing potassium as a species-forming cation are discussed in terms of the concept of transformational mineral species.an]Mis||Original Russian Text © R.K. Rastsvetaeva, S.M. Aksenov, K.A. Rozenberg, 2015, published in Kristallografiya, 2015, Vol. 60, No. 6, pp. 897–905.« less

Rubidium-strontium geochronology of the Oaxaca and Acatlan metamorphic areas of southern Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruiz Castellanos, M.

1979-01-01

A Rb-Sr study was carried out on crystalline basement rocks from two small separate areas of southern Mexico: Oaxaca area and the Acatlan area. The Oaxaca area consists mainly of orthogneisses and paragneisses of amphibolite to granulite grade metamorphism as well as granitic intrusives. In the present study the following dates and initial /sup 87/Sr//sup 86/Sr rates (Sr/sub 0/) were obtained from rocks of this area: El Cortijo gneisses 341 +/- 61 my, Sr/sub 0/ 0.7226 +/- 0.0027; Ojo de Agua pegmatite 975 +/- 25 my, assumed Sr/sub 0/ 0.710; El Catrin gneisses 1500 +/- 230 my, Sr/sub 0/ 0.7026more » +/- 0.0005; Suchilquitongo granite 272 +/- 8 my, Sr/sup 0/ 0.7047 +/- 0.0005; Laachila marble 901 +/- 24 my, Sr/sub 0/ 0.7062 +/- 0.0007; Laachila granitic dike 236 +/- 5 my, Sr/sub 0/ 0.8477 +/- 0.0009. The Acatlan area consists typically of greenschist facies metasedimentary rocks with similar structural and metamorphic characteristics through the area. In the present study, muscovite, biotite and whole rock data points from the typical Acatlan schists collected at different locations within the Acatlan Complex define two different linear arrays from which an age of 481 +/- 9 my, and two Sr/sub 0/ intercepts of 0.7075 +/- 0.0008 and 0.7112 +/- 0.0006 (95% confidence level) are obtained. The same date is obtained for 18 samples of the Piaxtla augen schist 480 +/- 84 my. Other dates obtained are: Caltepec granitic rocks 269 +/- 21 my, Sr/sub 0/ 0.7056 +/- 0.0004; Tepejillo intrusive bodies 207 +/- 10 my, Sr/sub 0/ 0.7037 +/- 0.0003 and Tepejillo pegmatite 173 +/- 0.3 my, Sr/sub 0/ 0.7044 +/- 0.0002. The tectonic histories of the Oaxaca and Acatlan areas are substantially different and have been unrelated at least until Late Paleozoic times.« less

Alpha Recoil Flux of Radon in Groundwater and its Experimental Measurement

NASA Astrophysics Data System (ADS)

Mehta, N.; Harvey, C. F.; Kocar, B. D.

2016-12-01

Groundwater Radon (Rn222) activity is primarily controlled by alpha recoil process (radioactive decay), however, evaluating the rate and extent of this process, and its impact on porewater radioactivity, remains uncertain. Numerous factors contribute to this uncertainty, including the spatial distribution of parent radionuclides (e.g. U238, Th232 , Ra226 and Ra228) within native materials, differences in nuclide recoil length in host matrix and the physical structure of the rock strata (pore size distribution and porosity). Here, we experimentally measure Radon activities within porewater contributed through alpha recoil, and analyze its variations as a function of pore structure and parent nuclide distribution within host matrices, including Marcellus shale rock and Serrie-Copper Pegmatite. The shale cores originate from the Marcellus formation in Mckean, Pennsylvania collected at depths ranging from 1000-7000 feet, and the U-Th-rich Pegmatite is obtained from South Platte District, Colorado. Columns are packed with granulated rock of varying surface area (30,000-60,000 cm2/g) and subjected to low salinity sodium chloride solution in a close loop configuration. The activity of Radon (Rn222) and radium (Ra226) in the saline fluid is measured over time to determine recoil supply rates. Mineralogical and trace element data for rock specimens are characterized using XRD and XRF, and detailed geochemical profiles are constructed through total dissolution and analysis using ICP-MS and ICP-OES. Naturally occurring Radium nuclides and its daughters are quantified using a low-energy Germanium detector. The parent nuclide (U238 and Th232) distribution in the host rock is studied using X-Ray Absorption Spectroscopy (XAS). Our study elucidates the contribution of alpha recoil on the appearance and distribution of Radon (Rn222) within porewater of representative rock matrices. Further, we illustrate the effects of chemical and physical heterogeneity on the rate of this process, which may inform models predicting the fate and transport of radionuclides in subsurface environments.

Elastic wave velocities, chemistry and modal mineralogy of crustal rocks sampled by the Outokumpu scientific drill hole: Evidence from lab measurements and modeling

NASA Astrophysics Data System (ADS)

Kern, H.; Mengel, K.; Strauss, K. W.; Ivankina, T. I.; Nikitin, A. N.; Kukkonen, I. T.

2009-07-01

The Outokumpu scientific deep drill hole intersects a 2500 m deep Precambrian crustal section comprising a 1300 m thick biotite-gneiss series (mica schists) at top, followed by a 200 m thick meta-ophiolite sequence, underlain again by biotite gneisses (mica schists) (500 m thick) with intercalations of amphibolite and meta-pegmatoids (pegmatitic granite). From 2000 m downward the dominating rock types are meta-pegmatoids (pegmatitic granite). Average isotropic intrinsic P- and S-wave velocities and densities of rocks were calculated on the basis of the volume fraction of the constituent minerals and their single crystal properties for 29 core samples covering the depth range 198-2491 m. The modal composition of the rocks is obtained from bulk rock (XRF) and mineral chemistry (microprobe), using least squares fitting. Laboratory seismic measurements on 13 selected samples representing the main lithologies revealed strong anisotropy of P- and S-wave velocities and shear wave splitting. Seismic anisotropy is strongly related to foliation and is, in particular, an important property of the biotite gneisses, which dominate the upper and lower gneiss series. At in situ conditions, velocity anisotropy is largely caused by oriented microcracks, which are not completely closed at the pressures corresponding to the relatively shallow depth drilled by the borehole, in addition to crystallographic preferred orientation (CPO) of the phyllosilicates. The contribution of CPO to bulk anisotropy is confirmed by 3D velocity calculations based on neutron diffraction texture measurements. For vertical incidence of the wave train, the in situ velocities derived from the lab measurements are significantly lower than the measured and calculated intrinsic velocities. The experimental results give evidence that the strong reflective nature of the ophiolite-derived rock assemblages is largely affected by oriented microcracks and preferred crystallographic orientation of major minerals, in addition to the lithologic control.

Structural analysis of Precambrian rocks at the Hot Dry Rock Site at Fenton Hill, New Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burns, K.L.; Potter, R.M.

1995-01-01

The subcrop of basement rock at Fenton HIll comprises Precambrian gneiss, schist, amphibolite, pegmatite, and granitoids with affinities in metamorphic and structural history to surface outcrops in the Tusas and Picuris Ranges. Televiewer measurements of structures were analyzed by taking advantage of the spatial continuity of foliations. Folds in the foliation are predominantly conical forms due to interference between structures formed in F2 and F3 tectonic events. Field observations of outcrops in the Picuris Range show that the fractures are predominantly an X-T network controlled by the lithological layering, and statistical evidence indicates that this layer-controlled network persists to depthmore » at Fenton Hill.« less

CONTRIBUTION TO THE GEOCHEMISTRY OF TANTALUM AND NIOBIUM IN THE HYDROTHERMAL-PNEUMATHOLYTIC PROCESS (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beus, A.A.; Sitnin, A.A.

1961-01-01

S>Data obtained as a result of geochemical investigations show that tantalum and niobium are typical elements of high-temperature postmagmatic processes (early albitization, greysening) connected with granites. The separation of tantalum and niobium in the hydrothermal-pneumatholytic process (greysening stage), which leads to the concentration of tantalum in albitized and greysenized granites (40 to 100 times compared to the average content in granites) is connected with the different mobility and stability of their acido- complex compounds (in particular fluor- and oxyfluorcomplexes), the existence of which in greysening solutions is suggested. A natural analogy in the behavior of both elements in the processesmore » of postmagmatic metasomatose in granites and granitic pegmatites is suggested. (tr-auth)« less

Origin of Archean migmatites from the Gwenoro Dam area, Zimbabwe-Rhodesia

NASA Astrophysics Data System (ADS)

Condie, Kent C.; Allen, Philip

1980-09-01

Archean migmatites in the vicinity of Gwenoro Dam in Zimbabwe-Rhodesia are composed chiefly of trondhjemite gneiss (TR), mafic tonalite (MT), amphibolite (AM), leuco-trondhjemite veins (LTR), and pegmatites. The gneiss is intruded in nearby areas with small tonalite plutons (TN). Geochemical model studies together with field relationships are consistent with the following model for migmatite production: AM is produced by partial melting of a partly depleted ultramafic parent in which neither garnet nor amphibole remain in the residue; TR and TN are produced by partial melting of undepleted to variably depleted amphibolite in which garnet does not remain in the residue; MT is produced by mixing of plagioclase-rich TR with AM; and LTR represents the solid residue after fractional crystallization of TR.

Maps showing geology, structure, and geophysics of the central Black Hills, South Dakota

USGS Publications Warehouse

Redden, Jack A.; DeWitt, Ed

2008-01-01

This 1:100,000-scale digital geologic map details the complex Early Proterozoic granitic rocks, Early Proterozoic supracrustal metamorphic rocks, and Archean crystalline basement of the Black Hills. The granitic rocks host pegmatite deposits renowned for their feldspar, mica, spodumene, and beryl. The supracrustal rocks host the Homestake gold mine, which produced more than 40 million ounces of gold over a 125-year lifetime. The map documents the Laramide deformation of Paleozoic and Mesozoic cover rocks; and shows the distribution of Laramide plutonic rocks associated with precious-metals deposits. Four 1:300,000-scale maps summarize Laramide structures; Early Proterozoic structures; aeromagnetic anomalies; and gravity anomalies. Three 1:500,000-scale maps show geophysical interpretations of buried Early Proterozoic to Archean rocks in western South Dakota and eastern Wyoming.

Preliminary geologic map of the Murrieta 7.5' quadrangle, Riverside County, California

USGS Publications Warehouse

Kennedy, Michael P.; Morton, Douglas M.

2003-01-01

The Murrieta quadrangle is located in the northern part of the Peninsular Ranges Province and includes parts of two structural blocks, or structural subdivisions of the province. The quadrangle is diagonally crossed by the active Elsinore fault zone, a major fault zone of the San Andreas fault system, and separates the Santa Ana Mountains block to the west from the Perris block to the east. Both blocks are relatively stable internally and within the quadrangle are characterized by the presence of widespread erosional surfaces of low relief. The Santa Ana Mountains block, in the Murrieta quadrangle, is underlain by undifferentiated, thick-layered, granular, impure quartzite and well-layered, fissile, phyllitic metamorphic rock of low metamorphic grade. Both quartzite and phyllitic rocks are Mesozoic. Unconformably overlying the metamorphic rocks are remnants of basalt flows having relatively unmodified flow surfaces. The age of the basalt is about 7-8Ma. Large shallow depressions on the surface of the larger basalt remnants form vernal ponds that contain an endemic flora. Beneath the basalt the upper part of the metamorphic rocks is deeply weathered. The weathering appears to be the same as the regional Paleocene saprolitic weathering in southern California. West of the quadrangle a variable thickness sedimentary rock, physically resembling Paleogene rocks, occurs between the basalt and metamorphic rock. Where not protected by the basalt, the weathered rock has been removed by erosion. The dominant feature on the Perris block in the Murrieta quadrangle is the south half of the Paloma Valley ring complex, part of the composite Peninsular Ranges batholith. The complex is elliptical in plan view and consists of an older ring-dike with two subsidiary short-arced dikes that were emplaced into gabbro by magmatic stoping. Small to large stoped blocks of gabbro are common within the ring-dikes. A younger ring-set of hundreds of thin pegmatite dikes occur largely within the central part of the complex. These pegmatite dikes were emplaced into a domal fracture system, apparently produced by cauldron subsidence, and include in the center of the complex, a number of flat-floored granophyre bodies. The granophyre is interpreted to be the result of pressure quenching of pegmatite magma. Along the eastern edge of the quadrangle is the western part of a large septum of medium metamorphic grade Mesozoic schist. A dissected basalt flow caps the Hogbacks northeast of Temecula, and represents remnants of a channel filling flow. Beneath the basalt is a thin deposit of stream gravel. Having an age of about 10Ma, this basalt is about 2-3Ma older than the basalt flows in the Santa Ana Mountains. The Elsinore fault zone forms a complex of pull-apart basins. The west edge of the fault zone, the Willard Fault, is marked by the high, steep eastern face of the Santa Ana Mountains. The east side of the zone, the Wildomar Fault, forms a less pronounced physiographic step. In the center of the quadrangle a major splay of the fault zone, the Murrieta Hot Springs Fault, strikes east. Branching of the fault zone causes the development of a broad alluvial valley between the Willard Fault and the Murrieta Hot Springs Fault. All but the axial part of the zone between the Willard and Wildomar Faults consist of dissected Pleistocene sedimentary units. The axial part of the zone is underlain by Holocene and latest Pleistocene sedimentary units.

Ti-in-Zircon Thermometer: Preliminary Results

NASA Astrophysics Data System (ADS)

Fu, B.; Cavosie, A. J.; Clechenko, C. C.; Fournelle, J.; Kita, N. T.; Lackey, J.; Page, F.; Wilde, S. A.; Valley, J. W.

2005-12-01

The titanium in zircon thermometer has been applied to 167 zircons from diverse rock types. These rocks include metamorphosed anorthosite and gabbro (1.15 Ga, intrusion age), and unmetamorphosed granitic pegmatite (0.9 Ga) from the Adirondack Highlands; metaluminous and peraluminous granites (114-90 Ma) of the Sierra Nevada Batholith; megacrysts from kimberlite pipes in southern Africa, Brazil, and Siberia; and detrital zircons (4.4-3.9 Ga) of metaconglomerate from Jack Hills, Western Australia. Titanium concentration in zircon was analysed using a CAMECA IMS-1280 ion microprobe (see Page et al., this volume). Spot analyses were correlated to U-Pb SHRIMP pits especially for Adirondack and Jack Hills zircons. The majority of zircons have Ti-content less than 10 ppm. Variability, in excess of analytical precision, within individual zircons is observed in about one-third of crystals. In general, there is no systematic change in Ti from core to rim (identified by cathodoluminescence) of zircons, or with regard to age, U content, Th/U ratio, or U-Pb age concordance for these non-metamict grains. The average temperatures for zircon crystallization in different rock suites using the experimental/empirical calibration of Watson and Harrison (W&H, 2005, Science 308:841), assuming the presence of rutile and quartz, are estimated to be: anorthosite 735±41°C (1SD, n=24; Ti = 10±5 ppm); metagabbro 714±31°C (n=19; Ti = 8±4 ppm); Adirondack pegmatite 500±16°C (n=5; Ti = 0.3±0.1 ppm); metaluminous and peraluminous granites from Sierra Nevada 681±67°C (n=53; Ti = 6±5 ppm) and 613±75°C (n=68; Ti = 3±3 ppm); kimberlite megacrysts 740±64°C (n=169; Ti = 14±13 ppm) (Page et al., this volume); and detrital zircons from Jack Hills metaconglomerate 718±63°C (n=64; Ti = 10±9 ppm). Most of the host rocks contain ilmenite or titanite suggesting that α(TiO2)>0.5, but rutile activity is unknown for megacrysts and detrital zircons. Pegmatite contains no Ti-rich minerals, permissive of low rutile activity. Peraluminous granites have lower whole-rock TiO2 content (0.02-0.21 wt.%) than metaluminous granites (0.54-0.91 wt.%), and both have similar zircon saturation temperatures (710-780°C). The low Ti content and apparent temperature in zircons from anorthosite and metagabbro (magmatic T = ca. 1000-1100°C) and the homogeneity of igneous zircon cores vs. metamorphic rims in metagabbro suggest that Ti content was reset during granulite-facies metamorphism (750°C, 1.0 Ga), in contrast to the current estimate of extremely low diffusivity of Ti in zircon. The Ti contents of >3.9 Ga Jack Hills detrital zircons are consistent with previously published data that were used to constrain magmatic temperature and thus the composition of unknown host rocks (W&H, 2005, Science 308:841). However, these values overlap those from both felsic and mafic rocks, and the Ti data are not sufficient to independently identify parent melt chemistry unless post-crystallization changes can be ruled out. The best evidence of pre-4 Ga evolved crust is provided by previously reported oxygen isotope ratios and felsic mineral inclusions in zircon (see Cavosie et al., 2005, EPSL 235:663).

Fe-bearing Olenite with Tetrahedrally Coordinated Al from an Abyssal Pegmatite at Kutna Hora, Czech Republic: Structure, Crystal Chemistry, Optical and XANES Spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cempirek,J.; Novak, M.; Ertl, A.

2006-01-01

The pale blue rim of olenite on a black crystal of olenite-schorl tourmaline from an abyssal pegmatite at the locality Kuklik, near Kutna Hora, Czech Republic, has been chemically and structurally characterized. The optimized formula, calculated using chemical and structural data, is {sup X}(Na{sub 0.54}Ca{sub 0.14}K{sub 0.01}{D'Alembertian}{sub 0.31}){sup Y}(Al{sub 2.15}Fe{sup 2+}{sub 0.06}Ti{sup 4+}{sub 0.01}) {sup Z}(Al{sub 5.90}Mg{sub 0.10}) {sup T}(Si{sub 5.60}Al{sub 0.40})B{sub 3}O{sub 27} {sup V}[(OH){sub 2.49}O{sub 0.51}] {sup W}(O{sub 0.99}F{sub 0.01}), with {alpha} 15.8838(3), c 7.1056(2) {angstrom} and R = 0.017. The relatively short bond-length, 1.992 {angstrom}, confirms the high content of Al at the Y site ({approx}2.1more » atoms per formula unit, apfu). It is similar to that of olenite from the type locality, though the olenite from Kuklik contains significant amounts of Fe at the Y site, and significant amounts of {sup [4]}Al ({approx}0.4 apfu) instead of {sup [4]}B in the T site. This finding is supported by results of the structure determination, which show an enlarged bond-length of {approx}1.626 {angstrom}. This sample of olenite shows that nonstoichiometric content of Si does not always imply {sup [4]}B in aluminous tourmaline. No H could be found at the O1 site by refinement, and the spherical distribution of electron density in the difference-Fourier map around the O1 site supports the conclusion that this site is only or mainly occupied by O and not by OH. On a bond-angle distortion ({sigma}{sub oct}{sup 2} of the ZO{sub 6} octahedron) - distance diagram, the olenite from Kuklik lies between compositions containing 3 (OH) at the V site, and natural buergerite, which contains 0.3 (OH) and 2.7 O at the V site (O3 site). The (OH) content with {approx}2.5 (OH) pfu, which was calculated for a charge-balanced formula, is in a good agreement with these findings and with the integrated intensity of the OH overtones in the 7000 cm{sup -1} region (690 cm{sup -2} per cm thickness), which is one of the lowest measured to date for tourmaline. The OH seems to be ordered strongly at the O3 site. The composition of this sample of olenite shows a trend toward the proposed olenite end-member formula, which contains only 1 OH group. The low content of F (0.01 apfu) is uncommon for natural Al-rich and Mg-poor tourmaline from granitic pegmatites. Synchrotron micro-XANES was used to detect the valence state of Fe in this crystal; it was found to have 93 {+-} 10% of the total Fe as Fe{sup 2+}. Optical absorption spectra show that the blue color is derived primarily from a combination of {sup [6]}Fe{sup 2+}, together with {sup [6]}Fe{sup 2+} interaction with a minor amount of {sup [6]}Fe{sup 3+}.« less

Low-rhenium molybdenite by metamorphism in northern Sweden: Recognition, genesis, and global implications

NASA Astrophysics Data System (ADS)

Stein, Holly J.

2006-04-01

Re-Os dating of molybdenite is an accurate means to date intrusions and intrusion-related ore deposits using the model age or isochron approach. But, molybdenite has a new niche in the greenschist- to granulite-facies metamorphic environment. Re-Os ages for metamorphic molybdenite may be used to construct regional metamorphic histories. Age significance and accuracy are established by analyzing multiple molybdenite separates extracted from single, petrographically-characterized molybdenite occurrences. In this study, twelve geologically distinct molybdenite-bearing samples from two small Mo districts in northern Sweden trace a 150 m.y. Paleoproterozoic Svecofennian metamorphic history from ˜1900 to 1750 Ma. These data reveal a little-known, widespread and protracted, Late Svecofennian anatexis in northern Sweden. The Kåtaberget Mo-(Cu, F) deposit is located in the Moskosel granite batholith north of the economically-renown Skellefte district. Four different molybdenite samples from outcrop at Kåtaberget indicate an intrusion age of 1895 ± 6 Ma with the formation of later pegmatite-aplite at 1875 ± 6 Ma. The Allebuoda (Björntjärn) and Munka Mo-(W) deposits in the Rappen district are represented by three outcrop and five drill core samples of molybdenite-bearing aplite-pegmatite-granite. These two deposits were previously described as intrusion-related Climax-type Mo mineralization. Re-Os ages for molybdenites from these deposits range from 1865 to 1750 Ma and, significantly, Re concentrations are markedly low, extending to the sub-ppm level. Age agreement within the deposits is conspicuously lacking, whereas, with one exception, age agreement within any single sample (geologic occurrence), as established by analysis of additional molybdenite separates, is very good. These data, together with fundamental geologic observations discussed in this paper, suggest that Mo-(W) mineralization in northern Sweden is not intrusion-related, but the local product of episodic melting of Archean-Paleoproterozoic supracrustal gneisses related to the Svecofennian orogeny. Petrographic traverses across the boundary between widespread, foliation-parallel units of aplitic to pegmatitic pink granite and hosting biotite gneiss directly capture the process of ore formation. Dehydration breakdown of zircon-rich biotite aligned with the foliation in the gneiss is accompanied by formation of new pristine, post-deformational biotite plus sulfides, oxides, hydrothermal zircon and fluorite, all associated with microcline-dominant leucosomes. This process has profound implication for the traditional leucogranite, intrusion-related genesis attributed to the broad classification of Mo-W-Sn-base and precious metal mineralization (e.g., South Mountain Batholith, Nova Scotia; Okiep, Namaqualand, South Africa; Mactung, Yukon; Pogo-Liese, Tintina, Alaska; Carajás and Goiás-Rio Tocantins, Brazil; New England Batholith, NSW, Australia; Bergslagen, Sweden; Nevoria, Western Australia; Alpeinerscharte, Austria; Erzgebirge, Germany; Sardinia-Corsica Batholith). In addition to biotite, metallogenic contributions (e.g., Mo, W, Sn, U, Bi, Cu, Pb, Zn, Fe, Ni, Co, Au, Ag, Te, As, Sb, REE) in various combinations may also be controlled by breakdown of amphibole. In effect, the trace element composition of dehydrating or recrystallizing components in a gneissic rock essentially defines the local and district metallogenic suite. In the absence of focusing structures (e.g., shear zones, sheeted vein development), this process will generally form small and disconnected subeconomic deposits with erratic and unpredictable grades. Low Re content in associated molybdenite is a key indicator for a subeconomic origin by local melting of biotite gneiss (Mo-W) or muscovite schist (Sn-W).

Micro-X-Ray computed tomography of natural and experimental melt segregations and other geological materials with small absorption contrasts

NASA Astrophysics Data System (ADS)

Baumgartner, L.; Wohlers, A.; Müller, T.

2003-04-01

Micro X-ray tomography is rapidly advancing to an important tool for non-destructive 3-D imaging of geological and engineering materials. We have been using a Skyscan 1072 system (Skyscan, Belgium) to successfully image as diverse geological materials as sandstones, foraminifers, run products of hydrothermal partial melting experiments, and metamorphic rocks. The system has a conical x-ray source with a spot size of about 5µm. The X-ray source is powered by a 10W, 20--100kV, tunable supply. Images are acquired with a scintillator coupled by glass fiber optics to a 1024×1024 pixel, 12-bit CCD. The sample is rotated for 180^o (or 360^o) in steps as small as 0.24^o. Transmission image are back projected, using a Feldkamp algorithm, into a stack of up to 1000 1K×1K images, each of which represents a horizontal cross section of the sample. We have succeeded to image very low contrast systems (feldspar/quartz and olivine/calcite/dolomite), by using extended acquisition times (up to 24 hours), and low excitation voltages (30--40kV) in combination with aluminum filters to reduce beam hardening. Some quartzites collected in the Little Cottonwood contact aureole have been infiltrated by a pegmatitic liquid. These liquids are the products of partial melting in intercalated meta-pelites. 2-D images (thin sections) clearly show, that poly-crystalline interstitial feldspar and mica represent precipitates from the infiltrated pegmatitic liquid (acute quartz-feldspar junctions similar to melting experiments). The micro-CT images reveal a thin mica-feldspar network. It forms highly anastomosing, multiply interconnected networks surrounding quartz grains. They connect larger, up to 1mm sized ponds, located in triple junctions. These results have important consequences for porous melt transport in shallow crustal rocks. Micro-CT images of spinifex textured olivine in marbles from the Ubehebe Peak contact aureole (Death Valley, California) reveal two preferential growth orientations of olivine, and irregular distribution of calcite haloes. These volumetric images suggesting that the growth of olivine is related to mass transport, rather than to their inherent crystallographic growth preferences.

Geology of Nicholson's point granite, Natal Metamorphic Province, South Africa: the chemistry of charnockitic alteration and origin of the granite

NASA Astrophysics Data System (ADS)

Grantham, G. H.; Allen, A. R.; Cornell, D. H.; Harris, C.

1996-10-01

In the Port Edward area of southern Kwa-Zulu Natal, South Africa, charnockitic aureoles up to ˜4 m in width are developed adjacent to contacts with Port Edward enderbite and pegmatites intruded into the normally garnetiferous Nicholson's Point granite. Other mineralogical differences between the aureoles and the granite include increased myrmekite and significantly less biotite in the former and the replacement of pyrite by pyrrhotite in the charnockitic rocks. No significant differences in major element chemistry between the garnet-biotite Nicholson's Point granite and charnockitic Nicholson's Point granite are seen, except possibly for higher CaO and TiO 2 in the charnockite. Higher Rb, Th, Nb and Y contents in the garnet-biotite granite suggest that these elements have been locally depleted from garnet-biotite granite during char nockitisation. This depletion is considered to be related to the reduction in biotite. Strontium and Ba contents are significantly higher in the charnockite. Generally higher S contents in the charnockite suggest S metasomatism, with S possibly being added from the enderbite. No differences in δ18O isotope data are seen between the garnetiferous and hypersthene bearing granite. In the charnockite the LREEs are weakly depleted whereas the HREEs show greater depletion compared to the garnetiferous granite. The depletions in REEs are thought to be related to the breakdown of garnet. Europium is marginally enriched or unchanged in the charnockite relative to the garnetiferous granite. Two-pyroxene thermometry on the Port Edward enderbite suggests that it was intruded at temperatures of ˜1000-1100°C. The replacement of pyrite by pyrrhotite is also consistent with a thermal auroele. Consequently the charnockitic zones developed around the intrusions of Port Edward enderbite may result from the thermally driven dehydration of biotite. The aureoles developed adjacent to pegmatites are not considered to have resulted from heat but probably by destabilisation of biotite by a low aH 20 fluid phase, possibly hypersaline brines. The Nicholson's Point granite has geochemical characteristics typical of within-plate granites, A-type granites and rapakivi granites, however the stable and radiogenic isotope characteristics suggest a significant crustal component in the source.

Can cathodoluminescence of feldspar be used as provenance indicator?

NASA Astrophysics Data System (ADS)

Scholonek, Christiane; Augustsson, Carita

2016-05-01

We have studied feldspar from crystalline rocks for its textural and spectral cathodoluminescence (CL) characteristics with the aim to reveal their provenance potential. We analyzed ca. 60 rock samples of plutonic, volcanic, metamorphic, and pegmatitic origin from different continents and of 16 Ma to 2 Ga age for their feldspar CL textures and ca. 1200 feldspar crystals from these rocks for their CL color spectra. Among the analyzed rocks, igneous feldspar is most commonly zoned, whereby oscillatory zoning can be confirmed to be typical for volcanic plagioclase. The volcanic plagioclase also less commonly contains twin lamellae that are visible in CL light than crystals from other rock types. Alkali feldspar, particularly from igneous and pegmatitic rocks, was noted to be most affected by alteration features, visible as dark spots, lines and irregular areas. The size of all textural features of up to ca. 150 μm, in combination with possible alteration in both the source area and the sedimentary system, makes the CL textures of feldspar possible to use for qualitative provenance research only. We observed alkali feldspar mostly to luminesce in a bluish color and sometimes in red, and plagioclase in green to yellow. The corresponding CL spectra are dominated by three apparent intensity peaks at 440-520 nm (mainly blue), 540-620 nm (mainly green) and 680-740 nm (red to infrared). A dominance of the peak in the green wavelength interval over the blue one for plagioclase makes CL particularly useful for the differentiation of plagioclase from alkali feldspar. An apparent peak position in red to infrared at < 710 nm for plagioclase mainly is present in mafic rocks. Present-day coastal sand from Peru containing feldspar with the red to infrared peak position mainly exceeding 725 nm for northern Peruvian sand and a larger variety for sand from southern Peru illustrates a discriminative effect of different source areas. We conclude that the provenance application particularly can reveal first-cycle input from mafic rocks and source variations for detritus from arid areas that has been affected by little feldspar alteration.

The magmatism and metamorphism at the Malayer area, Western Iran

NASA Astrophysics Data System (ADS)

Ahadnejad, V.; Valizadeh, M. V.; Esmaeily, D.

2009-04-01

The Malayer area is located in the NW-SE aligned Sanandaj-Sirjan metamorphic belt, western Iran and consists mainly of Mesozoic schists so-called Hamadan Phyllites, Jurassic to Tertiary intrusive rocks and related contact metamorphic aureoles, aplites and pegmatites. The Sanandj-Sirjan Zone is produced by oblique collisional event between Arabian plate and Central Iran microcontinent. Highest level of regional metamorphism in the area is greenschist facies and injection of felsic magmas is caused contact metamorphism. Magmatism is consist of a general northwest trend large felsic to intermediate intrusive bodies. The main trend of structural features i.e. faults, fractures and other structural features is NW-SE. The Malayer granitoid complex is ellipsoid in shape and has NW-SE foliation especially at the corners of the intrusions. Petrography of the magmatic rocks revealed recrystallization of quartz and feldspars, bending of biotite, and aligment of minerals paralle to the main trend of magmatic and metamorphic country rocks. These indicated that intrusion of felsic magma is coincide to the regional metamorphism and is syn-tectoinc. Non-extensive contact metamorphism aureoles and rareness of pegmatite and aplite in the area are interpreted as injection of felsic magmas into the high-strain metamorphic zone. The regional metamorphic rocks mainly consist of meta-sandstone, slate, phyllite, schist. These gray to dark metasedimentary rocks are consist of quartz, muscovite, turmaline, epidote, biotite and chlorite. Sheeted minerals form extended schistosity and study of porphyroblast-matrix relationships shows that injection of granitic magma into the country rocks is syn to post-tectonic. Syn-tectonic indicating porphyroblast growth synchronous with the development of the external fabric. The thermal contact area of the granite can be observed in the contact margin of granite and regional metamorphic rocks, where it produced hornfelses, andalusit-garnet schists and local feldspatisation. Hornfels has surrounded the Malayer intrusive body in its southern, eastern and to some extent northeastern parts. It shows a rather sharp contact with the granodiorite. According to field and microscopic investigations, an original clay-sandstone has been converted into hornfels due to contact metamorphism. Some small highly altered granitic patches are seen in the hornfels unit, especially close to its contact with the Malayer intrusive body.

HAFNIAN ZIRCONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

von Knorring, O.; Hornung, G.

1961-06-17

Two hafnia zircons were examined in detail, one from Mtoko in Southern Rhodesia, containing 21% HfO/sub 2/, and the other from Karibib in South-West Africa, with 31% HfO/sub 2/. In both cases the zircons are associated with the later tantalum-rich phase of mineralization. The Mtoko zircon forms small, mauve- colored, independent crystals in the albitic zone of the pegmatite. The zircon from Karibib occurs in larger reddish-brown masses, partly intergrown with minute manganotantalite crystals and set in a matrix of lithium-bearing mica, albite, quartz and kaolinized feldspar. Some crystals show dominant pyramid faces, with a suppressed prism. Both zircons exhibitmore » an intense golden-yellow fluorescence in UV light. The zircon from Karibib was found to be only weakly radioactive. Data are given concerning various properties of the two zircons. (P.C.H.)« less

Compositional variation in the chevkinite group: new data from igneous and metamorphic rocks

USGS Publications Warehouse

Belkin, Harvey E.; MacDonald, R.; Wall, F.; Baginski, B.

2009-01-01

Electron microprobe analyses are presented of chevkinite-group minerals from Canada, USA, Guatemala, Norway, Scotland, Italy and India. The host rocks are metacarbonates, alkaline and subalkaline granitoids, quartz-bearing pegmatites, carbonatite and an inferred K-rich tuff. The analyses extend slightly the range of compositions in the chevkinite group, e.g. the most MgO-rich phases yet recorded, and we report two further examples where La is the dominant cation in the A site. Patchily- zoned crystals from Virginia and Guatemala contain both perrierite and chevkinite compositions. The new and published analyses are used to review compositional variation in minerals of the perrierite subgroup, which can form in a wide range of host rock compositions and over a substantial pressure- temperature range. The dominant substitutions in the various cation sites and a generalized substitution scheme are described.

Reported industrial minerals occurrences and permissive areas for other occurrences in the Islamic Republic of Mauritania, (phase V, deliverable 89): Chapter R in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Langer, William H.

2015-01-01

Previous PRISM reports discuss a variety of industrial minerals. Gypsum, phosphate, salt, stone, sulfur, and ilmenite command the majority of the attention in the earlier geologic reports. (Ilmenite is evaluated in a separate U.S. Geological Survey report in the current study). Asbestos, arsenic, barite, fluorite, and kaolin are listed in indices (occurrence datasets) as potential mineral resources (Marsh and Anderson, 2015), but previous reports do not elaborate on their development potential. Beryl, described herein with the discussions of pegmatites, is also listed in indices of potential mineral resources, but has not been described in terms of its industrial mineral potential. Short discussions on the potential for cement (carbonate rocks), glass sand, peat, and sillimanite resources are included in this report.

Lithium: for harnessing renewable energy

USGS Publications Warehouse

Bradley, Dwight; Jaskula, Brian W.

2014-01-01

Lithium, which has the chemical symbol Li and an atomic number of 3, is the first metal in the periodic table. Lithium has many uses, the most prominent being in batteries for cell phones, laptops, and electric and hybrid vehicles. Worldwide sources of lithium are broken down by ore-deposit type as follows: closed-basin brines, 58%; pegmatites and related granites, 26%; lithium-enriched clays, 7%; oilfield brines, 3%; geothermal brines, 3%; and lithium-enriched zeolites, 3% (2013 statistics). There are over 39 million tons of lithium resources worldwide. Of this resource, the USGS estimates there to be approximately 13 million tons of current economically recoverable lithium reserves. To help predict where future lithium supplies might be located, USGS scientists study how and where identified resources are concentrated in the Earth’s crust, and they use that knowledge to assess the likelihood that undiscovered resources also exist.

Compositional variation in the chevkinite group: New data from igneous and metamorphic rocks

USGS Publications Warehouse

Macdonald, R.; Belkin, H.E.; Wall, F.; Baginski, B.

2009-01-01

Electron microprobe analyses are presented of chevkinite-group minerals from Canada, USA, Guatemala, Norway, Scotland, Italy and India. The host rocks are metacarbonates, alkaline and subalkaline granitoids, quartz-bearing pegmatites, carbonatite and an inferred K-rich tuff. The analyses extend slightly the range of compositions in the chevkinite group, e.g. the most MgO-rich phases yet recorded, and we report two further examples where La is the dominant cation in the A site. Patchilyzoned crystals from Virginia and Guatemala contain both perrierite and chevkinite compositions. The new and published analyses are used to review compositional variation in minerals of the perrierite subgroup, which can form in a wide range of host rock compositions and over a substantial pressure-temperature range. The dominant substitutions in the various cation sites and a generalized substitution scheme are described. ?? 2009 The Mineralogical Society.

Pre-impact tectonothermal evolution of the crystalline basement-derived rocks in the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure

USGS Publications Warehouse

Gibson, R.L.; Townsend, G.N.; Horton, J. Wright; Reimold, W.U.

2009-01-01

Pre-impact crystalline rocks of the lowermost 215 m of the Eyreville B drill core from the Chesapeake Bay impact structure consist of a sequence of pelitic mica schists with subsidiary metagraywackes or felsic metavolcanic rocks, amphibolite, and calc-silicate rock that is intruded by muscovite (??biotite, garnet) granite and granite pegmatite. The schists are commonly graphitic and pyritic and locally contain plagioclase porphyroblasts, fi brolitic sillimanite, and garnet that indicate middle- to upper-amphibolite-facies peak metamorphic conditions estimated at ??0.4-0.5 GPa and 600-670 ??C. The schists display an intense, shallowly dipping, S1 composite shear foliation with local micrometer- to decimeter-scale recumbent folds and S-C' shear band structures that formed at high temperatures. Zones of chaotically oriented foliation, resembling breccias but showing no signs of retrogression, are developed locally and are interpreted as shear-disrupted fold hinges. Mineral textural relations in the mica schists indicate that the metamorphic peak was attained during D1. Fabric analysis indicates, however, that subhorizontal shear deformation continued during retrograde cooling, forming mylonite zones in which high-temperature shear fabrics (S-C and S-C') are overprinted by progressively lower- temperature fabrics. Cataclasites and carbonate-cemented breccias in more competent lithologies such as the calc-silicate unit and in the felsic gneiss found as boulders in the overlying impactite succession may refl ect a fi nal pulse of low-temperature cataclastic deformation during D1. These breccias and the shear and mylonitic foliations are cut by smaller, steeply inclined anastomosing fractures with chlorite and calcite infill (interpreted as D2). This D2 event was accompanied by extensive chlorite-sericitecalcite ?? epidote retrogression and appears to predate the impact event. Granite and granite pegmatite veins display local discordance to the S1 foliation, but elsewhere they are affected by high-temperature mylonitic shear deformation, suggesting a late-D1 intrusive timing close to the metamorphic peak. The D1 event is tentatively interpreted as a thrusting event associated with westward-verging collision between Gondwana and Laurentia before or during the Permian-Carboniferous Alleghanian orogeny. It is unclear whether subsequent brittle deformation, described here as D2, could be part of regional dextral Alleghanian strike-slip faulting or younger Mesozoic normal faulting. ?? 2009 The Geological Society of America.

The role of lead and excess oxygen in uranite

USGS Publications Warehouse

Berman, Robert Morris

1957-01-01

Analysed samples of uraninite were x-rayed, annealed by heating to 550° and 900° for various times in a nitrogen atmosphere, and x-rayed again. A decrease in unit cell size was generally observed. Calculations on the basis of Vegard's Law showed that the ordering of the interstitial oxygen ions could account for the decrease in cell size on annealing. The interstitial oxygens are not necessarily completely disordered before annealing. The degree of original disorder is dependent on the Rare Earth/ThO2 ratio; for high ThO2 and low rare earths, the interstitial oxygens are completely random. The degree of disorder apparently depends solely on the composition, and not on the past history of the sample; this implies that the oxygens are being continuously disordered, perhaps by alpha particles, to the equilibrium point determined by the R.E./ThO2 ratio. The degree of ordering of the interstitial oxygens also accounts for the difference in cell size between vein pitchblendes and those from the sediments of the Colorado Plateau. A study was also made of the degree of oxidation of uraninites. Although the uranium in many pegmatitic uraninites is more oxidized than can be obtained with the cubic UO2 phase in the laboratory, if the atoms proxying for uranium are calculated into the structural formula, and the lead is assumed to be radiogenic and calculated as original uranium, almost all pegmatitic uraninites fall into the range of interstitial oxygen content obtainable in the laboratory. This fact supports the auto-oxidation hypothesis. Many of the vein and sedimentary pitchblendes have compositions close to U3O8, although they are cubic. They may gave crystallized as U3O8, the decomposed to the cubic phase and a amorphous phase. This suggests that the stability range of U3O8 includes only very exceptional natural conditions. Vegard's Law calculations, studies of zoning in crystals, differential leaching, polished section textures, and other lines of evidence indicate that lead, including radiogenic lead, is exsolved from uraninite. A study of x-ray line intensities indicates that it exsolves as oriented monomolecular layers of orthohombic PbO (massicot) along cube planes in the uraninite, separating the uraninite crystallites so that the x-ray reflections interfere destructively to different degrees for different reflections.

Clastic metasediments of the Early Proterozoic Broken Hill Group, New South Wales, Australia: Geochemistry, provenance, and metallogenic significance

USGS Publications Warehouse

Slack, J.F.; Stevens, B.P.J.

1994-01-01

Whole-rock analyses of samples of pelite, psammite, and psammopelite from the Early Proterozoic Broken Hill Group (Willyama Supergroup) in the Broken Hill Block, New South Wales, Australia, reveal distinctive geochemical signatures. Major-element data show high Al2O3 and K2O, low MgO and Na2O, and relatively high Fe2O3T MgO ratios, compared to average Early Proterozoic clastic metasediments. High field strength elements (HFSE) are especially abundant, including Nb (most 15-27 ppm), Ta (most 1.0-2.2 ppm), Th (17-36 ppm), Hf (4-15 ppm), and Zr (most 170-400 ppm); Y (33-74 ppm) is also high. Concentrations of ferromagnesian elements are generally low (Sc = < 20 ppm, Ni = ??? 62 ppm, Co = <26 ppm; Cr = most < 100 ppm). Data for rare earth elements (REEs) show high abundances of light REEs (LaCN = 116-250 ?? chondrite; LaCN = 437 in one sample), high LaCN YbCN ratios (5.6-13.9), and large negative Eu anomalies ( Eu Eu* = 0.32-0.57). The geochemical data indicate derivation of the metasedimentary rocks of the Broken Hill Group by the erosion mainly of felsic igneous (or meta-igneous) rocks. High concentrations of HFSE, Y, and REEs in the metasediments suggest a provenance dominanted by anorogenic granites and(or) rhyolites, including those with A-type chemistry. Likely sources of the metasediments were the rhyolitic to rhyodacitic protoliths of local quartz + feldspar ?? biotite ?? garnet gneisses (e.g., Potosi-type gneiss) that occur within the lower part of the Willyama Supergroup, or chemically similar basement rocks in the region; alternative sources may have included Early Proterozoic anorogenic granites and(or) rhyolites in the Mount Isa and(or) Pine Creek Blocks of northern Australia, or in the Gawler craton of South Australia. Metallogenic considerations suggest that the metasediments of the Broken Hill Block formed enriched source rocks during the generation of pegmatite-hosted deposits and concentrations of La, Ce, Nb, Ta, Th, and Sn in the region. Li, Be, B, W, and U in pegmatite minerals of the district may have been acquired during granulite-facies metamorphism of the local metasediments. ?? 1994.

A geochemical investigation of selected areas in Greenville and Laurens counties, South Carolina--implications for mineral resources

USGS Publications Warehouse

Jackson, John C.

1992-01-01

The purpose of this study is to geochemically evaluate three areas within the Greenville 1° x 2° quadrangle (see index map) that have been shown by previous studies to contain anomalously high amounts of tin. Jackson and Moore (1992) reported the presence of cassiterite (SnO2)-bearing heavy-mineral concentrates from stream sediment samples that were collected during a regional geochemical reconnaissance of the Greenville 1° x 2° quadrangle. The data reported here confirm identified in selected heavy-mineral concentrate samples. In addition, anomalously high concentrations of barium, beryllium, lanthanum, and thorium are also reported for parts of the same areas. No significant mineral deposits are known to occur in the study areas. There was, however, minor production of monazite from several nearby localities (Sloan, 1908), and gold was produced from deposits in the northeastern part of Greenville County and nearby Spartanburg County (McCauley and Butler, 1966). The three areas selected for resampling are located in the Inner Piedmont physiographic province of South Carolina (see index map). The generalized tectonic setting of the region and the locations of the study is just north of Greenville, S.C. Much of it is within the moderately to steeply sloped terrane of Paris Mountain State Park where elevations reach approximately 600 m. Simpsonville, S.C., is neat the center of the second study area, and the southernmost study area is near Hickory Tavern, S.C. Both the Simpsonville and Hickory Tavern study areas are in more gently rolling Piedmont terrane. Each of the sampled areas is drained by tributaries of the Enoree and Reedy Rivers. Parts of three different thrust sheets underlie the region covered by this study (fig. 1); in ascending structural position, they are the Six Mile, Paris Mountain, and Laurens thrust sheets (Nelson and others, 1987). Nelson (1988, p. 7) described the contacts between these sheets as being along unnamed faults. The rocks in and around the study areas have undergone sillimanite-muscovite-grade metamorphism (Nelson, 1988, p. 9). Nelson (1988, p. 13) reports that the Six Mile thrust sheet was metamorphosed about 344 Ma. The geology of these sheets as described in this study, including geologic contacts, rock descriptions, and unit names, generally follows that of Nelson and others (1987, 1989). Within the Paris Mountain study area, rocks of the Paris Mountain thrust sheet predominate (fig. 2) and consist of a biotite-muscovite-sillimanite schist (EZsp) that has extensive lenses of fine- to medium- grained biotite granite gneiss (Pzgp). Areas of biotite granite gneiss that occur in the southern part of the Paris Mountain study area contain extensive pegmatitic and leucogranitic phases. These pegmatitic zones consist mostly of coarse-grained microcline feldspar and quartz with minor amounts of muscovite, biotite, and garnet. Smaller pegmatite lenses (<0.5 m thick) that occur within the biotite-muscovite-sillimanite schist of the Paris Mountain study area are generally of similar mineralogy, although some contain tourmaline crystals up to 5 cm in length. The Six Mile thrust sheet underlies the northern edge of the Paris Mountain study area, where it is composed of gneissic biotitic granites of the Caesars Head Granite (figs. 1 and 2). The northwestern part of the Simpsonville study area (figs. 1 and 3), within the Paris Mountain thrust sheet, is underlain by a biotite-muscovite-sillimanite schist (EZsp) that contains lenses of biotite granite gneiss (Pzgp). In the southeastern part of the Simpsonville study area, within the Laurens thrust sheet, biotite gneiss (EZgl), biotite granite gneiss (Pzgf), and minor amphibolite (EZal) are interlayered biotite (EZgl), granite gneiss (Dgg), and amphibolite (EZal) of the Laurens thrust sheet (fig. 4).

Bedrock geologic map of the Uxbridge quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

USGS Publications Warehouse

Walsh, Gregory J.

2014-01-01

The bedrock geology of the 7.5-minute Uxbridge quadrangle consists of Neoproterozoic metamorphic and igneous rocks of the Avalon zone. In this area, rocks of the Avalon zone lie within the core of the Milford antiform, south and east of the terrane-bounding Bloody Bluff fault zone. Permian pegmatite dikes and quartz veins occur throughout the quadrangle. The oldest metasedimentary rocks include the Blackstone Group, which represents a Neoproterozoic peri-Gondwanan marginal shelf sequence. The metasedimentary rocks are intruded by Neoproterozoic arc-related plutonic rocks of the Rhode Island batholith. This report presents mapping by G.J. Walsh. The complete report consists of a map, text pamphlet, and GIS database. The map and text pamphlet are available only as downloadable files (see frame at right). The GIS database is available for download in ESRI™ shapefile and Google Earth™ formats, and includes contacts of bedrock geologic units, faults, outcrops, structural geologic information, geochemical data, and photographs.

Cryptic Disc Structures Resembling Ediacaran Discoidal Fossils from the Lower Silurian Hellefjord Schist, Arctic Norway.

PubMed

Kirkland, Christopher L; MacGabhann, Breandán A; Kirkland, Brian L; Daly, J Stephen

2016-01-01

The Hellefjord Schist, a volcaniclastic psammite-pelite formation in the Caledonides of Arctic Norway contains discoidal impressions and apparent tube casts that share morphological and taphonomic similarities to Neoproterozoic stem-holdfast forms. U-Pb zircon geochronology on the host metasediment indicates it was deposited between 437 ± 2 and 439 ± 3 Ma, but also indicates that an inferred basal conglomerate to this formation must be part of an older stratigraphic element, as it is cross-cut by a 546 ± 4 Ma pegmatite. These results confirm that the Hellefjord Schist is separated from underlying older Proterozoic rocks by a thrust. It has previously been argued that the Cambrian Substrate Revolution destroyed the ecological niches that the Neoproterozoic frond-holdfasts organisms occupied. However, the discovery of these fossils in Silurian rocks demonstrates that the environment and substrate must have been similar enough to Neoproterozoic settings that frond-holdfast bodyplans were still ecologically viable some hundred million years later.

The crystal structure of an iron-rich variety of zanazziite belonging to heteropolyhedral framework roscherite-group beryllophosphates

NASA Astrophysics Data System (ADS)

Rastsvetaeva, R. K.; Rozenberg, K. A.; Chukanov, N. V.; Möckel, S.

2009-07-01

The iron-rich variety of zanazziite Ca2[Mg0.65Fe0.35□1.0][Mg1.90Fe1.25Al0.5Mn0.35]Σ4Be4(PO4)6(OH)4(H2O,OH)2 · 4H2O, which is a heteropolyhedral framework roscherite-group beryllophos-phate from the Sapucaia pegmatite (Minas Gerais, Brazil), was studied by X-ray diffraction. The refinement was carried out in the triclinic and monoclinic systems. It was found that the cation distribution on octahedral sites in the crystal structure is in better agreement with the monoclinic symmetry ( a = 15.876 Å, b = 11.860 Å, c = 6.607 Å, β = 95.49°, sp. gr. C2/ c). In the sample under study, no ordering of Mg or Fe atoms in octahedral sites is observed in sp. gr. P bar 1 , unlike the more iron-rich member of the roscherite group (atencioite).

Cryptic Disc Structures Resembling Ediacaran Discoidal Fossils from the Lower Silurian Hellefjord Schist, Arctic Norway

PubMed Central

MacGabhann, Breandán A.; Kirkland, Brian L.; Daly, J. Stephen

2016-01-01

The Hellefjord Schist, a volcaniclastic psammite-pelite formation in the Caledonides of Arctic Norway contains discoidal impressions and apparent tube casts that share morphological and taphonomic similarities to Neoproterozoic stem-holdfast forms. U-Pb zircon geochronology on the host metasediment indicates it was deposited between 437 ± 2 and 439 ± 3 Ma, but also indicates that an inferred basal conglomerate to this formation must be part of an older stratigraphic element, as it is cross-cut by a 546 ± 4 Ma pegmatite. These results confirm that the Hellefjord Schist is separated from underlying older Proterozoic rocks by a thrust. It has previously been argued that the Cambrian Substrate Revolution destroyed the ecological niches that the Neoproterozoic frond-holdfasts organisms occupied. However, the discovery of these fossils in Silurian rocks demonstrates that the environment and substrate must have been similar enough to Neoproterozoic settings that frond-holdfast bodyplans were still ecologically viable some hundred million years later. PMID:27783643

Polygenetic Aspect of Unit Theory Oil Generation

NASA Astrophysics Data System (ADS)

Galant, Yuri

2015-04-01

In the framework of a unified theory Oil Generation one of important moments is the consideration of the distribution of oil in the Earth's Crust. Analysis of the distribution of oil deposits in the Earth's Crust showed that oil distributed throughout the stratigraphic section from ancient to modern sediments and from a depth of 12 kilometers to the Earth's surface. The distribution of oil almost meets all stages of metamorphism of rocks. Correlation of the section of oil distribution to genetic types of ore deposits showed that each genetic type ore deposits has its analogue oil field . So it is possible to classify oil fields on 1) endogenous: the actual magmatic, post-magmatic, contact-metasomatic (skarn), hydrothermal, exhalation, carbonatite, pegmatite, 2) exogenous: weathering, oxidation, sedimentary,3) metamorphogenic: metamorphosed, metamorphic. Model of such distribution of oil deposits can be a process of successive formation of oil deposits of mantle degassing tube. Thus oil is polygenic by way of formation of deposits, but their source is united.

40Ar/ 39Ar dating of micas from granites of NE Kibaran Belt (Karagwe-Ankolean), NW Tanzania

NASA Astrophysics Data System (ADS)

Ikingura, J. R.; Reynolds, P. H.; Watkinson, D. H.; Bell, K.

1992-11-01

40Ar/ 39Ar total gas ages of muscovites and biotites from granites associated with NE Kibaran belt (Karagwe-Ankolean) in NW Tanzanian are in the range of about 945-700 Ma, much less than the estimated age of the granites. Age gradients in the muscovite spectra are indicative of partial gas loss as a result of thermal overprinting. Evidence for at least two tectonothermal events, at ca. 950 Ma and ca. 700 Ma, is noted. The older of these correlates with the formation of tin-bearing pegmatites and hydrothermal veins in the Kibaran belt; the younger with vein emplacements in the Burundian and/or a deformational episode. Correlation of 40Ar/ 39Ar age data with K-Ar and Rb-Sr data from other parts of the Kibaran belt in Burundi, Rwanda and Zaire indicates that the NE Kibaran belt, east of the Western Rift, experienced a tectonothermal history similar to that of the western part of the during the late-Proterozoic.

Mineralogy and provenance of clays in miarolitic cavities of the Pikes Peak Batholith, Colorado

USGS Publications Warehouse

Kile, D.E.

2005-01-01

Clay samples from 105 cavities within miarolitic granitic pegmatites throughout the Pikes Peak batholith, in Colorado, were analyzed by powder X-ray diffraction (XRD). Smectite (beidellite), illite, and kaolinite were found within the cavities. Calculation of crystallite-thickness distribution (CTD), mean thickness of the crystallites, and variance in crystallite thickness, as deduced from XRD patterns, allowed a determination of provenance and mode of formation for illite and smectite. Authigenic miarolitic-cavity illite and smectite show lognormal CTDs and larger mean thicknesses of crystallites than do their soil-derived counterparts; non-lognormal illite in a cavity results from mixing of cavity and soil illite. Analysis of mean thickness and thickness variance shows that crystal growth of illite is initiated by a nucleation event of short duration, followed by surface-controlled kinetics. Crystallization of the miarolitic cavity clays is presumed to occur by neoformation from hydrothermal fluids. The assessment of provenance allows a determination of regional and local distributions of clay minerals in miarolitic cavities within the Pikes Peak batholith.

Geology of the Ralston Buttes district, Jefferson County, Colorado: a preliminary report

USGS Publications Warehouse

Sheridan, Douglas M.; Maxwell, Charles H.; Albee, Arden L.; Van Horn, Richard

1956-01-01

The Ralston Buttes district in Jefferson County is one of the most significant new uranium districts located east of the Continental Divide in Colorado. The district is east of the Colorado Front Range mineral belt, along the east front of the range. From November 1953 through October 1956, about 10,000 tons of uranium ore, much of which was high-grade pitchblende-bearing vein material, was shipped from the district. The ore occurs in deposits that range in size from bodies containing less than 50 tons to ore shoots containing over 1,000 tons. The only other mining activity in the area has been a sporadic production of beryl, feldspar, and scrap mica from Precambrian pegmatites, and quarrying of dimension stone, limestone, and clay from sedimentary rocks. Most of the Ralston Buttes district consists of complexly folded Precambrian metamorphic and igneous rocks - gneiss, schist, quartzite, amphibolite, and granodiorite. Paleozoic and Mesozoic sedimentary rocks crop out in the northeastern part of the district. These rocks are cut by northwesterly-trending fault systems of Laramide age and by small bodies of intrusive rocks that are Tertiary in age. The typical uranium deposits in the district are hydrothermal veins occupying openings in Laramide fault breccias or related fractures that cut the Precambrian rocks. Pitchblende and lesser amounts of secondary uranium minerals are associated with sparse base-mental sulfides in a gangue of carbonate minerals, potash feldspar, and, more rarely, quartz. Less common types of deposits consist of pitchblende and secondary uranium minerals that occupy fractures cutting pegmatites and quartz veins. The uranium deposits are concentrated in two areas, the Ralston Creek area and the Golden Gate Canyon area. The deposits in the Ralston Creek area are located along the Rogers fault system, and the deposits in the Golden Gate Canyon area are along the Hurricane Hill fault system. Two geologic factors were important to the localization of the uranium deposits: (1) favorable structural environment and (2) favorable host rocks. The deposits in each of the two major areas are located where a northwesterly-trending Laramide fault system splits into a complex network of faults. Also, most of the deposits appear to be localized where the faults cut Precambrian rocks rich in hornblende, biotite, or garnet and biotite. The ore controls recognized in this relatively new uranium district may have wider application in areas of similar geology elsewhere in the Front Range.

Geologic map of the Kings Mountain and Grover quadrangles, Cleveland and Gaston Counties, North Carolina, and Cherokee and York Counties, South Carolina

USGS Publications Warehouse

Horton, J. Wright

2006-01-01

This geologic map of the Kings Mountain and Grover 7.5-minute quadrangles, N.C.-S.C., straddles a regional geological boundary between the Inner Piedmont and Carolina terranes. The Kings Mountain sequence (informal name) on the western flank of the Carolina terrane in this area includes the Neoproterozoic Battleground and Blacksburg Formations. The Battleground Formation has a lower part consisting of metavolcanic rocks and interlayered schist, and an upper part consisting of quartz-sericite phyllite and schist interlayered with quartz-pebble metaconglomerate, aluminous quartzite, micaceous quartzite, manganiferous rock, and metavolcanic rocks. The Blacksburg Formation consists of phyllitic metasiltstone interlayered with thinner units of marble, laminated micaceous quartzite, hornblende gneiss, and amphibolite. Layered metamorphic rocks of the Inner Piedmont terrane include muscovite-biotite gneiss, muscovite schist, and amphibolite. The Kings Mountain sequence has been intruded by metatonalite and metatrondhjemite (Neoproterozoic), metadiorite and metagabbro (Paleozoic), and High Shoals Granite (Pennsylvanian). Layered metamorphic rocks of the Inner Piedmont in this area have been intruded by Toluca Granite (Ordovician?), Cherryville Granite and associated pegmatite (Mississippian), and spodumene pegmatite (Mississippian). Diabase dikes (early Jurassic) are locally present throughout the area. Ductile fault zones of regional scale include the Kings Mountain and Kings Creek shear zones. In this area, the Kings Mountain shear zone forms the boundary between the Inner Piedmont and Carolina terranes, and the Kings Creek shear zone separates the Battleground Formation from the Blacksburg Formation. Structural styles change across the Kings Mountain shear zone from steeply-dipping layers, foliations, and folds on the southeast to gently- and moderately-dipping layers, foliations, and recumbent folds on the northwest. Mineral assemblages in the Kings Mountain sequence show a westward decrease from upper amphibolite facies (sillimanite zone) near the High Shoals Granite on the east side of the map to greenschist (epidote-amphibolite) facies in the south-central part of the area near the Kings Mountain shear zone. Amphibolite-facies mineral assemblages in the Inner Piedmont terrane increase in grade from the kyanite zone near the Kings Mountain shear zone to the sillimanite zone in the northwest part of the map. Surficial deposits include alluvium in the stream valleys and colluvium along ridges and steep slopes. These quadrangles are unusual in their richness and variety of mineral deposits, which include spodumene (lithium), cassiterite (tin), mica, feldspar, silica, clay, marble, kyanite and sillimanite, barite, manganese, sand and gravel, gold, pyrite, and iron. (Abstract from pamphlet.)

Geologic Map of the Kings Mountain and Grover Quadrangles, Cleveland and Gaston Counties, North Carolina, and Cherokee and York Counties, South Carolina

USGS Publications Warehouse

Horton, J. Wright

2008-01-01

This geologic map of the Kings Mountain and Grover 7.5-min quadrangles, N.C.-S.C., straddles a regional geological boundary between the Inner Piedmont and Carolina terranes. The Kings Mountain sequence (informal name) on the western flank of the Carolina terrane in this area includes the Neoproterozoic Battleground and Blacksburg Formations. The Battleground Formation has a lower part consisting of metavolcanic rocks and interlayered schist and an upper part consisting of quartz-sericite phyllite and schist interlayered with quartz-pebble metaconglomerate, aluminous quartzite, micaceous quartzite, manganiferous rock, and metavolcanic rocks. The Blacks-burg Formation consists of phyllitic metasiltstone interlayered with thinner units of marble, laminated micaceous quartzite, hornblende gneiss, and amphibolite. Layered metamorphic rocks of the Inner Piedmont terrane include muscovite-biotite gneiss, muscovite schist, and amphibolite. The Kings Mountain sequence has been intruded by metatonalite and metatrondhjemite (Neoproterozoic), metagabbro and metadiorite (Paleozoic?), and the High Shoals Granite (Pennsylvanian). Layered metamorphic rocks of the Inner Piedmont in this area have been intruded by the Toluca Granite (Ordovician?), the Cherryville Granite and associated pegmatite (Mississippian), and spodumene pegmatite (Mississippian). Diabase dikes (early Jurassic) are locally present throughout the area. Ductile fault zones of regional scale include the Kings Mountain and Kings Creek shear zones. In this area, the Kings Mountain shear zone forms the boundary between the Inner Piedmont and Carolina terranes, and the Kings Creek shear zone separates the Battleground Formation from the Blacksburg Formation. Structural styles change across the Kings Mountain shear zone from steeply dipping layers, foliations, and folds on the southeast to gently and moderately dipping layers, foliations, and recumbent folds on the northwest. Mineral assemblages in the Kings Mountain sequence show a westward decrease from upper amphibolite facies (sillimanite zone) near the High Shoals Granite in the eastern side of the map area to upper greenschist (epidote-amphibolite) facies in the south-central part of the area near the Kings Mountain shear zone. Amphibolite-facies mineral assemblages in the Inner Piedmont terrane increase in grade from the kyanite zone near the Kings Mountain shear zone to the sillimanite zone in the northwestern part of the map area. Surficial deposits include alluvium in the stream valleys and colluvium along ridges and steep slopes. These quadrangles are unusual in the richness and variety of the mineral deposits that they contain, which include spodumene (lithium), cassiterite (tin), mica, feldspar, silica, clay, marble, kyanite and sillimanite, barite, manganese, sand and gravel, gold, pyrite, and iron.

Metamorphic charnockite in contact aureoles around intrusive enderbite from Natal, South Africa

NASA Astrophysics Data System (ADS)

van den Kerkhof, Alfons M.; Grantham, Geoffrey H.

In the Port Edward area of southern Kwa-Zulu Natal, South Africa, charnockitic aureoles up to 10m in width in the normally garnetiferous Nicholson's Point Granite, are developed adjacent to intrusive contacts with the Port Edward Enderbite and anhydrous pegmatitic veins. Mineralogical differences between the country rock and charnockitic aureole suggest that the dehydration reaction Bt+Qtz-->Opx+Kfs+H2O and the reaction of Grt+Qtz-->Opx+Pl were responsible for the charnockitization. The compositions of fluid inclusions show systematic variation with: (1) the Port Edward Enderbite being dominated by CO2 and N2 fluid inclusions; (2) the non-charnockitized granite by saline aqueous inclusions with 18-23 EqWt% NaCl; (3) the charnockitic aureoles by low-salinity and pure water inclusions (<7 EqWt% NaCl); (4) the pegmatites by aqueous inclusions of various salinity with minor CO2. As a result of the thermal event the homogenization temperatures of the inclusions in charnockite show a much larger range (up to 390°C) compared to the fluid inclusions in granite (mostly <250°C). Contrary to fluid-controlled charnockitization (brines, CO2) which may have taken place along shear zones away from the intrusive body, the present ``proximal'' charnockitized granite formed directly at the contact with enderbite. The inclusions indicate contact metamorphism induced by the intrusion of ``dry'' enderbitic magma into ``wet'' granite resulting in local dehydration. This was confirmed by cathodoluminescence microscopy showing textures indicative for the local reduction of structural water in the charnockite quartz. Two-pyroxene thermometry on the Port Edward Enderbite suggests intrusion at temperatures of 1000-1050°C into country rock with temperature of <700°C. The temperature of aureole formation must have been between 700°C (breakdown of pyrite to form pyrrhotite) and 1000°C. Charnockitization was probably controlled largely by heat related to anhydrous intrusions causing dehydration reactions and resulting in the release and subsequent trapping of dehydration fluids. The salinity of the metamorphic fluid in the contact zones is supposed to have been higher at an early stage of contact metamorphism, but it has lost its salt content by K-metasomatic reactions and/or the preferential migration of the saline fluids out of the contact zones towards the enderbite. The low water activity inhibited the localized melting of the granite. Mineral thermobarometry suggests that after charnockite aureole genesis, an isobaric cooling path was followed during which reequilibration of most of the aqueous inclusions occurred.

Gabbroic and Peridotitic Enclaves from the 2008 Kasatochi Eruption, Aleutian Islands, Alaska

NASA Astrophysics Data System (ADS)

Kentner, A.; Nadin, E. S.; Izbekov, P. E.; Nye, C. J.; Neill, O. K.

2012-12-01

Kasatochi volcano of the Andreanof Islands in the western Aleutian Arc violently erupted over a two day period from August 7-8, 2008. The eruption involved multiple explosive events generating pyroclastic flows, which included abundant mafic and ultramafic enclaves that have since weathered out and accumulated in talus along the coast. These and other mafic enclaves sampled by modern island arc lavas provide insight into subduction magmatism because they emerge from a section of the subduction system that is less likely than shallower zones to be modified by magmatic processes such as mixing, assimilation, or fractionation. We present new whole rock, clinopyroxene, amphibole, plagioclase, and melt compositions from Kasatochi enclaves of the 2008 eruption. The highly crystalline (~40 vol. % phenocryst content), medium-K basaltic andesite host rock contains ~52-55 wt. % SiO2 and 0.6-0.9 wt. % K2O, and is composed of plagioclase, ortho- and clinopyroxene, amphibole, and Ti-magnetite in a microlite-rich groundmass. Upon eruption, this magma sampled two distinct enclave populations: gabbro and peridotite. The gabbro has abundant amphibole (mostly magnesio-hastingsite) and plagioclase with minor clinopyroxene, olivine, and magnetite, while the peridotite is composed of olivine with minor amounts of clinopyroxene and orthopyroxene. There is little textural variation amongst the peridotitic samples collected, but the gabbroic samples vary from layered to massive and cover a range in grain size from fine-grained to pegmatitic. The layered gabbros display centimeter-scale bands of alternating plagioclase- and amphibole-rich layers, with a strong preferential alignment of the amphibole grains. The coarser-grained samples are very friable, with ~10% pore space; disaggregation of these upon host-magma ascent likely formed the amphibole and plagioclase xenocrysts in the andesitic host. Based on the textural and compositional differences, we divide the enclaves into four groups, (1) fine-grained gabbro, (2) medium- to coarse-grained gabbro, (3) pegmatitic gabbro with crystals up to 11 cm long, and (4) medium-grained peridotite. Bulk analyses of the gabbros using LA-ICP-MS show strong light rare-earth element depletion typical of primitive melts and arc volcanics such as the South Sandwich Arc. Our data suggest that the enclaves are primitive, with plagioclase compositions of An92-96 and crystallization temperatures of 900-1100 deg. C. Initial thermobarometric analyses from compositions of amphibole in the gabbroic samples suggest different temperature-pressure conditions for crystallization of fine-grained and very coarse-grained gabbros. We interpret these rocks as hydrous cumulate-melt mixtures with primitive geochemistry that is similar to Aleutian xenoliths of Kanaga Island.

Bedrock geologic map of the Nashua South quadrangle, Hillsborough County, New Hampshire, and Middlesex County, Massachusetts

USGS Publications Warehouse

Walsh, Gregory J.; Jahns, Richard H.; Aleinikoff, John N.

2013-01-01

The bedrock geology of the 7.5-minute Nashua South quadrangle consists primarily of deformed Silurian metasedimentary rocks of the Berwick Formation. The metasedimentary rocks are intruded by a Late Silurian to Early Devonian diorite-gabbro suite, Devonian rocks of the Ayer Granodiorite, Devonian granitic rocks of the New Hampshire Plutonic Suite including pegmatite and the Chelmsford Granite, and Jurassic diabase dikes. The bedrock geology was mapped to study the tectonic history of the area and to provide a framework for ongoing hydrogeologic characterization of the fractured bedrock of Massachusetts and New Hampshire. This report presents mapping by G.J. Walsh and R.H. Jahns and zircon U-Pb geochronology by J.N. Aleinikoff. The complete report consists of a map, text pamphlet, and GIS database. The map and text pamphlet are only available as downloadable files (see frame at right). The GIS database is available for download in ESRITM shapefile and Google EarthTM formats, and includes contacts of bedrock geologic units, faults, outcrops, structural geologic information, photographs, and a three-dimensional model.

Structure, age, and ore potential of the Burpala rare-metal alkaline massif, northern Baikal region

NASA Astrophysics Data System (ADS)

Vladykin, N. V.; Sotnikova, I. A.; Kotov, A. B.; Yarmolyuk, V. V.; Sal'nikova, E. B.; Yakovleva, S. Z.

2014-07-01

The Burpala alkaline massif is a unique geological object. More than 50 Zr, Nb, Ti, Th, Be, and REE minerals have been identified in rare-metal syenite of this massif. Their contents often reach tens of percent, and concentrations of rare elements in rocks are as high as 3.6% REE, 4% Zr, 0.5% Y, 0.5% Nb, 0.5% Th, and 0.1% U. Geological and geochemical data show that all rocks in the Burpala massif are derivatives of alkaline magma initially enriched in rare elements. These rocks vary in composition from shonkinite, melanocratic syenite, nepheline and alkali syenites to alaskite and alkali granite. The extreme products of magma fractionation are rare-metal pegmatites, apatite-fluorite rocks, and carbonatites. The primary melts were related to the enriched EM-2 mantle source. The U-Pb zircon ages of pulaskite (main intrusive phase) and rare-metal syenite (vein phase) are estimated at 294 ± 1 and 283 ± 8 Ma, respectively. The massif was formed as a result of impact of the mantle plume on the active continental margin of the Siberian paleocontinent.

Early Paleozoic magmatic events in the eastern Klamath Mountains, northern California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wallin, E.T.; Mattinson, J.M.; Potter, A.W.

1988-02-01

New U-Pb zircon ages for nine samples of tonalite and pegmatitic trondhjemite from the Trinity ophiolite and associated melange reveal a complex history of magmatic activity extending back into the earliest Cambrian, much older than previously believed. Earlier investigations, based on limited data, recognized lower Paleozoic crustal elements in the eastern Klamath terrane (EKT) ranging in age from Middle Ordovician to Early to Middle Devonian. The new work in the Yreka-Callahan area of the EKT confirms the Ordovician (440-475 Ma) and younger ages, but reveals for the first time the presence of tonalitic rocks that crystallized during a narrow timemore » interval at about 565-570 Ma. The authors also recognize younger, Late Silurian magmatism at 412 Ma. In the context of available mapping, these ages indicate that the Trinity ophiolite is broadly polygenetic because parts of it yield crystallization ages that span approximately 150 m.y. Superjacent dismembered units of probable early Paleozoic age may be tectonostratigraphically equivalent to the Sierra City melange in the northern Sierra Nevada.« less

Lithium brines: A global perspective: Chapter 14

USGS Publications Warehouse

Munk, LeeAnn; Hynek, Scott; Bradley, Dwight C.; Boutt, David; Labay, Keith A.; Jochens, Hillary; Verplanck, Philip L.; Hitzman, Murray W.

2016-01-01

Lithium is a critical and technologically important element that has widespread use, particularly in batteries for hybrid cars and portable electronic devices. Global demand for lithium has been on the rise since the mid-1900s and is projected to continue to increase. Lithium is found in three main deposit types: (1) pegmatites, (2) continental brines, and (3) hydrothermally altered clays. Continental brines provide approximately three-fourths of the world’s Li production due to their relatively low production cost. The Li-rich brine systems addressed here share six common characteristics that provide clues to deposit genesis while also serving as exploration guidelines. These are as follows: (1) arid climate; (2) closed basin containing a salar (salt crust), a salt lake, or both; (3) associated igneous and/or geothermal activity; (4) tectonically driven subsidence; (5) suitable lithium sources; and (6) sufficient time to concentrate brine. Two detailed case studies of Li-rich brines are presented; one on the longest produced lithium brine at Clayton Valley, Nevada, and the other on the world’s largest producing lithium brine at the Salar de Atacama, Chile.

Minasgeraisite, a new member of the gadolinite group from Minas Gerais, Brazil.

USGS Publications Warehouse

Foord, E.E.; Gaines, R.V.; Crock, J.G.; Simmons, W.B.; Barbosa, C.P.

1986-01-01

Minasgeraisite, Y2CaBe2Si2O10, a 9.833(2), b 7.562(1), c 4.702(1) A, beta 90.46(6)o, P21/a, Z = 2, is a new member of the gadolinite group. Found in quantities of only several hundred mg in the Jaguaracu pegmatite, Minas Gerais, Brazil, it occurs as 0.2 to 1.0 mm-diameter rosettes, coating and intergrown with milarite, albite, quartz and muscovite. The mineral is lavender to lilac purple and has a sheaf-like habit, with a grain size of 4.25, D(calc.) 4.90 g/cm3, lustre is earthy to subvitreous and the streak is pale purple. Minasgeraisite is slowly soluble in common acids. The mineral has one excellent cleavage, (100) by analogy with gadolinite, and another good cleavage (001). Minasgeraisite is biaxial positive with alpha (colourless) 1.740(4), beta (pale greyish yellow) 1.754(4), gamma (lavender purple) 1.786(4), 2Vgamma 68o. Strongest powder XRD lines include 3.11(100), 2.830(100), 2.540(90), 1.768(35) A.-J.A.Z.

Lithium in sediments and brines--how, why and where to search

USGS Publications Warehouse

Vine, James D.

1975-01-01

The possibility of using lithium in batteries to power electric vehicles and as fuel for thermonuclear power has focused attention on the limited resources of lithium other than in pegmatite minerals. The Clayton Valley, Nev., subsurface lithium brine has been the major source of lithium carbonate since about 1967, but the life of this brine field is probably limited to several more decades at the present rate of production. Lithium is so highly soluble during weathering and in sedimentary environments that no lithium-rich sedimentary minerals other than clays have been identified to date. The known deposits of lithium, such as the clay mineral hectorite and the lithium-rich brines, occur in closed desert basins of the Southwest in association with nonmarine evaporites. However, the ultimate source for the lithium in these deposits may be from hydrothermal solutions. The search for previously unreported deposits of nonpegmatitic lithium should consider its probable association, not only with nonmarine evaporite minerals, but also with recent volcanic and tectonic activity, as well as with deposits of boron, beryllium, fluorine, manganese, and possibly phosphate.

Melt inclusions come of age: Volatiles, volcanoes, and sorby's legacy

USGS Publications Warehouse

Lowenstern, J. B.

2003-01-01

Despite nearly forty years of modern research on silicate melt inclusions (MI), only within the past 10-15 years have volcanologists and petrologists come to regularly accept their utility for characterizing magmatic systems. Their relatively slow acceptance was likely due to a number of factors including: 1) Lack of reliable analytical techniques, 2) Concern that MI represent anomalous boundary-layer melts or are altered by leakage or post-entrapment crystallization, 3) Data sets indicative of heterogeneous melts and, 4) Homogenization temperatures greater than those calculated by other techniques. With improvements in analytical methods and careful studies of MI systematics, workers are increasingly convinced of the utility of these features to unravel the complexities of volcanic systems: melt inclusions have "come of age." Recent studies provide compelling evidence for the compositions of dissolved and exsolved volatiles in magma reservoirs. Evidence for immiscibility of gases, hydrosaline brines and pegmatitic fluids demonstrate that magmatic phase relations are often more complicated than can be inferred by inspection of crystalline phases alone. ?? 2003 Elsevier B.V. All rights reserved.

Crystal structure of ilyukhinite, a new mineral of the eudialyte group

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rastsvetaeva, R. K., E-mail: rast@crys.ras.ru; Rozenberg, K. A.; Chukanov, N. V.

The crystal structure of ilyukhinite, a new mineral of the eudialyte group, is studied by X-ray diffraction. The mineral found in pegmatite bodies of the Kukisvumchorr Mountain (Khibiny alkaline complex) is characterized by low sodium content, high degree of hydration, and predominance of manganese over iron. The trigonal cell has the following parameters: a = 14.1695(6) and c = 31.026(1) Å; space group R3m. The structure is refined to final R = 0.046 in the anisotropic approximation of atomic displacements using 1527F > 3σF. The idealized formula of ilyukhinite (Z = 3) is written as (H{sub 3}O,Na){sub 14}Ca{sub 6}Mn{sub 2}Zr{submore » 3}Si{sub 26}O{sub 72}(OH){sub 2} · 3H{sub 2}O. The new mineral differs from other representatives of the eudialyte group by the predominance of both oxonium in the N positions of extra-framework cations and manganese in the Ðœ2 position centering the tetragonal pyramid.« less

Mineralogy and origin of coarse-grained segregations in the pyrometallurgical Zn-Pb slags from Katowice-Wełnowiec (Poland)

NASA Astrophysics Data System (ADS)

Warchulski, R.; Gawęda, A.; Janeczek, J.; Kądziołka-Gaweł, M.

2016-10-01

The unique among pyrometallurgical slags, coarse-grained (up to 2.5 cm) segregations (up to 40 cm long) rimmed by "aplitic" border zones occur within holocrystalline historical Zn-smelting slag in Katowice, S Poland. Slag surrounding the segregations consists of olivine, spinel series, melilite, clinopyroxene, leucite, nepheline and sulphides. Ca-olivines, kalsilite and mica compositionally similar to oxykinoshitalite occur in border zones in addition to olivine, spinel series and melilite. Miarolitic and massive pegmatite-like segregations are built of subhedral crystals of melilite, leucite, spinel series, clinopyroxene and hematite. Melilite, clinopyroxenes and spinels in the segregations are enriched in Zn relatively to original slag and to fine-grained border zones. The segregations originated as a result of crystallization from residual melt rich in volatiles (presumably CO2). The volatile-rich melt was separated during fractional crystallization of molten slag under the cover of the overlying hot (ca. 1250 °C) vesicular slag, preventing the escape of volatiles. That unique slag system is analogous to natural magmatic systems.

New U-Pb zircon geochronology of the Choma-Kalomo Block (Zambia) and the Dete-Kamativi Inlier (Zimbabwe), with implications for the extent of the Zimbabwe Craton.

NASA Astrophysics Data System (ADS)

Glynn, Sarah; Wiedenbeck, Michael; Master, Sharad; Frei, Dirk

2015-04-01

The Choma-Kalomo Block is a north-east trending, Mesoproterozoic terrane located in southern Zambia. It is composed of as yet undated gneissic basement with a high-grade metamorphosed supracrustal metasedimentary sequence, which is intruded by hornblende granites and gneisses of the Choma-Kalomo Batholith, that is dated between ca. 1.37 and 1.18 Ga. Our new zircon U-Pb age data on metasedimentary rocks of the Choma-Kalomo Block identifies samples of different ages, with slightly different provenances. The oldest metasedimentary rock is a muscovite-biotite schist, which has only Palaeoproterozoic detrital zircons, the two age clusters around 2.03-2.02 Ga and 1.8-1.9 Ga, correspond to the ages of granitic intrusion, and metamorphism, in the Magondi Mobile Belt on the western side of the Archaean Zimbabwe Craton. The second sample is a garnetiferous paragneiss, which contains both Palaeoproterozoic (2.04 Ga), and Mesoproterozoic zircons, ca. 1.36 Ga, derived from the granites of the Choma-Kalomo Batholith. The third sample is a biotite-muscovite schist, in which the detrital zircon ages fall into four separate clusters: ca. 3.39 Ga, ca. 2.7-2.6 Ga, ca. 2.1-1.7 Ga (with a peak at ca. 1.18 Ga), and 1.55 - 1.28 Ga. The Archaean zircons in this sample are derived from the Zimbabwe Craton, while the Palaeoproterozoic samples come from the Magondi belt, and the youngest zircons come from both phases of the Choma-Kalomo Batholith. A possible connection between the Choma-Kalomo Block and the Dete-Kamativi Inlier - some 150 km to the south-east in western Zimbabwe - has been proposed on the basis of similarities in the nature of their Sn-Ta-muscovite pegmatite mineralisation. The Dete-Kamativi Inlier, which is part of the Magondi Mobile Belt, is a window into Palaeoproterozoic north-east trending belts of deformed and metamorphosed supracrustal rocks. By dating localities which we suspect form the basement to the surrounding younger sediments, along with selected pegmatites from within the inlier itself; we have concluded that the Choma-Kalomo Block and Dete-Kamativi Inlier are, in fact, coeval. Preliminary results for a number of these granites and gneisses give ages between 2.05 and 2.02 Ga; correlating well with the 2.03-2.02 Ga ages of detrital zircons from the Choma-Kalomo Block. While these basement rocks are not Archaean in age, we have identified Archaean aged zircons in both the Choma-Kalomo Block and the Dete-Kamativi Inlier, making them the Western most occurrences of Archaean granitoids, implying that the Zimbabwe Craton extends much further west under the Magondi Belt than previously thought.

Traditional and innovative methods applied to a crystalline aquifer for characterizing fault zone hydrology at different scales

NASA Astrophysics Data System (ADS)

Bour, O.; Ruelleu, S.; Le Borgne, T.; Boudin, F.; Moreau, F.; Durand, S.; Longuevergne, L.

2011-12-01

Crystalline rocks aquifers are difficult to characterize since flow is mainly localized in few fractures or faults. In particular, the geometry of the main flow paths and the connections of the aquifer with the sub-surface are often poorly constrained. Here, we present results from different geophysical and hydraulic methods to quantify fault zone hydrology of a crystalline confined aquifer (Ploemeur, French Brittany). This outstandingly productive crystalline rock aquifer is exploited at a rate of about 10 6 m3 per year since 1991. The pumping site is located at the intersection of two main structures: the contact zone between granite roof and overlying micaschists, and a steeply dipping fault striking North 20°, with combined dextral strike-slip and normal components. Core samples and borehole optical imagery reveals that the contact zone at the granite roof consists of alternating deformed granitic sheets and enclaves of micaschists, pegmatite and aplite dykes, as well as quartz veins. Locally, this contact is marked by mylonites and pegmatite-bearing breccias that are often but not systematically associated with major borehole inflows. Other significant inflows are localized within single fractures independently of the lithologies encountered. At the borehole scale the structural and hydraulic properties of the aquifer are thus highly variable. At the site scale - typically a kilometer squared - the water levels are monitored in 22 boreholes, 100 meters deep in average. The connectivity of the main flow paths and the hydraulic properties are relatively well constrained and quantified thanks to cross-borehole flowmeter tests and traditional pumping tests. In complement, long-base tiltmeters monitoring and ground-surface leveling allows to monitor sub-surface deformation. It provides a quantification of the hydro-mechanical properties of the aquifer and better constraints about the geometry of the main fault zone. Surprisingly, the storage coefficient of the confined aquifer is relatively high, in agreement with ground-surface deformation measurements that suggest a relativity high compressibility of the fault zone. At larger scale, we show through a high-resolution gravimetric survey that the highly fractured contact between granite and micaschists, which constitutes the main path for groundwater flow, is a gently dipping structure. A 3D gravimetric model confirms also the presence of sub-vertical faults that may constitute important drains for the aquifer recharge. In addition, groundwater temperature monitoring allows to shows that the main water supply comes from a depth of at least 300 meters. Such a depth in a low relief region involves relatively deep groundwater circulation that can be achieved only thanks to major permeable fault zone. This field example shows the advantages and limitations of some traditional and innovative methods to characterize fault zone hydrology in crystalline bedrock aquifers.

Interests of hydrogeological observatories for characterizing heterogeneous groundwater systems: the example of the Ploemeur hard-rock aquifer (French Brittany)

NASA Astrophysics Data System (ADS)

Bour, O.; Le Borgne, T.; Aquilina, L.; Labasque, T.; Lavenant, N.; Boudin, F.; Leray, S.; De Dreuzy, J.; Longuevergne, L.; Hochreutener, R.; Davy, P.

2012-12-01

Heterogeneous aquifers are often poorly constrained by the available data. There is a strong need of characterizing at multiple space and time scales heterogeneous groundwater systems to improve model predictions. Here, we present results from the site of Ploemeur (French Brittany) that belongs to the network of hydrogeological sites H+, and where complementarity approaches have been developed for almost fifteen years. This outstandingly heterogeneous crystalline rock aquifer is used for water supply at a rate of about 10^6 m3 per year since 1991. The geology of the area is relatively complex and involves two main structures: a highly fractured contact zone between the Ploemeur's granite and the overlying micaschists, and a steeply dipping fault striking North 20°. The contact zone in itself consists of alternating deformed granitic sheets and enclaves of micaschists, pegmatite and aplite dykes, and locally mylonites and pegmatite-bearing breccias that are often associated with major borehole inflows. At the site scale - typically a square kilometer - and at relatively shallow depth (100 to 150 m), the connectivity of the main flow paths and the hydraulic properties are relatively well constrained and quantified thanks to cross-borehole flowmeter tests and traditional pumping tests. However, such data are relatively limited in explaining the functioning of this confined groundwater system at the regional scale. Groundwater chemistry and groundwater dating permit to go further to identify distinct reservoirs and in particular a relatively deep groundwater component whose age is older than 50 years. Groundwater temperature measurements demonstrate the role of the pumping that influences greatly the spatial distribution of groundwater temperature and quality. Moreover, it suggests that the main water supply comes from a depth of at least 300 meters. This implies relatively deep groundwater circulation that can be achieved only thanks to major permeable fault zone. At the watershed scale - typically ten square kilometers - we show through a high-resolution gravimetric survey that the highly fractured contact between granite and micaschists, which constitutes the main path for groundwater flow, is a gently dipping structure towards the North. This is consistent with measurements of the ground surface deformation through long-base tiltmeters, which suggest that recharge of the aquifer come from the North. Finally, a numerical model of the site that combines hydraulic and age information confirms the geometry of the major permeable fault zone and the consistency of the different datasets. The Ploemeur example shows how multiple datasets at different scales may be combined to characterize and model heterogeneous groundwater systems. It also shows the interests of using specific sites as hydrogeological observatories to test novel field methods, to evaluate the relevance of numerical and theoretical models, to monitor groundwater changes and to improve our knowledge on groundwater systems.

Zincoberaunite, ZnFe3+ 5(PO4)4(OH)5ṡ6H2O, a new mineral from the Hagendorf South pegmatite, Germany

NASA Astrophysics Data System (ADS)

Chukanov, Nikita V.; Pekov, Igor V.; Grey, Ian E.; Price, Jason R.; Britvin, Sergey N.; Krzhizhanovskaya, Maria G.; Kampf, Anthony R.; Dünkel, Bernhard; Keck, Erich; Belakovskiy, Dmitry I.; MacRae, Colin M.

2017-06-01

The new mineral zincoberaunite, ideally ZnFe3+ 5(PO4)4(OH)5·6H2O, the Zn analogue of beraunite, is found in the Hagendorf South granitic pegmatite, Hagendorf, Bavaria, Germany, in two associations: (1) with potassium feldspar, quartz, jungite, phosphophyllite and mitridatite (the holotype) and (2) with flurlite, plimerite, Zn-bearing beraunite, schoonerite, parascholzite/scholzite, robertsite and altered phosphophyllite (the cotype). Zincoberaunite occurs as radial or randomly oriented aggregates of flexible fibers up to 1.5 mm long and up to 3 μm thick. D calc is 2.92 g/cm3 for the holotype and 2.94 g/cm3 for the cotype. Zincoberaunite is optically biaxial (-), α = 1.745(5), β = 1.760(5), γ = 1.770(5), 2 V meas = 80(5)°. Chemical composition of the holotype (electron probe microanalyser; H2O by gas chromatography of ignition products) is: MgO 0.28 wt%, CaO 0.47 wt%, ZnO 7.36 wt%, Al2O3 0.88 wt%, Fe2O3 42.42 wt%, P2O5 31.63 wt%, H2O 16.2 wt%, total 101.1 wt%. The empirical formula calculated on the basis of 27 oxygen atoms per formula unit is (Zn0.83Ca0.08Mg0.06)∑0.97(Fe3+ 4.88Al0.16)∑5.04(PO4)4.09(OH)4.78 · 5.86H2O. Zincoberaunite is monoclinic, space group C2 /c; refined unit cell parameters (for the holotype at room temperature and the cotype at 100 K, respectively) are: a 20.837(2) and 20.836(4), b 5.1624(4) and 5.148(1), c 19.250(1) and 19.228(4) Å, β 93.252(5) and 93.21(3)°, V 2067.3(3) and 2059.2(7) Å3, Z = 4. The crystal structure of the holotype specimen has been refined by the Rietveld method ( R p = 0.30 %; R B = 0.18 %) whereas the structure of the cotype has been solved from the single crystal data and refined to R 1 = 0.056 based on 1900 unique reflections with I > 2σ( I). The strongest reflections of the powder X-ray diffraction pattern of the holotype specimen [( d, Å) ( I, %) ( hkl)] are: 10.37 (100) (200), 9.58 (32) (002), 7.24 (26) (20-2), 4.817 (22) (111), 4.409 (13) (112), 3.483 (14) (11-4, 600), 3.431 (14) (404), 3.194 (15) (006, 31-4), 3.079 (33) (314).

Microbial nature of fibrous kerite of Volyn

NASA Astrophysics Data System (ADS)

Gorlenko, Vladimir M.; Zhmur, Stanislav I.; Duda, Vitalii I.; Osipov, George A.; Suzina, Natalia; Dmitriev, Vladimir V.

1999-12-01

For the last few years there have been a lot of publications in geological literature on the problem of formation of morphologically unique fine fibrous kerites, found in one of the objects of kamera pegmatites of Volyn (1800 - 1750 mln. years). According to the opinion of all researchers who deal with them, they are an excellent example of a biogenic, highly constructive carbon substance. The meeting of objectives set was carried out by means of the study of ultra-thin section and replicas of kerite cryofractures under high resolution electronic microscope. The similarity of fine structured fibrous kerite of Volyn (KV) to prokaryotic microorganisms is proved by availability in KV of clearly exposed cellular ultrastructures: multilayered cell wall, cross septa and cytoplasmatic membrane and `intracytoplasmic' inclusions. Fatty acids obtained from kerites contain a number of components typical of prokaryotic microbial community. Suggestions were made on the formation of fibrous Volyn's kerites as a result of mummification of the cyanobacterial mat components from freshwater thermal spring of moderate temperature. Thus, the detailed fine structure of microfossils and their fatty acid composition can be used to support evidence of biogenic origin of the bacteriomorphic elements in paleo- and space objects.

Bedrock geologic and joint trend map of the Pinardville quadrangle, Hillsborough County, New Hampshire

USGS Publications Warehouse

Burton, William C.; Armstrong, Thomas R.

2013-01-01

The bedrock geology of the Pinardville quadrangle includes the Massabesic Gneiss Complex, exposed in the core of a regional northeast-trending anticlinorium, and highly deformed metasedimentary rocks of the Rangeley Formation, exposed along the northwest limb of the anticlinorium. Both formations were subjected to high-grade metamorphism and partial melting: the Rangeley during the middle Paleozoic Acadian orogeny, and the Massabesic Gneiss Complex during both the Acadian and the late Paleozoic Alleghanian orogeny. Granitoids produced during these orogenies range in age from Devonian (Spaulding Tonalite) to Permian (granite at Damon Pond), each with associated pegmatite. In the latest Paleozoic the Massabesic Gneiss Complex was uplifted with respect to the Rangeley Formation along the ductile Powder Hill fault, which also had a left-lateral component. Uplift continued into the early Mesozoic, producing the 2-kilometer-wide Campbell Hill fault zone, which is marked by northwest-dipping normal faults and dilational map-scale quartz bodies. Rare, undeformed Jurassic diabase dikes cut all older lithologies and structures. A second map is a compilation of joint orientations measured at all outcrops in the quadrangle. There is a great diversity of strike trends, with northeast perhaps being the most predominant.

Mineral resources of the Castle Peaks Wilderness Study Area, San Bernardino County, California

USGS Publications Warehouse

Miller, David A.W.; Frisken, James G.; Jachens, Robert C.; Gese, Diann D.

1986-01-01

The Castle Peaks Wilderness Study Area (CDCA266) comprises approximately 45,000 acres in the northern New York Mountains, San Bernardino County, California. At the request of the Bureau of Land Management, 39,303 acres of the wilderness study area were studied. The area was investigated during 1982-1985 using combined geologic, geochemical, and geophysical methods. are considered preliminarily suitable for wilderness deignation. There are no mineral reserves or identified resources in the study area. Fluorspar, occurring in sparse veins, has moderate resource potential, as do silver and lead in fault zones, and gold and silver in sparse, high-grade veins and fault breccia. Each area of moderate resource potential encompasses less than one square mile. These same commodities have low resource potential in similar occurrences throughout much of the study area. In addition, there is low resource potential for gold in placer deposits, uranium in altered breccia and gouge, and rare-earth elements in pegmatite dikes. There is no resource potential for oil and gas resources over most of the study area, but the potential is unknown along its western margin. In this report, the area studied is referred to"the wilderness study area", or simply "the study area."

Geochemistry and mineralogy of the Dotson Zone HREE deposit in the Bokan Mountain peralkaline igneous complex, southeastern Alaska, USA

USGS Publications Warehouse

Taylor, Cliff D.; Lowers, Heather; Adams, David; Robinson, R. James

2017-01-01

The Bokan Mountain igneous complex (BMIC) is a typical example of a peralkaline intrusive system that has evolved to the point of developing late stage HFSE- and REE-rich silicic pegmatites and dikes. The Dotson Zone comprises a series of felsic dikes that extend from the southeast margin of the composite pluton and may represent an important resource of critical HREEs. Petrographically, the primary igneous mineral assemblage is altered by late-igneous and hydrothermal fluids resulting in redistribution and enrichment of REEs. An area of flexure in the southeastern end of the Dotson Zone was the primary locus of enrichment as shown by the pervasive alteration and consistently high REE+Y values. We favor a model in which the dikes were emplaced concurrently with the marginal intrusions, and then altered during emplacement of the inner, main intrusion in a relatively rapid series of overlapping intrusive and late magmatic fluid-high temperature hydrothermal events as the complex cooled. A much later sodic intrusive event focused on the BMIC may have resulted in additional silica-Na-Zr-rich alteration in proximity to the pluton.

The geochemical and genetic role of organic substances in postmagmatic derivatives of alkaline plutons

NASA Astrophysics Data System (ADS)

Ermolaeva, V. N.; Chukanov, N. V.; Pekov, I. V.; Kogarko, L. N.

2009-12-01

Solid bituminous substances (SBS) are common components of the late hydrothermal mineral assemblages of peralkaline pegmatites. SBS are formed in a reductive setting as a result of progressive sorption of minor carbon-bearing molecules (CO, CO2, CH4, C2H6, C2H4, etc.), their polymerization, transformation into aromatic compounds (reformation), and selective oxidation on microporous zeolite-like Ti-, Nb-, and Zrsilicates serving as sorbents and catalysts. The oxygen-bearing aromatic compounds with hydrophile functional groups (-OH, -C=O, -COOH, -COO) act as complexing agents with respect to Th, REE, U, Zr, Ti, Nb, Ba, Sr, Ca, resulting in transfer of these bitumenophile elements under low-temperature hydrothermal conditions in the form of water-soluble macroassociates of the micelle type. Th, REE, and to a lesser extent, U, Zr, Ti, and Nb concentrate at the late stage of the hydrothermal process as microphases impregnating SBS or macroscopic segregations of Th and REE minerals. At the final stage, homogeneous SBS break down into organic (partly together with Ca, Sr, Ba, and Pb) and mineral (with Th, Ln, Y, Ti, Nb, Ca, Na, K, Si) microphases.

Isukasia area: Regional geological setting (includes excursion guide)

NASA Technical Reports Server (NTRS)

Nutman, A. P.; Rosing, M.

1986-01-01

A brief account of the geology of the Isukasis area is given and is biased toward the main theme of the itinerary for the area: What has been established about the protoliths of the early Archean rocks of the area - the Isua supracrustal belt and the Amitsoq gneisses? The area's long and complex tectonometamorphic history of events can be divided into episodes using a combination of dike chronology, isotopic, and petrological studies. The earliest dikes, the ca 3700 Ma Inaluk dikes, intrude the earliest (tonalitic) components of the Amitsoq gneisses but are themselves cut up by the injection of the younger (granitic and pegmatitic) phases of the Amitsoq gneisses of the area. The areas of low late Archean deformation, strongly deformed early Archean mafic rocks have coarse grained metamorphic segregations and are cut by virtually undeformed mid-Archean Tarssartoq (Ameralik) dikes devoid of metamorphic segregations. The shows that the area was affected by regional amphibolite facies metamorphism in the early Archean. Late Archean and Proterozoic metamorphic imprints are marked to very strong in the area. Much of the early Archean gneiss complex was already highly deformed when the mid-Archean Tarssartoq dikes were intruded.

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

NASA Astrophysics Data System (ADS)

Macdonald, Ray; Bagiński, Bogusław; Kartashov, Pavel M.; Zozulya, Dmitry; Dzierżanowski, Piotr; Jokubauskas, Petras

2015-12-01

The results are presented of a textural and mineral chemical study of a previously undescribed type of hydrothermal alteration of chevkinite-(Ce) which occurs in a syenitic pegmatite from the Vishnevye Mountains, Urals Region, Russia. The progressive alteration of the chevkinite to a bastnäsite-(Ce)-ilmenite-columbite-(Fe) assemblage through a series of texturally complex intermediate stages is described and electron microprobe analyses are given of all the major phases. Unusual Nb ± Th-rich phases formed late in the alteration sequence provide evidence of local Nb mobility. The main compositional fluxes are traced, especially of the REE, HFSE, Th and U. It appears that almost all elements, with the exception of La, released from the chevkinite-(Ce) were reincorporated into later phases, such that they did not leave the alteration crust in significant amounts. The hydrothermal fluids are inferred to have been F- and CO2-rich, with variable levels of Ca activity, and with fO2 mainly between the nickel-nickel oxide and magnetite-hematite buffers. This occurrence represents a new paragenesis for a columbite-group mineral.

Penalobo "Castle Rocks" - First approach to valuing this geoforms.

NASA Astrophysics Data System (ADS)

Pinharandas, Carlos; Nobre, José; Gomes, Ana

2013-04-01

The village of Penalobo, located in the municipality of Sabugal (Portugal) is characterized by hercynian granites with interesting geological features, including pegmatite veins and quartz crystals with exotic forms, and presents some steep slopes and plateaus. From the mountainous configuration highlight some more pronounced elevations called "Castle Rocks". Such structures are composed by granites, which present greater fracturing at the top, which leads to the formation of large granite blocks. In less fractured zones it is possible to observe small folds. An excavation existing in one of those elevations allows us to observe a basic rock outcropping with clusters of crystals mottled with circular shape, which are indicative of the presence of late fluid during crystallization. In the zone of contact with the enclosing granite, there are small folds caused by magma intrusion. Those evidences led us to hypothesize that the peaks observed in the area of Penalobo village were due to the intrusion on basic magma. All this framework and geological environment becomes an asset for the scientific, educational and economic development of the region. On the other hand, it has a vital importance in the context of a strategy of forming a geological park, in the point of view of tourism, research and interpretation.

A Late Variscan Sn province: the Arburese region (SW Sardinia, Italy)

NASA Astrophysics Data System (ADS)

Naitza, Stefano; Secchi, Francesco; Oggiano, Giacomo; Cuccuru, Stefano

2015-04-01

Late Variscan Sn - rich European provinces (e. g. Erzgebirge, Cornwall) are of particular relevance as they offer key insights into crustal evolution, intrusive processes and ore genesis. In Sardinia (Italy), small Sn deposits are only known in the Arburese historical mining region (SW Sardinia), hosted in low-grade metamorphics close to the contacts with intrusives. This region is characterised by two late variscan intrusions, which differ in age and composition: the Arbus and the Monte Linas pluton, aging 304 ± 1 Ma, and 289 ± 1 Ma respectively. They emplaced at shallow crustal levels and crosscut the basal thrust between the alloctonous prism and the foreland of the Variscan belt of Sardinia. The Arbus Pluton (AP) is a composite intrusion of piroxene- and amphibole- granodiorites hosting minor amounts of monzogabbroic rocks and cordierite-bearing granites with a wide core of leuco-monzogranites. Tourmaline greisens and pegmatites garnish the contact between the border facies and the host metamorphic rocks. The Monte Linas Pluton (MLP) has biotite monzogranite composition. The pluton is internally zoned, from medium grained monzogranite in the core to hololeucocratic fine-grained rock-types at the top, where often F-greisen, fayalite-pegmatite pods and sill are common. In both plutons the igneous associations are high-K ilmenite series, suggesting derivation from low- fO2 magmas possibly linked to a common crustal contribution; however, in the Linas Pluton magnetite in the fine-grained facies may indicate an increase in oxygen fugacity. The AP-related Sn ores consist of high-temperature As-Sn quartz veins. They are vertically zoned, from quartz-chlorite-cassiterite to large quartz-arsenopyrite veins. Ore microscopy and SEM-EDS analyses evidenced a vein texture made of thick idiomorphic and frequently twinned cassiterite crystals, alternated with several generations of banded/geodic quartz. Chlinoclore aggregates are included into the quartz. The arsenopyrite ore shows alternating bands of microgranular to crystalline millimetric arsenopyrite with quartz. Field and analytical data suggest genetic mechanisms dominated by mobilization of residual Sn by chloride and other complexes in reducing, As- and S- rich, low- fO2 juvenile fluids. Cassiterite and successive arsenopyrite precipitation occurred under changing physicochemical conditions (e.g. oxygen contents; temperature decrease; pH). The MLP Sn metallogeny include Sn- Pb-Zn-Cu veins (Canale Serci old mine). Cassiterite occurs as fine-grained corroded crystals. Optical and SEM-EDS analyses evidence a high-temperature oxide stage (quartz-chlorite- cassiterite) followed, after brecciation, by mesothermal sulfide stages, with progressive deposition of sphalerite, pyrite, chalcopyrite, tetrahedrite, galena, marcasite. Arsenopyrite is strikingly absent. These evidences indicate possible derivation of the ore from residual, reducing juvenile fluids, capable to carry Sn- complexes from monzogranite magmas from which cassiterite precipitated in consequence of an increasing in fO2. Despite their limited amount, the Sn ores of SW Sardinia have high metallogenic relevance, indicating the persistence, of geochemical conditions,which lasted 15 Ma, favorable to the genesis of a Sn metallogenic province.

Crystallographic Orientation Relationships (CORs) between rutile inclusions and garnet hosts: towards using COR frequencies as a petrogenetic indicator

NASA Astrophysics Data System (ADS)

Griffiths, Thomas; Habler, Gerlinde; Schantl, Philip; Abart, Rainer

2017-04-01

Crystallographic orientation relationships (CORs) between crystalline inclusions and their hosts are commonly used to support particular inclusion origins, but often interpretations are based on a small fraction of all inclusions in a system. The electron backscatter diffraction (EBSD) method allows collection of large COR datasets more quickly than other methods while maintaining high spatial resolution. Large datasets allow analysis of the relative frequencies of different CORs, and identification of 'statistical CORs', where certain limited degrees of freedom exist in the orientation relationship between two neighbour crystals (Griffiths et al. 2016). Statistical CORs exist in addition to completely fixed 'specific' CORs (previously the only type of COR considered). We present a comparison of three EBSD single point datasets (all N > 200 inclusions) of rutile inclusions in garnet hosts, covering three rock systems, each with a different geological history: 1) magmatic garnet in pegmatite from the Koralpe complex, Eastern Alps, formed at temperatures > 600°C and low pressures; 2) granulite facies garnet rims on ultra-high-pressure garnets from the Kimi complex, Rhodope Massif; and 3) a Moldanubian granulite from the southeastern Bohemian Massif, equilibrated at peak conditions of 1050°C and 1.6 GPa. The present study is unique because all datasets have been analysed using the same catalogue of potential CORs, therefore relative frequencies and other COR properties can be meaningfully compared. In every dataset > 94% of the inclusions analysed exhibit one of the CORs tested for. Certain CORs are consistently among the most common in all datasets. However, the relative abundances of these common CORs show large variations between datasets (varying from 8 to 42 % relative abundance in one case). Other CORs are consistently uncommon but nonetheless present in every dataset. Lastly, there are some CORs that are common in one of the datasets and rare in the remainder. These patterns suggest competing influences on relative COR frequencies. Certain CORs seem consistently favourable, perhaps pointing to very stable low energy configurations, whereas some CORs are favoured in only one system, perhaps due to particulars of the formation mechanism, kinetics or conditions. Variations in COR frequencies between datasets seem to correlate with the conditions of host-inclusion system evolution. The two datasets from granulite-facies metamorphic samples show more similarities to each other than to the pegmatite dataset, and the sample inferred to have experienced the highest temperatures (Moldanubian granulite) shows the lowest diversity of CORs, low frequencies of statistical CORs and the highest frequency of specific CORs. These results provide evidence that petrological information is being encoded in COR distributions. They make a strong case for further studies of the factors influencing COR development and for measurements of COR distributions in other systems and between different phases. Griffiths, T.A., Habler, G., Abart, R. (2016): Crystallographic orientation relationships in host-inclusion systems: New insights from large EBSD data sets. Amer. Miner., 101, 690-705.

New geochronological constraints on the thermal and exhumation history of the Lesser and Higher Himalayan Crystalline Units in the Kullu–Kinnaur area of Himachal Pradesh (India)

PubMed Central

Thöni, M.; Miller, C.; Hager, C.; Grasemann, B.; Horschinegg, M.

2012-01-01

New geochronological, petrological and structural data from the Beas–Sutlej area of Himachal Pradesh (India) are used to reconstruct the tectonothermal and exhumation history of this part of the Himalayan orogen. Sm–Nd garnet ages at 40.5 ± 1.3 Ma obtained on a pegmatoid from the inverse metamorphic High Himalayan Crystalline (HHC) in the Malana–Parbati area probably mark local melting during initial decompression. Ongoing exhumation in ductilely deformed leuco-gneiss is constrained by Sm–Nd garnet ages at 29 ± 1 Ma and white mica Rb–Sr ages around 24–20 Ma, while Bt Rb–Sr ages indicate a drop of regional metamorphic temperatures below 300 °C between 15 and 12 Ma. The deep Sutlej gorge exposes medium-grade paragneisses and Proterozoic orthogneisses of the Lesser Himalayan Crystalline (LHC), overthrust by the HHC along the Main Central Thrust (MCT). Mica cooling ages in the HHC are in the range of 14–11 Ma. Above the extruded wedge of the HHC, the Leo Pargil leucogranite and associated dykes intrude the Haimanta Unit (HU) below the weakly metamorphic Palaeo-Mesozoic sediments of the Tethyan Himalayas (TH). The Leo Pargil leucogranite yielded a mean Sm–Nd garnet age of 19 ± 1 Ma and Rb–Sr muscovite and biotite cooling ages between 16.4 and 11.6 Ma. Marked young extrusion of LHC units resulted in differentiated exhumation/cooling of more frontal parts of the orogen. Very young ductile deformation of LHC gneisses near Wangtu is constrained by late-kinematic pegmatite intrusions crosscutting the main mylonitic foliation. Sm–Nd garnet and Rb–Sr muscovite ages of these pegmatites range between 7.9 ± 0.9 and 5.5 ± 0.1 Ma. Published apatite FT ages down to 0.6 Ma also document accelerated diachronous sub-recent exhumation of different parts of the orogen. Together with geochronological data from the literature, the new results demonstrate that the HHC and the HU were deformed by shortening and crustal thickening during the Eohimalayan phase (Late Eocene–Oligocene), followed by a strong thermal overprint and intrusions of granitoids during the Neohimalayan Phase (Early to Middle Miocene). The LHC experienced amphibolite facies metamorphic conditions in the Late Miocene prior to extrusion between the HHC and the very low-grade Lesser Himalayan sediments. In conjunction with climate changes, young tectonic activity in this central part of the Himalayan orogen may have strongly influenced fluvial incision and erosion, and therefore, contributed to the accelerated uplift, as indicated by extensive accumulation of Late Miocene to Early Pleistocene fluviatile–lacustrine sediments in the Zanda basin, the Transhimalayan headwaters of the Sutlej, in Western Tibet. PMID:27570473

Educational tools in the Museum of Rocks and Minerals

NASA Astrophysics Data System (ADS)

de Brito Barreto, S.; Ribeiro Sales, E.; de Lima Correia, A. Maria; Lima, M. Abreu e.; Bretas Bittar, S. Maria

2012-04-01

The Museum of Rocks and Minerals is a small museum which belongs to the Department of Geology of the Federal University of Pernambuco, Brazil. It was founded in the 1950's and its main exhibits are samples of scarns and pegmatites from the Northeast of Brazil, especially from the Borborema Pegmatitic Region. This museum has been visited by a wide variety of people, but mainly students from private and state schools on scheduled visits. Over the years museum staff felt the necessity to develop some mediating tools to develop a relationship between exhibits and visitors. Due to a lack of technical staff and finance to create interactive exhibits as well as space limitations, the museum decided to produce some games such as memory games, puzzles and dominoes. These fifteen games deal with different subjects of geosciences, especially those more interesting for children. The subjects chosen were: minerals, industrial minerals, gems, dimension stones, rock cycle, fossils, dinosaur footprints (Ichnofossils), wood fossils, Mohs scale. The games were created by the authors, and undergraduate students were responsible for researching concepts and images. Each game presents a concept and images related to it. The interns are undergraduate students of geology and mining engineering and this experience gives them an opportunity to review and improve some concepts and discuss what is important such as pedagogical actions in museums and geology teaching. To give an example, the subject of the industry mineral was treated using two games - a memory game and a puzzle. The first one shows images of minerals related each one to an industrial product and in the second, children can see different parts of a house labeled with the minerals used in the production of that space. Another interesting example is the puzzle about dinosaur footprints that uses an image of a dinosaur footprint, part of the paleontological collection of the Departament, and a representative ichnofossil from the Rio do Peixe Basin in the state of Paraíba, Brazil, the most important record of dinosaur prints in Brazil. The games are part of a playful activity used at the end of the visit called "NiFe", in reference to the Earth's core. The idea is for this to be a moment of concentration and an opportunity to share the museum experience, an activity which is coordinated by the interns of the museum. The "NiFe" is an educational activity for children, which aims to transform the visual and sensory experience into a complete experience, something that changes us through our experience. The objective is to make the visit a dynamic and educative experience in contrast to the inanimate characteristic of the kingdom of minerals and rocks. The intention is that these games will be adopted by the education secretaries of state and municipal governments in order to contribute to the teaching of geoscience mainly at primary and secondary of education and undergraduate level.

Mineralization related to Alvand pluton in the Hamadan, western Iran

NASA Astrophysics Data System (ADS)

Salehi, M. H.; Doosti, E. A.; Ahadnejad, V.

2009-04-01

The Alvand (Hamadan) plutonic batholith is one of the largest plutonic bodies in the Sanandaj-Sirjan metamorphic belt. This complex is consist of mafic part (gabbro-diorite-tonalite), intermediate (granite-granodiorite porphyroids), and hololeucocratic granitoids. Previous studies have shown that S-type granite-granodiorites are mostly peraluminous and calc-alkaline; the gabbro-diorite-tonalite suite is mostly metaluminous and tholeiitic to calc-alkaline (Sepahi, 2008). High initial 87Sr-86Sr ratios (0.7081 to 0.7115), low epsilon Nd values (-1.0 to -3.3), and peraluminous character reflects a different origin for the granites, possibly crustal sources (Ghalamghash et al, 2007). Aplite-pegmatite dikes are intruded in granitoide rocks, metamorphic rocks and the contact of Alvand granite with metamorphic rocks. The contact of Alvand granite with metamorphic rocks is sharp. By using heavy mineral studies on the alluvium of Alvand complex, it is recognized 28 minerals amongst Scheelite, Cassiterite, Ilmenite, Zircon and Garnet. Different geostatistical studies such as variant, bivariant and multivariant studies have been done on rough data of heavy minerals. They showed normal concentration of gold in studied rocks and low enrichment of tin and tungsten. The index of the ore elements average, frequeney distribution criteria of elements, the ratio of elements index and multielements show that Alvand granite is barren. Mineralography studies did not recognized any tin and tungsten minerals. The grains of gold was recognized in some of the microscopic thin sections. Calcopyrotite is the most important ore mineral that is accompanied with oxides and iron carbonates. The contacts of aplite-pegmatite dikes with granitoide rocks mostly are not prolific. For recognizing Scheelite, some samples of rocks studied by ultraviolet and few Scheelite is recognized in the samples. Some alteration zone observed in this area but they are not accompany with main mineralization. Although the expanded turmalinization has occurred but it is not seen any mineralization. Unless some small part of Alvand complex (i.e. stibnite in the Faghireh area, Maniijou and Aliani, 2000) and based on the main geochemical index, Alvand granitod pluton is classified as a barren type granite. References: Ghalamghash, J., Mirnejad, H., Rashid, H., Mohammadiha, K., Ghahraei-poor, M., Zakeri, M., 2007. Geochemistry of gabbro, granite and mafic enclaves of Alvand batholithe and their origin. 25th conference of geoscinces, Geological Survey of Iran. Maniijou, M., and Aliani, F., 2000. Stibnite mineralization in the Hamedan, west Iran. Mineral Deposits at the Beginning of the 21st Century: Proceedings of the Joint Sixth Biennial SGA-SEG Meeting, Krakow, Poland, 26-29 August 2001 By Adam Piestrzyński, Society for Geology Applied to Mineral Deposits, Society of Economic Geologists (U.S.) Published by Taylor & Francis. ISBN 9026518463, 9789026518461. 1148 pages. Sepahi, Ali A, 2008. Typology and petrogenesis of granitic rocks in the Sanandaj-Sirjan metamorphic belt, Iran: with emphasis on the Alvand plutonic complex. Neues Jahrbuch für Geologie Und Palaeontologie. Abhandlungen, 2008; 247 (3), 295-312.

The Phillips pluton, Maine, USA: evidence of heterogeneous crustal sources and implications for granite ascent and emplacement mechanisms in convergent orogens

NASA Astrophysics Data System (ADS)

Pressley, Rachel A.; Brown, Michael

1999-03-01

The Phillips pluton (age of 403.8±1.3 Ma) was assembled at a crustal level below the contemporary brittle-plastic transition during regional dextral-reverse transpressive deformation. The pluton is composed dominantly of medium- to coarse-grained leucogranite sensu lato (s.l.), but within its bounds includes decametric massive outcrop of fine- to medium-grained granodiorite (s.l.). In places, the leucogranite contains centimetric enclaves apparently of the granodiorite. Granodiorite is host to more biotite than muscovite, and more calcic, oscillatory-zoned plagioclase, compared to the leucogranite. Pegmatitic granite and composite pegmatite-aplite occur as metric sheets within the pluton and as larger bodies outside the pluton to the SW. Magmatic fabrics, defined by biotite schlieren, occur locally in the leucogranite; the attitude of these fabrics and layering within the leucogranite are concordant with the NE-striking, steeply-dipping country rock foliation. K 2O contents, Rb/Sr ratios, Rb, Sr and Ba covariations, and chondrite-normalized rare earth element (REE) patterns of leucogranite are consistent with high-to-moderate a(H 2O) muscovite dehydration equilibrium eutectic melting of a predominantly pelite source similar to metasedimentary rocks of the surrounding central Maine belt (CMB). The REE patterns and Rb/Sr ratios of granodiorite also suggest derivation from a metasedimentary source, but more likely by moderate-to-low a(H 2O) (muscovite-) biotite dehydration equilibrium eutectic to non-eutectic (minimum) melting of a protolith dominated by greywacke in which garnet and plagioclase were residual phases. Both granite (s.l.) types have heterogeneous initial Nd isotope compositions. Samples of granodiorite define a range in ɛNd (404 Ma) of -1.8 to +0.1 (±0.3 2 σ uncertainty), and samples of leucogranite define a range in ɛNd (404 Ma) of -8.0 to -5.3 (±0.3 2 σ uncertainty). This bimodal distribution suggests that melts were derived from a minimum of two sources. The data are consistent with these sources being CMB metasedimentary rocks ( ɛNd (404 Ma)<-4) for the leucogranite, and Avalon-like (peri-Gondwanan) metasedimentary crust ( ɛNd (404 Ma)>-4) for the granodiorite. The range of Nd isotope compositions within each granite type most likely reflects isotopic heterogeneity inherited from the source. These data imply that the integrity of individual melt batches was maintained during ascent, and that extensive mixing of melt batches during emplacement at this level in the pluton did not occur, although centimetric enclaves have intermediate Nd isotope compositions consistent with small-scale interactions between magmas. We infer that the Phillips pluton represents the root of a larger pluton, and that what remains of this larger pluton is the feeder constructed from multiple melt batches arrested during waning flow of granite magma through a crustal-scale shear zone system.

Sm-Nd and Rb-Sr isotopic systematics of the Pea Ridge Fe-P deposit and related rocks, southeast Missouri

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marikos, M.A.; Barton, M.D.

1993-03-01

Pea ridge is a discordant Middle Proterozoic Fe-P deposit hosted in rhyolite tuffs and flows of the 1.4--1.5 Ga St. Francois terrane. Host rocks and the deposit are cut by basalt and aplite/pegmatite dikes. The deposit overlies a blind pluton which is partially surrounded by a trachytic ring complex. In the deposit, which is mined for Fe, early Qtz+Amph+Mag+Ap rock is cut by Mag+Ap+Qtz rock. Subsequently, portions of the deposit and host rocks were brecciated, oxidized and silicified to produce a complex suite of rocks enriched in Hem+Qtz+Ksp+Mu. Late breccia pipes/dikes cut the complex and were mineralized with Bar+Ksp+Flu+Chl+Cc+REE-phosphates. Sm/Ndmore » and Rb/Sr isotopic systematics have been studied to: (1) constrain source(s) of igneous rocks and deposit components, (2) refine ages of magmatism, mineralization, and later hydrothermal activity, (3) begin regional comparison of isotopic systematics in SE Missouri Fe deposits, and (4) complement ongoing Missouri DGLS/USGS studies. Fourteen combined Sm-Nd and Rb-Sr analyses were done on materials including two host rhyolites, two nearby trachytes, two gneiss samples representing plausible basement, two intramineral dikes, and six samples of mineralization.« less

A vibrational spectroscopic study of the anhydrous phosphate mineral sidorenkite Na3Mn(PO4)(CO3)

NASA Astrophysics Data System (ADS)

Frost, Ray L.; López, Andrés; Scholz, Ricardo; Belotti, Fernanda Maria; Xi, Yunfei

2015-02-01

Sidorenkite is a very rare low-temperature hydrothermal mineral, formed very late in the crystallization of hyperagpaitic pegmatites in a differentiated alkalic massif (Mt. Alluaiv, Kola Peninsula, Russia). Sidorenkite Na3Mn(PO4)(CO3) is a phosphate-carbonate of sodium and manganese. Such a formula with two oxyanions lends itself to vibrational spectroscopy. The sharp Raman band at 959 cm-1 and 1012 cm-1 are assigned to the PO43- stretching modes, whilst the Raman bands at 1044 cm-1 and 1074 cm-1 are attributed to the CO32- stretching modes. It is noted that no Raman bands at around 800 cm-1 for sidorenkite were observed. The infrared spectrum of sidorenkite shows a quite intense band at 868 cm-1 with other resolved component bands at 850 and 862 cm-1. These bands are ascribed to the CO32- out-of-plane bend (ν2) bending mode. The series of Raman bands at 622, 635, 645 and 704 cm-1 are assigned to the ν4 phosphate bending modes. The observation of multiple bands supports the concept of a reduction in symmetry of the carbonate anion from D3h or even C2v.

Petrogenesis of mesozoic, peraluminous granites in the Lamoille canyon area, Ruby mountains, Nevada, USA

USGS Publications Warehouse

Lee, S.-Y.; Barnes, C.G.; Snoke, A.W.; Howard, K.A.; Frost, C.D.

2003-01-01

Two groups of closely associated, peraluminous, two-mica granitic gneiss were identified in the area. The older, sparsely distributed unit is equigranular (EG) with initial ??Nd ??? -8??8 and initial 87Sr/86Sr ???0??7098. Its age is uncertain. The younger unit is Late Cretaceous (???80 Ma), pegmatitic, and sillimanite-bearing (KPG), with ??Nd from -15??8 to -17??3 and initial 87Sr/86Sr from 0??7157 to 0??7198. The concentrations of Fe, Mg, Na, Ca, Sr, V, Zr, Zn and Hf are higher, and K, Rb and Th are lower in the EG. Major- and trace-element models indicate that the KPG was derived by muscovite dehydration melting (<35 km depth) of Neoproterozoic metapelitic rocks that are widespread in the eastern Great Basin. The models are broadly consistent with anatexis of crust tectonically thickened during the Sevier orogeny; no mantle mass or heat contribution was necessary. As such, this unit represents one crustal end-member of regional Late Cretaceous peraluminous granites. The EG was produced by biotite dehydration melting at greater depths, with garnet stable in the residue. The source of the EG was probably Paleoproterozoic metagraywacke. Because EG magmatism probably pre-dated Late Cretaceous crustal thickening, it required heat input from the mantle or from mantle-derived magma.

Small scale heterogeneity of Phanerozoic lower crust: evidence from isotopic and geochemical systematics of mid-Cretaceous granulite gneisses, San Gabriel Mountains, southern California

USGS Publications Warehouse

Barth, A.P.; Wooden, J.L.; May, D.J.

1992-01-01

An elongate belt of mid-Cretaceous, compositionally banded gneisses and granulites is exposed in Cucamonga terrane, in the southeastern foothills of the San Gabriel Mountains of southern California. Banded gneisses include mafic granulites of two geochemical types: type 1 rocks are similar to high Al arc basalts and andesites but have higher HFSE (high-field-strength-element) abundances and extremely variable LILE (largeion-lithophile-element) abundances, while type 2 rocks are relatively low in Al and similar to alkali rich MOR (midocean-ridge) or intraplate basalts. Intercalated with mafic granulites are paragneisses which include felsic granulites, aluminous gneisses, marble, and calc-silicate gneisses. Type 1 mafic granulites and calcic trondhjemitic pegmatites also oceur as cross-cutting, synmetamorphic dikes or small plutons. Small-scale heterogeneity of deep continental crust is indicated by the lithologic and isotopic diversity of intercalated ortho-and paragneisses exposed in Cucamonga terrane. Geochemical and isotopic data indicate that K, Rb, and U depletion and Sm/Nd fractionation were associated with biotite +/- muscovite dehydration reactions in type 1 mafic granulites and aluminous gneisses during high-grade metamorphism. Field relations and model initial isotopic ratios imply a wide range of protolith ages, ranging from Early Proterozoic to Phanerozoic. ?? 1992 Springer-Verlag.

Role of Precambrian compositions and fabrics in the development of foreland structures, southern Front Range, Colorado

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chase, R.B.

1985-01-01

The Front Range terminates to the south as three basement-cored uplifts located north and west of the Canon City embayment. Precambrian units consist of foliated and non-foliated granitic rocks, augen gneiss, interlayered schist and gneiss, amphibolite, quartzite, and pegmatite. Precambrian deformations include at least three phases of folding, two phases of crenulation cleavage development, and local mylonitization. Metamorphic conditions reached those of cordierite-sillimanite grade. Paleozoic and Mesozoic sediments surround and overlap the exposed uplifts to form south-plunging arches. Excellent three-dimensional exposure of structural relationships between Precambrian rocks and overlying Phanerozoic sediments is present. Deformation styles in the sedimentary cover aremore » strongly influenced by underlying Precambrian lithologies and structural orientations. Where the crystalline units are granitic, with steeply-dipping foliation or no directional fabric, uplifts are bounded by high angle faults. Some such faults show evidence of repeated movements and reversals dating back to Precambrian time. The boundary between mechanical basement and suprastructure is clearly not defined as the base of the sedimentary section. Balanced cross-sections constructed through the southern Front Range must include contemporaneous flexural folds and thrusts in Precambrian schistose and gneissic rocks as well as in Phanerozoic sedimentary layers.« less

Uranophane at Silver Cliff mine, Lusk, Wyoming

USGS Publications Warehouse

Wilmarth, Verl R.; Johnson, D.H.

1954-01-01

The uranium deposit at the Silver Cliff mine near Lusk, Wyo., consists primarily of uranophane which occurs as fracture fillings and small replacement pockets in faulted and fractured calcareous sandstone of Cambrian (?) age. The country rock in the vicinity of the mine is schist of pre-Cambrian age intruded by pegmatite dikes and is unconformably overlain by almost horizontal sandstone of Cambrian(?) age. The mine is on the southern end of the Lusk Dome, a local structure probably related to the Hartville uplift. In the immediate vicinity of the mine, the dome is cut by the Silver Cliff fault, a north-trending high-angle reverse fault about 1,200 feet in length with a stratigraphic throw of 70 feet. Uranophane, metatorbernite, pitchblende, calcite, native silver, native copper, chalcocite, azurite, malachite, chrysocolla, and cuprite have been deposited in fractured sandstone. The fault was probably mineralized throughout its length, but because of erosion, the mineralized zone is discontinuous. The principal ore body is about 800 feet long. The width and depth of the mineralized zone are not accurately known but are at least 20 feet and 60 feet respectively. The uranium content of material sampled in the mine ranges from 0.001 to 0.23 percent uranium, whereas dump samples range from 0.076 to 3.39 percent uranium.

Tectonic Evolution of the Careón Ophiolite (Northwest Spain): A Remnant of Oceanic Lithosphere in the Variscan Belt.

PubMed

Díaz García F; Arenas; Martínez Catalán JR; González del Tánago J; Dunning

1999-09-01

Analysis of the Careón Unit in the Ordenes Complex (northwest Iberian Massif) has supplied relevant data concerning the existence of a Paleozoic oceanic lithosphere, probably related to the Rheic realm, and the early subduction-related events that were obscured along much of the Variscan belt by subsequent collision tectonics. The ophiolite consists of serpentinized harzburgite and dunite in the lower section and a crustal section made up of coarse-grained and pegmatitic gabbros. An Early Devonian zircon age (395+/-2 Ma, U-Pb) was obtained in a leucocratic gabbro. The whole section was intruded by numerous diabasic gabbro dikes. Convergence processes took place shortly afterward, giving rise to a mantle-rooted synthetic thrust system, with some coeval igneous activity. Garnet amphibolite, developed in metamorphic soles, was found discontinuously attached to the thrust fault. The soles graded downward to epidote-amphibolite facies metabasite and were partially retrogressed to greenschist facies conditions. Thermobarometric estimations carried out at a metamorphic sole (T approximately 650 degrees C; P approximately 11.5 kbar) suggested that imbrications developed in a subduction setting, and regional geology places this subduction in the context of an early Variscan accretionary wedge. Subduction and imbrication of oceanic lithosphere was followed by underthrusting of the Gondwana continental margin.

Chemical and Sr isotopic characterization of North America uranium ores: Nuclear forensic applications

DOE PAGES

Balboni, Enrica; Jones, Nina; Spano, Tyler; ...

2016-08-31

This study reports major, minor, and trace element data and Sr isotope ratios for 11 uranium ore (uraninite, UO 2+x) samples and one processed uranium ore concentrate (UOC) from various U.S. deposits. The uraninite investigated represent ores formed via different modes of mineralization (e.g., high- and low-temperature) and within various geological contexts, which include magmatic pegmatites, metamorphic rocks, sandstone-hosted, and roll front deposits. In situ trace element data obtained by laser ablation-ICP-MS and bulk sample Sr isotopic ratios for uraninite samples investigated here indicate distinct signatures that are highly dependent on the mode of mineralization and host rock geology. Relativemore » to their high-temperature counterparts, low-temperature uranium ores record high U/Th ratios (>1000), low total rare earth element (REE) abundances (<1 wt%), high contents (>300 ppm) of first row transition metals (Sc, Ti, V, Cr, Mn, Co, Ni), and radiogenic 87Sr/ 86Sr ratios (>0.7200). Comparison of chondrite normalized REE patterns between uraninite and corresponding processed UOC from the same locality indicates identical patterns at different absolute concentrations. Lastly, this result ultimately confirms the importance of establishing geochemical signatures of raw, uranium ore materials for attribution purposes in the forensic analysis of intercepted nuclear materials.« less

Chemical and Sr isotopic characterization of North America uranium ores: Nuclear forensic applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balboni, Enrica; Jones, Nina; Spano, Tyler

This study reports major, minor, and trace element data and Sr isotope ratios for 11 uranium ore (uraninite, UO 2+x) samples and one processed uranium ore concentrate (UOC) from various U.S. deposits. The uraninite investigated represent ores formed via different modes of mineralization (e.g., high- and low-temperature) and within various geological contexts, which include magmatic pegmatites, metamorphic rocks, sandstone-hosted, and roll front deposits. In situ trace element data obtained by laser ablation-ICP-MS and bulk sample Sr isotopic ratios for uraninite samples investigated here indicate distinct signatures that are highly dependent on the mode of mineralization and host rock geology. Relativemore » to their high-temperature counterparts, low-temperature uranium ores record high U/Th ratios (>1000), low total rare earth element (REE) abundances (<1 wt%), high contents (>300 ppm) of first row transition metals (Sc, Ti, V, Cr, Mn, Co, Ni), and radiogenic 87Sr/ 86Sr ratios (>0.7200). Comparison of chondrite normalized REE patterns between uraninite and corresponding processed UOC from the same locality indicates identical patterns at different absolute concentrations. Lastly, this result ultimately confirms the importance of establishing geochemical signatures of raw, uranium ore materials for attribution purposes in the forensic analysis of intercepted nuclear materials.« less

Pre-Himalayan tectono-magmatic imprints in the Darjeeling-Sikkim Himalaya (DSH) constrained by 40Ar/39Ar dating of muscovite

NASA Astrophysics Data System (ADS)

Acharyya, Subhrangsu K.; Ghosh, Subhajit; Mandal, Nibir; Bose, Santanu; Pande, Kanchan

2017-09-01

The Lower Lesser Himalayan Sequence (L-LHS) in Darjeeling-Sikkim Himalaya (DSH) displays intensely deformed, low-grade meta-sedimentary rocks, frequently intervened by granite intrusives of varied scales. The principal motivation of our present study is to constrain the timing of this granitic event. Using 40Ar/39Ar geochronology, we dated muscovite from pegmatites emplaced along the earliest fabric in the low grade Daling phyllite, and obtained ∼1850 Ma Ar-Ar muscovite cooling age, which is broadly coeval with crystallization ages of Lingtse granite protolith (e.g., 1800-1850 Ma U-Pb zircon ages) reported from the L-LHS. We present here field observations to show the imprints (tectonic fabrics) of multiple ductile deformation episodes in the LHS terrain. The earliest penetrative fabric, axial planar to N-S trending reclined folds, suggest a regional tectonic event in the DSH prior to the active phase of Indo-Asia collision. Based on the age of granitic bodies and their structural correlation with the earliest fabric, we propose that the L-LHS as a distinct convergent tectono-magmatic belt, delineating the northern margin of Indian craton in the framework of the ∼1850 Ma Columbia supercontinent assembly.

Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria

NASA Astrophysics Data System (ADS)

Bayewu, Olateju O.; Oloruntola, Moroof O.; Mosuro, Ganiyu O.; Laniyan, Temitope A.; Ariyo, Stephen O.; Fatoba, Julius O.

2017-12-01

The geophysical assessment of groundwater in Awa-Ilaporu, near Ago Iwoye southwestern Nigeria was carried out with the aim of delineating probable areas of high groundwater potential. The area falls within the Crystalline Basement Complex of southwestern Nigeria which is predominantly underlain by banded gneiss, granite gneiss and pegmatite. The geophysical investigation involves the very low frequency electromagnetic (VLF-EM) and Vertical Electrical Sounding (VES) methods. The VLF-EM survey was at 10 m interval along eight traverses ranging between 290 and 700 m in length using ABEM WADI VLF-EM unit. The VLF-EM survey was used to delineate areas with conductive/fractured zones. Twenty-three VES surveys were carried out with the use of Campus Ohmega resistivity meter at different location and at locations areas delineated as high conductive areas by VLF-EM survey. The result of VLF-EM survey along its traverse was used in delineating high conductive/fractured zones, it is, however, in agreement with the delineation of the VES survey. The VES results showed 3-4 geoelectric layers inferred as sandy topsoil, sandy clay, clayey and fractured/fresh basement. The combination of these two methods, therefore, helped in resolving the prospecting location for the groundwater yield in the study area.

Petrochemical and Mineralogical Constraints on the Source and Processes of Uranium Mineralisation in the Granitoids of Zing-Monkin Area, Adamawa Massif, NE Nigeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haruna, I. V., E-mail: vela_hi@yahoo.co.uk; Orazulike, D. M.; Ofulume, A. B.

Zing-Monkin area, located in the northern part of Adamawa Massif, is underlain by extensive exposures of moderately radioactive granodiorites, anatectic migmatites, equigranular granites, porphyritic granites and highly radioactive fine-grained granites with minor pegmatites. Selected major and trace element petrochemical investigations of the rocks show that a progression from granodiorite through migmatite to granites is characterised by depletion of MgO, CaO, Fe{sub 2}O{sub 3,} Sr, Ba, and Zr, and enrichment of SiO{sub 2} and Rb. This trend is associated with uranium enrichment and shows a chemical gradation from the more primitive granodiorite to the more evolved granites. Electron microprobe analysis showsmore » that the uranium is content in uranothorite and in accessories, such as monazite, titanite, apatite, epidote and zircon. Based on petrochemical and mineralogical data, the more differentiated granitoids (e.g., fine-grained granite) bordering the Benue Trough are the immediate source of the uranium prospect in Bima Sandstone within the Trough. Uranium was derived from the granitoids by weathering and erosion. Transportation and subsequent interaction with organic matter within the Bima Sandstone led to precipitation of insoluble secondary uranium minerals in the Benue Trough.« less

Fe-dominated samarskite - a new member of the samarskite 'group'?

NASA Astrophysics Data System (ADS)

Nicolescu, S.; Davis, F. E.; Cornell, D.; Eckert, J., Jr.; Bojar, H.; Walter, F.; Luzik, E.

2013-12-01

Davis and Nicolescu (2011) alluded to the fact that Fe-dominated samarskite from the pegmatite at the Spinelli prospect in Glastonbury, CT is a potential new member of the samarskite mineral 'group'. Further work on untreated material from the same occurrence confirms Fe dominance at the A site, and based on 29 microprobe and four LA-ICP-MS analyses the following empirical formula is obtained: (Fe3+0.384[Y0.239Dy0.026Gd0.018Sm0.012Nd0.007Er0.006Tb0.005Yb0.005Ho0.003Ce0.003Pr0.001Tm0.001]Σ0.326U0.090Mn0.052Th0.047Ti0.033Ca0.009Pb0.006Mg0.003Al0.003Si0.001Sc0.001)0.956(Nb0.814Ta0.149Sn0.026W0.019)1.007O4. The corresponding simplified formula is (Fe3+,Y,U,REE)(Nb,Ta)O4. Due to its UO2 and ThO2 content (9.12 and 4.67 wt. %, respectively) and age of ~ 260 Ma, Spinelli prospect samarskite is completely metamict. Literature data (Simmons et al., 2006 and references therein) suggest that annealing metamict samarskite in a slightly reducing atmosphere of 95 % Ar - 5 % H2 for 12 hrs. at 1100° C will result in recrystallized samarskite. Repeated experiments conducted on powdered Spinelli prospect material under these conditions, at gas flow rates of 100 cm3/min. and 200 cm3/min., resulted in sintered material composed of an ill-defined mixture of fergusonite, columbite, possible samarskite and an unidentified phase. Moreover, in each of the 1100° C annealing experiments a black radioactive sublimate was deposited at the cold end of the annealing apparatus, suggesting significant changes in the chemistry of the annealed material. Annealing the powdered metamict phase for 21 hrs. at 650° C (Tomašić et al., 2004) in a 95 % Ar - 5 % H2 atmosphere at a flow rate of 100 cm3/min. resulted in a mineral phase yielding broad X-ray diffraction peaks, especially at elevated diffraction angles. Because of the broad diffraction peaks and one ambiguous peak impossible to index, attempts to calculate the unit cell parameters of the annealed phase were unsuccessful for either monoclinic or orthorhombic symmetry. Hence, the unambiguous structural characterization of the mineral phase failed. Fe-dominated samarskite does not seem to be restricted to the Spinelli prospect pegmatite. Of the 19 samarskite specimens discussed by Warner and Ewing (1993), 13 are Fe-dominated. Efforts to fully characterize the Spinelli prospect Fe-rich samarskite mineral phase are continuing. REFERENCES Davis & Nicolescu, 2011, Bull. Peabody Museum of Nat. History, 52(1), 135-152 Simmons et al., 2006, Can. Min., 44(5), 1119-1125 Tomašić et al., 2004, N. Jb. Miner. Mh., 2004(4), 163-175 Waren & Ewing, 1993, Am. Min., 78(3-4), 419-424

Geology of the Jabal Riah area, Kingdom of Saudi Arabia

USGS Publications Warehouse

Wells, J.D.

1982-01-01

The Jabal Riah area is in the southern part of the Jibal al Hamdah quadrangle (lat 19?00'00'' to 19?07'S0'' N., long 45?37'30'' to 43?45'00' E.) in the southeastern Precambrian Shield, Asir Province, Kingdom of Saudi Arabia. The Jabal Mahanid group of ancient gold mines, which is part of the Jabal Ishmas-Wadi Tathlith gold belt, is in the west-central part of the area. Rocks in the Jabal Riah area consist of Precambrian layered metasedimentary and metavolcanic rocks intruded by Precambrian igneous rocks. The metamorphic rocks are, from oldest to youngest, interlayered hornblende and biotite schist, quartz-biotite schist, hornblende schist, serpentinite, and chlorite schist. The igneous rocks are, from oldest to youngest, diorite-gabbro including dikes, granodiorite, monzogranite-granodiorite, leucocratic quartz porphyry, rhyolite, and aplite and pegmatite dikes. A large area of jasper replaces serpentinite. On the valley floors, recent alluvium and pediment deposits overlie the bedrock. The structure of the area is dominated by a dome centered over the eastern border of the area; leucocratic quartz porphyry forms the core of the dome. Minor folds and faults are present. The Jabal Mahanid group of ancient gold mines is on a northwest-trending vein system, and major ancient mine areas are found where the system splits or changes direction. The veins consist of zones of brecciated and crushed rock, which are generally less than 0.5 m wide but may be as wide as 1 m. These zones contain quartz and calcite stringers and commonly are along hornblende schist-serpentinite contacts; however, they also cut both units. Most aplite, pegmatite, and quartz dikes in the area are thin and discontinuous and are intruded along the vein trend. Similar veins, at the same stratigraphic interval, have been found beyond the northeastern part of the map area. The veins contain detectable gold and silver (median gold, approximately 0.14 ppm; median silver, approximately 1 ppm). Gold and silver are most abundant in calcium-rich rocks and veins; silver was not detected in igneous rocks. Altered wall-rock zones are mineralized as much as 10 m away from the veins. Away from the Jabal Mahanid vein-system, silver was detected in the jasper. Gold and silver were detected in minor brecciated and sheared structures and in metasedimentary rocks. Gold was detected in sericitized margins of the leucocratic quartz porphyry, in unaltered rhyolite, and in aplite dikes. The presence of unusual amounts of gold and silver over a wide area is indicated by the ancient gold mines along veins at or near the hornblende schist-serpentinite contact in the map area and to the south in the Hajrah-Hamdah area and by the widespread evidence of precious metals in igneous rocks and other vein structures. A domed-shaped area, approximately 30 km in diameter, is outlined by the hornblende schist-serpentinite contact and has leucocratic quartz prophyry in the middle. Additional study of this area might reveal economic concentrations of gold and silver.

Mechanisms of submicron inclusion re-equilibration during host mineral deformation

NASA Astrophysics Data System (ADS)

Griffiths, Thomas; Habler, Gerlinde; Abart, Rainer; Rhede, Dieter; Wirth, Richard

2014-05-01

Both brittle and ductile deformation can facilitate re-equilibration of mineral inclusions. The presence of inclusions also influences stress and strain distribution in the host. The processes governing feedbacks between brittle deformation, ductile deformation, and inclusion re-equilibration have been studied using unique microstructures in Permian meta-pegmatite garnets from the Koralpe, Eastern Alps, Austria. Sampled almandine-spessartine garnets contain highly abundant submicron-sized inclusions, which originated during or subsequent to magmatic garnet growth. The Permian magmatic assemblages were affected by eclogite facies metamorphism during the Cretaceous tectono-metamorphic event. The meta-pegmatite garnet deformed crystal-plastically at this metamorphic stage (Bestmann et al. 2008) and the host-inclusion system was affected by partial recrystallization. Trails of coarser inclusions (1-10µm diameter) crosscut the magmatic submicron inclusion density zoning in the garnet, defining curviplanar geometrical surfaces in 3D. In 10-40µm broad 'bleaching zones' flanking inclusion trails, the original ≤1µm sized inclusions are not seen in the optical microscope or SEM, however inclusions <100nm are still abundant in TEM foils from these areas. From their microstructural characteristics it is inferred that the trails formed at sites of healed brittle cracks. FEG-microprobe data showed that inclusion-trails and associated bleaching zones can be formed isochemically, although some trails showed non-isochemical coarsening. In both cases no change in garnet major element composition was observed. EBSD mapping revealed two phenomena that were investigated by cutting targeted TEM foils. Firstly, bleaching zones are associated with systematic very low angle (ca. 0.5°) garnet lattice orientation changes along discrete boundaries. TEM foils transecting such a boundary show a lower concentration of dislocations than expected for the lattice rotation inferred from EBSD data, and no subgrain boundaries. Secondly, garnet lattice rotation of up to 10° around rational garnet crystal axes is observed in connection with some already coarsened inclusions. Strain concentrations are widespread in some trails, but rare in others. A TEM foil transecting a garnet domain with concentrated lattice rotation in association with inclusions reveals well developed polygonal subgrain walls with few free dislocations. Where dislocation density is greatest, almost no <100nm inclusions are observed, whereas these are more abundant in unstrained garnet domains despite the foil being located entirely within the optically visible bleaching zone. Chlorite inclusions and formation of etch pits at dislocations at the garnet-chlorite interface demonstrate the presence of fluid along subgrain boundaries during this second bleaching process. In summary, brittle deformation in these garnets led to enhanced transport and inclusion re-equilibration by coarsening, forming inclusion trails. The precise mechanism allowing enhanced transport is still to be determined and may have involved fluid supply with or without pipe diffusion along introduced dislocations. Later ductile deformation via dislocations, concentrated at already coarsened inclusions and enhanced by fluid availability, further affected the nanoinclusion population. The inclusion trail microstructure records complex small-scale interaction between deformation and reaction, shedding light on the mechanisms by which re-equilibration and strain localisation can influence each other in deforming host-inclusion systems. Bestmann et al. (2008) Journal of Structural Geology 30: 777-790

A Raman micro-spectroscopic study of fluid inclusions in yellow danburite

NASA Astrophysics Data System (ADS)

Huong, Le T. T.; Krenn, Kurt; Hauzenberger, Christoph A.

2017-04-01

Danburite, a calcium borosilicate, CaB2Si2O8, can be associated genetically with rocks of magmatic (pegmatoid), metasomatic (skarn) and sedimentary (evaporite) origin. Yellow danburite belongs to the extremely rare gem group. Recently, several yellow danburite crystals were discovered in an alluvial deposit, in the Luc Yen mining area, northern Vietnam. The identification of sassolite crystals in fluid inclusions points to a pegmatite origin of the Luc Yen danburite (Smirnov et al., 2000) and this confirms with the low-density values of carbon dioxides which were obtained from Raman measurements using the Fermi doublet as a function of fluid density. Materials and Methods Three danburite crystals (158, 3.8 and 3.3 ct) were used for this study. Raman spectra of inclusions were collected in the confocal mode using a Jobin Yvon LabRam HR800 micro-spectrometer equipped with an Olympus BX41 optical microscope and a Si-based CCD (charged-coupled device) detector. Peak analysis of CO2 was performed with an OriginLab 9.0 professional software package, and the peaks were fitted using a Gauss-Lorentz function. Results and Discussion Fluid inclusions arrange as single or along trails inside the danburite crystal. Trails are oriented both parallel and perpendicular to the c-axis of the host crystals, composed of two- or multi-phase inclusions. Two-phase inclusions typically consist of a liquid (H2O-rich) phase and a vapor bubble (CO2) phase that differ in their degrees of fill suggesting heterogeneous entrapment of the dominant fluid during crystal growth. The dominant multi-phase is characterized by multiple sassolite crystals, a liquid H2O phase and a pure CO2 vapor bubble. The sassolite crystals appear usually as colourless pseudohexagonal plates showing more or less perfect crystal faces and vary from 5μm to 50μm in size. Sassolite shows two distinct bands at 500 and 880 cm-1 and two additional bands at 3165 and 3247 cm-1. Raman spectra of CO2 show two main bands at about 1388 cm-1 and 1285 cm 1 which are known as the Fermi diad. The separation between the Fermi diad bands (Δ) was found to be a function of CO2 density in fluid inclusions whereby the separation increases with increasing density of CO2. The Δ values fall in the range from 102.7 to 103.7 cm 1 which corresponds to densities lower than 0.4 g/cm3 (Wang et al., 2011). The low-density CO2 in liquid inclusions in danburite from Luc Yen is in accordance with those found in minerals of granitic pegmatite origin (Bakker and Schilli, 2016). References Bakker R.J. and Schilli S.E., 2016, Mineralogy and Petrology, 110, 43-63. Smirnov S.Z., Peretyazhko I.S., Prokofiev V.Y., Zagorskii V.E., and Shebanin A.P., 2000. Russian Geology and Geophysics, 41(2), 193-205. Wang X., Chou I., Hua W., Robert B., 2011. Geochimica et Cosmochimica Acta, 75, 4080-4093. Acknowledgment The support from ASEA-Uninet is gratefully acknowledged.

Fluid inclusion volatile analysis by gas chromatography with photoionization micro-thermal conductivity detectors: Applications to magmatic MoS 2 and other H 2O-CO 2 and H 2O-CH 4 fluids

NASA Astrophysics Data System (ADS)

Bray, C. J.; Spooner, E. T. C.

1992-01-01

Eighteen fluid inclusion volatile peaks have been detected and identified from 1-2 g samples (quartz) by gas chromatography using heated (~105°C) on-line crushing, helium carrier gas, a single porous polymer column (HayeSep R; 10' × 1/8″: 100/120#; Ni alloy tubing), two temperature programme conditions for separate sample aliquots, micro-thermal conductivity (TCD) and photoionization detectors (PID; 11.7 eV lamp), and off-line digital peak processing. In order of retention time these volatile peaks are: N 2, Ar, CO, CH 4, CO 2, C 2H 4, C 2H 6, C 2H 2, COS, C 3H 6, C 3H 8, C 3H 4 (propyne), H 2O (22.7 min at 80°C), SO 2, ± iso- C4H10 ± C4H8 (1-butene) ± CH3SH, C 4H 8 (iso-butylene), (?) C 4H 6 (1,3 butadiene) and ± n- C4H10 ± C4H8 (trans-2-butene) (80 and -70°C temperature programme conditions combined). H 2O is analysed directly. O 2 can be analysed cryogenically between N 2 and Ar, but has not been detected in natural samples to date in this study. H 2S, SO 2, NH 3, HCl, HCN, and H 2 ca nnot be analysed at present. Blanks determined by crushing heat-treated Brazilian quartz (800-900°C/4 h) are zero for 80°C temperature programme conditions, except for a large, unidentified peak at ~64 min, but contain H 2O, CO 2, and some low molecular weight hydrocarbons at -70°C temperature conditions due to cryogenic accumulation from the carrier gas and subsequent elution. TCD detection limits are ~30 ppm molar in inclusions; PID detection limits are ~ 1 ppm molar in inclusions and lower for unsaturated hydrocarbons (e.g., ~0.2 ppm for C 2H 4; ~ 1 ppb for C 2H 2; ~0.3 ppb for C 3H 6). Precisions (1σ) are ~ ±1-2% and ~ ± 13% for H 2O in terms of total moles detected; the latter value is equivalent to ±0.6 mol% at the 95 mol% H 2O level. Major fluid inclusion volatile species have been successfully analysed on a ~50 mg fluid inclusion section chip (~7 mm × ~10 mm × ~100 μm). Initial inclusion volatile analyses of fluids of interpreted magmatic origin from the Cretaceous Boss Mtn. monzogranite stock-related MoS 2 deposit, central British Columbia of ~97 mol% H 2O, ~3% CO 2, ~ 140-150 ppm N 2, and ~16-39 ppm CH 4 (~300-350°C) are reasonable in comparison with high temperature (~400-900°C) volcanic gas analyses from four, active calc-alkaline volcanoes; e.g., the H 2O contents of volcanic gases from the White Island (New Zealand), Mount St. Helens (Washington, USA), Merapi (Bali, Indonesia), and Momotombo (Nicaragua) volcanoes are 88-95%, >90% (often >95%), 88-95% and ~93%, respectively; CO 2 contents are ~3-10%, 1-10%, 3-8%, and ~3.5%. CO 2/N 2 ratios for the Boss Mtn. MoS 2 fluids of ~ 190-220 are in the range for known volcanic gas ratios (e.g., ~ 150- 240; White Island). The ∑S content of the Boss Mtn. MoS 2 fluid prior to S loss by sulphide precipitation may have been ~2 mol% since CO 2/∑S molar ratios of analysed high-temperature volcanic gases are ~ 1.5. This estimate is supported by ∑S contents for White Island, Merapi and Momotombo volcanic gases of ~2%, ~0.5-2.5%, and ~2%. COS has been determined in H 2O-CO 2 fluid inclusions of interpreted magmatic origin from the Boss Mtn. MoS 2 deposit and the Tanco zoned granitic pegmatite, S.E. Manitoba at ~50-100 ppm molar levels, which are consistent with levels in volcanic gases. It appears that low, but significant, concentrations of C 2-C 4 alkanes (~ 1-20 ppm), C 2-C 4 alkenes (~ 1-480 ppb) and alkynes (e.g., C 3H 4) have been detected in magmatically derived fluids (Boss Mtn. MoS 2 deposit; Tanco granitic pegmatite). Significantly higher, low molecular weight hydrocarbon concentrations have been determined in a CH 4-rich (~ 2%), externally derived fluid of possible metamorphic or deep crustal origin trapped as inclusions in metasomatic wall-rock tourmaline adjacent to the Tanco pegmatite (e.g., 300/470 ppm C 2H 6; 50/90 ppm C 3H 8; 3-60 ppm C 2H 4/C 3H 6 n-C 4H 10).

Empirical analysis of electromagnetic profiles for groundwater prospecting in rural areas of Ibadan, southwestern Nigeria

NASA Astrophysics Data System (ADS)

Ehinola, O. A.; Opoola, A. O.

2005-05-01

The Slingram electromagnetic (EM) survey using a coil separation of 60 and 100 meters was carried out in 10 villages in Akinyele area of Ibadan, southwestern Nigeria to aid in the development of groundwater. Five main rock types including an undifferentiated gneiss complex (Su), biotite-garnet schist/gneiss (Bs), quartzite and quartz schist (Q), migmatised undifferentiated biotite/hornblende gneiss (M) and pegmatite/quartz vein (P) underlie the study area. A total of 31 EM profiles was made to accurately locate prospective borehole sites in the field. Four main groups with different behavioural pattern were categorized from the EM profiles. Group 1 is characterized by high density of positive (HDP) or high density of negative (HDN) real and imaginary curves, Group 2 by parallel real and imaginary curves intersecting with negligible amplitude (PNA), Group 3 by frequent intersection of high density of negative minima (FHN) real and imaginary curves, and Group 4 by separate and approximately parallel (SAP) real and imaginary curves. Qualitative pictures of the overburden thickness and the extent of fracturing have been proposed from these behavioural patterns. A comparison of the borehole yield with the overburden thickness and the level of fracturing show that borehole yield depends more on the fracture density than on the overburden thickness. Asymmetry of the anomaly was also found useful in the determination of the inclination of the conductor/fracture.

Ultramafic rocks of the western Idaho suture zone: Asbestos Peak and Misery Ridge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Godchaux, M.M.; Bonnichsen, B.

1993-04-01

The Western Idaho Ultramafic Belt extends northward from the town of Weiser to the northern end of Dworshak Reservoir; in its northern portion most of the ultramafic bodies are localized along the suture zone where the Mesozoic oceanic accreted terranes meet the continental craton. Of the twenty bodies investigated, all are small, all are in fault contact with their metavolcanic and metasedimentary host rocks, all have been metamorphosed, and all display deformational fabrics in at least some portion of the outcrop area, suggesting that deformation continued after peak metamorphism. The degree of metamorphism ranges from incipient serpentinization to attainment ofmore » equilibrium in the upper amphibolite facies. Some bodies have been intruded by granitic dikes or pegmatite veins after emplacement, and have locally undergone contact metasomatism. Two particularly complex bodies, Asbestos Peak and Misery Ridge, were chosen for detailed petrographic and chemical study. Asbestos Peak is composed mostly of decussate anthophyllite-talc rock containing isolated patches of harzburgite protolith, and has blackwall border zones. Misery Ridge is composed mostly of coarse-grained sheared tremolite-talc schist without remnant protolith, and lacks true blackwall zones. Both bodies exhibit an unusual and enigmatic hornblende-poikiloblastic garnet-green spinel-skeletal ilmenite assemblage, present in some places as well-defined border zones and in other places as cross-cutting bodies.« less

The ultimate fate of a synmagmatic shear zone. Interplay between rupturing and ductile flow in a cooling granite pluton

NASA Astrophysics Data System (ADS)

Zibra, I.; White, J. C.; Menegon, L.; Dering, G.; Gessner, K.

2018-05-01

The Neoarchean Cundimurra Pluton (Yilgarn Craton, Western Australia) was emplaced incrementally along the transpressional Cundimurra Shear Zone. During syndeformational cooling, discrete networks of cataclasites and ultramylonites developed in the narrowest segment of the shear zone, showing the same kinematics as the earlier synmagmatic structures. Lithological boundaries between aplite/pegmatite veins and host granitic gneiss show more intense pre-cataclasite fabrics than homogeneous material, and these boundaries later became the preferred sites of shear rupture and cataclasite nucleation. Transient ductile instabilities established along lithological boundaries culminated in shear rupture at relatively high temperature (∼500-600 °C). Here, tensile fractures at high angles from the fault plane formed asymmetrically on one side of the fault, indicating development during seismic rupture, establishing the oldest documented earthquake on Earth. Tourmaline veins were emplaced during brittle shearing, but fluid pressure probably played a minor role in brittle failure, as cataclasites are in places tourmaline-free. Subsequent ductile deformation localized in the rheologically weak tourmaline-rich aggregates, forming ultramylonites that deformed by grain-size sensitive creep. The shape and width of the pluton/shear zone and the regime of strain partitioning, induced by melt-present deformation and established during pluton emplacement, played a key role in controlling the local distribution of brittle and then ductile subsolidus structures.

Airborne and ground reconnaissance of part of the syenite complex near Wausau, Marathon county, Wisconsin

USGS Publications Warehouse

Vickers, R.C.

1955-01-01

Airborne and ground reconnaissance for radioactive minerals in part of the syenite complex near Wausau, Marathon county, Wis., found 12 radioactive mineral localities. The rocks in the area are of Precambrian age and consist of syenite and nepheline syenite, which have intruded older granite, greenstone, quartzite, and argillite. There are very few outcrops, and much of the bedrock is deeply weathered and covered by residual soil. Thorium-bearing zircon pegatite float was found within the area of syenite and nepheline syenite at four localities. Reddish-brown euhedral to subeuhedral crystals of well-zoned zircon (variety cyrtolite) comprise more than 40 percent of some of the specimens. The radioactive mineral at four localities outside the area of syneites was identified as thorogummite, which occurred in nodular masses in residual soil. Alinement of the thorogummite float and associated radioactivity suggests that the thorogummite has resulted from weathering of narrow veins or pegmatites containing thorium-bearing minerals. Unidentified thorium-bearing minerals were found at three localities, and a specimen of allanite weighing about 2 pounds was found at one locality. Shallow trenches at two of the largest radioactivity anomalies showed that the radioactive material extended down into weathered bedrock. The occurrences might warrant additional physical exploration should there be sufficient demand for thorium. Further reconnaissance in the area would probably result in the discovery of additional occurrences.

Geochronology and geochemistry of lithologies of the Tabuaço W-prospect area (Northern Portugal)

NASA Astrophysics Data System (ADS)

Cerejo, Tiago; Francisco Santos, Jose; Sousa, Joao Carlos; Castanho, Nuno; Sergio, Gabriel; Ribeiro, Sara

2016-04-01

This work is focussed on lithologies occurring at Quinta de São Pedro das Águias, which is located in the Tabuaço prospect (an area of 45 km2 where exploration for W-skarn deposits is taking place, in northern Portugal, close to the Douro valley). At Quinta de São Pedro das Águias several lithologies are recognized: "normal" phyllites, black phyllites (graphite-bearing), marbles, calcsilicate (s.s.) rocks and skarns (sometimes, scheelite-bearing), belonging to the Bateiras Formation, of the Douro Group (one of the two major subdivisions of the Neoproterozoic-Cambrian Dúrico-Beirão Supergroup); Paredes da Beira-Tabuaço granite; several aplitic and pegmatitic bodies. The studied area belongs to the Central Iberian Zone, a geotectonic unit of the Iberian Variscan Chain. Rb-Sr isotope analyses done in the scope of this work, provided a 316 ± 7 Ma whole-rock isochron (MSWD = 1.7; initial 87Sr/86Sr = 0.7146) for the granitoids, using the 87Rb decay constant recently recommended by IUPAC-IUGS (Villa et al., 2015). This date is interpreted here as the emplacement age of those rocks, during a late stage of the Variscan D3. The granite revealed a S-type nature, namely because it is a muscovite granite, it shows a peraluminous composition (average A/CNK = 1.28), and the Sr and Nd isotope fingerprints (-8.9 ≤ ɛNd(316Ma) ≤ -7.8; +0.7105 ≤ 87Sr/86Sr(316Ma) ≤ 0.7182) fit into the composition of metasedimentary crust. The analysed phyllites show the following isotopic compositions: -9.7 ≤ ɛNd(316Ma) ≤ -8.2; +0.7148 ≤ 87Sr/86Sr(316Ma) ≤ 0.7188. Therefore, the isotope signatures, at 316 Ma, of the granite and of the studied metapelites overlap, suggesting that the parental magma was generated by anatexis of Grupo do Douro metasediments. According to their petrographic, geochemical and isotopic features, aplites and pegmatites are viewed as extreme differentiates from the granite. São Pedro das Águias metapelites show biotite zone parageneses. Geochemically, their REE normalized patterns are very similar to those displayed by NIBAS and by other upper crustal reference compositions. Isotopically, especially due to their lower ɛNd316, the studied metapelites are clearly distinct from the Grupo das Beiras metasediments (the other major division of the Dúrico-Beirão Supergroup), and, instead, they resemble other metasedimentary units of the Iberian Massif. Several lines of evidence, namely the isotope data (-8.1 ≤ ɛNd(316Ma) ≤ -6.4; +0.7090 ≤ 87Sr/86Sr(316Ma) ≤ 0.7102) and the occurrence of fine intercalations of sub-mm layers enriched in phyllosilicates, suggest that calcsilicate (s.l.) rocks owe their composition not only to metasomatism that accompanied the granite intrusion, but also to an inheritance from their protoliths, which should have resulted from mixed sedimentation, both chemical and terrigenous. This work was financially supported by: - FEDER funds trough Operational Programme Competitiveness Factors - COMPETE and by national funds through FCT - Fundação para a Ciência e a Tecnologia in the scope of projects Petrochron (PTDC/CTE-GIX/112561/2009) and Geobiotec (UID/GEO/04035/2013); - Colt Resources. Reference: Villa, I.M., De Bièvre, P., Holden, N.E., Renne, P.R., 2015. IUPAC-IUGS recommendation on the half life of 87Rb. Geochim. Cosmochim. Acta 164, 382-385.

Phosphoinnelite, Ba4Na3Ti3Si4O14(PO4,SO4)2(O,F)3, a new mineral species from peralkaline pegmatite of the Kovdor pluton, Kola Peninsula

NASA Astrophysics Data System (ADS)

Pekov, I. V.; Chukanov, N. V.; Kulikova, I. M.; Belakovsky, D. I.

2007-12-01

Phosphoinnelite, an analogue of innelite with P > S, has been found in a peralkaline pegmatite vein crosscutting calcite carbonatite at the phlogopite deposit, Kovdor pluton, Kola Peninsula. Cancrinite (partly replaced with thomsonite-Ca), orthoclase, aegirine-augite, pectolite, magnesioarfvedsonite, golyshevite, and fluorapatite are associated minerals. Phosphoinnelite occurs as lath-shaped crystals up to 0.2 × 1 × 6 mm in size, which are combined typically in bunch-, sheaf-, and rosettelike segregations. The color is yellow-brown, with vitreous luster on crystal faces and greasy luster on broken surfaces. The mineral is transparent. The streak is pale yellowish. Phosphoinnelite is brittle, with perfect cleavage parallel to the {010} and good cleavage parallel to the {100}; the fracture is stepped. The Mohs hardness is 4.5 to 5. Density is 3.82 g/cm3 (meas.) and 3.92 g/cm3 (calc.). Phosphoinnelite is biaxial (+), α = 1.730, β = 1.745, and γ = 1.764, 2V (meas.) is close to 90°. Optical orientation is Z^c ˜ 5°. Chemical composition determined by electron microprobe is as follows (wt %): 6.06 Na2O, 0.04 K2O, 0.15 CaO, 0.99 SrO, 41.60 BaO, 0.64 MgO, 1.07 MnO, 1.55 Fe2O3, 0.27 Al2O3, 17.83 SiO2, 16.88 TiO2, 0.74 Nb2O5, 5.93 P2O5, 5.29 SO3, 0.14 F, -O=F2 = -0.06, total is 99.12. The empirical formula calculated on the basis of (Si,Al)4O14 is (Ba3.59Sr0.13K0.01)Σ3.73(Na2.59Mg0.21Ca0.04)Σ3.04(Ti2.80Fe{0.26/3+}Nb0.07)Σ3.13[(Si3.93Al0.07)Σ4O14(P1.11S0.87)Σ1.98O7.96](O2.975F0.10)Σ3.075. The simplified formula is Ba4Na3Ti3Si4O14(PO4,SO4)2(O,F)3. The mineral is triclinic, space group P overline 1 or P1. The unit cell dimensions are a = 5.38, b = 7.10, c = 14.76 Å; α = 99.00°, β = 94.94°, γ = 90.14°; and V = 555 Å3, Z = 1. The strongest lines of the X-ray powder pattern [ d, Å in ( I)( hkl)] are: 14.5(100)(001), 3.455(40)(103), 3.382(35)(0overline 2 2), 2.921(35)(005), 2.810(40)(1overline 1 4), 2.683(90)(200, overline 2 01), 2.133(80)(overline 2 overline 2 2), 2.059(40)(204, 1overline 3 3, 221), 1.772(30)(0overline 4 1, 1overline 2 7, 2overline 3 2, 2overline 3 3). The infrared spectrum is demonstrated. An admixture of P substituting S has been detected in the innelite samples from the Inagli pluton (South Yakutia, Russia). An innelite-phosphoinnelite series with a variable S/P ratio has been discovered. The type material of phosphoinnelite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.

A structural analysis of the Minas da Panasqueira vein network and related fracture generations

NASA Astrophysics Data System (ADS)

Jacques, Dominique; Vieira, Romeu; Muchez, Philippe; Sintubin, Manuel

2014-05-01

The Minas da Panasqueira is a world-class W-Cu-Sn vein-type deposit, situated within the Central Iberian Zone of the Palaeozoic Iberian Massif (Portugal). The deposit consists of a network of subhorizontal, sill-like massive quartz veins situated above the southwestern extremity of a greisen cupola, within regionally metamorphosed, isoclinally folded, lower-greenschist slates and greywackes. The greisen cupola is part of a larger intrusive complex, emplaced during the late- to post-tectonic stage of the Variscan orogeny. The late-Variscan granitoid(s) underlying the Panasqueira deposit is considered to have served as a major metal source. The structure of the network of subhorizontal extension veins, consists of numerous planar vein lobes that are separated by host-rock bridges and merge at branch-points. A structural analysis demonstrates that not only within the Panasqueira mine, but also on a more regional scale, one or more generations of flat-lying fractures are present. The veins clearly exploited these pre-existing discontinuities, as confirmed by (1) the vein geometry being directly influenced by variations in the orientation of the initial fracture sets and (2) the geometry of the rock bridges and overlapping vein morphologies, consistently showing straight-line propagating crack tips. If veining is governed by a preferential, strongly developed anisotropy in the host rock, the hypothesis of vein lobes and rock bridges forming during propagation of the parent crack by tip-line bifurcation and confinement processes (Foxford et al., 2000) does not seem plausible. Instead, we propose that the rock bridges formed from several, initially separate and small veinlets that eventually overlapped in an en echelon arrangement during progressive propagation and inflation. Bending of the rock bridges and incipient vein rotation indicate that veining occurred near the brittle-ductile transition. Using a quantitative analysis of bridge orientations, vein aspect ratios and tip lines, we try to sort out if a dominant σ2 propagation direction, typical for hydrofractures, exists within the vein network. By doing so, we can evaluate whether the subhorizontal vein network formed under a compressive stress regime, or was mainly dictated by the strength anisotropy of the rocks under near-isotropic stress conditions of σhmax ≡ σhmin. The regional dominance of subhorizontal aplites, pegmatites and hydrothermal veins, exploiting subhorizontal fracture networks, occurs over a wide area of more than 100 km2 along the Serra de Estrela granitic massif (Derré et al., 1986). This orientation contrasts with the more common vertical attitude of granite-related hydrothermal veins, observed throughout the Iberian massif. A detailed orientation analysis of the fracture sets should allow to explore the possible causes of this particular late orogenic, flat-lying fracture network related to the granitic intrusion. References Derré, C., Lecolle, M., Roger, G., Tavares de Freitas Carvalho, J., 1986. Tectonics, magmatism, hydrothermalism and sets of flat joints locally filled by Sn-W, aplite-pegmatite and quartz veins, southeastern border of the Serra de Estrela granitic massif (Beira Baixa, Portugal). Ore Geology Reviews 1, 43-56. Foxford, K. A., Nicholson, R., Polya, D. A., and Hebblethwaite, R. P. B., 2000. Extensional failure and hydraulic valving at Minas da Panasqueira, Portugal; evidence from vein spatial distributions, displacements and geometries. Journal of Structural Geology 22, 1065-1086.

Geotectonic setting of the Suwałki Anorthosite Massif (NE-Poland) - constraints for 3D geological modelling

NASA Astrophysics Data System (ADS)

Wiszniewska, Janina; Petecki, Zdzislaw; Rosowiecka, Olga; Krzemińska, Ewa

2017-04-01

Suwałki Anorthosite Massif (SAM) is located within 200 km long Mesoproterozoic magmatic terrane called Mazury Complex (NE Poland) (Wiszniewska et al. 2002). This is a belt of granitoids and associated mafic and intermediate igneous rocks followed an E-W trending lineament extending from the Baltic Sea through northern Poland and southern Lithuania to western Belarus. Crystalline basement of the Suwałki region is covered by a thick pile (550-1300m) of Phanerozoic sedimentary rocks, which are dipping towards the SW East European Craton`s border. SAM is a complex structure composed primarily of magmatic massif type anorthosites, surrounded by a rim of norite-gabbronorite and diorite rocks. SAM is characterized by magnetic and gravimetric negative anomalies. The gravimetric one is related to anorthosite massif. It is surrounded by a few positive anomalies, which reflect occurrences of denser rocks such as granite, monzodiorite and granodiorite. The large magnetic anomaly is supposed to reflect an effect of an negative inclination of remanent magnetization of anorthosite rocks. This hypothesis was confirmed by magnetic modelling along DSS POLONAISE'97 profile P4 (Petecki, 2006). Existing measurements however do not show prevailing negative inclinations, even though they prove very high remanent magnetization of anorthosites. A pronounced residual magnetic anomalies of Udryń and Krzemianka are related to Fe-Ti-(V) ore deposits recognized by deep boreholes. Based on potential field data it was suggested that anorthosite bottom reaches 2,5-4,5 km depth. Thus it is evident that the geological architecture of SAM and its surrounding area is not fully recognized. The problem is supposed to be resolved using modern methods of geophysical transformations and 3D modelling using GeoModeller software. The final result of the research will be to recognize spatial structure of the SAM and its surrounding. Petrological, mineralogical, geochronological (U-Pb SHRIMP method on zircons and titanite) and tectonic testing from SAM were carried out. Structural analysis were also performed on a basis of the identified tectonic structures on selected cores. Recognition of possible connections of tectonic structures with magmatic processes and pegmatite, aplite, quartz veins including their mineral composition have been checked. For pegmatite, aplite, hydrothermal and quartz veins age determinations, U-Pb SHRIMP IIe method on zircon, monazite and titanite have been done. The primary age measurements of zircons from microgranite veins within anorthosite have shown consistent Paleoproterozoic ages of protolith ( 1844±11 Ma for Krzemianka 73) with Mezoproterozoic ages ( 1.5 Ga) of metamorphic rims, similar to monazite ages ( 1469±16 Ma). The microgranite veins are probably derived from the older Paleoproterozoic crust, carrying a relic zircons of 1.84 Ga ages but also some inherited older ages as 2.0 to 2.3 Ga. The future planned works will concern the genesis and evolution of igneous AMCG rocks suite and related ore mineralization of the SAM. Petecki Z., 2006: Integrated gravity and magnetic modelling along P4 seismic profile (in Polish). Pr. Państw. Inst. Geol. CLXI., 193p. Wiszniewska J., Claesson S., Stein H., Vander Auwera J., Duchense J-C., 2002: The north-eastern Polish anorthosite massifs: petrological, geochemical and isotopic evidence for a crustal derivation. Terra Nova 14, p.451-460 This is a contribution to the project " Determination of architecture and geological evolution of the Suwałki Anothosite Massif by 3D geological and geophysical data modelling method" NCN grant 51.2115.1601.09.0

Mineralogical and geochemical characteristics of BERYL (AQUAMARINE) from the Erongo Volcanic Complex, Namibia

NASA Astrophysics Data System (ADS)

Lum, Jullieta Enone; Viljoen, Fanus; Cairncross, Bruce; Frei, Dirk

2016-12-01

The granite hosted pegmatites of the Erongo Volcanic Complex in central Namibia are well known for the wide variety of minerals present, of considerable interest to mineral collectors. These include (amongst others) often spectacular, museum quality examples of beryl, schorl, jeremejevite, fluorite, quartz, goethite and cassiterite. The locality is particularly recognized for hosting a variety of beryl types, including green, yellow (heliodor), colorless (goshenite) and blue/greenish blue (aquamarine) variants. Comprehensive geochemical studies of the Erongo beryls are very limited. The present contribution serves to document the visual characteristics (colour, colour zoning, inclusion content) as well as the major and trace element chemistry of 42 blue, two green and one colorless beryl from Erongo, and to compare these with other localities worldwide. The beryls from Erongo are generally subhedral to euhedral with a well-formed prismatic habit. Idiomorphic crystals, characterised by strong hexagonal prisms, are common. Beryl is commonly associated with schorl, quartz, muscovite, alkali feldspar, plagioclase feldspar, iron oxides, foitite, rossmanite and cassiterite. Aquamarines range from pale blue to deep blue or greenish blue, with marked colour zoning seen in a number of samples. One of the two green beryls examined is of a medium green colour, and is heavily included, while the other specimen has a pale yellowish green colour. The goshenite sample is colourless, clear, and transparent. Numerous cracks are present in the samples examined, and these are usually filled by iron oxides. Inclusions species encountered in the beryl samples are schorl, quartz, muscovite, feldspar, iron oxides and cassiterite, clearly reflective of the host pegmatite mineralogy. Aquamarine and green beryl contain iron as the main chromophore while goshenite is devoid of chromophores. Fe contents in beryl increase with colour intensity, consistent with the known chromatic effects of Fe in blue, yellow and green beryl. Consistently low Cr contents in all studied beryls do not concur with Cr being a chromophore element for green beryl. Marked compositional zoning is present, with variable Fe (0.79-3.19 wt% FeOT), Na (0.09-0.35 wt% Na2O), Al (15.99-18.18 wt% Al2O3) in aquamarine. Zoning patterns range from simple core-to-rim transitions, to more complex sector and/or oscillatory zoning. Trace element contents vary amongst the beryl types examined, with the highest contents and most extreme variations observed in the aquamarines. This is probably partly due to sampling bias relating to the size of the sample set examined. Octahedral cation substitution is dominant, with Na incorporated (over Cs) at the channels, in order to maintain charge balance. Inferences based on charge balance arguments suggest that tetrahedral Be-Li substitution in these beryls may also be present. Cs, Sc, Ga and Mn are positively correlated with Rb, consistent with the incorporation of these elements at the octahedral site (Sc, Mn and minor Ga) or the channel site (Cs, Rb), in order to preserve charge balance. In contrast, Ca, Zn and Ti do not correlate with Rb, nor with Cs. This is unexpected, as Ti and Ca are known to substitute at the octahedral site in beryl, while Ca may also enter the 2a channel site of beryl. The major and trace element chemistry of the beryls are generally similar to other worldwide beryl deposits of similar colour and do not serve to distinguish beryls from Erongo.

Meurigite, a new fibrous iron phosphate resembling kidwellite

USGS Publications Warehouse

Birch, W.D.; Pring, A.; Self, P.G.; Gibbs, R.B.; Keck, E.; Jensen, M.C.; Foord, E.E.

1996-01-01

Meurigite is a new hydrated potassium iron phosphate related to kidwellite and with structural similarities to other late-stage fibrous ferric phosphate species. It has been found at four localities so far - the Santa Rita mine, New Mexico, U.S.A.; the Hagendorf-Sud pegmatite in Bavaria, Germany; granite pegmatite veins at Wycheproof, Victoria. Australia; and at the Gold Quarry Mine, Nevada, U.S.A. The Santa Rita mine is the designated type locality. Meurigite occurs as tabular, elongated crystals forming spherical and hemispherical clusters and drusy coatings. The colour ranges from creamy white to pale yellow and yellowish brown. At the type locality, the hemispheres may reach 2 mm across, but the maximum diameter reached in the other occurrences is usually less than 0.5 mm. A wide variety of secondary phosphate minerals accompanies meurigite at each locality, with dufrenite, cyrilovite. beraunite, rockbridgeite and leucophosphite amongst the most common. Vanadates and uranates occur with meurigite at the Gold Quarry mine. Electron microprobe analysis and separate determination of H2O and CO2 on meurigite from the type locality gave a composition for which several empirical formulae could be calculated. The preferred formula, obtained on the basis of 35 oxygen atoms, is (K0.85Na0.03)??0.88(Fe7.013+Al0.16Cu0.02)??7.19 (PO4)5.11(CO3)0.20(OH) 6.7??7-7.25H2O, which simplifies to KFe73+(PO4)5(OH) 7??8H2O. Qualitative analyses only were obtained for meurigite from the other localities, due to the softness and openness of the aggregates. Because of the fibrous nature of meurigite, it was not possible to determine the crystal structure, hence the exact stoichiometry remains uncertain. The lustre of meurigite varies from vitreous to waxy for the Santa Rita mine mineral, to silky for the more open sprays and internal surfaces elsewhere. The streak is very pale yellow to cream and the estimated Mohs hardness is about 3. Cleavage is perfect on {001] and fragments from the type material have a mean specific gravity of 2.96. The strongest lines in the X-ray powder pattern for the type material are (dobs,Iobs,hkl) 3.216(100)404; 4.84(90)111; 3.116(80)205; 4.32(70)112; 9.41(60)201; 3.470(60)800. The X-ray data were indexed on the basis of a monoclinic unit cell determined from electron diffraction patterns. The cell parameters, refined by least squares methods, are a = 29.52(4), b = 5.249(6), c = 18.26(1) A??, ?? = 109.27(7)??, V = 2672(3) A??3, and Z = 4. The calculated density is 2.89 gcm-3. The space group is either C2, Cm or C2/m. X-ray powder data for meurigite are closely similar to those for kidwellite and phosphofibrite, but meurigite appears to be characterised by a strong 14 A?? reflection. The relationship between these three minerals remains uncertain in the absence of structural data. On the available evidence, meurigite and kidwellite are not the respective K and Na-endmembers of a solid solution series. The meurigite cell parameters suggest it belongs to a structural family of fibrous ferric phosphates, such as rockbridgeite, dufrenite and beraunite, which have a discrete 5 A?? fibre axis. Meurigite occurs in widely varying environments, its formation probably favoured by late-stage solutions rich in K rather than Na.

Petrology and geochemistry of the orbicular granitoid of Caldera, northern Chile. Models and hypotheses on the formation of radial orbicular textures

NASA Astrophysics Data System (ADS)

Díaz-Alvarado, Juan; Rodríguez, Natalia; Rodríguez, Carmen; Fernández, Carlos; Constanzo, Ítalo

2017-07-01

The orbicular granitoid of Caldera, located at the northern part of the Chilean Coastal Range, is a spectacular example of radial textures in orbicular structures. The orbicular body crops out as a 375 m2 tabular to lensoidal intrusive sheet emplaced in the Lower Jurassic Relincho pluton. The orbicular structures are 3-7 cm in diameter ellipsoids hosted in a porphyritic matrix. The orbicules are comprised by a Qtz-dioritic core (3-5 cm in diameter) composed by Pl + Hbl + Qtz + Bt ± Kfs with equiaxial textures and a gabbroic shell (2-3 cm in diameter) characterized by feathery and radiate textures with a plagioclase + hornblende paragenesis. The radial shell crystals are rooted and orthogonally disposed in the irregular contact with the core. The radial shell, called here inner shell, is in contact with the granodioritic equiaxial interorbicular matrix through a 2-3 mm wide poikilitic band around the orbicule (outer shell). The outer shell and the matrix surrounding the orbicules are characterized by the presence of large hornblende and biotite oikocrystals that include fine-grained rounded plagioclase and magnetite. The oikocrystals of both the outer shell and the matrix have a circumferential arrangement around the orbicule, i.e. orthogonal to the radial inner shell. The coarse-grained granodioritic interorbicular matrix present pegmatitic domains with large acicular hornblende and K-feldspar megacrysts. This work presents a review of the textural characteristics of the orbicules and a complete new mineral and whole-rock geochemical study of the different parts of the orbicular granitoid, together with thermobarometric and crystallographic data, and theoretical modeling of the crystallization and element partitioning processes. We propose a model for the formation of the orbicular radial textures consisting of several processes that are suggested to occur fast and consecutively: superheating, volatile exsolution, undercooling, geochemical fractionation and columnar and equiaxial crystallization. According to the obtained results, the formation of the orbicular granitoid of Caldera may have initiated 1) during the generation of a magmatic fracture in the crystallization front of the Relincho pluton, where the water released by the host crystal mush was dissolved in the new batch of dioritic magma. 2) The high influx of water-rich liquids induced superheating conditions in the newly intruding magma that became a depolymerized liquid, where the only solid particules were the small irregular fragments of the host mush dragged from the fracture walls. 3) Volatile exsolution promoted crystallization under undercooling conditions. 4) Undercooling and nucleation around the core (cold germs) involved the physical and geochemical fractionation between two sub-systems: a gabbroic sub-system that comprises the solid paragénesis with a residual water-rich liquid and a granodioritic sub-system. 5) The orbicules, including core and inner shell, behaved as viscous bodies (crystals + residual liquid) floating in the granodioritic magma. 6) Higher undercooling rates occurred at the starting stage, close to the liquidus, promoting columnar crystallization around the cores and formation of the shells. Conversely, in the granodioritic matrix sub-system, equiaxial crystallization was promoted by low relative crystallization rates. 7) The rest of the crystallization process evolved later in the outer shell and the matrix, as suggested by the poikilitic textures observed in both sides of the orbicule contact, and under conditions close to the solidus of both sub-systems (shell and matrix). The water-rich residual liquid expelled during the orbicular shell crystallization was mingled with the partially crystallized matrix magma, generating the pegmatitic domains with large Kfs megacrysts.

Empirical analysis of electromagnetic profiles for groundwater prospecting in rural areas of Ibadan, southwestern Nigeria

NASA Astrophysics Data System (ADS)

Ehinola, O. A.; Opoola, A. O.; Adesokan, H. A.

2006-04-01

The Slingram electromagnetic (EM) survey using a coil separation of 60 and 100 m was carried out in ten villages in the Akinyele area of Ibadan, southwestern Nigeria to aid in the development of groundwater. Five main rock types including an undifferentiated gneiss complex (Su), biotite-garnet schist/gneiss (Bs), quartzite and quartz schist (Q), migmatized undifferentiated biotite/hornblende gneiss (M) and pegmatite/quartz vein (P) underlie the study area. A total of 31 EM profiles was made to accurately locate prospective borehole sites in the field. Four main groups with different behavioural patterns were categorized from the EM profiles. Group 1 is characterized by a high density of positive (HDP) or a high density of negative (HDN) real and imaginary curves, Group 2 by parallel real and imaginary curves intersecting with negligible amplitude (PNA), Group 3 by frequent intersection of a high density of negative minima (FHN) real and imaginary curves, and Group 4 by separate and approximately parallel (SAP) real and imaginary curves. Qualitative pictures of the overburden thickness and the extent of fracturing have been proposed from these behavioural patterns. A comparison of the borehole yield with the overburden thickness and the level of fracturing shows that the borehole yield depends more on the fracture density than on the overburden thickness. The asymmetry of the anomaly was also found to be useful in the determination of the inclination of the conductor/fracture.

Paralavas in the Cretaceous Paraná volcanic province, Brazil - A genetic interpretation of the volcanic rocks containing phenocrysts and glass.

PubMed

Baggio, Sérgio B; Hartmann, Léo A; Bello, Rosa M S

2016-01-01

The occurrences of glassy rocks containing long and curved phenocrysts in the Paraná volcanic province, South America, are here interpreted as paralavas. The large number of thin (0.1-0.5 m) dikes and sills of glassy volcanic rocks with hopper, hollow or curved, large crystals of clinopyroxene (up to 10 cm), plagioclase (up to 1 cm), magnetite and apatite are contained in the core of thick (>70 m) pahoehoe flows. They are strongly concentrated in the state of Paraná, coincident with the presence of the large number of dikes in the Ponta Grossa arch. These rocks were previously defined as pegmatites, although other names have also been used. A paralava is here interpreted as the product of melting of basaltic rocks following varied, successive processes of sill emplacement in high-kerogen bituminous shale and ascent of the resultant methane. As the gas reached the lower portion of the most recent lava flow of the volcanic pile, the methane reacted with the silicate and oxide minerals of the host volcanic rock (1,000 ºC) and thus elevated the local temperature to 1,600 ºC. The affected area of host rock remelted (possibly 75 wt.%) and injected buoyantly the central and upper portion of the core. This methane-related mechanism explains the evidence found in the paralavas from this volcanic province, one of the largest in the continents.

A Two-Phase Intergrowth in Genthelvite from Mont Saint-Hilaire, Quebec

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antao, Sytle M.; Hassan, Ishmael; West Indies)

Synchrotron high-resolution powder X-ray-diffraction (HRPXRD) data and Rietveld structure refinement were used to examine a two-phase intergrowth of genthelvite, ideally Zn{sub 8}[Be{sub 6}Si{sub 6}O{sub 24}]S{sub 2}, from the alkaline intrusive complex at Mont Saint-Hilaire, Quebec, where genthelvite occurs in nepheline syenite pegmatites. The structural parameters obtained for the two phases are slightly different from each other. The unit-cell parameters are 8.119190(7) {angstrom} (51% phase 1) and 8.128914(9) {angstrom} (49% phase 2). The refinement gives the chemical formulae and interstitial M cation in terms of Zn and Mn (the Fe content is practically zero) for the Mn-poor genthelvite phase 1 asmore » (Zn{sub 7.8}Mn{sub 0.2}){Sigma}{sub 8}[Be{sub 6}Si{sub 6}O{sub 24}]S{sub 2}, and the Mn-rich genthelvite phase 2 as (Zn{sub 7.0}Mn{sub 1.0}){Sigma}{sub 8}[Be{sub 6}Si{sub 6}O{sub 24}]S{sub 2}. These formulae are comparable to the Mn-poor and Mn-rich phases obtained by electron-microprobe analysis. The intergrowth indicates that diffusion is absent among the interstitial M cations of similar size (Zn{sup 2+}, Fe{sup 2+} and Mn{sup 2+}). Such intergrowths may form under distinct f(O{sub 2}) conditions and probably low temperature of crystallization that inhibits diffusion of M cations.« less

Rb-Sr geochronology of the region between the Antarctic Peninsula and the Transantarctic Mountains: Haag nunataks and Mesozoic granitoids

NASA Astrophysics Data System (ADS)

Millar, I. L.; Pankhurst, R. J.

Seventy-two new Rb-Sr whole-rock analyses are reported for Haag Nunataks, Mount Woollard, the Whitmore Mountains, the Pirrit and Nash hills, and Pagano Nunatak. For Haag Nunataks, three isochrons for gneisses and later aplogranite and microgranite sheets establish the age of crustal formation as 1000-1100 Ma. No other basement rocks of this age are known from the Antarctic Peninsula or Ellsworth Land. Results from the migmatite-pegmatite complex at Mount Woollard are inconclusive but do not suggest that this represents Precambrian crystalline basement. Provisional results for the Whitmore Mountains granites are compatible with crystallization of all components within error of a 182±5 Ma isochron for fine-grained microgranite, but variation in initial 87Sr/86Sr from 0.707 for porphyritic granites to 0.722 for the microgranite rule out simple crystal fractionation models which require a common parental magma. The granites of the Ellsworth-Thiel mountains ridge are well dated as Middle Jurassic by the new data: Pirrit Hills 173±3 Ma, Nash Hills 175±8 Ma, and Pagano Nunatak 175±8 Ma. Initial 87Sr/86Sr ratios of 0.707, 0.712, and 0.716, respectively, confirm that these are intracratonic S-type granites with a large crustal component involved in magma generation. The dolerite of Lewis Nunatak is shown by its Rb, Sr, and 87Sr/86Sr composition to be a member of the Jurassic Ferrar Supergroup.

Crystal structure of tveitite-(Y): Fractionation of rare-earth elements between positions and the variety of defects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yakubovich, O. V.; Massa, W.; Pekov, I. V.

2007-02-15

The crystal structure of the mineral tveitite-(Y) (Y{sub 0.883}Na{sub 0.106}) (Ca{sub 0.841}LREE{sub 0.159})(Ca{sub 0.716}Na{sub 0.204}HREE{sub 0.080})(Ca{sub 0.0=} 9{sub 2}Na{sub 0.074})F{sub 6.952} from amazonite pegmatites of Rov-Gora Mountain (Keivy, Kola Peninsula) is determined using X-ray diffraction (Stoe IPDS diffractometer, {lambda}MoK{sub {alpha}}, graphite monochromator, 2{theta}{sub max} = 63.5{sup o}, R = 0.051 for 1542 reflections). The main crystal data are as follows: a = 17.020(2) A, c = 9.679(2) A, V = 2428.2(4) A{sup 3}, space group R3-bar, Z = 18, and {rho}{sub calcd} = 4.00 g/cm{sup 3}. The idealized structural formula of the mineral is represented as (Y,Na){sub 6}(Ca,LREE){sub 6}(Ca,Na,HREE){sub 6}(Ca,Na)F{submore » 42} (Z = 3). The defect structure of the mineral manifests itself in a mixed occupation of all four independent cation positions and in a randomly disordered distribution of fluorine atoms over the majority of anion positions. It is shown that the crystal structure of tveitite-(Y) fulfills the function of an 'Eratosthenes sieve' for yttrium cations and two groups of lanthanide cations, so that these cations are distributed over three different positions.« less

Jinshanjiangite and bafertisite from the Gremyakha-Vyrmes Alkaline Complex, Kola Peninsula

NASA Astrophysics Data System (ADS)

Lykova, I. S.; Pekov, I. V.; Kononkova, N. N.; Shpachenko, A. K.

2010-12-01

Jinshanjiangite (acicular crystals up to 2 mm in length) and bafertisite (lamellar crystals up to 3 × 4 mm in size) have been found in alkali granite pegmatite of the Gremyakha-Vyrmes Complex, Kola Peninsula. Albite, microcline, quartz, arfvedsonite, zircon, and apatite are associated minerals. The dimensions of a monoclinic unit cell of jinshanjiangite and bafertisite are: a = 10.72(2), b=13.80(2), c = 20.94(6) Å, β = 97.0(5)° and a = 10.654(6), b = 13.724(6), c = 10.863(8) Å, β = 94.47(8)°, respectively. The typical compositions (electron microprobe data) of jinshanjiangite and bafertisite are: (Na0.57Ca0.44)Σ1.01(Ba0.57K0.44)Σ1.01 (Fe3.53Mn0.30Mg0.04Zn0.01)Σ3.88(Ti1.97Nb0.06Zr0.01)Σ2.04(Si3.97Al0.03O14)O2.00(OH2.25F0.73O0.02)Σ3.00 and (Ba1.98Na0.04K0.03)Σ2.05(Fe3.43Mn0.37Mg0.03)Σ3.83(Ti2.02Nb0.03)Σ2.05 (Si3.92Al0.08O14)(O1.84OH0.16)Σ2.00(OH2.39F1.61)Σ3.00, respectively. The minerals studied are the Fe-richest members of the bafertisite structural family.

Pressure-temperature-fluid constraints for the Emmaville-Torrington emerald deposit, New South Wales, Australia: Fluid inclusion and stable isotope studies

NASA Astrophysics Data System (ADS)

Loughrey, Lara; Marshall, Dan; Jones, Peter; Millsteed, Paul; Main, Arthur

2012-06-01

The Emmaville-Torrington emeralds were first discovered in 1890 in quartz veins hosted within a Permian metasedimentary sequence, consisting of meta-siltstones, slates and quartzites intruded by pegmatite and aplite veins from the Moule Granite. The emerald deposit genesis is consistent with a typical granite-related emerald vein system. Emeralds from these veins display colour zonation alternating between emerald and clear beryl. Two fluid inclusion types are identified: three-phase (brine+vapour+halite) and two-phase (vapour+liquid) fluid inclusions. Fluid inclusion studies indicate the emeralds were precipitated from saline fluids ranging from approximately 33 mass percent NaCl equivalent. Formational pressures and temperatures of 350 to 400 °C and approximately 150 to 250 bars were derived from fluid inclusion and petrographic studies that also indicate emerald and beryl precipitation respectively from the liquid and vapour portions of a two-phase (boiling) system. The distinct colour zonations observed in the emerald from these deposits is the first recorded emerald locality which shows evidence of colour variation as a function of boiling. The primary three-phase and primary two-phase FITs are consistent with alternating chromium-rich `striped' colour banding. Alternating emerald zones with colourless beryl are due to chromium and vanadium partitioning in the liquid portion of the boiling system. The chemical variations observed at Emmaville-Torrington are similar to other colour zoned emeralds from other localities worldwide likely precipitated from a boiling system as well.

Multiple Generations of Boudinage in a P-T Path: Insights from 3D Analysis of Amphibolite Boudins in Marble on Naxos, Greece

NASA Astrophysics Data System (ADS)

von Hagke, C.; Virgo, S.; Urai, J. L.

2016-12-01

Boudins are periodic structures in mechanically layered rocks deformed by layer parallel extension. At first sight, 2D sections of boudinaged layers are similar although 3D boudin patterns can be dramatically different. We aim to develop criteria to infer 3D strain from 2D outcrop observation of boudins. In marble quarries in the high grade complex on Naxos, Greece, we studied spectacular outcrops of amphibolite and pegmatite boudins, in combination with serial slicing of quarried blocks to reconstruct the 3D boudin structures. We identified multiple boudin generations, with early, high grade pinch and swell boudins followed by two generations of brittle shearband and torn boudins formed along the retrograde path under greenschist facies conditions. This shows how the rheological contract between marble and amphibolite changes from amphibolite to greenschist facies and suggests E-W shortening and N-S stretching in the footwall of the Naxos detachment. The later phases of boudinage interact with existing boudin geometries, producing complex structures in 3D. In 2D section the complexity is not directly apparent and reveals itself only in statistical analysis of long continuous sections. Our findings highlight the importance of 3D characterization of boudinage structures for boudin classification. The insights we gain from the analysis of multiphase boudinage structures on Naxos are the basis for quantitative boudin analysis to infer rheology, effective stress, vorticity and strain and establish a mechanics-based boudin classification scheme.

Characteristics of zircon suitable for REE extraction

NASA Astrophysics Data System (ADS)

Watanabe, Y.; Hoshino, M.

2011-12-01

Zircons (ZrSiO4) from Naegi and Ohro granitic pegmatites, Japan and from Saigon alkaline basalt, Vietnam, were mineralogically characterized by inductively couples plasma mass spectrometry (ICP-MS), electron-microprobe analysis (EMPA), X-ray powder diffraction, micro-Raman spectroscopy and leaching experiment. The powder XRD and Raman spectra analyses show that the degree of crystallinity decreases from Saigon, to Ohro and Naegi zircons. Quantitative analytical results by the EMPA indicate that the Naegi and Ohro zircon samples contain a large amount of REE2O3, while REE contents in Saigon zircon are below detection limit. The leaching experiments for the present zircons under the condition of a solvent 1M-HCl, at a room temperature to 250 °C and retention time of 30h resulted in about 100 %, 50 % and 1 % recoveries of REE from the Naegi, Ohro and Saigon zircons, respectively. Leaching experiments for the Naegi zircon under the condition of a solvent 1N-HCl, heating temperature of 50 °C, 100 °C, 150 °C and 200 °C, and retention time 30h, showed that a significant amount of REE was leached out at a temperature above 150 °C. However, the leaching experiments of the Naegi and Ohro zircons at room temperature (about 25 °C) show that REE were hard to be leached. These results indicates that both low crystallinity of zircon and higher leaching temperature are requisite for effective leaching of REE from zircon.

Anisotropic surface chemistry properties and adsorption behavior of silicate mineral crystals.

PubMed

Xu, Longhua; Tian, Jia; Wu, Houqin; Fang, Shuai; Lu, Zhongyuan; Ma, Caifeng; Sun, Wei; Hu, Yuehua

2018-03-07

Anisotropic surface properties of minerals play an important role in a variety of fields. With a focus on the two most intensively investigated silicate minerals (i.e., phyllosilicate minerals and pegmatite aluminosilicate minerals), this review highlights the research on their anisotropic surface properties based on their crystal structures. Four surface features comprise the anisotropic surface chemistry of minerals: broken bonds, energy, wettability, and charge. Analysis of surface broken bond and energy anisotropy helps to explain the cleavage and growth properties of mineral crystals, and understanding surface wettability and charge anisotropy is critical to the analysis of minerals' solution behavior, such as their flotation performance and rheological properties. In a specific reaction, the anisotropic surface properties of minerals are reflected in the adsorption strengths of reagents on different mineral surfaces. Combined with the knowledge of mineral crushing and grinding, a thorough understanding of the anisotropic surface chemistry properties and the anisotropic adsorption behavior of minerals will lead to the development of effective relational models comprising their crystal structure, surface chemistry properties, and targeted reagent adsorption. Overall, such a comprehensive approach is expected to firmly establish the connection between selective cleavage of mineral crystals for desired surfaces and designing novel reagents selectively adsorbed on the mineral surfaces. As tools to characterize the anisotropic surface chemistry properties of minerals, DLVO theory, atomic force microscopy (AFM), and molecular dynamics (MD) simulations are also reviewed. Copyright © 2017 Elsevier B.V. All rights reserved.

Airborne imaging spectrometer data of the Ruby Mountains, Montana: Mineral discrimination using relative absorption band-depth images

USGS Publications Warehouse

Crowley, J.K.; Brickey, D.W.; Rowan, L.C.

1989-01-01

Airborne imaging spectrometer data collected in the near-infrared (1.2-2.4 ??m) wavelength range were used to study the spectral expression of metamorphic minerals and rocks in the Ruby Mountains of southwestern Montana. The data were analyzed by using a new data enhancement procedure-the construction of relative absorption band-depth (RBD) images. RBD images, like bandratio images, are designed to detect diagnostic mineral absorption features, while minimizing reflectance variations related to topographic slope and albedo differences. To produce an RBD image, several data channels near an absorption band shoulder are summed and then divided by the sum of several channels located near the band minimum. RBD images are both highly specific and sensitive to the presence of particular mineral absorption features. Further, the technique does not distort or subdue spectral features as sometimes occurs when using other data normalization methods. By using RBD images, a number of rock and soil units were distinguished in the Ruby Mountains including weathered quartz - feldspar pegmatites, marbles of several compositions, and soils developed over poorly exposed mica schists. The RBD technique is especially well suited for detecting weak near-infrared spectral features produced by soils, which may permit improved mapping of subtle lithologic and structural details in semiarid terrains. The observation of soils rich in talc, an important industrial commodity in the study area, also indicates that RBD images may be useful for mineral exploration. ?? 1989.

Rb-Sr, Sm-Nd, and U-Pb geochronology of the rocks within the Khlong Marui shear zone, southern Thailand

NASA Astrophysics Data System (ADS)

Kanjanapayont, Pitsanupong; Klötzli, Urs; Thöni, Martin; Grasemann, Bernhard; Edwards, Michael A.

2012-08-01

In southern Thailand, the Khlong Marui shear zone is dominated by a NNE-SSW striking high topographic lozenge shaped area of ca. 40 km long and 6 km wide between the Khlong Marui Fault and the Bang Kram Fault. The geology within this strike-slip zone consists of strongly deformed layers of mylonitic meta-sedimentary rocks associated with orthogneisses, mylonitic granites, and pegmatitic veins with a steeply dipping foliation. The strike-slip deformation is characterized by dextral ductile deformation under amphibolite facies and low to medium greenschist facies. In situ U-Pb ages of inherited zircon cores from all zircons in the Khlong Marui shear zone indicate that they have the same material from the Archean. Late Triassic to Late Cretaceous ages obtained for zircon outer cores of the mylonitic granite are probably related to a period of magmatic activity that was significantly influenced by the West Burma and Shan-Thai collision and the subduction along the Sunda Trench. The early dextral ductile deformation phase of the Khlong Marui shear zone in the Early Eocene suggested by U-Pb ages of zircon rims, and the later dextral transpressional deformation in the Late Eocene indicated by mica Rb-Sr ages. Rb-Sr, Sm-Nd, and U-Pb dating correlation implies that the major exhumation period of the ductile lens was in the Eocene. This period was tectonically influenced in the SE Asia region by the early India-Asia collision.

Taeniolite, an uncommon lithium-mica from Coyote Peak, Humboldt County, California.

USGS Publications Warehouse

Erd, Richard C.; Czamanske, G.K.; Meyer, C.E.

1983-01-01

Taeniolite has been found in a late pegmatitic clot in a mafic alkalic diatreme at Coyote Peak; associated species are natrolite, pectolite, aegirine, barytolamprophyllite, rasvumite and sphalerite. The taeniolite is green-brown with sp. gr. (meas.) 2.85(1) and H. 31/2. Optically it is biaxial (-) with alpha 1.541(2), beta = gamma 1.570(2), 2V approx 0o and moderate pleochroism with gamma = beta reddish-brown, alpha pale greenish brown. Single-crystal precession photographs show it to be of the 1M type, with a 5.254(2), b 9.110(4), c 10.187(2) A, beta 99.85(4)o and V = 480.4(1) A3. Combined microprobe and ion probe analyses gave SiO2 53.5, Al2O3 3.00, TiO2 1.06, FeO 3.35, MnO 0.21, MgO 18.3, Li2O 2.4, K2O 11.3, Na2O 0.27, F 6.3 = 99.69; SrO and BaO are both <0.04 wt.%; B, Be, Ca and Cl were not detected. Assuming (F + OH) = 2 and assigning 1.30 wt.% H2O gives 409(K1.01Na0.04)(Al0.01Ti0.06Fe2+0.20Mn0.01Mg1.92Li0.68)(Si3.76Al0.24)O10- (F1.40OH0.60).-G.W.R.

Niobium (columbium) and tantalum resources of Brazil

USGS Publications Warehouse

White, Max Gregg

1975-01-01

Most of the niobium resources of Brazil occur as pyrochlore in carbonatites within syenitic intrusives of Late Cretaceous to early Tertiary age in western Minas Gerais and southeastern Goils. Minor amounts of it are produced together with tantalum from columbite-tantalite concentrates from pegmatites and placers adjacent to them, in the Sao Joao del Rei district in south-central Minas Gerais. All the niobium and tantalum produced in Brazil is exported. The only pyrochlore mined is from the Barreiro carbonatite deposit near Araxa in Minas Gerais where concentrates and ferroniobium are produced. Exploration work for pyrochlore and other mineral resources are being undertaken on other carbonatites, particularly at Catalao I in southeast Goias and at Tapira and Serra Negra in western Minas Gerais. Annual production and export from the Barreiro deposit are about 8,000 metric tons of pyrochlore concentrate containing about 60 percent Nb205 and about 2,700 metric tons of ferroniobium with 63 percent Nb2O5. The annual production capacity of the Barreiro plant is 18,000 tons of concentrate and 4,000 tons of ferroniobium. Ore reserves of the Barreiro deposit in all categories are 380 million tons with percent Nb2O5. Annual production of tantalite-columbite from the Sao Joao del Rei district, most of which is exported to the United States, is about 290 tons, of which about 79 percent is tantalite and about percent is columbite. Reserves of tantalite-columbite in the Sao Joao del Rei district are about 43,000 tons of proved and 73,000 tons of probable ore.

Preliminary report on uranium and thorium content of intrusive rocks in northeastern Washington and northern Idaho

DOE Office of Scientific and Technical Information (OSTI.GOV)

Castor, S.B.; Berry, M.R.; Robins, J.W.

1977-11-01

This study delineates favorable areas for uranium resources in northeastern Washington and northern Idaho by identifying granitic rocks with relatively large amounts of uranium and (or) thorium. Results are based on analysis of 344 rock samples. Uranium analyses obtained by gamma-ray spectrometric data correlate closely with fluorometric determinations. On the basis of cumulative frequency distribution curves, more than 8 ppM equivalent uranium and more than 20 ppM equivalent thorium are considered anomalous for granitic rocks in northeastern Washington and northern Idaho. Granitic rocks anomalously high in uranium and (or) thorium are concentrated in two northeast-trending belts. The most prominent, themore » Midnite-Hall Mountain belt, includes the Midnite and Sherwood uranium mines, and two lesser but productive areas farther north. This belt follows the contact between Precambrian and Paleozoic rocks, which is also the locus of the Kootenai arc fold belt. The second belt of anomalously radioactive granitic rocks is along the Republic graben, a prominent linear structure in an area with no recorded uranium production. Anomalously radioactive granitic rocks are generally massive quartz monzonite, alaskite, or pegmatite, which contain abundant quartz and potash feldspar. They are also characterized by pink potash feldspar, commonly as large phenocrysts, and by the presence of muscovite. Several uranium and thorium minerals have been identified in these rocks. The two belts of anomalously radioactive plutons are considered favorable for uranium resources. Deposits could occur in the intrusive rocks themselves or in favorable environments in adjacent rocks. 13 figs., 2 tables.« less

The Ackley City Batholith, southeastern Newfoundland: Evidence for crystal versus liquid-state fractionation

NASA Astrophysics Data System (ADS)

Whalen, J. B.

1983-08-01

The 345 ± 10 Ma old composite Ackley City Batholith of southeastern Newfoundland, consists largely of very felsic K-feldspar megacrystic granite and alaskite. Spatially related to the southeast contact of the alaskite are younger aplites and pegmatite, intrusive phases which are interpreted to be pan of a tilted, high level roof zone complex to the batholith. The compositions of the alaskite and roof zone complex define major and trace element gradients similar to those in voluminous high-silica eruptive suites; i.e., the alaskite is more chemically evolved (higher in Rb, lower in Ca, Fe, Mn, Ti, P, Sr, Ba and LREE) toward the roof. Apparently these chemical gradients in the batholith are restricted to the top 2 to 3 kms of the former magma chamber. Fractional crystallization is a plausible process for generating the chemical dispersion in the granites, although very high feldspar partition coefficients for Ba, Sr and Eu are required to generate the observed chemical gradients by a reasonable degree of fractional crystallization. Restriction of crystal fractionation to near the roof of the batholith may reflect a decreased viscosity which would facilitate crystal-liquid separation by processes such as filter pressing, flow differentiation or convective fractionation. The chemical gradients in these granites closely resemble those attributed in high-silica volcanics to the process of thermogravitational diffusion (TGD). Compositional gradients in the upper portion of a magma chamber are consistent with the TGD model. This model, although still poorly understood, is, like fractional crystallization, a plausible mechanism to generate the chemical features of the Ackley City granites.

Significance of the late Archaean granulite facies terrain boundaries, Southern West Greenland

NASA Technical Reports Server (NTRS)

Friend, C. R. L.; Nutman, A. P.; Mcgregor, V. R.

1988-01-01

Three distinct episodes and occurrences of granulite metamorphism in West Greenland are described: (1) the oldest fragmentary granulites occur within the 3.6-Ga Amitsoq gneisses and appear to have formed 200 Ma after the continental crust in which they lie (Spatially associated rapakivi granites have zircon cores as old as 3.8 Ga, but Rb-Sr, whole-rock Pb-Pb, and all other systems give 3.6 Ga, so these granulites apparently represent a later metamorphic event); (2) 3.0-Ga granulites of the Nordlandet Peninsula NW of Godthaab, developed immediately after crustal formation in hot, dry conditions, are carbonate-free, associated with voluminous tonalite, and formed at peak metamorphic conditions of 800 C and 7 to 8 kbar (Synmetamorphic trondhjemite abounds and the activity of H2O has been indicated by Pilar to have varied greatly); and (3) 2.8-Ga granulites south of Godthaab, lie to the south of retrogressed amphibolite terranes. Prograde amphibolite-granulite transitions are clearly preserved only locally at the southern end of this block, near Bjornesund, south of Fiskenaesset. Progressively deeper parts of the crust are exposed from south to north as a major thrust fault is approached. Characteristic big hornblende pegmatites, which outcrop close to the thrust in the east, have been formed by replacement of orthopyroxene. Comparable features were not seen in South Indian granulites. It was concluded that no one mechanism accounts for the origin of all granulites in West Greenland. Various processes have interacted in different ways, and what happened in individual areas must be worked out by considering all possible processes.

Second Projet de Renforcement Institutionnel du Secteur Minier de la République Islamique de Mauritanie (PRISM-II) Phase V

USGS Publications Warehouse

Taylor, Cliff D.

2015-12-30

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Crystal structure and chemistry of lithium-bearing trioctahedral micas-3T

USGS Publications Warehouse

Brigatti, M.F.; Kile, D.E.; Poppi, L.

2003-01-01

Chemical analyses and crystal structure refinements were performed on lithian siderophyllite-3T crystals from granitic pegmatites of the anorogenic Pikes Peak batholith (Colorado) to characterize the crystal chemistry and relations with trioctahedral lithium-bearing micas showing different stacking sequences. Chemical data show that the studied samples fall on the siderophyllite-polylithionite join, closer to the siderophyllite end-member. Single-crystal X-ray refinements were carried out on three samples (two of which were taken from core and rim of the same crystal) in space-group P31 12 (the agreement factor, Robs, varies between 0.034 and 0.036). Mean bond distances and mean electron counts of M1, M2 and M3 octahedral sites indicate an ordered cation distribution with M1 and M3 positions substantially larger than M2. In the sample with the largest iron content, the M2 mean electron count increases as well as the mean distance, whereas remains smaller than or . The tetrahedral cation-oxygen atom mean distances range from 1.614 to 1.638 A and from 1.663 to 1.678 A for T1 and T2 sites, respectively, being consistent with Al3+ enrichment in the T2 sites. The tetrahedral rotation angle, α, is generally small (3.1 ≤ α ≤ 4.6) and decreases with siderophyllite content. As Fe increases, the T1 tetrahedron becomes flatter (112.4 ≤ t1 ≤ 110.5??), whereas T2 tetrahedron distortion appears unchanged (110.7 ≤ T2 ≤ 110.9).

Petrologic Constraints on the Exhumation of the Sierra Blanca Metamorphic Core Complex (AZ)

NASA Astrophysics Data System (ADS)

Koppens, K. M.; Gottardi, R.

2017-12-01

The Sierra Blanca metamorphic core complex (SBMCC), located 90 miles west of Tucson, is part of the southern belt of metamorphic core complexes that stretches across southern Arizona. The SBMCC exposes Jurassic age sedimentary rocks that have been metamorphosed by intruding Late Cretaceous peraluminous granites and pegmatites. Evidence of this magmatic episode includes polysythetic twinning in plagioclase, albite exsolution of potassium feldspar resulting in myrmekitic texture, and garnet, mica and feldspar assemblages. The magmatic fabric is overprinted by a Tertiary (Miocene?) tectonic fabric, associated with the exhumation of the Sierra Blanca metamorphic core along a low-angle detachment fault, forming the SBMCC. The NW-SE elongated dome of metamorphic rocks forms the footwall of the detachment shear zone, and is separated from the hanging wall, composed of Paleozoic and Mesozoic metasedimentary rocks, by a low-angle detachment shear zone. Foliation is defined by gneissic layering and aligned muscovite, and is generally sub-horizontal, defining the dome. The NNW-SSE mineral stretching lineation is expressed by plagioclase and K-feldspar porphyroclasts, and various shear sense indicators are all consistent with a top-to the-NNW shear sense. Lineation trends in a NNW-SSE orientation; however, plunge changes across the domiform shape of the MCC. Much of the deformation is preserved in the blastomylonitic gneiss derived from the peraluminous granite, including epidote porphyroclasts, grain boundary migration in quartz, lozenged amphiboles, mica fish, and retrograde mineral alterations. Detailed petrologic observation and microstructural analysis presented here provide thermomechanical constraints on the evolution of the SBMCC.

Alkaline igneous rocks of Magnet Cove, Arkansas: Mineralogy and geochemistry of syenites

USGS Publications Warehouse

Flohr, M.J.K.; Ross, M.

1990-01-01

Syenites from the Magnet Cove alkaline igneous complex form a diverse mineralogical and geochemical suite. Compositional zoning in primary and late-stage minerals indicates complex, multi-stage crystallization and replacement histories. Residual magmatic fluids, rich in F, Cl, CO2 and H2O, reacted with primary minerals to form complex intergrowths of minerals such as rinkite, fluorite, V-bearing magnetite, F-bearing garnet and aegirine. Abundant sodalite and natrolite formed in pegmatitic segregations within nepheline syenite where Cl- and Na-rich fluids were trapped. During autometasomatism compatible elements such as Mn, Ti, V and Zr were redistributed on a local scale and concentrated in late-stage minerals. Early crystallization of apatite and perovskite controlled the compatible behavior of P and Ti, respectively. The formation of melanite garnet also affected the behaviour of Ti, as well as Zr, Hf and the heavy rare-earth elements. Pseudoleucite syenite and garnet-nepheline syenite differentiated along separate trends, but the two groups are related to the same parental magma by early fractionation of leucite, the presumed precursor of intergrowths of K-feldspar and nepheline. The Diamond Jo nepheline syenite group defines a different differentiation trend. Sphene-nepheline syenite, alkali syenite and several miscellaneous nepheline syenites do not consistently plot with the other syenite groups or each other on element and oxide variation diagrams, indicating that they were derived from still other parental syenite magmas. Mineral assemblages indicate that relatively high f{hook};O2, at or above the fayalite-magnetite-quartz buffer, prevailed throughout the crystallization history of the syenites. ?? 1990.

The zinc stable isotope signature of waste rock drainage in Arctic Canada

NASA Astrophysics Data System (ADS)

Matthies, Romy; Blowes, David

2014-05-01

Leachate emerging from a pilot-scale waste rock pile of the Diavik diamond mine, Northwest Territories, was monitored. The well-characterized waste rock consists of granite, pegmatitic granite and biotite schist with an average total sulfur and carbonate carbon concentration of 0.053 and 0.027 wt. %, respectively. During the field seasons of 2011 and 2012, the Zn stable isotope footprint was characterized alongside standard monitoring parameters. pH ranged between 4.3 and 6.8 and carbonate alkalinity was low or undetectable. Al and Fe concentrations averaged 6.78 mg L-1 and 175 µg L-1, respectively. The pH and metal mobility were governed by sulfide oxidation and sorption and co-precipitation onto iron and aluminium hydroxides. The main processes controlling zinc mobility in the range of 0.4 and 4.7 mg L-1 was the oxidative dissolution of sphalerite (ZnS) in the biotite schist and the attenuation of zinc onto secondary iron and aluminium hydroxides and desorption upon the pH declining below the pHpzc. The isotope ratios between -0.16 and +0.19 ‰ (δ66Zn, avg = +0.05 ‰, n = 43) are consistent with values reported from other sphalerite containing deposits. Zn isotope ratios and concentrations were largely uncorrelated suggesting that the processes affecting Zn mobility had little or no impact on the Zn isotope signature. Data indicate, that the Zn isotope ratios of the waste rock leachate may be used as a fingerprint to track anthropogenic, mine-derived Zn sources under varying environmental conditions.

Lithological architecture and petrography of the Mako Birimian greenstone belt, Kédougou-Kéniéba Inlier, eastern Senegal

NASA Astrophysics Data System (ADS)

Dabo, Moussa; Aïfa, Tahar; Gning, Ibrahima; Faye, Malick; Ba, Mamadou Fallou; Ngom, Papa Malick

2017-07-01

The new lithological and petrographic data obtained in the Mako sector are analyzed in the light of the geochemical data available in the literature. It consists of ultramaic, mafic rocks of tholeiitic affinities associated with intermediate and felsic rocks of calc-alkaline affinities and with intercalations of sedimentary rocks. The whole unit is intruded by Eburnean granitoids and affected by a greenschist to amphibolite facies metamorphism related to a high grade hydrothermalism. It consists of: (i) ultramafic rocks composed of a fractional crystallization succession of lherzolites, wehrlites and pyroxenites with mafic rock inclusions; (ii) layered, isotropic and pegmatitic metagabbros which gradually pass to metabasalts occur at the top; (iii) massive and in pillow metabasalts with locally tapered vesicles, completely or partially filled with quartzo-feldspathic minerals; (iv) quarzites locally overlying the mafic rocks and thus forming the top of the lower unit. This ultramafic-mafic lower unit presents a tholeiitic affinity near to the OIB or N-MORB. It represents the Mako Ophiolitic Complex (MOC), a lithospheric fragment of Birimian lithospheric crust. The upper unit is a mixed volcanic complex arranged in the tectonic corridors. From bottom to top it comprises the following: (i) andesitic, and (ii) rhyodacitic and rhyolitic lava flows and tuffs, respectively. They present a calc-alkaline affinity of the active margins. Three generations of Eburnean granitoids are recognized: (i) early (2215-2160 Ma); (ii) syn-tectonics (2150-2100 Ma) and post-tectonics (2090-2040 Ma). The lithological succession, geochemical and metamorphic characteristics of these units point to an ophiolitic supra-subduction zone.

Lu/Hf dating of garnet constrains timing of metamorphism and deformation, Prince Rupert Area, British Columbia

NASA Astrophysics Data System (ADS)

Wolf, D. E.; Andronicos, C. L.; Vervoort, J. D.; Mansfield, M.

2008-12-01

We present new Lu-Hf garnet ages that constrain the timing of deformation and metamorphism in the Western Metamorphic Belt (WMB), near Prince Rupert, British Columbia. We examined four samples of grt- bearing schist collected within the aureole to the Ecstall Pluton in the WMB. Garnets were separated from these rocks and dated using the Lu-Hf method at Washington State University. We determined geologically meaningful ages from three of these samples. The tectonic history of the Prince Rupert area is marked by phases of transpressive deformation, which included the development of crustal scale strike-slip shear zones and thrust slices with inverted metamorphic gradients. The Grenville Channel shear zone (GCSZ) is a crustal-scale sinistral-slip shear zone over 300 km long that strikes NW with a steep dip and shallow lineation. The GCSZ cuts through the WMB, a ductile fold and thrust belt composed of gneiss and schist with an inverted metamorphic sequence. Index minerals range from: chl and chd-grade units at the bottom of the sequence, str-bearing rocks in the middle, and ky-grt schist and local migmatites at the top of the thrust stack. The WMB was deformed and intruded by the Ecstall Pluton after the inverted metamorphic sequence had formed. The Ecstall is an epi-bearing hbl-qtz diorite emplaced between 91 and 93.5±1 Ma (Butler et al., 2001). Sample G-16A from Kumeleon Inlet (W of the Ecstall pluton) is a schist containing grt+biot+musc+qtz+epi+amph+sil, with small (<1 mm) euhedral grt. Kinematic indicators, including grt porphyroclasts, indicate left-lateral, top to the south, strike-slip shear. This sample yields a Lu-Hf age of 102±3.6 Ma (2σ, MSWD=1.5) based on seven grt and three whole-rock fractions, and a P-T estimate of 5.5±1 kbar and 590°±50° C from garnet-biotite thermobarometry. Sample 98-114A from Ridley Island (NW of Ecstall pluton) is a schist containing musc+biot+qtz+grt+ky+plag+chl+ill and with syn-tectonic euhedral garnet (1 cm). Grt contains sigmoidal inclusion trails that suggest rotation during left lateral shear, consistent with shear bands and C-S fabrics developed in the matrix of the sample. Grt in the sample produced a twelve-point isochron of 107.3±2.6 Ma (2σ, MSWD=1.6), indicating deformation and metamorphism at this time. Sample 06B-57, a garnet amphibolite migmatite from the inner aureole of the Ecstall pluton, contains grt up to 4 cm in diameter concentrated in leucosome layers. Qtz inclusion trails are consistent with rotation during reverse shear (pluton-side up), in addition to meso-scale folds, shear bands and dike arrays in adjacent rocks. This sample had complex systematics that record an older age of ~105 Ma with a younger overprinting of 90- 94 Ma during pluton emplacement. Pegmatite dikes contained within the Ecstall occur at high angles to the magmatic foliation, normal to the pluton margins, and indicate that the pluton was not folded after the pegmatite dikes were intruded. These new ages directly date garnet growth during metamorphism and deformation in the Prince Rupert area, and show that development of the inverted metamorphic sequence predated emplacement of the Ecstall pluton by 10 to 15 Ma. The data further indicate that left lateral strike slip shearing occurred between 107 and 102 Ma, at the same time much of the North American Cordillera was undergoing major contractional deformation.

Experimental constraints on the monazite-fluorapatite-allanite and xenotime-(Y,HREE)-rich fluorapatite-(Y,HREE)-rich epidote phase relations as a function of pressure, temperature, and Ca vs. Na activity in the fluid

NASA Astrophysics Data System (ADS)

Budzyń, Bartosz; Harlov, Daniel E.; Majka, Jarosław; Kozub, Gabriela A.

2014-05-01

Stability relations of monazite-fluorapatite-allanite and xenotime-(Y,HREE)-rich fluorapatite-(Y,HREE)-rich epidote are strongly dependent on pressure, temperature and fluid composition. The increased Ca bulk content expands stability field of allanite relative to monazite towards higher temperatures (Spear, 2010, Chem Geol 279, 55-62). It was also reported from amphibolite facies Alpine metapelites, that both temperature and bulk CaO/Na2O ratio control relative stabilities of allanite, monazite and xenotime (Janots et al., 2008, J Metam Geol 26, 5, 509-526). This study experimentally defines influence of pressure, temperature, high activity of Ca vs. Na in the fluid, and high vs. moderate bulk CaO/Na2O ratio on the relative stabilities of monazite-fluorapatite-allanite/REE-rich epidote and xenotime-(Y,HREE)-rich fluorapatite-(Y,HREE)-rich epidote. This work expands previous experimental study on monazite (Budzyń et al., 2011, Am Min 96, 1547-1567) to wide pressure-temperature range of 2-10 kbar and 450-750°C, utilizing most reactive fluids used in previous experiments. Experiments were performed using cold-seal autoclaves on a hydrothermal line (2-4 kbar runs) and piston-cylinder apparatus (6-10 kbar runs) over 4-16 days. Four sets of experiments, two for monazite and two for xenotime, were performed with 2M Ca(OH)2 and Na2Si2O5 + H2O fluids. The starting materials included inclusion-free crystals of monazite (pegmatite, Burnet County, TX, USA) or xenotime (pegmatite, Northwest Frontier Province, Pakistan) mixed with (1) labradorite (Ab37An60Kfs3) + K-feldspar + biotite + muscovite ± garnet + SiO2 + CaF2 + 2M Ca(OH)2 or (2) albite (Ab100) + K-feldspar + biotite + muscovite ± garnet + SiO2 + CaF2 + Na2Si2O5 + H2O. 20-35 mg of solids and 5 mg of fluid were loaded into 3x15 mm Au capsules and arc welded shut. The monazite alteration is observed in all runs. Newly formed REE-rich fluorapatite and/or britholite are stable in all experimental P-T range in the presence of both fluids. Alteration of monazite and subsequent formation of REE-rich epidote or allanite, REE-rich fluorapatite and britholite was promoted by high activity of Ca in the fluid, with high bulk CaO/Na2O ratio of ca. 11.5 in the system. In contrast, neither REE-rich epidote nor allanite does form in the presence of Na2Si2O5 + H2O fluid, with bulk CaO/Na2O ratio of ca. 1.0. Results indicating that stability field of allanite relative to monazite expands towards higher temperatures along with increased Ca bulk content are consistent with recent thermodynamic modeling of phase equilibria (Spear, 2010). Experiments also support natural observations from the amphibolite-facies Alpine metapelites regarding the influence of CaO/Na2O ratio in bulk content on the relative stabilities of monazite and REE-rich epidote (Janots et al., 2008). Alteration of xenotime is observed in all runs. (Y,HREE)-rich britholite or (Y,HREE)-rich fluorapatite always formed. In contrast to monazite experiments, (Y,HREE)-rich epidote formed only at 650°C and 8-10 kbar, in the presence of 2M Ca(OH)2. Results are partially consistent with natural observations showing that stability of (Y,HREE)-rich epidote is promoted by high Ca bulk content with high CaO/Na2O ratio (Janots et al., 2008). However, experimental results indicate that the relative stabilities of xenotime and (Y,HREE)-rich epidote are strongly controlled by pressure. Acknowledgements. The project was funded by the National Science Center of Poland, grant no. 2011/01/D/ST10/04588.

Mineral resources of the Turtle Mountains Wilderness Study Area, San Bernardino County, California

USGS Publications Warehouse

Howard, Keith A.; Nielson, Jane E.; Simpson, Robert W.; Hazlett, Richard W.; Alminas, Henry V.; Nakata, John K.; McDonnell, John R.

1988-01-01

At the request of the U.S. Bureau of Land Management, approximately 105,200 acres of the Turtle Mountains Wilderness Study Area (CDCA-307) were evaluated for mineral resources (known) and resource potential (undiscovered). In this report, the area studied is referred to as "the wilderness study area" or simply "the study area"; any reference to the Turtle Mountain Wilderness Study Area refers only to that part of the wilderness study area for which a mineral survey was requested by the U.S. Bureau of Land Management.The wilderness study area is in southeastern San Bernardino County, Calif. Gold, silver, copper, and lead have been mined within and adjacent to the study area. Copper-zinc-silver-gold mineral occurrences are found in the southern part and gold-silver mineral occurrences are found in the northern part of the study area; identified low- to moderate-grade gold-silver resources occur adjacent to the study area along the western boundary. Six areas in the south-central and northwestern parts of the study area have high resource potential, two broad areas have moderate resource potential, and part of the southwest corner has low resource potential for lode gold, silver, and associated copper, lead, zinc, molybdenum, and tungsten. Alluvium locally within one of these areas has moderate resource potential for placer gold and silver, and the entire area has low resource potential for placer gold and silver. There is low resource potential for perlite, ornamental stone (onyx marble and opal), manganese, uranium and thorium, pegmatite minerals, and oil and gas within the study area. Sand and gravel are abundant but are readily available outside the wilderness study area.

The timing of high-temperature retrogression in the Reynolds Range, central Australia: constraints from garnet and epidote Pb-Pb dating

NASA Astrophysics Data System (ADS)

Buick, Ian S.; Frei, Robert; Cartwright, Ian

Lower Calcsilicate Unit metasediments and underlying migmatitic Napperby Gneiss metagranite at Conical Hill in the Reynolds Range, central Australia, underwent regional high-grade ( 680 to 720°C), low-pressure/high-temperature metamorphism at 1594+/- 6Ma. The Lower Calcsilicate Unit is extensively quartz veined and epidotised, and discordant grandite garnet+epidote quartz veins may be traced over tens of metres depth into pegmatites that pooled at the Lower Calcsilicate Unit-Napperby Gneiss contact. The quartz veins were probably precipitated by water-rich fluids that exsolved from partial melts derived from the Napperby Gneiss during cooling from the peak of regional metamorphism to the wet granite solidus. Pb stepwise leaching (PbSL) on garnet from three discordant quartz veins yielded comparable single mineral isochrons of 1566+/-32Ma, 1576+/-3Ma and 1577+/-5Ma, which are interpreted as the age of garnet growth in the veins. These dates are in good agreement with previous Sensitive High Resolution Ion Microprobe (SHRIMP) ages of zircon and monazite formed during high-temperature retrogression (1586+/-5 to 1568+/-4Ma) elsewhere in the Reynolds Range. The relatively small age difference between peak metamorphism and retrograde veining suggests that partial melting and melt crystallisation controlled fluid recycling in the high-grade rocks. However, PbSL experiments on epidote intergrown with, and partially replacing, garnet in two of the veins yielded isochrons of 1454+/-34 and 1469+/- 26Ma. The 100-120Ma age difference between intergrown garnet and late epidote from the same vein suggests that the vein systems may have experienced multiple episodes of fluid flow.

Cooling and inferred uplift/erosion history of the Grenville Orogen, Ontario: Constraints from sup 40 Ar/ sup 39 Ar thermochronology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cosca, M.A.

1989-01-01

Thermochronological ({sup 40}Ar/{sup 39}Ar) data are presented from 76 mineral separates of hornblende, muscovite, biotite, phlogopite, and K-feldspar. Samples were selected from regionally metamorphosed gneiss, amphibolite, metasediment, marble, metagabbro and pegmatite across the two major metamorphic belts of the Grenville Province, the Central Metasedimentary Belt (CMB) and the Central Gneiss Belt (CGB). When combined with published temperature estimates for closure to argon diffusion in the phases analyzed, cooling rates from {approximately}500 C to {approximately}120 C of 1-4 C/MA are calculated across the entire Grenville Province of Ontario. Regional uplift/erosion rates for the Grenville Orogen of Ontario have been estimated frommore » the {sup 40}Ar/{sup 39}Ar data, a retrograde P-T path for rocks of the CGB, and an upper time constraint provided by flat, overlying Cambro-Ordovician sediments. Twenty-two of the hornblendes used for thermochronology have been quantitatively analyzed for major elements by microprobe, Fe{sup 2+}/Fe{sup 3+} by wet chemistry, and for H{sub 2}O by manometric measurement. Water activities calculated from hornblende equilibria are typically low (<0.01) because of the exponential dilutions in hornblende (tremolite) activity required by present activity-composition models. An oxyamphibole component of 25% further reduces any amphibole component and the H{sub 2}O activity by as much as 50% below that calculated with simplifying assumption. These findings indicate that different amphibole normalization schemes have a marked effect on the activity calculated for a specific amphibole or H{sub 2}O, and should be carefully evaluated.« less

Geologic map of the South Sierra Wilderness and South Sierra Roadless area, southern Sierra Nevada, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diggles, M.F.; Carter, K.E.

1993-04-01

The study area is underlain predominantly by granitoid rocks of the Sierra Nevada batholith. Metamorphic rocks are present in roof pendants mainly in the southwest corner of the study area and consist of quartz-biotite schist, phyllite, quartzite, marble, calc-silicate hornfels, and meta-dacite. Among the seven Triassic and (or) Jurassic plutons are three newly described units that consist of the gabbro of Deer Mountain, the tonalite of Falls Creek, and the quartz diorite of Round Mountain. The map shows one newly described unit that intrudes Triassic rocks: the granodiorite of Monache Creek which is a leucocratic, medium-grained, equi-granular, locally porphyritic biotitemore » hornblende granodiorite. Among the seven Cretaceous plutons are two newly described units. The Cretaceous rocks are generally medium- to coarse-grained, potassium-feldspar porphyritic granite with biotite and minor hornblende; it includes abundant pods of alaskite. The granite of Haiwee Creek is similar but only locally potassium-feldspar porphyritic and with only minor hornblende. Major-element data plotted on Harker diagrams show the older rocks to be higher in iron and magnesium and lower in silica than the younger rocks. There are abundant local pods of alaskite throughout the study area that consist of medium- to coarse-grained, leucocratic granite, alkali-feldspar granite and associated aplite and pegmatite bodies occurring as small pods and highly leucocratic border phases of nearby plutons. Tertiary and Quaternary volcanic rock include the rhyolite of Monache Mountain and Quaternary surficial deposits: fan, stream-channel, colluvium, talus, meadow-filling, rock-glacier, and glacial-moraine deposits. Important structures include the Sierran front fault and a possible extensional feature along which Bacon (1978) suggests Monache Mountain erupted.« less

Pressure determination in Hydrothermal Diamond Anvil Cell via laser interferometry: Investigation of hydrothermal melting of haplogranitic glass

NASA Astrophysics Data System (ADS)

Solferino, G.; Anderson, A. J.

2012-12-01

Pressure determination in HDAC experiments of hydrothermal melting of a haplogranitic glass at 130-830 MPa and 600-800 °C were performed employing in-situ visualization of alpha to beta quartz via laser interferometry. Hitherto, Raman spectroscopy of ruby, quartz, 13C and zircon has been used for the same purpose, with a best resolution of 40-50 MPa. Our method average uncertainty is just 3.4 MPa. This augmented precision is critical in estimate of the emplacement depth of mid to upper crustal magmatic bodies, e.g., intermediate-felsic intrusions, or definition of formation conditions of magmatic ores, like rare metal pegmatites. Moreover, thanks to this improved resolution on pressure measurements, we observed that actual run pressure, named Pα/β, is smaller than pressure computed using the equation of state (EOS) of pure water, here labeled PH2O for an ample range of pressures, up to 400 MPa. The absolute value of ΔP = Pα/β- PH2O decrease at higher pressure, and switches from negative to positive at P > 800 MPa. Since dissolution of the glass/melt into the pressure medium (water) leads to increment of the medium compressibility (density), then the medium should be able to impose a larger pressure than pure water for every observed temperature of alpha to beta transition (i.e., steeper isochor). A possible explanation of this discrepancy is found in the differential density between the pressure medium and the melt, and in the change of the volume occupied by the fluid for increasing temperature, as it emerges from a simplified model of dissolution of albite feldspar / albite melt in water, prepared for this study on the base of solubility data available in literature.

Fluid-assisted melting in a collisional orogen

NASA Astrophysics Data System (ADS)

Berger, A.; Burri, T.; Engi, M.; Roselle, G. T.

2003-04-01

The Southern Steep Belt (SSB) of the Central Alps is the location of backthrusting during syn- to post-collisional deformation. From its metamorphic evolution and lithological contents the SSB has been interpreted as a tectonic accretion channel (TAC [1]). The central part of the SSB is additionally characterized by anatexites, leucogranitic aplites and pegmatites. Dehydration melting of muscovite is rare but did occurr locally. Moreover, no evidence of dehydration melting of biotite has been formed in that products of incongruent melting reactions (garnet, opx or cordierite) are missing. The melts are mainly produced by the infiltration of an external aqueous fluid. The fluids must have originated from the breakdown of hydrous minerals at temperatures below the water saturated solidus of the quartz-feldspar-system, such that the liberated fluids could not been trapped in the melt. Using the thermal modeling program MELONPIT [2] and assuming that solid fragments ascended in combination with tectonic accreated radioactive material, a complex thermal evolution inside the TAC has been derived. During subduction of the downgoing plate, isotherms were locally inverted, then subsequently relaxed, when subduction slowed down. At the collisional stage a small region develope, where the isotherms were still bent, and where temperatures increased during decompression. Assuming that dehydration reactions were followed by upward flow of fluids released from this region fluid present partial melting was triggered. The flow direction of the fluid was controlled by the pressure gradient and the steeply oriented foliations in the SSB. According to the model, the area of upward flowing fluids should be limited to the SSB. This is consistent with the observed regional distribution of leucosomes derived from in-situ melts. [1] Engi et al. (2001) Geology 29: 1143-1146 [2] Roselle et al. (2002) Am. J. Sci. 302: 381-409

Fracture controls on valley persistence: the Cairngorm Granite pluton, Scotland

NASA Astrophysics Data System (ADS)

Hall, A. M.; Gillespie, M. R.

2017-09-01

Valleys are remarkably persistent features in many different tectonic settings, but the reasons for this persistence are rarely explored. Here, we examine the structural controls on valleys in the Cairngorms Mountains, Scotland, part of the passive margin of the eastern North Atlantic. We consider valleys at three scales: straths, glens and headwater valleys. The structural controls on valleys in and around the Cairngorm Granite pluton were examined on satellite and aerial photographs and by field survey. Topographic lineaments, including valleys, show no consistent orientation with joint sets or with sheets of microgranite and pegmatitic granite. In this granite landscape, jointing is not a first-order control on valley development. Instead, glens and headwater valleys align closely to quartz veins and linear alteration zones (LAZs). LAZs are zones of weakness in the granite pluton in which late-stage hydrothermal alteration and hydro-fracturing have greatly reduced rock mass strength and increased permeability. LAZs, which can be kilometres long and >700 m deep, are the dominant controls on the orientation of valleys in the Cairngorms. LAZs formed in the roof zone of the granite intrusion. Although the Cairngorm pluton was unroofed soon after emplacement, the presence of Old Red Sandstone (ORS) outliers in the terrain to the north and east indicates that the lower relief of the sub-ORS basement surface has been lowered by <500 m. Hence, the valley patterns in and around the Cairngorms have persisted through >1 km of vertical erosion and for 400 Myr. This valley persistence is a combined product of regionally low rates of basement exhumation and of the existence of LAZs in the Cairngorm pluton and sub-parallel Caledonide fractures in the surrounding terrain with depths that exceed 1 km.

Radiometric reconnaissance in the Garfield and Taylor park quadrangles, Chaffee and Gunnison counties, Colorado

USGS Publications Warehouse

Dings, M.G.; Schafer, Max

1953-01-01

During the summer of 1952 most of the mines and prospects in the Garfield and Taylor Park quadrangles of west-central Colorado were examined radiometrically by the U. S. Geological Survey to determine the extent, grade, and mode of occurrence of radioactive substances. The region contains a relatively large number of rock types, chiefly pre-Cambrian schists, gneisses, and granites; large and small isolated areas of sedimentary rocks of Paleozoic and Mesozoic ages; and a great succession of intrusive rocks of Tertiary age that range from andesite to granite and occur as stocks, chonoliths, sills, dikes, and one batholith. The prevailing structures are northwest-trending folds and faults. Ores valued at about $30,000,000 have been produced from this region. Silver, lead, zinc, and gold have accounted for most of this value, but small tonnages of copper, tungsten, and molybdenum have also been produced. The principal ore minerals are sphalerite, silver-bearing galena, cerussite, smithsonite, and gold-bearing pyrite and limonite; they occur chiefly as replacement bodies in limestone and as shoots in pyritic quartz veins. Anomalous radioactivity is uncommon and the four localities at which it is known are widely separated in space. The uranium content of samples from these localities is low. Brannerite, the only uranium-bearing mineral positively identified in the region, occurs sparingly in a few pegmatites and in one quartz-beryl-pyrite vein. Elsewhere radioactivity is associated with (l) black shale seams in the Manitou dolomite, (2) a quartz-pyrite-molybdenite vein, (3) a narrow border zone of oxidized material surrounding a small lead zinc ore body in the Manitou dolomite along a strong fault zone.

Reported industrial minerals occurrences and permissive areas for other occurrences in the Islamic Republic of Mauritania (phase V deliverable 88): Chapter R1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Langer, William H.; Anderson, Eric D.; Horton, John D.

2012-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Permissive tracts for iron oxide copper-gold deposits in Mauritania (phase V, deliverable 78 ): Chapter M1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Fernette, Gregory; Horton, John D.

2012-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Geologic map of Mauritania (phase V, deliverables 51a, 51b, and 51c): Chapter A1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Bradley, Dwight C.; Motts, Holly; Horton, John D.; Giles, Stuart A.; Taylor, Cliff D.

2015-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Permissive tracts for sediment-hosted lead-zinc-silver deposits in Mauritania (phase V, deliverable 72): Chapter J1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Mauk, Jeffrey L.; Horton, John D.

2012-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Permissive tracts for algoma-, superior-, and oolitic-type iron deposits in Mauritania (phase V, deliverable 82): Chapter O1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Taylor, Cliff D.; Horton, John D.

2012-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Mineral potential tracts for orogenic, Carlin-like, and epithermal gold deposits in the Islamic Republic of Mauritania, (phase V, deliverable 68): Chapter H1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Goldfarb, Richard J.; Marsh, Erin; Horton, John D.

2012-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Permissive tracts for volcanogenic massive sulfide deposits in Mauritania (phase V, deliverable 76): Chapter L1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Taylor, Cliff D.; Horton, John D.

2012-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Structure map of Mauritania (phase V, deliverables 52a and 52b): Chapter A2 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Bradley, Dwight C.; Horton, John D.; Motts, Holly A.; Taylor, Cliff D.

2015-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Geographic Information Systems (GIS) for la République Islamique de Mauritanie (PRISM-II) phase V (phase V, deliverable 92): Chapter T in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Horton, John D.; Taylor, Cliff D.

2015-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Permissive tracts for uranium deposits in Mauritania (phase V, deliverable 80): Chapter N1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Fernette, Gregory; Horton, John D.

2012-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Permissive tracts for nickel, copper, platinum group elements (PGE), and chromium deposits of Mauritania (phase V, deliverable 66): Chapter G1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Taylor, Cliff D.; Horton, John D.

2012-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Use of tourmaline as a potential petrogenetic indicator in the determination of host magma: CRS, XRD and PED-XRF methods

NASA Astrophysics Data System (ADS)

Gullu, Bahattin; Kadioglu, Yusuf Kagan

2017-08-01

Tourmaline defines a group of complex borosilicate forms as accessory mineral in igneous and metamorphic rocks and they act an important role in the interpretation of the chemical composition changes of the composition of the host fluid of the magma. The variety of tourmaline can be identified by using optical microscopy, X-Ray Diffraction (XRD) and by determining its chemical composition through Polarized Energy Dispersive X-Ray Fluorescence (PED-XRF) methods. However, microscopic investigations and XRD analyses are not quite adequate for detailed determination of tourmaline sub-groups. In addition, the use of chemical composition of tourmaline as a strict indicator of geochemical processes might be a misleading method. In this study, variable tourmaline crystals were collected from three different pegmatitic occurrences in Behrekdag, Yozgat and Karakaya granitic bodies of Central Anatolia to identify their chemical properties through Confocal Raman Spectroscopy (CRS), PED-XRF and XRD analyses. The confocal Raman spectrometry of collected tourmalines from the Behrekdag, Yozgat and Karakaya granites are in the compositions of schorl, schorl and elbaite respectively. The dominant compositional groups of these tourmalines are in the form of schorl. Raman shift values of tourmalines revealed four bands centered at almost 1050, 750, 400 and 300 cm- 1. The first group of the band arises from SiO stretching, the second from Bsbnd O stretching and the other two belong to bending modes of Osbnd Bsbnd O and Bsbnd Osbnd Al with symmetrical deformation of Sisbnd Osbnd Si. The strongest spectra near 360 cm- 1 should belong to the bonding of Alsbnd O. As a result, the confocal Raman studies are more sensitive for identification of tourmaline subgroup compositions and have a quite important in the explaining source of the magma.

The Jeffers Brook diorite-granodiorite pluton: style of emplacement and role of volatiles at various crustal levels in Avalonian appinites, Canadian Appalachians

NASA Astrophysics Data System (ADS)

Pe-Piper, Georgia; Piper, David J. W.

2018-04-01

Small appinite plutons ca. 610 Ma outcrop in the peri-Gondwanan Avalon terrane of northern Nova Scotia, with different structural levels exposed. Field mapping shows that the Jeffers Brook pluton is a laccolith emplaced along an upper crustal thrust zone, likely in a dilational jog in a regional dextral strike-slip system. The oldest rocks are probably mafic sills, which heated the area facilitating emplacement of intermediate magmas. Cross-cutting relationships show that both mafic and intermediate magmas were supplied throughout the history of pluton emplacement. The modal composition, mineral chemistry, and bulk chemistry of gabbro, diorite, tonalite, granodiorite, and granite have been studied in the main plutonic phases, dykes, and sills, and mafic microgranular enclaves. As with the type appinites in the Scottish Caledonides, the pluton shows evidence of high water content: the dominance of hornblende, locally within pegmatitic texture; vesicles and irregular felsic patches in enclaves; and late aplite dykes. Analyzed mafic microgranular enclaves are geochemically similar to larger diorite bodies in the pluton. Tonalite-granodiorite is distinct from the diorite in trace-element geochemistry and radiogenic isotopes. Elsewhere to the east, similar rocks of the same age form vertically sheeted complexes in major shear zones; hornblende chemistry shows that they were emplaced at a deeper upper crustal level. This implies that little of the observed geochemical variability in the Jeffers Brook pluton was developed within the pluton. The general requirements to form appinites are proposed to be small magma volumes of subduction-related magmas that reach the upper crust because of continual heating by mafic magmas moving through strike-slip fault pathways and trapping of aqueous fluids rather than venting through volcanic activity.

Uranium occurrences in the Golden Gate Canyon and Ralston Creek areas, Jefferson County, Colorado

USGS Publications Warehouse

Adams, John Wagstaff; Gude, A.J.; Beroni, E.P.

1953-01-01

Pitchblende, associated with base-metal sulfides, has been found at nine localities in the northern part of Jefferson County, Colo., in shear zones that cut pre-Cambrian metamorphic and igneous rocks, chiefly hornblende gneiss, biotite schist, and granite pegmatite. The known deposits are in the vicinity of Halston Creek and Golden Gate Canyon, in the foothills of the Colorado Front Range and about 15 miles east of the pitchblende-producing area of the Central City district. Two of the pitchblende occurrences were found by a local prospector in 1949; the seven other deposits were found by Geological Survey. personnel in 1951-52. The pitchblende deposits, with one exception, are in major shear zones that contain veinlike bodies of carbonate-rich breccia that ranges from 1 to 5 feet in thickness. The breccias probably are related to the Laramide faults, or 'breccia reefs' of similar trend, mapped by Loverinq and Goddard (1950). The breccias are composed of fragments of bleached and iron-stained wall rock, usually hornblende gneiss, that have been cut by veins and cemented by carbonate minerals, quartz, and orthoclase(?). Pitchblende and associated ore minerals, chiefly copper sulfides, occur in and along the margins of the breccias and apparently were introduced at a late stage of the carbonate deposition. At one deposit, the Buckman, the pitchblende is in narrow shear zones not closely related to any large breccia bodies. Secondary uranium minerals are subordinate except at the Schwartzwalder mine, where torbernite and metatorbernite are common. Some alteration of pitchblende to non-opaque materials, believed to be hydrated oxides, has been noted in ore from two of the deposits.

Exploration of dysprosium: the most critical element for Japan

NASA Astrophysics Data System (ADS)

Watanabe, Y.

2012-04-01

Dysprosium (Dy), one of the heavy rare earth elements, is used mainly as an additive for NdFeB permanent magnets which are installed in various modern industrial products such as voice coil motors in computers, factory automation machinery, hybrid and electric vehicles, home electronics, and wind turbine, to improve heat resistance of the magnets. Dy has been produced about 2,000t per year from the ores from ion adsorption type deposits in southern China. However, the produced amount of Dy was significantly reduced in 2011 in China due to reservation of heavy rare earth resources and protection of natural environment, resulting in soaring of Dy price in the world. In order to respond the increasing demand of Dy, unconventional supply sources are inevitably developed, in addition to heavy rare earth enriched ion adsorption type deposits outside China. Heavy rare earth elements including Dy are dominantly hosted in xenotime, fergusonite, zircon, eudialyte, keiviite, kainosite, iimoriite, etc. Concentration of xenotime is found in placer deposits in Malaysia and India, hydrothermal deposits associated with unconformity-type uranium mineralization (Athabasca basin in Canada, Western Australia), iron-oxide fluorite mineralization (South Africa) and Sn-bearing alkaline granite (Brazil). Zircon and fergusontie concentration is found as igneous and hydrothermal products in peralkaline syenite, alkaline granite and pegmatite (e.g., Nechalacho in Canada). Eudialyte concentration is found in some peralkaline syenite bodies in Greenland, Canada, Sweden and Russia. Among these sources, large Dy resources are estimated in the deposits hosted in peralkaline rocks (Nechalacho: 79,000t, Kvanefjeld: 49,000t, Norra Karr: 15,700t, etc.) compared to the present demand of Dy. Thus, Dy will be supplied from the deposits associated with peralkaline and alkaline deposits in future instead of ion adsorption type deposits in southern China.

Use of tourmaline as a potential petrogenetic indicator in the determination of host magma: CRS, XRD and PED-XRF methods.

PubMed

Gullu, Bahattin; Kadioglu, Yusuf Kagan

2017-08-05

Tourmaline defines a group of complex borosilicate forms as accessory mineral in igneous and metamorphic rocks and they act an important role in the interpretation of the chemical composition changes of the composition of the host fluid of the magma. The variety of tourmaline can be identified by using optical microscopy, X-Ray Diffraction (XRD) and by determining its chemical composition through Polarized Energy Dispersive X-Ray Fluorescence (PED-XRF) methods. However, microscopic investigations and XRD analyses are not quite adequate for detailed determination of tourmaline sub-groups. In addition, the use of chemical composition of tourmaline as a strict indicator of geochemical processes might be a misleading method. In this study, variable tourmaline crystals were collected from three different pegmatitic occurrences in Behrekdag, Yozgat and Karakaya granitic bodies of Central Anatolia to identify their chemical properties through Confocal Raman Spectroscopy (CRS), PED-XRF and XRD analyses. The confocal Raman spectrometry of collected tourmalines from the Behrekdag, Yozgat and Karakaya granites are in the compositions of schorl, schorl and elbaite respectively. The dominant compositional groups of these tourmalines are in the form of schorl. Raman shift values of tourmalines revealed four bands centered at almost 1050, 750, 400 and 300cm -1 . The first group of the band arises from SiO stretching, the second from BO stretching and the other two belong to bending modes of OBO and BOAl with symmetrical deformation of SiOSi. The strongest spectra near 360cm -1 should belong to the bonding of AlO. As a result, the confocal Raman studies are more sensitive for identification of tourmaline subgroup compositions and have a quite important in the explaining source of the magma. Copyright © 2017 Elsevier B.V. All rights reserved.

The mineral resources of the Borborema Province in Northeastern Brazil and its sedimentary cover: a review

NASA Astrophysics Data System (ADS)

Beurlen, H.

1995-10-01

The geotectonic Borborema Province in Northeast Brazil includes several NE-trending Proterozoic metamorphic belts which amalgamate some small older massifs. It has been known since the Second World War for the skarn-hosted scheelite mineralization and the TaLiBeSn-bearing pegmatites of the Seridó Region. With the drastic drop of the international tungsten prices, three mines were closed in the last decade and only the state-owned Bodó Mine remains working. Since 1961, when Brazilian universities begun to graduate geologists, several dozen mineral deposits were discovered and older prospects were reevaluated. These include the copper deposits of Aurora-State of Ceará (CE) and Serrote da Lage-State of Alagoas (AL), the nickel deposits of S. João do Piauí-State of Piauí (PI), the uranium deposits of Itataia-CE, a dozen gold prospects, the ilmenite deposit of Floresta-State of Pernambuco (PE), the vermiculite mine of Paulistana-PI, and the export quality granite at Bom Jardim-PE and Sumé-Congo-State of Paraíba (PB). In the mostly Cretaceous or Cainozoic sedimentary cover, the discovery includes two important oil and gas fields ((Carmópolis-State of Sergipe (SE) and Mossoró-Macau-State of Rio Grande do Norte (RN)); deposits of sulphur (Castanhal-SE), of KNaMg, salts (Carmópolis-SE, Sto. Antônio-AL), of phosphate (Olinda-PE and João Pessoa-PB), of gypsum (Araripe-PE/CE), of bentonite (Boa Vista-PB) and the Ti placers at Mataraca-PB. In the following pages the current knowledge about these deposits is summarized.

Amphibolite boudins in marble on Naxos, Greece: 3D analysis of multiphase deformation on a retrograde P-T path

NASA Astrophysics Data System (ADS)

Virgo, Simon; von Hagke, Christoph; Urai, Janos L.

2017-04-01

Boudins are periodic structures that form by layer parallel extension in mechanically layered rocks. The characteristics of boudins such as orientation and geometry provide constraints on the paleo stress field as well as the rheology of the rocks during deformation. However, most characterizations of boudinage are based on 2D observations and do not consider the 3-dimensional complexity and potentially non-coaxial polyphase genesis of boudinage structures. In marble quarries in the high grade complex on Naxos, Greece, we studied spectacular outcrops of amphibolite and pegmatite boudins, in combination with serial slicing of quarried blocks to reconstruct the 3D boudin structures. We identified five boudin generations with two distinct generations of early, high grade pinch-and-swell followed by two generations of brittle shearband and torn boudins formed along the retrograde path under greenschist facies conditions. The five generations of boudinage indicate that E-W compression is the main mode of deformation in the marbles. The axis of extension changes from subvertical during pinch-and swell deformation to subhorizontal N-S extension at later stages of deformation. Later phases of boudinage are influenced by existing boudin geometries, producing complex structures in 3D. In 2D section the complexity is not directly apparent and reveals itself only after statistical analysis of long continuous sections. Apart from implications for the regional geology, our findings highlight the importance of 3D characterization of boudinage structures for boudin classification. The insights we gain from the analysis of multiphase boudinage structures on Naxos are the basis for quantitative boudin analysis to infer rheology, effective stress, vorticity and strain, and establish a boudin classification scheme with appeal to a complete mechanics.

Age of the granitic magmatism and the W-Mo mineralization in skarns of the Seridó belt (NE Brazil) based on zircon U-Pb (SHRIMP) and molybdenite Re-Os dating

NASA Astrophysics Data System (ADS)

Hollanda, Maria Helena B. M. de; Souza Neto, João A.; Archanjo, Carlos J.; Stein, Holly; Maia, Ana C. S.

2017-11-01

Over five hundred W-Mo skarns have been reported in the Neoproterozoic Seridó belt in the northeastern Brazil. The origin of these mineralizations has been attributed to metasomatic reactions occuring after the infiltration of hydrothermal fluids that are mostly derived from the plutonic magmatic activity that ranged between approximately 600 and 525 Ma. Here we date molybdenite using N-TIMS on Re-Os analysis of three major scheelite deposits (Brejuí, Bonfim and Bodó) hosted in the skarn horizons of the metasedimentary sequence. Molybdenite is an integral part of the mineralizations that include scheelite in skarns and, in the Bonfim deposit, gold concentrate in late brittle faults. The Re-Os ages are 554 ± 2 Ma (Brejuí), 524 ± 2 Ma (Bonfim) and 510 ± 2 Ma (Bodó). The age of the Brejuí molybdenite, however, appears to be anomalous based on the local geology of the deposit, which is located next to the contact of a batholith dated ca. 575 Ma. In turn, the Bonfim molybdenite yields similar ages in replicated samples with variable high Re contents. New U-Pb SHRIMP ages of four biotite (leuco)granite plutons vary from 577 ± 5 Ma to 526 ± 8 Ma, which overlap with molybdenite crystallization. These results indicate a close connection between the W-Mo mineralizations and the plutonic activity that intruded the belt after the peak HT/LP metamorphism. The latest pulses of felsic magmatism, which were contemporaneous with the emplacement of Be-Ta-Nb-Li pegmatites, therefore constitute a potential guide in the Seridó belt for prospective W-Mo deposits.

Hydrogeochemistry and groundwater quality assessment along Wadi Al Showat, Khamis Mushiet District, Southwest Saudi Arabia

NASA Astrophysics Data System (ADS)

Alhumidan, S. M.; Alfaifi, H. J.; Ibrahim, E. K. E.; Abdel Rahman, K.

2015-12-01

In the present study, the hydrochemistry and geologic characteristics of the shallow groundwater aquifer along Wadi Al Showat, Khamis Mushiet District, Southwest Saudi Arabia was evaluated and assessed. Along this wadi the fractured/weathered basement rocks house significant quantity of groundwater that usually used by local people for agricultural and domestic purposes. Assessing and evaluation of the quality of the groundwater in such shallow aquifers is very important; especially the groundwater is generally occurred within the fractured basement rocks at shallow depths, thus exposing the groundwater to surface or near-surface contaminants is expected. For this purpose hydrochemical and biological analysis was conducted for 25 water samples collected from the available shallow dug wells along the studied wadi. The study reveals that the groundwater quality changed due to the agriculture and urbanization practices along the wadi. The effect of domestic waste water and septic tanks was obvious. In addition, the field investigation indicates that the basement rocks in the area is dissected by two main sets of fractures that oriented in the west-northwest and east-west directions. In some places, the basement rocks is intruded by coarse-grained, quartz-rich quartzite grained monzogranite, and pegmatite veins that have a coarse-grained weathering product, therefore, they tend to develop and preserve open joint systems between the granitic blocks. These fracturing system are important from the hydrogeological point of view, as they facilitate the storage, water flow movement through them and also facilitate the vertical infiltration of the surface pollutants. These results led to a better understanding of the groundwater characteristics that is important in groundwater management in the study area.

Role of Satellite Sensors in Groundwater Exploration

PubMed Central

Mukherjee, Saumitra

2008-01-01

Spatial as well as spectral resolution has a very important role to play in water resource management. It was a challenge to explore the groundwater and rainwater harvesting sites in the Aravalli Quartzite-Granite-Pegmatite Precambrian terrain of Delhi, India. Use of only panchromatic sensor data of IRS-1D satellite with 5.8-meter spatial resolution has the potential to infer lineaments and faults in this hard rock area. It is essential to identify the location of interconnected lineaments below buried pediment plains in the hard rock area for targeting sub-surface water resources. Linear Image Self Scanning sensor data of the same satellite with 23.5-meter resolution when merged with the panchromatic data has produced very good results in delineation of interconnected lineaments over buried pediment plains as vegetation anomaly. These specific locations of vegetation anomaly were detected as dark red patches in various hard rock areas of Delhi. Field investigation was carried out on these patches by resistivity and magnetic survey in parts of Jawaharlal Nehru University (JNU), Indira Gandhi national Open University, Research and Referral Hospital and Humayuns Tomb areas. Drilling was carried out in four locations of JNU that proved to be the most potential site with ground water discharge ranging from 20,000 to 30,000 liters per hour with 2 to 4 meters draw down. Further the impact of urbanization on groundwater recharging in the terrain was studied by generating Normalized difference Vegetation Index (NDVI) map which was possible to generate by using the LISS-III sensor of IRS-1D satellite. Selection of suitable sensors has definitely a cutting edge on natural resource exploration and management including groundwater. PMID:27879808

Bokan Mountain peralkaline granitic complex, Alexander terrane (southeastern Alaska): evidence for Early Jurassic rifting prior to accretion with North America

USGS Publications Warehouse

Dostal, Jaroslav; Karl, Susan M.; Keppie, J. Duncan; Kontak, Daniel J.; Shellnutt, J. Gregory

2013-01-01

The circular Bokan Mountain complex (BMC) on southern Prince of Wales Island, southernmost Alaska, is a Jurassic peralkaline granitic intrusion about 3 km in diameter that crosscuts igneous and metasedimentary rocks of the Alexander terrane. The BMC hosts significant rare metal (rare earth elements, Y, U, Th, Zr, and Nb) mineralization related to the last stage of BMC emplacement. U–Pb (zircon) and 40Ar/39Ar (amphibole and whole-rock) geochronology indicates the following sequence of intrusive activity: (i) a Paleozoic basement composed mainly of 469 ± 4 Ma granitic rocks; (ii) intrusion of the BMC at 177 ± 1 Ma followed by rapid cooling through ca. 550 °C at 176 ± 1 Ma that was synchronous with mineralization associated with vertical, WNW-trending pegmatites, felsic dikes, and aegirine–fluorite veins and late-stage, sinistral shear deformation; and (iii) intrusion of crosscutting lamprophyre dikes at >150 Ma and again at ca. 105 Ma. The peralkaline nature of the BMC and the WNW trend of associated dikes suggest intrusion during NE–SW rifting that was followed by NE–SW shortening during the waning stages of BMC emplacement. The 177 Ma BMC was synchronous with other magmatic centres in the Alexander terrane, such as (1) the Dora Bay peralkaline stock and (2) the bimodal Moffatt volcanic suite located ∼30 km north and ∼100 km SE of the BMC, respectively. This regional magmatism is interpreted to represent a regional extensional event that precedes deposition of the Late Jurassic – Cretaceous Gravina sequence that oversteps the Wrangellia and Alexander exotic accreted terranes and the Taku and Yukon–Tanana pericratonic terranes of the Canadian–Alaskan Cordillera.

Bokan Mountain peralkaline granitic complex, Alexander terrane (southeastern Alaska): evidence for Early Jurassic rifting prior to accretion with North America

USGS Publications Warehouse

Dostal, Jaroslav; Karl, Susan M.; Keppie, J. Duncan; Kontak, Daniel J.; Shellnutt, J. Gregory

2013-01-01

The circular Bokan Mountain complex (BMC) on southern Prince of Wales Island, southernmost Alaska, is a Jurassic peralkaline granitic intrusion about 3 km in diameter that crosscuts igneous and metasedimentary rocks of the Alexander terrane. The BMC hosts significant rare metal (rare earth elements, Y, U, Th, Zr, and Nb) mineralization related to the last stage of BMC emplacement. U–Pb (zircon) and 40Ar/39Ar (amphibole and whole-rock) geochronology indicates the following sequence of intrusive activity: (i) a Paleozoic basement composed mainly of 469 ± 4 Ma granitic rocks; (ii) intrusion of the BMC at 177 ± 1 Ma followed by rapid cooling through ca. 550 °C at 176 ± 1 Ma that was synchronous with mineralization associated with vertical, WNW-trending pegmatites, felsic dikes, and aegirine–fluorite veins and late-stage, sinistral shear deformation; and (iii) intrusion of crosscutting lamprophyre dikes at >150 Ma and again at ca. 105 Ma. The peralkaline nature of the BMC and the WNW trend of associated dikes suggest intrusion during NE–SW rifting that was followed by NE–SW shortening during the waning stages of BMC emplacement. The 177 Ma BMC was synchronous with other magmatic centres in the Alexander terrane, such as (1) the Dora Bay peralkaline stock and (2) the bimodal Moffatt volcanic suite located ~30 km north and ~100 km SE of the BMC, respectively. This regional magmatism is interpreted to represent a regional extensional event that precedes deposition of the Late Jurassic – Cretaceous Gravina sequence that oversteps the Wrangellia and Alexander exotic accreted terranes and the Taku and Yukon–Tanana pericratonic terranes of the Canadian–Alaskan Cordillera.

Mineralogy and Geochemistry of Granitic rocks within Lichen Hills, Outback Nunatak, Northern Victoria Land, Antarctica

NASA Astrophysics Data System (ADS)

KIM, T.; KIM, Y.; Lee, I.; Lee, J.; Woo, J.

2015-12-01

The study areas, Lichen Hills and Outback Nunatak are located in the Northern Victoria Land which is close to Pacific Ocean side of Transantarctic Mountain (TAM), Antarctica. According to the study of Zeller and Dreschoff (1990), the radioactivity values of Lichen hills and Frontier Mt. area in the Victoria Land were very high. To identify the geochemical characteristics of granitic rocks in these areas, 13 samples of Lichen Hills rocks and 4 samples of Outback Nunatak rocks are analyzed. For mineralogical study, samples were observed in macroscale as well as microscale including microscope electron probe analysis. Rock samples of Lichen Hills, Outback Nunatak are mainly leucogranite and granitic pegmatite. These rock samples are composed of quartz, k-feldspar, plagioclase, muscovite, garnet, tourmaline like granite. In SEM-EDS analysis, the observed light colored minerals show relatively high Th, U, Dy, Ce, Nb concentration. This suggests that rock samples may contain minerals such as fergusonite, monazite, thorite, allanite, karnasurtite which are considered to be REE-bearing minerals. Samples of related rocks have been analyzed in terms of major, trace and rare earth element (REE) concentrations using X-ray fluorescence (XRF) spectrometer and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). As concentration of SiO2 increase, Al2O3, TiO2, Fe2O3, MgO, P2O5 concentration decrease and Na2O, K2O, MnO concentration increase. Analyzed trace elements and REE are normalized using CI Chondrite, Primitive mantle. The normalized data show that LREE are enriched compared to HREE. The distinct negative anomalies of Eu, Sr are observed, indicating that rock-forming melts are fairly processed state of fractional crystallization. It means that Th, U, Nb, Ta are much enriched in the melts.

PRIMARY MINERALIZATION OF URANIUM-BEARING "SILICEOUS REEF" VEINS IN THE BOULDER BATHOLITH, MONTANA. PART I. THE HOST ROCKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wright, H.D.; Bieler, B.H.

1960-01-01

Between 1952 and 1956 a study was made of some of the uranium-bearing hydrothermal veins in the northern part of the Boulder batholith, Montana. Three mines, the W. Wilson, G. Washington, and Free Enterprise, were investigated in detail. The veins are characterized by a microcrystalline quartz gangue containing sparsely scattered, very fine-grained sulfide minerals and uraninite. Above the present water table, secondary uranium minerals are abundant locally. Throughout the area the veins --called "siliceous reefs"--strike east to northeast, are of steep dip, and vary in thickness from a fraction of an inch to several feet. The country rock is granodioritemore » containing, in order of abundance, plagioclase (An/sub 30/ to An/sub 36/), quartz, orthoclase, biotite, and hornblende, with apatite, zircon, and sphene. Small bodies of aplite, pegmatite, and alaskite occur along some veins. The granodiorite adjacent to the veins is rather strongly altered. The alteration is similar throughout all of the deposits studied, in barren and orebearing portions alike. The essential minerals show a characteristic sequence of alteration, in the order hornblende, andesine, biotite, orthoclase, and quartz. Successive zones of alteration are characterized, from the vein outward, by maximum development of sericite (muscovite polytype 1M, in part), kaolinite, and montmorillonite. Other alteration products are quartz, pyrite, calcite, leucoxene, and chlorite. The alteration resulted in an increase in silica and ferric iron, a decrease in alumina, total iron, ferrous iron, lime, soda, and magnesia, and little change in potash, titania, phosphorus, carbon dioxide, and sulfur. Consideration of the stability fields of the sheet structure silicate minerals indicates little basis for interpretation of the temperatures prevailing during mineralization. (auth)« less

Petrographic and geochemical comparisons between the lower crystalline basement-derived section and the granite megablock and amphibolite megablock of the Eyreville B core, Chesapeake Bay impact structure, USA

USGS Publications Warehouse

Townsend, G.N.; Gibson, R.L.; Horton, J. Wright; Reimold, W.U.; Schmitt, R.T.; Bartosova, K.

2009-01-01

The Eyreville B core from the Chesapeake Bay impact structure, Virginia, USA, contains a lower basement-derived section (1551.19 m to 1766.32 m deep) and two megablocks of dominantly (1) amphibolite (1376.38 m to 1389.35 m deep) and (2) granite (1095.74 m to 1371.11 m deep), which are separated by an impactite succession. Metasedimentary rocks (muscovite-quartz-plagioclase-biotite-graphite ?? fibrolite ?? garnet ?? tourmaline ?? pyrite ?? rutile ?? pyrrhotite mica schist, hornblende-plagioclase-epidote-biotite- K-feldspar-quartz-titanite-calcite amphibolite, and vesuvianite-plagioclase- quartz-epidote calc-silicate rock) are dominant in the upper part of the lower basement-derived section, and they are intruded by pegmatitic to coarse-grained granite (K-feldspar-plagioclase-quartz-muscovite ?? biotite ?? garnet) that increases in volume proportion downward. The granite megablock contains both gneissic and weakly or nonfoliated biotite granite varieties (K-feldspar-quartz-plagioclase-biotite ?? muscovite ?? pyrite), with small schist xenoliths consisting of biotite-plagioclase-quartz ?? epidote ?? amphibole. The lower basement-derived section and both megablocks exhibit similar middleto upper-amphibolite-facies metamorphic grades that suggest they might represent parts of a single terrane. However, the mica schists in the lower basement-derived sequence and in the megablock xenoliths show differences in both mineralogy and whole-rock chemistry that suggest a more mafi c source for the xenoliths. Similarly, the mineralogy of the amphibolite in the lower basement-derived section and its association with calc-silicate rock suggest a sedimentary protolith, whereas the bulk-rock and mineral chemistry of the megablock amphibolite indicate an igneous protolith. The lower basement-derived granite also shows bulk chemical and mineralogical differences from the megablock gneissic and biotite granites. ?? 2009 The Geological Society of America.

A study of the phosphate mineral kapundaite NaCa(Fe3+)4(PO4)4(OH)3ṡ5(H2O) using SEM/EDX and vibrational spectroscopic methods

NASA Astrophysics Data System (ADS)

Frost, Ray L.; López, Andrés; Xi, Yunfei; Scholz, Ricardo

2014-03-01

Vibrational spectroscopy enables subtle details of the molecular structure of kapundaite to be determined. Single crystals of a pure phase from a Brazilian pegmatite were used. Kapundaite is the Fe3+ member of the wardite group. The infrared and Raman spectroscopy were applied to compare the structure of kapundaite with wardite. The Raman spectrum of kapundaite in the 800-1400 cm-1 spectral range shows two intense bands at 1089 and 1114 cm-1 assigned to the ν1PO43- symmetric stretching vibrations. The observation of two bands provides evidence for the non-equivalence of the phosphate units in the kapundaite structure. The infrared spectrum of kapundaite in the 500-1300 cm-1 shows much greater complexity than the Raman spectrum. Strong infrared bands are found at 966, 1003 and 1036 cm-1 and are attributed to the ν1PO43- symmetric stretching mode and ν3PO43- antisymmetric stretching mode. Raman bands in the ν4 out of plane bending modes of the PO43- unit support the concept of non-equivalent phosphate units in the kapundaite structure. In the 2600-3800 cm-1 spectral range, Raman bands for kapundaite are found at 2905, 3151, 3311, 3449 and 3530 cm-1. These bands are broad and are assigned to OH stretching vibrations. Broad infrared bands are also found at 2904, 3105, 3307, 3453 and 3523 cm-1 and are attributed to water. Raman spectroscopy complimented with infrared spectroscopy has enabled aspects of the structure of kapundaite to be ascertained and compared with that of other phosphate minerals.

Geologic columns for the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure: Impactites and crystalline rocks, 1766 to 1096 m depth

USGS Publications Warehouse

Horton, J. Wright; Gibson, R.L.; Reimold, W.U.; Wittmann, A.; Gohn, G.S.; Edwards, L.E.

2009-01-01

The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville drill cores from the Chesapeake Bay impact structure provide one of the most complete geologic sections ever obtained from an impact structure. This paper presents a series of geologic columns and descriptive lithologic information for the lower impactite and crystalline-rock sections in the cores. The lowermost cored section (1766-1551 m depth) is a complex assemblage of mica schists that commonly contain graphite and fibrolitic sillimanite, intrusive granite pegmatites that grade into coarse granite, and local zones of mylonitic deformation. This basement-derived section is variably overprinted by brittle cataclastic fabrics and locally cut by dikes of polymict impact breccia, including several suevite dikes. An overlying succession of suevites and lithic impact breccias (1551-1397 m) includes a lower section dominated by polymict lithic impact breccia with blocks (up to 17 m) and boulders of cataclastic gneiss and an upper section (above 1474 m) of suevites and clast-rich impact melt rocks. The uppermost suevite is overlain by 26 m (1397-1371 m) of gravelly quartz sand that contains an amphibolite block and boulders of cataclasite and suevite. Above the sand, a 275-m-thick allochthonous granite slab (1371-1096 m) includes gneissic biotite granite, fine- and medium-to-coarse-grained biotite granites, and red altered granite near the base. The granite slab is overlain by more gravelly sand, and both are attributed to debris-avalanche and/or rockslide deposition that slightly preceded or accompanied seawater-resurge into the collapsing transient crater. ?? 2009 The Geological Society of America.

Models of corundum origin from alkali basaltic terrains: a reappraisal

NASA Astrophysics Data System (ADS)

Lin Sutherland, F.; Hoskin, Paul W. O.; Fanning, C. Mark; Coenraads, Robert R.

Corundums from basalt fields, particularly in Australia and Asia, include a dominant blue-green-yellow zoned ``magmatic'' suite (BGY suite) and subsidiary vari-coloured ``metamorphic'' suites. The BGY corundums have distinctive trace element contents (up to 0.04 wt% Ga2O3 and low Cr/Ga and Ti/Ga ratios <1). Different melt origins for BGY corundums are considered here from their inclusion and intergrowth mineralogy, petrologic associations and tectonic setting. Analysed primary inclusion minerals (over 100 inclusions) cover typical feldspars, zircon and Nb-Ta oxides and also include hercynite-magnetite, gahnospinel, rutile-ilmenite solid solution, calcic plagioclase, Ni-rich pyrrhotite, thorite and low-Si and Fe-rich glassy inclusions. This widens a previous inclusion survey; New England, East Australia corundums contain the most diverse inclusion suite known from basalt fields (20 phases). Zircon inclusion, intergrowth and megacryst rare earth element data show similar patterns, except for Eu which shows variable depletion. Temperature estimates from magnetite exsolution, feldspar compositions and fluid inclusion homogenization suggest that some corundums crystallized between 685-900°C. Overlap of inclusion Nb, Ta oxide compositions with new comparative data from niobium-yttrium-fluorine enriched granitic pegmatites favour a silicate melt origin for the corundums. The feasibility of crystallizing corundum from low-volume initial melting of amphibole-bearing mantle assemblages was tested using the MELTS program on amphibole-pyroxenite xenolith chemistry from basalts. Corundum appears in the calculations at 720-880°C and 0.7-1.1GPa with residual feldspathic assemblages that match mineral compositions found in corundums and their related xenoliths. A model that generates melts from amphibole-bearing lithospheric mantle during magmatic plume activity is proposed for BGY corundum formation.

The timing of tertiary metamorphism and deformation in the Albion-Raft River-Grouse Creek metamorphic core complex, Utah and Idaho

USGS Publications Warehouse

Strickland, A.; Miller, E.L.; Wooden, J.L.

2011-01-01

The Albion-Raft River-Grouse Creek metamorphic core complex of southern Idaho and northern Utah exposes 2.56-Ga orthogneisses and Neoproterozoic metasedimentary rocks that were intruded by 32-25-Ma granitic plutons. Pluton emplacement was contemporaneous with peak metamorphism, ductile thinning of the country rocks, and top-to-thewest, normal-sense shear along the Middle Mountain shear zone. Monazite and zircon from an attenuated stratigraphic section in the Middle Mountain were dated with U-Pb, using a SHRIMP-RG (reverse geometry) ion microprobe. Zircons from the deformed Archean gneiss preserve a crystallization age of 2532 ?? 33 Ma, while monazites range from 32.6 ?? 0.6 to 27.1 ?? 0.6 Ma. In the schist of the Upper Narrows, detrital zircons lack metamorphic overgrowths, and monazites produced discordant U-Pb ages that range from 52.8 ?? 0.6 to 37.5 ?? 0.3 Ma. From the structurally and stratigraphically highest unit sampled, the schist of Stevens Spring, narrow metamorphic rims on detrital zircons yield ages from 140-110 Ma, and monazite grains contained cores that yield an age of 141 ??2 Ma, whereas rims and some whole grains ranged from 35.5 ?? 0.5 to 30.0 ?? 0.4 Ma. A boudinaged pegmatite exposed in Basin Creek is deformed by the Middle Mountains shear zone and yields a monazite age of 27.6 ?? 0.2 Ma. We interpret these data to indicate two periods of monazite and metamorphic zircon growth: a poorly preserved Early Cretaceous period (???140 Ma) that is strongly overprinted by Oligocene metamorphism (???32-27 Ma) related to regional plutonism and extension. ?? 2011 by The University of Chicago.

Geology and market-dependent significance of rare earth element resources

NASA Astrophysics Data System (ADS)

Simandl, G. J.

2014-12-01

China started to produce rare earth elements (REEs) in the 1980s, and since the mid-1990s, it has become the dominant producer. Rare earth element export quotas first introduced by the Chinese government in the early 2000s were severely reduced in 2010 and 2011. This led to strong government-created disparity between prices within China and the rest of the world. Industrialized countries identified several REEs as strategic metals. Because of rapid price increases of REE outside of China, we have witnessed a world-scale REE exploration rush. The REE resources are concentrated in carbonatite-related deposits, peralkaline igneous rocks, pegmatites, monazite ± apatite veins, ion adsorption clays, placers, and some deep ocean sediments. REE could also be derived as a by-product of phosphate fertilizer production, U processing, mining of Ti-Zr-bearing placers, and exploitation of Olympic Dam subtype iron oxide copper gold (IOCG) deposits. Currently, REEs are produced mostly from carbonatite-related deposits, but ion adsorption clay deposits are an important source of heavy REE (HREE). Small quantities of REE are derived from placer deposits and one peralkaline intrusion-related deposit. The ideal REE development targets would be located in a politically stable jurisdiction with a pro-mining disposition such as Canada and Australia. REE grade, HREE/light REE (LREE) ratio of the mineralization, tonnage, mineralogy, and permissive metallurgy are some of the key technical factors that could be used to screen potential development projects. As REEs are considered strategic metals from economic, national security, and environmental points of view, technical and economic parameters alone are unlikely to be used in REE project development decision-making. Recycling of REE is in its infancy and unless legislated, in the short term, it is not expected to contribute significantly to the supply of REE.

Characterizing the nature of melt-rock reaction in peridotites from the Santa Elena Ophiolite, NW Costa Rica

NASA Astrophysics Data System (ADS)

Carr, D.; Loocke, M. P.; Snow, J. E.; Gazel, E.

2017-12-01

The Santa Elena Ophiolite (SEO), located on the northwestern coast of Costa Rica, consists primarily of preserved oceanic mantle and crustal rocks thrust above an accretionary complex. The SEO is predominantly characterized by mantle peridotites (i.e., primarily spinel lherzolite with minor amounts of harzburgite and dunite) cut and intruded by minor pegmatitic gabbros, layered gabbros, plagiogranites, and doleritic and basaltic dykes. Previous studies have concluded that the complex formed in a suprasubduction zone (SSZ) setting based on the geochemical nature of the layered gabbros and plagiogranites (i.e., depleted LREE and HFSE and enriched LILE and Pb), as well, as the peridotites (i.e., low-TiO2, Zr, and V, and high MgO, Cr, and Ni)(Denyer and Gazel, 2009). Eighteen ultramafic samples collected during the winter 2010/2011 field season (SECR11) exhibit abundant evidence for melt-rock reaction (e.g., disseminated plagioclase and plagioclase-spinel, clinopyroxene-spinel, and plagioclase-clinopyroxene symplectites) and provide a unique opportunity to characterize the textural and chemical nature of melt-rock reaction in the SEO. We present the results of a petrologic investigation (i.e., petrography and electron probe microanalysis) of 28 thin sections (19 spinel lherzolites, of which 14 are plagioclase-bearing, 4 pyroxenite veins, and 5 harzburgites) derived from the SECR11 sample set. The results of this investigation have the potential to better our understanding of the nature of melt generation and migration and melt-rock interaction in the SEO mantle section and shed further light on the complex petrogenetic history of the SEO. Denyer, P., Gazel, E., 2009, Journal of South American Earth Sciences, 28:429-442.

The molecular structure of the phosphate mineral beraunite Fe2+Fe53+(PO4)4(OH)5ṡ4H2O - A vibrational spectroscopic study

NASA Astrophysics Data System (ADS)

Frost, Ray L.; López, Andrés; Scholz, Ricardo; Xi, Yunfei; Lana, Cristiano

2014-07-01

The mineral beraunite from Boca Rica pegmatite in Minas Gerais with theoretical formula Fe2+Fe53+(PO4)4(OH)5ṡ4H2O has been studied using a combination of electron microscopy with EDX and vibrational spectroscopic techniques. Raman spectroscopy identifies an intense band at 990 cm-1 and 1011 cm-1. These bands are attributed to the PO43- ν1 symmetric stretching mode. The ν3 antisymmetric stretching modes are observed by a large number of Raman bands. The Raman bands at 1034, 1051, 1058, 1069 and 1084 together with the Raman bands at 1098, 1116, 1133, 1155 and 1174 cm-1 are assigned to the ν3 antisymmetric stretching vibrations of PO43- and the HOPO32- units. The observation of these multiple Raman bands in the symmetric and antisymmetric stretching region gives credence to the concept that both phosphate and hydrogen phosphate units exist in the structure of beraunite. The series of Raman bands at 567, 582, 601, 644, 661, 673, and 687 cm-1 are assigned to the PO43- ν2 bending modes. The series of Raman bands at 437, 468, 478, 491, 503 cm-1 are attributed to the PO43- and HOPO32- ν4 bending modes. No Raman bands of beraunite which could be attributed to the hydroxyl stretching unit were observed. Infrared bands at 3511 and 3359 cm-1 are ascribed to the OH stretching vibration of the OH units. Very broad bands at 3022 and 3299 cm-1 are attributed to the OH stretching vibrations of water. Vibrational spectroscopy offers insights into the molecular structure of the phosphate mineral beraunite.

International strategic minerals inventory summary report; natural graphite

USGS Publications Warehouse

Krauss, U.H.; Schmidt, H.W.; Taylor, H.A.; Sutphin, D.M.

1989-01-01

Natural graphite is a crystalline mineral of pure carbon which normally occurs in the form of platelet-shaped crystals. It has important properties, such as chemical inertness, low thermal expansion, and lubricity, that make it almost irreplaceable for certain uses such as refractories and steelmaking. Graphite ore types are crystalline (flake and lump} or 'amorphous' (cryptocrystalline}. Refractory applications use the largest total amount of natural graphite, while the most important use of crystalline graphite is in crucibles for handling molten metals. All graphite deposits being mined today are found in the following metamorphic environments: (1) contact metamorphosed coal generally is a source of amorphous graphite; (2)disseminated crystalline flake graphite comes from syngenetic metasediments; and (3) crystalline lump graphite is found in epigenetic veins in high-grade metamorphic regions. Graphite may also occur as a trace mineral in ultrabasic rocks and pegmatites, but these are economically insignificant. The world's identified economically exploitable resources of crystalline graphite in major deposits are estimated to be about 9.7 million metric tons of concentrate. In-place resources of amorphous graphite are about 11.5 million metric tons. Of these, less than 2 percent of the crystalline ore and less than 1 percent of the amorphous ore are in western industrial countries. World mining production of natural graphite rose from 347,000 metric tons in 1973 to 659,000 metric tons in 1986, while the proportion produced by central economy countries increased from about 50 percent for the period from 1973 to 1978 to more than 64 percent in 1979 to 1986. It is estimated that crystalline flake graphite accounts for at least 180,000 metric tons of total annual world mining production of natural graphite, and amorphous graphite makes up the rest.

Interpretation of core and well log physical property data from drill hole UPH-3, Stephenson County, Illinois

USGS Publications Warehouse

Daniels, J.J.; Olhoeft, G.R.; Scott, J.H.

1984-01-01

Laboratory and well log physical property measurements show variations in the mineralogy with depth in UPH-3. Gamma ray values generally decrease with depth in the drill hole, corresponding to a decrease in the felsic mineral components of the granite. Correspondingly, an increase with depth in mafic minerals in the granite is indicated by the magnetic susceptibility, and gamma ray measurements. These mineralogic changes indicated by the geophysical well logs support the hypothesis of fractionation during continuous crystallization of the intrusive penetrated by UPH-3. Two fracture zones, and an altered zone within the granite penetrated by drill hole UPH-3 are defined by the physical property measurements. An abnormally low magnetic susceptibility response in the upper portion of the drill hole can be attributed to alteration of the rock adjacent to the sediments overlying the granite. Fracture zones can be identified from the sonic velocity, neutron, and resistivity measurements. A fracture zone, characterized by low resistivity values and low neutron values, is present in the depth interval from 1150 to 1320 m. Low magnetic susceptibility and high gamma ray values indicate the presence of felsic-micaceous pegmatites within this fracture zone. An unfractured region present from a depth of 1380 m to the bottom of the hole is characterized by an absence of physical property variations. The magnetic susceptibility and gamma ray measurements indicate a change in the amount of mafic minerals at the base of this otherwise homogenous region of the drilled interval. Abrupt changes and repeated patterns of physical properties within the drill hole may represent interruptions in the crystallization process of the melt or they may be indicative of critical temperatures for specific mineral assemblages within the intrusive.

Petrochemical and Tectonogenesis of Granitoids in the Wuyo-Gubrunde Horst, Northeastern Nigeria: Implication for Uranium Enrichment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bolarinwa, Anthony Temidayo, E-mail: atbola@yahoo.com; Bute, Saleh Ibrahim

The Wuyo-Gubrunde Horst in the northeastern Nigeria consists of migmatite gneiss, unaltered, altered, and sheared porphyritic granites, pegmatites, aplites, basalts, and sandstone. Uranium has been reported in rhyolite, sheared rocks, and sandstone within the area. The petrogenesis of the granitoids and associated rocks in the area was evaluated in the light of new geochemical data, which showed that the U content of altered porphyritic granite is highest and hydrothermal-related. The granitoids are metaluminous, sub-alkaline, and S-type granite, and have evolved by partial melting of crustal material emplaced at moderate depth of 20–30 km in a syn-to late-collisional within-plate tectonic setting.more » The negative Eu/Eu* anomaly and high (La/Yb){sub N} ratio of the granitoids indicate magma fractionation. The low SiO{sub 2} (<53%) and high Fe{sub 2}O{sub 3} (10%) of the altered porphyritic granite compared to other similar rock units suggest pervasive alteration. The associated basalts are tholeiitic, emplaced within continental plate tectonic setting, and enriched in Ni, V, Nb, Sr, and light rare earth elements, and they have SiO{sub 2}, Fe{sub 2}O{sub 3}, V, Th, and Co contents that are similar to those of the altered porphyritic granites. The U occurrence in the Wuyo-Gubrunde Horst is believed to be sourced from the adjoining Bima sandstone in the Benue Trough, which locally contains carbonaceous zones with anomalously high concentrations of U. The Fe{sup 2+}/Fe{sup 3+} redox fronts formed by alteration of the iron-rich basalts provided the requisite geochemical barrier for U-bearing hydrothermal fluid, causing enrichment of U leached and mobilized from the sandstone through fractures in the rocks.« less

Metallogenetic systems associated with granitoid magmatism in the Amazonian Craton: An overview of the present level of understanding and exploration significance

NASA Astrophysics Data System (ADS)

Bettencourt, Jorge Silva; Juliani, Caetano; Xavier, Roberto P.; Monteiro, Lena V. S.; Bastos Neto, Artur C.; Klein, Evandro L.; Assis, Rafael R.; Leite, Washington Barbosa, Jr.; Moreto, Carolina P. N.; Fernandes, Carlos Marcello Dias; Pereira, Vitor Paulo

2016-07-01

The Amazonian Craton hosts world-class metallogenic provinces with a wide range of styles of primary precious, rare, base metal, and placer deposits. This paper provides a synthesis of the geological database with regard to granitoid magmatic suites, spatio temporal distribution, tectonic settings, and the nature of selected mineral deposits. The Archean Carajás Mineral Province comprises greenstone belts (3.04-2.97 Ga), metavolcanic-sedimentary units (2.76-2.74 Ga), granitoids (3.07-2.84 Ga) formed in a magmatic arc and syn-collisional setting, post-orogenic A2-type granites as well as gabbros (ca. 2.74 Ga), and anorogenic granites (1.88 Ga). Archean iron oxide-Cu-Au (IOCG) deposits were synchronous or later than bimodal magmatism (2.74-2.70 Ga). Paleoproterozoic IOCG deposits, emplaced at shallow-crustal levels, are enriched with Nb-Y-Sn-Be-U. The latter, as well as Sn-W and Au-EGP deposits are coeval with ca. 1.88 Ga A2-type granites. The Tapajós Mineral Province includes a low-grade meta-volcano-sedimentary sequence (2.01 Ga), tonalites to granites (2.0-1.87 Ga), two calc-alkaline volcanic sequences (2.0-1.95 Ga to 1.89-1.87 Ga) and A-type rhyolites and granites (1.88 Ga). The calc-alkaline volcanic rocks host epithermal Au and base metal mineralization, whereas Cu-Au and Cu-Mo ± Au porphyry-type mineralization is associated with sub-volcanic felsic rocks, formed in two continental magmatic arcs related to an accretionary event, resulting from an Andean-type northwards subduction. The Alta Floresta Gold Province consists of Paleoproterozoic plutono-volcanic sequences (1.98-1.75 Ga), generated in ocean-ocean orogenies. Disseminated and vein-type Au ± Cu and Au + base metal deposits are hosted by calc-alkaline I-type granitic intrusions (1.98 Ga, 1.90 Ga, and 1.87 Ga) and quartz-feldspar porphyries (ca. 1.77 Ga). Timing of the gold deposits has been constrained between 1.78 Ga and 1.77 Ga and linked to post-collisional Juruena arc felsic magmatism (e.g., Colíder and Teles Pires suites). The Transamazonas Province corresponds to a N-S-trending orogenic belt, consolidated during the Transamazonian cycle (2.26-1.95 Ga), comprising the Lourenço, Amapá, Carecuru, Bacajá, and Santana do Araguaia tectonic domains. They show a protracted tectonic evolution, and are host to the pre-, syn-, and post-orogenic to anorogenic granitic magmatism. Gold mineralization associated with magmatic events is still unclear. Greisen and pegmatite Sn-Nb-Ta deposits are related to 1.84 to 1.75 Ga late-orogenic to anorogenic A-type granites. The Pitinga Tin Province includes the Madeira Sn-Nb-Ta-F deposit, Sn-greisens and Sn-episyenites. These are associated with A-type granites of the Madeira Suite (1.84-1.82 Ga), which occur within a cauldron complex (Iricoumé Group). The A-type magmatism evolved from a post-collisional extension, towards a within-plate setting. The hydrothermal processes (400 °C-100 °C) resulted in albitization and formation of disseminated cryolite, pyrochlore columbitization, and formation of a massive cryolite deposit in the core of the Madeira deposit. The Rondônia Tin Province hosts rare-metal (Ta, Nb, Be) and Sn-W mineralization, which is associated with the São Lourenço-Caripunas (1.31-1.30 Ga), related to the post-collisional stage of the Rondônia San Ignácio Province (1.56-1.30 Ga), and to the Santa Clara (1.08-1.07 Ga) and Younger Granites of Rondônia (0.99-0.97 Ga) A-type granites. The latter are linked to the evolution of the Sunsás-Aguapeí Province (1.20-0.95 Ga). Rare-metal polymetallic deposits are associated with late stage peraluminous granites, mainly as greisen, quartz vein, and pegmatite types.

Genesis of the Silsilah tin deposit, Kingdom of Saudi Arabia

USGS Publications Warehouse

Kamilli, Robert J.; Criss, R.E.

1996-01-01

The Silsilah tin deposit (lat 25 degrees 06' N, long 42 degrees 40' E) consists of a group of pervasively greisenized, flat-topped granite cupolas within a 12-km-diam ring complex. The greisens contain varying amounts of disseminated cassiterite and wolframite. Several types of quartz veins are peripheral to the greisens; some of these contain minor wolframite. The deposit is genetically associated with a highly differentiated, peraluminous alkali-feldspar granite (587 + or - 8 Ma) that is part of a mostly peralkaline, igneous ring complex intruded into Late Proterozoic, immature sandstones of the Murdama Group. We recognize four distinct phases of the peraluminous granite. Only the smallest, most highly differentiated cupolas contain significant tin greisen mineralization. Greisens developed beneath aplitic carapaces that overlie the granite and created impermeable barriers to rising volatiles. The geometry of a cupola correlates strongly with the intensity of alteration; cupolas with the smallest cross sectional areas and steepest marginal contacts have the most intensely greisenized apexes. The paragenetic sequence can be divided into five stages: pegmatite formation, locally pervasive albitization, locally pervasive greisenization and deposition of cassiterite, deposition of quartz-wolframite veins, and deposition of quartz veins with minor base metal sulfides. Pressure-corrected fluid inclusion filling temperatures indicate that the hydrothermal system generally cooled as it evolved and that the delta 18O values of the hydrothermal quartz increased from 10.8 to 15.7 per mil. Calculated delta 18O values of the hydrothermal fluid varied concomitantly from the pegmatite stage (delta 18O fluid approximately 8.6ppm; T [asymp] 550 degrees C) to the greisen stage (5.4 and 5.6[ppm; T [asymp] 360 degrees C), the quartz-wolframite vein stage (6.3 and 7.5ppm; T [asymp] 390 degrees C), and the late vein stage (4.0 and 5.1ppm; T [asymp] 270 degrees C). This evolution probably reflects the admixture of generally increasing amounts of meteoric or formation water having a lower delta 18 O value into the cooling magmatic hydrothermal system. In delta 18O-delta 18O plots for mineral separates from fresh to altered samples of the peraluminous granite the values for quartz and feldspar conform to a steep, positive-sloped disequilibrium trend that indicates interaction with high 18O hydrothermal fluid, mirrored by a negative-sloped disequilibrium trend for quartz and mica. These complementary trends suggest strongly that individual granite cupolas were essentially closed systems during alteration. To our knowledge, this is the first oxygen isotope demonstration of a closed-system, hydrothermal metal deposit. The sandstone country rock has whole-rock delta 18O values of 12.4 + or - 2.0 per mil. The highest values (>13ppm) form a approximately 3-km-wide high delta 18O annulus immediately peripheral to the ring complex. The data suggest that the country rocks were pervasively exchanged with an outward-migrating, high delta 18O fluid moving down a temperature gradient. This fluid was probably formation water that flowed radially inward toward the pluton at a deeper level, forming a largely horizontal, unicellular flow system that had fluid-flow lines nearly vertical next to the intrusion, and directed upward and outward at higher levels. Low delta 18O fluids that formed quartz associated with the tin-tungsten mineralization and later veins are inferred to be the result of a subsequent and distinct phase of the hydrothermal system. Almost all the geologic processes necessary for the formation of an economically viable tin deposit occurred at Silsilah, but the lack of a strong localizing mechanism for cassiterite mineralization resulted in an economically marginal deposit. If the greisenized cupolas had been vertically stacked, as are the intrusions and ore zones in Climax-type molybdenum deposits, or if the mineralizing fluids had been channeled into veins, as in the tin deposits in Cornwall, England, a higher grade deposit might have formed. The generally closed-system behavior of the hydrothermal system at Silsilah may have prevented additional scavenging of metals and the formation of a larger, richer deposit.

Geology and fluorspar deposits, Northgate district, Colorado

USGS Publications Warehouse

Steven, Thomas A.

1960-01-01

The fluorspar deposits in the Northgate district, Jackson County, Colo., are among the largest in Western United States. The mines were operated intermittently during the 1920's and again during World War II, but production during these early periods of operation was not large. Mining was begun on a larger scale in 1951, and the district has assumed a prominent position among the fluorspar producers in the United States. Within the Northgate district, Precambrian metamorphic and igneous rocks crop out largely in the Medicine Bow Mountains, and later sedimentary rocks underlie North Park and fill old stream valleys in the mountains. The metamorphic rocks constitute a gneiss complex that formed under progressively changing conditions of regional metamorphism. They consist principally of hornblende-plagioclase gneiss (hornblende gneiss), quartz monzonite gneiss, pegmatite, biotite-garnet-quartz-plagioclase gneiss (biotite-garnet gneiss), hornblende-biotite-quartz-plagioclase gneiss (hornblende-biotite gneiss) and mylonite gneiss. The igneous rocks comprise some local fine-grained dacite porphyry dikes near the west margin of the district, and a quartz monzonitic stock and associated dikes in the central and eastern parts of the district. The sedimentary rocks in the district range in age from Permian to Recent. Folded Permian and Mesozoic rocks underlie the basin of North Park, and consist in sequence from oldest to youngest, of Satanka(?) shale (0-50 feet of brick-red shale) and Forelle(?) limestone (8-15 feet of pink to light-gray laminated limestone) of Permian age, Chugwater formation of Permian and Triassic age (690 feet of red silty shale and sandstone), Sundance formation of Late Jurassic age (145 feet of sandstone containing some shale and limestone), Morrison formation of Late Jurassic age (445 feet of variegated shale and minor sandstone and limestone), Dakota group as used by Lee (1927), now considered to be of Early Cretaceous age in this area (200-320 feet of pebbly sandstone, sandstone, and shale), Ben ton shale of Early and Late Cretaceous age (665 feet of dark-gray thin-bedded shale), Niobrara formation of Late Cretaceous age (865 feet of yellow to gray limy siltstone and shale), and Pierre shale of Late Cretaceous age (more than 60 feet of dark-gray fissile shale). Unconformities separate the Chugwater and Sundance formations, and the Morrison formation and the Dakota group.Nonmarine strata of the White River formation of Oligocene age and the North Park formation of Miocene and Pliocene (?) age fill Tertiary valleys cut in the Precambrian rocks of the mountain areas, and Quaternary terrace gravel, alluvium, and dune sand mantle much of the floor of North Park. The main outlines of the modern Rocky Mountains formed during the Laramide orogeny in late Mesozoic and early Tertiary time. Most of the Laramide structures that can be recognized in the Northgate district involve the sedimentary rocks underlying North Park which are folded into northwest-trending anticlines and synclines. The folds are open and in most the beds dip 60° or less. Yet many anticlines are cut by reverse faults of widely different trends and directions of offset. Transverse faults offset some of the folds, and the character of folding commonly is markedly different on opposing sides of these faults. The North Park basin is cut off on the north by the east-trending Independence Mountain fault, a north-dipping reverse fault along which hard Precambrian rocks have been thrust up across the trend of the earlier Laramide structures. The North Park basin is still a major structure where it is interrupted by the Independence Mountain fault, and the original basin must have extended much farther north. Disrupted gradients at the base of pre-White River valleys suggest that the Northgate district and adjacent areas may have been deformed in middle Tertiary time, but the evidence is not conclusive. A more definite period of deformation took place in Pliocene time following deposition of the North Park formation. North Park strata in south-central North Park were folded into a northwest-trending syncline, and the central part of the Northgate district probably was warped up along a north- or northwestward-trending axis. Four north- to northwestward-trending faults cut the Precambrian rocks and White River formation on Pinkham Mountain and the area to the southeast. Similar faults 2½ and 15 miles west of the Northgate district cut rocks of the North Park formation, and all probably formed during the Pliocene period of deformation. The known commercial fluorspar deposits are localized along the two larger faults of the Northgate district, and they have been studied in detail. The White River formation in early Oligocene time covered a hilly terrain drained by southward-flowing streams. By late Miocene, the northward-flowing streams had cut to about the same levels reached by the pre-White River streams and had partly exhumed and modified the older terrain. During late Miocene and early Pliocene (?) time, the Northgate area was buried beneath the clays, sands, and gravels of the North Park formation. Subsequent erosion removed the higher part of the North Park formation, cut a surface of low relief across the exhumed Precambrian rocks, and removed all topographic evidence of the Pliocene period of deformation. The present courses of the major streams were superimposed across the buried terrains during this period of erosion. Rejuvenation during middle Pleistocene caused all major streams to become incised in sharp canyons. Copper minerals occur in small concentrations in some of the pegmatite masses in the gneiss complex. The copper-rich masses rarely exceed a few feet in diameter and constitute only a small part of the associated pegmatite body.Vermiculite is exposed in prospect pits and mine workings along the west margin of the Northgate district. All the venniculite that was seen is associated with small masses of horablendite, massive chlorite, or serpentinite where these masses are near or are cut by pegmatite bodies. Some of the deposits may be potential producers of commercial-grade vermiculite, but most are small and erratic in shape or grade.Fluorspar is the main mineral commodity that has been produced from the Northgate district. It was deposited during two distinct periods of mineralization, but only the younger deposits have been productive. Small bodies of silicified breccia containing minor coarsely crystalline fluorite occur along the Independence Mountain fault, and in a few places along other Laramide faults. The fluorspar is an integral part of the fault breccia and apparently was deposited while the enclosing fault was still active. The largest deposits of fluorspar in the Northgate district occur along the late Tertiary (?) faults on Pinkham Mountain. The fluorspar consists typically of botryoidal layers that formed as successive encrustations along open fractures, or as finely granular aggregates replacing and cementing fault gouge and White River formation. Many incompletely filled cavities, called water courses, still exist. Fluorite is the principal vein material; fragments of country rock constitute the chief impurity although finely granular quartz or chalcedony is common locally. Soft powdery manganese oxide coats many fractures and in places is associated with a fine white clay. Fluorspar was deposited in or adjacent to open spaces along the late Tertiary (?) faults. Fractures in hard granitic rocks tended to remain open after faulting and were the favored sites for fluorspar deposition; fractures in the less competent hornblende and hornblende-biotite gneiss and schist generally were tight and little fluorspar was deposited. The White River rocks, although soft, were permeable and were widely impregnated or replaced by fluorspar. Both of the main vein zones are along faults that have predominant rightlateral strike-slip displacement. As they theoretically should be, the vein zones are narrower and contain less fluorspar where the containing fault is deflected to the left than where the fault is deflected to the right and the fractures remained open. The crustified, vuggy structure of the fluorspar and the common association with chalcedony or finely granular quartz suggest deposition in a very shallow environment, but no direct evidence bearing on the depth at which the fluorspar formed was seen. Fluorspar was deposited throughout a vertical range of 600 feet or more on each of the main vein zones, and for a vertical range of 1,050 feet for the district as a whole. None of the deposits had been bottomed at the time this report was prepared. Exploration at depth beneath known ore bodies is favorable for developing large tonnages of fluorspar. The best possibilities for finding new ore bodies near the surface are along the northwestern and southeastern parts of the Fluorine-Camp Creek vein zone where large bodies of granitic rocks are intersected by the fault. These areas are generally mantled by a thick overburden, and have been inadequately tested so far.

Lithium in Jack Hills zircons: Evidence for extensive weathering of Earth's earliest crust

NASA Astrophysics Data System (ADS)

Ushikubo, Takayuki; Kita, Noriko T.; Cavosie, Aaron J.; Wilde, Simon A.; Rudnick, Roberta L.; Valley, John W.

2008-08-01

In situ Li analyses of 4348 to 3362 Ma detrital zircons from the Jack Hills, Western Australia by SIMS reveal that the Li abundances (typically 10 to 60 ppm) are commonly over 10,000 times higher than in zircons crystallized from mantle-derived magmas and in mantle-derived zircon megacrysts (typically < 2 ppb). High Li concentrations in zircons (10 to 250 ppm) have also been found in igneous zircons from three continental parent rocks: granites, Li-rich pegmatites, and migmatites in pelitic metasediment. The substitution of trivalent cations (REEs and Y) in zircon correlates with Li + 1 and P + 5 , suggesting that an interstitial site for Li, as well as the xenotime substitution for P, provides charge balance for REEs. Li is thus fixed in the zircon structure by coupled substitutions, and diffusive changes in [Li] composition are rate-limited by slow diffusion of REEs. The Jack Hills zircons also have fractionated lithium isotope ratios ( δ7Li = - 19 to + 13‰) about five times more variable than those recorded in primitive ocean floor basalts (2 to 8‰), but similar to continental crust and its weathering products. Values of δ7Li below - 10‰ are found in zircons that formed as early as 4300 Ma. The high Li compositions indicate that primitive magmas were not the source of Jack Hills zircons and the fractionated values of δ7Li suggest that highly weathered regolith was sampled by these early Archean magmas. These new Li data provide evidence that the parent magmas of ancient zircons from Jack Hills incorporated materials from the surface of the Earth that interacted at low temperature with liquid water. These data support the hypothesis that continental-type crust and oceans existed by 4300 Ma, within 250 million years of the formation of Earth and the low values of δ7Li suggest that weathering was extensive in the early Archean.

The geology and ore deposits of Upper Mayflower Gulch, Summit County, Colorado

USGS Publications Warehouse

Randall, John Alexander

1958-01-01

Upper Mayflower Gulch is on the highly glaciated western side of the Tenmile Range near Kokomo in central Colorado. Somewhat less than $500,000 in silver and gold has been produced from the area since the first mining in the 1880' s. In the mapped area high grade regional metamorphism has produced two varieties of gneiss and a granulite. Total thickness of the rocks is about 5,000 feet. Relict bedding is preserved in compositional banding which strikes north to N. 20 ? E. and dips 70 ? to 80 ? southeast. No significant folding was observed. Normal faulting has occurred since the Precambrian; two major sets of faults are recognizable: (1) a set striking N. 70 ? to 85 ? E. and dipping 75?-85 ? NW; and (2) a set striking N. 70?-50 ? W. and dipping 50?-60 ? SW. Tabular bodies of pegmatite and retrogressively metamorphosed schist along many faults indicate Precambrian movement. The Mayflower fault, a 90 to 300 foot wide zone of siltification and shattered rock, strikes about N. 40 ? W. It extends the entire length of the gulch and appears to form the northern terminus for the northeast trending Mosquito Fault. The Mayflower fault shows repeated movement since the Precambrian, totaling about 3,000 feet of apparent dip slip and 640 feet of apparent strike slip. Faulting during the Tertiary includes both additional movement along Precambrian faults and development of shears trending N. to N. 20 ? E. The shears served as channels for the intrusion of two varieties of quartz latite porphyry dikes. Specular hematite and base-metal sulfide mineralization followed intrusion of the porphyry dikes; the minerals were deposited in open fault zones by high temperature solutions in a low pressure environment. The principal metallic minerals in order of deposition are: hematite, pyrite, chalcopyrite, sphalerite, galena, and rarer argentite. The major mines are the Gold Crest, Payrock, Nova Scotia Boy, and Bird's Nest.

Structural mechanism of the formation of mineral Na-tveitite-a new type of phase with a fluorite-derivative structure-in the NaF-CaF{sub 2}-(Y,Ln)F{sub 3} natural system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golubev, A. M., E-mail: fluorides@ns.crys.ras.ru; Otroshchenko, L. P.; Sobolev, B. P.

2012-03-15

Relationships between the chemical compositions and structures of the mineral tveitite from the southern Norway pegmatites (with the idealized formula Ca{sub 14}Y{sub 5}F{sub 43}) and Na-tveitite from the Rov mountain (Keivy, Kola Peninsula) Na{sub 2.5}Ca{sub 10}Ln{sub 1.5}Y{sub 5}F{sub 42} are considered. According to the structural mechanism of its formation, Na-tveitite is a nanocomposite crystal based on the crystalline matrix Ca{sub 14}Y{sub 5}F{sub 43} with the ordered arrangement of {l_brace}Ca{sub 8}[CaY{sub 5}]F{sub 69}{r_brace} clusters which contain anionic {l_brace}F{sub 13}{r_brace} cuboctahedra with F{sup 1-} at the center. When Na-tveitite is formed, 29% of these clusters are statistically replaced by Na-'Y' clusters {l_brace}[Na{submore » 0.5}(Y,Ln){sub 0.5}]{sub 14}F{sub 64}{r_brace} with {l_brace}F{sub 8}{r_brace} cubes at the center (analogs of matrix fluorite groups {l_brace}Ca{sub 14}F{sub 64}{r_brace}). This replacement gives rise to composition-imperfect (Na, Ca, 'Y') cationic positions and occupancy-deficient F positions, which correspond to {l_brace}F{sub 13}{r_brace} cuboctahedra and the {l_brace}F{sub 8}{r_brace} cubes that replace them. The difference between Na-tveitite and fluorite phases M{sub 1-x}R{sub x}F{sub 2+x} is as follows: its matrix is the structure of the ordered phase (tveitite) into which Na-containing rare earth fragments of fluorite-type structure are incorporated instead of ordered-phase structural blocks (clusters).« less

Radioactive rare-earth deposit at Scrub Oaks mine, Morris County, New Jersey

USGS Publications Warehouse

Klemic, Harry; Heyl, A.V.; Taylor, Audrey R.; Stone, Jerome

1959-01-01

A deposit of rare-earth minerals in the Scrub Oaks iron mine, Morris County, N. J., was mapped and sampled in 1955. The rare-earth minerals are mainly in coarse-grained magnetite ore and in pegmatite adjacent to it. Discrete bodies of rare-earth-bearing magnetite ore apparently follow the plunge of the main magnetite ore body at the north end of the mine. Radioactivity of the ore containing rare earths is about 0.2 to 0.6 mllliroentgens per hour. The principal minerals of the deposit are quartz, magnetite, hematite, albiteoligoclase, perthite and antiperthite. Xenotime and doverite aggregates and bastnaesite with intermixed leucoxene are the most abundant rare-earth minerals, and zircon, sphene, chevkinite, apatite, and monazite are of minor abundance in the ore. The rare-earth elements are partly differentiated into cerium-rich bastnaesite, chevkinite, and monazite, and yttrium-rich xenotime and doverite. Apatite, zircon, and sphene contain both cerium and yttrium group earths. Eleven samples of radioactive ore and rock average 0.009 percent uranium, 0.062 percent thorium, 1.51 percent combined rare-earth oxides including yttrium oxide and 24.8 percent iron. Scatter diagrams of sample data show a direct correlation between equivalent uranium, uranium, thorium, and combined rare^ earth oxides. Both cerium- and yttrium-group earths are abundant in the rare-earth minerals. Radioactive magnetite ore containing rare-earth minerals probably formed as a variant of the magnetite mineralization that produced the main iron ore of the Scrub Oaks deposit. The rare-earth minerals and the iron ore were deposited contemporaneously. Zircon crystals, probably deposited at the same time, have been determined by the Larsen method to be about 550 to 600 million years old (late Precambrian age). Uranium, thorium, and rare-earth elements are potential byproducts of iron in the coarse-grained magnetite ore.

Discrimination of iron ore deposits of granulite terrain of Southern Peninsular India using ASTER data

NASA Astrophysics Data System (ADS)

Rajendran, Sankaran; Thirunavukkarasu, A.; Balamurugan, G.; Shankar, K.

2011-04-01

This work describes a new image processing technique for discriminating iron ores (magnetite quartzite deposits) and associated lithology in high-grade granulite region of Salem, Southern Peninsular India using visible, near-infrared and short wave infrared reflectance data of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Image spectra show that the magnetite quartzite and associated lithology of garnetiferrous pyroxene granulite, hornblende biotite gneiss, amphibolite, dunite, and pegmatite have absorption features around spectral bands 1, 3, 5, and 7. ASTER band ratios ((1 + 3)/2, (3 + 5)/4, (5 + 7)/6) in RGB are constructed by summing the bands representing the shoulders of absorption features as a numerator, and the band located nearest the absorption feature as a denominator to map iron ores and band ratios ((2 + 4)/3, (5 + 7)/6, (7 + 9)/8) in RGB for associated lithology. The results show that ASTER band ratios ((1 + 3)/2, (3 + 5)/4, (5 + 7)/6) in a Red-Green-Blue (RGB) color combination identifies the iron ores much better than previously published ASTER band ratios analysis. A Principal Component Analysis (PCA) is applied to reduce redundant information in highly correlated bands. PCA (3, 2, and 1 for iron ores and 5, 4, 2 for granulite rock) in RGB enabled the discrimination between the iron ores and garnetiferrous pyroxene granulite rock. Thus, this image processing technique is very much suitable for discriminating the different types of rocks of granulite region. As outcome of the present work, the geology map of Salem region is provided based on the interpretation of ASTER image results and field verification work. It is recommended that the proposed methods have great potential for mapping of iron ores and associated lithology of granulite region with similar rock units of granulite regions of Southern Peninsular India. This work also demonstrates the ability of ASTER's to provide information on iron ores, which is valuable for mineral prospecting and exploration activities.

Crystalline basement map of Mauritania derived from filtered aeromagnetic data (deliverable 54_1), Aeromagnetic and geological structure map of Mauritania (phase V, deliverable 54_2), Maximum depth to basement map of Mauritania derived from Euler analysis of Aeromagnetic data (phase V, deliverable 54_3), and color composite image of radioelement data (added value): Chapter B1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Finn, Carol A.; Horton, John D.

2015-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Evolution of crystalline target rocks and impactites in the chesapeake bay impact structure, ICDP-USGS eyreville B core

USGS Publications Warehouse

Horton, J. Wright; Kunk, Michael J.; Belkin, Harvey E.; Aleinikoff, John N.; Jackson, John C.; Chou, I.-Ming

2009-01-01

The 1766-m-deep Eyreville B core from the late Eocene Chesapeake Bay impact structure includes, in ascending order, a lower basement-derived section of schist and pegmatitic granite with impact breccia dikes, polymict impact breccias, and cataclas tic gneiss blocks overlain by suevites and clast-rich impact melt rocks, sand with an amphibolite block and lithic boulders, and a 275-m-thick granite slab overlain by crater-fill sediments and postimpact strata. Graphite-rich cataclasite marks a detachment fault atop the lower basement-derived section. Overlying impactites consist mainly of basement-derived clasts and impact melt particles, and coastal-plain sediment clasts are underrepresented. Shocked quartz is common, and coesite and reidite are confirmed by Raman spectra. Silicate glasses have textures indicating immiscible melts at quench, and they are partly altered to smectite. Chrome spinel, baddeleyite, and corundum in silicate glass indicate high-temperature crystallization under silica undersaturation. Clast-rich impact melt rocks contain α-cristobalite and monoclinic tridymite. The impactites record an upward transition from slumped ground surge to melt-rich fallback from the ejecta plume. Basement-derived rocks include amphibolite-facies schists, greenschist(?)-facies quartz-feldspar gneiss blocks and subgreenschist-facies shale and siltstone clasts in polymict impact breccias, the amphibolite block, and the granite slab. The granite slab, underlying sand, and amphibolite block represent rock avalanches from inward collapse of unshocked bedrock around the transient crater rim. Gneissic and massive granites in the slab yield U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon dates of 615 ± 7 Ma and 254 ± 3 Ma, respectively. Postimpact heating was <~350 °C in the lower basement-derived section based on undisturbed 40Ar/39Ar plateau ages of muscovite and <~150 °C in sand above the suevite based on 40Ar/39Ar age spectra of detrital microcline.

Investigating Magmatic Processes in the Lower Levels of Mantle-derived Magmatic Systems: The Age & Emplacement of the Kunene Anorthosite Complex (SW Angola)

NASA Astrophysics Data System (ADS)

Hayes, B.; Bybee, G. M.; Owen-Smith, T.; Lehmann, J.; Brower, A. M.; Ashwal, L. D.; Hill, C. M.

2017-12-01

Our understanding of mantle-derived magmatic systems has shifted from a notion of upper crustal, melt-dominated magma chambers that feed short-lived volcanic eruptions, to a view of more long-lived trans-crustal, mush-dominated systems. Proterozoic massif-type anorthosite systems are voluminous, plagioclase-dominated plutonic suites with ubiquitous intermediate compositions (An 50 ± 10) that represent mantle-derived magmas initially ponded at Moho depths and crystallized polybarically until emplacement at mid-crustal levels. Thus, these systems provide unique insight into magma storage and processing in the lower reaches of the magma mush column, where such interpretation has previously relied on cumulate xenoliths in lavas, geophysical data and experimental/numerical modeling. We present new CA-ID-TIMS ages and a series of detailed field observations from the largest Proterozoic anorthosite massif on Earth, the Kunene Anorthosite Complex (KAC) of SW Angola. Field structures indicate that (i) the bulk of the material was emplaced in the form of crystal mushes, as both plutons and sheet-like intrusions; (ii) prolonged magmatism led to cumulate disaggregation (block structure development) and remobilization, producing considerable textural heterogeneity; (iii) crystal-rich magmatic flow induced localized recrystallization and the development of protoclastic (mortar) textures; and (iv) late residual melts were able to migrate locally prior to complete solidification. Dating of pegmatitic pods entrained from cumulate zones at the base of the crust (1500 ± 13 Ma) and their host anorthosites (1375-1438 Ma) reveals time periods in the range of 60-120 Myr between the earliest products of the system and the final mushes emplaced at higher crustal levels. Therefore, the KAC represents a complex, mushy magmatic system that developed over a long period of time. Not only do these observations help in refining our understanding of Proterozoic anorthosite petrogenesis, they also allow us to place constraints on the types of magmatic processes that operate in the lower levels of other trans-crustal magmatic systems.

Mesozoic intra-arc tectonics in the NE Mojave Desert, CA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stephens, K.A.; Schermer, E.R.; Walker, J.D.

1993-04-01

Field and U-Pb zircon geochronological data from the Tiefort Mts. (TM) and surrounding areas in the NE Mojave Desert provide new constraints on Precambrian to Paleozoic paleogeography and Mesozoic intra-arc tectonics. Amphibolite facies metasediments appear to correlate with lower Paleozoic miogeoclinal sequences. Coarse-grained K-feldspar augen gneiss occurs in sharp contact with the metasedimentary rocks; U-Pb dating yields a 1393[+-]12 Ma age. This gneiss is interpreted to represent cratonal basement of North America. A texturally and compositionally heterogeneous amphibolite-facies monzonitic complex which intrudes the basement and metasediments yields a mid-Jurassic age. Felsite and biotite granite that intrude the foliated monzonitic complexmore » locally contain the mylonitic fabric and appear to be syn-late kinematic. Undeformed pegmatite, granite, and microdiorite appear as dikes throughout the region. Vertical silicic dikes at southern TM trend N5-25E and are dated at 148[+-]14 Ma, coeval with the Independence dike swarm (IDS). Similar dikes that occur at TM trend N60-80E. Undeformed granite cross-cuts the foliated monzonite; some granitic rocks cut dikes of the IDs and are likely to be Cretaceous in age. The E- to SE-vergence and mid-late Jurassic age of ductile shear zones in the TM region are similar to that in nearby parts of the East Sierra Thrust System (ESTS). If NE and NNE dikes are IDS-equivalent, this implies clockwise, vertical-axis rotation of 30[degree]--90[degree] by younger structures. The authors interpret this to be related to late Cenozoic strike-slip faults. Restoration of folds and the IDS to the regional NW trend results in top to the E to NE sense of shear during Jurassic deformation. Deformation in the TM and areas to the north connects the ESTS from the Garlock fault to the central Mojave region indicating a region in which mid-crustal levels of the arc and cratonal basement experienced contractional tectonism during mid-Jurassic time.« less

Vibrational spectroscopy of the phosphate mineral lazulite--(Mg, Fe)Al2(PO4)2·(OH)2 found in the Minas Gerais, Brazil.

PubMed

Frost, Ray L; Xi, Yunfei; Beganovic, Martina; Belotti, Fernanda Maria; Scholz, Ricardo

2013-04-15

This research was done on lazulite samples from the Gentil mine, a lithium bearing pegmatite located in the municipality of Mendes Pimentel, Minas Gerais, Brazil. Chemical analysis was carried out by electron microprobe analysis and indicated a magnesium rich phase with partial substitution of iron. Traces of Ca and Mn, (which partially replaced Mg) were found. The calculated chemical formula of the studied sample is: (Mg0.88, Fe0.11)Al1.87(PO4)2.08(OH)2.02. The Raman spectrum of lazulite is dominated by an intense sharp band at 1060 cm(-1) assigned to PO stretching vibrations of of tetrahedral [PO4] clusters presents into the HPO4(2-) units. Two Raman bands at 1102 and 1137 cm(-1) are attributed to both the HOP and PO antisymmetric stretching vibrations. The two infrared bands at 997 and 1007 cm(-1) are attributed to the ν1PO4(3-) symmetric stretching modes. The intense bands at 1035, 1054, 1081, 1118 and 1154 cm(-1) are assigned to the ν3PO4(3-) antisymmetric stretching modes from both the HOP and tetrahedral [PO4] clusters. A set of Raman bands at 605, 613, 633 and 648 cm(-1) are assigned to the ν4 out of plane bending modes of the PO4, HPO4 and H2PO4 units. Raman bands observed at 414, 425, 460, and 479 cm(-1) are attributed to the ν2 tetrahedral PO4 clusters, HPO4 and H2PO4 bending modes. The intense Raman band at 3402 and the infrared band at 3403 cm(-1) are assigned to the stretching vibration of the OH units. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral lazulite to be understood. Copyright © 2013 Elsevier B.V. All rights reserved.

Duration of convergence at the Pacific-Gondwana plate margin: insights from accessory phase petrochronology of the Alpine Schist, New Zealand

NASA Astrophysics Data System (ADS)

Briggs, S. I.; Cottle, J. M.; Smit, M. A.; Arnush, N. F.

2016-12-01

The timing, duration and along-strike synchroneity of metamorphism and anataxis in the Alpine Schist of New Zealand is a matter of considerable debate. Our preliminary data indicate that metamorphism resulting in garnet growth occurred from 97 - 75 Ma, and anatectic melting occurred from 80 - 51 Ma. These events are contemporaneous with rifting of Zealandia from East Gondwana, and Tasman Sea spreading from 83 - 52 Ma. An important implication of these results is that Late Cretaceous convergence along the Zealandia segment of the Pacific-Gondwana plate margin may have persisted much later than previously thought, and that convergence and extension occurred coevally in adjacent areas. This poses the question: for how long did convergence continue along the Pacific-Gondwana plate margin during East Gondwana breakup? To fully decipher the multiple stages of the complex metamorphic history recorded in the Alpine Schist, we combine Lu-Hf garnet geochronology with U-Th/Pb and REE analyses of zircon and monazite. We use the newly developed `single-shot laser ablation split stream' (SS-LASS) analysis method to obtain depth profiles through 5-10 µm metamorphic zircon overgrowths at 100 nm depth resolution to constrain both the timing and petrological context of discrete metamorphic zircon (re-)crystallization events recorded in the Alpine Schist. We also employ high spatial resolution LASS analysis to target rare 5 - 20 µm monazite in thin section to augment garnet and zircon data. Our multi-accessory phase petrochronology approach is capable of resolving discrete short-duration thermal events, strengthening the geological interpretation of `mean' Lu-Hf garnet ages and discerning between an episodic versus a prolonged history of metamorphism. In addition, comparison with geochronology from anatectic pegmatites clarifies the temporal relationship between metamorphism and melting in the Alpine Schist, while providing direct constraints on the timing and duration of convergence along the Zealandia segment of the Pacific-Gondwana margin.

Constraining the 40K decay constant with 87Rb-87Sr - 40K-40Ca chronometer intercomparison

NASA Astrophysics Data System (ADS)

Naumenko-Dèzes, Maria O.; Nägler, Thomas F.; Mezger, Klaus; Villa, Igor M.

2018-01-01

A literature survey reveals that the K-Ar chronometer gives ages that are ca. 1% younger than U-Pb ages. This offset is generally attributed to an inaccurate 40K decay constant. Three geological samples selected from a shortlist of eight with known U-Pb ages were investigated using detailed petrological methods and subsequently the Rb-Sr and K-Ca chronometers in order (a) to evaluate if they meet the requirement of a geological history reflecting a ;point-like; event (i.e. isochronous formation and subsequent ideal closure of chronometers) and (b) to narrow down the systematic uncertainty on the 40K decay constant by investigating the metrologically traceable K-Ca decay branch. Lepidolite of the Rubikon pegmatite, Namibia, was dated with Rb-Sr at 504.7 ± 4.2 Ma and the phlogopite and apatite from the Phalaborwa carbonatite complex, South Africa, yielded a Rb-Sr age of 2058.9 ± 5.2 Ma. Both Rb-Sr ages agree with published U-Pb ages. The Rb-Sr age of the late Archean Siilinjärvi carbonatite, Finland, records a later regional metamorphic event at 1869 ± 10 Ma. Only the samples from the Phalaborwa complex represent a ;point-like; magmatic event and meet all the criteria to make them suitable for the 40K decay constant intercalibration. The Phalaborwa K-Ca isochron has a slope of 1.878 ± 0.012. Forcing the K-Ca isochron to coincide with the U-Pb and Rb-Sr ages gives one equation with two unknowns. Assuming that the branching ratio of the K-Ca branch, BCa, lies in the interval (k = 2) of all published references, 0.8925 < BCa < 0.8963, then the most reliable uncertainty interval (k = 2) for the total 40K decay constant, λtot, is calculated as 5.484 × 10-10 a-1 < λtot < 5.498 × 10-10 a-1. This confirms that the currently used IUGS recommendation is inaccurate.

Photograph of the month

NASA Astrophysics Data System (ADS)

2016-10-01

Complex fold pattern superposition in the migmatite core of the Archean Yalgoo Dome, Yilgarn Craton, WA (Myers, J.S. et al., 1985. Geology 13, 778). East-trending F1 axial traces are folded around N-trending F2 axial traces, and truncated by S2, filled with axial planar leucosome. Note that most D2 leucosomes are subparallel to F2 axial traces, but not exactly located along them. Fold interference pattern types 1, 2 and 3 (Ramsay, J. G., 1967) seem to coexist in different portions of this platform. The transition between interference types is likely due to the highly non-cylindrical character of F1 folds. Furthermore, the "dome and basin" pattern, highlighted by ring-shaped layers, results from a subhorizontal cut through the culmination of F1 sheath folds. Such interpretation is supported by: (i) existence of F1 sheath folds in areas unaffected by F2 folds, and (ii) subhorizontal F2 axes, rather than the vertical observed, would be required in order to generate "dome and basin" pattern by fold superposition. The tonalite protolith of the migmatite was emplaced at c. 2.95Ga, and then deformed together with host greenstones (D1 event). Layering in the migmatite is due to alternating biotite-rich melanosomes, leucosomes bearing thin selvages, mesocratic tonalite gneiss and pegmatite to aplite veins. The pervasive, E-W trending S1 is associated with subvertical stretching lineation and is axial planar to subvertical, m- to km-scale highly sheath folds. At c. 2.75Ga, the tonalite-greenstone complex recorded a second episode of syndeformational melting (D2), accompanied by the emplacement of granites surrounding the tonalite. In migmatites, S2 occurs as N-trending, subvertical leucosomes and dykes, that are axial planar to N-trending, open to isoclinal vertical folds. 28°42‧S, 116°39‧E. Photograph© Ivan Zibra and Roberto Weinberg.

Initial yield to depth relation for water wells drilled into crystalline bedrock - Pinardville quadrangle, New Hampshire

USGS Publications Warehouse

Drew, L.J.; Schuenemeyer, J.H.; Amstrong, T.R.; Sutphin, D.M.

2001-01-01

A model is proposed to explain the statistical relations between the mean initial water well yields from eight time increments from 1984 to 1998 for wells drilled into the crystalline bedrock aquifer system in the Pinardville area of southern New Hampshire and the type of bedrock, mean well depth, and mean well elevation. Statistical analyses show that the mean total yield of drilling increments is positively correlated with mean total well depth and mean well elevation. In addition, the mean total well yield varies with rock type from a minimum of 46.9 L/min (12.4 gpm) in the Damon Pond granite to a maximum of 74.5 L/min (19.7 gpm) in the Permian pegmatite and granite unit. Across the eight drilling increments that comprise 211 wells each, the percentages of very low-yield wells (1.9 L/min [0.5 gpm] or less) and high-yield wells (151.4 L/min [40 gpm] or more) increased, and those of intermediate-yield wells decreased. As housing development progressed during the 1984 to 1998 interval, the mean depth of the wells and their elevations increased, and the mix of percentages of the bedrock types drilled changed markedly. The proposed model uses a feed-forward mechanism to explain the interaction between the increasing mean elevation, mean well depth, and percentages of very low-yielding wells and the mean well yield. The increasing percentages of very low-yielding wells through time and the economics of the housing market may control the system that forces the mean well depths, percentages of high-yield wells, and mean well yields to increase. The reason for the increasing percentages of very low-yield wells is uncertain, but the explanation is believed to involve the complex structural geology and tectonic history of the Pinardville quadrangle.

A Geothermochronologic Investigation of the Coyote Mountains Metamorphic Core Complex (AZ)

NASA Astrophysics Data System (ADS)

Borel, M.; Gottardi, R.; Casale, G.

2017-12-01

The Coyote Mountains metamorphic core complex (CM-MCC) makes up the northern end of the Baboquivari Mountain complex, which is composed of Mesozoic rocks, Tertiary granites, pegmatites, and metasediments. The CM-MCC expose the Pan Tak granite, a 58 Ma intrusive muscovite-biotite-garnet peraluminous granite. The Pan Tak and other intrusions within the Baboquivari Mountains have been interpreted as anatectic melts representing the culmination of a Laramide crustal shortening orogenic event started in the Late Cretaceous ( 70 Ma). Evidence of this magmatic episode includes polysynthetic twinning in plagioclase, myrmekitic texture in alkali feldspars, and garnet, mica and feldspar assemblages. The magmatic fabric is overprinted by a Tertiary tectonic fabric, associated with the exhumation of the CM-MCC along the Ajo road décollement and associated shear zone. In the shear zone, the Pan Tak mylonite display N-dipping foliation defined by gneissic layering and aligned muscovite, and N-trending mineral stretching lineation. Various shear sense indicators are all consistent with a top-to the-N shear sense. Preliminary argon geochronology results suggest that the shear zone was exhumed 29 Ma ago, an age similar to the onset of detachment faulting in other nearby MCCs (Catalina, Rincon, Pinaleño). In the Pan Tak mylonite, quartz grains display regime 2 to 3 microstructures and shows extensive recrystallization by subgrain rotation and grain boundary migration. The recrystallized grain size ranges between 20 and 50 µm in all samples. Quartz crystallographic preferred orientation measured using electron backscatter diffraction (EBSD) shows that recrystallization was accommodated by dominant prism and minor rhomb slip, suggesting deformation temperature ranging from 450°C to 550°C. These preliminary results constrain the timing of uplift and exhumation, and thermomechanical evolution of the CM-MCC, and improve our understanding of recycling of the continental crust in southern Arizona.

Petrographic and geochemical comparisons between the lower crystalline basement-derived section and the granite megablock and amphibolite megablock of the Eyreville-B core, Chesapeake Bay impact structure

USGS Publications Warehouse

Townsend, Gabrielle N.; Gibson, Roger L.; Horton, J. Wright; Reimold, Wolf Uwe; Schmitt, Ralf T.; Bartosova, Katerina

2009-01-01

The Eyreville B core from the Chesapeake Bay impact structure, Virginia, USA, contains a lower basement-derived section (1551.19 m to 1766.32 m deep) and two megablocks of dominantly (1) amphibolite (1376.38 m to 1389.35 m deep) and (2) granite (1095.74 m to 1371.11 m deep), which are separated by an impactite succession. Metasedimentary rocks (muscovite-quartz-plagioclase-biotite-graphite ± fibrolite ± garnet ± tourmaline ± pyrite ± rutile ± pyrrhotite mica schist, hornblende-plagioclase-epidote-biotite-K-feldspar-quartz-titanite-calcite amphibolite, and vesuvianite-plagioclase-quartz-epidote calc-silicate rock) are dominant in the upper part of the lower basement-derived section, and they are intruded by pegmatitic to coarse-grained granite (K-feldspar-plagioclase-quartz-muscovite ± biotite ± garnet) that increases in volume proportion downward. The granite megablock contains both gneissic and weakly or nonfoliated biotite granite varieties (K-feldspar-quartz-plagioclase-biotite ± muscovite ± pyrite), with small schist xenoliths consisting of biotite-plagioclase-quartz ± epidote ± amphibole. The lower basement-derived section and both megablocks exhibit similar middle- to upper-amphibolite-facies metamorphic grades that suggest they might represent parts of a single terrane. However, the mica schists in the lower basement-derived sequence and in the megablock xenoliths show differences in both mineralogy and whole-rock chemistry that suggest a more mafic source for the xenoliths. Similarly, the mineralogy of the amphibolite in the lower basement-derived section and its association with calc-silicate rock suggest a sedimentary protolith, whereas the bulk-rock and mineral chemistry of the megablock amphibolite indicate an igneous protolith. The lower basement-derived granite also shows bulk chemical and mineralogical differences from the megablock gneissic and biotite granites.

Geology of the Wood and East Calhoun mines, Central City District, Gilpin County, Colorado

USGS Publications Warehouse

Drake, Avery Ala

1955-01-01

The Wood-East Calhoun mine area is underlain by complexly folded Precambrian gneiss and pegmatite. The major fold in the area is an anticline that trends about N. 60° E. The Precambrian rocks are intruded by bostonite porphyry dikes of Tertiary age. All the rocks are cut by east- to northeast - trending faults that have been filled by precious metal-sulfide veins which have been worked chiefly for gold. The Wood vein occurs in an east-trending fault; the Calhoun vein occurs in a northeast-trending fault. Much of the uranium production of the Central City district has come from the Wood vein on Quartz Hill. The veins consist chiefly of quartz; pyrite is the chief metallic mineral and chalcopyrite is next in abundance. Sphalerite, galena, tetrahedrite-tennantite, and pitchblende are locally present. Deposition began with alteration-stage quartz and pyrite followed in order by pitchblend, light-yellow pyrite, massive quartz, yellow pyrite, shalerite, comb quartz, chalcopyrite, tetrahedrite-tennantite, galena, chalcopyrite, pyrite, and gray to light-brown fine-grained quartz. The veins of the Central City district are zoned, with quartz-pyrite veins near the center and galena-sphalerite veins on the periphery. The known pitchblende bodies are in the transition between these, but paragenetically, the pitchblende is earlier than all other metallic minerals. A trace element study of the ore indicates an association of zirconium and molybdenum with uranium, of bismuth, antimony, and arsenic with copper, and of cadmium with zinc. The pitchblende and other ore minerals are concentrated in ore shoots. The shoots are in open spaces controlled by the competency of the wall rocks, the presence of a prevailing direction of weakness in the rocks, and changes in strike and dip of the vein. The pitchblende is thought to be a local constituent of the quartz-pyrite ores and to owe its origin to residual solutions from the quartz bostonite magma.

Observations on the crystallization of spodumene from aqueous solutions in a hydrothermal diamond-anvil cell

USGS Publications Warehouse

Li, Jianking; Chou, I-Ming; Yuan, Shunda; Burruss, Robert A.

2013-01-01

Crystallization experiments were conducted in a new type of hydrothermal diamond-anvil cell (HDAC; type V) using LiAlSi2O6 (S) gel and H2O (W) as starting materials. A total of 21 experiments were performed at temperatures up to 950°C and pressures up to 788 MPa. In the samples with relatively low W/S ratios, many small crystals formed in the melt phase during cooling. In those with high W/S ratios, only a few crystals with smooth surfaces crystallized from the aqueous fluid in the presence of melt droplets, which were gradually consumed during crystal growth, indicating rapid transfer of material from the melt to the crystals through the aqueous fluid. The nucleation of crystals started at 710 (±70)°C and 520 (±80) MPa, and crystal growth ended at 570 (±40)°C and 320 (±90) MPa, with the cooling P-T path within the stability field of spodumene + quartz in the S-W system. The observed linear crystal growth rates in the aqueous phase, calculated by dividing the maximum length of a single crystal by the duration of the entire growth step, were 4.7 × 10−6 and 5.7 × 10−6 cm s−1 for the cooling rates of 0.5 and 1°C min−1, respectively. However, a rapid crystal growth rate of 3.6 × 10−5 cm s−1 in the aqueous fluid was observed when the components were supplied by nearby melt droplets. Our results show that when crystals nucleate in the aqueous fluid instead of the melt phase, there are fewer nuclei formed, and they grow much faster due to the low viscosity of the aqueous fluid, which accelerates diffusion of components for the growth of crystals. Therefore, the large crystals in granitic pegmatite can crystallize directly from aqueous fluids rather than hydrosilicate melt.

Experimental Study into the Stability of Whitlockite and Hydroxylapatite in Basaltic Magmas

NASA Technical Reports Server (NTRS)

McCubbin, F. M.; Barnes, J. J.; Vander Kaaden, K. E.; Srinivasan, P.; Whitson, E. S.; Turner, A.; Reppart, J. J.

2018-01-01

Apatite (Ca5(PO4)3(F,Cl,OH)), merrillite (Ca18Na2Mg2(PO4)14), and whitlockite (Ca9(Mg,Fe(2+))(PO4)6[PO3(OH)]) are the primary phosphate minerals found in most planetary materials including rocks from Earth, Moon, Mars, and asteroids. For many years, the terms merrillite and whitlockite have been used interchangeably in the meteorite literature. Much of the confusion regarding the relationship between terrestrial and extraterrestrial 'whitlockite' is based on the presence or absence of hydrogen in the mineral structure. Whitlockite has approximately 8500 ppm H2O, and the term 'merrillite' has been adopted to identify the hydrogen-free form of whitlockite. The atomic structures of merrillite and whitlockite were examined in detail by Hughes et al.. On Earth, whitlockite has been found in rocks from evolved pegmatitic systems and in some mantle rocks. Furthermore, terrestrial whitlockite has been shown to have some merrillite component. For the meteoritic and lunar materials that have been investigated, merrillite appears to be far more common than whitlockite, and it has been proposed that the whitlockite component is unique to terrestrial samples. There are some reports of 'whitlockite' in the meteorite literature; however, these may represent misidentifications of merrillite because there have been no reports of extraterrestrial whitlockite that have been verified through crystal structural studies or analyzed for their H contents. Hughes et al. reported the atomic arrangement of lunar merrillite and demonstrated that the phase is similar to meteoritic merrillite and, predictably, devoid of hydrogen. In a follow-up study, Hughes et al. reported the atomic arrangements of two natural samples of whitlockite, one synthetic whitlockite, and samples of synthetic whitlockite that were heated at 500 C or 1050 C for 24 h. The crystal chemistry and crystal structures of the phases were compared, and it was discovered that the latter treatment resulted in the dehydrogenation of whitlockite to form merrillite.

Cambro-Ordovician post-collisional granites of the Ribeira belt, SE-Brazil: A case of terminal magmatism of a hot orogen

NASA Astrophysics Data System (ADS)

Valeriano, Claudio de Morisson; Mendes, Julio Cezar; Tupinambá, Miguel; Bongiolo, Everton; Heilbron, Monica; Junho, Maria do Carmo Bustamante

2016-07-01

This work presents an overview of the geology and chemical composition of the Cambrian-Ordovician post-collisional (COPC) granites and associated rocks of Ribeira belt, SE-Brazil. These COPC granites make up some of the most picturesque and highest (>2000 m) rocky peaks and cliffs of Rio de Janeiro state, an accessible case of post-orogenic granitic magmatism associated with the terminal stages of a hot Ediacaran-Cambrian (Brasiliano-Panafrican) orogen. The COPC magmatism intruded tonalitic to granitic orthogneisses of the Rio Negro arc (∼790-600 Ma) and associated paragneisses of the São Fidelis Group. Post-collisional magmatism started ∼10 m.y. after the latest collisional event, the Buzios Orogeny, lasting discontinuously from ∼510 Ma until ∼470 Ma. The 15 largest intrusive bodies in Rio de Janeiro State are referred to in the literature as the Parati/Mangaratiba, Vila Dois Rios, Pedra Branca, Suruí, Silva Jardim, Favela, Andorinha, Teresópolis, Frade, Nova Friburgo, Conselheiro Paulino, São José do Ribeirão, Sana and Itaoca granites. They crop out as rounded/elliptical stocks or gently-dipping sheets, always with sharp contacts with the country rocks, along with pegmatite and aplitic veins and dykes. COPC granites are grey and pink undeformed medium-grained biotite monzogranites with (K-feldspar) porphyritic, mega-crystic, equigranular and serial textures. Magmatic flow foliation is frequently observed. Peripheric xenolith zones are common as well as isolated xenoliths from the country rocks. In a compilation of more than 100 chemical compositions, SiO2 contents display a major mode at 71wt%. The COPC magmatism generated high-K calc-alkaline granites and quartz monzonites with predominantly metaluminous granites. Meso to melanocratic gabbroic and dioritic enclaves also have calc-alkaline affinity and likely represent more resistant mafic xenoliths from the Rio Negro Arc.

From ocean depths to mountain tops: uplift of the Troodos Massif (Cyprus) constrained by (U-Th)/He thermochronology and geomorphic analysis

NASA Astrophysics Data System (ADS)

Morag, N.; Haviv, I.; Katzir, Y.

2013-12-01

The Troodos Massif of Cyprus, rising to nearly 2000 meters above sea level, encompasses one of the world's classic ophiolites. Following its formation at a seafloor spreading center in Late Cretaceous times, this slice of the NeoTethyan oceanic lithosphere was uplifted and eventually exposed on mountain tops during the Neogene. The final uplift and exhumation of the Troodos was previously assigned to Pleistocene age by observations in the circum-Troodos sedimentary strata. However, quantitative thermochronological and geomorphological data from the Massif itself were not available. Here we use apatite (U-Th)/He low-temperature thermochronology complemented by zircon (U-Th)/He and apatite fission track data, and combined with geomorphic analysis to constrain the exhumation and uplift history of the Troodos ophiolite. Apatite (U-Th)/He ages vary with depth from ~ 22 Ma at the top of the Gabbro sequence to ~ 6 Ma at the bottom of the sequence. The deepest sample from a Gabbro pegmatitic dyke intruding the ultramafic sequence yielded an age of ~ 3 Ma. Thermal modeling of apatite (U-Th)/He and fission track data delineates Plio - Pleistocene initiation of rapid uplift and exhumation of the Troodos ophiolite. The estimated cumulative exhumation since its initiation is 2-3 km. No evidence was found for significant uplift of the central Troodos area prior to that time. The geomorphic analysis delineates a bull's-eye zone at the center of the Troodos Massif, where local relief and channel steepness index are highest. The boundaries of this zone roughly correspond with the Mt. Olympus mantle outcrop and suggest recent, differential uplift of this zone relative to its surroundings. The most likely mechanism, which could drive such a focused bull's-eye uplift pattern is hydration of ultramafic rocks (serpentinization) leading to a decrease in rock density and subsequent diapiric uplift of the serpentinized lithospheric mantle.

Quantitative Analysis of Piezoelectric and Seismoelectric Anomalies in Subsurface Geophysics

NASA Astrophysics Data System (ADS)

Eppelbaum, Lev

2017-04-01

The piezoelectric and seismo-electrokinetic phenomena are manifested by electrical and electromagnetic processes that occur in rocks under the influence of elastic oscillations triggered by shots or mechanical impacts (hits) (e.g., Neishtadt and Osipov, 1958; Neishtadt, 1961; Parkhomenko, 1971; Neishtadt et al., 1986; Maxwell et al., 1992; Butler et al., 1994; Kepic et al., 1995; Neishtadt et al., 1996; Mikhalov et al., 1997; Boulytchov, 2000; Dupuis et al., 2009; Schakel et al., 2011; Neishtadt and Eppelbaum, 2012; Jouniaux and Zyserman, 2016). The developed classification divides the above phenomena into the following types: (1) the seismo-electrokinetic (electrokinetic) phenomenon E, which occurs in polyphase media due to the mutual displacement of the solid and liquid phases; (2) the piezoelectric phenomenon, which occurs in rocks that contain piezoactive minerals; (3) the shot-triggered phenomenon, which is observed in rocks in the vicinity of a shot or hit point; (4) the seismoelectric phenomenon I, manifested by the change of the electric current passing through rocks, and (5) high-frequency impulse electromagnetic radiation, which is generated by massive base-metal bodies. This paper describes the above phenomena in detail, describing their nature, manifestation patterns, and registration techniques. Because the manifestation patterns of the above phenomena are different in different rocks, these phenomena can be used as a basis for geophysical exploration techniques. The piezoelectric method is an example of a successful application of piezoelectric and seismo-electrokinetic phenomena in exploration geophysics. It has been successfully applied in mineral exploration and environmental features research in Russia, USA, Canada, Australia, Belorussia, Azerbaijan, Georgia, Israel and other countries. This method uses comparatively new geophysical parameter - piezoelectric activity of rocks, ores, and minerals. It enables direct exploration for pegmatite, apatite-nepheline, essentially sphalerite, and ore-quartz deposits of gold, tin, tungsten, molybdenum, zinc, crystal, and other raw materials. This method also enables differentiation of rocks such as bauxites, kimberlites, etc., from the host rocks, by their electrokinetic properties. Classification of some rocks, ores, and minerals by their piezoactivity is given in Table 1. These objects (targets) transform wave elastic oscillations into electromagnetic ones. It should be taken into account that anomalous bodies may be detected not only by positive, but also by negative anomalies, if low-piezoactive body occurs in the higher piezoactive medium. The piezoelectric method is an example of successful application of piezoelectric and seismo-electrokinetic phenomena in exploration and environmental geophysics and designed for delineation of targets differing from the host media by piezoelectric properties (Neishtadt et al., 2006, Neishtadt and Eppelbaum, 2012). This method is employed in surface, downhole, and underground modes. Recent testing of piezeoelectric effects of archaeological samples composed from fired clay have shown values of 2.0 - 3.0 ṡ 10-14 C/N. However, absence of reliable procedures for solving the direct and inverse problems of piezoelectric anomalies (PEA), drastically hampers further progression of the method. Therefore, it was suggested to adapt the tomography procedure, widely used in the seismic prospecting, to the PEA modeling. Diffraction of seismic waves has been computed for models of circular cylinder, thin inclined bed and thick bed (Alperovich et al., 1997). As a result, spatial-time distribution of the electromagnetic field caused by the seismic wave has been found. The computations have shown that effectiveness and reliability of PEA analysis may be critically enhanced by considering total electro- and magnetograms as differentiated from the conventional approaches. Distribution of the electromagnetic field obtained by solving the direct problem was the basis for an inverse problem, i.e. revealing depth of a body occurrence, its location in a space as well as determining physical properties. At the same time, this method has not received a wide practical application taking into account complexity of real geological media. Careful analysis piezo- and seismoelectric anomalies shows the possibility of application of quantitative analysis of these effects advanced methodologies developed in magnetic prospecting for complex physical-geological conditions (Eppelbaum et al., 2000, 2001, 2010; Eppelbaum, 2010; 2011, 2015). Employment of these methodologies (improved modifications of tangents, characteristic points areal methods) for obtaining quantitative characteristics of ore bodies, environmental features and archaeological targets (models of horizontal circular cylinder, sphere, thin bed, thick bed and thin horizontal plate were utilized) have demonstrated their effectiveness. Case study at the archaeological site Tel Kara Hadid Field piezoelectric observations were conducted at the ancient archaeological site Tel Kara Hadid with gold-quartz mineralization in southern Israel within the Precambrian terrain at the northern extension of the Arabian-Nubian Shield (Neishtadt et al., 2006). The area of the archaeological site is located eight kilometers north of the town of Eilat, in an area of strong industrial noise. Ancient river alluvial terraces (extremely heterogeneous at a local scale, varying from boulders to silt) cover the quartz veins and complicate their identification. Piezoelectric measurements conducted over a quartz vein covered by surface sediments (approximately of 0.4 m thickness) produced a sharp (500 μV ) piezoelectric anomaly. Values recorded over the host rocks (clays and shales of basic composition) were close to zero. The observed piezoelectric anomaly was successfully interpreted by the use of methodologies developed in magnetic prospecting. For effective integration of piezo- and seismoelectric interpretation results with other geophysical methods, some schemes developed in theory of information (Eppelbaum, 2014) and wavelet theory (Eppelbaum et al., 2011) can be effectively applied. Table 1. Classification of some rocks, ores, and minerals by their piezoactivity d (10-14 Coulomb/Newton) (after Neishdadt et al., 2006 and Neishtadt and Eppelbaum, 2012, with modifications) Piezoactivity groupRock, Ore, Mineral dmin - dmaxdaver Quartz-tourmaline-cassiterite ore 0.8-28 15.7 Antimonite-quartz ore 0.2-1.35 0.6 I Apatite-nepheline ore 0-5 0.9 Galenite-sphalerite ore 0.2-7.7 3.3 Ijolite 0.1-8 1.2 Melteigite 0.2-5 1.6 Pegmatite 0.1-4.8 1.3 Skarn with galenite-sphalerite mineralization0.1-3 0.6 II Sphalerite-galenite ore 0.3-7.7 3.8 Turjaite 0.9-4.8 2.2 Urtite 0.1-32.5 3.4 Juvite 0.2-5.4 1.8 Aleurolite silicificated 0-0.5 0.2 Aplite 0-1.7 0.6 Breccia aleurolite-quartz 0.1-0.4 0.2 Gneiss 0-1.4 0.2 Granite 0-1.6 0.4 Granodiorite 0-0.2 0.1 Quartzite 0-3.3 0.6 III Pegmatite ceramic 0-1 0.15 Sandstone silicificated and tourmalinised 0.1-1.4 0.5 Feldspars 0-0.4 0.15 Porphyrite 0-0.3 0.1 Ristschorrite 0.3-0.9 0.5 Schist argillaceous 0-0.6 0.2 Hornfels 0-0.4 0.2 Skarn sphaleritic-garnet 0-1 0.3 Skarn pyroxene-garnet 0-0.2 0.1 Aleurolite, amphibolites, andesite, gabbro, 0-0.1 0.05 IV greisens, diabase, sandstone Argillite, beresite, dacite, diorite-porphyrite, 0 0 felsite-liparite, limestone, tuff, fenite I - highly active — piezo-activity of samples is greater than 5.0 ṡ 10-14 C/N II - moderately active — piezo-activity of samples is (0.5 - 5.0) ṡ 10-14 C/N III - weakly active — piezo-activity of samples is lower than 0.5 ṡ 10-14 C/N IV - non-active — piezo-activity of samples are near zero. REFERENCES Alperovich, L.S., Neishtadt, N.M., Berkovitch, A.L. and Eppelbaum, L.V., 1997. Tomography approach and interpretation of the piezoelectric data. Trans. of IX General Assembly of the European Geophysical Society. Strasbourg, France, 59/4P02, p. 546. Boulytchov, A., 2000, Seismic-electric effect method on guided and reflected waves. Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy, 25, No.4, 333-336. Butler, K.E., Russell, R.D., Kepic A.W. and Maxwell, M., 1994. Mapping of a stratigraphic boundary by its seismoelectric response. SAGEEP '94 Conference Proceedings, 689-699. Eppelbaum, L.V., 2010. Archaeological geophysics in Israel: Past, Present and Future. Advances in Geosciences, 24, 45-68. Dupuis, J.C., Butler, K.E., Kepic, A.W. and Harris, B.D., 2009. Anatomy of a seismoelectric conversion: Measurements and conceptual modeling in boreholes penetrating a sandy aquifer. Journal of Geophysical Research, 114, B10306, doi:10.1029/2008JB005939 Eppelbaum, L.V., 2011. Study of magnetic anomalies over archaeological targets in urban conditions. Physics and Chemistry of the Earth, 36, No. 16, 1318-1330. Eppelbaum, L.V., 2014. Geophysical observations at archaeological sites: Estimating informational content. Archaeological Prospection, 21, No. 2, 25-38. Eppelbaum, L.V., 2015. Quantitative interpretation of magnetic anomalies from thick bed, horizontal plate and intermediate models under complex physical-geological environments in archaeological prospection. Archaeological Prospection, 23, No. 2, 255-268. Eppelbaum, L.V., Alperovich, L., Zheludev, V. and Pechersky, A., 2011. Application of informational and wavelet approaches for integrated processing of geophysical data in complex environments. Proceed. of the 2011 SAGEEP Conference, Charleston, South Carolina, USA, 24, 24-60. Eppelbaum, L.V., Itkis, S.E. and Khesin, B.E., 2000. Optimization of magnetic investigations in the archaeological sites in Israel, In: Special Issue of Prospezioni Archeologiche "Filtering, Modeling and Interpretation of Geophysical Fields at Archaeological Objects", 65-92. Eppelbaum, L.V., Khesin, B.E. and Itkis, S.E., 2001. Prompt magnetic investigations of archaeological remains in areas of infrastructure development: Israeli experience. Archaeological Prospection, 8, No.3, 163-185. Eppelbaum, L.V., Khesin, B.E. and Itkis, S.E., 2010. Archaeological geophysics in arid environments: Examples from Israel. Journal of Arid Environments, 74, No. 7, 849-860. Jouniaux, L. and Zyserman, F., 2016. A review on electrokinetically induced seismo-electrics, electro-seismics, and seismo-magnetics for Earth sciences. Solid Earth, 7, 249-284. Kepic, A.W., Maxwell, M. and Russell, R.D., 1995. Field trials of a seismoelectric method for detecting massive sulfides. Geophysics, 60, 365-373. Maxwell, M., Russel, R.D., Kepic, A.W. and Butler, K.E., 1992. Electromagnetic responses from seismically excited targets: Non-Piezoelectric Phenomena. Exploration Geophysics, 23, 201-208. Mikhailov, O.V., Haarsten, M.W. and Toksoz, N., 1997. Electroseismic investigation of the shallow subsurface: Field measurements and numerical modeling. Geophysics, 62, No. 1, 97-105. Neishtadt, N.M., 1961. Searching pegmatites using seismo-electric effect of the second kind. Soviet Geology, No.1, 121-127. Neishtadt, N.M. and Eppelbaum, L.V., 2012. Perspectives of application of piezoelectric and seismoelectric methods in applied geophysics. Russian Geophysical Journal, Nos. 51-52, 63-80. Neishtadt, N., Eppelbaum, L. and Levitski, A., 2006. Application of seismo-electric phenomena in exploration geophysics: Review of Russian and Israeli experience. Geophysics, 71, No. 2, B41-B53. Neishdadt, N.M., Mazanova, Z.V., and Suvorov, N.D., 1986. The application of piezoelectric method for searching ore-quartz deposits in Yakutia. In: Seismic Methods of Studying Complex Media in Ore Regions. NPO Rudgeofizika, Leningrad, 109-116 (in Russian). Neishdadt, N.M., and Osipov, L.N., 1958. On using of seismoelectric effects of the second type observed by pegmatites searching. Trans. of VITR (All-Union Institute of Technical Prospecting Methods), 11, 63-71 (in Russian). Parkhomenko, E.I., 1971. Electrification Phenomena in Rocks. Plenum Press, New York. Schakel, M.D., Smeulders, D.M.J., Slob, E.C. and Heller, H.K.J., 2011. Seismoelectric interface response: Experimental results and forward model. Geophysics, 76, No. 4, p. N29-N36.

The Nolans Bore rare-earth element-phosphorus-uranium mineral system: geology, origin and post-depositional modifications

NASA Astrophysics Data System (ADS)

Huston, David L.; Maas, Roland; Cross, Andrew; Hussey, Kelvin J.; Mernagh, Terrence P.; Fraser, Geoff; Champion, David C.

2016-08-01

Nolans Bore is a rare-earth element (REE)-U-P fluorapatite vein deposit hosted mostly by the ~1805 Ma Boothby Orthogneiss in the Aileron Province, Northern Territory, Australia. The fluorapatite veins are complex, with two stages: (1) massive to granular fluorapatite with inclusions of REE silicates, phosphates and (fluoro)carbonates, and (2) calcite-allanite with accessory REE-bearing phosphate and (fluoro)carbonate minerals that vein and brecciate the earlier stage. The veins are locally accompanied by narrow skarn-like (garnet-diopside-amphibole) wall rock alteration zones. SHRIMP Th-Pb analyses of allanite yielded an age of 1525 ± 18 Ma, interpreted as the minimum age of mineralisation. The maximum age is provided by a ~1550 Ma SHRIMP U-Pb age for a pegmatite that predates the fluorapatite veins. Other isotopic systems yielded ages from ~1443 to ~345 Ma, implying significant post-depositional isotopic disturbance. Calculation of initial ɛNd and 87Sr/86Sr at 1525 Ma and stable isotope data are consistent with an enriched mantle or lower crust source, although post-depositional disturbance is likely. Processes leading to formation of Nolans Bore began with north-dipping subduction along the south margin of the Aileron Province at 1820-1750 Ma, producing a metasomatised, volatile-rich, lithospheric mantle wedge. About 200 million years later, near the end of the Chewings Orogeny, this reservoir and/or the lower crust sourced alkaline low-degree partial melts which passed into the mid- and upper-crust. Fluids derived from these melts, which may have included phosphatic melts, eventually deposited the Nolans Bore fluorapatite veins due to fluid-rock interaction, cooling, depressurisation and/or fluid mixing. Owing to its size and high concentration of Th (2500 ppm), in situ radiogenic heating caused significant recrystallisation and isotopic resetting. The system finally cooled below 300 °C at ~370 Ma, possibly in response to unroofing during the Alice Springs Orogeny. Surface exposure and weathering of fluorapatite produced acidic fluids and intense, near-surface kaolinitised zones that include high-grade, supergene-enriched cheralite-rich ores.

Source of boron in the Palokas gold deposit, northern Finland: evidence from boron isotopes and major element composition of tourmaline

NASA Astrophysics Data System (ADS)

Ranta, Jukka-Pekka; Hanski, Eero; Cook, Nick; Lahaye, Yann

2017-06-01

The recently discovered Palokas gold deposit is part of the larger Rompas-Rajapalot gold-mineralized system located in the Paleoproterozoic Peräpohja Belt, northern Finland. Tourmaline is an important gangue mineral in the Palokas gold mineralization. It occurs as tourmalinite veins and as tourmaline crystals in sulfide-rich metasomatized gold-bearing rocks. In order to understand the origin of tourmaline in the gold-mineralized rocks, we have investigated the major element chemistry and boron isotope composition of tourmaline from three areas: (1) the Palokas gold mineralization, (2) a pegmatitic tourmaline granite, and (3) the evaporitic Petäjäskoski Formation. Based on textural evidence, tourmaline in gold mineralization is divided into two different types. Type 1 is located within the host rock and is cut by rock-forming anthophyllite crystals. Type 2 occurs in late veins and/or breccia zones consisting of approximately 80% tourmaline and 20% sulfides, commonly adjacent to quartz veins. All the studied tourmaline samples belong to the alkali-group tourmaline and can be classified as dravite and schorl. The δ11B values of the three localities lie in the same range, from 0 to -4‰. Tourmaline from the Au mineralization and from the Petäjäskoski Formation has similar compositional trends. Mg is the major substituent for Al; inferred low Fe3+/Fe2+ ratios and Na values (<0.8 atoms per formula unit (apfu)) of all tourmaline samples suggest that they precipitated from reduced, low-salinity fluids. Based on the similar chemical and boron isotope composition and the Re-Os age of molybdenite related to the tourmaline-sulfide-quartz veins, we propose that the tourmaline-forming process is a result of a single magmatic-hydrothermal event related to the extensive granite magmatism at around 1.79-1.77 Ga. Tourmaline was crystallized throughout the hydrothermal process, which resulted in the paragenetic variation between type 1 and type 2. The close association of tourmaline and gold suggests that the gold precipitated from the same boron-rich source as tourmaline.

Strides in Preservation of Malawi's Natural Stone

NASA Astrophysics Data System (ADS)

Kamanga, Tamara; Chisenga, Chikondi; Katonda, Vincent

2017-04-01

The geology of Malawi is broadly grouped into four main lithological units that is the Basement Complex, the Karoo Super group, Tertiary to Quaternary sedimentary deposits and the Chilwa Alkaline province. The basement complex rocks cover much of the country and range in age from late Precambrian to early Paleozoic. They have been affected by three major phases of deformation and metamorphism that is the Irumide, Ubendian and The Pan-African. These rocks comprise gneisses, granulites and schists with associated mafic, ultramafic, syenites and granite rocks. The Karoo System sedimentary rocks range in age from Permian to lower Jurassic and are mainly restricted to two areas in the extreme North and extreme Alkaline Province - late Jurassic to Cretaceous in age, preceded by upper Karoo Dolerite dyke swarms and basaltic lavas, have been intruded into the Basement Complex gneisses of southern Malawi. Malawi is endowed with different types of natural stone deposits most of which remain unexploited and explored. Over twenty quarry operators supply quarry stone for road and building construction in Malawi. Hundreds of artisanal workers continue to supply aggregate stones within and on the outskirts of urban areas. Ornamental stones and granitic dimension stones are also quarried, but in insignificant volumes. In Northern Malawi, there are several granite deposits including the Nyika, which is the largest single outcrop occupying approximately 260.5 km2 , Mtwalo Amazonite an opaque to translucent bluish -green variety of microcline feldspar that occurs in alkali granites and pegmatite, the Ilomba granite (sodalite) occurring in small areas within biotite; apatite, plagioclase and calcite. In the Center, there are the Dzalanyama granites, and the Sani granites. In the South, there are the Mangochi granites. Dolerite and gabbroic rocks spread across the country, treading as black granites. Malawi is also endowed with many deposits of marble. A variety of other igneous, metamorphic and sedimentary rocks are also used as dimension stones. Discovery and preservation of more natural stone deposits through research is essential in the country .Natural stone preservation has not only the potential to generate significant direct and indirect economic benefits for Malawi but also to preserve its heritage .

Petrogenesis of cataclastic rocks within the San Andreas fault zone of Southern California U.S.A.

NASA Astrophysics Data System (ADS)

Lawford Anderson, J.; Osborne, Robert H.; Palmer, Donald F.

1980-08-01

This paper petrologically characterizes cataclastic rocks derived from four sites within the San Andreas fault zone of southern California. In this area, the fault traverses an extensive plutonic and metamorphic terrane and the principal cataclastic rock formed at these upper crustal levels is unindurated gouge derived from a range of crystalline rocks including diorite, tonalite, granite, aplite, and pegmatite. The mineralogical nature of this gouge is decidedly different from the "clay gouge" reported by Wu (1975) for central California and is essentially a rock flour with a quartz, feldspar, biotite, chlorite, amphibole, epidote and oxide mineralogy representing the milled-down equivalent of the original rock. Clay development is minor (less than 4 wt. %) to nonexistent and is exclusively kaolinite. Alterations involve hematitic oxidation, chlorite alteration on biotite and amphibole, and local introduction of calcite. Electron microprobe analysis showed that in general the major minerals were not reequilibrated with the pressure—temperature regime imposed during cataclasis. Petrochemically, the form of cataclasis that we have investigated is largely an isochemical process. Some hydration occurs but the maximum amount is less than 2.2% added H 2O. Study of a 375 m deep core from a tonalite pluton adjacent to the fault showed that for Si, Al, Ti, Fe, Mg, Mn, K, Na, Li, Rb, and Ba, no leaching and/or enrichment occurred. Several samples experienced a depletion in Sr during cataclasis while lesser number had an enrichment of Ca (result of calcite veining). Texturally, the fault gouge is not dominated by clay-size material but consists largely of silt and fine sand-sized particles. An intriguing aspect of our work on the drill core is a general decrease in particulate size with depth (and confining pressure) with the predominate shifting sequentially from fine sand to silt-size material. The original fabric of these rocks is commonly not disrupted during the cataclasis. It is evident that the gouge development in these primarily igneous crystalline terranes is largely an in situ process with minimal mixing of rock types. Fabric analyses reveal that brecciation (shattering), not shearing, is the major deformational mechanism at these upper crustal levels.

Petrography, mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core, Chesapeake Bay impact structure

USGS Publications Warehouse

Bartosova, Katerina; Gier, Susanne; Horton, J. Wright; Koeberl, Christian; Mader, Dieter; Dypvik, Henning

2010-01-01

The ICDP–USGS Eyreville drill cores in the Chesapeake Bay impact structure reached a total depth of 1766 m and comprise (from the bottom upwards) basement-derived schists and granites/pegmatites, impact breccias, mostly poorly lithified gravelly sand and crystalline blocks, a granitic slab, sedimentary breccias, and postimpact sediments. The gravelly sand and crystalline block section forms an approximately 26 m thick interval that includes an amphibolite block and boulders of cataclastic gneiss and suevite. Three gravelly sands (basal, middle, and upper) are distinguished within this interval. The gravelly sands are poorly sorted, clast supported, and generally massive, but crude size-sorting and subtle, discontinuous layers occur locally. Quartz and K-feldspar are the main sand-size minerals and smectite and kaolinite are the principal clay minerals. Other mineral grains occur only in accessory amounts and lithic clasts are sparse (only a few vol%). The gravelly sands are silica rich (~80 wt% SiO2). Trends with depth include a slight decrease in SiO2 and slight increase in Fe2O3. The basal gravelly sand (below the cataclasite boulder) has a lower SiO2 content, less K-feldspar, and more mica than the higher sands, and it contains more lithic clasts and melt particles that are probably reworked from the underlying suevite. The middle gravelly sand (below the amphibolite block) is finer-grained, contains more abundant clay minerals, and displays more variable chemical compositions than upper gravelly sand (above the block). Our mineralogical and geochemical results suggest that the gravelly sands are avalanche deposits derived probably from the nonmarine Potomac Formation in the lower part of the target sediment layer, in contrast to polymict diamictons higher in the core that have been interpreted as ocean-resurge debris flows, which is in agreement with previous interpretations. The mineralogy and geochemistry of the gravelly sands are typical for a passive continental margin source. There is no discernible mixing with marine sediments (no glauconite or Paleogene marine microfossils noted) during the impact remobilization and redeposition. The unshocked amphibolite block and cataclasite boulder might have originated from the outer parts of the transient crater.

Note on the Occurrence of Thorite at Alter Pedroso (Portugal). Report No. 29; NOTA SOBRE UMA OCORRENCIA DE TORITE EM ALTER PEDROSO. Memoria No. 29

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pacheco, J.T.; Gomes, R.A.D.

1960-01-01

The first known occurrence of thorite in Portugal is reported. The mineral was found as small dark reddishbrown euhedral grains scattered in a soil sample from the hyper-alkaline syerdte region of Alter Pedroso, in prospecting for radioactive materials. Zircon, riebeckite, aegirine, feldspar, biotite, magnetite (all of these common minerals of the hyper-alkaline syenite), and a few other urddentified minerals were found in the soil associated with thorite. This suggests the weathering of a local pegmatitic differentiation of the syenite as the origin of the thorite. Microscopic examination shows the mineral to be only partially metumict, and it is probably alteredmore » to a variable degree. Euhedral grains are constituted by several nearly colorless anisotropic nuclei (n/sub p/ near 1.69, n/sub g/ near 1.71, and sometimes anomalous B+ with variable 2V averaging 10/sup 0/) surrounded by a golden-brown isotropic material (n about 1.67). Specific gravity determinations were somewhat impaired by zircon inclusions and led to a value of 4.79. The chemical composition was determined by emission and x-ray fluorescence spectrography and shows a high yttrium content. A partial semiquantitative analysis gave the following results: ThO/sub 2/ (58.0%), SiO/sub 2/ (14.5%), Fe/sub 2/O/sub 3/ (2.5%), Y/sub 2/O/sub / 3>i (2.5%), CaO (l.1%), U/sub 3/O/sub 8/ (0.5%), and PbO (0.2%). The elements Be, Mg, Al, Mn, and P were also detected. X-raypowder patterns obtained before and after heating the sample to 1000 ts C for 1 hr in air confirmed the mineral to be only slightly metamict and showed that the tetragonal phase still prevails above 950 ts C. Calculations based on these patterns led to a tetragonal unit cell with a/sub 0/ = 7.05 0.01 A, c/sub 0/ = 6.27 0.01 A, and c/sub 0//a/sub 0/ = 0.889. (auth).« less

Mineral equilibria and zircon, garnet and titanite U-Pb ages constraining the PTt path of granite-related hydrothermal systems at the Big Bell gold deposit, Western Australia

NASA Astrophysics Data System (ADS)

Mueller, Andreas G.; McNaughton, Neal J.

2018-01-01

The Big Bell deposit (75 t gold) is located in a narrow spur of the Meekatharra greenstone belt, Yilgarn Craton, Western Australia. Two ore bodies are located in a calcic-potassic contact alteration zone overprinting lineated granodiorite dykes and amphibolite: almandine-cummingtonite-hornblende skarn (1-3 g/t Au, 1700 g/t As, 330 g/t W) and the muscovite-microcline gneiss (3-5 g/t Au, 580 g/t Sb, 620 g/t W) of the Main Lode. Genetic models vary from pre- to post-metamorphic replacement. Hornblende-plagioclase pairs in amphibolite constrain peak metamorphic temperature to 670 ± 50 °C. In contrast, garnet-biotite thermometry provides estimates of 578 ± 50 and 608 ± 50 °C for garnet-cordierite-biotite schist bordering the skarn and enveloping the Main Lode. Garnet-cordierite and garnet-hornblende pairs extend the range of fluid temperature to 540 ± 65 °C, well below peak metamorphic temperature. At 540-600 °C, the alteration assemblage andalusite + sillimanite constrains pressure to 300-400 MPa corresponding to 11-14 km crustal depth. Published U-Pb ages indicate that metamorphism took place in the aureole of the southeast granodiorite-tonalite batholith (2740-2700 Ma), followed by gold mineralization at 2662 ± 5 Ma and by the emplacement of biotite granite and Sn-Ta-Nb granite-pegmatite dykes at 2625-2610 Ma. Amphibolite xenoliths in granite northwest of the deposit record the lowest temperature (628 ± 50 °C), suggesting it lacks a metamorphic aureole. The rare metal dykes are spatially associated with epidote-albite and andradite-diopside skarns (≤1.5 g/t Au), mined where enriched in the weathered zone. We analysed hydrothermal zircon intergrown with andradite. Concordant U-Pb ages of 2612 ± 7 and 2609 ± 10 Ma confirm the presence of a second granite-related system. The zircons display oscillatory zoning and have low Th/U ratios (0.05-0.08). Low-Th titanite from an albite granite dyke has a concordant but reset U-Pb age of 2577 ± 7 Ma.

Kyanite-bearing migmatites in the central Adirondack Mountains: Implications for late to post-orogenic metamorphism and melting in a collisional orogen

NASA Astrophysics Data System (ADS)

Reeder, J.; Metzger, E. P.; Bickford, M. E.; Leech, M. L.

2016-12-01

Sillimanite-rich felsic migmatites exposed at Ledge Mountain in the Central Adirondack Highlands (AH) represent the only location in the AH where kyanite is found. The texturally young kyanite is overprinted on sillimanite in largely undeformed pegmatitic leucosomes, suggesting a late episode of melting taking place deeper than previously thought, and requiring a counter-clockwise P-T path. A final phase of anatexis ca. 1050 Ma in the Eastern AH is consistent with an influx of fluid or decompression from extension in sillimanite-bearing migmatites. Temperatures both from this study and previous work are consistent with granulite-facies metamorphism; however, the presence of kyanite requires higher pressure conditions corresponding to deeper burial of rocks exposed in the central Adirondacks. The Adirondacks are associated with the Grenville Province of eastern North America, that formed during four orogenic events. The most recent (Grenville) orogeny consisted of two stages: crustal thickening and granulite facies metamorphism during the Ottawan phase (ca 1090-1020) then metamorphism and melting in the kyanite field during the much shorter Rigolet pulse (ca 1005-980 Ma). Preliminary U-Pb SHRIMP zircon ages from Ledge Mountain kyanite-bearing migmatites suggest that melting in the Central AH persisted into the Rigolet phase. On the basis of mineral composition and chemistry and the presence of distinctive quartz-sillimanite nodules, the Ledge Mountain migmatites closely resemble the K-rich phase of the Ottawan-age Lyon Mountain granite (LMG) and may represent LMG that was metamorphosed to sillimanite grade and then overprinted by a higher pressure, lower temperature assemblage. Kyanite-bearing felsic anatectites of Rigolet age have previously been observed only in the western portion of the Grenville Province. Documentation of a counterclockwise P-T path and post-Ottawan melting in the Ledge Mountain migmatites requires re-evaluation of current tectonic models for the Grenville Province and its Adirondacks outlier. Further analysis of age, geochemical, and petrographic data will help develop a better-defined P-T-t path and may lead to the development of a new tectonic model to be compared with other collisional orogens such as Himalaya or the Bohemian Massif of the Variscan orogenic belt.

Brittle structures and their role in controlling porosity and permeability in a complex Precambrian crystalline-rock aquifer system in the Colorado Rocky Mountain front range

USGS Publications Warehouse

Caine, Jonathan S.; Tomusiak, S.R.A.

2003-01-01

Expansion of the Denver metropolitan area has resulted in substantial residential development in the foothills of the Rocky Mountain Front Range. This type of sub-urban growth, characteristic of much of the semiarid intermountain west, often relies on groundwater from individual domestic wells and is exemplified in the Turkey Creek watershed. The watershed is underlain by complexly deformed and fractured crystalline bedrock in which groundwater resources are poorly understood, and concerns regarding groundwater mining and degradation have arisen. As part of a pilot project to establish quantitative bounds on the groundwater resource, an outcrop-based geologic characterization and numerical modeling study of the brittle structures and their controls on the flow system was initiated. Existing data suggest that ground-water storage, flow, and contaminant transport are primarily controlled by a heterogeneous array of fracture networks. Inspections of well-permit data and field observations led to a conceptual model in which three dominant lithologic groups underlying sparse surface deposits form the aquifer system-metamorphic rocks, a complex array of granitic intrusive rocks, and major brittle fault zones. Pervasive but variable jointing of each lithologic group forms the "background" permeability structure and is an important component of the bulk storage capacity. This "background" is cut by brittle fault zones of varying structural styles and by pegmatite dikes, both with much higher fracture intensities relative to "background" that likely make them spatially complex conduits. Probabilistic, discrete-fracture-network and finite-element modeling was used to estimate porosity and permeability at the outcrop scale using fracture network data collected in the field. The models were conditioned to limited aquifer test and borehole geophysical data and give insight into the relative hydraulic properties between locations and geologic controls on storage and flow. Results from this study reveal a complex aquifer system in which the upper limits on estimated hydraulic properties suggest limited storage capacity and permeability as compared with many sedimentary-rock and surficial-deposit aquifers.

Geologic Map of the Clark Peak Quadrangle, Jackson and Larimer Counties, Colorado

USGS Publications Warehouse

Kellogg, Karl S.; Ruleman, Chester A.; Shroba, Ralph R.; Braddock, William A.

2008-01-01

The Clark Peak quadrangle encompasses the southern end of the Medicine Bow Mountains and the northernmost end of the Mummy Range. The Continental Divide traverses the map area and Highway 14 cross the Divide at Cameron Pass, in the southeastern corner of the map. Approximately the eastern half of the map, and a few areas to the west, are underlain by Early Proterozoic plutonic and metamorphic rocks. Most of these basement rocks are part of the ~1,715 Ma Rawah batholith, composed mostly of pinkish, massive to moderately foliated monzogranite and granodiorite intruded by numerous, large pegmatite- aplite bodies. The metamorphic rocks, many of which form large inclusions in the granitic rocks of the Rawah batholith, include biotite-hornblende gneiss, hornblende gneiss, amphibolite, and biotite schist. The crystalline basement rocks are thrust westward along the Medicine Bow thrust over a sequence of sedimentary rocks as old as the Upper Permian Satanka Shale. The Satanka Shale, Middle and Lower Triassic Chugwater group, and a thin sandstone tentatively correlated with the Lower Jurassic and Upper Triassic Jelm Formation are combined as one map unit. This undivided unit is overlain sequentially upward by the Upper Jurassic Sundance Formation, Upper Jurassic Morrison Formation, Lower Cretaceous Dakota Group, Upper and Lower Cretaceous Benton Group, Upper Cretaceous Niobrara Formation, and the Eocene and Paleocene Coalmont Formation. The Late Cretaceous to early Eocene Medicine Bow thrust is folded in places, and several back thrusts produced a complicated thrust pattern in the south part of the map. Early Oligocene magmatism produced rhyolite tuff, dacite and basalt flows, and intermediate dikes and small stocks. A 40Ar/39Ar date on sanidine from one rhyolite tuff is ~28.5 Ma; a similar whole-rock date on a trachybasalt is ~29.6 Ma. A very coarse, unsorted probably pre-Quaternary ridge-top diamicton crops out in the southern part of the quadrangle. Numerous glacial deposits (mostly of Pinedale age), rock glaciers, block-slope deposits, landslide deposits, talus deposits, fan deposits, colluvium, and alluvium comprise the surficial deposits of the map area.

Kyanite-Bearing Migmatites at Ledge Mountain, Adirondack Highlands

NASA Astrophysics Data System (ADS)

Swanson, B.; Leech, M.; Metzger, E. P.

2017-12-01

Sillimanite-rich felsic migmatites exposed at Ledge Mountain represent the only location in the Adirondack Highlands where kyanite has been found. The texturally young kyanite is overprinted on sillimanite in largely undeformed pegmatitic leucosomes, suggesting a late episode of melting taking place deeper than previously thought, and requiring a counter-clockwise P-T path. A final phase of anatexis ca. 1050 Ma in the Eastern Adirondack Highlands is consistent with an influx of fluid or decompression from extension in sillimanite-bearing migmatites. Temperatures both from this study and previous work are consistent with granulite-facies metamorphism, however the presence of kyanite requires higher pressure conditions corresponding to deeper burial of these central Adirondack rocks. We used Perple_X to model phase equilibria using XRF+ICP-MS whole-rock chemistries for the kyanite-bearing migmatites. Pseudosection models suggest that the peak P-T mineral assemblage kyanite + mesoperthite + garnet + rutile formed at approximately 15-20kb and 1000°C which is higher than previously proposed for granulites in the region. These P-T conditions for peak metamorphism are similar to those reported for the distinctive and relatively rare assemblage that we observe kyanite + hypersolvus feldspar (now mesoperthite) + garnet + rutile. We have evidence of isothermal decompression to <11kb and 880°-1000°C based on Grt + Pl equilibrium in the assemblage Grt + Pl ± Kfs + Qz + Ilm + melt. The leucocratic melt phase comprises 16 vol. % of the rock at these P-T conditions which is sufficient for ductile flow in the deep crust. This melt phase is present syn-exhumation and helped to buoyantly exhume Ledge Moutain rocks beneath bounding normal faults as a granitic gneiss dome. Preliminary U-Pb SHRIMP zircon ages from Ledge Mountain kyanite-bearing migmatites show anatexis continuing well after high-grade metamorphism is believed to have ceased in the range. A counter-clockwise P-T path is consistent with the mechanisms in the current model, and this study indicates anatectic melting persisted into the Rigolet phase. The Ledge Mountain migmatite may represent the Hawkeye granite and/or Lyon Mountain Gneiss that were metamorphosed to sillimanite grade and then overprinted by a higher pressure, lower temperature assemblage.

Juxtaposition of contrasting structural regimes across a portion of the Norumbega fault system in the northern Casco Bay region of Maine

NASA Astrophysics Data System (ADS)

West, D. P., Jr.; Hussey, A. M., II

2015-12-01

It has long been recognized that Paleozoic stratified rocks in some regions of central New England are dominated by relatively flat structural features (e.g., recumbent folds, shallow dipping foliation) while other areas are dominated by near vertical upright structures. The northern Casco Bay region of coastal Maine (Brunswick 7.5' quadrangle and adjacent areas) provides an excellent venue for studying the relationships between these two structural regimes as they are in close proximity due to juxtaposition by high angle faulting associated with the Norumbega fault system. Stratified rocks exposed west of the Flying Point fault in northern Casco Bay are dominated by moderately east dipping foliation (ave. = 025o, 37o), moderate northeast plunging mineral lineations, and recumbent to gently inclined minor folds. In stark contrast, immediately east of the Flying Point fault, stratified rocks are dominated by steep east dipping foliation (ave. = 014o, 73o), subhorizontal mineral lineations, and upright to steeply inclined minor folds. The structural differences correspond directly to differences in the thermal histories preserved in these rocks as revealed by earlier thermochronological studies. Rocks in the zone of upright structures east of the Flying Point fault were last subjected to high grade metamorphic conditions and granitic plutonism in the Late Devonian and were relatively cold (<300oC) by Late Carboniferous time. In contrast, flat lying rocks west of the Flying Point fault were over 500oC in the Early Permian and Permian pegmatites are common. Geochronological studies north of the study area have revealed that the two distinctly different structural styles are not the product of strain partitioning during the same deformational episode, but rather they represent two temporally and kinematically distinct deformational events. Swanson (1999), originally suggested flat structures west of the Flying Point fault are consistent with an episode of northwest directed thrusting and our findings are consistent with this interpretation. However, this flat phase of deformation significantly post-dates the older upright structures preserved to the east and thus models for the structural evolution of the region must integrate both the kinematic and temporal differences in this deformation.

The mantle source of island arc magmatism during early subduction: Evidence from Hf isotopes in rutile from the Jijal Complex (Kohistan arc, Pakistan)

NASA Astrophysics Data System (ADS)

Ewing, Tanya A.; Müntener, Othmar

2018-05-01

The Cretaceous-Paleogene Kohistan arc complex, northern Pakistan, is renowned as one of the most complete sections through a preserved paleo-island arc. The Jijal Complex represents a fragment of the plutonic roots of the Kohistan arc, formed during its early intraoceanic history. We present the first Hf isotope determinations for the Jijal Complex, made on rutile from garnet gabbros. These lithologies are zircon-free, but contain rutile that formed as an early phase. Recent developments in analytical capabilities coupled with a careful analytical and data reduction protocol allow the accurate determination of Hf isotope composition for rutile with <30 ppm Hf for the first time. Rutile from the analysed samples contains 5-35 ppm Hf, with sample averages of 13-17 ppm. Rutile from five samples from the Jijal Complex mafic section, sampling 2 km of former crustal thickness, gave indistinguishable Hf isotope compositions with εHf(i) ranging from 11.4 ± 3.2 to 20.1 ± 5.7. These values are within error of or only slightly more enriched than modern depleted mantle. The analysed samples record variable degrees of interaction with late-stage melt segregations, which produced symplectitic overprints on the main mineral assemblage as well as pegmatitic segregations of hydrous minerals. The indistinguishable εHf(i) across this range of lithologies demonstrates the robust preservation of the Hf isotope composition of rutile. The Hf isotope data, combined with previously published Nd isotope data for the Jijal Complex garnet gabbros, favour derivation from an inherently enriched, Indian Ocean type mantle. This implies a smaller contribution from subducted sediments than if the source was a normal (Pacific-type) depleted mantle. The Jijal Complex thus had only a limited recycled continental crustal component in its source, and represents a largely juvenile addition of new continental crust during the early phases of intraoceanic magmatism. The ability to determine the Hf isotope composition of rutile with low Hf contents is an important development for zircon-free mafic lithologies. This study highlights the potential of Hf isotope analysis of rutile to characterise the most juvenile deep arc crust cumulates worldwide.

Coarse muscovite veins and alteration deep in the Yerington batholith, Nevada: insights into fluid exsolution in the roots of porphyry copper systems

NASA Astrophysics Data System (ADS)

Runyon, Simone E.; Steele-MacInnis, Matthew; Seedorff, Eric; Lecumberri-Sanchez, Pilar; Mazdab, Frank K.

2017-04-01

Veins and pervasive wall-rock alteration composed of coarse muscovite±quartz±pyrite are documented for the first time in a porphyritic granite at Luhr Hill in the Yerington District, Nevada. Coarse muscovite at Luhr Hill occurs at paleodepths of 6-7 km in the roots of a porphyry copper system and crops out on the scale of tens to hundreds of meters, surrounded by rock that is unaltered or variably altered to sodic-calcic assemblages. Coarse muscovite veins exhibit a consistent orientation, subvertical and N-S striking, which structurally restores to subhorizontal at the time of formation. Along strike, coarse muscovite veins swell from distal, millimeter-thick muscovite-only veinlets to proximal, centimeter-thick quartz-sulfide-bearing muscovite veins. Crosscutting relationships between coarse muscovite veins, pegmatite dikes, and sodic-calcic veins indicate that muscovite veins are late-stage magmatic-hydrothermal features predating final solidification of the Luhr Hill porphyritic granite. Fluid inclusions in the muscovite-quartz veins are high-density aqueous inclusions of 3-9 wt% NaCl eq. and <1 mol% CO2 that homogenize between 150 and 200 °C, similar to fluid inclusions from greisen veins in Sn-W-Mo vein systems. Our results indicate that muscovite-forming fluids at Luhr Hill were mildly acidic, of low to moderate salinity and sulfur content and low CO2 content, and that muscovite in deep veins and alteration differs in texture, composition, and process of formation from sericite at shallower levels of the hydrothermal system. Although the definition of greisen is controversial, we suggest that coarse muscovite alteration is more similar to alteration in greisen-type Sn-W-Mo districts worldwide than to sericitic alteration at higher levels of porphyry copper systems. The fluids that form coarse muscovite veins and alteration in the roots of porphyry copper systems are distinct from fluids that formed copper ore or widespread, shallower, acidic alteration. We propose that this style of veins and alteration at Luhr Hill represents degassing of moderate volumes of overpressured hydrothermal fluid during late crystallization of deep levels of the Yerington batholith.

Altitude and Configuration of the Potentiometric Surface in the Upper White Clay Creek and Lower West Branch Brandywine Creek Basins including Portions of Penn, London Grove, New Garden, Londonderry, West Marlborough, Highland, and East Fallowfield Townships and West Grove, Avondale, Modena, and South Coatesville boroughs, Chester County, Pennsylvania, May through July 2006

USGS Publications Warehouse

Hale, Lindsay B.

2007-01-01

INTRODUCTION Since 1984, the U.S. Geological Survey (USGS) has been mapping the altitude and configuration of the potentiometric surface in Chester County as part of an ongoing cooperative program to measure and describe the water resources of the county. These maps can be used to determine the general direction of ground-water flow and are frequently referenced by municipalities and developers to evaluate ground-water conditions for water supply and resource-protection requirements. For this study, the potentiometric surface was mapped for an area in south-central Chester County. The northern part of the map includes portions of Highland, East Fallowfield, Londonderry, and West Marlborough Townships and South Coatesville and Modena Boroughs. The southern part of the map includes portions of Londonderry, West Marlborough, Penn, London Grove, and New Garden Townships and West Grove and Avondale Boroughs. The study area is mostly underlain by metamorphic rocks of the Glenarm Supergroup including Peters Creek Schist, Octoraro Phyllite, Wissahickon Schist, Cockeysville Mrable, and Setters Quartzite; and by pegmatite, mafic gneiss, felsic gneiss, and diabase. Ground water is obtained from these bedrock formations by wells that intercept fractures. The altitude and configuration of the potentiometric surface was contoured from water levels measured on different dates in available wells during May through July 2006 and from the altitude of springs and perennial streams. Topography was used as a guide for contouring so that the altitude of the potentiometric surface was inferred nowhere to be higher than the land surface. The potentiometric surface shown on this map is an approximation of the water table. The altitude of the actual potentiometric surface may differ from the water table, especially in areas where wells are completed in a semi-confined zone or have long open intervals that reflect the composite hydraulic head of multiple water-yielding fractures. A composite head may differ from the potentiometric-surface altitude, particularly beneath hilltops and valleys where vertical hydraulic gradients are significant.

Pre-Alpine contrasting tectono-metamorphic evolutions within the Southern Steep Belt, Central Alps

NASA Astrophysics Data System (ADS)

Roda, Manuel; Zucali, Michele; Li, Zheng-Xiang; Spalla, Maria Iole; Yao, Weihua

2018-06-01

In the Southern Steep Belt, Italian Central Alps, relicts of the pre-Alpine continental crust are preserved. Between Valtellina and Val Camonica, a poly-metamorphic rock association occurs, which belongs to the Austroalpine units and includes two classically subdivided units: the Languard-Campo nappe (LCN) and the Tonale Series (TS). The outcropping rocks are low to medium grade muscovite, biotite and minor staurolite-bearing gneisses and micaschists, which include interlayered garnet- and biotite-bearing amphibolites, marbles, quartzites and pegmatites, as well as sillimanite-bearing gneisses and micaschists. Permian intrusives (granitoids, diorites and minor gabbros) emplaced in the metamorphic rocks. We performed a detailed structural, petrological and geochronological analysis focusing on the two main lithotypes, namely, staurolite-bearing micaschists and sillimanite-bearing paragneisses, to reconstruct the Variscan and Permian-Triassic history of this crustal section. The reconstruction of the tectono-metamorphic evolution allows for the distinction between two different tectono-metamorphic units during the early pre-Alpine evolution (D1) and predates the Permian intrusives, which comprise rocks from both TS and LCN. In the staurolite-bearing micaschists, D1 developed under amphibolite facies conditions (P = 0.7-1.1 GPa, T = 580-660 °C), while in the sillimanite-bearing paragneisses formed under granulite facies conditions (P = 0.6-1.0 GPa, T> 780 °C). The two tectono-metamorphic units coupled together during the second pre-Alpine stage (D2) under granulite-amphibolite facies conditions at a lower pressure (P = 0.4-0.6 GPa, T = 620-750 °C) forming a single tectono-metamorphic unit (Languard-Tonale Tectono-Metamorphic Unit), which comprised the previously distinguished LCN and TS. Geochronological analyses on zircon rims indicate ages ranging between 250 and 275 Ma for D2, contemporaneous with the emplacement of Permian intrusives. This event developed under a high thermal state, which is compatible with an extensional tectonic setting that occurred during the exhumation of the Languard-Tonale Tectono-Metamorphic Unit. The extensional regime is interpreted as being responsible for the thinning of the Adriatic continental lithosphere during the Permian, which may be related to an early rifting phase of Pangea.

Multi-azimuth Anisotropic Velocity Measurements in Fractured Crystalline Rock From the International Continental Drilling Program Outokumpu Borehole, Finland

NASA Astrophysics Data System (ADS)

Schijns, H.; Duo, X.; Heinonen, S.; Schmitt, D. R.; Kukkonen, I. T.; Heikkinen, P.

2008-12-01

A high resolution seismic survey consisting of a multi-depth multi-azimuth VSP, a zero-offset VSP and a reflection/refraction survey was conducting in May, 2006, near the town of Outokumpu, Finland, using the International Continental Scientific Drilling Program 2.5 km deep fully cored scientific borehole. The survey was undertaken in order to create an anisotropic velocity model for future micro-seism studies as well as to provide a higher resolution reflection profile through the area than was previously available. The seismic survey high frequency seismic vibrator as a source, employing 8 s linear taper sweeps from 15-250 Hz at 20 m shot spacing. Receivers were 14 Hz single component geophones on the surface and a three component geophone downhole. The walk-away VSP included measurements over two azimuths with the receiver at depths of 1000, 1750 and 2500 m, while the zero-offset VSP used a 2 m depth increment. Surface geophones were located along the same seismic lines as employed in the walk-away VSP and were nominally 4 m apart. The survey area is located on the Fennoscandian shield, and the glacial history of the area required significant static corrections to account for the variable overburden overlying the mica-rich schist and pegmatitic granite composing the bedrock. These were calculated using travel-time inversion of the refraction data and were applied to the walk-away VSP and reflection profiles, significantly improving the quality of both. Anisotropic velocity analysis was performed using a plane-wave decomposition of the processed walk-away VSP. The maximum anisotropy was observed in the walk-away VSPs along the Southeastern azimuth, with the P-wave phase velocity ranging from 5330-5950 m/s between 50-1000 m in depth, and up to 6150 m/s between 1000-1750 m in depth. Shear wave splitting was observed in the Northeastern direction. Preliminary analysis of the zero-offset VSP has revealed shown good agreement with the relevant portions of the anisotropic velocity measurements and the reflection profile.

Niobium and tantalum

USGS Publications Warehouse

Schulz, Klaus J.; Piatak, Nadine M.; Papp, John F.; Schulz, Klaus J.; DeYoung,, John H.; Seal, Robert R.; Bradley, Dwight C.

2017-12-19

Niobium and tantalum are transition metals that are almost always found together in nature because they have very similar physical and chemical properties. Their properties of hardness, conductivity, and resistance to corrosion largely determine their primary uses today. The leading use of niobium (about 75 percent) is in the production of high-strength steel alloys used in pipelines, transportation infrastructure, and structural applications. Electronic capacitors are the leading use of tantalum for high-end applications, including cell phones, computer hard drives, and such implantable medical devices as pacemakers. Niobium and tantalum are considered critical and strategic metals based on the potential risks to their supply (because current production is restricted to only a few countries) and the significant effects that a restriction in supply would have on the defense, energy, high-tech industrial, and medical sectors.The average abundance of niobium and tantalum in bulk continental crust is relatively low—8.0 parts per million (ppm) niobium and 0.7 ppm tantalum. Their chemical characteristics, such as small ionic size and high electronic field strength, significantly reduce the potential for these elements to substitute for more common elements in rock-forming minerals and make niobium and tantalum essentially immobile in most aqueous solutions. Niobium and tantalum do not occur naturally as pure metals but are concentrated in a variety of relatively rare oxide and hydroxide minerals, as well as in a few rare silicate minerals. Niobium is primarily derived from the complex oxide minerals of the pyrochlore group ((Na,Ca,Ce)2(Nb,Ti,Ta)2(O,OH,F)7), which are found in some alkaline granite-syenite complexes (that is, igneous rocks containing sodium- or potassium-rich minerals and little or no quartz) and carbonatites (that is, igneous rocks that are more than 50 percent composed of primary carbonate minerals, by volume). Tantalum is derived mostly from the mineral tantalite ((Fe,Mn)(Ta,Nb)2O6), which is found as an accessory mineral in rare-metal granites and pegmatites that are also enriched in lithium and cesium (termed lithium-cesium-tantalum (LCT)-type pegmatites).Brazil and Canada are the leading nations that produce niobium mineral concentrates, but Brazil is by far the leading producer, accounting for about 90 percent of production, which comes mostly from weathered material derived from carbonatites. Brazil and Canada also have the largest identified niobium resources; additional resources, although they are less well reported, occur in Angola, Australia, China, Greenland, Malawi, Russia, and South Africa. Australia and Brazil have been the leading producers of tantalum mineral concentrates, although recently Ethiopia and Mozambique have also been significant suppliers of tantalum. Artisanal mining of columbite-tantalite (also called coltan) is practiced in many countries, particularly Burundi, the Democratic Republic of the Congo (Congo [Kinshasa]), Nigeria, Rwanda, and Uganda. Brazil has about 40 percent of the identified tantalum resources; other countries and regions with identified tantalum resources include, in decreasing order of resources, Australia, Asia, Russia and the Middle East, Africa, North America, and Europe. Identified niobium and tantalum resources in the United States are small, low grade, and difficult to recover and process, and are thus not commercially recoverable at current prices. Consequently, the United States meets its current and expected future needs for niobium and tantalum through imports of primary mineral concentrates and alloys and through recovery from foreign and domestic alloy scrap that contain the metals.Environmentally, the main issues related to niobium and tantalum mining are land disruptions, the volume of waste materials and their disposal, and the radioactivity of some tailings and waste materials that contain thorium and uranium. Because of the relative biological inertness of niobium and tantalum, human and ecological health concerns are generally minimal under most natural conditions.Demand for both niobium and tantalum is expected to increase as the world economy continues to recover from the downturn that began in 2008. Increased demand for niobium is linked to increased consumption of microalloyed steel, which is used in the manufacture of cars, buildings, ships, and refinery equipment. Demand for these steels will likely increase with continued economic development in such countries as Brazil, China, and India. In addition, increased global demand for cars, cell phones, computers, superconducting magnets, and other high-tech devices will likely spur increased demand for both niobium and tantalum. The estimated global reserves and resources of niobium and tantalum are large and appear more than sufficient to meet global demand for the foreseeable future, possibly the next 500 years. The sale of “conflict coltan” attributed to rebel forces waging a civil war in Congo (Kinshasa) has been of recent concern and has highlighted the need for a transparent and traceable global supply chain that can exclude illegal columbite-tantalite from the conventional market while discerning legitimate artisanal mine production in central Africa.

Emplacement and deformation of the A-type Madeira granite (Amazonian Craton, Brazil)

NASA Astrophysics Data System (ADS)

Siachoque, Astrid; Salazar, Carlos Alejandro; Trindade, Ricardo

2017-04-01

The Madeira granite is one of the Paleoproterozoic (1.82 Ga) A-type granite intrusions in the Amazonian Craton. It is elongated in the NE-SW direction and is composed of four facies. Classical structural techniques and the anisotropy of magnetic susceptibility (AMS) method were applied to the study of its internal fabric. Magnetic susceptibility measurements, thermomagnetic curves, remanent coercivity spectra, optical microscopy and SEM (scanning electron microscopy) analyses were carried out on the earlier and later facies of the Madeira granite: the rapakivi granite (RG) and the albite granite (AG) respectively. The last one is subdivided into the border albite granite (BAG) and the core albite granite (CAG) subfacies. AMS fabric pattern is controlled by pure magnetite in all facies, despite significant amounts of hematite in the BAG subfacies. Microstructural observations show that in almost all sites, magnetic fabric correlates to magmatic state fabrics that are defined by a weak NE-SW orientation of mafic and felsic silicates. However, strain mechanisms in both subfacies of AG also exhibit evidence for solid-state deformation at high to moderate temperatures. Pegmatite dyke, strike slip fault (SFA-B-C), hydrothermal vein, normal fault (F1-2) and joint (J) structures were observed and their orientation and kinematics is consistent with the magmatic and solid-state structures. Dykes, SFA-C and F1, are usually orientated along the N70°E/40°N plane, which is nearly parallel to the strike of AMS and magmatic foliations. In contrast, veins, SFB, F2 and some J are oriented perpendicular to the N70°E trend. Kinematic analysis in these structures shows evidence for a dextral sense of movement in the system in the brittle regime. The coherent structural pattern for the three facies of Madeira granite suggests that the different facies form a nested pluton. The coherence in orientation and kinematics from magmatic to high-temperature solid-state, and into the brittle regime indicates the continuity in the stress regime from the last magmatic stages until the complete cooling of the pluton, likely along a NE-SW dextral corridor related to the regional deformation in the Uatumã-Anauá Domain of the Amazonian Craton.

Geological setting, emplacement mechanism and igneous evolution of the Atchiza mafic-ultramafic layered suite in north-west Mozambique

NASA Astrophysics Data System (ADS)

Ibraimo, Daniel Luis; Larsen, Rune B.

2015-11-01

The Atchiza mafic and ultramafic-layered suite (hereafter, "Atchiza Suite) crops out in an area 330 km2 west of the Mozambican Tete province. In an early account of the geology of this intrusion, it was considered the continuation of the Great Dyke of Zimbabwe, an idea that was aborted after detailed studies. Nevertheless, the Ni concentrations in the Atchiza outcrop rocks are considerable. Our investigation used field evidence, hand specimens and petrography descriptions, mineral chemistry studies using electron microprobe analysis and tectonic analysis to arrive at a plausible mineralogical composition and understanding of the tectonic setting for the igneous evolution. The mineral composition from the Atchiza Suite indicates that these are cumulates. The magmatic segregation from the petrographic and mineral composition reasoning indicates that dunite-lherzolitic peridotite-olivine gabbro-gabbronorite-gabbro-pegmatitic gabbro is the rock formation sequence. Olivine and chromite were the first phases formed, followed by pyroxene and plagioclase. In addition, it is shown that these minerals are near-liquidus crystallization products of basaltic magma with olivine Fo: 87.06 in dunite, mean values of clinopyroxene are (Wo: 36.4, En: 48.0, Fs: 15.2), orthopyroxene (Wo: 2.95, En: 73.0, Fs: 24.2) and plagioclase An: 71.3, respectively. Opaque minerals comprise Fe-Ti oxides and (Fe, Cr) spinel up to 4.8 vol.%, but chromitite layers are not present. Most of the opaque minerals are interstitial to pyroxene. Sulphides are common in gabbros, with pyrrhotite, pentlandite, chalcopyrite, pyrite and covellite together comprising 0.4-2.0 vol.%. The whole rock Rare Earth Element (REE) concentrations are mainly a result of differentiation, but slight crustal contamination/assimilation contributed to the REE contents. In addition, they also show Eu enrichment, suggesting that plagioclase fractionation was important in the rock. The Atchiza Suite preserves a deep-seated plumbing system of the continental rift environment. The intrusion resulted from the emplacement of mafic magma in space created by extensional forces. Space was created through a connecting fault generated as a result of overall extensional, torsion and slab displacement in a rift system. The geometry of the body is tectonically controlled, and it agrees with the tectonic framework of the Zambezi Belt during the Rodinia breakup in the early Neoproterozoic.

Helium Diffusion in Natural Xenotime

NASA Astrophysics Data System (ADS)

Anderson, A. J.; Hodges, K. V.; Van Soest, M. C.; Hanchar, J. M.

2017-12-01

Xenotime (nominally YPO4) occurs as an accessory mineral in felsic igneous rocks, pegmatites, and gneisses, often incorporating weight percent levels of U, Th, and REEs. Although commonly used for precise U-Pb geochronology, xenotime is seldom used for (U-Th)/He thermochronometry despite the fact that its high radionuclide content allows for the rapid accumulation of radiogenic He that could potentially allow for the precise dating of very young cooling events in active geologic settings. Xenotime's likely high concentrations of radiogenic 4He also make it a promising candidate for laser microprobe (U-Th)/He dating. Unfortunately, limited data are currently available for He diffusion in xenotime, and previous experimental studies of natural and synthetic xenotime have led to discrepant results (1). Published estimates of the (U-Th)/He closure temperature for xenotime based on these experiments range from 60˚C to 300˚C. In this contribution, we report new results for incremental step heating `bulk' 4He diffusion experiments on a fragment of a natural xenotime crystal from the Torghar district of the Khyber Agency in the Federally Administered Tribal Areas of Pakistan. Laser ablation 238U/206Pb dating of this crystal yields a crystallization age of 28.82 ± 0.13 Ma. The results of our He diffusion experiments- which display excellent linearity on an Arrhenius plot assuming a spherical geometry - indicate kinetic parameters of E 133 kJ/mol and ln(D0/a2) 10.9 s-1. Our results imply a preliminary (U-Th)/He closure temperature of 80˚C for xenotime crystals with a diffusion dimension of 220 μm. This closure temperature is much lower than that previously estimated for natural xenotime (1), and it is possible, perhaps likely, that He diffusion in natural xenotime crystals display a strong compositional dependency (1). Nevertheless, our experimental data suggest that near-end member (YPO4) xenotime has an intrinsic helium diffusivity consistent with a closure temperature comparable to that of the apatite (U-Th)/He thermochronometer. As a consequence, xenotime He chronometry may serve as a higher-precision alternative to apatite He chronometry for revealing low temperature cooling histories of rocks in which it crystallized. References: 1) Farley, 2007, Geochimica et Cosmochimica Acta, v. 71.

Mineralogical Control on Microbial Diversity in a Weathered Granite?

NASA Astrophysics Data System (ADS)

Gleeson, D.; Clipson, N.; McDermott, F.

2003-12-01

Mineral transformation reactions and the behaviour of metals in rock and soils are affected not only by physicochemical parameters but also by biological factors, particularly by microbial activity. Microbes inhabit a wide range of niches in surface and subsurface environments, with mineral-microbe interactions being generally poorly understood. The focus of this study is to elucidate the role of microbial activity in the weathering of common silicate minerals in granitic rocks. A site in the Wicklow Mountains (Ireland) has been identified that consists of an outcrop surface of Caledonian (ca. 400 million years old) pegmatitic granite from which large intact crystals of variably weathered muscovite, plagioclase, K-feldspar and quartz were sampled, together with whole-rock granite. Culture-based microbial approaches have been widely used to profile microbial communities, particularly from copiotrophic environments, but it is now well established that for oligotrophic environments such as those that would be expected on weathering faces, perhaps less than 1% of microbial diversity can be profiled by cultural means. A number of culture-independent molecular based approaches have been developed to profile microbial diversity and community structure. These rely on successfully isolating environmental DNA from a given environment, followed by the use of the polymerase chain reaction (PCR) to amplify the typically small quantities of extracted DNA. Amplified DNA can then be analysed using cloning based approaches as well as community fingerprinting systems such as denaturing gradient gel electrophoresis (DGGE), terminal restriction fragment length polymorphism (TRFLP) and ribosomal intergenic spacer analysis (RISA). Community DNA was extracted and the intergenic spacer region (ITS) between small (16S) and large (23S) bacterial subunit rRNA genes was amplified. RISA fragments were then electrophoresed on a non-denaturing polyacrylamide gel. Banding patterns suggest that the bacterial population in whole rock, which contained approximately 30 separated bands (indicative of the number of bacterial ribotypes), is greater than muscovite (20), K-feldspar (15), and plagioclase feldspar (12) with quartz exhibiting the lowest number (6). These bands were excised from the gel for sequencing, allowing identification of the major populations. An automated approach was also used to assess similarity of bacterial communities present on each sample type, and this allowed for a statistical evaluation of bacterial diversity. Petrographic studies were carried out to assess mineral alteration effects. Scanning electron microscopy (SEM) was used to visualise in-situ bacterial cells.

Carbonate and silicate rock standards for cosmogenic 36Cl

NASA Astrophysics Data System (ADS)

Mechernich, Silke; Dunai, Tibor J.; Binnie, Steven A.; Goral, Tomasz; Heinze, Stefan; Dewald, Alfred; Benedetti, Lucilla; Schimmelpfennig, Irene; Phillips, Fred; Marrero, Shasta; Akif Sarıkaya, Mehmet; Gregory, Laura C.; Phillips, Richard J.; Wilcken, Klaus; Simon, Krista; Fink, David

2017-04-01

The number of studies using cosmogenic nuclides has increased multi-fold during the last two decades and several new dedicated target preparation laboratories and Accelerator Mass Spectrometry (AMS) facilities have been established. Each facility uses sample preparation and AMS measurement techniques particular to their needs. It is thus desirable to have community-accepted and well characterized rock standards available for routine processing using identical target preparation procedures and AMS measurement methods as carried out for samples of unknown cosmogenic nuclide concentrations. The usefulness of such natural standards is that they allow more rigorous quality control, for example, the long-term reproducibility of results and hence measurement precision, or the testing of new target preparation techniques or newly established laboratories. This is particularly pertinent for in-situ 36Cl studies due to the multiplicity of 36Cl production pathways that requires a variety of elemental and isotopic determinations in addition to AMS 36Cl assay. We have prepared two natural rock samples (denoted CoCal-N and CoFsp-N) to serve as standard material for in situ-produced cosmogenic 36Cl analysis. The sample CoCal-N is a pure limestone prepared from pebbles in a Namibian lag deposit, while the alkali-feldspar CoFsp-N is derived from a single crystal in a Namibian pegmatite. The sample preparation took place at the University of Cologne, where first any impurities were removed manually from both standards. CoCal-N was leached in 10 % HNO3 to remove the outer rim, and afterwards crushed and sieved to 250-500 μm size fractions. CoFsp-N was crushed, sieved to 250-500 μm size fractions and then leached in 1% HNO3 / 1% HF until 20% of the sample were removed. Both standards were thoroughly mixed using a rotating sample splitter before being distributed to other laboratories. To date, a total of 28 CoCal-N aliquots (between 2 and 16 aliquots per facility) and 31 CoFsp-N aliquots (between 2 and 20 aliquots per facility) have been analyzed by six target preparation laboratories employing five different AMS facilities. Currently, the internal reproducibility of the measurements underlines the homogeneity of both standards. The inter-laboratory comparison suggests low over-dispersion. Further measurements are pending and should allow meaningful statistical analysis. Both standard materials are freely available and can be obtained from Tibor Dunai tdunai@uni-koeln.de).

High-temperature metamorphism and its relation with magmatism (Svecofennian Belt, the Ladoga region, Russia)

NASA Astrophysics Data System (ADS)

Baltybaev, Shauket

2010-05-01

The Ladoga region, situated in the south-eastern part of the Fennoscandian shield, is subdivided into the Archean (ARD) and the Proterozoic (PRD) domains. The boundary between them is a wide shear-zone. The ARD consists mostly of AR-PR middle-low temperature gneisses and the PRD consists of turbidites, pelites, volcanics metamorphosed under HT-conditions (granulite facies). Metamorphism within the PRD is culminated at T= 800-900C and P=5-6 kbar. The peak of metamorphism of granulite facies is dated at 1881 Ma by Pb-Pb stepwise leaching method of rock-forming minerals of the granulites. Pb-Pb results are within error limits coeval with the U-Pb ages of metamorphic monazites. The same (1881Ma) age has gabbro-enderbites. Next stage of metamorphism lasts from 1881 to 1860 Ma under conditions of amphibolite facies. It was restricted with U-Pb, Pb-Pb, Sm-Nd data based on the closure temperature of zircon, monazite, garnet, sillimanite from gneisses, leucosomes of migmatites and synmetamorphic diorites and tonalites. The lowermost point of the trend shows P-T: ~3-4 kbar, 600C. By the time 1860 Ma K-rich granites were emplaced and the uppermost limit for granulite metamorphism comes from the ages of the aplitic/pegmatitic veins (1860-1850 Ma), which cut the K-rich granites. Thermal and tectonic settings can be described based on spatial and temporal changes during magma emplacement. The granulites of the PRD were produced by the emplacement of the extensive basic intrusion (gabbro-enderbites) into the lower-middle crust. A prolonged thermal flux over all area was supported by new generated dioritic and tonalitic melts, which were intruded into the middle crust. The final stage of tectono-metamorphic evolution was marked by emplacement of the K-rich granites. Numerical simulation of the process of magma emplacement (sequences: gabbro-enderbites, diorites and tonalites) and related heat production shows good correlation between intrusive activity and metamorphism of the surrounding rocks. Baltybaev Sh. K., Levchenkov O. A., Levsky L. K., Eklund O., Kilpeläinen T. 2006. Two metamorphic stages in the Svecofennian Domain: evidence from the isotopic geochronological study of the Ladoga and Sulkava metamorphic complexes. Petrology, 14(3), 247-261.

The importance of intracrustal magmatic heat advection in large hot orogens: the Ediacaran-Cambrian ultrahigh-temperature domain of southern Madagascar.

NASA Astrophysics Data System (ADS)

Holder, R. M.; Hacker, B. R.

2016-12-01

Ultrahigh temperature metamorphism (UHTM) represents the thermal extremes of crustal metamorphism and is integral to our understanding of orogenic systems and continental evolution. The relative importance of advective and radiogenic heating in UHTM is often unclear, however, due to retrogression of UHT mineral assemblages and lack of robust chronology. We report the first observation of osumilite, pseudosections, feldspar thermometry, and monazite LASS U-Th-Pb chronology from the Ediacaran-Cambrian Anosyen domain of southern Madagascar to evaluate P-T-time paths and assess the relative importance of advective and radiogenic heating. Pseudosections of an osumilite-bearing assemblage, a garnet-orthopyroxene gneiss, and a garnet-spinel leucogneiss indicate peak conditions of 930-1010 C, 4-6 kbar; 900-950 C, 6-7 kbar; and 970-1000 C, 4.5-5.5 kbar, respectively. Feldspar thermometry indicates T > 915 ± 30 C. These conditions were reached along a low-P prograde path, as implied by cordierite and sillimanite inclusions in garnet. Monazite and zircon U/Th-Pb dating indicates that prograde metamorphism began 625 Ma and lasted 60 Myr. The timing of peak metamorphism is constrained to a 16 ± 2.5 Myr period between 566 ± 2 and 550 ± 1.5 Ma, by monazite inclusions in pseudomorphs after osumilite and monazite from a leucosome in the same outcrop. Peak T was achieved immediately following emplacement of voluminous charnockites (emplaced 1000-1100 C) and related magmas of the Anosyen Batholith. Crystallization of pegmatite dikes, leucosomes, and smaller plutons during cooling lasted from 550 to 510 Ma. This broad thermal history is also recorded by metamorphic monazite Eu/Eu*, which indicate progressive melt generation and extraction prior to 550 Ma followed by melt accumulation and crystallization after 550 Ma. Although the duration of prograde metamorphism is consistent with radiogenic heating models of large hot orogens, peak T was 100-200 C higher in southern Madagascar than in models, implying that UHTM in southern Madagascar cannot be explained by radiogenic heating alone. We attribute this thermal discrepancy to heat advected by the Anosyen Batholith. Published Nd isotope data (ɛNd = -22) indicate that these magmas were primarily sourced from the even hotter (>1000 C) lower crust of the orogen.

The role of hydrothermal processes in the granite-hosted Zr, Y, REE deposit at Strange Lake, Quebec/Labrador: Evidence from fluid inclusions

NASA Astrophysics Data System (ADS)

Salvi, Stefano; Williams-Jones, Anthony E.

1990-09-01

The Strange Lake Zr, Y, REE, Nb, and Be deposit is hosted by a small, high-level, Late-Proterozoic peralkaline granite stock that intruded into high-grade metamorphic gneisses on the Quebec-Labrador border. The stock is extensively altered. Early alteration is manifested by the replacement of arfvedsonite with aegirine. Later alteration involved Ca-Na exchange. Zr, Ti, Y, REEs, Nb, and Be are concentrated in Ca-bearing minerals that, together with quartz, commonly pseudomorph Na-bearing minerals. Fluid inclusions in pseudomorphs comprise several distinct types: high-salinity (13 to 24 wt% NaCl eq.), Ca-rich aqueous inclusions that homogenize to liquid between 135 and 195°C; mixed aqueousmethane inclusions; methane inclusions; and solid-bearing inclusions. Aqueous-methane inclusions represent heterogeneous entrapment of immiscible high-salinity aqueous liquid and methane. Bastnäsite (tentatively identified by SEM analysis) occurs as a daughter mineral. Other daughter or trapped minerals include a Y, HREE-bearing mineral, possibly gagarinite, and hematite, galena, sphalerite, fluorite, pyrochlore, kutnahorite (?), and griceite (?). The first three inclusion types also occur in quartz in pegmatites and veins together with lower-temperature, lower-salinity, Na-dominated aqueous inclusions. The entrapment temperature inferred for the aqueous inclusions from microthermometry and the Na-K-Ca geothermometer range from 155 to 195°C for the higher-salinity inclusions and 100 to 165°C for the low-salinity inclusions. A model is proposed in which the intrusion of a peralkaline granite to high crustal levels initiated a ground/formational water-dominated hydrothermal system in adjacent gabbroic, calc-silicate, and graphitic gneisses. Reaction of the high-salinity, Ca-rich liquid with the graphitic gneisses led to the production of an immiscible methane gas. Subsequent interaction of this liquid with the granite led to extensive replacement of sodic minerals by calcium analogues at temperatures of less than 200°C. Some time after the onset of Ca metasomatism the high-salinity liquid mixed with a Ca-poor, low-salinity, low-temperature liquid that had leached F and rare metals from the granite. Yttrium and REE mineral deposition occurred as a result of the decreased ligand concentration that accompanied fluorite deposition during mixing of the Ca-rich and Ca-poor aqueous liquids.

An evolved axial melt lens in the Northern Ibra Valley, Southern Oman Ophiolite

NASA Astrophysics Data System (ADS)

Loocke, M. P.; Lissenberg, C. J.; MacLeod, C. J.

2014-12-01

The axial melt lens (AML) is a common feature lying at the base of the upper crust at fast-spreading mid-ocean ridges. It is thought to play a major role in the evolution of MORB and, potentially, accretion of the plutonic lower crust. In order to better understand the petrological processes that operate in AMLs we have examined the nature and variability of the horizon equivalent to the AML preserved in the Oman ophiolite. We present the results of a detailed investigation of a section east of Fahrah in the Ibra Valley. Here, a suite of 'varitextured' gabbros separates the sheeted dykes above from foliated gabbros below. It comprises 3 distinct units: an ophitic gabbro with pegmatitic patches (patchy gabbro; 70 m thick), overlain by a spotty gabbro (50 m), capped by a quartz-diorite (120 m). The sheeted dykes are observed to root in the quartz-diorite. Contacts between the plutonic units are gradational and subhorizontal. All of the units are isotropic. A total of 110 samples were collected for detailed petrographic and chemical analysis. With the exception of a small number of the diorites, all of the samples have a 'cumulate' component. Primary igneous amphibole is ubiquitous, present even as a minor phase in the foliated gabbros beneath, and indicating extensive differentiation and/or the presence of water in the primary liquid. France et al. (2014, Lithos) report patches of granoblastic material from this horizon in the Fahrah area, and suggest they represent the restites of partially melted pieces of the sheeted dykes. We did not, however, find any such granoblastic material, nor can the quartz-diorites represent partial melt; instead, preliminary geochemical modeling suggests that all of the units can be related by simple progressive fractional crystallization of an Oman axial ('V1' or 'Geotimes') melt. Along with the field relationships, as well as the basaltic andesite to dacite composition of the overlying sheeted dykes, this suggests that the AML was the locus of formation of the highly evolved melts. This contrasts with the more primitive AML and sheeted dyke complex documented in Wadi Abyad. From this we conclude that there is significant lateral variability in AML compositions along the Oman ridge axis.

Provenance of Carboniferous sedimentary rocks in the northern margin of Dabie Mountains, central China and the tectonic significance: constraints from trace elements, mineral chemistry and SHRIMP dating of zircons

NASA Astrophysics Data System (ADS)

Li, Renwei; Li, Shuangying; Jin, Fuquan; Wan, Yusheng; Zhang, Shukun

2004-04-01

A suite of slightly metamorphosed Carboniferous sedimentary strata occurs in the northern margin of the Dabie Mountains, central China. It consists, in ascending order, of the upper Huayuanqiang Formation (C 1), the Yangshan Formation (C 1), the Daorenchong Formation (C 1-2), the most widely distributed Huyoufang Formation (C 2) and the Yangxiaozhuang Formation (C 2). The provenance of the Carboniferous sedimentary rocks is constrained by the integration of trace elements, detrital mineral chemistry and sensitive high resolution ion microprobe (SHRIMP) dating of detrital zircons, which can help to understand the connection between the provenance and the Paleozoic tectonic evolution of the Qinling-Dabie Orogen. The trace element compositions indicate that the source terrain was probably a continental island arc. Detrital tourmalines were mainly derived from aluminous and Al-poor metapelites and metapsammites, and some are sourced from Li-poor granitoids, pegmatites and aplites. Detrital garnets, found only in the uppermost Huyoufang Formation, are almandine and Mn-almandine garnets, indicating probable sources mainly from garnetiferous schists, and partly from granitoid rocks. The detrital white K-micas are muscovitic in the Huayuanqiang, Daorenchong and Huyoufang Formations, and phengitic with Si contents (p.f.u.) from 3.20 up to max. 3.47-3.53 in the uppermost Huyoufang and the Yangxiaozhuang Formations, a meta-sedimentary source. Major components in the detrital zircon age structure for the Huyoufang Formation range from 506 to 363 Ma, centering on ˜400 and ˜480 Ma, which is characteristic of the Qinling and Erlangping Groups in the Qinling and Tongbai Mountains, central China. Evidently, the major source of the Carboniferous sedimentary rocks in the northern margin of Dabie Mountains was from the southern margin of the Sino-Korean Craton represented by the Qinling and Erlangping Groups. The source area was an island-arc system during the Early Paleozoic that collided with the Sino-Korea plate towards the end of the Early Paleozoic or during the Devonian. A prominent feature in the detrital zircon age structure of the Huyoufang Formation is the Neoproterozoic detritus, which could be derived only from the Yangtze Craton. Reasonable interpretation of the two distinct source materials for the Huyoufang Formation is that the two plates were juxtaposed through collision before the late Carboniferous.

Quaternary geologic map of the Havre 1° x 2° quadrangle

USGS Publications Warehouse

Compilations by Fullerton, David S.; Colton, Roger B.; Bush, Charles A.

2012-01-01

The Havre quadrangle encompasses approximately 16,084 km2 (6,210 mi2). The northern boundary is the Montana/Saskatchewan (U.S./Canada) boundary. The quadrangle is in the Northern Plains physiographic province and it includes parts of the Bearpaw Mountains, the Little Rocky Mountains, and the Boundary Plateau. The primary river is the Milk River. The ancestral Missouri River was diverted south of the Bearpaw Mountains by a Laurentide ice sheet. The fill in the buried ancestral valley at and southwest of Havre contains a complex stratigraphy of fluvial, glaciofluvial, ice-contact, glacial, lacustrine, and eolian deposits. The old valley east of Havre now is occupied by the Milk River. The map units are surficial deposits and materials, not landforms. Deposits that comprise some constructional landforms (e.g., ground-moraine deposits, end-moraine deposits, stagnation-moraine deposits, all composed of till) are distinguished for purposes of reconstruction of glacial history. Surficial deposits and materials are assigned to 24 map units on the basis of genesis, age, lithology or composition, texture or particle size, and other physical, chemical, and engineering characteristics. It is not a map of soils that are recognized in engineering geology, or of substrata or parent materials in which pedologic or agronomic soils are formed. Glaciotectonic (ice-thrust) structures and deposits are mapped separately, represented by a symbol. On the glaciated plains and on the Boundary Plateau the surficial deposits are glacial, ice-contact, glaciofluvial, catastrophic flood, alluvial, lacustrine, eolian, and colluvial deposits. In the Bearpaw Mountains and Little Rocky Mountains beyond the limit of Quaternary glaciation they are fluvial, colluvial, and mass-wasting deposits and residual materials. Tills of late Wisconsin and Illinoian ages are represented by map units. Tills of two pre-Illinoian glaciations are not mapped but are widespread in the subsurface and are identified in stratigraphic sections. Thirteen stratigraphic sections document a complex glacial and interglacial history in the quadrangle. Pliocene continental glaciation possibly is represented by erratic blocks of garnet gneiss and pegmatite from the Canadian Shield, perched high on drainage divides in the western Bearpaw Mountains. Glacial striations on bedrock, two boulder trains, and linear ice-molded landforms (primarily drumlins) indicate the possible presence of an east-southeast flowing ice stream in the Havre glacial lobe during late Wisconsin glaciation.

In situ rutile petrochronology: texture-related T, Paleoproterozoic inheritance and a Pan-African overprint in the oldest subduction-related eclogites, Usagaran Orogen, Tanzania

NASA Astrophysics Data System (ADS)

Moeller, A.; Kraus, K.; Herms, P.; Appel, P.; Raase, P.

2014-12-01

Rutile U-Pb thermochronology is applied successfully by both TIMS and beam methods to date cooling events in mafic and metapelitic rocks, as well as in detrital studies. The Zr-in-rutile thermometer is very robust to thermal diffusion, and generally requires complete recrystallization to change recorded crystallization temperatures. Evidence for diffusion of HFSE elements in rutile is sparse; whereas U-Pb chronology generally records diffusion controlled cooling from the last event. This study follows conventional thermobarometry and U-Pb TIMS results on monazite, sphene and rutile of Möller et al. (1995) establishing a 2 Ga eclogite facies event from MORB-like metabasic, and metapelitic rocks in the Usagaran Orogen of Tanzania, interpreted to be the oldest outcrops of subduction-related eclogites. Rutile from both rock types were discordant near a ca. 500 Ma lower intercept, confirming a thermal overprint postulated on the basis of K-Ar and Rb-Sr mica ages by e.g. Wendt et al. (1972). The age of the eclogite-facies event was confirmed by U-Pb zircon dating of a 1991±2 Ma crosscutting pegmatite (Collins et al., 1999). We present in situ LA-ICP-MS rutile petrochronology on five metabasic and metapelitic eclogite facies samples with variable retrograde amphibolite-facies recrystallization. Thermometry confirms conventional Fe-Mg results, including higher peak temperatures in metabasites. Traverses on rutile inclusions in large garnet prophyroblasts in metapelites show increasing temperatures from cores outwards and a slight decrease towards outermost rims, with peak T coinciding with highest Mg# and highest grossular content, hence consistent with preservation of prograde zoning in the garnets and a brief eclogite facies event. Large rutiles (800μm) in recrystallized samples record temperature zoning profiles. U-Pb results show inheritance of near concordant 2 Ga domains, but dominantly confirm the ca. 490 Ma amphibolite facies overprint. The study is an excellent example of the potential of in-situ rutile petrochronology in complex, polymetamorphic rocks when meticulous attention is given to textural context. Möller et al., 1995, Geology, v. 23, p. 1067-1070. Collins et al., 2004, Earth Planet. Sci. Lett., v. 224, p. 175-192. Wendt et al., 1972, 24th Internat. Geol. Congr., Proc., p. 295-314.

Granodiorite - one of the most significant Slovenian natural stones

NASA Astrophysics Data System (ADS)

Kramar, Sabina; Trajanova, Mirka; Rogan-Šmuc, Nastja; Gutman, Maja; Bedjanič, Mojca; Mladenovič, Ana

2015-04-01

The paper provides a description of the petrographic and mechanical characteristics of granodiorite from the Pohorje Mountains (NE Slovenia) and of its use as a natural stone. This stone, which is a calc-alkaline igneous rock of Miocene age (18.7 Ma), is characterised by its grey colour and by its thick white aplite-pegmatite veins. It mainly consists of plagioclase, quartz, and K-feldspar, which are light coloured constituents, with biotite and a small amount of hornblende as dark coloured minerals. Some other minerals are found in traces, among which pyrite is considered to be the most problematic. However, due to the presence of a small amount of arsenic, the pyrite is quite stable and not prone to alteration. In Slovenia currently two quarries are located in granodiorite, both protected as valuable natural geological features; an active quarry at Cezlak which is the largest quarry in magmatic rocks in Slovenia and the abandoned quarry in Josipdol. Granodiorite is considered the highest quality natural stone in Slovenia. It is characterised by high density, low water absorption, and low open porosity, so that it exhibits high frost and salt resistance, as well as a high compressive strength and an extremely high flexural strength, which is due to its pronounced oriented structure. It is widely recognized throughout Slovenia by its durability and its decorative white veins, and is currently the most frequently used natural stone in Slovenia. It is mainly used as paving and cladding material for residential buildings, churches, and other structures, as well as for squares, thus giving a special character to many of Slovenia's largest towns and cities. Several important buildings are decorated by means of this stone, such as the Slovenian Parliament, the Republic Square business complex, the Maximarket department store, and the Faculty of Law of the University of Ljubljana, all of which are located in Ljubljana, some of them having been declared as cultural monuments of national importance. Since 1940 granodiorite has also been widely used by sculptors for various monuments and fountains. An unusual type of degradation of cladding panels, in the form of bowing, was detected on the façades of the above-mentioned Maximarket, which was constructed in 1971. This phenomenon is one among the very few documented cases of the bowing of magmatic rocks.

Geology, market and supply chain of niobium and tantalum—a review

NASA Astrophysics Data System (ADS)

Mackay, Duncan A. R.; Simandl, George J.

2014-12-01

Tantalum (Ta) and niobium (Nb) are essential metals in modern society. Their use in corrosion prevention, micro-electronics, specialty alloys and high-strength low-alloy (HSLA) steel earns them a strategic designation in most industrialised countries. The Ta market is unstable due in part to historic influx of `conflict' columbite-tantalite concentrate, or "Coltan," that caused Ta mines in Australia and Canada to be placed on care and maintenance. More recently, the growing appetite of modern society for consumer goods made of `conflict-free' minerals or metals has put pressure on suppliers. Pegmatites, rare-element-enriched granites, related placer deposits and weathered crusts overlying carbonatite and peralkaline complexes account for the majority of Ta production. Several carbonatite-related deposits (e.g. Upper Fir and Crevier, Canada) are being considered for potential co-production of Ta and Nb. Pyrochlore (Nb-Ta), columbite-tantalite (Nb-Ta), wodginite (Ta, Nb and Sn) and microlite (Ta and Nb) are the main ore minerals. Approximately 40 % of Ta used in 2012 came from Ta mines, 30 % from recycling, 20 % from tin slag refining and 10 % from secondary mine concentrates. Due to rapid industrialisation and increased use of Nb in steel making in countries such as China and India, demand for Nb is rising. Weathered crusts overlying carbonatite complexes in Brazil and one hard rock carbonatite deposit in Canada account for about 92 and 7 % of Nb world mine production, respectively. Since the bulk of the production is geographically and politically restricted to a single country, security of supply is considered at risk. Other prospective resources of Nb, beside carbonatites and associated weathered crusts, are peralkaline complexes (e.g. Nechalacho; where Nb is considered as a potential co-product of REE and zirconium). Economically, significant deposits of Ta and Nb contain pyrochlore, columbite-tantalite, fersmite, loparite and strüverite. Assuming continued elasticity of Ta and Nb prices and that the law of the supply and demand applies, new sources of these metals can be developed. In the long term, there is no need to worry about Ta and Nb availability. Temporary disruptions in Ta and Nb supply are possible and could be difficult to cope with, so new sources of supply may be developed to diversify geographic sources of supply for strategic reasons.

Uniform Distribution of Yttrium and Heavy Rare Earth Elements in Round Top Mountain Rhyolite Deposit , Sierra Blanca Texas, USA: Data, Significance, and Origin

NASA Astrophysics Data System (ADS)

Pingitore, N. E., Jr.; Clague, J. W.; Gorski, D.

2014-12-01

The Round Top Mountain peraluminous rhyolite, exposed at the surface in Sierra Blanca, Hudspeth County, west Texas, USA, is enriched in yttrium and heavy rare earth elements (YHREEs). Other potentially valuable elements in the deposit include Be, Li, U, Th, Sn, F, Nb, and Ta. Texas Rare Earth Resources Corp. proposes to extract the YHREEs from the host mineral variety yttrofluorite by inexpensive heap leaching with dilute sulfuric acid, which also releases some of the Be, Li, U, F, and Th from other soluble minor minerals. Data: Feldspars and quartz comprise 90-95% of the rhyolite, with pheonocrysts of up to 250 microns set in an aphanitic matrix that hosts the typically sub-micron target yttrofluorite. Reverse circulation cuttings from some 100 drill holes, two drill cores, and outcrop and trench observations suggest striking physical homogeneity through this billion-plus ton surface-exposed laccolith, about 1200 feet high and a mile in diameter (375 x 1600 m). Gray to pink, and other minor hues, color variation derives from magnetite—hematite redox reaction. Plots of Y, 13 REEs, U, Th, and Nb analyses from over 1500 samples collected from 64 drill holes (color codes in figure) exhibit remarkably little variation in the concentration of these elements with geographic position or depth within the laccolith. Importance: Uniform mineralization grades help insure against the mining production surprises often associated with vein deposits and heterogeneous open pit deposits. At Round Top, mine feedstock can be relatively constant over the life of the mine (multiple decades), so the mechanical mining process can be optimized early on and not need expensive alterations later. Likewise, the chemical and physical parameters of the heap leach can be perfected. The sensitive and expensive process of extraction of elements and element groups from the pregnant leach solution and purification also can be optimized. Origin: The remarkable homogeneity of the YHREE distribution through the laccolith suggest YHREE and associated mineralization from a late-stage fluorine vapor generated within the magma in situ, rather than from injection of a F-rich fluid from an external source. The micron-scale cavities that produce up to 5% original porosity in the rhyolite may be nano-analogues of the cavities associated with granite pegmatites.

Homogenous stretching or detachment faulting? Which process is primarily extending the Aegean crust

NASA Astrophysics Data System (ADS)

Kumerics, C.; Ring, U.

2003-04-01

In extending orogens like the Aegean Sea of Greece and the Basin-and-Range province of the western United States, knowledge of rates of tectonic processes are important for understanding which process is primarily extending the crust. Platt et al. (1998) proposed that homogeneous stretching of the lithosphere (i.e. vertical ductile thinning associated with a subhorizontal foliation) at rates of 4-5 km Myr-1 is the dominant process that formed the Alboran Sea in the western Mediterranean. The Aegean Sea in the eastern Mediterranean is well-known for its low-angle normal faults (detachments) (Lister et al., 1984; Lister &Forster, 1996) suggesting that detachment faulting may have been the primary agent achieving ~>250 km (McKenzie, 1978) of extension since the Miocene. Ring et al. (2003) provided evidence for a very fast-slipping detachment on the islands of Syros and Tinos in the western Cyclades, which suggests that normal faulting was the dominant tectonic process that formed the Aegean Sea. However, most extensional detachments in the Aegean do not allow to quantify the amount of vertical ductile thinning associated with extension and therefore a full evaluation of the significance of vertical ductile thinning is not possible. On the Island of Ikaria in the eastern Aegean Sea, a subhorizontal extensional ductile shear zone is well exposed. We studied this shear zone in detail to quantify the amount of vertical ductile thinning associated with extension. Numerous studies have shown that natural shear zones usually deviate significantly from progressive simple shear and are characterized by pronounced shortening perpendicular to the shear zone. Numerous deformed pegmatitic veins in this shear zone on Ikaria allow the reconstruction of deformation and flow parameters (Passchier, 1990), which are necessary for quantifying the amount of vertical ductile thinning in the shear zone. Furthermore, a flow-path and finite-strain study in a syn-tectonic granite, which intruded into the shear zone, was carried out. Consistent results show that the mean kinematic vorticity number in the shear zone was close to 1, indicating that the bulk deformation path was close to simple shear. This in turn indicates that vertical ductile thinning was not important during extensional faulting. We conclude that detachment faulting was the primary agent that extended the Aegean crust.

Earthquake Hazard Assessment Based on Geological Data: An approach from Crystalline Terrain of Peninsular India

NASA Astrophysics Data System (ADS)

John, B.

2009-04-01

Earthquake Hazard Assessment Based on Geological Data: An approach from Crystalline Terrain of Peninsular India Biju John National Institute of Rock Mechanics b_johnp@yahoo.co.in Peninsular India was for long considered as seismically stable. But the recent earthquake sequence of Latur (1993), Jabalpur (1997), Bhuj (2001) suggests this region is among one of the active Stable Continental Regions (SCRs) of the world, where the recurrence intervals is of the order of tens of thousands of years. In such areas, earthquake may happen at unexpected locations, devoid of any previous seismicity or dramatic geomorphic features. Even moderate earthquakes will lead to heavy loss of life and property in the present scenario. So it is imperative to map suspected areas to identify active faults and evaluate its activities, which will be a vital input to seismic hazard assessment of SCR area. The region around Wadakkanchery, Kerala, South India has been experiencing micro seismic activities since 1989. Subsequent studies, by the author, identified a 30 km long WNW-ESE trending reverse fault, dipping south (45°), that influenced the drainage system of the area. The macroscopic and microscopic studies of the fault rocks from the exposures near Desamangalam show an episodic nature of faulting. Dislocations of pegmatitic veins across the fault indicate a cumulative dip displacement of 2.1m in the reverse direction. A minimum of four episodes of faulting were identified in this fault based on the cross cutting relations of different structural elements and from the mineralogic changes of different generations of gouge zones. This suggests that an average displacement of 52cm per event might have occurred for each event. A cyclic nature of faulting is identified in this fault zone in which the inter-seismic period is characterized by gouge induration and fracture sealing aided by the prevailing fluids. Available empirical relations connecting magnitude with displacement and rupture length show that each event might have produced an earthquake of magnitude ≥ 6.0, which could be a damaging one to an area like peninsular India. Electron Spin Resonance dating of fault gouge indicates a major event around 430ka. In the present stress regime this fault can be considered as seismically active, because the orientation of the fault is favorable for reactivation.

Provenance analysis and thermo-dynamic studies of multi-type Holocene duricrusts (1700 BC) in the Sua Salt Pan, NE Botswana

NASA Astrophysics Data System (ADS)

Dill, Harald G.; Dohrmann, R.; Kaufhold, S.; Techmer, A.

2014-08-01

Multi-type duricrusts, composed of silcretes, calcretes, halcretes and sulcretes developed during the Holocene at the northern rim of the Sua Salt Pan, NE Botswana. They were investigated for their light (quartz/chalcedony, feldspar, analcime, clinoptilolite, calcite, kaolinite/halloysite, illite-smectite mixed-layers, halite) and heavy minerals (baryte, clinozoisite-epidote s.s.s., amphibole, corundum, tourmaline, ilmenite, rutile, sphene, kyanite, andalusite, staurolite, garnet, zircon, apatite, monazite, cassiterite, garnet, biotite) using petrographic microscopy, X-ray fluorescence and diffraction analyses, radio-carbon dating, scanning electron microscopy equipped with an EDX-system, cation exchange capacity and infrared spectroscopy. Detrital minerals predominantly derived from the erosion of rocks belonging to the Archaean Basement Complex, the Stormberg Volcanites and the Kalahari sediments. Of particular interest to exploration geologists, geikielite-enriched ilmenite fragments are a hint to kimberlitic pipes. Biodetritus was derived from invertebrates and from vertebrates (fish bones?). A man-made impact on the heavy mineral suite has to be invoked from small fragments of cassiterite fragments that derived from processing of sulfidic and pegmatitic Sn-bearing ore. In the salt-pan-derived duricrusts mainly the aeolian and to a lesser degree fluvial inputs were responsible for the concentration of clasts in these multi-type duricrusts. Moreover, their variegated mineralogy enables us to constrain the physical-chemical regime, prevalently as to the pH and the chemical composition of the major constituents. All duricrusts developed in a self-sufficient chemically closed system where quartz and feldspar provided the elements Si, Na, K, Ca, and Ba to produce the encrustations. The spatial and temporal trend in the Sua Salt Pan rim encrustations may be described as follows: (1) sulcrete-silcretes, (2) silcretes with kaolinite-group minerals towards more recent stages at the rim and smectite-illite mixed-layers and clinoptilolite towards the basin center, (3) calcretes with analcite towards the basin center, (4) halcretes (and soda ash at a more central position). In the sulcrete-silcrete facies the pH decreases from pH 14 down to 4. In the calcretes and halcretes it increases from pH 8 to pH > 13. marking a chemical hiatus between stages 1 plus 2 and stages 3 plus 4. Mineral assemblages forming more basinward tend to have derived from more alkaline fluids than those near the edge of the salt pan.

The sources and evolution of mineralising fluids in iron oxide-copper-gold systems, Norrbotten, Sweden: Constraints from Br/Cl ratios and stable Cl isotopes of fluid inclusion leachates

NASA Astrophysics Data System (ADS)

Gleeson, S. A.; Smith, M. P.

2009-10-01

We have analysed the halogen concentrations and chlorine stable isotope composition of fluid inclusion leachates from three spatially associated Fe-oxide ± Cu ± Au mineralising systems in Norrbotten, Sweden. Fluid inclusions in late-stage veins in Fe-oxide-apatite deposits contain saline brines and have a wide range of Br/Cl molar ratios, from 0.2 to 1.1 × 10 -3 and δ 37Cl values from -3.1‰ to -1.0‰. Leachates from saline fluid inclusions from the Greenstone and Porphyry hosted Cu-Au prospects have Br/Cl ratios that range from 0.2 to 0.5 × 10 -3 and δ 37Cl values from -5.6‰ to -1.3‰. Finally, the Cu-Au deposits hosted by the Nautanen Deformation Zone (NDZ) have Br/Cl molar ratios from 0.4 to 1.1 × 10 -3 and δ 37Cl values that range from -2.4‰ to +0.5‰, although the bulk of the data fall within 0‰ ± 0.5‰. The Br/Cl ratios of leachates are consistent with the derivation of salinity from magmatic sources or from the dissolution of halite. Most of the isotopic data from the Fe-oxide-apatite and Greenstone deposits are consistent with a mantle derived source of the chlorine, with the exception of the four samples with the most negative values. The origin of the low δ 37Cl values in these samples is unknown but we suggest that there may have been some modification of the Cl-isotope signature due to fractionation between the mineralising fluids and Cl-rich silicate assemblages found in the alteration haloes around the deposits. If such a process has occurred then a modified crustal source of the chlorine for all the samples cannot be ruled out although the amount of fractionation necessary to generate the low δ 37Cl values would be significantly larger. The source of Cl in the NDZ deposits has a crustal signature, which suggests the Cl in this system may be derived from (meta-) evaporites or from input from crustal melts such as granitic pegmatites of the Lina Suite.

Syn-orogenic magmatism over 100 m.y. in high crustal levels of the central Grenville Province: Characteristics, age and tectonic significance

NASA Astrophysics Data System (ADS)

Groulier, Pierre-Arthur; Indares, Aphrodite; Dunning, Gregory; Moukhsil, Abdelali; Jenner, George

2018-07-01

The Escoumins Supracrustal Belt (ESB) represents higher levels of the infrastructure of a large hot orogen, exposed in a broadly dome and basin pattern. It consists of remnants of a Pinwarian-age (1.52-1.46 Ga) oceanic arc and arc-rift sequence, preserved in the low-P Belt of the central Grenville Province, and was intruded by diverse Grenvillian-age plutons. The plutonic rocks range from quartz monzodiorite to granite and have intrusion ages covering a time interval of 100 My, that represents the entire range of the Grenvillian orogeny. Moreover, the ages, field relations and geochemical signatures of the different intrusions can be matched with different documented stages of the orogeny. The oldest pluton, the magnesian, biotite-bearing Bon-Désir granite (1086 ± 2 Ma), has positive εNd (+0.6), TDM = 1.52 Ga, and is attributed to melting of a juvenile Pinwarian crust as a result of slab break-off, at the onset of continental collision. The ferroan and Ba-Sr enriched, biotite-, amphibole- and clinopyroxene-bearing Michaud plutonic suite (1063 ± 3 Ma) and biotite-rich felsic sill (1045 ± 3 Ma) have εNd (-0.01 - +0.8) and TDM = 1.45-1.48 Ga. Their geochemistry is consistent with fractionation of a mafic magma derived from melting of a Geon 14 subduction-modified subcontinental lithospheric mantle. This magmatism is consistent with convective thinning of subcontinental lithosphere, potentially linked to tectonic extrusion and orogenic collapse. This collapse ultimately led to the juxtaposition of the low-P Belt with the high-T mid-P Belt in the hinterland of the Grenville Province and to amphibolite-facies metamorphism in the former, producing metamorphic zircon overgrowths at 1037 ± 10 Ma. Finally, 988 ± 5 Ma to 983 ± 5 Ma syn-kinematic peraluminous two-mica garnetiferous leucogranite bodies and pegmatites with inherited 1055 ± 2 Ma metamorphic monazite were derived from melting of previously metamorphosed deeper levels of the low-P Belt. This is consistent with a high geothermal gradient linked to thinning of the crust in a Basin and Range setting. The geochemical and age pattern of Grenvillian-age magmatism in the ESB, in conjunction with the overall architecture of the Province, suggests that Laurentia was the upper plate during the Grenvillian orogeny.

Comparing REE distribution in GEMAS agricultural soils and FOREGS topsoils-subsoils in Italy and Sweden

NASA Astrophysics Data System (ADS)

Petrosino, Paola; Sadeghi, Martiya; Andersson, Madelen; Albanese, Stefano; Dinelli, Enrico; Valera, Paolo; Ladenberger, Anna; Morris, George; Uhlbäck, Jo; Lima, Annamaria; De Vivo, Benedetto

2014-05-01

Scientific interest on Rare Earth Elements (REEs)-bearing media is increasing as a consequence of the rapidly growing demand of these important chemical resources, which are currently used in a large number of technical applications. In this study, Italian and Swedish REE data from the FOREGS database on topsoil and subsoils samples have been compared to the distribution of REEs in the GEMAS samples of agricultural soil (Ap), pertaining to regularly ploughed land to a depth of 20 cm. Principal Component Analysis (PCA) was carried out to identify patterns within both data sets. Investigation of the spatial distribution of REEs in FOREGS topsoil-subsoil and GEMAS Ap media for both countries revealed the prominent role of the geogenic component in the general REE geochemical pattern of the three solid media. Despite a similar REE content in the underlying parent material or bedrocks (alkaline igneous rocks, both intrusive and effusive in Italy, alkaline granites and pegmatites in Sweden), several distinct differences emerged between the two countries driven by climate, topography, age of the rock units and sediments, presence of mineralisations, type of soils and presence of glacial deposits. GEMAS agricultural soils form both countries show higher REEs contents than the corresponding subsoils and topsoils, which could be ascribed to the analytical method specifically set for REEs and the last generation ICP-MS instrument used by SGS Lab to analyze REEs in Ap soils. The REE content in Italian topsoil and subsoil is similar and there is a good agreement between the topsoils and Ap soils, which were collected from similar depth. Swedish subsoil is on the contrary more enriched in REEs with respect to topsoil, and Ap soils even display REE contents higher than subsoils. This anomalous REE concentrations in agricultural soil may originate from the fact that most of the arable land in Sweden has been located on glacial and postglacial deposits, rich in clay which has tendency to accumulate secondary REEs. We concluded that the fingerprints of anthropic activity due to agricultural activities does not influence the geogenic signal. Both in Italy and Sweden, in fact, REE trends in GEMAS agricultural soils are well comparable with those obtained for FOREGS soils sampled from unoccupied and undisturbed regions.

Demonstration Of A Portable Approach For Rb-Sr Geochronology On The Boulder Creek Granite: Implications For Planetary Exploration

NASA Astrophysics Data System (ADS)

Anderson, F.; Nowicki, K.; Whitaker, T.

2011-12-01

We have succeeded at producing a Rubidium-Strontium (Rb-Sr) geochronology measurement of the Boulder Creek Granite of 1.369±0.144 Ga (MSWD=1; actual value 1.34±0.07 Ga [0]) in under 5 hours using a laser desorption resonance ionization mass spectrometer (LDRIMS) that can be miniaturized for portable use. The LDRIMS approach would enable new in-situ radiometric measurements for the Moon and Mars that would significantly improve geologic interpretation of these complex surfaces and constrain impactor flux throughout the solar system. Models of the age error based on existing Rb-Sr measurements of Mars meteorites using 100-1000 LDRIMS measurements at ±0.1% (1σ) accuracy show that analytical uncertainties <±50 Ma are possible [1]. The LDRIMS technique avoids the interference and mass resolution issues associated with other geochronology measurements [2]. Our current prototype can measure the isotope ratio of lab standards with 10 ppm net Sr or Rb to a precision of ±0.1% (1σ), with a sensitivity of 1:1010 in ~15 minutes. The speed of the LDRIMS measurement allows thousands of samples to be measured in significantly shorter periods of time than traditional methods, with little or no sample preparation. This abstract focuses on samples of the Boulder Creek Granite from Elephant Butte located in Boulder, Colorado, composed of a "gneissic quartz monzonite and granodiorite with local facies of aplite, alaskite, hornblende diorite, and pegmatite" [3]. We rough cut a block of Boulder Creek Granite to fit our sample holder, verifying that a range of quartz, plagioclase, hornblende and biotite were visible, and placing it in our sample chamber. 3000 laser desorption shots were acquired at each of 97 spots manually separated in a rastering fashion by ~300-500 μm. For this initial experiment, no attempt was made to localize desorption to a single mineral, or identify the mineral under desorption. The age error of ±144 m.y. is consistent with our analytical models for a small number of measurements at moderate precision, however, when more measurements are completed, we anticipate that the age error will improve to <50-100 m.y. values [1]. Finally, the instrument can also be used to measure the chemistry of a sample using laser desorption secondary ionization mass spectrometry (LDSIMS), simply by turning up the power of the RI lasers. In addition to geochronology, the TOF has demonstrated resolution of 80K+, enabling us to separate light isotopes and measure heavy organics relevant for astrobiology.

Solution-mass transfer and grain boundary sliding in mafic shear zones - comparison between experiments and nature

NASA Astrophysics Data System (ADS)

Marti, Sina; Heilbronner, Renée; Stünitz, Holger; Plümper, Oliver; Drury, Martyn

2017-04-01

Grain size sensitive creep (GSSC) mechanisms are widely recognized to be the most efficient deformation mechanisms in shear zones. With or without initial fracturing and fluid infiltration, the onset of heterogeneous nucleation leading to strong grain size reduction is a frequently described process for the initiation of GSSC. Phase mixing due to reaction and heterogeneous nucleation during GSSC impedes grain growth, sustaining small grain sizes as a prerequisite for GSSC. Here we present rock deformation experiments on 'wet' plagioclase - pyroxene mixtures at T=800°C, P=1.0 and 1.5GPa and strain rates of 2e-5 - 2e-6 1/s, performed with a Griggs-type solid medium deformation apparatus. Microstructural criteria are used to show that both, grain boundary sliding (GBS) and solution-mass transfer processes are active and are interpreted to be the dominant strain accommodating processes. Displacement is localized within shear bands formed by fine-grained ( 300 - 500nm) plagioclase (Pl) and the syn-kinematic reaction products amphibole (Amph), quartz (Qz) and zoisite (Zo). We compare our experiments with a natural case - a sheared mafic pegmatite (P-T during deformation 0.7 - 0.9 GPa, 610 - 710 °C; Getsinger et al., 2013) from Northern Norway. Except for the difference in grain size of the experimental and natural samples, microstructures are strikingly alike. The experimental and natural P- and especially T-conditions are very similar. Consequently, extrapolation from experiments to nature must be made without a significant 'temperature-time' trade-off, which is normally taken advantage of when relating experimental to natural strain rates. We will discuss under which assumptions extrapolation to nature in our case is likely feasible. Syn-kinematic reactions during GBS and solution-mass transport are commonly interpreted to result in an ordered (anticlustered) phase mixture. However, phase mixing in our case is restricted: Mixing is extensive between Pl + Zo + Qz and Amph + Qz, but clustering is common between Pl + Amph. We present microstructural evidences, that phase mixing between Pl and Amph (the most abundant phases) is enhanced by the presence of quartz. Accordingly, quartz forming reactions or external sources (e.g. through fluid infiltration) may play a crucial role in deformation of mafic rocks, which has not been recognized thus far. Getsinger, A.J., Hirth, G., Stünitz, H., Goergen, E.T., 2013. The Influence of Water on Rheology and Strain Localization in the Lower Continental Crust. Geochemistry Geophysics Geosystems 14, 2247 - 2264.

Geochemical and isotopic evidence for the petrogenesis and emplacement tectonics of the Serra dos Órgãos batholith in the Ribeira belt, Rio de Janeiro, Brazil

NASA Astrophysics Data System (ADS)

Machado, Rômulo; Philipp, Ruy Paulo; McReath, Ian; Peucat, Jean Jacques

2016-07-01

The Serra dos Órgãos batholith in the State of Rio de Janeiro (Brazil) is a NE-SW-trending elongated body that occupies ca. 5000 km2 in plan view. It is a foliated intrusion, especially at its borders and is crosscut by syn-magmatic shear zones, with foliations that are moderately-to steeply-dipping to the northwest and moderately-to shallow-dipping in the center and to the southeast, in a configuration of a large laccolith. It was emplaced between 560 and 570 Ma, during an extensional episode that was part of a series of events that comprise the Brasiliano Orogeny in SE Brazil, and which includes deformation, metamorphism and granite intrusion during the interval between 630 and 480 Ma. The two main rock types in the batholith are biotite-hornblende monzogranite, and biotite leucogranite, with subordinate tonalite, granodiorite, diorite, quartz diorite (enclaves), aplite and pegmatite. Harker-type diagrams help show two rock groups with similar trends of evolution: a dioritic and a granitic. The first one is tholeiitic, whereas the second is calc-alkaline, with medium-to high-K calc-alkaline affinity and metaluminous to slightly peraluminous character. In both groups strong decrease in Al2O3, MgO, FeOT and CaO relative to silica contents are observed, which is compatible with trends of fractional crystallization involving clinopyroxene and/or hornblende, plagioclase, opaque minerals, apatite, microcline and biotite. The Sr and Nd isotopic data suggest recycling of a Paleoproterozoic crust as an important petrological process to generate the batholith rocks. Geothermometry (amphibole composition) and geobarometry (saturation in zircon and apatite) indicate that most of the batholith solidified at mid to lower crustal levels at about 750 °C and between 5 and 5.5 kbar. We consider that Serra dos Órgãos crustal protoliths underwent melting caused by the interaction with hotter mafic magma at the base of the crust. These two magmas, with distinct initial compositions and rheology, probably underwent mixing and mingling. This process continued during the rise of the magma through the crust, which was accompanied by magmatic differentiation. The main feature that characterizes the post-collisional Serra dos Órgãos granite magmatism is the connection with high angle ductile shear zones of continental scale and presence to a greater or lesser extent of mafic magmas.

The Early Jurassic Bokan Mountain peralkaline granitic complex (southeastern Alaska): geochemistry, petrogenesis and rare-metal mineralization

USGS Publications Warehouse

Dostal, Jaroslav; Kontak, Daniel J.; Karl, Susan M.

2014-01-01

The Early Jurassic (ca. 177 Ma) Bokan Mountain granitic complex, located on southern Prince of Wales Island, southernmost Alaska, cross-cuts Paleozoic igneous and metasedimentary rocks of the Alexander terrane of the North American Cordillera and was emplaced during a rifting event. The complex is a circular body (~3 km in diameter) of peralkaline granitic composition that has a core of arfvedsonite granite surrounded by aegirine granite. All the rock-forming minerals typically record a two-stage growth history and aegirine and arfvedsonite were the last major phases to crystalize from the magma. The Bokan granites and related dikes have SiO2 from 72 to 78 wt. %, high iron (FeO (tot) ~3-4.5 wt. %) and alkali (8-10 wt.%) concentrations with high FeO(tot)/(FeO(tot)+MgO) ratios (typically >0.95) and the molar Al2O3/(Na2O+K2O) ratio Nd values which are indicative of a mantle signature. The parent magma is inferred to be derived from an earlier metasomatized lithospheric mantle by low degrees of partial melting and generated the Bokan granitic melt through extensive fractional crystallization. The Bokan complex hosts significant rare-metal (REE, Y, U, Th, Nb) mineralization that is related to the late-stage crystallization history of the complex which involved the overlap of emplacement of felsic dikes, including pegmatite bodies, and generation of orthomagmatic fluids. The abundances of REE, HFSE, U and Th as well as Pb and Nd isotopic values of the pluton and dikes were modified by orthomagmatic hydrothermal fluids highly enriched in the strongly incompatible trace elements, which also escaped along zones of structural weakness to generate rare-metal mineralization. The latter was deposited in two stages: the first relates to the latest stage of magma emplacement and is associated with felsic dikes that intruded along the faults and shear deformations, whereas the second stage involved ingress of hydrothermal fluids that both remobilized and enriched the initial magmatic mineralization. Mineralization is mostly composed of new minerals. Fluorine complexing played a role during the transportation of REE and HFSE in hydrothermal fluids and oxygen isotopes in the granites and quartz veins negate the significant incursion of an external fluid and support a dominantly orthomagmatic hydrothermal system. Many other REE-HFSE deposits hosted by peralkaline felsic rocks (nepheline syenites, peralkaline granites and peralkaline trachytes) were formed by a similar two stage process.

The origin and geochemical characteristics of rutile in eluvial and fluvial-alluvial placers and quartz veins of the Menderes Massif from the Neoproterozoic Pan-African Belt, Western Turkey

NASA Astrophysics Data System (ADS)

Kuşcu, Mustafa; Cengiz, Oya; Işık, Kayhan; Gül, E. Kübra

2018-07-01

Rutile occur in important amounts within Quaternary detrital sediments, and quartz veins which cut down the Paleozoic aged Eşme formation in the Menderes Massif on the Neoproterozoic Pan-Afrikan Belt in the west of Turkey. As a result of erosion, transport and accumulation of rutile-bearing quartz veins in the mica schists of the Eşme formation outcropped between Eşme (Uşak) and Kula (Manisa), the placer rutile occurrences occur in terraces, fluvial-alluvial and eluvial deposits. This study investigates the element content of rutile, oxygen isotope ratios of rutile and quartz, and formation temperature of rutile related to titanium source rock. Field observations show that rutiles are located in quartz veins that cut the schists. After these veins were fragmented and eroded, blocks of quartz with rutile and rutile grains are transported into clastic sediments in slope debris (eluvial), terraces and recent fluvial-alluvial deposits. Whereas quartz, rutile, ilmenite, and albite are found in the paragenesis of the rutile-bearing quartz vein fragments, the placers forming the terraces and current fluvial-alluvial deposits contain quartz, albite, muscovite, orthoclase, kaolinite, rutile, dravite, ilmenite, and zircon. The rutile grains in the examined placers and quartz vein fragments have grain sizes ranging from mm fractions to 5-6 cm. The major oxide compositions of the rutile grains have average values of 94 wt.% TiO2, 1.5 wt.% Fe2O3, 0.5 wt.% SiO2, and 0.3 wt.% Al2O3. The rutile samples have average values Nb of 1424 ppm, V of 980 ppm, W of 192 ppm, Ta of 94 ppm, and Zr of 73 ppm. The rutiles in the study area are defined as iron-rich rutile "nigrine" due to high iron content. Quartz veins are host rocks of rutile grains in the terrace and fluvial-aluvial sediments. The rutile-bearing quartz veins may be sourced from the Lower-Middle Miocene aged granites which are intruded the rocks in the Menderes Massif. Based on the analysis results of the methods of Zr thermometer from Zr values containing rutile and quartz-rutile geothermometer from oxygen isotope results (13.5‰ and 6‰) of quartz and rutile samples, the formation temperature of the rutile-bearing quartz veins were found to be at temperatures of 537 °C and 561 °C, respectively. These temperatures indicate that the rutile-bearing quartz veins may be in a temperature range between pegmatitic and/or hydrothermal stages.

Rare earth element deposits in China

USGS Publications Warehouse

Xie, Yu-Ling; Hou, Zeng-qian; Goldfarb, Richard J.; Guo, Xiang; Wang, Lei

2016-01-01

China is the world’s leading rare earth element (REE) producer and hosts a variety of deposit types. Carbonatite- related REE deposits, the most significant deposit type, include two giant deposits presently being mined in China, Bayan Obo and Maoniuping, the first and third largest deposits of this type in the world, respectively. The carbonatite-related deposits host the majority of China’s REE resource and are the primary supplier of the world’s light REE. The REE-bearing clay deposits, or ion adsorption-type deposits, are second in importance and are the main source in China for heavy REE resources. Other REE resources include those within monazite or xenotime placers, beach placers, alkaline granites, pegmatites, and hydrothermal veins, as well as some additional deposit types in which REE are recovered as by-products. Carbonatite-related REE deposits in China occur along craton margins, both in rifts (e.g., Bayan Obo) and in reactivated transpressional margins (e.g., Maoniuping). They comprise those along the northern, eastern, and southern margins of the North China block, and along the western margin of the Yangtze block. Major structural features along the craton margins provide first-order controls for REE-related Proterozoic to Cenozoic carbonatite alkaline complexes; these are emplaced in continental margin rifts or strike-slip faults. The ion adsorption-type REE deposits, mainly situated in the South China block, are genetically linked to the weathering of granite and, less commonly, volcanic rocks and lamprophyres. Indosinian (early Mesozoic) and Yanshanian (late Mesozoic) granites are the most important parent rocks for these REE deposits, although Caledonian (early Paleozoic) granites are also of local importance. The primary REE enrichment is hosted in various mineral phases in the igneous rocks and, during the weathering process, the REE are released and adsorbed by clay minerals in the weathering profile. Currently, these REE-rich clays are primarily mined from open-pit operations in southern China. The complex geologic evolution of China’s Precambrian blocks, particularly the long-term subduction of ocean crust below the North and South China blocks, enabled recycling of REE-rich pelagic sediments into mantle lithosphere. This resulted in the REE-enriched nature of the mantle below the Precambrian cratons, which were reactivated and thus essentially decratonized during various tectonic episodes throughout the Proterozoic and Phanerozoic. Deep fault zones within and along the edges of the blocks, including continental rifts and strike-slip faults, provided pathways for upwelling of mantle material.

Metallogeny of The Sierra de Guanajuato Range, Central México

NASA Astrophysics Data System (ADS)

Pedro F., Z. D.

2004-12-01

The Sierra de Guanajuato Range (SGR), trending N315° at Central México, is an orographic feature extending over a distance of 80 km. SGR comprises three well defined lithostratigraphic units: (1) a cretaceous basement including an arc-derived terrane named Guanajuato Arc (GA) made of gabbro, diorite and basaltic pillowed lava, and volcano-sedimentary rocks belonging to Arperos fore-arc basin which are geochemically anomalous in Au (0.15 ppm), Ag (3 ppm), Cu (40 ppm), Pb (50 ppm) and Zn (15 ppm); (2) Early Tertiary intrusive rocks, e.g., Comanja Granite which is affected by the presence of tourmalinized (schörl) aplito-pegmatite dykes mineralized with rare earths elements, and (3) Eocene redbeds (1,500-2000 m) and Oligocene-Miocene volcanics cover. The metallogeny of the SGR shows a multiple origin in time and space: volcano-sedimentary, granitic and volcanic, being possible to define three metallogenic epochs: cretaceous, paleocene and oligocene. Cretaceous epoch includes: (a) volcanogenic massive sulphide deposits (VMS) of bimodal-siliclastic type belonging to León-Guanajuato district; wallrock of VMS is made of felsic-internediate volcanics and black argillite; at Los Gavilanes deposit paragenesis is next: chalcopyrite > sphalerite > galena, pyrite > pyrrhotite > marcasite; grade is as follows: Au: .02-.07 g/t; Ag: 157-18.5 g/t; Cu: 2.24-0.81%, Pb: 4.16-0.03%; Zn: 10.35-3.02 %; (b) lens-shaped stratiform bodies of massive pyrite (i. ex., San Ignacio prospect; ˜ 4,000 ton) of exhalative-sedimentary origin with chalcopyrite and sphalerite microveins. Paleocene epoch includes both quartz-cordierite-sanidine veins and replacement bodies of hydrothermal metamorphic filliation (W +Se-Bi, Pb, Zn, Cu), and pyrometasomatic bodies [Cu, Pb, Zn (Ag), W] which genetically are linked to Comanja Granite emplacement. The wallrock at El Maguey mine (35,000 ton; 0.6% WO3) is made of hornfel and the vein (1.8-3.2m width) has a banding structure made of : \\{quartz & K-feldspar\\}, \\{(schörl) & specular hematite\\} and epidote alternating bands; ore minerals are scheelite and tetradymite. Oligocene epoch includes quartz-calcite-adulaire epithermal veins (Ag-Au) of geothermal-volcanic filliation. At Guanajuato mining District; ore minerals are: Au, electrum, acanthite, aguilarite, naumannite, polybasite, proustite, fischesserite (?); chalcopyrite, sphalerite and galena. Ore grade at Las Torres mine are: Ag 300 g/t, Au 2 g/t. At El Cubo mine because of the presence of rhyolitic domes gold grade reaches 100 g/t. Since Early Cretaceous Epoch, metallogenic concepts of heritage and permanence are valid in SG ore deposits.

Origin and Evolution of Li-rich Brines at Clayton Valley, Nevada, USA

NASA Astrophysics Data System (ADS)

Munk, L. A.; Bradley, D. C.; Hynek, S. A.; Chamberlain, C. P.

2011-12-01

Lithium is the key component in Li-ion batteries which are the primary energy storage for electric/hybrid cars and most electronics. Lithium is also an element of major importance on a global scale because of interest in increasing reliance on alternative energy sources. Lithium brines and pegmatites are the primary and secondary sources, respectively of all produced Li. The only Li-brine in the USA that is currently in production exists in Clayton Valley, NV. The groundwater brines at Clayton Valley are located in a closed basin with an average evaporation rate of 142 cm/yr. The brines are pumped from six aquifer units that are composed of varying amounts of volcanic ash, gravel, salt, tufa, and fine-grained sediments. Samples collected include spring water, fresh groundwater, groundwater brine, and meteoric water (snow). The brines are classified as Na-Cl waters and the springs and fresh groundwater have a mixed composition and are more dilute than the brines. The Li content of the waters in Clayton Valley ranges from less than 1 μg/L (snow) up to 406.9 mg/L in the lower ash aquifer system (one of six aquifers in the basin). The cold springs surrounding Clayton Valley have Li concentrations of about 1 mg/L. A hot spring located just east of Clayton Valley contains 1.6 mg/L Li. The Li concentration of the fresh groundwater is less than 1 mg/L. Hot groundwater collected in the basin contain 30-40 mg/L Li. Water collected from a geothermal drilling north of Silver Peak, NV, had water with 4.9 mg/L Li at a depth of >1000m. The δD and δ18O isotopic signatures of fresh groundwater and brine form an evaporation path that extends from the global meteoric water line toward the brine from the salt aquifer system (the most isotopically enriched brine with ave. δD = -3.5, ave. δ18O = -67.0). This suggests that mixing of inflow water with the salt aquifer brine could have played an important role in the evolution of the brines. Along with mixing, evaporation appears to be an important process in the brine evolution. This is evident because of the increase in Na concentration as a function of enrichment in δD for most brine samples. In contrast the non-brine waters flowing into the basin show an increase in Na at relatively constant δD indicating little evaporation. The δD of clays sampled throughout a sediment core extending to 354 m below the surface show fluctuations that likely indicate warmer and cooler periods through time. Further investigation of the relationship of past climate and Li accumulation is in progress.

Archean crustal evolution of the Narryer Gneiss Terrane, Western Australia, as revealed by the U-Pb age and Hf-isotope compositions of zircon from the granitic gneisses

NASA Astrophysics Data System (ADS)

Sylvester, P.; Souders, K.; Crowley, J. L.; Myers, J.

2011-12-01

The Narryer Gneiss Terrane of the Yilgarn Craton, Western Australia, is an important area for studies of early crustal evolution because of the preservation of (1) detrital zircons of Hadean to Archean age in the Jack Hills and Mt. Narryer metasedimentary belts, and (2) several widespread units of granitic gneisses emplaced between ca. 3.7 and 2.6 Ga. We have analyzed the U-Pb geochronology and Hf-isotope geochemistry of magmatic zircons from 38 samples of the granitic gneisses using laser ablation - (multicollector) - ICPMS. The sample suite is dominated by the Meeberrie gneiss, a banded quartz-microcline-oligoclase-biotite gneiss of monzogranite to granodiorite composition, and the Dugel gneiss, a leucocratic, pegmatite-layered syenogranite gneiss, but gneisses of dioritic to tonalitic composition, as well as less deformed granite sheets, are also represented. Magmatic zircons were identified on the basis of the preservation of oscillatory zoning in BSE and CL images, igneous Th/U ratios (>0.2), and concordant U-Pb isotopic systematics with low common Pb contents. The results indicate many of the gneisses are composed of the products of multiple magmatic events, as has been reported previously for samples of the Meeberrie gneiss (Kinny & Nutman, 1996, Precambrian Res. 78, 165-178). Major ages of magmatism preserved in the gneisses occurred at ca. 3685-3665 Ma, 3620-3565 Ma, 3495-3440 Ma, 3375-3330 Ma, and 3300-3260 Ma. The late granite sheets crystallized at 2710-2645 Ma. Hf-isotope compositions of the zircons trend to less radiogenic values with decreasing age, with ɛHf values of ca. 0 to -5 for 3.7-3.4 Ga gneisses, ca. -1 to -9 for 3.4-3.2 Ga gneisses and ca. -5 to -20 for the late granite sheets. The array of the Hf isotopic compositions with time for the entire sample set are fit well by a regression indicating a source reservoir with a 176Lu/177Hf of 0.022 extracted from the depleted mantle at 3.9 Ga. This suggests that the Narryer gneisses and late granite sheets were derived by repeated partial melting of an Eoarchean mafic to intermediate crustal source that persisted throughout the Archean. The ɛHf evolution trend for the Narryer gneisses plots distinctly above the ɛHf trend of the Hadean mafic crustal reservoir inferred for the source of the Hadean detrital zircons from the Jack Hills. The implication is that the inferred Hadean crustal reservoir was not an important source of the Narryer gneisses, either because it was largely isolated from zones of melting in the crust of the Narryer Gneiss Terrane during the Archean, or because it was simply of limited volume.

Clast Rotation and Nature of Strain Localization in Thick Ultramylonites: the El Pichao Shear Zone (Sierra de Quilmes), NW Argentina.

NASA Astrophysics Data System (ADS)

Hasalova, Pavlina; Hunter, Nicholas James; Weinberg, Roberto; Finch, Melanie

2013-04-01

Ultramylonite formation is integral to understanding the accommodation of high strain in ductile shear zones, mountain building and crustal movement. The El Pichao Shear Zone (PSZ) is 3-7km thick ductile thrust zone in the Sierra de Quilmes, NW Argentina. Sinistral thrusting along the PSZ has placed granulite facies migmatites of the Tolombón Complex on top of amphibolite metasedimentary rocks of the Agua del Sapo Complex, separated by a sheared granitic body intruded by pegmatites. The fabric varies from protomylonite to ultramylonite. Ultramylonites in the core of the shear zone reach ~1km in thickness. Ultramylonites of this thickness are extremely rare, and thus the El Pichao Shear Zone provides a unique opportunity to investigate the origin of such high strain rocks. We used microstructural and quantitative textural analysis, quartz crystallographic preferred orientation (CPO), clast vorticity and geochemical data to investigate the origin of the thick ultramylonites, and variable strain accommodation associated with the mylonitization process. The mylonitic rocks have granitic composition and consist of a matrix of Bt+Qtz+Ms+Pl+Kfs, Qtz ribbons, mica bands and feldspar porphyroclasts. Feldspar clasts have been variably rotated and their deformation behaviour varies between brittle faulting and partial to complete dynamic recrystallisation. In the ultramylonite Qtz ribbons or strong S-C fabrics are lacking and the matrix tends to be homogeneous with only weak foliation defined by the preferred orientation of micas. There is also a systematic decrease in matrix grain size and mica connectivity towards ultramylonite. Quartz CPO suggests changes in deformation mechanisms associated with strain increase. The transition between mylonite and ultramylonite in the PSZ occurred due to a switch from dominant dislocation creep to dominant diffusion creep. Major and trace element data show no geochemical variation between samples, indicating that the mylonite-ultramylonite transition took place in a closed system with fixed P-T conditions. We argue that the formation of thick ultramlyonites can occur where strain is high enough to instigate intense clast rotation. The homogenization of the originally banded mylonite results from continual rotation of clasts, which disaggregated the anisotropic matrix and thus inhibited strain localisation. The relative rotation of clasts in the matrix was a function of their vorticity and geometry, which may have influenced the variable deformation behaviours of feldspars in the mylonites. Strain softening at the clast matrix interface may have also played a role in increasing the vorticity of clasts and promoting rotation-induced strain accomodation. Ultramylonite thickness may be explained, at least in part, by the homogenisation of the matrix by clast rotation, where the loss of effective slip planes resulted in strain being dispersed over larger areas in the ultramylonite.

Magmatic evolution and controls on rare metal-enrichment of the Strange Lake A-type peralkaline granitic pluton, Québec-Labrador

NASA Astrophysics Data System (ADS)

Siegel, Karin; Vasyukova, Olga V.; Williams-Jones, Anthony E.

2018-05-01

Although it is well known that A-type granites are enriched in the rare earth elements (REE) and other high field strength elements (HFSE), the magmatic processes that concentrate these elements are still poorly understood. The 1.24 Ga Strange Lake pluton in northern Québec-Labrador provides an extraordinary example of hyper-enrichment in the REE, Zr, and Nb in a peralkaline A-type granite. The pluton consists of two hypersolvus granite units (southern and northern) and a transsolvus granite, all of which contain perthitic alkali feldspar as the earliest major mineral; the transsolvus granite also contains separate albite and microcline crystals. Arfvedsonite, a sodic amphibole, occurs exclusively as phenocrysts in the transsolvus granite, whereas in the hypersolvus granite it is present as a late, interstitial phase. The primary HFSE minerals are zircon, monazite-(Ce), gagarinite-(Ce) and the pyrochlore group minerals. Magma evolution was monitored by the alumina content in the bulk rock, which decreases from the southern to the northern hypersolvus granite and is lowest in the transsolvus granite. Alkalinity indices and bulk Si, Fe, Rb, REE, Zr, Nb concentrations show the opposite trend. Alkali feldspar compositions mirror the trend shown by the bulk rock, i.e., decreasing Al contents are accompanied by increasing Si, Fe3+, REE, Zr and Nb contents. The major driving forces for the evolution of the hypersolvus magma prior to emplacement were the early separation of a fluoride melt from the silicate melt and the crystallization of alkali feldspar and HFSE-rich phases (zircon, monazite-(Ce), pyrochlore group). An alkali feldspar-rich crystal-mush containing LREE-fluoride melt droplets was emplaced as the least evolved southern hypersolvus granite. Massive fractionation of alkali feldspar led to a sharp increase in ƒH2O and F- activity in the magma chamber that triggered the crystallization of arfvedsonite and was followed by emplacement of the northern hypersolvus granite, which contained a higher proportion of LREE-fluoride melt droplets. Further evolution in the magma chamber led to a transition from a miaskitic to an agpaitic composition. The transsolvus granite was intruded in the form of a low viscosity crystal mush of alkali feldspar, quartz, arfvedsonite (after appreciable crystallization of arfvedsonite) and LREE-fluoride melt droplets. Upon emplacement, arfvedsonite (and gagarinite-(Ce)) crystals segregated as cumulates in response to a combination of flow differentiation and gravity settling. The immiscible fluoride melt accumulated in a volatile-rich residual silicate magma, which migrated to the top of the pluton where it formed the F-REE-rich cores of highly mineralized pegmatites.

Minimum age of the Neoproterozoic Seven Hundred Acre Island Formation and the tectonic setting of the Islesboro Formation, Islesboro block, Maine

USGS Publications Warehouse

Stewart, D.B.; Tucker, R.D.; Ayuso, R.A.; Lux, D.R.

2001-01-01

Two platformal stratigraphic sequences occur on Islesboro, Penobscot Bay, Maine. The older Seven Hundred Acre Island Formation is at least 200 m thick, its base is not exposed, and it makes up fault-bounded blocks of siliceous colour-banded dolomitic marble, muscovite-rich quartzite, coarse-grained splendent muscovite-garnet-staurolite-andalusite schist, and calcareous metapelite, with minor garnet amphibolite and amphibolite. It was initially metamorphosed to lower amphibolite facies and was later to lower greenschist facies. The lower amphibolite facies metamorphism is Neoproterozoic (670 to 650 Ma) as inferred from the 40Ar/39Ar high temperature release spectra of hornblende separates. A U-Pb zircon age of 646.7 ?? 2.7 Ma obtained for a pegmatite that intruded deformed rocks is taken to be the minimum age of the Formation. The platformal Islesboro Formation probably unconformably overlies the Seven Hundred Acre Island Formation. It is primarily turbiditic pelite with many beds of quartzite, impure dolomitic marble, some conglomerate, and a few feldsparrich volcaniclastic beds and is thought to be either Neoproterozoic or Cambrian. It was metamorphosed only to lower greenschist facies, possibly in the same event that retrograded the Seven Hundred Acre Island Formation. Geochemical interpretations of minor and trace element analyses of six amphibolite and four schist samples from the Seven Hundred Acre Island Formation show that the protoliths of the amphibolite samples were intermediate between tholeiitic and within-plate type basaltic flows or dikes that intruded attenuated continental crust, or were eroded from these basalts. Four amphibolite and three schist samples analyzed for Pb isotopes were found to be enriched in radiogenic Pb. The Pb isotopic compositions are similar to those in peri-Gondwanan basement rocks from Atlantic Canada. The peri-Gondwanan Islesboro block was placed against the peri-Gondwanan Middle and Late Cambrian Ellsworth terrane on the east by significant Late Silurian strike-slip faulting. The Late Silurian or Early Devonian Turtle Head dextral strike-slip fault separates the Islesboro block from the peri-Gondwanan St. Croix terrane to the west. The timing and nature of the movements of these faults are given from offsets of the isograds around the zircon-dated Late Silurian Sedgwick Granite (419.5 ?? 1.4 Ma) and South Penobscot Intrusive Suite (419.2 ?? 2.2 Ma). These terranes and others like them in Atlantic Canada make up a composite terrane that is different from the composite Avalonian terranes sensu stricto of southeastern New England and Atlantic Canada. The composite peri-Gondwanan terrane that included the Islesboro block was amalgamated with the margin of ancestral North America in the Silurian.

Sulfide minerals as new Sm-Nd geochronometers for ore genesis dating of mafic-ultramafic layered intrusions

NASA Astrophysics Data System (ADS)

Serov, Pavel; Ekimova, Nadezhda; Bayanova, Tamara

2014-05-01

The main method of dating the ore process was the Re-Os method of sulfides (Luck, Allegre, 1983; Walker et. al., 1991). However, studies of Re-Os systematics of sulfide minerals do not always give the correct ages and showing the disturbances of the Re-Os systematics. At the same time, Sm-Nd age of sulfides in good agreement with the U-Pb dating on zircon and baddeleyite and suggests that the Sm-Nd system of sulfides is more resistant to secondary alteration processes. Our studies have shown that along with rock-forming, ore minerals (sulfides) can be used to determine the ore genesis time of industrially important geological sites, since exactly with the sulfides the industry Pt-Pd mineralization is closely connected. The Sm-Nd investigations steadily employ new minerals-geochronometers. Of these, sulfides of PGE-bearing layered intrusions are quite important in terms of dating the process of ore origin. Studying the REE distribution in the sulfides of MOR hydrothermal sources has shown possible REE presence in the sulfide lattice (Rimskaya-Korsakova et. al., 2003). These are difficult to carry out because the concentrations of Sm and Nd isotopes in sulfides are much lower than chondrites (Rimskaya-Korsakova et. al., 2003). For the first time in Russia with sulfide and rock-forming minerals and WR in Sm-Nd method have been dated impregnated and brecciform ores of the following objects: Pilguyarvi Cu-Ni deposits, Pechenga (1965±87 Ma); impregnated (2433±83 Ma) and redeposited (1903±24 Ma) ores of Ahmavaara intrusion (Finland); ore gabbronorites of Penikat PGE-bearing layered intrusion (2426±38 Ma (Ekimova et.al., 2011); Pt-Pd gabbro-pegmatite ores (2476± 41 Ma, which agrees with the U-Pb zircon age - 2470±9 Ma (Bayanova, 2004) and gabbronorites (2483±86 Ma) of PGE Kievei deposit and Fedorova Tundra metagabbroids (2494±54 Ma); Monchetundra gabbronorites - 2489±49 Ma. In (Kong et. al., 2000) sulfides from two metamorphosed chondrites studied by instrumental neutron activation analysis (INAA) and ion probe. As shown, the level of REE in the sulfide phase determined by the ion probe is quite similar to that obtained by INAA. Although the concentrations of REE in the enstatite and the Fe, Si, Cr-rich inclusions are comparable to those in sulfide, estimates based on mass balance calculations show that the silicate inclusions would not noticeably contribute to the REE budget in sulfides (Kong et. al., 2000). These studies were supported by the RFBR 13-05-00493, OFI-M 13-05-12055, State Earth Division Program #4 and IGCP-599.

Geochemical Analysis for Sedimentary Emerald Mineralization in Western Emerald belt, Colombia

NASA Astrophysics Data System (ADS)

Nino Vasquez, Gabriel Felipe; Song, Sheng-Rong

2017-04-01

1Gabriel Felipe Nino Vasquez and 1Sheng-Rong Song 1Department of Geosciences, National Taiwan University Colombia hosts a large quantity of mineral resources due to its complex tectonic arrangement, and emerald deposits are one of the most representatives for the country. Emeralds in Colombia occur mainly in black shale, and are located in eastern Andes Cordillera with two parallel belts separated by approximately 130 Km: the Western belt (WB) and the Eastern belt (EB). The geological, mineralogical and tectonic features from these belts are quite similar (Buenaventura 2002). Previous researchers concluded that emeralds in Colombia came from hydrothermal sedimentary processes without any magmatic influence, and suggested that the source of Cr, V and Be (which are important components of the beryl) was the host rock. According to their results, the process which allowed the shale to release these cations was the metasomatism (albitization and carbonization), which was resulted from the interaction between the rocks and the alkaline brines. Fractures and fault planes originated by these tectonic movements were fulfilled by enriched fluids, which they allowed emeralds and the other minerals precipitation with decreasing alkalinity and pressure (Giuliani et al. 1994). However, there were several pitfalls of conclusions drawn from previous researches. Firstly, Cr and V were widely distributed and come from mafic and ultramafic rocks, and Be was mostly found in pegmatites, finding these elements in sedimentary rocks suggest that probably the ultramafic rocks occurred not far from the deposits. Secondly, there was an inconsistency in the estimated temperatures of emeralds formation, i.e. temperature of hydrothermal sedimentary deposits was only 200° C, while laboratory analysis showed that the formation of emeralds was higher than 300° C. Therefore, there might still be an allocthonus influence on emerald formation that significantly increases the temperature. This research is going to contribute information in order to clarify these inconsistencies, We have done the O and C isotopes in calcite and S isotope in pyrite and shale from different mines along the (WB) in order to determine the main fluid source of the mineralization. Selected samples will also be analyzed with EDS, RAMAN and ICP-MS methods to obtain the exact compositions of elements with extremely low concentrations in host rock, metazomatized host rock and mineralization (productive and not productive veins); the main purpose is to measure how strong were the fluid-rock interaction to leach elements out from the black shale. Thin sections from the altered shale and vein have been analyzed with the purpose of identify paragenesis and microstructures in the mineralization. Finally, we would like to gather the results from different sectors and compare it with the previous studies.

Data from geologic investigations in the Yemen Arab Republic during 1976

USGS Publications Warehouse

Grolier, Maurice J.; Domenico, J.A.; Donato, Mary; Tibbitts, G.C.; Overstreet, W.C.; Ibrahim, Mohammad Mukred

1977-01-01

The results of semiquantitative spectrographic analyses for 31 elements in 126 specimens of rocks from the Yemen Arab Republic, collected mainly during February 1976 from the Precambrian area in the southeastern part of the country, provide background data for use in geochemical evaluation of areas potentially favorable for mineral deposits. Gold and thorium were undetected; the lower limits of determination are 10 parts per million (ppm) and 20 ppm, respectively. For the other elements, the abundances follow geochemical norms for crustal distribution: (1) Fe, Nb, and Zr in Holocene weathering products; (2) Ca and Sr in Pliocene limestone; (3) Mo in Pliocene(?) or Miocene(?) dikes; (4) Be, La, and Sn in Miocene(?) alkalic granite; (5) As, Be, and La in Tertiary and/or Cretaceous felsic tuff; (6) V in Tertiary and/or Cretaceous carbonaceous sedimentary rocks interbedded with volcanic rocks; (7) Be, La, Sn, and Zr in Tertiary and/or Cretaceous undivided volcanics; (8) Sn and W in Precambrian felsite and pegmatite; (9) Co, Cr, Ni, and Ti in Precambrian mafic rocks; (10) Mg and Sr in Precambrian marble and calcsilicate rocks; (11) Y in Precambrilan schist; (12) B and Sc dispersed in rocks of many ages; and (13) Ag, Ba, Bi, Cd, Cu, Mn, Pb, Sb, Sn, and Zn in a hydrothermal replacement deposit in Precambrian sediment. None of the rocks contained as much as 205 ppm equivalent uranium. The highest values for Ag, Cu, Pb, Zn, and Cd were obtained on a sample of hydrothermally altered siltstone not personally collected by the writers. It was said to have come from the Ma'rib area in the eastern part of the Yemen Arab Republic. The source must be studied, because this single sample is high-grade base-metal ore. Among the samples collected by the writers, the economically most significant are altered tuffs, ignimbrites, and felsites exposed between Jibal Hufash and Manakhah on the road from Hudaydah to San'a'. They are strongly anomalous for As and weakly anomalous, variously, for Hg, Mo, and Pb, which elements may constitute an epigenetic dispersion pattern from hidden sulfide deposits. Inasmuch as chalcopyrite and native copper have been reported in the vicinity of Jabal Haraz in the Manakhah area, the rocks of the Yemen Volcanics in this region should be explored for base-metal sulfide deposits. The first results of paleontologic examinations of fossils collected during 1975 and 1976 are presented, as are a list of Landsat images covering the Yemen Arab Republic, and a selected bibliography of reports on geology and the allied sciences relating to the Yemen Arab Republic.

Ilyukhinite (H3O,Na)14Ca6Mn2Zr3Si26O72(OH)2 • 3H2O, a New Mineral of the Eudialyte Group

NASA Astrophysics Data System (ADS)

Chukanov, N. V.; Rastsvetaeva, R. K.; Rozenberg, K. A.; Aksenov, S. M.; Pekov, I. V.; Belakovsky, D. I.; Kristiansen, R.; Van, K. V.

2017-12-01

A new eudialyte-group mineral, ilyukhinite, ideally (H3O,Na)14Ca6Mn2Zr3Si26O72(OH)2 · 3H2O, has been found in peralkaline pegmatite at Mt. Kukisvumchorr, Khibiny alkaline pluton, Kola Peninsula, Russia. It occurs as brownish orange, with vitreous luster anhedral grains up to 1 mm across in hydrothermally altered peralkaline rock, in association with aegirine, murmanite, albite, microcline, rhabdophane-(Ce), fluorite, sphalerite and molybdenite. The Mohs hardness is 5; cleavage is not observed. D meas 2.67(2), D calc 2.703 g/cm3. Ilyukhinite is optically uniaxial (-): ω = 1.585(2), ɛ = 1.584(2). The IR spectrum is given. The average chemical composition of ilyukhinite (wt %; electron microprobe, ranges given in parentheses; H2O determined by gas chromatography) is as follows: 3.07 (3.63-4.43) Na2O, 0.32 (0.28-0.52) K2O, 10.63 (10.26-10.90) CaO, 3.06 (2.74-3.22) MnO, 1.15 (0.93-1.37) FeO, 0.79 (0.51-0.89) La2O3, 1.21 (0.97-1.44) Ce2O3, 0.41 (0.30-0.56) Nd2O3, 0.90 (0.77-1.12) TiO2, 10.94 (10.15-11.21) ZrO2, 1.40 (0.76-1.68) Nb2O5, 51.24 (49.98-52.28) SiO2, 1.14 (0.89-1.37) SO3, 0.27 (0.19—0.38) Cl, 10.9(5 )H2O,-0.06-O = C1, total is 98.27. The empirical formula is H36.04(Na3.82K0.20)(Ca5.65Ce0.22La0.14Nd0.07)(Mn1.285Fe0.48)(Zr2.645Ti0.34)Nb0.31Si25.41S0.42Cl0.23O86.82. The crystal structure has been solved ( R = 0.046). Ilyukhinite is trigonal, R3 m; a = 14.1695(6) Å, b = 31.026(1) Å, V = 5394.7(7) Å3, Z = 3. The strongest XRD reflections [ d, Å (I, %) ( hkl)] are 11.44 (82) (101), 7.09 (70) (110), 6.02 (44) (021), 4.371 (89) 205), 3.805 (47) (303, 033), 3.376 (41) (131), 2.985 (100) (315, 128), 2.852 (92) (404). Ilyukhinite was named in memory of Vladimir V. Ilyukhin (1934-1982), an outstanding Soviet crystallographer. The type specimen of ilyukhinite has been deposited in the collection of the Natural History Museum, University of Oslo, Norway.

Layered Fault Rocks Below the West Salton Detachment Fault (WSDF), CA Record Multiple Seismogenic? Slip Events and Transfer of Material to a Fault Core

NASA Astrophysics Data System (ADS)

Axen, G. J.; Luther, A. L.; Selverstone, J.; Mozley, P.

2011-12-01

Unique layered cataclasites (LCs) occur locally along footwall splays, S of the ~N-dipping, top-E WSDF. They are well exposed in a NW-plunging antiform that folds the LCs and their upper and lower bounding faults. Layers range from very fine-grained granular shear zones 1-2 mm thick and cm's to m's long, to medium- to coarse-grained isotropic granular cataclasite with floating clasts up to 4-5 cm diameter in layers up to ~30 cm thick and 3 to >10 m long. The top, N-flank contact is ~5 m structurally below the main WSDF. Maximum thickness of the LCs is ~5 m on the S flank of the antiform, where the upper 10-50 cm of LCs are composed of relatively planar layers that are subparallel to the upper fault, which locally displays ultracataclasite. Deeper layers are folded into open to isoclinal folds and are faulted. Most shear-sense indicators show N-side-to-E or -SE slip, and include: (1) aligned biotite flakes and mm-scale shear bands that locally define a weak foliation dipping ~ESE, (2) sharp to granular shears, many of which merge up or down into fine-grained layers and, in the base of the overlying granodiorite, (3) primary reidel shears and (4) folded pegmatite dikes. Biotite is unaltered and feldspars are weakly to strongly altered to clays and zeolites. Zeolites also grew in pores between clasts. XRF analyses suggest minimal chemical alteration. The upper fault is sharp and relatively planar, carries granular to foliated cataclasitic granodiorite that grades up over ~2-4 m into punky, microcracked but plutonic-textured rock with much of the feldspar alteration seen in LC clasts. Some upper-plate reidels bend into parallelism with the top fault and bound newly formed LC layers. The basal fault truncates contorted layers and lacks evidence of layers being added there. We infer that the deeper, contorted layers are older and that the LC package grew upward by transfer of cataclasized slices from the overlying granodiorite while folding was ongoing. Particle-size distributions reflect constrained comminution and shear localization (slopes of ~3-3.5 on log-log plots of grain size vs. no. of grains > grain size). The LCs require episodic slip events that probably record dozens of seismic cycles. Foliation likely records post- or interseismic creep. Geometric complexities among the WSDF footwall splays presumably caused episodic dilation that allowed accumulation and folding of the LCs. Mechanical processes dominated over chemical processes. A key question is why the LCs apparently were stronger than the overlying granodiorite, leading to formation of new LC layers rather than significant reworking of older layers.

Reconnaissance for radioactive materials in northeastern United States during 1952

USGS Publications Warehouse

McKeown, Francis A.; Klemic, Harry

1953-01-01

Reconnaissance for radioactive materials was made in parts of Maine, New York, New Jersey, and Pennsylvania. The primary objective was to examine the iron ore deposits and associated rocks in the Adirondack Mountains of New York and the Highlands of New Jersey. In addition, several deposits known or reported to contain radioactive minerals were examined to delimit their extent. Most of the deposits examined are not significant as possible sources of radioactive elements and the data pertaining to them are summarized in table form. Deposits that do warrant more description than can be given in table form are: Benson Mines, St. Lawrence County, N. Y.; Rutgers mine, Clinton County, N. Y.; Mineville Mines, Essex County, N. Y.l Canfield phosphate mine, Morris County, N. J.; Mullgan quarry, Hunterdon County, N. J.; and the Chestnut Hill-Marble Mountain area, Pennsylvania and New Jersey. The Old Bed in the Mineville district is the only deposit that may be economically significant. Apatite from Old Bed ore contains as much as 4.9 percent total rare earth. 0.04 percent thorium, and 0.018 percent uranium. Magnetite ore at the Rutgers mine contains radioactive zircon and apatite. Radioactivity measurements of outcrops and dump material show that the ore contains from 0.005 to 0.010 percent equivalent uranium. One sample of lean magnetite ore contains 0.006 percent equivalent uranium. Garnet-rich zones in the Benson Mines magnetite deposit contain as much as 0.017 equivalent uranium. Most of the rock and ore, however, contains about 0.005 percent equivalent uranium. Available data indicate that the garnet-rich zones are enriched in radioactive allanite. A shear zone in the Kittatinny limestone of Cambrian age at the Mulligan quarry contains uraniferous material. Radioactivity anomalies elsewhere in the quarry and in adjacent fields indicate that there may be other uraniferous shear zones. Assays of samples and measurements of outcrop radioactivity indicate that the uranium content of these zones is low; samples contain from 0.008 to 0.068 percent equivalent uranium. The anomalies, however, may indicate greater concentrations of uranium below surficial leached zones. The Chestnut Hill-Marble Mountain area contains radioactivity anomalies for about 2 miles along the strike of the contact of pre-Cambrian Pickering gneiss and Franklin limestone formations. In places this contact is injected with pegmatite, which probably was the source of the radioelements. The most favorable area for further study is at Marble Mountain, where a nearly continuous anomaly extends for about 1500 feet. Samples from part of this area contain as much as 0.044 percent equivalent uranium and 0.005 percent uranium. Radioactive hematite and florencite, in which thorium may have substituted for cerium, are the only radioactive minerals observed in the Marble Mountain area.

Beyond Colorado's Front Range - A new look at Laramide basin subsidence, sedimentation, and deformation in north-central Colorado

USGS Publications Warehouse

Cole, James C.; Trexler, James H.; Cashman, Patricia H.; Miller, Ian M.; Shroba, Ralph R.; Cosca, Michael A.; Workman, Jeremiah B.

2010-01-01

This field trip highlights recent research into the Laramide uplift, erosion, and sedimentation on the western side of the northern Colorado Front Range. The Laramide history of the North Park?Middle Park basin (designated the Colorado Headwaters Basin in this paper) is distinctly different from that of the Denver basin on the eastern flank of the range. The Denver basin stratigraphy records the transition from Late Cretaceous marine shale to recessional shoreline sandstones to continental, fluvial, marsh, and coal mires environments, followed by orogenic sediments that span the K-T boundary. Upper Cretaceous and Paleogene strata in the Denver basin consist of two mega-fan complexes that are separated by a 9 million-year interval of erosion/non-deposition between about 63 and 54 Ma. In contrast, the marine shale unit on the western flank of the Front Range was deeply eroded over most of the area of the Colorado Headwaters Basin (approximately one km removed) prior to any orogenic sediment accumulation. New 40Ar-39Ar ages indicate the oldest sediments on the western flank of the Front Range were as young as about 61 Ma. They comprise the Windy Gap Volcanic Member of the Middle Park Formation, which consists of coarse, immature volcanic conglomerates derived from nearby alkalic-mafic volcanic edifices that were forming at about 65?61 Ma. Clasts of Proterozoic granite, pegmatite, and gneiss (eroded from the uplifted core of the Front Range) seem to arrive in the Colorado Headwaters Basin at different times in different places, but they become dominant in arkosic sandstones and conglomerates about one km above the base of the Colorado Headwaters Basin section. Paleocurrent trends suggest the southern end of the Colorado Headwaters Basin was structurally closed because all fluvial deposits show a northward component of transport. Lacustrine depositional environments are indicated by various sedimentological features in several sections within the >3 km of sediment preserved in the Colorado Headwaters Basin, suggesting this basin may have remained closed throughout the Paleocene and early Eocene. The field trip also addresses middle Eocene(?) folding of the late Laramide basin-fill strata, related to steep reverse faults that offset the Proterozoic crystalline basement. Late Oligocene magmatic activity is indicated by dikes, plugs, and eruptive volcanic rocks in the Rabbit Ears Range and the Never Summer Mountains that span and flank the Colorado Headwaters Basin. These intrusions and eruptions were accompanied by extensional faulting along predominantly northwesterly trends. Erosion accompanied the late Oligocene igneous activity and faulting, leading to deposition of boulder conglomerates and sandstones of the North Park Formation and high-level conglomerates across the landscape that preserve evidence of a paleo-drainage network that drained the volcanic landscape.

Application of Cathodoluminescence to The Study of Feldspars: Imaging and Spectrometry

NASA Astrophysics Data System (ADS)

Fonseca, Rute; Couto, Helena

2017-12-01

Cathodoluminescence (CL) studies were carried out on polished thin sections of different feldspar samples (from migmatites, granites, aplite-pegmatites and granitic aggregates) using a hot cathode CL equipment HC3-LM coupled to an optical microscope and to a spectrometer (SpectraPro 2300i and a CCD Pixis 400B detector and the software Winspec32) from the Faculty of Sciences of University of Porto. The system was operated at 14kV and a filament current of 0.18 mA. The samples were coated with a thin gold film using a Cressington 108 Auto device. Luminescence images were acquired during the CL analysis with an adapted digital video-camera (KAPPA PS 40C-285 (DX) with dual stage Peltier cooling) and an acquisition time between 351ms and 3,52s. The CL study, including imaging and spectrometry, proved to be an important tool to complement the feldspar petrography as it contributes to the identification of features not observed under optical microscope. The application of the Cathodoluminescence to feldspar allows distinguishing between potassic feldspar and plagioclase, differentiating generations of feldspar and displaying internal zoning and growth areas, among other. The spectrometry complements the CL imaging. It allows obtaining a qualitative level of emission intensity, which permits the interpretation of the nature of this luminescence in each feldspar. Bands shown in the spectra are related to the existing activator elements. In the present study, it was found an association of each feldspar to different spectra and respective colour. The plagioclases exhibit yellow or green luminescence. The activator element is Mn2+, showing a broad emission band between 550 - 570 nm specially detected on this type of feldspars, due to the replacement of K+ for Mn2+. The potassium feldspars have more or less intense blue colour associated with various activators elements: the activator element is Cu2+ showing a broad emission band between 420±5 nm. This emission band can be detected either in potassium feldspar or in plagioclases, but when associated with the blue colour, it indicates that it is a potassium feldspar. Spectra with a wavelength of 460±10 nm, associated to the element activator/synthesizer Ti3+, which is initially deposited as Ti4+, replacing Al, as temperature rise. The emission band with a wavelength of 860 nm correspond to the activator element Pb+, and occurs specially in potassium feldspar like adularia and orthoclase. The activator element Al - O - Al, show a broad emission band between 450-480 nm. This emission in CL is caused by the replacement of Al3+ and Si4+ in feldspars.

Soil contamination of heavy metals in the Katedan Industrial Development Area, Hyderabad, India.

PubMed

Govil, P K; Sorlie, J E; Murthy, N N; Sujatha, D; Reddy, G L N; Rudolph-Lund, Kim; Krishna, A K; Rama Mohan, K

2008-05-01

Studies on quantitative soil contamination due to heavy metals were carried out in Katedan Industrial Development Area (KIDA), south of Hyderabad, Andhra Pradesh, India under the Indo-Norwegian Institutional Cooperation Programme. The study area falls under a semi-arid type of climate and consists of granites and pegmatite of igneous origin belonging to the Archaean age. There are about 300 industries dealing with dyeing, edible oil production, battery manufacturing, metal plating, chemicals, etc. Most of the industries discharge their untreated effluents either on open land or into ditches. Solid waste from industries is randomly dumped along roads and open grounds. Soil samples were collected throughout the industrial area and from downstream residential areas and were analysed by X-ray Fluorescence Spectrometer for fourteen trace metals and ten major oxides. The analytical data shows very high concentrations of lead, chromium, nickel, zinc, arsenic and cadmium through out the industrial area. The random dumping of hazardous waste in the industrial area could be the main cause of the soil contamination spreading by rainwater and wind. In the residential areas the local dumping is expected to be the main source as it is difficult to foresee that rain and wind can transport the contaminants from the industrial area. If emission to air by the smokestacks is significant, this may contribute to considerable spreading of contaminants like As, Cd and Pb throughout the area. A comparison of the results with the Canadian Soil Quality Guidelines (SQGL) show that most of the industrial area is heavily contaminated by As, Pb and Zn and local areas by Cr, Cu and Ni. The residential area is also contaminated by As and some small areas by Cr, Cu, Pb and Zn. The Cd contamination is detected over large area but it is not exceeding the SQGL value. Natural background values of As and Cr exceed the SQGL values and contribute significantly to the contamination in the residential area. However, the availability is considerably less than anthropogenic contaminants and must therefore be assessed differently. The pre- and post-monsoon sampling over two hydrological cycles in 2002 and 2003 indicate that the As, Cd and Pb contaminants are more mobile and may expect to reach the groundwater. The other contaminants seem to be much more stable. The contamination is especially serious in the industrial area as it is housing a large permanent residing population. The study not only aims at determining the natural background levels of trace elements as a guide for future pollution monitoring but also focuses on the pollution vulnerability of the watershed. A plan of action for remediation is recommended.

Elemental fingerprints of isotopic contamination of hebridean Palaeocene mantle-derived magmas by archaean sial

NASA Astrophysics Data System (ADS)

Thompson, R. N.; Dickin, A. P.; Gibson, I. L.; Morrison, M. A.

1982-06-01

One of the major puzzles presented by the geochemistry of the Palaeocene plateau lavas of Skye and Mull (N.W. Scotland) is that, although a very strong case can be made that the magmas are variably isotopically contaminated by Archaean Lewisian continental crust, little evidence has been gleaned to date from their major- and trace-element compositions to illuminate this hypothetical process. The combined results of published Sr-, Nd- and Pb-isotope studies of these lavas allow the basalts and hawaiites to be divided into three broad groups: essentially uncontaminated; contaminated with granulite-facies Archaean crust; contaminated with amphibolite-facies Archaean crust. Members of each group show distinctive chondrite-normalised incompatible-element patterns. The processes which gave rise to isotopic contamination of these lavas also affected the abundances and ratios of Ba, Rb, Th, K, Sr and light REE in the magmas, whilst having negligible effects on their abundances and ratios of Nb, Ta, P, Zr, Hf, Ti, Y and middle-heavy REE. Because such a wide range of elements were affected by the contamination process, it is postulated that the contaminant was a silicate melt of one or more distinctive crustal rock types, rather than an aqueous or similar fluid causing selective elemental movements from wall rocks into the magmas. As previous experimental and isotopic studies have shown that the Skye and Mull basic magmas were not constrained by cotectic equilibria at the time when they interacted with sial, the compositions of the contaminated lavas have been modelled in terms of simple magma-crust mixtures. Very close approximations to both the abundances and ratios of incompatible elements in the two groups of contaminated basalts may be obtained by adding 15% to 20% of Lewisian leucogneisses to uncontaminated Palaeocene basalt. Nevertheless, major-element constraints suggest that the maximum amount of granitic contaminant which has been added to these magmas lies between 5% and 10%. These estimates may be reconciled by postulating that the contaminants were large-fraction cotectic partial melts of Lewisian leucogneisses, leaving plagioclase residua. A corollary of this hypothesis is that it is necessary to postulate that the “magma chambers” where the sialic contamination occurred were, in fact, dykes or (more probably) sills. The very large surface-to-volume ratios of such magmas bodies would permit the systematic stripping, by partial melting, of the most-easily-fusible leucogneisses and pegmatites from the Lewisian crust, whilst failing to melt its major rock types. A present-day analogue to this situation may be the extensive sill-like magma bodies detected by geophysical methods within the continental crust beneath the Rio Grande Rift, southwestern U.S.A.

Mineral chemistry and shrimp U-Pb Geochronology of mesoproterozoic polycrase-titanite veins in the sullivan Pb-Zn-Ag Deposit, British Columbia

USGS Publications Warehouse

Slack, J.F.; Aleinikoff, J.N.; Belkin, H.E.; Fanning, C.M.; Ransom, P.W.

2008-01-01

Small polycrase-titanite veins 0.1-2 mm thick cut the tourmalinite feeder zone in the deep footwall of the Sullivan Pb-Zn-Ag deposit, southeastern British Columbia. Unaltered, euhedral crystals of polycrase and titanite 50-100 ??m in diameter are variably replaced by a finer-grained alteration-induced assemblage composed of anhedral polycrase and titanite with local calcite, albite, epidote, allanite, and thorite or uranothorite (or both). Average compositions of the unaltered and altered polycrase, as determined by electron-microprobe analysis, are (Y0.38 REE0.49 Th0.10 Ca0.04 Pb0.03 Fe0.01U0.01) (Ti1.48 Nb0.54 W0.04 Ta0.02)O6 and (Y0.42 REE0.32 Th0.15 U0.06 Ca0.04 Pb0.01 Fe0.01) (Ti1.57 Nb0.44 W0.04 Ta0.02)O6, respectively. The unaltered titanite has, in some areas, appreciable F (to 0.15 apfu), Y (to 0.40 apfu), and Nb (to 0.13 apfu). SHRIMP U-Pb geochronology of eight grains of unaltered polycrase yields a weighted 207Pb/206Pb age of 1413 ?? 4 Ma (2??) that is interpreted to be the age of vein formation. This age is 50-60 m.y. younger than the ca. 1470 Ma age of synsedimentary Pb-Zn-Ag mineralization in the Sullivan deposit, which is based on combined geological and geochronological data. SHRIMP ages for altered polycrase and titanite suggest later growth of minerals during the ???1370-1320 Ma East Kootenay and ???1150-1050 Ma Grenvillian orogenies. The 1413 ?? 4 Ma age for the unaltered polycrase in the veins records a previously unrecognized post-ore (1370 Ma) mineralizing event in the Sullivan deposit and vicinity. The SHRIMP U-Pb age of the polycrase and high concentrations of REE, Y, Ti, Nb, and Th in the veins, together with elevated F in titanite and the absence of associated sulfides, suggest transport of these high-field-strength elements (HFSE) by F-rich and S-poor hydrothermal fluids unrelated to the fluids that formed the older Fe-Pb-Zn-Ag sulfide ores of the Sullivan deposit. Fluids containing abundant REE, HFSE, and F may have been derived from a geochemically specialized magma such as those that form alkaline granites, pegmatites, or carbonatites. In an alternative model. preferred here, these fluids were associated with a rift-related, crustal metasomatic event in the region. Determination of a Mesoproterozoic age for the polycrase-titanite veins establishes the first known occurrence of pre-Grenvillian REE-rich mineralization in the Belt-Purcell basin.

Metasomatic Reaction Zones as Monitors of Trace Element Transfer at the Slab-Mantle Interface: the Case of the Hochwart Peridotite (Ulten Zone, Italy)

NASA Astrophysics Data System (ADS)

Marocchi, M.; Hermann, J.; Bargossi, G. M.; Mair, V.; Morten, L.

2006-12-01

Ultramafic blocks belonging to the Hochwart peridotite outcrop (Ulten Zone, Italian Alps) preserve a series of metasomatic mineral zones generated by infiltration of Si-rich hydrous fluids which occurred at the gneiss- peridotite interface. The age of the high pressure metamorphism for the Hochwart complex has been constrained at 330 Ma (Tumiati et al., 2003, EPSL, 210, 509-526). The country rocks are stromatic gneisses consisting mainly of quartz, K-feldspar, garnet, kyanite, biotite and muscovite. The ultramafic body consists of strongly serpentinized metaperidotites which are exposed as a hectometre-size lens along a steep gully, associated to monomineralic zones that developed at the contact between the peridotite body and the garnet gneiss country rocks. The composition of the metasomatic zones has been investigated in detail and records an order of metasomatic zoning formed by phlogopite-rich to tremolite-anthophyllite-rich rocks going from the host gneiss towards the peridotite. In some cases, the ultramafics fade into the gneisses developing serpentine and talc which has replaced, presumably at lower temperatures, the serpentine matrix and occurs in association with chlorite. Phlogopite aggregates (phlogopitite) with accessory minerals (quartz + zircon + apatite) and metabasic pods (phlogopite and hornblende) also occur. Black tourmaline (schorl-dravite solid solution) has been found for the first time in the contact near the phlogopite zone, suggesting an external addition of elements (boron and fluorine) to the system at high temperature. The formation of the metasomatic zones composed exclusively of hydrous phases must have involved extensive H2O-metasomatism as already documented for the Ulten peridotites. The source for these fluids can be a system of trondhjemitic-pegmatitic dikes cutting the peridotite that would have channelled aqueous fluids into the ultramafic rocks. Whole-rock geochemistry and trace element (LA ICP-MS) composition of hydrous phases (phlogopite and amphibole) in different metasomatic zones indicate mobility of many elements, including elements such as Ta which are considered to have scarce mobility in fluids. Trace element composition of accessory minerals in the phlogopite-rich zone suggests that the trace element signature of subduction zone fluids may be fractionated in this zone. The progressive depletion in some trace elements (LREE) and enrichment in LILE and Li from the peridotite towards the gneiss suggests a strong influence of bulk composition on the trace element budget of hydrous minerals. Since the ultramafic blocks can be representative of metasomatic processes occurring at the slab-mantle interface, we can infer that metasomatic reactions between slab-derived fluids and ultramafic mantle wedge will follow a specific series of reactions, creating mineral zonation similar to those observed in this study. Our results further favour the evidence that the primary composition of subduction zone fluids is modified substantially by metasomatic reactions occurring in the mantle wedge.

Geochemistry and geochronology of Tobago Island: a preliminary re-appraisal

NASA Astrophysics Data System (ADS)

Neill, I.; Kerr, A. C.; Snoke, A. W.; Hastie, A.; Pindell, J. L.; Chamberlain, K.; Millar, I. L.

2009-12-01

A unifying model to constrain the sources, polarity and geometry of the Great Arc of the Caribbean during the Jurassic-Cretaceous remains elusive. The arc was the leading edge of the Caribbean plate prior to, and during, its late Cretaceous tectonic emplacement between the Americas1,2. Tobago Island in the SE Caribbean has long been considered a partial cross-section through at least two generations of mid-Cretaceous Great Arc magmatism3. ICP-OES/MS and Nd-Hf-Pb radiogenic isotope whole rock determinations are combined with three new U-Pb zircon LA-ICP-MS and several existing mineral ages to present a geochemical and geochronological re-appraisal of the origin of the igneous suites on Tobago. The North Coast Schist (>115 Ma3) is a suite of tholeiitic mafic-felsic tuffs and volcanic breccias with variable Nb-Ta, Ti and slight Th depletions indicative of an arc or back-arc origin. This suite was deformed and metamorphosed to greenschist facies prior to the formation of the Tobago pluton and volcanic suite. The pluton (104±1 Ma3) comprises peridotite cumulates, gabbro-diorites and hornblende pegmatites. It is cogenetic with the volcanic suite, which consists of mafic volcanic breccias, tuffs and lavas (~104 Ma3), and a suite of mafic dykes (~105-91 Ma3). The volcano-plutonic suite has a tholeiitic island arc composition and appears geochemically similar to the North Coast Schist. A 6 km-long tonalite body cross-cuts the pluton and has a trondhjemitic composition, with high Si, Al, La/Yb and Sr/Y, low MgO, Y and Nb. It may be derived from partial melting of an enriched, garnet-bearing basaltic or amphibolitic source region. Furthermore, several mafic-to-granitic dykes have non-arc highly enriched signatures consistent with a plume source and may be related to the ~90 Ma Caribbean Oceanic Plateau2. The data indicate a more complex magmatic history for the igneous rocks of Tobago than suggested by previous studies3 and thus they require a more detailed tectonomagmatic interpretation. Radiogenic isotopes provide a unique opportunity to study in detail the changing nature of the mantle sources involved in both arc and plume magmatism on Tobago and to test potential links with arc outcrops of a similar age throughout the Caribbean. A vital test will be to place constraints upon whether or not subduction polarity reversal occurred between eruption of the North Coast Schist and the Tobago Volcanic Group, a key tenet of the work by Pindell et al.1. 1: Pindell, J.L. et al., 2009. In: James, K., Lorente, M. A. & Pindell, J. (eds), The geology and evolution of the region between North and South America, Geological Society, London, Special Publication, in press. 2: Kerr, A.C. et al., 2003. AAPG Memoir 79: 126-168. 3: Snoke, A.W. et al., 2001. GSA Special Paper 354: pp.54.

Optimization of the thermodynamic properties and phase diagrams of P2O5-containing systems

NASA Astrophysics Data System (ADS)

Hudon, Pierre; Jung, In-Ho

2014-05-01

P2O5 is an important oxide component in the late stage products of numerous igneous rocks such as granites and pegmatites. Typically, P2O5 combines with CaO and crystallizes in the form of apatite, while in volatile-free conditions, Ca-whitlockite is formed. In spite of their interest, the thermodynamic properties and phase diagrams of P2O5-containg systems are not well known yet. In the case of the pure P2O5 for example, no experimental thermodynamic data are available for the liquid and the O and O' solid phases. As a result, we re-evaluated all the thermodynamic and phase diagram data of the P2O5 unary system [1]. Optimization of the thermodynamic properties and phase diagrams of the binary P2O5 systems was then performed including the Li2O-, Na2O-, MgO-, CaO-, BaO-, MnO-, FeO-, Fe2O3-, ZnO-, Al2O3-, and SiO2-P2O5 [2] systems. All available thermodynamic and phase equilibrium data were simultaneously reproduced in order to obtain a set of model equations for the Gibbs energies of all phases as functions of temperature and composition. In particular, the Gibbs energy of the liquid solution was described using the Modified Quasichemical Model [3-5] implemented in the FactSage software [6]. Thermodynamic modeling of the Li2O-Na2O-K2O-MgO-CaO-FeO-Fe2O3-Al2O3-SiO2 system, which include many granite-forming minerals such as nepheline, leucite, pyroxene, melilite, feldspar and spinel is currently in progress. [1] Jung, I.-H., Hudon, P. (2012) Thermodynamic assessment of P2O5. J. Am. Ceram. Soc., 95 (11), 3665-3672. [2] Rahman, M., Hudon, P. and Jung, I.-H. (2013) A coupled experimental study and thermodynamic modeling of the SiO2-P2O5 system. Metall. Mater. Trans. B, 44 (4), 837-852. [3] Pelton, A.D. and Blander, M. (1984) Computer-assisted analysis of the thermodynamic properties and phase diagrams of slags. Proc. AIME Symp. Metall. Slags Fluxes, TMS-AIME, 281-294. [4] Pelton, A.D. and Blander, M. (1986) Thermodynamic analysis of ordered liquid solutions by a modified quasichemical approach application to silicate slags. Metall. Trans. B, 17, 805-815. [5] A.D. Pelton, S.A. Decterov, G. Eriksson, C. Robelin and Y. Dessureault (2000) The modified quasichemical model - I Binary solutions. Metall. Mater. Trans. B, 31, 651-660. [6] C.W. Bale, P. Chartrand, S.A. Decterov, G. Eriksson, K. Hack, R. Ben Mahfoud, J. Melançon, A.D. Pelton and S. Petersen. (2002) FactSage Thermochemical Software and Databases. Calphad, 26, 189-228.

Evaluation of ASR potential of quartz-rich rocks by alkaline etching of polished rock sections

NASA Astrophysics Data System (ADS)

Šachlová, Šárka; Kuchařová, Aneta; Pertold, Zdeněk; Přikryl, Richard

2015-04-01

Damaging effect of alkali-silica reaction (ASR) on concrete structures has been observed in various countries all over the World. Civil engineers and real state owners are demanding reliable methods in the assessment of ASR potential of aggregates before they are used in constructions. Time feasible methods are expected, as well as methods which enable prediction of long-term behaviour of aggregates in concrete. The most frequently employed accelerated mortar bar test (AMBT) quantifies ASR potential of aggregates according to the expansion values of mortar bars measured after fourteen days testing period. Current study aimed to develop a new methodical approach facilitating identification and quantification of ASR potential of aggregates. Polished rock sections of quartz and amorphous SiO2 (coming from orthoquartzite, quartz meta-greywacke, pegmatite, phyllite, chert, and flint) were subjected to experimental leaching in 1M NaOH solution at 80°C. After 14 days of alkaline etching, the rock sections were analyzed employing scanning electron microscope combined with energy dispersive spectrometer. Representative areas were documented in back scattered electron (BSE) images and measured using fully-automatic petrographic image analysis (PIA). Several features connected to alkaline etching were observed on the surface of polished rock sections: deep alkaline etching, partial leach-out of quartz and amorphous particles, alkaline etching connected to quartz grain boundaries, and alkaline etching without any connection to grain boundaries. All features mentioned above had significant influence on grey-scale spectrum of BSE images. A specific part of the grey-scale spectrum (i.e. grey-shade 0-70) was characteristic of areas affected by alkaline etching (ASR area). By measuring such areas we quantified the extent of alkaline etching in studied samples. Very good correlation was found between the ASR area and ASR potential of investigated rocks measured according to the standard AMBT (folowing ASTM C1260). The etching experiment is regarded to be feasible method to quantify ASR potential of quartz- (resp. SiO2-) rich rocks. Employement of the method: (1) decreases potential error from less experienced operator; (2) minimizes the volume of the rock need to be analyzed; (3) enables to visualize microscopic features where ASR originates; and (4) enables to identify alkali-reactive components in the rocks. The main disadvatage of the method is regarded in the restriction to quartz- (resp. SiO2-) rich rocks. If other minerals are included in the rocks their role in ASR should be considered. These minerals can be excluded from the analysis in case they are not reactive and if their content is very low (e.g. accesory minerals). If the minerals contribute to ASR (e.g. albite, micas), these mineral phases should be included in the analysis. Then the application of PIA needs to be modified in respect to different grey shades of individual minerals.

Analytical fingerprint for tantalum ores from African deposits

NASA Astrophysics Data System (ADS)

Melcher, F.; Graupner, T.; Sitnikova, M.; Oberthür, T.; Henjes-Kunst, F.; Gäbler, E.; Rantitsch, G.

2009-04-01

Illegal mining of gold, diamonds, copper, cobalt and, in the last decade, "coltan" has fuelled ongoing armed conflicts and civil war in a number of African countries. Following the United Nations initiative to fingerprint the origin of conflict materials and to develop a traceability system, our working group is investigating "coltan" (i.e. columbite-tantalite) mineralization especially in Africa, also within the wider framework of establishing certified trading chains (CTC). Special attention is directed towards samples from the main Ta-Nb-Sn provinces in Africa: DR Congo, Rwanda, Mozambique, Ethiopia, Egypt and Namibia. The following factors are taken into consideration in a methodological approach capable of distinguishing the origin of tantalum ores and concentrates with the utmost probability: (1) Quality and composition of coltan concentrates vary considerably. (2) Mineralogical and chemical compositions of Ta-Nb ores are extremely complex due to the wide range of the columbite-tantalite solid solution series and its ability to incorporate many additional elements. (3) Coltan concentrates may contain a number of other tantalum-bearing minerals besides columbite-tantalite. In our approach, coltan concentrates are analyzed in a step-by-step mode. State-of-the-art analytical tools employed are automated scanning electron microscopy (Mineral Liberation Analysis; MLA), electron microprobe analysis (major and trace elements), laser ablation-ICP-MS (trace elements, isotopes), and TIMS (U-Pb dating). Mineral assemblages in the ore concentrates, major and trace element concentration patterns, and zoning characteristics in the different pegmatites from Africa distinctly differ from each other. Chondrite-normalized REE distribution patterns vary significantly between columbite, tantalite, and microlite, and also relative to major element compositions of columbites. Some locations are characterized by low REE concentrations, others are highly enriched. Samples with Kibaran age either show flat patterns for most tantalites, rising values from the LREE to the HREE, or trough-like patterns. Eu anomalies are strongly negative in columbite-tantalite from the Alto Ligonha Province in Mozambique, from the Namaqualand Province (Namibia, South Africa), and from Zimbabwe. Four main age populations of coltan deposits in Africa were revealed: (1) Archean (>2.5 Ga), (2) Paleoproterozoic (2.1-1.9 Ga), (3) early Neoproterozoic ("Kibaran", 1.0-0.9 Ga), and (4) late Neoproterozoic to early Paleozoic (Pan-African; ca. 0.6-0.4 Ga). Currently, we focus on the resolution of the fingerprinting system from region via ore province down to deposit scale, establishing a large and high-quality analytical data base, and developing fast-screening and low-cost methods. Analytical flow-charts and identification schemes for coltan ores will be presented at the Conference. The analytical results obtained so far indicate that a certification scheme including fingerprinting of sources of coltan ores is feasible. The methodology developed is capable to assist in the establishment of a control instrument in an envisaged certification of the production and trade chain of coltan.

Mineral resources of Elko County, Nevada

USGS Publications Warehouse

Smith, Roscoe Maurice

1976-01-01

Of the 66 named mining districts in Elko County, 56 have been productive of one or more of 19 different commodities: 11 metals--copper, gold, silver, lead, zinc, mercury, tungsten, manganese, iron, uranium, and antimony; 8 nonmetals--sand and gravel, stone, barite, diatomite, gems, oil shale, volcanic ash, and clay. In addition to the commodities produced, at least 5 others--beryllium, molybdenum, tin, phosphorite, and petroleum, occur in amounts sufficient to warrant exploration. The other districts have been explored, but no production has been recorded. Total value-when-sold of production recorded through 1969 was nearly $91 million; actual production was considerably greater, especially if sand and gravel, barite, and other nonmetallic products before 1953 are included. In value of metals produced, the five highest districts are Mountain City ($26 million), Tuscarora ($11 million), Jarbidge ($10 million), Aura ($6 million), and Railroad (nearly $5 million). The Rio Tinto copper mine in the Mountain City district yielded $21 million. Of the 17 districts that produced nonmetallic minerals, Bootstrap .is the largest producer, containing the Rossi mine, one of the two largest barite mines in the United States. Most of /he metals produced name from veins and replacement deposits in limestone or dolomite near granitic stocks; exceptions are manganese and mercury, which are not associated with known or inferred stocks; mercury is further excepted because it occurs in volcanic rocks, as do a few deposits of the major metals. The largest deposit--the Rio Tinto lode--was a combination of fissure filling and replacement along a bedding plane shear zone 150 ft wide and 1,200 ft long in carbonaceous shale of the Valmy Formation; this deposit is apparently older than the Mountain City stock and its mineralization may be related to Paleozoic mafic volcanism later than a major thrust fault, inferred to underlie the area at a depth of about 5,000 ft. Most of the nonmetallic minerals mined were sedimentary bedded deposits, but mica was mined from pegmatite deposits, and turquoise from both placer and hydrothermal deposits. The largest known reserves of metals (1973) are of porphyry copper in the Dolly Varden district and gold in the Bootstrap district. Reserves of barite also are presumed to be large. The greatest potential for future production of metals, notably copper and gold, appears to be in the known districts or extensions of them and peripheral to deposits that are related to known or concealed plutons and thrust faults. Potential resources in deposits too low in grade to be worked profitably at the present time include all commodities that have been produced and, in addition, known, deposits of beryllium, molybdenum, tin, and phosphorite. Speculative resources in undiscovered deposits may reasonably be predicted to include all known commodities as well as others that are unsuspected. Petroleum may yet be produced from the Elko Formation and geothermal energy from the Ruby Valley and Elko areas.

Tectonic evolution and crustal-scale structure of Kyrgyz Central Asian Orogenic Belt: new insights from the Darius programme

NASA Astrophysics Data System (ADS)

Rolland, Yann; Loury, Chloé; Guillot, Stéphane; Mikolaichuk, Alexander

2014-05-01

Mechanisms and history of the Late Palaeozoic accretion followed by formation of trunscurrent strike-slip faults were studied in the southern segment of the Central Asian Orogenic Belt (CAOB) within Kyrgyz South Tianshan. 1. South Tianshan Suture: ending accretion process after docking of Tarim craton This study gives insights into the crustal-scale structure and Upper Paleozoic history of this mountain belt, currently intensely reactivated by the India-Asia collision. Structural, petrological and geochronological studies were carried out within South Tianshan suture east of the Talas-Ferghana Fault (TFF). New data highlight a south-dipping structure featured by a HP metamorphic core complex comprised of c. 320 Ma continental and oceanic eclogites exhumed by top-to-North motion. A large massif (10 x 50 km) of continental HP rocks in the Atbashi Range is comprised of hectometric boudins of eclogites embedded in metapelites and gneissesMetamorphic units exhibit blueschist to eclogite facies conditions, with oceanic (MORB) rocks in the blueschist facies representing the accretionary oceanic prism being thrusted by oceanic rocks and a continental unit in the eclogite facies (510 ± 50°C and 24 ± 2 kbar). Evidence for eclogite facies both in metasediments and mafic lithologies and geological structure are in agreement with a previously thinned continental margin. Subduction of this thinned COT (Continent-Ocean Transition) probably occurred by slab pull in a south-dipping subduction zone, while another north-dipping subduction was active below Middle Tianshan. Final stacking of Middle and South Tianshan occurred at 320-310 Ma. These opposite subduction zones are still reflected in the main structures of Tianshan. Reactivation of the South-dipping structures since 30-25 Ma is ascribed to explain the current Tianshan intra-continental subduction from seismology. 2. Talas-Ferghana Fault (TFF) activity & Basin formation After this accretionary episode, the South Tianshan suture was cross-cut by the TFF, which was active in several stages from 320 Ma to present. The main events of basin formation are ascribed to the activity of the dextral TFF (Rolland et al. 2013, JAES). Ar-Ar dating undertaken on syn-kinematic minerals that feature the phases of motion of the TFF show a first stage of activation occurred at 312 ± 4 Ma, followed by a main stage of dextral motion in the Late Permian at 256 - 250 Ma, while late stages of reactivation of TFF is featured by emplacement of 195 ± 3 Ma pegmatitic dykes, formation of transtensional basins during Jurassic, dextral offsets of river valleys and ongoing seismicity. 3. Reactivation of South Tian Shan Suture Most prominent topography in Central Asia corresponds to the former South Tianshan suture which has been reactivated since about 30 Ma, the former Carboniferous thrusts are reactivated in a pop-up structure with top-north and top-south faults bounding the high mountains of Khan Tengri and Pobeda peaks (7440 m a.s.l.).

Ar-Ar and U-Pb ages of marble-hosted ruby deposits from Central and South-east Asia

NASA Astrophysics Data System (ADS)

Garnier, V.; Giuliani, G.; Maluski, H.; Ohnenstetter, D.; Deloule, E.

2003-04-01

Marble-hosted ruby deposits represent the first source of gemstones in Asia. The deposits from Jegdalek (Afghanistan), Hunza Valley (Pakistan), Nangimali (Azad-Kashmir), Chumar, Ruyil (Nepal), Mogok (Myanmar), Luc Yen, Yen Bai and Quy Chau (Vietnam) were dated using the 40Ar-39Ar laser stepwise heating technique on syngenetic micas. The following ages were obtained : 24.7 ± 0.3 Ma at Jegdalek ; 10.8 ± 0.3 to 5.4 ± 0.3 Ma at Hunza ; 17.2 ± 0.2 to 15.3 ± 0.1 Ma at Nangimali ; 4.6 ± 0.1 Ma at Ruyil ; 5.6 ± 0.4 Ma at Chumar ; 18.7 ± 0.2 to 17.1 ± 0.2 Ma at Mogok ; 33.8 ± 0.4 to 30.8 ± 0.8 Ma at Luc Yen ; 24.4 ± 0.4 to 23.2 ± 0.6 Ma at Yen Bai, 22.1 ± 0.6 to 21.6 ± 0.7 Ma at Quy Chau. These ages represent cooling ages and thus minimum ages for ruby formation. The ages obtained for Nangimali are close to the Ar-Ar cooling age of 19 Ma recorded in the Chichi granite, North to the ruby deposit. However, (C,O)-isotopic studies of the ruby-bearing marbles show no genetic relation between granite emplacement and ruby deposition in this area. The age found at Jegdalek is similar to the K-Ar ages obtained on the Sairobi pegmatitic dykes (20-26 Ma) and of the Jalalabad pluton (25 Ma), located close to the ruby deposit. At Mogok, the ruby deposits yield ages close to those obtained on high grade metamorphic and foliated intrusive regional rocks (15.8 ± 0.7 - 19.5 ± 1.0 Ma). The ages obtained at Chumar and Ruyil agree with those of the Lesser Himalaya Formation (12 - 6 Ma). Those found at Quy Chau agree with those found for the shear zone activity. Furthermore, U-Pb dating was done on zircons included in a ruby from Luc Yen and spinels in marble from Luc Yen and Hunza. The wide range of 238U-206Pb ages obtained for Luc Yen (266 - 45 Ma) evidences a complex metamorphic history. Ruby crystallised at 45 Ma during ductile activity of the Red River shear zone. At Hunza, an 238U-206Pb age of 94.0 ± 2.1 Ma obtained on inherited zircons confirms the U-Pb age obtained on zircons from the Karakorum batholith (95 Ma). Asian marble-hosted ruby deposits are directly linked with the tectonometamorphic activity of Cenozoic structures resulting from deformation of the Asian plate during India-Asia collision. Geochemical studies evidence that these rubies have a metamorphic origin and thus dating of these deposits provide an essential clue to decipher the timing of continental collision in Central and South-east Asia.

Anthropogenic and natural lead isotopes in Fe-hydroxides and Fe-sulphates in a watershed associated with arsenic-enriched groundwater, Maine, USA

USGS Publications Warehouse

Ayuso, Robert A.; Foley, Nora K.

2008-01-01

A survey of the natural and anthropogenic sources of lead contributing to secondary minerals in sulphidic schists associated with arsenic-enriched groundwater in Coastal Maine shows that the most likely source is natural Pb, particularly from coexisting sulphide minerals. The secondary minerals also reflect notable contributions from anthropogenic Pb. The Pb isotopes establish pathways by which Pb, and by inference As, could have been transported from As-bearing minerals (arsenian pyrite, arsenopyrite, lollingite, orpiment, arsenic oxide and others), via sulphide oxidation or carbonation reactions into multiple generations of secondary minerals (goethite, hematite, jarosite, natrojarosite and others). Lead isotopic compositions of the sulphides and secondary minerals determined by thermal ionization mass spectrometry (n=53) range widely. Lead and As contents of the sulphides and secondary minerals overlap, and are generally positively correlated. Pyrite, the dominant sulphide in sulphidic schists associated with As-enriched groundwater in Coastal Maine, has values of 206Pb/204Pb from 18.186 to 18.391, 207Pb/204Pb from 15.617 to 15.657, 208Pb/204Pb from 38.052 to 38.210, 206Pb/207Pb from c. 1.1625 to 1.1760 and 208Pb/207Pb from c. 2.4276 to 2.4394. Mixtures of Fe-hydroxide and oxide minerals (predominantly goethite and hematite) and secondary Fe-sulphate minerals (jarosite, natrojarosite, rozenite and melanterite) in the sulphidic schists have overlapping but generally higher values of 206Pb/204Pb from 18.495 to 19.747 (one sample at 21.495), 207Pb/204Pb from 15.595 to 15.722 (one sample at 15.839), 208Pb/204Pb from 38.186 to 39.162,206Pb/207Pb from c.1.1860 to 1.2575 (one sample at 1.3855) and 208Pb/207Pb from c. 2.4441 to 2.4865 than the sulphides. Sulphides from Zn-Pb metal mines are somewhat less radiogenic than sulphides from the schists. Other sulphides (mostly pyrite) associated with pegmatites and granitic rocks are heterogeneous and more radiogenic than the pyrite-rich sulphidic schists. Sulphides from other regional bedrock units also have heterogeneous isotope values. Lead isotopic compositions of the sulphides from the sulphidic schists and coexisting Fe-oxides and Fe-sulphates produced by weathering and alteration overlap, but the secondary minerals extend toward more radiogenic values that broadly indicate the addition of Pb from anthropogenic origin. As a component of Pb from extensively used arsenical pesticides may also be present in the secondary minerals, the range in Pb isotope values is consistent with multiple sources: natural Pb from the schists and anthropogenic Pb (industrial and possibly from agricultural activities). Contributions from past mining activities or from other bedrock sources are not implicated.

A new mineral species rossovskyite, (Fe3+,Ta)(Nb,Ti)O4: crystal chemistry and physical properties

NASA Astrophysics Data System (ADS)

Konovalenko, Sergey I.; Ananyev, Sergey A.; Chukanov, Nikita V.; Rastsvetaeva, Ramiza K.; Aksenov, Sergey M.; Baeva, Anna A.; Gainov, Ramil R.; Vagizov, Farit G.; Lopatin, Oleg N.; Nebera, Tatiana S.

2015-11-01

A new mineral rossovskyite named after L.N. Rossovsky was discovered in granite pegmatites of the Bulgut occurrence, Altai Mts., Western Mongolia. Associated minerals are microcline, muscovite, quartz, albite, garnet of the almandine-spessartine series, beryl, apatite, triplite, zircon, pyrite, yttrobetafite-(Y) and schorl. Rossovskyite forms flattened anhedral grains up to 6 × 6 × 2 cm. The color of the mineral is black, and the streak is black as well. The luster is semi-metallic, dull. Mohs hardness is 6. No cleavage or parting is observed. Rossovskyite is brittle, with uneven fracture. The density measured by the hydrostatic weighing method is 6.06 g/cm2, and the density calculated from the empirical formula is 6.302 g/cm3. Rossovskyite is biaxial, and the color in reflection is gray to dark gray. The IR spectrum contains strong band at 567 cm-1 (with shoulders at 500 and 600 cm-1) corresponding to cation-oxygen stretching vibrations and weak bands at 1093 and 1185 cm-1 assigned as overtones. The reflection spectrum in visible range is obtained. According to the Mössbauer spectrum, the ratio Fe2+:Fe3+ is 35.6:64.4. The chemical composition is as follows (electron microprobe, Fe apportioned between FeO and Fe2O3 based on Mössbauer data, wt%): MnO 1.68, FeO 5.92, Fe2O3 14.66, TiO2 7.69, Nb2O5 26.59, Ta2O5 37.51, WO3 5.61, total 99.66. The empirical formula calculated on four O atoms is: {{Mn}}_{0.06}^{2 + } {{Fe}}_{0.21}^{2 + } {{Fe}}_{0.47}^{3 + } Ti0.25Nb0.51Ta0.43W0.06O4. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is monoclinic, space group P2/ c, a = 4.668(1), b = 5.659(1), c = 5.061(1) Å, β = 90.21(1)º; V = 133.70(4) Å3, Z = 2. Topologically, the structure of rossovskyite is analogous to that of wolframite-group minerals. The crystal-chemical formula of rossovskyite is [(Fe3+, Fe2+, Mn)0.57Ta0.32Nb0.11][Nb0.40Ti0.25Fe0.18Ta0.11W0.06]O4. The strongest lines of the powder X-ray diffraction pattern [ d, Å (I, %) ( hkl)] are as follows: 3.604 (49) (110), 2.938 (100) (-1-11), 2.534 (23) (002), 2.476 (29) (021), 2.337 (27) (200), 1.718 (26) (-202), 1.698 (31) (-2-21), 1.440 (21) (-311). The type specimen of rossovskyite is deposited in the Mineralogical Museum of the Tomsk State University, Tomsk, 634050 Russia, with the inventory number 20927.

Lithium Resources for the 21st Century

NASA Astrophysics Data System (ADS)

Kesler, S.; Gruber, P.; Medina, P.; Keolian, G.; Everson, M. P.; Wallington, T.

2011-12-01

Lithium is an important industrial compound and the principal component of high energy-density batteries. Because it is the lightest solid element, these batteries are widely used in consumer electronics and are expected to be the basis for battery electric vehicles (BEVs), hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs) for the 21st century. In view of the large incremental demand for lithium that will result from expanded use of various types of EVs, long-term estimates of lithium demand and supply are advisable. For GDP growth rates of 2 to 3% and battery recycling rates of 90 to 100%, total demand for lithium for all markets is expected to be a maximum of 19.6 million tonnes through 2100. This includes 3.2 million tonnes for industrial compounds, 3.6 million tonnes for consumer electronics, and 12.8 million tonnes for EVs. Lithium-bearing mineral deposits that might supply this demand contain an estimated resource of approximately 39 million tonnes, although many of these deposits have not been adequately evaluated. These lithium-bearing mineral deposits are of two main types, non-marine playa-brine deposits and igneous deposits. Playa-brine deposits have the greatest immediate resource potential (estimated at 66% of global resources) and include the Salar de Atacama (Chile), the source of almost half of current world lithium production, as well as Zabuye (China/Tibet) and Hombre Muerto (Argentina). Additional important playa-brine lithium resources include Rincon (Argentina), Qaidam (China), Silver Peak (USA) and Uyuni (Bolivia), which together account for about 35% of the estimated global lithium resource. Information on the size and continuity of brine-bearing aquifers in many of these deposits is limited, and differences in chemical composition of brines from deposit to deposit require different extraction processes and yield different product mixes of lithium, boron, potassium and other elements. Numerous other brines in playas (Great Salt Lake, Searles Lake), geothermal systems (Salton Sea) and oil fields contain lithium, but in low concentrations that add relatively little to estimated global resources. Igneous deposits, which constitute 26% of estimated global resources, consist largely of pegmatites, including past and present producers at Kings Mountain-Bessemer City (USA), Greenbushes (Australia) and Bikita (Zimbabwe), as well as numerous active prospects, especially in Canada and China. Amenability of these deposits to economic extraction is controlled by mineralogy and zoning of lithium, which vary considerably from deposit to deposit. An additional 8% of global lithium resources is estimated to be present in unusual deposits including largely hectorite clays in volcaniclastic rocks at Kings Valley (USA) and jadarite in lacustrine evaporite deposits (Serbia), which present new challenges to both mining and processing. If this highly varied population of deposits can be converted to reserves, lithium supplies for the 21st century EV market are relatively secure.

Experimental Study into the Stability of Whitlockite in Basaltic Magmas

NASA Technical Reports Server (NTRS)

McCubbin, F. M.; Barnes, J. J.; Srinivasan, P.; Whitson, E. S.; Vander Kaaden, K. E.; Boyce, J. W.

2017-01-01

Apatite Ca5(PO4)3(F,Cl,OH), merrillite Ca18Na2Mg2(PO4)14, and whitlockite Ca9(Mg,Fe2+)(PO4)6[PO3(OH)] are the primary phosphate minerals found in most planetary materials including rocks from Earth, Moon, Mars, and asteroids [1-2]. For many years, the terms merrillite and whitlockite have been used interchangeably in the meteorite literature. Much of the confusion regarding the relationship between terrestrial and extraterrestrial "whitlockite" is based on the presence or absence of hydrogen in the mineral structure. Whitlockite has approximately 8500 ppm H2O, and the term "merrillite" has been adopted to identify the hydrogen-free form of whitlockite [2]. The atomic structures of merrillite and whitlockite were examined in detail by Hughes et al. [3-4]. On Earth, whitlockite has been found in rocks from evolved pegmatitic systems [2-4] and in some mantle rocks [e.g., 5]. Furthermore, terrestrial whitlockite has been shown to have some merrillite component [4]. For the meteoritic and lunar materials that have been investigated, merrillite appears to be far more common than whitlockite, and it has been proposed that the whitlockite component is unique to terrestrial samples [4]. There are some reports of "whitlockite" in the meteorite literature; however, these likely represent misidentifications of merrillite because there have been no reports of extraterrestrial whitlockite that have been verified through crystal structural studies or analyzed for their H contents. Hughes et al. [3] reported the atomic arrangement of lunar merrillite and demonstrated that the phase is similar to meteoritic merrillite and, predictably, devoid of hydrogen. In a follow-up study, Hughes et al. [4] reported the atomic arrangements of two natural samples of whitlockite, one synthetic whitlockite, and samples of synthetic whitlockite that were heated at 500degC and 1050degC for 24 h. The crystal chemistry and crystal structures of the phases were compared, and it was discovered that the latter treatment resulted in the dehydrogenation of whitlockite to form merrillite. The presence of merrillite vs. whitlockite was widely thought to serve as an indication that magmas were anhydrous [e.g., 6-7]. However, McCubbin et al., [8] determined that merrillite in the martian meteorite Shergotty had no discernible whitlockite component despite its coexistence with OH-rich apatite. Consequently, McCubbin et al., (2014) speculated that the absence of a whitlockite component in Shergotty merrillite and other planetary merrillites may be a consequence of the limited thermal stability of H in whitlockite (stable only at T less than1050degC), which would prohibit merrillite-whitlockite solid-solution at high temperatures. In the present study, we have aimed to test this hypothesis experimentally by examining the stability of whitlockite in basaltic magmas at 1.2 GPa and a temperature range of -1000- 1300degC.

Geology and geochronology of granitoid and metamorphic rocks of late Archean age in northwestern Wisconsin

USGS Publications Warehouse

Sims, P.K.; Peterman, Z.E.; Zartman, R.E.; Benedict, F.C.

1985-01-01

Granitoid rocks of the Puritan Quartz Monzonite and associated biotite gneiss and amphibolite in northwestern Wisconsin compose the southwestern part of the Puritan batholith of Late Archean age. They differ from rocks in the Michigan segment of the batholith in having been deformed by brittle-ductile deformation and partly recrystallized during shearing accompanying development of the midcontinent rift system of Keweenawan (Middle Proterozoic) age. Granitoid rocks ranging in composition from granite to tonalite are dominant in the Wisconsin part of the batholith. To the north of the Mineral Lake fault zone, they are massive to weakly foliated and dominantly of granite composition, whereas south of the fault zone they are more strongly foliated and mainly of tonalite composition. Massive granite, leucogranite, and granite pegmatite cut the dominant granitoid rocks. Intercalated with the granitoid rocks in small to large conformable bodies are biotite gneiss, amphibolite, and local tonalite gneiss. Metagabbro dikes of probable Early Proterozoic age as much as 15 m thick cut the Archean rocks. Rubidium-strontium whole-rock data indicate a Late Archean age for the granitoids and gneisses, but data points are scattered and do not define a single isochron. Zircon from two samples of tonalitic gneiss for uranium-thorium-Iead dating define a single chord on a concordia diagram, establishing an age of 2,735?16 m.y. The lower intercept age of 1,052?70 m.y. is in close agreement with rubidium-strontium and potassium-argon biotite ages from the gneisses. Two episodes of deformation and metamorphism are recorded in the Archean rocks. Deformation during the Late Archean produced a steep west-northwest-oriented foliation and gently plunging fold axes and was accompanied by low amphibolite-facies metamorphism of the bedded rocks. A younger deformation resulting from largely brittle fracture was accompanied by retrogressive metamorphism; this deformation is most evident adjacent to the Mineral Lake fault and took place during Keweenawan rifting about 1,050 m.y. ago. The Mineral Lake fault is one of several northwest-trending faults in the Lake Superior region that originated in the Late Archean and were reactivated intermittently during the Proterozoic, including Keweenawan time. The faults dominantly have right-lateral displacements. The Archean rocks of the Puritan batholith exposed in northwestern Wisconsin compose part of the greenstone-granite terrane, as defined in the Lake Superior region. These rocks were formed 2,7502,600 m.y. ago. The long dimension of the Puritan batholith as well as that of several batholiths in adjacent Minnesota are oriented sub parallel to the boundary between the greenstone-granite terrane and the older gneiss terrane, to the south. This conformity in trend is interpreted as indicating that the granite probably was emplaced after the two basement crustal segments had been joined.

Chromite and other mineral deposits in serpentine rocks of the Piedmont Upland, Maryland, Pennsylvania, and Delaware

USGS Publications Warehouse

Pearre, Nancy C.; Heyl, Allen V.

1960-01-01

The Piedmont Upland in Maryland, Pennsylvania, and Delaware is about 160 miles long and at the most 50 miles wide. Rocks that underlie the province are the Baltimore gneiss of Precambrian age and quartzite, gneiss, schist, marble, phyllite, and greenstone, which make up the Glenarm series of early Paleozoic (?) age. These are intruded by granitic, gabbroic, and ultramaflc igneous rocks. Most of the ultramaflc rocks, originally peridotite, pyroxenite, and dunite, have been partly or completely altered to serpentine and talc; they are all designated by the general term serpentine. The bodies of serpentine are commonly elongate and conformable with the enclosing rocks. Many have been extensively quarried for building, decorative, and crushed stone. In addition, chromite, titaniferous magnetite, rutile, talc and soapstone, amphibole asbestos, magnesite, sodium- rich feldspar (commercially known as soda spar), and corundum have been mined or prospected for in the serpentine. Both high-grade massive chromite and lower grade disseminated chromite occur in very irregular and unpredictable form in the serpentine, and placer deposits of chromite are in and near streams that drain areas underlain by serpentine. A group of unusual minerals, among them kammererite, are typical associates of high-grade massive chromite but are rare in lower grade deposits. Chromite was first discovered in the United States at Bare Hills, Md., around 1810. Between 1820 and 1850, additional deposits were discovered and mined in Maryland and Pennsylvania, including the largest deposit of massive chromite ever found in the United States the Wood deposit, in the State Line district. A second period of extensive chromite mining came during the late 1860's and early 1870's. Production figures are incomplete and conflicting. Estimates from the available data indicate that the aggregate production from 27 of 40 known mines before 1900 totaled between 250,000 and 280,000 tons of lode-chromite ore; information is lacking for the other 13. Placer deposits produced considerably more than 15,000 tons of chromite concentrates. Exploratory work in several of the mines and placer deposits during World War I produced about 1,500 long tons of chromite ore, 920 tons of which was sold.Most of the chromite from Maryland and Pennsylvania was used to manufacture chemical compounds, pigments, and dyes before metallurgical and refractory uses for chromite were developed. Available analyses of the ores indicate that they would satisfy modern requirements for chemical-grade chromite. With the exception of such deposits as the Line Pit and Red Pit mines, the chromite contains too much iron for the best metallurgical grade, but many would be satisfactory low-grade metallurgical chromite. Perhaps 30,000 to 50,000 tons of chromite concentrates that would range from 30 to 54 percent Cr2O3 could be obtained from placer deposits in the State Line and Soldiers Delight districts. A small tonnage of chromite remains in dumps at six of the old mines. Lode and placer deposits in the Philadelphia district, placers in Montgomery County, Md., and possible downward extensions of known ore bodies below the floors of high-grade mines now flooded have not been completely explored. Although other chromite deposits probably lie concealed at relatively shallow depths, no practical method of finding them has been developed.Small deposits of titaniferous iron ore in serpentine were mined for iron before 1900, but the titanium content troubled furnace operators. Ore bodies are similar in occurrence to chromite deposits; they are massive or disseminated and are found near the edges of serpentine intrusive rocks. The small size of the deposits and comparatively low titanium content limit their importance as a potential source of titanium. A single rutile deposit in Harford County, Md., has been prospected but not mined. Pockets in schistose chlorite rock, probably altered from pyroxenite, contain as much as 16 percent rutile and average 8 percent. Rutile-bearing rock has been proved to a depth of about 58 feet. Talc and soapstone deposits that have been worked in the State Line and Jarrettsville-Dublin districts are the result of steatitization of serpentine at its contact with intrusive sodium-rich pegmatites. Deposits in the Marriottsville and Philadelphia districts seem to be related to shear or crush zones in the serpentine, which served as channelways for steatitizing solutions. Massive soapstone was extensively used in the 19th century for furnace, fireplace, and stove linings and for washtubs and bathtubs. Every year from 1906 until 1960 talc and soapstone have been produced from one or more of the deposits in Maryland and Pennsylvania. Deposits near Dublin and Marriottsville, Md., have produced steadily for years and production continues. Lava-grade steatite from Dublin, Md., is manufactured into ceramic products for electrical and refractory purposes. Slip-fiber amphibole asbestos deposits were known in the area as early as 1837, but early production was limited. The product was used mostly for linings of safes, boiler covers, and paints. During World War I the demand for domestic asbestos for chemical filters led to further development of deposits in Maryland. Between 1916 and 1940 many small veins of good-quality tremolite and anthophyllite were mined, and the fiber was prepared for market at Woodlawn, Md. Only the upper parts of veins, softened by weathering, were usable. Because prospecting was reportedly fairly thorough and known deposits are said to be mined out, and because demand for amphibole asbestos is limited, the possibility of future asbestos production from the area seems small, except as a byproduct of talc quarrying. Magnesite from several mines in Pennsylvania and Maryland was much in demand between 1828 and 1871 for the manufacture of epsom salt. Exploratory work at the old Goat Hill mines in 1921 indicated that the product could not be profitably prepared for market at that time. Although reportedly high grade, the magnesite veins are thin and small in comparison with other domestic deposits.Sodium-rich feldspar and corundum deposits occur in pegmatites that are unusual because they characteristically contain little or no quartz and mica and because, insofar as known, they are confined to serpentine rocks. Many of the known deposits of sodium-rich feldspar commercial soda-spar are reportedly mined out. It is possible, however, that other commercial deposits will be found in the area. At various times from 1825 until about 1892 in Pennsylvania, corundum mined or found at the surface was used to meet a demand of the abrasives industry. The increased use of artificial abrasives has diminished the demand for natural corundum, and interest in the small, irregular Pennsylvania deposits is at present largely historical or mineralogical.

Evidences for the austroalpine - southalpine up-doming after the end of the variscan orogenesis (central and eastern alps)

NASA Astrophysics Data System (ADS)

Martin, S.; Tumiati, S.

2003-04-01

The structural and petrographic studies of the basement units in the Alpine region, independently from their present tectonic setting in the nappe pile, suggest that at the end of the Variscan orogenesis they were in such a position that they suffered relevant up-doming and cooling since Late Carboniferous (Thöni, 1981; Mottana et al., 1985; Martin et al., 1996; Bertotti et al., 1999). This up-doming has been interpreted as due to an isostatic rebound related to the detachment of the slab after the cessation of the subduction at the end of the Variscan orogenesis (Neubauer and Handler, 2000; Ranalli, 2003). The metamorphic setting of the Southalpine basement between the Tonale pass and Lake Maggiore in the Southern Alps, is due to processes which, by extension denudation and erosion, locally took to the surface portions of middle-to-high grade basement, within a horst-graben environment (Cassinis et al., 1997). The basements of the Orobic, Lake Como and Lake Maggiore areas are composed of kyanite-garnet or sillimanite-bearing schists (e.g., Gneiss di Morbegno, Scisti di Edolo, Scisti dei Laghi; Boriani et al., 1990; Siletto et al., 1993), or of low grade schists (e.g., Filladi di Ambria) intruded by Early Permian plutons, covered by continental and volcanic deposits of Late Carboniferous to Permian age, after a marked unconformity (Cadel et al., 1996). The thickness of this clastic cover ranges between a few hundreds to thousands of meters; the clast compositions suggest a low-grade basement as a dominant source; the structures indicate alternance of uplift and collapse and continue deformation during sedimentation (Cassinis et al., 1974). Most of the Upper Austroalpine units of the central and eastern Alps (e.g., Tonale nappe, Languard, Ortles and Campo units) have structural and lithological similarities with the Orobic, Lake Como and Lake Maggiore basement units confirming their appartenance to the same pre-Alpine paleogeographic environment which suffered up-doming and collapse (Martin et al., 1996). The Austroalpine units have a sedimentary cover including basal clastic sediments younger (Late Permian, Verrucano; Furrer, 1985), than the Orobic ones (Late Carboniferous-Permian) indicating erosion and sedimentation diachronous in respect to the Orobic and Lake Como areas. Most of the lower Austroalpine basement units are composed of middle-to-high grade rocks (e.g., Margna) and are covered by very thin Permian sediments, or directly by carbonatic sequences (Campo and Bernina units) typical of a rapid drowning of the passive margin after erosion (Froitzheim and Manatschal, 1996). In this picture, the Variscan basement of the central and eastern Alps suffered a relevant, even if diachronous, up-doming during Late Carboniferous-Permian time. This involved the basement which at present corresponds to the Lower Austroalpine (e.g., Err, Bernina and Margna) and to the Upper Austroalpine units (e.g.; Ortles, Languard and Campo). The up-doming is mostly evidenced by structural and petrographic observations rather than the geochronology because these basements have been thermally re-setted by intrusion of several Early Permian plutons which altered their cooling history. In some places the magmatic activity continued up to Trias with hydrothermal veins and pegmatites, which slowed the cooling evolution down to the Jurassic time. Rb-Sr cooling ages from high grade Austroalpine and Southalpine basements cumulate around Late Jurassic confirming this time as the end of the pre-alpine thermal evolution of the Variscan basement in the Alps (Sanders et al., 1996). References: BERTOTTI G., SEWARD D., WIJBRANS J., VOORDE M.TER, HURFORD A.J. (1999) - Crustal thermal regime prior to, during, and after rifting: A geochronological and modeling study of the Mesozoic South Alpine rifted margin. Tectonics, 18-2: 185-200 BORIANI A., GIOBBI ORIGONI E., BORGHI A., CAIRONI V. (1990) - The evolution of the "Serie dei Laghi" (Strona-Ceneri and Scisti dei Laghi): upper component of the Ivrea-Verbano crustal section; Southern Alps, North Italy and Ticino, Switzerland. Tectonophysics, 182: 103-118 CADEL G., COSI M., PENNACCHIONI G., SPALLA M.I. (1996) - A new map of the Permo-Carboniferous cover and Variscan metamorphic basement in the central Orobic Alps, Southern Alps, Italy: Structural and stratigraphical data. Mem. Sci. Geol., Padova, 48:1-53 CASSINIS G., MONTRASIO A., POTENZA R., VON RAUMER J.F., SACCHI R., ZANFERRARI A. (1974) - Tettonica ercinica nelle Alpi. Mem. Soc. Geol. Ital., Vol. XIII, suppl. 1, 289-318 CASSINIS G., PEROTTI C.R., VENTURINI C. (1997) - Examples of late Hercynian transtensional tectonics in the Southern Alps (Italy). In: Late Paleozoic and Early Mesozoic Circum Pacific Events and Their Global Correlation (Ed. Dickins J.M., Yang Z., Yin H., Lucas S.G., Acharyya S.K.), Cambridge University Press. DEL MORO A., NOTARPIETRO A. (1987) - Rb-Sr Geochemistry of some Hercynian granitoids overprinted by eo-Alpine metamorphism in the Upper Valtellina, Central Alps. Schweiz. Mineral. Petrogr. Mitt., 67: 295-306 FROITZHEIM N., MANATSCHAL G. (1996) - Kinematics of Jurassic rifting, mantle exhumation, and passive-margin formation in the Austroalpine and Penninic nappes (eastern Switzerland). GSA Bull., 108-9: 1120-1133 FURRER H. ed. (1985) - Field workshop on Triassic and Jurassic sediments in the Eastern Alps of Switzerland. Mitt. Geol. Inst. ETH u. Univ. Zürich, N.F., v. 248, 82 p. MARTIN S., ZATTIN M., DEL MORO A., MACERA P. (1996) - Chronologic constraints for the evolution of the Giudicarie belt (Eastern Alps, NE Italy). Annales Tectonicae, Vol. X, N. 1-2, 60-79 MOTTANA A., NICOLETTI M., PETRUCCIANI C., LIBORIO G., DE CAPITANI L., BOCCHIO R. (1985) - Pre-alpine and alpine eolution of the South-alpine basement of the Orobic Alps. Geol. Rundsch., 74-2: 353-366 NEUBAUER F., HANDLER R. (2000) - Variscan orogeny in the Eastern Alps and Bohemian Massif: How do these units correlate?. Mitt. Österr. Geol. Ges., 92:35-39 RANALLI G. (2003) - A model of Palaeozoic subduction and exhumation of continental crust: Ulten unit, Tonale Nappe, Eastern Austroalpine. Transalp workshop, Trieste 10-12 February. SANDERS C.A.E., BERTOTTI G., TOMMASINI S., DAVIES G.R., WIJBRANS J.R. (1996) - Triassic pegmatites in the Mesozoic middle crust of the Southern Alps (Italy): Fluid inclusions, radiometric dating and tectonic implications. Eclogae Geol. Helv., 89-1: 505-525 SILETTO G.B., SPALLA M.I., TUNESI A., LARDEAUX J.M., COLOMBO A. (1993) - Pre-Alpine structural and metamorphic histories in the Orobic Southern Alps, Italy. In: Pre-Mesozoic geology in the Alps (Ed. By von Raumer J.F. &Neubauer F.), 585-598 THÖNI M. (1981) - Degree and Evolution of the Alpine Metamorphism in the Austroalpine Unit W of the Hohe Tauern in the light of K/Ar and Rb/Sr Age Determinations on Micas. Jahrb. Geol. B.-A., 124-1: 111-174

Pseudotachylitic breccia in mafic and felsic rocks

NASA Astrophysics Data System (ADS)

Kovaleva, Elizaveta; Huber, Matthew S.

2017-04-01

Impact-produced pseudotachylitic breccia (PTB) is abundant in the core of the Vredefort impact structure and was found in many pre-impact lithologies (e.g., Reimold and Colliston, 1994; Gibson et al., 1997). The mechanisms involved in the process of forming this rock remain highly debated, and various authors have discussed many possible models. We investigate PTB from two different rock types: meta-granite and meta-gabbro and test how lithology controls the development of PTB. We also report on clast transport between different lithologies. In the core of the Vredefort impact structure, meta-granite and meta-gabbro are observed in contact with each other, with an extensive set of PTB veins cutting through both lithologies. Microstructural analyses of the PTB veins in thin sections reveals differences between PTBs in meta-granite and meta-gabbro. In granitic samples, PTB often develops along contacts of material with different physical properties, such as a contact with a migmatite or pegmatite vein. Nucleation sites of PTB have features consistent with ductile deformation and shearing, such as sigmoudal-shaped clasts and dragged edges of the veins. Preferential melting of mafic and hydrous minerals takes place (e.g., Reimold and Colliston, 1994; Gibson et al., 2002). Refractory phases remain in the melt as clasts and form reaction rims. In contrast, PTB in meta-gabbro develop in zones with brittle deformation, and do not exploit existing physical contacts. Cataclastic zones develop along the faults and progressively produce ultracataclasites and melt. Thus, PTB veins in meta-gabbro contain fewer clasts. Clasts usually represent multi-phase fragments of host rock and not specific phases. Such fragments often originate from the material trapped between two parallel or horse-tail faults. The lithological control on the development of PTB does not imply that PTB develops independently in different lithologies. We have observed granitic clasts within PTB veins in meta-gabbro, demonstrating clast transport between lithologies. PT melt in meta-gabbro has a two-phase structure: a phase free of granitic clasts, and a phase that contains granitic clasts. This also indicates that melt in both rock types was mobile during the same period of time, and that physical mixing and chemical exchange occurred between the two melts. Thus, PTB cuts across the contact between granite and gabbro, and is not restricted by the contact (e.g., Reimold and Colliston, 1994). These differences in nucleation and propagation of PTB based on rock type must be considered when discussing the formation mechanisms of impact-generated PTB. References: Gibson R.L., Reimold W.U., Ashley A.J., Koeberl C. (2002) Metamorphism of the Moon: A terrestrial analogue in the Vredefort dome, South Africa? Geology 30:475-478. Gibson R.L., Reimold W.U., Wallmach T. (1997) Origin of pseudotachylite in the lower Witwatersrand Supergroup, Vredefort Dome (South Africa): constraints from metamorphic studies. Tectonophysics 283:241-262. Reimold W.U., Colliston W.P. (1994) Pseudotachylites of the Vredefort Dome and the surrounding Witwatersrand Basin, South Africa. Geological Society of America Special Papers 293:177-196.

Aegirine as a late-stage phase in an alkaline pluton associated with carbonate assimilation

NASA Astrophysics Data System (ADS)

Barnes, C. G.; Prestvik, T.; Hiller, J.

2006-12-01

The Hortavaer Complex in north-central Norway is a well-documented example of formation of an alkaline magmatic suite due to assimilation of carbonate and calc-silicate rocks (Vogt 1916; Gustavson & Prestvik, 1979; Barnes et al., 2003, 2005). The alkaline nature developed primarily as the result of increased stability and fractionation of Ca-pyroxene at the expense of olivine, resulting in enrichment of Na and K compared to Si. Calcic pyroxene is a common mineral in rocks that range from gabbro through diorite and monzonite to syenite, with a compositional range from augite to hedenbergite. In addition to calcic pyroxene, glassy, pale green aegirine occurs in veins near skarn-like assemblages in a zone where dioritic sheets were emplaced into syenite. Other vein minerals are biotite, albite, K-feldspar, calcite, and ilmenite. The aegirine is almost pure NaFeSi2O6 (Ae = 91.1%, Jd = 7.4%, Q = 1.5%; where Ae is the aegirine component, Jd the jadeite component, and Q the "quadrilateral" pyroxene component). Laser-ablation ICP-MS analysis shows that the aegirine crystals are typically lower in trace element concentrations than the calcic cpx. For example, Sr is < 2 ppm in the aegirine but > 20 ppm in cpx from evolved syenites and > 85 ppm in cpx from dioritic samples. Chondrite-normalized rare earth element (REE) patterns show a prominent cup shape and light REE abundances range from ~0.1X > 10X chondrites. Aegirine occurs in many locations in Norway (Neumann 1985), where it is generally related to alkaline rocks. Compared to the Hortavaer locality, aegirine from the type area in the Permian Oslo Region has 77% of the NaFeSi2O6 (Ae) component, whereas acmite has 89% Ae. Larsen and Raade (1997) presented c. 30 XRF and EMP analyses of pyroxenes from syenite pegmatites of the southern part of Oslo Region. There is a wide range in composition, and some have up to 95% of the Ae component. Most of the Na-rich pyroxenes (Ae > 90) are low in the Jd component (1.6 to 4.7%), and Q varies in the 4 to 6% range. Thus, compared to pyroxenes similarly high in Ae (> 90%) from the Oslo Region, the Hortavaer aegirine has more of the Jd component and less of the "quadrilateral" component. This feature is striking because host rocks to the Hortavaer aegirine are exceptionally rich in CaO. We suggest that aegirine from Hortavaer is distinct from aegirine from the Oslo region for at least two reasons. First, the Oslo occurrences are associated with rift-related magmatic rocks in which alkalinity resulted by fractionation of an alkaline parent. In contrast, alkalinity in the Hortavær complex developed due to in situ assimilation of carbonate rocks by a sub-alkaline parent. Assimilation resulted in a fluid-rich environment that provided Na, it enhanced the stability of titanite and suppressed magnetite stability. This sequestered Ti and made ferric iron available for aegirine growth. The higher Al may have resulted from differentiation of Hortavaer magmas in a deep-seated magmatic arc.

High-temperature carbonates in the Stillwater Complex, Montana, USA

NASA Astrophysics Data System (ADS)

Aird, H. M.; Boudreau, A. E.

2012-12-01

The processes involved in the petrogenesis of the sulphide-hosted platinum-group-element (PGE) deposits of the Stillwater Complex are controversial, with theories ranging from the purely magmatic to those involving an aqueous fluid. To further constrain these models, we have been examining the trace phase assemblages in rocks away from the ore zones. High-temperature carbonates have been observed in association with sulphide minerals below the platiniferous J-M Reef of the Stillwater Complex. The carbonate assemblage consists of dolomite with exsolved calcite and is found in contact with sulphide minerals: chalcopyrite and pyrrhotite in the Peridotite Zone; and pyrrhotite with pentlandite, pyrite and chalcopyrite in Gabbronorite I of the Lower Banded Series. The minimal silicate alteration and the lack of greenschist minerals in association with the mineral assemblage are consistent with a high-temperature origin for the carbonates. The calcite-dolomite geothermometer [1] yields a minimum formation temperature of ~900°C for the unmixed assemblages. A reaction rim surrounds the carbonate-sulphide assemblages, showing an alteration of the host orthopyroxene to a more Ca-enriched, Fe-depleted composition. This is consistent with diffusive exchange between carbonates and pyroxenes at high temperatures, mediated by an aqueous fluid. The highly variable molar MnO/FeO ratios in both the high-temperature carbonates and their associated altered pyroxene rims also imply their interaction with a fluid. The carbonate assemblages are consistent with Stillwater fluid inclusion studies [2], showing that fluids comprising coexisting Cl-rich brine and carbonic fluid were trapped in pegmatitic quartz at 700-715°C, some of which also contained "accidental" calcite inclusions. The high Cl-content of apatite [3] found below the platiniferous J-M Reef is further evidence that a Cl-rich fluid was migrating through the rocks beneath the Reef. Carbonates have been shown to be stabilized by Cl-rich fluids [4]. The association of high-temperature carbonates with sulphides beneath the J-M reef supports the hydromagmatic theory which involves a late-stage chloride-carbonate fluid percolating upwards, dissolving PGE and sulphides and redepositing them at a higher stratigraphic level. [1] Anovitz, L.M., and Essene, E.J., 1987, Phase Equilibria in the System CaCO3-MgCO3-FeCO3: Journal of Petrology, v. 28, p. 389-414. [2] Hanley, J.J., Mungall, J.E., Pettke, T., Spooner, E.T.C., and Bray, C.J., 2008, Fluid and Halide Melt Inclusions of Magmatic Origin in the Ultramafic and Lower Banded Series, Stillwater Complex, Montana, USA: Journal of Petrology, v. 49, p. 1133-1160. [3] Boudreau, A.E., and McCallum, I.S., 1989, Investigations of the Stillwater Complex: Part V. Apatites as indicators of evolving fluid composition: Contributions to Mineralogy and Petrology, v. 102, p. 138-153. [4] Newton, R.C., and Manning, C.E., 2002, Experimental determination of calcite solubility in H2O-NaCl solutions at deep crust/upper mantle pressures and temperature: implications for metasomatic processes in shear zones: American Mineralogist, v. 87, p. 1401-1409.

Reconnaissance geology and geochronology of the Precambrian of the Granite Mountains, Wyoming

USGS Publications Warehouse

Peterman, Zell E.; Hildreth, Robert A.

1978-01-01

The Precambrian of the western part of the Granite Mountains, Wyoming, contains a metamorphic complex of gneisses, schists, and amphibolites that were derived through amphibolite-grade metamorphism from a sedimentary-volcanic sequence perhaps similar to that exposed in the southeastern Wind River Mountains. Whole-rock Rb-Sr dating places the time of metamorphism at 2,860?80 million years. A high initial 87Sr/ 86 S r ratio of 0.7048 suggests that either the protoliths or the source terrane of the sedimentary component is several hundred million years older than the time of metamorphism. Following an interval of 300:t100 million years for which the geologic record is lacking or still undeciphered, the metamorphic complex was intruded by a batholith and satellite bodies of medium- to coarse-grained, generally massive biotite granite and related pegmatite and aplite. The main body of granite is dated at 2,550?60 million years by the Rb-Sr method. Limited data suggest that diabase dikes were emplaced and nephrite veins were formed only shortly after intrusion of the granite. Emplacement of the granite at about 2,550 million years ago appears to be related to a major period of regional granitic plutonism in the Precambrian of southern and western Wyoming. Granites, in the strict sense, that are dated between 2,450 and 2,600 million years occur in the Teton Range, the Sierra Madre, the Medicine Bow Mountains and the Laramie Range. This episode of granitic plutonism occured some 50 to 100 million years later than the major tonalitic to granitic plutonism in the Superior province of northern Minnesota and adjacent Ontario-the nearest exposed Precambrian W terrane that is analogous to the Wyoming province. Initial 87Sr / 86Sr ratios of some of the Wyoming granites are higher than expected if the rocks had been derived from juvenile magmas and it is likely that older crustal rocks were involved to some degree in the generation of these granites. Slightly to highly disturbed Rb-Sr and K-Ar mineral ages are obtained on rocks of the metamorphic complex and on the granite. These ages range from about 2,400 to 1,420 million years and are part of a regional pattern of lowered mineral ages of Precambrian W rocks of southern Wyoming. A major discontinuity in these mineral ages occurs along a line extending from the northern Laramie Range, through the northern part of the Granite Mountains, to the southeastern Wind River Mountains. North of this line, Rb-Sr and K-Ar biotite ages are 2,300 million years or greater, whereas to the south, the biotite ages decrease drastically over a short distance, to a common range of 1,600-1,400 million years. We suggest that these lowered ages represent regional cooling below the 300 0 C isotherm as a consequence of uplift and erosion of the large crustal block occurring south of the age discontinuity. In this interpretation, the westerly-trending age discontinuity would be a zone of major crustal dislocation that resulted from vertical tectonics in late Precambrian X or early Precambrian Y time.

Natural radioactivity in stream sediments of Oltet River, Romania

NASA Astrophysics Data System (ADS)

Ion, Adriana

2017-04-01

The concentration of naturally occurring radionuclides (U-238, Th-232 and K-40) in stream sediments of the Oltet River was measured in order to establish the primary sources of radionuclides, the transport pathways and the geochemical factors favouring their mobilisation and concentration in the existing geological context. The Oltet River has a length of 185 Km and crosses the southern central part of the country, being the right tributary of the Olt River. The range in elevation of the watercourse varies between 1963 m in the springs area (Parîng Mountains) and 200 m at the confluence with the Olt River, whereas the relief of the Oltet Basin has a varied character, manifested by the presence of diverse forms of relief, starting with major mountainous heights and ending with low-lying plains regions. In cross section from North to South, the Olteț River cuts metamorphic rocks (schist, gneisses, quartzite, marble, mica-schist's), magmatic rocks (granite and granitoid massifs - intruded by veins of microgranite, aplite, pegmatite and lamprophyre) and limestone, followed by deposits composed of clays, marls, sands and gravels, that are characterized by the presence of lignite seams. 44 stream sediment samples were collected in summer of 2016 from sampling points distributed along the river with an equidistance of about 4 - 5 km. The activity concentrations of the U-238, Th-232 and K-40 were measured by gamma ray spectrometry using HPGe detector (ORTEC) with 26% relative efficiency in multilayer shielding. The reference materials used were IAEA - RGK-1 and IAEA - 314. Analysis was performed on the <2 mm fraction of sediment sample, each sample was counted for 24,000 s. U-238 specific activity in the stream sediments varies between 6.18 and 68.76 Bq/Kg and Th-232 specific activity from 8.12 to 89.28 Bq/Kg, whereas the K-40 specific activity in sediments ranges from 99.01 to 312.16 Bq/Kg. In the upper sector of the Oltet River, concentrations of U-238, Th-232 and K-40 show a good correlation between them and reflect the lithological features, the mechanical degradation of the rocks overcomes their chemical decomposition. In the middle part of the river as result of almost abrupt passage between mountain and hilly terrains increases and concentration of radionuclides; effect of large quantities of clastic material deposited by torrents. The mechanical migration of resistant uranium, thorium and potassium bearing mineral determines the movement of rock particles under moving water effect, and redistribution in alluvial sediments with preservation of the native features. In this zone under the action of biochemical processes and other chemical weathering agents, uranium is released from rocks and penetrates in the superficial circulation area or groundwater. Through this geochemical process the amounts of thorium and potassium released are modest, leaching of uranium being the dominant feature (uranyl ion). The downstream lignite seams are the secondary geochemical barriers in accumulation of uranium; the radiometric data obtained for stream sediments emphasize this enrichment.

Ore genesis dating: implication of Sm-Nd method using sulfide minerals for mafic-ultramafic layered intrusions of Fennoscandian Shield

NASA Astrophysics Data System (ADS)

Serov, Pavel; Bayanova, Tamara; Steshenko, Ekaterina; Ekimova, Nadezhda

2015-04-01

The main method of dating the ore process was the Re-Os method of sulfides (Luck, Allegre, 1983; Walker et. al., 1991). However, studies of Re-Os systematics of sulfide minerals do not always give the correct ages and showing the disturbances of the Re-Os systematics. At the same time, Sm-Nd age of sulfides in good agreement with the U-Pb dating on zircon and baddeleyite and suggests that the Sm-Nd system of sulfides is more resistant to secondary alteration processes. Our studies have shown that along with rock-forming, ore minerals (sulfides) can be used to determine the ore genesis time of industrially important geological sites, since exactly with the sulfides the industry Pt-Pd mineralization is closely connected. In to Sm-Nd measurements steadily introduce new minerals-geochronometers (i.e. titanite, burbancite, eudialite etc.). Of these, sulfides of PGE-bearing layered intrusions are quite important in terms of dating the process of ore origin. Studying the REE distribution in the sulfides of MOR hydrothermal sources has shown possible REE presence in the sulfide lattice (Rimskaya-Korsakova et. al., 2003). These are difficult to carry out because the concentrations of Sm and Nd isotopes in sulfides are much lower than those in chondrites (Rimskaya-Korsakova et. al., 2003). In (Kong et. al., 2000) sulfides from two metamorphosed chondrites were studied by instrumental neutron activation analysis (INAA) and ion probe. As shown, the level of REE in the sulfide phase determined by the ion probe is quite similar to that obtained by INAA. Although the concentrations of REE in the enstatite and the Fe, Si, Cr-rich inclusions are comparable to those in sulfide, estimates based on mass balance calculations show that the silicate inclusions would not noticeably contribute to the REE budget in sulfides (Kong et. al., 2000). For the first time in Russian geochemistry laboratories using sulfide and rock-forming minerals and WR in Sm-Nd method have been dated impregnated and brecciform ores of the following objects - Pilguyarvi Cu-Ni deposits, Pechenga (1965±87 Ma); impregnated (2433±83 Ma) and redeposited (1903±24 Ma) ores of Ahmavaara intrusion (Finland); Kolvitsa massif metagabbro (1990±92 Ma, which reflect the age of Sm-Nd system closure in sulfide minerals); olivine orthopyroxenites of Sopcha 'Ore bed' (2442±59 Ma); ore gabbronorites of Penikat PGE-bearing layered intrusion (2426±38 Ma (Ekimova et.al., 2011); Pt-Pd gabbro-pegmatite ores (2476± 41 Ma, which agrees well with the U-Pb zircon age - 2470±9 Ma (Bayanova, 2004) and gabbronorites (2483±86 Ma) of PGE Kievey deposit and Fedorova Tundra metagabbroids (2494±54 Ma); Monchetundra gabbronorites - 2489±49 Ma. All investigations are devoted to memory of academician RAS, professor F. Mitrofanov (Russia), he was a leader of scientific school for geology, geochemistry and metallogenesis of ore deposits. The studies were supported by the RFBR 13-05-00493, OFI-M 13-05-12055, Department of Earth Sciences RAS (programs 2 and 4), IGCP-599.

The role of national regulations in RPAS-based mapping projects in the monitoring of natural hazards that could involve infrastructures: the example of the Val Venosta Railway (Northern Italy - Bolzano).

NASA Astrophysics Data System (ADS)

Gandolfo, Luca; Busnardo, Enrico; Castellarin, Nicola; Canella, Claudio; Canella, Federico; Stabile, Marco; Curci, Francesco; Petrillo, Giovanni

2016-04-01

Italy has adopted National Regulations for the use of RPAS in its country's airspace in December 2013, issued by the Italian Civil Aviation Authority (ENAC). Despite the issued regulations, over the past months an increasing number of unauthorized and unsafe operations have been performed and the attention to safety is growing quickly in the public opinion. For this reason "Critical Operations" is permitted only to those RPAS Operators which have received special authorization by ENAC after a very demanding Aeronautical procedure. According to the Regulations, the flight close to-over urban areas, industrial plants, highways and railways, implies that only authorized RPAS Operators may perform such activities. An example of a "Critical" operation were the RPAS flights performed along the Venosta railway line to evaluate the current situation of two areas affected by geological instability and laid the basis for a future high accurate monitoring. The Venosta Valley is located in the western part of South Tyrol (Norhtern Italy). The valley possesses some unique features compared to the entire Alps, the particularly dry climate and the presence of huge alluvional fans, which give rise to different levels of altitude in the valley. From geological point of view, the Venosta Valley is characterized by the presence of the Austroalpine domain. In particular, there are two different geological units in this area: (i) the crystalline schists of the basement, which includes paragneiss, gneiss, granitoid pegmatites, garnet micaschists, quartzites and phyllites. (ii) The Mesozoic coverage divided into various complexes with successions of phyllites, volcanics and magmatiti. The railway line that runs through the Venosta Valley (Merano - Malles) unfolds along a path of 59,8 kilometers and covers an altitude difference of about 700 meters. In particular, three tunnels characterized the first section, including the M. Giuseppe tunnel, which required extensive consolidations both inside and outside. The mission's scope was to achieve high precision photogrammetry data to reconstruct sub-centimetric 3D models of the retaining wall and the unstable rock mass. Flights have been performed with two different RPAS, a multicopter and an helicopter, controlled by a crew composed by three members: two pilots (Command and Backup Pilot) operating redundant data links for flight control and a payload operator and Aeronautical Flight procedures have been applied. The payload operated the camera to achieve the best images for the data acquisition and 3D model reconstruction. The flights have been conducted with manual piloting flight procedures because of the RPAS on board GPS is significantly affected by the mountain slope proximity. For this reason, for the georeferencing procedure, ground control points have been acquired by using an high precision GPS. Finally, using RPAS data it has been possible to assess the lateral earth pressure on the retaining wall of the railway embankment, while in the second case the aim was to accurately reconstruct the volumes of an unstable rock mass.

Geologic setting of the Mountain Pass rare earth deposits, San Bernardino County, California

USGS Publications Warehouse

Olson, Jerry Chipman

1952-01-01

The Mountain Pass district is in a block of pre-Cambrian metamorphic rocks bounded on the east and south by the alluvium of Ivanpah Valley. This block is separated from Paleozoic and Mesozoic sedimentary and volcanic rocks on the west by the Clark Mountain normal fault, and the northern boundary of the district is a prominent transverse fault. The pre-Cambrian metamorphic complex comprises a great variety of lithologic types including garnetiferous mica gneisses and schists; biotite-garnet-sillimenite gneiss; hornblende gneiss, schist, and amphibolite; biotite gneiss and schist; granitic gneisses and migmatites; pegmatites; and minor amounts of foliated mafic rocks. The rare earth-bearing carbonate rocks are related to potash-rich igneous rocks, of uncertain age, that cut the metamorphic complex. The larger potash-rich intrusive masses, 300 or more feet wide, comprise one granite, two syenite, and four composite shonkinite-syenite bodies. One of the shonkinite-syenite stocks is more than a mile long. Several hundred relatively thin dikes of these potash-rich rocks range in composition, and generally decreasing age, from biotite shonkinite through syenite to granite. A few thin fine-grained shonkinite dikes cut the granite. These potash-rich rocks are cut by east-trending andesitic dikes and by faults. Veins of carbonate rock are most abundant in and near the southwest side of the largest shonkinite-syenite body. Although most veins are less than 6 feet thick, one mass of carbonate rock near the Sulphide Queen min4e is 600 feet in maximum width and 2,400 feet long. About 200 veins have been mapped in the district; their aggregate surface area is probably less than one-tenth that of the large carbonate mass. The carbonate materials, which make up about 60 percent of the veins and the large carbonite body, are chiefly calcite, dolomite, ankerite, and siderite. The other constituents are barite, bastnaesite and perisite, quartz, and variable small quantities of crocidolite, biotite, phlogopite, chlorite, muscovite, apatite, iron oxides, fluorite, monazite, galena, allanite, sphene, pyrite, chalcopyrite, tetrahedrite, malachite, azurite, corussite, wulfenite, aragonite, and thorite. The rare earth oxide content in most of the carbonate rock is less than 13 percent, but in some local concentrations of bastnaesite the content is as high as 40 percent. The origin of the carbonate rocks and related potash-rich igneous rocks is considered in the light of similar associations of carbonate and alkalinic rocks in Sweden, Norway, Russia, South Africa, and the United States. The carbonate rock may have originated (1) as a pre-Cambrian limestone or evaporate sequence in the gneisses; (2) by reaction between magma and the Paleozoic dolomite and limestone overlying the pre-Cambrian complex; (3) by alteration of pre-Cambrian gneisses by emanations from an unknown deep-seated source; or (4) by differentiation of an alkaline magma from shonkinite to syenite to granite, leading to a final carbonate-rich fraction, containing the rare elements, which was emplaced either as a concentrated or a dilute solution. The fourth hypothesis is considered the most plausible.

When the CA-TIMS therapy fails: the over-enthusiastic, the mixed-up, and the stubborn zircon

NASA Astrophysics Data System (ADS)

Corfu, F.

2009-12-01

Mattinson’s CA-TIMS technique has proven to be highly successful in efficiently removing disturbed domains of zircon, thus enabling the determination of precise and accurate ages in a variety of geological situations. The method generally produces equal or better results than mechanical abrasion. There are, however, cases where CA-TIMS fails to achieve perfect concordance, and occasionally actually increases the degree of discordance. Such a behaviour (the over-reaction) is observed for example in U-rich (>1000 ppm) but texturally homogeneous zircon, a type quite common in highly differentiated portions of mafic intrusions, in granitic pegmatites, and in some metamorphic rocks. Because of their internal uniformity, such zircons do not exhibit large contrasts in crystallinity and solubility and after the baking stage of the CA-TIMS procedure they will either totally dissolve in the first HF attack, or produce discordant results. By contrast, mechanical abrasion of this type of zircon can isolate alteration-free zircon domains that yield concordant and reproducible data. This is due to the homogeneity of the crystals, the lack of zoning limiting contrasts in the degrees of metamictization and brittleness and preventing fracturing. The absence of fractures helps to confine alteration of zircon to the marginal domains, and these can be removed very efficiently by mechanical abrasion. This behaviour is exemplified by zircon populations from 252.0 Ma and 182.5 Ma mafic sills in Siberia and the Karoo basin. Another class of zircons that in general does not, or only partially comply with CA-TIMS includes populations from metamorphic and poly-orogenic rocks, typical of many Proterozoic orogens. The metamorphic reprocessing of zircon into low-U domains can freeze-in old Pb-loss patterns that cannot be undone by any technique. New metamorphic zircon growth can also create mixtures of different aged domains that cannot be resolved by CA-TIMS. In favourable circumstances, however, CA-TIMS could provide elegant ways to isolate the metamorphic components. A third category includes zircon populations that fail to achieve consistent ages, or concordant plateaus in multi-step partial dissolutions, even though they may have all the attributes of ideal CA-TIMS objects. The category is exemplified by a 62 Ma magmatic suite with a simple geological history and good quality zircon populations. The zircons have moderate U contents, regular growth zoning and few visible imperfections, yet the data reveal very extensive Pb loss requiring the almost total dissolution of the zircon before reaching the concordant residues. Baking of some of these zircon populations turns the colourless crystals brick-red (but still transparent), the red colour persisting long into the partial dissolution procedure. These features suggest that Pb loss may be related to a submicroscopic network of impurities and primary defects in the crystal structures which form pathways for the diffusion of Pb. Subsequent annealing appears to make the discordant domains impervious to partial dissolution. In conclusion, it is evident that CA-TIMS is a very helpful new technique for U-Pb geochronology, but some limitations must be considered that require case-by-case judgment and good Krogh-type abraders in reserve.

Distribution of lithium in agricultural and grazing land soils at European continental scale (GEMAS project)

NASA Astrophysics Data System (ADS)

Negrel, Philippe; Reimann, Clemens; Ladenberger, Anna; Birke, Manfred

2017-04-01

The environmental chemistry of Li has received attention because Li has been shown to have numerous and important implications for human health and agriculture and the stable isotope composition of lithium is a powerful geochemical tool that provides quantitative information about Earth processes such as sediment recycling, global chemical weathering and its role in the carbon cycle, hydrothermal alteration, and groundwater evolution. However, the role of bedrock sources, weathering and climate changes in the repartition of Li at the continental scale has been scarcely investigated. Agricultural soil (Ap-horizon, 0-20 cm) and grazing land soil (Gr-horizon, 0-10 cm) samples were collected from a large part of Europe (33 countries, 5.6 million km2) as a part of the GEMAS (GEochemical Mapping of Agricultural and grazing land Soil) soil mapping project. GEMAS soil data have been used to provide a general view of element mobility and source rocks at the continental scale, either by reference to average crustal abundances or to normalized patterns of element mobility during weathering processes. The survey area includes a diverse group of soil parent materials with varying geological history, a wide range of climate zones and landscapes. The concentrations of Li in European soil were determined by ICP-MS after a hot aqua regia extraction, and their spatial distribution patterns generated by means of a GIS software. Due to the partial nature of the aqua regia extraction, the mean concentration of Li in the European agricultural soil (ca 11.4 mg/kg in Ap and Gr soils) is about four times lower than in the Earth's upper continental crust (UCC = 41 mg/kg). The combined plot histogram - density trace one- dimensional scattergram - boxplot of the aqua regia data displays the univariate data distribution of Li. The one-dimensional scattergram and boxplot highlight the existence of many outliers at the lower end of the Li distribution and very few at the upper end. Though the density trace, histogram and boxplot suggest a slight skew, the data distributions are still rather symmetrical in the log-scale. The median values of the Ap and Gr samples do overlap, demonstrating they are not statistically different at the 5 % significance level. The maps of Li in the aqua regia extraction show a distinct difference between northern Europe with predominantly low concentrations (median 6.4 mg/kg) and southern Europe with significantly higher values (median 15 mg/kg). The maximum extent of the last glaciation is visible as a discrete concentration break on the maps. The principal Li anomalies occur spatially associated with the granitic rocks and Li-pegmatites and their weathering products throughout Europe, e.g. in central Sweden (Central Scandinavian Clay Belt) and in the western part of the Alpine Region (higher Li concentrations). Even the new Li-deposit near Wolfsberg, Austria is marked by a clear anomaly. In southern Europe, high Li values occurring over limestone areas can be attributed to secondary Li enrichment during weathering controlled by climate (temperature and precipitation).

Geology of the Midnite uranium mine area, Washington: maps, description, and interpretation

USGS Publications Warehouse

Nash, J. Thomas

1977-01-01

Bedrock geology of about 12 km2 near the Midnite mine has been mapped at the surface, in mine exposures, and from drilling, at scales from 1:600 to 1:12,000 and is presented here at 1:12,000 to provide description of the setting of uranium deposits. Oldest rocks in the area are metapelitic and metacarbonate rocks of the Precambrian (Y) Togo Formation. The chief host for uranium deposits is graphitic and pyritic mica phyllite and muscovite schist. Ore also occurs in calc-silicate hornfels and marble at the western edge of a calcareous section about 1,150 m thick. Calcareous rocks of the Togo are probably older than the pelitic as they are interpreted to be near the axis of a broad anticline. The composition and structural position of the calcareous unit suggests correlation with less metamorphosed carbonate-bearing rocks of the Lower Wallace Formation, Belt Supergroup, about 200 km to the east. Basic sills intrusive into the Togo have been metamorphosed to amphibolite. Unmetamorphosed rocks in the mine area are Cretaceous(?) and Eocene igneous rocks. Porphyritic quartz monzonite of Cretaceous age, part of the Loon Lake batholith, is exposed over one third of the mine area. It underlies the roof pendant of Precambrian rocks in which the Midnite mine occurs at depths of generally less than 300 m. The pluton is a two-mica granite and exhibits pegmatitic and aplitic textural features indicative of water saturation and pressure quenching. Eocene intrusive and extrusive rocks in the area provide evidence that the Eocene surface was only a short distance above the present uranium deposits. Speculative hypotheses are presented for penesyngenetic, hydrothermal, and supergene modes of uranium emplacement. The Precambrian Stratigraphy, similar in age and pre-metamorphic lithology to that of rocks hosting large uranium deposits in Saskatchewan and Northern Territory, Australia, suggests the possibility of uranium accumulation along with diagenetic pyrite in carbonaceous muds in a marine shelf environment. This hypothesis is not favored by the author because there is no evidence for stratabound uranium such as high regional radioactivity in the Togo. A hydrothermal mode of uranium emplacement is supported by the close apparent ages of mineralization and plutonism, and by petrology of the pluton. I speculate that uranium may have become enriched in postmagmatic fluids at the top of the pluton, possibly by hydrothermal leaching of soluble uranium associated with magnetite, and diffused outward into metasedimentary wall rocks to create an aureole about 100 m thick containing about 100 ppm uranium. Chemistry of the hydrothermal process is not understood, but uranium does not appear to have been transported by an oxidizing fluid, and the fluid did not produce veining and alteration comparable to that of base-metal sulfide deposits. Uranium in the low-grade protore is believed to have been redistributed into permeable zones in the Tertiary to create ore grades. Geologic and isotopic ages of uranium mineralization, and the small volume of porphyritic quartz monzonite available for leaching, are not supportive of supergene emplacement of uranium.

Mapping contact metamorphic aureoles in Extremadura, Spain, using Landsat thematic mapper images

USGS Publications Warehouse

Rowan, L.C.; Anton-Pacheco, C.; Brickey, D.W.; Kingston, M.J.; Payas, A.

1987-01-01

In the Extremadura region of western Spain, Ag, Pb, Zn, and Sn deposits occur in the pieces of late Hercynian granitic plutons and near the pluton contacts in late Proterozoic slate and metagraywacke that have been regionally metamorphosed to the green schist facies. The plutons generally are well exposed and have distinctive geomorphological expression and vegetation; poor exposures of the metasedimentary host rocks and extensive cultivation, however, make delineation of the contact aureoles difficult. Landsat Thematic Mapper (TM) images have been used to distinguish soil developed on the contact metamorphic rocks from soil formed on the stratigraphically equivalent slate-metagraywacke sequence. The mineral constituents of these soils are similar, except that muscovite is more common in the contact metamorphic soil; carbonaceous material is common in both soils. Contact metamorphic soil have lower reflectance, especially in the 1.6-micrometers wavelength region (TM 5), and weaker Al-OH, Mg-OH, and Fe3+ absorption features than do spectra of the slate-metagraywacke soil. The low-reflectance and subdued absorption features exhibited by the contact metamorphic soil spectra are attributed to the high absorption coefficient f the carbonaceous material caused by heating during emplacement of the granitic plutons. These spectral differences are evident in a TM 4/3, 4/5, 3/1 color-composite image. Initially, this image was used to outline the contact aureoles, but digital classification of the TM data was necessary for generating internally consistent maps of the distribution of the exposed contact metamorphic soil. In an August 1984, TM scene of the Caceras area, the plowed, vegetation-free fields were identified by their low TM 4/3 values. Then, ranges of TM 4/5 and 3/1 values were determine for selected plower fields within and outside the contact aureoles; TM 5 produced results similar to TM 4/5. Field evaluation, supported by X-ray diffraction and petrographic studies, confirmed the presence of more extensive aureoles than shown in published geologic maps; few misclassified areas were noted. Additional plowed fields consisting of exposed contact metamorphic soil were mapped digitally in an August 1985 TM scene. Subsequently, this approach was used to map two 1-km-wide linear zones of contact metamorphosed rock and oil in the San Nicolas-Sn-W Mine area, which is located approximated 125 km southeast of the Caceras study area. Exposures of granite in the San Nicolas area are limited to a few unaltered granitic dikes in the mine and a small exposure of unaltered pegmatite-bearing granite in a quarry about 1.5 km west of the mine. The present of coarsely crystalline biotite and beryl in the granite in the quarry and of contact metamorphosed slate up to 2.5 km from the nearest granite exposure suggest that only the apical part of a pluton is exposed in the quarry and that a larger, shallowly buried body is probably present. These results indicate that potential application of TM image analysis to mineral exploration in lithologically similar areas that are cultivated in spite of poor rock exposures.

UNEXMIN H2020 Project: an underwater explorer for flooded mines

NASA Astrophysics Data System (ADS)

Lopes, Luís; Zajzon, Norbert; Bodo, Balázs; Henley, Stephen; Žibret, Gorazd; Almeida, José; Vörös, Csaba; Horvath, Janos; Dizdarevič, Tatjana; Rossi, Claudio; McLoughlin, Mike

2017-04-01

UNEXMIN (Underwater Explorer for Flooded Mines, Grant Agreement No. 690008, www.unexmin.eu) is a project funded by the European Commission's HORIZON2020 Framework Programme. The project is developing a multi-platform robotic system for the autonomous exploration and mapping of Europe's flooded mines. The robotic system - UX-1 - will use non-invasive methods for the 3D mapping of abandoned flooded mines, bringing new important geological and mineralogical data that cannot be currently obtained by any other means. This technology will allow the development or update of geological models at local and regional levels. The data collected will then be used to consider new exploration scenarios for the possible re-opening of some of Europe's abandoned mines which may still contain valuable resources of strategic minerals. The deployment of a multi-robotic system in such a confined environment poses challenges that must be overcome so that the robots can work autonomously, without damaging the equipment and the mine itself. Key challenges are related to the i) structural design for robustness and resilience, ii) localization, navigation and 3D mapping, iii) guidance, propulsion and control, iv) autonomous operation and supervision, v) data processing, interpretation and evaluation. The scientific instrument array is currently being tested, built and tailored for the submersible: pH, electrical conductivity, pressure and temperature analyzers and a water sampler (water sampling methods), a magnetic field analyzer, a gamma-ray counter and a sub-bottom profiler (geophysical methods) and a multispectral and UV fluorescence imaging units (optical observation methods). The instruments have been selected to generate data of maximum geoscientific interest, considering the limiting factors of the submerged underground environment, the necessary robotic functions, the size for the robot and other constraints. Other crucial components for the robot's functionality (such as movement, control, autonomy, mapping, interpretation and evaluation) include cameras, SONARs, thrusters, DVL, inertial navigation system, laser scanner, computer, batteries and the integrated pressure hull. The UNEXMIN project is currently ongoing with the development of the first mechanical model as well as the scientific instruments. The robot prototype is being developed with a spherical shape with a diameter such that will allow it to fit into the sometimes narrow underground mine openings and to freely move around them, to a depth of 500m. Component/instrument validations and simulations are being worked out to understand the behavior of the technology in the flooded mine environment. At the same time post-processing and data analysis tools are also being developed and prepared. After the groundwork and setup phases, the first robot prototype is going to be tested in four sites under real life conditions corresponding to increasingly difficult mission objectives in terms of mine layout, geometry and topology. The test sites include the Kaatiala pegmatite mine in Finland, the Urgeiriça uranium mine in Portugal and the Idrija mercury mine in Slovenia. The final, most ambitious demonstration will occur in the UK with the resurveying of the entire flooded section of the Ecton underground copper mine that nobody has seen for over 150 years.

Present-day stress state in the Outokumpu deep drill hole, Finland

NASA Astrophysics Data System (ADS)

Pierdominici, Simona; Ask, Maria; Kukkonen, Ilmo; Kueck, Jochem

2017-04-01

This study aims to investigate the present-day stress field in the Outokumpu area, eastern Finland, using interpretation of borehole failure on acoustic image logs in a 2516 m deep hole. Two main objectives of this study are: i. to constrain the orientation of maximum horizontal stress by mapping the occurrence of stress-induced deformation features using two sets of borehole televiewer data, which were collected in 2006 and 2011; and ii. to investigate whether any time dependent deformation of the borehole wall has occurred (creep). The Outokumpu deep hole was drilled during 2004-2005 to study deep structures and seismic reflectors within the Outokumpu formation and conducted within the International Continental Scientific Drilling Program (ICDP). The hole was continuously core-drilled into Paleoproterozoic formation of metasediments, ophiolite-derived altered ultrabasic rocks and pegmatitic granite. In 2006 and 2011 two downhole logging campaigns were performed by the Operational Support Group of ICDP to acquire a set of geophysical data. Here we focus on a specific downhole logging measurement, the acoustic borehole televiewer (BHTV), to determine the present-day stress field in the Outokumpu area. We constrain the orientation and magnitude of in situ stress tensor based on borehole wall failures detected along a 2516 m deep hole. Horizontal stress orientation was determined by interpreting borehole breakouts (BBs) and drilling-induced tensile fractures (DIFs) from BHTV logs. BBs are stress-induced enlargements of the borehole cross section and occur in two opposite zones at angles around the borehole where the wellbore stress concentration (hoop stress) exceeds the value required to cause compressive failure of intact rock. DIFs are caused by tensile failure of the borehole wall and form at two opposite spots on the borehole where the stress concentration is lower than the tensile strength of the rock. This occurs at angles 90° apart from the center of the breakout zone. Acoustic imaging logs provide a high-resolution oriented picture of the borehole wall that allows for the direct observation of BBs, which appear as two almost vertical swaths on the borehole image separated by 180°. BBs show poor sonic reflectivity and long travel times due to the many small brittle fractures and the resulting spalling. DIFs appear as two narrow stripes of low reflectivity separated by 180° and typically sub-parallel or slightly inclined to the borehole axis. The analysis of these images shows a distinct compressive failure area consistent with major geological and tectonic lineaments of the area. Deviations from this trend reflect local structural perturbations. Additionally, the 2006 and 2011 dataset are used to compare the changes of breakout geometry and to quantify the growth of the breakouts in this time span from differences in width, length and depth to estimate the magnitude of the horizontal stress tensors. Our study contributes to understand the structure of the shallow crust in the Outokumpu area by defining the current stress field. Furthermore, a detailed understanding of the regional stress field is a fundamental contribution in several research areas such as exploration and exploitation of underground resources, and geothermal reservoir studies.

Building The Bigger Picture - Using a field study geology programme to link and contextualise classroom topics.

NASA Astrophysics Data System (ADS)

Allen, Lesley

2013-04-01

Cornwall, UK, has been designated a World Heritage Site for industrial heritage, based on the extensive mining history built around hydrothermal deposits of tin and copper suite deposits. These deposits are found in a very varied and complex geological setting. The tectonic activity which emplaced the deposits also produced intense folding and faulting of Carboniferous and Devonian marine sediments, major and minor igneous intrusions, regional and contact metamorphism, and the emplacement of an ophiolite sequence on the Lizard peninsula. The region is targeted by college and university geology student groups from across the UK. It is also the home of the world famous Camborne School of Mines, part of the University of Exeter. We have developed a comprehensive series of field visits to cover all these geological aspects. We also use the history of mining as a context within which to teach the social, environmental and economic aspects of the geology curriculum at A Level. By this means we can reveal how disparate geological topics link together through 3 physical dimensions plus time. Field visits motivate students; they enthuse and excite them and help them to understand the large-scale and 3D visualisation aspects of geology, the timescales involved, and also assist students in developing observational and practical field and mapping skills. The series of visits also helps to bring many aspects of the curriculum together into a more complete picture. Site 1 - Bude. Intense folding of marine sediments with tectonic and sedimentary structures in cyclical sands and shales and some turbidites. Competent and incompetent rocks, axial planar cleavage, etc. Site 2 - Praa Sands. Minor porphyritic intrusion with baked & chilled margins and flow aligned feldspars. (Also incidental raised beach due to post-glacial isostatic rebound.) Site 3 - Rinsey Cove. Contact zone where 'roof' of major granitic intrusion intrudes slates. Pegmatites, classic marginal features, xenoliths, stoping and faulting visible. Site 4 - Polurrian Cove. Western end of boundary thrust fault between metamorphosed subterranean lava flows (hornblende schists)above and crustal Devonian slates below can be observed. Site 5 - Coverack Cove to Godrevy Cove. The beach rocks change from olivine rich serpentinised peridotite to gabbro as you move across the Moho boundary zone. Further along the coast at Dean Point, dolerite dykes are quarried and basalt dykes are found at neighbouring Godrevy Cove - the complete ophiolite sequence in a few miles! Site 6 - Holmans Mine. Camborne School of Mines' training mine where students can experience blasting and see methods of rock stabilisation. They can also see mineral veins in situ underground and investigate mining techniques. Site 7 - Carnon Valley. Once known as the 'richest square mile in the World' due to the amount of tin and copper being produced. The Wheal Jane pollution incident (1992) caused widespread alarm and was dealt with by chemical and biological treatment systems still in operation. Historical and current tailings dams can be seen and compared, and the ecology of environmentally damaged ground observed. Mine dumps still yield mineral specimens and the streams are still acidic after heavy rain.

Siudaite, Na8(Mn2+ 2Na)Ca6Fe3+ 3Zr3NbSi25O74(OH)2Cl·5H2O: a new eudialyte-group mineral from the Khibiny alkaline massif, Kola Peninsula

NASA Astrophysics Data System (ADS)

Chukanov, Nikita V.; Rastsvetaeva, Ramiza K.; Kruszewski, Łukasz; Aksenov, Sergey M.; Rusakov, Vyacheslav S.; Britvin, Sergey N.; Vozchikova, Svetlana A.

2018-03-01

The new eudialyte-group mineral siudaite, ideally Na8(Mn2+ 2Na)Ca6Fe3+ 3Zr3NbSi25O74(OH)2Cl·5H2O, was discovered in a peralkaline pegmatite situated at the Eveslogchorr Mt., Khibiny alkaline massif, Kola Peninsula, Russia. The associated minerals are aegirine, albite, microcline, nepheline, astrophyllite, and loparite-(Ce). Siudaite forms yellow to brownish-yellow equant anhedral grains up to 1.5 cm across. Its lustre is vitreous, and the streak is white. Cleavage is none observed. The Mohs' hardness is 4½. Density measured by hydrostatic weighing is 2.96(1) g/cm3. Density calculated using the empirical formula is equal to 2.973 g/cm3. Siudaite is nonpleochroic, optically uniaxial, negative, with ω = 1.635(1) and ɛ = 1.626(1) (λ = 589 nm). The IR spectrum is given. The chemical composition of siudaite is (wt%; electron microprobe, H2O determined by HCN analysis): Na2O 8.40, K2O 0.62, CaO 9.81, La2O3 1.03, Ce2O3 1.62, Pr2O3 0.21, Nd2O3 0.29, MnO 6.45, Fe2O3 4.51. TiO2 0.54, ZrO2 11.67, HfO2 0.29, Nb2O5 2.76, SiO2 47.20, Cl 0.54, H2O 3.5, -O = Cl - 0.12, total 99.32. According to Mössbauer spectroscopy data, all iron is trivalent. The empirical formula (based on 24.5 Si atoms pfu, in accordance with structural data) is [Na7.57(H2O)1.43]Σ9(Mn1.11Na0.88Ce0.31La0.20Nd0.05Pr0.04K0.41)Σ3(H2O)1.8(Ca5.46Mn0.54)Σ6(Fe3+ 1.76Mn2+ 1.19)Σ2.95Nb0.65(Ti0.20Si0.50)Σ0.71(Zr2.95Hf0.04Ti0.01)Σ3Si24.00Cl0.47O70(OH)2Cl0.47·1.82H2O. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is trigonal, space group R3m, with a = 14.1885(26) Å, c = 29.831(7) Å, V = 5200.8(23) Å3 and Z = 3. Siudaite is chemically related to georgbarsanovite and is its analogue with Fe3+-dominant M2 site. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 6.38 (60) (-114), 4.29 (55) (-225), 3.389 (47) (131), 3.191 (63) (-228). 2.963 (100) (4-15), 2.843 (99) (-444), 2.577 (49) (3-39). Siudaite is named after the Polish mineralogist and geochemist Rafał Siuda (b. 1975).

A Geophysical Study in Grand Teton National Park and Vicinity, Teton County, Wyoming: With Sections on Stratigraphy and Structure and Precambrian Rocks

USGS Publications Warehouse

Behrendt, John Charles; Tibbetts, Benton L.; Bonini, William E.; Lavin, Peter M.; Love, J.D.; Reed, John C.

1968-01-01

An integrated geophysical study - comprising gravity, seismic refraction, and aeromagnetic surveys - was made of a 4,600-km2 area in Grand Teton National Park and vicinity, Wyoming, for the purpose of obtaining a better understanding of the structural relationships in the region. The Teton range is largely comprised of Precambrian crystalline rocks and layered metasedimentary gneiss, but it also includes granitic gneiss, hornblende-plagioclase gneiss, granodiorite, and pegmatite and diabase dikes. Elsewhere, the sedimentary section is thick. The presence of each system except Silurian provides a chronological history of most structures. Uplift of the Teton-Gros Ventre area began in the Late Cretaceous; most of the uplift occurred after middle Eocene time. Additional uplift of the Teton Range and downfaulting of Jackson Hole began in the late Pliocene and continues to the present. Bouguer anomalies range from -185 mgal over Precambrian rocks of the Teton Range to -240 mgal over low-density Tertiary and Cretaceous sedimentary rocks of Jackson Hole. The Teton fault (at the west edge of Jackson Hole), as shown by steep gravity gradients and seismic-refraction data, trends north-northeast away from the front of the Teton Range in the area of Jackson Lake. The Teton fault either is shallowly inclined in the Jenny Lake area, or it consists of a series of fault steps in the fault zone; it is approximately vertical in the Arizona Creek area. Seismic-refraction data can be fitted well by a three-layer gravity model with velocities of 2.45 km per sec for the Tertiary and Cretaceous rocks above the Cloverly Formation, 3.9 km per sec for the lower Mesozoic rocks, and 6.1 km per sec for the Paleozoic (limestone and dolomite) and Precambrian rocks. Gravity models computed along two seismic profiles are in good agreement (sigma=+- 2 mgal) if density contrasts with the assumed 2.67 g per cm2 Paleozoic and Precambrian rocks are assumed to be -0.35 and -0.10 g per cm2 for the 2.45 and 3.9 km per sec velocity layers, respectively. The Teton Range has a maximum vertical uplift of about 7 km, as inferred from the maximum depth to basement of about 5 km. Aeromagnetic data show a 400gamma positive anomaly in the Gros Ventre Range, which trends out of the surveyed area at the east edge. Exposed Precambrian rocks contain concentrations of magnetite and hematite. A prominent anomaly of about 100gamma is associated with the Gros Ventre Range, and 100gamma anomalies are associated with the layered gneiss of the Teton Range. On this basis the unmapped Precambrian rocks of the Gross Ventre Range are interpreted as layered gneiss. The sources of the magnetic anomalies, as indicated by depth determination, are at the surface of the Precambrian rocks. A model fitted to a profile across the Gros Ventre Range gives a depth to the Precambrian surface and a susceptibility of 0.0004 emu (electromagnetic units) for the source, which is consistent with modal analyses of the layered gneisses. A residual magnetic map shows that the granitic rocks and layered gneiss probably continue beneath the floor of Jackson Hole east of the Teton fault. The location of aeromagnetic anomalies is consistent with the interpretation that the Teton fault diverges from the front of the Teton Range.

Preliminary report on deposit models for sand and gravel in the Cache la Poudre River valley

USGS Publications Warehouse

Langer, W.H.; Lindsey, D.A.

1999-01-01

The stratigraphy, sedimentary features, and physical characteristics of gravel deposits in the Cache la Poudre River valley were studied to establish geologic models for these deposits. Because most of the gravel mined in the valley is beneath the low terraces and floodplain, the quality of these deposits for aggregate was studied in detail at eight sites in a 25.5-mile reach between Fort Collins and Greeley, Colorado. Aggregate quality was determined by field and laboratory measurements on samples collected under a consistent sampling plan. The Broadway terrace is underlain by Pleistocene alluvium and, at some places, by fine-grained wind-blown deposits. The Piney Creek terrace, low terraces, and floodplain are primarily underlain by Holocene alluvium. Pleistocene alluvium may underlie these terraces at isolated locations along the river. Gravels beneath the Piney Creek terrace, low terraces, and floodplain are divisible into two units that are poorly distinguishable at the upstream end of the study area, but are readily distinguishable about 7 miles downstream. Where distinguished, the two gravel units are separated by a sharp, locally erosional, contact. The upper gravel is probably of Holocene age, but the lower gravel is considered to be Holocene and Pleistocene. The primary variation in particle size of the gravels beneath the floodplain and low terraces of the Cache la Poudre River valley is the downstream decrease in the proportion of particles measuring 3/4 inch and larger. Above Fort Collins, about 60 pct of the gravel collects on the 3/4 inch sieve, whereas about 50 pct of gravel collects on the same sieve size at Greeley. For 1.5-inch sieves, the corresponding values are about 50 pct for Fort Collins and only about 30 pct for Greeley. Local differences in particle size and sorting between the upper and lower gravel units were observed in the field, but only the coarsest particle sizes appear to have been concentrated in the lower unit. Field measurements of aggregate quality, pebble lithology, and shape show little significant downstream variation. Pebble lithology is about 25 percent granite; 48 percent pegmatite; 5-7 percent each of gneiss, quartz, and quartzite; and minor amounts of diabase, schist, volcanic porphyry, and sandstone. Among the rock types, only the volcanic porphyries might be reactive with Portland cement. Pebble shape is dominantly equidimensional with a tendency to form thick, disc-shaped particles. Disc-shaped and spherical particles comprise about 39 percent and 31 percent of the pebble-size fraction, respectively. Rod and blade shapes comprise about 18 and 12 percent of the pebble-size fraction, respectively. The relatively large proportion of equidimensional particles in the Cache la Poudre may be due to the small proportion of layered gneiss in gravel. Pebbles having axial ratios less than 0.5, which might be structurally weak, are rare. The two gravel units show subtle local differences and evidence for derivation of the younger gravel from the older gravel. At many sites, the upper gravel unit tends to contain more quartz plus quartzite, has poorer physical quality, and contains more angular pebbles than the lower gravel. Weathering, followed by transport in the river, might be expected to concentrate quartz and quartzite, degrade physical quality, and break pebbles into angular fragments. This conclusion is consistent with local evidence of an erosional contact between the two gravel units.

The Yale Peabody Museum Mineral Collection: Past, Present, and Future

NASA Astrophysics Data System (ADS)

Nicolescu, S.; Ague, J.

2012-12-01

The beginnings of what became the Yale Peabody Museum (YPM) mineral collection are intimately associated with the emergence of science teaching and scientific research in the US. In 1802 Yale College graduate Benjamin Silliman was offered the first Yale "Chymistry" and Natural History professorship. In order to fulfill his academic duties he needed a mineral collection, but in 1802 only a few specimens were available to him. Through his determined efforts and with the critical support of two Yale College presidents, by 1825 Yale was in possession of what was arguably the best mineral collection in the US. The quality of the scientific education pioneered by Silliman attracted many bright students, including future pillars of 19th century science J. D. Dana, O. C. Marsh and G. J. Brush. Silliman was also the founder of an illustrious mineralogical "dynasty", members of which, starting with his son-in-law J. D. Dana and continuing with son, B. Silliman, Jr. and grandson E. S. Dana, contributed in seminal ways to the development of mineralogy. Having access to specimens collected by the Sillimans, or the many ones described in successive editions of Dana's System of Mineralogy, is a rare privilege. The YPM was founded in 1866 and the mineral collection started by Silliman became part of it. The collection has now grown to some 40,000 specimens, at least 38 of which are type minerals (roughly one percent of all presently known mineral species). Any collection is a valuable asset only if it is "alive" through use and development; hence, further enhancing the holdings of the YPM mineral collection is a continuing effort. Preservation of historic and scientifically relevant specimens is only one of many purposes served by the collection. An important intellectual value resides in the fact that many specimens are from localities lost to anthropogenic activities. The REE and U-Th bearing pegmatites at Barringer Hill, TX are such an example. Barringer Hill has been under the waters of Lake Buchanan since 1938. However, a significant mineral suite collected in the late 1800s/early 1900s is preserved in the YPM. The same holds true for mineral specimens from localities on Manhattan Island, NY, lost to urban development over the last 100 plus years, and many other US and world localities. Following the tradition instilled by Silliman, the specimens of the YPM mineral collection are actively used for undergraduate and graduate teaching in a large spectrum of Yale classes in several disciplines, ranging from Geology to Art and Architecture. Yale graduate and post-graduate students, as well as faculty and research personnel, are actively using collection material for research. Moreover, ongoing US and international projects are making use of YPM mineral specimens either for refining or redefining mineral chemical and structural data. In line with this last line of research, one of our future projects is the in-depth investigation of the type mineral specimens in the collection using state-of-the-art analytical techniques. The Petrology Collection, which also dates back to the 19th century, was recently acquired from the Yale Department of Geology and Geophysics and will be the focus of future research projects as well.

Middendorfite, K3Na2Mn5Si12(O,OH)36 · 2H2O, a new mineral species from the Khibiny pluton, Kola Peninsula

NASA Astrophysics Data System (ADS)

Pekov, I. V.; Chukanov, N. V.; Dubinchuk, V. T.; Zadov, A. E.

2007-12-01

Middendorfite, a new mineral species, has been found in a hydrothermal assemblage in Hilairite hyperperalkaline pegmatite at the Kirovsky Mine, Mount Kukisvumchorr apatite deposit, Khibiny alkaline pluton, Kola Peninsula, Russia. Microcline, sodalite, cancrisilite, aegirine, calcite, natrolite, fluorite, narsarsukite, labuntsovite-Mn, mangan-neptunite, and donnayite are associated minerals. Middendorfite occurs as rhombshaped lamellar and tabular crystals up to 0.1 × 0.2 × 0.4 mm in size, which are combined in worm-and fanlike segregations up to 1 mm in size. The color is dark to bright orange, with a yellowish streak and vitreous luster. The mineral is transparent. The cleavage (001) is perfect, micalike; the fracture is scaly; flakes are flexible but not elastic. The Mohs hardness is 3 to 3.5. Density is 2.60 g/cm3 (meas.) and 2.65 g/cm3 (calc.). Middendorfite is biaxial (-), α = 1.534, β = 1.562, and γ = 1.563; 2 V (meas.) = 10°. The mineral is pleochroic strongly from yellowish to colorless on X through brown on Y and to deep brown on Z. Optical orientation: X = c. The chemical composition (electron microprobe, H2O determined with Penfield method) is as follows (wt %): 4.55 Na2O, 10.16 K2O, 0.11 CaO, 0.18 MgO, 24.88 MnO, 0.68 FeO, 0.15 ZnO, 0.20 Al2O3, 50.87 SiO2, 0.17 TiO2, 0.23 F, 7.73 H2O; -O=F2-0.10, total is 99.81. The empirical formula calculated on the basis of (Si,Al)12(O,OH,F)36 is K3.04(Na2.07Ca0.03)Σ2.10(Mn4.95Fe0.13Mg0.06Ti0.03Zn0.03)Σ5.20(Si11.94Al0.06)Σ12O27.57(OH)8.26F0.17 · 1.92H2O. The simplified formula is K3Na2Mn5Si12(O,OH)36 · 2H2O. Middenforite is monoclinic, space group: P21/ m or P21. The unit cell dimensions are a = 12.55, b = 5.721, c = 26.86 Å; β = 114.04°, V = 1761 Å3, Z = 2. The strongest lines in the X-ray powder pattern [ d, Å, ( I)( hkl)] are: 12.28(100)(002), 4.31(81)(11overline 4 ), 3.555(62)(301, 212), 3.063(52)(008, 31overline 6 ), 2.840(90)(312, 021, 30overline 9 ), 2.634(88)(21overline 9 , 1.0.overline 1 0, 12overline 4 ), 2.366(76)(22overline 6 , 3.1.overline 1 0, 32overline 3 ), 2.109(54)(42 33, 42 44, 51overline 9 , 414), 1.669(64)(2.2.overline 1 3, 3.2.overline 1 3, 62overline 3 , 6.1.overline 1 3), 1.614(56)(5.0.overline 1 6, 137, 333, 71overline 1 ). The infrared spectrum is given. Middendorfite is a phyllosilicate related to bannisterite, parsenttensite, and the minerals of the ganophyllite and stilpnomelane groups. The new mineral is named in memory of A.F. von Middendorff (1815 1894), an outstanding scientist, who carried out the first mineralogical investigations in the Khibiny pluton. The type material of middenforite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.

Vigrishinite, Zn2Ti4 - x Si4O14(OH,H2O,□)8, a new mineral from the Lovozero alkaline complex, Kola Peninsula, Russia

NASA Astrophysics Data System (ADS)

Pekov, I. V.; Britvin, S. N.; Zubkova, N. V.; Chukanov, N. V.; Bryzgalov, I. A.; Lykova, I. S.; Belakovskiy, D. I.; Pushcharovsky, D. Yu.

2013-12-01

A new mineral vigrishinite, epistolite-group member and first layer titanosilicate with species-defining Zn, was found at Mt. Malyi Punkaruaiv, in the Lovozero alkaline complex, Kola Peninsula, Russia. It occurs in a hydrothermally altered peralkaline pegmatite and is associated with microcline, ussingite, aegirine, analcime, gmelinite-Na, and chabazite-Ca. Vigrishinite forms rectangular or irregularly shaped lamellae up to 0.05 × 2 × 3 cm flattened on [001]. They are typically slightly split and show blocky character. The mineral is translucent to transparent and pale pink, yellowish-pinkish or colorless. The luster is vitreous. The Mohs' hardness is 2.5-3. Vigrishinite is brittle. Cleavage is {001} perfect. D meas = 3.03(2), D calc = 2.97 g/cm3. The mineral is optically biaxial (-), α = 1.755(5), β = 1.82(1), γ = 1.835(8), 2 V meas = 45(10)°, 2 V calc = 50°. IR spectrum is given. The chemical composition (wt %; average of 9 point analyses, H2O is determined by modified Penfield method) is as follows: 0.98 Na2O, 0.30 K2O, 0.56 CaO, 0.05 SrO, 0.44 BaO, 0.36 MgO, 2.09 MnO, 14.39 ZnO, 2.00 Fe2O3, 0.36 Al2O3, 32.29 SiO2, 29.14 TiO2, 2.08 ZrO2, 7.34 Nb2O5, 0.46 F, 9.1 H2O, -0.19 O=F2, total is 101.75. The empirical formula calculated on the basis of Si + Al = 4 is: H7.42(Zn1.30Na0.23Mn0.22Ca0.07Mg0.07K0.05Ba0.02)Σ1.96(Ti2.68Nb0.41Fe{0.18/3+}Zr0.12)Σ3.39(Si3.95Al0.05)Σ4 20.31F0.18. The simplified formula is: Zn2Ti4- x Si4O14(OH,H2O,□)8 ( x < 1). Vigrishinite is triclinic, space group P , a = 8.743(9), b = 8.698(9), c = 11.581(11)Å, α = 91.54(8)°, β = 98.29(8)°, γ = 105.65(8)°, V = 837.2(1.5) Å3, Z = 2. The strongest reflections in the X-ray powder pattern ( d, Å, - I[ hkl]) are: 11.7-67[001], 8.27-50[100], 6.94-43[01, 10], 5.73-54[11, 002], 4.17-65[020, 2, 200], and 2.861-100[30, 22, 004, 11]. The crystal structure model was obtained on a single crystal, R = 0.171. Vigrishinite and murmanite are close in the structure of the TiSiO motif, but strongly differ from each other in part of large cations and H-bearing groups. Vigrishinite is named in honor of Viktor G. Grishin (b. 1953), a Russian amateur mineralogist and mineral collector, to pay tribute to his contribution to the mineralogy of the Lovozero Complex. The type specimen is deposited in the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.

Cr(III) solubility in aqueous fluids at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Watenphul, Anke; Schmidt, Christian; Jahn, Sandro

2014-02-01

Trivalent chromium is generally considered relatively insoluble in aqueous fluids and melts. However, numerous counterexamples in nature indicate Cr(III) mobilization by aqueous fluids during metamorphism or hydrothermal alteration of chromite-bearing rocks, or by pegmatite melts. So far, very little is known about the chromium concentrations and speciation in such fluids. In this study, the solubility of eskolaite (Cr2O3) in 1.6-4.2 m aqueous HCl solutions was determined in situ at elevated pressures up to 1 GPa and temperatures ranging between 400 and 700 °C using synchrotron micro-X-ray fluorescence spectroscopy (μ-XRF). Determined concentrations of dissolved Cr ranged between about 900-18,000 ppm, with the highest concentrations found at 500 °C and 861 MPa. The Cr(III) solubility in aqueous HCl fluids is retrograde in the studied temperature range and increases with pressure. In addition, Cr(III) complexation in these fluids was explored by Raman spectroscopy on a 12.3 mass% HCl fluid in equilibrium with eskolaite at 400 and 600 °C, 0.3-1.6 GPa. All spectra show two prominent Cr-Cl stretching bands at about 275 and 325 cm-1, which display some fine structure, and in some spectra weak bands in the region between 380 and 500 cm-1. The sum of the integrated intensities of the two dominant bands reveals qualitatively the same changes with temperature along an isochore, with pressure at constant temperature, and with the time required for equilibration as the Cr(III) concentrations in the fluid determined by μ-XRF. Complementary ab initio molecular dynamics simulations of a 4 m HCl solution at two different densities (0.8 and 0.97 g/cm3) and temperatures (427 and 727 °C) were performed to investigate the vibrational properties of various(O)y3-x and (O)y(OH)z3-x-z complexes with 3⩽x+z⩽4 and 0⩽y⩽2. Quasi-normal mode analysis reveals that both the tetrahedral symmetric and antisymmetric Cr-Cl stretching vibrations of CrCl4(H2O)0-2- have characteristic frequencies in the range of the two strongest experimentally observed Raman bands, whereas Cr-O stretching vibrations of hydroxy-chloride complexes occur at wavenumbers above 400 cm-1. Solubility and complexation of Cr(III) depend strongly on the activities of Cl- and H+. At high H+ and Cl- activity, the results are consistent with CrCl(H2O)0-2-1-0 complexes as major Cr(III) species, the Cr coordination number of which increases with pressure by becoming more aquated. At low Cl- activity, i.e. in our study at high-temperature low-pressure conditions, the data indicate mixed CrClx((OH)z3-x-z complexes with Cl-Cr ratios less than three. In situ μ-XRF solubility experiments conducted with eskolaite + (H2O + 29 mass% Na2CO3) and kosmochlor + (H2O + 44 mass% Na2Si3O7) resulted in dissolved Cr concentrations at or below the detection limit of 500 ppm. Thus, acidic chloridic fluids seem to be more efficient agents for Cr(III) mobilization and transport at crustal conditions than aqueous alkali carbonate or silicate solutions.

Eocene to post-Miocene kinematic evolution of the central Cyclades (Greece)

NASA Astrophysics Data System (ADS)

Draganits, E.; Huet, B.; Grasemann, B.; Schneider, D.; Ertl, A.

2012-04-01

Due to the extraordinary geotectonic location of the Aegean above an active subduction zone and an exceptional high seismicity, this area and especially the Cyclades have been in the focus of structural investigations for several decades. The present deformation is the result of ongoing plate tectonic movements in this area since at least the Miocene. The ductile structures of the Miocene extension and related metamorphic core type deformation are quite well studied and understood. Equally well investigated are the active tectonic deformation and associated brittle structures through several decades of seismic records. However, due to the difficulties of dating brittle faults, the kinematic evolution from the early to middle Miocene ductile structures, to later Miocene brittle-ductile and brittle faults is much less understood. For these reasons detailed structural fieldwork, combined with Ar-Ar geochronology and P-T studies, have been carried out on the uninhabited island of Despotiko, SW of Antiparos, which is situated virtually in the center of the Cycladic islands. This island has been selected because the existence of metamorphic rocks penetrated by Messinian rhyolite pipes and Pleistocene eolianites provide exceptional age constraints for Eocene to post-Miocene deformation structures. Despotiko is part of lower structural levels of the polymetamorphic Blueschist Unit of the Attic-Cycladic Metamorphic Belt and correlated lithologically with the Parikia gneisses and Marathi unit of Paros. Foliation is shallowly dipping towards the SSW. The main lithologies of the island, from the footwall to the hanging wall, consist of dark to pale grey, strongly foliated, mylonitic granite gneiss with abundant pegmatite dikes. The gneiss is overlain by prominent white, strongly foliated, mylonitic gneiss. Above are medium-grained, white calcite marble followed by greenish-white, mylonitic gneiss and an alternation of mica schist, greenschist, thin marble layers and some small serpentinite lenses. The structurally highest levels, in the south and southwest of the island, comprise several tens of meters of dolomite marble. This metamorphic succession has been cut by six Messinian rhyolitic volcanic vents and all crystalline rocks have been covered by late Pleistocene eolianites. The kinematic evolution of the investigation area can be divided based on the deformation style and age. (1) The ductile deformation results in NE-SW trending stretching lineation and shear senses both top-to NE and top-to SW. Ar-Ar white mica cooling ages indicate an early Miocene age for this ductile deformation. (2) The brittle/ductile structures, which gradually advance from the previous ductile deformation, start with small but pervasive flanking folds, followed by larger shear bands and finally faults with tourmaline slickenlines. The shear sense is consistently top-to SW with middle to late Miocene age constrained by Ar-Ar white mica cooling ages and zircon fission-track data from Paros. (3a) Large, subvertical, sinistral strike-slip faults cross-cut the metamorphic rocks and show up to hundreds of meters displacement. Late Miocene age is constrained by apatite fission-track data from Paros and the observation that these faults are sealed by Messinian rhyolites. (3b) The Messinian volcanic rocks are almost exclusively deformed by E-W striking conjugate brittle normal faults, which started already during the formation of the volcanic rocks. No unequivocal tectonic deformation structures have been observed in the Pleistocene eolianites.

40K-40Ca and 87Rb-86Sr Dating by SIMS: The Double-Plus Advantage

NASA Astrophysics Data System (ADS)

Harrison, T. M.; McKeegan, K. D.; Schmitt, A. K.

2009-12-01

The decay of 40K to 40Ar forms the basis of the potassium-argon dating method, although only one out of every 10 parent atoms decays to daughter 40Ar. The other 90% decay to 40Ca giving, in principle, the 40K-40Ca decay system great potential for dating samples with high K/Ca. This method, however, has not been utilized as an ion-microprobe-based geochronometer, largely because these isotopes require a very high mass resolving power (MRP) of ~25k for full separation. We found that limiting secondary ion transmission in our ims1270 ion microprobe to ~20% permits sufficient separation of 40K from 40Ca (MRP≈ 20k) to permit isotope ratio analysis, albeit with 40Ca+ on the shoulder of the more intense 40K+ peak. A pegmatitic muscovite from Jack Hills (K-Ca age = 2.54 Ga; Fletcher et al., Chem. Geol. 138, 289) yields ~104 cps of both 40K+ and 40Ca+ with a 15 μm primary spot size and O- beam current of 10 nA. The 40Ca+ signal is >90% radiogenic and reflects a “common” Ca content of ≤ 100 ppm. However, application of the relative sensitivity factor (RSF) calculated from the Jack Hills muscovite to unknowns yields relatively high age dispersion, perhaps related to the incompletely separated mass interferences. Theorizing that the noble gas electronic structure of K+ would likely resist further electron loss, we investigated an alternative approach involving analysis of Ca++/K++. The double-plus method provides an important advantage in that K++ species are suppressed by a factor of ~103 relative to K+, thereby effectively removing 40K++ from the spectrum at m/e≈ 20 and leaving 40Ca++ free from any significant interferences at an MRP≈ 4k. Measurement of the much more abundant 39K++ then permits 40Ca++/40K++ to be calculated from the known 39K/40K ratio. We applied this approach to Precambrian muscovite samples obtaining ages similar to, but generally younger than, their associated 40Ar/39Ar ages. This could reflect a minor matrix effect or a lower intrinsic retentivity of 40Ca* relative to 40Ar* in white micas. This approach offers the potential to develop a branched-decay thermochronometer (K-Ca-Ar) permitting simultaneous solution of temperature-time history from μm-scale isotopic variations. A further advantage is that even low resolution SIMS instruments (e.g., ims7f) can utilize the double-plus method. Initial investigations using the same double-plus approach for Rb-Sr dating show promise. While resolving 87Rb+ from 87Sr+ requires an MRP of ~290k, unattainable using any current SIMS instrument, 87Rb++ is so strongly suppressed that determination of 87Sr++ is possible with minor peak stripping. 87Rb/86Sr can be determined either from 85Rb+/88Sr+ at MRP≈ 8k or by the use of energy filtering. In addition to micas, these approaches may be applicable to any mineral systems enriched in alkali metals relative to alkaline earths, such as alkali feldspars, feldspathoids, and alkaline halides.

Davinciite, Na12K3Ca6Fe{3/2+}Zr3(Si26O73OH)Cl2, a New K,Na-Ordered mineral of the eudialyte group from the Khibiny Alkaline Pluton, Kola Peninsula, Russia

NASA Astrophysics Data System (ADS)

Khomyakov, A. P.; Nechelyustov, G. N.; Rastsvetaeva, R. K.; Rozenberg, K. A.

2013-12-01

This paper presents a description of a new zirconosilicate of the eudialyte group, which was named davinciite in honor of Leonardo da Vinci (1452-1519), a famous Italian scientist, painter, sculptor and architect. The new mineral has been found in hyperagpaitic pegmatite at the Rasvumchorr Mountain, Khibiny Pluton, Kola Peninsula, as relict inclusions, up to 1-2 mm in size in a rastsvetaevite matrix. It is associated with nepheline, sodalite, potassium feldspar, delhayelite, aegirine, shcherbakovite, villiaumite, nitrite, nacaphite, rasvumite, and djerfisherite. Davinciite is dark lavender and transparent, with a vitreous luster and white streak. The new mineral is brittle, with conchoidal fracture; the Mohs' hardness is 5. No indications of cleavage or parting were observed. The measured density is 2.82(2) g/cm3 (volumetric method); the calculated density is 2.848 g/cm3. Davinciite is optically uniaxial, positive; ω = 1.603(2), ɛ = 1.605(2). It is nonpleochroic and nonfluorescent in UV light. The new mineral slowly breaks down and gelates in 50% HCl and HNO3. It is trigonal, space group R3m. The unit-cell dimensions are a = 14.2956(2), c = 30.0228(5) Å, V=5313.6(2) Å3. The strongest reflections in the X-ray powder diffraction pattern [ d, Å ( I, %) ( hkl)] are as follows: 2.981(100)(315), 2.860(96)(404), 4.309(66)(205), 3.207(63)(208), 6.415(54)(104), 3.162(43)(217). The chemical composition (electron microprobe, H2O calculated from X-ray diffraction data) is as follows, wt %: 12.69 Na2O, 3.53 K2O, 11.02 CaO, 0.98 SrO, 0.15 BaO, 5.33 FeO, 0.37 MnO, 0.07 Al2O3, 51.20 SiO2, 0.39 TiO2, 11.33 ZrO2, 0.21HfO2, 0.09 Nb2O5, 1.89 Cl, 0.93H2O, -O = Cl2 0.43; total is 99.75. The empirical formula calculated on the basis of Si + Al + Zr + Hf + Ti + Nb = 29 ( Z = 3) is (Na1l.75Sr0.29Ba0.03)Σ12.07(K2.28Na0.72)Σ3Ca5.99(Fe2.26Mn0.16)Σ2.42(Zr2.80Ti0.15Hf0.03Nb0.02) Σ3(Si1.96Al0.04)Σ2[Si3O9]2 [Si9O27]2[(OH)1.42O0.58]Σ2[Cl1.62(H2O)0.38]Σ2 · 0.48H2O. The simplified formula is Na12K3Ca6Fe{3/2+}Zr3(Si26O73OH)Cl2. The IR-spectrum is given and the crystal structure is described. The position of davinciite in the crystal chemical taxonomy of the eudialyte group is shown, and its relationships with the other eudialyte-group minerals (acentric eudialyte, andrianovite, and kentbrooksite) are characterized. The type material of davinciite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.

Petrology and geochemistry of late-stage intrusions of the A-type, mid-Proterozoic Pikes Peak batholith (Central Colorado, USA): Implications for petrogenetic models

USGS Publications Warehouse

Smith, D.R.; Noblett, J.; Wobus, R.A.; Unruh, D.; Douglass, J.; Beane, R.; Davis, C.; Goldman, S.; Kay, G.; Gustavson, B.; Saltoun, B.; Stewart, J.

1999-01-01

The ~1.08 Ga anorogenic, A-type Pikes Peak batholith (Front Range, central Colorado) is dominated by coarse-grained, biotite ?? amphibole syenogranites and minor monzogranites, collectively referred to as Pikes Peak granite (PPG). The batholith is also host to numerous small, late-stage plutons that have been subdivided into two groups (e.g. Wobus, 1976. Studies in Colorado Field Geology, Colorado School of Mines Professional Contributions, Colorado): (1) a sodic series (SiO2= ~44-78 wt%; K/Na=0.32-1.36) composed of gabbro, diabase, syenite/quartz syenite and fayalite and sodic amphibole granite; and (2) a potassic series (SiO2= ~ 70-77 wt%; K/Na=0.95-2.05), composed of biotite granite and minor quartz monzonite. Differences in major and trace element and Nd isotopic characteristics for the two series indicate different petrogenetic histories. Potassic granites of the late-stage intrusions appear to represent crustal anatectic melts derived from tonalite sources, based on comparison of their major element compositions with experimental melt products. In addition, Nd isotopic characteristics of the potassic granites [??(Nd)(1.08 Ga) = -0.2 to -2.7] overlap with those for tonalites/granodiorites [ca 1.7 Ga Boulder Creek intrusions; ??(Nd)(1.08 Ga) = -2.4 to -3.6] exposed in the region. Some of the partial melts evolved by fractionation dominated by feldspar. The late-stage potassic granites share geochemical characteristics with most of the PPG, which is also interpreted to have an anatectic origin involving tonalitic crust. The origin of monzogranites associated with the PPG remains unclear, but mixing between granitic and mafic or intermediate magmas is a possibility. Syenites and granites of the sodic series cannot be explained as crustal melts, but are interpreted as fractionation products of mantle-derived mafic magmas with minor crustal input. High temperature and low oxygen fugacity estimates (e.g. Frost et al., 1988. American Mineralogist 73, 727-740) support a basalt fractionation origin, as do ??(Nd) values for sodic granitoids [??(Nd)(1.08 Ga) = +2.2 to -0.7], which are higher than ??(Nd) values for Colorado crust at 1.08 Ga (ca -1.0 to -4.0). Enrichments in incompatible elements (e.g. rare earth elements, Rb, Y) and depletions in compatible elements (e.g. Cr, Sr, Ba) in the sodic granitoids compared to coeval mafic rocks are also consistent with fractionation. Accessory mineral fractionation, release of fluorine-rich volatiles and/or removal of pegmatitic fluids could have modified abundances of Ce, Nb, Zr and Y in some sodic granitoid magmas. Gabbros and mafic dikes associated with the sodic granitoids have ??(Nd)(1.08 Ga) of -3.0 to +3.5, which are lower than depleted mantle at 1.08 Ga, and their trace element characteristics suggest derivation from mantle sources that were previously affected by subduction-related processes. However, it is difficult to characterize the mantle component in these magmas, because assimilation of crust during magma ascent could also result in their observed geochemical features. The Pikes Peak batholith is composed of at least two petrogenetically different granite types, both of which exhibit geochemical characteristics typical of A-type granites. Models proposed for the petrogenesis of the granitoids imply the existence of mafic rocks at depth and addition of juvenile material to the crust in central Colorado at ~ 1.1 Ga.

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes in central Iran: New geological data, relationships and tectonic implications

NASA Astrophysics Data System (ADS)

Bagheri, Sasan; Stampfli, Gérard M.

2008-04-01

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes occupy the NW part of the Central-East Iranian Microcontinent and are juxtaposed with the Great Kavir block and Sanandaj-Sirjan zone. Our recent findings redefine the origin of these complexes, so far attributed to the Precambrian-Early Paleozoic orogenic episodes, and now directly related to the tectonic evolution of the Paleo-Tethys Ocean. This tectonic evolution was initiated by Late Ordovician-Early Devonian rifting events and terminated in the Triassic by the Eocimmerian collision event due to the docking of the Cimmerian blocks with the Asiatic Turan block. The "Variscan accretionary complex" is a new name we proposed for the most widely distributed metamorphic rocks connected to the Anarak and Jandaq complexes. This accretionary complex exposed from SW of Jandaq to the Anarak and Kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal-sea ophiolitic remnants, including gabbro-basalts with a supra-subduction-geochemical signature. New 40Ar/ 39Ar ages are obtained as 333-320 Ma for the metamorphism of this sequence under greenschist to amphibolite facies. Moreover, the limy intercalations in the volcano-sedimentary part of this complex in Godar-e-Siah yielded Upper Devonian-Tournaisian conodonts. The northeastern part of this complex in the Jandaq area was intruded by 215 ± 15 Ma arc to collisional granite and pegmatites dated by ID-TIMS and its metamorphic rocks are characterized by some 40Ar/ 39Ar radiometric ages of 163-156 Ma. The "Variscan" accretionary complex was northwardly accreted to the Airekan granitic terrane dated at 549 ± 15 Ma. Later, from the Late Carboniferous to Triassic, huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the Anarak and Kabudan. This new period of accretion is supported by the 280-230 Ma 40Ar/ 39Ar ages for the Anarak mild high-pressure metamorphic rocks and a 262 Ma U-Pb age for the trondhjemite-rhyolite association of that area. The Triassic Bayazeh flysch filled the foreland basin during the final closure of the Paleo-Tethys Ocean and was partly deposited and/or thrusted onto the Cimmerian Yazd block. The Paleo-Tethys magmatic arc products have been well-preserved in the Late Devonian-Carboniferous Godar-e-Siah intra-arc deposits and the Triassic Nakhlak fore-arc succession. On the passive margin of the Cimmerian block, in the Yazd region, the nearly continuous Upper Paleozoic platform-type deposition was totally interrupted during the Middle to Late Triassic. Local erosion, down to Lower Paleozoic levels, may be related to flexural bulge erosion. The platform was finally unconformably covered by Liassic continental molassic deposits of the Shemshak. One of the extensional periods related to Neo-Tethyan back-arc rifting in Late Cretaceous time finally separated parts of the Eocimmerian collisional domain from the Eurasian Turan domain. The opening and closing of this new ocean, characterized by the Nain and Sabzevar ophiolitic mélanges, finally transported the Anarak-Jandaq composite terrane to Central Iran, accompanied by large scale rotation of the Central-East Iranian Microcontinent (CEIM). Due to many similarities between the Posht-e-Badam metamorphic complex and the Anarak-Jandaq composite terrane, the former could be part of the latter, if it was transported further south during Tertiary time.

The late Variscan ferroan granite magmatism of southern Sardinia: inferences from Mo metallogenesis

NASA Astrophysics Data System (ADS)

Naitza, Stefano; Conte, Aida Maria; Cuccuru, Stefano; Fadda, Sandro; Fiori, Maddalena; Oggiano, Giacomo; Secchi, Francesco

2017-04-01

Metallogeny is a powerful tool to investigate crustal evolution; a good example is offered by the Variscan basement of Sardinia and its Mo deposits. Mo ores are poorly represented in Variscan metallogenic provinces of Europe: however, in Sardinia, numerous small Mo deposits, often associated to Sn, W and F ores, are present, invariably related to an early Permian intrusive peak bracketed at about 290 Ma (Fadda et al., 2015; Naitza et al., 2017). In Sardinia, two main magmatic peaks have been schematized at pre-300 and 290 Ma. In southern Sardinia, the 290 magmatic peak is made up of several intrusive F-bearing rock-suites (Conte et al., 2016), belonging to ilmenite series, showing a slight peraluminous character and mostly classifiable as ferroan granites (sensu Frost and Frost, 2011). Mo-bearing granites form a distinct suite of relatively small plutons, emplaced at very shallow depth (about 1kb) in an exhumed Variscan low-grade basement. Peculiar characters of Mo-bearing granites are the occurrence of greisenized microgranite and granophyre cupolas, with fayalite-bearing pegmatites, and ilmenite, xenotime-(Y), monazite, fluorite, and local topaz as accessory phases. Recently, Conte et al. (2016) interpreted these granites as originated by partial melting of low crustal felsic metaigneous photoliths enriched in granophiles (Mo, Sn, W). Mo ores occur as: a) endo- and exo- quartz-muscovite greisens with molybdenite±Fe-Cu sulphides, and b) quartz-molybdenite±wolframite±Fe-Cu-Zn sulphides±fluorite±topaz hydrothermal veins and stockworks, hosted in granites or in country rocks. Redox state of magmas exerts a strong control on Mo metallogeny, as in Mo districts worldwide ores are usually hosted by high-fO2 magnetite series intrusions (Ishihara, 1981). The close field association of Sardinian Mo mineralization with ferroan, low-fO2 ilmenite-series granites may be explained in terms of Mo-enriched crustal sources of magmas, and very efficient geochemical concentration processes. Mo concentration occurred during latest intrusive phases in granitic cupolas, as local subsolidus reactions. They involve: 1) leaching of Mo5+ and Mo6+ from their primary hosts (e.g., biotites) by Cl- and F-rich fluids under decreasing pH and increasing fH2O and fO2, and 2) transport of Mo cations towards intrusive contacts, where they quickly reacted with Sulphur from country rocks to be reduced as MoS2. Overall, the late Variscan Mo metallogenic peak in Sardinia is a single event located in a short timespan at around 290 Ma. In the early Permian extensional setting of Corsica-Sardinia batholith, a distinct HT/LP event related to melting of mantle lithosphere (Rossi et al., 2015), triggered partial melting of Mo-bearing deep crustal sources, producing the F-bearing ferroan magmas. The singular concentration of Mo-bearing granites could indicate a peculiar compositional character of the Sardinian lower crust. References: Conte A.M. et al. (2016). Proc. 2nd European Mineralogical Conference, Rimini, Italy, 154. Fadda et al. (2015). Proc. 13th Biennial SGA Meeting, Nancy, France, Vol. 2, 721-724. Frost, C. D. and Frost R. B. (2011). J. Petrol. 52, 39-53. Ishihara S. (1981). Econ. Geol., 75th Anniversary Volume, 458-484. Naitza S. et al. (2017). Ore Geol. Rev. 80, 1259-1278. Rossi et al. (2015). Bull. Soc. Géol. France 186, 171-192.

Summary of reconnaissance for radioactive deposits in Alaska, 1945-1954, and an appraisal of Alaskan uranium possibilities

USGS Publications Warehouse

Wedow, Helmuth

1956-01-01

In the period 1945-1954 over 100 investigations for radioactive source materials were made in Alaska. The nature of these investigations ranged from field examinations of individual prospects or the laboratory analysis of significantly radioactive samples submitted by prospectors to reconnaissance studies of large districts. In this period no deposits of uranium or thorium that would warrant commercial exploitation were discovered. The investigations, however, disclosed that radioactive materials occur in widely scattered areas of Alaska and in widely diverse environments. Many igneous rocks throughout Alaska are weakly radioactive because of uranium- and thorium-bearing accessory minerals, such as allanite, apatite, monazite, sphene, xenotime, and zircon; more rarely the radioactivity of these rocks is due to thorianite or thorite and their uranoan varieties. The felsic rocks, for example, granites and syenites, are generally more radioactive than the mafic igneous rocks. Pegmatites, locally, have also proved to be radioactive, but they have little commercial significance. No primary uranium oxide minerals have been found yet in Alaskan vein deposits, except, perhaps, for a mineral tentatively identified as pitchblende in the Hyder district of southeastern Alaska. However, certain occurrences of secondary uranium minerals, chiefly those of the uranite group, on the Seward Peninsula, in the Russian Mountains, and in the vicinity of Kodiak suggest that pitchblende-type ores may occur at depth beneath zones of alteration. Thorite-bearing veins have been discovered on Prince of Wales Island in southeastern Alaska. Although no deposits or carnotite-type minerals have been found in Alaska, several samples containing such minerals have been submitted by Alaskan prospectors. Efforts to locate the deposits from which these minerals were obtained have been unsuccessful, but review of available geologic data suggests that several Alaskan areas are potentially favorable for carnotite-type deposits. The chief of these areas is the Alaska Peninsula-Cook Inlet area which encompasses most of the reported occurrences of the prospectors' carnotite-type samples. Alaska is also potentially favorable for the occurrence of large bodies of the very low-grade uraniferous sedimentary rocks, such as phosphorites and black shales. This type of deposit, however, has not received much study because of the emphasis on the search for bonanza-type high-grade ores. Uraniferous phosphorites similar to those of Idaho, Montana, and Wyoming occur in northern Alaska on the north flank of the Brooks Range; black shales comparable to the uraniferous shales of the Chattanooga formation of southeastern United States have been noted along the Yukon River near the international boundary. Placer deposits in Alaska have some small potential for the production of the radioactive elements as byproducts of gold- and tin-placer mining. the placer area believed to have the relatively greatest potential in Alaska lies in the Kahiltna River valley where concentrates are known to contain such commercial minerals as ilmenite, cassiterite, platinum, and gold in addition to uranothorianite and monazite. The possibilities of the natural fluids--water and petroleum--have not yet been tested in Alaska to any great extent. Studies of fluids are in progress to determine whether they may be used to discover and define areas potentially favorable for the occurrence of uraniferous lodes.

Geologic map of Colorado National Monument and adjacent areas, Mesa County, Colorado

USGS Publications Warehouse

Scott, Robert B.; Harding, Anne E.; Hood, William C.; Cole, Rex D.; Livaccari, Richard F.; Johnson, James B.; Shroba, Ralph R.; Dickerson, Robert P.

2001-01-01

New 1:24,000-scale geologic mapping in the Colorado National Monument Quadrangle and adjacent areas, in support of the USGS Western Colorado I-70 Corridor Cooperative Geologic Mapping Project, provides new interpretations of and data for the stratigraphy, structure, geologic hazards in the area from the Colorado River in Grand Valley onto the Uncompahgre Plateau. The plateau drops abruptly along northwest-trending structures toward the northeast 800 m to the Redlands area and the Colorado River in Grand Valley. In addition to common alluvial and colluvial deposits, surficial deposits include Holocene and late Pleistocene charcoal-bearing valley-fill deposits, late to middle Pleistocene river-gravel terrace deposits, Holocene to middle Pleistocene younger, intermediate, and old fan-alluvium deposits, late to middle Pleistocene local gravel deposits, Holocene to late Pleistocene rock-fall deposits, Holocene to middle Pleistocene young and old landslide deposits, Holocene to late Pleistocene sheetwash deposits and eolian deposits, and Holocene Cienga-type deposits. Only the lowest part of the Upper Cretaceous Mancos Shale is exposed in the map area near the Colorado River. The Upper and Lower? Cretaceous Dakota Formation and the Lower Cretaceous Burro Canyon Formation form resistant dipslopes in the Grand Valley and a prominent ridge on the plateau. Less resistant strata of the Upper Jurassic Morrison Formation consisting of the Brushy Basin, Salt Wash, and Tidwell Members form slopes on the plateau and low areas below the mountain front of the plateau. The Middle Jurassic Wanakah Formation nomenclature replaces the previously used Summerville Formation. Because an upper part of the Middle Jurassic Entrada Formation is not obviously correlated with strata found elsewhere, it is therefore not formally named; however, the lower rounded cliff former Slickrock Member is clearly present. The Lower Jurassic silica-cemented Kayenta Formation forms the cap rock for the Lower Jurassic carbonate-cemented Wingate Sandstone, which forms the impressive cliffs of the monument. The Upper Triassic Chinle Formation was deposited on the eroded and weathered Middle Proterozoic meta-igneous gneiss, pegmatite dikes, and migmatitic gneiss. Structurally the area is deceptively challenging. Nearly flat-lying strata on the plateau are folded by northwest-trending fault-propagation folds into at least two S-shaped folds along the mountain front of the plateau. Strata under Grand Valley dip at about 6 degrees to the northeast. In the absence of local evidence, the uplifted plateau is attributed to Laramide deformation by dated analogous structures elsewhere in the Colorado Plateau. The major exposed fault records high-angle reverse relationships in the basement rocks but dissipates strain as a triangular zone of distributed microfractures and cataclastic flow into overlying Mesozoic strata that absorb the fault strain, leaving only folds. Evidence for younger, probably late Pliocene or early Pleistocene, uplift does exist at the antecedent Unaweep Canyon south and east of the map area. To what degree this younger deformation affected the map area is unknown. Several geologic hazards affect the area. Middle and late Pleistocene landslides involving the smectite-bearing Brushy Basin Member of the Morrison Formation are extensive on the plateau and common in the Redlands below the plateau. Expansive clay in the Brushy Basin and other strata create foundation stability problems for roads and homes. Flash floods create a serious hazard to people on foot in narrow canyons in the monument and to homes close to water courses downstream from narrow restrictions close to the monument boundary.

Contact metamorphism, partial melting and fluid flow in the granitic footwall of the South Kawishiwi Intrusion, Duluth Complex, USA

NASA Astrophysics Data System (ADS)

Benko, Z.; Mogessie, A.; Molnar, F.; Severson, M.; Hauck, S.; Lechler, P.; Arehart, G.

2012-04-01

The footwall of the South Kawishiwi Intrusion (SKI) a part of the Mesoproterozoic (1.1 Ga) Duluth Complex consists of Archean granite-gneiss, diorite, granodiorite (Giant Range Batholith), thin condensed sequences of Paleoproterozoic shale (Virginia Fm.), as well as banded iron formation (Biwabik Iron Fm). Detailed (re)logging and petrographic analysis of granitic footwall rocks in the NM-57 drillhole from the Dunka Pit area has been performed to understand metamorphic processes, partial melting, deformation and geochemical characteristics of de-volatilization or influx of fluids. In the studied drillhole the footwall consists of foliated metagranite that is intersected by mafic (dioritic) dykes of older age than the SKI. In the proximal contact zones, in the mafic dykes, the orthopyroxene+clinopyroxene+plagioclase+quartz+Fe-Ti-oxide+hornblende±biotite porphyroblasts embedded in a plagioclase+K-feldspar+orthopyroxene+apatite matrix indicate pyroxene-hornfels facies conditions. Migmatitization is revealed by the euhedral crystal faces of plagioclase and pyroxene against anhedral quartz crystals in the in-situ leucosome and by the presence of abundant in-source plagioclase±biotite leucosome veinlets. Amphibole in the melanosome of mafic dykes was formed with breakdown of biotite and implies addition of H2O to the system during partial melting. Towards the deeper zones, the partially melted metatexite-granite can be characterized by K-feldspar+plagioclase+quartz+ortho/clinopyroxene+biotite+Fe-Ti-oxide+apatite mineral assemblage. The felsic veins with either pegmatitic or aplititic textures display sharp contact both to the granite and the mafic veins. They are characterized by K-feldspar+quartz±plagioclase±muscovite mineral assemblage. Sporadic occurrence of muscovite suggest local fluid saturated conditions. Emplacement of gabbroic rocks of the SKI generated intense shear in some zones of the granitic footwall resulting in formation of biotite-rich mylonites with lepidoblastic texture. High modal content of syn-tectonic biotite in these shear zones indicate involvement of large amount of fluids during deformation. Apatite is an omnipresent accessory mineral in all rock types, with up to 1-3% modal proportion. Crystal habit is columnar or rarely needle-like. XCl/XF and XOH/XF ratios of apatite were compared with depth in the drillhole and in relation to the host rock type. Apatite in the metagranite and in the mafic dyke is fluorine-rich (XFgranite≈1,27-1,63; XFmafic dyke≈1,51-1,83) and their XCl/XFgranite≈0,083 to 0,051 and XCl/XFmafic dyke≈0,051 to 0,044 ratios decrease towards the distal parts of the contact. Apatite in biotite-rich mylonite, as well as in the porphyroblasts of mafic dykes, is extremely depleted in chlorine- and hydroxyl-anions (XCl/XFmylonite≈0,02 and XOH/XFmylonite≈0,14), whereas apatite in felsic dykes and in the in-source leucosome are enriched in hydroxyl and chlorine relative to fluorine (XCl/XFfelsic vein≈0,21 and XOH/XFfelsic vein≈0,37). These variations suggest release of chlorine enriched fluids from the partially melted contact zones and movement and enrichments of these fluids in migration channels of partial melts. It has been for a long time accepted that fluids emerging from the metamorphosed Virginia Formation played an essential role in the formation of the Cu-Ni sulphide and PGE mineralization at the bottom of the gabbroic intrusions in the northwestern marginal zones of the Duluth Complex. Our study proves that the granitic footwall was also an important source of fluids and melts. We acknowledge the Austrian Science Found (FWF P23157-N21) to A. Mogessie for the financial support.

Geologic Setting of the Hamme Tungsten District, North Carolina and Virginia

USGS Publications Warehouse

Parker, John Mason

1963-01-01

The Hamme tungsten district is in the eastern part of the Piedmont province, mainly in Vance County, North Carolina, but it extends a few miles into Virginia. The district is underlain by a central lenticular pluton of albite granodiorite that trends north-northeastward and is flanked on both sides by metamorphic rocks of low and medium grade that dip steeply westward. The relative ages of the metamorphic rocks are uncertain. The oldest rocks are likely to be the biotite gneisses in the eastern part of the district; successively younger units expose westward across the district are sericite-chlorite phyllites, greenstone, metafelsites, and metabasalts. The biotite gneisses and minor intercalated hornblende gneiss, which have a total thickness of many thousand feet, were derived from sediments. Some of the gneiss grades into phyllites and as probably formed by metasomatic alteration of the phyllites. Sericite-chlorite phyllite, epidote-quartz meta siltstone, quartzite, and conglomeratic phyllite occur principally in a wide belt on the west side of the central albite granodiorite. This unit is some 10,000 feet thick and originally consisted mainly of sediments of the graywacke suite. Greenstone totaling about 500 feet in thickness lies west of the phyllite and was derived from maflc lava flows and andesitic tuff. Metamorphosed massive aphanitic and porphyritic flows and dikes that range in composition from dacite to rhyolite, and phyllitic metatuffs and tuffaceous breccia are exposed west of the greenstone. These total at least 3,000 feet in thickness. Massive metabasalt that resembles greenstone but is less altered is common in the area between the Hamme district and the Virgilina district to the west. The thickness of the metabasalt is about 600 to 6,000 feet. The metamorphic rocks of the Hamme and Virgilina districts are parts of the Carolina slate belt, but map units cannot be directly correlated. Rocks in the Hamme district are thought by the writer to have been derived mainly from graywackes and volcanic flows, and subordinately from pyroclastic materials, whereas the rocks of the Virgilina district were interpreted by earlier workers as being mainly volcanic with much pyroclastic material but little sediment. Igneous, and perhaps pseudo igneous, rocks in the district include hornblende gabbro, albite granodiorite, aplite, and pegmatite--all of which are probably middle Paleozoic in age--and diabase and hypersthene tonalite of Late Triassic age. The gabbro forms three lenticular to subcircular bodies up to 2% miles in width in the western part of the area. Albite granodiorite forms a pluton with a maximum width of 7 miles which occupies the center of the area. At its northeastern end the pluton narrows abruptly to a point. Phyllite forms the wall rocks on all sides of the albite granodiorite. The contact is gradational and conformable in most places, but on the northwest side it cuts across wall structure for about 3 miles. Near its western edge the albite granodiorite includes a northeast-trending zone of schistose wall rock in and near which are localized the tungsten deposits. The origin of the albite granodiorite is uncertain, but it may have formed by the metasomatic replacement of the wallrocks, during which albite porphyroblasts developed first and were followed by microcline and quartz. Diabase and hypersthene tonalite occur as dikes and sills along four northward-trending belts. The dikes are a few feet to more than 300 feet thick, and several extend along strike for more than 10 miles. The Hamme district Is in the eastern part of the Carolina slate belt, and the Virg1l1na district lies along the western side of the belt. Rocks in the Hamme district dip mostly westward and in the Vifg1lina district dip mainly eastward into a syncline. This syncline, here named the Spewmarrow syncline, may be a structure of regional significance. Tungsten in the Hamme district occurs mainly

Numerical simulation of ground-water flow through glacial deposits and crystalline bedrock in the Mirror Lake area, Grafton County, New Hampshire

USGS Publications Warehouse

Tiedeman, Claire; Goode, Daniel J.; Hsieh, Paul A.

1997-01-01

This report documents the development of a computer model to simulate steady-state (long-term average) flow of ground water in the vicinity of Mirror Lake, which lies at the eastern end of the Hubbard Brook valley in central New Hampshire. The 10-km2 study area includes Mirror Lake, the three streams that flow into Mirror Lake, Leeman's Brook, Paradise Brook, and parts of Hubbard Brook and the Pemigewasset River. The topography of the area is characterized by steep hillsides and relatively flat valleys. Major hydrogeologic units include glacial deposits, composed of till containing pockets of sand and gravel, and fractured crystalline bedrock, composed of schist intruded by granite, pegmatite, and lamprophyre. Ground water occurs in both the glacial deposits and bedrock. Precipitation and snowmelt infiltrate to the water table on the hillsides, flow downslope through the saturated glacial deposits and fractured bedrock, and discharge to streams and to Mirror Lake. The model domain includes the glacial deposits, the uppermost 150m of bedrock, Mirror Lake, the layer of organic sediments on the lake bottom, and streams and rivers within the study area. A streamflow routing package was included in the model to simulate baseflow in streams and interaction between streams and ground water. Recharge from precipitation is assumed to be areally uniform, and riparian evapotranspiration along stream banks is assumed negligible. The spatial distribution of hydraulic conductivity is represented by dividing the model domain into several zones, each having uniform hydraulic properties. Local variations in recharge and hydraulic conductivities are ignored; therefore, the simulation results characterize the general ground-water system, not local details of ground-water movement. The model was calibrated using a nonlinear regression method to match hydraulic heads measured in piezometers and wells, and baseflow in three inlet streams to Mirror Lake. Model calibration indicates that recharge from precipitation to the water table is 26 to 28 cm/year. Hydraulic conductivities are 1.7 x 10-6 to 2.7 x 10-6 m/s for glacial deposits, about 3 x 10-7 m/s for bedrock beneath lower hillsides and valleys, and about 6x10-8 m/s for bedrock beneath upper hillsides and hilltops. Analysis of parameter uncertainty indicates that the above values are well constrained, at least within the context of regression analysis. In the regression, several attributes of the ground-water flow model are assumed perfectly known. The hydraulic conductivity for bedrock beneath upper hillsides and hilltops was determined from few data, and additional data are needed to further confirm this result. Model fit was not improved by introducing a 10-to-1 ration of horizontal-to-vertical anisotropy in the hydraulic conductivity of the glacial deposits, or by varying hydraulic conductivity with depth in the modeled part (uppermost 150m) of the bedrock. The calibrated model was used to delineate the Mirror Lake ground-water basin, defined as the volumes of subsurface through which ground water flows from the water table to Mirror Lake or its inlet streams. Results indicate that Mirror Lake and its inlet streams drain an area of ground-water recharge that is about 1.5 times the area of the surface-water basin. The ground-water basin extends far up the hillside on the northwestern part of the study area. Ground water from this area flows at depth under Norris Brook to discharge into Mirror Lake or its inlet streams. As a result, the Mirror Lake ground-water basin extends beneath the adjacent ground-water basin that drains into Norris Brook. Model simulation indicates that approximately 300,000 m3/year of precipitation recharges the Mirror Lake ground-water basin. About half the recharge enters the basin in areas where the simulated water table lies in glacial deposits; the other half enters the basin in areas where the simulated water table lies in be

Genesis of a zoned granite stock, Seward Peninsula, Alaska

USGS Publications Warehouse

Hudson, Travis

1977-01-01

A composite epizonal stock of biotite granite has intruded a diverse assemblage of metamorphic rocks in the Serpentine Hot Springs area of north-central Seward Peninsula, Alaska. The metamorphic rocks include amphibolite-facies orthogneiss and paragneiss, greenschist-facies fine-grained siliceous and graphitic metasediments, and a variety of carbonate rocks. Lithologic units within the metamorphic terrane trend generally north-northeast and dip moderately toward the southeast. Thrust faults locally juxtapose lithologic units in the metamorphic assemblage, and normal faults displace both the metamorphic rocks and some parts of the granite stock. The gneisses and graphitic metasediments are believed to be late Precambrian in age, but the carbonate rocks are in part Paleozoic. Dating by the potassium-argon method indicates that the granite stock is Late Cretaceous. The stock has sharp discordant contacts, beyond which is a well-developed thermal aureole with rocks of hornblende hornfels facies. The average mode of the granite is 29 percent plagioclase, 31 percent quartz, 36 percent K-feldspar, and 4 percent biotite. Accessory minerals include apatite, magnetite, sphene, allanite, and zircon. Late-stage or deuteric minerals include muscovite, fluorite, tourmaline, quartz, and albite. The stock is a zoned complex containing rocks with several textural facies that are present in four partly concentric zones. Zone 1 is a discontinuous border unit, containing fine- to coarse-grained biotite granite, that grades inward into zone 2. Zone 2 consists of porphyritic biotite granite with oriented phenocrysts of pinkish-gray microcline in a coarse-grained equigranular groundmass of plagioclase, quartz, and biotite. It is in sharp, concordant to discordant contact with rocks of zone 3. Zone 3 consists of seriate-textured biotite granite that has been intruded by bodies of porphyritic biotite granite containing phenocrysts of plagioclase, K-feldspar, quartz, and biotite in an aplitic groundmass. Flow structures, pegmatite and aplite segregations, and miarolitic cavities are common in the seriate-textured granite. Zone 4, which forms the central part of the complex, consists of fine- to medium-grained biotite granite and locally developed leucogranite. Small miarolitic cavities are common within it. Eight textural facies have been defined within the complex, and mineralogic, petrographic, modal, and chemical variations are broadly systematic within the facies sequence. Study of these variations shows that the gradational facies of zones l and 2 systematically shift toward more mafic compositions inward within the complex. Seriate-textured rocks of zone 3 are similar in composition to those of zone 2, but porphyritic rocks of zone 3 and rocks of zone 4 mark shifts to more felsic compositions. These late-crystallizing felsic rocks are products of an interior residual magma system. This system was enriched in water and certain trace elements including tin, lithium, niobium, lead, and zinc. The complex as a whole has higher concentrations of these elements than many other granites. The nature of this geochemical specialization is particularly well demonstrated by the trace-element composition of biotite. The crystallization history of the pluton was complex. The available data suggest that this history could have included: (1) chilling and metasomatic alteration adjacent to the contact, (2) in-situ crystallization in several marginal facies accompanied by some transfer of residual constituents toward interior parts of the pluton, (3) slight upward displacement of magma that was subjacent to the crystallized walls, accompanied by disequilibrium crystallization and local vapor saturation, (4) upward displacement of part of the residual water-rich interior magma, accompanied by rapid loss of a separated vapor phase, and (5) displacement of the margins of the pluton by normal faults, accompanied by loss of an exsolved vapor phase from th

Fluorine, fluorite, and fluorspar in central Colorado

USGS Publications Warehouse

Wallace, Alan R.

2010-01-01

Fluorine (F) is a widespread element that was deposited in a variety of rocks, minerals, and geologic environments in central Colorado. It occurs as a trace element, as a major component of the mineral fluorite (CaFs), and as a major economic source of fluorine in fluorspar deposits, which are massive concentrations of fluorite. This study has compiled available geochemical analyses of rocks, both unmineralized and mineralized, to determine the distribution of fluorine in specific age-lithologic categories, ranging from 1.8-giga-annum (Ga) metamorphic rocks to modern soils, throughout central Colorado. It also draws upon field studies of fluorine-rich mineral deposits, including fluorspar deposits, to decipher the nearly two-billion-year-long geologic history of fluorine in the study area, with implications for mineral-resource evaluations and exploration. The resulting compilation provides an important inventory of the naturally occurring levels and sources of fluorine that ultimately weather, erode, and become part of surface waters that are used for domestic water supplies in densely populated areas along the Colorado Front Range. Most commonly, fluorine is a trace element in virtually all rocks in the region. In the 3,798 unmineralized rocks that were analyzed for fluorine in the study area, the average fluorine content was 1,550 parts per million (ppm). The median was 640 ppm, nearly identical to the average crustal abundance of 650 ppm, and some high-fluorine rocks in the Pikes Peak area skewed the average to a value much greater than the median. Most unmineralized age-lithologic rock suites, including Proterozoic metamorphic rocks, 1.7- and 1.4-Ga granitic batholiths, Cambrian igneous rocks, Phanerozoic sedimentary rocks, and Laramide and Tertiary igneous rocks, had median fluorine values of 400 to 740 ppm fluorine. In all suites, however, a small number of analyzed samples contained more than 1 percent (10,000 ppm) fluorine. The 1.1-Ga plutonic rocks related to the Pikes Peak batholith had a mean fluorine content of 1,700 ppm, and primary magmatic fluorite and fluorite-bearing pegmatites are common throughout that igneous mass. Fluorine was deposited in many types of economic mineral deposits in central Colorado, and it currently is a significant trace element in some thermal springs. In the fluorspar deposits, fluorine contents were as high as 37 percent. Some fluorine-rich porphyry systems, such as Jamestown, had fluorine values that ranged from 200 ppm to nearly 37 percent fluorine, and veins in other deposits contained hydrothermal fluorite, although it was not ubiquitous. For the 495 samples from non-fluorspar mining districts (and excluding Jamestown), however, the median fluorine content was 990 ppm. This is above the crustal average but still relatively modest compared to the fluorspar deposits, and it indicates that the majority of the mineralizing systems in central Colorado did not deposit large amounts of fluorine. Nevertheless, the fluorine- and fluorite-rich mineral deposits could be used as guides for the evaluation and discovery of related but concealed porphyry and epithermal base- and precious-metal deposits. The Cenozoic geologic history of central Colorado included multiple periods during which fluorine-bearing rocks and mineral deposits were exposed, weathered, and eroded. This protracted history has released fluorine into soils and regoliths, and modern rainfall and snowmelt interact with these substrates to add fluorine to the hydrosphere. This study did not evaluate the fluorine contents of water or make any predictions about what areas might be major sources for dissolved fluorine. However, the abundant data that are available on fluorine in surface water and ground water can be coupled with the results of this study to provide additional insight into natural sources of fluorine in domestic drinking water.

Genesis of the central zone of the Nolans Bore rare earth element deposit, Northern Territory, Australia

NASA Astrophysics Data System (ADS)

Schoneveld, Louise; Spandler, Carl; Hussey, Kelvin

2015-08-01

The Nolans Bore rare earth element (REE) deposit consists of a network of fluorapatite-bearing veins and breccias hosted within Proterozoic granulites of the Reynolds Range, Central Australia. Mineralisation is divided into three zones (north, central, and south-east), with the north and south-east zones consisting of massive REE-bearing fluorapatite veins, with minor brecciation and carbonate infill. The central zone is distinctively different in mineralogy and structure; it features extensive brecciation, a high allanite content, and a large, epidote-rich enveloping alteration zone. The central zone is a reworking of the original solid apatite veins that formed during the Chewings Orogeny at ca. 1525 Ma. These original apatite veins are thought to derive from phosphate-rich magmatic-hydrothermal fluid exsolved from as-yet unrecognised alkaline magmatic bodies at depth. We define four ore breccia types (BX1-4) in the central zone on the basis of detailed petrological and geochemical analysis of drillcore and thin sections. BX1 ore comprises fluorapatite with minor crackle brecciation with carbonate infill and resembles ore of the north and south-east zones. Breccia types BX2, BX3, and BX4 represent progressive stages of ore brecciation and development of calc-silicate mineral (amphibole, epidote, allanite, calcite) infill. Comparison of bulk ore sample geochemistry between breccia types indicates that REEs were not mobilised more than a few centimetres during hydrothermal alteration and brecciation. Instead, most of the REEs were partitioned from the original REE fluorapatite into newly formed allanite, REE-poor fluorapatite and minor REE carbonate in the breccias. Negative europium (Eu) anomalies in the breccia minerals are accounted for by a large positive Eu anomaly in epidote from the alteration zones surrounding the ore breccias. This observation provides a direct link between ore recrystallisation and brecciation, and the formation of the alteration halo in the surrounding host rocks. Where allanite and fluorapatite are texturally related, the fluorapatite is relatively depleted in the light rare earth elements (LREEs), whereas allanite is relatively LREE enriched, suggesting co-crystallisation. We tentatively date the BX1 ore stage to 1440 ± 80 Ma based on U-Pb dating of thorianite. Sm-Nd isotope isochrons derived from in situ isotope analysis of cognate apatite and allanite date the BX2 and BX3 events to ca. 400 Ma, while U-Pb dating of late-stage monazite from the BX4 ore stage returned an age of ca. 350 Ma. Therefore, formation of the central zone at Nolans Bore involved multiple alteration/brecciation events that collectively span over 1 billion years in duration. We suggest that the BX1-type veins and breccias were formed from REE-rich, saline (F- and Cl-bearing) fluids that infiltrated the granulite-grade host rocks in association with either shear activation events of the Redbank Shear Zone (1500-1400 Ma) or intrusion of late-stage pegmatites of the Mt Boothby area. BX2, BX3, and BX4 events record deformation and hydrothermal alteration associated with the Alice Springs Orogeny (400-350 Ma). These hydrothermal events occurred at temperatures of 450 to ~600 °C, due to inflow of highly acidic hydrous fluids derived from a magmatic source, or from mixing of meteoric and metamorphic fluids. Our data testify to the long and complex geological history of not only the Nolans Bore REE deposit, but also of the rocks of the eastern Reynolds Range, and demonstrate the great utility of using hydrothermally derived REE minerals to trace the timing of crustal deformation events and source of associated hydrothermal fluids.

Borehole-geophysical investigation of the University of Connecticut landfill, Storrs, Connecticut

USGS Publications Warehouse

Johnson, Carole D.; Haeni, F.P.; Lane, John W.; White, Eric A.

2002-01-01

A borehole-geophysical investigation was conducted to help characterize the hydrogeology of the fractured-rock aquifer and the distribution of unconsolidated glacial deposits near the former landfill and chemical waste-disposal pits at the University of Connecticut in Storrs, Connecticut. Eight bedrock boreholes near the landfill and three abandoned domestic wells located nearby were logged using conventional and advanced borehole-geophysical methods from June to October 1999. The conventional geophysical-logging methods included caliper, gamma, fluid temperature, fluid resistivity, and electromagnetic induction. The advanced methods included deviation, optical and acoustic imaging of the borehole wall, heat-pulse flowmeter, and directional radar reflection. Twenty-one shallow piezometers (less than 50-feet deep) were logged with gamma and electromagnetic induction tools to delineate unconsolidated glacial deposits. Five additional shallow bedrock wells were logged with conventional video camera, caliper, electromagnetic induction, and fluid resistivity and temperature tools. The rock type, foliation, and fracturing of the site were characterized from high-resolution optical-televiewer (OTV) images of rocks penetrated by the boreholes. The rocks are interpreted as fine- to medium-grained quartz-feldspar-biotite-garnet gneiss and schist with local intrusions of quartz diorite and pegmatite and minor concentrations of sulfide mineralization similar to rocks described as the Bigelow Brook Formation on regional geologic maps. Layers containing high concentrations of sulfide minerals appear as high electrical conductivity zones on electromagnetic-induction and borehole-radar logs. Foliation in the rocks generally strikes to the northeast-southwest and dips to the west, consistent with local outcrop observations. The orientation of foliation and small-scale gneissic layering in the rocks, however, varies locally and with depth in some of the boreholes. In two of the boreholes, the foliation strikes predominantly to the northwest and dips to the northeast. Although small-scale faults and lithologic discontinuities were observed in the OTV data, no large-scale faults were observed that appear on regional geologic maps. Fractures were located and characterized through the use of conventional geophysical, OTV, acoustic-televiewer (ATV), and borehole-radar logs. The orientation of fractures varies considerably across the site; some fractures are parallel to the foliation, whereas others cross-cut the foliation. Many of the transmissive fractures in the bedrock boreholes strike about N170?E and N320?E with dips of less than 45?. Other transmissive fractures strike about N60?E with dips of more than 60?. Most of the transmissive fractures in the domestic wells strike about N60?E and N22?E with dips of more than 45?. The strike of N60?E is parallel to the trend of a thrust fault that appears on regional geologic maps. Vertical flow in the boreholes was measured with the heat-pulse flowmeter under ambient and (or) pumping conditions. Results of ATV, OTV, and conventional logs were used to locate specific zones for flowmeter testing. Ambient downflow was measured in three boreholes, ambient upflow was measured in two other boreholes, and both ambient downflow and upflow were measured in a sixth borehole. The other five bedrock boreholes and domestic wells did not have measurable vertical flow. The highest rate of ambient flow was measured in the background borehole in which upflow and downflow converged and exited the borehole at a fracture zone near a depth of 62 feet. Ambient flow of about 340 gallons per day was measured. In the other five wells, ambient flow of about 20 to 35 gallons per day was measured. Under low-rate pumping (0.25 to 1 gallon per minute), one to six inflow zones were identified in each well. Usually the fractures that are active under ambient conditions contribute to the well under pumping conditions. To prevent

Petrogenesis of Oxidized Arfvedsonite Granite Gneiss from Dimra Pahar, Hazaribagh, Eastern India: Constraints from Mineral Chemistry and Trace Element Geochemistry

NASA Astrophysics Data System (ADS)

Basak, Ankita; Goswami, Bapi

2017-04-01

The arfvedsonite granite gneiss of Dimra Pahar occurs along the North Purulia Shear Zone (NPSZ) which pivots the Proterozoic Chotannagpur Gneissic Complex (CGC), Eastern India. Although minerals like arfvedsonite and aegirine depict the peralkaline nature of the pluton, the geochemistry of the rock reflects its composition varying from peralkaline to mildly peraluminous. K-feldspar, quartz, arfvedsonite, albite with accessory aegirine, titaniferous iron oxides and zircon form the dominant mineralogy of this alkali feldspar granite (IUGS, 2000) gneiss. The zircon saturation temperature corresponds to 747oC-1066oC. The granitic magma contains low water content evidenced by the absence of any pegmatite associated with this pluton. Geochemically these granites are classified as ferroan and alkalic (cf. Frost et al., 2001). These highly evolved granites possess enrichment of SiO2, Na2O + K2O, FeO(t)/MgO, Ga/Al, Zr, Nb, Ga, Y, Ce and rare earth elements (REE) with low abundance of CaO, MgO, Ba and Sr which characterize their A-type nature while standard discrimination diagrams ( cf. Eby, 1992; Grebennikov, 2014) help to further discriminate them as A1 type. Tectonic discriminations diagrams (Pearce et al., 1984; Maniar and Piccoli, 1989; Batchelor and Bowden, 1985) constrain the tectonic setting of the magma to be anorogenic, within plate, rift-related one. The REE compositions show moderately fractionated patterns with (La/Yb)N 2.57-10.5 and Eu/Eu* 0.16-0.70. Multielement spider diagram and various trace element ratio together with oxidized nature (ΔNNO: +2) of these granites further suggest that these have been derived from OIB-type parental magma. The peralkaline nature of the granite and its lack of subduction- related geochemical features are consistent with an origin in a zone of regional extension. The extremely high Rb/Sr ratios combined with the extreme Sr, Ba, P, Ti and Eu depletions clearly indicate that these A-type granites were highly evolved and require advanced fractional crystallization in upper crustal conditions. Major element mass-balance models that use observed phases are consistent with an origin by fractional crystallization from a basaltic parent. The high Sr, Eu and Ba anomalies strongly suggest plagioclase and alkali feldspar fractionation. The abundance of Nb relative to Y reflects pyroxene and amphibole fractionation during differentiation process. EPMA studies of arfvedsonite, aegirine, k-feldspar and albite reveal the pure end-member composition of all the minerals which in turn reflects metamorphism has superimposed on the pluton. The elongated nature of the pluton, metamorphism together with the shear- related deformation as evidenced from the petrographic studies of the rocks suggest syn-tectonic emplacement of the pluton in relation to the kinematics of the North Purulia Shear Zone during 1000Ma (Goswami and Bhattacharyya, 2014). Derivation from basaltic parental magmas indicates that the Dimrapahar pluton represents addition of juvenile material to the crust. References Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J. and Frost, C.D., (2001): A geochemical classification for granitic rocks. Journal of petrology, 42(11):2033-2048. Eby, G.N (1992): Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology, 20(7): 641-644. Le Bas, M. J. (2000). IUGS reclassification of the high-Mg and picritic volcanic rocks. Journal of Petrology, 41(10): 1467-1470. Grebennikov, A. V. (2014): A-type granites and related rocks: petrogenesis and classification. Russian Geology and Geophysics, 55.(11): 1353-1366. Pearce, J.A., Harris, N.B. and Tindle, A.G. (1984): Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of petrology, 25(4): 956-983. Maniar, P.D. and Piccoli, P.M. (1989): Tectonic discrimination of granitoids. Geological society of America bulletin, 101(5): 635-643. Batchelor, R.A. and Bowden, P. (1985): Petrogenetic interpretation of granitoid rock series using multicationic parameters. Chemical geology, 48(1-4): 43-55. Goswami, B. and Bhattacharyya, C. (2014): Petrogenesis of shoshonitic granitoids, eastern India: implications for the late Grenvillian post-collisional magmatism. Geoscience Frontiers, 5(6): 821-843.

Evidence of Nb-Ta mobility in high temperature F-rich fluids evidenced by the La Bosse quartz-Nb-ferberite stockwork (Echassières, French Massif Central).

NASA Astrophysics Data System (ADS)

Marignac, C.; Cuney, M.

2012-04-01

In the Echassières district (northern French Massif Central), the 310 Ma Beauvoir granite (a P-rich peraluminous RMG) overprints a quartz-ferberite stockwork. The 900 m-deep GPF1 scientific hole shows that the stockwork is split into two parts by the gently dipping Beauvoir intrusion: the upper section (~ 100m thick) occurs in the La Bosse quarry, , and the lower section (≥ 60 m thick) below the granite floor. The root of the stockwork (hypothetic La Bosse granite) has not been reached. The stockwork comprises flat-lying quartz veins (≤ 0.6 m thick) concordant to the regional schistosity of surrounding micaschists, and steep N10-N50°E quartz veins (≤ 0.2 m thick). The two sets result from hydraulic fracturing, and consistently display crack seal features. A family of aplites and aplo-pegmatites dikes follow the same set of fractures, being either later (with partial dissolution of pre-existing quartz veins) or earlier, than the quartz veins. There is no alteration, nor associated mineral other than ferberite, at the La Bosse quarry, whereas micaceous selvages are observed in the lower section. Ferberite display a trend of ferberite enrichment with increasing depth (0.71 to 0.95 Fb mole%). In the La Bosse quarry, three ferberite habitus are present: acicular, lanceolate and prismatic. Acicular crystals are typically nicely zoned, with alternating Nb-rich (4.95±0.94 % Nb2O5) and Nb-poor (1.57±0.38 % Nb2O5) growth bands. Ta (up to 0.30 Ta2O5), Ti and Sn are also enriched in the Nb-rich bands. Nb and Ta incorporation into the ferberite is in the form of columbite, as either true solid solution or nanoinclusions. Lanceolate crystals have a similarly zoned acicular core and a Nb-poor rim (1.08±0.66 % Nb2O5). Prismatic crystals are unzoned and Nb-poor (0.67±0.20 % Nb2O5). In the lower part of the stockwork, the Nb contents are lower (2.17 % Nb2O5 in the Nb-rich bands, 1.36 % in the Nb-poor bands, 0.08 % in the unzoned cortex, 0.15 % in the unzoned prisms). Thus the unusual Nb content of the La Bosse ferberites is correlated to the apparently very distal setting of this quartz system relatively to the parent granite, in contrast with most quartz-W systems in the French Massif Central (Aïssa et al. 1987). When invaded by aplites or aplopegmatites, the ferberite-bearing quartz veins are dissolved, but the ferberites remain apparently unaffected - they are not dissolved by the granite melt. Yet, the acicular and lanceolate crystals have lost their Nb-zoning and display uniform homogenised Nb content. The emplacement of the Beauvoir granite was associated with late magmatic exsolution of an Al- and F-rich, silica undersaturated, hydrothermal fluid that percolated upwards in the surrounding schists (Cuney et al. 1992). When interacting with the quartz veins of the La Bosse stockwork, this fluid precipitated topazites. Again, included ferberites remain apparently unaffected. However, they display microscopic vuggy cavities, successively filled by a Nb-rich ferberite (up to 8.91% Nb2O5) with significant Ta content (up to 0.35 % Ta2O5), a wolframo-ixiolite and a Ta-rich columbite. Later Li-phengite was precipitated from the same magmatic fluid, and was associated with hubnerite enrichment of pre-existing ferberites along Li-phengite-bearing microcracks (down to 0.20 mole % Fb). Ta and Nb are known for their poor solubility in hydrothermal fluids, but the Nb and Ta enrichments observed in the wolframite of La Bosse stockwork show that they can be transported to some extent by F-rich fluids. Aïssa, M., Marignac, C., Weisbrod, A. (1987). Le stockwerk à ferbérite d'Echassières : évolution spatiale et temporelle; cristallochimie des ferbérites. In : Cuney, M., Autran, A. (eds), Echassières : le forage scientifique d'Echassières (Allier). Une clé pour la compréhension des mécanismes magmatiques et hydrothermaux associés aux granites à métaux rares. Mém. GPF, tome 1, 311-334. M Cuney, C Marignac, A Weisbrod (1992). The Beauvoir topaz-lepidolite albitic granite (Massif Central, France). A highly specialized granite with disseminated Sn-Li-Ta-Nb-Be mineralization of magmatic origin. Economic Geology 87, 1776-1794.

Strategic graphite, a survey

USGS Publications Warehouse

Cameron, Eugene N.; Weis, Paul L.

1960-01-01

Strategic graphite consists of certain grades of lump and flake graphite for which the United States is largely or entirely dependent on sources abroad. Lump graphite of high purity, necessary in the manufacture of carbon brushes, is imported from Ceylon, where it occurs in vein deposits. Flake graphite, obtained from deposits consisting of graphite disseminated in schists and other metamorphic rocks, is an essential ingredient of crucibles used in the nonferrous metal industries and in the manufacture of lubricants and packings. High-quality flake graphite for these uses has been obtained mostly from Madagascar since World War I. Some flake graphite of strategic grade has been produced, however, from deposits in Texas, Alabama, and Pennsylvania. The development of the carbon-bonded crucible, which does not require coarse flake, should lessen the competitive advantage of the Madagascar producers of crucible flake. Graphite of various grades has been produced intermittently in the United States since 1644. The principal domestic deposits of flake graphite are in Texas, Alabama, Pennsylvania, and New York. Reserves of flake graphite in these four States are very large, but production has been sporadic and on the whole unprofitable since World War I, owing principally to competition from producers in Madagascar. Deposits in Madagascar are large and relatively high in content of flake graphite. Production costs are low and the flake produced is of high quality. Coarseness of flake and uniformity of the graphite products marketed are cited as major advantages of Madagascar flake. In addition, the usability of Madagascar flake for various purposes has been thoroughly demonstrated, whereas the usability of domestic flake for strategic purposes is still in question. Domestic graphite deposits are of five kinds: deposits consisting of graphite disseminated in metamorphosed siliceous sediments, deposits consisting of graphite disseminated in marble, deposits formed by thermal or dynamothermal metamorphism of coal beds or other highly carbonaceous sediments, vein deposits, and contact metasomatic deposits in marble. Only the first kind comprises deposits sufficiently large and rich in flake graphite to be significant potential sources of strategic grades of graphite. Vein deposits in several localities are known, but none is known to contain substantial reserves of graphite of strategic quality.Large resources of flake graphite exist in central Texas, in northeastern Alabama, in eastern Pennsylvania, and in the eastern Adirondack Mountains of New York. Tonnages available, compared with the tonnages of flake graphite consumed annually in the United States, are very large. There have been indications that flake graphite from Texas, Alabama, and Pennsylvania can be used in clay-graphite crucibles as a substitute for Madagascar flake, and one producer has made progress in establishing markets for his flake products as ingredients of lubricants. The tonnages of various commercial grades of graphite recoverable from various domestic deposits, however, have not been established; hence, the adequacy of domestic resources of graphite in a time of emergency is not known.The only vein deposits from which significant quantities of lump graphite have been produced are those of the Crystal Graphite mine, Beaverhead County, Mont. The deposits are fracture fillings in Precambrian gneiss and pegmatite. Known reserves in the deposits are small. In Texas, numerous flake-graphite deposits occur in the Precambrian Packsaddle schist in Llano and Burnet Counties. Graphite disseminated in certain parts of this formation ranges from extremely fine to medium grained. The principal producer has been the mine of the Southwestern Graphite Co., west of the town of Burnet. Substantial reserves of medium-grained graphite are present in the deposit mined by the company. In northeastern Alabama, flake-graphite deposits occur in the Ashland mica schist in two belts that trend northeastward across Clay, Goosa, and Chilton Counties. The northeastern belt has been the most productive. About 40 mines have been operated at one time or another, but only a few have been active during or since World War I. The deposits consist of flake graphite disseminated in certain zones or "leads" consisting of quartz-mica-feldspar schists and mica quartzite. Most of past production has come from the weathered upper parts of the deposits, but unweathered rock has been mined at several localities. Reserves of weathered rock containing 3 to 5 percent graphite are very large, and reserves of unweathered rock are even greater. Flake graphite deposits in Chester County, Pa., have been worked intermittently since about 1890. The deposits consist of medium- to coarse-grained graphite disseminated in certain belts of the Pickering gneiss. The most promising deposit is one worked in the Benjamin Franklin and the Eynon Just mines. Reserves of weathered rock containing 1.5 percent graphite are of moderate size; reserves of unweathered rock are large. In the eastern Adirondack Mountains in New York there are two principal kinds of flake-graphite deposits: contact-metasomatic deposits and those consisting of flake graphite disseminated in quartz schist. The contact-metasomatic deposits are small, irregular, and very erratic in graphite content. The deposits in quartz schist are very large, persistent, and uniform in grade. There are large reserves of schist containing 3 to 5 percent graphite, but the graphite is relatively fine grained.

Tin

USGS Publications Warehouse

Kamilli, Robert J.; Kimball, Bryn E.; Carlin, James F.; Schulz, Klaus J.; DeYoung,, John H.; Seal, Robert R.; Bradley, Dwight C.

2017-12-19

Tin (Sn) is one of the first metals to be used by humans. Almost without exception, tin is used as an alloy. Because of its hardening effect on copper, tin was used in bronze implements as early as 3500 B.C. The major uses of tin today are for cans and containers, construction materials, transportation materials, and solder. The predominant ore mineral of tin, by far, is cassiterite (SnO2).In 2015, the world’s total estimated mine production of tin was 289,000 metric tons of contained tin. Total world reserves at the end of 2016 were estimated to be 4,700,000 metric tons. China held about 24 percent of the world’s tin reserves and accounted for 38 percent of the world’s 2015 production of tin.The proportion of scrap used in tin production is between 10 and 25 percent. Unlike many metals, tin recycling is relatively efficient, and the fraction of tin in discarded products that get recycled is greater than 50 percent.Only about 20 percent of the world’s identified tin resources occur as primary hydrothermal hard-rock veins, or lodes. These lodes contain predominantly high-temperature minerals and almost invariably occur in close association with silicic, peraluminous granites. About 80 percent of the world’s identified tin resources occur as unconsolidated secondary or placer deposits in riverbeds and valleys or on the sea floor. The largest concentration of both onshore and offshore placers is in the extensive tin belt of Southeast Asia, which stretches from China in the north, through Thailand, Burma (also referred to as Myanmar), and Malaysia, to the islands of Indonesia in the south. Furthermore, tin placers are almost always found closely allied to the granites from which they originate. Other countries with significant tin resources are Australia, Bolivia, and Brazil.Most hydrothermal tin deposits belong to what can be thought of as a superclass of porphyry-greisen deposits. The hydrothermal tin deposits are all characterized by a close spatial, temporal, and genetic association with highly differentiated, peraluminous porphyritic granite intrusions. The intrusions form pegmatites; disseminated ore; parallel or subparallel, greisen-bordered sheeted veins that either cross-cut the intrusion or are peripheral to it; skarns; and (or) limestone replacements that contain different amounts of cassiterite, molybdenite, and wolframite.The tectonic settings of tin-bearing granites are relatively well understood and of limited variety. Tin and tungsten deposits and their associated igneous rocks are found mainly in continental settings.Historically, prospecting for tin has been carried out by the time-honored methods of panning, drilling, trenching, and assaying. Geophysical and geochemical surveys have been employed to cover large areas more rapidly, isolating areas of possible tin deposits so that drilling can be more effective and less costly. Elemental concentrations and relationships of the lithophile elements, especially barium, lithium, niobium, potassium, rubidium, and zirconium, are the most reliable chemical indicators of ore-forming processes and tin-bearing potential.The average human diet includes an intake of about 10 milligrams per day of tin. Ingestion of tin in significantly greater amounts than 10 milligrams per day may lead to a stomach ache, anemia, and liver and kidney problems. Exposure to some organo-tin compounds can interfere with brain and nervous system function and, in severe cases, can cause death. Extended inhalation of tin oxide—an issue mainly for those people who work in the tin industry—results in a higher potential to develop stannosis, which is a mild disease of the lungs caused by the inhalation of tin-bearing dust. Inorganic tin is poorly absorbed by the body, and no evidence exists for the carcinogenicity of metallic tin and tin compounds in humans.Most placer tin deposits are mined by open pit and (or) dredging methods. Mining of alluvial placers in modern streambeds and riverbeds is likely to increase the amount of sediment delivered downstream. This, combined with potential diversion of rivers and streams, may negatively affect downstream ecosystems. Many of the placer deposits located in Burma, Indonesia, Malaysia, and Thailand are located offshore. Most offshore placer tin deposits are mined by dredging methods, which have the potential to negatively affect benthic, midwater, and pelagic ecosystems.In a congressionally mandated U.S. Department of Defense study of strategic minerals published in 2013, tin has the greatest shortfall amount (insufficient supply to meet demand) at \\$416 million; this amount is more than twice that of antimony ($182 million), which is the strategic mineral with the next largest shortfall amount (U.S. Department of Defense, 2013). The United States imported 75 percent of its tin supply in 2015. During the period 2012–15, these imports were from, in descending order of amount imported, Peru, Indonesia, Malaysia, and Bolivia.A promising advancement concerning research into the origin of tin deposits is the recent development of a reliable method of analyzing tin isotopes in cassiterite. Although the mechanism of transport and deposition of tin is fairly well understood, the means by which tin is incorporated into the parent magma at the points of magma generation and ascent needs further investigation.Tin metallogenic provinces worldwide are well known. Consequently, any undiscovered tin deposits will likely be spatially close to known deposits or extensions of the same.