Znaczenie analizy minerałów ciężkich w badaniach osadów czwartorzędowych Polski

NASA Astrophysics Data System (ADS)

Racinowski, Roman

2008-01-01

In most regions of Poland the composition of heavy minerals assemblage permits to distinguish the Quaternary deposits from the older ones. The pre-Quaternary deposits are characterized by high content of glauconite, carbonate-ferruginous-manganese concretions, muscovite and chlorites. In their transparent heavy minerals spectrum the following minerals predominate: zircon, tourmaline, rutile, staurolite, disthene. However, the Tertiary deposits in the Carpathians and their foreland contain a significant amount of garnet, and sometimes also amphiboles, pyroxenes and biotite. Pyroxenes and sillimanite are found in the Sudetes foreland. In many Tertiary deposits of the northwestern and western Poland there are rather high contents of amphiboles, biotite, pyroxenes, garnets, rutile. In all Quaternary deposits in Poland the qualitative composition of heavy minerals assemblage is similar but the contents of particular minerals are different depending on the examined grain fraction. In tills (Table 1) and glaciofluvial deposits (Table 2), with the decreasing grain diameter the contents of zircon, rutile, and partly epidote increase, and those of amphiboles and garnets decrease. In rubble of coastal zone in the Polish Baltic Sea, with the decreasing grain diameter the contents of zircon, rutile and epidote increase, and those of amphibole, biotite and pyroxenes decrease (Tables 3-7). In Poland, glacial, glaciofluvial and glaciolacustrine deposits are characterized by quantitatively similar composition of heavy minerals assemblage. Amphiboles, biotite, epidotes, garnets and pyroxenes are typical transparent minerals (Tables 8 and 9). Young Pleistocene and Holocene sands of river terraces and dune fields in the upland zone of Poland differ from glacial deposits in low contents of amphiboles, biotite and pyroxenes, and higher contents of garnets and epidotes (Tables 8 and 9). Fossil river and lacustrine deposits of Polish Lowlands have very similar assemblage of heavy minerals to that found in glacial deposits. Both glacial and glaciofluvial deposits have similar composition of heavy minerals assemblage irrespective of their age (Tables 10, 11 and 12). This principle concerns also loesses (Table 13a, b) but the youngest ones are characterized by higher contents of amphiboles and epidotes. The composition of heavy minerals assemblage is useful for determining the source of material forming the Quaternary deposits. In the case of glacial deposits, the enrichment in glauconite, chlorites, and even zircon, rutile, tourmaline, staurolite indicates that material from local older substratum was supplied to the Quaternary deposits. Heavy minerals spectrum of non-glacial deposits can directly indicate the source material that formed a deposit. Conversely, it is difficult to draw the conclusions about fossil and modern weathering-soil horizons in loesses from the composition of heavy minerals assemblage (Tables 14 and 15). The results of heavy minerals analysis are useful for lithodynamic and lithofacial interpretation of flowing water environments, e.g. river (Table 16), glaciofluvial (Table 17) and sea coastal (Table 18).

Geothermobarometry for ultramafic assemblages from the Emeishan Large Igneous Province, Southwest China and the Nikos and Zulu Kimberlites, Nunavut, Canada

NASA Astrophysics Data System (ADS)

Zhao, D.

2009-05-01

To understand and contrast the origins of ultramafic assemblages from basaltic and kimberlitic rocks and their associated deposits, such as V-Ti magnetite and Ni-Cu-(PGE) sulfide deposits and diamond, applicable thermobarometers were evaluated and applied to the ultramafic assemblages from the Emeishan Large Igneous Province (ELIP), Southwest China and from the Nikos and Zulu Kimberlites of Nunavut, Canada. The ELIP is located in the Yangtze Block, Southwest China and composed of Permian Emeishan Flood basalt (EFB) and associated layered mafic-ultramafic intrusions. Some of these intrusions host V-Ti magnetite deposits; while others contain Ni-Cu-(PGE) sulfide deposits. It is not clear why some intrusions host magnetite deposits and others contain sulfide deposits. The P-T conditions for the ultramafic assemblages from the mafic-ultramafic intrusions in the ELIP were calculated in order to understand the origins and the associated mineral deposits. The ultramafic assemblages are peridotite, olivine pyroxenite, pyroxenite in the layered intrusions and the common minerals include spinel, olivine, clinopyroxene, orthopyroxene, and minor magnetite and ilmenite. Using a two pyroxene thermometer and a Ca-Mg exchange barometer between olivine and clinopyroxene, a spinel-olivine-clinopyroxene-orthopyroxene assemblage from the Xinjie intrusion yields a T-P of 905°C and 17 kbar; and a similar assemblage from the Jinbaoshan intrusion yields a T-P of 1124°C and 31 kbar. The Nikos kimberlite, near Elwin Bay on Somerset Island, is located at the northeast end of the northeast-southwest kimberlite zone; and the Zulu kimberlite is located on the neighboring Brodeur Peninsula of Baffin Island, Nunavut. The ultramafic assemblages from the Canadian Kimberlites include garnet lherzolite, garnet-spinel lherzolite, spinel lherzolite, dunite, garnet websterite, spinel websterite and garnet clinopyroxenite. The calculated P-T conditions are in the range of 760 to 1180°C and 25 to 60 kbar, follow a continental geotherm, and overlap the stability field of diamond. The ultramafic assemblages from the ELIP, Southwest China and from the Canadian Kimberlites were sampled from different depths in the lithosphere.

Chemistry of the surface and lower atmosphere of Venus

NASA Technical Reports Server (NTRS)

Fegley, B., Jr.; Treiman, A.

1992-01-01

A comprehensive overview of the chemical interactions between the atmosphere and surface of Venus is presented. Earth-based, earth-orbital, and spacecraft data on the composition of the atmosphere and surface of Venus are presented and applied to quantitative evaluations of the chemical interactions between carbon, hydrogen, sulfur, chlorine, fluorine, and nitrogen-containing gases and possible minerals on the Venus surface. The calculation results are used to predict stable minerals and mineral assemblages on the Venus surface to determine which, if any, atmospheric gases are buffered by mineral assemblages on the surface, and to critically review and assess prior work on atmosphere-surface chemistry on Venus. It is concluded that the CO2 pressure on Venus is comparable to the CO2 equilibrium partial pressure developed by the calcite + wollastonite + quartz assemblage at the mean Venus surface temperature of 740 K.

Brucite-driven CO2 uptake in serpentinized dunites (Ligurian Ophiolites, Montecastelli, Tuscany)

NASA Astrophysics Data System (ADS)

Boschi, Chiara; Dini, Andrea; Baneschi, Ilaria; Bedini, Federica; Perchiazzi, Natale; Cavallo, Andrea

2017-09-01

Understanding the mechanism of serpentinite weathering at low temperature - that involves carbonate formation - has become increasingly important because it represents an analog study for a cost-efficient carbon disposal strategy (i.e. carbon mineralization technology or mineral Carbon dioxide Capture and Storage, CCS). At Montecastelli (Tuscany, Italy), on-going spontaneous mineral CO2 sequestration is enhanced by brucite-rich serpentinized dunites. The dunites are embedded in brucite-free serpentinized harzburgites that belong to the ophiolitic Ligurian Units (Northern Apennine thrust-fold belt). Two main serpentinization events produced two distinct mineral assemblages in the reactive dunite bodies. The first assemblage consists of low-T pseudomorphic, mesh-textured serpentine, Fe-rich brucite (up to 20 mol.% Fe(OH)2) and minor magnetite. This was overprinted by a non-pseudomorphic, relatively high-T assemblage consisting of serpentine, Fe-poor brucite (ca. 4 mol% Fe(OH)2) and abundant magnetite. The harzburgite host rock developed a brucite-free paragenesis made of serpentine and magnetite. Present-day interaction of serpentinized dunites with slightly acidic and oxidizing meteoric water, enhances brucite dissolution and leads to precipitation of both Mg-Fe layered double hydroxides (coalingite-pyroaurite, LDHs) and hydrous Mg carbonates (hydromagnesite and nesquehonite). In contrast, the brucite-free serpentinized harzburgites are not affected by the carbonation process. In the serpentinized dunites, different carbonate minerals form depending on brucite composition (Fe-rich vs Fe-poor). Reactions in serpentinized dunites containing Fe-rich brucite produce a carbonate assemblage dominated by LDHs and minor amount of hydromagnesite. Serpentinites with a Fe-poor brucite assemblage contain large amounts of hydromagnesite and minor LDHs. Efficiency of CO2 mineral sequestration is different in the two cases owing to the distinct carbon content of LDHs (ca. 1.5 wt.%) and hydromagnesite (ca. 10 wt.%). Here, for the first time, we link the mineral composition of serpentinized ultramafic rocks to carbonate formation, concluding that Fe-poor brucite maximizes the mineral CCS efficiency.

Alteration minerals in impact-generated hydrothermal systems - Exploring host rock variability

NASA Astrophysics Data System (ADS)

Schwenzer, Susanne P.; Kring, David A.

2013-09-01

Impact-generated hydrothermal systems have been previously linked to the alteration of Mars’ crust and the production of secondary mineral assemblages seen from orbit. The sensitivity of the resultant assemblages has not yet been evaluated as a function of precursor primary rock compositions. In this work, we use thermochemical modeling to explore the variety of minerals that could be produced by altering several known lithologies based on martian meteorite compositions. For a basaltic host rock lithology (Dhofar 378, Humphrey) the main alteration phases are feldspar, zeolite, pyroxene, chlorite, clay (nontronite, kaolinite), and hematite; for a lherzolithic host rock lithology (LEW 88516) the main alteration phases are amphibole, serpentine, chlorite, clay (nontronite, kaolinite), and hematite; and for an ultramafic host rock lithology (Chassigny) the main minerals are secondary olivine, serpentine, magnetite, quartz, and hematite. These assemblages and proportions of phases in each of those cases depend on W/R and temperature. Integrating geologic, hydrologic and alteration mineral evidence, we have developed a model to illustrate the distribution of alteration assemblages that occur in different levels of an impact structure. At the surface, hot, hydrous alteration affects the ejecta and melt sheet producing clay and chlorite. Deeper in the subsurface and depending on the permeability of the rock, a variety of minerals - smectite, chlorite, serpentine, amphiboles and hematite - are produced in a circulating hydrothermal system. These modeled mineral distributions should assist with interpretation of orbital observations and help guide surface exploration by rovers and sample return assets.

Diagenesis and clay mineral formation at Gale Crater, Mars

PubMed Central

Bridges, J C; Schwenzer, S P; Leveille, R; Westall, F; Wiens, R C; Mangold, N; Bristow, T; Edwards, P; Berger, G

2015-01-01

The Mars Science Laboratory rover Curiosity found host rocks of basaltic composition and alteration assemblages containing clay minerals at Yellowknife Bay, Gale Crater. On the basis of the observed host rock and alteration minerals, we present results of equilibrium thermochemical modeling of the Sheepbed mudstones of Yellowknife Bay in order to constrain the formation conditions of its secondary mineral assemblage. Building on conclusions from sedimentary observations by the Mars Science Laboratory team, we assume diagenetic, in situ alteration. The modeling shows that the mineral assemblage formed by the reaction of a CO2-poor and oxidizing, dilute aqueous solution (Gale Portage Water) in an open system with the Fe-rich basaltic-composition sedimentary rocks at 10–50°C and water/rock ratio (mass of rock reacted with the starting fluid) of 100–1000, pH of ∽7.5–12. Model alteration assemblages predominantly contain phyllosilicates (Fe-smectite, chlorite), the bulk composition of a mixture of which is close to that of saponite inferred from Chemistry and Mineralogy data and to that of saponite observed in the nakhlite Martian meteorites and terrestrial analogues. To match the observed clay mineral chemistry, inhomogeneous dissolution dominated by the amorphous phase and olivine is required. We therefore deduce a dissolving composition of approximately 70% amorphous material, with 20% olivine, and 10% whole rock component. PMID:26213668

Diagenesis and clay mineral formation at Gale Crater, Mars

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

Bridges, J. C.; Schwenzer, S. P.; Leveille, R.

The Mars Science Laboratory rover Curiosity found host rocks of basaltic composition and alteration assemblages containing clay minerals at Yellowknife Bay, Gale Crater. On the basis of the observed host rock and alteration minerals, we present results of equilibrium thermochemical modeling of the Sheepbed mudstones of Yellowknife Bay in order to constrain the formation conditions of its secondary mineral assemblage. Building on conclusions from sedimentary observations by the Mars Science Laboratory team, we assume diagenetic, in situ alteration. The modeling shows that the mineral assemblage formed by the reaction of a CO₂-poor and oxidizing, dilute aqueous solution (Gale Portage Water)more » in an open system with the Fe-rich basaltic-composition sedimentary rocks at 10–50°C and water/rock ratio (mass of rock reacted with the starting fluid) of 100–1000, pH of ~7.5–12. Model alteration assemblages predominantly contain phyllosilicates (Fe-smectite, chlorite), the bulk composition of a mixture of which is close to that of saponite inferred from Chemistry and Mineralogy data and to that of saponite observed in the nakhlite Martian meteorites and terrestrial analogues. To match the observed clay mineral chemistry, inhomogeneous dissolution dominated by the amorphous phase and olivine is required. We therefore deduce a dissolving composition of approximately 70% amorphous material, with 20% olivine, and 10% whole rock component.« less

Diagenesis and clay mineral formation at Gale Crater, Mars

DOE PAGES

Bridges, J. C.; Schwenzer, S. P.; Leveille, R.; ...

2015-01-18

The Mars Science Laboratory rover Curiosity found host rocks of basaltic composition and alteration assemblages containing clay minerals at Yellowknife Bay, Gale Crater. On the basis of the observed host rock and alteration minerals, we present results of equilibrium thermochemical modeling of the Sheepbed mudstones of Yellowknife Bay in order to constrain the formation conditions of its secondary mineral assemblage. Building on conclusions from sedimentary observations by the Mars Science Laboratory team, we assume diagenetic, in situ alteration. The modeling shows that the mineral assemblage formed by the reaction of a CO₂-poor and oxidizing, dilute aqueous solution (Gale Portage Water)more » in an open system with the Fe-rich basaltic-composition sedimentary rocks at 10–50°C and water/rock ratio (mass of rock reacted with the starting fluid) of 100–1000, pH of ~7.5–12. Model alteration assemblages predominantly contain phyllosilicates (Fe-smectite, chlorite), the bulk composition of a mixture of which is close to that of saponite inferred from Chemistry and Mineralogy data and to that of saponite observed in the nakhlite Martian meteorites and terrestrial analogues. To match the observed clay mineral chemistry, inhomogeneous dissolution dominated by the amorphous phase and olivine is required. We therefore deduce a dissolving composition of approximately 70% amorphous material, with 20% olivine, and 10% whole rock component.« less

Factors influencing the composition of detrital heavy mineral suites in Holocene sands of the Apure River drainage basin, Venezuela

USGS Publications Warehouse

Morton, Andrew C.

1993-01-01

Heavy mineral assemblages in rivers in the Apure River drainage basin of Venezuela and Colombia closely reflect the nature of the source regions, which lie in the Andean orogenic terranes to the west and northwest. The Caribbean Mountains, largely composed of greenschist-facies pelites, phyllites, carbonates, and metavolcanics, supply assemblages dominated by epidote and calcic amphibole. Minor amounts of the high-pressure index minerals glaucophane and lawsonite indicate the presence of blueschistfacies rocks, reflecting the origin of the Caribbean Mountains by subduction-related tectonism. The northern Mérida Andes, which comprise basement gneisses and granites overlain by unmetamorphosed to low-grade metamorphosed clastics, supply two types of assemblage reflecting these two lithological types: garnet-sillimanite-staurolite-amphibole suites from the basement rocks, and epidote-amphibole suites from the overlying cover sequence. The southern Mérida Andes supply stable heavy mineral suites reflecting recycling from the extensive unmetamorphosed sandstones that occur at outcrop. By considering suites from different physiographical provinces, the effects of short-term alluvial storage in the Llanos on heavy mineral assemblages have been evaluated. Weathering during alluvial storage appears to be effective in modifying the apatite-tourmaline ratio, which shows a steady, marked decline with distance from the mountain front, resulting from the removal of apatite during weathering. Clinopyroxene and garnet may also show evidence of loss through weathering, although the trends are poorly constrained statistically. Epidote and amphibole proportions remain essentially constant, possibly through a balance between loss through weathering and continual resupply from the breakdown of rock fragments. In general, the heavy mineral assemblages are less affected than the bulk mineralogy by alluvial storage on the Llanos.

Copernicus crater central peak: lunar mountain of unique composition.

PubMed

Pieters, C M

1982-01-01

Olivine is identified as the major mafic mineral in a central peak of Copernicus crater. Information on the mineral assemblages of such unsampled lunar surface material is provided by near infrared reflectance spectra (0.7 to 2.5 micrometers) obtained with Earth-based telescopes. The composition of the deep-seated material comprising the Copernicus central peak is unique among measured areas. Other lunar terra areas and the wall of Copernicus exhibit spectral characteristics of mineral assemblages comparable to the feldspathic breccias returned by the Apollo missions, with low-calcium orthopyroxene being the major mafic mineral.

Copernicus crater central peak - Lunar mountain of unique composition

NASA Technical Reports Server (NTRS)

Pieters, C. M.

1982-01-01

Olivine is identified as the major mafic mineral in a central peak of Copernicus crater. Information on the mineral assemblages of such unsampled lunar surface material is provided by near infrared reflectance spectra (0.7 to 2.5 micrometers) obtained with earth-based telescopes. The composition of the deep-seated material comprising the Copernicus central peak is unique among measured areas. Other lunar terra areas and the wall of Copernicus exhibit spectral characteristics of mineral assemblages comparable to the feldspathic breccias returned by the Apollo missions, with low-calcium orthopyroxene being the major mafic mineral.

An evaluation and geochemical survey of the Farah Garan East Prospect, Southeast Asir, Kingdom of Saudi Arabia

USGS Publications Warehouse

Bookstrom, Arthur A.; El Komi, Mohamed; Christian, Ralph P.; Bazzari, Maher A.

1990-01-01

Ore minerals in outcrops, and geochemically anomalous concentrations of gold, silver, copper, lead, zinc, arsenic, antimony, and tellurium are present in carbonate-rich rocks of the hot-spring assemblage. This indicates that the ore minerals and elements were deposited originally as constituents of the hot-spring assemblage. However, exposed ore-mineral occurrences are small and sparse, and geochemical anomalies are small, irregularly distributed, and of subeconomic grade. Furthermore, weak electromagnetic anomalies do not indicate the presence of subsurface bodies of concentrated, conductive ore minerals. Therefore, no drilling is recommended.

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.

Mineralogy, mineral chemistry, and paragenesis of gold, silver, and base-metal ores of the North Amethyst vein system, San Juan Mountains, Mineral County, Colorado

USGS Publications Warehouse

Foley, Nora K.; Caddey, Stanton W.; Byington, Craig B.; Vardiman, David M.

1993-01-01

Mineralogic, lead-isotopic, and fluid-inclusion characteristics of the younger association are similar to those of ores of the southern and central parts of the Creede mining district. In contrast, the gold and manganese-silicate assemblages of the older association are rare to absent in the southern and central parts of the district. The local and early occurrence of the manganese and gold assemblages may indicate that they formed in a small hydrothermal cell that predated the extensive hydrothermal system from which ores of the central and southern parts of the Creede district are proposed to have been deposited (Bethke, 1988). If similar early-stage cells were present in the southern and central parts of the district, they may have been replaced or overprinted by later assemblages, and they may remain to be discovered. In the latter case, mineral assemblages that formed at early stages in the paragenesis hold the most promise for gold exploration.

Secondary Sulfate Mineralization and Basaltic Chemistry of Craters of the Moon National Monument, Idaho: Potential Martian Analog

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

C. Doc Richardson; Nancy W. Hinman; Lindsay J. McHenry

2012-05-01

Secondary deposits associated with the basaltic caves of Craters of the Moon National Monument (COM) in southern Idaho were examined using X-ray powder diffraction, X-ray fluorescence spectrometry, Fourier transform infrared spectrometry, and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The secondary mineral assemblages are dominated by Na-sulfate minerals (thenardite, mirabilite) with a small fraction of the deposits containing minor concentrations of Na-carbonate minerals. The assemblages are found as white, efflorescent deposits in small cavities along the cave walls and ceilings and as localized mounds on the cave floors. Formation of the deposits is likely due to direct and indirectmore » physiochemical leaching of meteoritic water through the overlying basalts. Whole rock data from the overlying basaltic flows are characterized by their extremely high iron concentrations, making them good analogs for martian basalts. Understanding the physiochemical pathways leading to secondary mineralization at COM is also important because lava tubes and basaltic caves are present on Mars. The ability of FTICR-MS to consistently and accurately identify mineral species within these heterogeneous mineral assemblages proves its validity as a valuable technique for the direct fingerprinting of mineral species by deductive reasoning or by comparison with reference spectra.« less

Asteroid surface materials: Mineralogical characterizations from reflectance spectra

NASA Technical Reports Server (NTRS)

Gaffey, M. J.; Mccord, T. B.

1977-01-01

Mineral assemblages analogous to most meteorite types, with the exception of ordinary chondritic assemblages, have been found as surface materials of Main Belt asteroids. C1- and C2-like assemblages (unleached, oxidized meteoritic clay minerals plus opaques such as carbon) dominate the population throughout the Belt, especially in the outer Belt. A smaller population of asteroids exhibit surface materials similar to C3 (CO, CV) meteoritic assemblages (olivine plus opaque, probably carbon) and are also distributed throughout the Belt. The majority of remaining studied asteroids (20) of 65 asteroids exhibit spectral reflectance curves dominated by the presence of metallic nickel-iron in their surface materials. The C2-like materials which dominate the main asteroid belt population appear to be relatively rare on earth-approaching asteroids.

Earth physics and phase transformations program: A concept and proposal

NASA Technical Reports Server (NTRS)

Bonavito, N. L.; Tanaka, T.

1971-01-01

A program to study the geophysical characteristics of the earth is presented as an integration of the different disciplines that constitute the earth sciences, through the foundation of a generalized geodynamic theory of earth physics. A program is considered for defining the physical constants of the earth's material which parametrize the hydrodynamic equation in the microscopic solid state behavior of the crystals of the lithosphere. In addition, in order to lay the foundation for a generalized theory in earth physics, specific research areas are considered, such as the nature of the kinetics of the phase transitions in mineral assemblages, the equilibrium thermodynamic properties of crystals which are major constituents of mineral assemblages, and the transport properties of pure crystals which are major constituents of mineral assemblages.

The electrical resistivity signature of a fault controlling gold mineralization and the implications for Mesozoic mineralization: a case study from the Jiaojia Fault, eastern China

NASA Astrophysics Data System (ADS)

Zhang, Kun; Lü, Qingtian; Yan, Jiayong; Hu, Hao; Fu, GuangMing

2017-08-01

We use 3D audio magnetotelluric method to the south segment of Jiaojia fault belt, and obtain the 3D electrical model of this area. Regional geophysical data were combined in an analysis of strata and major structural distribution in the study area, and included the southern segment of the Jiaojia fault zone transformed into two fault assemblages. Together with the previous studies of the ore-controlling action of the Jiaojia fault belt and deposit characteristics, the two faults are considered to be favorable metallogenic provinces, because some important features coupled with them, such as the subordinate fault intersection zone and several fault assemblages in one fault zone. It was also suggested the control action of later fault with reversed downthrows to the ore distribution. These studies have enabled us to predict the presence of two likely target regions of mineralization, and are prospecting breakthrough in the southern section of Jiaojia in the Shandong Peninsula, China.

Utility of high-altitude infrared spectral data in mineral exploration: Application to Northern Patagonia Mountains, Arizona

USGS Publications Warehouse

Berger, B.R.; King, T.V.V.; Morath, L.C.; Phillips, J.D.

2003-01-01

Synoptic views of hydrothermal alteration assemblages are of considerable utility in regional-scale minerals exploration. Recent advances in data acquisition and analysis technologies have greatly enhanced the usefulness of remotely sensed imaging spectroscopy for reliable alteration mineral assemblages mapping. Using NASA's Airborne Visible Infrared Imaging Spectrometer (AVIRIS) sensor, this study mapped large areas of advanced argillic and phyllic-argillic alteration assemblages in the southeastern Santa Rita and northern Patagonia mountains, Arizona. Two concealed porphyry copper deposits have been identified during past exploration, the Red Mountain and Sunnyside deposits, and related published hydrothermal alteration zoning studies allow the comparison of the results obtained from AVIRIS data to the more traditional field mapping approaches. The AVIRIS mapping compares favorably with field-based studies. An analysis of iron-bearing oxide minerals above a concealed supergene chalcocite deposit at Red Mountain also indicates that remotely sensed data can be of value in the interpretation of leached caps above porphyry copper deposits. In conjunction with other types of geophysical data, AVIRIS mineral maps can be used to discriminate different exploration targets within a region.

Occurrence modes of As, Sb, Te, Bi, Ag in sulfide assemblages of gold deposits of the Urals

NASA Astrophysics Data System (ADS)

Vikent'eva, O.; Vikentev, I.

2016-04-01

Review of occurrence modes of trace toxic elements ("potential pollutants") in ores from large gold deposits (the Urals) of different genetic types is presented. Mineral forms of these elements as well as their presence in main minerals from gold-bearing sulfide assemblages according to SEM, EPMA, INAA, ICP-MS and LA-ICP-MS are demonstrated.

Orogenic-type copper-gold-arsenic-(bismuth) mineralization at Flatschach (Eastern Alps), Austria

NASA Astrophysics Data System (ADS)

Raith, Johann G.; Leitner, Thomas; Paar, Werner H.

2015-10-01

Structurally controlled Cu-Au mineralization in the historic Flatschach mining district (Styria, Austria) occurs in a NE-SW to NNE-WSW oriented vein system as multiple steep-dipping calcite-(dolomite)-quartz veins in amphibolite facies metamorphic rocks (banded gneisses/amphibolites, orthogneisses, metagranitoids) of the poly-metamorphosed Austroalpine Silvretta-Seckau nappe. Vein formation postdated ductile deformation events and Eoalpine (Late Cretaceous) peak metamorphism but predated Early to Middle Miocene sediment deposition in the Fohnsdorf pull-apart basin; coal-bearing sediments cover the metamorphic basement plus the mineralized veins at the northern edge of the basin. Three gold-bearing ore stages consist of a stage 1 primary hydrothermal (mesothermal?) ore assemblage dominated by chalcopyrite, pyrite and arsenopyrite. Associated minor minerals include alloclasite, enargite, bornite, sphalerite, galena, bismuth and matildite. Gold in this stage is spatially associated with chalcopyrite occurring as inclusions, along re-healed micro-fractures or along grain boundaries of chalcopyrite with pyrite or arsenopyrite. Sericite-carbonate alteration is developed around the veins. Stage 2 ore minerals formed by the replacement of stage 1 sulfides and include digenite, anilite, "blue-remaining covellite" (spionkopite, yarrowite), bismuth, and the rare copper arsenides domeykite and koutekite. Gold in stage 2 is angular to rounded in shape and occurs primarily in the carbonate (calcite, Fe-dolomite) gangue and less commonly together with digenite, domeykite/koutekite and bismuth. Stage 3 is a strongly oxidized assemblage that includes hematite, cuprite, and various secondary Cu- and Fe-hydroxides and -carbonates. It formed during supergene weathering. Stage 1 and 2 gold consists mostly of electrum (gold fineness 640-860; mean = 725; n = 46), and rare near pure gold (fineness 930-940; n = 6). Gold in stage 3 is Ag-rich electrum (fineness 350-490, n = 12), and has a high Hg content (up to 11 mass %). The Cu-Au deposits in the Flatschach area show similarities with meso- to epizonal orogenic lode gold deposits regarding the geological setting, the structural control of mineralization, the type of alteration, the early (stage 1) sulfide assemblage and composition of gold. Unique about the Flatschach district is the lower-temperature overprint of copper arsenides (domeykite and koutekite) and copper sulfides (djurleite, yarrowite/spionkopite) on earlier formed sulfide mineralization. Based on mineralogical considerations temperature of stage 2 mineralization was between about 70 °C and 160 °C. Gold was locally mobilized during this low-temperature hydrothermal overprint as well as during stage 3 supergene oxidation and cementation processes.

Alunite in the Pascua-Lama high-sulfidation deposit: Constraints on alteration and ore deposition using stable isotope geochemistry

USGS Publications Warehouse

Deyell, C.L.; Leonardson, R.; Rye, R.O.; Thompson, J.F.H.; Bissig, T.; Cooke, D.R.

2005-01-01

The Pascua-Lama high-sulfidation system, located in the El Indio-Pascua belt of Chile and Argentina, contains over 16 million ounces (Moz) Au and 585 Moz Ag. The deposit is hosted primarily in granite rocks of Triassic age with mineralization occurring in several discrete Miocene-age phreatomagmatic breccias and related fracture networks. The largest of these areas is Brecha Central, which is dominated by a mineralizing assemblage of alunite-pyrite-enargite and precious metals. Several stages of hydrothermal alteration related to mineralization are recognized, including all types of alunite-bearing advanced argillic assemblages (magmatic-hydrothermal, steam-heated, magmatic steam, and supergene). The occurrence of alunite throughout the paragenesis of this epithermal system is unusual and detailed radiometric, mineralogical, and stable isotope studies provide constraints on the timing and nature of alteration and mineralization of the alunite-pyiite-enargite assemblage in the deposit. Early (preore) alteration occurred prior to ca. 9 Ma and consists of intense silicic and advanced argillic assemblages with peripheral argillic and widespread propylitic zones. Alunite of this stage occurs as fine intergrowths of alunite-quartz ?? kaolinite, dickite, and pyrophyllite that selectively replaced feldspars in the host rock. Stable isotope systematics suggest a magmatic-hydrothermal origin with a dominantly magmatic fluid source. Alunite is coeval with the main stage of Au-Ag-Cu mineralization (alunite-pyrite-enargite assemblage ore), which has been dated at approximately 8.8 Ma. Ore-stage alunite has an isotopic signature similar to preore alunite, and ?? 34Salun-py data indicate depositional temperatures of 245?? to 305??C. The ??D and ?? 18O data exclude significant involvement of meteoric water during mineralization and indicate that the assemblage formed from H2S-dominated magmatic fluids. Thick steam-heated alteration zones are preserved at the highest elevations in the deposit and probably formed from oxidation of H2S during boiling of the magmatic ore fluids. Coarsely crystalline magmatic steam alunite (8.4 Ma) is restricted to the near-surface portion of Brecha Central. Postmineral alunite ?? jarosite were previosly interpreted to be supergene crosscutting veins and overgrowths, although stable isotope data suggest a mixed magmatic-meteoric origin for this late-stage alteration. Only late jarosite veinlets (8.0 Ma) associated with fine-grained pseudocubic alunite have a supergene isotopic signature. The predominanca of magmatic fluids recorded throughout the paragenesis of the Pascua system is atypical for high-sulfidation deposits, which typically envolve significant meteoric water in near-surface and peripheral alteration and, in some systems, even ore deposition. A Pascua, the strong magmatic signature of both alteration and main-stage (alunite-pyrite-enargite assemblage) ore is attributed to limited availability of meteoric fluids. This is in agreement with published data for the El Indio-Pascua belt, indicating an event of uplift and subsequent pediment incision, as well as a transition from semiarid to arid climatic conditions, during the formation of the deposit in the mid to late Miocene. ?? 2005 Society of Economic Geologists, Inc.

Persistency-field Eh-pH diagrams for sulfides and their application to supergene oxidation and enrichment of sulfide ore bodies

USGS Publications Warehouse

Sato, M.

1992-01-01

At temperatures prevailing near the Earth's surface, metastable co-existence of chemical substances is common because chemical reactions that would directly lead to the attainment of thermody-namically most stable equilibria are often blocked by high activation energy barriers. The persistency of a metastable assemblage is then governed by alternative reaction paths that provide lower activation energy barriers. Comparison of observed mineral assemblages in the supergene oxidized and enriched sulfide ores with corresponding stability Eh-pH diagrams reveals that the supergene assemblages are mostly metastable due primarily to the persistency of sulfide minerals beyond stability boundaries. A new set of diagrams called persistency-field Eh-pH diagrams has been constructed for binary metal sulfides on the basis of electrochemical and other experimental data. Each diagram delineates the persistency field, which is a combined field of thermodynamic stability and reaction path-controlled metastability, for a specific sulfide mineral. When applied to the supergene assemblages, these new diagrams show much better correspondence to the field observations. Although there may still be room for further refinement, the new diagrams appear to provide a strong visual aid to the understanding of the behavior of sulfide minerals in the supergene conditions. ?? 1992.

Behaviour of phase functions of Olivine and Augite assemblages in the wavelength range 0.3-18 μm

NASA Astrophysics Data System (ADS)

Salgueiro da Silva, M. A.; Seixas, T. M.; Maturilli, A.; Helbert, J.

2017-09-01

We tested the validity of the wavelength-independent phase function assumption by measuring BDR of olivine and augite mineral assemblages in the extended spectral range 0.3-18 μm. Because quasi-isotropic scattering is present in both OL and AUG assemblages with grain-size dependent features, it is not clear that this is an intrinsic effect attributed to the wavelength dependence of the optical constants of olivine and augite minerals. Our results show that the application of Hapke model to olivine and augite BDR spectra in the MIR range requires a wavelength- and, possibly, grain size-dependent phase function.

Fate of organo-mineral particles in streams: Microbial degradation by streamwater & biofilm assemblages

NASA Astrophysics Data System (ADS)

Hunter, W. R.; Raich, M.; Wanek, W.; Battin, T. J.

2013-12-01

Inland waters are of global biogeochemical importance. They receive carbon inputs of ~ 4.8 Pg C/ y of which, 12 % is buried, 18 % transported to the oceans, and 70 % supports aquatic secondary production. However, the mechanisms that determine the fate of organic matter (OM) in these systems are poorly defined. One aspect of this is the formation of organo-mineral complexes in aquatic systems and their potential as a route for OM transport and burial vs. their use as carbon (C) and nitrogen (N) sources within aquatic systems. Organo-mineral particles form by sorption of dissolved OM to freshly eroded mineral surfaces and may contribute to ecosystem-scale particulate OM fluxes. We experimentally tested the availability of mineral-sorbed OM as a C & N source for streamwater microbial assemblages and streambed biofilms. Organo-mineral particles were constructed in vitro by sorption of 13C:15N-labelled amino acids to hydrated kaolin particles, and microbial degradation of these particles compared with equivalent doses of 13C:15N-labelled free amino acids. Experiments were conducted in 120 ml mesocosms over 7 days using biofilms and water sampled from the Oberer Seebach stream (Austria). Each incubation experienced a 16:8 light:dark regime, with metabolism monitored via changes in oxygen concentrations between photoperiods. The relative fate of the organo-mineral particles was quantified by tracing the mineralization of the 13C and 15N labels and their incorporation into microbial biomass. Here we present the initial results of 13C-label mineralization, incorporation and retention within dissolved organic carbon pool. The results indicate that 514 (× 219) μmol/ mmol of the 13:15N labeled free amino acids were mineralized over the 7-day incubations. By contrast, 186 (× 97) μmol/ mmol of the mineral-sorbed amino acids were mineralized over a similar period. Thus, organo-mineral complexation reduced amino acid mineralization by ~ 60 %, with no differences observed between the streamwater and biofilm assemblages. Throughout the incubations, biofilms were observed to leach dissolved organic carbon (DOC). However, within the streamwater assemblage the presence of both organo-mineral particles and kaolin particles was associated with significant DOC removal (-1.7 % and -7.5 % respectively). Consequently, the study demonstrates that mineral and organo-mineral particles can limit the availability of DOC in aquatic systems, providing nucleation sites for flocculation and fresh mineral surfaces, which facilitate OM-sorption. The formation of these organo-mineral particles subsequently restricts microbial OM degradation, potentially altering the transport and facilitating the burial of OM within streams.

Unmixing Magnetic Hysteresis Loops

NASA Astrophysics Data System (ADS)

Heslop, D.; Roberts, A. P.

2012-04-01

Magnetic hysteresis loops provide important information in rock and environmental magnetic studies. Natural samples often contain an assemblage of magnetic particles composed of components with different origins. Each component potentially carries important environmental information. Hysteresis loops, however, provide information concerning the bulk magnetic assemblage, which makes it difficult to isolate the specific contributions from different sources. For complex mineral assemblages an unmixing strategy with which to separate hysteresis loops into their component parts is therefore essential. Previous methods to unmix hysteresis data have aimed at separating individual loops into their constituent parts using libraries of type-curves thought to correspond to specific mineral types. We demonstrate an alternative approach, which rather than decomposing a single loop into monomineralic contributions, examines a collection of loops to determine their constituent source materials. These source materials may themselves be mineral mixtures, but they provide a genetically meaningful decomposition of a magnetic assemblage in terms of the processes that controlled its formation. We show how an empirically derived hysteresis mixing space can be created, without resorting to type-curves, based on the co-variation within a collection of measured loops. Physically realistic end-members, which respect the expected behaviour and symmetries of hysteresis loops, can then be extracted from the mixing space. These end-members allow the measured loops to be described as a combination of invariant parts that are assumed to represent the different sources in the mixing model. Particular attention is paid to model selection and estimating the complexity of the mixing model, specifically, how many end-members should be included. We demonstrate application of this approach using lake sediments from Butte Valley, northern California. Our method successfully separates the hysteresis loops into sources with a variety of terrigenous and authigenic origins.

Isotopic fractionation of oxygen and carbon in decomposed lower-mantle inclusions in diamond

DOE PAGES

Kaminsky, Felix; Matzel, Jennifer; Jacobsen, Ben; ...

2015-07-25

Two carbonatitic mineral assemblages, calcite + wollastonite and calcite + monticellite, which are encapsulated in two diamond grains from the Rio Soriso basin in the Juina area, Mato Grosso State, Brazil, were studied utilizing the NanoSIMS technique. The assemblages were formed as the result of the decomposition of the lower-mantle assemblage calcite + CaSi-perovskite + volatile during the course of the diamond ascent under pressure conditions from 15 to less than 0.8 GPa. The oxygen and carbon isotopic compositions of the studied minerals are inhomogeneous. They fractionated during the process of the decomposition of primary minerals to very varying values:more » δ 18O from –3.3 to +15.4 ‰ SMOW and δ 13C from –2.8 to +9.3 ‰ VPDB. As a result, these values significantly extend the mantle values for these elements in both isotopically-light and isotopically-heavy areas.« less

The fate of iron on Mars: Mechanism of oxidation of basaltic minerals to ferric-bearing assemblages

NASA Technical Reports Server (NTRS)

Burns, Roger G.

1992-01-01

Perhaps the most conspicuous indication that chemical weathering has occurred on the surface of Mars is the overall color of the red planet and the spectroscopic features that identify ferric-bearing assemblages in the martian regolith. Apparently, Fe(2+) ions in primary minerals in parent igneous rocks on the martian surface have been oxidized to ferric iron, which occurs in degradation products that now constitute the regolith. The mineralogy of the unweathered igneous rocks prior to weathering on the martian surface is reasonably well constrained, mainly as a result of petrographic studies of the SNC meteorites. However, the alteration products resulting from oxidative weathering of these rocks are less well-constrained. The topics covered include the following: primary rocks subjected to chemical weathering; dissolution processes; oxidation of dissolved Fe(2+); mechanism of polymerization of hydrous ferric oxides; terrestrial occurrences of ferromagnesian smectites; and dehydroxylated Mg-Fe smectites on Mars.

Late-stage anhydrite-gypsum-siderite-dolomite-calcite assemblages record the transition from a deep to a shallow hydrothermal system in the Schwarzwald mining district, SW Germany

NASA Astrophysics Data System (ADS)

Burisch, Mathias; Walter, Benjamin F.; Gerdes, Axel; Lanz, Maximilian; Markl, Gregor

2018-02-01

The majority of hydrothermal vein systems of economic interest occur at relatively shallow crustal levels, although many of them formed at significantly greater depths. Their present position is a consequence of uplift and erosion. Although, many aspects of their formation are well constrained, the temporal chemical evolution of such systems during uplift and erosion is still poorly understood. These vein minerals comprise calcite, dolomite-ankerite, siderite-magnesite, anhydrite and gypsum forming the last gangue assemblages in Jurassic and Tertiary sulphide-fluorite-quartz-barite veins of the Schwarzwald mining district, SW Germany. Mineral textures of samples from nine localities reveal that in these sequences, mineral precipitation follows a recurring pattern: early calcite is followed by anhydrite or gypsum, siderite and/or dolomite. This succession may repeat up to three times. In-situ (LA-ICP-MS) U-Pb age dating of 15 carbonates from three subsequent generations of the late-stage vein assemblage yield robust ages between 20 and 0.6 Ma. Each mineral sequence forms in a distinctive period of about 2-5 Ma. These ages clearly relate these late-stage mineral phases to the youngest geological episode of the Schwarzwald, which is associated with the Cenozoic Rhine Graben rifting and basement uplift. Based on thermodynamic modelling, the formation of the observed mineral assemblages required an deeply sourced Mg-, Fe- and SO4-rich fluid (b), which was episodically mixed with a shallow crustal HCO3-rich fluid (a). As a consequence of fluid mixing, concentrations of Mg, Fe and SO4 temporarily increased and initiated the formation of the observed sulphate-carbonate mineral sequences. This discontinuous large-scale vertical fluid mixing was presumably directly related to episodes of active tectonics associated with the Cenozoic strike-slip regime of the Upper Rhine Graben. Analogously, episodic fluid mixing is a major key in the formation of older (Jurassic to early Tertiary) Pb-Zn-fluorite-quartz-barite assemblages in the same specific vein systems, albeit involving different fluid compositions. Late-stage hydrothermal (∼20-70 °C) vein assemblages reported in this study record the transition from deep (>2 km) to very shallow (0-1 km) crustal conditions. As a consequence of successive uplift, increasing proportions of shallower and cooler (∼50-70 °C) fluids could take part in such mixing processes. Associated changes in the fluid composition caused the vein mineralogy to change from sulphide-quartz-fluorite-barite to calcite-anhydrite/gypsum-siderite-dolomite, as the system passively ascended closer to the surface.

Fluid-induced Blueschist Preservation on Syros, Cyclades, Southern Greece

NASA Astrophysics Data System (ADS)

Kleine, B. I.; Huet, B.; Skelton, A. D. L.

2012-04-01

Local examples of preservation of high-pressure, low-temperature (HP-LT) mineral assemblages within retrograde metamorphosed greenschist are recorded from the Cyclades, Greece. Several models have been proposed to explain the preservation of HP-LT rocks in these areas. On Sifnos, a capping effect of impermeable marble units below the preserved blueschists caused diversion of the upward, cross-layer infiltration of retrograde fluids [1]. On Tinos, blueschist preservation occurred due to retrograde fluid flow channelization along lithological contacts with high flux rates [2]. HP-LT minerals were preserved in regions adjacent to these contacts where fluid fluxes were smaller. We propose a different mechanism of blueschist preservation based on observations from a costal section near Fabrika on Syros. At this locality a high strain zone cuts through a retrograde greenschist. Along the fault a dark blue halo occurs within the greenschist. Whole rock analyses along a profile from the fault into the greenschist show that only the areas directly adjacent to the deformation zone show chemical evidence of metasomatism, whereas the areas further away are chemically similar to greenschist. Point counting of 1000 evenly spaced points in thin sections of the profile shows a clear blueschist to greenschist transition with a blueschist mineral assemblage (glaucophane+phengite+calcite) nearer to the metasomatic zone and a typical greenschist mineral assemblage (epidote+chlorite+albite) farther away. We propose the following model to explain preservation of HP-LT mineral assemblage in this locality. During retrograde metamorphism a water-rich fluid infiltrated the blueschist rock from below. This occurred close to the brittle-ductile transition. This fluid caused a reaction front to propagate into the overlying blueschist at which its mineral assemblage glaucophane+phengite+calcite was replaced by the greenschist mineral assemblage epidote+albite+chlorite. Upwards-flowing fluid passing through the reaction front is buffered to higher X(CO2) by the reaction glaucophane+phengite+calcite+H2O=albite+chlorite+epidote+quartz+CO2. This fluid travels faster along paths of structural weakness (e.g. shear zones, faults). If this fluid reaches colder regions more rapidly such that the fluid chemistry is unable to "keep up" with the position of the reaction equilibria as the temperature falls, X(CO2) will be effectively shifted back into the blueschist stability field and blueschist will be preserved, specifically within high flux regions, such as shear zones and faults. [1] Matthews & Schliestedt (1984), Contributions to Mineralogy and Petrology, 88, 150-163. [2] Breeding et al. (2003), Geochemistry Geophysics Geosystems, 4, 1-11.

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.

Spatial and temporal zoning of hydrothermal alteration and mineralization in the Sossego iron oxide-copper-gold deposit, Carajás Mineral Province, Brazil: Paragenesis and stable isotope constraints

USGS Publications Warehouse

Monteiro, Lena V.S.; Xavier, R.P.; Carvalho, E.R.; Hitzman, M.W.; Johnson, C.A.; Souza, Filho C.R.; Torresi, I.

2008-01-01

The Sossego iron oxide–copper–gold deposit (245 Mt @ 1.1% Cu, 0.28 g/t Au) in the Carajás Mineral Province of Brazil consists of two major groups of orebodies (Pista–Sequeirinho–Baiano and Sossego–Curral) with distinct alteration assemblages that are separated from each other by a major high angle fault. The deposit is located along a regional WNW–ESE-striking shear zone that defines the contact between metavolcano–sedimentary units of the ∼2.76 Ga Itacaiúnas Supergroup and tonalitic to trondhjemitic gneisses and migmatites of the ∼2.8 Ga Xingu Complex. The deposit is hosted by granite, granophyric granite, gabbro, and felsic metavolcanic rocks. The Pista–Sequeirinho–Baiano orebodies have undergone regional sodic (albite–hematite) alteration and later sodic–calcic (actinolite-rich) alteration associated with the formation of massive magnetite–(apatite) bodies. Both these alteration assemblages display ductile to ductile–brittle fabrics. They are cut by spatially restricted zones of potassic (biotite and potassium feldspar) alteration that grades outward to chlorite-rich assemblages. The Sossego–Curral orebodies contain weakly developed early albitic alteration and very poorly developed subsequent calcic–sodic alteration. These orebodies contain well-developed potassic alteration assemblages that were formed during brittle deformation that resulted in the formation of breccia bodies. Breccia matrix commonly displays coarse mineral infill suggestive of growth into open space. Sulfides in both groups of deposits were precipitated first with potassic alteration and more importantly with a later assemblage of calcite–quartz–epidote–chlorite. In the Sequeirinho orebodies, sulfides range from undeformed to deformed; sulfides in the Sossego–Curral orebodies are undeformed. Very late, weakly mineralized hydrolytic alteration is present in the Sossego/Currral orebodies. The sulfide assemblage is dominated by chalcopyrite with subsidiary siegenite, and millerite. Pyrrhotite and pyrite are minor constituents of ore in the Sequerinho orebodies while pyrite is relatively abundant in the Sossego–Curral bodies. Oxygen isotope partitioning between mineral pairs constrains temperatures in the deposit spatially and through time. In the Sequeirinho orebody, the early sodic–calcic alteration stage was characterized by temperatures exceeding 500°C and δ18OH2O values for the alteration fluid of 6.9 ± 0.9‰. Temperature declines outward and upward from the zone of most intense alteration. Paragenetically later copper–gold mineralization displays markedly lower temperatures (<300°C) and was characterized by the introduction of 18O-depleted hydrothermal fluids −1.8 ± 3.4‰. The calculated δDH2O and δ18OH2O values suggest that the fluids that formed the early calcic–sodic alteration assemblage were of formational/metamorphic or magmatic origin. The decrease of δ18OH2O values through time may reflect influx of surficially derived waters during later alteration and mineralization events. Influx of such fluids could be related to episodic fluid overpressure, resulting in dilution and cooling of the metalliferous fluid, causing deposition of metals transported as metal chloride complexes.

Phase equilibrium modelling of granite magma petrogenesis: B. An evaluation of the magma compositions that result from fractional crystallization

NASA Astrophysics Data System (ADS)

Garcia-Arias, Marcos; Stevens, Gary

2017-04-01

Several fractional crystallization processes (flow segregation, gravitational settling, filter-pressing), as well as batch crystallization, have been investigated in this study using thermodynamic modelling (pseudosections) to test whether they are able to reproduce the compositional trends shown by S-type granites. Three starting compositions comprising a pure melt phase and variable amounts of entrained minerals (0, 20 and 40 wt.% of the total magma) have been used to study a wide range of likely S-type magma compositions. The evolution of these magmas was investigated from the segregation from their sources at 0.8 GPa until emplacement at 0.3 GPa in an adiabatic path, followed by isobaric cooling until the solidus was crossed, in a closed-system scenario. The modelled magmas and the fractionated mineral assemblages are compared to the S-type granites of the Peninsula pluton, Cape Granite Suite, South Africa, which have a composition very similar to most of the S-type granites. The adiabatic ascent of the magmas digests partially the entrained mineral assemblage of the magmas, but unless this entrained assemblage represents less than 1 wt.% of the original magma, part of the mineral fraction survives the ascent up to the chosen pressure of emplacement. At the level of emplacement, batch crystallization produces magmas that only plot within the composition of the granites of the Peninsula pluton if the bulk composition of the original magmas already matched that of the granites. Flow segregation of crystals during the ascent and gravitational settling fractional crystallization produce bodies that are generally more mafic than the most mafic granites of the pluton and the residual melts have an almost haplogranitic composition, producing a bimodal compositional distribution not observed in the granites. Consequently, these two processes are ruled out. Filter-pressing fractional crystallization produces bodies in an onion-layer structure that become more felsic with increasing crystallization, culminating in a haplogranitic melt, and is able to reproduce the compositional trends of the granites, but only if the original magmas already had the composition of the granites. Filter-pressing fractionation produces a mineral assemblage that is 1.5 times more mafic than the magma fraction from which it is derived. However, the mineral assemblages produced by crystallization of an originally pure melt phase are still too felsic to account for the bulk of the granites of the Peninsula pluton. For filter-pressing to produce the most mafic granites of the pluton, the original magmas must already contain an entrained mafic mineral assemblage and have the same composition of the granites, otherwise the modelled trends do not match the maficity (FeO + MgO) or the slope against maficity of the granites. Crystallization of the magma in filter-pressing releases a free water phase, whose amount depends on the amount of water of the original magma, and whose behaviour may be controlled by a water-saturation front. In summary, the main control in the composition of S-type granites is the amount and nature of the entrained mineral assemblage, and filter-pressing fractional crystallization can only modify slightly the compositions of the granitic bodies derived from these magmas.

Geochemical models of metasomatism in ultramafic systems: Serpentinization, rodingitization, and sea floor carbonate chimney precipitation

USGS Publications Warehouse

Palandri, J.L.; Reed, M.H.

2004-01-01

In a series of water-rock reaction simulations, we assess the processes of serpentinization of harzburgite and related calcium metasomatism resulting in rodingite-type alteration, and seafloor carbonate chimney precipitation. At temperatures from 25 to 300??C (P = 10 to 100 bar), using either fresh water or seawater, serpentinization simulations produce an assemblage commonly observed in natural systems, dominated by serpentine, magnetite, and brucite. The reacted waters in the simulations show similar trends in composition with decreasing water-rock ratios, becoming hyper-alkaline and strongly reducing, with increased dissolved calcium. At 25??C and w/r less than ???32, conditions are sufficiently reducing to yield H2 gas, nickel-iron alloy and native copper. Hyperalkalinity results from OH- production by olivine and pyroxene dissolution in the absence of counterbalancing OH- consumption by alteration mineral precipitation except at very high pH; at moderate pH there are no stable calcium minerals and only a small amount of chlorite forms, limited by aluminum, thus allowing Mg2+ and Ca2+ to accumulate in the aqueous phase in exchange for H+. The reducing conditions result from oxidation of ferrous iron in olivine and pyroxene to ferric iron in magnetite. Trace metals are computed to be nearly insoluble below 300??C, except for mercury, for which high pH stabilizes aqueous and gaseous Hg??. In serpentinization by seawater at 300??C, Ag, Au, Pd, and Pt may approach ore-forming concentrations in sulfide complexes. Simulated mixing of the fluid derived from serpentinization with cold seawater produces a mineral assemblage dominated by calcite, similar to recently discovered submarine, ultramafic rock-hosted, carbonate mineral deposits precipitating at hydrothermal vents. Simulated reaction of gabbroic or basaltic rocks with the hyperalkaline calcium- and aluminum-rich fluid produced during serpentinization at 300??C yields rodingite-type mineral assemblages, including grossular, clinozoisite, vesuvianite, prehnite, chlorite, and diopside. ?? 2004 Elsevier Ltd.

Metamorphic mineral assemblages of slightly calcic pelitic rocks in and around the Taconic Allochthon, southwestern Massachusetts and adjacent Connecticut and New York

USGS Publications Warehouse

Zen, E-an

1981-01-01

The mineral assemblages from metamorphosed slightly calcic pelitic rocks of the Taconic Range in southwestern Massachusetts and adjacent areas of Connecticut and New York were studied petrographically and chemically. These rocks vary in metamorphic grade from those below the chloritoid zone through the chloritoid and garnet zones into the kyanite-staurolite zone. Microprobe data on the ferromagnesian minerals show that the sequence of increasing Fe/ (Fe+Mg) value is, from the lowest, chlorite, biotite, hornblende, chloritoid, staurolite, garnet. Hornblende, epidote, garnet, and plagioclase are the most common minerals that carry significant calcium. Biotite is persistently deficient in alkali but is abnormally rich in octahedral aluminum to such an extent that the overall charge balance can be ascribed to an AI=K+ (Fe,Mg) diadochy. Muscovite contains small though persistent amounts of iron and magnesium in octahedral positions but has a variable K/Na ratio, which is potentially useful as a geothermometer. One low-grade muscovite is highly phengitic, but the white micas in rocks from metamorphic grades higher than chloritoid zone do not contain significant phengite components. Chlorite is persistently high in aluminum and so its ratio of divalent ions to aluminum is approximately that of garnet. Many garnets show pronounced zoning in manganese and less pronounced zoning in calcium. Garnet coexisting with hornblende contains a high proportion of the grossularitic component. The calcium content is significant in all the analyzed garnets, except those from a cummingtonite-bearing sample that is free of muscovite. This suggests that in slightly calcic pelitic rocks, calcium-free garnet cannot coexist with muscovite. Most of the mineral assemblages formed in the presence of excess quartz and muscovite. The phase-petrologic analysis, made with the aid of an eight-phase multisystematic model, shows the following major points: 1. Chloritoid and staurolite coexist in a definite interval of prograde metamorphism. 2. Biotite-chloritoid does not constitute an alternative assemblage to garnet-chlorite-muscovite, because the former combination is found predominantly in the presence of the latter combination. Because the garnet contains lime, all five phases are stable together in lowlime pelitic rocks. 3. The first appearance of staurolite in the area does not correspond to the reaction leading to the first intrinsic stable existence of this phase. Inasmuch as the first appearanc,e of staurolite is always in chlorite-bearing as semblages, I suggest that the mapped staurolite zone marker corresponds to a reaction whereby staurolitechlorite becomes stable. The probable lower grade chemical equivalent, for example, chloritoid-aluminum silicate, however, has not been found in the area of study. Several staurolite-forming reactions discussed in the literature are ruled out because of the relative siderophility of the minerals. A second staurolite isograd involves the reaction, chloritoid+chlorite+muscovite= staurolite+biotite. A third isograd involves staurolite+ chlorite=biotite+kyanite; this reaction is postulated on the basis of the observed assemblage biotite-kyanitesta urolite-garnet-muscoviteplagioclase-quartzilmenite. 4. In low-grade rocks, epidote is stable considerably before the first appearance of chloritoid. The nature of the high-aluminum phase in low-grade rocks that leads to the formation of chloritoid remains obscure. The epidote is always rich in ferric iron (pistacite content of about 1/ 4 to 1/3). Garnet-bearing assemblages (with or without epidote) are formed next as metamorphic grade increases. The next more calcium-rich silicate is hornblende, and despite the meager data on assemblages that include hornblende, the first intrinsic appearance of this phase has probably been recorded. At highstaurolite grade, the most calcium-rich assemblage in pelitic rocks is hornblende-garnet-biotite-plagioclase (bytownit

Platinum-group mineralization at the margin of the Skaergaard intrusion, East Greenland

NASA Astrophysics Data System (ADS)

Andersen, Jens C. Ø.; Rollinson, Gavyn K.; McDonald, Iain; Tegner, Christian; Lesher, Charles E.

2017-08-01

Two occurrences of platinum-group elements (PGEs) along the northern margin of the Skaergaard intrusion include a sulfide-bearing gabbro with slightly less than 1 ppm PGE + Au and a clinopyroxene-actinolite-plagioclase-biotite-ilmenite schist with 16 vol% sulfide and 1.8 ppm PGE + Au. Both have assemblages of pyrrhotite, pentlandite, and chalcopyrite typical for orthomagmatic sulfides. Matching platinum-group mineral assemblages with sperrylite (PtAs2), kotulskite (Pd(Bi,Te)1-2), froodite (PdBi2), michenerite (PdBiTe), and electrum (Au,Ag) suggest a common origin. Petrological and geochemical similarities suggest that the occurrences are related to the Skaergaard intrusion. The Marginal Border Series locally displays Ni depletion consistent with sulfide fractionation, and the PGE fractionation trends of the occurrences are systematically enriched by 10-50 times over the chilled margin. The PGE can be explained by sulfide-silicate immiscibility in the Skaergaard magma with R factors of 110-220. Nickel depletion in olivine suggests that the process occurred within the host cumulate, and the low R factors require little sulfide mobility. The sulfide assemblages are different to the chalcopyrite-bornite-digenite assemblage found in the Skaergaard Layered Series and Platinova Reef. These differences can be explained by the early formation of sulfide melt, while magmatic differentiation or sulfur loss caused the unusual sulfide assemblage within the Layered Series. The PGEs indicate that the sulfides formed from the Skaergaard magma. The sulfides and PGEs could not have formed from the nearby Watkins Fjord wehrlite intrusion, which is nearly barren in sulfide. We suggest that silicate-sulfide immiscibility led to PGE concentration where the Skaergaard magma became contaminated with material from the Archean basement.

Metaultramafic schists and dismembered ophiolites of the Ashe Metamorphic Suite of northwestern North Carolina, USA

USGS Publications Warehouse

Raymond, Loren A.; Merschat, Arthur J.; Vance, R. Kelly

2016-01-01

Metaultramafic rocks (MUR) in the Ashe Metamorphic Suite (AMS) of northwestern North Carolina include quartz ± feldspar-bearing QF-amphibolites and quartz-deficient, locally talc-, chlorite-, and/or Mg-amphibole-bearing TC-amphibolites. Some workers divide TC-amphibolites into Todd and Edmonds types, based on mineral and geochemical differences, and we provisionally add a third type – olivine ± pyroxene-rich, Rich Mountain-type rocks. Regionally, MUR bodies range from equant, Rich Mountain- to highly elongate, Todd-TC-amphibolite-type bodies. The MURs exhibit three to five mineral associations containing assemblages with olivine, anthophyllitic amphibole, Mg-hornblende, Mg-actinolite, cummingtonite, and serpentine representing decreasing eclogite to greenschist facies grades of metamorphism over time. MUR protoliths are difficult to determine. Southwestern MUR bodies have remnant olivine ± pyroxene-rich assemblages representing ultrabasic-basic, dunite-peridotite-pyroxenite protoliths. Northeastern TC-amphibolite MURs contain hornblende and actinolitic amphiboles plus chlorites – aluminous and calcic assemblages suggesting to some that metasomatism of basic, QF-amphibolites yields all TC-amphibolites. Yet MgO-CaO-Al2O3 and trace element chemistries of many TC-amphibolites resemble compositions of plagioclase peridotites. We show that a few AMS TC-amphibolites had basaltic/gabbroic protoliths, while presenting arguments opposing application of the metasomatic hypothesis to all TC-amphibolites. We establish that MUR bodies are petrologically heterolithic and that TC-amphibolites are in contact with many rock types; that those with high Cr, Ni, and Mg have olivine- or pyroxene-dominated protoliths; that most exhibit three or more metamorphic mineral associations; and that contacts thought to be metasomatic are structural. Clearly, different MUR bodies have different chemistries representing various protoliths, and have different mineral assemblages, reflecting both chemical composition and metamorphic history. Spot sampling of heterolithic MUR bodies does not reveal MUR body character or history or allow ‘type’ designations. We recommend that the subdivision of MUR bodies into ‘types’ be abandoned and that the metasomatic hypothesis be carefully applied. AMS MURs and associated metamafic rocks likely represent fragments of dismembered ophiolites from various ophiolite types.

Borate mineral assemblages in the system Na2OCaOMgOB2O3H2O

USGS Publications Warehouse

Christ, C.L.; Truesdell, A.H.; Erd, Richard C.

1967-01-01

he significant known hydrated borate mineral assemblages (principally of the western United States) in the system Na2OCaOz.sbnd;MgOB2O3H2O are expressible in three ternary composition diagrams. Phase rule interpretation of the diagrams is consistent with observation, if the activity of H2O is generally considered to be determined by the geologic environment. The absence of conflicting tie-lines on a diagram indicates that the several mineral assemblages of the diagram were formed under relatively narrow ranges of temperature and pressure. The known structural as well as empirical formulas for the minerals are listed, and the more recent (since 1960) crystal structure findings are discussed briefly. Schematic Gibbs free energy-composition diagrams based on known solubility-temperature relations in the systems Na2B4O7-H2O and Na2B4O7-NaCl-H2O, are highly useful in the interpretation and prediction of the stability relations in these systems; in particular these diagrams indicate clearly that tincalconite, although geologically important, is everywhere a metastable phase. Crystal-chemical considerations indicate that the same thermodynamic and kinetic behavior observed in the Na2B4O7-H2O system will hold in the Ca2B6O11-H2O system. This conclusion is confirmed by the petrologic evidence. The chemical relations among the mineral assemblages of a ternary diagram are expressed by a schematic "activity-activity" diagram. These activity-activity diagrams permit the tracing-out of the paragenetic sequences as a function of changing cation and H2O activities. ?? 1967.

Long-term controls on continental-scale bedrock river terrace deposition from integrated clast and heavy mineral assemblage analysis: An example from the lower Orange River, Namibia

NASA Astrophysics Data System (ADS)

Nakashole, Albertina N.; Hodgson, David M.; Chapman, Robert J.; Morgan, Dan J.; Jacob, Roger J.

2018-02-01

Establishing relationships between the long-term landscape evolution of drainage basins and the fill of sedimentary basins benefits from analysis of bedrock river terrace deposits. These fragmented detrital archives help to constrain changes in river system character and provenance during sediment transfer from continents (source) to oceans (sink). Thick diamondiferous gravel terrace deposits along the lower Orange River, southern Namibia, provide a rare opportunity to investigate controls on the incision history of a continental-scale bedrock river. Clast assemblage and heavy mineral data from seven localities permit detailed characterisation of the lower Orange River gravel terrace deposits. Two distinct fining-upward gravel terrace deposits are recognised, primarily based on mapped stratigraphic relationships (cross-cutting relationships) and strath and terrace top elevations, and secondarily on the proportion of exotic clasts, referred to as Proto Orange River deposits and Meso Orange River deposits. The older early to middle Miocene Proto Orange River gravels are thick (up to 50 m) and characterised by a dominance of Karoo Supergroup shale and sandstone clasts, whereas the younger Plio-Pleistocene Meso Orange River gravels (6-23 m thick) are characterised by more banded iron formation clasts. Mapping of the downstepping terraces indicates that the Proto gravels were deposited by a higher sinuosity river, and are strongly discordant to the modern Orange River course, whereas the Meso deposits were deposited by a lower sinuosity river. The heavy minerals present in both units comprise magnetite, garnet, amphibole, epidote and ilmenite, with rare titanite and zircon grains. The concentration of amphibole-epidote in the heavy minerals fraction increases from the Proto to the Meso deposits. The decrease in incision depths, recorded by deposit thicknesses above strath terraces, and the differences in clast character (size and roundness) and type between the two units, are ascribed to a more powerful river system during Proto-Orange River time, rather than reworking of older deposits, changes in provenance or climatic variations. In addition, from Proto- to Meso-Orange River times there was an increase in the proportion of sediments supplied from local bedrock sources, including amphibole-epidote in the heavy mineral assemblages derived from the Namaqua Metamorphic Complex. This integrated study demonstrates that clast assemblages are not a proxy for the character of the matrix, and vice versa, because they are influenced by the interplay of different controls. Therefore, an integrated approach is needed to improve prediction of placer mineral deposits in river gravels, and their distribution in coeval deposits downstream.

ARSENIC MINERALS AS INDICATORS OF CONDITIONS OF GOLD DEPOSITION IN CARLIN-TYPE GOLD DEPOSITS.

USGS Publications Warehouse

Rytuba, James J.

1984-01-01

Arsenic minerals commonly occurring in Carlin-type gold deposits include orpiment and realgar and, more rarely, native arsenic and arsenopyrite. Other arsenic-bearing phases present include arsenian pyrite and stibnite and a number of thallium and mercury sulfides. Under conditions of constant temperature and pressure, the relative stability of arsenic minerals is a function of sulfur activity. At high sulfur activity, orpiment is the stable phase. As sulfur activity is decreased, more sulfur-deficient arsenic phases become stable with the progressive formation of realgar, native arsenic, arsenopyrite, and finally, loellingite at very low sulfur activity. Three univariant equilibrium assemblages: orpiment plus realgar, realgar plus native arsenic and native arsenic plus arsenopyrite are useful indicators of sulfur activity and commonly occur in the epithermal environment.

Low-Fe(III) Greenalite Was a Primary Mineral From Neoarchean Oceans

NASA Astrophysics Data System (ADS)

Johnson, Jena E.; Muhling, Janet R.; Cosmidis, Julie; Rasmussen, Birger; Templeton, Alexis S.

2018-04-01

Banded iron formations (BIFs) represent chemical precipitation from Earth's early oceans and therefore contain insights into ancient marine biogeochemistry. However, BIFs have undergone multiple episodes of alteration, making it difficult to assess the primary mineral assemblage. Nanoscale mineral inclusions from 2.5 billion year old BIFs and ferruginous cherts provide new evidence that iron silicates were primary minerals deposited from the Neoarchean ocean, contrasting sharply with current models for BIF inception. Here we used multiscale imaging and spectroscopic techniques to characterize the best preserved examples of these inclusions. Our integrated results demonstrate that these early minerals were low-Fe(III) greenalite. We present potential pathways in which low-Fe(III) greenalite could have formed through changes in saturation state and/or iron oxidation and reduction. Future constraints for ancient ocean chemistry and early life's activities should include low-Fe(III) greenalite as a primary mineral in the Neoarchean ocean.

Direct Visualization of Aggregate Morphology and Dynamics in a Model Soil Organic–Mineral System

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

Hufschmid, Ryan; Newcomb, Christina J.; Grate, Jay W.

Interactions between mineral surfaces and organic matter are ubiquitous in soils and the environment. Through both physical and chemical mechanisms, organic-mineral assemblages prevent decomposition of soil organic matter by limiting accessibility or reducing efficacy of enzymes and microbes. To understand the mechanisms underlying organic-mineral interactions, researchers have begun to interrogate these systems at smaller length scales. Current techniques that maintain a hydrated state and allow researchers to characterize nanometer length scales are limited. Here we chose a model organic-mineral system and performed complementary imaging techniques that enable direct nanoscale observations in environmentally relevant conditions: cryogenic TEM and in-situ liquid cellmore » TEM. We observed a three-fold increase in aggregate size of goethite nanoparticles upon addition of a model organic phosphate ligand and quantification of nanoparticle orientation reveals a preference for side-to-side interactions independent of the addition of an organic ligand. Additionally, in-situ liquid cell TEM experiments provides a dynamic view of the interactions allowing us to report velocities of mineral assemblages during aggregation and disaggregation, which could potentially provide binding energetics and kinetic parameters about organic-mineral and mineral-mineral systems.« less

Mineralogy of new Antarctic achondrites with affinity to Lodran and a model of their evolution in an asteroid

NASA Technical Reports Server (NTRS)

Takeda, Hiroshi; Mori, Hiroshi; Hiroi, Takahiro; Saito, Jun

1994-01-01

We studied five new Antartic achondrites, MacAlpine Hills (MAC) 88177, Yamato (Y)74357, Y75274, Y791491 and Elephant Moraine (EET)84302 by mineralogical techniques to gain a better understanding of the mineral assemblages of a group of meteorites with an affinity to Lodran (stony-iron meteorite) and their formation processes. This group is being called lodranites. These meteorites contain major coarse-grained orthopyroxene (Opx) and olivine as in Lodran and variable amounts of FeNi metal and troilite etc. MAC88177 has more augite and less FeNi than Lodran; Y74357 has more olivine and contains minor augite; Y791491 contains in addition plagioclase. EET84302 has an Acapulco-like chondritic mineral assembladge and is enriched in FeNi metal and plagioclase, but one part is enriched in Opx and chromite. The EET84302 and MAC88177 Opx crystals have dusty cores as in Acapulco. EET84302 and Y75274 are more Mg-rich than other members of the lodranite group, and Y74357 is intermediate. Since these meteorites all have coarse-grained textures, similar major mineral assemblages, variable amounts of augite, plagioclase, FeNi metal, chromite and olivine, we suggest that they are related and are linked to a parent body with modified chondritic compositions. The variability of the abundances of these minerals are in line with a proposed model of the surface mineral assemblages of the S asteroids. The mineral assemblages can best be explained by differing degrees of loss or movements of lower temperature partial melts and recrystallization, and reduction. A portion of EET84302 rich in metal and plagioclase may represent a type of component removed from the lodranite group meteorites. Y791058 and Caddo County, which were studied for comparison, are plagioclase-rich silicate inclusions in IAB iron meteorites and may have been derived by similar process but in a different body.

Simulated space weathering of Fe- and Mg-rich aqueously altered minerals using pulsed laser irradiation

NASA Astrophysics Data System (ADS)

Kaluna, H. M.; Ishii, H. A.; Bradley, J. P.; Gillis-Davis, J. J.; Lucey, P. G.

2017-08-01

Simulated space weathering experiments on volatile-rich carbonaceous chondrites (CCs) have resulted in contrasting spectral behaviors (e.g. reddening vs bluing). The aim of this work is to investigate the origin of these contrasting trends by simulating space weathering on a subset of minerals found in these meteorites. We use pulsed laser irradiation to simulate micrometeorite impacts on aqueously altered minerals and observe their spectral and physical evolution as a function of irradiation time. Irradiation of the mineral lizardite, a Mg-phyllosilicate, produces a small degree of reddening and darkening, but a pronounced reduction in band depths with increasing irradiation. In comparison, irradiation of an Fe-rich aqueously altered mineral assemblage composed of cronstedtite, pyrite and siderite, produces significant darkening and band depth suppression. The spectral slopes of the Fe-rich assemblage initially redden then become bluer with increasing irradiation time. Post-irradiation analyses of the Fe-rich assemblage using scanning and transmission electron microscopy reveal the presence of micron sized carbon-rich particles that contain notable fractions of nitrogen and oxygen. Radiative transfer modeling of the Fe-rich assemblage suggests that nanometer sized metallic iron (npFe0) particles result in the initial spectral reddening of the samples, but the increasing production of micron sized carbon particles (μpC) results in the subsequent spectral bluing. The presence of npFe0 and the possible catalytic nature of cronstedtite, an Fe-rich phyllosilicate, likely promotes the synthesis of these carbon-rich, organic-like compounds. These experiments indicate that space weathering processes may enable organic synthesis reactions on the surfaces of volatile-rich asteroids. Furthermore, Mg-rich and Fe-rich aqueously altered minerals are dominant at different phases of the aqueous alteration process. Thus, the contrasting spectral slope evolution between the Fe- and Mg-rich samples in these experiments may indicate that space weathering trends of volatile-rich asteroids have a compositional dependency that could be used to determine the aqueous histories of asteroid parent bodies.

Hydrothemal Alteration Mapping Using Feature-Oriented Principal Component Selection (fpcs) Method to Aster DATA:WIKKI and Mawulgo Thermal Springs, Yankari Park, Nigeria

NASA Astrophysics Data System (ADS)

Abubakar, A. J.; Hashim, M.; Pour, A. B.

2017-10-01

Geothermal systems are essentially associated with hydrothermal alteration mineral assemblages such as iron oxide/hydroxide, clay, sulfate, carbonate and silicate groups. Blind and fossilized geothermal systems are not characterized by obvious surface manifestations like hot springs, geysers and fumaroles, therefore, they could not be easily identifiable using conventional techniques. In this investigation, the applicability of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were evaluated in discriminating hydrothermal alteration minerals associated with geothermal systems as a proxy in identifying subtle Geothermal systems at Yankari Park in northeastern Nigeria. The area is characterized by a number of thermal springs such as Wikki and Mawulgo. Feature-oriented Principal Component selection (FPCS) was applied to ASTER data based on spectral characteristics of hydrothermal alteration minerals for a systematic and selective extraction of the information of interest. Application of FPCS analysis to bands 5, 6 and 8 and bands 1, 2, 3 and 4 datasets of ASTER was used for mapping clay and iron oxide/hydroxide minerals in the zones of Wikki and Mawulgo thermal springs in Yankari Park area. Field survey using GPS and laboratory analysis, including X-ray Diffractometer (XRD) and Analytical Spectral Devices (ASD) were carried out to verify the image processing results. The results indicate that ASTER dataset reliably and complementarily be used for reconnaissance stage of targeting subtle alteration mineral assemblages associated with geothermal systems.

The influence of minerals on decomposition of the n-alkyl-α-amino acid norvaline under hydrothermal conditions

NASA Astrophysics Data System (ADS)

McCollom, Thomas M.

2013-03-01

Laboratory experiments were conducted to observe the effect of iron oxide and sulfide minerals on decomposition reactions of norvaline, a representative of a group of alkyl-α-amino acids observed in meteorites and prebiotic synthesis experiments. The primary products observed during heating of aqueous solutions of norvaline at temperatures of 156-186 °C in the presence of minerals included CO2, NH3, butyric acid, and valeric acid. The products indicated that norvaline predominantly decomposed by a combination of pathways that included both decarboxylation followed rapidly by oxidative deamination (norvaline → butanamide + CO2 → butyric acid + NH3) and deamination directly to valeric acid (norvaline → valeric acid + NH3). An experiment performed with alanine under similar conditions showed it decomposed by analogous reactions that produced acetic and propionic acids along with CO2 and NH3. For both amino acids, the presence of minerals accelerated decomposition rates as well as altered the final products of reaction, when compared with decomposition in the absence of mineral substrates. In addition, decomposition of norvaline was found to proceed much faster in the presence of the mineral assemblage hematite-magnetite-pyrite (HMP) than with the assemblage pyrite-pyrrhotite-magnetite (PPM), a trend that has been observed for several other organic compounds. The influence of minerals on decomposition reactions of these amino acids appears to be attributable to a combination of surface catalysis and production of dissolved sulfur compounds. Overall, the results indicate that minerals may exert a substantial influence on amino acid stability in many geologic environments, and emphasize the need to consider the impact of minerals when evaluating the lifetimes and decomposition rates of amino acids in terrestrial and planetary systems. Estimated half-lives for alkyl-α-amino acids based on the experimental results indicate that moderately hot hydrothermal environments (<˜100 °C) would have been the most favorable for accumulation of these amino acids in the early solar system, and that the predominance of alkyl-α-amino acids in some meteorites may only be compatible with temperature remaining below about 60 °C following their formation.

Mineral Selection for Multicomponent Equilibrium Geothermometry

DOE PAGES

Plamer, C. D.; Ohly, S. R.; Smith, R. W.; ...

2015-04-01

Multicomponent geothermometry requires knowledge of the mineral phases in the reservoir with which the geothermal fluids may be equilibrated. These minerals phases are most often alteration products rather than primary minerals. We have reviewed the literature on geothermal systems representing most major geologic environments typically associated with geothermal activity and identified potential alteration products in various environments. We have included this information in RTEst, a code we have developed to estimate reservoir conditions (temperature, CO 2 fugacity) from the geochemistry of near-surface geothermal waters. The information has been included in RTEst through the addition of filters that decrease the potentialmore » number of minerals from all possibilities based on the basis species to those that are more relevant to the particular conditions in which the user is interested. The three groups of filters include host rock type (tholeiitic, calc-alkaline, silicic, siliciclastic, carbonate), water type (acidic, neutral), and the temperature range over which the alteration minerals were formed (low, medium, high). The user-chosen mineral assemblage is checked to make sure that it does not violate the Gibbs phase rule. The user can select one of three mineral saturation weighting schemes that decrease the chance the optimization from being skewed by reaction stoichiometry or analytical uncertainty.« less

Identification of hydrated silicate minerals on Mars using MRO-CRISM: Geologic context near Nili Fossae and implications for aqueous alteration

USGS Publications Warehouse

Ehlmann, B.L.; Mustard, J.F.; Swayze, G.A.; Clark, R.N.; Bishop, J.L.; Poulet, F.; Des Marais, D.J.; Roach, L.H.; Milliken, R.E.; Wray, J.J.; Barnouin-Jha, O.; Murchie, S.L.

2009-01-01

The Noachian terrain west of the Isidis basin hosts a diverse collection of alteration minerals in rocks comprising varied geomorphic units within a 100,000 km2 region in and near the Nili Fossae. Prior investigations in this region by the Observatoire pour l'Min??ralogie, l'Eau, les Glaces, et l'Activit?? (OMEGA) instrument on Mars Express revealed large exposures of both mafic minerals and iron magnesium phyllosilicates in stratigraphic context. Expanding on the discoveries of OMEGA, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) has found more spatially widespread and mineralogically diverse alteration minerals than previously realized, which represent multiple aqueous environments. Using CRISM near-infrared spectral data, we detail the basis for identification of iron and magnesium smectites (including both nontronite and more Mg-rich varieties), chlorite, prehnite, serpentine, kaolinite, potassium mica (illite or muscovite), hydrated (opaline) silica, the sodium zeolite analcime, and magnesium carbonate. The detection of serpentine and analcime on Mars is reported here for the first time. We detail the geomorphic context of these minerals using data from high-resolution imagers onboard MRO in conjunction with CRISM. We find that the distribution of alteration minerals is not homogeneous; rather, they occur in provinces with distinctive assemblages of alteration minerals. Key findings are (1) a distinctive stratigraphy, in and around the Nili Fossae, of kaolinite and magnesium carbonate in bedrock units always overlying Fe/Mg smectites and (2) evidence for mineral phases and assemblages indicative of low-grade metamorphic or hydrothermal aqueous alteration in cratered terrains. The alteration minerals around the Nili Fossae are more typical of those resulting from neutral to alkaline conditions rather than acidic conditions, which appear to have dominated much of Mars. Moreover, the mineralogic diversity and geologic context of alteration minerals found in the region around the Nili Fossae indicates several episodes of aqueous activity in multiple distinct environments. Copyright 2009 by the American Geophysical Union.

Petrology of enstatite chondrites and anomalous enstatite achondrites

NASA Astrophysics Data System (ADS)

van Niekerk, Deon

2012-01-01

Chondrites are meteorites that represent unmelted portions of asteroids. The enstatite chondrites are one class of chondrites. They consist of reduced mineral assemblages that formed under low oxygen fugacity in the solar nebula, prior to accretion into asteroids. There are two groups of enstatite chondrites---EH and EL. I studied EL3 meteorites, which are understood to be unmetamorphosed and thus to only preserve primitive nebular products. I show in a petrographic study that the EL3s are in fact melt--breccias in which impact-melting produced new mineral assemblages and textures in portions of the host chondrites, after accretion. I document meta- land sulfide assemblages that are intergrown with silicate minerals (which are often euhedral), and occur outside chondrules; these assemblages probably represent impact-melting products, and are different from those in EH3 chondrites that probably represent nebular products. In situ siderophile trace element compositions of the metal in EL3s, obtained by laser ablation inductively coupled plasma mass spectrometry, are consistent with an impact-melting hypothesis. The trace element concentrations show no clear volatility trend, and are thus probably not the result of volatile-driven petrogenetic processes that operated in the solar nebula. Trace element modeling suggests that the character of the trace element patterns together with deviations from the mean bulk EL metal pattern is consistent with metal that crystallized in a coexisting liquid-solid metal system in which dissolved carbon influenced element partitioning. I also conducted a petrographic and mineral-chemistry study of several anomalous enstatite meteorites. These have igneous textures, but unfractionated mineralogy similar to unmelted chondrites. I show that with the exception of one, the meteorites are related to each other, and probably formed by crystallization from an impact melt instead of metamorphism through the decay of short lived radionuclides. The broad importance of these studies lies in documenting the petrology of extraterrestrial materials that reveal the geological history of the young solar system prior to the existence of planets. Furthermore, they serve to identify which mineral assemblages record nebular processes and which record processes on asteroids, so that future studies may select the correct material to address particular questions.

Heterogeneous mineral assemblages in martian meteorite Tissint as a result of a recent small impact event on Mars

NASA Astrophysics Data System (ADS)

Walton, E. L.; Sharp, T. G.; Hu, J.; Filiberto, J.

2014-09-01

The microtexture and mineralogy of shock melts in the Tissint martian meteorite were investigated using scanning electron microscopy, Raman spectroscopy, transmission electron microscopy and synchrotron micro X-ray diffraction to understand shock conditions and duration. Distinct mineral assemblages occur within and adjacent to the shock melts as a function of the thickness and hence cooling history. The matrix of thin veins and pockets of shock melt consists of clinopyroxene + ringwoodite ± stishovite embedded in glass with minor Fe-sulfide. The margins of host rock olivine in contact with the melt, as well as entrained olivine fragments, are now amorphosed silicate perovskite + magnesiowüstite or clinopyroxene + magnesiowüstite. The pressure stabilities of these mineral assemblages are ∼15 GPa and >19 GPa, respectively. The ∼200-μm-wide margin of a thicker, mm-size (up to 1.4 mm) shock melt vein contains clinopyroxene + olivine, with central regions comprising glass + vesicles + Fe-sulfide spheres. Fragments of host rock within the melt are polycrystalline olivine (after olivine) and tissintite + glass (after plagioclase). From these mineral assemblages the crystallization pressure at the vein edge was as high as 14 GPa. The interior crystallized at ambient pressure. The shock melts in Tissint quench-crystallized during and after release from the peak shock pressure; crystallization pressures and those determined from olivine dissociation therefore represent the minimum shock loading. Shock deformation in host rock minerals and complete transformation of plagioclase to maskelynite suggest the peak shock pressure experienced by Tissint ⩾ 29-30 GPa. These pressure estimates support our assessment that the peak shock pressure in Tissint was significantly higher than the minimum 19 GPa required to transform olivine to silicate perovskite plus magnesiowüstite. Small volumes of shock melt (<100 μm) quench rapidly (0.01 s), whereas thermal equilibration will occur within 1.2 s in larger volumes of melt (1 mm2). The apparent variation in shock pressure recorded by variable mineral assemblages within and around shock melts in Tissint is consistent with a shock pulse on the order of 10-20 ms combined with a longer duration of post-shock cooling and complex thermal history. This implies that the impact on Mars that shocked and ejected Tissint at ∼1 Ma was not exceptionally large.

Analysis of mixed-layer clay mineral structures

USGS Publications Warehouse

Bradley, W.F.

1953-01-01

Among the enormously abundant natural occurrences of clay minerals, many examples are encountered in which no single specific crystallization scheme extends through a single ultimate grain. The characterization of such assemblages becomes an analysis of the distribution of matter within such grains, rather than the simple identification of mineral species. It having become established that the particular coordination complex typified by mica is a common component of many natural subcrystalline assemblages, the opportunity is afforded to analyze scattering from random associations of these complexes with other structural units. Successful analyses have been made of mixed hydration states of montmorillonite, of montmorillonite with mica, of vermiculite with mica, and of montmorillonite with chlorite, all of which are variants of the mica complex, and of halloysite with hydrated halloysite.

Geology, mineralization, and fluid inclusion characteristics of the Skrytoe reduced-type W skarn and stockwork deposit, Sikhote-Alin, Russia

NASA Astrophysics Data System (ADS)

Soloviev, Serguei G.; Kryazhev, Sergey G.

2017-08-01

The Skrytoe deposit (>145 Kt WO3, average grade 0.449% WO3) in the Sikhote-Alin orogenic system (Eastern Russia) is situated in a metallogenic belt of W, Sn-W, Au, and Au-W deposits formed in a late to post-collisional tectonic environment after cessation of active subduction. It is localized within a mineralized district of reduced-type skarn W and veined Au (±W) deposits and occurrences related to the Early Cretaceous ilmenite-series plutonic suite. The deposit incorporates large stockworks of scheelite-bearing veinlets related to propylitic (amphibole, chlorite, quartz) and phyllic (quartz, sericite, albite, apatite, and carbonate) hydrothermal alteration. The stockwork cuts flat-lying mafic volcanic rocks and limestone partially replaced by pyroxene skarn that host the major W orebodies. Scheelite is associated with pyrrhotite and/or arsenopyrite, with minor chalcopyrite and other sulfide minerals; the late phyllic stage assemblages hosts Bi and Au mineralization. The fluid evolution included low-salinity moderate-temperature, moderate-pressure (˜370-390 °C, ˜800 bars) methane-dominated carbonic-aqueous fluids that formed post-skarn propylitic alteration assemblages. Then, at the phyllic stage, there has been an evolution from methane-dominated, moderate-temperature (330-360 °C), low-salinity (<12.3 wt% NaCl equiv.) fluids forming the early quartz-sericite-albite-arsenopyrite assemblage, through lower temperature (290-330 °C) methane-dominated, low-salinity (˜9-10 wt% NaCl equiv.) fluids forming the intermediate quartz-sericite-albite-scheelite-pyrrhotite assemblage, to yet lower temperature (245-320 °C) CO2-dominated carbonic-aqueous low-salinity (˜1-7 wt% NaCl equiv.) fluids forming the late quartz-sericite-sulfide-Bi-Au assemblage. Recurrent fluid immiscibility (phase separation) and cooling probably affected W solubility and promoted scheelite deposition. The stable isotope data support a sedimentary source of carbon (δ13Cfluid = ˜-21 to -10 ‰), a magmatic source for water (δ18OH2O = +7.4 to +7.7 ‰), and dominantly crustal-derived source of sulfur (δ34S = -4.6 to -2.9 ‰) in the hydrothermal fluids. This is consistent with the development of larger, longer crystallizing crustal intermediate to felsic magma chambers in the late to post-collisional tectonic environment, with their protracted magmatic evolution advancing magmatic differentiation and partitioning of W into magmatic-hydrothermal fluid. The dominating role of the crustal-derived magmatic water, sulfur, and carbon appears to be an important feature of reduced W skarn deposits related to ilmenite-series granitoids.

A study of the trace sulfide mineral assemblages in the Stillwater Complex, Montana, USA

NASA Astrophysics Data System (ADS)

Aird, Hannah M.; Ferguson, Katherine M.; Lehrer, Malia L.; Boudreau, Alan E.

2017-03-01

The sulfide assemblages of the Stillwater Complex away from the well-studied ore zones are composed mainly of variable proportions of pyrrhotite, chalcopyrite, pentlandite, and ±pyrite. Excluding vein assemblages and those affected by greenschist and lower temperature alteration, the majority can be classified into two broad assemblages, defined here as pristine (multiphase, often globular in shape) or volatile-bearing (multiphase, high-temperature, volatile-rich minerals such as biotite, hornblende, or an unmixed calcite-dolomite assemblage). The volatile-bearing assemblages are mainly found within and below the J-M reef, where native copper and sphalerite are also locally present. Pristine sulfides are found throughout the stratigraphy. Both groups can be affected by apparent S loss in the form of pyrite being converted to magnetite and chalcopyrite to a Cu-Fe-oxide (delafossite), with little to no silicate alteration. An upward trend from pentlandite-rich to pyrrhotite-rich to pyrite-rich assemblages is observed in the footwall rocks in upper GN-I, and the same trend repeats from just below the reef and continues into the overlying N-II and GN-II. Modeling suggests that the sulfide Ni in the Peridotite Zone is largely controlled by silicate Ni. When taken together, observations are most readily explained by the remobilization of selected elements by a high-temperature fluid with the apparent loss of S > Cu > Ni. This could concentrate ore metals by vapor refining, eventually producing a platinum group element-enriched sulfide ore zone, such as the J-M reef.

The Friningen Garnet Peridotite (central Swedish Caledonides). A good example of the characteristic PTt path of a cold mantle wedge garnet peridotite

NASA Astrophysics Data System (ADS)

Gilio, Mattia; Clos, Frediano; van Roermund, Herman L. M.

2015-08-01

We present pseudosections of Cr-bearing garnet peridotite that together with new mineral-chemical data allow quantification of the early PT conditions of the original lithospheric mantle assemblage (M1) of the Friningen Garnet Peridotite (FGP) located in the central/middle belt of the Seve Nappe Complex in central Sweden. Results indicate that the early, coarse grained, olivine + orthopyroxene + clinopyroxene + "high Cr" garnet assemblage (M1a) was formed at 1100 ± 100 °C and 5.0 ± 0.5 GPa. These metamorphic conditions were followed by an inferred late Proterozoic exhumation event down to 850-900 °C and 1.5 GPa (M1b). The latter PT estimate is based on the breakdown of high-Cr M1a garnet (Cr# = 0.065) + olivine into an orthopyroxene + clinopyroxene + spinel (Cr# = 0.15-0.25) ± pargasite kelyphite (M1b) and the exsolution of garnet from Al-rich orthopyroxene and clinopyroxene. The M1b kelyphite is overprinted by an early-Caledonian UHPM mineral assemblage (M2; T = 800 °C and P = 3.0 GPa), equivalent to the earlier discovered UHP assemblage within an eclogitic dyke that cross-cuts FGP. In the garnet peridotite M2 is displayed by low-Cr garnet (Cr# = 0.030) growing together with spinel (Cr# = 0.35-0.45), both these minerals form part of the olivine + orthopyroxene + clinopyroxene + garnet + spinel + pargasite M2 assemblage. The formation of plagioclase + diopside symplectites after omphacite and breakdown of kyanite to sapphirine + albite in internal eclogite and the breakdown of M2 olivine + garnet to amphibole + orthopyroxene + spinel assemblages (M3) in garnet peridotite indicate post-UHP isothermal decompression down to 750-800 °C and 0.8-1.0 GPa (= M3). Multiphase solid-and fluid inclusion assemblages composed of Sr-bearing magnesite, dolomite or carbon decorate linear defect structures within M1a-b minerals and/or form subordinate local assemblages together with M2 minerals. The latter are interpreted as evidence for infiltration of early-Caledonian COH-bearing subduction zone fluids. The well-defined PTt-deformation path of the FGP resembles that of a mantle wedge garnet peridotite. The M1 assemblage originates from the base of a cold, old and thick subcontinental lithospheric mantle that is inferred to extend asymmetrically leading to extreme exhumation of FGP down to lithospheric conditions around 1.5 GPa and 850-900 °C. After that the FGP became incorporated into the subducting continental crust of the SNC during "early-Caledonian" subduction (M2) down to UHPM conditions (800 °C/3.0 GPa), subsequently followed by eduction back to sub-crustal levels. As such, FGP is the first locality in the Swedish Caledonides from which two UHP metamorphic events are described, the first event can be related to the formation of an ancient (> 1.0 Ga) lithosphere underneath a craton (Rodinia) and the second is of early-Caledonian age.

Chemical composition and osmium-isotope systematics of primary and secondary PGM assemblages from high-Mg chromitite of the Nurali lherzolite massif, the South Urals, Russia

NASA Astrophysics Data System (ADS)

Malitch, K. N.; Anikina, E. V.; Badanina, I. Yu.; Belousova, E. A.; Pushkarev, E. V.; Khiller, V. V.

2016-01-01

The isotopic and geochemical characteristics of PGE mineralization in high-Mg chromitite from the banded dunite-wehrlite-clinopyroxenite complex of the Nurali lherzolite massif, the South Urals, Russia is characterized for the first time. Electron microprobe analysis and LA MC-ICP-MS mass spectrometry are used for studying Cr-spinel and platinum-group minerals (PGM). Two processes synchronously develop in high-Mg chromitite subject to metamorphism: (1) the replacement of Mg-Al-rich Cr-spinel, orthopyroxene, and diopside by chromite, Cr-amphibole, chlorite, and garnet; (2) the formation of a secondary mineral assemblage consisting of finely dispersed ruthenium or Ru-hexaferrum aggregate and silicate-oxide or silicate matter on the location of primary Ru-Os-sulfides of the laurite-erlichmanite solid solution series. Similar variations of Os-isotopic composition in both primary and secondary PGM assemblages are evidence for the high stability of the Os isotope system in PGM and for the possibility of using model 187Os/188Os ages in geodynamic reconstructions.

Metamorphic style and development of the blueschist- to eclogite-facies rocks, Cyclades, Greece

NASA Astrophysics Data System (ADS)

Schumacher, J. C.; Brady, J. B.; Cheney, J. T.

2008-07-01

The island of Syros, Greece is part of the Attic-Cycladic blueschist belt, formed during Mesozoic Eurasia-Africa subduction. The rocks of Syros can be broadly divided into three tectono-stratigraphic units: (I) metamorphosed sedimentary and volcanic rocks (marble-schist sequence), (II) remnants of oceanic crust with fault-bounded packages of blueschist/eclogite-facies mafic rocks and serpentinite (mafic-ultramafic rocks) and (III) the Vari gneiss, which is a tectonic klippe. Low-temperature, high-pressure assemblages are found on several islands in the Cyclades. The best preserved of these rocks are on Syros and Sifnos islands. Mineral compositions and peak metamorphic assemblages are similar on both islands. Both islands are considered to share similar P-T histories with highest-pressure mineral assemblages reflecting conditions of at least 15 kbar and about 500°C.

Clues on Acid-Sulfate Alteration and Hematite Formation on Earth and Mars From Iron Isotopic Analyses of Terrestrial Analogues From Hawaii

NASA Technical Reports Server (NTRS)

Nie, N. X.; Dauphas, N.; Morris, R. V

2017-01-01

The Mars Exploration Rover mission revealed the presence of rocks and minerals indicative of water-rock interactions on Mars. A range of mineralogies have been identified, including hematite spherules (i.e., blueberries), jarosite, Mg-, Ca-sulfates, silica-rich materials and silicate relics from basaltic rocks. The mineral assemblages have been interpreted to be derived from acid-sulfate alteration of basaltic materials. Indeed, the chemical compositions of rocks and soils at Home Plate in Gusev Crater follow the trends expected for acid-sulfate alteration.

Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

NASA Astrophysics Data System (ADS)

Lang, Helen M.; Gilotti, Jane A.

2015-06-01

Pseudosection modeling constrains the pressure-temperature (P-T) exhumation path of partially melted ultrahigh-pressure (UHP) metapelites exposed in the North-East Greenland UHP terrane. A robust peak P and T estimate of 3.6 GPa and 970 °C based on mineral assemblages in nearby kyanite eclogites is the starting point for the P-T path. Although the peak assemblage for the metapelite is not preserved, the calculated modeled peak assemblage contained substantial clinopyroxene, garnet, phengite, K-feldspar and coesite with minor kyanite and rutile. Combining the pseudosection and observed textures, the decompression path crosses the coesite-quartz transition before reaching the dry phengite dehydration melting reaction where phengite is abruptly consumed. In the range of 2.5 to 2.2 GPa, clinopyroxene is completely consumed and garnet grows to its maximum volume and grossular content, matching the high grossular rims of relict megacrysts. Plagioclase joins the assemblage and the pseudosection predicts up to 12-13 vol.% melt in the supersolidus assemblage, which contained garnet, liquid, K-feldspar, plagioclase, kyanite, quartz and rutile. At this stage, the steep decompression path flattened out and became nearly isobaric. The melt crystallization assemblage that formed when the path crossed the solidus with decreasing temperature contains phengite, garnet, biotite, 2 feldspars, kyanite, quartz and rutile. Therefore, the path must have intersected the solidus at approximately 1.2 GPa, 825 °C. The pseudosection predicts that garnet is consumed on the cooling path, but little evidence of late garnet consumption or other retrograde effects is observed. This may be due to partial melt loss from the rock. Isochemical PT-n and PT-X sections calculated along the P-T path display changes in mineral assemblage and composition that are consistent with preserved assemblages.

Thermodynamic modeling using BINGO-ANTIDOTE: A new strategy to investigate metamorphic rocks

NASA Astrophysics Data System (ADS)

Lanari, Pierre; Duesterhoeft, Erik

2016-04-01

BINGO-ANTIDOTE is a new program, combing the achievements of the two petrological software packages XMAPTOOLS[1] and THERIAK-DOMINO[2]. XMAPTOOLS affords information about compositional zoning in mineral and local bulk composition of domains at the thin sections scale. THERIAK-DOMINO calculates equilibrium phase assemblages from given bulk rock composition, temperature T and pressure P. Primarily BINGO-ANTIDOTE can be described as an inverse THERIAK-DOMINO, because it uses the information provided by XMAPTOOLS to calculate the probable P-T equilibrium conditions of metamorphic rocks. Consequently, the introduced program combines the strengths of forward Gibbs free energy minimization models with the intuitive output of inverse thermobarometry models. In order to get "best" P-T equilibrium conditions of a metamorphic rock sample and thus estimating the degree of agreement between the observed and calculated mineral assemblage, it is critical to define a reliable scoring strategy. BINGO uses the THERIAKD ADD-ON[3] (Duesterhoeft and de Capitani, 2013) and is a flexible model scorer with 3+1 evaluation criteria. These criteria are the statistical agreement between the observed and calculated mineral-assemblage, -proportions (vol%) and -composition (mol). Additionally, a total likelihood, consisting of the first three criteria, allows the user an evaluation of the most probable equilibrium P-T condition. ANTIDOTE is an interactive user interface, displaying the 3+1 evaluation criteria as probability P-T-maps. It can be used with and without XMAPTOOLS. As a stand-alone program, the user is able to give the program macroscopic observations (i.e., mineral names and proportions), which ANTIDOTE converts to a readable BINGO input. In this manner, the use of BINGO-ANTIDOTE opens up thermodynamics to students and people with only a basic knowledge of phase diagrams and thermodynamic modeling techniques. This presentation introduces BINGO-ANTIDOTE and includes typical examples of its functionality, such as the determination of P-T conditions of high-grade rocks. BINGO-ANTIDOTE is still under development and will soon be freely available online. References: [1] Lanari P., Vidal O., De Andrade V., Dubacq B., Lewin E., Grosch E. G. and Schwartz S. (2013) XMapTools: a MATLAB©-based program for electron microprobe X-ray image processing and geothermobarometry. Comput. Geosci. 62, 227-240. [2] de Capitani C. and Petrakakis K. (2010) The computation of equilibrium assemblage diagrams with Theriak/Domino software. Am. Mineral. 95, 1006-1016. [3] Duesterhoeft E. and de Capitani C. (2013) Theriak_D: An add-on to implement equilibrium computations in geodynamic models. Geochem. Geophys. Geosyst. 14, 4962-4967.

Lead Isotope Characteristics of the Mindyak Gold Deposit, Southern Urals: Evidence for the Source of Metals

NASA Astrophysics Data System (ADS)

Chugaev, A. V.; Znamensky, S. E.

2018-01-01

The isotopic composition of Pb in pyrite of the Mindyak orogenic gold deposit located in the Main Ural Fault Zone, the Southern Urals, has been studied by the high-precision MC-ICP-MS method. Orebodies at the deposit are composed of early pyrite and late polysulfide-carbonate-quartz mineral assemblages. The orebodies are localized in olistostrome with carbonaceous clayey-cherty cement. Pyrites from early and late mineral assemblages are close in Pb isotope ratios. For early pyrite 206Pb/204Pb = 18.250-18.336, 207Pb/204Pb = 15.645-15.653, 208Pb/204Pb = 38.179-38.461; while for late pyrite 206Pb/204Pb = 18.102-18.378, 207Pb/204Pb = 15.635-15.646, 208Pb/204Pb = 38.149-38.320. The model parameters μ2 (238U/204Pb = 9.91 ± 2), ω2 (232Th/204Pb = 38.5 ± 4), and 232Th/238U = 3.88 ± 3 indicate that an upper crustal Pb source played a leading role in ore formation. Carbonaceous shale as an olistostrome cement and syngenetic sulfide mineralization are considered to be the main Pb sources of both early and late mineral assemblages. An additional recept in apparently magmatic lead is suggested for the late veinlet mineralization. The involvement of lead from several sources in ore formation is consistent with the genetic model, which assumes a two-stage formation of orebodies at the Mindyak deposit.

Submicron-scale mineralogy of lithotypes and the implications for trace element associations: Blue Gem coal, Knox County, Kentucky

DOE PAGES

Hower, James C.; Berti, Debora; Hochella, Michael F.; ...

2018-04-16

Transmission electron microscopy accompanied by energy-dispersive spectroscopy and selected area electron diffraction of density-gradient separates from two lithotypes of the low-ash, low-sulfur Blue Gem coal, eastern Kentucky, revealed an array of previously unrecognized (in this coal, and arguable in most others) sub-micron minerals, some <10 nm in size. The first sample representing the 1.22–1.24 specific gravity fraction of the middle bench contains a mineral identified as a La-, Ce-, Nd-bearing monazite; other minerals with CrFe, CuFeS, FeZn-S, and Pb; and areas, probably comprising agglomerates of several grains, if not several minerals, with concentrations of Mg, Ca, Ti, Fe, Zn, Zr,more » and Mo. The second sample representing the 1.30–1.31 specific gravity fraction of the basal lithotype has aggregates of particles enriched in Mg, Ca, Ti, and Fe. Individual grains not specifically quantified include CrNiMnCuFeS, AgS, and CuS. Detailed investigation of one area (most of the variation within a <4 μm 2 region) demonstrates the presence of greenockite (CdS); minute phases containing NiCoGe and AgCdBi, the latter with a more evident S association than the former; metallic Bi; nisnite (Ni 3Sn); silver cadmium; manganosite (MnO); and siderite. Some minerals, such as the monazite, are most likely of detrital or tuffaceous origin. Many of the other assemblages could be of hydrothermal origin, a hypothesis supported by known regional geochemical and coal rank trends, but not previously demonstrated in mineral assemblages at the 10's of nm scale in this region.« less

Submicron-scale mineralogy of lithotypes and the implications for trace element associations: Blue Gem coal, Knox County, Kentucky

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

Hower, James C.; Berti, Debora; Hochella, Michael F.

Transmission electron microscopy accompanied by energy-dispersive spectroscopy and selected area electron diffraction of density-gradient separates from two lithotypes of the low-ash, low-sulfur Blue Gem coal, eastern Kentucky, revealed an array of previously unrecognized (in this coal, and arguable in most others) sub-micron minerals, some <10 nm in size. The first sample representing the 1.22–1.24 specific gravity fraction of the middle bench contains a mineral identified as a La-, Ce-, Nd-bearing monazite; other minerals with CrFe, CuFeS, FeZn-S, and Pb; and areas, probably comprising agglomerates of several grains, if not several minerals, with concentrations of Mg, Ca, Ti, Fe, Zn, Zr,more » and Mo. The second sample representing the 1.30–1.31 specific gravity fraction of the basal lithotype has aggregates of particles enriched in Mg, Ca, Ti, and Fe. Individual grains not specifically quantified include CrNiMnCuFeS, AgS, and CuS. Detailed investigation of one area (most of the variation within a <4 μm 2 region) demonstrates the presence of greenockite (CdS); minute phases containing NiCoGe and AgCdBi, the latter with a more evident S association than the former; metallic Bi; nisnite (Ni 3Sn); silver cadmium; manganosite (MnO); and siderite. Some minerals, such as the monazite, are most likely of detrital or tuffaceous origin. Many of the other assemblages could be of hydrothermal origin, a hypothesis supported by known regional geochemical and coal rank trends, but not previously demonstrated in mineral assemblages at the 10's of nm scale in this region.« less

Physical-chemical conditions of ore deposition

USGS Publications Warehouse

Barton, P.B.

1981-01-01

Ore deposits form under a wide range of physical and chemical conditions, but those precipitating from hot, aqueous fluids-i.e. the hydrothermal deposits-form generally below 700??C and at pressures of only 1 or 2 kbar or less. Natural aqueous fluids in rocks may extract metal and sulfur from a variety of rock types or may acquire them as a residual heritage from a crystallizing silicate magma. Ore-forming hydrothermal fluids never appear as hot springs (except in deep, submarine situations) because they boil, mix with surface waters, and cool, thereby losing their ore-bearing ability before reaching the surface. Mineral systems function as chemical buffers and indicators just as buffers and indicators function in a chemical laboratory. By reading the record written in the buffer/indicator assemblages of minerals one can reconstruct many aspects of the former chemical environment. By studying the record of changing conditions one may deduce information regarding the processes functioning to create the succession of chemical environments and the ore deposits they represent. The example of the OH vein at Creede, Colorado, shows a pH buffered by the K-feldspar + muscovite + quartz assemblage and the covariation of S2 and O2 buffered by the assemblage chlorite + pyrite + quartz. Boiling of the ore fluid led to its oxidation to hematite-bearing assemblages and simultaneously produced an intensely altered, sericitic capping over the vein in response to the condensation of vapors bearing acidic components. The solubility of metals as calculated from experimental and theoretical studies of mineral solubility appears too low by at least one or two powers of ten to explain the mineralization at Creede. In contrast to Creede where the mineral stabilities all point to a relatively consistent chemistry, the Mississippi Valley type deposits present a puzzle of conflicting chemical clues that are impossible to reconcile with any single equilibrium situation. Thus we must seriously consider metastable equilibria; those most likely involve redox disequilibrium among the sulfur species in solution and perhaps also involve organic compounds. ?? 1981.

Blueschist preservation in a retrograded, high-pressure, low-temperature metamorphic terrane, Tinos, Greece: Implications for fluid flow paths in subduction zones

NASA Astrophysics Data System (ADS)

Breeding, Christopher M.; Ague, Jay J.; BröCker, Michael; Bolton, Edward W.

2003-01-01

The preservation of high-pressure, low-temperature (HP-LT) mineral assemblages adjacent to marble unit contacts on the Cycladic island of Tinos in Greece was investigated using a new type of digital outcrop mapping and numerical modeling of metamorphic fluid infiltration. Mineral assemblage distributions in a large blueschist outcrop, adjacent to the basal contact of a 150-meter thick marble horizon, were mapped at centimeter-scale resolution onto digital photographs using a belt-worn computer and graphics editing software. Digital mapping reveals that while most HP-LT rocks in the outcrop were pervasively retrograded to greenschist facies, the marble-blueschist contact zone underwent an even more intense retrogression. Preservation of HP-LT mineral assemblages was mainly restricted to a 10-15 meter zone (or enclave) adjacent to the intensely retrograded lithologic contact. The degree and distribution of the retrograde overprint suggests that pervasively infiltrating fluids were channelized into the marble-blueschist contact and associated veins and flowed around the preserved HP-LT enclave. Numerical modeling of Darcian flow, based on the field observations, suggests that near the marble horizon, deflections in fluid flow paths caused by flow channelization along the high-permeability marble-blueschist contact zone likely resulted in very large fluid fluxes along the lithologic contact and significantly smaller fluxes (as much as 8 times smaller than the input flux) within the narrow, low-flux regions where HP-LT minerals were preserved adjacent to the contact. Our results indicate that lithologic contacts are important conduits for metamorphic fluid flow in subduction zones. Channelization of retrograde fluids into these discrete flow conduits played a critical role in the preservation of HP-LT assemblages.

Hyperspectral mapping of alteration assemblages within a hydrothermal vug at the Haughton impact structure, Canada

NASA Astrophysics Data System (ADS)

Greenberger, Rebecca N.; Mustard, John F.; Osinski, Gordon R.; Tornabene, Livio L.; Pontefract, Alexandra J.; Marion, Cassandra L.; Flemming, Roberta L.; Wilson, Janette H.; Cloutis, Edward A.

2016-12-01

Meteorite impacts on Earth and Mars can generate hydrothermal systems that alter the primary mineralogies of rocks and provide suitable environments for microbial colonization. We investigate a calcite-marcasite-bearing vug at the 23 km diameter Haughton impact structure, Devon Island, Nunavut, Canada, using imaging spectroscopy of the outcrop in the field (0.65-1.1 μm) and samples in the laboratory (0.4-2.5 μm), point spectroscopy (0.35-2.5 μm), major element chemistry, and X-ray diffraction analyses. The mineral assemblages mapped at the outcrop include marcasite; marcasite with minor gypsum and jarosite; fibroferrite and copiapite with minor gypsum and melanterite; gypsum, Fe3+ oxides, and jarosite; and calcite, gypsum, clay, microcline, and quartz. Hyperspectral mapping of alteration phases shows spatial patterns that illuminate changes in alteration conditions and formation of specific mineral phases. Marcasite formed from the postimpact hydrothermal system under reducing conditions, while subsequent weathering oxidized the marcasite at low temperatures and water/rock ratios. The acidic fluids resulting from the oxidation collected on flat-lying portions of the outcrop, precipitating fibroferrite + copiapite. That assemblage then likely dissolved, and the changing chemistry and pH resulting from interaction with the calcite-rich host rock formed gypsum-bearing red coatings. These results have implications for understanding water-rock interactions and habitabilities at this site and on Mars.

Origin of primary PGM assemblage in сhromitite from a mantle tectonite at Harold's Grave (Shetland Ophiolite Complex, Scotland)

NASA Astrophysics Data System (ADS)

Badanina, Inna Yu.; Malitch, Kreshimir N.; Lord, Richard A.; Meisel, Thomas C.

2013-12-01

In this paper we present textural and mineral chemistry data for a PGM inclusion assemblage and whole-rock platinum-group element (PGE) concentrations of chromitite from Harold's Grave, which occurrs in a dunite pod in a mantle tectonite at Unst in the Shetland Ophiolite Complex (SOC), Scotland. The study utilized a number of analytical techniques, including acid digestion and isotope dilution (ID) ICP-MS, hydroseparation and electron microprobe analysis. The chromitite contains a pronounced enrichment of refractory PGE (IPGE: Os, Ir and Ru) over less refractory PGE (PPGE: Rh, Pt and Pd), typical of mantle hosted `ophiolitic' chromitites. A `primary' magmatic PGM assemblage is represented by euhedrally shaped (up to 60 μm in size) single and composite inclusions in chromite. Polyphase PGM grains are dominated by laurite and osmian iridium, with subordinate laurite + osmian iridium + iridian osmium and rare laurite + Ir-Rh alloy + Rh-rich sulphide (possibly prassoite). The compositional variability of associated laurite and Os-rich alloys at Harold's Grave fit the predicted compositions of experiment W-1200-0.37 of Andrews and Brenan (Can Mineral 40: 1705-1716, 2002) providing unequivocal information on conditions of their genesis, with the upper thermal stability of laurite in equilibrium with Os-rich alloys estimated at 1200-1250 °C and f(S2) of 10-0.39-10-0.07.

Superficial alteration mineralogy in active volcanic systems: An example of Poás volcano, Costa Rica

NASA Astrophysics Data System (ADS)

Rodríguez, Alejandro; van Bergen, Manfred J.

2017-10-01

The alteration mineralogy in the crater area of Poás volcano (Costa Rica) has been studied to constrain acid fluid-rock interaction processes and conditions relevant for the formation of sulphate-bearing mineral assemblages found on the surface of Mars. Individual sub-environments, which include the hyperacid lake (Laguna Caliente), ephemeral hot springs, fumarole vents and areas affected by acid rain and/or spray from the lake, are marked by distinct secondary mineral associations, with sulphates commonly as prevailing component. The sulphates occur in a wide mineralogical diversity comprising gypsum/anhydrite, various polyhydrated Al-sulphates, alunite-jarosite group minerals, halotrichite-, voltaite- and copiapite-group minerals, epsomite and römerite. Depending on the sub-environment, they are variably associated with clay minerals (kaolinite-group and smectite-group), zeolites, SiO2-polymorphs, Fe-(hydro)oxides, Ti-oxides, native sulphur, sulphides, chlorides, fluorides, phosphates and carbonates. Geochemical modelling was performed to identify mechanisms responsible for the formation of the secondary minerals found in the field, and to predict their possible stability under conditions not seen at the surface. The results indicate that the appearance of amorphous silica, hematite, anhydrite/gypsum, pyrite, anatase and kaolinite is relatively insensitive to the degree of acidity of the local aqueous system. On the other hand, alunite-jarosite group minerals, elemental sulphur and Al(OH)SO4 only form under acidic conditions (pH < 4). The presence of polyhydrated Mg- and Fe2 +-sulphates is restricted to olivine-bearing rocks exposed to acid rain or brine spray. Modelling suggests that their formation required a repetitive sequence of olivine dissolution and evaporation in an open system involving limited amounts of fluid. The mineral variety in the crater of Poás is remarkably similar to sulphate-bearing assemblages considered to be the product of acid-sulphate alteration on Mars. The analogy suggests that comparable fluid-rock interaction controls operated in Martian volcanic environments.

Apollo 15 Mg- and Fe-norites - A redefinition of the Mg-suite differentiation trend

NASA Technical Reports Server (NTRS)

Lindstrom, M. M.; Marvin, U. B.; Mittlefehldt, D. W.

1989-01-01

The Apollo 15 highland rocks from the Apennine Front include clasts of mafic plutonic rocks from deep in the lunar crust that were brought to the surface by the Imbrium and Serenitatis impacts. The Apollo 15 norites exhibit wide variations in mineral and bulk compositions and include Fe-norites that plot between the three major pristine rock fields on a diagram of Mg' in mafic minerals vs An in paglioclase. Based on assemblages and compositions of minerals, and on ratios of elemental abundances, it is concluded that these Apollo 15 Fe-norites are differentiated members of the Mg-norite suite. The Apollo 15 and 17 norites and troctolites form a closely related suite of rocks, whose variations in mineral compositions represent the main differentiation trend of the Mg-suite. This trend in mineral compositions has a steeper slope than the previous Mg-suite field. The parent magmas for these Mg-suite rocks formed by partial melting deep in the lunar mantle. Differentiation by fractional crystallization may also have included assimilation of crustal components as the magmas rose from the mantle and crystallized plutons in the lower crust.

Magnetic minerals in soils across the forest-prairie ecotone in NW Minnesota

NASA Astrophysics Data System (ADS)

Maxbauer, D.; Feinberg, J. M.; Fox, D. L.; Nater, E. A.

2016-12-01

Soil pedogenesis results in a complex assemblage of iron oxide minerals that can be disentangled successfully using sensitive magnetic techniques to better delineate specific soil processes. Here, we evaluate the variability in soil processes within forest, prairie, and transitional soils along an 11 km transect of anthropogenically unaltered soils that span the forest-to-prairie ecotone in NW Minnesota. All soils in this study developed on relatively uniform topography, similar glacial till parent material, under a uniform climate, and presumably over similar time intervals. The forest-to-prairie transition zone in this region is controlled by naturally occurring fires, affording the opportunity to evaluate differences in soil processes related to vegetation (forest versus prairie) and burning (prairie and transitional soils). Results suggest that the pedeogenic fraction of magnetite/maghemite in soils is similar in all specimens and is independent of soil type, vegetation, and any effects of burning. Magnetically enhanced horizons have 45% of remanence held by a low-coercivity pedogenic component (likely magnetite/maghemite) regardless of vegetation cover and soil type. Enhancement ratios for magnetic susceptibility and low-field remanences, often used as indicators of pedogenic magnetic minerals, are more variable but remain statistically equivalent across the transect. These results support the hypothesis that pedogenic magnetic minerals in soils mostly reflect ambient climatic conditions regardless of the variability in soil processes related to vegetation and soil type. The non-pedogenic magnetic mineral assemblage shows clear distinctions between the forest, prairie, and transitional soils in hysteresis properties (remanence and coercivity ratios; Mr/Ms and Bc/Bcr, respectively), suggesting that variable processes in these settings influence the local magnetic mineral assemblage, and that it may be possible to use magnetic minerals in paleosols to constrain these processes. This work highlights the importance of isolating the magnetic behavior of pedogenic and non-pedogenic minerals in environmental magnetism studies in order to provide the most rigorous interpretation of past environmental conditions.

Hydrothermal processes in the Edmond deposits, slow- to intermediate-spreading Central Indian Ridge

NASA Astrophysics Data System (ADS)

Cao, Hong; Sun, Zhilei; Zhai, Shikui; Cao, Zhimin; Jiang, Xuejun; Huang, Wei; Wang, Libo; Zhang, Xilin; He, Yongjun

2018-04-01

The Edmond hydrothermal field, located on the Central Indian Ridge (CIR), has a distinct mineralization history owing to its unique magmatic, tectonic, and alteration processes. Here, we report the detailed mineralogical and geochemical characteristics of hydrothermal metal sulfides recovered from this area. Based on the mineralogical investigations, the Edmond hydrothermal deposits comprise of high-temperature Fe-rich massive sulfides, medium-temperature Zn-rich sulfide chimney and low-temperature Ca-rich sulfate mineral assemblages. According to these compositions, three distinctive mineralization stages have been identified: (1) low-temperature consisting largely of anhydrite and pyrite/marcasite; (2) medium-high temperature distinguished by the mineral assemblage of pyrite, sphalerite and chalcopyrite; and (3) low-temperature stage characterized by the mineral assemblage of colloidal pyrite/marcasite, barite, quartz, anglesite. Several lines of evidence suggest that the sulfides were influenced by pervasive low-temperature diffuse flows in this area. The hydrothermal deposits are relatively enriched in Fe (5.99-18.93 wt%), Zn (2.10-10.00 wt%) and Ca (0.02-19.15 wt%), but display low Cu (0.28-0.81 wt%). The mineralogical varieties and low metal content of sulfides in the Edmond hydrothermal field both indicate that extensive water circulation is prevalent below the Edmond hydrothermal field. With regard to trace elements, the contents of Pb, Ba, Sr, As, Au, Ag, and Cd are significantly higher than those in other sediment-starved mid-ocean ridges, which is indicative of contribution from felsic rock sources. Furthermore, the multiphase hydrothermal activity and the pervasive water circulation underneath are speculated to play important roles in element remobilization and enrichment. Our findings deepen our understanding about the complex mineralization process in slow- to intermediate-spreading ridges globally.

Composition and genesis of the Konevinsky gold deposit, Eastern Sayan, Russia

NASA Astrophysics Data System (ADS)

Damdinov, B. B.; Zhmodik, S. M.; Roshchektaev, P. A.; Damdinova, L. B.

2016-03-01

The Konevinsky gold deposit in southeast Eastern Sayan is distinguished from most known deposits in this region (Zun-Kholba, etc.) by the geological setting and composition of mineralization. To elucidate the cause of the peculiar mineralization, we have studied the composition, formation conditions, and origin of this deposit, which is related to the Ordovician granitoid pluton 445-441 Ma in age cut by intermediate and basic dikes spatially associated with metavolcanic rocks of the Devonian-Carboniferous Ilei Sequence. Four mineral assemblages are recognized: (1) quartz-pyrite-molybdenite, (2) quartz-gold-pyrite, (3) gold-polysulfide, and (4) telluride. Certain indications show that the ore was formed as a result of the superposition of two distinct mineral assemblages differing in age. The first stage dated at ~440 Ma is related to intrusions generating Cu-Mo-Au porphyry mineralization and gold-polysulfide veins. The second stage is controlled by dikes pertaining to the Devonian-Carboniferous volcanic-plutonic association. The second stage is characterized by gain of Hg and Te and formation of gold-mercury-telluride paragenesis.

Weathering of almandine garnet: influence of secondary minerals on the rate-determining step, and implications for regolith-scale Al mobilization

Treesearch

Jason R. Price; Debra S. Bryan-Ricketts; Diane Anderson; Michael A. Velbel

2013-01-01

Secondary surface layers form by replacement of almandine garnet during chemical weathering. This study tested the hypothesis that the kinetic role of almandine's weathering products, and the consequent relationships of primary-mineral surface texture and specific assemblages of secondary minerals, both vary with the solid-solution-controlled variations in Fe and...

Greenstone-hosted lode-gold mineralization at Dungash mine, Eastern Desert, Egypt

NASA Astrophysics Data System (ADS)

Zoheir, Basem; Weihed, Pär

2014-11-01

The auriferous quartz ± carbonate veins at Dungash mine, central Eastern Desert of Egypt, are confined to ∼E-trending dilation zones within variably foliated/sheared metavolcanic/volcaniclastic rocks. The vein morphology and internal structures demonstrate formation concurrent with a dextral shear system. The latter is attributed to flexural displacement of folded, heterogeneous rock blocks through transpression increment, late in the Neoproterozoic deformation history of the area. Geochemistry of the host metavolcanic/metavolcaniclastic rocks from the mine area suggests derivation from a low-K, calc-alkaline magma in a subduction-related, volcanic arc setting. In addition, chemistry of disseminated Cr-spinels further constrain on the back-arc basin setting and low-grade metamorphism, typical of gold-hosting greenstone belts elsewhere. Mineralogy of the mineralized veins includes an early assemblage of arsenopyrite-As-pyrite-gersdorffite ± pyrrhotite, a transitional pyrite-Sb-arsenopyrite ± gersdorffite assemblage, and a late tetrahedrite-chalcopyrite-sphalerite-galena-gold assemblage. Based on arsenopyrite and chlorite geothermometers, formation of gold-sulfide mineralization occurred between ∼365 and 280 °C. LA-ICP-MS measurements indicate the presence of refractory Au in arsenian pyrite (up to 53 ppm) and Sb-bearing arsenopyrite (up to 974 ppm). Abundant free-milling gold associated with the late sulfide assemblage may have been mobilized and re-distributed by circulating, lower temperature ore fluids in the waning stages of the hydrothermal system. Based on the isotopic values of vein quartz and carbonate, the calculated average δ18OH2O values of the ore fluids are 5.0 ± 1.4‰ SMOW for quartz, and 3.3 ± 1.4‰ for vein carbonate. The measured carbonate δ13C values correspond to ore fluids with δ13CCO2 = -6.7 ± 0.7‰ PDB. These results suggest a mainly metamorphic source for ore fluids, in good agreement with the vein morphology, textures and hydrothermal alteration. The calculated δ34SH2S values for early, transitional, and late sulfide assemblages define three distinct ranges (∼1.5-3.6‰), (∼0.4-1.0‰), and (-3.7‰ to -1.9‰), respectively. The systematic evolution towards lighter δ34S values may be attributed to recrystallization, or to ore fluid buffering under variable physicochemical conditions. The shear zone-related setting, mineralogy and isotopic characteristics of gold mineralization in Dungash mine are comparable with other orogenic gold deposits in the region (e.g., Barramiya deposit), which may suggest a regional setting controlling gold metallogeny of the region. This setting should guide future exploration programs in the central Eastern Desert province.

Hydrothermal and Diagenetic Mineralization on Mars

NASA Astrophysics Data System (ADS)

Ehlmann, B. L.; Quinn, D. P.

2015-12-01

Predicted by geophysical modeling, the mineraolgic record of early Mars groundwater has only recently been discovered. First, rover exploration in sedimentary basins reveals diagenesis. At Meridiani, sandstone porosity is occluded by precipitation of secondary sulfates, hematite, and silica. Multiple alteration episodes are indicated by crystal vugs, disruption of preexisting textures by hematite concretions, and grain coatings (e.g. McLennan et al., 2005). At Gale crater, raised ridges in mudstones, interpreted to be early diagenetic features, are crossed by later-emplaced hydrated calcium sulfate veins (e.g. Grotzinger et al., 2014). Waters in Gale were likely circumneutral while jarosite mineralogy at Meridiani implies acidic waters. Second, systems of raised ridges at 100-m scale are observed from orbit in multiple Martian sedimentary rock units. An outstanding example is sulfate-bearing sediments exhumed at the northern margin of the Syrtis Major lavas (e.g. Quinn & Ehlmann, 2015). Polygonal and with no clearly preferred orientation, the ridges rise 5-30 m above the surrounding terrain. Parallel light-toned grooves with dark interiors (indicative of isopachous fills) and jarosite in ridge mineralogy point to mineralization by acidic waters. Third, some mineral assemblages observed from orbit represent the products of subsurface aqueous alteration at elevated temperatures (Ehlmann et al., 2011). These are globally distributed, exposed in scarps and by impact cratering. Mineral assemblages variously include (a) serpentine and carbonate; (b) prehnite and chlorite, and (c) zeolites. Collectively, these datasets indicate that groundwaters were spatially widespread on ancient Mars, contributing to the sustenance of lakes and to the alteration of bedrock to >1 km depths. While the Martian surface may have always been relatively inhospitable, a warmer, wetter subsurface provided a long-term potentially habitable environment. Key outstanding questions remaining include groundwater sources, their composition and compositional variability, and subsurface transport distances. Continued exploration of Mars, combined with studies of analogous bedrock mineralization on Earth, will advance understanding of environments with liquid water during Mars' first billion years.

Lead isotope compositions as guides to early gold mineralization: The North Amethyst vein system, Creede district, Colorado

USGS Publications Warehouse

Foley, Nora K.; Ayuso, Robert A.

1994-01-01

Pb isotope compositions from the late stage of the North Amethyst vein system and from the Bondholder and central and southern Creede mining districts are more radiogenic than the host volcanic rocks of the central cluster of the San Juan volcanic field. Our Pb isotope results indicate that early Au mineralization of the North Amethyst area may represent the product of an older and relatively local hydrothermal system distinct from that of the younger base metal and Ag mineralization found throughout the region. Fluids that deposited Au minerals may have derived their Pb isotope composition by a greater degree of interaction with shallow, relatively less radiogenic volcanic wall rocks. The younger, base metal and Ag-rich mineralization that overprints the Au mineralization in the North Amethyst area clearly has a more radiogenic isotopic signature, which implies that the later mineralization derived a greater component of its Pb from Proterozoic source rocks, or sediments derived from them.Paragenetically early sulfide-rich vein assemblages have the least radiogenic galenas and generally also have the highest Au contents. Thus, identification of paragenetically early vein assemblages with relatively unradiogenic Pb isotope compositions similar to those of the North Amethyst area provides an additional exploration tool for Au in the central San Juan Mountains area.

Minerals and clay minerals assemblages in organic-rich facies: the case study of the Sinemurian-Pliensbachian carbonate deposits of the western Lusitanian Basin (Portugal)

NASA Astrophysics Data System (ADS)

Caniço, Ana; Duarte, Luís V.; Silva, Ricardo L.; Rocha, Fernando; Graciano Mendonça Filho, João

2015-04-01

The uppermost Sinemurian-Pliensbachian series of the western part of the Lusitanian Basin is composed by hemipelagic carbonates particularly enriched in organic matter. Great part of this succession, considered to be one of the most important potential source rock intervals of Portugal, crops out in the S. Pedro de Moel and Peniche sectors, belonging to the Água de Madeiros and Vale das Fontes formations. In this study, supported by a detailed and integrated stratigraphic framework, we analyzed 98 marly samples (whole-rock mineralogy and clay minerals assemblages) from the aforementioned formations in the S. Pedro de Moel and Peniche sectors. X-ray Diffraction analysis followed the standard procedures and the semi-quantification of the different mineral phases was calculated using MacDiff 4.2.6. The goals of this work are to demonstrate the vertical variability of the mineral composition of these two units and investigate the relationship between the clay minerals assemblages and the content in organic matter (Total organic carbon: TOC). Besides the abundance of calcite and phyllosilicates, whole-rock mineralogy revealed the presence of quartz, potassium feldspar, dolomite, and pyrite (trace amounts). Other minerals like anhydrite, barite and gypsum occur sporadically. The clay minerals assemblages are dominated by illite+illite/smectite mixed-layers (minimum of 59%), always associated with kaolinite (maximum of 37%) and chlorite (maximum of 25%); sporadically smectite occurs in trace amounts. Generally, high TOC levels (i.e., black shale facies with TOC reaching up to 22 wt.% in both units, see Duarte et al., 2010), show a major increase in chlorite and kaolinite (lower values of illite+illite/smectite mixed layers). A kaolinite enrichment is also observed just above the Sinemurian-Pliensbachian boundary (base of Praia da Pedra Lisa Member of Água de Madeiros Formation; values varying between 30 and 37%). This event is associated with a second-order regressive phase, and marks the disappearance of the organic-rich facies and increase of carbonate sedimentation. This enrichment was likely favored by the development of more humid conditions at the Sinemurian-Pliensbachian transition. References Duarte, L.V., Silva, R.L., Oliveira, L.C.V., Comas-Rengifo, M.J., Silva, F. 2010. Organic-rich facies in the Sinemurian and Pliensbachian of the Lusitanian Basin, Portugal: Total Organic Carbon distribution and relation to transgressive-regressive facies cycles. Geologica Acta 8, 325-340.

Biogenic Weathering: Solubilization of Iron from Minerals by Epilithic Freshwater Algae and Cyanobacteria

PubMed Central

2018-01-01

A sandstone outcrop exposed to freshwater seepage supports a diverse assemblage of photosynthetic microbes. Dominant taxa are two cyanophytes (Oscillatoria sp., Rivularia sp.) and a unicellular green alga (Palmellococcus sp.). Less abundant taxa include a filamentous green alga, Microspora, and the desmid Cosmarium. Biologic activity is evidenced by measured levels of chlorophyll and lipids. Bioassay methods confirm the ability of these microbes to dissolve and metabolize Fe from ferruginous minerals. Chromatographic analysis reveals citric acid as the likely chelating agent; this low molecular weight organic acid is detectable in interstitial fluid in the sandstone, measured as 0.0756 mg/mL. Bioassays using a model organism, Synechoccus elongates strain UTEX 650, show that Fe availability varies among different ferruginous minerals. In decreasing order of Fe availability: magnetite > limonite > biotite > siderite > hematite. Biotite was selected for detailed study because it is the most abundant iron-bearing mineral in the sandstone. SEM images support the microbiologic evidence, showing weathering of biotite compared to relatively undamaged grains of other silicate minerals. PMID:29342973

Preliminary mineralogic, fluid inclusion, and stable isotope study of the Mahd adh Dhahab gold mine, Kingdom of Saudi Arabia

USGS Publications Warehouse

Rye, Robert O.; Hall, W.E.; Cunningham, C.G.; Czamanske, G.K.; Afifi, A.M.; Stacey, J.S.

1983-01-01

The Mahd adh Dhahab mine, located about 280 km northeast of Jiddah, Kingdom of Saudi Arabia, has yielded more than 2 million ounces of gold from periodic production during the past 3,000 years. A new orebody on the southern side of the ancient workings, known as the South orebody, is being developed by Gold Fields-Mahd adh Dhahab Limited. A suite of samples was collected from the newly exposed orebody for preliminary mineralogic, stable isotope, fluid inclusion, and geochemical studies. The Mahd adh Dhahab deposit is in the carapace of a Proterozoic epizonal rhyolite stock that domed pyroclastic and metasedimentary rocks of the Proterozoic Halaban group. Ore of gold, silver, copper, zinc, tellurium, and lead is associated with north-trending, steeply dipping quartz veins in a zone 1,000 m long and 400 m wide. The veins include an assemblage of quartz-chlorite-pyrite-hematite-chalcopyrite-sphalerite-precious metals, which is similar to the mineral assemblage at the epithermal deposit at Creede, Colorado. The primary ore contains abundant chalcopyrite, sphalerite, and pyrite in addition to a complex precious metal assemblage. Gold and silver occur principally as minute grains of telluride minerals disseminated in quartz-chlorite-hematite and as inclusions in chalcopyrite and sphalerite. Telluride minerals include petzite, hessite, and sylvanite. Free gold is present but not abundant. All of the vein-quartz samples contained abundant, minute inclusions of both low-density, vapor-rich fluids and liquid-rich fluids. Primary fluid inclusions yielded homogenization temperatures of from 110? to 238? C. Preliminary light-stable isotope studies of the sulfide minerals and quartz showed that all of the d34S values are between 1.2 and 6.3 per mil, which is a typical range for hydrothermal sulfide minerals that derive their sulfur from an igneous source. The data-suggest that the sulfide sulfur isotope geochemistry was controlled by exchange with la large sulfur isotope reservoir at depth. The d18O values of all stages of vein quartz in the South orebody range between 8.5 and 11.1 per mil. This range is similar to that for quartz from the North orebody and indicates that the hydrothermal system consisted of dominantly exchanged meteoric water, which was uniform in temperature and d18O content throughout the area during the entire period of mineralization. Lead isotope analyses of two galena samples indicate that the lead in the South orebody is less radiogenic than that from the North orebody and confirm that the lead was derived from oceanic crust approximately 700 Ma ago.

Eudialyte Composition and Decomposition Assemblage of the Sushina Syenite Gneisss, India

NASA Astrophysics Data System (ADS)

Chakrabarty, A.; Ren, M.

2012-12-01

Eudialyte group of minerals (EGM) were not recognized from the Indian subcontinent until recently an occurrence of eudialyte bearing nepheline syenite from the Sushina Hill region of West Bengal is made. The rocks of the Sushina hill region had undergone poly-phase post formational magmato-thermal activity and the studied unit of nepheline syenite can be better termed as 'nepheline syenite gneiss' in their present form. This under saturated syenite gneiss is present as intrusive body and hosted by the phyllites and schists of the Proterozoic Chandil Formation covering an area of about 1500m2. There is not much information available on the detailed mineralogy of this nepheline gneiss. The main purpose of this study is to present precise in-depth chemistry of the individual minerals with special emphasis on the EGM along with the decomposition assemblage(s) formed after eudialyte. The ortho-, late- and post-magmatic assemblages were observed throughout the studied unit of syenite gneiss. The ortho-magmatic assemblage is defined by the discrete subhedral grains of albite, orthoclase, nepheline and aegirine. Compositionally all the feldspars represent near end-member compositions. Nepheline compositions are falling well within the range of Morozewicz-Buerger convergence field for plutonic low-temperature nepheline. Eudialyte is the dominant phase associated with the late-magmatic assemblage. Anhedral aegirine grains are frequently present within the complex aggregate of eudialyte and related decomposition assemblages which indicate that the aegirine predates eudialyte during the crystallization history. The studied EGM are essentially Mn-Nb-Ca-Zr rich variety and comparable to the other occurrences of the Ilímaussaq (Greenland), Tamazeght (Morocco), Mont-Saint Hilaire (Canada) and Pilansberg (South Africa). The studied eudialytes are characterized by very high Mn content (6.6-9.7 wt.%) relative to all other eudialyte reported world-wide. Such Mn-rich eudialytes are usually formed at the late-magmatic to hydrothermal stage from a highly evolved parent nephelinitic melt. These eudialytes are also characterized by the significant amount of REE and the REE2O3 goes up to ~3.5 wt%. Owing to the high content of Mn-Nb-Ca-Zr, decomposition assemblage formed after eudialyte at the post-magmatic stage is quite unique. Two distinct eudialyte decomposition assemblages were observed. The first alteration assemblage resulted from the complete breakdown of eudialyte to numerous complex Na-Zr silicates (NZS) namely catapleiite/gaidonnayite and hilairite. However, at places discrete grains of catapleiite/gaidonnayite was found without any associated eudialyte. Thus it is not always conclusive that these NZS were essentially formed after eudialyte. Other type of alteration include a symplectitic breakdown of eudialyte in to pectolite-serandite assemblage. No vein or vein-lets were seen in the near vicinity of the studied unit of the syenite gneiss. This indicates that the fluid responsible for the late- to post-magmatic assemblages were essentially a system derived deuteric fluid. This is also well documented by the extensive alteration of precursor alumino-silicates to natrolite consanguineous to eudialyte crystallization at late-magmatic stage.

Silicate petrography and origin of the mesosiderites: a preliminary investigation of their relationships to the howardite-eurite-diogenite suite

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

Floran, R. J

1978-04-01

Results are reported from a petrographic study of 20 mesosiderites that reveals that most contain a complex assemblage of mineral, lithic, and metal clasts. Mineral fragments dominate the clast population and consist primarily of orthopyroxene, plagioclase, and olivine.

Tectono-metallogenetic evolution of the Fe-Cu deposit of Dominga, northern Chile

NASA Astrophysics Data System (ADS)

Veloso, E.; Cembrano, J.; Arancibia, G.; Heuser, G.; Neira, S.; Siña, A.; Garrido, I.; Vermeesch, P.; Selby, D.

2017-04-01

The Dominga district in northern Chile (2082 Mt at 23.3 % Fe, 0.07 % Cu) shows a spatial and genetic affinity among distinctive structural elements and Fe-Cu-rich paragenetic mineral assemblages. Deep seated, NE-to-E striking structural elements form a right-lateral duplex-like structural system (early structural system, ESS) that cuts a regionally extensive alteration (stage I) zone. The EES system served as a locus and as path for the emplacement of biotite-magnetite alteration/mineralization (stage IIa) as veins and Fe-bearing layers following altered volcano sedimentary strata. NW-striking actinolite-magnetite hydrothermal breccias, coeval with and part of the ESS, include apatite (stage IIb) crystallized at 127 ± 15 Ma (U-Pb, 2σ). The ESS was also the locus of subsequent alteration/mineralization represented by K-feldspar, epidote, and albite (stage IIIa) and Fe-Cu-rich (vermiculite-anhydrite-chalcopyrite, stage IIIb) mineral associations. Shallowly developed, NNE-striking, left-lateral structural elements defining the El Tofo Structural System (ETSS)—probably part of the Atacama Fault System—clearly crosscut the ESS. Minerals associated with alteration/mineralization stage IIIb also occur as veins and as part of hydrothermal breccias of the ETSS, marking the transition from the ESS to ETSS. Molybdenite associated with alteration/mineralization stage IIIb yielded a Re-Os age of 127.1 ± 0.7 Ma (2σ). Both the ESS and ETSS were cut by left-lateral, NW- to E-striking shallowly developed structural elements (Intermediate Structural System, ISS) on which a hematite-calcite assemblage (stage IV) occurs mostly as infill material of veins and fault veins. The ISS is cut by N-striking, left-lateral, and shallowly developed structural elements (Late Structural System, LSS) showing no evidence of alteration/mineralization. Estimated strain and stress fields indicate an overall NW-trending shortening/compression and NE-trending stretching/tension strike-slip regime probably due to oblique subduction during the Mesozoic. However, the orientations of the stress and strain fields calculated for each structural system suggest a back-and-forth rotation pattern during transition from one structural system to the other—as they change between transtension and transpression—and between alteration/mineralization stages.

Effects of two lubricant oils on marine nematode assemblages in a laboratory microcosm experiment.

PubMed

Beyrem, H; Louati, H; Essid, N; Aïssa, P; Mahmoudi, E

2010-05-01

The effects of two lubricating oils on nematode assemblages of a Tunisian lagoon were investigated in a microcosm experiment. Sediment from a pristine site in Ghar El Melh lagoon (Western Mediterranean) was treated with either mineral oil (Mobil 20 W-50), a synthetic lubricant (Mobil 0 W-40), the same two lubricants after use in a vehicle, and effects were examined after 5 weeks. Univariate analysis showed significant differences between most univariate indices of the nematode assemblages in all the lubricant treatments as compared to the control. Total nematode abundance (I), species richness (d) and number of species (S) decreased significantly in all lubricant contaminated microcosms. However, evenness was not affected in all treated replicates except in used mineral lubricant treatment where it was significantly higher than in the control. Diversity (H') was only altered in synthetic lubricant treatments. Results from multivariate analyses of the species abundance data demonstrated that responses of nematode species to the two lubricants treatments were varied: Daptonema trabeculosum was eliminated in all lubricant treatments and seemed to be an intolerant species to oil contamination. Spirinia gerlachi increased in mineral lubricant treatments ("clean" and used) but was eliminated in all synthetic lubricant treatments. This species could be categorized as "resistant" to mineral oil contamination and intolerant to synthetic lubricant contamination. Terschellingia longicaudata increased only in synthetic lubricant treatments ("clean" and used) and appeared to be a "synthetic oil-resistant" species. Copyright 2009 Elsevier Ltd. All rights reserved.

Thermometers and thermobarometers in granitic systems

USGS Publications Warehouse

Anderson, J.L.; Barth, A.P.; Wooden, J.L.; Mazdab, F.; ,

2008-01-01

The ability to determine the thermal and barometric history during crystallization and emplacement of granitic plutons has been enhanced by several new calibrations applicable to granitic mineral assemblages. Other existing calibrations for granitic plutons have continued to be popular and fairly robust. Recent advances include the trace element thermometers Ti-in-quartz, Ti-in-zircon, and Zr-in-sphene (titanite), which need to be further evaluated on the roles of reduced activities due to lack of a saturating phase, the effect of pressure dependence (particularly for the Ti-in-zircon thermometer), and how resistive these thermometers are to subsolidus reequilibration. As zircon and sphene are also hosts to radiogenic isotopes, these minerals potentially also provide new insights into the temperature - time history of magmas. When used in conjunction with pressure-sensitive mineral equilibria in the same rocks, a complete assessment of the P-T-t (pressure-temperature-time) path is possible given that the mineralogy of plutons can reflect crystallization over a range of pressure and temperature during ascent and emplacement and that many intrusions are now seen as forming over several millions of years during the protracted history of batholith construction. Accessory mineral saturation thermometers, such as those for zircon, apatite, and allanite, provide a different and powerful perspective, specifically that of the temperature of the onset of crystallization of these minerals, which can allow an estimate of the range of temperature between the liquidus and solidus of a given pluton. In assessment of the depth of crystallization and emplacement of granitic plutons, the Al-in-hornblende remains popular for metaluminous granites when appropriately corrected for temperature. For peraluminous granites, potential new calibrations exist for the assemblages bearing garnet, biotite, plagioclase, muscovite, and quartz. Other thermometers, based on oxygen abundance, and including Fe-Ti oxides, pyroxene, fayalitic olivine, quartz, sphene, and/or biotite, some of which have been recently revised, can provide additional information on temperature and oxygen fugacity. Oxygen fugacity can range over several orders of magnitude in different magmatic systems and can have profound influence on the mineralogy and mineral compositions in granitic magmas. It also forms the foundation of the popular magnetite- versus ilmenite-series granite classification. Copyright ?? Mineralogical Society of America.

Identifying areas of high economic-potential copper mineralization using ASTER data in the Urumieh-Dokhtar Volcanic Belt, Iran

NASA Astrophysics Data System (ADS)

Pour, Amin Beiranvand; Hashim, Mazlan

2012-02-01

This study investigates the application of spectral image processing methods to ASTER data for mapping hydrothermal alteration zones associated with porphyry copper mineralization and related host rock. The study area is located in the southeastern segment of the Urumieh-Dokhtar Volcanic Belt of Iran. This area has been selected because it is a potential zone for exploration of new porphyry copper deposits. Spectral transform approaches, namely principal component analysis, band ratio and minimum noise fraction were used for mapping hydrothermally altered rocks and lithological units at regional scale. Spectral mapping methods, including spectral angle mapper, linear spectral unmixing, matched filtering and mixture tuned matched filtering were applied to differentiate hydrothermal alteration zones associated with porphyry copper mineralization such as phyllic, argillic and propylitic mineral assemblages.Spectral transform methods enhanced hydrothermally altered rocks associated with the known porphyry copper deposits and new identified prospects using shortwave infrared (SWIR) bands of ASTER. These methods showed the discrimination of quartz rich igneous rocks from the magmatic background and the boundary between igneous and sedimentary rocks using the thermal infrared (TIR) bands of ASTER at regional scale. Spectral mapping methods distinguished the sericitically- and argillically-altered rocks (the phyllic and argillic alteration zones) that surrounded by discontinuous to extensive zones of propylitized rocks (the propylitic alteration zone) using SWIR bands of ASTER at both regional and district scales. Linear spectral unmixing method can be best suited for distinguishing specific high economic-potential hydrothermal alteration zone (the phyllic zone) and mineral assemblages using SWIR bands of ASTER. Results have proven to be effective, and in accordance with the results of field surveying, spectral reflectance measurements and X-ray diffraction (XRD) analysis. In conclusion, the image processing methods used can provide cost-effective information to discover possible locations of porphyry copper and epithermal gold mineralization prior to detailed and costly ground investigations. The extraction of spectral information from ASTER data can produce comprehensive and accurate information for copper and gold resource investigations around the world, including those yet to be discovered.

Geology of central Libya Montes, Mars: Aqueous alteration history from mineralogical and morphological mapping

NASA Astrophysics Data System (ADS)

Tirsch, D.; Bishop, J. L.; Voigt, J. R. C.; Tornabene, L. L.; Erkeling, G.; Jaumann, R.

2018-11-01

We analyze the emplacement chronology and aqueous alteration history of distinctive mineral assemblages and related geomorphic units near Hashir and Bradbury impact craters located within the Libya Montes, which are part of the southern rim of the Isidis Basin on Mars. We derive our results from a spectro-morphological mapping project that combines spectral detections from CRISM near-infrared imagery with geomorphology and topography from HRSC, CTX, and HiRISE imagery. Through this combination of data sets, we were able to use the morphology associated with specific mineral detections to extrapolate the possible extent of the units hosting these compositions. We characterize multiple units consistent with formation through volcanic, impact, hydrothermal, lacustrine and evaporative processes. Altered pyroxene-bearing basement rocks are unconformably overlain by an olivine-rich unit, which is in turn covered by a pyroxene-bearing capping unit. Aqueously altered outcrops identified here include nontronite, saponite, beidellite, opal, and dolomite. The diversity of mineral assemblages suggests that the nature of aqueous alteration at Libya Montes varied in space and time. This mineralogy together with geologic features shows a transition from Noachian aged impact-induced hydrothermal alteration and the alteration of Noachian bedrock by neutral to slightly basic waters via Hesperian aged volcanic emplacements and evaporative processes in lacustrine environments followed by Amazonian resurfacing in the form of aeolian erosion.

Sediment transport mechanisms inferred from heavy mineral assemblages on the 2010 Chilean tsunami deposit

NASA Astrophysics Data System (ADS)

Cascalho, João; Costa, Pedro; Lario, Javier

2017-04-01

Characterization of heavy mineral (HM) assemblages in tsunami deposits has been applied to infer inundation and backwash phases and to establish sediment sources. In ideal conditions and due to their specific density (>2.9 g/cm3), heavy minerals are the most suitable component of a sediment assemblage that can provide information regarding flow competence. Having these features in consideration, sandy tsunamigenic samples from Arauco and Mataquito areas (central Chile) were retrieved after the 27th of February 2010 tsunami that affected the Chilean coastline. Twenty seven samples (a total of 54 thin sections) tsunamigenic and beach samples were prepared to observe HM under the petrographic microscope. After dividing the samples in 4 fractions (<63 µm, 63- 125 µm, 125-500µm and >500 µm), HM were separated using bromoform and two fractions (63- 125 µm and 125-500µm) were individually mounted using Canada balsam resin on glass slides. About 300 heavy minerals per slide were identified and counted. Both assemblages were mainly composed of magnetite, pyrrhotite, amphiboles, pyroxenes, olivine, micas and zircon (this specie particularly abundant in the finer fraction analyzed). In Arauco (Ar), average HM percentages in the 125-500 µm fraction was 17.9% while in Mataquito (Ma) it was 25.7%. In the 63-125 µm fraction HM average percentages were 36.9% and 56.1%, for Ar and Ma respectively. In the 125-500 µm fraction the percentage of magnetic minerals (the densest of the denser HM) correspond to 13.2% in Ar and 2.7% in Ma. While in the finer fraction these percentages are of 0.24% and 0.1% In Ar it was possible to perceive that the highest concentration in HM and magnetic minerals was observed in the NE sector (Llico) of the embayment, where the highest run-up was observed. In this specific sector an inland decrease of HM and magnetic minerals was detected along a 300m profile, with HM percentages varying from 27% to 9% and magnetic minerals from 16% to 5%, thus suggesting a progressive energy decrease with inundation extent. In Ma only an inland decrease in magnetic minerals was observed (in Lloca sector) with values decreasing from 4.9% to 2.5% with 175m. This also indicates a decrease in sediment transport competence by the incoming tsunami waves. Here, the potential of HM is confirmed as a useful sedimentological tool to better understand tsunami events retrieving relevant information regarding to infer energy of tsunami waves. This work was supported by the Spanish Government Project CGL2013-42847-R. and through FCT- Instituto Dom Luiz UID/GEO/50019/2013. This is a contribution to the UNESCO IGCP Project 639 "Sea Level Change from Minutes to Millennia".

A Critical Appraisal of the "Day" Diagram

NASA Astrophysics Data System (ADS)

Roberts, Andrew P.; Tauxe, Lisa; Heslop, David; Zhao, Xiang; Jiang, Zhaoxia

2018-04-01

The "Day" diagram (Day et al., 1977, https://doi.org/10.1016/0031-9201(77)90108-X) is used widely to make inferences about the domain state of magnetic mineral assemblages. Based on theoretical and empirical arguments, the Day diagram is demarcated into stable "single domain" (SD), "pseudo single domain" ("PSD"), and "multidomain" (MD) zones. It is straightforward to make the necessary measurements for a sample and to plot results within the "domain state" framework based on the boundaries defined by Day et al. (1977, https://doi.org/10.1016/0031-9201(77)90108-X). We discuss 10 issues that limit Day diagram interpretation, including (1) magnetic mineralogy, (2) the associated magnetocrystalline anisotropy type, (3) mineral stoichiometry, (4) stress state, (5) surface oxidation, (6) magnetostatic interactions, (7) particle shape, (8) thermal relaxation, (9) magnetic particle mixtures, and (10) definitional/measurement issues. In most studies, these variables are unknowns and cannot be controlled for, so that hysteresis parameters for single bulk samples are nonunique and any data point in a Day diagram could result from infinite combinations of relevant variables. From this critical appraisal, we argue that the Day diagram is fundamentally ambiguous for domain state diagnosis. Widespread use of the Day diagram has also contributed significantly to prevalent but questionable views, including underrecognition of the importance of stable SD particles in the geological record and reinforcement of the unhelpful PSD concept and of its geological importance. Adoption of approaches that enable correct domain state diagnosis should be an urgent priority for component-specific understanding of magnetic mineral assemblages and for quantitative rock magnetic interpretation.

Depositional and diagenetic history and petroleum geology of the Jurassic Norphlet Formation of the Alabama coastal waters area and adjacent federal waters area

USGS Publications Warehouse

Kugler, R.L.; Mink, R.M.

1999-01-01

The discovery of deep (>20,000 ft) gas reservoirs in eolian sandstone of the Upper Jurassic Norphlet Formation in Mobile Bay and offshore Alabama in the late 1970s represents one of the most significant hydrocarbon discoveries in the nation during the past several decades. Estimated original proved gas from Norphlet reservoirs in the Alabama coastal waters and adjacent federal waters is 7.462 trillion ft3 (Tcf) (75% recovery factor). Fifteen fields have been established in the offshore Alabama area. Norphlet sediment was deposited in an arid environment in alluvial fans, alluvial plains, and wadis in updip areas. In downdip areas, the Norphlet was deposited in a broad desert plain, with erg development in some areas. Marine transgression, near the end of Norphlet deposition, resulted in reworking of the upper part of the Norphlet Formation. Norphlet reservoir sandstone is arkose and subarkose, consisting of a simple assemblage of three minerals, quartz, albite, and K-feldspar. The present framework grain assemblage of the Norphlet is dominantly diagenetic, owing to albitization and dissolution of feldspar. Despite the simple framework composition, the diagenetic character of the Norphlet is complex. Important authigenic minerals include carbonate phases (calcite, dolomite, Fe-dolomite, and breunnerite), feldspar (albite and K-feldspar), evaporite minerals (anhydrite and halite), clay minerals (illite and chlorite), quartz, and pyrobitumen. The abundance and distribution of these minerals varies significantly between onshore and offshore regions of Norphlet production. The lack of sufficient internal sources of components for authigenic minerals, combined with unusual chemical compositions of chloride (Mg-rich), breunnerite, and some minor authigenic minerals, suggests that Louann-derived fluids influenced Norphlet diagenesis. In offshore Alabama reservoirs, porosity is dominantly modified primary porosity. Preservation of porosity in deep Norphlet reservoirs is due to a combination of factors, including a lack of sources of cement components and lack of pervasive early cement, so that fluid-flow pathways remained open during burial. Below the dominantly quartz-cemented tight zone near the top of the Norphlet, pyrobitumen is a major contributor to reduction in reservoir quality in offshore Alabama. The highest reservoir quality occurs in those wells where the present gas-water contact is below the paleohydrocarbon-water contact. Thiz zone of highest reservoir quality is between the lowermost occurrence of pyrobitumen and the present gas-water contact.The Upper Jurassic Norphlet Formation sediment was deposited in an arid environment in alluvial fans, alluvial plains, and wadis in undip areas. In downdip areas, the Norphlet was deposited in a broad desert plain, with erg development in some areas. Marine transgression, near the end of Norphlet deposition resulted in reworking of the upper part of the formation. he present framework grain assemblage of the Norphlet is dominantly diagenetic, owing to albitization and dissolution of feldspar. Despite the simple framework composition, the diagenetic character of the Norphlet is complex.

Heavy Minerals in Palaeotsunami Deposits: Assemblages, Spatial Distribution and Microtextural Imprints

NASA Astrophysics Data System (ADS)

Costa, P. J.; Andrade, C.; Cascalho, J.; Dawson, A. G.; Freitas, M. C.; Dawson, S.; Mahaney, W. C.

2013-12-01

The sedimentological record provides a database useful to characterize and evaluate recurrence of tsunamis, which contributes to assessing the vulnerability of any coastal area to this natural hazard. Thus, the enhancement of our ability to recognize signatures specific of tsunami activity imprinted in coastal sediments is of unquestionable interest. The aim of this study is to discuss and further contribute to the improvement of the characterization of (palaeo)tsunami deposits, and of their source materials. With that purpose the vertical and horizontal distribution of heavy mineral (HM) assemblages in sand-sized tsunamigenic deposits from six locations exhibiting a varied suite of coastal contexts and corresponding to three inundation events -(8200yrs BP - Scotland, 1500yrs BP - Scotland, AD 1755 - Portugal) were studied. In general, results from paleotsunami sediments show that site-specific effects prevent 'blind' extrapolations; instead, the bulk of the HM assemblages reflect local specificities related with the regional geology. In the Portuguese sediments (Martinhal, Boca do Rio and Salgados) ca. 90% of the non-opaque HM population consists of tourmaline, andalusite and staurolite, whereas amphiboles are dominant (> 90% of the assemblage) in the Scottish sediments (Scasta Voe, Basta Voe and Whale Firth). Principal Components Analyses revealed that the first 2 components explain more than 2/3 of the total variance found in each site. Horizontal and vertical variations in the HM were observed and especially in the heavier mineral species. Although, in some of the studied cases, the deposit was macroscopically massive, data on HM allowed the distinction of backwash layer(s), related with incorporation of inland materials. In what concerns sources, results indicate that palaeotsunami sediments share fewer compositional similarities with present-day inshore and offshore materials and more resemblances with dune and beach sediment, thus indicating these as the more likely source areas. In addition, preliminary results of SEM analysis of microtextural features imprinted in the surface of heavy minerals indicate an increase in the number of mechanical marks in the surface of palaeotsunami grains when compared with potential source materials (beach, dune, inshore and offshore samples). This work further reveals the potential to use heavy minerals as a complementary sedimentological tool in the study of palaeotsunami deposits.

Textural and isotopic development of marble assemblages during the Barrovian-style M2 metamorphic event, Naxos, Greece

NASA Astrophysics Data System (ADS)

Baker, Judy; Matthews, Alan

1994-03-01

A detailed petrological analysis of the marble assemblages observed within the M2 metamorphic complex on Naxos is presented. Two distinct periods of mineral growth are documented; the first is associated with prograde M2 metamorphism and the second with retrograde M2 metamorphism occurring during ductile extensional thinning of the complex. The textural and miner-alogical characteristics and the carbon and oxygen isotope compositions of each generation are described, and the P-T-X CO 2 conditions at which these two mineral generations were stable, and the compositions of the fluids present during metamorphism are characterised. Whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution, the retrograde mineral generation is shown to have grown as a result of the infiltration of a water-rich fluid phase that transported silica, Al2O3, Na2O and FeO into the host rocks. This observation, together with the stable isotope compositions of the retrograde calcite, and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas ( T>600° C) of the metamorphic complex, suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures. The existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on Naxos, because many of the unusually low δ18O compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde M2 fluids, rather than with prograde fluids.

Specificity of pyrometamorphic minerals of the ellestadite group

NASA Astrophysics Data System (ADS)

Zateeva, S. N.; Sokol, E. V.; Sharygin, V. V.

2007-12-01

Numerous rare and new mineral species are synthesized during the process of pyrometamorphism (Gross, 1977; Chesnokov et al., 1987; Chesnokov and Shcherbakova, 1991; Chesnokov, 1999), including silicooxides, chloride-, fluoride, and sulfate-silicates, carbonate-sulfides, chloride-oxides, etc. Having made sense of numerous findings of compounds of this type, Chesnokov (1999) set forth the concept of the crystallochemical transition at extreme temperatures attaining 1200-1450°C in pyrogenic systems. First of all, intertype transitions (oxygen-bearing-oxygen-free) and interclass transitions (chloride-silicate, carbonate-sulfide, chlorideoxide) are realized. The specificity of pyrometamorphic mineral assemblages consists in the abundance of silicates with additional anions (F-, Cl-, (CO3)2-) (Sokol et al., 2005). Minerals of the ellestadite group Ca10(SiO4)3 - x (SO4)3 - x (PO4)2 x (OH,F,Cl)2 are a spectacular example of these features. In the general case, they are silicate-sulfate-phosphate-hydroxide-chlorides-fluorides. The detailed description of these minerals based on the study of the original collection of pyrometamorphic minerals is presented in this paper.

Origin and prospectivity of heavy mineral enriched sand deposits along the Somaliland coastal areas

NASA Astrophysics Data System (ADS)

Ali, M. Y.; Hibberd, P.; Stoikovich, B.

2018-04-01

Sixty-one heavy mineral enriched samples along the Somaliland coast from Eil Sheikh to Ras Khatib, a distance of about 130 km, were analyzed using X-ray Fluorescence, X-ray Diffraction and SEM-EDS techniques. This study reveals that a considerable amount of heavy minerals is present along the Somaliland coast and confirms the presence of high concentration titanium and iron bearing minerals. However, the backshore deposits in the mouths of Waaheen and Biyo Gure ephemeral rivers as well as raised paleo-beaches in the east of port city of Berbera demonstrate the highest level of titaniferous heavy minerals with most samples showing concentration greater than 50 wt %. The titanium detected in geochemical analysis occurs in the form of ilmenite, rutile, titanite and titaniferous magnetite. Also, present in minor or trace amounts, are garnet, zircon and monazite. Heavy mineral accumulations in the east and west of Berbera have different mineralogical assemblages. The east of Berbera is dominated by quartz with moderate concentration of plagioclase, K-feldspar, magnetite, hematite and titanium bearing minerals, whereas in the west of Berbera, the dominant minerals are quartz, K-feldspar and plagioclase with variable proportions of ilmenite, rutile, mica, amphibole and pyroxene. These variations in mineral assemblages suggest different composition of the catchment areas that supply sediment to these deposits. The catchment area in the east of Berbera consists mainly of Proterozoic crystalline basement of the Qabri Bahar complex, Gabbro-Synenite belt and granitic intrusions that outcrop in Hudiso, Tulo Dibijo and surrounding areas. The primary sources of heavy minerals in the west of Berbera comprise of high-grade metamorphic rocks of the Mora and Qabri Bahar complexes as well as the Miocene volcanics that outcrop in Laferug and Hagabo areas. The heavy mineral sand deposits observed along the Somaliland coast have the potential to provide commercially important heavy minerals, in particular ilmenite. It appears that prospects for development of the heavy mineral sands in the east of Berbera are better than those to the west of Berbera. In general, east of Berbera has wider beaches, better heavy mineral sands in the upper horizons and dune areas with heavier mineral sands. Furthermore, a series of raised paleo-beaches with high concentrations of heavy mineral sands are observed 1-2 km behind the shoreline. However, further investigation, including drilling and laboratory analyses, still needs to be carried out, particularly close to the entrance of Waaheen and Biyo Gure ephemeral rivers to evaluate the potential quality and scale of the deposits.

Granitoid-associated gold mineralization in Egypt: a case study from the Atalla mine

NASA Astrophysics Data System (ADS)

Zoheir, Basem; Deshesh, Fatma; Broman, Curt; Pitcairn, Iain; El-Metwally, Ahmed; Mashaal, Shabaan

2018-06-01

Gold-bearing sulfide-quartz veins cutting mainly through the Atalla monzogranite intrusion in the Eastern Desert of Egypt are controlled by subparallel NE-trending brittle shear zones. These veins are associated with pervasive sericite-altered, silicified, and ferruginated rocks. The hosting shear zones are presumed as high-order structures of the Najd-style faults in the Central Eastern Desert ( 615-585 Ma). Ore minerals include an early pyrite-arsenopyrite (±pyrrhotite) mineralization, partly replaced by a late pyrite-galena-sphalerite-chalcopyrite (±gold/electrum ± tetrahedrite ± hessite) assemblage. Gold occurs as small inclusions in pyrite and arsenopyrite, or more commonly as intergrowths with galena and sphalerite/tetrahedrite in microfractures. Arsenopyrite geothermometry suggests formation of the early Fe-As-sulfide mineralization at 380-340 °C, while conditions of deposition of the late base metal-gold assemblage are assumed to be below 300 °C. Rare hessite, electrum, and Bi-galena are associated with sphalerite and gold in the late assemblage. The early and late sulfide minerals show consistently a narrow range of δ34S ‰ (3.4-6.5) that overlaps with sulfur isotopic values in ophiolitic rocks. The Au-quartz veins are characterized by abundant CO2 and H2O ± CO2 ± NaCl inclusions, where three-dimensional clusters of inclusions show variable aqueous/carbonic proportions and broad range of total (bimodal) homogenization temperatures. Heterogeneous entrapment of immiscible fluids is interpreted to be caused by unmixing of an originally homogenous, low salinity ( 2 eq. mass % NaCl) aqueous-carbonic fluid, during transition from lithostatic to hydrostatic conditions. Gold deposition occurred generally under mesothermal conditions, i.e., 1.3 kbar and 280 °C, and continued during system cooling to < 200 °C and pressure decrease to 0.1 kbar. Based on the vein textures, sulfur isotope values, composition of ore fluids, and conditions of ore formation, we suggest that the Atalla monzogranite intrusion acted only as a competent structural host for ore deposition from shear-related, metal-rich fluids migrated up from depth. This model is also presumed for most granitoid-associated Au deposits in the region, considering the similarity in their structural control, alteration pattern and mineralogy, and chemistry of the ore fluids.

Mount St. Augustine volcano fumarole wall rock alteration: Mineralogy, zoning, composition and numerical models of its formation process

USGS Publications Warehouse

Getahun, A.; Reed, M.H.; Symonds, R.

1996-01-01

Intensely altered wall rock was collected from high-temperature (640??C) and low-temperature (375??C) vents at Augustine volcano in July 1989. The high-temperature altered rock exhibits distinct mineral zoning differentiated by color bands. In order of decreasing temperature, the color bands and their mineral assemblages are: (a) white to grey (tridymite-anhydrite); (b) pink to red (tridymite-hematite-Fe hydroxide-molysite (FeCl3) with minor amounts of anhydrite and halite); and (c) dark green to green (anhydrite-halite-sylvite-tridymite with minor amounts of molysite, soda and potash alum, and other sodium and potassium sulfates). The alteration products around the low-temperature vents are dominantly cristobalite and amorphous silica with minor potash and soda alum, aphthitalite, alunogen and anhydrite. Compared to fresh 1986 Augustine lava, the altered rocks exhibit enrichments in silica, base metals, halogens and sulfur and show very strong depletions in Al in all alteration zones and in iron, alkali and alkaline earth elements in some of the alteration zones. To help understand the origins of the mineral assemblages in altered Augustine rocks, we applied the thermochemical modeling program, GASWORKS, in calculations of: (a) reaction of the 1987 and 1989 gases with wall rock at 640 and 375??C; (b) cooling of the 1987 gas from 870 to 100??C with and without mineral fractionation; (c) cooling of the 1989 gas from 757 to 100??C with and without mineral fractionation; and (d) mixing of the 1987 and 1989 gases with air. The 640??C gas-rock reaction produces an assemblage consisting of silicates (tridymite, albite, diopside, sanidine and andalusite), oxides (magnetite and hercynite) and sulfides (bornite, chalcocite, molybdenite and sphalerite). The 375??C gas-rock reaction produces dominantly silicates (quartz, albite, andalusite, microcline, cordierite, anorthite and tremolite) and subordinate amounts of sulfides (pyrite, chalcocite and wurtzite), oxides (magnetite), sulfates (anhydrite) and halides (halite). The cooling calculations produce: (a) anhydrite, halite, sylvite; (b) Cu, Mo, Fe and Zn sulfides; (c) Mg fluoride at high temperature (> 370??C); (d) chlorides, fluorides and sulfates of Mn, Fe, Zn, Cu and Al at intermediate temperature (170-370??C); and (e) hydrated sulfates, liquid sulfur, crystalline sulfur, hydrated sulfuric acid and water at low temperature ( 0.41 (> 628??C). This is followed by precipitation of sulfates of Fe, Cu, Pb, Zn and Al at lg/a ratios between 0.41 and -0.4 (628-178??C). At a lg/r ratio of < - 0.4 (178??C), anhydrous sulfates are replaced by their hydrated forms and hygroscopic sulfuric acid forms. At these low g/a ratios, hydrated sulfuric acid becomes the dominant phase in the system. Comparison of the thermochemical modeling results with the natural samples suggests that the alteration assemblages include: (1) minerals that precipitate from direct cooling of the volcanic gas; (2) phases that form by volcanic gases mixing with air; and (3) phases that form by volcanic gas-air-rock reaction. A complex interplay of the three processes produces the observed mineral zoning. Another implication of the numerical simulation results is that most of the observed incrustation and sublimate minerals apparently formed below 700??C.

Soil mineral assemblage influences on microbial communities and carbon cycling under fresh organic matter input

NASA Astrophysics Data System (ADS)

Finley, B. K.; Schwartz, E.; Koch, B.; Dijkstra, P.; Hungate, B. A.

2017-12-01

The interactions between soil mineral assemblages and microbial communities are important drivers of soil organic carbon (SOC) cycling and storage, although the mechanisms driving these interactions remain unclear. There is increasing evidence supporting the importance of associations with poorly crystalline, short-range order (SRO) minerals in protection of SOC from microbial utilization. However, how the microbial processing of SRO-associated SOC may be influenced by fresh organic matter inputs (priming) remains poorly understood. The influence on SRO minerals on soil microbial community dynamics is uncertain as well. Therefore, we conducted a priming incubation by adding either a simulated root exudate mixture or conifer needle litter to three soils from a mixed-conifer ecosystem. The parent material of the soils were andesite, basalt, and granite and decreased in SRO mineral content, respectively. We also conducted a parallel quantitative stable isotope probing incubation by adding 18O-labelled water to the soils to isotopically label microbial DNA in situ. This allowed us to characterize and identify the active bacterial and archaeal community and taxon-specific growth under fresh organic matter input. While the granite soil (lowest SRO content), had the largest total mineralization, the least priming occurred. The andesite and basalt soils (greater SRO content) had lower total respiration, but greater priming. Across all treatments, the granite soil, while having the lowest species richness of the entire community (249 taxa, both active and inactive), had a larger active community (90%) in response to new SOC input. The andesite and basalt soils, while having greater total species richness of the entire community at 333 and 325 taxa, respectively, had fewer active taxa in response to new C compared to the granite soil (30% and 49% taxa, respectively). These findings suggest that the soil mineral assemblage is an important driver on SOC cycling under fresh organic matter inputs, as well as on the activity and diversity of the microbial community. Often, microbial diversity is associated with function. Our results suggest that the soil environment, in this case SRO mineral content, may be more important on SOC cycling and storage than microbial diversity alone.

Heavy mineral assemblages of the Storegga tsunami deposit

NASA Astrophysics Data System (ADS)

Cascalho, J.; Costa, P.; Dawson, S.; Milne, F.; Rocha, A.

2016-04-01

This study applies heavy mineral analysis to the Storegga tsunami deposit across a range of locations (Whale Firth, Maggie's Kettle Loch and Scatsta Voe) in Shetland (Scotland). The usefulness of this proxy is tested in the identification and characterization of these palaeotsunami units. Furthermore, provenance relationships are established based on the mineralogical content of tsunami deposits and their potential source. Finally, the capability of identifying different phases of tsunami inundation in an 8200 years old tsunami deposit is attempted. Our results show that, overall, tsunamigenic samples presented a clear dominance of garnets and amphiboles. While Whale Firth presented a more balanced distribution between these two mineral groups, in Maggie's Kettle Loch and Scatsta Voe the tsunamigenic samples are dominated by amphiboles (> 90% of transparent heavy minerals). Focusing on the two dominant heavy minerals (garnets and amphiboles) and their vertical variation, one could observe that garnets mimic the heavy mineral concentration variability - higher values at the base and decreasing values to the top. This effect of concentration of the heaviest of the heavy minerals assemblage presents similarities with the formation of beach placer deposits. In fact, based on the heavy mineral vertical variation of the tsunami deposits in Maggie's Kettle Loch, Scatsta Voe and Whale Firth it is possible to conclude that hornblende (most likely amphibole of the assemblage) has the lowest concentration factor indicating that its transport process is more efficient and consequently most of its particles eventually may have moved offshore in the backwash phase of the tsunami. Furthermore, the more platy shape of amphiboles also favours a slower deposition. The opposite can be observed for garnets, which require more energy to be transported (i.e. they are more difficult to entrain by the tsunami waves) and tend to be more easily preserved in the formation of a tsunamigenic (placer) deposit. The work presented here is of particular relevance for future high resolution sedimentological studies aiming to distinguish different inundation phases of the Storegga tsunami, and assess the degree of preservation of these deposits, especially considering the specific geomorphological and stratigraphic depositional setting of Scotland.

A CO2-Silica Geothermometer for Low Temperature Geothermal Resource Assessment, with Application to Resources in the Safford Basin, Arizona

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

Witcher, James C.; Stone, Claudia

1983-11-01

Geothermics is the study of the earth's heat energy, it's affect on subsurface temperature distribution, it's physical and chemical sources, and it's role in dynamic geologic processes. The term, geothermometry, is applied to the determination of equilibrium temperatures of natural chemical systems, including rock, mineral, and liquid phases. An assemblage of minerals or a chemical system whose phase composition is a function of temperature and pressure can be used as a geothermometer. Thus a geothermometer is useful to determine the formation temperature of rock or the last equilibrium temperature of a flowing aqueous solution such as ground water and hydrothermalmore » fluids.« less

U-Pb zircon and 40Ar/39Ar geochronology of sericite from hydrothermal alteration zones: new constraints for the timing of Ediacaran gold mineralization in the Sukhaybarat area, western Afif terrane, Saudi Arabia

NASA Astrophysics Data System (ADS)

Harbi, Hesham M.; Ali, Kamal A.; McNaughton, Neal J.; Andresen, Arild

2018-04-01

The Sukhaybarat East and Red Hill deposits, in the northeastern part of the Arabian Shield, are mesothermal vein-type gold deposits hosted by late Cryogenian-Ediacaran intrusive rocks of the Idah suites (diorite, tonalite, granodiorite) and, at Sukhaybarat East, also by Ediacaran metasedimentary rocks. Gold mineralization comprises quartz-arsenopyrite veins (Sukhaybarat East), quartz-carbonate-pyrite veins (Red Hill), and subordinate gold-base metal sulfide veins. In the Red Hill deposit, alteration is complicated due to multiple overprinting hydrothermal events and is characteristically affected by pervasive, pink quartz-K-feldspar-hematite alteration which is overprinted by potassic alteration characterized by a quartz-biotite-carbonate-muscovite/sericite-rutile-apatite assemblage. This assemblage is associated with molybdenite veins which appear to form late in the paragenetic sequence and may represent either evolution of the ore fluid composition, or a later, unrelated mineralized fluids. Hydrothermal alteration at the Sukhaybarat East deposit is dominated by quartz-carbonate-sericite-arsenopyrite assemblages. Zircon from ore-hosting tonalite at Sukhaybarat East yields a U-Pb age of 629 ± 6 Ma, and biotite from the same rock gives an 40Ar/39Ar age of 622 ± 23 Ma. The 40Ar/39Ar age is within the uncertainty range for the U-Pb age of the host intrusion and is interpreted as a minimally disturbed cooling age for the tonalite. In the Red Hill area, granodiorite was emplaced at 615 ± 5 Ma, whereas muscovite/sericite separated from a mineralized sample of a quartz-carbonate-pyrite vein, that was overprinted by molybdenite-bearing veinlets, yields an 40Ar/39Ar age of 597 ± 8 Ma. We interpreted this age to represent the maximum age of the molybdenite mineralization and the probable minimum age of gold mineralization in the Red Hill deposit.

Abiotic CO2 reduction during geologic carbon sequestration facilitated by Fe(II)-bearing minerals

NASA Astrophysics Data System (ADS)

Nielsen, L. C.; Maher, K.; Bird, D. K.; Brown, G. E.; Thomas, B.; Johnson, N. C.; Rosenbauer, R. J.

2012-12-01

Redox reactions involving subsurface minerals and fluids and can lead to the abiotic generation of hydrocarbons from CO2 under certain conditions. Depleted oil reservoirs and saline aquifers targeted for geologic carbon sequestration (GCS) can contain significant quantities of minerals such as ferrous chlorite, which could facilitate the abiotic reduction of carbon dioxide to n-carboxylic acids, hydrocarbons, and amorphous carbon (C0). If such reactions occur, the injection of supercritical CO2 (scCO2) could significantly alter the oxidation state of the reservoir and cause extensive reorganization of the stable mineral assemblage via dissolution and reprecipitation reactions. Naturally occurring iron oxide minerals such as magnetite are known to catalyze CO2 reduction, resulting in the synthesis of organic compounds. Magnetite is thermodynamically stable in Fe(II) chlorite-bearing mineral assemblages typical of some reservoir formations. Thermodynamic calculations demonstrate that GCS reservoirs buffered by the chlorite-kaolinite-carbonate(siderite/magnesite)-quartz assemblage favor the reduction of CO2 to n-carboxylic acids, hydrocarbons, and C0, although the extent of abiotic CO2 reduction may be kinetically limited. To investigate the rates of abiotic CO2 reduction in the presence of magnetite, we performed batch abiotic CO2 reduction experiments using a Dickson-type rocking hydrothermal apparatus at temperatures (373 K) and pressures (100 bar) within the range of conditions relevant to GCS. Blank experiments containing CO2 and H2 were used to rule out the possibility of catalytic activity of the experimental apparatus. Reaction of brine-suspended magnetite nanoparticles with scCO2 at H2 partial pressures typical of reservoir rocks - up to 100 and 0.1 bars respectively - was used to investigate the kinetics of magnetite-catalyzed abiotic CO2 reduction. Later experiments introducing ferrous chlorite (ripidolite) were carried out to determine the potential for heterogeneous catalysis in GCS systems.

Heavy-mineral provenance in an estuarine environment, Willapa Bay, Washington, USA: palaeogeographic implications and estuarine evolution

USGS Publications Warehouse

Luepke Bynum, Gretchen

2007-01-01

Modern sediments from representative localities in Willapa Bay, Washington, comprise two principal heavy-mineral suites. One contains approximately equivalent amounts of hornblende, orthopyroxene, and clinopyroxene; this is derived from the Columbia River, which discharges into the Pacific Ocean a short distance south of the bay. The other suite, dominated by clinopyroxene, is restricted to sands of rivers flowing into the bay from the east. The heavy-mineral distributions within the bay suggest that sand discharged from the Columbia River, borne north by longshore transport and carried into the bay by tidal currents, accounts for nearly all of the sand within the interior of Willapa Bay today. Pleistocene deposits on the east side of the bay contain three heavy-mineral assemblages, two of which are identical to the modern assemblages described above. These assemblages reflect the relative influence of tidal and fluvial processes on the Late Pleistocene deposits (100,000–200,000 BP. Amino acid racemization in Quaternary shell deposits at Willapa Bay, Washington. Geochimica et Cosmochimica Acta 43, 1505–1520). They are also consistent with those processes inferred on the basis of sedimentary structures and stratigraphic relations in about two-thirds of the samples examined. Anomalies can be explained by recycling of sand from older deposits. The persistence of the two heavy-mineral suites suggests that the pattern of estuarine sedimentation in Late Pleistocene deposits closely resembled that of the modern bay. The third heavy-mineral suite is enriched in epidote and occurs in a few older Pleistocene units. On the north side of the bay, the association of this suite with southwest-directed foresets in cross-bedded gravel indicates derivation from the northeast, perhaps from an area of glacial outwash. The presence of this suite in ancient estuarine sands exposed on the northeast side of the bay suggests that input from this northerly source may have intermittently dominated Willapa Bay deposition in the past.

Carbonate mineral solubility at low temperatures in the Na-K-Mg-Ca-H-Cl-SO 4-OH-HCO 3-CO 3-CO 2-H 2O system

NASA Astrophysics Data System (ADS)

Marion, Giles M.

2001-06-01

Carbonate minerals have played an important role in the geochemical evolution of Earth, and may have also played an important role in the geochemical evolution of Mars and Europa. Several models have been published in recent years that describe chloride and sulfate mineral solubilities in concentrated brines using the Pitzer equations. Few of these models are parameterized for subzero temperatures, and those that are do not include carbonate chemistry. The objectives of this work are to estimate Pitzer-equation bicarbonate-carbonate parameters and carbonate mineral solubility products and to incorporate them into the FREZCHEM model to predict carbonate mineral solubilities in the Na-K-Mg-Ca-H-Cl-SO 4-OH-HCO 3-CO 3-CO 2-H 2O system at low temperatures (≤25°C) with a special focus on subzero temperatures. Most of the Pitzer-equation parameters and equilibrium constants are taken from the literature and extrapolated into the subzero temperature range. Solubility products for 14 sodium, potassium, magnesium, and calcium bicarbonate and carbonate minerals are included in the model. Most of the experimental data are at temperatures ≥ -8°C; only for the NaHCO 3-NaCl-H 2O and Na 2CO 3-NaCl-H 2O systems are there bicarbonate and carbonate data to temperatures as low as -21.6°C. In general, the fit of the model to the experimental data is good. For example, calculated eutectic temperatures and compositions for NaHCO 3, Na 2CO 3, and their mixtures with NaCl and Na 2SO 4 salts are in good agreement with experimental data to temperatures as low as -21.6°C. Application of the model to eight saline, alkaline carbonate waters give predicted pHs ranging from 9.2 to 10.2, in comparison with measured pHs that range from 8.7 to 10.2. The model suggests that the CaCO 3 mineral that precipitates during seawater freezing is probably calcite and not ikaite. The model demonstrates that a proposed salt assemblage for the icy surface of Europa consisting of highly hydrated MgSO 4 salts and natron (Na 2CO 3 · 10H 2O) is an incompatible salt assemblage.

Heavy minerals in the 2011 Tohoku-oki tsunami deposits—insights into sediment sources and hydrodynamics

NASA Astrophysics Data System (ADS)

Jagodziński, Robert; Sternal, Beata; Szczuciński, Witold; Chagué-Goff, Catherine; Sugawara, Daisuke

2012-12-01

The 2011 Tohoku-oki tsunami left sand and mud deposits more than 4 km inland on the coastal plain of Sendai, Japan. The tsunami deposits, pre-tsunami soils and beach sediments were analysed for grain size, and heavy mineral content and assemblages to test the applicability of heavy mineral analyses in the identification of tsunami deposits and interpretation of associated sedimentation processes. Heavy minerals comprised on average 35% of the tsunami deposit in the 0.125-0.25 mm grain size fraction. The most common were orthopyroxenes, clinopyroxenes, amphiboles, limonites and opaque minerals. Heavy mineral concentrations and assemblages were similar in the tsunami deposits, beach and pre-tsunami soils and sediments and thus tsunami deposits could not simply be identified based on their heavy minerals. Sediment provenance analysis revealed that tsunami deposits left within 1.5 km of the shoreline were mostly eroded from the beach, dune and local soils, while deposits farther inland (> 1.5 km) were mostly derived from local soil erosion. No evidence was found for a significant contribution of offshore sediments. Detailed analyses revealed that the lowermost portion of tsunami deposits was mostly of local origin, while the sediment source of the upper portion was variable. A comparison with a previous study of heavy minerals in 2004 IOT deposits confirms that heavy minerals in tsunami deposits are mostly source-dependent and may represent a useful supplementary tool in studies of tsunami deposits. However, the interpretation must always be placed in the local geological context and corroborated with other "tsunami proxies".

Organo-mineral complexation alters carbon and nitrogen cycling in stream microbial assemblages

NASA Astrophysics Data System (ADS)

Hunter, William Ross; Wanek, Wolfgang; Prommer, Judith; Mooshammer, Maria; Battin, Tom

2014-05-01

Inland waters are of global biogeochemical importance receiving carbon inputs of ~ 4.8 Pg C y-1. Of this 12 % is buried, 18 % transported to the oceans, and 70 % supports aquatic secondary production. However, the mechanisms that determine the fate of organic matter (OM) in these systems are poorly defined. One important aspect is the formation of organo-mineral complexes in aquatic systems and their potential as a route for OM transport and burial vs. microbial utilization as organic carbon (C) and nitrogen (N) sources. Organo-mineral particles form by sorption of dissolved OM to freshly eroded mineral surfaces and may contribute to ecosystem-scale particulate OM fluxes. We tested the availability of mineral-sorbed OM as a C & N source for streamwater microbial assemblages and streambed biofilms. Organo-mineral particles were constructed in vitro by sorption of 13C:15N-labelled amino acids to hydrated kaolin particles, and microbial degradation of these particles compared with equivalent doses of 13C:15N-labelled free amino acids. Experiments were conducted in 120 ml mesocosms over 7 days using biofilms and streamwater sampled from the Oberer Seebach stream (Austria), tracing assimilation and mineralization of 13C and 15N labels from mineral-sorbed and dissolved amino acids. Here we present data on the effects of organo-mineral sorption upon amino acid mineralization and its C:N stoichiometry. Organo-mineral sorption had a significant effect upon microbial activity, restricting C and N mineralization by both the biofilm and streamwater treatments. Distinct differences in community response were observed, with both dissolved and mineral-stabilized amino acids playing an enhanced role in the metabolism of the streamwater microbial community. Mineral-sorption of amino acids differentially affected C & N mineralization and reduced the C:N ratio of the dissolved amino acid pool. The present study demonstrates that organo-mineral complexes restrict microbial degradation of OM and may, consequently, alter the carbon and nitrogen cycling dynamics within aquatic ecosystems.

Genesis and evolution of the Baid al Jimalah tungsten deposit, Kingdom of Saudi Arabia

USGS Publications Warehouse

Kamilli, Robert J.

1986-01-01

Baid al Jimalah is similar in character and origin to other tungsten-tin greisen deposits in the world, especially the Hemerdon deposit in Devon, England. It is also analogous to Climax-type molybdenum deposits, which contain virtually identical mineral assemblages, but with the relative intensities of the molybdenum and tungsten mineralization reversed.

Mineralogy, paragenesis, and mineral zoning of the Bulldog Mountain vein system, Creede District, Colorado

USGS Publications Warehouse

Plumlee, Geoffrey S.; Heald Whitehouse-Veaux, Pamela

1994-01-01

The Bulldog Mountain vein system, Creede district, Colorado, is one of four major epithermal vein systems from which the bulk of the district's historical Ag-Pb-Zn-Cu production has come. Ores deposited along the vein system were discovered in 1965 and were mined from 1969 to 1985.Six temporally gradational mineralization stages have been identified along the Bulldog Mountain vein system, each with a characteristic suite of minerals deposited or leached and a characteristic distribution within the vein system; some of these stages are also strongly zoned within the vein system. Stage A was dominated by deposition of rhodochrosite along the lower levels of the Bulldog Mountain ore zone. Stage B in the northern parts of the ore zone is characterized by abundant fine-grained sphalerite and galena, with lesser tetrahedrite and minor chlorite and hematite. With increasing elevation to the south, stage B ores become progressively more barite and silver rich, with alternating barite and fine-grained sphalerite + galena generations; native silver + or - acanthite assemblages are also locally abundant within southern stage B barite sulfide ores, whereas chalcopyrite and other Cu and Ag sulfides and sulfosalts are present erratically in minor amounts. Stage C in the upper and northern portions of the ore zone is characterized by abundant quartz and fluorite, minor adularia, hematite, Mn siderite, sphalerite, and galena, and major leaching of earlier barite; to the south, some barite and sulfides may have been deposited. Stage D sphalerite and galena were deposited in the upper and northern portions of the ore zone; a barite- and silver-rich facies of this stage may also be present in the southern portions of the vein system. Late in stage D, mineralogically complex assemblages containing chalcopyrite, tetrahedrite, polybasite, bornite, pyrargyrite, and a variety of other sulfides and sulfosalts were deposited in modest amounts throughout the vein system. This complex assemblage marked the transition to stage E. During stage E, the final sulfide stage, abundant botryoidal pyrite and marcasite with lesser stibnite, sphalerite, and sulfosalts were deposited primarily along the top of the Bulldog Mountain ore zone. Stage F, the final mineralization stage along the vein system, is marked by wire silver and concurrent leaching of earlier sulfides and sulfosalts; this stage may reflect the transition to a supergene environment.The sequence of mineralization stages identified in this study along the Bulldog Mountain system can be correlated with corresponding stages identified by other researchers along the OH and P veins, and the southern Amethyst vein system. Mineral zoning patterns identified along the Bulldog Mountain vein system also parallel larger scale zoning patterns across the central and southern Creede district.The complex variations in mineral assemblages documented in time and space along the Bulldog Mountain vein system were produced by the combined effects of many processes. Large-scale changes in vein mineralogy over time produced discrete mineralization stages. Short-term mineralogical fluctuations produced complex interbanding of mineralogically distinct generations. Fluid chemistry evolution within the vein system produced large-scale lateral zoning patterns within certain stages. Hypogene leaching substantially modified the distributions of some minerals. Finally, structural activity, mineral deposition, and mineral leaching modified fluid flow pathways repeatedly during mineralization, and so added to the complex mineral distribution patterns within the vein system.

Geographic information systems (GIS) spatial data compilation of geodynamic, tectonic, metallogenic, mineral deposit, and geophysical maps and associated descriptive data for northeast Asia

USGS Publications Warehouse

Naumova, Vera V.; Patuk, Mikhail I.; Kapitanchuk, Marina Yu.; Nokleberg, Warren J.; Khanchuk, Alexander I.; Parfenov, Leonid M.; Rodionov, Sergey M.; Miller, Robert J.; Diggles, Michael F.

2006-01-01

This is the online version of a CD-ROM publication. It contains all of the data that are on the disc but extra files have been removed: index files, software installers, and Windows autolaunch files. The purpose of this publication is to provide a high-quality spatial data compilation (Geographical Information System or GIS) of geodynamic, mineral deposit, and metallogenic belt maps, and descriptive data for Northeast Asia for customers and users. This area consists of Eastern Siberia, Russian Far East, Mongolia, northern China, South Korea, and Japan. The GIS compilation contains integrated spatial data for: (1) a geodynamics map at a scale of 1:5,000,000; (2) a mineral deposit location map; (3) metallogenic belt maps; (4) detailed descriptions of geologic units, including tectonostratigraphic terranes, cratons, major melange zones, and overlap assemblages, with references; (5) detailed descriptions of metallogenic belts with references; (6) detailed mineral deposit descriptions with references; and (7) page-size stratigraphic columns for major terranes.

Geochemical and textural characterization of phosphate accessory phases in the vein assemblage and metasomatically altered Llallagua tin porphyry

NASA Astrophysics Data System (ADS)

Betkowski, Wladyslaw B.; Rakovan, John; Harlov, Daniel E.

2017-09-01

Petrographic and geochemical characterization of phosphate accessory minerals represents a powerful tool in understanding the mineralization and metasomatic history of one of the world's biggest tin deposits, the Siglo XX mine, Salvadora stock, Llallagua, Bolivia. The Llallagua tin deposit lies in a hydrothermally altered porphyry stock that is part of the subduction-related Bolivian tin belt. Despite numerous studies, there is still a debate over the timing and characteristics of mineralization history of the deposit. Primary igneous fluorapatite and monazite (for the first time) were recognized in the altered porphyry. The igneous monazite is enriched in Th, unlike the hydrothermal monazite that is recognized for its low Th concentration. Fluorapatite, monazite, and xenotime also coexist with cassiterite within the hydrothermal vein assemblage. Fluorapatite and xenotime are essentially pristine. Monazite, however, shows various degrees of alteration in the form of regenerative mineral replacement (RMR). This exemplifies differential reactivity and selective mineral replacement/alteration of three accessory phosphate minerals, that are all important geochemical tracers of magmatic and hydrothermal processes, and which can all be used as geochronometers. Mineral textures and composition in the altered porphyry and vein assemblages have been evaluated. Monazite-xenotime geothermometry indicates monazite crystallization beginning around 550 °C. Monazite continues to grow as temperatures gradually decrease to about 300 °C, when most of cassiterite precipitation occurred in the samples studied. The primary mechanism of phosphate alteration has been identified as a coupled dissolution-reprecipitation process, which led to REE exchange in the igneous fluorapatite and hydrothermal monazite. In Type I local alteration, La and Pr-Nd show continuity across the pre- and post- alteration concentric zones indicating that they were not affected by alteration. This is an example of a selective elemental exchange during coupled dissolution-precipitation. Type II, pervasive post-growth alteration, is evident by the presence of micro-porosity and the formation of secondary, reaction induced minerals. Release of HREE from the monazite goes into the formation of void filling xenotime inclusions; the first documentation of this metasomatic alteration product in monazite. A well-documented discrepancy exists among ages determined from the zircon, fluorapatite, monazite, and altered porphyry minerals. These observations, regarding selective alteration of fluorapatite and monazite, may help to elucidate the reasons for this discrepancy.

Coesite Assemblages in Deep Continental Lithosphere: Additional Evidence for a Protolith from Subduction of Oceanic Crust

NASA Astrophysics Data System (ADS)

Sobolev, N.

2005-12-01

Inclusions in diamonds (DIs) represent an important source of information about the composition of continental lithospheric mantle. The isolated coesite inclusions in two diamonds (Harris, 1968) and a full set of eclogitic minerals (coesite (Cs), garnet (Ga), omphacite Cpx)) in two Yakutian diamonds (Sobolev et al., 1976), followed by finds of Cs-eclogite xenoliths (Smyth and Hatton, 1977; Ponomarenko et al., 1977) testify to the importance of coesite as a constituent of eclogitic rocks in deep lithospheric environment. Since these earlier times, coesite has been documented in more than 250 natural diamonds from 25 localities worldwide. Some 40 xenoliths of Cs-eclogites were found both in South African and Yakutian kimberlites. However, >50% of DIs of coesite are related to only four (4) diamond localities, including Guaniamo, Venezuela (Sobolev et al., 1998, 2003), Argyle (Jaques et al., 1989; Sobolev et al., 1989), New South Wales, all Australia (Sobolev et al., 1984; Meyer et al., 1997), and North Yakutian alluvials (Sobolev et al., 1999). All described DIs with coesite are from a wide range of assemblages: websterites to kyanite eclogites; grospydites and calcsilicate assemblages, with a large range in Gt [3.7-28.7 wt.% CaO] and Cpx [ 0.9-8.8 wt.% Na2O] compositions. In spite of these occurrences in diamonds, to the present, no coesite has been detected within the assemblage of minerals making up some 400 diamondiferous-eclogite xenoliths; similarly, no diamonds have been found in any Cs-eclogite xenoliths. This apparent paradox may be caused by coesite alteration in the diamondiferous eclogites, whereas coesite eclogites may have formed only outside of the diamond stability field. Indeed, coesite eclogites (without diamonds) may occupy a shallower position within continental lithosphere compared with the normal E-type diamond source. This indicates a broadly basaltic chemistry of the deep eclogitic environment, additional evidence for a protolith from the subduction of oceanic crust.

Geologic setting of the Fortymile River area - Polyphase deformational history within part of the eastern Yukon-Tanana uplands of Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998

USGS Publications Warehouse

Day, Warren C.; Gamble, Bruce M.; Henning, Mitchell W.; Smith, Bruce D.

2000-01-01

The Fortymile River area lies within the Yukon-Tanana lithotectonic terrane of east-central Alaska. This terrane is a mosaic of several lithotectonic assemblages, each with a coherent lithologic, metamorphic, and deformational history. Previous workers have shown that the Fortymile River area is underlain by rocks of the Seventymile, Taylor Mountain, and Nisutlin assemblages. The Taylor Mountain tectonostratigraphic assemblage is the most widespread within study area and is made up of amphibolite-grade Paleozoic(?) metamorphosed supracrustal rocks that have been intruded by plutonic rocks. The protoliths for the supracrustal rocks include mafic volcanic(?) rocks, graywacke, sulfide-rich siliciclastic sediments, quartz-rich sandstone, pelite, and marble, all of which are cut by late sulfide-bearing quartz veins. The mafic metavolcanic(?) rocks are of both tholeiitic and calc-alkalic affinity and have distinctly different rare-earth-element abundances. The supracrustal rocks are interpreted to have been deposited on a continental margin and (or) distal to an island-arc complex in a back-arc basin.The Steele Creek Dome Tonalite is defined herein as a composite body of foliated biotite-hornblende tonalitic orthogneiss containing country-rock rafts of paragneiss. The complex lies within the Taylor Mountain assemblage and has been tectonized and presumably recrystallized during regional Early Jurassic ductile deformation. The tonalite is compositionally similar to other volcanic-arc granites. The entire sequence was intruded by a Early Jurassic(?) hornblende monzodioritediorite-quartz diorite suite.The area has been subjected to at least three phases of deformation. The first (D1) produced a strong regional S1 schistosity and local mineral lineations. The second (D2) deformation generated tight to isoclinal F2 folds, folding the S1 schistosity and L1 mineral lineations, and was accompanied by a weak axial-planar S2 cleavage and both L2 mineral and stretching lineations. The question remains if the D1 and D2 tectonic fabrics either (1) record end members of a continuous, relatively long lived, progressive ductile deformation associated with the peak regional metamorphism and northward-directed thrusting; or (2) were separate and distinct pulses of tectonism. The youngest deformation recognized (D3) folded the ductile fabric elements about south-plunging, east-vergent, open folds and records east-west-directed tectonic shortening.

Discrimination of hydrothermal alteration mineral assemblages at Virginia City, Nevada, using the airborne imaging spectrometer

NASA Technical Reports Server (NTRS)

Hutsinpiller, Amy

1988-01-01

The purpose of this study is to use airborne imaging spectrometer data to discriminate hydrothermal alteration mineral assemblages associated with silver and gold mineralization at Virginia City, NV. The data is corrected for vertical striping and sample gradients, and converted to flat-field logarithmic residuals. Log residual spectra from areas known to be altered are compared to field spectra for kaolinitic, illitic, sericitic, and propylitic alteration types. The areal distributions of these alteration types are estimated using a spectral matching technique. Both visual examination of spectra and the matching techniques are effective in distinguishing kaolinitic, illitic, and propylitic alteration types from each other. However, illitic and sericitic alteration cannot be separated using these techniques because the spectra of illite and sericite are very similar. A principal components analysis of 14 channels in the 2.14-2.38 micron wavelength region is also successful in discriminating and mapping illitic, kaolinitic, and propylitic alteration types.

Mineral Reactions Involving Sapphirine and Their Application for Characterization of Metamorphic Conditions

NASA Astrophysics Data System (ADS)

Podlesskii, K. K.

2008-05-01

Assemblages of sapphirine, once considered to be a rare mineral, have in recent years been recognized as important indicators of high-temperature metamorphism. They occur in rocks that have undergone different tectono-metamorphic histories, with the P-T range of formation being estimated from below 700°C and 0.5 GPa to above 1100°C and 1.5 GPa. Sapphirine associated with quartz is attributed exclusively to the highest temperature conditions of crustal metamorphism referred to as ultrahigh-temperatiure metamorphism. Although experimental data involving sapphirine extend over an even wider P-T range, the quantitative interpretation of sapphirine-bearing assemblages remains ambiguous. Thermodynamic properties of magnesian sapphirine end-members have been optimized on the basis of experimentally constrained phase relations with the equation of state developed by Gerya et al., 2004. They differ from the model used in THERMOCALC (Kelsey et al., 2004), and the differences in the estimated stability of assemblages of sapphirine with quartz, kyanite and forsterite, to which a special attention have been paid due to their petrologic importance, look dramatic and may change interpretations of petrogenetic processes.

Nontronite and Montmorillonite as Nutrient Sources for Life on Mars

NASA Technical Reports Server (NTRS)

Craig, P. I.; Mickol, R. L.; Archer, P. D.; Kral, T. A.

2017-01-01

Clay minerals have been identified on Mars' oldest (Noachian) terrain and their presence suggests long-term water-rock interactions. The most commonly identified clay minerals on Mars to date are nontronite (Fe-smectite) and montmorillonite (Al-smectite) [1], both of which contain variable amounts of water both adsorbed on their surface and within their structural layers. Over Mars' history, these clay miner-al-water assemblages may have served as nutrient sources for microbial life.

Parkerite and bismutohauchecornite in chromitites of the Urals: Example of the Uralian Emerald Mines

NASA Astrophysics Data System (ADS)

Koroteev, V. A.; Popov, M. P.; Erokhin, Yu. V.; Khiller, V. V.

2017-04-01

An unusual ore mineralization represented by parkerite, millerite, bismutohauchecornite, bismuthinite, and nickeline was registered in altered chromitite from the Mariinsk emerald-beryllium deposit. Such mineralization is typical of Cu-Ni sulfide ores and hydrothermal veins from the five-element formation. This mineral assemblage was not registered in ophiolitic ultrabasic rocks and related chromitites. The find of bismutohauchecornite is the first in the Urals; the find of parkerite is the third.

Iron mineralization and associated skarn development around southern contact of the Eğrigöz pluton (northern Menderes Massif-Turkey)

NASA Astrophysics Data System (ADS)

Uǧurcan, Okşan Gökçen; Oyman, Tolga

2016-11-01

The Eğrigöz pluton is located in the northern portion of the Menderes Massif, which is the largest known metamorphic core complex that is also characterized by large-scale extension. Kalkan and Karaağıl skarn deposits are located on the southern border of the Eğrigöz Pluton, whereas Katrandağ mineralization developed along the roof pendant. Skarnization in these three areas is associated with the peraluminous, I-type, calc-alkaline, high-K calc-alkaline Eğrigöz Pluton. Geochemical characteristics of the pluton indicate that it was generated in a continental arc setting. Kalkan, Karaağıl, and Katrandağ skarns are hosted in marble bands in two-mica gneiss of the Kalkan Formation, a locally dolomitic and clay-bearing limestone of the Arıkaya Formation and locally dolomitised limestone of the Balıkbaşı Formation, respectively. Skarn development occurred sequentially in two stages, prograde and retrograde. In Kalkan skarn, prograde stage is characterized by clinopyroxene (Di56-73 Hd26-43 Joh1-2), garnet (Adr45-69 Grs30-52 Alm0-1.4 Sps0.7-2.3), amphibole, and magnetite, whereas retrograde stage is dominated by epidote, amphibole, chlorite, quartz, and calcite. In Karaağıl, both calcic and magnesian skarn association occurred as a result of local variations in dolomite content in Arıkaya Formation. The prograde assemblage of magnesian skarn is composed chiefly of spinel, amphibole and olivine. These mineral assemblages were, partially or fully, altered to serpentine, talc, and chlorite during retrograde alteration. Mesh textures of the serpentine indicates that the serpentine was altered from olivine. Olivine was completely destroyed during retrograde alteration without relict grains remaining. Calcic skarn paragenesis include garnet (Grs36-80Adr20-62Alm0-2.2Sps0.2-2.6), clinopyroxene (Di81-92 Hd7-19 Jo0-1), and plagioclase, that belongs to the earlier stage, and amphibole of the retrograde stage. High grossular end member of the garnet probably reflects host rock composition. The Katrandağ area differs from Kalkan and Karaağıl deposits in terms of initial metal content and gossan alteration due to the supergene alteration of galena dominated mineralization. In the Katrandağ, skarn that associated with iron and lead mineralization, both contain clinopyroxene and garnet. In the Kalkan skarn, fluid inclusion assemblages of prograde skarn association yield homogenization temperatures from 379 °C to over 600 °C, whereas those of retrograde minerals vary between 235 °C and 412 °C. Salinity values of the inclusions which obtained from prograde and retrograde assemblages are 9.2-22.4 and 6.4-20.1 wt%NaCl eq., respectively. Homogenization temperatures and salinity values of inclusions in clinopyroxene of Karaağıl calcic skarn are 420 to over 600 °C and 21-30 wt%NaCl eq., respectively.

An AEM-TEM study of weathering and diagenesis, Abert Lake, Oregon. (1) Weathering reactions in the volcanics

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

Banfield, J.F.; Veblen, D.R.; Jones, B.F.

1991-10-01

Abert Lake in south-central Oregon provides a site suitable for the study of sequential weathering and diagenetic events. In this first of two papers, transmission electron microscopy was used to characterize the igneous mineralogy, subsolidus alteration assemblage, and the structural and chemical aspects of silicate weathering reactions that occur in the volcanic rocks that outcrop around the lake. Olivine and pyroxene replacement occurred topotactically, whereas feldspar and glass alteration produced randomly oriented smectite in channels and cavities. The tetrahedral, octahedral, and interlayer compositions of the weathering products, largely dioctahedral smectites, varied with primary mineral composition, rock type, and as themore » result of addition of elements released from adjacent reaction sites. The variability within and between the smectite assemblages highlights the microenvironmental diversity, fluctuating redox conditions, and variable solution chemistry associated with mineral weathering reactions in the surficial environment. Late-stage exhalative and aqueous alteration of the volcanics redistributed many components and formed a variety of alkali and alkali-earth carbonate, chloride, sulfate, and fluoride minerals in vugs and cracks. Overall, substantial Mg, Si, Na, Ca, and K are released by weathering reactions that include the almost complete destruction of the Mg-smectite that initially replaced olivine. The leaching of these elements from the volcanics provides an important source of these constituents in the lake water. The nature of subsequent diagenetic reactions resulting from the interaction between the materials transported to the lake and the solution will be described in part.« less

Abiotic versus biotic iron mineral transformation studied by a miniaturized backscattering Mössbauer spectrometer (MIMOS II), X-ray diffraction and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Markovski, C.; Byrne, J. M.; Lalla, E.; Lozano-Gorrín, A. D.; Klingelhöfer, G.; Rull, F.; Kappler, A.; Hoffmann, T.; Schröder, C.

2017-11-01

Searching for biomarkers or signatures of microbial transformations of minerals is a critical aspect for determining how life evolved on Earth, and whether or not life may have existed in other planets, including Mars. In order to solve such questions, several missions to Mars have sought to determine the geochemistry and mineralogy on the Martian surface. This research includes the two miniaturized Mössbauer spectrometers (MIMOS II) on board the Mars Exploration Rovers Spirit and Opportunity, which have detected a variety of iron minerals on Mars, including magnetite (Fe2+Fe3+2O4) and goethite (α-FeO(OH)). On Earth, both minerals can derive from microbiological activity (e.g. through dissimilatory iron reduction of ferrihydrite by Fe(III)-reducing bacteria). Here we used a lab based MIMOS II to characterize the mineral products of biogenic transformations of ferrihydrite to magnetite by the Fe(III)-reducing bacteria Geobacter sulfurreducens. In combination with Raman spectroscopy and X-ray diffraction (XRD), we observed the formation of magnetite, goethite and siderite. We compared the material produced by biogenic transformations to abiotic samples in order to distinguish abiotic and biotic iron minerals by techniques that are or will be available onboard Martian based laboratories. The results showed the possibility to distinguish the abiotic and biotic origin of the minerals. Mossbauer was able to distinguish the biotic/abiotic magnetite with the interpretation of the geological context (Fe content mineral assemblages and accompanying minerals) and the estimation of the particle size in a non-destructive way. The Raman was able to confirm the biotic/abiotic principal peaks of the magnetite, as well as the organic principal vibration bands attributed to the bacteria. Finally, the XRD confirmed the particle size and mineralogy.

Late-stage magmatic to deuteric/metasomatic accessory minerals from the Cerro Boggiani agpaitic complex (Alto Paraguay Alkaline Province)

NASA Astrophysics Data System (ADS)

Comin-Chiaramonti, Piero; Renzulli, Alberto; Ridolfi, Filippo; Enrich, Gaston E. R.; Gomes, Celso B.; De Min, Angelo; Azzone, Rogério G.; Ruberti, Excelso

2016-11-01

This work describes rare accessory minerals in volcanic and subvolcanic silica-undersaturated peralkaline and agpaitic rocks from the Permo-Triassic Cerro Boggiani complex (Eastern Paraguay) in the Alto Paraguay Alkaline Province. These accessory phases consist of various minerals including Th-U oxides/silicates, Nb-oxide, REE-Sr-Ba bearing carbonates-fluorcarbonates-phosphates-silicates and Zr-Na rich silicates. They form a late-stage magmatic to deuteric/metasomatic assemblage in agpaitic nepheline syenites and phonolite dykes/lava flows made of sodalite, analcime, albite, fluorite, calcite, ilmenite-pyrophanite, titanite and zircon. It is inferred that carbonatitic fluids rich in F, Na and REE percolated into the subvolcanic system and metasomatically interacted with the Cerro Boggiani peralkaline and agpaitic silicate melts at the thermal boundary layers of the magma chamber, during and shortly after their late-stage magmatic crystallization and hydrothermal deuteric alteration.

Comparison of the mineralogy of the Boss-Bixby, Missouri copper-iron deposit, and the Olympic Dam copper-uranium-gold deposit, South Australia

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

Brandom, R.T.; Hagni, R.D.; Allen, C.R.

1985-01-01

An ore microscopic examination of 80 polished sections prepared from selected drill core specimens from the Boss-Bixby, Missouri copper-iron deposit has shown that its mineral assemblage is similar to that of the Olympic Dam (Roxby Downs) copper-uranium-gold deposit in South Australia. A comparison with the mineralogy reported for Olympic Dam shows that both deposits contain: 1) the principal minerals, magnetite, hematite, chalcopyrite, and bornite, 2) the cobalt-bearing phases, carrollite and cobaltian pyrite, 3) the titanium oxides, rutile and anatase, 4) smaller amounts of martite, covellite, and electrum, 5) fluorite and carbonates, and 6) some alteration minerals. The deposits also aremore » similar with regard to the sequence of mineral deposition: 1) early oxides, 2) then sulfide minerals, and 3) a final oxide generation. The deposits, however, are dissimilar with regard to their host rock lithologies and structural settings. The Boss-Bixby ores occupy breccia zones within a hydrothermally altered basic intrusive and intruded silicic volcanics, whereas the Olympic Dam ores are contained in sedimentary breccias in a graben or trough. Also, some minerals have been found thus far to occur at only one of the deposits. The similarity of mineralogy in these deposits suggests that they were formed from ore fluids that had some similarities in character and that the St. Francois terrane of Missouri is an important region for further exploration for deposits with this mineral assemblage.« less

Blueschists and eclogites from southern Sifnos (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Weil, Jonas; Petrakakis, Konstantin; Grasemann, Bernhard; Iglseder, Christoph

2010-05-01

Eclogite/blueschist facies rocks from northern Sifnos (Cyclades) are well known and have been described by many authors. A small occurrence of similar rocks in the south-west of Sifnos has been investigated and is compared to other occurrences in terms of their mineral assemblages, chemistry, petrography and structural position. The tectono-metamorphic evolution on Sifnos is characterized by a regional blueschist / eclogite facies metamorphism (M1) during the Eocene, followed by a regional Oligo-Miocene medium pressure overprint (M2). The investigated rocks from the Fikiada Bay area formed during M1 but were overprinted by a brittle / ductile M2 event. The high-pressure rock assemblage of Fikiada bay represents a sequence of metabasites, metaacidites, and metasediments with a foliation-parallel compositional layering. Rootless isoclinal folding of the regional foliation is common with fold axes trending roughly NW-SE; hinges are overprinted by later axial foliation planes. The foliation is well developed and mostly dips to N to E, the main pervasive stretching lineation is shallow and plunging to NE. Grt- rich dark blueschists, bearing eclogite-boudins of some dm size, alternate with lighter Qtz-rich Grt-bearing, cm to m thick layers. Massive, very coarse grained Ep+Chl+Ab -rich gneisses form layers with up to 3 m thickness. Metasediments comprise light Cal-rich gneisses as well as metapelites and quartzites. These lithologies are overlain by highly strained calcite marbles bearing boudins of Dol-marble. Foliation, stretching lineation and isoclinal folds show the same orientation as in the silicates. The blueschists show the characteristic assemblage Gln + Grt + Ep + Ab + Phg + Pg +Qtz (+Cal) + Mag. Inclusions in large poikiloblastic Grt reveal an earlier compositional layering: Domains with conserved foam microstructures of Qtz and domains of massive Grt including relics of Jd (XNa = 0.9), Ctd, Ep, Rt and Mag. Gln shows a zonal pattern with Mg-rich cores to ferro-glaucophane and crossite- richer rims. Ep is zoned too with decreasing Fe from core to rim, while Grt-poikiloblasts are nearly homogeneous in composition. Eclogitic assemblages consist of Grt + Omp + Ep + Phg + Gln ± Qtz. A greenschist-facies overprint accompanied by Fe- and CO2- rich fluids is mostly evident along shear bands of variable thickness from thin section to outcrop scale. It is best documented by the growth of syntectonic Ab+Chl neoblasts. Metabasite layers intercalated with the marble show a pervasive greenschist-facies overprint with extensive, neoblastic growth of Chl an Ab. Early Ep remains unaffected, but Gln and Grt are preserved only as relics. Petrography and mineral chemistry of southern Sifnos HP-rocks comply with the occurrence in northern Sifnos (e.g. comprehensive description by Schliestedt 1986) References: Schliestedt, M., 1986. Eclogite-blueschist relationships as evidenced by mineral equilibria in the high-pressure rocks of Sifnos (Cycladic islands), Greece. Journal of Petrology, 27,1437-1459 Mineral abbreviations after Kretz, 1983: Symbols for rock-forming minerals. American Mineralogist, 68, 277-279

Tectono-metamorphic evolution of meta-ophiolitic units along Susa Valley (Italian Western Alps): new suggestions for the exhumation processes

NASA Astrophysics Data System (ADS)

Ghignone, Stefano; Borghi, Alessandro; Balestro, Gianni; Gattiglio, Marco

2017-04-01

In the inner Western Alps, meta-ophiolite units (i.e., the Piemonte Zone) show different stages of the tectono-metamorphic evolution, since the early phases of subduction to the latest exhumation steps. Tectono-metamorphic data collected through the meta-ophiolite units of the Piemonte Zone along the middle Susa Valley allowed to infer new ideas about the exhumation processes that developed in the (U)HP units. In this area, Zermatt-Saas-like meta-ophiolite unit (i.e., the eclogite-facies Internal Piemonte Zone, IPZ) are tectonically overlain by Combin-like ones (i.e., the blueschist-facies External Piemonte Zone, EPZ), through a thick shear zone (i.e., the Susa Shear Zone, SSZ). Metamorphic history was achieved by analyzing basic rocks (metabasalt and Fe-Ti metagabbro) and sedimentary rocks derived from reworking basic rocks in oceanic environment (basic sandstones and conglomerates, and ophiolitic breccia). Different P-T paths were inferred for IPZ and EPZ, according with mineral assemblages and realizations of pseudosections. In the IPZ, four tectono-metamorphic events, developed under variables metamorphic conditions, were recognized. The first (peak-P) event shows (U)HP conditions, defined by the occurrence of relic mineral assemblage (Grt I+ Omp I + Rt). The paragenesis is completed by Zo + Pg pseudomorphs, implying that Lws-eclogite facies were reached. The discovery in Grt (and Rt) relics inclusions of black euhedral pseudomorphs of disordered graphite, suggesting to be derived from original microdiamonds, agree with other petrologic constrains. The second event, marked by the Grt II + Omp II + Ph + Gln + Zo assemblage, developed under epidote-eclogite facies conditions. Following a retrograde and decompressional trajectory, the IPZ was then re-equilibrated under greenschist-facies conditions and a new assemblage (Ab + Chl + Mu + Czo + Ttn + Act) overprinted HP paragenesis. The last event is marked by a weak heating, with crystallization of Bt + Ep + Olig + Hbl (Prg) + Ms. The EPZ shows a different metamorphic evolution, where only two events were recognized. The first event developed under blueschist-facies conditions, with relics of mineral assemblages consisting of Gln + Rt + Ph. Then, a retrograde trajectory re-equilibrated EPZ under greenschist-facies conditions and a new stable mineral assemblage (Ab + Chl + Mu + Ttn + Act + Czo) grew. The inferred P-T path suggests, for the IPZ, a first isothermal exhumation stage, likely driven by buoyancy forces from the base of the orogenic wedge. In the EPZ, HP peak occurs at the same gradient of the second event in the IPZ, suggesting that, during exhumation of the IPZ, the EPZ was still subducted. The strong re-equilibration under greenschist-facies conditions suggests a stage of slow exhumation rate, which can be related to the coupling between IPZ and EPZ.

The potential for prebiotic synthesis in hydrothermal systems. [Abstract only

NASA Technical Reports Server (NTRS)

Ferris, James P.

1994-01-01

Contemporary hydrothermal systems provide a reducing environment where organic compounds are formed and may react to generate the molecules used in the first living systems. The organic compounds percolate through mineral assemblages at a variety of temperatures so the proposed synthetic reactions are driven by heat and catalyzed by minerals (Ferris, 1992). Some examples of potential prebiotic reactions are discussed.

On protolith-, metamorphic overprint, microstructure and rheology of mineral assemblages in orogenic peridotites of the central Scandinavian Caledonides

NASA Astrophysics Data System (ADS)

Gilio, Mattia; Clos, Frediano; Van Roermund, Herman L. M.

2013-04-01

The Scandinavian Caledonides (SC) are a deeply eroded Alpine-type orogenic belt formed by closure of the Iapetus ocean and collision between Baltica and Laurentia (500-380 Ma). The SC consists of a stack of Nappe Complexes (from bottom to top called Lower, Middle, Upper and Uppermost Allochthons) thrusted to the east over the Baltic Shield (Brueckner and Van Roermund, 2004; Gee et al., 2008). Fossil lithospheric mantle fragments, called orogenic peridotites, have been found within the (upper part of) middle, upper and uppermost Allochthons, as well as in the reworked basement gneisses (a.o Western Gneiss Complex (WGC)) along the Norwegian west coast. They occur as isolated lenses that contain diverse mineral parageneses and/or bulk rock compositions. Crustal incorporation of orogenic peridotite is classically interpreted to be the result of plate collisional processes related to orogeny (Brueckner and Medaris, 2000). The WGC and parts of the upper part of the Middle Allochthon (a.o. Seve Nappe Complex (SNC) in N Jämtland/S Västerbotten, central Sweden), are well known for the occurrence of high (HP) and ultrahigh pressure (UHP) metamorphic terranes (of Caledonian age). The (U)HPM evidence clearly demonstrates the deep metamorphic origin of these rocks interpreted to be caused by continental subduction and/or collision. Other metamorphic rocks (of Caledonian age) exposed in allochthonous nappes are solely characterised by greenschist-, amphibolite- and/or MP granulite "facies" mineral assemblages that can be interpreted, in the absence of retrogression, to have formed in less deeply subducted (and/or metamorphic) environments. This duality in metamorphic "facies" allows for a discrimination (at least theoretically) between "deep" versus "shallow" rooted nappes (in central parts of the Scandinavian Caledonides). Conform this reasoning, this duality should also be present within the Caledonian mineral assemblages (= metamorphic overprint) of orogenic peridotites (in central parts of the orogen), which, at least in the allochtonous nappes, have been interpreted to be "isofacial" with their host country rocks (Bucher, 1991). The latter strongly contrast to the interpretation of their "primary" (="protolith"- related) mineral assemblage(s) which clearly suggest a bimodal origin: here called thick (>80 km) versus thin (< 70 km) rooted lithospheric mantle protoliths. Distinction can be made on the basis of the presence of the stable (minimal Proterozoic) garnet-olivine assemblages in the protolith (i.e. much older than the Scandian collision event (Brueckner et al., 2010). For this reason orogenic garnet peridotite was first called "relict" garnet peridotite (Brueckner and Medaris, 2000), later rephrased into mantle wedge garnet peridotite (MWgp) by Van Roermund (2009). MWgp occurs in the WGC and in the SNC of the Upper Allochthon in central Sweden (Zhang et al., 2009). Most (All?) other protolith assemblages of orogenic peridotite in the CSC belong to the thin-rooted protolith subtype. No examples are known to us in which thin rooted prototypes became overprinted (during the Caledonian orogeny) by (U)HP metamorphic minerals, except for the subduction zone garnet peridotites (SZgp) in the WGC (Van Roermund, 2009). The latter can thus savely be interpreted as being enclosed within normal "MP" (or lower pressure) nappe sequences. As such it will be clear that this duality in protolith (and/or metamorphic) mineral assemblages of orogenic peridotite can be used to identify former, but now strongly retrogressed, (U)HP metamorphic terranes in other parts of the CSC (Gee et al, 2012). For this reason a comparative study has been made concerning field, (micro-)structural, mineral-chemical and/or geochemical aspects of two major orogenic peridotites from the SNC, central Sweden; here called the Friningen Garnet Peridotite (FGP) and the Kittelfjäll Spinel Peridotite (KSP), both exposed within the central belt of the SNC in central Sweden. The ultimate aim was to investigate whether the MWgp sub-type can be extended towards (Al-poor) spinel-bearing protolith assemblages or not. Results, including some hitherto unexpected mechanical effects, will be presented. References: Brueckner, H.K., Carswell, D.A., Griffin, W.L., Medaris, L.G., Van Roermund, H.L.M., Cuthbert, S.J. (2010). The mantle and crustal evolution of two garnet peridotite suites from the Western Gneiss Region, Norwegian Caledonides: An isotopic investigation. Lithos, 117, 1-19. doi:10.1016/j. Lithos.2010.01.011 Brueckner, H.K.and Medaris, L.G. (2000). A general model for the intrusion and evolution of "mantle" garnet peridotites in high-pressure and ultra-high-pressure metamorphic terranes. J. Metamorphic Geol., 18, 123-133. Brueckner H.K. and Van Roermund,H.L.M. (2004). Dunk tectonics: A multiple subduction//eduction model for the evolution of the Scandinavian Caledonides. Tectonics, 23, TC2004, doi:10.1029/2003tc001502. Bucher, K. (1991). Mantle fragments in the Scandinavian Caledonides. Tectonophysics, 190, 173-192. Gee, D.G., Fossen, H., Henriksen, N., Higgins, K. (2008). From the Early Paleozoic Platforms of Baltica and Laurentia to the Caledonide Orogen of Scandinavia and Greenland. Episodes, 31, 44-51. Gee, D.G., Janak, M., Majka, J., Robinson, P., Van Roermund, H.L.M (2012). UHP metamorphism along the Baltoscandian outer margin: evidence from the Seve Nappe Complex of the Swedish Caledonides. Lithosphere, in press. Janak, M., Van Roermund, H., Majka, J., Gee, D. (2012). UHP metamorphism recorded by kyanite-bearing eclogite in the Seve Nappe Complex of northern Jämtland, Swedish Caledonides. Gondwana Research, in press. Van Roermund, H.L.M. (2009). Mantle-wedge garnet peridotites from the northernmost ultra-high pressure domain of the Western Gneiss Region, SW Norway. Eur. J. Mineralogy, 21, 1085-1096. Zhang, C., Van Roermund, H.L.M., Zhang, L.F (2011). 16 - Orogenic Garnet Peridotites: Tools to Reconstruct Paleo-Geodynamic Settings of Fossil Continental Collision Zones. In: Ultrahigh Pressure Metamorphism, 25 Years After The Discovery Of Coesite And Diamond. London. Doi:10.1016/B978-0-12-385144-4.00015-1

Nanomineralogy as a new dimension in understanding elusive geochemical processes in soils: The case of low-solubility-index elements

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

Schindler, Michael; Hochella, Michael F.

2016-05-20

Nanomineralogy is a new dimension in understanding chemical processes in soils. These processes are revealed at the nanoscale within the structures and compositions of phases that heretofore were not even known to exist in the soils in which they are found. The discovery and understanding of soil chemistry in this way is best accessible via a combination of focused ion beam technology (for sample preparation) and high resolution, analytical transmission electron microscopy (for phase identification). We have used this scientific framework and these techniques to decipher past and present chemical processes in a soil in Sudbury, Ontario, Canada that hasmore » been impacted by both smelter contamination (acidification) and subsequent remediation within the past century. In this study, we use these methods to investigate mobilization and sequestration of the relatively immobile elements Al, Ti and Zr. In a micrometer-thick alteration layer on an albite grain, a first generation of clay minerals represents weathering of the underlying mineral prior to the acidification of the soils. Complex assemblages of Ti- and Zr-bearing nanophases occur on the surfaces of Fe-(hydr)oxide crystals and are the result of the dissolution of silicates and oxides and the mobilization of Ti- and Zr-bearing colloids under acidic conditions. These phases include anatase (TiO2), kleberite (Fe3+Ti6O11(OH)5) Ti4O7, baddelyite (ZrO2), a structural analogue to kelyshite (NaZr[Si2O6(OH)]) and authigenic zircon (ZrSiO4). Subsequent remediation of the acidic soils has resulted in the sequestration of Al and in the neoformation of the clay minerals kaolinite, smectite and illite. These complex mineral assemblages form a porous layer that controls the interaction of the underlying mineral with the environment.« less

Partitioning in REE-saturating minerals - Theory, experiment, and modelling of whitlockite, apatite, and evolution of lunar residual magmas

NASA Technical Reports Server (NTRS)

Jolliff, Bradley L.; Haskin, Larry A.; Colson, Russell O.; Wadhwa, Meenakshi

1993-01-01

Compositions, including REEs determined by ion microprobe, of apatite and whitlockite in lunar rock assemblages rich in incompatible trace elements, are presented. Concentrations of REEs in lunar whitlockites are high, ranging from about 1.2 to 2.1 REEs (lanthanides + Y) per 56 oxygens. This slightly exceeds the level of two REE atoms per 56 oxygens at which the dominant substitution theoretically becomes saturated. This saturation effect leads to whitlockite REE(3+) D values at typical lunar whitlockite REE concentrations which are 30-40 percent lower than the D values at low concentrations. The halogen-to-phosphorous ratio in lunar melts is a key factor determining the REE distribution with crystalline assemblages. As long as P and REE concentrations of melts are in KREEP-like proportions, one or both of the phosphates will saturate in melts at similar REE concentrations.

The origin of Ag-Au-S-Se minerals in adularia-sericite epithermal deposits: constraints from the Broken Hills deposit, Hauraki Goldfield, New Zealand

NASA Astrophysics Data System (ADS)

Cocker, Helen A.; Mauk, Jeffrey L.; Rabone, Stuart D. C.

2013-02-01

The 7.1 Ma Broken Hills adularia-sericite Au-Ag deposit is currently the only producing rhyolite-hosted epithermal deposit in the Hauraki Goldfield of New Zealand. The opaque minerals include pyrite, electrum, acanthite (Ag2S), sphalerite, and galena, which are common in other adularia-sericite epithermal deposits in the Hauraki Goldfield and elsewhere worldwide. Broken Hills ores also contain the less common minerals aguilarite (Ag4SeS), naumannite (Ag2Se), petrovskaite (AuAgS), uytenbogaardtite (Ag3AuS2), fischesserite (Ag3AuSe2), an unnamed silver chloride (Ag2Cl), and unnamed Ag ± Au minerals. Uytenbogaardtite and petrovskaite occur with high-fineness electrum. Broken Hills is the only deposit in the Hauraki Goldfield where uytenbogaardtite and petrovskaite have been identified, and these phases appear to have formed predominantly from unmixing of a precursor high-temperature phase under hypogene conditions. Supergene minerals include covellite, chalcocite, Au-rich electrum, barite, and a variety of iron oxyhydroxide minerals. Uytenbogaardtite can form under supergene and hypogene conditions, and textural relationships between uytenbogaardtite and associated high-fineness electrum may be similar in both conditions. Distinguishing the likely environment of formation rests principally on identification of other supergene minerals and documenting their relationships with uytenbogaardtite. The presence of aguilarite, naumannite, petrovskaite, and fischesserite at Broken Hills reflects a Se-rich mineral assemblage. In the Hauraki Goldfield and the western Great Basin, USA, Se-rich minerals are more abundant in provinces that are characterized by bimodal rhyolite-andesite volcanism, but in other epithermal provinces worldwide, the controls on the occurrences of Se-bearing minerals remain poorly constrained, in spite of the unusually high grades associated with many Se-rich epithermal deposits.

Modeling hot spring chemistries with applications to martian silica formation

NASA Astrophysics Data System (ADS)

Marion, G. M.; Catling, D. C.; Crowley, J. K.; Kargel, J. S.

2011-04-01

Many recent studies have implicated hydrothermal systems as the origin of martian minerals across a wide range of martian sites. Particular support for hydrothermal systems include silica (SiO 2) deposits, in some cases >90% silica, in the Gusev Crater region, especially in the Columbia Hills and at Home Plate. We have developed a model called CHEMCHAU that can be used up to 100 °C to simulate hot springs associated with hydrothermal systems. The model was partially derived from FREZCHEM, which is a colder temperature model parameterized for broad ranges of temperature (<-70 to 25 °C), pressure (1-1000 bars), and chemical composition. We demonstrate the validity of Pitzer parameters, volumetric parameters, and equilibrium constants in the CHEMCHAU model for the Na-K-Mg-Ca-H-Cl-ClO 4-SO 4-OH-HCO 3-CO 3-CO 2-O 2-CH 4-Si-H 2O system up to 100 °C and apply the model to hot springs and silica deposits. A theoretical simulation of silica and calcite equilibrium shows how calcite is least soluble with high pH and high temperatures, while silica behaves oppositely. Such influences imply that differences in temperature and pH on Mars could lead to very distinct mineral assemblages. Using measured solution chemistries of Yellowstone hot springs and Icelandic hot springs, we simulate salts formed during the evaporation of two low pH cases (high and low temperatures) and a high temperature, alkaline (high pH) sodic water. Simulation of an acid-sulfate case leads to precipitation of Fe and Al minerals along with silica. Consistency with martian mineral assemblages suggests that hot, acidic sulfate solutions are plausibility progenitors of minerals in the past on Mars. In the alkaline pH (8.45) simulation, formation of silica at high temperatures (355 K) led to precipitation of anhydrous minerals (CaSO 4, Na 2SO 4) that was also the case for the high temperature (353 K) low pH case where anhydrous minerals (NaCl, CaSO 4) also precipitated. Thus we predict that secondary minerals associated with massive silica deposits are plausible indicators on Mars of precipitation environments and aqueous chemistry. Theoretical model calculations are in reasonable agreement with independent experimental silica concentrations, which strengthens the validity of the new CHEMCHAU model.

Modeling hot spring chemistries with applications to martian silica formation

USGS Publications Warehouse

Marion, G.M.; Catling, D.C.; Crowley, J.K.; Kargel, J.S.

2011-01-01

Many recent studies have implicated hydrothermal systems as the origin of martian minerals across a wide range of martian sites. Particular support for hydrothermal systems include silica (SiO2) deposits, in some cases >90% silica, in the Gusev Crater region, especially in the Columbia Hills and at Home Plate. We have developed a model called CHEMCHAU that can be used up to 100??C to simulate hot springs associated with hydrothermal systems. The model was partially derived from FREZCHEM, which is a colder temperature model parameterized for broad ranges of temperature (<-70 to 25??C), pressure (1-1000 bars), and chemical composition. We demonstrate the validity of Pitzer parameters, volumetric parameters, and equilibrium constants in the CHEMCHAU model for the Na-K-Mg-Ca-H-Cl-ClO4-SO4-OH-HCO3-CO3-CO2-O2-CH4-Si-H2O system up to 100??C and apply the model to hot springs and silica deposits.A theoretical simulation of silica and calcite equilibrium shows how calcite is least soluble with high pH and high temperatures, while silica behaves oppositely. Such influences imply that differences in temperature and pH on Mars could lead to very distinct mineral assemblages. Using measured solution chemistries of Yellowstone hot springs and Icelandic hot springs, we simulate salts formed during the evaporation of two low pH cases (high and low temperatures) and a high temperature, alkaline (high pH) sodic water. Simulation of an acid-sulfate case leads to precipitation of Fe and Al minerals along with silica. Consistency with martian mineral assemblages suggests that hot, acidic sulfate solutions are plausibility progenitors of minerals in the past on Mars. In the alkaline pH (8.45) simulation, formation of silica at high temperatures (355K) led to precipitation of anhydrous minerals (CaSO4, Na2SO4) that was also the case for the high temperature (353K) low pH case where anhydrous minerals (NaCl, CaSO4) also precipitated. Thus we predict that secondary minerals associated with massive silica deposits are plausible indicators on Mars of precipitation environments and aqueous chemistry. Theoretical model calculations are in reasonable agreement with independent experimental silica concentrations, which strengthens the validity of the new CHEMCHAU model. ?? 2011 Elsevier Inc.

Mineralogical gradients associated with alvinellids at deep-sea hydrothermal vents

NASA Astrophysics Data System (ADS)

Zbinden, Magali; Le Bris, Nadine; Compère, Philippe; Martinez, Isabelle; Guyot, François; Gaill, Françoise

2003-02-01

Alvinella pompejana and Alvinella caudata live in organic tubes on active sulphide chimney walls at deep-sea hydrothermal vents. These polychaete annelids are exposed to extreme thermal and chemical gradients and to intense mineral precipitation. This work points out that mineral particles associated with Pompeii worm ( A. pompejana and A. caudata) tubes constitute useful markers for evaluating the chemical characteristics of their micro-environment. The minerals associated with these worm tubes were analysed on samples recovered from an experimental alvinellid colony, at different locations in the vent fluid-seawater interface. Inhabited tubes from the most upper and lower parts of the colony were analysed by light and electron microscopies, X-ray microanalysis and X-ray diffraction. A change was observed from a Fe-Zn-S mineral assemblage to a Zn-S assemblage at the millimeter scale from the outer to the inner face of a tube. A similar gradient in proportions of minerals was observed at a decimeter scale from the lower to the upper part of the colony. The marcasite/pyrite ratio of iron disulphides also displays a steep decrease along the few millimeters adjacent to the external tube surface. The occurrence of these gradients indicates that the micro-environment within the tube differs from that outside the tube, and suggests that the tube wall acts as an efficient barrier to the external environment.

Two cryptic anatectic events within a syn-collisional granitoid from the Araçuaí orogen (southeastern Brazil): Evidence from the polymetamorphic Carlos Chagas batholith

NASA Astrophysics Data System (ADS)

Melo, M. G.; Stevens, G.; Lana, C.; Pedrosa-Soares, A. C.; Frei, D.; Alkmim, F. F.; Alkmin, L. A.

2017-04-01

From the earliest (ca. 630 Ma) pre-collisional plutons to the latest (ca. 480 Ma) post-collisional intrusions, the Araçuaí orogen (SE Brazil) records an outstanding succession of granite production events in space and time. The Carlos Chagas batholith (CCB) is the largest ( 14,000 km2) granitic body ascribed to the collisional plutonism (G2 supersuite) in the back-arc region of the Araçuaí orogen, to the east of the Rio Doce magmatic arc. A wide range of monazite and zircon ages (> 725 Ma to ca. 490 Ma) have been found in CCB granites, recording a rich history of crustal recycling and inheritance, magmatic crystallization and anatexis. The CCB includes a dominant granite richer in garnet than in biotite, in which three mineral assemblages can be identified: 1) Qz + Pl + Kfs + Bt + Grt + Ilm ± Rt; 2) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil; and 3) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil + Spl. Rocks which contain mineral assemblage 2 and 3 all contain two generations of garnet. Textural evidence for the presence of former melt, recognized in all studied CCB samples, includes: silicate melt inclusions in poikiloblastic garnet, pseudomorphed thin films of melt surrounding both generations of garnet, pseudomorphed melt pools adjacent to garnet and biotite, and plagioclase and quartz with cuspate-lobate shapes occurring among matrix grains. Both generations of garnet crystals (Grt1 and Grt2) are unzoned in terms of major element concentration, contain small rounded inclusions of Ti-rich biotite and, in addition, the Grt2 crystals also contain inclusions of remnant sillimanite needles. Microstructural evidence, in combination with mineral chemistry, indicates that the garnet crystals grew during two distinct metamorphic-anatectic events, as the peritectic products of fluid-absent melting reactions which consumed biotite, quartz and plagioclase, in the case of Grt1, and which consumed biotite, quartz, plagioclase and sillimanite in the case of Grt2. P-T pseudosections calculated via Theriak-Domino, in combination with in situ U-Pb monazite and zircon dating, provide new constraints on the thermal evolution of the back-arc region of the Araçuaí orogen. Data from assemblage 1 suggests P-T conditions for the first granulite-facies metamorphic event (M1) at 790-820 °C and 9.5-10.5 kbar, while the assemblage 2 records P-T conditions for a second granulite-facies metamorphism (M2) of around 770 °C and 6.6 kbar. Monazite and zircon within garnets from the different assemblages give age peaks at 570-550 Ma (M1) and 535-515 Ma (M2), recording two anatectic events in the CCB during a single orogenic cycle. The PT conditions for these metamorphic events can be related to: i) M1, striking crustal thickening, probably involving thrusting of the magmatic arc onto the back-arc region; and ii) M2, decompression related to the gravitational collapse of the Araçuaí orogen.

Hydrothermal alteration and Cu–Ni–PGE mobilization in the charnockitic rocks of the footwall of the South Kawishiwi intrusion, Duluth Complex, USA

PubMed Central

Benkó, Zsolt; Mogessie, Aberra; Molnár, Ferenc; Krenn, Kurt; Poulson, Simon R.; Hauck, Steven; Severson, Mark; Arehart, Greg B.

2015-01-01

In the Neoarchean (~ 2.7 Ga) contact metamorphosed charnockitic footwall of the Mesoproterosoic (1.1 Ga) South Kawishiwi intrusion of the Duluth Complex, the primary metamorphic mineral assemblage and Cu–Ni–PGE sulfide mineralization is overprinted by an actinolite + chlorite + cummingtonite + prehnite + pumpellyite + quartz + calcite hydrothermal mineral assemblage along 2–3 cm thick veins. In calcite, hosted by the hydrothermal alteration zones and in a single recrystallized quartz porphyroblast, four different fluid inclusion assemblages are documented; the composition of these fluid inclusions provide p–T conditions of the fluid flow, and helps to define the origin of the fluids and evaluate their role in the remobilization and reprecipitation of the primary metamorphic sulfide assemblage. Pure CO2 fluid inclusions were found as early inclusions in recrystallized quartz porphyroblast. These inclusions may have been trapped during the recrystallization of the quartz during the contact metamorphism of the footwall charnockite in the footwall of the SKI. The estimated trapping pressure (1.6–2.0 kbar) and temperature (810–920 °C) conditions correspond to estimates based on felsic veins in the basal zones of the South Kawishiwi intrusion. Fluid inclusion assemblages with CO2–H2O–NaCl and CH4–N2–H2O–NaCl compositions found in this study along healed microfractures in the recrystallized quartz porphyroblast establish the heterogeneous state of the fluids during entrapment. The estimated trapping pressure and temperature conditions (240–650 bar and 120–150 °C for CO2–H2O–NaCl inclusions and 315–360 bar and 145–165 °C for CH4–N2–H2O–NaCl inclusions) are significantly lower than the p–T conditions (> 700 °C and 1.6–2 kbar) during the contact metamorphism, indicating that this fluid flow might not be related to the cooling of the Duluth Complex and its contact aureole. The presence of chalcopyrite inclusions in these fluid inclusions and in the trails of these fluid inclusion assemblages confirms that at least on local scale these fluids played a role in base metal remobilization. No evidences have been observed for PGE remobilization and transport in the samples. The source of the carbonic phase in the carbonic assemblages (CO2; CH4) could be the graphite, present in the metasedimentary hornfelsed inclusions in the basal zones of the South Kawishiwi intrusion. The hydrothermal veins in the charnockite can be characterized by an actinolite + cummingtonite + chlorite + prehnite + pumpellyite + calcite (I–II) + quartz mineral assemblage. Chlorite thermometry yields temperatures around 276–308 °C during the earliest phase of the fluid flow. In the late calcite (II) phase, high salinity (21.6–28.8 NaCl + CaCl2 equiv. wt.%), low temperature (90–160 °C), primary aqueous inclusions were found. Chalcopyrite (± sphalerite ± millerite), replacing and intersecting the early hydrothermal phases, are associated to the late calcite (II) phase. The composition of the formational fluids in the Canadian Shield is comparable with the composition of the studied fluid inclusions. This suggests that the composition of the fluids did not change in the past 2 Ga and base metal remobilization by formational fluids could have taken place any time after the formation of the South Kawishiwi intrusion. Sulfur isotope studies carried out on the primary metamorphic (δ34S = 7.4–8.9‰) and the hydrothermal sulfide mineral assemblage (δ34S = 5.5–5.7‰) proves, that during the hydrothermal fluid flow the primary metamorphic ores were remobilized. PMID:26594080

Mineral assemblage transformation of a metakaolin-based waste form after geopolymer encapsulation

NASA Astrophysics Data System (ADS)

Williams, Benjamin D.; Neeway, James J.; Snyder, Michelle M. V.; Bowden, Mark E.; Amonette, James E.; Arey, Bruce W.; Pierce, Eric M.; Brown, Christopher F.; Qafoku, Nikolla P.

2016-05-01

Mitigation of hazardous and radioactive waste can be improved through conversion of existing waste to a more chemically stable and physically robust waste form. One option for waste conversion is the fluidized bed steam reforming (FBSR) process. The resulting FBSR granular material was encapsulated in a geopolymer matrix referred to here as Geo-7. This provides mechanical strength for ease in transport and disposal. However, it is necessary to understand the phase assemblage evolution as a result of geopolymer encapsulation. In this study, we examine the mineral assemblages formed during the synthesis of the multiphase ceramic waste form. The FBSR granular samples were created from waste simulant that was chemically adjusted to resemble Hanford tank waste. Another set of samples was created using Savannah River Site Tank 50 waste simulant in order to mimic a blend of waste collected from 68 Hanford tank. Waste form performance tests were conducted using the product consistency test (PCT), the Toxicity Characteristic Leaching Procedure (TCLP), and the single-pass flow-through (SPFT) test. X-ray diffraction analyses revealed the structure of a previously unreported NAS phase and indicate that monolith creation may lead to a reduction in crystallinity as compared to the primary FBSR granular product.

Magnetic Minerals in Soils and Paleosols as Recorders of Paleoclimate

NASA Astrophysics Data System (ADS)

Maxbauer, Daniel P.

It is a fundamental challenge for geologists to create quantitative estimates of rainfall and temperature in past climates. Yet, records of past climates are integral for understanding the complexities of earth system dynamics. The research presented in this dissertation begins to establish a framework for reconstructing paleoclimates using the magnetic properties of fossilized soils. Magnetic minerals are ubiquitous in soils, and their composition, grain size, and concentration is often directly related to the ambient climatic conditions that were present during soil formation. Using rock magnetic methods, it is possible to sensitively characterize the magnetic mineral assemblages in natural materials - including soils and paleosols. The fundamentals of rock magnetism and many of the common methods used in rock magnetic applications are presented in chapter 2 and chapter 3, respectively. Chapter 4 reviews the physical, chemical, and biological factors that affect magnetic mineral assemblages in soils, the magnetic methods we use to characterize them, and the known relationships between magnetic minerals in soils and climate. A critical component to developing replicable tools for reconstructing paleoclimate is developing analytical and statistical tools that are accessible to the greater community. Chapter 5 introduces a new model, MAX UnMix, that was developed as an open-source, online tool for rock magnetic data processing that is designed to be user-friendly and accessible. Two case studies, on both fossil (Chapter 7) and modern (Chapter 6) soils, are presented and discuss many issues related to applying magnetic paleoprecipitation proxies in deep time. Chapter 7 discusses difficulties in disentangling the effects of pedogenesis, diagenesis, and recent surficial weathering in Paleocene-Eocene ( 56-55 Ma) paleosols. Chapter 6 explores the relative influence of soil forming factors (vegetation vs. climate) on controlling the pedogenic formation of magnetic minerals in soils developing across the forest-to-prairie ecotone in NW Minnesota. The body of research presented in this dissertation provides many challenges to future workers, while at the same time highlighting that rock magnetism should be a useful tool for researchers interested in deep time paleoclimates moving forward.

An X-ray diffraction method for semiquantitative mineralogical analysis of Chilean nitrate ore

USGS Publications Warehouse

Jackson, J.C.; Ericksent, G.E.

1997-01-01

Computer analysis of X-ray diffraction (XRD) data provides a simple method for determining the semiquantitative mineralogical composition of naturally occurring mixtures of saline minerals. The method herein described was adapted from a computer program for the study of mixtures of naturally occurring clay minerals. The program evaluates the relative intensities of selected diagnostic peaks for the minerals in a given mixture, and then calculates the relative concentrations of these minerals. The method requires precise calibration of XRD data for the minerals to be studied and selection of diffraction peaks that minimize inter-compound interferences. The calculated relative abundances are sufficiently accurate for direct comparison with bulk chemical analyses of naturally occurring saline mineral assemblages.

An x-ray diffraction method for semiquantitative mineralogical analysis of chilean nitrate ore

USGS Publications Warehouse

John, C.; George, J.; Ericksen, E.

1997-01-01

Computer analysis of X-ray diffraction (XRD) data provides a simple method for determining the semiquantitative mineralogical composition of naturally occurring mixtures of saline minerals. The method herein described was adapted from a computer program for the study of mixtures of naturally occurring clay minerals. The program evaluates the relative intensities of selected diagnostic peaks for the minerals in a given mixture, and then calculates the relative concentrations of these minerals. The method requires precise calibration of XRD data for the minerals to be studied and selection of diffraction peaks that minimize inter-compound interferences. The calculated relative abundances are sufficiently accurate for direct comparison with bulk chemical analyses of naturally occurring saline mineral assemblages.

Using Vanadium in Spinel as a Sensor of Oxygen Fugacity in Meteorites: Applications to Mars, Vesta, and Other Asteroids

NASA Technical Reports Server (NTRS)

Righter, K.; Sutton, S.; Danielson, L.; Le, L.; Newville, M.; Pando, K.

2009-01-01

Igneous and metamorphic rocks commonly contain a mineral assemblage that allows oxygen fugacity to be calculated or constrained such as FeTi oxides, olivine-opx-spinel, or some other oxybarometer [1]. Some rocks, however, contain a limited mineral assemblage and do not provide constraints on fO2 using mineral equilibria. Good examples of the latter are orthopyroxenites or dunites, such as diogenites, ALH 84001, chassignites, or brachinites. In fact it is no surprise that the fO2 of many of these samples is not well known, other than being "reduced" and below the metal saturation value. In order to bridge this gap in our understanding, we have initiated a study of V in chromites in natural meteorite samples. Because the V pre-edge peak intensity and energy in chromites varies with fO2 (Fig. 1) [2], and this has been calibrated over a large fO 2 range, we can apply this relation to rocks for which we otherwise have no fO2 constraints.

Effect of pressure on ore mineral solubilities under hydrothermal conditions.

USGS Publications Warehouse

Hemley, J.J.; Cygan, G.L.; d'Angelo, W. M.

1986-01-01

The combined solubilities of Fe, Zn and Pb sulphides were determined at elevated P and T in chloride solutions buffered in pH by a silicate assemblage of quartz monzonite composition plus added muscovite, and buffered in fS2 and fO2 by the assemblage pyrite-pyrrhotite-magnetite. Higher T and higher chloride concentration favour higher metal solubilities, but the P effect is opposite. At 500oC, 0.5 kbar and 1 M total chloride, Fe, Zn, Pb solubilities were 8500, 4300 and 8700 ppm, respectively, whereas at 1 kbar they were 4200, 2400 and 2600 ppm, and at 2 kbar, 1700, 800 and 1200 ppm. The P effect is of considerable importance to problems of ore-mineral transport; the metal could be carried over long distances on a decreasing P gradient so long as the T decreases were sufficient; this condition could be approximated by a near-adiabatic transport cooling path. Such a condition is probably common for hydrothermal processes involving fairly deep-seated sources of heat and mineral components.-L.C.H.

Plumbing the depths of batholiths

USGS Publications Warehouse

Zen, E.-A.

1989-01-01

Knowledge of the pressure of consolidation of a pluton and the pressure-time history of magmatic evolution should allow better understanding of the tectonic and thermal history of the crust. Available methods to estimate pressures of plutons are mainly for those of consolidation. These are either extrinsic, based on geological context, or intrinsic, based on mineral texture, mineral assemblage, fluid inclusions, mineral inclusions, apparent cooling rates, and mineral chemistry. The methods of lattice-dimension matching of mineral inclusions and of detailed chemistry for zoned minerals could lead to pressure-time reconstructions. Future barometers based on mineral chemistry should use atomic species that have low diffusion coefficients and whose values are not sensitive to computational schemes and cumulative analytical errors. Aluminum and silicon in coexisting hornblende, biotite, pyroxene, plagioclase, or garnet are reasonable candidate phases for barometry. -from Author

Contrasting fluids and reservoirs in the contiguous Marcona and Mina Justa iron oxide-Cu (-Ag-Au) deposits, south-central Perú

NASA Astrophysics Data System (ADS)

Chen, Huayong; Kyser, T. Kurtis; Clark, Alan H.

2011-10-01

The Marcona-Mina Justa deposit cluster, hosted by Lower Paleozoic metaclastic rocks and Middle Jurassic shallow marine andesites, incorporates the most important known magnetite mineralization in the Andes at Marcona (1.9 Gt at 55.4% Fe and 0.12% Cu) and one of the few major iron oxide-copper-gold (IOCG) deposits with economic Cu grades (346.6 Mt at 0.71% Cu, 3.8 g/t Ag and 0.03 g/t Au) at Mina Justa. The Middle Jurassic Marcona deposit is centred in Ica Department, Perú, and the Lower Cretaceous Mina Justa Cu (Ag, Au) prospect is located 3-4 km to the northeast. New fluid inclusion studies, including laser ablation time-of-flight inductively coupled plasma mass spectrometry (LA-TOF-ICPMS) analysis, integrated with sulphur, oxygen, hydrogen and carbon isotope analyses of minerals with well-defined paragenetic relationships, clarify the nature and origin of the hydrothermal fluid responsible for these contiguous but genetically contrasted deposits. At Marcona, early, sulphide-free stage M-III magnetite-biotite-calcic amphibole assemblages are inferred to have crystallized from a 700-800°C Fe oxide melt with a δ18O value from +5.2‰ to +7.7‰. Stage M-IV magnetite-phlogopite-calcic amphibole-sulphide assemblages were subsequently precipitated from 430-600°C aqueous fluids with dominantly magmatic isotopic compositions (δ34S = +0.8‰ to +5.9‰; δ18O = +9.6‰ to +12.2‰; δD = -73‰ to -43‰; and δ13C = -3.3‰). Stages M-III and M-IV account for over 95% of the magnetite mineralization at Marcona. Subsequent non-economic, lower temperature sulphide-calcite-amphibole assemblages (stage M-V) were deposited from fluids with similar δ34S (+1.8‰ to +5.0‰), δ18O (+10.1‰ to +12.5‰) and δ13C (-3.4‰), but higher δD values (average -8‰). Several groups of lower (<200°C, with a mode at 120°C) and higher temperature (>200°C) fluids can be recognized in the main polymetallic (Cu, Zn, Pb) sulphide stage M-V and may record the involvement of modified seawater. At Mina Justa, early magnetite-pyrite assemblages precipitated from a magmatic fluid (δ34S = +0.8‰ to +3.9‰; δ18O = +9.5‰ to +11.5‰) at 540-600°C, whereas ensuing chalcopyrite-bornite-digenite-chalcocite-hematite-calcite mineralization was the product of non-magmatic, probably evaporite-sourced, brines with δ34S ≥ +29‰, δ18O = 0.1‰ and δ13C = -8.3‰. Two groups of fluids were involved in the Cu mineralization stage: (1) Ca-rich, low-temperature (approx. 140°C) and high-salinity, plausibly a basinal brine and (2) Na (-K)-dominant with a low-temperature (approx. 140°C) and low-salinity probably meteoric water. LA-TOF-ICPMS analyses show that fluids at the magnetite-pyrite stage were Cu-barren, but that those associated with external fluids in later stages were enriched in Cu and Zn, suggesting such fluids could have been critical for the economic Cu mineralization in Andean IOCG deposits.

Base and precious metal occurrences along the San Andreas Fault, Point Delgada, California

USGS Publications Warehouse

McLaughlin, Robert J.; Sorg, D.H.; Ohlin, H.N.; Heropoulos, Chris

1979-01-01

Previously unrecognized veins containing lead, zinc, and copper sulfide minerals at Point Delgada, Calif., are associated with late Mesozoic(?) and Tertiary volcanic and sedimentary rocks of the Franciscan assemblage. Sulfide minerals include pyrite, sphalerite, galena, and minor chalcopyrite, and galena-rich samples contain substantial amounts of silver. These minerals occur in a quartz-carbonate gangue along northeast-trending faults and fractures that exhibit (left?) lateral and vertical slip. The sense of fault movement and the northeasterly strike are consistent with predicted conjugate fault sets of the present San Andreas fault system. The sulfide mineralization is younger than the Franciscan rocks of Point Delgada and King Range, and it may have accompanied or postdated the inception of San Andreas faulting. Mineralization largely preceded uplift, the formation of a marine terrace, and the emplacement of landslide-related debris-flow breccias that overlie the mineralized rocks and truncate the sulfide veins. These field relations indicate that the sulfide mineralization and inception of San Andreas faulting were clearly more recent than the early Miocene and that the mineralization could be younger than about 1.2 m.y. The sulfide veins at Point Delgada may be of economic significance. However, prior to any exploitation of the occurrence, economic and environmental conflicts of interest involving private land ownership, the Shelter Cove home development, and proximity of the coast must be resolved.

Remote sensing characterization of the Animas River watershed, southwestern Colorado, by AVIRIS imaging spectroscopy

USGS Publications Warehouse

Dalton, J.B.; Bove, D.J.; Mladinich, C.S.

2005-01-01

Visible-wavelength and near-infrared image cubes of the Animas River watershed in southwestern Colorado have been acquired by the Jet Propulsion Laboratory's Airborne Visible and InfraRed Imaging Spectrometer (AVIRIS) instrument and processed using the U.S. Geological Survey Tetracorder v3.6a2 implementation. The Tetracorder expert system utilizes a spectral reference library containing more than 400 laboratory and field spectra of end-member minerals, mineral mixtures, vegetation, manmade materials, atmospheric gases, and additional substances to generate maps of mineralogy, vegetation, snow, and other material distributions. Major iron-bearing, clay, mica, carbonate, sulfate, and other minerals were identified, among which are several minerals associated with acid rock drainage, including pyrite, jarosite, alunite, and goethite. Distributions of minerals such as calcite and chlorite indicate a relationship between acid-neutralizing assemblages and stream geochemistry within the watershed. Images denoting material distributions throughout the watershed have been orthorectified against digital terrain models to produce georeferenced image files suitable for inclusion in Geographic Information System databases. Results of this study are of use to land managers, stakeholders, and researchers interested in understanding a number of characteristics of the Animas River watershed.

Hydrothermal alteration mapping using ASTER data in Baogutu porphyry deposit, China

NASA Astrophysics Data System (ADS)

Li, Q.; Zhang, B.; Lu, L.; Lin, Q.

2014-03-01

Remote sensing plays an important role in mineral exploration. One of its proven applications is extracting host-rock lithology and alteration zones that are related to porphyry copper deposits. An Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) was used to map the Baogutu porphyry deposit alteration area. A circular alteration mineral zoning pattern was clearly observed in the classification result of potassic, phyllic, argillic, propylitic zones. The potassic is characterized by biotite and anhydrite with an absorption feature centered at 1.94 and 2.1um. The phyllic zone is characterized by illite and sericite that indicates an intense Al-OH absorption feature centered at 2.20um. The narrower argillic zone including kaolinite and alunite displays a secondary Al-OH absorption feature at 2.17 um. The mineral assemblages of the outer propylitic zone are epidote, chlorite and calcite that exhibit absorption features at 2.335um.The performance of Principal Component Analysis(PCA), Minimum Noise Fraction (MNF), band ratio(BR) and Constrained Energy Minimization(CEM) has been evaluated. These techniques identified new prospects of porphyry copper mineralization in the study areas. These results indicate that ASTER is a powerful tool in the initial steps of mineral exploration.

PyXRD v0.6.7: a free and open-source program to quantify disordered phyllosilicates using multi-specimen X-ray diffraction profile fitting

NASA Astrophysics Data System (ADS)

Dumon, M.; Van Ranst, E.

2016-01-01

This paper presents a free and open-source program called PyXRD (short for Python X-ray diffraction) to improve the quantification of complex, poly-phasic mixed-layer phyllosilicate assemblages. The validity of the program was checked by comparing its output with Sybilla v2.2.2, which shares the same mathematical formalism. The novelty of this program is the ab initio incorporation of the multi-specimen method, making it possible to share phases and (a selection of) their parameters across multiple specimens. PyXRD thus allows for modelling multiple specimens side by side, and this approach speeds up the manual refinement process significantly. To check the hypothesis that this multi-specimen set-up - as it effectively reduces the number of parameters and increases the number of observations - can also improve automatic parameter refinements, we calculated X-ray diffraction patterns for four theoretical mineral assemblages. These patterns were then used as input for one refinement employing the multi-specimen set-up and one employing the single-pattern set-ups. For all of the assemblages, PyXRD was able to reproduce or approximate the input parameters with the multi-specimen approach. Diverging solutions only occurred in single-pattern set-ups, which do not contain enough information to discern all minerals present (e.g. patterns of heated samples). Assuming a correct qualitative interpretation was made and a single pattern exists in which all phases are sufficiently discernible, the obtained results indicate a good quantification can often be obtained with just that pattern. However, these results from theoretical experiments cannot automatically be extrapolated to all real-life experiments. In any case, PyXRD has proven to be useful when X-ray diffraction patterns are modelled for complex mineral assemblages containing mixed-layer phyllosilicates with a multi-specimen approach.

Metasomatic Evolution in Tectonically Mixed Zones (Mélange) and Significance for Geochemical Evolution of the Slab-Mantle Interface

NASA Astrophysics Data System (ADS)

Bebout, G. E.; King, R. L.

2012-12-01

Fluid flow focused in highly deformed zones (shear zones), and the physical juxtaposition of chemically disparate rocks (via mechanical mixing) in such zones, can lead to extensive metasomatism, including volume strain, and result in rocks with hybridized compositions little resembling the compositions of the incorporated rock types [1-5]. In the Catalina Schist (California), lawsonite-albite, lawsonite-blueschist, and amphibolite-facies units contain shear zones at scales of meters to kilometers, each containing "blocks" (with more spherical or more tabular dimensions) co-facial in grade with the "matrix" surrounding these blocks [1-3]. Oxygen isotope data for these "mélange" units, and adjacent more "coherent" expanses, indicate enhanced fluid flow in the more strongly deforming mélange zones while fluid flow in coherent domains was dominantly fracture-controlled and episodic. The amphibolite-facies mélange unit shows evidence for km-scale equilibration of varying mineral assemblages with H2O-rich fluids with uniform O and H isotope compositions consistent with a lower-grade metasedimentary source. This unit is believed to have formed largely by mechanical mixing of mafic and ultramafic compositions, partly because of the scarcity of sedimentary blocks. However, the mélange matrix in this unit preserves a number of sedimentary chemical/isotopic characteristics (e.g., Pb isotope compositions [3]) that could reflect the incorporation of sedimentary rocks, with or without fluid-related fractionation, and possibly fluid-mediated additions. Tectonically mixed zones such as these, if volumetrically significant at the slab-mantle interface, could exert disproportionate control on the compositions of hydrous fluids or silicate melts emanating from subducting slabs and entering the forearc to backarc mantle wedge, including those contributing to arc magmatism [1-5]. Geochemical studies of arc lavas should consider the possibility that the "fluids" contributed from slabs to arc source regions bear chemical/isotopic signatures reflecting their interaction with these hybridized zones produced by mixing of varying proportions of sedimentary, mafic, and ultramafic compositions. Also, the high-variance hydrous mineral assemblages created by these coeval mechanical and metasomatic processes (e.g., nearly monomineralic chlorite, talc, and amphibole schists) could play an important role in the volatiles budgets at subduction zones (i.e., having stabilities to P and T significantly higher than those for mineral assemblages in metabasaltic and metasedimentary rocks containing the same mineral phases [1,4]). Field, petrologic/geochemical, theoretical, and geophysical studies should work toward assessment of the volumetric significance, physical properties, and devolatilization histories of these hybridized compositions. [1] Bebout and Barton (2002) Chem. Geol. 187:79-106 [2] King et al. (2006) Ear. Planet. Sci. Lett. 246:288-304 [3] King et al. (2007) Chem. Geol. 239:305-322 [4] Spandler et al. (2008) Contrib. Mineral. Petrol. 155:181-198 [5] Miller et al. (2009) Lithos 107:53-67

Clay mineral distribution and provenance in the Heuksan mud belt, Yellow Sea

NASA Astrophysics Data System (ADS)

Cho, Hyen Goo; Kim, Soon-Oh; Kwak, Kyeong Yoon; Choi, Hunsoo; Khim, Boo-Keun

2015-12-01

The Heuksan mud belt (HMB), located in the southeastern Yellow Sea, runs parallel to the southwest coast of Korea. In this study, the distribution and relative contribution of four major clay minerals are investigated using 101 surface sediment samples collected in the course of KIOST (2001, 2010, 2011) and KIGAM (2012) cruises, as well as 33 river sediment samples (four from the Huanghe River, three from the Changjiang River, and 26 from Korean rivers) in order to clarify the provenance of fine-grained sediments in the HMB. Based on this currently largest and most robust dataset available for interpretation, the clay mineral assemblages of the fine-grained sediments in the HMB are found to be on average composed of 64.7% illite, 17.9% chlorite, 11.4% kaolinite, and 5.9% smectite. Overall, the clay mineral assemblages are similar in both the northern and the southern parts of the HMB, although smectite seems to be relatively enriched in the southern part, whereas kaolinite is slightly more dominant in the northern part. This clearly indicates that the clays are mostly derived from Korean rivers and, in the southern part of the HMB, partly also from the Huanghe River in China. The new data thus confirm and strengthen the tentative interpretation of some earlier work based on a more limited dataset.

Thermochemical Constraints For the Formation Conditions of the Hydrothermal Alteration Mineralogy of Home Plate and Columbia Hills

NASA Astrophysics Data System (ADS)

Filiberto, J.; Schwenzer, S. P.

2012-12-01

Home Plate is a plateau in the Columbia Hills of Gusev Crater. It is dominated by igneous minerals (olivine, pyroxene, and magnetite) with small amounts of alteration minerals (hematite and nanophase oxides). Surrounding Home Plate are deposits containing diverse secondary mineral assemblages: Fe3+-sulfates deposits at Paso Robles, Dead Sea, Shredded, Arad, Tyrone, and Troy; Hematite-rich outcrops between Home Plate and Tyrone; SiO2-rich deposits possibly containing pyrite and/or marcasite at Fuzzy Smith; SiO2-rich, possibly opaline silica, deposits at Northern Valley, Eastern Valley, and Tyrone; and Mg-Fe-carbonate outcrops at Comanche in the Columbia Hills [1-4]. Here, we focus on using thermochemical modeling to understand the secondary alteration mineralogy at the Home Plate outcrop and surrounding Columbia Hills region in Gusev Crater. We use CHILLER [5] to evaluate mineral assemblages that are likely to form from the Martian Home Plate, Barn-Hill class rock Fastball in contact with a dilute fluid at various pressures, temperatures, and water-rock ratios. For details see [6]. In our models, hematite dominates the alteration assemblage at high W/R at 150°C, but is generally produced at W/R above 10. Goethite only forms at low temperature and W/R above 40 with a maximum around 100 and again around 100,000. Pyrite is produced at all temperatures but only at relatively high W/R. These results imply intermediate to high W/R and low to intermediate temperatures during alteration of the Home Plate region. Additional acidic brine, while not strictly excluded, is not required to form many of the observed phases. In contrast, the phyllosilicates recently invoked from orbital observations [4] indicate neutral to alkaline conditions - either accompanying the silica precipitation or as a separate event. For future exploration, our results emphasize that the observation of assemblages is critically important to understand mineral formation conditions and that minor phases such as fluorite can give valuable insights into host rock chemistry and alteration conditions. REFS: [1] Ruff S.W. et al. (2011) JGR 116, doi.10.1029/2010je003767. [2] Morris R.V. et al. (2008) JGR 113, doi.10.1029/2008je003201. [3] Morris R.V. et al. (2010) Science 329, 421-424. [4] Carter J. and Poulet F. (2012) Icarus 219, 250-253. [5] Reed M.H. and Spycher N.F. (2006) User Guide for CHILLER: A Program for Computing Water-Rock Reactions, Boiling, Mixing, and Other Reaction Processes in Squeous-Mineral-Gas Systems and Minplot Guide (3rd ed.), Eugene, Oregon: University of Oregon. [6] Schwenzer S.P. and Kring D.A. (2009) Geology 37, 1091-1094.

Reconstruction of Ancestral Hydrothermal Systems on Mount Rainier Using Hydrothermally Altered Rocks in Holocene Debris Flows and Tephras

NASA Astrophysics Data System (ADS)

John, D. A.; Breit, G. N.; Sisson, T. W.; Vallance, J. W.; Rye, R. O.

2005-12-01

Mount Rainier is the result of episodic stages of edifice growth during periods of high eruptive activity and edifice destruction during periods of relative magmatic quiescence over the past 500 kyr. Edifice destruction occurred both by slow erosion and by catastrophic collapses, some of which were strongly influenced by hydrothermal alteration. Several large-volume Holocene debris-flow deposits contain abundant clasts of hydrothermally altered rocks, most notably the 4-km3 clay-rich Osceola Mudflow which formed by collapse of the northeast side and upper 1000+ m of the edifice about 5600 ya and flowed >120 km downstream into Puget Sound. Mineral assemblages and stable isotope data of hydrothermal alteration products in Holocene debris-flow deposits indicate formation in distinct hydrothermal environments, including magmatic-hydrothermal, steam-heated (including a large fumarolic component), magmatic steam (including a possible fumarolic component), and supergene. The Osceola Mudflow and phreatic components of coeval tephras contain the highest-temperature and inferred most deeply formed alteration minerals; assemblages include magmatic-hydrothermal quartz-alunite, quartz-topaz, quartz-pyrophyllite and quartz-illite (all +pyrite), in addition to steam-heated opal-alunite-kaolinite and abundant smectite-pyrite. In contrast, the Paradise lahar, which formed by a collapse of the surficial upper south side of the edifice, contains only steam-heated assemblages including those formed largely above the water table from condensation of fumarolic vapor (opal-alunite-jarosite). Younger debris-flow deposits on the west side of the volcano (Round Pass lahar and Electron Mudflow) contain only smectite-pyrite alteration, whereas an early 20th century rock avalanche on Tahoma Glacier also contains magmatic-hydrothermal alteration that is exposed in the avalanche headwall of Sunset Amphitheater. Mineralogy and isotopic composition of the alteration phases, geologic and geophysical data, as well as analog fossil hydrothermal systems in volcanoes elsewhere, constrain hydrothermal alteration geometry on the pre-Osceola-collapse edifice of Mount Rainier. Relatively narrow zones of acid magmatic-hydrothermal alteration in the central core of the volcano grade to more widely distributed smectite-pyrite alteration farther out on the upper flanks, capped by steam-heated alteration with a large component of alteration resulting from condensation of fumarolic vapor above the water table. Alteration was polygenetic in zones formed episodically, and was strongly controlled by fluxes of heat and magmatic fluid and by local permeability.

Mars weathering analogs - Secondary mineralization in Antarctic basalts

NASA Technical Reports Server (NTRS)

Berkley, J. L.

1982-01-01

Alkalic basalt samples from Ross Island, Antarctica, are evaluated as terrestrial analogs to weathered surface materials on Mars. Secondary alteration in the rocks is limited to pneumatolytic oxidation of igneous minerals and glass, rare groundmass clay and zeolite mineralization, and hydrothermal minerals coating fractures and vesicle surfaces. Hydrothermal mineral assemblages consist mainly of K-feldspar, zeolites (phillipsite and chabazite), calcite, and anhydrite. Low alteration rates are attributed to cold and dry environmental factors common to both Antarctica and Mars. It is noted that mechanical weathering (aeolian abrasion) of Martian equivalents to present Antarctic basalts would yield minor hydrothermal minerals and local surface fines composed of primary igneous minerals and glass but would produce few hydrous products, such as palagonite, clay or micas. It is thought that leaching of hydrothermal vein minerals by migrating fluids and redeposition in duricrust deposits may represent an alternate process for incorporating secondary minerals of volcanic origin into Martian surface fines.

An isotopic study of mafic microgranular enclaves in the Katsuragi adakitic tonalite, southwestern Japan.

NASA Astrophysics Data System (ADS)

Tezuka, N.; Tsuboi, M.; Asahara, Y.

2017-12-01

The Cretaceous Katsuragi tonalite in southwestern Japan has been regarded as adakite formed by the partial melting of lower crust a) b). The tonalite is 10 x 15 km in areal extent, is composed of hornblende-biotite tonalite with a mineral assemblage of plagioclase, biotite, quartz and hornblende, and contains mafic microgranular enclaves (MME). The MME has dioritic composition with a mineral assemblage of plagioclase, biotite, hornblende and quartz. The boundary between the tonalite and the MME is sharp. To reveal the relationship between the MME and adakitic feature of the host tonalite, we have focused on the chemical and Sr-Nd isotopic compositions of the MME in the Katsuragi tonalite. Three models have been proposed for the origin of MME: restite, magma-mixing, and cumulate c). In the restite model, MME is regarded as a residual material of partial melting, and therefore chemical compositions of MME and host should show a linear trend on the Harker's diagram. However, the Katsuragi tonalite and its MME do not show one linear trend. Based on mixing of two magmas, initial 87Sr/86Sr (SrI) value of MME is basically different from that of its host. However, the SrI value of the MME is 0.70725-0.70749 and is identical to the value of 0.70728 in the Katsuragi tonalite d), indicating one magma source for the MME and its host. According to the cumulate model, MME forms from cumulate piles by subsequent feeding of congenetic magma immediately after the early crystallized minerals are solidified. The concordance of the age and SrI between the Katsuragi tonalite and its MME strongly indicate the cumulate origin c). Furthermore, the mineral assemblage of the MME resembles with the common mineral assemblage of andesitic cumulate such as plagioclase, hornblende and quartz c), and this is consistent with the cumulate model. Based on the cumulate origin of the MME, the adakitic feature of chemical composition in the host rock is potentially formed by the separation of cumulate. In the presentation, we evaluate the adakitic, chemical composition of the Katsuragi tonalite by calculation of MME separation from parental magma. a) K. Takemura, M. Tsuboi, 2014, MAGMA, 96, 31, 44. b) Y. Nishioka, 2008, 115th Ann. Meet. Geol. Soc. Japan, Abstr., 131.c) S. Chen et al., 2016, Lithos, 248, 251, 455, 468. d) K. Morioka et al., 2000, Island Arc, 9, 46, 54.

Postmagmatic magnetite-apatite assemblage in mafic intrusions: a case study of dolerite at Olympic Dam, South Australia

NASA Astrophysics Data System (ADS)

Apukhtina, Olga B.; Kamenetsky, Vadim S.; Ehrig, Kathy; Kamenetsky, Maya B.; McPhie, Jocelyn; Maas, Roland; Meffre, Sebastien; Goemann, Karsten; Rodemann, Thomas; Cook, Nigel J.; Ciobanu, Cristiana L.

2016-01-01

An assemblage of magnetite and apatite is common worldwide in different ore deposit types, including disparate members of the iron-oxide copper-gold (IOCG) clan. The Kiruna-type iron oxide-apatite deposits, a subtype of the IOCG family, are recognized as economic targets as well. A wide range of competing genetic models exists for magnetite-apatite deposits, including magmatic, magmatic-hydrothermal, hydrothermal(-metasomatic), and sedimentary(-exhalative). The sources and mechanisms of transport and deposition of Fe and P remain highly debatable. This study reports petrographic and geochemical features of the magnetite-apatite-rich vein assemblages in the dolerite dykes of the Gairdner Dyke Swarm (~0.82 Ga) that intruded the Roxby Downs Granite (~0.59 Ga), the host of the supergiant Olympic Dam IOCG deposit. These symmetrical, only few mm narrow veins are prevalent in such dykes and comprise besides usually colloform magnetite and prismatic apatite also further minerals (e.g., calcite, quartz). The genetic relationships between the veins and host dolerite are implied based on alteration in the immediate vicinity (~4 mm) of the veins. In particular, Ti-magnetite-ilmenite is partially to completely transformed to titanite and magmatic apatite disappears. We conclude that the mafic dykes were a local source of Fe and P re-concentrated in the magnetite-apatite veins. Uranium-Pb ages for vein apatite and titanite associated with the vein in this case study suggest that alteration of the dolerite and healing of the fractures occurred shortly after dyke emplacement. We propose that in this particular case the origin of the magnetite-apatite assemblage is clearly related to hydrothermal alteration of the host mafic magmatic rocks.

Approaches to modelling uranium (VI) adsorption on natural mineral assemblages

USGS Publications Warehouse

Waite, T.D.; Davis, J.A.; Fenton, B.R.; Payne, T.E.

2000-01-01

Component additivity (CA) and generalised composite (GC) approaches to deriving a suitable surface complexation model for description of U(VI) adsorption to natural mineral assemblages are pursued in this paper with good success. A single, ferrihydrite-like component is found to reasonably describe uranyl uptake to a number of kaolinitic iron-rich natural substrates at pH > 4 in the CA approach with previously published information on nature of surface complexes, acid-base properties of surface sites and electrostatic effects used in the model. The GC approach, in which little pre-knowledge about generic surface sites is assumed, gives even better fits and would appear to be a method of particular strength for application in areas such as performance assessment provided the model is developed in a careful, stepwise manner with simplicity and goodness of fit as the major criteria for acceptance.

57Fe Mössbauer spectroscopy of mineral assemblages in mantle spinel lherzolites from Cenozoic alkali basalt, eastern China: Petrological applications

NASA Astrophysics Data System (ADS)

Hao, Xi-Luo; Li, Yi-Liang

2013-01-01

Mineral assemblages in spinel lherzolite xenoliths from the Cenozoic alkali basalt of eastern China were analyzed by 57Fe Mössbauer spectroscopy for Fe3+/ΣFe and distribution of Fe2+/Fe3+ in non-equivalent crystal cites. Orthopyroxene, clinopyroxene and spinel have 0.08-0.13, 0.19-0.31 and 0.13-0.23 Fe3+/ΣFe, respectively. The cation-exchange equilibrium temperatures, Fe3+ partition coefficient and oxygen fugacity of the upper mantle peridotites were calculated. The equilibrium temperatures are between 1103 K and 1405 K consistent with those reported elsewhere. The oxygen fugacities of spinel lherzolites calculated with olivine-orthopyroxene-spinel (ΔlogƒO2 from - 1.1 to 0) and clinopyroxene-olivine-orthopyroxene oxybarometers (ΔlogƒO2 from - 2.0 to 0.7) are consistent with previously reported upper mantle values.

Quantitative Mineralogical Analysis of Mars Analogues Using CHEMIN Data and Rietveld Refinement

NASA Technical Reports Server (NTRS)

Bish, D. L.; Sarrazin, P.; Chipera, S. J.; Vaniman, D. T.; Blake, D.

2004-01-01

Mineralogical analysis is a critical component of planetary surface exploration. Chemical data alone leave serious gaps in our understanding of the surfaces of planets where complex minerals may form in combination with H, S, and halogens. On such planets (e.g., Mars) a single chemical composition may represent a range of mineral assemblages. For example, Viking chemical analyses of excavated duricrust indicate that Mg and S are correlated and 10% MgSO4 (anhydrous weight) is a likely cementing agent. Pathfinder chemical data support a similar abundance of MgSO4 in the most altered materials. However, there are many possible Mg-sulfates with widely varying hydration states (including dehydrated and 1-, 2-, 3-, 4-, 5-, 6-, and 7-hydrates). In addition, other sulfate minerals such as gypsum (CaSO4 .2H2O) and other salts containing Cl may also exist. X-ray diffraction (XRD) has the ability to decipher mixtures of these phases that would be difficult, if not impossible to unravel using only chemical or spectral data.

A discovery of extremely-enriched boehmite from coal in the Junger Coalfield, the northeastern Ordos Basin

USGS Publications Warehouse

Dai, S.; Ren, D.; Li, S.; Chou, C.

2006-01-01

The authors found an extremely-enriched boehmite and its associated minerals for the first time in the super-thick No. 6 coal seam from the Junger Coalfield in the northeastern Ordos Basin by using technologies including the X-ray diffraction analysis (XRD), scanning electron microscope equipped with an energy dispersive X-ray spectrometer, and optical microscope. The content of boehmite is as high as 13.1%, and the associated minerals are goyazite, zircon, rutile, goethite, galena, clausthalite, and selenio-galena. The heavy minerals assemblage is similar to that in the bauxite of the Benxi Formation from North China. The high boehmite in coal is mainly from weathering crust bauxite of the Benxi Formation from the northeastern coal-accumulation basin. The gibbsite colloidstone solution was removed from bauxite to the peat mire, and boehmite was formed via compaction and dehydration of gibbsite colloidstone solution in the period of peat accumulation and early period of diagenesis.

Effects of chemical alteration on fracture mechanical properties in hydrothermal systems

NASA Astrophysics Data System (ADS)

Callahan, O. A.; Eichhubl, P.; Olson, J. E.

2015-12-01

Fault and fracture networks often control the distribution of fluids and heat in hydrothermal and epithermal systems, and in related geothermal and mineral resources. Additional chemical influences on conduit evolution are well documented, with dissolution and precipitation of mineral species potentially changing the permeability of fault-facture networks. Less well understood are the impacts of chemical alteration on the mechanical properties governing fracture growth and fracture network geometry. We use double-torsion (DT) load relaxation tests under ambient air conditions to measure the mode-I fracture toughness (KIC) and subcritical fracture growth index (SCI) of variably altered rock samples obtained from outcrop in Dixie Valley, NV. Samples from southern Dixie Valley include 1) weakly altered granite, characterized by minor sericite in plagioclase, albitization and vacuolization of feldspars, and incomplete replacement of biotite with chlorite, and 2) granite from an area of locally intense propylitic alteration with chlorite-calcite-hematite-epidote assemblages. We also evaluated samples of completely silicified gabbro obtained from the Dixie Comstock epithermal gold deposit. In the weakly altered granite KIC and SCI are 1.3 ±0.2 MPam1/2 (n=8) and 59 ±25 (n=29), respectively. In the propylitic assemblage KIC is reduced to 0.6 ±0.1 MPam1/2 (n=11), and the SCI increased to 75 ±36 (n = 33). In both cases, the altered materials have lower fracture toughness and higher SCI than is reported for common geomechanical standards such as Westerly Granite (KIC ~1.7 MPam1/2; SCI ~48). Preliminary analysis of the silicified gabbro shows a significant increase in fracture toughness, 3.6 ±0.4 MPam1/2 (n=2), and SCI, 102 ±45 (n=19), compared to published values for gabbro (2.9 MPam1/2 and SCI = 32). These results suggest that mineralogical and textural changes associated with different alteration assemblages may result in spatially variable rates of fracture initiation and growth in different parts of hydrothermal systems. Contrasting fracture mechanical properties between alteration assemblages may constitute a new mechanism of chemical-mechanical feedback that contributes to the localization of conduits in hydrothermal systems.

Cenozoic exhumation and tectonic evolution of the Qimen Tagh Range, northern Tibetan Plateau: Insights from the heavy mineral compositions, detrital zircon U-Pb ages and seismic interpretations

NASA Astrophysics Data System (ADS)

Zhu, W.; Wu, C.; Wang, J.; Zhou, T.; Zhang, C.; Li, J.

2017-12-01

The Qaidam Basin is the largest intermountain basin within the Tibetan Plateau. The Cenozoic sedimentary flling characteristics of the basin was significantly influenced by the surrounding tectonic belt, such as the Altyn Tagh Range to the north-west and Qimen Tagh Range to the south. The tectonic evolution of the Qimen Tagh Range and the structural relationship between the Qaidam Basin and Qimen Tagh Range remain controversial. To address these issues, we analyzed thousands of heavy mineral data, 720 detrital zircon ages and seismic data of the Qaidam Basin. Based on the regional geological framework and our kinematic analyses, the Cenozoic tectonic evolution of the Qimen Tagh Range can be divided into two stages. From the Early Eocene to the Middle Miocene, the Devonian (400-360 Ma) and Permian to Triassic (300-200 Ma) zircons which were sourced from the Qimen Tagh Range and the heavy mineral assemblage of zircon-leucoxene-garnet-sphene on the north flank of the Qimen Tagh Range indicated that the Qimen Tagh Range has been exhumed before the Eocene and acted as the primary provenance of the Qaidam Basin. The Kunbei fault system (i.e. the Kunbei, Arlar and Hongliuquan faults) in the southwest of the Qaidam Basin, which can be seen as a natural study window of the Qimen Tagh Range, was characterized by left-lateral strike-slip faults and weak south-dipping thrust faults based on the seismic sections. This strike-slip motion was generated by the uplift of the Tibetan Plateau caused by the onset of the Indian-Eurasian collision. Since the Middle Miocene, the primary mineral assemblages along the northern flank of the Qimen Tagh Range changed from the zircon-leucoxene-garnet-sphene assemblage to the epidote-hornblende-garnet-leucoxene assemblage. Simultaneously, the Kunbei fault system underwent intense south-dipping thrusting, and a nearly 2.2-km uplift can be observed in the hanging wall of the Arlar fault. We attributed these variations to the rapid uplift event of the Qimen Tagh Range. The intense tectonic activity is the far-feld effect of the full collision that occurred between the Indian-Eurasian plates.This work was financially supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China (2017ZX05008-001).

Magmatic anhydrite and calcite in the ore-forming quartz-monzodiorite magma at Santa Rita, New Mexico (USA): genetic constraints on porphyry-Cu mineralization

NASA Astrophysics Data System (ADS)

Audétat, A.; Pettke, T.; Dolejš, D.

2004-02-01

A quartz-monzodioritic dike associated with the porphyry-Cu mineralized stock at Santa Rita, NM, has been studied to constrain physico-chemical factors ( P, T, fO 2, and volatile content) responsible for mineralization. The dike contains a low-variance mineral assemblage of amphibole, plagioclase (An 30-50), quartz, biotite, sphene, magnetite, and apatite, plus anhydrite and calcite preserved as primary inclusions within the major phenocryst phases. Petrographic relationships demonstrate that anhydrite originally was abundant in the form of phenocrysts (1-2 vol.%), but later was replaced by either quartz or calcite. Hornblende-plagioclase thermobarometry suggests that several magmas were involved in the formation of the quartz-monzodiorite, with one magma having ascended directly from ≥14 km depth. Rapid magma ascent is supported by the presence of intact calcite inclusions within quartz phenocrysts. The assemblage quartz+sphene+magnetite+Mg-rich amphibole in the quartz-monzodiorite constrains magmatic oxygen fugacity at log fO 2>NNO+1, in agreement with the presence of magmatic anhydrite and a lack of magmatic sulfides. The same reasoning generally applies for rocks hosting porphyry-Cu deposits, seemingly speaking against a major role of magmatic sulfides in the formation of such mineralizations. There is increasing evidence, however, that magmatic sulfides play an important role in earlier stages of porphyry-Cu evolution, the record of which is often obliterated by later processes.

Mineralogical compositions of fault rocks from surface ruptures of Wenchuan earthquake and implication of mineral transformation during the seismic cycle along Yingxiu-Beichuan fault, Sichuan Province, China

NASA Astrophysics Data System (ADS)

Dang, Jiaxiang; Zhou, Yongsheng; He, Changrong; Ma, Shengli

2018-06-01

There are two co-seismic bedrock surface ruptures from the Mw 7.9 Wenchuan earthquake in the northern and central parts of the Beichuan-Yingxiu fault, Sichuan Province, southwest China. In this study, we report on the macrostructure of the fault rocks and results from X-ray powder diffraction analysis of minerals from rocks in the fault zone. The most recent fault gouge (the gouge produced by the most recent co-seismic fault movement) in all the studied outcrops is dark or grayish-black, totally unconsolidated and ultrafine-grained. Older fault gouges in the same outcrops are grayish or yellowish and weakly consolidated. X-ray powder diffraction analysis results show that mineral assemblages in both the old fault gouge and the new fault gouge are more complicated than the mineral assemblages in the bedrock as the fault gouge is rich in clay minerals. The fault gouge inherited its major rock-forming minerals from the parent rocks, but the clay minerals in the fault gouge were generated in the fault zone and are therefore authigenic and synkinematic. In profiles across the fault, clay mineral abundances increase as one traverses from the bedrock to the breccia to the old gouge and from the old gouge to the new gouge. Quartz and illite are found in all collected gouge samples. The dominant clay minerals in the new fault gouge are illite and smectite along the northern part of the surface rupture and illite/smectite mixed-layer clay in the middle part of the rupture. Illite/smectite mixed-layer clay found in the middle part of the rupture indicates that fault slip was accompanied by K-rich fluid circulation. The existence of siderite, anhydrite, and barite in the northern part of the rupture suggests that fault slip at this locality was accompanied by acidic fluids containing ions of Fe, Ca, and Ba.

Hydrothermal simulation experiments as a tool for studies of the origin of life on Earth and other terrestrial planets: a review.

PubMed

Holm, Nils G; Andersson, Eva

2005-08-01

The potential of life's origin in submarine hydrothermal systems has been evaluated by a number of investigators by conducting high temperature-high pressure experiments involving organic compounds. In the majority of these experiments little attention has been paid to the importance of constraining important parameters, such as the pH and the redox state of the system. This is particularly revealed in the apparent difficulties in interpreting experimental data from hydrothermal organic synthesis and stability studies. However, in those cases where common mineral assemblages have been used in an attempt to buffer the pH and redox conditions to geologically and geochemically realistic values, theoretical and experimental data seem to converge. The use of mineral buffer assemblages provides a convenient way by which to constrain the experimental conditions. Studies at high temperatures and pressure in the laboratory have revealed a number of reactions that proceed rapidly in hydrothermal fluids, including the Strecker synthesis of amino acids. In other cases, the verification of postulated abiotic reaction mechanisms has not been possible, at least for large molecules such as large fatty acids and hydrocarbons. This includes the Fischer-Tropsch synthesis reaction. High temperature-high pressure experimental methods have been developed and used successfully for a long time in, for example, mineral solubility studies under hydrothermal conditions. By taking advantage of this experimental experience new and, at times, unexpected directions can be taken in bioorganic geochemistry, one being, for instance, primitive two-dimensional information coding. This article critically reviews some of the organic synthesis and stability experiments that have been conducted under simulated submarine hydrothermal conditions. We also discuss some of the theoretical and practical considerations that apply to hydrothermal laboratory studies of organic molecules related to the origin of life on Earth and probably also to the other terrestrial planets.

Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: 40Ar/39Ar data from metamorphic and plutonic rocks

USGS Publications Warehouse

Dusel-Bacon, C.; Lanphere, M.A.; Sharp, W.D.; Layer, P.W.; Hansen, V.L.

2002-01-01

We present new 40Ar/39Ar ages for hornblende, muscovite, and biotite from metamorphic and plutonic rocks from the Yukon-Tanana Upland, Alaska. Integration of our data with published 40Ar/39Ar, kinematic, and metamorphic pressure (P) and temperature (T) data confirms and refines the complex interaction of metamorphism and tectonism proposed for the region. The oldest metamorphic episode(s) postdates Middle Permian magmatism and predates the intrusion of Late Triassic (215-212 Ma) granitoids into the Fortymile River assemblage (Taylor Mountain assemblage of previous papers). In the eastern Eagle quadrangle, rapid and widespread Early Jurassic cooling is indicated by ???188-186 Ma 40Ar/39Ar plateau ages for hornblende from plutons that intrude the Fortymile River assemblage, and for metamorphic minerals from the Fortymile River assemblage and the structurally underlying Nasina assemblage. We interpret these Early Jurassic ages to represent cooling resulting from northwest-directed contraction that emplaced the Fortymile River assemblage onto the Nasina assemblage to the north as well as the Lake George assemblage to the south. This cooling was the final stage of a continuum of subduction-related contraction that produced crustal thickening, intermediate- to high-P metamorphism within both the Fortymile River assemblage and the structurally underlying Lake George assemblage, and Late Triassic and Early Jurassic plutonism in the Fortymile River and Nasina assemblages. Although a few metamorphic samples from the Lake George assemblage yield Jurassic 40Ar/39Ar cooling ages, most yield Early Cretaceous 40Ar/39Ar ages: hornblende ???135-115 Ma, and muscovite and biotite ???110-108 Ma. We interpret the Early Cretaceous metamorphic cooling, in most areas, to have resulted from regional extension and exhumation of the lower plate, previously tectonically thickened during Early Jurassic and older convergence.

Occurrence and Mineralogical Characteristics of Tremolite Asbestos Occurred in Boryeong area, Chungnam, South Korea

NASA Astrophysics Data System (ADS)

Yoon, K.; Hwang, J.; Oh, J.; Lee, H.

2009-12-01

Abandoned tremolite mines, which had been exploited for several decades since 1930, are distributed in Boryeong, Chungnam. It is known that tremolite asbestos is approximately 100 times more harmful than chrysotile asbestos. Recently, it become a regional social problem because lung disease (mesothelioma and lung cancer) suspect patients are largely found among the residents of the mining area. Therefore, Korean government making every endeavor to remove asbestos risk in the area. However, there is insufficiency geological and mineralogical studies for tremolite asbestos. In the present study, the occurrence and mineralogical characteristics of tremolite asbestos were studied using polarization microscope, XRD, XRF, EPMA, SEM and TEM. Mica-schist of precambrian metasedimentary rock, which is widely distributed in the area, is the host rock of tremolite deposits. The rocks are largely disturbed by faults and folds, and shows sudden changes in strike and slope of strata. Tremolite ore bodies, which show relatively light colored, mainly occur as stratiform or veinlet and some occurs in brecciated rock fragments. Tremolite is a major asbestos mineral, and chrysotile, talc, mica, chlorite and quartz occurs as associated minerals. Considerable amount of ore containing pure tremolite is found, and ores having mineral assemblages of tremolite+talc, tremolite+quartz and chrysotile+talc also occurs. From optical microscope observations, most tremolites are asbestos from that meets to the criterion (length > 5 μm, diameter < 3 μm, aspect ratio > 3:1) defined by the international organization (WHO, ILO), but non-asbestos form tremolites are also included. Most asbestos form tremolites have the size range of 1.0-2.0 μm width and 5-10 μm length. The length can be shorten with crushing experiments, but the width remains unchanged. Non-asbestos form hardly change to asbestos form by mechanical crushing. From comprehensive studies for geological occurrence and mineral assemblage, it is considered that tremolite is formed within Mg-rich strata, which is intercalated in precambrian mica-schist, by hydrothermal alteration associated with faults movements.

Bulk rock composition and geochemistry of olivine-hosted melt inclusions in the Grey Porri Tuff and selected lavas of the Monte dei Porri volcano, Salina, Aeolian Islands, southern Italy

USGS Publications Warehouse

Doherty, Angela L.; Bodnar, Robert J.; De Vivo, Benedetto; Bohrson, Wendy A.; Belkin, Harvey E.; Messina, Antonia; Tracy, Robert J.

2012-01-01

The Aeolian Islands are an arcuate chain of submarine seamounts and volcanic islands, lying just north of Sicily in southern Italy. The second largest of the islands, Salina, exhibits a wide range of compositional variation in its erupted products, from basaltic lavas to rhyolitic pumice. The Monte dei Porri eruptions occurred between 60 ka and 30 ka, following a period of approximately 60,000 years of repose. The bulk rock composition of the Monte dei Porri products range from basaltic-andesite scoria to andesitic pumice in the Grey Porri Tuff (GPT), with the Monte dei Porri lavas having basaltic-andesite compositions. The typical mineral assemblage of the GPT is calcic plagioclase, clinopyroxene (augite), olivine (Fo72−84) and orthopyroxene (enstatite) ± amphibole and Ti-Fe oxides. The lava units show a similar mineral assemblage, but contain lower Fo olivines (Fo57−78). The lava units also contain numerous glomerocrysts, including an unusual variety that contains quartz, K-feldspar and mica. Melt inclusions (MI) are ubiquitous in all mineral phases from all units of the Monte dei Porri eruptions; however, only data from olivine-hosted MI in the GPT are reported here. Compositions of MI in the GPT are typically basaltic (average SiO2 of 49.8 wt %) in the pumices and basaltic-andesite (average SiO2 of 55.6 wt %) in the scoriae and show a bimodal distribution in most compositional discrimination plots. The compositions of most of the MI in the scoriae overlap with bulk rock compositions of the lavas. Petrological and geochemical evidence suggest that mixing of one or more magmas and/or crustal assimilation played a role in the evolution of the Monte dei Porri magmatic system, especially the GPT. Analyses of the more evolved mineral phases are required to better constrain the evolution of the magma.

Equilibrium-disequilibrium relations in the Monte Rosa Granite, Western Alps: Petrological, Rb-Sr and stable isotope data

USGS Publications Warehouse

Frey, M.; Hunziker, J.C.; O'Neil, J.R.; Schwander, H.W.

1976-01-01

Nine samples from the Monte Rosa Granite have been investigated by microscopic, X-ray, wet chemical, electron microprobe, stable isotope and Rb-Sr and K-Ar methods. Two mineral assemblages have been distinguished by optical methods and dated as Permian and mid-Tertiary by means of Rb-Sr age determinations. The Permian assemblage comprises quartz, orthoclase, oligoclase, biotite, and muscovite whereas the Alpine assemblage comprises quartz, microcline, albite+epidote or oligoclase, biotite, and phengite. Disequilibrium between the Permian and Alpine mineral assemblages is documented by the following facts: (i) Two texturally distinguishable generations of white K-mica are 2 M muscovite (Si=3.1-3.2) and 2 M or 3 T phengite (Si=3.3-3.4). Five muscovites show Permian Rb-Sr ages and oxygen isotope fractionations indicating temperatures between 520 and 560 ?? C; however, K-Ar ages are mixed or rejuvenated. Phengite always shows mid-Tertiary Rb-Sr ages, (ii) Two biotite generations can be recognized, although textural evidence is often ambiguous. Three out of four texturally old biotites show mid-Tertiary Rb-Sr cooling ages while the oxygen isotopic fractionations point to Permian, mixed or Alpine temperatures, (iii) Comparison of radiogenic and stable isotope relations indicates that the radiogenic isotopes in the interlayer positions of the micas were mobilized during Alpine time without recrystallization, that is, without breaking Al-O or Si-O bonds. High Ti contents in young muscovites and biotites also indicate that the octahedral (and tetrahedral) sites remained undisturbed during rejuvenation. (iv) 'Isotopic reversals' in the order of O18 enrichment between K-feldspar and albite exist. Arguments for equilibrium during Permian time are meagre because of Alpine overprinting effects. Texturally old muscovites show high temperatures and Permian Rb-Sr ages in concordancy with Rb-Sr whole rock ages. For the tectonically least affected samples, excellent concordance between quartz-muscovite and quartz-biotite 'Permian temperatures' implies oxygen isotope equilibrium in Permian time which was undisturbed during Alpine metamorphism. Arguments for equilibrium during the mid-Tertiary metamorphism are as follows: (i) Mid-Tertiary Rb-Sr mineral isochrons of up to six minerals exist, (ii) Oxygen isotope temperatures of coexisting Alpine phengites and biotites are concordant. The major factor for the adjustment of the Permian assemblages to Alpine conditions was the degree of Alpine tectonic overprinting rather than the maximum temperatures reached during the mid-Tertiary Alpine metamorphism. The lack of exchange with externally introduced fluid phases in the samples least affected by tectonism indicates that the Monte Rosa Granite 'stewed in its own juices'. This seems to be the major cause for the persistence of Permian ages and corresponding temperatures. ?? 1976 Springer-Verlag.

Mineral assemblage transformation of a metakaolin-based waste form after geopolymer encapsulation

DOE PAGES

Williams, Benjamin D.; Neeway, James J.; Snyder, Michelle M. V.; ...

2015-12-23

We can improve mitigation of hazardous and radioactive waste through conversion of existing waste to a more chemically stable and physically robust waste form. One option for waste conversion is the fluidized bed steam reforming (FBSR) process. The resulting FBSR granular material was encapsulated in a geopolymer matrix referred to here as Geo-7. This provides mechanical strength for ease in transport and disposal. But, it is necessary to understand the phase assemblage evolution as a result of geopolymer encapsulation. In this study, we examine the mineral assemblages formed during the synthesis of the multiphase ceramic waste form. The FBSR granularmore » samples were created from waste simulant that was chemically adjusted to resemble Hanford tank waste. Another set of samples was created using Savannah River Site Tank 50 waste simulant in order to mimic a blend of waste collected from 68 Hanford tank. Waste form performance tests were conducted using the product consistency test (PCT), the Toxicity Characteristic Leaching Procedure (TCLP), and the single-pass flow-through (SPFT) test. Finally, X-ray diffraction analyses revealed the structure of a previously unreported NAS phase and indicate that monolith creation may lead to a reduction in crystallinity as compared to the primary FBSR granular product.« less

The First Finding of Sapphirine in Granulites of the Angara-Kan Block: Evidence of Ultra-High-Temperature Metamorphism in the SW Siberian Craton

NASA Astrophysics Data System (ADS)

Sukhorukov, V. P.; Gladkochub, D. P.; Turkina, O. M.

2018-04-01

This work reports the first discovery of sapphirine-bearing mineral parageneses in granulites of the Angara-Kan block, information on the mineral assemblage of rocks, and the mineral composition. Based on mineral geothermometers utilizing alumina content in orthopyroxene, reconstruction of the composition of ternary feldspar, and the titanium content in zircon, it was revealed that the peak temperatures of metamorphism reached 1100°C, after which the rocks underwent cooling under sub-isobaric conditions. It is assumed that the pulse of ultra-high-temperature metamorphism correlates with processes of extension and intraplate magmatism during the age interval of 1.78-1.75 Ga.

Heavy-Mineral Placer Potential Map of the U.S. Continental Shelf, Western and Northern Gulf of Mexico

USGS Publications Warehouse

Shideler, Gerald L.

1988-01-01

The establishment of the Exclusive Economic Zone (EEZ) in 1983 by Presidential Proclamation opened for natural resource exploration a vast offshore frontier area contiguous to the United States and its territories. The EEZ extends from the seaward limit of state waters (3 nautical mi from shore) to 200 nautical mi offshore, and it includes the continental shelves. Within the context of the EEZ natural resource assessment effort, the purpose of this study is to delineate, on a regional basis, the potential for heavy-mineral placers on the U.S. Continental Shelf in the western and northern Gulf of Mexico from the United States-Mexico border to the Alabama-Florida state line. This map is intended to serve as a general guide for placer exploration. It shows favorable sea-floor areas for placer occurrence in water depths ranging from 0 to 100 fathoms (600 ft). The map can be used as a guide for focusing costly exploratory efforts, such as coring operations and geophysical surveys. The potential economic value of heavy-mineral placer concentrations on the U.S. Continental Shelf is a function of both geologic and economic variables. Geologic variables include the composition and concentration of the heavy-mineral assemblages and their environment of deposition. Economic variables include the current world market price of extracted metals, as well as the cost of mining, processing, and marketing the metals. These economic factors, in turn, are tempered by the nation1s socio-political climate, which determines its need for specific mineral resources at any given time.

10 CFR 960.4-2-2 - Geochemistry.

Code of Federal Regulations, 2013 CFR

2013-01-01

.... Considering the likely chemical interactions among radionuclides, the host rock, and the ground water, the... the rock matrix, or sorption of radionuclides; inhibit the formation of particulates, colloids... transport of radionuclides by particulates, colloids, or complexes. (3) Mineral assemblages that, when...

10 CFR 960.4-2-2 - Geochemistry.

Code of Federal Regulations, 2014 CFR

2014-01-01

.... Considering the likely chemical interactions among radionuclides, the host rock, and the ground water, the... the rock matrix, or sorption of radionuclides; inhibit the formation of particulates, colloids... transport of radionuclides by particulates, colloids, or complexes. (3) Mineral assemblages that, when...

APPLICATION OF THE SURFACE COMPLEXATION CONCEPT TO COMPLEX MINERAL ASSEMBLAGES

EPA Science Inventory

Two types of modeling approaches are illustrated for describing inorganic contaminant adsorption in aqueous environments: (a) the component additivity approach and (b) the generalized composite approach. Each approach is applied to simulate Zn2+ adsorption by a well-characterize...

V Xanes in Spinels as an Oxy-Barometer in Meteorites with Implications for Redox Variations in the Inner Solar System

NASA Technical Reports Server (NTRS)

Righter, K.; Sutton, S.; Danielson, L.; Pando, K.; Le, L.; Newville, M.

2015-01-01

The variation of oxygen fugacity within inner solar system materials spans a range of nearly 15 orders of magnitude. Igneous and metamorphic rocks commonly contain a mineral assemblage that allows oxygen fugacity to be calculated or con-strained such as FeTi oxides, olivine-opx-spinel, or some other oxy-barometer. Some rocks, however, contain a limited mineral assemblage and do not provide constraints on fO2 using mineral equilibria. Good examples of the latter are orthopyroxenites or dunites, such as diogenites, ALH 84001, chassignites, or brachinites. In fact it is no surprise that the fO2 of many of these achondrites is not well known, other than being "reduced" and below the metal saturation value. In order to bridge this gap in our understanding, we have initiated a study of V in chromites in achondrite. Because the V pre-edge peak intensity and energy in chromites varies with fO2, and this has been calibrated over a large fO2 range, we can apply this relation to rocks for which we otherwise have no fO2 constraints.

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.

Subsolidus cooling of mid-ocean ridge peridotites and implications for the oxygen fugacity of the oceanic upper mantle

NASA Astrophysics Data System (ADS)

Birner, S.; Davis, F. A.; Cottrell, E.; Warren, J. M.; Kelley, K. A.

2017-12-01

Peridotites dredged from mid-ocean ridges provide a window into the chemistry of Earth's upper mantle. At equilibrium, mineral assemblages within peridotite record intrinsic properties, including oxygen fugacity (fO2). During cooling below the solidus, however, reactions affect the chemical compositions and modal abundances of minerals, directly affecting the fO2 recorded by these mineral assemblages. The slow kinetics of subsolidus diffusion also prevent full re-equilibration of peridotite during cooling, and different reactions have different closure temperatures. As a result, peridotites measured at the surface record neither equilibrium nor asthenospheric conditions. In order to quantify the effect of subsolidus diffusion on fO2, we analyzed minerals from abyssal peridotites dredged from the Southwest Indian Ridge (SWIR), which we then used as a basis for modeling potential subsolidus reactions. We first examined exchange reactions where no modal changes occur. We considered both Fe-Mg exchange between olivine and spinel [1] and Al-Cr exchange between orthopyroxene and spinel [2], and combined these models with spinel oxybarometry [3] to determine the effect of these reactions on fO2. Our results indicate that as peridotites cool from 1300°C to 900°C, these exchange processes together increase recorded fO2 by 0.3 log units relative to the approach in which compositional changes are not considered. Some reactions additionally change mineral modal abundances during cooling, in particular the Tschermak exchange in orthopyroxene [2], which consumes olivine and Al-rich orthopyroxene and produces spinel and Al-poor orthopyroxene as temperature decreases. Depending on partitioning of Fe3+ between phases, this reaction may dilute the concentration of Fe3+ in spinel and decrease recorded fO2 as temperature decreases. Preliminary results suggest that the magnitude of this effect is strongly sensitive to both initial spinel mode and partitioning of Fe3+ between orthopyroxene and spinel. Finally, we compare the fO2 recorded by SWIR peridotites to the fO2 recorded by basalts, projected to source conditions. [1] Li et al., 1995; [2] Voigt and von der Handt, 2011; [3] Davis et al., 2017

Evaporation pathways and solubility of Fe-Ca-Mg-rich salts in acid sulfate waters. A model for Martian ancient surface waters

NASA Astrophysics Data System (ADS)

Sobron, P.; Sansano, A.; Sanz, A.

2011-12-01

It has been suggested that Martian iron rich sulfate and oxyhydroxide deposits were precipitated from meltwaters[1], thought to have been acidic. Alternatively, iron(III)-rich hydrated sulfates from oxidized sulfides observed in the outcrops may occur as a result of long-term reactions[4]. Recent analysis of Martian materials support that they come from hydrothermal activity[5], which is highly consistent with the observation of enriched in iron, magnesium, silicon and calcium materials[2]. Independently of the nature of the sulfate formation paths on Mars, characterizing the interaction of saline mineral assemblages and the aqueous solutions necessary for their formation is significance in assessing Mars' hydrological and mineralogical evolution history. In this work we have characterized a layered deposit(Fig. 1) formed from the evaporation of stream water from Rio Tinto, Spain, a relevant Mars analog site[6]. The minerals detected in-situ, confirmed later via high resolution laser Raman spectroscopy in the laboratory, are, from bottom to top: (A) mixture of goethite and probably schwermannite; (B) goethite; (C) mixture of gypsum and highly hydrated ferric sulfates; (D) hexahydrite; and (E) mixture of hexahydrite and epsomite. What we observed in this deposit is the precipitation of relatively insoluble hydroxysulfates (schwermannite admixed with goethite), followed by the precipitation of other relatively insoluble ferric and gypsum, and finally the occurrence of the very soluble Mg-sulfates. We are currently investigating the correlation of this evaporite deposit with the hydrochemistry of the stream water from which it evaporated through dedicated laboratory analysis of natural mineral and aqueous samples. A solubility model including the minerals identified in this work will be reported at the conference. The study of this particular acid sulfate system (with analog mineralogy to that observed in Meridiani[3]) provides constraints on the evaporation pathways that may lead to a better understanding of the composition of ancient surface waters on Mars from which certain complex mineral assemblages are thought to have been formed.

Sulfide-associated mineral assemblages in the Bushveld Complex, South Africa: platinum-group element enrichment by vapor refining by chloride-carbonate fluids

NASA Astrophysics Data System (ADS)

Kanitpanyacharoen, W.; Boudreau, A. E.

2013-02-01

The petrology of base metal sulfides and associated accessory minerals in rocks away from economically significant ore zones such as the Merensky Reef of the Bushveld Complex has previously received only scant attention, yet this information is critical in the evaluation of models for the formation of Bushveld-type platinum-group element (PGE) deposits. Trace sulfide minerals, primarily pyrite, pyrrhotite, pentlandite, and chalcopyrite are generally less than 100 microns in size, and occur as disseminated interstitial individual grains, as polyphase assemblages, and less commonly as inclusions in pyroxene, plagioclase, and olivine. Pyrite after pyrrhotite is commonly associated with low temperature greenschist alteration haloes around sulfide grains. Pyrrhotite hosted by Cr- and Ti-poor magnetite (Fe3O4) occurs in several samples from the Marginal to Lower Critical Zones below the platiniferous Merensky Reef. These grains occur with calcite that is in textural equilibrium with the igneous silicate minerals, occur with Cl-rich apatite, and are interpreted as resulting from high temperature sulfur loss during degassing of interstitial liquid. A quantitative model demonstrates how many of the first-order features of the Bushveld ore metal distribution could have developed by vapor refining of the crystal pile by chloride-carbonate-rich fluids during which sulfur and sulfide are continuously recycled, with sulfur moving from the interior of the crystal pile to the top during vapor degassing.

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.

Soil ecosystem function under native and exotic plant assemblages as alternative states of successional grasslands

NASA Astrophysics Data System (ADS)

Spirito, Florencia; Yahdjian, Laura; Tognetti, Pedro M.; Chaneton, Enrique J.

2014-01-01

Old fields often become dominated by exotic plants establishing persistent community states. Ecosystem functioning may differ widely between such novel communities and the native-dominated counterparts. We evaluated soil ecosystem attributes in native and exotic (synthetic) grass assemblages established on a newly abandoned field, and in remnants of native grassland in the Inland Pampa, Argentina. We asked whether exotic species alter soil functioning through the quality of the litter they shed or by changing the decomposition environment. Litter decomposition of the exotic dominant Festuca arundinacea in exotic assemblages was faster than that of the native dominant Paspalum quadrifarium in native assemblages and remnant grasslands. Decomposition of a standard litter (Triticum aestivum) was also faster in exotic assemblages than in native assemblages and remnant grasslands. In a common garden, F. arundinacea showed higher decay rates than P. quadrifarium, which reflected the higher N content and lower C:N of the exotic grass litter. Soil respiration rates were higher in the exotic than in the native assemblages and remnant grasslands. Yet there were no significant differences in soil N availability or net N mineralization between exotic and native assemblages. Our results suggest that exotic grass dominance affected ecosystem function by producing a more decomposable leaf litter and by increasing soil decomposer activity. These changes might contribute to the extended dominance of fast-growing exotic grasses during old-field succession. Further, increased organic matter turnover under novel, exotic communities could reduce the carbon storage capacity of the system in the long term.

Mapping playa evaporite minerals with AVIRIS data: A first report from death valley, California

USGS Publications Warehouse

Crowley, J.K.

1993-01-01

Efflorescent salt crusts in Death Valley, California, were mapped by using Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data and a recently developed least-squares spectral band-fitting algorithm. Eight different saline minerals were remotely identified, including three borates, hydroboracite, pinnoite, and rivadavite, that have not been previously reported from the Death Valley efflorescent crusts. The three borates are locally important phases in the crusts, and at least one of the minerals, rivadavite, appears to be forming directly from brine. Borates and other evaporite minerals provide a basis for making remote chemical measurements of desert hydrologic systems. For example, in the Eagle Borax Spring area, the AVIRIS mineral maps pointed to elevated magnesium and boron levels in the ground waters, and to the action of chemical divides causing subsurface fractionation of calcium. Many other chemical aspects of playa brines should have an expression in the associated evaporite assemblages. Certain anhydrous evaporites, including anhydrite, glauberite, and thenardite, lack absorption bands in the visible and near-infrared wavelength range, and crusts composed of these minerals could not be characterized by using AVIRIS. In these situations, thermal-infrared remote sensing data may complement visible and near-infrared data for mapping evaporites. Another problem occurred in wet areas of Death Valley, where water absorption caused low signal levels in the 2.0-2.5 ??m wavelength region that obscured any spectral features of evaporite minerals. Despite these difficulties, the results of this study demonstrate the potential for using AVIRIS and other imaging spectrometer data to study playa chemistry. Such data can be useful for understanding chemical linkages between evaporites and ground waters, and will facilitate studies of how desert ground-water regimes change through time in response to climatic and other variables. ?? 1993.

Microtectonic-assisted P-T determination on low-grade Alpine metamorphic rocks from the "Tisia Mega-Unit" of the Slavonian Mountains in Croatia

NASA Astrophysics Data System (ADS)

Balen, Dražen; Lihter, Iva; Massonne, Hans-Joachim

2016-04-01

The internal structure of the Tisia (Tisza) Mega-Unit in the Alpine-Carpathian-Dinaridic orogenic system encompasses large Alpine nappe systems brought to its present-day position by complex regional-scale movements. The Slavonian Mountains are part of the Bihor nappe system which is below the Codru and above the Mecsek nappe systems. The low-grade metamorphic schist unit of the Slavonian Mountains includes numerous rocks which were previously related to Precambrian and/or Lower Paleozoic orogeneses. However, recent studies (e.g. Balen, 2014, European Geosciences Union General Assembly, EGU 2014-6122) show that the metapelites of this unit should be attributed to the Alpine orogeny and the poorly known P-T conditions, which they experienced, should be refined. Although metapelites can be sensitive to changes of metamorphic conditions and, therefore, be suitable for the P-T estimation of metamorphic event(s), the extraction of mineral assemblages, being in equilibrium, and associated microtectonic data for particular low-grade metamorphic rocks is not straightforward. On the contrary, due to lack of suitable minerals and complex mictotectonic features, one can be faced with a severe problem concerning (dis)equilibrium. To avoid this, the observation scale in the research was set to the sub-mm level taking into account microtectonic positions of minerals. The investigated samples from the Slavonian Mountains are fine-grained schists consisting of chlorite (15-30 vol. %), white mica (15-25 vol. %), quartz (10-25 vol. %), feldspars (albite 10-15 vol. %; some K-feldspar), biotite (<5 vol. %), opaques (<5 vol. %), and accessory minerals (zircon, monazite, xenotime, apatite, chalcopyrite, pyrite, barite, parisite-(Ce), rutile). The schists show complex microtectonic fabric including well-developed foliations, pervasive folding, crenulation and cleavage. Foliations are defined by the preferred orientation of phyllosilicates and thin quartz and feldspar ribbons. Chlorite and white mica oriented along the S1 foliation are up to 50 μm long grains whereas those oriented along the S2 foliation are as large as 500 μm. Chlorite is ripidolite; potassic white mica is muscovite to phengite. Both minerals show a systematic variation in chemical composition such as higher Si contents in white mica and lower XFe in chlorite of the S1 assemblage compared to the S2 assemblage. The application of classical chlorite thermometers, based on Si, Al, Fe, and Mg contents of chlorite, and phengite gave P-T conditions of 325-350 °C around 4.6 kbar and 315-330 °C around 3.8 kbar for the S1 and S2 minerals, respectively. Constructions of pseudosections in the system MnNCKFMASHTO with PERPLEX confirmed these P-T ranges yielding 3.1-4.7 kbar and 300-360 °C based on intersections of XFe (chlorite) and Si (phengite) isopleths. The P-T range is in accordance with the critical reaction chlorite + K-feldspar = biotite + K-white mica in the presence of quartz and H2O. The presented refinement of the P-T data for the studied metapelites combined with two sets of known monazite ages (113±20 and 82±23 Ma; Balen, 2014) has a significance in clarifying details of the geodynamic evolution during the Alpine orogeny. Financial support by the Croatian Science Foundation (IP-2014-09-9541) and T. Theye's help during microprobe work is greatly acknowledged.

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.

The 'North American shale composite' - Its compilation, major and trace element characteristics

NASA Technical Reports Server (NTRS)

Gromet, L. P.; Dymek, R. F.; Haskin, L. A.; Korotev, R. L.

1984-01-01

North American shale composite (NASC) major element composition and compilation are presented, together with rare earth element (REE) redeterminations obtained by high precision analytical methods. The major element composition of the NASC compares closely with other average shale compositions, and significant portions of the REE and some other trace elements are contained in minor phases. The uneven REE distribution in NASC powder appears to yield the heterogeneity in analyzed aliquants. REE distributions of detrital sediments may to some extent be dependent on their minor mineral assemblages and the sedimentological factors controlling these assemblages.

Metamorphic ore remobilization in the Hällefors district, Bergslagen, Sweden: constraints from mineralogical and small-scale sulphur isotope studies

NASA Astrophysics Data System (ADS)

Wagner, Thomas; Jonsson, Erik; Boyce, Adrian J.

2005-07-01

The marble- and metavolcanic-hosted Pb Zn (Ag Sb As) deposits of the Hällefors district, located in the Palaeoproterozoic Bergslagen ore province, south central Sweden, comprise both stratabound sulphides and discordant, Ag-rich sulphide sulphosalt veins. The complex sulphide sulphosalt assemblages of the Alfrida-Jan Olof mines at Hällefors were investigated by a combination of ore microscopy, electron-microprobe analysis, and in situ laser sulphur isotope analysis. The massive ore is characterized by positive and homogeneous δ34S (+1.4‰ to +2.7‰ V-CDT), whereas vein-hosted sulphides and sulphosalts exhibit similar, but generally less positive to slightly negative δ34S (-0.6‰ to +2.0‰). Comparison of the observed ore mineral assemblages with calculated phase equilibria in the system Fe As S O H and isotopic fractionation as a function of temperature, oxygen fugacity and pH indicates that the vein-type mineralization was formed from relatively reduced and rather alkaline hydrothermal fluids. At these reduced conditions, fractionation of δ34S via changes of fO2 is insignificant, and thus the isotopic signatures of the vein minerals directly reflect the composition of the sulphur source. We therefore conclude that the vein-type ore essentially inherited the sulphur isotope signature from the pre-existing massive sulphides via metamorphic remobilization at approximately 300 400°C and 2 3 kbar. Scales of remobilization observable are on the order of about 5 mm to 30 cm. Overall, the sulphide sulphosalt assemblages from the Alfrida-Jan Olof mines exhibit δ34S values which are comparable to a majority of metasupracrustal-hosted deposits in the Bergslagen province, thereby suggesting a common origin from ca. 1.90 1.88 Ga volcanic-hydrothermal processes.

Formation of ore minerals in metamorphic rocks of the German continental deep drilling site (KTB)

NASA Astrophysics Data System (ADS)

Kontny, A.; Friedrich, G.; Behr, H. J.; de Wall, H.; Horn, E. E.; Möller, P.; Zulauf, G.

1997-08-01

The German Continental Deep Drilling Program (KTB) drilled a 9.1 km deep profile through amphibolite facies metamorphic rocks and reached in situ temperatures of 265°C. Each lithologic unit is characterized by typical ore mineral assemblages related to the regional metamorphic conditions. Paragneisses contain pyrrhotite + rutile + ilmenite ± graphite, metabasic units bear ilmenite + rutile + pyrrhotite ± pyrite, and additionally, the so-called variegated units yield pyrrhotite + titanite assemblages. In the latter unit, magnetite + ilmenite + rutile + titanite assemblages related to the lower amphibolite facies breakdown of ilmenite-hematite solid solution also occur locally. Retrograde hydrothermal mineralization which commenced during Upper Carboniferous times is characterized by the following geochemical conditions: (1) low saline Na-K-Mg-Cl fluids with sulfur and oxygen fugacities at the pyrite-pyrrhotite buffer and temperatures of 400-500°C, (2) fluids with CO2, CH4±N2, andpH, Eh, sulfur, and oxygen fugacity in the stability field of graphite + pyrite at temperatures of 280-350° and (3) moderate to high saline Ca-Na-Cl fluids with CH4+ N2; sulfur and oxygen fugacity are in the stability field of pyrrhotite at temperatures <300°C. The latter environment is confirmed by in situ conditions found at the bottom of the deep drilling. Monoclinic, ferrimagnetic pyrrhotite is the main carrier of magnetization which disappears below about 8.6 km, corresponding to in situ temperatures of about 250°C. Below this depth, hexagonal antiferromagnetic pyrrhotite with a Curie temperature of 260°C is the stable phase. Temperature-dependent transformation of pyrrhotite and the reaching of its Curie isotherm within the Earth crust are one of the striking results of the KTB deep drilling project.

Textural, mineralogical and stable isotope studies of hydrothermal alteration in the main sulfide zone of the Great Dyke, Zimbabwe and the precious metals zone of the Sonju Lake Intrusion, Minnesota, USA

USGS Publications Warehouse

Li, C.; Ripley, E.M.; Oberthur, T.; Miller, J.D.; Joslin, G.D.

2008-01-01

Stratigraphic offsets in the peak concentrations of platinum-group elements (PGE) and base-metal sulfides in the main sulfide zone of the Great Dyke and the precious metals zone of the Sonju Lake Intrusion have, in part, been attributed to the interaction between magmatic PGE-bearing base-metal sulfide assemblages and hydrothermal fluids. In this paper, we provide mineralogical and textural evidence that indicates alteration of base-metal sulfides and mobilization of metals and S during hydrothermal alteration in both mineralized intrusions. Stable isotopic data suggest that the fluids involved in the alteration were of magmatic origin in the Great Dyke but that a meteoric water component was involved in the alteration of the Sonju Lake Intrusion. The strong spatial association of platinum-group minerals, principally Pt and Pd sulfides, arsenides, and tellurides, with base-metal sulfide assemblages in the main sulfide zone of the Great Dyke is consistent with residual enrichment of Pt and Pd during hydrothermal alteration. However, such an interpretation is more tenuous for the precious metals zone of the Sonju Lake Intrusion where important Pt and Pd arsenides and antimonides occur as inclusions within individual plagioclase crystals and within alteration assemblages that are free of base-metal sulfides. Our observations suggest that Pt and Pd tellurides, antimonides, and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration. Experimental studies of magmatic crystallization and hydrothermal transport/deposition in systems involving arsenides, tellurides, antimonides, and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in controlling the distribution of PGE in mineralized layered intrusions of this type. ?? Springer-Verlag 2007.

Mineral parageneses, regional architecture, and tectonic evolution of Franciscan metagraywackes, Cape Mendocino-Garberville-Covelo 30' x 60' quadrangles, northwest California

USGS Publications Warehouse

Ernst, W.G.; McLaughlin, Robert J.

2012-01-01

The Franciscan Complex is a classic subduction-zone assemblage. In northwest California, it comprises a stack of west vergent thrust sheets: westernmost Eastern Belt outliers; Central Belt mélange; Coastal Belt Yager terrane; Coastal Belt Coastal terrane; Coastal Belt King Range/False Cape terranes. We collected samples and determined P-T conditions of recrystallization for 88 medium-fine-grained metasandstones to assess their subduction-exhumation histories and assembly of the host allochthons. Feebly recrystallized Yager, Coastal, and King Range strata retain clear detrital features. Scattered neoblastic prehnite occurs in several Coastal terrane metasandstones; traces of possible pumpellyite are present in three Yager metaclastic rocks. Pumpellyite ± lawsonite ± aragonite-bearing Central Belt metasandstones are moderately deformed and reconstituted. Intensely contorted, thoroughly recrystallized Eastern Belt affinity quartzose metagraywackes contain lawsonite + jadeitic pyroxene ± aragonite ± glaucophane. We microprobed neoblastic phases in 23 rocks, documenting mineral parageneses that constrain the tectonic accretion and metamorphic P-T evolution of these sheets. Quasi-stable mineral assemblages typify Eastern Belt metasandstones, but mm-sized domains in the Central and Coastal belt rocks failed to achieve chemical equilibrium. Eastern Belt slabs rose from subduction depths approaching 25–30 km, whereas structurally lower Central Belt mélanges returned from ∼15–18 km. Coastal Belt assemblages suggest burial depths less than 5–8 km. Eastern and Central belt allochthons sequentially decoupled from the downgoing oceanic lithosphere and ascended into the accretionary margin; K-feldspar-rich Coastal Belt rocks were stranded along the continental edge without undergoing appreciable subduction, probably during Paleogene unroofing of the older, deeply subducted units of the Franciscan Complex in east-vergent crustal wedges.

Petrogenesis of incipient charnockite in the Ikalamavony sub-domain, south-central Madagascar: New insights from phase equilibrium modeling

NASA Astrophysics Data System (ADS)

Endo, Takahiro; Tsunogae, Toshiaki; Santosh, M.; Shaji, E.; Rambeloson, Roger A.

2017-06-01

Incipient charnockites representing granulite formation on a mesoscopic scale occur in the Ambodin Ifandana area of Ikalamavony sub-domain in south-central Madagascar. Here we report new petrological data from these rocks, and discuss the process of granulite formation on the basis of petrography, mineral equilibrium modeling, and fluid inclusion studies. The incipient charnockites occur as brownish patches, lenses, and layers characterized by an assemblage of biotite + orthopyroxene + K-feldspar + plagioclase + quartz + magnetite + ilmenite within host orthopyroxene-free biotite gneiss with an assemblage of biotite + K-feldspar + plagioclase + quartz + magnetite + ilmenite. Lenses and layers of calc-silicate rock (clinopyroxene + garnet + plagioclase + quartz + titanite + calcite) are typically associated with the charnockite. Coarse-grained charnockite occurs along the contact between the layered charnockite and calc-silicate rock. The application of mineral equilibrium modeling on the mineral assemblages in charnockite and biotite gneiss employing the NCKFMASHTO system as well as fluid inclusion study on coarse-grained charnockite defines a P-T range of 8.5-10.5 kbar and 880-900 °C, which is nearly consistent with the inferred P-T condition of the Ikalamavony sub-domain (8.0-10.5 kbar and 820-880 °C). The result of T versus H2O activity (a(H2O)) modeling demonstrates that orthopyroxene-bearing assemblage in charnockite is stable under relatively low a(H2O) condition of 0.42-0.43, which is consistent with the popular models of incipient-charnockite formation related to the lowering of water activity and stabilization of orthopyroxene through dehydration of biotite. The occurrence of calc-silicate rocks adjacent to the charnockite suggests that the CO2-bearing fluid that caused dehydration and incipient-charnockite formation might have been derived through decarbonation of calc-silicate rocks during the initial stage of decompression slightly after the peak metamorphism. The calc-silicate rocks might have also behaved as a cap rock that trapped CO2 infiltrated from an external source. 'CO2-rich fluid ponds' formed beneath calc-silicate layers could have enhanced dehydration of biotite to orthopyroxene, and produced layers of coarse-grained charnockite adjacent to calc-silicate layers.

The occurrence of fluor-wagnerite in UHT granulites and its implications towards understanding fluid regimes in the evolution of deep crust: a case study from the Eastern Ghats Belt, India

NASA Astrophysics Data System (ADS)

Das, Kaushik; Tomioka, Naotaka; Bose, Sankar; Ando, Jun-ichi; Ohnishi, Ichiro

2017-06-01

We report the occurrence of a rare phosphate mineral, fluor-wagnerite (Mg1.91-1.94Fe0.06-0.07Ca<0.01) (P0.99-1.00O4)(OH0.02-0.17F0.98-0.83) from the Eastern Ghats Belt of India, an orogenic belt evolved during Meso- to Neoproterozoic time. The host rock, i.e. high- to ultrahigh temperature (UHT) granulites ( 1000 °C, 8-9 kbar) of the studied area was retrogressed after emplacement to mid-crustal level (800-850 °C, 6-6.5 kbar) as deduced from their pressure -temperature histories. Based on mineral chemical data and micro-Raman analyses, we document an unusual high Mg-F-rich chemistry of the F-wagnerite, which occur both in peak metamorphic porphyroblastic assemblages as well as in the retrograde matrix assemblage. Therefore, in absence of other common phosphates like apatite, fluor-wagnerite can act as an indicator for the presence of F-bearing fluids for rocks with high X Mg and/or fO2. The occurrence of F-rich minerals as monitors for fluid compositions has important implications for the onset of biotite dehydration melting and hence melt production in the deep crust. We propose that fluor-wagnerite can occur as an accessory mineral associated with F-rich fluids in lower-mid crustal rocks, and F in coexisting minerals should be taken into consideration when reconciling the petrogenetic grid of biotite-dehydration melting.

REE enrichment due to fenitization of Devonian granites, Rodeo de Los Molles, Central Argentina

NASA Astrophysics Data System (ADS)

Lorenz, M.; Altenberger, U.; Trumbull, R. B.; Lira, R.; Lopez De Luchi, M. G.; Viñas, N.

2017-12-01

The Rodeo de Los Molles rare earth element (REE) mineralization is characterized by an uncommon REE-bearing assemblage located within a fenitized biotite-monzogranite. The fenitization is found in a NNE-SSW trending, possibly fault related elliptical body in the northern margin of the Devonian Las Chacras-Piedras Coloradas Batholith, San Luis province, Central Argentina. The fenite was produced by the metasomatic addition of K and Na, as well as the loss of Ca and Sr, leading to the transformation of monzogranite to (quartz) alkali-feldspar syenite composition. Whole-rock geochemistry revealed a local enrichment in light rare earth elements within the fenitized zone. Drill-core samples from a mineral exploration campaign (Lira et al., 1999) and new surface samples are the basis for the present investigation, which aims to decipher the fluid evolution and REE-mineralization. REE-bearing minerals are located in irregularly patches and nodules ranging from a few millimeters to more than one meter in diameter. The REE-rich assemblage comprises an intergrowth of primary britholite (Ce,Ca)5(SiO4, PO4)3(OH,F), allanite and apatite with aegirine-augite, titanite, fluorite, bastnaesite and, quartz as well as complex thorium-rich accessory minerals. In more intensely altered areas clinochlore, spherolitic quartz, calcite, kaolinite, hematite and phlogopite also occur. Britholite is an extraordinary mineral belonging to the apatite group, usually described as an accessory mineral. Aside from being one of only three localites in the world where it occurs in ore quantities, Rodeo de Los Molles further contains atypical huge aggregates of the rare mineral. In general, britholite is thought to form by late-magmatic crystallization or alteration of primary minerals in alkali-rich granites (Uher et al., 2015). Its origin as an abundant phase in the Rodeo de Los Molles mineralization is one focus of this study. Lira, R., Barbieri, M., Ripley, E.M., Viñas, N.A. (1999) Actas II South American Symposium on Isotope Geology, p.219-222. Uher, P., Ondrejka, M., Bačík, P., Broska, I., & Konečný, P. (2015) Lithos, 236, p.212-225.

Proceedings of West Coast Regional Coastal Design Conference Held on 7-8 November 1985 at Oakland, California.

DTIC Science & Technology

1986-04-01

Lon- don, 53 2p. Yancey, T.E. and Lee, J.W. 1972. Major heavy mineral assemblages and heavy mineral provinces of the central California Coast Region...sites have been collected. A data base and a user-friendly retrieval system have been de - veloped and are presently undergoing evaluation before they are...Continental Margin The tectonic evolution of the Oregon coastline appears to be controlled at present by the underthrusting of the Juan de Fuca plate beneath

Porphyry deposits of the Canadian Cordillera

USGS Publications Warehouse

McMillan, W.J.; Thompson, J.F.H.; Hart, C.J.R.; Johnston, S.T.

1996-01-01

Porphyry deposits are intrusion-related, large tonnage low grade mineral deposits with metal assemblages that may include all or some of copper, molybdenum, gold and silver. The genesis of these deposits is related to the emplacement of intermediate to felsic, hypabyssal, generally porphyritic intrusions that are commonly formed at convergent plate margins. Porphyry deposits of the Canadian Cordillera occur in association with two distinctive intrusive suites: calc-alkalic and alkalic. In the Canadian Cordillera, these deposits formed during two separate time periods: Late Triassic to Middle Jurassic (early Mesozoic), and Late Cretaceous to Eocene (Mesozoic-Cenozoic). Deposits of the early Mesozoic period occur in at least three different arc terranes (Wrangellia, Stikinia and Quesnellia) with a single deposit occurring in the oceanic assemblage of the Cache Creek terrane. These terranes were located outboard from continental North America during formation of most of their contained early Mesozoic porphyry deposits. Some of the deposits of this early period may have been emplaced during terrane collisions. Metal assemblages in deposits of the calc-alkalic suite include Mo-Cu (Brenda), Cu-Mo (Highland Valley, Gibraltar), Cu-Mo-Au-Ag (Island Copper, Schaft Creek) and Cu-Au (Kemess, Kerr).The alkalic suite deposits are characterized by a Cu-Au assemblage (Copper Mountain, Afton-Ajax, Mt. Milligan, Mount Polley, Galore Creek). Although silver is recovered from calc-alkalic and alkalic porphyry copper mining operations, silver data are seldom included in the published reserve figures. Those available are in the range of 1-2 grams per tonne (g??t-1). Alkalic suite deposits are restricted to the early Mesozoic and display distinctive petrology, alteration and mineralization that suggest a similar tectonic setting for both Quesnellia and Stikinia in Early Jurassic time. The younger deposits, late Mesozoic to Cenozoic in age, formed in an intracontinental setting, after the outboard host arc and related terranes accreted to the western margin of North America. These deposits are interpreted to occur in continental arc settings, and individual deposits are hosted by a variety of older country rocks. These younger deposits also show a spectrum of metal associations: Cu-Mo (Huckleberry, Berg), Cu-Au (-Mo) (Bell, Granisle, Fish Lake, Casino), Mo (Endako, Boss Mountain, Kit-sault, Quartz Hill), Mo-W (Logtung), Au-W (Dublin Gulch) and Au (Ft. Knox). There may be a continuum between Mo, Mo-W, Au-Mo-W and Au deposits. The distribution and timing of these post-accretion deposits likely reflect major crustal structures and subduction geometry. Cordilleran porphyry metallic deposits show the full range of morphological and depth relationships found in porphyry deposits worldwide. In addition, the Cordillera contains numerous alkalic suite deposits, which are rare worldwide: the unusual, possibly syntectonic Gibraltar deposit; and end-member gold-rich granite-hosted deposits, such as Ft. Knox (Alaska).

10 CFR 960.4-2-2 - Geochemistry.

Code of Federal Regulations, 2010 CFR

2010-01-01

... REPOSITORY Postclosure Guidelines § 960.4-2-2 Geochemistry. (a) Qualifying condition. The present and... future, not affect or would favorably affect the ability of the geologic repository to isolate the waste... subjected to expected repository conditions, would remain unaltered or would alter to mineral assemblages...

MULTIVARIATE ANALYSIS OF MACROINVERTEBRATE ASSEMBLAGES TO DETERMINE IMPACTS ON ROCKY MOUNTAIN STREAM ECOSYSTEMS

EPA Science Inventory

Using reduncancy (RDA) and canonical correlation analysis (CCA) we assessed relationships between chemical and physical characteristics and periphyton at 105 stream sites sampled by REMAP in the mineral belt of the southern Rockies ecoregion in Colorado. We contrasted results ob...

Microphytoplankton variations during coral spawning at Los Roques, Southern Caribbean

PubMed Central

Zubillaga, Ainhoa L.; Bastidas, Carolina

2016-01-01

Phytoplankton drives primary productivity in marine pelagic systems. This is also true for the oligotrophic waters in coral reefs, where natural and anthropogenic sources of nutrients can alter pelagic trophic webs. In this study, microphytoplankton assemblages were characterized for the first time in relation to expected coral spawning dates in the Caribbean. A hierarchical experimental design was used to examine these assemblages in Los Roques archipelago, Venezuela, at various temporal and spatial scales for spawning events in both 2007 and 2008. At four reefs, superficial water samples were taken daily for 9 days after the full moon of August, including days before, during and after the expected days of coral spawning. Microphytoplankton assemblages comprised 100 microalgae taxa at up to 50 cells per mL (mean ± 8 SD) and showed temporal and spatial variations related to the coral spawning only in 2007. However, chlorophyll a concentrations increased during and after the spawning events in both years, and this was better matched with analyses of higher taxonomical groups (diatoms, cyanophytes and dinoflagellates), that also varied in relation to spawning times in 2007 and 2008, but asynchronously among reefs. Heterotrophic and mixotrophic dinoflagellates increased in abundance, correlating with a decrease of the diatom Cerataulina pelagica and an increase of the diatom Rhizosolenia imbricata. These variations occurred during and after the coral spawning event for some reefs in 2007. For the first time, a fresh-water cyanobacteria species of Anabaena was ephemerally found (only 3 days) in the archipelago, at reefs closest to human settlements. Variability among reefs in relation to spawning times indicated that reef-specific processes such as water residence time, re-mineralization rates, and benthic-pelagic coupling can be relevant to the observed patterns. These results suggest an important role of microheterotrophic grazers in re-mineralization of organic matter in coral reef waters and highlight the importance of assessing compositional changes of larger size fractions of the phytoplankton when evaluating primary productivity and nutrient fluxes. PMID:27019774

Shock-induced kelyphite formation in the core of a complex impact crater

NASA Astrophysics Data System (ADS)

Deseta, Natalie; Boonsue, Suporn; Gibson, Roger L.; Spray, John G.

2017-10-01

We present a compositional and textural analysis of shock-induced microtextures in garnet porphyroblasts in migmatitic garnet-cordierite-biotite paragneisses from the centre of the Vredefort impact structure, South Africa. Detailed imaging and major element analysis of deformation features in, and adjacent to, the garnet porphyroblasts record a complex, heterogeneous distribution of shock effects at the microscale. As the most competent silicate mineral in the assemblage, with the highest Hugoniot Elastic Limit and a wide pressure-temperature stability field, the porphyroblastic garnet preserves a more diverse shock deformation response compared to minerals such as quartz and feldspar, which underwent more comprehensive shock metamorphism and subsequent annealing. The garnet porphyroblasts display pre-impact fractures that are overprinted by later intra-granular Hertzian and distinctive planar fractures associated with the impact event. Shock-induced strain localization occurred along internal slip planes and defects, including pre-existing fractures and inclusion boundaries in the garnet. Symplectitic (kelyphitic) coronas commonly enclose the garnet porphyroblasts, and inhabit intra-granular fractures. The kelyphite assemblage in fractures with open communication beyond garnet grain boundaries is characterized by orthopyroxene—cordierite—sapphirine. Conversely, the kelyphite assemblage in closed-off intra-granular fractures is highly variable, comprising spatially restricted combinations of a secondary garnet phase with a majoritic component, Al-rich orthopyroxene, sapphirine and cordierite. The impedance contrast between garnet porphyroblasts and their inclusions further facilitated the formation of shock-induced features (Al-rich orthopyroxene coronas). Together, the textural and mineralogical data suggest that these features provide a record of oscillatory shock perturbations initiated under confining pressure beneath the transient crater floor. This occurred as the shocked rock volume underwent post-shock expansion, forming the core of the central uplift, and was followed by variable textural re-equilibration. This study thus provides a microtextural and mineralogical perspective of the shock regime within confined crust immediately prior to and during central uplift formation.

Alteration Map Showing Major Faults and Veins and Associated Water-Quality Signatures of the Animas River Watershed Headwaters Near Silverton, Southwest Colorado

USGS Publications Warehouse

Bove, Dana J.; Yager, Douglas B.; Mast, M. Alisa; Dalton, J. Brad

2007-01-01

This map was produced to provide hard-copy and digital data for alteration assemblages in the historical mining area centered on the Tertiary San Juan and Silverton calderas. The data have direct application to geoenvironmental and mineral exploration objectives. This dataset represents alteration mapping for the upper Animas River watershed near Silverton, Colorado. The map is based on detailed 1:12,000-scale field mapping, X-ray diffraction (XRD) analysis, mineral mapping by remote sensing (AVIRIS) data, and 1:24,000-scale aerial photographic interpretation. Geologic structures were compiled and generalized from multiple published and unpublished sources (Burbank and Luedke, 1964; Steven and others, 1974; Luedke and Burbank 1975a, b; Lipman, 1976; Luedke and Burbank, 1987; Luedke, 1996) (see Index Map). Unpublished mapping of the Ironton quadrangle by D.J. Bove and J.P. Kurtz in 1997-1999 was included.

Definitive Mineralogical Analysis of Mars Analog Rocks Using the CheMin XRD/XRF Instrument

NASA Technical Reports Server (NTRS)

Blake, D. F.; Sarrazin, P.; Bish, D. L.; Feldman, S.; Chipera, S. J.; Vaniman, D. T.; Collins, S.

2004-01-01

Mineral identification is a critical component of Mars Astrobiological missions. Chemical or elemental data alone are not definitive because a single elemental or chemical composition or even a single bonding type can represent a range of substances or mineral assemblages. Minerals are defined as unique structural and compositional phases that occur naturally. There are about 15,000 minerals that have been described on Earth, all uniquely identifiable via diffraction methods. There are likely many minerals yet undiscovered on Earth, and likewise on Mars. If an unknown phase is identified on Mars, it can be fully characterized by structural (X-ray Diffraction, XRD) and elemental analysis (X-ray Fluorescence, XRF) without recourse to other data because XRD relies on the principles of atomic arrangement for its determinations. XRD is the principal means of identification and characterization of minerals on Earth.

Visible and near-infrared (0.4-2.5 μm) reflectance spectra of playa evaporite minerals

USGS Publications Warehouse

Crowley, James K.

1991-01-01

Visible and near-infrared (VNIR; 0.4–2.4 μm) reflectance spectra were recorded for 35 saline minerals that represent the wide range of mineral and brine chemical compositions found in playa evaporite settings. The spectra show that many of the saline minerals exhibit diagnostic near-infrared absorption bands, chiefly attributable to vibrations of hydrogen-bonded structural water molecules. VNIR reflectance spectra can be used to detect minor hydrate phases present in mixtures dominated by anhydrous halite or thenardite, and therefore will be useful in combination with X ray diffraction data for characterizing natural saline mineral assemblages. In addition, VNIR reflectance spectra are sensitive to differences in sample hydration state and should facilitate in situ studies of minerals that occur as fragile, transitory dehydration products in natural salt crusts. The use of spectral reflectance measurements in playa studies should aid in mapping evaporite mineral distributions and may provide insight into the geochemical and hydrological controls on playa mineral and brine development.

PERMEABILITY CHANGES IN CRYSTALLINE ROCKS DUE TO TEMPERATURE: EFFECTS OF MINERAL ASSEMBLAGE.

USGS Publications Warehouse

Morrow, C.A.; Moore, Diane E.; Byerlee, J.D.; ,

1985-01-01

The change in permeability with time of granite, quartzite, anorthosite and gabbro was measured while these rocks were subjected to a temperature gradient. Permeability reductions of up to two orders of magnitude were observed, with the greatest reactions occurring in the quartzite. These changes are thought to be caused by dissolution of minerals at high temperatures, and redeposition of the dissolved material at lower temperatures. Quartz appears to be an important mineral in this self-sealing process. If very low permeability is desired around a nuclear waste repository in crystalline rocks, then a quartz-rich rock may be the most appropriate host.

P-T composition and evolution of paleofluids in the Paleoproterozoic Mag Hill IOCG system, Contact Lake belt, Northwest Territories, Canada

NASA Astrophysics Data System (ADS)

Somarin, A. Karimzadeh; Mumin, A. Hamid

2014-02-01

The Echo Bay stratovolcano complex and Contact Lake Belt of the Great Bear Magmatic Zone, Northwest Territories, host a series of coalescing Paleoproterozoic hydrothermal systems that affected an area of several hundred square kilometers. They were caused by intrusion of synvolcanic diorite-monzodioritic plutons into andesitic host rocks, producing several characteristic hydrothermal assemblages. They include early and proximal albite, magnetite-actinolite-apatite, and potassic (K-feldspar) alteration, followed by more distal hematite, phyllic (quartz-sericite-pyrite), and propylitic (chlorite-epidote-carbonate±sericite±albite±quartz) alteration, and finally by late-stage polymetallic epithermal veins. These alteration types are characteristic of iron oxide copper-gold deposits, however, with distal and lower-temperature assemblages similar to porphyry Cu systems. Magnetite-actinolite-apatite alteration formed from high temperature (up to 560 °C) fluids with average salinity of 12.8 wt% NaCl equivalent. The prograde propylitic and phyllic alteration stages are associated with fluids with temperatures varying from 80 to 430 °C and a wide salinity range (0.5-45.6 wt% NaCl equivalent). Similarly, wide fluid temperature (104-450 °C) and salinity (4.2-46.1 wt% NaCl equivalent) ranges are recorded for the phyllic alteration. This was followed by Cu-Ag-U-Zn-Co-Pb sulfarsenide mineralization in late-stage epithermal veins formed at shallow depths and temperatures from 270 °C to as low as 105 °C. The polymetallic veins precipitated from high salinity (mean 30 wt% NaCl equivalent) dense fluids (1.14 g/cm3) with a vapor pressure of 3.8 bars, typical of epithermal conditions. Fluid inclusion evidence indicates that mixed fluids with evolving physicochemical properties were responsible for the formation of the alteration assemblages and mineralization at Mag Hill. An early high temperature, moderate salinity, and magmatic fluid was subsequently modified variably by boiling, mixing with cooler low-salinity meteoric water, and simple cooling. The evidence is consistent with emplacement of the source plutons and stocks into an epithermal environment within ~1 km of surface. This generated near-surface high-temperature alteration in a dynamic hydrothermal system that collapsed (telescoped) resulting in widespread evidence of boiling and epithermal mineralization superimposed on earlier stages of alteration.

Sedimentary carbonate-hosted giant Bayan Obo REE-Fe-Nb ore deposit of Inner Mongolia, China; a cornerstone example for giant polymetallic ore deposits of hydrothermal origin

USGS Publications Warehouse

Chao, E.C.T.; Back, J.M.; Minkin, J.A.; Tatsumoto, M.; Junwen, Wang; Conrad, J.E.; McKee, E.H.; Zonglin, Hou; Qingrun, Meng; Shengguang, Huang

1997-01-01

Detailed, integrative field and laboratory studies of the textures, structures, chemical characteristics, and isotopically determined ages and signatures of mineralization of the Bayan Obo deposit provided evidence for the origin and characteristics favorable for its formation and parameters necessary for defining giant polymetallic deposits of hydrothermal origin. Bayan Obo is an epigenetic, metasomatic, hydrothermal rare earth element (REE)-Fe-Nb ore deposit that is hosted in the metasedimentary H8 dolostone marble of the Middle Proterozoic Bayan Obo Group. The metasedimentary sequence was deposited on the northern continental slope of the North China craton. The mine area is about 100 km south of the suture marking Caledonian subduction of the Mongolian oceanic plate from the north beneath the North China craton. The mineralogy of the deposit is very complex, consisting of more than 120 different minerals, some of which are epigenetic minerals introduced by hydrothermal solutions, and some of which are primary and secondary metamorphic minerals. The major REE minerals are monazite and bastnaesite, whereas magnetite and hematite are the dominant Fe-ore minerals, and columbite is the most abundant Nb mineral. Dolomite, alkali amphibole, fluorite, barite, aegirine augite, apatite, phlogopite, albite, and microcline are the most widespread gangue minerals. Three general types of ores occur at Bayan Obo: disseminated, banded, and massive ores. Broad zoning of these ore types occurs in the Main and East Orebodies. Disseminated ores are in the outermost zone, banded ores are in the intermediate zone, and massive ores are in the cores of the orebodies. On the basis of field relations, host rocks, textures, structures, and mineral assemblages, many varieties of these three types of ores have been recognized and mapped. Isotopic dating of monazite, bastnaesite, aeschynite, and metamorphic and metasomatic alkali amphiboles associated with the deposit provides constraints on the ages of mineralization and the history of the deposit. Textural relations, differences in chemical composition, and 232Th/208Pb internal isochron ages of monazite and bastnaesite samples indicate that many episodes of REE mineralization occurred at Bayan Obo, ranging from about 555 Ma to about 398 Ma. Initial 208Pb/204Pb ratios suggest different sources of REE's for different generations of REE minerals. Relative ages of Fe mineralization were deduced from textural relationships of Fe minerals with other, dated mineral phases in the deposit. Most Nb mineralization was in the area of the West Orebodies and resulted in disseminated ore. Aeschynite, an early stage of Nb mineralization (438+-25.1 Ma), occurs with huanghoite and alkali amphiboles in veins. The 40Ar/39Ar ages of amphiboles, as well as petrographic textures, were used to distinguish three periods of regional metamorphism in the Bayan Obo mine area: (1) Late Proterozoic, about 890 Ma, which recrystallized H8 carbonate to marble and crystallized lineated alkali amphiboles along foliation planes in the marble; (2) Caledonian, about 425-395 Ma, which resulted in metamorphic and metasomatic-metamorphic alkali amphiboles; and (3) Hercynian, about 300 Ma, based on biotite 40Ar/39Ar analyses from biotite schist and folded banded ores. The 40Ar/39Ar ages of metasomatic alkali amphiboles also place time constraints on the hydrothermal history of the ore deposit. Metasomatic amphiboles represent periods of intense hydrothermal activity, which began as early as 1.26 Ga; that date is based on the age of amphibole from a vein that crosscuts the H6 quartzite that underlies the H8 dolostone marble. Although much of the metasomatic amphibole formed during periods that overlapped the peak period of REE mineralization of banded ores, REE and alkali amphibole phases generally occur in different mineral assemblages or are of very different ages in the same assemblage and, therefore, may have been derived from

Cretaceous plutonic rocks in the Donner Lake-Cisco Grove area, northern Sierra Nevada, California

USGS Publications Warehouse

Kulow, Matthew J.; Hanson, Richard E.; Girty, Gary H.; Girty, Melissa S.; Harwood, David S.

1998-01-01

The northernmost occurrences of extensive, glaciated exposures of the Sierra Nevada batholith occur in the Donner Lake-Cisco Grove area of the northern Sierra Nevada. The plutonic rocks in this area, which are termed here the Castle Valley plutonic assemblage, crop out over an area of 225 km2 and for the most part are shown as a single undifferentiated mass on previously published geological maps. In the present work, the plutonic assemblage is divided into eight separate intrusive units or lithodemes, two of which each consist of two separate plutons. Compositions are dominantly granodiorite and tonalite, but diorite and granite form small plutons in places. Spectacular examples of comb layering and orbicular texture occur in the diorites. U-Pb zircon ages have been obtained for all but one of the main units and range from ~120 to 114 Ma, indicating that the entire assemblage was emplaced in a narrow time frame in the Early Cretaceous. This is consistent with abundant field evidence that many of the individual phases were intruded penecontemporaneously. The timing of emplacement correlates with onset of major Cretaceous plutonism in the main part of the Sierra Nevada batholith farther south. The emplacement ages also are similar to isotopic ages for gold-quartz mineralization in the Sierran foothills west of the study area, suggesting a direct genetic relationship between the voluminous Early Cretaceous plutonism and hydrothermal gold mineralization.

Geologic and mineralogic controls on acid and metal-rich rock drainage in an alpine watershed, Handcart Gulch, Colorado

USGS Publications Warehouse

Bove, Dana J.; Caine, Jonathan S.; Lowers, Heather

2012-01-01

The surface and subsurface geology, hydrothermal alteration, and mineralogy of the Handcart Gulch area was studied using map and drill core data as part of a multidisciplinary approach to understand the hydrology and affects of geology on acid-rock drainage in a mineralized alpine watershed. Handcart Gulch was the locus of intense hydrothermal alteration that affected an area of nearly 3 square kilometers. Hydrothermal alteration and accompanied weak mineralization are spatially and genetically associated with small dacite to low-silica rhyolite stocks and plugs emplaced about 37-36 Ma. Felsic lithologies are commonly altered to a quartz-sericite-pyrite mineral assemblage at the surface, but alteration is more variable in the subsurface, ranging from quartz-sericite-pyrite-dominant in upper core sections to a propylitic variant that is more typical in deeper drill core intervals. Late-stage, hydrothermal argillic alteration [kaolinite and(or) smectite] was superimposed over earlier-formed alteration assemblages in the felsic rocks. Smectite in this late stage assemblage is mostly neoformed resulting from dissolution of chlorite, plagioclase, and minor illite in more weakly altered rocks. Hydrothermally altered amphibolites are characterized by biotitic alteration of amphibole, and subsequent alteration of both primary and secondary biotite to chlorite. Whereas pyrite is present both as disseminations and in small veinlets in the felsic lithologies, it is mostly restricted to small veinlets in the amphibolites. Base-metal sulfides including molybdenite, chalcopyrite, sphalerite, and galena are present in minor to trace amounts in the altered rocks. However, geologic data in conjunction with water geochemical studies indicate that copper mineralization may be present in unknown abundance in two distinct areas. The altered rocks contain an average of 8 weight percent fine pyrite that is largely devoid of metals in the crystal structure, which can be a significant source of trace metals in other areas with acid rock drainage. Thus, elevated base-metal concentrations in the trunk stream and discrete springs in the study area, as determined in previous studies, are likely derived from discrete metal-rich sources, rather than the abundant pyrite veins or disseminations. Pyrite is oxidized in nearly all outcrops examined. Drill core data show that zones of pyrite oxidation range in depth from 100 meters below the surface at higher elevations to just a few meters depth at the lowest elevations in the study area. However, discrete pyrite oxidation zones are present in drill core to depths of several hundred meters below the pervasive near-surface oxidation zones. These deeper discrete oxidation zones, which are present where fresh pyrite predominates, are spatially associated with fractures, small faults, and breccias. Quartz-sericite-pyrite-altered rocks containing unoxidized pyrite likely have the highest acid-generating capacity of all alteration assemblages in the study area. Hydrothermal alteration has left these rocks base-cation leached and thus acid-neutralizing potential is negligible. In contrast, propylitic-altered felsic rocks commonly contain trace to minor calcite and abundant chlorite, which provide some amount of acid-neutralization despite the presence of a few percent pyrite.

The Sandvik peridotite, Gurskøy, Norway: Three billion years of mantle evolution in the Baltica lithosphere

NASA Astrophysics Data System (ADS)

Lapen, Thomas J.; Medaris, L. Gordon, Jr.; Beard, Brian L.; Johnson, Clark M.

2009-05-01

The Sandvik ultramafic body, Island of Gurskøy, Western Gneiss Region, Norway, is a mantle fragment that contains polymetamorphic mineral assemblages and affords a unique view into the response of subcontinental lithospheric mantle to repeated orogenic/magmatic events. The Sandvik peridotite body and nearby outcrops record four paragenetic stages: 1) pre-exsolution porphyroclasts of ol + grt + opx (high-Ca ) + cpx (low-Ca), which equilibrated at 1100-1200 °C and 6.5-7.0 GPa; 2) kelyphite containing ol + grt + spl +opx (low-Ca) + am (high-Al), as well as exsolved pyroxene containing opx + cpx + spl in equilibrium with matrix olivine, at 725 °C and 1.5 GPa; 3) granoblastic matrix of ol + spl + opx (low-Ca) + am (high-Al), at 700 °C and 1.0 GPa. A nearby outcrop contains a fourth assemblage consisting of ol + chl + opx + am. Lu-Hf and Re-Os model ages of garnet peridotite indicate melt depletion at 3.3 Ga [Beyer, E.E., Brueckner, H.K., Griffin, W.L., O'Reilly, S.Y., Graham, S., 2004. Archean mantle fragments in Proterozoic crust, Western Gneiss Region, Norway. Geology 32, 609-612.; Lapen, T.J., Medaris, L.G. Jr., Johnson, C.M., and Beard, B.L., 2005. Archean to Middle Proterozoic evolution of Baltica subcontinental lithosphere: evidence from combined Sm-Nd and Lu-Hf isotope analyses of the Sandvik ultramafic body, Norway. Contributions to Mineralogy and Petrology 150, 131-145.], marking the time of separation from the convecting mantle. Lu-Hf whole rock and mineral isochron ages of constituent garnet peridotite and garnet pyroxenite layers in the Sandvik body reflect cooling and emplacement at ~ 1.25 Ga and ~ 1.18 Ga, respectively, whereas Sm-Nd whole rock and mineral ages of the garnet pyroxenite layers and the garnet peridotite are consistent with metasomatic alteration at ~ 1.15 Ga [Lapen, T.J., Medaris, L.G. Jr., Johnson, C.M., and Beard, B.L., 2005. Archean to Middle Proterozoic evolution of Baltica subcontinental lithosphere: evidence from combined Sm-Nd and Lu-Hf isotope analyses of the Sandvik ultramafic body, Norway. Contributions to Mineralogy and Petrology 150, 131-145.]. The isochron ages likely record lithospheric modification associated with the 1.25-1.00 Ga Sveconorwegian orogeny and represent the youngest age of the Stage 1 mineral assemblage equilibration. A 606 ± 39 Ma Sm-Nd isochron age of the Stage 2 kelyphite assemblage is consistent with partial re-equilibration of the porphyroclastic assemblage during continental rifting associated with opening of the Iapetus Ocean between Baltica and Laurentia at ~ 600 Ma, or extension between Baltica and Siberia that may have been associated with opening of the Ægir Sea. The age of kelyphite, therefore, places the Sandvik peridotite in the uppermost mantle prior to Silurian shortening between the Baltic and Laurentian continents.

Causes of Different Vivid Colors in Chalcedonies: Kutahya-Turkey

NASA Astrophysics Data System (ADS)

Ozcan Kilic, Cumhur; Kagan Kadıoglu, Yusuf

2016-04-01

Chalcedony is a silicate mineral which is a mixture of fibrous quartz (trigonal) and granular moganite (monoclinic) minerals. They are both SiO2 in composition but differs in crystal system. Chalcedony is widely used as semi-precious gemstone in many countries. It has many different kinds due to their various colors and structures. The colour changes in mineral depends on different causes. Most important causes are transition metal impurities in minerals chemical composition and charge transfer between ions. Different chalcedony types have different colors due to their elemental composition. Chalcedony can be show almost every colour strating from white, black, gray, red, blue, green to brown or a combinations of more than one color in case of agates and jasper formations. Although they have same major oxide compositions,chrysopras (green chalcedony) have Ni which gives the green color and carnelian (orange chalcedony) have Fe+3 which gives the orange color. Kutahya, Eskisehir, Ankara, Manisa, Balıkesir, Canakkale and Yozgat represent the most cities which chalcedony can be mostly observed in Turkey. In Kutahya, chalcedony occurs in cavity or vein fillings in pyroclastic rocks such as tuff and formed by precipitation of silica bearing fluids in low temperatures. They can be also formed within the hydrothermal alteration zone of ultramafic rocks. Although chalcedonies in Kutahya form under almost same condition, they have various colors within the same unit. To specify the cause of the different colors, chemical analysis and Confocal Raman studies performed on Kutahya chalcedonies. Firstly, samples are crushed to 2 mm. size. After that, different colors of chalcedonies are separated by hand picking under binocular microscope and grouped into different color sets such as white, blue, dark yellow, light orange, dark orange and claret red. Each color set is measured by PED-XRF method to obtain chemical compositions. Also Raman studies performed to identify the effect of Fe element and OH bonds in each color set groups. Due to chemical results, 'Fe2O3-TiO2'assemblage gives claret red-dark orange, only "Fe2O3"gives claret red, 'Fe2O3-Ni' assemblage gives orange to claret red, 'Cr-Ni-Co' assemblage gives light orange, 'As' gives yellow, 'Fe2O3-Cu' assemblage gives claret red to orange, 'As-Zr' and 'Cr2O3-MgO' assemblage gives blue color to chalcedonies in Kutahya. Also 'Fe' Raman shift is figured in Raman studies in Fe containing orange-claret red colored samples. The vivid colors in all the sets derived from the OH Raman shift bonds of the chalcedony. Chemical results show that the colour differences in chalcedony is not related with only one element.The mobility and charge of Fe element with some other (Co, Mn, Cu, Cr, Ni etc.) elements also effects the variability of the colour.

Late Quarternary Sedimentation in the Eastern Angola Basin.

DTIC Science & Technology

1973-11-01

Angola diapir field. Illite and montmorillonite are abundant in the southern part of the basin, reflecting the source in soils of South West Africa and...northward transport in the Benguela Current system. Kaolinite dominates the clay-mineral assemblage in the north-central part of the basin

Asteroid surface mineralogy: Evidence from earth-based telescope observations

NASA Technical Reports Server (NTRS)

Mccord, T. B.

1978-01-01

The interpretation of asteroid reflectance spectrophotometry in terms of mineralogical types gives inferred mineral assemblages for about 60 asteroids. Asteroid surface materials are compared with similar materials that make up many meteorites. The absence of asteroids with spectra that match identically the ordinary chondrites is noted.

The Kongsberg silver deposits, Norway: Ag-Hg-Sb mineralization and constraints for the formation of the deposits

NASA Astrophysics Data System (ADS)

Kotková, Jana; Kullerud, Kåre; Šrein, Vladimír; Drábek, Milan; Škoda, Radek

2018-04-01

The Kongsberg silver district has been investigated by microscopy and electron microprobe analysis, focusing primarily on the Ag-Hg-Sb mineralization within the context of the updated mineral paragenesis. The earliest mineralization stage is represented by sulfides, including acanthite, and sulfosalts. Native silver formed initially through breakdown of early Ag-bearing phases and later through influx of additional Ag-bearing fluids and silver remobilization. The first two generations of native silver were separated in time by the formation of Ni-Co-Fe sulfarsenides and the monoarsenide niccolite along rims of silver crystals. The presence of As-free sulfosalts and the absence of di- and tri-arsenides suggest a lower arsenic/sulfur activity ratio for the Kongsberg deposits compared to other five-element deposits. Native silver shows binary Ag-Hg and Ag-Sb solid solutions, in contrast to the ternary Ag-Hg-Sb compositions typical for other deposits of similar type. Antimonial silver together with allargentum, dyscrasite, and pyrargyrite was documented exclusively from the northern area of the district. Elsewhere, the only Sb-bearing minerals are polybasite and tetrahedrite/freibergite. Hg-rich silver (up to 21 wt% Hg) has been documented only in the central-western area. Myrmekite of freibergite and chalcopyrite reflects exsolution from an original Ag-poor tetrahedrite upon cooling, while myrmekite of pyrite and silver, forming through breakdown of low-temperature phases (argentopyrite or lenaite) upon heating, characterizes the Kongsberg silver district. Based on the stabilities of minerals and mineral assemblages, the formation of the silver mineralization can be constrained to temperatures between 180 and 250 °C.

Using ASD data to identify the altered minerals for exploring of gold deposit in the Beishan area, North China

NASA Astrophysics Data System (ADS)

Ren, G. L.; Yi, H.; Yang, M.; Liang, N.; Li, J. Q.; Yang, J. L.

2016-11-01

Hyperspectral information of altered minerals plays an important role in the identifications of mineralized zones. In this study, the altered minerals of two gold deposits from Fangshankou-Laojinchang regions of Beishan metallogenic belt were measured by ASD field Spectrometer. Many gold deposits would have a close relationship with Variscan magma intrusion, which have been found in study region. The alteration minerals have been divided six types by the spectral results, i.e. sericite, limonite, dolomite, chlorite, epidote and calcite. The distribution characteristics and formations of altered minerals were discussed here. By the ASD, the spectral curve of different geological units in the Jintanzi and Fangshankou gold deposits were analysed and summarized. The results show that the sericite and limonite are mainly related with the gold mineralization and widely occurred in the gold deposits. Therefore, we proposed that the sericite and limonite are the iconic alteration mineral assemblages for gold mineralization and the models of altered minerals for gold deposits could be established in this region.

Characteristics, extent and origin of hydrothermal alteration at Mount Rainier Volcano, Cascades Arc, USA: Implications for debris-flow hazards and mineral deposits

USGS Publications Warehouse

John, D.A.; Sisson, T.W.; Breit, G.N.; Rye, R.O.; Vallance, J.W.

2008-01-01

Hydrothermal alteration at Mount Rainier waxed and waned over the 500,000-year episodic growth of the edifice. Hydrothermal minerals and their stable-isotope compositions in samples collected from outcrop and as clasts from Holocene debris-flow deposits identify three distinct hypogene argillic/advanced argillic hydrothermal environments: magmatic-hydrothermal, steam-heated, and magmatic steam (fumarolic), with minor superimposed supergene alteration. The 3.8??km3 Osceola Mudflow (5600??y BP) and coeval phreatomagmatic F tephra contain the highest temperature and most deeply formed hydrothermal minerals. Relatively deeply formed magmatic-hydrothermal alteration minerals and associations in clasts include quartz (residual silica), quartz-alunite, quartz-topaz, quartz-pyrophyllite, quartz-dickite/kaolinite, and quartz-illite (all with pyrite). Clasts of smectite-pyrite and steam-heated opal-alunite-kaolinite are also common in the Osceola Mudflow. In contrast, the Paradise lahar, formed by collapse of the summit or near-summit of the edifice at about the same time, contains only smectite-pyrite and near-surface steam-heated and fumarolic alteration minerals. Younger debris-flow deposits on the west side of the volcano (Round Pass and distal Electron Mudflows) contain only low-temperature smectite-pyrite assemblages, whereas the proximal Electron Mudflow and a < 100??y BP rock avalanche on Tahoma Glacier also contain magmatic-hydrothermal alteration minerals that are exposed in the avalanche headwall of Sunset Amphitheater, reflecting progressive incision into deeper near-conduit alteration products that formed at higher temperatures. The pre-Osceola Mudflow alteration geometry is inferred to have consisted of a narrow feeder zone of intense magmatic-hydrothermal alteration limited to near the conduit of the volcano, which graded outward to more widely distributed, but weak, smectite-pyrite alteration within 1??km of the edifice axis, developed chiefly in porous breccias. The edifice was capped by a steam-heated alteration zone, most of which resulted from condensation of fumarolic vapor and oxidation of H2S in the unsaturated zone above the water table. Weakly developed smectite-pyrite alteration extended into the west and east flanks of the edifice, spatially associated with dikes that are localized in those sectors; other edifice flanks lack dikes and associated alteration. The Osceola collapse removed most of the altered core and upper east flank of the volcano, but intensely altered rocks remain on the uppermost west flank. Major conclusions of this study are that: (1) Hydrothermal-mineral assemblages and distributions at Mount Rainier can be understood in the framework of hydrothermal processes and environments developed from studies of ore deposits formed in analogous settings. (2) Frequent eruptions supplied sufficient hot magmatic fluid to alter the upper interior of the volcano hydrothermally, despite the consistently deep (??? 8??km) magma reservoir which may have precluded formation of economic mineral deposits within or at shallow depths beneath Mount Rainier. The absence of indicator equilibrium alteration-mineral assemblages in the debris flows that effectively expose the volcano to a depth of 1-1.5??km also suggests a low potential for significant high-sulfidation epithermal or porphyry-type mineral deposits at depth. (3) Despite the long and complex history of the volcano, intensely altered collapse-prone rocks were spatially restricted to near the volcano's conduit system and summit, and short distances onto the upper east and west flanks, due to the necessary supply of reactive components carried by ascending magmatic fluids. (4) Intensely altered rocks were removed from the summit, east flank, and edifice interior by the Osceola collapse, but remain on the upper west flank in the Sunset Amphitheater area and present a continuing collapse hazard. (5) Visually conspicuous rocks on the lower east and mid-to-lower

Concealed basalt-matrix diatremes with Cu-Au-Ag-(Mo)-mineralized xenoliths, Santa Cruz Porphyry Cu-(Mo) System, Pinal County, Arizona

USGS Publications Warehouse

Vikre, Peter; Graybeal, Frederick T.; Koutz, Fleetwood R.

2014-01-01

The Santa Cruz porphyry Cu-(Mo) system near Casa Grande, Arizona, includes the Sacaton mine deposits and at least five other concealed, mineralized fault blocks with an estimated minimum resource of 1.5 Gt @ 0.6% Cu. The Late Cretaceous-Paleocene system has been dismembered and rotated by Tertiary extension, partially eroded, and covered by Tertiary-Quaternary basin-fill deposits. The mine and mineralized fault blocks, which form an 11 km (~7 miles) by 1.6 km (~1 mile) NE-SW–trending alignment, represent either pieces of one large deposit, several deposits, or pieces of several deposits. The southwestern part of the known system is penetrated by three or more diatremes that consist of heterolithic breccia pipes with basalt and clastic matrices, and subannular tuff ring and maar-fill sedimentary deposits associated with vents. The tephra and maar-fill deposits, which are covered by ~485 to 910 m (~1,600–3,000 ft) of basin fill, lie on a mid-Tertiary erosion surface of Middle Proterozoic granite and Late Cretaceous porphyry, which compose most xenoliths in pipes and are the host rocks of the system. Some igneous xenoliths in the pipes contain bornite-chalcopyrite-covellite assemblages with hypogene grades >1 wt % Cu, 0.01 ounces per ton (oz/t) Au, 0.5 oz/t Ag, and small amounts of Mo (<0.01 wt %). These xenoliths were derived from mineralized rocks that have not been encountered in drill holes, and attest to additional, possibly higher-grade deposits within or subjacent to the known system.The geometry, stratigraphy, and temporal relationships of pipes and tephras, interpreted from drill hole spacing and intercepts, multigenerational breccias and matrices, reequilibrated and partially decomposed sulfide-oxide mineral assemblages, melted xenoliths, and breccia matrix compositions show that the diatremes formed in repeated stages. Initial pulses of basalt magma fractured granite, porphyry, and other crustal rocks during intrusion, transported multi-sized fragments of these rocks upward, and partially melted small fragments. Rapid decompression of magma induced catastrophic devolatilization that ruptured overlying rocks to the surface, and generated fragment-volatile suspensions that abraded conduits into near-vertical cylindrical structures. Fragments entrained in suspensions were milled and sorted, and ejected as basal surge, pyroclastic deposits, and airfall tephra that built tuff rings around vents and filled vent depressions. Comminuted m- to mm-sized fragments of wall rocks in magma and suspensions that remained in conduits solidified as heterolithic breccias. Subsequent pulses of basalt magma ascended through the same conduits, brecciated older heterolithic breccias, devolatilized, and quenched, leaving two or more generations of nested and mingled heterolithic breccias and internal zones of fluidized fragments. Tephra and maar-fill deposits from later eruptions are composed of more hydrous and oxidized minerals than earlier tephras, reflecting a higher proportion of water in transport fluid which, based on fluid inclusion populations in mineralized xenoliths, was saline water and CO2. The large vertical extent (~600 m; ~2,000 ft) of basalt matrix in pipes, near-paleosurface matrix vesiculation, and plastically deformed basalt lapilli indicates that diatreme eruptions were predominantly phreatic.Diatreme xenoliths represent crustal stratigraphy and, as in the Santa Cruz system, provide evidence of concealed mineral resources that can guide exploration drilling through cover. Vectors to the source of bornite-dominant xenoliths containing >1% Cu and significant Au and Ag could be determined by refinement of breccia pipe geometries, by reassembly of mineralized fault blocks using modal, chemical, and temporal characteristics of hydrothermal mineral assemblages and fluid inclusions, and by paleodrainage analysis.

The role of metasomatism in the balance of halogens in ore-forming process at porphyry Cu-Mo deposits

NASA Astrophysics Data System (ADS)

Berzina, A. N.

2009-04-01

Volatile components play an important role in the evolution of ore-magmatic systems and their ore potential. Of special interest are fluorine and chlorine compounds that principally control the transportation of ore elements by the fluid in a magmatic process and under high-temperature hydrothermal conditions. Study of the evolution of fluorine-chlorine activity in the ore-forming process and their source is usually based on analysis of their magmatic history, whereas the additional source of fluorine and chlorine released during metasomatic alteration of rocks hosting mineralization is poorly discussed in the existing literature. Based on microprobe data on Cl and F abundances in halogen-containing minerals (biotite, amphibole, apatite, titanite) in intrusive rocks and their hydrothermally altered varieties, the role of metasomatic processes in the balance of volatiles in the ore-forming system is discussed by the example of porphyry Cu-Mo deposits of Siberia (Russia) and Mongolia. Two groups of the deposits are considered: copper-molybdenum (Erdenetiin Ovoo, Mongolia and Aksug, Russia) with prevailing propylitic and phyllic alteration and molybdenum-copper (Sora, Russia), with predominant potassic alteration. All types of hydrothermal alterations have led to drastic decrease in Cl contents in metasomatic minerals as compared with halogen-containing magmatic minerals. All studied deposits (particularly those where propylitic and phyllic alteration were developed) show a nearly complete chlorine removal from altered halogen-containing rock-forming minerals (biotite and amphibole). The Cl content in amphibole decreases several times at the stage of replacement with actinolite in the process of propylitization. In the later chlorites (ripidolite and brunsvigite) that replace amphibole, actinolite, and biotite, chlorine is not detected by microprobe (detection limit 0.01-0.02% Cl). Chlorine was also not detected in white micas (muscovite-phengite series) in quartz-sericite alteration zones. No Cl-bearing minerals were revealed in ore-metasomatic assemblages with the exception of extremely low Cl contents in secondary biotite and very rare low-Cl apatite in the early potassic alteration zone. In contrast, fluorine concentrates in chlorites and white micas; however, the F content in them is commonly lower than in dark minerals, especially in biotite from altered rocks. The highest F contents are typical of biotites related to potassic alteration (K-feldspar + biotite + quartz assemblage). For example, the F content at the Sora deposit ranges from 2.5-2.7 wt.% in the metasomatic biotite to 0.44-1.63 wt.% in the rock-forming biotite of host granitoids. At this deposit, fluorite is a major mineral of the ore-metasomatic assemblage. The Mo-rich Sora deposit drastically differs from the Cu-rich Erdenetiin Ovoo and Aksug deposits by extremely low (0.02-0.08 wt.%) Cl contents in dark minerals from all of the host rocks. The considerable quantity of chlorine released as a result of large-scale propylitic and phyllic alteration from halogen-bearing dark minerals at Cu-rich deposits considerably affected the general Cl budget in the ore-metasomatic system. This could significantly promote the generation of Cl-rich (up to 50-70 wt.% NaCl-equiv.) ore-forming solutions at such deposits. At the Sora deposit characterized by less concentrated ore-bearing solutions (12-20 wt.% NaCl-equiv.), the metasomatic alteration of host rocks was not accompanied by an appreciable removal of Cl. At the studied deposits, huge volumes of enclosing rocks were involved in metasomatism. The large amounts of halogens released during the metasomatic alteration of host rocks might have significantly influenced the balance of volatiles in the ore forming system, including the increase in the salinity of hydrothermal solutions.

Partitioning of Cu between mafic minerals, Fe-Ti oxides and intermediate to felsic melts

NASA Astrophysics Data System (ADS)

Liu, Xingcheng; Xiong, Xiaolin; Audétat, Andreas; Li, Yuan

2015-02-01

This study used improved capsule technique i.e., Pt95Cu05 or Au95Cu05 alloy capsules as Cu sources to determine Cu partitioning between mafic minerals, Fe-Ti oxides and intermediate to felsic melts at 0.5-2.5 GPa, 950-1100 °C and various oxygen fugacities (fO2). In combination with the data from the mafic composition systems, the results demonstrate that Cu is generally highly incompatible in mafic minerals and moderately incompatible to compatible in Fe-Ti oxides. The general order of mineral/melt Cu partition coefficients (DCu) is garnet (0.01-0.06) ⩽ olivine (0.04-0.20) ≈ opx (0.04-0.24) ≈ amphibole (0.04-0.20) ⩽ cpx (0.04-0.45) ⩽ magnetite, titanomagnetite and Cr-spinel (0.18-1.83). The variations in DCu depend mainly on temperature, fO2 or mineral composition. In general, DCu for olivine (and perhaps opx) increases with decreasing temperature and increasing fO2. DCu increases for cpx with Na+ (pfu) in cpx, for magnetite and Cr-spinel with Fe3+ (pfu) in these phases and for titanomagnetite with Ti4+ (pfu) in this phase. The large number of DCu data (99 pairs) serves as a foundation for quantitatively understanding the behavior of Cu during magmatic processes. The generation of intermediate to felsic magmas via fractional crystallization or partial melting of mafic rocks (magmas) at deep levels of crust involves removal of or leaving assemblages of mafic minerals + Fe-Ti oxides ± sulfides. With our DCu data on mafic minerals and Fe-Ti oxides, DCubulk values around 0.2 were obtained for the sulfide-free assemblages. Cu will thus be concentrated efficiently in the derived melts during these two processes if sulfides are absent or negligible, explaining that high fO2 and sulfide-destabilization are favorable to formation of the porphyry Cu system.

Clay Mineralogy of AN Alluvial Aquifer in a Mountainous, Semiarid Terrain, AN Example from Rifle, Colorado

NASA Astrophysics Data System (ADS)

Elliott, W. C.; Lim, D.; Zaunbrecher, L. K.; Pickering, R. A.; Williams, K. H.; Navarre-Sitchler, A.; Long, P. E.; Noel, V.; Bargar, J.; Qafoku, N. P.

2015-12-01

Alluvial sediments deposited along the Colorado River corridor in the semi-arid regions of central to western Colorado can be important hosts for legacy contamination including U, V, As and Se. These alluvial sediments host aquifers which are thought to provide important "hot spots" and "hot moments" for microbiological activity controlling organic carbon processing and fluxes in the subsurface. Relatively little is known about the clay mineralogy of these alluvial aquifers and the parent alluvial sediments in spite of the fact that they commonly include lenses of silt-clay materials. These lenses are typically more reduced than coarser grained materials, but zones of reduced and more oxidized materials are present in these alluvial aquifer sediments. The clay mineralogy of the non-reduced parent alluvial sediments of the alluvial aquifer located in Rifle, CO (USA) is composed of chlorite, smectite, illite, kaolinite and quartz. The clay mineralogy of non-reduced fine-grained materials at Rifle are composed of the same suite of minerals found in the sediments plus a vermiculite-smectite intergrade that occurs near the bottom of the aquifer near the top of the Wasatch Formation. The clay mineral assemblages of the system reflect the mineralogically immature character of the source sediments. These assemblages are consistent with sediments and soils that formed in a moderately low rainfall climate and suggestive of minimal transport of the alluvial sediments from their source areas. Chlorite, smectite, smectite-vermiculite intergrade, and illite are the likely phases involved in the sorption of organic carbon and related microbial redox transformations of metals in these sediments. Both the occurrence and abundance of chlorite, smectite-vermiculite, illite and smectite can therefore exert an important control on the contaminant fluxes and are important determinants of biogeofacies in mountainous, semiarid terrains.

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.

Latest Paleocene lithologic and biotic events in neritic deposits of southwestern New Jersey

USGS Publications Warehouse

Gibson, Thomas G.; Bybell, Laurel M.; Owens, James P.

1993-01-01

In the southwestern New Jersey Coastal Plain, four drill holes contain continuous neritic sedimentation across the Paleocene/Eocene boundary (calcareous nannofossil Zone NP 9/NP 10 boundary). Significant lithologic and biotic changes occur in these strata near the top of the Paleocene. Global warming, increased precipitation, and other oceanographic and climatic events that have been recognized in high-latitude, deep-oceanic deposits of the latest Paleocene also influenced mid-latitude, shallow-marine, and terrestrial environments of the western North Atlantic. The diverse, well-preserved calcareous nannofossil flora that is present throughout the entire New Jersey boundary section accurately places these events within the uppermost part of the upper Paleocene Zone NP 9. Several rapid but gradational changes occur within a 1.1-m interval near the top of Zone NP 9. The changes include (1) a change in lithology from glauconitic quartz sand to clay, (2) a change in clay mineral suites from illite/smectite-dominated to kaolinite-dominated, (3) a change in benthic foraminiferal assemblages to a lower diversity fauna suggestive of low-oxygen environments, (4) a significant increase in planktonic foraminiferal abundance, and (5) an increased species turnover rate in marine calcareous nannofossils. Pollen was sparse in the New Jersey drill holes, but terrestrial sporomorph species in Virginia exhibit increased turnover rates at a correlative level. Foraminiferal assemblages and lithology indicate that relative sea level rose in New Jersey at the same time as these late Paleocene events occurred in late Biochron NP 9. The higher sea levels influenced sediment type and absolute abundance of planktonic foraminifers in the deposits. Above the initial increase of kaolinite in the upper part of Zone NP 9, the kaolinite percentage continues to increase, and the maximum kaolinite value occurs in the uppermost part of Zone NP 9. There are few changes in either the sediments or the biota precisely at the Zone NP 9/NP 10 boundary in New Jersey. The clay-rich deposits with a high kaolinite clay mineral suite, the lowered diversity benthic foraminiferal assemblages, the abundant planktonic foraminiferal specimens, and the calcareous nannofossil assemblages continued essentially unchanged into the earliest Eocene Zone NP 10. Within the lower part of Zone NP 10, the kaolinite percentage decreased to very low values.

Derivation and calibration of semi-empirical gas geothermometers for Mahanagdong Geothermal Project, Philippines

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

Sanchez, D.R.

1996-12-31

The dissolved CO{sub 2}, H{sub 2}S, and H{sub 2} gases in Mahanagdong aquifer fluids are controlled by specific gas-mineral equilibria. At temperature range of 250 to 310 {degrees}C, CO{sub 2} is buffered by clinozoisite + K-feldspar + calcite + muscovite (illite) + quartz mineral assemblage. For H{sub 2}S and H{sub 2} dissolved gases, they are more likely buffered by pyrrhotite + pyrite + magnetite mineral assemblage at similar temperature range. Calibration of five Mahanagdong (MG) gas geothermometers is presented, three of which used CO{sub 2}, H{sub 2}S, and H{sub 2} concentration in steam. The remaining two use CO{sub 2}/H{sub 2}more » and H{sub 2}S/H{sub 2} ratios. The calibration is based on the relation between gas content of drillhole discharges and measured aquifer temperatures. After establishing the gas content in the aquifer, gas concentrations were computed in steam after adiabatic boiling to atmospheric condition (100 {degrees}C), to obtain gas geothermometry functions. These functions could also be used in evaluating fraction of steam condensation and temperature of phase separation. A demonstration given the Mahanagdong fumarole data, indicates that there is generally a fair relation between computed temperatures using Mahanagdong gas geothermometers and the actual field trend`s temperatures.« less

Deep-sea nematode assemblage has not recovered 26 years after experimental mining of polymetallic nodules (Clarion-Clipperton Fracture Zone, Tropical Eastern Pacific)

NASA Astrophysics Data System (ADS)

Miljutin, Dmitry M.; Miljutina, Maria A.; Arbizu, Pedro Martínez; Galéron, Joëlle

2011-08-01

We investigated nematode assemblages inhabiting the 26-year-old track created by experimental deep-sea mining of polymetallic nodules, and two adjacent, undisturbed sites, one with nodules and one without nodules. The aim was to compare density, assemblage structure, and diversity indices in order to assess the process of recovery of the nematode assemblage inhabiting the disturbed site. This experimental dredging was conducted in 1978 by the Ocean Minerals Company (USA) in the area of a French mining claim in the Clarion-Clipperton Fracture Zone (Tropical Eastern Pacific) at a depth of about 5000 m. The nematode assemblage had not returned its initial state 26 years after the experimental dredging: the total nematode density and biomass within the dredging track were significantly lower than outside the track; the biodiversity indices showed significantly lower nematode diversity within the track; and the structure of the nematode assemblage within the track differed significantly from those in the two undisturbed sites outside the track. However, there were no significant differences in the mean body volumes of adult nematodes and adult-juvenile ratios between the track and reference sites. Parameters such as the rate of sediment restoration (which depends on local hydrological conditions) and the degree and character of the disturbance appeared to be of considerable importance for the recovery rate of the deep-sea nematode assemblages and their ability to recolonize disturbed areas. The rates of recolonization and recovery may vary widely in different deep-sea regions.

A hydrothermal system associated with the Siljan impact structure, Sweden--implications for the search for fossil life on Mars.

PubMed

Hode, Tomas; von Dalwigk, Ilka; Broman, Curt

2003-01-01

The Siljan ring structure (368 +/- 1.1 Ma) is the largest known impact structure in Europe. It isa 65-km-wide, eroded, complex impact structure, displaying several structural units, including a central uplifted region surrounded by a ring-shaped depression. Associated with the impact crater are traces of a post-impact hydrothermal system indicated by precipitated and altered hydrothermal mineral assemblages. Precipitated hydrothermal minerals include quartz veins and breccia fillings associated with granitic rocks at the outer margin of the central uplift, and calcite, fluorite, galena, and sphalerite veins associated with Paleozoic carbonate rocks located outside the central uplift. Two-phase water/gas and oil/gas inclusions in calcite and fluorite display homogenization temperatures between 75 degrees C and 137 degrees C. With an estimated erosional unloading of approximately 1 km, the formation temperatures were probably not more than 10-15 degrees C higher. Fluid inclusion ice-melting temperatures indicate a very low salt content, reducing the probability that the mineralization was precipitated during the Caledonian Orogeny. Our findings suggest that large impacts induce low-temperature hydrothermal systems that may be habitats for thermophilic organisms. Large impact structures on Mars may therefore be suitable targets in the search for fossil thermophilic organisms.

RARE EARTH ELEMENTS: A REVIEW OF PRODUCTION, PROCESSING, RECYCLING, AND ASSOCIATED ENVIRONMENTAL ISSUES

EPA Science Inventory

Rare earth elements (REEs) are a group of 15 chemical elements in the periodic table, specifically the lanthanides. Two other elements, scandium and yttrium, have a similar physiochemistry to the lanthanides, are commonly found in the same mineral assemblages, and are often refe...

Thermobarometric studies on the Levack Gneisses: Footwall rocks to the Sudbury Igneous Complex

NASA Technical Reports Server (NTRS)

James, R. S.; Peredery, W.; Sweeny, J. M.

1992-01-01

Granulite and amphibolite facies gneisses and migmatites of the Levack Gneiss Complex occupy a zone up to 8 km wide around the northern part of the Sudbury Igneous Complex (SIC). Orthopyroxene- and garnet-bearing tonalitic and semipelitic assemblages of granulite facies grade occur within 3 km of the SIC together with lenses of mafic and pyroxenitic rock compositions normally represented by an amphibole +/- cpx-rich assemblage; amphibolite facies assemblages dominate elsewhere in this terrain. These 2.711-Ga gneisses were introduced by (1) the Cartier Granite Batholith during late Archaean to early Proterozoic time and (2) the SIC, at 1.85 Ga, which produced a contact aureole 1-1.5 km wide in which pyroxene hornfelses are common within 200-300 m of the contact. A suite of 12 samples including both the opx-gt and amphibole-rich rock compositions have been studied. Garnets in the semipelitic gneisses are variably replaced by a plg-bio assemblage. Thermobarometric calculations using a variety of barometers and thermometers reported in the literature suggest that the granulite facies assemblages formed at depths in the 21-28 km range (6-8 kbar). Textures and mineral chemistry in the garnet-bearing semipelitic rocks indicate that this terrain underwent a second metamorphic event during uplift to depth in the 5-11 km range (2-3 kbar) and at temperatures as low as 500-550 C. This latter event is distinct from thermal recrystallization caused by the emplacement of the SIC; it probably represents metamorphism attributable to intrusion of the Cartier Granite Batholith. These data allow two interpretations for the crustal uplift of the Levack Gneisses: (1) The gneisses were tectonically uplifted prior to the Sudbury Event (due to intrusion of the Cartier Batholith); or (2) the gneisses were raised to epizonal levels as a result of meteorite impact at 1.85 Ga.

Comparative mineral mapping in the Colorado Mineral Belt using AVIRIS and ASTER remote sensing data

USGS Publications Warehouse

Rockwell, Barnaby W.

2013-01-01

This report presents results of interpretation of spectral remote sensing data covering the eastern Colorado Mineral Belt in central Colorado, USA, acquired by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensors. This study was part of a multidisciplinary mapping and data integration project at the U.S. Geological Survey that focused on long-term resource planning by land-managing entities in Colorado. The map products were designed primarily for the regional mapping and characterization of exposed surface mineralogy, including that related to hydrothermal alteration and supergene weathering of pyritic rocks. Alteration type was modeled from identified minerals based on standard definitions of alteration mineral assemblages. Vegetation was identified using the ASTER data and subdivided based on per-pixel chlorophyll content (depth of 0.68 micrometer absorption band) and dryness (fit and depth of leaf biochemical absorptions in the shortwave infrared spectral region). The vegetation results can be used to estimate the abundance of fire fuels at the time of data acquisition (2002 and 2003). The AVIRIS- and ASTER-derived mineral mapping results can be readily compared using the toggleable layers in the GeoPDF file, and by using the provided GIS-ready raster datasets. The results relating to mineral occurrence and distribution were an important source of data for studies documenting the effects of mining and un-mined, altered rocks on aquatic ecosystems at the watershed level. These studies demonstrated a high correlation between metal concentrations in streams and the presence of hydrothermal alteration and (or) pyritic mine waste as determined by analysis of the map products presented herein. The mineral mapping results were also used to delineate permissive areas for various mineral deposit types.

Hydrothermal barite mineralization at Chenarvardeh deposit, Markazi Province, Iran: Evidences from REE geochemistry and fluid inclusions

NASA Astrophysics Data System (ADS)

Ehya, Farhad; Mazraei, Shaghayegh Moalaye

2017-10-01

Barite mineralization occurs at Chenarvardeh deposit as layers and lenses in Upper Eocene volcanic and pyroclastic rocks. The host rocks are intensely saussuritized in most places. Barite is accompanied by calcite, Mn-oxides, galena and malachite as subordinate minerals. The amount of Sr in barites is low and varies between 0.11 and 0.30 wt%. The concentration of Rb, Zr, Y, Ta and Hf is also low (<5 ppm) in barite samples. The amount of total REEs (∑REE) is low in barites, ranging from 7.51 to 30.50 ppm. Chondrite-normalized REE patterns reveal LREE enrichment with respect to HREE, and positive Ce anomalies. Fluid inclusions are common in barite samples, being dominantly from liquid-rich two phase (L + V) type. Salinity values in fluid inclusions range from 9.41 to 18.69 wt% NaCl equivalent with most frequent salinities falling in the range of 10-15 wt% NaCl equivalent. Homogenization temperatures (Th) range between 160 and 220 °C, being the 180-200 °C range as the most common Th interval. A combination of factors, including geologic setting, host rock, mineral assemblages, REE geochemistry and fluid inclusion data are consistent with a submarine volcanic hydrothermal model for barite formation at the Chenarvardeh deposit. Mineral-forming fluids originated from solutions related to submarine hydrothermal activities deposited barite on seafloor as they encountered sulfate-bearing seawater.

Metabasalts from the Mid-Atlantic Ridge: new insights into hydrothermal systems in slow-spreading crust

NASA Astrophysics Data System (ADS)

Gillis, Kathryn M.; Thompson, Geoffrey

1993-12-01

An extensive suite of hydrothermally altered rocks were recovered by Alvin and dredging along the MARK [Mid-Atlantic Ridge, south of the Kane Fracture Zone (23 24°N)] where detachment faulting has provided a window into the crustal component of hydrothermal systems. Rocks of basaltic composition are altered to two assemblages with these characteristics: (i) type I: albitic plagioclase (An02 10)+mixed-layer smectite/chlorite or chlorite±actinolite±quartz±sphene, <10% of the clinopyroxene is altered, and there is no trace metal mobility; (ii) type II: plagioclase (An10 30)+amphibole (actinolite-magnesio-hornblende) +chlorite+sphene, >20% of the clinopyroxene is altered, and Cu and Zn are leached. The geochemical signature of these alteration types reflects the relative proportion and composition of secondary minerals, and the degree of alteration of primary phases, and does not show simple predictive relationships. Element mobilities indicate that both alteration types formed at low water/rock ratios. The MARK assemblages are typical of the greenschist and transition to the amphibolite facies, and represent two distinct, albeit overlapping, temperature regimes: type I-180 to 300°C and type II-250 to 450°C. By analogy with DSDP/ODP Hole 504B and many ophiolites, the MARK metabasalts were altered within the downwelling limb of a hydrothermal cell and type I and II samples formed in the upper and lower portions of the sheeted like complex, respectively. Episodic magmatic and hydrothermal events at slow-spreading ridges suggest that these observed mineral assemblages represent the cumulative effects of more than one hydrothermal event. Groundmass and vein assemblages in the MARK metabasalts indicate either that alteration conditions did not change during successive hydrothermal events or that these assemblages record only the highest temperature event. Lack of retrograde reactions or overprinting of lower temperature assemblages (e.g., zeolites) suggests that there is a continuum in alteration conditions while crustal segments remain in the ridge axis environment. The type II samples may be representative of the reaction zone where compositions of hydrothermal fluids actively venting at the seafloor today become fixed. This prediction necessitates interaction between hydrothermal fluids and intersertal glass and/or mafic phases, in addition to plagioclase, in order to produce the observed range in vented fluid pH.

Temporal and spatial distribution of alteration, mineralization and fluid inclusions in the transitional high-sulfidation epithermal-porphyry copper system at Red Mountain, Arizona

USGS Publications Warehouse

Lecumberri-Sanchez, Pilar; Newton, M. Claiborne; Westman, Erik C.; Kamilli, Robert J.; Canby, Vertrees M.; Bodnar, Robert J.

2013-01-01

Red Mountain, Arizona, is a Laramide porphyry Cu system (PCD) that has experienced only a modest level of erosion compared to most other similar deposits in the southwestern United States. As a result, the upper portion of the magmatic–hydrothermal system, which represents the transition from shallower high-sulfidation epithermal mineralization to deeper porphyry Cu mineralization, is well preserved. Within the Red Mountain system, alteration, mineralization and fluid inclusion assemblages show a systematic distribution in both time and space. Early-potassic alteration (characterized by the minerals biotite and magnetite) is paragenetically earlier than late-potassic alteration (K-feldspar–anhydrite) and both are followed by later phyllic (sericite–pyrite) alteration. Advanced argillic alteration (pyrophyllite–alunite–other clay minerals) is thought to be coeval with or postdate phyllic alteration. Minerals characteristic of advanced argillic alteration are present in the near surface. Phyllic alteration extends to greater depths compared to advanced argillic alteration. Early-potassic and late-potassic alteration are only observed in the deepest part of the system. Considerable overlap of phyllic alteration with both early-potassic and late-potassic alteration zones is observed. The hypogene mineralization contains 0.4–1.2% Cu and is spatially and temporally related to the late-potassic alteration event. Molybdenum concentration is typically In the deepest part of the system, an early generation of low-to-moderate density and salinity liquid + vapor inclusions with opaque daughter minerals is followed in time by halite-bearing inclusions that also contain opaque daughter minerals indicating that an early intermediate-density magmatic fluid evolved to a high-density, high-salinity mineralizing fluid. The increase in density and salinity of fluids with time observed in the deeper parts of the system may be the result of immiscibility (“boiling”) of the earlier magmatic fluids or may reflect the compositional evolution of fluids that exsolved from the magma. Trails of inclusions consisting of only vapor-rich inclusions are common in the shallow parts of the system, and are associated with advanced argillic alteration, suggesting that intense boiling (“flashing”) occurred at (or below) this level. Fluid inclusion assemblages consisting of coexisting vapor-rich and halite-bearing inclusions are observed in samples extending from the surface to the upper part of the late-potassic zone, indicating that fluid immiscibility occurred within this depth interval.

Genetic environment of germanium-bearing gold-silver vein ores from the Wolyu mine, Republic of Korea

NASA Astrophysics Data System (ADS)

Yun, Seong-Taek; So, Chil-Sup; Choi, Sang-Hoon; Shelton, Kevin L.; Koo, Ja-Hak

1993-04-01

The Wolyu mine is one of the largest vein-type gold-silver-bearing epithermal systems in the Youngdong district and is the first gold-silver deposit in Korea found to contain significant germanium, in the form of argyrodite (Ag8GeS6). Mineralized veins (78.9 ± 1.2 Ma) crosscutting Late Cretaceous hostrock tuff and quartz porphyry (81.5 ± 1.8 Ma) consist of three stages of quartz and carbonates, the first of which contains pyrite, basemetal sulfides and Au-Ag-minerals. Stage I Au-Ag-Ge-mineralized veins show a systematic variation of mineral assemblage with time: (1) quartz + pyrite; (2) quartz + pyrite + sphalerite + electrum + argentite; (3) carbonate + quartz + sphalerite + electrum + argentite; (4) carbonate + native silver + argentite + Ag-sulfosalts + argyrodite + sphalerite. Calculated values of temperature and sulfur activity are: assemblage (1), 360-280°C and 10-7-10-10; (2), 280-210°C and 10-10-10-14; (3), 210-180°C and 10-14-10-16; (4), 180-155°C and 10-17-10-18. These data, the frequent association of gold with sulfides, and the abundance of pyrite in alteration zones indicate that decreasing sulfur activity and cooling were important in triggering gold deposition. Hydrogen and oxygen isotope compositions of ore fluids display a systematic variation with increasing time. Within the main Ag-Au-Ge mineralization, δD and δ 18O values decrease with the transition from quartz to carbonate deposition (from -78 and -2.8% to -90 and -8.7%., respectively), indicating increasing involvement (mixing) of less evolved meteoric water which resulted in progressive cooling and dilution of ore fluids in the shallow (≈ 370 600 m) Wolyu epithermal system.

High-Pressure Minerals in Meteorites: Constraints on Shock Conditions and Duration

NASA Technical Reports Server (NTRS)

Sharp, Thomas G.

2004-01-01

The objective of this research was to better understand the conditions and duration of shock metamorphism in meteorites through microstructural and microanalytical characterization of high-pressure minerals. A) Continue to investigate the mineralogy and microstructures of melt-veins in a suite of chondritic samples ranging from shock grades S3 through S6 to determine how the mineral assemblages that crystallize at high-pressure and are related to shock grade. B) Investigate the chemical, mineralogical, and microstructural heterogeneities that occur across melt veins to interpret crystallization histories. C) Use static high-pressure experiments to simulate crystallization of melt veins for mineralogical and textural comparisons with the melt veins of naturally shocked samples. D) Characterize the compositions and defect microstructures of polycrystalline ringwoodite, wadsleyite, majorite, (Mg,Fe)Si03-ilmenite and (Mg,Fe)SiO3-perovskite in S6 samples to understand the mechanisms of phase transformations that occur during shock. These results will combined with kinetic data to constrain the time scales of kinetic processes. E) Investigate the transformations of metastable high-pressure minerals back to low- pressure forms to constrain post-shock temperatures and estimates of the peak shock pressure. Of these objectives, we have obtained publishable data on A, B and D. I am currently doing difficult high-pressure melting and quench experiments on an L chondrite known as Mbale. These experiments will provide additional constraints on the mineral assemblages that are produced during rapid quench of an L chondrite at pressures of 16 to 25 GPa. Results from published or nearly published research is presented below. Lists of theses, dissertations and publications are given below.

A thermodynamic evaluation of the potential for cryptic formation of incidental Au-Fe alloy catalysts during flexible cell experimental studies of abiotic alkanogenesis during serpentinization

NASA Astrophysics Data System (ADS)

Lazar, C.

2017-12-01

The formation of abiotic alkanes via CO2 reduction during serpentinization is an important process in astrobiology and geochemistry. Aqueous alkane concentrations in natural settings are often non-equilibrated, thus motivating many experimental studies of CO2 reduction kinetics. A well-established result of such studies is the strong catalytic effect of metallic Feo on the conversion rate of CO2 to alkanes. Because alkanogenetic serpentinization experiments often feature Fe-bearing minerals contained in gold vessels, incidental metallic Feo may precipitate during an experiment as Au-Fe alloy. Such alloy may be catalytic, potentially leading to artificially rapid alkanogenesis and an overestimation of the catalytic strength of nominally nonmetallic Fe-bearing minerals, even if isotopically labeled 13C is used. To evaluate this potential for Au-Fe alloying, a thermodynamic analysis of the effect of oxygen fugacity on Au-Fe mixing has been performed at metamorphic grades relevant to experimental alkanogenesis. The results show that even relatively oxidized metal-free mineral assemblages such as the quartz-fayalite-magnetite buffer (QFM) can stably coexist with an Au-Fe alloy containing a few hundred ppm Fe. Given the strong catalytic effect of metallic Fe, any hydrocarbons generated during a hypothetical experiment containing, for example, the QFM assemblage might be catalyzed by trace Fe in an Au-Fe alloy, not by a QFM mineral. The effect is stronger for assemblages more reducing than QFM, which are notably common in serpentinites. This is a source of experimental uncertainty in reusable flexible gold cell apparatus that cannot be assessed by traditional blank experiments, which only demonstrate the effectiveness of post-run acid-cleaning procedures. A more effective approach would be the chemical analysis of a small, recoverable gold chip embedded into the experimental materials. By assuming that the experimental materials interact identically with the Au chip and with the Au vessel wall, it would be possible to explicitly evaluate whether catalytic Au-Fe alloy formed in situ in a given experiment.

Analysis of Mineral Assemblages Containing Unstable Hydrous Phases

NASA Astrophysics Data System (ADS)

Vaniman, D. T.; Wilson, S. A.; Bish, D. L.; Chipera, S.

2011-12-01

Minerals in many environments can be treated as durable phases that preserve a record of their formation. However many minerals, especially those with hydrogen-bonded H2O molecules as part of their structure, are ephemeral and are unlikely to survive disturbance let alone removal from their environment of formation. Minerals with exceptionally limited stability such as meridianiite (Mg-sulfate 11 hydrate), ikaite (Ca-carbonate 6 hydrate), and mirabilite (Na-sulfate 10 hydrate) are very susceptible to destabilization during analysis, and even modest changes in temperature or relative humidity can lead to change in hydration state or deliquescence. The result may be not only loss of the salt hydrate but dissolution of other salts present, precipitation of new phases, and ion exchange between the concentrated solution and otherwise unaffected phases. Exchange of H2O molecules can also occur in solid-vapor systems without any liquid involvement; moreover, recent work has shown that cation exchange between smectite and sulfate hydrates can occur without any liquid phase present other than a presumed thin film at the salt-silicate interface. Among hydrous silicates, clay minerals are susceptible to cation exchange and similar alteration can be expected for zeolites, palagonite, and possibly other hydrous silicate alteration products. Environmentally sensitive phases on Mars, such as meridianiite, may occur at higher latitudes or in the subsurface where permafrost may be present. Accurate determination of the presence and paragenesis of such minerals will be important for understanding the near-surface hydrogeology of Mars, and in situ analysis may be the only way to obtain this information. Access to the subsurface may be required, yet the act of exposure by excavation or drilling can itself lead to rapid degradation as the sample is exposed or brought to the surface for analysis. Mars is not the only body with which to be concerned, for similar concerns can be raised for sampling cold-environment deposits at the lunar poles, at the poles of Mercury, on icy satellites, and on many other bodies that may host hydrous minerals. The problem of adequate in situ analysis of such mutable assemblages extends to Earth as well, for example in the need for improved understanding of polar and permafrost regions, deep sea clathrates, cave minerals, and mine dump efflorescence. Advanced methods of in situ analysis are needed, including but not limited to contact instruments and instrumentation that can be inserted by probe or operated within a borehole that could be advanced with minimal thermal disturbance. One of the lessons of robotic analysis is that field instruments, which by necessity are less capable than laboratory equivalents, provide greatly improved interpretations if data from several different instruments can be compared.

Gas-path leakage seal for a gas turbine

DOEpatents

Wolfe, C.E.; Dinc, O.S.; Bagepalli, B.S.; Correia, V.H.; Aksit, M.F.

1996-04-23

A gas-path leakage seal is described for generally sealing a gas-path leakage-gap between spaced-apart first and second members of a gas turbine (such as combustor casing segments). The seal includes a generally imperforate foil-layer assemblage which is generally impervious to gas and is located in the leakage-gap. The seal also includes a cloth-layer assemblage generally enclosingly contacting the foil-layer assemblage. In one seal, the first edge of the foil-layer assemblage is left exposed, and the foil-layer assemblage resiliently contacts the first member near the first edge to reduce leakage in the ``plane`` of the cloth-layer assemblage under conditions which include differential thermal growth of the two members. In another seal, such leakage is reduced by having a first weld-bead which permeates the cloth-layer assemblage, is attached to the metal-foil-layer assemblage near the first edge, and unattachedly contacts the first member. 4 figs.

Gas-path leakage seal for a gas turbine

DOEpatents

Wolfe, Christopher E.; Dinc, Osman S.; Bagepalli, Bharat S.; Correia, Victor H.; Aksit, Mahmut F.

1996-01-01

A gas-path leakage seal for generally sealing a gas-path leakage-gap between spaced-apart first and second members of a gas turbine (such as combustor casing segments). The seal includes a generally imperforate foil-layer assemblage which is generally impervious to gas and is located in the leakage-gap. The seal also includes a cloth-layer assemblage generally enclosingly contacting the foil-layer assemblage. In one seal, the first edge of the foil-layer assemblage is left exposed, and the foil-layer assemblage resiliently contacts the first member near the first edge to reduce leakage in the "plane" of the cloth-layer assemblage under conditions which include differential thermal growth of the two members. In another seal, such leakage is reduced by having a first weld-bead which permeates the cloth-layer assemblage, is attached to the metal-foil-layer assemblage near the first edge, and unattachedly contacts the first member.

Geologic map of the Ahankashan-Rakhna basin, Badghis, Ghor, and Herat Provinces, Afghanistan, modified from the 1974 original map compilation of Y.I. Shcherbina and others

USGS Publications Warehouse

Tucker, Robert D.; Stettner, Will R.; Masonic, Linda M.; Bogdanow, Anya K.

2014-01-01

The Ahankashan and Rakhna prospect area is one of several gold and copper deposits within west-central Afghanistan. Here, various felsic to intermediate igneous porphyries intrude Lower Triassic to lower Paleogene sedimentary rocks, producing mineral and ore-bearing zones related to hydrothermal alteration, skarns, silicification, and crushing (brecciation). Mineralized skarns contain assemblages such as magnetite, magnetite-hematite, epidote-hematite, and epidote-garnet, as well as disseminations of chalcopyrite, covellite, chalcocite, cuprite, malachite, and azurite. Gold mineralization is mainly associated with zones of crushing along faults, and with small silicified igneous veins within granite and quartz porphyry.

Quantifying the Complete Mineral Assemblages in Rocks of GUSEV Crater, Mars

NASA Technical Reports Server (NTRS)

McSween, H. Y.; Ruff, S. W.; Morris, R. V.; Gellert, R.

2007-01-01

Determining the complete mineralogy of Mars rocks by remote sensing has remained a challenge, because of inherent limitations in the minerals that can be detected and uncertainties in spectral modeling. A subset of the igneous rocks of Gusev crater provide a unique opportunity to determine modal mineralogy, because of limited alteration and the analytical capabilities of the Athena instrument package. Here we estimate the absolute (wt. %) abundances of Fe-bearing minerals from Moessbauer spectra (previously reported only as "areas for component subspectra"), and compare these results to the normative mineralogy calculated from APXS elemental analyses. We also test our preferred mineralogy by comparison of Mini-TES spectra with synthetic thermal emission spectra.

Hingganite-(Y) from a small aplite vein in granodiorite from Oppach, Lusatian Mts., E-Germany

NASA Astrophysics Data System (ADS)

Thomas, Rainer; Davidson, Paul

2017-12-01

Crystals of hingganite-(Y) occur co-trapped in quartz crystals from miarolitic cavities in an aplite vein in the Cadomian granodiorite from Oppach/Lusatian, Germany. We describe the chemical composition and provide a reference Raman spectrum of this mineral, for which little useful spectral data has been published. In addition, we provide some inferences as to the genesis of this mineral in relationship to melt and fluid inclusions in quartz. The paragenetic sequence of minerals conserved only as small crystal inclusions in quartz, demonstrates an unusual occurrence in the Lusatian aplites, characterized by an unusual, extremely water-rich, near-supercritical melt-fluid system with high concentrations in alkali carbonates and sulfates. We propose that a sulfate-rich system was responsible for the fixation of Be and REE as hingganite-(Y), rather than the more common beryl + REE mineral assemblage. This may provide an explanation for the formation of this otherwise rare mineral

Impact Crater Hydrothermal Niches for Life on Mars: Question of Scale

NASA Technical Reports Server (NTRS)

Pope, K. O.; Ames, D. E.; Kieffer, S. W.; Ocampo, A. C.

2000-01-01

A major focus in the search for fossil life on Mars is on ancient hydrothermal deposits. Nevertheless, remote sensing efforts have not found mineral assemblages characteristic of hydrothermal activity. Future remote sensing work, including missions with higher spatial resolution, may detect localized hydrothermal deposits, but it is possible that dust mantles will prohibit detection from orbit and lander missions will be required. In anticipation of such missions, it is critical to develop a strategy for selecting potential hydrothermal sites on Mars. Such a strategy is being developed for volcanogenic hydrothermal systems, and a similar strategy is needed for impact hydrothermal systems.

Mineralogy and stratigraphy of phyllosilicate-bearing and dark mantling units in the greater Mawrth Vallis/west Arabia Terra area: Constraints on geological origin

USGS Publications Warehouse

Noe Dobrea, E.Z.; Bishop, J.L.; McKeown, N.K.; Fu, R.; Rossi, C.M.; Michalski, J.R.; Heinlein, C.; Hanus, V.; Poulet, F.; Mustard, R.J.F.; Murchie, S.; McEwen, A.S.; Swayze, G.; Bibring, J.-P.; Malaret, E.; Hash, C.

2010-01-01

Analyses of MRO/CRISM images of the greater Mawrth Vallis region of Mars affirm the presence of two primary phyllosilicate assemblages throughout a region ∼1000 × 1000 km. These two units consist of an Fe/Mg-phyllosilicate assemblage overlain by an Al-phyllosilicate and hydrated silica assemblage. The lower unit contains Fe/Mg-smectites, sometimes combined with one or more of these other Fe/Mg-phyllosilicates: serpentine, chlorite, biotite, and/or vermiculite. It is more than 100 m thick and finely layered at meter scales. The upper unit includes Al-smectite, kaolin group minerals, and hydrated silica. It is tens of meters thick and finely layered as well. A common phyllosilicate stratigraphy and morphology is observed throughout the greater region wherever erosional windows are present. This suggests that the geologic processes forming these units must have occurred on at least a regional scale. Sinuous ridges (interpreted to be inverted channels) and narrow channels cut into the upper clay-bearing unit suggesting that aqueous processes were prevalent after, and possibly during, the deposition of the layered units. We propose that layered units may have been deposited at Mawrth Vallis and then subsequently altered to form the hydrated units. The Fe/Mg-phyllosilicate assemblage is consistent with hydrothermal alteration or pedogenesis of mafic to ultramafic rocks. The Al-phyllosilicate/hydrated silica unit may have formed through alteration of felsic material or via leaching of basaltic material through pedogenic alteration or a mildly acidic environment. These phyllosilicate-bearing units are overlain by a darker, relatively unaltered, and indurated material that has probably experienced a complex geological history.

Modelling metamorphism in the Hoosac Schist, Western Massachusetts: new approaches to a New England problem

NASA Astrophysics Data System (ADS)

Bidgood, Anna; Waters, Dave; Gardiner, Nick

2015-04-01

Along the western margin of the metamorphic Appalachians in New England, Taconic (Ordovician) tectonism and metamorphism are overprinted towards the east by Acadian (Devonian) structures and metamorphism. The Hoosac Schist, a probable correlate of the well-known Gassetts Schist of Vermont, lies in the region of overprinting. It forms a narrow N-S-trending tectonically-bound zone crossing several Barrovian mineral-assemblage zones from garnet to kyanite grade. Highly aluminous units containing cm-sized garnets (Cheney & Brady, 1992) are noted for the occurrence of textural unconformities within the garnets, separating inclusion-rich cores from inclusion-poor rims. Matrix domains contain both paragonite and muscovite. Muscovite is present in at least two compositionally distinct generations, with broad later laths cutting across a microfolded earlier fabric. Rutile is restricted to inclusions in garnet, whereas the matrix Ti- phase is ilmenite. These features suggest a polymetamorphic history, potentially recording the superimposition of Acadian metamorphism on Taconic, but it has not yet proved possible to demonstrate the presence of two metamorphic cycles. This study aims to test and employ the new and revised activity models recently developed for metapelites in the full system MnNCKFMASHTO (White et al, 2014), for use with the Holland & Powell data-set 6. Features that can now be more explicitly modelled include garnet zonation in relation to its inclusion suites and microstructural features, the occurrence, texture and distribution of Ti-bearing accessory minerals, and the assemblages and compositional trends in white micas. Preliminary modelling, correlated with microstructural observation, indicates (1) some confirmation of the concern expressed by White et al (2014) that the stability of margarite-bearing assemblages may be somewhat overestimated, (2) that apart from this, the early growth history of garnet is consistent with its suite of trapped inclusions at 8-9 kbar, 500-540°C, (3) that the progression from rutile to ilmenite via an interval of coexistence may be consistent with a single prograde process, and (4) that the marked transition from phengitic to low-Si, high-Na muscovite probably occurred during the growth of the cross-cutting mica generation, but after the growth of ilmenite micropoikiloblasts at the expense of rutile. Cheney, JT & Brady, JB (1992), Petrology of the high-alumina Hoosac Schist from the chloritoid+garnet through the kyanite+biotite zones in western Massachusetts, in: Robinson, P and Brady, JB, editors, Guidebook for Field Trips in the Connecticut Valley Region of Massachusetts and Adjacent States, NEIGC 84th Meeting, Amherst, MA, 332-357. White, RW, Powell, R & Johnson, TE (2014), The effect of Mn on mineral stability in metapelites revisited: new a-x relations for manganese-bearing minerals, Journal of Metamorphic Geology, 32, 809-828.

A Model of the Chicxulub Impact Basin Based on Evaluation of Geophysical Data, Well Logs, and Drill Core Samples

NASA Technical Reports Server (NTRS)

Sharpton, Virgil L.; Marin, Luis E.; Carney, John D.; Lee, Scott; Ryder, Graham; Schuraytz, Benjamin C.; Sikora, Paul; Spudis, Paul D.

1996-01-01

Abundant evidence now shows that the buried Chicxulub structure in northern Yucatan, Mexico, is indeed the intensely sought-after source of the ejecta found world-wide at the Cretaceous-Tertiary (K/T) boundary. In addition to large-scale concentric patterns in gravity and magnetic data over the structure, recent analyses of drill-core samples reveal a lithological assemblage similar to that observed at other terrestrial craters. This assemblage comprises suevite breccias, ejecta deposit breccias (Bunte Breccia equivalents), fine-grained impact melt rocks, and melt-matrix breccias. All these impact-produced lithologies contain diagnostic evidence of shock metamorphism, including planar deformation features in quartz, feldspar, and zircons; diaplectic glasses of quartz and feldspar; and fused mineral melts and whole-rock melts. In addition, elevated concentrations of Ir, Re, and Os, in meteoritic relative proportions, have been detected in some melt-rock samples from the center of the structure. Isotopic analyses, magnetization of melt-rock samples, and local stratigraphic constraints identify this crater as the source of K/T boundary deposits.

Phase equilibria of HP mica schists from the Kamieniec Metamorphic Belt (Sudetes, NE Bohemian Massif)

NASA Astrophysics Data System (ADS)

Szczepanski, Jacek; Golen, Marcin; Anczkiewicz, Robert

2017-04-01

The Kamieniec Metamorphic Belt (KMB), situated in the north-eastern part of the Bohemian Massif, represents the easternmost part of the Variscan Belt of Europe and is interpreted as a fragment of Central Sudetic accretionary wedge containg vestiges of the Saxothuringian crust (Mazur et al., 2015). The KMB comprises a volcano-sedimentary succession dominated by mica schists with intercalations of quartzo-feldspatic schists and subordinate marbles, amphibolites and eclogites. These rocks bear an imprint of Variscan tectonometamorphic reworking. PT conditions of these events were previously estimated at ca. 550 - 590 oC and 7.5 up to 12 kbars (Nowak, 1998; Józefiak, 2000) for mica schists and at 15 kbar and 575 oC for eclogites (Achramowicz et al., 1997). The metamorphic evolution of micaschists comprise the early HP/LT assemblage M1 with Cld+Phe and also earlier reported pseudomorphs after lawsonite (Nowak, 1998) followed by MP/MT mineral assemblage M2 comprising Grt+Pl+Bt+Ms+Qtz±St. Minerals of the M1 and M2 metamorphic events were overprinted by the LP/MT assemblage M3 containing Pl+Chl+Bt+Ms+Qtz±And. Thermodynamic modelling suggests that mineral assemblages record peak-pressure conditions of 20-25 kbar at 520 oC (M1) followed by nearly isothermal decompression to 6-7 kbar, and subsequent metamorphism with record of temperature progression from 500 to 600 oC at 10 kbar (M2) and final retrogression to 3 kbar and 550 oC (M3). The calculated PT conditions indicate a surprisingly low geothermal gradient during the M1 event of 5.5-7.1 oC/km. However, similar eclogitic mica schists with recognised geothermal gradient of ca. 8 oC/km were documented elsewhere from the Saxothuringian domain (Konopásek, 2001). Presented data provides the first report on mica schists from the KMB metamorphosed under eclogite-facies conditions at such low geothermal gradient. Acknowledgements: The study was supported from NCN research grant UMO-2015/17/B/ST10/02212. References Achramowicz, S., Muszynski, A., Schliestedt, M., 1997. The northeasternmost eclogite occurrence in the Saxothuringian Zone, West Sudetes (Poland). Chem. ERDE-Geochem. 57, 51-61. Józefiak, D., 2000. Geothermobarometry in staurolilte-grade mica schists from the southern part of the Niemcza-Kamieniec Metamorphic Complex (Fore-Sudetic Block, SW Poland). Neues Jahrb. Für Mineral. - Abh. 175, 223-248. Konopásek, J., 2001. Eclogitic micaschists in the central part of the Krušné hory Mountains (Bohemian Massif). Eur. J. Mineral. 13, 87-100. Mazur, S., Turniak, K., Szczepański, J., McNaughton, N.J., 2015. Vestiges of Saxothuringian crust in the Central Sudetes, Bohemian Massif: Zircon evidence of a recycled subducted slab provenance. Gondwana Res. Nowak, I., 1998. Polyphase exhumation of eclogite-bearing high-pressure mica schists from the Fore-Sudetic Block, SW Poland. Geol. Sudet. 31, 3-31.

Shock Pressures, Temperatures and Durations in L Chondrites: Constraints from Shock-Vein Mineralogy

NASA Astrophysics Data System (ADS)

Xie, Z.; Aramovish Weaver, C.; Decarli, P. S.; Sharp, T. G.

2003-12-01

Shock effects in meteorites provide a record of major impact events on meteorite parent bodies. Shock veins in chondrites, which result from local melting during shock loading, are the location of all high-pressure minerals. Shock veins contain igneous assemblages, produced by the crystallization of shock-induced melt, and metamorphic assemblages, produced by solid-state transformation in entrained host-rock clasts and wall rock. The mineralogy, distribution of high-pressure minerals and microstructures in shock veins provide a record of crystallization pressures and quench histories that can be used to constrain shock pressures and pulse duration. Here we report mineralogical and microstructural studies of shock-induced melt veins in L chondrites that provide insight into the impact history of the L-chondrite parent body. Eight L6 chondrites were investigated using FESEM and TEM and Raman spectroscopy: RC 106 (S6), Tenham (S6), Umbarger (S4-S6), Roy (S3-S5), Ramsdorf (S4), Kunashak (S4), Nakhon Pathon (S4) and La Lande (S4). Igneous melt-vein assemblages, combined with published phase equilibrium data (Agee et al. 1996), indicate crystallization pressures from less than 2.5 GPa for Kunashack and LaLande to approximately 25 GPa for Tenham. Because shock veins quench primarily by thermal conduction, crystallization starts at vein edges and progresses inward. Variation in the igneous assemblage across shock veins, combined with thermal modelling, provides constraints on quench times and pressure variation during quench. Most samples appear to have crystallized prior to shock release, whereas Kunashack and LaLande apparently crystallized after pressure release. RC 106 and Tenham (both S6), which have thick melt veins with uniform igneous assemblages, crystallized under equilibrium shock pressures of approximately 22-25 GPa during shock events that lasted at least 500 ms and 50ms, respectively. The fact that S6 samples do not appear to have crystallized at a pressures greater than about 25 GPa, suggest that the impacts that produced shock veins in chondrites had low relative impact velocities.

Iron Oxidation Processes During Asteroidal Fluid-Rock Interactions: a Nanoscale Study of Serpentine-bearing Alteration Assemblages in the Murray Meteorite

NASA Astrophysics Data System (ADS)

Elmaleh, A.; Bourdelle, F.; Benzerara, K.; Caste, F.; Leroux, H.; Devouard, B.

2014-12-01

Carbonaceous chondrites of the CM and CI groups contain large amounts of water bound in minerals, attesting to early water-rock interactions on their parent bodies. In CM2 chondrites such as the Murray meteorite the alteration assemblages mostly consist of serpentines with variable chemical compositions. Even though chondritic serpentines formed from anoxic fluids, they contain significant amounts of ferric iron. In order to evaluate mass transfers and redox processes during alteration, we performed a study of a heavily altered calcium-aluminium-rich inclusion (CAI), at the nanometer scale (Transmission Electron Microscopy and Soft x-Ray Scanning Transmission Spectro-Microscopy, on ultra-thin sections prepared by Focused Ion Beam - FIB - milling). Using x-ray absorption spectroscopy at the Fe L2,3-edges, and based on literature references and on measurements of crystallographically oriented FIB foils of cronstedtite (the mixed-valence Fe endmember of serpentine) we estimated over 50% Fe3+ in alteration assemblages. We measured higher ferric iron proportions in mixed Fe,Mg,Al-serpentine/hydroxide disordered phases than in well-crystallized Al,Mg-bearing cronstedtite. We suggest that aqueous Fe2+ was transported to the initially Fe-depleted CAI. There, local changes in pH conditions and / or mineral catalysis would have promoted the partial oxidation of Fe. Later input of Al- and Mg-rich solutions might then have destabilized the initial serpentine, yielding assemblages un-equilibrated from the structural, chemical and redox point of views, similar to the polysomatic assemblages observed in terrestrial hydrothermal systems. Here, we illustrate the usefulness of such a combined study for better understanding the processes of hydration on the parent body of carbonaceous chondrites. Interestingly, as the reactions proposed for the oxidation of Fe generate hydrogen, reduction reactions - involving carbon species, for instance - are expected to follow the ones described here. Alternatively, given the high rate of diffusion of hydrogen some degree of H2 escape may be expected too, which would have induced increasingly oxidizing conditions during aqueous alteration.

Mass change calculations of hydrothermal alterations within the volcanogenic metasediments hosted Cu-Pb (-Zn) mineralization at Halilar area, NW Turkey

NASA Astrophysics Data System (ADS)

Kiran Yildirim, Demet; Abdelnasser, Amr; Doner, Zeynep; Kumral, Mustafa

2016-04-01

The Halilar Cu-Pb (-Zn) mineralization that is formed in the volcanogenic metasediments of Bagcagiz Formation at Balikesir province, NW Turkey, represents locally vein-type deposit as well as restricted to fault gouge zone directed NE-SW along with the lower boundary of Bagcagiz Formation and Duztarla granitic intrusion in the study area. Furthermore, This granite is traversed by numerous mineralized sheeted vein systems, which locally transgress into the surrounding metasediments. Therefore, this mineralization closely associated with intense hydrothermal alteration within brecciation, and quartz stockwork veining. The ore mineral assemblage includes chalcopyrite, galena, and some sphalerite with covellite and goethite formed during three phases of mineralization (pre-ore, main ore, and supergene) within an abundant gangue of quartz and calcite. The geologic and field relationships, petrographic and mineralogical studies reveal two alteration zones occurred with the Cu-Pb (-Zn) mineralization along the contact between the Bagcagiz Formation and Duztarla granite; pervasive phyllic alteration (quartz, sericite, and pyrite), and selective propylitic alteration (albite, calcite, epidote, sericite and/or chlorite). This work, by using the mass balance calculations, reports the mass/volume changes (gain and loss) of the chemical components of the hydrothermal alteration zones associated with Halilar Cu-Pb (-Zn) mineralization at Balikesir area (Turkey). It revealed that the phyllic alteration has enrichments of Si, Fe, K, Ba, and LOI with depletion of Mg, Ca, and Na reflect sericitization of alkali feldspar and destruction of ferromagnesian minerals. This zone has high Cu and Pb with Zn contents represents the main mineralized zone. On the other hand, the propylitic zone is characterized by addition of Ca, Na, K, Ti, P, and Ba with LOI and Cu (lower content) referring to the replacement of plagioclase and ferromagnesian minerals by albite, calcite, epidote, and sericite with chlorite. Keywords: Mass balance calculations; hydrothermal alterations; Cu-Pb (-Zn) mineralization; Halilar area; NW Turkey

Alteration assemblages in the Miller Range and Elephant Moraine regions of Antarctica: Comparisons between terrestrial igneous rocks and Martian meteorites

NASA Astrophysics Data System (ADS)

Hallis, L. J.

2013-02-01

The weathering products present in igneous terrestrial Antarctic samples were analyzed, and compared with those found in the four Miller Range nakhlite Martian meteorites. The aim of these comparisons was to determine which of the alteration phases in the Miller Range nakhlites are produced by terrestrial weathering, and what effect rock composition has on these phases. Antarctic terrestrial samples MIL 05031 and EET 96400, along with the Miller Range nakhlites MIL 03346 and 090032, were found to contain secondary alteration assemblages at their externally exposed surfaces. Despite the difference in primary mineralogy, the assemblages of these rocks consist mostly of sulfates (jarosite in MIL 05031, jarosite and gypsum in EET 96400) and iddingsite-like Fe-clay. As neither of the terrestrial samples contains sulfur-bearing primary minerals, and these minerals are rare in the Miller Range nakhlites, it appears that SO42-, possibly along with some of the Na+, K+, and Ca+ in these phases, was sourced from wind-blown sea spray and biogenic emissions from the southern ocean. Cl enrichment in the terrestrially derived "iddingsite" of MIL 05031 and MIL 03346, and the presence of halite at the exterior edge of MIL 090032, can also be explained by this process. However, jarosite within and around the olivine-bound melt inclusions of MIL 090136 is present in the interior of the meteorite and, therefore, is probably the product of preterrestrial weathering on Mars.

Minearl associated microbial communities from The Cedars, associate with specific geological features

NASA Astrophysics Data System (ADS)

Rowe, A. R.; Wanger, G. P.; Bhartia, R.

2017-12-01

The Cedars, an area of active serpentinization located in the Russian River area of Northern California, represents one of the few terrestrial areas on Earth undergoing active serpentinization. One of the products of the serpentinization reaction is the formation of hydroxyl radicals making the springs of the Cedars some of the most alkaline natural waters on Earth. These waters, with very high pH (pH>11), low EH and, low concentrations of electron acceptors are extremely inhospitible; however microbial life has found a way to thrive and a distinct microbial community is observed in the spring waters. Previous work with environmental samples and pure culture isolates [3] derived from The Cedars has suggested the importance of minearal association to these characteristic microbes. Here we show the results combined spectroscopic and molecular studies on aseries of mineral colonization experiemnts performed with a pure culture Cedar's isolate (Serpentenamonas str. A1) and in situ at CS spring. Centimeter scale, polished coupons of a variety of mminerals were prepared in the lab, spectroscopically characterized (Green Raman, DUV Raman, and DUV Fluorescence maps) and deployed into the springs for three months. The coupons were recovered and the distribution of the microbes on the minerals was mapped using a deep-UV native fluorescent mapping sustem that allows for non-destructive mapping of organics and microbes on surfaces. Subsequently the DNA from the minerals was extracted for community structure analysis. The MOSAIC (i.e. deep UV Fluorescence) showed extensicve colonization of the minerals and in some cases we were able to correlate microbial assemblages with specific geological features. In one example, organisms tended to associate strongly with carbonate features on Chromite mineral surfaces (Figure 1). The 16s rDNA revealed the microbial assemblages from each slide was dominated by active Cedars community memebers (i.e., Serpentinamonas and Silanimonas species), however the relative distribution oc bacterial types varied across mineral type and from the original spring community itself.

A granulometry and secondary mineral fingerprint of chemical weathering in periglacial landscapes and its application to blockfield origins

NASA Astrophysics Data System (ADS)

Goodfellow, Bradley W.

2012-12-01

A review of published literature was undertaken to determine if there was a fingerprint of chemical weathering in regoliths subjected to periglacial conditions during their formation. If present, this fingerprint would be applied to the question of when blockfields in periglacial landscapes were initiated. These blocky diamicts are usually considered to represent remnants of regoliths that were chemically weathered under a warm, Neogene climate and therefore indicate surfaces that have undergone only a few metres to a few 10s of metres of erosion during the Quaternary. Based on a comparison of clay and silt abundances and secondary mineral assemblages from blockfields, other regoliths in periglacial settings, and regoliths from non-periglacial settings, a fingerprint of chemical weathering in periglacial landscapes was identified. A mobile regolith origin under, at least seasonal, periglacial conditions is indicated where clay(%) ≤ 0.5*silt(%) + 8 across a sample batch. This contrasts with a mobile regolith origin under non-periglacial conditions, which is indicated where clay(%) ≥ 0.5*silt(%) - 6 across a sample batch with clay(%) ≥ 0.5*silt(%) + 8 in at least one sample. A range of secondary minerals, which frequently includes interstratified minerals and indicates high local variability in leaching conditions, is also commonly present in regoliths exposed to periglacial conditions during their formation. Clay/silt ratios display a threshold response to temperature, related to the freezing point of water, but there is little response to precipitation or regolith residence time. Lithology controls clay and silt abundances, which increase from felsic, through intermediate, to mafic compositions, but does not control clay/silt ratios. Use of a sedigraph or Coulter Counter to determine regolith granulometry systematically indicates lower clay abundances and intra-site variability than use of a pipette or hydrometer. In contrast to clay/silt ratios, secondary mineral assemblages vary according to regolith residence time, temperature, and/or precipitation. A microsystems model is invoked as a conceptual framework in which to interpret the concurrent formation of the observed secondary mineral ranges. According to the fingerprint of chemical weathering in periglacial landscapes, there is generally no evidence of blockfield origins under warm Neogene climates. Nearly all blockfields appear to be a product of Quaternary physical and chemical weathering. A more dominant role for periglacial processes in further bevelling elevated, low relief, non-glacial surface remnants in otherwise glacially eroded landscapes is therefore indicated.

Coesite-Diamond Assemblage in Ultrahigh Pressure Crustal and Mantle rocks: Evidence for Carbon Recycling

NASA Astrophysics Data System (ADS)

Sobolev, N. V.

2010-12-01

Coesite, a high-pressure polymorph of silica, was first discovered as part of a coesite-eclogite assemblage (coesite, garnet, omphacite) in equilibrium with diamond as diamond inclusion (DI) in Siberian diamond placers (Sobolev et al., 1976, Dokl. Akad. Nauk SSSR, 230: 1442). In recent years, coesite has become a key mineral coexisting with diamond both in kimberlite (DIs) and in UHP metamorphic rocks of the Kokchetav massif, Kazakhstan (diamondiferous gneisses and calcsilicate rocks). In the UHPM rocks of Kokchetav massif, coesite was first detected as inclusions in zircon associated with diamonds (Sobolev et al., 1991, Dokl. Akad. Nauk SSSR, 321: 184), as a result of the initial studies that had identified diamonds as inclusions in garnets and zircons (Sobolev, Shatsky, 1990, Nature, 343: 742). Garnet and omphacitic clinopyroxene are the principal primary minerals associated with coesite and diamond in UHP mantle and crustal rocks. Their compositions plot distinctly within the eclogitic compositional field and substantiate the existence of coesite presence as DIs in eclogitic (E-type) diamonds, as well as sometimes in xenoliths of diamondiferous eclogites (Shatsky et al., 2008, Lithos, 105:289). One of the major significant features of these eclogitic minerals in both UHPM and kimberlitic mantle occurrences is the K2O contents of the clinopyroxenes, reaching 1.6 wt.%, with Na2O and MnO in Ca-Mg-Fe garnets reaching 0.3 and 6.0 wt.%, respectively. Stable isotope data for C in diamonds and O in garnet, pyroxene and coesite have resulted in establishing a very wide range for these isotopes most typical for crustal conditions - i.e., atypical of mantle values. This is clearly shown for coesite DIs (Schulze et al., 2003, Nature, 428:68), garnets from diamondiferous eclogite xenoliths from Siberian kimberlites (Spetsius et al., 2008, Eur. J. Min., 20:375), garnets and clinopyroxenes from UHP calcsilicate diamondiferous rocks of the Kokchetav massif (Sobolev et al., in press, Contr. Min. Petr.). This extensive wide range in δ13C (PDB) for coesite-bearing diamonds, from -28 to +1.5 ‰, along with common crustal δ18O (SMOW) values from the principal rock-forming minerals (garnet and clinopyroxene) and accessory mineral (coesite), is typical for diamondiferous mantle eclogites, crustal UHPM rocks, and DIs. The petrogenetic evidences from all these rocks and minerals are indicative of major subduction of crustal protoliths (Ringwood, 1972, EPSL, 14:233), including the recycling of crustal carbon into diamonds in mantle eclogites, first speculated on by V.S. Sobolev and N.V. Sobolev (1980, Dokl. Akad. Nauk SSSR, 249: 1217).

An eclogite-bearing continental tectonic slice in the Zermatt-Saas high-pressure ophiolites at Trockener Steg (Zermatt, Swiss Western Alps)

NASA Astrophysics Data System (ADS)

Weber, Sebastian; Bucher, Kurt

2015-09-01

The Theodul Glacier Unit (TGU) at "Trockener Steg" represents a continental slice, embedded within the ophiolitic Zermatt-Saas Zone. The Zermatt-Saas Zone is the remnant of the Piemonte-Liguria oceanic lithosphere, formed in the middle Jurassic and subducted up to eclogite facies conditions in the Early Tertiary. The close spatial association of the TGU to the Zermatt-Saas Zone permits a comparison of the metamorphic evolution of the units by detailed field mapping and a petrological investigation of eclogites. The eclogites from both tectono-metamorphic units can be clearly distinguished by their textures, mineral assemblages and by mineral and bulk-rock composition. Geothermobarometry and computed assemblage stability diagrams for the TGU eclogites indicate P-T conditions of 2.2 ± 0.1 GPa and 580 ± 50 °C. These derived P-T conditions must be considered as minimum peak metamorphic conditions the rocks achieved during subduction. The P-T data are different from those derived for eclogites of Zermatt-Saas Zone adjacent to the Theodul Glacier Unit, that reached maximal burial depths at 2.3-2.4 GPa and 500 ± 50 °C. While the estimates of the eclogites of Zermatt-Saas Zone are in good agreement with some of the previous studies, the contrasting P-T estimates for the TGU eclogites suggest that the Zermatt-Saas complex must be subdivided into several tectonic subunits. The non-uniform peak conditions over the "Trockener Steg" area and the maximum pressures conditions reported from ultra-high pressure localities within Zermatt-Saas Zone suggest, that individual tectonic slices have been assembled after detachment from the slab at the return-point, i.e. along the exhumation path. Detached packages of rocks may range from small tectonic slices up to several kilometer-sized fragments. The TGU is separated from the surrounding rocks of the ophiolite unit by two major tectonic contacts. In addition, the formation of biotite-rich crusts along the basal contact of the TGU is evidence of prolonged fluid channeling along the basal thrust. The presence of hydrous decompression assemblages replacing earlier formed high-pressure mineral assemblages within the studied eclogite suggests that fluids were present throughout most of the TGU exhumation history.

Petrography and geochemistry of granitoids from the Samphire Pluton, South Australia: Implications for uranium mineralisation in overlying sediments

NASA Astrophysics Data System (ADS)

Domnick, Urs; Cook, Nigel J.; Bluck, Russel; Brown, Callan; Ciobanu, Cristiana L.

2018-02-01

The Blackbush uranium deposit (JORC Inferred Resource: 12,580 tonnes U), located on the north-eastern Eyre Peninsula, is currently the only sediment-hosted U deposit investigated in detail in the Gawler Craton. Uranium is hosted within Eocene sandstone of the Kanaka Beds, overlying Mesoproterozoic granites of the Samphire pluton, affiliated with the Hiltaba Intrusive Suite ( 1.6 Ga). These are considered the most probable source rocks for uranium mineralisation. By constraining the petrography and mineralogy of the granites, insights into the post-emplacement evolution can be gained, which may provide an exploration indicator for other sediment-hosted uranium systems. Three geochemically distinct granite types were identified in the Samphire Pluton and correspond to domains interpreted from geophysical data. All granites show complex alteration overprints and textures with increasing intensity closer to the deposit, as well as crosscutting veining. Alkali feldspar has been replaced by porous K-feldspar and albite, and plagioclase is overprinted by an assemblage of porous albite + sericite ± calc-silicates (prehnite, pumpellyite and epidote). This style of feldspar alteration is regionally widespread and known from Hiltaba-aged granites associated with iron-oxide copper-gold mineralisation at Olympic Dam and in the Moonta-Wallaroo region. In two granite types biotite is replaced by calcic garnet. Calc-silicates are indicative of Ca-metasomatism, sourced from the anorthite component of altered plagioclase. Minor clay alteration of feldspars is present in all samples. Mineral assemblages in veins include quartz + hematite, hematite + coffinite, fluorite + quartz, and clay minerals. Minor chlorite and sericite are found in all vein types. All granite types are anomalously rich in U (concentrations between 10 and 81 ppm). Highly variable Th/U ratios, as well as hydrothermal U minerals (mostly coffinite) in granites and veins, are clear evidence for U mobility. Uranium may have been preconcentrated in veins in the upper parts of the pluton, and was subsequently leached after deposition of the sediment.

Relationship between dissolved organic matter quality and microbial community composition across polar glacial environments.

PubMed

Smith, H J; Dieser, M; McKnight, D M; SanClements, M D; Foreman, C M

2018-05-14

Vast expanses of Earth's surface are covered by ice, with microorganisms in these systems affecting local and global biogeochemical cycles. We examined microbial assemblages from habitats fed by glacial meltwater within the McMurdo Dry Valleys, Antarctica, and on the west Greenland Ice Sheet, (GrIS) evaluating potential physicochemical factors explaining trends in community structure. Microbial assemblages present in the different Antarctic dry valley habitats were dominated by Sphingobacteria and Flavobacteria, while Gammaproteobacteria and Sphingobacteria prevailed in west GrIS supraglacial environments. Microbial assemblages clustered by location (Canada Glacier, Cotton Glacier, west GrIS) and were separated by habitat type (i.e. ice, cryoconite holes, supraglacial lakes, sediment, and stream water). Community dissimilarities were strongly correlated with dissolved organic matter (DOM) quality. Microbial meltwater assemblages were most closely associated with different protein-like components of the DOM pool. Microbes in environments with mineral particles (i.e. stream sediments, cryoconite holes) were linked to DOM containing more humic-like fluorescence. Our results demonstrate the establishment of distinct microbial communities within ephemeral glacial meltwater habitats, with DOM-microbe interactions playing an integral role in shaping communities on local and polar spatial scales.

Subglacial hydrothermal alteration minerals in Jökulhlaup deposits of Southern Iceland, with implications for detecting past or present habitable environments on Mars.

PubMed

Warner, Nicholas H; Farmer, Jack D

2010-06-01

Jökulhlaups are terrestrial catastrophic outfloods, often triggered by subglacial volcanic eruptions. Similar volcano-ice interactions were likely important on Mars where magma/lava may have interacted with the planet's cryosphere to produce catastrophic floods. As a potential analogue to sediments deposited during martian floods, the Holocene sandurs of Iceland are dominated by basaltic clasts derived from the subglacial environment and deposited during jökulhlaups. Palagonite tuffs and breccias, present within the deposits, represent the primary alteration lithology. The surface abundance of palagonite on the sandurs is 1-20%. X-ray diffraction (XRD) analysis of palagonite breccias confirms a mineral assemblage of zeolites, smectites, low-quartz, and kaolinite. Oriented powder X-ray diffractograms (< 2 microm fraction) for palagonite breccia clasts and coatings reveal randomly ordered smectite, mixed layer smectite/illite, zeolites, and quartz. Visible light-near infrared (VNIR) and shortwave infrared (SWIR) lab spectroscopic data of the same palagonite samples show H2O/OH(-) absorptions associated with clays and zeolites. SWIR spectra derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images of the sandurs reveal Al-OH(-) and Si-OH(-) absorption features. The identified alteration mineral assemblage is consistent with low temperature (100-140 degrees C) hydrothermal alteration of basaltic material within the subglacial environment. These results suggest that potential martian analog sites that contain a similar suite of hydrated minerals may be indicative of past hydrothermal activity and locations where past habitable environments for microbial life may be found.

Sand dunes on the central Delmarva Peninsula, Maryland and Delaware

USGS Publications Warehouse

Denny, Charles Storrow; Owens, James Patrick

1979-01-01

Inconspicuous ancient sand dunes are present in parts of the central Delmarva Peninsula, Maryland and Delaware. Many dunes are roughly V-shaped, built by northwest winds, especially on the east sides of some of the large rivers. On the uplands, the form and spacing of the dunes are variable. A surficial blanket composed mainly of medium and fine-grained sand-the Parsonsburg Sand-forms both the ancient dunes and the broad plains between the dunes. The sand that forms the dunes is massive and intensely burrowed in the upper part; traces of horizontal or slightly inclined bedding appear near the base. Quartz is the dominant mineral constituent of the sand. Microline is abundant in the very fine to fine sand fraction. The heavy-mineral assemblages (high zircon, tourmaline, rutile) are more mature than in most of the possible source rocks. The most abundant minerals in the clay-sized fraction are dioctahedral vermiculite, kaolinite, illite, montmorillonite, and gibbsite. The first four minerals are common in deposits of late Wisconsin and Holocene age. The gibbsite may be detrital, coming from weathered rocks of Tertiary age. The soil profile in the dune sand is weakly to moderately developed. At or near the base of the Parsonsburg Sand are peaty beds that range in age from about 30,000 to about 13,000 radiocarbon years B.P. Microfloral assemblages in the peaty beds suggest that the dunes on the uplands formed in a spruce parkland during the late Wisconsin glacial maximum. The river dunes may also be of late Wisconsin age, but could be Holocene.

Local variation of inundation, sedimentary characteristics, and mineral assemblages of the 2011 Tohoku-oki tsunami on the Misawa coast, Aomori, Japan

NASA Astrophysics Data System (ADS)

Nakamura, Yugo; Nishimura, Yuichi; Putra, Purna Sulastya

2012-12-01

The 2011 Tohoku-oki tsunami caused severe damage to the coastal regions of eastern Japan and left a sediment veneer over affected areas. We discuss differences in depositional characteristics of the 2011 Tohoku-oki tsunami from the viewpoint of the sediment source, coastal topography and flow height. The study area on the Misawa coast, northern Tohoku, includes a 20 km long coastline with sandy beaches, coastal dunes and a gently sloping lowland. This landscape assemblage provides an opportunity to examine the effects of topography on the characteristics of the tsunami deposit. During field surveys conducted from April 10 to May 2, 2011, we described the thickness, facies, and structure of the tsunami deposit. We also collected sand samples at approximately 20 m intervals along 13 shore-perpendicular transects extending up to 550 m inland, for grain size and mineral assemblage analysis. The tsunami flow height was estimated by measuring the elevation of debris found in trees, broken tree limbs, or water marks on buildings. The nature of the coastal lowland affected the flow height and inundation distance. In the southern part of the study area, where there is a narrow, 100 m wide low-lying coastal strip, the run-up height reached 10 m on the landward terrace slopes. To the north, the maximum inundation reached 550 m with a run-up height of 3.2 m on the wider, low-lying coastal topography. The average flow height was 4-5 m. The tsunami eroded coastal dunes and formed small scarps along the coast. Immediately landward of the coastal dunes the tsunami deposit was more than 20 cm thick, but thinned markedly inland from this point. Close to the dunes the deposit was composed largely of medium sand (1-2 Φ) with planar and parallel bedding, but with no apparent upward fining or coarsening. The grain size was similar to that of the coastal dune and we infer that the dunes were the local source material for the tsunami deposit at this point. The mineral assemblage of the tsunami deposit was dominated by orthopyroxene and clinopyroxene and was also similar to the dune and beach sand. At sites more than half the inundation distance inland, the thinner tsunami deposit consisted mainly of fine sand (2.375 Φ) with some upward fining. The difference in grain size and sedimentary characteristics was probably caused by differences in sediment transportation and depositional processes. We infer that the well-sorted, finer sediments were deposited out of suspension, whereas the relatively coarse sands were laid down from traction flows. The depositional characteristics of the 2011 Tohoku-oki tsunami deposit appeared to have been affected mainly by the coastal topography and the extent of erosion at any one point, as opposed to flow height.

Mineralogy of Nicobar Fan turbidites (IODP Leg 362): Himalayan provenance and diagenetic control.

NASA Astrophysics Data System (ADS)

Limonta, M.; Garzanti, E.; Ando, S.; Carter, A.; Milliken, K. L.; Pickering, K. T.

2017-12-01

In this study we use quantitative petrographic and heavy-mineral data on silt-sized and sand-sized sediments from the Nicobar Fan turbiditic depositional system to unravel their provenance and discriminate between pre-depositional and post-depositional processes controlling sediment mineralogy. Eighteen samples from the two drill sites U1480 e U1481, collected down to a depth of 1400 m during International Ocean Discovery Expedition 362, were selected for analysis. A complete section of the sedimentary section overlying oceanic basaltic basement was recovered at the U1480 drill site, whereas the U1481 drill site, located 35 km to the southeast, focused on the deeper interval of the sedimentary section overlying oceanic basement. Here we illustrate the compositional trends observed throughout the recovered succession, and compare heavy-mineral suites characterizing sediments drilled at the two U1480 and U1481 sites to check for potential differences in sediment provenance over a relatively short distance in trench settings. Diagenetic control with increasing burial depth was also specifically investigated. In Pleistocene sediments at depths of a few tens of meters only, rich heavy-mineral assemblages include mainly hornblende, epidote, and garnet, associated with apatite, clinopyroxene, tourmaline, sillimanite, kyanite, zircon, titanite, and rare staurolite and rutile, testifying to long-distance provenance from the Himalayan range via the Ganga-Brahmaputra fluvio-deltaic-turbiditic system. Heavy-mineral concentration shows a progressive decrease with burial depth, pointing to selective diagenetic dissolution of less durable detrital minerals. Clinopyroxene becomes rare below 400 m depth and was not recorded below 500 m depth, where amphibole decreases notably in relative abundance. More durable heavy minerals, including zircon, tourmaline, apatite, garnet and epidote, consequently tend to be relatively enriched with increasing age and burial depth. Petrographic and heavy-mineral data, combined with biostratigraphic, paleomagnetic, and geochemical evidence, allow us to unravel the sedimentary history of the Nicobar Fan as related to Himalayan uplift, erosion, and monsoon development during the last 10 Ma.

Structural and metamorphic evolution of serpentinites and rodingites recycled in the Alpine subduction wedge

NASA Astrophysics Data System (ADS)

Zanoni, D.; Rebay, G.; Spalla, M. I.

2015-12-01

Hydration-dehydration of mantle rocks affects the viscosity of the mantle wedge and plays a prominent role in subduction zone tectonics, facilitating marble cake-type instead of large-slice dynamics. An accurate structural and petrologic investigation of serpentinites from orogenic belts, supported by their long-lived structural memory, can help to recognize pressure-sensitive mineral assemblages for deciphering their P-prograde and -retrograde tectonic trajectories. The European Alps preserve large volumes of the hydrated upper part of the oceanic lithosphere that represents the main water carrier into the Alpine subduction zone. Therefore, it is important to understand what happens during subduction when these rocks reach P-T conditions proximal to those that trigger the break-down of serpentine, formed during oceanic metamorphism, to produce olivine and clinopyroxene. Rodingites associated with serpentinites are usually derived from metasomatic ocean floor processes but rodingitization can also happen in subduction environments. Multiscale structural and petrologic analyses of serpentinites and enclosed rodingites have been combined to define the HP mineral assemblages in the Zermatt-Saas ophiolites. They record 3 syn-metamorphic stages of ductile deformation during the Alpine cycle, following the ocean floor history that is testified by structural and metamorphic relics in both rock types. D1 and D2 developed under HP to UHP conditions and D3 under lower P conditions. Syn-D2 assemblages in serpentinites and rodingites indicate conditions of 2.5 ± 0.3 GPa and 600 ± 20°C. This interdisciplinary approach shows that the dominant structural and metamorphic imprint of the Zermatt-Saas eclogitized serpentinites and rodingites developed during the Alpine subduction and that subduction-related serpentinite de-hydration occurred exclusively at Pmax conditions, during D2 deformation. In contrast, in the favourable rodingite bulk composition (Ca-rich), hydrated minerals such as vesuvianite are stable up to the estimated P-climax conditions.

Using MicroFTIR to Map Mineral Distributions in Serpentinizing Systems

NASA Astrophysics Data System (ADS)

Johnson, A.; Kubo, M. D.; Cardace, D.

2016-12-01

Serpentinization, the water-rock reaction forming serpentine mineral assemblages from ultramafic precursors, can co-occur with the production of hydrogen, methane, and diverse organic compounds (McCollom and Seewald, 2013), evolving water appropriate for carbonate precipitation, including in ophiolite groundwater flow systems and travertine-producing seeps/springs. Serpentinization is regarded as a geologic process important to the sustainability of the deep biosphere (Schrenk et al., 2013) and the origin of life (Schulte et al., 2006). In this study, we manually polished wafers of ultramafic rocks/associated minerals (serpentinite, peridotite, pyroxenite, dunite; olivine, diopside, serpentine, magnetite), and travertine/constituent minerals (carbonate crusts; calcite, dolomite), and observed mineral boundaries and interfaces using µFTIR analysis in reflection mode. We used a Thermo Nicolet iS50 FTIR spectrometer coupled with a Continuum IR microscope to map minerals/boundaries. We identify, confirm, and document FTIR wavenumber regions linked to serpentinite- and travertine-associated minerals by referencing IR spectra (RRUFF) and aligning with x-ray diffraction. The ultramafic and carbonate samples are from the following field localities: McLaughlin Natural Reserve - a UC research reserve, Lower Lake, CA; Zambales, PH; Ontario, CA; Yellow Dog, MI; Taskesti, TK; Twin Sisters Range, WA; Sharon, MA; Klamath Mountains, CA; Dun Mountain, NZ; and Sussex County, NJ. Our goals are to provide comprehensive µFTIR characterization of mineral profiles important in serpentinites and related rocks, and evaluate the resolving power of µFTIR for the detection of mineral-encapsulated, residual organic compounds from biological activity. We report on µFTIR data for naturally occurring ultramafics and travertines and also estimate the limit of detection for cell membrane components in mineral matrices, impregnating increasing mass proportions of xanthan gum in a peridotite sand derived from drilling at the Coast Range Ophiolite Microbial Observatory (CROMO, Cardace et al., 2013). Preservation and well resolved description of organic compounds in secondary minerals in ultramafic rocks may allow assessment of changing habitability of past microenvironments fueled by serpentinization.

First Radiological Study of a Complete Dental Ontogeny Sequence of an Extinct Equid: Implications for Equidae Life History and Taphonomy.

PubMed

Domingo, M Soledad; Cantero, Enrique; García-Real, Isabel; Chamorro Sancho, Manuel J; Martín Perea, David M; Alberdi, M Teresa; Morales, Jorge

2018-05-31

The sequence of cheek teeth mineralization, eruption, and replacement of an extinct horse species is here documented with radiological techniques for the first time thanks to the exceptional preservation of Hipparion sp. mandibles from Cerro de los Batallones (Madrid Basin, Spain). The sequence of dental ontogeny in mammals provides valuable insights about life history traits, such as the pace of growth, and about the mode of formation of fossiliferous assemblages. We have determined that the order of permanent cheek teeth mineralization and eruption of hipparionine horses is m1, m2, (p2, p3), p4, m3. Cheek teeth mineralization timing of hipparionine horses coincides with the one observed in modern equids. In turn, there are differences in the eruption timing of the p4 and m3 between horses belonging to the Anchitheriinae and Hipparionini compared to equids of the Equus genus that might be related to the shorter durability of the deciduous tooth dp4 in anchitheriine and hipparionine horses and, more broadly, to an increased durability of equid teeth through their evolutionary history. Based on the dental eruption sequence, hipparionine horses are slow-growing, long-living mammals. The Hipparion sp. assemblage from Batallones-10 conforms to an attritional model, as individuals more vulnerable to natural mortality predominate.

Deposition conditions and distribution features of native gold individuals in the veins of the Tokur mesothermal deposit, Russia

NASA Astrophysics Data System (ADS)

Ostapenko, N. S.; Neroda, O. N.

2016-05-01

The paper discusses factors in the deposition and concentration of native gold and the spatial distribution of its individuals within the sufide-poor gold-quartz veins at the mesoabyssal Tokur deposit. The major factors in deposition of gold were sealing of the hydrothermal system, a sudden drop in fluid pressure, and repeated immiscibility in the fluid. Native gold was deposited in relation to initial acts of prolonged and discrete opening and preopening of cavities in three mineral assemblages of the productive association II. Most native gold individuals with a visible size of 0.1-1.5 mm were together with the early generation of quartz 2 on cavity walls adjacent to altered rocks. This is caused by the high content of Au complexes in initial hydrothermal solutions favoring rapid oversaturation during cavity formation. Gold fills interstices between grains of quartz 2 throughout the deposit and mineral assemblages. The vertical-flow distribution of gold has been established in economic veins; the upper and middle levels are enriched in gold, and samples with the greatest gold grade of 100-500 g/t or higher are concentrated there. This is caused both by the predominance of mineral association II at these levels and probable natural flotation of gold grains contained in the gold-gas associate for immiscibility of the hydrothermal fluid at the second stage of the ore-forming process.

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.

Study of Deformation Bands in Ignimbrites in Shihtiping, Eastern Taiwan

NASA Astrophysics Data System (ADS)

Lin, S. T.; Huang, W. J.

2014-12-01

Shihtiping is located at the coast of eastern Taiwan, where rocks are the products of subaerial eruption by Chimei Volcano in late Miocene. The major lithology is ignimbrite along with pyroclasts in various sizes. Deformation bands ubiquitously appear in such loose, high-porosity, rocks. This study aims at documenting the occurrence of the deformation bands, understanding their formation mechanism and discussing their tectonic implications. There are two sets of deformation bands with orientations of N60°~80°E and N50°~70°W, respectively, in Shihtiping. The dip angles of both range from 70° to 90°. Commonly, the deformation bands are exposed as single trace or braided trace composed of several individuals. They can be traced easily because they are protruding owning to more weathering-resistant than the host rock. Thickness and separation of single deformation band are in the order of millimeter and millimeter to centimeter, respectively. Thickness of zone of deformation band ranges from few mm to tens of cm and total separation is commonly tens of cm. Based on microscopic examination, mineral assemblages in deformation bands usually include plagioclase, hornblende and augite. Although mineral assemblages are the same as host rock, clasts in deformation bands are rounder and smaller. Thus, it results in closed packing and porosity reduction within deformation bands. Summed up the observations, the deformation bands in Shihtiping were formed by cataclasis and can be classified as cataclastic band. They may reflect the regional paelostress state but not accompanied with any tectonic fault.

Syn- and post-sedimentary controls on clay mineral assemblages in a tectonically active basin, Andean Argentinean foreland

NASA Astrophysics Data System (ADS)

Do Campo, Margarita; Nieto, Fernando; del Papa, Cecilia; Hongn, Fernando

2014-07-01

In the northern part of the Calchaquí Valley (NW Argentina), Palaeogene Andean foreland sediments are represented by a 1400-metre-thick continental succession (QLC: Quebrada de Los Colorados Formation) consisting of claystones, siltstones, sandstones, and conglomerates representing sedimentation in fluvial-alluvial plains and alluvial fan settings. To understand the main syn- and postsedimentary variables controlling the clay mineral assemblages of this succession, we have studied the fine-grained clastic sediments by X-ray diffraction and electron microscopy, along with a detailed sedimentary facies analysis, for two representative sections. In the northern section, the whole succession was sampled and analysed by XRD, whereas in the second section, a control point 15 km to the south, only the basal levels were analysed. The XRD study revealed a strong contrast in clay mineral assemblages between these two sections as well as with sections in the central Calchaquí Valley studied previously. In the northernmost part of the study area, a complete evolution from smectite at the top to R3 illite/smectite mixed-layers plus authigenic kaolinite at the bottom, through R1-type mixed-layers in between, has been recognized, indicating the attainment of late diagenesis. In contrast, the clay mineral assemblages of equivalent foreland sediments cropping out only 15 km to the south contain abundant smectite and micas, subordinate kaolinite and chlorite, and no I/S mixed-layers to the bottom of the sequence. Early diagenetic conditions were also inferred in a previous study for equivalent sediments of the QLC Formation cropping out to the south, in the central Calchaquí Valley, as smectite occurs in basal strata. Burial depths of approximately 3000 m were estimated for the QLC Formation in the central and northern Calchaquí Valley; in addition, an intermediate to slightly low geothermal gradient can be considered likely for both areas as foreland basins are regarded as hypothermal basins. Consequently, the attainment of late diagenesis in the northernmost study area cannot be explained by significant differences in burial depth nor in geothermal gradient in relation to the section 15 km to the south nor with the central Calchaquí Valley. The formation of R3 mixed-layer I/S and authigenic kaolinite in the northern study area was most likely controlled by the circulation of hot, deep fluids along the reverse faults that bounded the Calchaquí valley. These faults were active during the Cenozoic, as evidenced by the syndepositional deformation features preserved in the studied sediments. Stress could also have been a driving force in burial diagenesis at the R3 mixed-layer I/S stage in these young continental sediments.

Calc-silicate mineralization in active geothermal systems

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

Bird, D.K.; Schiffman, P.; Elders, W.A.

The detailed study of calc-silicate mineral zones and coexisting phase relations in the Cerro Prieto geothermal system were used as examples for thermodynamic evaluation of phase relations among minerals of variable composition and to calculate the chemical characteristics of hydrothermal solutions compatible with the observed calc-silicate assemblages. In general there is a close correlation between calculated and observed fluid compositions. Calculated fugacities of O{sub 2} at about 320{degrees}C in the Cerro Prieto geothermal system are about five orders of magnitude less than that at the nearby Salton Sea geothermal system. This observation is consistent with the occurrence of Fe{sup 3+}more » rich epidotes in the latter system and the presence of prehnite at Cerro Prieto.« less

Bacterial diversity patterns of the intertidal biofilm in urban beaches of Río de la Plata.

PubMed

Piccini, C; García-Alonso, J

2015-02-28

Intertidal benthic ecosystems in estuaries are productive sites where microbial processes play critical roles in nutrients mineralization, primary production and trophic web. In this groundwork study we analyzed the bacterial community of intertidal biofilms from Río de la Plata beaches with different anthropogenic impacts. Several environmental parameters were measured and bacterial assemblages were analyzed by 16S-rDNA pyrosequencing. The average OTU found per sample was 527.3±122.5, showing similar richness and diversity among them. However, sites having the highest and lowest salinity displayed higher bacterial diversity. Assemblages from a site nearby an oil refinery, showing the lowest salinity and oxygen concentration, were clearly distinct from the rest. The weight of this splitting relied on OTUs belonging to Thauera, known by its ability to metabolize aromatic compounds. Our results suggest that intertidal bacterial assemblages would be structured by major estuarine variables such as salinity, and that anthropogenic-induced environmental parameters might also be relevant. Copyright © 2014 Elsevier Ltd. All rights reserved.

Chemistry and petrography of calcite in the KTB pilot borehole, Bavarian Oberpfalz, Germany

USGS Publications Warehouse

Komor, S.C.

1995-01-01

The KTB pilot borehole in northeast Bavaria, Germany, penetrates 4000 m of gneiss, amphibolite, and subordinate calc-silicate, lamprophyre and metagabbro. There are three types of calcite in the drilled section: 1) metamorphic calcite in calc-silicate and marble; 2) crack-filling calcite in all lithologies; and 3) replacement calcite in altered minerals. Crack-filling and replacement calcite postdate metamorphic calcite. Multiple calcite generations in individual cracks suggest that different generations of water repeatedly flowed through the same cracks. Crack-filling mineral assemblages that include calcite originally formed at temperatures of 150-350??C. Presently, crack-filling calcite is in chemical and isotopic equilibrium with saline to brackish water in the borehole at temperatures of ???120??C. The saline to brackish water contains a significant proportion of meteoric water. Re-equilibration of crack-filling calcite to lower temperatures means that calcite chemistry tells us little about water-rock interactions in the crystal section of temperatures higher than ~120??C. -from Author

The response of vegetation to geochemical conditions

NASA Technical Reports Server (NTRS)

Mouat, D. A.

1983-01-01

An understanding of the factors of vegetation response to changes in the geochemistry of the environment may give exploration geologists and other researchers an additional and effective tool for rock type discrimination. The factors of vegetation response can be grouped into three principal categories: structural or morphological factors, taxonomic factors which include indicator flora as well as vegetation assemblages, and spectral factors which represent the manner in which the vegetation interacts with electromagnetic radiation. The response of these factors over areas of anomalous mineralization is often unique and may be due to nutrient deficiencies and/or imbalances, toxicity and stress caused by anomalous mineral concentrations in the soil, low water retention, and plant competition. The successful use of geobotanical techniques results from the integration of the geobotanical observations with other techniques. The use of remote sensing in such a program must be predicated on those factors which can be discriminated within the constraints of the spatial, spectral, radiometric, and temporal resolutions of the sensing system and with appropriate analytical techniques.

Metal endowment reflected in chemical composition of silicates and sulfides of mineralized porphyry copper systems, Urumieh-Dokhtar magmatic arc, Iran

NASA Astrophysics Data System (ADS)

Zarasvandi, Alireza; Rezaei, Mohsen; Raith, Johann G.; Pourkaseb, Houshang; Asadi, Sina; Saed, Madineh; Lentz, David R.

2018-02-01

The present work attempts to discriminate between the geochemical features of magmatic-hydrothermal systems involved in the early stages of mineralization in high grade versus low grade porphyry copper systems, using chemical compositions of silicate and sulfide minerals (i.e., plagioclase, biotite, pyrite and chalcopyrite). The data indicate that magmatic plagioclase in all of the porphyry copper systems studied here has high An% and Al content with a significant trend of evolution toward AlAl3SiO8 and □Si4O8 endmembers, providing insight into the high melt water contents of the parental magmas. Comparably, excess Al and An% in the high grade deposits appears to be higher than that of selected low grade deposits, representing a direct link between the amounts of exsolving hydrothermal fluids and the potential of metal endowment in porphyry copper deposits (PCDs). Also, higher Al contents accompanied by elevated An% are linked to the increasing intensity of disruptive alteration (phyllic) in feldspars from the high grade deposits. As calculated from biotite compositions, chloride contents are higher in the exsolving hydrothermal fluids that contributed to the early mineralization stages of highly mineralized porphyry systems. However, as evidenced by scattered and elevated log (fH2O)/(fHF) and log (fH2O)/(fHCl) values, chloride contents recorded in biotite could be influenced by post potassic fluids. Geothermometry of biotite associated with the onset of sulfide mineralization indicates that there is a trend of increasing temperature from high grade to low grade porphyry systems. Significantly, this is coupled with a sharp change in copper content of pyrite assemblages precipitated at the early stages of mineralization such that Cu decreased with increasing temperature. Based on EMPA and detailed WDS elemental mapping, trace elements do not exhibit complex compositional zoning or solid solution in the sulfide structure. Nevertheless, significant amounts of Cu and Au are contained in pyrite assemblages as micro- to nano-sized inclusions, especially in the high grade fertile porphyry deposits. However, unexpectedly high concentrations of Te, Se, and Re may be associated with early stage of sulfide mineralization, especially when there is no epithermal lithocap. This may highlight the significance of trace metals partitioning in the sulfides formed at the early stages of mineralization in PCDs.

Biologically agglutinated eukaryotic microfossil from Cryogenian cap carbonates.

PubMed

Moore, K R; Bosak, T; Macdonald, F A; Lahr, D J G; Newman, S; Settens, C; Pruss, S B

2017-07-01

Cryogenian cap carbonates that overlie Sturtian glacial deposits were formed during a post-glacial transgression. Here, we describe microfossils from the Kakontwe Formation of Zambia and the Taishir Formation of Mongolia-both Cryogenian age, post-Sturtian cap carbonates-and investigate processes involved in their formation and preservation. We compare microfossils from these two localities to an assemblage of well-documented microfossils previously described in the post-Sturtian Rasthof Formation of Namibia. Microfossils from both new localities have 10 ± 1 μm-thick walls composed of carbonaceous matter and aluminosilicate minerals. Those found in the Kakontwe Formation are spherical or ovoid and 90 ± 5 μm to 200 ± 5 μm wide. Structures found in the Taishir Formation are mostly spherical, 50 ± 5 μm to 140 ± 5 μm wide, with distinct features such as blunt or concave edges. Chemical and mineralogical analyses show that the walled structures and the clay fraction extracted from the surrounding sediments are composed of clay minerals, especially muscovite and illite, as well as quartz, iron and titanium oxides, and some dolomite and feldspar. At each locality, the mineralogy of the microfossil walls matched that of the clay fractions of the surrounding sediment. The abundance of these minerals in the walled microfossils relative to the surrounding carbonate matrix and microbial laminae, and the presence of minerals that cannot precipitate from solution (titanium oxide and feldspar), suggests that the composition represents the original mineralogy of the structures. Furthermore, the consistency in mineralogy of both microfossils and sediments across the three basins, and the uniformity of size and shape among mineral grains in the fossil walls indicate that these organisms incorporated these minerals by primary biological agglutination. The discovery of new, mineral-rich microfossil assemblages in microbially laminated and other fine-grained facies of Cryogenian cap carbonates from multiple localities on different palaeocontinents demonstrates that agglutinating eukaryotes were widespread in carbonate-dominated marine environments in the aftermath of the Sturtian glaciation. © 2017 John Wiley & Sons Ltd.

Inclusions of crichtonite-group minerals in Cr-pyropes from the Internatsionalnaya kimberlite pipe, Siberian Craton: Crystal chemistry, parageneses and relationships to mantle metasomatism

NASA Astrophysics Data System (ADS)

Rezvukhin, Dmitriy I.; Malkovets, Vladimir G.; Sharygin, Igor S.; Tretiakova, Irina G.; Griffin, William L.; O'Reilly, Suzanne Y.

2018-05-01

Cr-pyrope xenocrysts and associated inclusions of crichtonite-group minerals from the Internatsionalnaya kimberlite pipe were studied to provide new insights into processes in the lithospheric mantle beneath the Mirny kimberlite field, Siberian craton. Pyropes are predominantly of lherzolitic paragenesis (Cr2O3 2-6 wt%) and have trace-element spectra typical for garnets from fertile mantle (gradual increase in chondrite-normalized values from LREE to MREE-HREE). Crichtonite-group minerals commonly occur as monomineralic elongated inclusions, mostly in association with rutile, Mg-ilmenite and Cr-spinel within individual grains of pyrope. Sample INT-266 hosts intergrowth of crichtonite-group mineral and Cl-apatite, while sample INT-324 contains polymineralic apatite- and dolomite-bearing assemblages. Crichtonite-group minerals are Al-rich (1.1-4.5 wt% Al2O3), moderately Zr-enriched (1.3-4.3 wt% ZrO2), and are Ca-, Sr-, and occasionally Ba-dominant in terms of A-site occupancy; they also contain significant amounts of Na and LREE. T-estimates and chemical composition of Cr-pyropes imply that samples represent relatively low-T peridotite assemblages with ambient T ranging from 720 to 820°С. Projected onto the 35 mW/m2 cratonic paleogeotherm for the Mirny kimberlite field (Griffin et al., 1999b. Tectonophysics 310, 1-35), temperature estimates yield a P range of 34-42 kbar ( 110-130 km), which corresponds to a mantle domain in the uppermost part of the diamond stability field. The presence of crichtonite-group minerals in Cr-pyropes has petrological and geochemical implications as evidence for metasomatic enrichment of some incompatible elements in the lithospheric mantle beneath the Mirny kimberlite field. The genesis of Cr-pyropes with inclusions of crichtonite-group minerals is attributed to the percolation of Ca-Sr-Na-LREE-Zr-bearing carbonate-silicate metasomatic agents through Mg- and Cr-rich depleted peridotite protoliths. The findings of several potentially new members of the crichtonite group as inclusions in garnet extend existing knowledge on the compositions and occurrences of exotic titanates stable in the lithospheric mantle.

Magnetic Mineral diagenesis in changing water environments in the Black Sea since ˜41.6 ka

NASA Astrophysics Data System (ADS)

Liu, Jiabo; Nowaczyk, Norbert; Frank, Ute; Arz, Helge

2017-04-01

Magnetic mineral diagenesis plays a key role in the global iron cycle. To understand the authigenic magnetic mineral formation by diagenesis is also fundamentally important for the interpretation of environmental magnetic as well as paleomagnetic signals. Core MSM33-55-1, recovered from the SW Black Sea, was subjected to rock-magnetic and SEM studies. The results demonstrate that four different magnetic mineral assemblages associated to specific water conditions can be observed. Between ˜41.6 ka and ˜19 ka, magnetite and greigite are alternatively in dominance in the sediment. Due to low organic matter input during the late MIS 3 and the last glacial maximum (LGM), oxygenated bottom water in the Black Sea was favourable for preserving detrital magnetite. Greigite in this interval have irregular shapes and assemble in spots, which were formed in a micro environment with limited sulfate availability. Between ˜19 ka and ˜16.5 ka, black layers were deposited as a result of organic matter accumulation induced by productivity blooming and riverine discharge soaring after the LGM. Hence less oxygenated bottom water conditions developed, and more fine grained greigite was formed. After melt-water pulse (MWP) events (˜16.5 ka), both primary productivity and the sea level were continuously rising until ˜8.3 ka, leading to the depletion of oxygen in bottom water. In addition to greigite, pyrite was also formed and gradually in dominance as approaching the Holocene. The influx of salt water masses from the Mediterranean Sea after ˜8.3 ka contributed to the establishment of the anoxic Black Sea, which resulted in the formation of ubiquitous frambiods of pyrite. Additionally, bacterial magnetic minerals are likely present in the sediment younger than ˜8.3 ka as indicated by rock magnetic results. In this paper, four different magnetic mineral assemblages, reflecting gradual changes from an oxic to an anoix Black Sea, were identified, yielding insights into the relation between magnetic minerals diagenesis and bottom water conditions.

Early Triassic change in the erosional level in the eastern part of the Bohemian Massif revealed by detrital garnet assemblages from the Buntsandstein siliciclastics of southern Poland

NASA Astrophysics Data System (ADS)

Kowal-Linka, Monika; Walczak, Klaudia

2017-04-01

Garnets, as constituents of various magmatic and metamorphic rocks, show different chemical compositions depending on the type of magma or primary rock, the temperature, and the pressure. This diversity of chemical compositions makes detrital garnets a very useful tool for provenance analysis and deciphering changes in erosional levels of source areas. Preliminary works reveal that the Lower and Middle Buntsandstein terrigenous and marine sandstones cropping out in southern Poland (50˚ 28'20"N, 18˚ 04'33"E and 50˚ 27'35"N, 18˚ 07'23"E) are characterized by very different heavy mineral assemblages (HMA) and types of detrital garnets. The aim of the research is to recognize the source areas and causes of these distinct variations using petrographic analysis, heavy mineral analysis, and electron probe microanalysis. During the Early Triassic, the area under study was located between two landmasses: the eastern margin of the Bohemian Massif (BM) to the west and Pre-Carpathian Land (PCL) to the east. Presently, the sampled area is situated ˜50 km from the NE margin of the BM, which consists of many garnet-bearing rocks and is a presumable source area for the examined grains. The PCL was hidden under the Carpathians during the Alpine orogeny and knowledge of its composition is very limited. Petrographic analysis shows that the older sandstones are red to rusty quartz arenites with a hematite-rich matrix and well-rounded grains (aeolian deposits). The younger sandstones are bicolored quartz wackes (dirty pink with grey patches) with a calcite matrix and angular to rounded grains (shallow marine deposits). The arenites contain zircon, tourmaline, and rutile grains accompanied by garnet, staurolite, apatite, and topaz. The opaque heavy minerals include ilmenite, ilmenite-rutile aggregates, magnetite and rarely chromian spinel. In contrast, the HMA from the wackes consist mostly of garnets, while the minerals listed above occur in subordinate amounts. The garnets from the older sandstones are rich in pyrope molecule. They include peridotite-derived pyropes (Prp(62)66-73Alm4-21(23)Grs(1)4-9(14)Uv(1)2-9(14)Sps1And<1), which are accompanied by pyrope-almandine-grossular garnets with a wide range of compositions (Prp(11)18-62Alm17-49Grs10-38(44)Uv<1-3Sps1-2And<1-1), derived from garnet pyroxenites and eclogites. By contrast, the garnets occurring in the wackes reveal definitely higher content of almandine molecule. The most abundant are the HP felsic granulite-derived almandine-pyrope garnets with low content of grossular molecule (Prp(25)27-49(54)Alm(42)45-65(68)Grs1-15Uv<1Sps1-2And<1). They are accompanied by almandine-pyrope-grossular garnets derived from mafic granulites, amphibolites, and eclogites. The other types of garnets occur with lower frequency. The examined HMA and garnet assemblages show different compositions in comparison with all the previously investigated Carboniferous, Permian, and Early Triassic HMA from the nearby areas in Poland and the Czech Republic. Detailed comparative analysis indicated the Moldanubian Zone as the most probable and important source area for the majority of the detrital garnets. The differences between the HMA and the garnet assemblages suggest a distinct change in the erosional level of the eastern part of the Moldanubian Zone during the Early Triassic. Combined tectonic and surficial process likely caused the change in the types of the exhumed rocks subjected to erosion. M. Kowal-Linka is supported by NCN grant 2014/13/B/ST10/02102.

Fluid inclusion chemistry of adularia-sericite epithermal Au-Ag deposits of the southern Hauraki Goldfield, New Zealand

USGS Publications Warehouse

Simpson, Mark P.; Strmic Palinkas, Sabina; Mauk, Jeffrey L.; Bodnar, Robert J.

2015-01-01

LA-ICP-MS analyses show that in some cases different fluid inclusion assemblages (FIAs) within a single sample trapped fluids with variable chemistries. These differences likely reflect modification of a single parent fluid through mineral dissolution and precipitation, water/rock interactions, boiling and vapor loss, conductive cooling, and mixing.

Manganese-rich red tourmaline from the Fowler talc belt, New York.

USGS Publications Warehouse

Ayuso, R.A.; Brown, C. Erwin

1984-01-01

Red uvite containing up to 4.34 wt.% MnO is found in the Arnold talc mine near Fowler, New York, USA. Microprobe analyses give a composition of 51% uvite in the uvite-dravite series. Associated minerals in this manganiferous metamorphic assemblage (possibly an evaporite) are manganese-rich tremolite (hexagonite) braunite and quartz.-R.A.G.

The age and thermal history of Cerro Rico de Potosi, Bolivia

USGS Publications Warehouse

Cunningham, C.G.; Zartman, R.E.; McKee, E.H.; Rye, R.O.; Naeser, C.W.; Sanjines, V.O.; Ericksen, G.E.; Tavera, V.F.

1996-01-01

Cerro Rico de Potosi, Bolivia, is the world's largest silver deposit and has been mined since the sixteenth century for silver, and for tin and zinc during the twentieth century, together with by-product copper and lead. The deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia. The deposit is compositionally and thermally zoned, having a core of cassiterite, wolframite, bismuthinite, and arsenopyrite surrounded by a peripheral, lower-temperature mineral assemblage consisting principally of sphalerite, galena, lead sulfosalt, and silver minerals. The low-temperature assemblage also was superim-posed on the high-temperature assemblage in response to cooling of the main hydrothermal system. Both the dacite dome and the ore fluids were derived from a larger magmatic hydrothermal source at depth. The dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement. The dome was extruded at 13.8 ?? 0.2 Ma (2??), based on U-Th-Pb dating of zircon. Mineralization and alteration occurred within about 0.3 my of dome emplacement, as indicated by a 40Ar/39Ar date of 13.76 ?? 0.10 Ma (1??) for sericite from the pervasive quartz-sericite-pyrite alteration associated with the main-stage, high-temperature, mineralization. The last thermal event able to reset zircon fission tracks occurred no later than 12.5 ?? 1.1 Ma (1??). as indicated by fission-tract dating. Minor sericite. and magmatic-steam alunite veins, were episodically formed around 11 Ma and between 8.3 and 5.7 Ma; the younger episodes occurring at the time of extensional fracturing at Cerro Rico and widespread volcanism in the adjacent Los Frailes volcanic field. None of these younger events appear to be signific-ant thermal/mineralizing events: the exceptionally flat thermal release pattern of 39Ar from sericite and the results of the fission-tract dating of zircon show that none of the younger events was hot enough, and lasted long enough, to cause significant loss of Ar or annealing of zircon fission tracks. U-Th-Pb dating of zircon cores dicates a Precambrian progenitor for some zircons, and REE analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive Eu anomaly, which constrains interpretations of the origin and evolution of the magmatic/hydrothermal system.

Igneous activity and related ore deposits in the western and southern Tushar Mountains, Marysvale volcanic field, west-central Utah

USGS Publications Warehouse

Steven, Thomas A.

1984-01-01

PART A: Igneous activity in the Marysvale volcanic field of western Utah can be separated into many episodes of extrusion, intrusion, and hydrothermal activity. The rocks of the western Tushar Mountains, near the western part of the volcanic field, include intermediate-composition, calc-alkalic volcanic rocks erupted from scattered volcanoes in Oligocene through earliest Miocene time and related monzonitic intrusions emplaced 24-23 m.y. ago. Beginning 22-21 m.y. ago and extending through much of the later Cenozoic, a bimodal basalt-rhyolite assemblage was erupted widely throughout the volcanic field. Only volcanic and intrusive rocks belonging to the rhyolitic end member of this bimodal assemblage are present in the western Tushar Mountains; most of these rocks either fill the Mount Belknap caldera (19 m.y. old) or are part of the rhyolite of Gillies Hill (9---8 m.y. old). Episodic hydrothermal activity altered and mineralized rocks at many places in the western Tushar Mountains during Miocene time. The earliest activity took place in and adjacent to monzonitic calcalkalic intrusions emplaced in the vicinity of Indian Creek and Cork Ridge. These rocks were widely propylitized, and gold-bearing quartz-pyrite-carbonate veins formed in local fractures. Hydrothermal activity associated with the Mount Belknap caldera mobilized and redeposited uranium contained in the caldera-fill rocks and formed primary concentrations of lithophile elements (including molybdenum and uranium) in the vicinity of intrusive bodies. Hydrothermal activity associated with the rhyolite of Gillies Hill altered and mineralized rocks at several places along the fault zone that marks the western margin of the Tushar Mountains; the zoned alunite and gold deposits at Sheep Rock, the gold deposit at the Sunday Mine, and an alunite deposit near Indian Creek were thus produced. Resetting of isotopic ages suggests that another center of hydrothermally altered rocks associated with a buried pluton about 16 m.y. old may exist near Indian Creek just west of the Mount Belknap caldera. Geophysical evidence confirms the probability of a buried pluton near Indian Creek, and also indicates that another buried pluton probably exists beneath the 9-m.y.-old mineralized area at Sheep Rock. The mineral potential of the different hydrothermal systems, and the types of minerals deposited probably vary considerably from one period of mineralization to another and from one depth environment to another within a given system. PART B: The Big John caldera, on the western flank of the Tushar Mountains in the Marysvale volcanic field in west-central Utah, formed 23-22 m.y. ago in response to ash-flow eruptions of the Delano Peak Tuff Member of the Bullion Canyon Volcanics. These eruptions were near the end of the period of Oligocene-early Miocene calc-alkalic igneous activity that built a broad volcanic plateau in this part of Utah. About 22 m.y. ago, the composition of rocks erupted changed to a bimodal assemblage of mafic and silicic volcanics that was erupted episodically through the remainder of Cenozoic time. The alkali rhyolites are uranium rich in part, and are associated with all the known uranium deposits in the Marysvale volcanic field. The Big John caldera was a broad drained basin whose floor was covered by a layer of stream gravels when ash flows from the western source area of the Mount Belknap Volcanics filled the caldera with the Joe Lott Tuff Member about 19 m.y. ago. Devitrified and zeolitized rocks in the caldera fill have lost one-quarter to one-half of the uranium contained in the original magma. This mobilized uranium probably moved into the hydrologic regime, and some may have been redeposited in stream gravels underlying the Joe Lott within the caldera, or in gravels filling the original drainage channel that extended south from the caldera.

Iron disulfide minerals and the genesis of roll-type uranium deposits.

USGS Publications Warehouse

Reynolds, R.L.; Goldhaber, M.B.

1983-01-01

Studies of the distribution of and textural relationships among pyrite and marcasite in host rocks for a number of roll-type sedimentary U deposits have enabled identification of several generations of FeS2 minerals. A critical factor influencing mineral formation is the complex relationship of pH and the S species that are precursors of FeS2 minerals. The presence or absence of intrinsic organic matter for bacterial sulphate reduction also plays a key role. In deposits lacking such organic matter, the pre-ore is often euhedral pyrite and the ore-stage is marcasite. In contrast, in deposits containing organic matter the pre-ore is pyrite occurring as framboids or as replacements of plant material, and the ore-stage is also pyrite. These contrasting FeS2 assemblages and their respective modes of origin are consistent with previously proposed biogenic and nonbiogenic theories of the genesis of roll-type U deposits. -J.E.S.

The mangazeya Ag-Pb-Zn vein deposit hosted in sedimentary rocks, Sakha-Yakutia, Russia: Mineral assemblages, fluid inclusions, stable isotopes (C, O, S), and origin

NASA Astrophysics Data System (ADS)

Anikina, E. Yu.; Bortnikov, N. S.; Klubnikin, G. K.; Gamyanin, G. N.; Prokof'ev, V. Yu.

2016-05-01

The succession of mineral assemblages, chemistry of gangue and ore minerals, fluid inclusions, and stable isotopes (C, O, S) in minerals have been studied in the Mangazeya silver-base-metal deposit hosted in terrigenous rocks of the Verkhoyansk Fold-Thrust Belt. The deposit is localized in the junction zone of the Kuranakh Anticlinorium and the Sartanga Synclinorium at the steep eastern limb of the Endybal Anticline. The deposit is situated at the intersection of the regional Nyuektame and North Tirekhtyakh faults. Igneous rocks are represented by the Endybal massif of granodiorite porphyry 97.8 ± 0.9 Ma in age and dikes varying in composition. One preore and three types of ore mineralization separated in space are distinguished: quartz-pyrite-arsenopyrite (I), quartz-carbonate-sulfide (II), and silver-base-metal (III). Quartz and carbonate (siderite) are predominant in ore veins. Ore minerals are represented by arsenopyrite, pyrite, sphalerite, galena, fahlore, and less frequent sulfosalts. Three types of fluid inclusions in quartz differ in phase compositions: two- or three-phase aqueous-carbon dioxide (FI I), carbon dioxide gas (FI II), and two-phase (FI III) containing liquid and a gas bubble. The homogenization temperature and salinity fall within the ranges of 367-217°C and 13.8-2.6 wt % NaCl equiv in FI I; 336-126°C and 15.4-0.8 wt % NaCl equiv in FI III. Carbon dioxide in FI II was homogenized in gas at +30.2 to +15.3°C and at +27.2 to 29.0°C in liquid. The δ34S values for minerals of type I range from-1.8 to +4.7‰ (V-CDT); of type II, from-7.4 to +6.6‰; and of type III, from-5.6 to +7.1‰. δ13C and δ18O vary from-7.0 to-6.7‰ (V-PDB) and from +16.6 to +17.1 (V-SMOW) in siderite-I; from-9.1 to-6.9‰ (V-PDB) and from +14.6 to +18.9 (V-SMOW) in siderite-II; from-5.4 to-3.1‰ (V-PDB) and from +14.6 to +19.5 (V-SMOW) in ankerite; and from-4.2 to-2.9‰ (V-PDB) and from +13.5 to +16.8 (V-SMOW) in calcite. The data on mineral assemblages, fluid inclusions, and ratios of stable isotopes allow us to speak about the formation of the Mangazeya deposit in relation to the activity of the hydrothermal-magmatic system. The latter combines emplacement of subvolcanic granitic stocks and involvement of fluids variable in salinity and temperature in ore deposition zone. The fluids released from crystallizing felsic magma and were formed in a convective cell by heating of meteoric and marine waters. The mechanism of ore deposition is related to phase separation (boiling) and mixing of fluids.

A speciation solver for cement paste modeling and the semismooth Newton method

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

Georget, Fabien, E-mail: fabieng@princeton.edu; Prévost, Jean H., E-mail: prevost@princeton.edu; Vanderbei, Robert J., E-mail: rvdb@princeton.edu

2015-02-15

The mineral assemblage of a cement paste may vary considerably with its environment. In addition, the water content of a cement paste is relatively low and the ionic strength of the interstitial solution is often high. These conditions are extreme conditions with respect to the common assumptions made in speciation problem. Furthermore the common trial and error algorithm to find the phase assemblage does not provide any guarantee of convergence. We propose a speciation solver based on a semismooth Newton method adapted to the thermodynamic modeling of cement paste. The strong theoretical properties associated with these methods offer practical advantages.more » Results of numerical experiments indicate that the algorithm is reliable, robust, and efficient.« less

Characteristics, extent and origin of hydrothermal alteration at Mount Rainier Volcano, Cascades Arc, USA: Implications for debris-flow hazards and mineral deposits

NASA Astrophysics Data System (ADS)

John, David A.; Sisson, Thomas W.; Breit, George N.; Rye, Robert O.; Vallance, James W.

2008-08-01

Hydrothermal alteration at Mount Rainier waxed and waned over the 500,000-year episodic growth of the edifice. Hydrothermal minerals and their stable-isotope compositions in samples collected from outcrop and as clasts from Holocene debris-flow deposits identify three distinct hypogene argillic/advanced argillic hydrothermal environments: magmatic-hydrothermal, steam-heated, and magmatic steam (fumarolic), with minor superimposed supergene alteration. The 3.8 km 3 Osceola Mudflow (5600 y BP) and coeval phreatomagmatic F tephra contain the highest temperature and most deeply formed hydrothermal minerals. Relatively deeply formed magmatic-hydrothermal alteration minerals and associations in clasts include quartz (residual silica), quartz-alunite, quartz-topaz, quartz-pyrophyllite, quartz-dickite/kaolinite, and quartz-illite (all with pyrite). Clasts of smectite-pyrite and steam-heated opal-alunite-kaolinite are also common in the Osceola Mudflow. In contrast, the Paradise lahar, formed by collapse of the summit or near-summit of the edifice at about the same time, contains only smectite-pyrite and near-surface steam-heated and fumarolic alteration minerals. Younger debris-flow deposits on the west side of the volcano (Round Pass and distal Electron Mudflows) contain only low-temperature smectite-pyrite assemblages, whereas the proximal Electron Mudflow and a < 100 y BP rock avalanche on Tahoma Glacier also contain magmatic-hydrothermal alteration minerals that are exposed in the avalanche headwall of Sunset Amphitheater, reflecting progressive incision into deeper near-conduit alteration products that formed at higher temperatures. The pre-Osceola Mudflow alteration geometry is inferred to have consisted of a narrow feeder zone of intense magmatic-hydrothermal alteration limited to near the conduit of the volcano, which graded outward to more widely distributed, but weak, smectite-pyrite alteration within 1 km of the edifice axis, developed chiefly in porous breccias. The edifice was capped by a steam-heated alteration zone, most of which resulted from condensation of fumarolic vapor and oxidation of H 2S in the unsaturated zone above the water table. Weakly developed smectite-pyrite alteration extended into the west and east flanks of the edifice, spatially associated with dikes that are localized in those sectors; other edifice flanks lack dikes and associated alteration. The Osceola collapse removed most of the altered core and upper east flank of the volcano, but intensely altered rocks remain on the uppermost west flank. Major conclusions of this study are that: (1) Hydrothermal-mineral assemblages and distributions at Mount Rainier can be understood in the framework of hydrothermal processes and environments developed from studies of ore deposits formed in analogous settings. (2) Frequent eruptions supplied sufficient hot magmatic fluid to alter the upper interior of the volcano hydrothermally, despite the consistently deep (≥ 8 km) magma reservoir which may have precluded formation of economic mineral deposits within or at shallow depths beneath Mount Rainier. The absence of indicator equilibrium alteration-mineral assemblages in the debris flows that effectively expose the volcano to a depth of 1-1.5 km also suggests a low potential for significant high-sulfidation epithermal or porphyry-type mineral deposits at depth. (3) Despite the long and complex history of the volcano, intensely altered collapse-prone rocks were spatially restricted to near the volcano's conduit system and summit, and short distances onto the upper east and west flanks, due to the necessary supply of reactive components carried by ascending magmatic fluids. (4) Intensely altered rocks were removed from the summit, east flank, and edifice interior by the Osceola collapse, but remain on the upper west flank in the Sunset Amphitheater area and present a continuing collapse hazard. (5) Visually conspicuous rocks on the lower east and mid-to-lower west flanks are not intensely altered and probably have not significantly weakened the rock, and thus do not present significant collapse hazards. (6) Alteration developed most intensely within breccia units, because of their high permeability and porosity. Volcanoes with abundant near-conduit upper-edifice breccias are prone to alteration increasing the possibility of collapse, whereas those that are breccia-poor (e.g., massive domes) are less prone to alteration.

Mineral textural evolution and PT-path of relict eclogite-facies rocks in the Paleoproterozoic Nagssugtoqidian Orogen, South-East Greenland

NASA Astrophysics Data System (ADS)

Müller, Sascha; Dziggel, Annika; Kolb, Jochen; Sindern, Sven

2018-01-01

The Nagssugtoqidian Orogen in South-East Greenland is a deeply eroded, Paleoproterozoic collision orogen. It consists of a variety of Archean and Paleoproterozoic rocks, most notably TTG gneiss, a variety of supracrustal rocks and basic dykes. This study aims at providing new insight into the geodynamic processes and subduction depth of this orogen by investigating the metamorphic evolution of garnet pyroxenite, retrogressed eclogite and amphibolite-facies rocks that are exposed within the Kuummiut Terrane of the Nagssugtoqidian Orogen. The garnet-pyroxenite has a dominant mineral assemblage of garnet, orthopyroxene, clinopyroxene and hornblende, while garnet-amphibolite and garnet-kyanite schist are made up of garnet, hornblende, plagioclase and quartz, and garnet, kyanite, biotite and quartz, respectively. Relicts of, and pseudomorphs after, eclogite-facies mineral assemblages are frequently found within basic metavolcanic rocks and Paleoproterozoic discordant basic dykes. In the retrogressed eclogite, the retrograde mineral reactions ceased prior to completion, resulting in the formation of two domains. A clinopyroxene domain consists of diopside-plagioclase symplectites, which are interpreted to have grown at the expense of omphacite. The symplectites are surrounded and partly replaced by hornblende and plagioclase. Omphacite (XJd 25-42) is preserved in a Na-rich sample, where it occurs in the core of large clinopyroxene and as inclusion in garnet and hornblende. In a garnet domain, garnet is variably replaced by an inner corona of plagioclase and an outer corona of amphibole +/- orthopyroxene and clinopyroxene. The degree of retrogression as well as the type of the retrograde assemblage in both domains appears to be dependent on fluid activity. Large garnet grains preserve Ca-rich cores, interpreted as prograde in origin, while Mg-rich garnet rims formed during eclogite-facies metamorphism and later re-equilibration. Pseudosection modelling combined with conventional geothermobarometry reveals a clockwise PT-evolution, involving eclogite-facies conditions of 17-19 kbar and 740-810 °C, followed by near-isothermal decompression to medium-pressure granulite-facies conditions (13.8-15.4 kbar, 760-880 °C) and subsequent decompression with minor cooling to high-pressure amphibolite-facies grades (8.8-10.9 kbar, 660-840 °C). These data show that rocks of the Kuummiut Terrane were exhumed from 70 to about 30 km into the mid- and lower crust. The PT-path implies that exhumation initially was rapid and tectonically-controlled.

Hydrothermal Alteration of the Lower Oceanic Crust: Insight from OmanDP Holes GT1A and GT2A.

NASA Astrophysics Data System (ADS)

Harris, M.; Zihlmann, B.; Mock, D.; Akitou, T.; Teagle, D. A. H.; Kondo, K.; Deans, J. R.; Crispini, L.; Takazawa, E.; Coggon, J. A.; Kelemen, P. B.

2017-12-01

Hydrothermal circulation is a fundamental Earth process that is responsible for the cooling of newly formed ocean crust at mid ocean ridges and imparts a chemical signature on both the crust and the oceans. Despite decades of study, the critical samples necessary to resolve the role of hydrothermal circulation during the formation of the lower ocean crust have remained poorly sampled in the ocean basins. The Oman Drilling Project successfully cored 3 boreholes into the lower crust of the Semail ophiolite (Holes GT1A layered gabbros, GT2A foliated gabbros and GT3A dike/gabbro transition). These boreholes have exceptionally high recovery ( 100%) compared to rotary coring in the oceans and provide an unrivalled opportunity to quantitatively characterise the hydrothermal system in the lower oceanic crust. Hydrothermal alteration in Holes GT1A and GT2A is ubiquitous and manifests as secondary minerals replacing primary igneous phases and secondary minerals precipitated in hydrothermal veins and hydrothermal fault zones. Hole GT1A is characterised by total alteration intensities between 10 -100%, with a mean alteration intensity of 60%, and shows no overall trend downhole. However, there are discrete depth intervals (on the scale of 30 -100 m) where the total alteration intensity increases with depth. Alteration assemblages are dominated by chlorite + albite + amphibole, with variable abundances of epidote, clinozoisite and quartz. Hole GT1A intersected several hydrothermal fault zones, these range from 2-3 cm up to >1m in size and are associated with more complex secondary mineral assemblages. Hydrothermal veins are abundant throughout Hole GT1A, with a mean density of 37 vein/m. Hole GT2A is characterised by total alteration intensities between 6-100%, with a mean alteration intensity of 45%, and is highly variable downhole. Alteration halos and patches are slightly more abundant than in Hole GT1A. The secondary mineral assemblage is similar to Hole GT1A, but Hole GT2A has higher abundances of epidote, clinozoisite, quartz, laumontite and iron-oxydroxides. Vein density in Hole GT2A is 61 veins/m. In both holes, cross cutting vein relationships indicate a relative timing from earliest to latest of: amphibole; epidote + zoisite + qtz; chlorite + prehnite + qtz, calcite-laumontite-anhydrite; gypsum.

Deportment of PGE and semimetals in the Volspruit deposit: the most ultramafic PGE horizon of the Bushveld Complex

NASA Astrophysics Data System (ADS)

Tanner, D.; McDonald, I.; Harmer, R. E. J.; Hughes, H. S. R.; Muir, D. D.

2017-12-01

The Volspruit deposit is a zone of disseminated magmatic sulphides carrying Ni-PGE (platinum-group element) mineralization in the Northern Limb of the Bushveld Complex, South Africa. It is one of the few known PGE prospects hosted by the lower ultramafic portion of a layered intrusion and the only known example in the Bushveld Complex. Volspruit therefore provides a unique insight into the processes governing mineralisation early in the Bushveld magmatic system. This study presents a detailed analysis from the northern portion of the Volspruit orebody combining mineralogical and textural observations with sulphide mineral trace element compositions. Electron microscopy reveals a diverse assemblage of Pt-, Pd- and Rh- dominant platinum-group minerals (PGM), electrum, Ag tellurides, Pb-chlorides, Pb-sulphides, U-oxide and monazite. Laser ablation ICP-MS has demonstrated that the Volspruit base metal sulphides have elevated PGE tenors but a range of S/Se values 1414-19319 - greater than other magmatic sulphide deposits in the northern Bushveld. The S/Se values are typical of crustal S and in agreement with previous S isotope data. These data imply a magma with initially high tenor sulphide liquid experienced local contamination from sedimentary S, leading to reduced tenors and elevated S/Se in sulphides coupled with a propensity of Pb- and Zn-bearing minerals (e.g., Pb-sulphide, Pb-chloride and sphalerite) in association with archetypal orthomagmatic sulphide assemblages. Our data demonstrate that assimilation of sedimentary rocks can modify sulphide melt evolution through the addition of metals such as Pb and Zn, not just contamination by sulphur. The Volspruit deposit illustrates the complexity of multi-stage processes governing mineralisation in the ultramafic portions of layered mafic intrusions.

Plant community change mediates the response of foliar δ(15)N to CO 2 enrichment in mesic grasslands.

PubMed

Polley, H Wayne; Derner, Justin D; Jackson, Robert B; Gill, Richard A; Procter, Andrew C; Fay, Philip A

2015-06-01

Rising atmospheric CO2 concentration may change the isotopic signature of plant N by altering plant and microbial processes involved in the N cycle. CO2 may increase leaf δ(15)N by increasing plant community productivity, C input to soil, and, ultimately, microbial mineralization of old, (15)N-enriched organic matter. We predicted that CO2 would increase aboveground productivity (ANPP; g biomass m(-2)) and foliar δ(15)N values of two grassland communities in Texas, USA: (1) a pasture dominated by a C4 exotic grass, and (2) assemblages of tallgrass prairie species, the latter grown on clay, sandy loam, and silty clay soils. Grasslands were exposed in separate experiments to a pre-industrial to elevated CO2 gradient for 4 years. CO2 stimulated ANPP of pasture and of prairie assemblages on each of the three soils, but increased leaf δ(15)N only for prairie plants on a silty clay. δ(15)N increased linearly as mineral-associated soil C declined on the silty clay. Mineral-associated C declined as ANPP increased. Structural equation modeling indicted that CO2 increased ANPP partly by favoring a tallgrass (Sorghastrum nutans) over a mid-grass species (Bouteloua curtipendula). CO2 may have increased foliar δ(15)N on the silty clay by reducing fractionation during N uptake and assimilation. However, we interpret the soil-specific, δ(15)N-CO2 response as resulting from increased ANPP that stimulated mineralization from recalcitrant organic matter. By contrast, CO2 favored a forb species (Solanum dimidiatum) with higher δ(15)N than the dominant grass (Bothriochloa ischaemum) in pasture. CO2 enrichment changed grassland δ(15)N by shifting species relative abundances.

Authigenic carbonate precipitation in Lake Acigöl, a hypersaline lake in southwestern Turkey

NASA Astrophysics Data System (ADS)

Balci, Nurgul; Menekse, Meryem; Gül Karagüler, Nevin; Seref Sönmez, M.; Meister, Patrick

2014-05-01

Lake Acigöl (Bitter Lake) is a hypersaline lake in southwestern Turkey at an elevation of 836 m above sea level showing authigenic precipitation of several different carbonate mineral phases. It is a perennial lake and closed drainage basin where a semiarid continental climate dominates. Due to the extreme water chemistry (salinity 8-200 mg/l; SO4 112-15232 mg/l; Cl 290-35320 mg/l; Mg, 82-3425 mg/l; Ca 102-745 mg/l) unique microorganisms flourish in the lake. We studied microbial diversity from enrichment cultures and performed precipitation experiments using similar water chemistry and adding bacterial enrichment cultures from lake sediments in order to elucidate whether the mineral assemblages found in the lake can be reproduced. Experiments using moderately halophilic bacteria obtained from the lake sediments demonstrate the formation of various calcium-/magnesium-carbonates: hydromagnesite, dypingite, huntite, monohydrocalcite and aragonite. The relative amounts of different mineral phases, particularly monohydrocalcite, hydromagnesite and dypingite, could be controlled by varying the sulphate concentration in the media from 0 to 56 mM. The similar mineral assemblages identified in the sediments of Lake Acigöl and in the experiments point to similar thermodynamic conditions and kinetics of crystal growth. In particular, the similar spherical morphology points to a rapid crystal growth under strong kinetic inhibition, possibly by organic polymers that are commonly produced by microbial communities. Our results demonstrate that the authigenic carbonate paragenesis of hypersaline lakes as Lake Acigöl can be reproduced in halophilic bacterial cultures. The exact thermodynamic conditions and precipitation kinetics under seasonally changing water chemistry or in batch experiment, however, still have to be constrained in order to establish a microbial model for carbonate precipitation in such environments.

Magmatic-vapor expansion and the formation of high-sulfidation gold deposits: Structural controls on hydrothermal alteration and ore mineralization

USGS Publications Warehouse

Berger, Byron R.; Henley, Richard W.

2011-01-01

High-sulfidation copper–gold lode deposits such as Chinkuashih, Taiwan, Lepanto, Philippines, and Goldfield, Nevada, formed within 1500 m of the paleosurface in volcanic terranes. All underwent an early stage of extensive advanced argillic silica–alunite alteration followed by an abrupt change to spatially much more restricted stages of fracture-controlled sulfide–sulfosalt mineral assemblages and gold–silver mineralization. The alteration as well as ore mineralization stages of these deposits were controlled by the dynamics and history of syn-hydrothermal faulting.At the Sulfate Stage, aggressive advanced argillic alteration and silicification were consequent on the in situ formation of acidic condensate from magmatic vapor as it expanded through secondary fracture networks alongside active faults. The reduction of permeability at this stage due to alteration decreased fluid flow to the surface, and progressively developed a barrier between magmatic-vapor expansion constrained by the active faults and peripheral hydrothermal activity dominated by hot-water flow. In conjunction with the increased rock strength resulting from alteration, subsequent fault-slip inversion in response to an increase in compressional stress generated new, highly permeable fractures localized by the embrittled, altered rock. The new fractures focused magmatic-vapor expansion with much lower heat loss so that condensation occurred. Sulfide Stage sulfosalt, sulfide, and gold–silver deposition then resulted from destabilization of vapor phase metal species due to vapor decompression through the new fracture array. The switch from sulfate to sulfide assemblages is, therefore, a logical consequence of changes in structural permeability due to the coupling of alteration and fracture dynamics rather than to changes in the chemistry of the fluid phase at its magmatic source.

Submarine hydrothermal processes, mirroring the geotectonic evolution of the NE Hungarian Jurassic Szarvaskő Unit

NASA Astrophysics Data System (ADS)

Kiss, Gabriella B.; Zagyva, Tamás; Pásztor, Domokos; Zaccarini, Federica

2018-05-01

The Jurassic pillow basalt of the NE Hungarian Szarvaskő Unit is part of an incomplete ophiolitic sequence, formed in a back-arc- or marginal basin of Neotethyan origin. Different, often superimposing hydrothermal processes were studied aiming to characterise them and to discover their relationship with the geotectonic evolution of the region. Closely packed pillow, pillow-fragmented hyaloclastite breccia and transition to peperitic facies of a submarine lava flow were observed. The rocks underwent primary and cooling-related local submarine hydrothermal processes immediately after eruption at ridge setting. Physico-chemical data of this process and volcanic facies analyses revealed distal formation in the submarine lava flow. A superimposing, more extensive fluid circulation system resulted in intense alteration of basalt and in the formation of mostly sulphide-filled cavities. This lower temperature, but larger-scale process was similar to VMS systems and was related to ridge setting. As a peculiarity of the Szarvaskő Unit, locally basalt may be completely altered to a grossular-bearing mineral assemblage formed by rodingitisation s.l. This unique process observed in basalt happened in ridge setting/during spreading, in the absence of known large ultramafic blocks. Epigenetic veins formed also during Alpine regional metamorphism, related to subduction/obduction. The observed hydrothermal minerals represent different steps of the geotectonic evolution of the Szarvaskő Unit, from the ridge setting and spreading till the subduction/obduction. Hence, studying the superimposing alteration mineral assemblages can be a useful tool for reconstructing the tectonic history of an ophiolitic complex. Though the found mineral parageneses are often similar, careful study can help in distinguishing the processes and characterising their P, T, and X conditions.

Precious metal-bearing epithermal deposits in western Patagonia (NE Lago Fontana region), Argentina

NASA Astrophysics Data System (ADS)

Lanfranchini, Mabel Elena; Etcheverry, Ricardo Oscar; de Barrio, Raúl Ernesto; Recio Hernández, Clemente

2013-04-01

Precious metal-bearing quartz veins occur at the northeastern sector of the Lago Fontana region in southwestern Argentina, within the context of the Andean continental magmatic arc environment. The deposits and their associated alteration zones are spatially related to a Cretaceous calc-alkaline magmatism represented by silicic dikes and hypabyssal intrusions, and hosted by a Late Jurassic to Cretaceous volcano-sedimentary sequence. The veins and related veinlets crop out discontinuously, in general terms in a NW-SE belt. The primary vein mineral assemblage is composed mostly of pyrite ± galena ± chalcopyrite > hematite ± arsenopyrite in silica gangue minerals. Chemical analyses of grab samples from selected quartz veins show as much as 5.7 ppm Au and 224 ppm Ag, as well as elevated Pb, Cu, and Zn. Hydrothermal fluids caused an innermost silicification and adularia-sericite alteration assemblage, and an external propylitic halo. Sulfur isotope values measured for sulfides (δSS from -1.90 to +1.56‰), and oxygen and hydrogen isotopes measured on quartz crystals and extracted primary fluid inclusion waters (δOO = -2.85 to +5.40‰; δDO = -106.0 to -103.4‰) indicate that mineralization probably formed from magmatic fluids, which were mixed with meteoric waters. Also, fluid inclusion data from quartz veins point out that these fluids had low salinity (1.7-4.2 wt% NaCl equiv.), and temperatures of homogenization between 180 and 325 °C. Mineralogical, petrographic and geochemical features for mineralized surface exposures indicate a typical adularia-sericite, low sulfidation epithermal system in the Lago Fontana area that represents a promising target for further exploration programs.

A comparison of the influences of urbanization in contrasting environmental settings on stream benthic algal assemblages

USGS Publications Warehouse

Potapova, M.; Coles, J.F.; Giddings, E.M.P.; Zappia, H.

2005-01-01

Patterns of stream benthic algal assemblages along urbanization gradients were investigated in three metropolitan areas-Boston (BOS), Massachusetts; Birmingham (BIR), Alabama; and Salt Lake City (SLC), Utah. An index of urban intensity derived from socioeconomic, infrastructure, and land-use characteristics was used as a measure of urbanization. Of the various attributes of the algal assemblages, species composition changed along gradients of urban intensity in a more consistent manner than biomass or diversity. In urban streams, the relative abundance of pollution-tolerant species was often higher than in less affected streams. Shifts in assemblage composition were associated primarily with increased levels of conductivity, nutrients, and alterations in physical habitat. Water mineralization and nutrients were the most important determinants of assemblage composition in the BOS and SLC study areas; flow regime and grazers were key factors in the BIR study area. Species composition of algal assemblages differed significantly among geographic regions, and no particular algal taxa were found to be universal indicators of urbanization. Patterns in algal biomass and diversity along urban gradients varied among study areas, depending on local environmental conditions and habitat alteration. Biomass and diversity increased with urbanization in the BOS area, apparently because of increased nutrients, light, and flow stability in urban streams, which often are regulated by dams. Biomass and diversity decreased with urbanization in the BIR study area because of intensive fish grazing and less stable flow regime. In the SLC study area, correlations between algal biomass, diversity, and urban intensity were positive but weak. Thus, algal responses to urbanization differed considerably among the three study areas. We concluded that the wide range of responses of benthic algae to urbanization implied that tools for stream bioassessment must be region specific. ?? 2005 by the American Fisheries Society.

The presence of carbonates on Mars: origin, terrestrial analogues and analytical tecniques ambiguity

NASA Astrophysics Data System (ADS)

Marinangeli, Lucia; Liberi, Francesca; Pompilio, Loredana; Piluso, Eugenio; Rosatelli, Gianluigi; Tranquilli, Andrea; Pepe, Monica

2013-04-01

The most common cause of carbonates formation on Earth is the chemical deposition from Ca-rich waters in sedimentary basins, mostly in shallow water. The lack of widespread exposure of carbonates on the Mars' surface in areas where geomorphological and sedimentological mapping confirms the presence of water for a long period of the Martian history, led us to look for a potential different origin of the carbonates identified on CRISM data [1, 2,3]. We suggest the presence of carbonatites on Mars and we have also investigated the capabilities of analytical tecniques for mineralogical analysis to recognise these peculiar type of rocks. Carbonatites are igneous rocks containing more than 50 percent of carbonate minerals and associated silicate minerals as olivine, pyroxene and phyllosilicates. Carbonatites are associated with alkali silicate rocks that are usually of nephelinitic or melilititic affinity. The Martian carbonates are often present in layered rocks and in association with hydrated Fe-Mg silicates (clays family) and kaolinite-group minerals at places [1]. This mineralogical association is very similar to an water-altered carbonatite. We have compared the compositional and mineralogical affinity of some carbonatite samples from different alkaline-carbonatite complexes from Uganda, Spain and Italy, with the mineralogy described for the carbonate- and phyllosolicate rich rocks on Mars, using the XRD and IR analyses. The mineral assemblage has been defined through petrographic analyses as well. It is important to stress that only with XRD analysis some minerals diagnos-tic of carbonatitic assemblage (i.e. melilite) were identified. The relationships between carbonatites and their associated silicate rocks are complex and are still not fully understood on Earth as well, however, it deserves further investigations to better explain the carbonates and silicate volcanic rocks on Mars and its crustal dynamics. References: [1] Michalski and Niles, 2010, Nature Geoscience, 751-755. [2] Helmann et al., 2008, Science, 322, 1828-1832. [3] Morris et al., 2010, Science, 329, 421-424.

Bismuth selenides from St. Andreasberg, Germany: an oxidised five-element style of mineralisation and its relation to post-Variscan vein-type deposits of central Europe

NASA Astrophysics Data System (ADS)

Cabral, Alexandre Raphael; Ließmann, Wilfried; Jian, Wei; Lehmann, Bernd

2017-10-01

Carbonate veinlets at Roter Bär, a former underground mine in the polymetallic St. Andreasberg vein district of the Harz Mountains, Germany, host selenide minerals that are characterised as Bi-Ag-bearing clausthalite (PbSe), tiemannite (HgSe), guanajuatite (Bi2Se3) and a number of selenides of Bi, Zn, Cu, Ag and Pd. An unnamed Bi-Pb-Ag selenide species with some Hg and Cu, ideally Bi4Pb3Ag2Se10, is reported here. Specular hematite is disseminated within the clausthalite, at the marginal zones of which other selenide minerals are located. The occurrence of bohdanowiczite (AgBiSe2) and umangite (Cu3Se2) constrains the formation temperature to ≤120 °C, and the selenide-hematite assemblage (plus barite in the carbonate gangue) identifies highly oxidised conditions. Selenide assemblages of Pb, Bi, Ag, with and without Co and Ni, occur in many parts of the Variscan basement of central Europe (Harz, Erzgebirge, Schwarzwald and Bohemian Massif) and represent a high-oxidation variety of five-element (Ag-As-Bi-Co-Ni) veins.

Fahlore and Sphalerite from the Darasun Gold Deposit in the Eastern Transbaikal Region, Russia: I. Mineral Assemblages and Intergrowths, Chemical Composition, and Its Evolution

NASA Astrophysics Data System (ADS)

Lyubimtseva, N. G.; Bortnikov, N. S.; Borisovsky, S. E.; Prokofiev, V. Yu.; Vikent'eva, O. V.

2018-03-01

The mineral assemblages, mode of occurrence, and chemical compositions of coexisting fahlore and sphalerite from the Darasun gold deposit have been described. Three generations of fahlore and three generations of sphalerite have been recognized. The FeS content in sphalerite coexisting with fahlore ranges from 0.8 to 9.4 mol %. The complete solid solution series Fe-tetrahedrite-Zn-tetrahedrite-Fe-tennantite-Zn-tennantite reflected in Sb/(Sb + As) and Fe/(Fe + Zn) ratios ranging from 0 to 0.97 and from 0.07 to 1.00, respectively, with a predominant negative relationship between these ratios has been identified for the first time at the deposit. Stepped, oscillatory, and combined stepped-oscillatory growth zonings within fahlore grains and heterogeneous aggregates of fahlore have been found. Fahlore is enriched in As with respect to Sb, and Zn-tetrahedrite is followed by Fe- and Zn-tennantite from early to late generation; Zn-tetrahedrite is followed by Fe-tennantite in zoned grains and overgrown rims; sphalerite crystallized at decreased temperature and sulfur fugacity. The evolution of the chemical composition of fahlores was caused by the evolving temperature, fluid salinity, and conditions of metal migration.

New geochronologic and stratigraphic evidence confirms the paleocene age of the dinosaur-bearing ojo alamo sandstone and animas formation in the San Juan Basin, New Mexico and Colorado

USGS Publications Warehouse

Fassett, J.E.

2009-01-01

Dinosaur fossils are present in the Paleocene Ojo Alamo Sandstone and Animas Formation in the San Juan Basin, New Mexico, and Colorado. Evidence for the Paleo-cene age of the Ojo Alamo Sandstone includes palynologic and paleomagnetic data. Palynologic data indicate that the entire Ojo Alamo Sandstone, including the lower dinosaur-bearing part, is Paleocene in age. All of the palynomorph-productive rock samples collected from the Ojo Alamo Sandstone at multiple localities lacked Creta-ceous index palynomorphs (except for rare, reworked specimens) and produced Paleocene index palynomorphs. Paleocene palynomorphs have been identified strati-graphically below dinosaur fossils at two separate localities in the Ojo Alamo Sand-stone in the central and southern parts of the basin. The Animas Formation in the Colorado part of the basin also contains dinosaur fossils, and its Paleocene age has been established based on fossil leaves and palynology. Magnetostratigraphy provides independent evidence for the Paleocene age of the Ojo Alamo Sandstone and its dinosaur-bearing beds. Normal-polarity magnetochron C29n (early Paleocene) has been identified in the Ojo Alamo Sandstone at six localities in the southern part of the San Juan Basin. An assemblage of 34 skeletal elements from a single hadrosaur, found in the Ojo Alamo Sandstone in the southern San Juan Basin, provided conclusive evidence that this assemblage could not have been reworked from underlying Cretaceous strata. In addition, geochemical studies of 15 vertebrate bones from the Paleocene Ojo Alamo Sandstone and 15 bone samples from the underlying Kirtland Formation of Late Creta-ceous (Campanian) age show that each sample suite contained distinctly different abundances of uranium and rare-earth elements, indicating that the bones were miner-alized in place soon after burial, and that none of the Paleocene dinosaur bones ana-lyzed had been reworked. ?? U.S. Geological Survey, Public Domain April 2009.

Reconnaissance of uranium and copper deposits in parts of New Mexico, Colorado, Utah, Idaho, and Wyoming

USGS Publications Warehouse

Gott, Garland B.; Erickson, Ralph L.

1952-01-01

Because of the common association of uranium and copper in several of the commercial uranium deposits in the Colorado Plateau Province, a reconnaissance was made of several known deposits of copper disseminated through sandstone to determine whether they might be a source of uranium. In order to obtain more information regarding the relationship between copper, uranium and carbonaceous materials, some of the uraniferious asphaltrite deposits in the Shinarump conglomerate along the west flank of the San Rafael Swell were also investigated briefly. During this reconnaissance 18 deposits were examined in New Mexico, eight in Utah, two in Idaho, and one each in Wyoming and Colorado. No uranium deposits of commercial grade are associated with the copper deposits that were examined. The uraniferous asphaltites in the Shinarump conglomerate of Triassic age on the west flank of the San Rafael Swell, however, are promising from the standpoint of commercial uranium production. Spectrographic analyses of crude oil, asphalt, and bituminous shales show a rather consistent suite of trace metals including vanadium, nickel, copper, cobalt, chromium, lead zinc, and molybdenum. The similarity of the metal assemblage, including uranium of the San Rafael Swell asphaltites, to the metal assemblage in crude oil and other bituminous materials suggests that these metals were concentrated in the asphaltites from petroleum. However, the hypothesis that uranium minerals were already present before the hydrocarbons were introduced and that some sort of replacement or uranium minerals by carbon compounds was effected after the petroleum migrated into the uranium deposit should not be disregarded. The widespread association of uranium with asphaltic material suggests that it also may have been concentrated by some agency connected with the formation of petroleum. The problem of the association of uranium and other trace metals with hydrocarbons should be studied further both in the field and in the laboratory.

Splint coals of the Central Appalachians: Petrographic and geochemical facies of the Peach Orchard No. 3 split coal bed, southern Magoffin County, Kentucky

USGS Publications Warehouse

Hower, James C.; Ruppert, Leslie F.

2011-01-01

The Bolsovian (Middle Pennsylvanian) Peach Orchard coal bed is one of the splint coals of the Central Appalachians. Splint coal is a name for the dull, inertinite-rich lithologies typical of coals of the region. The No. 3 Split was sampled at five locations in Magoffin County, Kentucky and analyzed for petrography and major and minor elements. The No. 3 Split coals contain semifusinite-rich lithologies, up to 48% (mineral-free basis) in one case. The nature of the semifusinite varies with position in the coal bed, containing more mineral matter of detrital origin in the uppermost durain. The maceral assemblage of these terminal durains is dominated by detrital fusinite and semifusinite, suggesting reworking of the maceral assemblage coincident with the deposition of the detrital minerals. However, a durain in the middle of the coal bed, while lithologically similar to the uppermost durains, has a degraded, macrinite-rich, texture. The inertinite macerals in the middle durain have less distinct edges than semifusinites in the uppermost terminal durains, suggesting degradation as a possible path to inertinite formation. The uppermost durain has higher ash and semifusinite contents at the eastern sites than at the western sites. The difference in the microscopic petrology indicates that megascopic petrology alone can be a deceptive indicator of depositional environments and that close attention must be paid to the individual macerals and their implications for the depositional setting, especially within the inertinite group.

Mineralogical assemblages forming at hyperalkaline warm springs hosted on ultramafic rocks: A case study of Oman and Ligurian ophiolites

NASA Astrophysics Data System (ADS)

Chavagnac, Valérie; Ceuleneer, Georges; Monnin, Christophe; Lansac, Benjamin; Hoareau, Guilhem; Boulart, Cédric

2013-07-01

We report on the mineralogical assemblages found in the hyperalkaline springs hosted on Liguria and Oman ophiolites based on exhaustive X-ray diffraction and scanning electron microprobe analyses. In Liguria, hyperalkaline springs produce a thin brownish calcite precipitate that covers the bedrock due to the concomitant atmospheric CO2 uptake and neutralization of the hyperalkaline waters. No brucite and portlandite minerals are observed. The discharge of alkaline waters in Oman ophiolite forms white-orange precipitates. Calcium carbonate minerals (calcite and/or aragonite) are the most abundant and ubiquitous precipitates and are produced by the same mechanism as in Liguria. This process is observed as a thin surface crust made of rhombohedral calcite. Morphological features of aragonite vary from needle-, bouquet-, dumbbell-, spheroidal-like habitus according to the origin of carbon, temperature, and ionic composition of the hyperalkaline springs, and the biochemical and organic compounds. Brucite is observed both at hyperalkaline springs located at the thrust plane and at the paleo-Moho. The varying mixing proportions between the surface runoff waters and the hyperalkaline ones control brucite precipitation. The layered double hydroxide minerals occur solely in the vicinity of hyperalkaline springs emerging within the bedded gabbros. Finally, the dominant mineralogical associations we found in Oman (Ca-bearing carbonates and brucite) in a serpentinizing environment driven by the meteoric waters are surprisingly the same as those observed at the Lost City hydrothermal site in a totally marine environment.

A Study of Olivine Alteration to Iddingsite Using Raman Spectroscopy

NASA Technical Reports Server (NTRS)

Kuebler, K. E.; Wang, Alian; Haskin, L. A.; Jolliff, B. L.

2003-01-01

A crucial task of Mars surface science is to determine past environmental conditions, especially aqueous environments and their nature. Identification of mineral alteration by water is one way to do this. Recent work interprets TES spectra as indicating altered basalt on Mars. Olivine, a primary basaltic mineral, is easily altered by aqueous solutions. Alteration assemblages of olivine may be specific to deuteric, hydrothermal, surface water, or metamorphic environments. Raman spectra are produced by molecular vibrations and provide direct means for studying and identifying alteration products. Here, we present a combined study of changes in the chemical composition and Raman spectra of an olivine as it alters to iddingsite. Iddingsite is found in some SNC meteorites and is presumably present on Mars. The term 'iddingsite' has been used as a catch-all term to describe reddish alteration products of olivine, although some authors ascribe a narrower definition: an angstrom-scale intergrowth of goethite and smectite (presumably saponite) formed in an oxidizing and fluid-rich environment. Alteration conserves Fe (albeit oxidized) but requires addition of Al and H2O and removal of Mg and Si. The smectite that forms may be removed by continued alteration. Dehydration of the goethite forms hematite. Our purpose is to study the mineral assemblage, determine the structural and chemical variability of the components with respect to the degree of alteration, and to find spectral indicators of alteration that will be useful during in-situ analyses on Mars.

Shelf gradients of echinoid assemblages from the Miocene of Sardinia

NASA Astrophysics Data System (ADS)

Nebelsick, James; Andrea, Mancosu

2017-04-01

Well exposed Miocene echinoid assemblages from Sardinia representing various environmental settings including both siliciclastics and carbonates have been studied with respect to reconstructing palaeoenvironmental conditions along a shelf gradient. The basis of this study includes 1) detailed logging of sedimentary facies in the field, 2) interpreting their behavior and life habits of the preserved echinoids by applying functional morphological reconstructions of the echinoid skeletons and comparing them to related Recent echinoid taxa, 3) quantifying taphonomic features of test preservation including predation, abrasion, fragmentation, encrustation and bioerosion, and finally 4) analyzing accompanying fauna and flora as well as trace fossils. The assemblages included clypeasteroid dominated assemblages in shallow water settings where often mass accumulations of sand dollars are present. Spatangoid dominated assemblages are found in more offshore settings where diversity is determined by varying burrowing depths, feeding strategies and resource partitioning accompanied by varying rates of bioturbation and episodes of sediment deposition by storms. Mixed assemblages also occur ranging from shallow to deeper water with varying substrates including sea grass, as well as coarser and finer sediments. Finally, deeper water monotypic assemblages are present in storm-dominated siliciclastic shelf environments including both regular and irregular echinoids. In general, echinoid presence is determined by the ecological preferences of the taxa involved, their propensities for gregarious behavior, the differential preservation potentials of the varied skeletal architectures present as well as sedimentary environment in which they occur.

South Asian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the Andaman Sea

NASA Astrophysics Data System (ADS)

Ali, Sajid; Hathorne, Ed C.; Frank, Martin; Gebregiorgis, Daniel; Stattegger, Karl; Stumpf, Roland; Kutterolf, Steffen; Johnson, Joel E.; Giosan, Liviu

2015-02-01

The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial-interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd, and Pb isotope compositions of the detrital clay-size fraction and clay mineral assemblages obtained from sediment core NGHP Site 17 in the Andaman Sea to reconstruct the variability of the South Asian monsoon during the past 60 kyr. Over this time interval ɛNd values changed little, generally oscillating between -7.3 and -5.3 and the Pb isotope signatures are essentially invariable, which is in contrast to a record located further northeast in the Andaman Sea. This indicates that the source of the detrital clays did not change significantly during the last glacial and deglaciation suggesting the monsoon was spatially stable. The most likely source region is the Irrawaddy river catchment including the Indo-Burman Ranges with a possible minor contribution from the Andaman Islands. High smectite/(illite + chlorite) ratios (up to 14), as well as low 87Sr/86Sr ratios (0.711) for the Holocene period indicate enhanced chemical weathering and a stronger South Asian monsoon compared to marine oxygen isotope stages 2 and 3. Short, smectite-poor intervals exhibit markedly radiogenic Sr isotope compositions and document weakening of the South Asian monsoon, which may have been linked to short-term northern Atlantic climate variability on millennial time scales. This article was corrected on 18 MAR 2015. See the end of the full text for details.

Rock magnetic and geochemical evidence for authigenic magnetite formation via iron reduction in coal-bearing sediments offshore Shimokita Peninsula, Japan (IODP Site C0020)

NASA Astrophysics Data System (ADS)

Phillips, Stephen C.; Johnson, Joel E.; Clyde, William C.; Setera, Jacob B.; Maxbauer, Daniel P.; Severmann, Silke; Riedinger, Natascha

2017-06-01

Sediments recovered at Integrated Ocean Drilling Program (IODP) Site C0020, in a fore-arc basin offshore Shimokita Peninsula, Japan, include numerous coal beds (0.3-7 m thick) that are associated with a transition from a terrestrial to marine depositional environment. Within the primary coal-bearing unit (˜2 km depth below seafloor) there are sharp increases in magnetic susceptibility in close proximity to the coal beds, superimposed on a background of consistently low magnetic susceptibility throughout the remainder of the recovered stratigraphic sequence. We investigate the source of the magnetic susceptibility variability and characterize the dominant magnetic assemblage throughout the entire cored record, using isothermal remanent magnetization (IRM), thermal demagnetization, anhysteretic remanent magnetization (ARM), iron speciation, and iron isotopes. Magnetic mineral assemblages in all samples are dominated by very low-coercivity minerals with unblocking temperatures between 350 and 580°C that are interpreted to be magnetite. Samples with lower unblocking temperatures (300-400°C), higher ARM, higher-frequency dependence, and isotopically heavy δ56Fe across a range of lithologies in the coal-bearing unit (between 1925 and 1995 mbsf) indicate the presence of fine-grained authigenic magnetite. We suggest that iron-reducing bacteria facilitated the production of fine-grained magnetite within the coal-bearing unit during burial and interaction with pore waters. The coal/peat acted as a source of electron donors during burial, mediated by humic acids, to supply iron-reducing bacteria in the surrounding siliciclastic sediments. These results indicate that coal-bearing sediments may play an important role in iron cycling in subsiding peat environments and if buried deeply through time, within the subsequent deep biosphere.

The application of microtextural and heavy mineral analysis to discriminate between storm and tsunami deposits

USGS Publications Warehouse

Costa, Pedro J.M.; Gelfenbaum, Guy R.; Dawson, Sue; La selle, Seanpaul; Milne, F; Cascalho, J.; Ponte Lira, C.; Andrade, C.; Freitas, M. C.; Jaffe, Bruce E.

2017-01-01

Recent work has applied microtextural and heavy mineral analyses to sandy storm and tsunami deposits from Portugal, Scotland, Indonesia and the USA. We looked at the interpretation of microtextural imagery (scanning electron microscopy) of quartz grains and heavy mineral compositions. We consider inundation events of different chronologies and sources (the AD 1755 Lisbon and 2004 Indian Ocean tsunamis, the Great Storm of 11 January 2005 in Scotland, and Hurricane Sandy in 2012) that affected contrasting coastal and hinterland settings with different regional oceanographic conditions. Storm and tsunami deposits were examined along with potential source sediments (alluvial, beach, dune and nearshore sediments) to determine provenance.Results suggest that tsunami deposits typically exhibit a significant spatial variation in grain sizes, microtextures and heavy minerals. Storm deposits show less variability, especially in vertical profiles. Tsunami and storm quartz grains had more percussion marks and fresh surfaces compared to potential source material. Moreover, in the studied cases, tsunami samples had fewer fresh surfaces than storm deposits.Heavy mineral assemblages are typically site-specific. The concentration of heavy minerals decreases upwards in tsunamigenic units, whereas storm sediments show cyclic concentrations of heavy minerals, reflected in the laminations observed macroscopically in the deposits.

Biostratigraphy and structure of paleozoic host rocks and their relationship to Carlin-type gold deposits in the Jerritt Canyon mining district, Nevada

USGS Publications Warehouse

Peters, S.G.; Armstrong, A.K.; Harris, A.G.; Oscarson, R.L.; Noble, P.J.

2003-01-01

The Jerritt Canyon mining district in the northern Independence Range, northern Nevada, contains multiple, nearly horizontal, thrust masses of platform carbonate rocks that are exposed in a series of north- to northeast-elongated, tectonic windows through rocks of the Roberts Mountains allochthon. The Roberts Mountains allochthon was emplaced during the Late Devonian to Early Mississippian Antler orogeny. These thrust masses contain structurally and stratigraphically controlled Carlin-type gold deposits. The gold deposits are hosted in tectonically truncated units of the Silurian to Devonian Hanson Creek and Roberts Mountains Formations that lie within structural slices of an Eastern assemblage of Cambrian to Devonian carbonate rocks. In addition, these multiply thrust-faulted and folded host rocks are structurally interleaved with Mississippian siliciclastic rocks and are overlain structurally by Cambrian to Devonian siliciclastic units of the Roberts Mountains allochthon. All sedimentary rocks were involved in thrusting, high-angle faulting, and folding, and some of these events indicate substantial late Paleozoic and/or Mesozoic regional shortening. Early Pennsylvanian and late Eocene dikes also intrude the sedimentary rocks. These rocks all were uplifted into a northeast-trending range by subsequent late Cenozoic Basin and Range faulting. Eocene sedimentary and volcanic rocks flank part of the range. Pathways of hydrothermal fluid flow and locations of Carlin-type gold orebodies in the Jerritt Canyon mining district were controlled by structural and host-rock geometries within specific lithologies of the stacked thrust masses of Eastern assemblage rocks. The gold deposits are most common proximal to intersections of northeast-striking faults, northwest-striking dikes, and thrust planes that lie adjacent to permeable stratigraphic horizons. The host stratigraphic units include carbonate sequences that contained primary intercrystalline permeability, which provided initial pathways for fluid flow and later served as precipitation sites for ore minerals. Alteration, during, and perhaps prior to mineralization, enhanced primary permeability by dissolution, by removal of calcite, and by formation of dolomite. Ore-stage sulfide minerals and alteration minerals commonly precipitated in pore spaces among dolomite grains. Microveinlets and microbrecciation in zones of intense alteration also provided networks of secondary permeability that further enhanced fluid flux and produced additional sites for ore deposition.

Development of inverted metamorphic isograds in the western metamorphic belt, Juneau, Alaska

USGS Publications Warehouse

Himmelberg, G.R.; Brew, D.A.; Ford, A.B.

1991-01-01

An inverted metamorphic gradient is preserved in the western metamorphic belt near Juneau, Alaska. Detailed mapping of pelitic single-mineral isograds, systematic changes in mineral assemblages, and silicate geothermometry indicate that thermal peak metamorphic conditions increase structurally upward over a distance of about 8 km. Silicate geobarometry suggests that the thermal peak metamorphism occurred under pressures of 9-11 kbar. Our preferred interpretation of the cause of the inverted gradient is that it formed during compression of a thickened wedge of relatively wet and cool rocks in response to heat flow associated with the formation and emplacement of tonalite sill magma. -from Authors

Novel Microbial Assemblages Dominate Weathered Sulfide-Bearing Rock from Copper-Nickel Deposits in the Duluth Complex, Minnesota, USA

PubMed Central

Lapakko, Kim A.; Wenz, Zachary J.; Olson, Michael C.; Roepke, Elizabeth W.; Novak, Paige J.; Bailey, Jake V.

2017-01-01

ABSTRACT The Duluth Complex in northeastern Minnesota hosts economically significant deposits of copper, nickel, and platinum group elements (PGEs). The primary sulfide mineralogy of these deposits includes the minerals pyrrhotite, chalcopyrite, pentlandite, and cubanite, and weathering experiments show that most sulfide-bearing rock from the Duluth Complex generates moderately acidic leachate (pH 4 to 6). Microorganisms are important catalysts for metal sulfide oxidation and could influence the quality of water from mines in the Duluth Complex. Nevertheless, compared with that of extremely acidic environments, much less is known about the microbial ecology of moderately acidic sulfide-bearing mine waste, and so existing information may have little relevance to those microorganisms catalyzing oxidation reactions in the Duluth Complex. Here, we characterized the microbial communities in decade-long weathering experiments (kinetic tests) conducted on crushed rock and tailings from the Duluth Complex. Analyses of 16S rRNA genes and transcripts showed that differences among microbial communities correspond to pH, rock type, and experimental treatment. Moreover, microbial communities from the weathered Duluth Complex rock were dominated by taxa that are not typically associated with acidic mine waste. The most abundant operational taxonomic units (OTUs) were from the genera Meiothermus and Sulfuriferula, as well as from diverse clades of uncultivated Chloroflexi, Acidobacteria, and Betaproteobacteria. Specific taxa, including putative sulfur-oxidizing Sulfuriferula spp., appeared to be primarily associated with Duluth Complex rock, but not pyrite-bearing rocks subjected to the same experimental treatment. We discuss the implications of these results for the microbial ecology of moderately acidic mine waste with low sulfide content, as well as for kinetic testing of mine waste. IMPORTANCE Economic sulfide mineral deposits in the Duluth Complex may represent the largest undeveloped source of copper and nickel on Earth. Microorganisms are important catalysts for sulfide mineral oxidation, and research on extreme acidophiles has improved our ability to manage and remediate mine wastes. We found that the microbial assemblages associated with weathered rock from the Duluth Complex are dominated by organisms not widely associated with mine waste or mining-impacted environments, and we describe geochemical and experimental influences on community composition. This report will be a useful foundation for understanding the microbial biogeochemistry of moderately acidic mine waste from these and similar deposits. PMID:28600313

Novel Microbial Assemblages Dominate Weathered Sulfide-Bearing Rock from Copper-Nickel Deposits in the Duluth Complex, Minnesota, USA.

PubMed

Jones, Daniel S; Lapakko, Kim A; Wenz, Zachary J; Olson, Michael C; Roepke, Elizabeth W; Sadowsky, Michael J; Novak, Paige J; Bailey, Jake V

2017-08-15

The Duluth Complex in northeastern Minnesota hosts economically significant deposits of copper, nickel, and platinum group elements (PGEs). The primary sulfide mineralogy of these deposits includes the minerals pyrrhotite, chalcopyrite, pentlandite, and cubanite, and weathering experiments show that most sulfide-bearing rock from the Duluth Complex generates moderately acidic leachate (pH 4 to 6). Microorganisms are important catalysts for metal sulfide oxidation and could influence the quality of water from mines in the Duluth Complex. Nevertheless, compared with that of extremely acidic environments, much less is known about the microbial ecology of moderately acidic sulfide-bearing mine waste, and so existing information may have little relevance to those microorganisms catalyzing oxidation reactions in the Duluth Complex. Here, we characterized the microbial communities in decade-long weathering experiments (kinetic tests) conducted on crushed rock and tailings from the Duluth Complex. Analyses of 16S rRNA genes and transcripts showed that differences among microbial communities correspond to pH, rock type, and experimental treatment. Moreover, microbial communities from the weathered Duluth Complex rock were dominated by taxa that are not typically associated with acidic mine waste. The most abundant operational taxonomic units (OTUs) were from the genera Meiothermus and Sulfuriferula , as well as from diverse clades of uncultivated Chloroflexi , Acidobacteria , and Betaproteobacteria Specific taxa, including putative sulfur-oxidizing Sulfuriferula spp., appeared to be primarily associated with Duluth Complex rock, but not pyrite-bearing rocks subjected to the same experimental treatment. We discuss the implications of these results for the microbial ecology of moderately acidic mine waste with low sulfide content, as well as for kinetic testing of mine waste. IMPORTANCE Economic sulfide mineral deposits in the Duluth Complex may represent the largest undeveloped source of copper and nickel on Earth. Microorganisms are important catalysts for sulfide mineral oxidation, and research on extreme acidophiles has improved our ability to manage and remediate mine wastes. We found that the microbial assemblages associated with weathered rock from the Duluth Complex are dominated by organisms not widely associated with mine waste or mining-impacted environments, and we describe geochemical and experimental influences on community composition. This report will be a useful foundation for understanding the microbial biogeochemistry of moderately acidic mine waste from these and similar deposits. Copyright © 2017 American Society for Microbiology.

Metagabbro associated with the shear zone on Prins Karls Forland (Svalbard, Arctic)

NASA Astrophysics Data System (ADS)

Maraszewska, Maria; Manecki, Maciej; Czerny, Jerzy; Schneider, David; Myhre, Per Inge; Faehnrich, Karol; Barnes, Christopher

2016-04-01

Prins Karls Forland (PKF) is a N-S elongated island situated west of Spitsbergen in the Svalbard archipelago, High Arctic. The northern part of the island is dominated by siliciclastic metasediments regionally metamorphosed to greenshist facies assemblages during one distinct stage of tectonism. Amphibolite facies garnet-mica schists, mica schists, quartzites and carbonate-silicate rocks exhibiting evidence of at least two distinct, strong deformation episodes (including mylonitization) locally outcrop on the east coast of PKF, termed the Pinkie Unit. A ~1 km wide shear zone containing ductile to brittle structures and distinct outcrops of greenstones (metagabbros and greenschists), associated with magnetite ore, separates these two contrasting tectonic units. Ten samples of greenstones were collected on the slopes of Lauratzonfjellet and Boureefjellet for petrologic and geochemical analyses. Despite intense localized shearing, the metagabbros are undeformed and preserve coarse crystalline, magmatic texture, which is locally poikilitic. The primary magmatic assemblage consists of brown hornblende, plagioclase, biotite and opaque minerals, with accessory apatite and titanite. No relicts of pyroxenes are preserved. Formation of secondary uralite, sericite and chlorite is observed. Metamorphic assemblage consists of actinolite pseudomorhs after hornblende, epidote, and second generation biotite. Blue amphibole is observed in one sample from Boureefjellet; greenschists from Boureefjellet also contain fibrous blue amphibole, as well as garnets, actinolite, epidote and biotite. Some rocks sampled on Boureefjellet are more strongly deformed and exhibit probably two stages of metamorphism: amphibolite facies metamorphism resulting in blue amphibole-garnet assemblage followed by greenschist facies metamorphism resulting in actinolite-epidote-biotite paragenesis. Parallel and overlapping patterns on chondrite-normalized REE diagrams and spider diagrams indicate that these metagabbros are comagmatic. Enrichment in incompatible lighter elements and position of projections on discrimination diagrams suggest ocean island basalt (OIB) character of primary magmas. The age of these rocks is unknown and is an objective of ongoing investigation. This work is partially funded by AGH research grant no 11.11.140.319.

Challenging the Standard Model: Equation of State of Natural Peridotite at Lower-Mantle Conditions

NASA Astrophysics Data System (ADS)

Jeanloz, R.; Lee, K. K.; Shim, S.

2002-12-01

High-resolution x-ray diffraction of natural peridotite, before and after (subsolidus) laser heating at pressures as high as 107 GPa, yields results challenging the paradigm that the Earth's mantle is a homogeneously mixed layer having the bulk composition of pyrolite. The starting material for the experiments is representative of fertile upper mantle, and is indistinguishable from Ringwood's pyrolite compositions. It transforms to an assemblage of 76 (2)% (Mg0.88Fe0.06Al0.12Si0.94)O3 orthorhombic perovskite (opv) by volume at zero pressure, 17 (2)% (Mg0.80Fe0.20)O magnesiow\\x81stite (mw) and 7 (1)% CaSiO3 perovskite (cpv), and room-temperature isotherms for each phase within the assemblage are in good agreement with past results on the individual mineral phases. Different measurement techniques yield reproducible results, with the observed scatter being well explained by the (small) compositional variations within the mineral phases of the natural starting material. We find values of the opv/mw Fe/Mg partition coefficient consistent with prior results, 0.20 (0.10) with no evidence of any pressure dependence, and recent work on CaSiO3 perovskite shows that its structure exhibits slight tetragonal distortion at lower-mantle pressures. The thermal equation of state of the high-pressure assemblage, described in terms of the Debye temperature, Gruneisen parameter and its volume dependence, is well determined if past measurements at high pressures and temperatures are reanalysed in terms of internally-consistent calibration standards. In particular, one model for the thermal equation of state of gold that has been used to calibrate several key experiments is faulty and yields biased results. Our re-analysis shows that all experiments point to relatively high values for the thermal expansion of opv (hence of the entire high-pressure assemblage), compatible with earlier rather than more recent analyses. The resulting high-pressure, high-temperature bulk modulus of the high-pressure assemblage is constrained to about 5% at lower-mantle conditions, and is expected to be relatively insensitive to Fe abundance. Minimum temperatures of about 2000 K at 700 km depth rising to about 3000 K at 2500 km depth are required for the bulk modulus of the high-pressure assemblage to match the seismologically observed bulk modulus of the lower mantle. These values of temperature are in good accord with current estimates. The density of the pyrolite-composition high-pressure assemblage is then found to be at least 2 (1)%, (and plausibly 4 (2)%) lower than the seismologically determined density at corresponding depths. The density mismatch is partly attributable to the effect of Al on the volume of opv, as also found by others. Uncertainties in the measurements and analysis appear to be well constrained, and rule out pyrolite as a viable bulk composition for the preponderance of the mantle.

Experimental Constraints on Hot Spring Fluid Chemistry in Back Arc Basins

NASA Astrophysics Data System (ADS)

Schaen, A. T.; Saccocia, P. J.; Seewald, J.

2010-12-01

Many axial hot springs from back-arc basins are characterized by low pH and high metal concentrations compared to fluids from the mid-ocean ridge. Such differences are likely related to the presence of felsic crust and the involvement of acidic magmatic fluids in back-arc hydrothermal systems. Previous experiments that reacted fresh andesite with seawater at elevated T and P yielded pH values significantly higher than those observed in back-arc basin hot springs. Moreover, ocean drilling beneath back-arc basin hot springs revealed acid-sulfate alteration assemblages, suggesting at least transient involvement of magmatic fluids. Here we report the results of two laboratory experiments designed to assess fluid chemistry in equilibrium with acid-sulfate alteration assemblages at sub-seafloor conditions typically associated with back-arc hot springs. Both experiments reacted a K-Ca-Na-Cl fluid with a pyrophyllite-pyrite-anhydrite-quartz assemblage (PPAQ). In addition, alunite was added to the assemblage in one experiment (PPAQA). Both experiments were conducted in a flexible-cell hydrothermal apparatus utilizing an inert Au-Ti reaction cell. Fluid samples were withdrawn from the reaction cell as a function of time and temperature and analyzed for major anions, cations, pH (25C), H2, and H2S to monitor reaction progress. In the PPAQ experiment, pH varied from 3.1 to 3.4 from 350 to 365C at 0.25 Kb. At 385C, 0.26 Kb, pH dropped to 2.74, close to the value observed in many BAB hot springs. H2S varied from 2 mmol/kg at 350C, 0.25 Kb to 11 mmol/kg at 385C, 0.26 Kb. In general, K decreased and Ca increased with increasing T and decreasing P while SO4 remained low (<1 mmol/kg). In the PPAQA experiment, fluid pH was much lower, varying from 2.2 to 1.5 from 250 to 350C, 0.25 Kb. H2S was low (<1 mmol/kg) at these same conditions. Similarly, H2 was <0.003 mmol/kg, consistent with relatively oxidizing conditions. K concentration remained nearly constant while Ca increased with decreasing T. SO4 varied inversely with Ca, varying from 35 to 4 mmol/kg from 350 to 250C, respectively. Thus, the presence of alunite in the alteration assemblage yields an extremely acid fluid, depleted in H2S and enriched in SO4 compared to fluids from the PPAQ experiment. These results suggest that the composition of hot spring fluids from back-arc environments is consistent with fluid-mineral equilibria involving acid-sulfate mineral assemblages. Such assemblages may be produced by previous episodes of magmatic degassing. Accordingly, the presence of highly acidic vent fluids may reflect an important role for magmatic fluids during crustal alteration processes, but does not require the presence of an actively degassing magma chamber.

Distribution of clay minerals in surface sediments of the western Gulf of Thailand: Sources and transport patterns

NASA Astrophysics Data System (ADS)

Shi, Xuefa; Liu, Shengfa; Fang, Xisheng; Qiao, Shuqing; Khokiattiwong, Somkiat; Kornkanitnan, Narumol

2015-06-01

A high density sampling program during two joint China-Thailand scientific cruises in 2011-2012 included collection of 152 gravity box cores in the Gulf of Thailand (GoT). Samples from the top 5 cm of each core were analyzed by X-ray diffraction for clay mineral content. Several systemic analytical approaches were applied to examine the distribution pattern and the constraint factors of clay minerals in the surface sediments of the western GoT. The clay minerals mainly comprise illite, kaolinite, chlorite and smectite, having the average weight percent distributions of 50%, 34%, 14% and 2%, respectively. Based on the spatial distribution characteristics and statistical results, the study area can be classified into three provinces. Province I contains high concentrations of smectite, and covers the northern GoT, sediments in this province are mainly from rivers discharging into the upper GoT, especially the Chao Phraya and Mae Klong Rivers. Sediments in Province II are characterized by higher values of illite, located in the central GoT, where fine sediments are contributed by the Mekong River and from the South China Sea. Province Ш, in the coastal regions of southwestern GoT close to Malaysia, exhibits a clay mineral assemblage with complex distribution patterns, and may contain terrestrial materials from the Mae Klong River as well as re-suspended sediments. Results of integrative analysis also demonstrate that the hydrodynamic environment in the study area, especially the seasonal various circumfluence and eddies, play an important role in the spatial distribution and dispersal of clay fraction in sediments.

Targeting Hydrothermal Alterations Utilizing LANDSAT-8 Andaster Data in Shahr-E Iran

NASA Astrophysics Data System (ADS)

Safari, M.; Pour, A. B.; Maghsoudi, A.; Hashim, M.

2017-10-01

Shahr-e-Babak tract of the Kerman metalogenic belt is one of the most potential segments of Urumieh-Dokhtar (Sahand-Bazman) magmatic arc. This area encompasses several porphyry copper deposits in exploration, development and exploitation hierarchy. The aim of this study is to map hydrothermal alterations caused by early Cenozoic magmatic intrusions in Shahr-e-Babak area. To this purpose, mineral mapping methods including band combinations, ratios and multiplications as well as PCA and MNF data space transforms in SWIR and VNIR for both ASTER and OLI sensors. Alteration zones according to spectral signatures of each type of alteration mineral assemblages such as argillic, phyllic and propylitic are successfully mapped. For enhancing the target areas false color composites and HSI-RGB color space transform are performed on developed band combinations. Previous studies have proven the robust application of ASTER in geology and mineral exploration; nonetheless, the results of this investigation prove applicability of OLI sensor from landsat-8 for alteration mapping. According to the results, evidently OLI sensor data can accurately map alteration zones. Additionally, the 12-bit quantization of OLI data is its privilege over 8-bit data of ASTER in VNIR and SWIR, thus OLI high quality results, which makes it easy to distinguish targets with enhanced color contrast between the altered and unaltered rocks.

Littoral zone fish assemblages of northern Cayuga Lake.

USGS Publications Warehouse

McKenna, James E.

2001-01-01

Fish assemblages from northern Cayuga Lake were examined for patterns in temporal structure. Fish assemblages changed significantly between seasons. Bluegill (Lepomis macrochirus), bluntnose minnow (Pimephales notatus), and smallmouth bass (Micropterus dolomieu) formed the basis for most assemblages, but the spring assemblage was dominated by common carp (Cyprinus carpio). Correlations between community structure and abiotic factors were identified. Ten abiotic factors strongly influenced species assemblages, including phosphorus concentration, but could not fully explain differences between assemblages. Results indicate that the seasonal pattern of fish assemblage structure and abundance of fish that tend to feed in the water column were related to the annual cycle of productivity in the lake and behavioral adaptations of the fish.

Rotational spectral variations of asteroid (8) Flora Implications for the nature of the S-type asteroids and for the parent bodies of the ordinary chondrites

NASA Technical Reports Server (NTRS)

Gaffey, M. J.

1984-01-01

The surface material and the surface material heterogeneities of the asteroid Flora are characterized using the best available data sets and the most sophisticated interpretive calibrations. Five spectrally derived mineralogic and patrologic properties of the surface assemblage of Flora which are relevant to whether this body is a differentiated or undifferentiated object are considered: bulk mineralogy, mafic mineral assemblage, metallic phase, pyroxene composition and structural type, and mineralogic variation. All of these properties indicate that Flora is a differentiated body. Flora is probably the residual core of an intensely heated, thermally evolved, and magnetically differentiated planetesimal which was subsequently disrupted. The present surface sample layers formed at or near the core-mantle boundary in the parent body.

Evidence of a Volcanogenic Massive Sulfide (Znsbnd Pbsbnd Cusbnd Ag) district within the Tiébélé Birimian (Paleoproterozoic) Greenstone Belts, Southern Burkina Faso (West - Africa)

NASA Astrophysics Data System (ADS)

Ilboudo, Hermann; Lompo, Martin; Wenmenga, Urbain; Napon, Salif; Naba, Seta; Ngom, Papa Malick

2017-05-01

Twenty years after the discovery of the Perkoa Znsbnd Ag deposit, another type of Znsbnd Cusbnd Pb ± Ag Volcanogenic Massive Sulfide (VMS) subgroup of occurrences forming a district has been highlighted within the Paleoproterozoic Birimian Greenstone Belts of the West African Craton in Burkina Faso. The geology of the area is characterized by a series of dominantly mafic volcanic rocks with intercalated black shales which increase in proportion upwards in the stratigraphy. This stratigraphic package is overlain by a felsic volcanic sequence comprising reworked tuff and rhyolite. Although mineralization is locally associated with sedimentary rocks, it is more commonly found in rhyolites. The metamorphic grade is dominantly greenschist facies. The main lithologies in the mafic sequence range from basalt to andesite with associated gabbro. The felsic sequence consists of dacite to rhyolite with associated granitoids (granite-granodiorite-tonalite). The volcanic rocks are commonly tholeiitic (Zr/Y = 2-4.5) with relatively high Zr and Y content, although a limited number of samples plot in transitional (Zr/Y = 4.5-7) or calc-alkaline (Zr/Y = 7-25) fields. Rhyolites, which constitute the main mineralized rocks at Tiébélé, have similar key trace element signatures to other rhyolites-related known VMS systems worldwide. Both have low Zr/Y (<7) and low LaN/YbN (<6), which suggests low crustal residence times of magmas in extensional settings. Detailed investigations identified at least four VMS targets notably at Koubongo, Nabenia, Loubel and AVV (Aménagement de la Vallée des Voltas) extending over an area of 332 km2. Typical mineral assemblages defining VMS occurrences are mainly hosted by meta-sedimentary rocks and rhyolite but are also found as veins in tonalite. These assemblages can be grouped into four different styles: (i) Variably banded massive sulfides dominated by sphalerite over galena, pyrite, and chalcopyrite within metasediments; (ii) Pyrite-rich or pyrrhotite banded type associated with sphalerite, chalcopyrite, and galena within silicified and carbonatized units; (iii) Disseminated and finely oriented sulfides, including pyrite - pyrrhotite - magnetite ± sphalerite within quartz-phyric rhyolite; and (iv) Fracture filling pyrrhotite-rich - magnetite - sphalerite mineralization possibly within tonalite. Irrespective of the style of the mineralization, chemistry of altered and least altered rhyolite reveals a significant increase in Mg ± Fe and H2O, and a loss of K within mineralization associated alteration. This may suggest sea water leaching of underlying (?) mafic and sedimentary rocks, with Mgsbnd Fe transfer into the rhyolites concomitant with the loss of K. This paper highlights the features of new occurrences of VMS mineralization type within the Birimian system of West Africa. We think this could help for new discoveries along the belts. Exploration based upon ground mapping, geochemistry and geophysics is highly recommended.

Seafloor massive sulfide deposits support unique megafaunal assemblages: Implications for seabed mining and conservation.

PubMed

Boschen, Rachel E; Rowden, Ashley A; Clark, Malcolm R; Pallentin, Arne; Gardner, Jonathan P A

2016-04-01

Mining of seafloor massive sulfides (SMS) is imminent, but the ecology of assemblages at SMS deposits is poorly known. Proposed conservation strategies include protected areas to preserve biodiversity at risk from mining impacts. Determining site suitability requires biological characterisation of the mine site and protected area(s). Video survey of a proposed mine site and protected area off New Zealand revealed unique megafaunal assemblages at the mine site. Significant relationships were identified between assemblage structure and environmental conditions, including hydrothermal features. Unique assemblages occurred at both active and inactive chimneys and are particularly at risk from mining-related impacts. The occurrence of unique assemblages at the mine site suggests that the proposed protected area is insufficient alone and should instead form part of a network. These results provide support for including hydrothermally active and inactive features within networks of protected areas and emphasise the need for quantitative survey data of proposed sites. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Reconstructing the Jurassic Talkeetna Intra-oceanic Arc of Alaska Using Thermobarometry

NASA Astrophysics Data System (ADS)

Hacker, B. R.; Mehl, L.; Kelemen, P. B.; Rioux, M.; Greene, A.

2005-12-01

The Talkeetna arc is one of two intra-oceanic arcs where the entire section from the upper mantle tectonite through the sediments capping the volcanic carapace is well exposed. The objective of this study is to reconstruct the vertical section of the Talkeetna arc by determining the (re) crystallization pressures at various structural levels. This information is crucial if the Talkeetna arc is to be exploited as an archetypal cross section for purposes as diverse as understanding the evolution of the Earth's crust, assessing rates and mechanisms of arc growth, and understanding the tectonic history arcs in general. The base of the arc crust exposed at Bernard and Scarp Mtns includes rare gabbro(norites) with metamorphic garnets-mineral assemblages excellent for thermobarometry. Broad core-to-rim garnet zoning toward lower Mg#, pyroxenes with near-rim, steep increases in Mg# and Al2O3, and unzoned plagioclase document cooling following core crystallization at ~900- 1025 °C and 0.9-1.0 GPa. Hornblende gabbros with magmatic garnet exposed in the Klanelneechena klippe indicate significantly lower P-T of ~700-835°C, 0.69- 0.77 GPa. Hornblende gabbro (norites) that comprise the bulk of the arc were studied in the Tazlina, Barnette, Scarp, and Pippin Ridge sections. Differences in mineral composition indicate qualitatively that the Tazlina, Barnette, and Scarp sections crystallized at successively greater depths. Temperature was calculated using hbl- plg [Holland and Blundy, 1994] and cpx-opx [QUILF; Andersen et al., 1993] net- transfer equilibria, and P was constrained using high δV/δS equilibria among plg, amph, opx, and cpx. Poorly known amphibole and pyroxene Tschermak-component activity models yield large uncertainties for P, but relative P differences can be anchored to the better-determined garnet gabbro P's, revealing that the rocks from the Barnette Creek section crystallized at ~0.40-0.55 GPa and the Tazlina and Pippin sections formed at ~0.25-0.35 GPa. Al-in-hornblende barometry indicates 0.23 GPa for granodiorites intruding the volcanic section. Calc-silicate rocks within the arc include metasedimentary wall rocks and carbonate veins cutting igneous rock. Grossular-andradite + diopside + calcite +/- sphene + quartz +/- wollastonite +/- scapolite mineral assemblages were strongly overprinted by a prehnite-pumpellyite facies alteration that includes datolite. Calculating P-T for the calc-silicate rocks is tenuous for several reasons-including large calculated Fe3+ in garnet and cpx, complete replacement of plagioclase, extreme partitioning of Mg into cpx, and ill-constrained aCO2--but a general correspondence between P-T inferred for the calc-silicate rocks and nearby metamafic rocks suggests that the calc-silicate assemblages grew during the magmatic development of the arc. Metamorphic rocks in float of the McHugh Complex(?) structurally beneath the Klanelneechena Klippe contain a strong amphibolite-facies fabric formed at 500°C and 1.0 ± 0.1 GPa. In summary, the granodiorites intruded at c. 6-10 km into a volcanic section estimated from stratigraphy to be 7 km thick [Clift et al., 2005]. The shallowest, Tazlina and Pippin, gabbros cooled at ~9-12 km; the Barnette section at ~14-19 km; the Klanelneechena klippe at ~24-26 km; and the base of the arc at ~30-34 km depth. Thus, the arc consists of a volcanic:plutonic ratio of ~28:72, and the current 5-7 km structural thickness of the plutonic section of the arc is ~20-35% of the original 20-26 km thickness.

ARO - Terrestrial Research Program, Methodologies and Protocols for Characterization of Geomaterials

DTIC Science & Technology

2015-05-14

of ice involves melting, digestion, and analysis using inductively coupled plasma – mass spectrometry (ICPMS). ICP-MS analysis established elemental...4] have distinct chemical compositions. Knowledge of the chemical composition of the mineral assemblage present in a rock is critical to...activation analysis (INAA), to inductively-coupled plasma analysis and mass spectrometry (ICP & ICP-MS), mass spectrometry (MS), and laser-ablation

Tamarugite in the Steam-Condensate Alteration Paragenesis in Diana Cave (SW Romania)

NASA Astrophysics Data System (ADS)

Puscas, C. M.; Onac, B. P.; Effenberger, H. S.; Povară, I.

2012-12-01

The double-salt hydrate tamarugite [NaAl(SO4)2 6H2O] is an uncommon mineral in the cave environment, forming as a result of chemical reactions between water and bedrock only under very specific conditions. The Diana Cave hosts a unique tamarugite occurrence, the first one to be reported from a typical karst environment. The cave is located within the limits of Băile Herculane township in the Cerna Mountains, SW Romania. It consists of a 14 m long, westward-oriented single passage, developed along the Diana Fault. In 1974 a concrete-clad mine gallery was created to channel the thermal water (Diana 1+2 Spring) flowing through the cave to a pumping station. The spring's chemical and physical parameters fluctuated through time, averaging 51.98° C, discharge of 0.96 Ls-1, pH of 7.46, 5768.66 ppm TDS, 9303 μScm-1 conductivity, 5.02 salinity. The major chemical components of the thermo-mineral water in Diana Cave are, Na+ (1392.57 ppm), K+ (58.55 ppm), Ca2+ (725.16 ppm), Mg2+ (10.78 ppm), Cl- (3376.83 ppm), and SO42- (92.27 ppm), and H2S (24.05 ppm), with traces of Si, Fe2+, Br+, I-, and Li+. The general air circulation pattern within the cave is fairly simple: cold air from the outside sweeps into the cave along the floor, heats up at the contact with the thermo-mineral water, ascends, and exists the cave along the ceiling. At the contact with the cold walls of the Diana Cave, the hot steam condenses and gives rise to a rich and exotic sulfate-mineral paragenesis (including halotrichite-series minerals, gypsum, bassanite, anhydrite, epsomite, alunite, halite, native sulfur, etc.). The most exotic minerals precipitate at or below the contact between the Tithonic - Neocomian limestone and the overlaying Cretaceous shaly limestone, as a result of steam-condensate alteration. Minerogenetic mechanisms responsible for the peculiar sulfate mineral assemblage in Diana Cave are evaporation, oxidation, hydrolysis, double exchange reactions, and deposition from vapours or possibly aerosols. This highly aggressive alteration of the carbonate rock (known as sulfuric acid speleogenesis) extends from the ceiling of the cave downward to, or slightly below, the water table and is responsible for further enlargement of cave passages. Given the availability of SO42-, gypsum replacement crusts form in the subaerial part of the cave, as well as thin gypsum rafts at the water surface. The presence of tamarugite indicates sufficiently strong acid conditions in the steam-condensate film to dissolve clay minerals, releasing Na+ and Al3+ into the geochemical system. Conditions conducive to tamarugite precipitation in carbonate caves seem to be the presence of: 1) thermo-mineral water, which through surface evaporation and condensation on the cold cave walls causes steam-condensate alteration processes, 2) sulfuric acid, and 3) a constant source of Al3+ and Na+. Such conditions are seldom fulfilled in any ordinary limestone caves. The bedrock geology and the particular tectonics and hydrogeology of the Băile Herculane area seem to be the essential prerequisites, not only for the development of hypogene karst, but also for producing an outstanding cave mineral assemblage.

Tectonic and climatic control of Paleogene sedimentation in the Rhenodanubian Flysch basin (Eastern Alps, Austria)

NASA Astrophysics Data System (ADS)

Egger, Hans; Homayoun, Mandana; Schnabel, Wolfgang

2002-10-01

The Paleocene to lowermost Eocene formations of the Rhenodanubian Flysch were deposited in an abyssal environment at the continental rise to the south of the European Plate. The pattern of paleocurrents indicates a number of small distributary systems for the turbiditic material that entered the basin from the north and was deflected to the east and to the west. Heavy mineral assemblages in the turbidites suggest the erosion of medium-grade metasediments in the Danian and the progressive erosion of underlying metamorphic magmatic rocks in the Thanetian and Ypresian. The most obvious sedimentary event is the breakdown in turbidite sedimentation during the late Danian to the early Thanetian. Remarkably, this starvation of turbidites is associated with high values of chlorite in the clay mineral assemblages of interturbidite shales, indicating increased mechanical erosion of the adjoining land areas. Tectonic uplift of these areas and associated block faulting and tilting is assumed to be responsible for this increase in erosion as well as for the synchronous cutting off of the basin from the source area of the turbidites. This tectonic activity is related to the onset of the collision of the European and the Adriatic Plates. A second major event documented in the Paleogene record is the change from a predominantly siliciclastic system to a carbonate system in the latest Thanetian. Associated with the global negative carbon isotope excursion (CIE) in the upper part of calcareous nannozone NP9, calcareous mudturbidites become the prevailing rock type. Eutrophication of surface waters is indicated by acmes of diatoms, radiolaria and dinoflagellates at the level of the CIE. Together with slightly increased values of kaolinite in the clay mineral assemblages of interturbidite shales, this can be interpreted as a result of increased continental run-off due to high precipitation rates in a humid climate. The top of the increased kaolinite input is poorly constrained because of a very high input of smectite due to volcanic activity in sub-zone NP10a. This igneous activity is assigned to the opening of the Northern Atlantic Ocean and has no geodynamic relevance for the Rhenodanubian Basin.

Marble-hosted ruby deposits of the Morogoro Region, Tanzania

NASA Astrophysics Data System (ADS)

Balmer, Walter A.; Hauzenberger, Christoph A.; Fritz, Harald; Sutthirat, Chakkaphan

2017-10-01

The ruby deposits of the Uluguru and Mahenge Mts, Morogoro Region, are related to marbles which represent the cover sequence of the Eastern Granulites in Tanzania. In both localities the cover sequences define a tectonic unit which is present as a nappe structure thrusted onto the gneissic basement in a north-western direction. Based on structural geological observations the ruby deposits are bound to mica-rich boudins in fold hinges where fluids interacted with the marble-host rock in zones of higher permeability. Petrographic observations revealed that the Uluguru Mts deposits occur within calcite-dominated marbles whereas deposits in the Mahenge Mts are found in dolomite-dominated marbles. The mineral assemblage describing the marble-hosted ruby deposit in the Uluguru Mts is characterised by corundum-dolomite-phlogopite ± spinel, calcite, pargasite, scapolite, plagioclase, margarite, chlorite, tourmaline whereas the assemblage corundum-calcite-plagioclase-phlogopite ± dolomite, pargasite, sapphirine, titanite, tourmaline is present in samples from the Mahenge Mts. Although slightly different in mineral assemblage it was possible to draw a similar ruby formation history for both localities. Two ruby forming events were distinguished by textural differences, which could also be modeled by thermodynamic T-XCO2 calculations using non-ideal mixing models of essential minerals. A first formation of ruby appears to have taken place during the prograde path (M1) either by the breakdown of diaspore which was present in the original sedimentary precursor rock or by the breakdown of margarite to corundum and plagioclase. The conditions for M1 metamorphism was estimated at ∼750 °C at 10 kbar, which represents granulite facies conditions. A change in fluid composition towards a CO2 dominated fluid triggered a second ruby generation to form. Subsequently, the examined units underwent a late greenschist facies overprint. In the framework of the East African Orogen we assume that the prograde ruby formation occurred at the commonly observed metamorphic event around 620 Ma. At the peak or during beginning of retrogression the fluid composition changed triggering a second ruby generation. The late stage greenschist facies overprint could have occurred at the waning stage of this metamorphic episode which is in the range of ∼580 Ma.

A new barometer from stress fields around inclusions

NASA Astrophysics Data System (ADS)

Avadanii, Diana; Hansen, Lars; Wallis, David; Waters, David

2017-04-01

A key step in understanding geological and geodynamic processes is modelling the pressure-temperature paths of metamorphic rocks. Traditional thermobarometry relies on mineral assemblage equilibria and thermodynamic modelling to infer the pressures and temperatures of chemical equilibration. This approach requires the presence of specific mineral assemblages and compositions, which narrows its applicability. In this study we aim to develop a geobarometer based on mechanical interactions between inclusions and their host grains. Exhumation of minerals with inclusions causes heterogeneous residual stress fields due to the different, and often anisotropic, elastic properties of the inclusion and host. Recent studies measure residual mean stresses within inclusions using Raman spectroscopy and use those stresses as a barometer. In contrast, we map each component of the stress tensor around inclusions using high angular-resolution electron backscatter diffraction (HR-EBSD). This technique provides both higher spatial resolution and increased sensitivity to elastic strains relative to Raman spectroscopy. We focus on quartz inclusions in garnet, a common feature in metamorphic rocks. This assemblage also provides an opportunity to test our results with compositional thermobarometry. We analyse samples metamorphosed at pressures ranging from ˜ 300 MPa to ˜ 1600 MPa, as recorded by independent geobarometers. HR-EBSD reveals symmetric and lobate signals around inclusions, with elastic strains and residual stresses of the order 10-3 and ±102 -103 MPa, respectively. We solve Eshelby's problem for the 'inhomogeneous inclusion' case to simulate the elastic strain/stress field around an anisotropic ellipsoidal inclusion surrounded by an isotropic, homogeneous, infinite matrix. This model calculates the stress disturbances caused by differential expansion of an inclusion and host subjected to decompression. We additionally account for differential expansion related to cooling by imposing an eigenstrain in the inclusion, according to the thermal expansivity of quartz. Thermal contraction in the host garnet is accounted for by modifying the macroscopic pressure. The simulations reproduce the general pattern of the elastic fields that we observe from HR-EBSD and account for different geometries of the inclusion. The simulations provide the basis for quantitatively relating the stress fields measured by HR-EBSD to the entrapment pressures of inclusions.

Li Isotopes as Tracers of Fluid-Rock Interactions in Oceanic Hydrothermal Systems: Evidence From the Hess Deep Rift

NASA Astrophysics Data System (ADS)

Brant, C. O.; Coogan, L. A.; Gillis, K. M.

2004-12-01

Li isotopes have the potential to be powerful tracers of fluid-rock interactions at mid-ocean ridge hydrothermal systems due to the large isotopic difference between seawater (δ7Li = 31‰) and fresh MORB (δ7Li = 1.5 to 5.6 ‰). Sampling programs along tectonic escarpments at Hess Deep provide an ideal suite to examine the spatial variability of Li mobility and Li isotopic content within young (1 Ma) lavas and sheeted dikes formed at the fast-spreading East Pacific Rise towards the end of a segment. Previous work has shown that the lavas are relatively fresh, with minor alteration to clay minerals and Fe oxyhydroxides. Sheeted dikes are variably altered to amphibole-dominated assemblages, with localized zones where chlorite dominates. Sr and O isotope data correlate with these regional patterns. Preliminary data, collected by Thermo X-series quadrupole ICP-MS, show that the lavas have similar Li concentrations to fresh MORB (5 to 6 ppm) and are slightly enriched in δ7Li (4.1 to 7.7 ‰). There is a positive correlation between Li content and δ7Li within the lavas, however, the trend is not a simple mixing line between seawater and fresh MORB, being offset to lower δ7Li in the altered component. Similar to previous studies, these relationships support the prediction that 6Li is preferentially retained in low temperature clay minerals. Sheeted dykes are depleted in Li (0.8-4.63 ppm) and most samples are enriched in δ7Li (6.7-15.4 ‰) relative to fresh MORB. These samples show an inverse relationship between decreasing concentration and increasing isotopic enrichment. This implies that 6Li is not simply preferentially retained in the replacement mineral assemblages. The degree of isotopic enrichment appears to increase with increasing clinopyroxene alteration, and is greatest for amphibolite dominated assemblages. A broad positive correlation between Li concentration and δ18O is observed in the dikes. Thus Li isotopes are sensitive indicators of the nature and extent of hydrothermal interactions for both high and low temperature processes.

Li Isotopes as Tracers of Fluid-Rock Interactions in Oceanic Hydrothermal Systems: Evidence From the Hess Deep Rift

NASA Astrophysics Data System (ADS)

Brant, C. O.; Coogan, L. A.; Gillis, K. M.

2007-12-01

Li isotopes have the potential to be powerful tracers of fluid-rock interactions at mid-ocean ridge hydrothermal systems due to the large isotopic difference between seawater (δ7Li = 31‰) and fresh MORB (δ7Li = 1.5 to 5.6 ‰). Sampling programs along tectonic escarpments at Hess Deep provide an ideal suite to examine the spatial variability of Li mobility and Li isotopic content within young (1 Ma) lavas and sheeted dikes formed at the fast-spreading East Pacific Rise towards the end of a segment. Previous work has shown that the lavas are relatively fresh, with minor alteration to clay minerals and Fe oxyhydroxides. Sheeted dikes are variably altered to amphibole-dominated assemblages, with localized zones where chlorite dominates. Sr and O isotope data correlate with these regional patterns. Preliminary data, collected by Thermo X-series quadrupole ICP-MS, show that the lavas have similar Li concentrations to fresh MORB (5 to 6 ppm) and are slightly enriched in δ7Li (4.1 to 7.7 ‰). There is a positive correlation between Li content and δ7Li within the lavas, however, the trend is not a simple mixing line between seawater and fresh MORB, being offset to lower δ7Li in the altered component. Similar to previous studies, these relationships support the prediction that 6Li is preferentially retained in low temperature clay minerals. Sheeted dykes are depleted in Li (0.8-4.63 ppm) and most samples are enriched in δ7Li (6.7-15.4 ‰) relative to fresh MORB. These samples show an inverse relationship between decreasing concentration and increasing isotopic enrichment. This implies that 6Li is not simply preferentially retained in the replacement mineral assemblages. The degree of isotopic enrichment appears to increase with increasing clinopyroxene alteration, and is greatest for amphibolite dominated assemblages. A broad positive correlation between Li concentration and δ18O is observed in the dikes. Thus Li isotopes are sensitive indicators of the nature and extent of hydrothermal interactions for both high and low temperature processes.

Trace fossils revealed through x-radiography in facies analysis of Smackover Formation, southwest Alabama

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

Esposito, R.A.; King, D.T. Jr.

The use of x-radiography has been applied to slabbed cores of Jurassic Smackover limestones from southwestern Alabama to enhance the complete petrologic description of the rocks. Through x-radiography, trace fossils have been revealed in what would otherwise appear to be homogeneous rock. In these biogenic structures, organic material, partly fecal in origin, is concentrated as infill packing in actively filled burrows. A microreducing environment within the burrow results in the mineralization by finely disseminated FeS/sub 2/. The density difference between FeS/sub 2/, which has a high absorption coefficient, and the surrounding calcium carbonate highlights the burrows in the x-radiographs. Thismore » characteristic burrow mineralization is shown well in the Smackover where a Zoophycus-Thalassinoides trace-fossil assemblage has been identified. Zoophycus, a feeding structure, is characterized by concave-upward traces with whorled peaks, and is best seen in slabs cut perpendicular to bedding. Thalassinoides is a dwelling structure characterized by a boxwork burrow system and is best seen in cores cut parallel to bedding. This assemblage is restricted to facies that is laterally persistent throughout the Smackover in most of Escambia County, Alabama. This trace-fossil assemblage is found in an oolitic pelletal packstone. This unit is overlain by an oolitic grainstone and is stratigraphically above a sparsely fossiliferous, laminated wackestone and packstone. Trace fossils in this horizon are abundant, but the traces are not found in stratigraphically adjacent lithofacies. Detecting these otherwise unseen trace fossils by x-radiography assisted the paleoenvironmental interpretation of this depositional facies as a low-energy subwave-base carbonate-shelf deposit.« less

Copper speciation in sulfidic solutions at low sulfur activity: Further evidence for cluster complexes?

NASA Astrophysics Data System (ADS)

Thompson, Richard A.; Helz, George R.

1994-07-01

The solubility of two as0-buffering assemblages in the Cu-S system have been studied: chalcocite-djurleite (Cc-Dj) and anilite-covellite (An-Cv). Ion activity products, [Cu +]HS -] 1/2[H +] - 1/2 (25°C, I = 0) at equilibrium, derived from solubility measurements in penicillamine solutions, are 10 -17.01 ± 0.05 (Cc-Dj) and 10 -17.14 ± 0.10 (An-Cv), from which ΔG° f = -82.11 kJ/mol for Cc and -74.77 kJ/mol for An. In the An-Cv assemblage, aCu2S = 0.55 (2 σ = 0.2) vs. 1.00 in the Cc-containing assemblage. The difference in aCu2S between the two assemblages is used in a novel way to estimate stoichiometry of Cu-HS complexes. The solubility of both assemblages (0.7-0.01 M NaHS, pH 7-12.5, 25°C) can be fit with a model incorporating the same two chemical species, one containing an odd number of Cu atoms (Cu(HS) 2-3, CU 3S 4H 2-3, or a higher multimer) and the other containing an even number of Cu atoms (Cu 2S(HS) 22-, Cu 4S 4H 22-, etc.). The trimer-tetramer model fits the combined data for the two assemblages distinctly better than the monomer-dimer model, but this result is very sensitive to uncertainty in aCu2S. Along with EXAFS results, the weight of the evidence favors small cluster complexes (2-5 Cu atoms), but is inconclusive at the present level of resolution. Multimers can be rationalized because condensation of metal-centered monomers to clusters provides a means for soft acid/base elements to maintain favored coordination geometries at low ligand to metal ratios. Based on the fitting methods developed here, previous covellite solubility data from this laboratory are reinterpreted in terms of Cu 2S 2(HS) 33-, Cu 2S 3)(S 4) 2-, and Cu(S 9)S 10) 3-; the last of these could also be represented by the trimer, Cu 3(S 7) 33-, which is homologous with a known complex. With the measured equilibrium constants, the speciation of Cu in the sulfidic zone of the Black Sea is calculated. Covellite is the stable Cu-S mineral, but the sulfidic water column is vastly supersaturated with respect to it. Most of the sulfidic water column is modestly (2.5-5.5 times) supersaturated with respect to Cc, hinting that this mineral metastably controls ΣCu. The slight supersaturation suggests that Cc occurs as 10-100 nm particles.

Formation of recent Pb-Ag-Au mineralization by potential sub-surface microbial activity

NASA Astrophysics Data System (ADS)

Tornos, Fernando; Velasco, Francisco; Menor-Salván, César; Delgado, Antonio; Slack, John F.; Escobar, Juan Manuel

2014-08-01

Las Cruces is a base-metal deposit in the Iberian Pyrite Belt, one of the world’s best-known ore provinces. Here we report the occurrence of major Pb-Ag-Au mineralization resulting from recent sub-surface replacement of supergene oxyhydroxides by carbonate and sulphide minerals. This is probably the largest documented occurrence of recent microbial activity producing an ore assemblage previously unknown in supergene mineralizing environments. The presence of microbial features in the sulphides suggests that these may be the first-described natural bacteriomorphs of galena. The low δ13C values of the carbonate minerals indicate formation by deep anaerobic microbial processes. Sulphur isotope values of sulphides are interpreted here as reflecting microbial reduction in a system impoverished in sulphate. We suggest that biogenic activity has produced around 3.1 × 109 moles of reduced sulphur and 1010 moles of CO2, promoting the formation of ca. 1.19 Mt of carbonates, 114,000 t of galena, 638 t of silver sulphides and 6.5 t of gold.

Cortlandtitic enclaves associated with calc-alkaline granites from Tapia-Asturias (Hercynian Belt, northwestern Spain)

NASA Astrophysics Data System (ADS)

Galán, G.; Suárez, O.

1989-10-01

Petrographic and mineralogical characteristics of amphibole-olivine- and pyroxene-bearing ultramafic rocks from Asturias (NW Spain) are dealt with in this paper. These rocks are of cortlandtitic type and occur as small rare enclaves in basic rocks related to Hercynian calc-alkaline, post-tectonic epizonal granites, in the northwest of the Iberian Peninsula. These particular ultramafic enclaves are characterized by poikilitic cumulate microtexture. Olivine (Fo 77-81), spinel, from chromite to pleonaste composition, enstatite, subordinated diopside and sulphides are included in large brown calcic amphibole crystals displaying an irregular zonation. Phlogopite and plagioclase are also found, in a much lower proportion, between the large amphibole crystals. Mineral assemblage and chemical composition of minerals indicate formation conditions of 1150°C, 7-8 kbar of Ptotal and PH 2O < Ptotal. These rocks could represent the earlier products of fractional crystallization from a hydrated high-alumina basalt involved in the genesis of the calc-alkaline granites. This basic magma would start crystallizing at a relatively deep level, carrying up the first products of its crystallization during its ascent.

Implications of using broadband photometry for compositional remote sensing of icy objects. [including natural satellites and asteroids

NASA Technical Reports Server (NTRS)

Clark, R. N.

1982-01-01

The validity and limitations of assuming bright surfaces are icy and dark surfaces are stony are investigated, and the limitations of JHK colorimetry for distinguishing icy versus stony objects are studied. The broadband JHK reflectances of a large range of minerals and mineral assemblages were computed, the visual albedo obtained, and the J-H and H-K colors computed. Visual reflectance was found to vary easily from 0.15 to 1.0 when the surface contains 99 percent or more water by weight. The effect of varying particulate weight fraction and grain size are described. Visual albedo is found to give no indication of the purity of an icy surface. The JHK colors of an ice and particulate mixture can fall anywhere in the classical J-H versus H-K diagram, and thus the diagram cannot be used to distinguish a predominantly rock surface from a predominantly ice one in a specific case, except where both J-H and H-K colors are less than about -0.2.

Evidence of phyllosilicates in Wooly Patch, an altered rock encountered at West Spur, Columbia Hills, by the Spirit rover in Gusev crater, Mars

USGS Publications Warehouse

Wang, A.; Korotev, R.L.; Jolliff, B.L.; Haskin, L.A.; Crumpler, L.; Farrand, W. H.; Herkenhoff, K. E.; de Souza, Jr.; Kusack, A.G.; Hurowitz, J.A.; Tosca, N.J.

2006-01-01

On its traverse to Columbia Hills, the Mars Exploration Rover Spirit investigated an outcrop designated "Wooly Patch" that exhibited morphological, mineralogical, and geochemical characteristics at the extreme ends of ranges observed among rocks studied at West Spur, a westward projecting salient near the foot of the Columbia Hills, Gusev crater. The major-element composition and Fe-mineralogy, as determined by the Alpha-Particle X-ray Spectrometer and Mo??ssbauer Spectrometer, are inconsistent with any reasonable assemblage of basaltic minerals in that there is an excess of Si and Al. The combined data are best explained by the presence of 14-17% phyllosilicate minerals. Phyllosilicates that account for the composition and cation ratios include members of the kaolinite, serpentine, chlorite, and septechlorite groups. The potential existence of kaolinite-type Al-rich phyllosilicates within the Wooly Patch outcrop suggests a mildly acidic environment (pH 4-6) in the past and an open hydrologic system with good drainage conditions in the environment where these rocks were altered. Copyright 2006 by the American Geophysical Union.

Spatial-temporal and genetic relationships between gold and antimony mineralization at gold-sulfide deposits of the Ob-Zaisan folded zone

NASA Astrophysics Data System (ADS)

Kalinin, Yu. A.; Naumov, E. A.; Borisenko, A. S.; Kovalev, K. R.; Antropova, A. I.

2015-05-01

The Ob-Zaisan folded zone is a fragment of a single structure composed of Paleozoic sedimentary and volcanogenic rocks (mainly black shale), which was formed at the margin of the Siberian continent and features a common set of magmatic complexes and mineral systems. However, there are some differences that determine the specific geological and metallogenic features of the Irtysh-Zaisan and Kolyvan-Tomsk fragments of the Ob-Zaisan folded zone. In the gold deposits of the West Kalba and Kolyvan-Tomsk auriferous belt, the main gold-sulfide mineralization is controlled by zones of shearing and dynamic metamorphism in carbonaceous carbonate-terrigenous rocks. This type of mineralization was formed in tectonic blocks in a compressional setting. Antimony mineralization is characterized by brecciated textures and the vein-like morphology of ore bodies, reflecting extensional tectonics. At some deposits (Zherek, Mirazh, Dalny), Sb mineralization is spatially separated from the main gold-sulfide ores and shows cross-cutting relations to the principal ore-controlling structures. In other gold deposits, stibnite is spatially associated with disseminated gold-sulfide ores and forms mineral assemblages with Ni, Co, Au, Pb, and Fe (Alimbet, Zhanan, Legostaevskoe, Semiluzhenskoe, and Kamenskoe deposits). This study reveals no direct correlation between Au and Sb in gold-sulfide ores of these deposits. SEM analysis indicated the absence of free gold in stibnite veins. However, atomic absorption and electron microprobe analysis indicated the presence of "invisible gold" from a few ppm to several tens of ppm in the stibnite. High gold contents in the gold-sulfide ores overprinted by antimony mineralization (Suzdalskoe, Zhanan, and Legostaevskoe deposits) can be explained by the processes of regeneration and redeposition. The results of microstructural observations, isotope geochronology, studies of mineral assemblages and fluid inclusions in the ores from gold deposits of the Ob-Zaisan folded zone suggest that antimony mineralization was formed at gold-polysulfide stage, which was separated from the early ore pyrite-arsenopyrite stage by a 30 Ma time gap. It can be assumed that the essentially stibnite mineralization was formed at a separate stage and was separated from the gold-polysulfide mineralization by a 7 Ma interval of tectonic activity. Our Ar-Ar data on sericite from ore samples, combined with U-Pb data on zircons from igneous rocks and previous data from the literature show that there were two major stages of ore formation: the Early Permian (282-270 Ma) and the Early Triassic (250-240 Ma). Most researchers suggest that these stages of mineralization can be related to the epochs of intraplate magmatism that led to the formation of the Tarim (280 Ma) and Siberian (250 Ma) large igneous provinces. These global geological events are generally connected with the influence of Tarim and Siberian mantle plumes.

Redox processes in subducting oceanic crust recorded by sulfide-bearing high-pressure rocks and veins (SW Tianshan, China)

NASA Astrophysics Data System (ADS)

Li, Ji-Lei; Gao, Jun; Klemd, Reiner; John, Timm; Wang, Xin-Shui

2016-09-01

The oxidized nature of the sub-arc mantle and hence arc magmas is generally interpreted as a result of the migration of subduction-related oxidizing fluids or melts from the descending slab into the mantle wedge. This is of particular importance seeing that the oxidization state of sub-arc magmas seems to play a key role in the formations of arc-related ore deposits. However, direct constraints on the redox state of subducted oceanic crust are sparse. Here, we provide a detailed petrological investigation on sulfide- and oxide-bearing eclogites, blueschists, micaschists, eclogite-facies and retrograde veins from the Akeyazi high-pressure (HP) terrane (NW China) in order to gain insight into the redox processes recorded in a subducting oceanic slab. Sulfides in these rocks are mainly pyrite and minor pyrrhotite, chalcopyrite, bornite, molybdenite, sphalerite and chalcocite, including exsolution textures of bornite-chalcopyrite intergrowth. Magnetite, ilmenite and pyrite occur as inclusions in garnet, whereas sulfides are dominant in the matrix. Large pyrite grains in the matrix contain inclusions of garnet, omphacite and other HP index minerals. However, magnetite replacing pyrite textures are commonly observed in the retrograded samples. The eclogite-facies and retrograde veins display two fluid events, which are characterized by an early sulfide-bearing and a later magnetite-bearing mineral assemblage, respectively. Textural and petrological evidences show that the sulfides were mainly formed during HP metamorphism. Mineral assemblage transitions reveal that the relative oxygen fugacity of subducted oceanic crust decreases slightly with increasing depths. However, according to oxygen mass balance calculations, based on the oxygen molar quantities ( nO2), the redox conditions remain constant during HP metamorphism. At shallow levels (<60 km) in the subduction channel, interaction with oxidized fluid seems to have caused an increase of the oxygen fugacity and the oxidation state of exhuming HP rocks. This study suggests that oxygen components are not released in significant amounts during HP metamorphism of subducted oceanic crust and, thus, cannot be responsible for oxidizing the mantle wedge and increasing the oxidation state of sub-arc mantle melts.

Alteration and geochemical zoning in Bodie Bluff, Bodie mining district, eastern California

USGS Publications Warehouse

Herrera, P.A.; Closs, L.G.; Silberman, M.L.

1993-01-01

Banded, epithermal quartz-adularia veins have produced about 1.5 million ounces of gold and 7 million ounces of silver from the Bodie mining district, eastern California. The veins cut dacitic lava flows, pyroclastic rocks and intrusions. Sinter boulders occur in a graben structure at the top of Bodie Bluff and fragments of sinter and mineralized quartz veins occur in hydrothermal breccias nearby. Explosive venting evidently was part of the evolution of the ore-forming geothermal systems which, at one time, must had reached the paleosurface. Previous reconnaissance studies at Bodie Bluff suggested that the geometry of alteration mineral assemblages and distribution of some of the major and trace elements throughout the system correspond to those predicted by models of hot-spring, volcanic rock hosted precious metal deposits (Silberman, 1982; Silberman and Berger, 1985). The current study was undertaken to evaluate these sugestions further. About 500 samples of quartz veins and altered rocks, including sinter, collected over a vertical extent of 200 meters within Bodie Bluff were petrographically examined and chemically analyzed for trace elements by emission spectrographic and atomic absorption methods. Sixty-five samples were analyzed for major elements by X-ray fluorescence methods. The results of these analyses showed that, in general, alteration mineral assemblage and vertical geochemical zoning patterns follow those predicted for hot-spring deposits, but that geochemical zoning patterns for sinter and quartz veins (siliceous deposits), and altered wall rocks are not always similar. The predicted depth-concentration patterns for some elements, notably Au, Ag, Hg, and Tl in quartz veins, and Hg, As and Ag in wall rocks were not as expected, or were perturbed by the main ore producing zone. For both quartz veins and altered wall rocks, the main ore zone had elevated metal contents. Increased concentration of many of these elements could indicate proximity to this zone. However, irregularities in the distribution of some key elements, such as Au and Ag, relative to the predictive models suggest that a larger suite of elements be considered for exploration for ore zones within the district. ?? 1993.

A Critical Appraisal of the `Day' Diagram

NASA Astrophysics Data System (ADS)

Roberts, A. P.; Tauxe, L.; Heslop, D.

2017-12-01

The `Day' diagram [Day et al., 1977; doi:10.1016/0031-9201(77)90108-X] is used widely to infer the mean domain state of magnetic mineral assemblages. The Day plot coordinates are the ratios of the saturation remanent magnetization to saturation magnetization (Mrs/Ms) and the coercivity of remanence to coercivity (Bcr/Bc), as determined from a major hysteresis loop and a backfield demagnetization curve. Based on theoretical and empirical arguments, Day plots are typically demarcated into stable single domain (SD), `pseudosingle domain' (`PSD'), and multidomain (MD) zones. It is a simple task to determine Mrs/Ms and Bcr/Bc for a sample and to assign a mean domain state based on the boundaries defined by Day et al. [1977]. Many other parameters contribute to variability in a Day diagram, including surface oxidation, mineral stoichiometry, stress state, magnetostatic interactions, and mixtures of magnetic particles with different sizes and shapes. Bulk magnetic measurements usually lack detailed independent evidence to constrain each free parameter, which makes the Day diagram fundamentally ambiguous. This raises questions about its usefulness for diagnosing magnetic particle size variations. The Day diagram is also used to make inferences about binary mixing of magnetic particles, where, for example, mixtures of SD and MD particles give rise to a bulk `PSD' response even though the concentration of `PSD' grains could be zero. In our assessment of thousands of hysteresis measurements of geological samples, binary mixing occurs in a tiny number of cases. Ternary, quaternary, and higher order mixing are usually observed. Also, uniaxial SD and MD end-members are nearly always inappropriate for considering mixing because uniaxial SD particles are virtually non-existent in igneous rocks. Thus, use of mixing lines in Day diagrams routinely provides unsatisfactory representations of particle size variations. We critically appraise the Day diagram and argue that its many ambiguities limit its use so severely that it should be abandoned. A suitable alternative is not obvious, but new approaches need to be developed to understand the magnetic properties of individual magnetic components in samples with mixed magnetic mineral assemblages.

Mechanical properties and leaching modeling of activated incinerator bottom ash in Portland cement blends

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

Onori, Roberta, E-mail: Roberta.onori@uniroma1.it; Polettini, Alessandra; Pomi, Raffaella

2011-02-15

In the present study the evolution of mechanical strength and the leaching behavior of major and trace elements from activated incinerator bottom ash/Portland cement mixtures were investigated. Chemical and mechanical activation were applied with the purpose of improving the reactivity of bottom ash in cement blends. Chemical activation made use of NaOH, KOH, CaCl{sub 2} or CaSO{sub 4}, which were selected for the experimental campaign on the basis of the results from previous studies. The results indicated that CaCl{sub 2} exhibited by far the best effects on the evolution of the hydration process in the mixtures; a positive effect onmore » mechanical strength was also observed when CaSO{sub 4} was used as the activator, while the gain in strength produced by KOH and NaOH was irrelevant. Geochemical modeling of the leaching solutions provided information on the mineral phases responsible for the release of major elements from the hardened materials and also indicated the important role played by surface sorption onto amorphous Fe and Al minerals in dictating the leaching of Pb. The leaching of the other trace metal cations investigated (Cu, Ni and Zn) could not be explained by any pure mineral included in the thermodynamic database used, suggesting they were present in the materials in the form of complex minerals or phase assemblages for which no consistent thermodynamic data are presently available in the literature.« less

Mechanical properties and leaching modeling of activated incinerator bottom ash in Portland cement blends.

PubMed

Onori, Roberta; Polettini, Alessandra; Pomi, Raffaella

2011-02-01

In the present study the evolution of mechanical strength and the leaching behavior of major and trace elements from activated incinerator bottom ash/Portland cement mixtures were investigated. Chemical and mechanical activation were applied with the purpose of improving the reactivity of bottom ash in cement blends. Chemical activation made use of NaOH, KOH, CaCl(2) or CaSO(4), which were selected for the experimental campaign on the basis of the results from previous studies. The results indicated that CaCl(2) exhibited by far the best effects on the evolution of the hydration process in the mixtures; a positive effect on mechanical strength was also observed when CaSO(4) was used as the activator, while the gain in strength produced by KOH and NaOH was irrelevant. Geochemical modeling of the leaching solutions provided information on the mineral phases responsible for the release of major elements from the hardened materials and also indicated the important role played by surface sorption onto amorphous Fe and Al minerals in dictating the leaching of Pb. The leaching of the other trace metal cations investigated (Cu, Ni and Zn) could not be explained by any pure mineral included in the thermodynamic database used, suggesting they were present in the materials in the form of complex minerals or phase assemblages for which no consistent thermodynamic data are presently available in the literature. Copyright © 2010 Elsevier Ltd. All rights reserved.

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

Metamorphic P-T path and zircon U-Pb dating of HP mafic granulites in the Yushugou granulite-peridotite complex, Chinese South Tianshan, NW China

NASA Astrophysics Data System (ADS)

Zhang, Lu; Zhang, Lifei; Xia, Bin; Lü, Zeng

2018-03-01

Co-existing granulite and peridotite may represent relics of the paleo-suture zone and provides an optimal opportunity for better understanding of orogeny between two blocks. In this study, we carried out petrological and U-Pb zircon dating investigation on the HP mafic granulites associated with peridotite complex at Yushugou in Chinese South Tianshan. The studied samples include garnet-bearing high-pressure mafic granulites which can be subdivided into two types: Type I orthopyroxene-free and Type II orthopyroxene-bearing granulites and amphibolite. Type I granulite (Y21-2) has a mineral assemblage of garnet (33 vol.%), clinopyroxene (32 vol.%) and plagioclase (30 vol.%); and Type II granulite (Y18-8) has a mineral assemblage of garnet (22 vol.%), clinopyroxene (10 vol.%), orthopyroxene (14 vol.%), plagioclase (45 vol.%) and quartz. Garnet in both granulites exhibits core-rim structure characterized by increasing grossular and decreasing pyrope from core to rim. Petrographic observations and phase equilibrium modeling using THERMOCALC in the NCFMASHTO system for the mafic granulites (Y21-2 and Y18-8) show three stages of metamorphism: Stage I (granulite facies) was recognized by the large porphyroblastic garnet core, with P-T conditions of 9.8-10.4 Kbar and 860-900 °C (Y21-2) and 9.9-10.6 Kbar and 875-890 °C (Y18-8), respectively; Stage II (HP granulite facies) has peak P-T conditions of 12.1 Kbar at 755 °C (Y21-2) and 13.8 Kbar at 815 °C (Y18-8) using mineral assemblages combining with garnet rim compositions with maximum grossular and minimum pyrope contents; Stage III (amphibolite facies) was characterized by the development of calcic amphibole in granulites with temperature of 446-563 °C. Therefore, an anticlockwise P-T path characterized by simultaneous temperature-decreasing and pressure-increasing was inferred for the Yushugou HP mafic granulite. Studies of zircon morphology and inclusions, combined with zircon U-Pb dating and REE geochemistry indicate that their protolith's ages of the mafic granulites were ∼430 Ma, while the metamorphism could occur at three stages with ages of ∼390 Ma, ∼340 Ma and ∼320 Ma, which may correspond to Stage I, II and III, respectively. We interpret the HP mafic granulites from the Yushugou granulite-peridotite complex to be formed by the cooling subduction of the lower crustal rocks from the hanging wall of central Tianshan block during the northward subduction of the south Tianshan paleo-ocean from Devonian to Carboniferous.

Examining Metasomatism in Low fO2 Environments: Exploring Sulfidation Reactions in Various Planetary Bodies

NASA Technical Reports Server (NTRS)

Srinivasan, P.; Shearer, C. K.; McCubbin, F. M.; Bell, A. S.; Agee, C. B.

2016-01-01

Hydrothermal systems are common on Earth in a variety of tectonic environments and at different temperature and pressure conditions. These systems are commonly dominated by H2O, and they are responsible for element transport and the production of ore deposits. Unlike the Earth (fO2FMQ), many other planetary bodies (e.g., Moon and asteroids) have fO2 environments that are more reduced (IW+/-2), and H2O is not the important solvent responsible for element transport. One example of a texture that could result from element transport and metasomatism, which appears to occur on numerous planetary bodies, is sulfide-silicate intergrowths. These subsolidus assemblages are interpreted to form as a result of sulfidation reactions from a S-rich fluid phase. The composition of fluids may vary within and among parent bodies and could be sourced from magmatic (e.g. Moon) or impact processes (e.g. HED meteorites and Moon). For example, it has been previously demonstrated on the Moon that the interaction of olivine with a hydrogen- and sulfur-bearing vapor phase altered primary mineral assemblages, producing sulfides (e.g. troilite) and orthopyroxene. Formation of these types of "sulfidation" assemblages can be illustrated with the following reaction: Fe2SiO4(ol) + 1/2 S(2 system) = FeS(troi)+ FeSiO3(opx) + 1/2 O2 system. The products of this reaction, as seen in lunar rocks, is a vermicular or "worm-like" texture of intergrown orthopyroxene and troilite. Regardless of the provenance of the S-bearing fluid, the minerals in these various planetary environments reacted in the same manner to produce orthopyroxene and troilite. Although similar textures have been identified in a variety of parent bodies, a comparative study on the compositions and the origins of these sulfide-silicate assemblages has yet to be undertaken. The intent of this study is to examine and compare sulfide-silicate intergrowths from various planetary bodies to explore their petrogenesis and examine the nature of low fO2 (IW+/-2) element migration and sulfidation reactions.

Mineralogy and geochemistry of the Lower Cretaceous siliciclastic rocks of the Morita Formation, Sierra San José section, Sonora, Mexico

NASA Astrophysics Data System (ADS)

Madhavaraju, J.; Pacheco-Olivas, S. A.; González-León, Carlos M.; Espinoza-Maldonado, Inocente G.; Sanchez-Medrano, P. A.; Villanueva-Amadoz, U.; Monreal, Rogelio; Pi-Puig, T.; Ramírez-Montoya, Erik; Grijalva-Noriega, Francisco J.

2017-07-01

Clay mineralogy and geochemical studies were carried out on sandstone and shale samples collected from the Sierra San José section of the Morita Formation to infer the paleoclimate and paleoweathering conditions that prevailed in the source region during the deposition of these sediments. The clay mineral assemblages (fraction < 2 μm) of the Sierra San José section are composed of chlorite and illite. The abundance of illite and chlorite in the studied samples suggest that the physical weathering conditions were dominant over chemical weathering. Additionally, the illite and chlorite assemblages reflect arid or semi-arid climatic conditions in the source regions. K2O/Al2O3 ratio of shales vary between 0.15 and 0.26, which lie in the range of values for clay minerals, particularly illite composition. Likewise, sandstones vary between 0.06 and 0.13, suggesting that the clay minerals are mostly kaolinte and illite types. On the chondrite-normalized diagrams, sandstone and shale samples show enriched light rare earth elements (LREE), flat heavy rare earth elements (HREE) patterns and negative Eu anomalies. The CIA and PIA values and A-CN-K plot of shales indicate low to moderate degree of weathering in the source regions. However, the sandstones have moderate to high values of CIA and PIA suggesting a moderate to intense weathering in the source regions. The SiO2/Al2O3 ratios, bivariate and ternary plots, discriminant function diagram and elemental ratios indicate the felsic source rocks for sandstone and shale of the Morita Formation.

Oxygen isotope evidence for submarine hydrothermal alteration of the Del Puerto ophiolite, California

USGS Publications Warehouse

Schiffman, P.; Williams, A.E.; Evarts, R.C.

1984-01-01

The oxygen isotope compositions and metamorphic mineral assemblages of hydrothermally altered rocks from the Del Puerto ophiolite and overlying volcaniclastic sedimentary rocks at the base of the Great Valley sequence indicate that their alteration occurred in a submarine hydrothermal system. Whole rock ??18O compositions decrease progressively down section (with increasing metamorphic grade): +22.4??? (SMOW) to +13.8 for zeolite-bearing volcaniclastic sedimentary rocks overlying the ophiolite; +19.6 to +11.6 for pumpellyite-bearing metavolcanic rocks in the upper part of the ophiolite's volcanic member; +12.3 to +8.1 for epidote-bearing metavolcanic rocks in the lower part of the volcanic member; +8.5 to +5.7 for greenschist facies rocks from the ophiolite's plutonic member; +7.6 to +5.8 for amphibolite facies or unmetamorphosed rocks from the plutonic member. Modelling of fluid-rock interaction in the Del Puerto ophiolite indicates that the observed pattern of upward enrichment in whole rock ??18O can be best explained by isotopic exchange with discharging 18O-shifted seawater at fluid/rock mass ratios near 2 and temperatures below 500??C. 18O-depleted plutonic rocks necessarily produced during hydrothermal circulation were later removed as a result of tectonism. Submarine weathering and later burial metamorphism at the base of the Great Valley sequence cannot by itself have produced the zonation of hydrothermal minerals and the corresponding variations in oxygen isotope compositions. The pervasive zeolite and prehnite-pumpellyite facies mineral assemblages found in the Del Puerto ophiolite may reflect its origin near an island arc rather than deep ocean spreading center. ?? 1984.

Fish assemblages in borrow-pit lakes of the Lower Mississippi River

USGS Publications Warehouse

Miranda, Leandro E.; Killgore, K. J.; Hoover, J.J.

2013-01-01

Borrow-pit lakes encompass about a third of the lentic water habitats (by area) in the active floodplain of the Lower Mississippi River, yet little is known about their fish assemblages. We investigated whether fish assemblages supported by borrow-pit lakes resembled those in oxbow lakes to help place the ecological relevance of borrow-pit lakes in context with that of natural floodplain lakes. In all, we collected 75 fish species, including 65 species in eight borrow-pit lakes, 52 species in four riverside oxbow lakes, and 44 species in eight landside oxbow lakes. Significant differences in several species richness metrics were evident between borrow-pit lakes and landside oxbow lakes but not between borrow-pit lakes and riverside oxbow lakes. All three lake types differed in fish assemblage composition. Borrow-pit lakes and riverside oxbow lakes tended to include a greater representation of fish species that require access to diverse environments, including lentic, lotic, and palustrine habitats; fish assemblages in landside oxbow lakes included a higher representation of lacustrine species. None of the fish species collected in borrow-pit lakes was federally listed as threatened or endangered, but several were listed as species of special concern by state governments in the region, suggesting that borrow-pit lakes provide habitat for sensitive riverine and wetland fish species. Differences in fish assemblages among borrow-pit lakes were linked to engineered morphologic features, suggesting that diversity in engineering can contribute to diversity in fish assemblages; however, more research is needed to match engineering designs with fish assemblage structures that best meet conservation needs.

Precious metals associated with Late Cretaceous-early Tertiary igneous rocks of southwestern Alaska

USGS Publications Warehouse

Bundtzen, Thomas K.; Miller, Marti L.; Goldfarb, Richard J.; Miller, Lance D.

1997-01-01

Placer gold and precious metal-bearing lode deposits of southwestern Alaska lie within a region 550 by 350 km, herein referred to as the Kuskokwim mineral belt. This mineral belt has yielded 100,240 kg (3.22 Moz) of gold, 12, 813 kg (412,000 oz) of silver, 1,377,412 kg (39,960 flasks) of mercury, and modest amounts of antimony and tungsten derived primarily from the late Cretaceous-early Tertiary igneous complexes of four major types: (1) alkali-calcic, comagmatic volcanic-plutonic complexes and isolated plutons, (2) calc-alkaline, meta-aluminous reduced plutons, (3) peraluminous alaskite or granite-porphyry sills and dike swarms, and (4) andesite-rhyolite subaerial volcanic rocks.About 80 percent of the 77 to 52 Ma intrusive and volcanic rocks intrude or overlie the middle to Upper Cretaceous Kuskokwim Group sedimentary and volcanic rocks, as well as the Paleozoic-Mesozoic rocks of the Nixon Fork, Innoko, Goodnews, and Ruby preaccretionary terranes.The major precious metal-bearing deposit types related to Late Cretaceous-early Tertiary igneous complexes of the Kuskokwim mineral belt are subdivided as follows: (1) plutonic-hosted copper-gold polymetallic stockwork, skarn, and vein deposits, (2) peraluminous granite-porphory-hosted gold polymetallic deposits, (3) plutonic-related, boron-enriched silver-tin polymetallic breccia pipes and replacement deposits, (4) gold and silver mineralization in epithermal systems, and (5) gold polymetallic heavy mineral placer deposits. Ten deposits genetically related to Late Cretaceous-early Tertiary intrusions contain minimum, inferred reserves amounting to 162,572 kg (5.23 Moz) of gold, 201,015 kg (6.46 Moz) silver, 12,160 metric tons (t) of tin, and 28,088 t of copper.The lodes occur in veins, stockworks, breccia pipes, and replacement deposits that formed in epithermal to mesothermal temperature-pressure conditions. Fluid inclusion, isotopic age, mineral assemblage, alteration assemblage, and structural data indicate that many of the mineral deposits associated with Late Cretaceous-early tertiary volcanic and plutonic rocks represent geologically and spatially related, vertically zoned hydrothermal systems now exposed at several erosional levels.Polymetallic gold deposits of the Kuskokwim mineral belt are probably related to 77 to 52 Ma plutonism and volcanism associated with a period of rapid, north-directed subduction of the Kula plate. The geologic interpretation suggests that igneous complexes of the Kuskokwim mineral belt formed in an intracontinental back-arc setting during a period of extensional, wrench fault tectonics.The Kuskokwim mineral belt has many geologic and metallogenic features similar to other precious metal-bearing systems associated with arc-related igneous rocks such as the Late Cretaceous-early Tertiary Rocky Mountain alkalic province, the Jurassic Mount Milligan district of central British Columbia, the Andean orogen of South America, and the Okhotsk-Chukotka belt of northeast Asia.

Mineralogy and Microstructures of Shock-Induced Melt Veins in Chondrites

NASA Technical Reports Server (NTRS)

Sharp, Thomas G.

2000-01-01

The applicability of phase equilibrium data to the interpretation of shock-induced melt veins can only be tested by a detailed study of melt- vein mineralogy to see how high-pressure assemblages vary as a function of shock conditions inferred from other indicators. We have used transmission electron microscopy (TEM), analytical electron microscopy (AEM), scanning electron microscopy (SEM), electron microprobe analysis (EMA) and optical petrography to characterize the mineralogy, microstructures, and compositions of melt veins and associated high-pressure minerals in shocked chondrites and SNC meteorites. In the processes, we have gained a better understanding of what melt veining can tell us about shock conditions and we have discovered new mineral phases in chondritic and SNC meteorites.

Experimental aqueous alteration of the Allende meteorite under oxidizing conditions: Constraints on asteroidal alteration

NASA Astrophysics Data System (ADS)

Jones, Catherine L.; Brearley, Adrian J.

2006-02-01

We have performed an experimental study of the aqueous alteration of the Allende CV3 carbonaceous chondrite under highly oxidizing conditions, in order to examine the alteration behavior of Allende's anhydrous mineralogy. The experiments were carried out at temperatures of 100, 150, and 200 °C, for time periods between 7 and 180 days, with water/rock ratios ranging from 1:1 to 9:1. Uncrushed cubes of Allende were used so that the spatial relationships between reactant and product phases could be examined in detail. Scanning electron microscope studies show that in all the experiments, even those of short duration (7 days), soluble salts of Ca and Mg (CaSO 4, CaCO 3, and MgSO 4) precipitated on the sample surface, indicating that these elements are rapidly mobilized during alteration. In addition, iron oxides and hydroxides formed on the sample surfaces. The sulfates, carbonates, and the majority of the iron-bearing secondary minerals are randomly distributed over the surface of samples. In some instances the iron oxides and hydroxides are constrained to the boundaries of altering mineral grains. Transmission electron microscope studies show that the FeO-rich olivine in the interior of the samples has altered to form interlayered serpentine/saponite and Fe-oxyhydroxides. The degree of alteration increases significantly with increasing water/rock ratio, and to a lesser extent with increasing duration of heating. The serpentine/saponite forms both by direct replacement of the olivine in crystallographically oriented intergrowths, and by recrystallization of an amorphous Si-rich phase that precipitates in pore space between the olivine grains. The alteration assemblage bears many similarities to those found in altered carbonaceous chondrites, although in detail there are important differences, which we attribute to (a) the relatively high temperatures of our experiments and (b) comparatively short reaction times compared with the natural examples. In terms of mineral assemblage, our experiments most closely resemble alteration in the CI chondrites, although the degree of alteration of our experiments is much lower. CI chondrites contain serpentine/saponite intergrowths and veins of Ca-sulfate and Ca-carbonate as well as the Fe-oxyhydroxide, ferrihydrite. However, the phyllosilicate phases formed in our experiments are somewhat coarser-grained than the finest phyllosilicate fraction present in CI chondrites, suggesting that alteration of the CI chondrites occurred at lower temperatures. In terms of mineral assemblage, our experiments also appear to come close to matching CR chondrites, although we infer that CR alteration probably occurred at temperatures <100 °C, based on the very fine-grained size of phyllosilicates in CR matrices.

Mineralogical composition of the meteorite El Pozo (Mexico): a Raman, infrared and XRD study.

PubMed

Ostrooumov, Mikhail; Hernández-Bernal, Maria del Sol

2011-12-01

The Raman (RMP), infrared (IR) and XRD analysis have been applied to the examination of mineralogical composition of El Pozo meteorite (an ordinary chondrite L5 type; village Valle of Allende, founded in State of Chihuahua, Mexico: 26°56'N and 105°24'W, 1998). RMP measurements in the range of 100-3500 cm(-1) revealed principal characteristic bands of the major minerals: olivine, two polymorph modifications of pyroxene (OPx and CPx) and plagioclase. Some bands of the minor minerals (hematite and goethite) were also identified. All these minerals were clearly distinguished using IR and XRD techniques. XRD technique has shown the presence of some metallic phases such as kamacite and taenite as well as troilite and chromite. These minerals do not have characteristic Raman spectra because Fe-Ni metals have no active modes for Raman spectroscopy and troilite is a weak Raman scatterer. Raman mapping microspectroscopy was a key part in the investigation of El Pozo meteorite's spatial distribution of the main minerals because these samples are structurally and chemically complex and heterogeneous. The mineral mapping by Raman spectroscopy has provided information for a certain spatial region on which a spatial distribution coexists of the three typical mineral assemblages: olivine; olivine+orthopyroxene; and orthopyroxene. Copyright © 2011 Elsevier B.V. All rights reserved.

Phosphatized algal-bacterial assemblages in Late Cretaceous phosphorites of the Voronezh Anteclise

NASA Astrophysics Data System (ADS)

Maleonkina, Svetlana Y.

2003-01-01

Late Cretaceous phosphogenesis of the Voronezh Anteclise has occurred during Cenomanian and Early Campanian. SEM studies show the presence of phosphatized algal-bacterial assemblages both in Cenomanian and Campanian phosphorites. In some Cenomanian nodular phosphorite samples revealed empty tubes 1 - 5 microns in diameter, which are most likely trichomes of cyanobacterial filaments. Other samples contained accumulations of spheres 0,5-3 microns, similar to coccoidal bacteria. Complicated tubular forms with variable diameter 2 - 5 microns occur on surface of some quartz grains in nodules. They are probably pseudomorphs after algae. We found similar formations in the Campanian phosphate grains. Frequently, grain represents a cyanobacterial mat, which is sometimes concentrically coated by phosphatic films. The films of some grains retain the primary structure, their concentric layers are formed by pseudomorphs after different bacterial types and obviously they represent oncolite. In other cases, the primary structure is unobservable because of recrystallization process erases them. Occasionally, the central part retains the coccoidal structure and the recrystallization affects only films. Besides the core of such oncolite can be represented not only by phosphatic grain, but also by grains of other minerals, such as quartz, glauconite and heavy minerals, which serve as a substrate for cyanobacterial colonies. Bacteria also could settle on cavity surfaces and interiors frames of sponge fragments, teeth and bones.

Geochemical and mineralogical characterization of a neutral, low-sulfide/high-carbonate tailings impoundment, Markušovce, eastern Slovakia.

PubMed

Hiller, Edgar; Petrák, Marián; Tóth, Roman; Lalinská-Voleková, Bronislava; Jurkovič, L'ubomír; Kučerová, Gabriela; Radková, Anežka; Sottník, Peter; Vozár, Jaroslav

2013-11-01

Tailings deposits generated from mining activities represent a potential risk for the aquatic environment through the release of potentially toxic metals and metalloids occurring in a variety of minerals present in the tailings. Physicochemical and mineralogical characteristics of tailings such as total concentrations of chemical elements, pH, ratio of acid-producing to acid-neutralizing minerals, and primary and secondary mineral phases are very important factors that control the actual release of potentially toxic metals and metalloids from the tailings to the environment. The aims of this study are the determination of geochemical and mineralogical characteristics of tailings deposited in voluminous impoundment situated near the village of Markušovce (eastern Slovakia) and identification of the processes controlling the mobility of selected toxic metals (Cu, Hg) and metalloids (As, Sb). The studied tailings have unique features in comparison with the other tailings investigated previously because of the specific mineral assemblage primarily consisting of barite, siderite, quartz, and minor sulfides. To meet the aims, samples of the tailings were collected from 3 boreholes and 15 excavated pits and subjected to bulk geochemical analyses (i.e., determination of chemical composition, pH, Eh, acid generation, and neutralization potentials) combined with detailed mineralogical characterization using optical microscopy, X-ray diffraction (XRD), electron microprobe analysis (EMPA), and micro-X-ray diffraction (μ-XRD). Additionally, the geochemical and mineralogical factors controlling the transfer of potentially toxic elements from tailings to waters were also determined using short-term batch test (European norm EN 12457), sampling of drainage waters and speciation-equilibrium calculations performed with PHREEQC. The tailings mineral assemblage consists of siderite, barite, quartz, and dolomite. Sulfide minerals constitute only a minor proportion of the tailings mineral assemblage and their occurrence follows the order: chalcopyrite > pyrite > tetrahedrite>arsenopyrite. The mineralogical composition of the tailings corresponds well to the primary mineralization mined. The neutralization capacity of the tailings is high, as confirmed by the values of neutralization potential to acid generation potential ratio, ranging from 6.7 to 63.9, and neutral to slightly alkaline pH of the tailings (paste pH 7.16-8.12) and the waters (pH 7.00-8.52). This is explained by abundant occurrence of carbonate minerals in the tailings, which readily neutralize the acidity generated by sulfide oxidation. The total solid-phase concentrations of metal(loid)s decrease as Cu>Sb>Hg>As and reflect the proportions of sulfides present in the tailings. Sulfide oxidation generally extends to a depth of 2 m. μ-XRD and EMPA were used to study secondary products developed on the surface of sulfide minerals and within the tailings. The main secondary minerals identified are goethite and X-ray amorphous Fe oxyhydroxides and their occurrence decreases with increasing tailings depth. Secondary Fe phases are found as mineral coatings or individual grains and retain relatively high amounts of metal(loid)s (up to 57.6 wt% Cu, 1.60 wt% Hg, 23.8 wt% As, and 2.37 wt% Sb). Based on batch leaching tests and lysimeter results, the mobility of potentially toxic elements in the tailings is low. The limited mobility of metals and metalloids is due to their retention by Fe oxyhydroxides and low solubilities of metal(loid)-bearing sulfides. The observations are consistent with PHREEQC calculations, which predict the precipitation of Fe oxyhydroxides as the main solubility-controlling mineral phases for As, Cu, Hg, and Sb. Waters discharging from tailings impoundment are characterized by a neutral to slightly alkaline pH (7.52-7.96) and low concentrations of dissolved metal(loid)s (<5-7.0 μg/L Cu, <0.1-0.3 μg/L Hg, 5.0-16 μg/L As, and 5.0-43 μg/L Sb). Primary factors influencing aqueous chemistry at the site are mutual processes of sulfide oxidation and carbonate dissolution as well as precipitation reactions and sorption onto hydrous ferric oxides abundantly present at the discharge of the impoundment waters. The results of the study show that, presently, there are no threats of acid mine drainage formation at the site and significant contamination of natural aquatic ecosystem in the close vicinity of the tailings impoundment.

Fractional ultrabasic-basic evolution of upper-mantle magmatism: Evidence from xenoliths in kimberlites, inclusions in diamonds and experiments

NASA Astrophysics Data System (ADS)

Litvin, Yuriy; Kuzyura, Anastasia

2017-04-01

Ultrabasic peridotites and pyroxenites together with basic eclogites are the upper-mantle in situ rocks among xenoliths in kimberlites. Occasionally their diamond-bearing varieties have revealed within the xenoliths. Therewith the compositions of rock-forming minerals demonstrate features characteristic for primary diamond-included minerals of peridotite and eclogite parageneses (the elevated contents of Cr-component in peridotitic garnets and Na-jadeitic component in eclogitic clinopyroxenes). High-pressure experimental study of melting equilibria on the multicomponent peridotie-pyroxenite system olivine Ol - orthopyroxene Opx - clinopyroxene Cpx - garnet Grt showed that Opx disappeared in the peritectic reaction Opx+L→Cpx (Litvin, 1991). As a result, the invariant peritectic equilibrium Ol+Opx+Cpx+Grt+L of the ultrabasic system was found to transform into the univariant cotectic assemblage Ol+Cpx+Grt+L. Further experimental investigation showed that olivine reacts with jadeitic component (Jd) with formation of garnet at higher 4.5 GPa (Gasparik, Litvin, 1997). Study of melting relations in the multicomponent system Ol - Cpx - Jd permits to discover the peritectic point Ol+Omph+Grt+L (where Omph - omphacitic clinopyroxene) at concentration 3-4 wt.% Jd-component in the system. The reactionary loss of Opx and Ol makes it possible to transform the 4-phase garnet lherzolite ultrabasic association into the bimineral eclogite assemblage. The regime of fractional Ol, Cpx and Grt crystallization must be accompanied by increasing content of jadeitic component in residual melts that causes the complete "garnetization of olivine". In the subsequent evolution, the melts would have to fractionate for basic SiO2-saturated compositions responsible for petrogenesis of eclogite varieties marked with accessory corundum Crn, kyanite Ky and coesite Coe. Both the peritectic mechanisms occur in regime of fractional crystallization. The sequence of the upper-mantle fractional ultrabasic-basic magmatic evolution and petrogenesis may be controlled by the following melting relations: from Ol, Opx, L field to cotectic curve Ol, Opx, Cpx, L, peritectic point Ol, Opx, Cpx, Grt, L (loss of Opx), cotectic curve Ol, (Cpx+Jd), Grt, L, peritectic point Ol, (Cpx→Omph), Grt, L (loss of Ol), divariant field Omph,Grt,L, cotectic curve Ky, Omph, Grt, L, eutectic point Ky,Coe,Omph, Grt,L, subsolidus assemblage Ky,Coe,Omph, Grt. The fractional ultrabasic-basic evolution of the upper-mantle silicate-carbonate-carbon melts-solutions, which are responsible for genesis of diamond-and-inclusions associations and diamond-bearing peridotites and eclogites, follows the similar physico-chemical mechanisms (Litvin et al., 2016). This is illustrated by fractional syngenesis diagram for diamonds and associated minerals which construction is based on evidence from high pressure experiments. References Gasparik T., Litvin Yu.A (1997). Stability of Na2Mg2Si2O7 and melting relations on the forsterite - jadeite join at pressures up to 22 GPa. Eur, J. Mineral. 9(2), 311-326. Litvin Yu.A. (1991). Physico-Chemical Study of Melting of Materials from the Deep Earth. Moscow: Nauka. 312 p. Litvin Yu.A., Spivak A.V., Kuzyura A.V. (2016). Fundamentals of the mantle-carbonatite concept of diamond genesis, Geochemistry Internat. 34(10), 839-857.

Experimental Alteration of Basalt to Support Interpretation of Remote Sensing and In Situ Meausrements from Mars

NASA Technical Reports Server (NTRS)

Bell, M. S.

2014-01-01

Major occurrences of hydrous alteration minerals on Mars have been found in Noachian impact craters formed in basaltic targets and detected using visible/near infrared (VNIR) spectroscopy. Until recently phyllosilicates were detected only in craters in the southern hemisphere [1, 2]. However, it has been reported that at least nine craters in the northern plains apparently excavated thick layers of lava and sediment to expose phyllosilicates [3] as well. The MER (Mars Exploration Rovers) rovers previously reported results of in situ measurement indicating the presence of alteration minerals on Mars [4,5] and it was recently reported that the Mars Curiosity rover has detected alteration phases in situ at Yellowknife Bay in Gale crater as well [6,7]. An important discovery for Mars geochronology is that the Chemistry and Mineralogy (CheMin) x-ray diffraction (XRD) instrument on Curiosity detected phyllosilicates indicating that phyllosilicate formation on Mars extended beyond the Noachian Epoch [8]. These discoveries indicate that Mars was globally altered by water in the past but does not constrain formation conditions for alteration phase occurrences, which have important implications for the evolution of the surface and the biological potential on Mars. Understanding the alteration assemblages produced by a range of conditions is vital for the interpretation of phyllosilicate spectral signatures as well as in situ measurements and to decipher the environment and evolution of early Mars. The martian surface has been intensely altered by meteorite impacts whose effects include brecciation and melting of target materials as well as the initiation of hydrothermal circulation in a hydrous target [9,10,11,12]. Impact effects may facilitate aqueous alteration of a basaltic target because the rate of silicate dissolution is a function of the degree of crystallinity, surface area, and temperature. The resultant alteration mineralogies from shocked basaltic target material are a function of the original mineral assemblage in the parent rocks, the chemistry of fluids that interacted with the rocks, and physico-chemical conditions (pH, temperatures, and pressure) during the time of mineral formation. Understanding the alteration assemblages produced by a range of conditions is vital for the interpretation of phyllosilicate spectral signatures and to decipher the environment and evolution of early Mars, and especially for identifying habitable niches in which life could be initiated and sustained. No experimentally controlled and well characterized analog materials that simulate martian shock metamorphism and alteration conditions currently exist for calibrating either remote sensing or in situ measurements of Mars. A series of experiments was initiated to assess the effects of systematic changes in the physico-chemical conditions on Mars analog materials thereby providing samples to ground-truth Mars remote sensing observations from CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) and in situ measurements from Opportunity's Mössbauer and Curiosity's CHEMIN (Chemistry and Mineralogy X-Ray Diffraction/XRay Fluorescence) instruments. Results of initial experimental runs as analysed by SEM-EDS (Secondary Electron Microscopy -Energy Dispersive Spectroscopy) and X-ray Diffraction (XRD) analysis are reported here and lay the foundation for comparison with shocked and altered samples that will be characterized in the next phase of this work.

Soft X-ray spectromicroscopy study of mineral-organic matter associations in pasture soil clay fractions.

PubMed

Chen, Chunmei; Dynes, James J; Wang, Jian; Karunakaran, Chithra; Sparks, Donald L

2014-06-17

There is a growing acceptance that associations with soil minerals may be the most important overarching stabilization mechanism for soil organic matter. However, direct investigation of organo-mineral associations has been hampered by a lack of methods that can simultaneously characterize organic matter (OM) and soil minerals. In this study, STXM-NEXAFS spectroscopy at the C 1s, Ca 2p, Fe 2p, Al 1s, and Si 1s edges was used to investigate C associations with Ca, Fe, Al, and Si species in soil clay fractions from an upland pasture hillslope. Bulk techniques including C and N NEXAFS, Fe K-edge EXAFS spectroscopy, and XRD were applied to provide additional information. Results demonstrated that C was associated with Ca, Fe, Al, and Si with no separate phase in soil clay particles. In soil clay particles, the pervasive C forms were aromatic C, carboxyl C, and polysaccharides with the relative abundance of carboxyl C and polysaccharides varying spatially at the submicrometer scale. Only limited regions in the soil clay particles had aliphatic C. Good C-Ca spatial correlations were found for soil clay particles with no CaCO3, suggesting a strong role of Ca in organo-mineral assemblage formation. Fe EXAFS showed that about 50% of the total Fe in soils was contained in Fe oxides, whereas Fe-bearing aluminosilicates (vermiculite and Illite) accounted for another 50%. Fe oxides in the soil were mainly crystalline goethite and hematite, with lesser amounts of poorly crystalline ferrihydrite. XRD revealed that soil clay aluminosilicates were hydroxy-interlayered vermiculite, Illite, and kaolinite. C showed similar correlation with Fe to Al and Si, implying a similar association of Fe oxides and aluminosilicates with organic matter in organo-mineral associations. These direct microscopic determinations can help improve understanding of organo-mineral interactions in soils.

Submarine hydrothermal metamorphism of the Del Puerto ophiolite, California.

USGS Publications Warehouse

Evarts, R.C.; Schiffman, P.

1983-01-01

Metamorphic zonation overprinted on the volcanic member and overlying volcanogenic sediments of the ophiolite complex increases downward in grade and is characterized by the sequential appearance with depth of zeolites, ferric pumpellyite and pistacitic epidote. Metamorphic assemblages of the plutonic member of the complex are characterized by the presence of calcic amphibole. The overprinting represents the effects of hydrothermal metamorphism resulting from the massive interaction between hot igneous rocks and convecting sea-water in a submarine environment. A thermal gradient of 100oC/km is postulated to account for the zonal recrystallization effects in the volcanic member. The diversity and sporadic distribution of mineral assemblages in the amphibole zone are considered due to the limited availability of H2O in the deeper part of the complex. Details of the zonation and representative microprobe analyses are tabulated.-M.S.

Weathering and hydrothermal alteration of basalts in Iceland: mineralogy from VNIR, TIR, XRD, and implications for Mars

NASA Astrophysics Data System (ADS)

Ehlmann, B. L.; Mustard, J. F.; Bish, D. L.

2009-12-01

Recent orbital investigations have revealed that aqueous alteration on early Mars took place in diverse alteration environments indicated by distinctive assemblages of minerals (Murchie et al., 2009, JGR). There is growing evidence for past diagenetic or low-temperature/pressure hydrothermal activity on Mars at neutral to alkaline pH, indicated by the presence of Fe/Mg smectites, chlorite, prehnite, serpentine, opaline silica, and zeolites such as analcime in Noachian terrains (Ehlmann et al., 2009, JGR). In recent investigations of terrestrial Mars analog sites, neutral to alkaline pH alteration of basalt, both pedogenic and hydrothermal, has been understudied in favor of sulfur-rich, acidic systems including those at the Hawaiian volcanoes and Rio Tinto, Spain. We began study of the alteration of basalt lava flows in Iceland as a geochemical analog for Noachian Mars. Because the basaltic bedrock is recently formed (<16Ma) with few localities of more highly evolved composition and has poorly formed soils and spare vegetation, the ground and surface waters are broadly similar to those which might have existed on Noachian Mars. Iceland has a variety of geothermal spring systems--low T, low S; low T, high S; and high T, high S--each of which creates distinctive mineralogic assemblages. Here we examine rocks of the Hvalfjordur peninsula, collected from basalt flows that were in some places altered at the surface by pedogenesis and in other locations were hydrothermally altered by non-sulfurous groundwater circulation (low T, low S) following the emplacement of a later hot basalt flow. Rock samples were surveyed in the field using a portable VNIR spectrometer. Altered and unaltered rocks that were typical for the locality were collected as were altered rocks whose spectra were most similar to those measured by CRISM from Mars orbit. Ten rocks were ultimately selected for detailed laboratory analyses: zeolitized basaltic rocks bearing minerals including analcime and thomsonite, basalts with silica/quartz-bearing veins, basalts bearing celadonite, and basalts partially altered to montmorillonite, Fe/Mg smectite, or mixed smectite-chlorite. Analyses included: (1) measurement of reflectance spectra of the whole rock by the ASD; (2) measurement of VNIR and TIR spectra in RELAB of particle-size separates (<25um and <125um) derived from the bulk rock and from precipitated minerals extracted from the vesicles; (3) measurement of X-ray diffraction (XRD) patterns, including quantitative XRD; and (4) electron microprobe chemical analyses. These data emulate orbital data from CRISM, OMEGA, and TES, which detect the infrared active components, linked to in-situ data on whole rock modal mineralogy such as will be measured by the ChemMin instrument on the MSL rover.

Holocene oceanographic and climatic variability of the Vega Drift deduced through foraminiferal interpretation

USGS Publications Warehouse

Szymcek, Phillip; Ishman, Scott E.; Domack, Eugene W.; Leventer, Amy

2007-01-01

fusiformis assemblages. Most agglutinated forms tend to decrease downcore, and comparisons to modern analogues imply post-depositional disintegration, while calcareous taxa indicate non-corrosive bottom waters. The lower to middle Holocene Vega Drift sediments are characterized by the calcareous S. fusiformis assemblage and glacial plume sediments. This assemblage is characterized by calcareous forms including Globocassidulina biora, G. subglobosa, and Nonionella iridea. The planktic species Neogloboquadrina pachyderma is associated with the S. fusiformis assemblage. The S. fusiformis assemblage is faunally similar to assemblages described in fjords of the western Antarctic Peninsula and indicates non-corrosive bottom water. Sediments of the mid to upper Holocene interval are characterized by the T. wiesneri and M. arenacea assemblages and indicate the presence of Hyper Saline Shelf Water. These assemblages are similar to modern assemblages directly to the south in the Prince Gustav Channel. The upper Holocene is marked by several small intervals with taxonomic characteristics similar to the S. fusiformis assemblage, indicating periodic introduction of non-corrosive bottom water to the Vega Drift

Re-assessing the vertical distribution of testate amoeba communities in surface peats: Implications for palaeohydrological studies.

PubMed

Roe, Helen M; Elliott, Suzanne M; Patterson, R Timothy

2017-08-01

Testate amoeba-derived transfer functions are frequently used in peatland palaeohydrological studies and involve the development of training sets from surficial peats. However, within acrotelmic peats, considerable vertical variation in assemblage composition can occur, particularly along Sphagnum stems, which may limit the representation of the associated 'contemporary' testate amoeba samples as analogues for the peatland surface. This paper presents contiguous testate amoeba assemblage data from nine monoliths collected from different peatland microforms (hummock, hollow, lawn) in three Sphagnum dominated ombrotrophic peatlands in Ontario and Quebec, eastern Canada. The aim is to: (i) gain a greater understanding of the vertical distribution of xerophilous/hygrophilous taxa along Sphagnum stems; (ii) determine the vertical extent of live/encysted taxa along this gradient; and (iii) assess the significance of this distribution on surface sampling protocols. The results show that testate amoeba communities in the uppermost acrotelmic peat layers display considerable variability. This may reflect a complex interplay of abiotic and biotic controls, including moisture, temperature, light and other characteristics, food availability, and mineral particle availability for test construction. These findings underline the complexity of testate amoeba community structure and highlight the importance of analysing both living and dead Sphagnum stem sections when developing calibration sets. Copyright © 2017 Elsevier GmbH. All rights reserved.

1.45 Ga granulites in the southwestern Grenville province: Geologic setting, P-T conditions, and U-Pb geochronology

NASA Astrophysics Data System (ADS)

Ketchum, J. W. F.; Jamieson, R. A.; Heaman, L. M.; Culshaw, N. G.; Krogh, T. E.

1994-03-01

In the southwestern Grenville province, the parautochthonous Britt domain includes a variety of pre-Grenvillian metamorphic and plutonic rocks that were reworked at upper amphibolite facies during the Grenvillian orogeny. Near Pointe-au-Baril, Ontario, a crustal block containing pre-Grenvillian granulite facies mineral assemblages and pre-Grenvillian to early Grenvillian tectonic fabrics has been identified. The block is bounded on the northwest and southeast by extensional shear zones that may have isolated it from regional late Gren- villian deformation. Multiequilibria pressure-temperature (P-T) calculations for orthopyroxene-bearing mafic rocks suggest conditions of 625-700 °C and 7.2-8.4 kbar for the pre-Grenvillian metamorphism. The granulite facies assemblages were locally overprinted during higher pressure Grenvillian metamorphism, which peaked at 720-775 °C and 10.8-11.5 kbar. U-Pb zircon data from migmatitic, mafic supracrustal gneiss indicate metamorphism and leucosome development at ca. 1450-1430 Ma, in agreement with other pre-Grenvillian metamorphic ages for the Central gneiss belt and Grenville Front tectonic zone. An expanding data base on pre-Grenvillian events in the southwestern Grenville province indicates that high-grade metamorphism at ca. 1450-1430 Ma affected a large region of crust and was coeval with widespread felsic to intermediate plutonism.

Petro-mineralogical Studies of the Paleoproterozoic Phosphorites in the Sonrai basin, Lalitpur District, Uttar Pradesh, India

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

Dar, Shamim A., E-mail: sjshamim@gmail.com; Khan, K. F.; Khan, Saif A.

2015-09-15

The Paleoproterozoic phosphorites constitute an economically significant component of the Sonrai basin of Lalitpur district. These are associated with ferruginous shale, ironstone, limestone and quartz breccia. Petro-mineralogical studies of samples of the phosphorites, using X-ray diffractometry and scanning electron microscopy, reveal that the collophane (carbonate-fluorapatite) is the dominant phosphate mineral. Calcite, dolomite, quartz, mica and haematite are the dominant gangue constituents. The phosphate minerals occur as oolites mutually replaced by carbonate and silica. The presence of iron oxides has been found in most of the thin sections. There is meagre evidence of organic matter in the form of filaments ofmore » microbial phosphate laminae in the samples of phosphorite. The mineral assemblages, their texture and various forms in these phosphorites may be due to some environmental vicissitudes followed by replacement processes and biogenic activities.« less

Geology and genesis of the Baid al Jimalah tungsten deposit, Kingdom of Saudi Arabia

USGS Publications Warehouse

Kamilli, R.J.; Cole, J.C.; Elliott, J.E.; Criss, R.E.

1993-01-01

The Baid ad Jimalah tungsten deposit in Saudi Arabia consists predominantly of swarms of steeply dipping, subparallel, tungsten-bearing quartz veins and of less abundant, smaller stockwork veins. It is spatially, temporally, and genetically associated with a 569 Ma, highly differentiated, porphyritic, two-feldspar granite that intrudes Late Proterozoic immature sandstones. Baid al Jimalah is similar in character and origin to Phanerozoic tungsten-tin greisen deposits throughout the world, especially the Hemerdon deposit in Devon, England. It is also analogous to Climax-type molybdenum deposits, which contain virtually identical mineral assemblages, but with the relative proportions of molybdenum and tungsten mineralization reversed, primarily owing to differences in oxygen fugacity. This similarity in mineralization styles and fluid histories indicates that metallogenic processes in granite-related deposits in the late Precambrian were similar to those seen in the Phanerozoic. -from Authors

Secondary mineral growth in fractures in the Miravalles geothermal system, Costa Rica

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

Rochelle, C.A.; Milodowski, A.E.; Savage, D.

1989-01-01

A mineralogical, fluid-chemical, and theoretical study of hydrothermal alteration in veins from drillcore from the Miravalles geothermal field, Costa Rica has revealed a complex history of mineral-fluid reaction which may be used to characterize changes in temperature and fluid composition with time. Mineralogical and mineral-chemical data are consistent with hydrothermal alteration in the temperature range 200{sup 0}-270{sup 0}C, with deeper portions of the system having undergone temperatures in excess of 300{sup 0}C. Thermodynamic calculations suggest that the observed alteration assemblage is not equilibrium with current well fluids, unless estimates of reservoir pH are incorrect. Fe-Al zoning of prehnite and epidotemore » in veins is consistent with rapid, isothermal fluctuations in fluid composition at current reservoir temperatures, and may be due to changes in volatile content of the fluid due to tectonic activity.« less

Characterization of Spitsbergen Disks by Transmission Electron Microscopy and Raman Spectroscopy

NASA Technical Reports Server (NTRS)

Thomas-Keprta, K. L.; Clemett, S. J.; Le, L.; Ross, K.; McKay, David S.; Gibson, E. K., Jr.

2010-01-01

'Carbonate disks' found in the fractures and pores spaces of peridotite xenoliths and basalts from the island of Spitsbergen in the Norwegian Svalbard archipelago have been suggested to be "The best (and best documented) terrestrial analogs for the [Martian meteorite] ALH84001 carbonate globules ..." Previous studies have indicated that Spitsbergen carbonates show broadly comparable internal layering and mineral compositions to ALH84001 carbonate-magnetite disks. We report here for the first time, the detailed mineral characterization of Spitsbergen carbonates and their spatial relationship to the host mineral assemblages in the xenolith, using high resolution TEM (as used previously for ALH84001 carbonate disks). These studies were conducted in concert with complementary Raman and SEM analysis of the same samples. Our results indicate that there are significant chemical and physical differences between the disks in Spitsbergen and the carbonates present in ALH84001.

Reptile assemblage response to restoration of fire-suppressed longleaf pine sandhills.

PubMed

Steen, David A; Smith, Lora L; Conner, L M; Litt, Andrea R; Provencher, Louis; Hiers, J Kevin; Pokswinski, Scott; Guyer, Craig

2013-01-01

Measuring the effects of ecological restoration on wildlife assemblages requires study on broad temporal and spatial scales. Longleaf pine (Pinus palustris) forests are imperiled due to fire suppression and subsequent invasion by hardwood trees. We employed a landscape-scale, randomized-block design to identify how reptile assemblages initially responded to restoration treatments including removal of hardwood trees via mechanical methods (felling and girdling), application of herbicides, or prescribed burning alone. Then, we examined reptile assemblages after all sites experienced more than a decade of prescribed burning at two- to thee-year return intervals. Data were collected concurrently at reference sites chosen to represent target conditions for restoration. Reptile assemblages changed most rapidly in response to prescribed burning, but reptile assemblages at all sites, including reference sites, were generally indistinguishable by the end of the study. Thus, we suggest that prescribed burning in longleaf pine forests over long time periods is an effective strategy for restoring reptile assemblages to the reference condition. Application of herbicides or mechanical removal of hardwood trees provided no apparent benefit to reptiles beyond what was achieved by prescribed fire alone.

A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter

USGS Publications Warehouse

Murchie, S.L.; Mustard, J.F.; Ehlmann, B.L.; Milliken, R.E.; Bishop, J.L.; McKeown, N.K.; Noe Dobrea, E.Z.; Seelos, F.P.; Buczkowski, D.L.; Wiseman, S.M.; Arvidson, R. E.; Wray, J.J.; Swayze, G.; Clark, R.N.; Des Marais, D.J.; McEwen, A.S.; Bibring, J.-P.

2009-01-01

Martian aqueous mineral deposits have been examined and characterized using data acquired during Mars Reconnaissance Orbiter's (MRO) primary science phase, including Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral images covering the 0.4-3.9 ??m wavelength range, coordinated with higher-spatial resolution HiRISE and Context Imager images. MRO's new high-resolution measurements, combined with earlier data from Thermal Emission Spectrometer; Thermal Emission Imaging System; and Observatoire pour la Min??ralogie, L'Eau, les Glaces et l'Activiti?? on Mars Express, indicate that aqueous minerals are both diverse and widespread on the Martian surface. The aqueous minerals occur in 9-10 classes of deposits characterized by distinct mineral assemblages, morphologies, and geologic settings. Phyllosilicates occur in several settings: in compositionally layered blankets hundreds of meters thick, superposed on eroded Noachian terrains; in lower layers of intracrater depositional fans; in layers with potential chlorides in sediments on intercrater plains; and as thousands of deep exposures in craters and escarpments. Carbonate-bearing rocks form a thin unit surrounding the Isidis basin. Hydrated silica occurs with hydrated sulfates in thin stratified deposits surrounding Valles Marineris. Hydrated sulfates also occur together with crystalline ferric minerals in thick, layered deposits in Terra Meridiani and in Valles Marineris and together with kaolinite in deposits that partially infill some highland craters. In this paper we describe each of the classes of deposits, review hypotheses for their origins, identify new questions posed by existing measurements, and consider their implications for ancient habitable environments. On the basis of current data, two to five classes of Noachian-aged deposits containing phyllosilicates and carbonates may have formed in aqueous environments with pH and water activities suitable for life. Copyright 2009 by the American Geophysical Union.

Orbital evidence for clay and acidic sulfate assemblages on Mars based on mineralogical analogs from Rio Tinto, Spain

NASA Astrophysics Data System (ADS)

Kaplan, Hannah H.; Milliken, Ralph E.; Fernández-Remolar, David; Amils, Ricardo; Robertson, Kevin; Knoll, Andrew H.

2016-09-01

Outcrops of hydrated minerals are widespread across the surface of Mars, with clay minerals and sulfates being commonly identified phases. Orbitally-based reflectance spectra are often used to classify these hydrated components in terms of a single mineralogy, although most surfaces likely contain multiple minerals that have the potential to record local geochemical conditions and processes. Reflectance spectra for previously identified deposits in Ius and Melas Chasma within the Valles Marineris, Mars, exhibit an enigmatic feature with two distinct absorptions between 2.2 and 2.3 μm. This spectral 'doublet' feature is proposed to result from a mixture of hydrated minerals, although the identity of the minerals has remained ambiguous. Here we demonstrate that similar spectral doublet features are observed in airborne, field, and laboratory reflectance spectra of rock and sediment samples from Rio Tinto, Spain. Combined visible-near infrared reflectance spectra and X-ray diffraction measurements of these samples reveal that the doublet feature arises from a mixture of Al-phyllosilicate (illite or muscovite) and jarosite. Analyses of orbital data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) shows that the martian spectral equivalents are also consistent with mixtures of Al-phyllosilicates and jarosite, where the Al-phyllosilicate may also include kaolinite and/or halloysite. A case study for a region within Ius Chasma demonstrates that the relative proportions of the Al-phyllosilicate(s) and jarosite vary within one stratigraphic unit as well as between stratigraphic units. The former observation suggests that the jarosite may be a diagenetic (authigenic) product and thus indicative of local pH and redox conditions, whereas the latter observation may be consistent with variations in sediment flux and/or fluid chemistry during sediment deposition.

Can rove beetles (Staphylinidae) be excluded in studies focusing on saproxylic beetles in central European beech forests?

PubMed

Parmain, G; Bouget, C; Müller, J; Horak, J; Gossner, M M; Lachat, T; Isacsson, G

2015-02-01

Monitoring saproxylic beetle diversity, though challenging, can help identifying relevant conservation sites or key drivers of forest biodiversity, and assessing the impact of forestry practices on biodiversity. Unfortunately, monitoring species assemblages is costly, mainly due to the time spent on identification. Excluding families which are rich in specimens and species but are difficult to identify is a frequent procedure used in ecological entomology to reduce the identification cost. The Staphylinidae (rove beetle) family is both one of the most frequently excluded and one of the most species-rich saproxylic beetle families. Using a large-scale beetle and environmental dataset from 238 beech stands across Europe, we evaluated the effects of staphylinid exclusion on results in ecological forest studies. Simplified staphylinid-excluded assemblages were found to be relevant surrogates for whole assemblages. The species richness and composition of saproxylic beetle assemblages both with and without staphylinids responded congruently to landscape, climatic and stand gradients, even when the assemblages included a high proportion of staphylinid species. At both local and regional scales, the species richness as well as the species composition of staphylinid-included and staphylinid-excluded assemblages were highly positively correlated. Ranking of sites according to their biodiversity level, which either included or excluded Staphylinidae in species richness, also gave congruent results. From our results, species assemblages omitting staphylinids can be taken as efficient surrogates for complete assemblages in large scale biodiversity monitoring studies.

Petrogenetic grids for sapphirine-bearing granulites

NASA Astrophysics Data System (ADS)

Podlesskii, Konstantin K.

2010-05-01

Phase relations involving sapphirine, garnet, spinel, orthopyroxene, olivine, cordierite, alumina silicates, corundum, and quartz have been calculated in the system FeO-MgO-Al2O3-SiO2 based on internally consitent thermodynamic properties of both the end-member minerals and the solid solutions (Gerya et al., 2004; Podlesskii et al., 2008). The derived P-T diagrams imply stable invariant points and stability fields of key assemblages that differ from those proposed by other authors (Kelsey et al., 2004; Harley 2008). The sapphirine + quartz assemblage, which is widely recognized as indicative of ultrahigh-temperature metamorphism, can be stable down to 835° C and ~6 kbar. The sapphirine + kyanite assemblage has been found stable at temperatures below 860° C and 11.3 kbar, whereas the sapphirine + forsterite assemblage may be stable below 800° C only under specific conditions of a very low activity of water. The existing constraints on the thermodynamic properties of sapphirine are considered insufficient to make decisive conclusions about metamorphic conditions. Granulites containing the sapphirine + quartz assemblage have been investigated with the microprobe to apply both the conventional thermobarometry and thermometry based on Ti contents of quartz (TitaniQ, Wark & Watson, 2006). The results demonstrate that, in some cases, this assemblage might have formed at relatively low temperatures during retrograde stages of metamorphism. The research has been supported by the RFBR grant 09-05-00193. References Gerya,T.V., Perchuk,L.L., & Podlesskii,K.K. In: Zharikov,V.A. & Fed'kin,V.V. (eds.) Experimental Mineralogy: Some Results on the Century's Frontier. Moscow: Nauka, Vol. 2, 188-206 (2004). Harley,S.L. Refining the P-T records of UHT crustal metamorphism. Journal of Metamorphic Geology, 26, 125-154 (2008). Kelsey,D.E., White,R.W., Holland,T.J.B., & Powell,R. Journal of Metamorphic Geology, 22, 559-578 (2004). Podlesskii,K.K., Aranovich,L.Y., Gerya,T.V., & Kosyakova,N.A. Sapphirine-bearing assemblages in the system MgO-Al2O3-SiO2: A continuing ambiguity. European Journal of Mineralogy, 20, 721-734 (2008). Wark,D.A. & Watson,E.B. TitaniQ: a titanium-in-quartz geothermometer. Contributions to Mineralogy and Petrology, 152, 743-754 (2006).

Paleoproterozoic multistage metamorphic events in Jining metapelitic rocks from the Khondalite Belt in the North China Craton: Evidence from petrology, phase equilibria modelling and U-Pb geochronology

NASA Astrophysics Data System (ADS)

Cai, Jia; Liu, Fulai; Liu, Pinghua

2017-05-01

Metapelitic rocks of the Jining Complex (sillimanite-cordierite-garnet (Sil-Crd-Grt) gneisses, sillimanite-garnet (Sil-Grt) gneisses and quartzofeldspathic rocks) are exposed in the eastern segment of the Khondalite Belt (KB) in the North China Craton (NCC). The Sil-Crd-Grt gneisses have preserved polyphase mineral assemblages and microstructural evidence of anatexis, resulting from biotite dehydration melting. Petrological observations revealed that the Sil-Crd-Grt gneisses contain three metamorphic assemblages: a peak assemblage of garnet porphyroblast and matrix biotite + sillimanite + K-feldspar + plagioclase + quartz + ilmenite + magnetite, a post-peak near-isothermal decompressional assemblage of garnet + cordierite + biotite + sillimanite + K-feldspar + plagioclase + quartz + ilmenite + magnetite, and a decompressional cooling assemblage of garnet + biotite + cordierite + K-feldspar + plagioclase + quartz + ilmenite + magnetite. A clockwise P-T path was defined involving the inferred peak stage followed by post-peak near-isothermal decompression and decompressional cooling stages, with P-T conditions of 790-825 °C and 9-10 kbar, 810-890 °C and 6.0-6.5 kbar, and 780-810 °C and 4.0-5.5 kbar, respectively. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb analyses of the Sil-Crd-Grt gneisses and Sil-Grt gneisses for the detrital and metamorphic zircons yielded a protolith age of ∼2.0 Ga and the late Paleoproterozoic metamorphic age of 1895-1885 Ma. The results reveal that the metapelitic rocks of the Jining Complex underwent continent-continent subduction or collision in the peak metamorphic stage, followed by a post-collisional exhumation event in the post-peak decompressional stage, and a subsequent decompressional cooling stage between the Yinshan and Ordos blocks to form the Paleoproterozoic KB.

The distribution and composition of REE-bearing minerals in placers of the Atlantic and Gulf coastal plains, USA

USGS Publications Warehouse

Bern, Carleton R.; Shah, Anjana K.; Benzel, William M.; Lowers, Heather A.

2016-01-01

Rare earth element (REE) resources are currently of great interest because of their importance as raw materials for high-technology manufacturing. The REE-phosphates monazite (light REE enriched) and xenotime (heavy REE enriched) resist weathering and can accumulate in placer deposits as part of the heavy mineral assemblage. The Atlantic and Gulf coastal plains of the southeastern United States are known to host heavy mineral deposits with economic concentrations of zircon, ilmenite and rutile. This study provides a perspective on the distribution and composition of REE phosphate minerals in the region. The elemental chemistry and mineralogy of sands and associated heavy-mineral assemblages from new and archived sediment samples across the coastal plains are examined, along with phase-specific compositions of monazite, xenotime and zircon. Both monazite and xenotime are present across the coastal plains. The phase-specific compositions allow monazite content to be estimated using La as a geochemical proxy. Similarly, both Y and Yb are geochemical proxies for xenotime, but their additional presence in zircon and monazite require a correction to prevent overestimation of xenotime content. Applying this correction, maps of monazite and xenotime content across the coastal plains were generated using sample coverage from the National Geochemical Database (NGS) and National Uranium Resource Evaluation (NURE). The NGS and NURE approach of sampling stream sediments in small watersheds links samples to nearby lithologies. The results show an approximately 40 km-wide band of primarily Cretaceous, marine sediments bordering the Piedmont province from North Carolina to Alabama in which monazite and xenotime content are relatively high (up to 4.4 wt. % in < 150 μm bulk sediment). Strong correlations between concentrations of the two phases were found, with estimated monazite:xenotime ratios ranging approximately 6:1 to 12:1 depending upon the dataset analyzed. From a resource perspective, xenotime correlation with monazite indicates a heavy REE potential in coastal plain placers, and exploration may be warranted within the identified coastal plain band along the boundary of the Piedmont region.

The Role of Halogens in High-Grade Metamorphism and Anatexis

NASA Astrophysics Data System (ADS)

Aranovich, L.; Safonov, O.

2016-12-01

We review factors controlling the distribution of the two major halogens, F and Cl, in high-grade metamorphic rocks; their compositional correlations and partitioning between minerals; experimental data on stability and phase equilibria of the halogen-bearing minerals; the influence of halogens on Fe-Mg exchange reactions; and the means of estimating concentrations/activity of halogen species concentration/ activity in the fluid phase ("chlorimetry and fluorimetry") via calculation of equilibrium conditions for mineral assemblages containing halogen-bearing phases. Clear negative correlation between the F content and XFe=Fe/(Fe+Mg) suggests that natural biotite and amphibole obey the Fe-F avoidance rule. A strong positive correlation exists between K and Cl in amphibole. A scattering of points on the XFe -Cl and TiO2- Cl diagrams indicate the possible involvement of an exotic Cl-rich phase (fluid or melt) during the formation of Cl-bearing biotite and amphibole. Fluorine and Cl substituting for OH-groups substantially stabilize minerals relative to dehydration and melting. They should also strongly affect partitioning of Fe and Mg between biotite, amphibole and anhydrous minerals. This effect is quantified for Fe-Mg exchange reactions involving biotite (Zhu and Sverjensky, 1992), but remains to be evaluated for amphibole. Calculations based on recent thermodynamic systematics show that the relatively Mg-rich, Cl-poor biotite (for example, XFe = 0.4 and about 0.2 wt.% Cl) may coexist with a fairly Cl-rich fluid, i.e. total Cl/(Cl+H2O) from 0.1-0.3, depending on the assemblage, under granulite facies P-T conditions. Alkali (and Ca) metasomatism caused by interaction of high grade rocks with halogen-bearing fluids has major impact on the subsolidus phase transformations and melting processes during high-grade metamorphism and anatexis. For example, an increase in sodium content in plagioclase (Pl) by 20 mol% due to infiltration of Na- fluid into the quartz (Qtz)-bearing rocks decreases melting temperature by about 50o. Similar effect may occur in the originally Qtz-absent rocks due to interaction with Ca-rich fluids. Acknowledgements: This work was supported by RFBR grant 15-05-01053.

Geology of coal fires: case studies from around the world

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

Glenn B. Stracher

2008-01-15

Coal fires are preserved globally in the rock record as burnt and volume-reduced coal seams and by pyrometamorphic rocks, explosion breccias, clinker, gas-vent-mineral assemblages, fire-induced faulting, ground fissures, slump blocks, and sinkholes. Coal fires are responsible for coronary and respiratory diseases and fatalities in humans, as well as arsenic and fluorine poisoning. Their heat energy, toxic fumes, and solid by-products of combustion destroy floral and faunal habitats while polluting the air, water, and soil. This volume includes chapters devoted to spontaneous combustion and greenhouse gases, gas-vent mineralogy and petrology, paralavas and combustion metamorphic rocks, geochronology and landforms, magnetic signatures andmore » geophysical modeling, remote-sensing detection and fire-depth estimation of concealed fires, and coal fires and public policy.« less

Mineral complexities as evidence for open-system processes in intermediate magmas of the Mount Baker volcanic field, northern Cascade arc

NASA Astrophysics Data System (ADS)

Escobar-Burciaga, R. D.; DeBari, S. M.

2015-12-01

The petrogenesis of intermediate magmas in arcs is a critical contribution to crustal growth. Andesites are commonly thought of as a hybrid product, the result of two endmember magmas mixing. At the Mount Baker volcanic field (MBVF), northern Cascade arc, andesites are the predominantly erupted lavas since 1 Ma and yet their origin is poorly constrained. Previous studies have suggested that open-system processes play a dominant role. However, the studies rely heavily on bulk rock compositions and overlook complex mineral textures and compositions. To better understand the complex processes at work at MBVF, we focus on establishing mineral and crystal clot populations in three andesitic flow units (55-59% SiO2). Petrographic and geochemical analyses suggest that variable-composition crystal clot and phenocryst populations in a single flow are related. We interpret the crystal clots to represent cumulates entrained in the erupting host magma and that related phenocrysts are disaggregates of crystal clots. The existence of common, multiple phenocryst and crystal clot populations in each flow of different age and SiO2 content provides strong evidence that intermediate magmas of MBVF are more than just the end product of mixing between two magmas. Furthermore, we suggest that most phenocrysts do not represent equilibrium products of their host liquid, evident from wide compositional ranges of ferromagnesian minerals (e.g. augite core Mg# 70-87). In fact, the most primitive phenocryst populations show the least amount of disequilibrium texture but represent assemblages expected to fractionate from basaltic to basaltic-andesitic liquids rather than equilibrium assemblages from their host bulk rock "liquid" composition. As a result, we interpret the variable SiO2 signature of the three andesitic flow units to have been obtained through the incorporation of cumulates/liquids as basaltic to basaltic-andesitic magma ascends.

Eclogite-facies guyanaite, carmichaelite and eskolaite in xenoliths of Cr-omphacitite from Navajo diatremes, Utah: Hydration and dehydration in the subducted Farallon plate

NASA Astrophysics Data System (ADS)

Schulze, D. J.; Helmstaedt, H.

2013-12-01

The mantle-derived xenolith suite in the Navajo serpentinized ultramafic diatremes includes low-temperature metamorphic rocks such as lawsonite- and phengite-bearing eclogites, Cr-pyrope xenocrysts with inclusions of hydrous minerals and hydrated peridotites and pyroxenites containing minerals such as chlorite, pargasite, tremolite and antigorite. We have now also identified a suite of bright green Cr-rich clinopyroxenites from the Moses Rock and Mule's Ear diatremes that contain unusual assemblages of dark to opaque accessory minerals such as guyanaite [CrOOH], carmichaelite [(Ti,Cr)2-x(OH)x], eskolaite [Cr2O3], chromite and rutile. The xenoliths are dominated by omphacitic pyroxenes (most in the range 10-55 mole% jadeite) that are locally enriched in Cr adjacent to clots of accessory minerals (to 35 mole% kosmochlor). Most samples have small clusters of scattered accessory minerals (individual grains on the scale of tens of microns) but one sample has clusters to 2 mm dominated by guyanaite blades intergrown with Cr-rich omphacite. Thin grains of eskolaite traverse the guyanaite and occur at the guyanaite-omphacite interfaces. Patches of zincian chromite (to 5.7 wt% ZnO) are associated with some of the guyanaite-dominated clusters and consist of lamellar intergrowths of two texturally and compositionally different types of chromite, interpreted as an exsolution feature and precursor to hydration and metasomatic development of guyanaite-omphacite intergrowths. Minor carmichaelite occurs in these clusters. In another sample carmichaelite with finely intergrown patches of rutile dominates the clusters. Equilibration conditions of these assemblages are poorly constrained, but the reaction guyanaite = eskolaite + H2O (Jahn et al., Eur. J. Min., 2012) is consistent with an estimate for equilibration conditions of a phengite eclogite (700oC, 3.4GPa - Smith et al., GGG, 2013). We interpret these rocks to be Na-metasomatized and hydrated basalts (small clusters) and peridotites (clusters to 2mm), formed in serpentinites during subduction of the Farallon Plate under the Colorado Plateau in Laramide time, based on similarities with subduction-origin Cr-jade bodies associated with serpentinites (e.g., Myanmar). At the time of entrainment in the host diatremes, these rocks were undergoing dehydration reactions (guyanaite to eskolaite, carmichaelite to rutile) providing water to the overlying subcrustal mantle section and contributing to Plateau uplift. The occurrence of carmichaelite as inclusions armoured within pyrope garnet xenocrysts from the nearby Garnet Ridge diatreme is now linked to the presence of carmichaelite in the open system of the upper mantle in these Cr-omphacitites (the only two known occurrences of carmichaelite), complicating interpretation of the pyropes as being derived from subcontinental upper mantle formed by Proterozoic subduction.

Processes of high-T fluid-rock interaction during gold mineralization in carbonate-bearing metasediments: the Navachab gold deposit, Namibia

NASA Astrophysics Data System (ADS)

Dziggel, A.; Wulff, K.; Kolb, J.; Meyer, F. M.

2009-08-01

The Navachab gold deposit in the Damara belt of central Namibia is hosted by a near-vertical sequence of amphibolite facies shelf-type metasediments, including marble, calc-silicate rock, and biotite schist. Petrologic and geochemical data were collected in the ore, alteration halos, and the wall rock to evaluate transport of elements and interaction between the wall rock and the mineralizing fluid. The semi-massive sulfide lenses and quartz-sulfide veins are characterized by a complex polymetallic ore assemblage, comprising pyrrhotite, chalcopyrite, sphalerite, and arsenopyrite, native bismuth, gold, bismuthinite, and bismuth tellurides. Mass balance calculations indicate the addition of up to several orders of magnitude of Au, Bi, As, Ag, and Cu. The mineralized zones also record up to eightfold higher Mn and Fe concentrations. The semi-massive sulfide lenses are situated in the banded calc-silicate rock. Petrologic and textural data indicate that they represent hydraulic breccias that contain up to 50 vol.% ore minerals, and that are dominated by a high-temperature (T) alteration assemblage of garnet-clinopyroxene-K-feldspar-quartz. The quartz-sulfide veins crosscut all lithological units. Their thickness and mineralogy is strongly controlled by the composition and rheological behavior of the wall rocks. In the biotite schist and calc-silicate rock, they are up to several decimeters thick and quartz-rich, whereas in the marble, the same veins are only a few millimeters thick and dominated by sulfides. The associated alteration halos comprise (1) an actinolite-quartz alteration in the biotite schist, (2) a garnet-clinopyroxene-K-feldspar-quartz alteration in the marble and calc-silicate rock, and (3) a garnet-biotite alteration that is recorded in all rock types except the marble. The hydrothermal overprint was associated with large-scale carbonate dissolution and a dramatic increase in CO2 in the ore fluid. Decarbonation of wall rocks, as well as a low REE content of the ore fluid resulted in the mobilization of the REE, and the decoupling of the LREE from the HREE. The alteration halos not only parallel the mineralized zones, but may also follow up single layers away from the mineralization. Alteration is far more pronounced facing upward, indicating that the rocks were steep when veining occurred. The petrologic and geochemical data indicate that the actinolite-quartz- and garnet-clinopyroxene-K-feldspar-quartz alterations formed in equilibrium with a fluid (super-) saturated in Si, and were mainly controlled by the composition of the wall rocks. In contrast, the garnet-biotite alteration formed by interaction with a fluid undersaturated in Si, and was mainly controlled by the fluid composition. This points to major differences in fluid-rock ratios and changes in fluid composition during alteration. The alteration systematics and geometry of the hydrothermal vein system are consistent with cyclic fluctuations in fluid pressure during fault valve action.

Reactive transport modeling of ferroan dolomitization by seawater interaction with mafic igneous dikes and carbonate host rock at the Latemar platform, Italy

NASA Astrophysics Data System (ADS)

Blomme, Katreine; Fowler, Sarah Jane; Bachaud, Pierre

2017-04-01

The Middle Triassic Latemar carbonate platform, northern Italy, has featured prominently in the longstanding debate regarding dolomite petrogenesis [1-4]. Recent studies agree that ferroan and non-ferroan dolomite replaced calcite in limestone during reactive fluid flow at <0.1 GPa and 40-80°C. Regional igneous activity drove heating that provided kinetically favorable conditions for the replacement reaction. However, the origin of the dolomitizing fluid is unclear. Seawater may have been an important component, but its Fe concentrations are insufficient to account for ferroan dolomite. New field, petrographic, XRD, and geochemical data document a spatial, temporal, and geochemical link between ferroan replacement dolomite and altered mafic igneous dikes that densely intrude the platform. A critical observation is that ferroan dolomite abundances increase towards the dikes. We hypothesize that seawater interacted with mafic minerals in the dikes, leading to Fe enrichment in the fluid that subsequently participated in dolomitization. This requires that dolomite formation was preceded by dike alteration reactions that liberated Fe and did not consume Mg. Another requirement is that ferroan and non-ferroan dolomite (instead of other Fe- and Mg-bearing minerals) formed during fluid circulation within limestone host rock. We present reactive transport numerical simulations (Coores-Arxim, [5]) that predict equilibrium mineral assemblages and the evolution of fluid dolomitizing potential from dike crystallization, through dike alteration by seawater, to replacement dolomitization in carbonate host rock. The simulations are constrained by observations. A major advantage of the simulations is that stable mineral assemblages are identified based on a forward modeling approach. In addition, the dominant igneous minerals (plagioclase, clinopyroxene olivine and their alteration products) are solid solutions. Most reactive transport simulations of carbonate petrogenesis do not share these benefits (e.g. [6]). Predicted alteration mineral assemblages are consistent with observations on dikes and with ferroan and non-ferroan dolomite genesis. The simulation results also show that fluid dolomitizing potential (Mg/Ca and Fe/Mg) increases during dissolution of igneous solid solution minerals. Enrichment in fluid Fe concentration is sufficient to stabilize ferroan replacement dolomite. Consistent with field observations, ferroan dolomite forms closest to dikes due to the abundance of Fe associated with the dikes. This leads to depletion of Fe in fluid flowing away from dikes and formation of non-ferroan replacement dolomite further afield. References S.K. Carmichael, J.M. Ferry, W.F. McDonough, Formation of replacement dolomite in the Latemar carbonate buildup, Dolomites, Northern Italy: Part 1. Field relations, mineralogy and geochemistry, Am. J. Sci. 308 (2008) 851-884. J.M. Ferry, B.H. Passey, C. Vasconcelos, J.M. Eiler, Formation of dolomite at 40 - 80 °C in the Latemar carbonate buildup, Dolomites, Italy, from clumped isotope thermometry, Geology. 39 (2011) 571-574. C. Jacquemyn, M. Huysmans, D. Hunt, G. Casini, R. Swennen, Multi-scale three-dimensional distribution of fracture- and igneous intrusion- controlled hydrothermal dolomite from digital outcrop model, Latemar platform, Dolomites, northern Italy, Am. Assoc. Pet. Geol. Bull. 99 (2015) 957-984. C. Jacquemyn, H. El Desouky, D. Hunt, G. Casini, R. Swennen, Dolomitization of the Latemar platform: Fluid flow and dolomite evolution, Mar. Pet. Geol. 55 (2014) 43-67. L. Trenty, A. Michel, E. Tillier, Y. Le Gallo, A Sequential Splitting Strategy for CO2 Storage Modelling, in: ECMOR X - 10th Eur. Conf. Math. Oil Recover., 2006. T. Gabellone, F. Whitaker, Secular variations in seawater chemistry controlling dolomitisation in shallow reflux systems: Insights from reactive transport modelling, Sedimentology. 63 (2016) 1233-1259.

Geochemistry and provenance of some detrital heavy minerals of alluvial sediments from Neagra Şarului River, Eastern Carpathians, Romania

NASA Astrophysics Data System (ADS)

Ciortescu, Catalina; Iancu, Ovidiu Gabriel; Bulgariu, Dumitru; Popa, Ciprian

2014-05-01

The present work focuses on the analyses of a selection of heavy mineral assemblages sampled from the Neagra Şarului River's alluvia, in order to determine their provenance and distribution, using their geochemical and physical characteristics. The study focused on a mountain river of about 30 km long, located in the north-western part of the Eastern Carpathians, an important tributary of the Bistria River. The bedrocks in the river drainage basin are constituted mainly by igneous rocks from Călimani Volcanic Complex in the west, and secondarily by a small area of low to medium grade metamorphic rocks, part of Crystalline-Mesozoic Zone, in the east. In order to trace the source of each individual mineral species, we prepared our samples via field separation and subsequent laboratory sieving using 8 different size fractions. An electromagnetic separator (Frantz Isodynamic) was used to separate and classify each heavy minerals species, depending on their magnetic susceptibility. Thus prepared, more than 500 grains per samples (from the 0.5-1 mm size fraction) were mounted on thin sections and analyzed using a Cambridge Microscan M9 with EDS system. These analyses served for mineral identification and relative abundance determination. The classification of the minerals and the nature of their inclusions are derived from the major element compositions computed from SEM-EDX analysis. We also used a stereo microscope in order to determine complementary properties of the grains, such as: color, degree of roundness and degree of alteration. In order of abundance, the main heavy minerals are magnetite, hematite, pyroxene, pyrite, manganese oxides, garnet, apatite, titanium oxides (ilmenite, titanite and rutile/anatase), chlorite, olivine, epidote, biotite and rhodochrosite. A particularity of the studied area is the presence of an altered magnetite caused first by the hydrothermal alteration and strong weathering of the source rocks and second by the river's acid water. Manganese oxides are present only in grain fractions greater than 0.25 mm due to higher susceptibility to weathering and dissolution of the Mn aggregates in the river bed. Despite low distribution of the metamorphic units in the river's studied basin, the garnets almandine (Alm 13-88%) and spessartine (Sps 0.5-87%), specific to the medium grade metamorphic rocks, have a relative high frequency. In this study, heavy mineral assemblages generally reflect the composition of primary (augite, almandine) and accessory minerals present in source rocks. The last ones are both primary (apatite) and secondary, which are mainly derived from hydrothermal deposition (e. g. pyrite) and from supergene alterations (e. g. manganese, iron oxides/ hydroxides, and other altered product of magnetite). Therefore, the mineral analyses were not limited to only tracking the source of each mineral species, but they also revealed the characteristics of their parent rocks.

New occurrences of ferroselite (FeSe2)

USGS Publications Warehouse

Coleman, R.G.

1959-01-01

Iron selenide from the uranium-vanadium ores of the Colorado Plateau was under investigation when ferroselite was described as a new mineral in Russia by Bur'yanova and Komkov (1955). Association of ferroselite with selenian pyrite and marcasite within discrete areas of these uranium-vanadium deposits suggests an unusual environment of formation. Its association with apparent low temperature assemblages in the United States and Bussia indicates that its minimum temperature of formation is quite low. Chemical analyses of ferroselite agree well with the theoretical formula FeSe2; material from the Virgin no. 3 mine, Montrose County, Colorado, gives the formula FeSe2.07 and that from the A.E.C. no. 8 mine, Temple Mountain, Utah, gives the formula (Fe, Co)Se2.08. The similarity of hastite and ferroselite suggests that a complete series FeSe2-CoSe2 may exist. In contrast to this, pyrite associated with ferroselite apparently will camouflage only 4 per cent (molecular) FeSe2 within its structure. Ferroselite cannot be distinguished from rammelsbergite (FeAs2) by X-ray or in polished section; therefore, the exact identification of these two minerals can be made only by specific tests for As or Se. As hastite (CoSe2) and marcasite are in the same structure group as ferroselite and rammelsbergite, identification of these minerals should include qualitative chemical determinations. ?? 1959.

Interpreting U-Pb data from primary and secondary features in lunar zircon

NASA Astrophysics Data System (ADS)

Grange, M. L.; Pidgeon, R. T.; Nemchin, A. A.; Timms, N. E.; Meyer, C.

2013-01-01

In this paper, we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon U-Pb isotopic systems and the significance of these features for understanding lunar processes. Lunar zircons can be classified according to: (i) textural relationships between zircon and surrounding minerals in the host breccias, (ii) the internal microstructures of the zircon grains as identified by optical microscopy, cathodoluminescence (CL) imaging and electron backscattered diffraction (EBSD) mapping and (iii) results of in situ ion microprobe analyses of the Th-U-Pb isotopic systems. Primary zircon can occur as part of a cogenetic mineral assemblage (lithic clast) or as an individual mineral clast and is unzoned, or has sector and/or oscillatory zoning. The age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data. A secondary set of microstructures, superimposed on primary zircon, include localised recrystallised domains, localised amorphous domains, crystal-plastic deformation, planar deformation features and fractures, and are associated with impact processes. The first two secondary microstructures often yield internally consistent and close to concordant U-Pb ages that we interpret as dating impact events. Others secondary microstructures such as planar deformation features, crystal-plastic deformation and micro-fractures can provide channels for Pb diffusion and result in partial resetting of the U-Pb isotopic systems.

Carbon isotope geochemistry of graphite vein deposits from New Hampshire, U.S.A.

NASA Astrophysics Data System (ADS)

Rumble, Douglas, III; Hoering, Thomas C.

1986-06-01

Graphite veins of hydrothermal origin occur throughout central New Hampshire. Veins truncate sillimanite-grade, metasedimentary rocks of Early Devonian-Silurian age and range in size from microscopic to meters in thickness. In addition to graphite, veins may contain quartz, tourmaline, ilmenite, rutile, sillimanite, muscovite or chlorite. Vein mineralogy is generally compatible with wall rock mineral assemblages. Mineralization structures include wall-rock alteration zones, coxcomb graphite crystals on vein walls, and botryoidal, concentrically layered graphite-silicate nodules. The δ13C values of graphite in 14 deposits studied range from - 28%. (PDB) to - 9%. Veins whose textures give evidence of a single stage of mineralization have a narrow range of δ13C values (± 0.2%.). Other veins record successive episodes of graphite precipitation and have ranges of 3-6%. In one sample, adjacent layers of graphite differ by 3%. The wide range of δ13C may be explained by mixing carbon from two crustal reservoirs: biogenic, reduced carbon and carbonate. Precipitation of graphite results from mixing two or more aqueous fluids with different CO 2/CH 4 ratios. Parental fluids are produced by devolatilization during metamorphism. Water-rich fluids with CH4 > CO2 and low δ13C are derived from pelites that contained organic matter; whereas fluids with CO2 > CH4 and high δ13C come from siliceous carbonates.

Geobiochemistry: Placing Biochemistry in Its Geochemical Context

NASA Astrophysics Data System (ADS)

Shock, E.; Boyer, G. M.; Canovas, P. A., III; Prasad, A.; Dick, J. M.

2014-12-01

Goals of geobiochemistry include simultaneously evaluating the relative stabilities of microbial cells and minerals, and predicting how the composition of biomolecules can change in response to the progress of geochemical reactions. Recent developments in theoretical geochemistry make it possible to predict standard thermodynamic properties of proteins, nucleotides, lipids, and many metabolites including the constituents of the citric acid cycle, at all temperatures and pressures where life is known to occur, and beyond. Combining these predictions with constraints from geochemical data makes it possible to assess the relative stabilities of biomolecules. Resulting independent predictions of the environmental occurrence of homologous proteins and lipid side-chains can be compared with observations from metagenomic and metalipidomic data to quantify geochemical driving forces that shape the composition of biomolecules. In addition, the energetic costs of generating biomolecules from within a diverse range of habitable environments can be evaluated in terms of prevailing geochemical variables. Comparisons of geochemical bioenergetic calculations across habitats leads to the generalization that the availability of H2 determines the cost of autotrophic biosynthesis relative to the aquatic environment external to microbial cells, and that pH, temperature, pressure, and availability of C, N, P, and S are typically secondary. Increasingly reduced conditions, which are determined by reactions of water with mineral surfaces and mineral assemblages, allow many biosynthetic reactions to shift from costing energy to releasing energy. Protein and lipid synthesis, as well as the reverse citric acid cycle, become energy-releasing processes under these conditions. The resulting energy balances that determine habitability contrast dramatically with assumptions derived from oxic surface conditions, such as those where human biochemistry operates.

Petrography and geochemistry of modern river sediments in an equatorial environment (Rwenzori Mountains and Albertine rift, Uganda) - Implications for weathering and provenance

NASA Astrophysics Data System (ADS)

Schneider, Sandra; Hornung, Jens; Hinderer, Matthias; Garzanti, Eduardo

2016-05-01

In hot-humid equatorial climate chemical weathering may be so strong that provenance signatures may be largely lost and even detritus derived from crystalline basement rocks reduced to quartzose sand. We tested this hypothesis in western Uganda, where stable plateau areas contrast with the active tectonic setting of the Albertine Rift (western branch of the East African Rift System, EARS), culminating in the strongly exhumed fault block of the > 5000 m high Rwenzori Mountains. In this setting, sediments derived from similar types of basement rocks including gneiss, schist, amphibolite, metasediments and granites can be traced from rapidly eroding high-altitude areas to low-altitude areas undergoing prolonged weathering. Sand and mud carried by 51 rivers overall in these two contrasting landscapes were sampled to study how and to what extent detrital modes are modified by the selective loss of unstable detrital minerals. Sediments generated in the high-relief Rwenzori Mountains show abundant feldspar (up to 32%) and rock fragments (up to 52%), which together with low SiO2/Al2O3 ratio and composition close to the Upper Continental Crust (UCC standard) reflect erosion in weathering-limited conditions. In the central Rwenzoris, low Th/Sc and Zr/Sc ratios, weak negative Eu anomaly, lower LaN/YbN values, and heavy-mineral assemblages with hornblende and epidote reflect the lithology of source rocks in the Buganda-Toro-Greenstone Belt. In contrast, sediments produced on the low-relief plateau have quartz content up to 98% and higher SiO2/Al2O3 ratio. Systematic loss of mobile elements is indicated by high chemical weathering indices CIA, PIA and WIP. However, provenance from metamorphic basement rocks is still indicated by heavy-mineral assemblages dominated by epidote and amphibole, whereas provenance from granitic rocks is revealed by high Th/Sc and Zr/Sc ratio, negative Eu anomaly and higher LaN/YbN values. We conclude that first-cycle sediments generated in high-relief areas preserve the original imprint of parent lithologies even in very humid equatorial climate. In low-relief areas, although weathering processes have proceeded over millions of years turning basement-derived detritus into an almost pure quartzose resistate, provenance signals are not erased entirely, and can be still retrieved from the residual heavy-mineral suite and relative abundance of high-field-strength trace elements.

Geochemistry and mineralogy of Pd in the magnetitite layer within the upper gabbro of the Mesoarchean Nuasahi Massif (Orissa, India)

NASA Astrophysics Data System (ADS)

Prichard, Hazel M.; Mondal, Sisir K.; Mukherjee, Ria; Fisher, Peter C.; Giles, Nicolas

2018-04-01

Palladium concentrations of 1-3 ppm with an average Pt/Pd ratio of 0.15 have been located for the first time in a magnetitite layer in the Nuasahi Massif in Orissa India. This layer occurs at a high stratigraphic level in the complex and is nearly 4-km long and 5-12-m thick. The sections of the Pd-rich zone identified to date extend over a distance of 1 km at the southern end of the layer. Several phases of mineralization are evident. The first, primary assemblage of platinum-group minerals (PGM) contains Pd-sulfides (vysotskite), Pd-Pb alloys (zvyagintsevite), and a Pd-In alloy, a mineral probably new to mineralogy. These PGM are confined to central magnetite grains in the magnetitites. The magnetite grains with exsolved fine laths of ilmenite at centers are referred to as central magnetite grains. These central magnetite grains are commonly surrounded by blebs of ilmenite and magnetite that contain the majority of the PGM. These are dominated by Pd-antimonides, variably altered to Pd-oxides, and other PGM including PtAs2 (sperrylite), RuS2 (laurite), and IrRhAsS (irarsite/hollingwothite). Many of these PGM also occur in the interstitial silicates, with rare occurrences in the central magnetite grains. We propose that the platinum-group elements (PGE) crystallized during a minor sulfide saturation event that occurred as the magnetitites crystallized. This event produced the minor Cu-sulfides in these magnetitites. Later introduction of antimony and arsenic, during the alteration event that produced the blebby ilmenite and magnetite, led to the more primary PGM being succeeded by the main PGM assemblage, dominated by Pd-antimonides. These are associated with secondary Cu minerals and sperrylite. Subsequent oxidation during weathering in the hot wet Indian climate produced the Pd-oxides. The Nuasahi Massif is a sill-like Archean layered ultramafic-mafic intrusion genetically linked to high-Mg siliceous basalt or boninites and is characterized by unusually thick layers of chromitite. PGE are concentrated in these chromitites and in the base metal sulfide-bearing breccias in the overlying gabbro. The Pd in the magnetitites described here indicates the presence of a third level where PGE are concentrated and a magma that crystallized to produce PGE concentrations at three stratigraphic levels in the massif. This indicates that similar thin sill-like intrusions, hosting unusually thick chromitites, may also have PGE concentrations at a number of stratigraphic levels.

Magmatism, metasomatism, tectonism, and mineralization in the Humboldt Range, Pershing County, Nevada

USGS Publications Warehouse

Vikre, Peter

2014-01-01

Introduction The Humboldt Range, Pershing County, Nevada, predominantly consists of Mesozoic igneous and sedimentary rocks that were modified several times by magmatism, metasomatism, and tectonism, and contain a variety of metallic (Ag, Au, Pb, Zn, Sb, W, Hg) and non-metallic (dumortierite, pinite, fluorite) mineral deposits (Knopf, 1924; Kerr and Jenney, 1935; Kerr, 1938; Cameron, 1939; Campbell, 1939; Kerr, 1940; Page et al., 1940; Johnson, 1977; Vikre, 1978; 1981; Crosby, 2012). Early Triassic Koipato Group volcanic rocks, which are widely exposed in the range, have been altered to quartz, muscovite (sericite), chlorite, pyrite, and other minerals during emplacement of Mesozoic intrusions and by crustal thickening. Most hydrothermal alteration of volcanic rocks and formation of mineral deposits involved externally derived water and other volatiles, although some volcanic strata were apparently altered by pore or dehydration water. Cospatial hydrothermal mineral assemblages and associations, produced by events widely spaced in time, are difficult to separate because of common mineralogy (quartz, sericite, and pyrite), partial to complete recrystallization, thermally compromised Ar geochronology, and lack of comprehensive investigations of volatile sources and deformational fabric. Distinguishing between metasomatic and metamorphic processes that affected rocks in the Humboldt Range is not straightforward.

Experimental alteration of artificial and natural impact melt rock from the Chesapeake Bay impact structure

USGS Publications Warehouse

Declercq, J.; Dypvik, H.; Aagaard, Per; Jahren, J.; Ferrell, R.E.; Horton, J. Wright

2009-01-01

The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mj??lnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 ??C) in order to reproduce conditions found in meltbearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples. In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment. ?? 2009 The Geological Society of America.

Geochemical constraints on the Hadean environment from mineral fingerprints of prokaryotes.

PubMed

Novoselov, Alexey A; Silva, Dailto; Schneider, Jerusa; Abrevaya, Ximena Celeste; Chaffin, Michael S; Serrano, Paloma; Navarro, Margareth Sugano; Conti, Maria Josiane; Souza Filho, Carlos Roberto de

2017-06-21

The environmental conditions on the Earth before 4 billion years ago are highly uncertain, largely because of the lack of a substantial rock record from this period. During this time interval, known as the Hadean, the young planet transformed from an uninhabited world to the one capable of supporting, and inhabited by the first living cells. These cells formed in a fluid environment they could not at first control, with homeostatic mechanisms developing only later. It is therefore possible that present-day organisms retain some record of the primordial fluid in which the first cells formed. Here we present new data on the elemental compositions and mineral fingerprints of both Bacteria and Archaea, using these data to constrain the environment in which life formed. The cradle solution that produced this elemental signature was saturated in barite, sphene, chalcedony, apatite, and clay minerals. The presence of these minerals, as well as other chemical features, suggests that the cradle environment of life may have been a weathering fluid interacting with dry-land silicate rocks. The specific mineral assemblage provides evidence for a moderate Hadean climate with dry and wet seasons and a lower atmospheric abundance of CO 2 than is present today.

A probabilistic approach to remote compositional analysis of planetary surfaces

USGS Publications Warehouse

Lapotre, Mathieu G.A.; Ehlmann, Bethany L.; Minson, Sarah E.

2017-01-01

Reflected light from planetary surfaces provides information, including mineral/ice compositions and grain sizes, by study of albedo and absorption features as a function of wavelength. However, deconvolving the compositional signal in spectra is complicated by the nonuniqueness of the inverse problem. Trade-offs between mineral abundances and grain sizes in setting reflectance, instrument noise, and systematic errors in the forward model are potential sources of uncertainty, which are often unquantified. Here we adopt a Bayesian implementation of the Hapke model to determine sets of acceptable-fit mineral assemblages, as opposed to single best fit solutions. We quantify errors and uncertainties in mineral abundances and grain sizes that arise from instrument noise, compositional end members, optical constants, and systematic forward model errors for two suites of ternary mixtures (olivine-enstatite-anorthite and olivine-nontronite-basaltic glass) in a series of six experiments in the visible-shortwave infrared (VSWIR) wavelength range. We show that grain sizes are generally poorly constrained from VSWIR spectroscopy. Abundance and grain size trade-offs lead to typical abundance errors of ≤1 wt % (occasionally up to ~5 wt %), while ~3% noise in the data increases errors by up to ~2 wt %. Systematic errors further increase inaccuracies by a factor of 4. Finally, phases with low spectral contrast or inaccurate optical constants can further increase errors. Overall, typical errors in abundance are <10%, but sometimes significantly increase for specific mixtures, prone to abundance/grain-size trade-offs that lead to high unmixing uncertainties. These results highlight the need for probabilistic approaches to remote determination of planetary surface composition.

Mineralogical and geochemical characterization of supergene Cu-Pb-Zn-V ores in the Oriental High Atlas, Morocco

NASA Astrophysics Data System (ADS)

Verhaert, Michèle; Bernard, Alain; Dekoninck, Augustin; Lafforgue, Ludovic; Saddiqi, Omar; Yans, Johan

2017-10-01

In the Moroccan High Atlas, two sulfide deposits hosted by Jurassic dolostones underwent significant weathering. In the Cu deposit of Jbel Klakh, several stages of supergene mineralization are distinguished: (1) the replacement of hypogene sulfides in the protolith (chalcopyrite) by secondary sulfides in the cementation zone (bornite, digenite, chalcocite, covellite), (2) the formation of oxidized minerals in the saprolite (malachite, azurite, brochantite) where the environment becomes more oxidizing and neutral, and (3) the precipitation of late carbonates (calcite) and iron (hydr-)oxides in the laterite. The precipitation of carbonates is related to the dissolution of dolomitic host rocks, which buffers the fluid acidity due to the oxidation of sulfides. In the Jbel Haouanit Pb-Zn deposit, the mineral assemblage is dominated by typical calamine minerals, Cu minerals (chalcocite, covellite, malachite), and a Cu-Pb-Zn vanadate (mottramite). Galena is successively weathered in anglesite and cerussite. Sphalerite is weathered in smithsonite, which is rapidly replaced by hydrozincite. Late iron (hydr-)oxides are mainly found at the top of both deposits (laterite). Both deposits are thus characterized by specific mineral zoning, from laterite to protolith, related to variations in the mineralogy and ore grades and probably caused by varying Eh-pH conditions.

Age of uranium mineralization at the Jabiluka and Ranger deposits, Northern Territory, Australia: New U- Pb isotope evidence.

USGS Publications Warehouse

Ludwig, K. R.; Grauch, R.I.; Nutt, C.J.; Nash, J.T.; Frishman, D.; Simmons, K.R.

1987-01-01

The Ranger and Jabiluka uranium deposits are the largest in the Alligator Rivers uranium field, which contains at least 20% of the world's low-cost uranium reserves. Ore occurs in early Proterozoic metasediments, below an unconformity with sandstones of the 1.65 b.y.-old Kombolgie Formation. This study has used U-Pb isotope data from a large number of whole-rock drill core samples with a variety of mineral assemblages and textures. Both Ranger and Jabiluka reflect a common, profound isotopic disturbance at about 400 to 600 m.y. This disturbance, which was especially pronounced at Jabiluka, may correspond to the development of basins and associated basalt flows to the W and SW.-from Authors

Sorption of Eu(III) on granite: EPMA, LA-ICP-MS, batch and modeling studies.

PubMed

Fukushi, Keisuke; Hasegawa, Yusuke; Maeda, Koushi; Aoi, Yusuke; Tamura, Akihiro; Arai, Shoji; Yamamoto, Yuhei; Aosai, Daisuke; Mizuno, Takashi

2013-11-19

Eu(III) sorption on granite was assessed using combined microscopic and macroscopic approaches in neutral to acidic conditions where the mobility of Eu(III) is generally considered to be high. Polished thin sections of the granite were reacted with solutions containing 10 μM of Eu(III) and were analyzed using EPMA and LA-ICP-MS. On most of the biotite grains, Eu enrichment up to 6 wt % was observed. The Eu-enriched parts of biotite commonly lose K, which is the interlayer cation of biotite, indicating that the sorption mode of Eu(III) by the biotite is cation exchange in the interlayer. The distributions of Eu appeared along the original cracks of the biotite. Those occurrences indicate that the prior water-rock interaction along the cracks engendered modification of biotite to possess affinity to the Eu(III). Batch Eu(III) sorption experiments on granite and biotite powders were conducted as functions of pH, Eu(III) loading, and ionic strength. The macroscopic sorption behavior of biotite was consistent with that of granite. At pH > 4, there was little pH dependence but strong ionic strength dependence of Eu(III) sorption. At pH < 4, the sorption of Eu(III) abruptly decreased with decreased pH. The sorption behavior at pH > 4 was reproducible reasonably by the modeling considering single-site cation exchange reactions. The decrease of Eu(III) sorption at pH < 4 was explained by the occupation of exchangeable sites by dissolved cationic species such as Al and Fe from granite and biotite in low-pH conditions. Granites are complex mineral assemblages. However, the combined microscopic and macroscopic approaches revealed that elementary reactions by a single mineral phase can be representative of the bulk sorption reaction in complex mineral assemblages.

Inferring crustal viscosity from seismic velocity: Application to the lower crust of Southern California

NASA Astrophysics Data System (ADS)

Shinevar, William J.; Behn, Mark D.; Hirth, Greg; Jagoutz, Oliver

2018-07-01

We investigate the role of composition on the viscosity of the lower crust through a joint inversion of seismic P-wave (Vp) and S-wave (Vs) velocities. We determine the efficacy of using seismic velocity to constrain viscosity, extending previous research demonstrating robust relationships between seismic velocity and crustal composition, as well as crustal composition and viscosity. First, we calculate equilibrium mineral assemblages and seismic velocities for a global compilation of crustal rocks at relevant pressures and temperatures. Second, we use a rheological mixing model that incorporates single-phase flow laws for major crust-forming minerals to calculate aggregate viscosity from predicted mineral assemblages. We find a robust correlation between crustal viscosity and Vp together with Vs in the α-quartz regime. Using seismic data, geodetic surface strain rates, and heat flow measurements from Southern California, our method predicts that lower crustal viscosity varies regionally by four orders of magnitude, and lower crustal stress varies by three orders of magnitude at 25 km depth. At least half of the total variability in stress can be attributed to composition, implying that regional lithology has a significant effect on lower crustal geodynamics. Finally, we use our method to predict the depth of the brittle-ductile transition and compare this to regional variations of the seismic-aseismic transition. The variations in the seismic-aseismic transition are not explained by the variations in our model rheology inferred from the geophysical observations. Thus, we conclude that fabric development, in conjunction with compositional variations (i.e., quartz and mica content), is required to explain the regional changes in the seismic-aseismic transition.

Petrography and trace element signatures in silicates and Fe-Ti-oxides from the Lanjiahuoshan deposit, Panzhihua layered intrusion, Southwest China

NASA Astrophysics Data System (ADS)

Gao, Wenyuan; Ciobanu, Cristiana L.; Cook, Nigel J.; Huang, Fei; Meng, Lin; Gao, Shang

2017-12-01

Permian mafic-ultramafic layered intrusions in the central part of the Emeishan Large Igneous Province (ELIP), Southwestern China, host Fe-Ti-V-oxide ores that have features which distinguish them from other large layered intrusion-hosted deposits. The origin of these ores is highly debated. Careful petrographic examination, whole rock analysis, electron probe microanalysis, and measurement and mapping of trace element concentrations by laser ablation inductively coupled plasma mass spectrometry in all major and minor minerals (clinopyroxene, plagioclase, olivine, amphibole, titanomagnetite, ilmenite, pleonaste and pyrrhotite) has been undertaken on samples from the Lanjiahuoshan deposit, representing the Middle, Lower and Marginal Zone of the Panzhihua intrusion. Features are documented that impact on interpretation of intrusion petrology and with implications for genesis of the Fe-Ti-V-oxide ores. Firstly, there is evidence, as symplectites between clinopyroxene and plagioclase, for introduction of complex secondary melts. Secondly, reaction between a late hydrothermal fluid and clinopyroxene is recognized, which has led to formation of hydrated minerals (pargasite, phlogopite), as well as a potassium metasomatic event, postdating intrusion solidification, which led to formation of K-feldspar. Lastly, partitioning of trace elements between titanomagnetite and silicates needs to consider scavenging of metals by ilmenite (Mn, Sc, Zr, Nb, Sn, Hf and Ta) and sulfides, as well as the marked partitioning of Co, Ni, Zn, Ga, As and Sb into spinels exsolved from titanomagnetite. The role of these less abundant phases may have been understated in previous studies, highlighting the importance of petrographic examination of complex silicate-oxide-sulfide assemblages, as well as the need for a holistic approach to trace element analysis, acknowledging all minerals within the assemblage.

Provenance Analysis of Lower Miocene Sediments in the Lower Austrian Molasse Basin

NASA Astrophysics Data System (ADS)

Knierzinger, Wolfgang; Palzer, Markus; Wagreich, Michael

2015-04-01

In the Early Miocene (Late Ottnangian) a global drop of the sea level and the continuous rise of the Alps caused a regression of the Paratethys. During this time interval the Traisen Formation (formerly Oncophora beds) was deposited in the Lower Austrian Molasse Basin. These yellowish-brownish to greyish mica-rich and carbonate-free sands and silts with clayish interlayers were originally named after a brackish water bivalve ("Oncophora"- now Rzehakia). The southeastern part of the TF partly interfingers with finer sands of the Dietersdorf Formation (DF). The Pixendorf Group combines the TF and the DF [coarse sands, conglomerates, blocks] of the Upper Ottnangian lithostratigraphic units in Lower Austria. West to the Waschberg Zone a deeper-water environment (so called Oncophora beds in former literature, herein [informally] renamed to Wildendürnbach Member) with sediment gravity flows (turbidites, muddy/sandy slumps) is inferred from OMV well data. Examinations of these fine sandstones, silts and laminated pelites have been carried out on the basis of the Wildendürnbach-4 OMV drilling core. Analyses of the TF revealed rather homogenous heavy mineral assemblages, dominated by high amounts of garnet (~65%) and relatively high amounts of epidote/zoisite (~10%) and amphiboles (~10%). Conducted surveys point towards a primary influence of metamorphic (metapelitic) source rocks of Austroalpine Crystalline Complexes of the rising Eastern Alps. Heavy mineral analysis of the WDK-4 drilling core showed even higher amounts of garnet (~80%) combined with minor amounts of rutile, staurolite, apatite, epidote/zoisite, tourmalines, zircon and amphiboles. Consistent heavy mineral assemblages and chemical data (EMPA) suggest a stratigraphical correlation with the Křepice Formation and the Ždánice-Hustopeče Formation in the Czech Republic and sedimentary influence from the Western Carpathian Flysch Belt.

The mineralogical consequences and behavior of descending acid-sulfate waters: An example from the Karaha - Telaga Bodas geothermal system, Indonesia

USGS Publications Warehouse

Moore, J.N.; Christenson, B.W.; Allis, R.G.; Browne, P.R.L.; Lutz, S.J.

2004-01-01

Acidic steam condensates in volcanic systems or shallow, oxygenated geothermal environments are typically enriched in SO4 and poor in Cl. These fluids produce distinctive alteration-induced assemblages as they descend. At Karaha - Telaga Bodas, located on the flank of Galunggung Volcano, Indonesia, neutralization of descending acid waters has resulted in the successive appearance of 1) advanced argillic alteration characterized by alunite, clay minerals and pyrite, 2) anhydrite, pyrite and interlayered sheet silicates, and 3) carbonates. Minor tourmaline, fluorite and native sulfur also are present locally, reflecting interactions with discharging magmatic gases. Water rock interactions were modeled at temperatures up to 250??C using the composition of acidic lake water from Telaga Bodas and that of a typical andesite as reactants. The simulations predict mineral distributions consistent with the observed assemblages and a decrease in the freezing-point depression of the fluid with increasing temperature. Fluids trapped in anhydrite, calcite and fluorite display a similar decrease in their freezing-point depressions, from 2.8?? to 1.5??C, as homogenization temperatures increase from 160?? to 205??C. The simulations indicate that the progressive change in fluid composition is due mainly to the incorporation of SO4 into the newly formed hydrothermal minerals. The salinities of fluid inclusions containing Cl-deficient steam condensates are better expressed in terms of H2SO4 equivalents than the commonly used NaCl equivalents. At solute concentrations >1.5 molal, freezing-point depressions represented as NaCl equivalents overestimate the salinity of Cl-poor waters. At lower concentrations, differences between apparent salinities calculated as NaCl and H2SO 4 equivalents are negligible.

Clay mineralogical record on the upper continental slope of the northwestern South China Sea since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

CHEN, Q.; Liu, Z.; Stattegger, K.

2012-12-01

Clay mineralogy of two gravity cores (18428 and 18429) on the upper continental slope of the northwestern South China Sea was investigated in order to understand terrigenous sediment sources and to evaluate the contribution from the Red River since the Late Glacial Maximum. Planktonic foraminiferal oxygen isotope and carbonate stratigraphies suggest that Core 18428 is constrained in Holocene while Core 18429 covers the period of MIS 1-2. Clay mineral assemblages of two cores are composed mainly of smectite (18-57%) and illite (21-41%), with minor chlorite (12-21%) and kaolinite (8-26%). In despite of relatively constant values of illite crystallinity, ranging among 0.14°-0.20° Δ2θ, the time series variation in clay mineral distributions indicates a strong glacial-interglacial shift. Contents of illite, chlorite, and kaolinite (Core 18429) in the Holocene are lower than in the glacial period, and vice versa for the smectite content. The provenance analysis based on clay mineralogy suggests the Red River as a predominant sedimentary source of illite, chlorite, and kaolinite during all the depositional period of MIS 1-2. The sea level change actually controlled the variations of clay mineral assemblages on the upper slope since the Last Glacial Maximum. When the sea level was low during the last glacial period, more terrigenous sediments from the Red River could reach the continental slope in the northwestern South China Sea. However, when the sea level is closed to the present situation during the Holocene, most of Red River sediments could be trapped in the Gulf of Tonkin, instead of draining in the deep South China Sea.

BurnMan: Towards a multidisciplinary toolkit for reproducible deep Earth science

NASA Astrophysics Data System (ADS)

Myhill, R.; Cottaar, S.; Heister, T.; Rose, I.; Unterborn, C. T.; Dannberg, J.; Martin-Short, R.

2016-12-01

BurnMan (www.burnman.org) is an open-source toolbox to compute thermodynamic and thermoelastic properties as a function of pressure and temperature using published mineral physical parameters and equations-of-state. The framework is user-friendly, written in Python, and modular, allowing the user to implement their own equations of state, endmember and solution model libraries, geotherms, and averaging schemes. Here we introduce various new modules, which can be used to: Fit thermodynamic variables to data from high pressure static and shock wave experiments, Calculate equilibrium assemblages given a bulk composition, pressure and temperature, Calculate chemical potentials and oxygen fugacities for given assemblages Compute 3D synthetic seismic models using output from geodynamic models and compare these results with global seismic tomographic models, Create input files for synthetic seismogram codes. Users can contribute scripts that reproduce the results from peer-reviewed articles and practical demonstrations (e.g. Cottaar et al., 2014).

The role of minerals in the thermal alteration of organic matter. III - Generation of bitumen in laboratory experiments

NASA Technical Reports Server (NTRS)

Huizinga, Bradley J.; Tannenbaum, Eli; Kaplan, I. R.

1987-01-01

A series of pyrolysis experiments, utilizing two different immature kerogens (from the Monterey and Green River Formations) mixed with common sedimentary minerals (calcite, illite, or Na-montmorillonite), was conducted to study the impact of the mineral matrix on the bitumen that was generated. Calcite has no significant influence on the thermal evolution of bitumen and also shows virtually no adsorption capacity for any of the pyrolysate. In contrast, montmorillonite (M) and illite, to a lesser extent, alter bitumen during dry pyrolysis. M and illite also display strong adsorption capacities for the polar constituents of bitumen. By this process, hydrocarbons are substantially concentrated within the pyrolysate that is not strongly adsorbed on the clay matrices. The effects of the clay minerals are significantly reduced during hydrous pyrolysis. The strong adsorption capacities of M and illite, as well as their thermocatalytic properties, may in part explain why light oils and gases are generated from certain argillaceous source-rock assemblages, whereas heavy immature oils are often derived from carbonate source rocks.

Corrosion of heavy minerals during weathering and diagenesis: A catalog for optical analysis

NASA Astrophysics Data System (ADS)

Andò, Sergio; Garzanti, Eduardo; Padoan, Marta; Limonta, Mara

2012-12-01

A practical classification of surface textures observed on detrital grains in sands and sandstones is proposed, in order to enhance data reproducibility among operators and to implement the use of high-resolution heavy-mineral data in studies of sediment-generation, provenance, and diagenesis. Five stages of progressive weathering (unweathered, corroded, etched, deeply etched, skeletal) are recognized for diverse detrital minerals. Archetypal grains displaying increasing degrees of corrosion are illustrated in numerous color tables for visual comparison. This catalog, specifically devised to systematically collect valuable information for paleoclimatic or diagenetic interpretation during routine grain-counting under the microscope, is here shown to represent a useful subsidiary tool to reveal the different degrees of weathering for diverse minerals in modern sands of equatorial Africa, and to identify post-depositional modifications of detrital assemblages in buried orogenic sediments of the Bengal Basin. The data thus obtained need to be interpreted by carefully considering the concentration of heavy minerals in each sample, which provides the fundamental clue to quantify the degree of heavy-mineral depletion caused by either pre-depositional or post-depositional processes. The scrutiny of dissolution effects has applications in the study of the chemical properties of minerals and of diagenetic evolution, helping us to understand the development of secondary porosity and to assess the potential of water and hydrocarbon reservoirs.

Numerically Simulating Carbonate Mineralization of Basalt with Injection of Carbon Dioxide into Deep Saline Formations

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

White, Mark D.; McGrail, B. Peter; Schaef, Herbert T.

2006-07-08

The principal mechanisms for the geologic sequestration of carbon dioxide in deep saline formations include geological structural trapping, hydrological entrapment of nonwetting fluids, aqueous phase dissolution and ionization, and geochemical sorption and mineralization. In sedimentary saline formations the dominant mechanisms are structural and dissolution trapping, with moderate to weak contributions from hydrological and geochemical trapping; where, hydrological trapping occurs during the imbibition of aqueous solution into pore spaces occupied by gaseous carbon dioxide, and geochemical trapping is controlled by generally slow reaction kinetics. In addition to being globally abundant and vast, deep basaltic lava formations offer mineralization kinetics that makemore » geochemical trapping a dominate mechanism for trapping carbon dioxide in these formations. For several decades the United States Department of Energy has been investigating Columbia River basalt in the Pacific Northwest as part of its environmental programs and options for natural gas storage. Recently this nonpotable and extensively characterized basalt formation is being reconsidered as a potential reservoir for geologic sequestration of carbon dioxide. The reservoir has an estimated storage capacity of 100 giga tonnes of carbon dioxide and comprises layered basalt flows with sublayering that generally alternates between low permeability massive and high permeability breccia. Chemical analysis of the formation shows 10 wt% Fe, primarily in the +2 valence. The mineralization reaction that makes basalt formations attractive for carbon dioxide sequestration is that of calcium, magnesium, and iron silicates reacting with dissolved carbon dioxide, producing carbonate minerals and amorphous quartz. Preliminary estimates of the kinetics of the silicate-to-carbonate reactions have been determined experimentally and this research is continuing to determine effects of temperature, pressure, rock composition and mineral assemblages on the reaction rates. This study numerically investigates the injection, migration and sequestration of supercritical carbon dioxide in deep Columbia River basalt formations using the multifluid subsurface flow and reactive transport simulator STOMP-CO2 with its ECKEChem module. Simulations are executed on high resolution multiple stochastic realizations of the layered basalt systems and demonstrate the migration behavior through layered basalt formations and the mineralization of dissolved carbon dioxide. Reported results include images of the migration behavior, distribution of carbonate formation, quantities of injected and sequestered carbon dioxide, and percentages of the carbon dioxide sequestered by different mechanisms over time.« less

New data towards the development of a comprehensive taphonomic framework for the Late Jurassic Cleveland-Lloyd Dinosaur Quarry, Central Utah

PubMed Central

Warnock, Jonathan P.; Eberhart, Shawn L.; Clawson, Steven R.; Noto, Christopher R.

2017-01-01

The Cleveland-Lloyd Dinosaur Quarry (CLDQ) is the densest deposit of Jurassic theropod dinosaurs discovered to date. Unlike typical Jurassic bone deposits, it is dominated by the presence of Allosaurus fragilis. Since excavation began in the 1920s, numerous hypotheses have been put forward to explain the taphonomy of CLDQ, including a predator trap, a drought assemblage, and a poison spring. In an effort to reconcile the various interpretations of the quarry and reach a consensus on the depositional history of CLDQ, new data is required to develop a robust taphonomic framework congruent with all available data. Here we present two new data sets that aid in the development of such a robust taphonomic framework for CLDQ. First, x-ray fluorescence of CLDQ sediments indicate elevated barite and sulfide minerals relative to other sediments from the Morrison Formation in the region, suggesting an ephemeral environment dominated by periods of hypereutrophic conditions during bone accumulation. Second, the degree of abrasion and hydraulic equivalency of small bone fragments dispersed throughout the matrix were analyzed from CLDQ. Results of these analyses suggest that bone fragments are autochthonous or parautochthonous and are derived from bones deposited in the assemblage rather than transported. The variability in abrasion exhibited by the fragments is most parsimoniously explained by local periodic re-working and re-deposition during seasonal fluctuations throughout the duration of the quarry assemblage. Collectively, these data support previous interpretations that the CLDQ represents an attritional assemblage in a poorly-drained overbank deposit where vertebrate remains were introduced post-mortem to an ephemeral pond during flood conditions. Furthermore, while the elevated heavy metals detected at the Cleveland-Lloyd Dinosaur Quarry are not likely the primary driver for the accumulation of carcasses, they are likely the result of multiple sources; some metals may be derived from post-depositional and diagenetic processes, and others are potentially produced from an abundance of decomposing vertebrate carcasses. These new data help to support the inferred depositional environment of the quarry as an ephemeral pond, and represent a significant step in understanding the taphonomy of the bonebed and Late Jurassic paleoecology in this region. PMID:28603668

Different origins of garnet in high pressure to ultrahigh pressure metamorphic rocks

NASA Astrophysics Data System (ADS)

Xia, Qiong-Xia; Zhou, Li-Gang

2017-09-01

Garnet in high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in subduction zone commonly shows considerable zonation in major and trace elements as well as mineral inclusions, which bears information on its growth mechanism via metamorphic or peritectic reactions in coexistence with relic minerals and metamorphic fluids or anatectic melts at subduction-zone conditions. It provides an important target to retrieve physicochemical changes in subduction-zone processes, including those not only in pressure and temperature but also in the durations of metamorphism and anatexis. Garnet from different compositions of HP to UHP metamorphic rocks may show different types of major and trace element zonation, as well as mineral inclusions. Discrimination between the different origins of garnet provides important constraints on pressure and temperature and the evolution history for the HP to UHP metamorphic rocks. Magmatic garnet may occur as relics in granitic gneisses despite metamorphic modification at subduction-zone conditions, with spessartine-increasing or flat major element profiles from inner to outer core and exceptionally higher contents of trace elements than metamorphic mantle and rim. Metamorphic garnet can grow at different metamorphic stages during prograde subduction and retrograde exhumation, with spessartine-decreasing from core to rim if the intracrystalline diffusion is not too fast. The compositional profiles of metamorphic garnet in the abundances of grossular, almandine and pyrope are variable depending on the composition of host rocks and co-existing minerals. Peritectic garnet grows through peritectic reactions during partial melting of HP to UHP rocks, with the composition of major elements to be controlled by anatectic P-T conditions and the compositions of parental rocks and anatectic melts. Trace element profiles in garnet with different origins are also variable depending on the coexisting mineral assemblages, the garnet-forming reactions and the property of metamorphic fluids or anatectic melts. Mineral inclusions not only present key clues to identify the different origins of garnet, but also serve as sound candidates for the temporal constraint on garnet growth.

Upper mantle fluids evolution, diamond formation, and mantle metasomatism

NASA Astrophysics Data System (ADS)

Huang, F.; Sverjensky, D. A.

2017-12-01

During mantle metasomatism, fluid-rock interactions in the mantle modify wall-rock compositions. Previous studies usually either investigated mineral compositions in xenoliths and xenocrysts brought up by magmas, or examined fluid compositions preserved in fluid inclusions in diamonds. However, a key study of Panda diamonds analysed both mineral and fluid inclusions in the diamonds [1] which we used to develop a quantitative characterization of mantle metasomatic processes. In the present study, we used an extended Deep Earth Water model [2] to simulate fluid-rock interactions at upper mantle conditions, and examine the fluids and mineral assemblages together simultaneously. Three types of end-member fluids in the Panda diamond fluid inclusions include saline, rich in Na+K+Cl; silicic, rich in Si+Al; and carbonatitic, rich in Ca+Mg+Fe [1, 3]. We used the carbonatitic end-member to represent fluid from a subducting slab reacting with an excess of peridotite + some saline fluid in the host environment. During simultaneous fluid mixing and reaction with the host rock, the logfO2 increased by about 1.6 units, and the pH increased by 0.7 units. The final minerals were olivine, garnet and diamond. The Mg# of olivine decreased from 0.92 to 0.85. Garnet precipitated at an early stage, and its Mg# also decreased with reaction progress, in agreement with the solid inclusions in the Panda diamonds. Phlogopite precipitated as an intermediate mineral and then disappeared. The aqueous Ca, Mg, Fe, Si and Al concentrations all increased, while Na, K, and Cl concentrations decreased during the reaction, consistent with trends in the fluid inclusion compositions. Our study demonstrates that fluids coming from subducting slabs could trigger mantle metasomatism, influence the compositions of sub-lithospherc cratonic mantle, precipitate diamonds, and change the oxygen fugacity and pH of the upper mantle fluids. [1] Tomlinson et al. EPSL (2006); [2] Sverjensky, DA et al., GCA (2014), Huang, F, Ph. D. thesis, Johns Hopkins University, (2017); [3] Shirey et al., Rev. Mineral. Geochem. (2013)

Some mineral stability relations in the system CaOMgOSiO2H2OHCl

USGS Publications Warehouse

Luce, R.W.; Cygan, G.L.; Hemley, J.J.; d'Angelo, W. M.

1985-01-01

Mineral-aqueous solution equilibria for the assemblages talc-quartz, tremolite-talc-quartz, diopside-tremolite-quartz, wollastonite-diopside-quartz and wollastonite-quartz have been studied at 2 kb total pressure, 500?? to 700??C and chloride concentrations from 0.03 to 6.0 molal. Most work was at 1 m chloride. Both buffered and unbuffered data were obtained and a recalibration of the Ag-AgCl buffer is presented. Log equilibrium quotients at 500??, 600?? and 700??C are respectively: Ta-Qz ( mMgCl2 mHCl2) 2.57, 1.71, 0.73; Tr-Ta-Qz and Di-Tr-Qz ( mCaCl2 mMgCl2mHCl2) 4.98, 3.99, 2.21 and 7.29, 5.30, 3.56; WoDi-Qz ( mCaCl2 mMgCl2) 3.30, 3.00, 2.79: Wo-Qz ( mCaCl2 mHCl2) 5.15, 3.95, 2.68. Mineral stability fields plotted in terms of these concentration data more tangibly represent the compositional character of real systems and the mass transfer capabilities of their fluids than do the analogous theoretical activity diagrams. Overall dissociation constants of MgCl2 and CaCl2 were calculated from the experimental data using the calculated ionic activity constants for the reactions and the established dissociation constants of HCl. The negative log values are respectively: 3.88. 6.63, 9.20 for CaCl2 and 4.60, 7.54, 10.37 for MgCl2 at 500??, 600?? and 700??C, 2 kb. The Ca values are about an order of magnitude more positive than the conductance-derived values by Frantz and Marshall (1982). The phase relations developed in this study have application to the genesis of talc, tremolite, and diopside-bearing assemblages in some regional metamorphic rocks, but more specifically to the calcsilicate skarn assemblages of many metasomatic aureoles. The equilibrium fluids are characterized by high concentrations of Ca relative to Mg and increasing Ca Mg ratios with decreasing temperatures. The stability fields of talc, tremolite, and quartz expand relative to those of diopside and wollastonite with decreasing temperature, hence their more common appearance as retrograde products in skarn systems. ?? 1985.

Thermal infrared spectral analysis of compacted fine-grained mineral mixtures: implications for spectral interpretation of lithified sedimentary materials on Mars

NASA Astrophysics Data System (ADS)

Pan, C.; Rogers, D.

2012-12-01

Characterizing the thermal infrared (TIR) spectral mixing behavior of compacted fine-grained mineral assemblages is necessary for facilitating quantitative mineralogy of sedimentary surfaces from spectral measurements. Previous researchers have demonstrated that TIR spectra from igneous and metamorphic rocks as well as coarse-grained (>63 micron) sand mixtures combine in proportion to their volume abundance. However, the spectral mixing behavior of compacted, fine-grained mineral mixtures that would be characteristic of sedimentary depositional environments has received little attention. Here we characterize the spectral properties of pressed pellet samples of <10 micron mineral mixtures to 1) assess linearity of spectral combinations, 2) determine whether there are consistent over- or under-estimations of different types of minerals in spectral models and 3) determine if model accuracy can be improved by including both fine- and coarse-grained end-members. Major primary and secondary minerals found on the Martian surface including feldspar, pyroxene, smectite, sulfate and carbonate were crushed with an agate mortar and pestle and centrifuged to obtain less than 10 micron size. Pure phases and mixtures of two, three and four components were made in varying proportions by volume. All of the samples were pressed into pellets at 15000PSI to minimize volume scattering. Thermal infrared spectra of pellets were measured in the Vibrational Spectroscopy Laboratory at Stony Brook University with a Thermo Fisher Nicolet 6700 Fourier transform infrared Michelson interferometer from ~225 to 2000 cm-1. Our preliminary results indicate that some pelletized samples have contributions from volume scattering, which leads to non-linear spectral combinations. It is not clear if the transparency features (which arise from multiple surface reflections of incident photons) are due to minor clinging fines on an otherwise specular pellet surface or to partially transmitted energy through optically thin grains in the compacted mixture. Inclusion of loose powder (<10 μm) sample spectra improves mineral abundance estimates for some mixtures. In general, mineral abundances are predicted to within +/- 10% (absolute) for approximately 60% of our samples; thus far, there are no clear trends in which cases produce better model results. With the exception of pyroxene/feldspar ratios being consistently overestimated, there are no consistent trends in over- or under-estimation of minerals. The results described here are based on the unsubstantiated assumption that areal abundance on the pellet surface is equal to the volume abundance. Thus future work will include micro-imaging of our samples to constrain areal abundance. We will also prepareclay mixtures using a wetting/drying sequence rather than pressure, and expand our set of samples to include additional mixture combinations to further characterize the spectral behavior of compacted mixtures. This work will be directly applicable to analysis of TES and Mini-TES data of lithified sedimentary deposits.

An Example of Cyprus type Volcanogenic Massive Sulfide Deposit in the Southeast of Turkey

NASA Astrophysics Data System (ADS)

Kang, J.; Lee, I.; Donmez, C.; Yildirim, N.; Chang, S.

2013-12-01

Ortaklar mineral deposit of Gaziantep province in Turkey is located in the Southeast Anatolian orogenic belt which was developed as a result of closure of Neotethyan ocean, between Tauride (at north) and Arabian platform (at south), during upper Cretaceous-Miocene periods. Copper mineralization is in spilitic basalt and pillow lavas of Kocali complex. The complex includes oceanic fragments that represent serpentinite, mafic and ultramafic cumulates, isotropic gabbros, sheeted dyke complexes, spilitic basalt, pillow lavas, and radiolarian chert. The deposit is generally parallel to the thrust lines (E-W/30-60 North). Ore minerals occur in massive form and also as stockwork or disseminated forms at subsurface. Oxidized zone appears about 1 km in width at surface. The orebody is underlain and contacted with radiolarian chert. The samples mainly have been collected from open pit but also include some core samples. The samples were examined with unaided eyes and under microscope. In basalts, clino-pyroxenes subophitically enclose laths of plagioclases. Amygdales are filled with calcite in spilitic basalts and it is heavily chloritized and cut by calcite veins. In some parts of basalt, crystobalite is intergrowth with plagioclas. Globules between laths of plagioclase are also observed due to liquid immiscibility. Cherts have spherical radiolaria skeletons and their long thin spines. A lot of carbonate veinlets are developed as well. Few samples of cherts have radialfibrous quartz, known as chalcedonic quartz. Serpentinites in the study area are divided into two types on the basis of the existence of relics of the original minerals. One has relict crystals of olivine or pyroxene within the network of serpenitine and the other has no mineral remnants. Both types have opaque iron oxides with some brown stains among small blocks by numerous veinlets. Major ore minerals consist of chalcopyrite, pyrite, magnetite, and hematite. Minor ore minerals are composed of bornite, covellite, chalcocite, sphalerite, and Fe-oxide. Pyrite occurs as a typical cube shape or shows cataclastic texture. And intergrowth of chalcopyrite with magnetite and massive chalcopyrite are observed in the samples. Goethite and lepidocrocite occur in needle or lath shape in the samples from the iron cap as the secondary minerals. It is also shown that pyrite and chalcopyrite are replaced by anhedral bornite and chalcocite. Sulfide textures also indicate grain-coarsening and crystallization under hydrothermal conditions. Electron microprobe was used to identify several minerals and to find out the difference of trace elements such as Cr, Ni, Co, As, Zn, and Pb within mineral grains. Ortaklar copper deposit in Gaziantep resembles Cyprus type volcanogenic massive sulfide deposit based on ore mineralogy, mineral assemblages, textures, and host rock relationship. To investigate more detail characteristics of the deposit, trace elements and rare earth elements were analyzed using inductively coupled plasma mass spectrometer.

Curiosity Rover's CheMin Instrument Investigates Mineralogy of Gale Crater and Implications for Diagenesis

NASA Astrophysics Data System (ADS)

Fendrich, Kim; Rampe, Elizabeth; Vaniman, David; Bish, David; Blake, David; Treiman, Allan; Ming, Doug; Morris, Richard; Bristow, Tom; Cavanagh, Patrick; Downs, Robert; Morrison, Shaunna; Chipera, Steve; Achilles, Cherie; Farmer, Jack; Sarrazin, Philippe; Crisp, Joy; Morookian, John Michael; Yen, Albert; Gellert, Ralf

2015-04-01

The Mars Science Laboratory rover Curiosity employs a suite of instruments to investigate past or present habitability of Mars, as observed at Gale crater and particularly in the lower strata of the crater's central mound, informally named Mount Sharp. The X-ray diffractometer on board, CheMin, is used to assess the quantitative mineralogy of scooped soil samples and drilled rock powders. Methods of modeling diffraction peak positions and intensities to evaluate the abundances of minerals include Rietveld refinement and FULLPAT (full-pattern fitting). Each of the samples analyzed by CheMin contains X-ray amorphous material. The amorphous component chemistry is resolved by subtracting the chemistry of the crystalline composition, as determined by X-ray diffraction data, from the bulk sample chemistry, as determined by the Alpha Particle X-ray Spectrometer (APXS). Diffraction results have been obtained on five samples thus far to include Rocknest, John Klein, Cumberland, Windjana and Confidence Hills. Soil samples collected at Rocknest, an aeolian bedform in Gale crater, were the first to be analyzed in situ by CheMin. The Rocknest mineral assemblage is basaltic (plagioclase, Fe-forsterite, augite, pigeonite) and contains amorphous material that is compositionally similar to palagonitic volcanic soils found on Earth, with the addition of sulfur and chlorine. The four drill analyses are characteristic of deposition in a variety of fluvio-lacustrine environments and exhibit evidence of low-temperature diagenesis. Both John Klein and Cumberland are part of the Sheepbed mudstone at Yellowknife Bay, where the first drilled samples were acquired as well as the first evidence of a habitable environment on Mars. Drilled three meters apart from each other, the two samples reveal basaltic minerals similar to those at Rocknest, as well as phyllosilicates, Fe-oxides/hydroxides, Ca-sulfates, Fe-sulfides, and amorphous materials. The nature and hydration of interlayer cations within the phyllosilicates differs between the two samples, which implies localized diagenesis. The Windjana sandstone at the Kimberley location differs from the Sheepbed mudstone in that it contains more pyroxene and magnetite and abundant K-feldspar, as well as phyllosilicates and amorphous material. These phases may represent potassium-rich basaltic provenance or aqueous alteration by potassium-bearing fluids. While the Confidence Hills sample is still in the preliminary stages of evaluation, major crystalline phases observed in this fine-grained sedimentary rock include plagioclase, pyroxene, K-feldspar and phyllosilicates; hematite, rare in all previous samples, is notably abundant and jarosite is present. The findings suggest localized mobilization of iron-bearing fluids and acidic conditions. The more oxidized assemblage of Confidence Hills marks the transition into the lower strata of Mount Sharp.

Determinism in fish assemblages of floodplain lakes of the vastly disturbed Mississippi Alluvial Valley

USGS Publications Warehouse

Miranda, L.E.; Lucas, G.M.

2004-01-01

The Mississippi Alluvial Valley between southern Illinois and southern Louisiana contains hundreds of floodplain lakes, most of which have been adversely affected by landscape modifications used to control flooding and support agriculture. We examined fish assemblages in lakes of this region to determine whether deterministic patterns developed in relation to prominent abiotic lake characteristics and to explore whether relevant abiotic factors could be linked to specific assemblage structuring mechanisms. The distributions of 14 taxa in 29 lakes were governed primarily by two gradients that contrasted assemblages in terms of lake area, lake elongation, and water clarity. The knowledge of whether a lake was clear or turbid, large or small, and long or short helped determine fish assemblage characteristics. Abiotic factors influenced fish assemblage structures, plausibly through limitations on foraging and physiological tolerances. Determinism in assemblage organization of floodplain lakes relative to recurrence in physicochemical features has been documented for unaltered rivers. Whereas the Mississippi Alluvial Valley has been subjected to vast anthropogenic disturbances and is not a fully functional floodplain river, fish assemblages in its floodplain lakes remain deterministic and organized by the underlying factors that also dictate assemblages in unaltered rivers. In advanced stages of lake aging, fish assemblages in these lakes are expected to largely include species that thrive in turbid, shallow systems with few predators and low oxygen concentrations. The observed patterns related to physical characteristics of these lakes suggest three general conservation foci, including (1) watershed management to control erosion, (2) removal of sediments or increases in water level to alleviate depth reductions and derived detriments to water physicochemistry, and (3) management of fish populations through stockings, removals, and harvest regulations.

Petrography and character of the bedrock surface beneath western Cape Cod, Massachusetts

USGS Publications Warehouse

Hallett, B.W.; Poppe, L.J.; Brand, S.G.

2004-01-01

Cores collected during recent drilling in western Cape Cod, Massachusetts provide insight into the topography and petrology of the underlying bedrock. 62 drill sites spread over a ???140 km2 study area produced cores of granitoids (31), orthogneisses (20), basalts/diabases (4), amphibolites (3), felsic mylonites (2), and dolomitic rock (2). Granitoid cores range in composition from granite to tonalite to quartz diorite, but are dominated by single-mica granites. Alteration is common in nearly all cores examined in this study, and is evidenced by the secondary growth of chlorite and epidote. The granitoids resemble rocks of the Dedham and Fall River terranes (Wones and Goldsmith 1991). Gneisses from the study area generally contain the mineral assemblage hornblende+plagioclase+quartz+biotite+epidote??chlorite?? sphene??K-feldspar??sericite+oxides. Based on mineral assemblages, we estimate peak metamorphic grade to be of lower amphibolite facies. X-ray powder diffraction of unmetamorphosed dolomitic cores shows presence of layered silicates (clays), plagioclase, and possible magnesite. Contours of the bedrock surface show locally irregular topography suggesting erosion by glacial scour. The distribution of lithologies suggests a possible continuation of the New Bedford gneissic terrane that outcrops 25 km to the west. Dolomitic rocks may represent a lithified fault gouge material at the eastern edge of the gneissic zone. Basalts/diabases are interpreted to be post-metamorphic dikes of Late Paleozoic age, or possibly associated with Mesozoic rifting.

Late-stage sulfides and sulfarsenides in Lower Cambrian black shale (stone coal) from the Huangjiawan mine, Guizhou Province, People's Republic of China

USGS Publications Warehouse

Belkin, H.E.; Luo, K.

2008-01-01

The Ni-Mo Huangjiawan mine, Guizhou Province, People's Republic of China, occurs in Lower Cambrian black shale (stone coal) in an area where other mines have recently extracted ore from the same horizon. Detailed electron microprobe (EMPA) and scanning electron microscope (SEM) analyses of representative thin sections have revealed a complex assemblage of sulfides and sulfarsenides. Early sulfidic and phosphatic nodules and host matrix have been lithified, somewhat fractured, and then mineralized with later-stage sulfides and sulfarsenides. Gersdorffite, millerite, polydymite, pyrite, sphalerite, chalcopyrite, galena, and clausthalite have been recognized. EMPA data are given for the major phases. Pyrite trace-element distributions and coeval Ni-, As-sulfides indicate that in the main ore layer, the last sulfide deposition was Ni-As-Co-rich. Mo and V deposition were early in the petrogenesis of these rocks. The assemblages gersdorffite-millerite-polydymite (pyrite) and millerite-gersdorffite (pyrite) and the composition of gersdorffite indicate a formation temperature of between 200?? and 300??C suggesting that the last solutions to infiltrate and mineralize the samples were related to hydrothermal processes. Environmentally sensitive elements such as As, Cd, and Se are hosted by sulfides and sulfarsenides and are the main source of these elements to residual soil. Crops grown on them are enriched in these elements, and they may be hazardous for animal and human consumption. ?? Springer-Verlag 2007.

Giardia spp. Are Commonly Found in Mixed Assemblages in Surface Water, as Revealed by Molecular and Whole-Genome Characterization

PubMed Central

Tsui, Clement K.-M.; Hsiao, William W. L.; Uyaguari-Diaz, Miguel I.; Ho, Jordan; Tang, Patrick; Isaac-Renton, Judith

2015-01-01

Giardia is the most common parasitic cause of gastrointestinal infections worldwide, with transmission through surface water playing an important role in various parts of the world. Giardia duodenalis (synonyms: G. intestinalis and G. lamblia), a multispecies complex, has two zoonotic subtypes, assemblages A and B. When British Columbia (BC), a western Canadian province, experienced several waterborne giardiasis outbreaks due to unfiltered surface drinking water in the late 1980s, collection of isolates from surface water, as well as from humans and beavers (Castor canadensis), throughout the province was carried out. To better understand Giardia in surface water, 71 isolates, including 29 from raw surface water samples, 29 from human giardiasis cases, and 13 from beavers in watersheds from this historical library were characterized by PCR. Study isolates also included isolates from waterborne giardiasis outbreaks. Both assemblages A and B were identified in surface water, human, and beavers samples, including a mixture of both assemblages A and B in waterborne outbreaks. PCR results were confirmed by whole-genome sequencing (WGS) for one waterborne outbreak and supported the clustering of human, water, and beaver isolates within both assemblages. We concluded that contamination of surface water by Giardia is complex, that the majority of our surface water isolates were assemblage B, and that both assemblages A and B may cause waterborne outbreaks. The higher-resolution data provided by WGS warrants further study to better understand the spread of Giardia. PMID:25956776

The Archean komatiite-hosted, PGE-bearing Ni-Cu sulfide deposit at Vaara, eastern Finland: evidence for assimilation of external sulfur and post-depositional desulfurization

NASA Astrophysics Data System (ADS)

Konnunaho, J. P.; Hanski, E. J.; Bekker, A.; Halkoaho, T. A. A.; Hiebert, R. S.; Wing, B. A.

2013-12-01

Archean komatiites host important resources of Ni, Cu, Co, and PGE, particularly in Western Australia and Canada. In Finland, several small, low-grade sulfide deposits have been found in komatiites, including the ca. 2.8 Ga Vaara deposit in the Archean Suomussalmi greenstone belt. It occurs in the central part of the serpentinized olivine cumulate zone of a komatiitic extrusive body and is composed of disseminated interstitial sulfides consisting of pyrite, pentlandite, millerite, violarite, and chalcopyrite accompanied by abundant magnetite. Although currently subeconomic, the mineralization is interesting due to the very high chalcophile element contents of the sulfide fraction (38 wt% Ni, 3.4 wt% Cu, 0.7 wt% Co, 22.4 ppm Pd, and 9.5 ppm Pt). The sulfides occur in relatively Cr-poor olivine cumulates suggesting involvement of a chromite-undersaturated magma. The parental magma was an Al-undepleted komatiite with an estimated MgO content of at least 24 wt%. In contrast to the common komatiite types in the eastern Finland greenstone belts, the Vaara rocks are moderately enriched in LREE relative to MREE, suggesting that crustal contamination played an important role in the genesis of the Vaara deposit. Multiple sulfur isotope data reveal considerable mass-independent sulfur isotope fractionation both in country rock sedimentary sulfides (Δ33S ranges from -0.50 to +2.37 ‰) and in the Vaara mineralization (Δ33S ranges from +0.53 to +0.66 ‰), which provides strong evidence for incorporation of crustal sulfur. Extensive replacement of interstitial sulfides by magnetite and the presence of millerite- and violarite-bearing, pyrrhotite-free sulfide assemblages indicate significant post-magmatic, low-temperature hydrothermal oxidation of the primary magmatic pyrrhotite-pentlandite-chalcopyrite assemblages and associated sulfur loss that led to a significant upgrading of the original metal tenors of the Vaara deposit.

Proterozoic metamorphism and uplift history of the north-central Laramie Mountains, Wyoming, USA

USGS Publications Warehouse

Patel, S.C.; Frost, B.R.; Chamberlain, K.R.; Snyder, G.L.

1999-01-01

The Laramie Mountains of south-eastern Wyoming contain two metamorphic domains that are separated by the 1.76 Ga. Laramie Peak shear zone (LPSZ). South of the LPSZ lies the Palmer Canyon block, where apatite U-Pb ages are c. 1745 Ma and the rocks have undergone Proterozoic kyanite-grade Barrovian metamorphism. In contrast, in the Laramie Peak block, north of the shear zone, the U-Pb apatite ages are 2.4-2.1 Ga, the granitic rocks are unmetamorphosed and supracrustal rocks record only low-T amphibolite facies metamorphism that is Archean in age. Peak mineral assemblages in the Palmer Canyon block include (a) quartz-biotite-plagioclase-garnet-staurolite-kyanite in the pelitic schists; (b) quartz-biotite-plagioclase-low-Ca amphiboles-kyanite in Mg-Al-rich schists, and locally (c) hornblende-plagioclase-garnet in amphibolites. All rock types show abundant textural evidence of decompression and retrograde re-equilibration. Notable among the texturally late minerals are cordierite and sapphirine, which occur in coronas around kyanite in Mg-Al-rich schists. Thermobarometry from texturally early and late assemblages for samples from different areas within the Palmer Canyon block define decompression from > 7 kbar to < 3 kbar. The high-pressure regional metamorphism is interpreted to be a response to thrusting associated with the Medicine Bow orogeny at c. 1.78-1.76 Ga. At this time, the north-central Laramie Range was tectonically thickened by as much as 12 km. This crustal thickening extended for more than 60 km north of the Cheyenne belt in southern Wyoming. Late in the orogenic cycle, rocks of the Palmer Canyon block were uplifted and unroofed as the result of transpression along the Laramie Peak shear zone to produce the widespread decompression textures. The Proterozoic tectonic history of the central Laramie Range is similar to exhumation that accompanied late-orogenic oblique convergence in many Phanerozoic orogenic belts.

Preliminary mineralogical data on epithermal ore veins associated with Rosia Poieni porphyry copper deposit, Apuseni Mountains, Romania

NASA Astrophysics Data System (ADS)

Iatan, E. L.; Popescu, Gh. C.

2012-04-01

Rosia Poieni is the largest porphyry copper (±Au±Mo) deposits associated with Neogene magmatic rocks from the South Apuseni Mountains, being located approximately 8 km northeast of the town of Abrud. During a recent examination of some epithermal mineralized veins, crosscutting the porphyry mineralization from the Roşia Poieni deposit, two species of tellurides and one tellurosulfide minerals were identified. The studied samples were collected from the + 1045 m level, SW side of the open pit and are represented by epithermal veins, crosscutting the porphyry copper mineralized body. The thickness of the veins is almost 4 cm. Following reflected-polarized light microscopy to identify the ore-mineral assemblages, the polished sections were studied with a Scanning Electron Microscope (SEM) equipped with a back-scattered electron (BSE) detector to study fine-sized minerals. Quantitative compositional data were determined using a Cameca SX 50 electron microprobe (EMP). Based on optical microscopy, SEM and EMPA three mineral associations have been separated inside the epithermal vein, from the margins to the centre: 1. quartz+tennantite-tetrahedrite+goldfieldite+pyrite+sphalerite; 2. quartz+pyrite+tellurobismutite; 3. chalcopyrite+hessite+vivianite. Goldfieldite occurs in anhedral grains and it is associated with tennantite-tetrahedrite and quartz. The electron microprobe analysis gave a variable content in Te between 13.28-13.39 wt.%, 43.34 wt.% Cu, 0.1 wt. % Fe, 0.2 wt.% Zn, 14.68 wt.% As, 4.35 wt.% Sb and 24.84 wt.% S. The calculated formula for the goldfieldite is Cu11.8Te1.8(Sb,As)4S13.4. The EPM analyses on tetrahedrite-tennantite revealed a low content in Te (0.02-0.03 wt.%) and 42.23 wt.% Cu, 2.67 wt.% Fe, 7.34 wt.% Zn, 0.04 wt.% Sb, 19.28 wt.% As and 28.4 wt.% S. The calculated formula is Cu9.8(Fe,Zn)2.4(Sb,As,Te)3.8S13. The variable ratio of the Te content may reflect a variable content of Te in the hydrothermal fluids from which the tellurian tetrahedrite precipitated. Hessite lies close to the grain boundary between the calchopyrite grains, which is associated with vivianite. Electron microprobe analysis gave 57.73 wt.% Ag and 42.27 wt.% Te with calculated stoichiometric formula Ag1.9Te1.1 . Tellurobismuthite it forms irregular grains and it is associated with quartz and pyrite. Electron microprobe analysis gave 57.20 wt.% Bi and 42.80 wt.% Te with calculated stoichiometric formula Bi2.2Te2.8. Based on the mineral assemblages separated inside the ore vein and on the ratio of the Te content for the different identified tellurium bearing minerals, we can conclude that the Te content of the fluids from which they precipitated, increased from the margins to the centre of the vein. In summary, this study of specimens from Rosia Poieni porphyry copper deposit, has resulted in the recognition of some tellurium-bearing minerals, not reported by previous workers. These minerals are represented by tellurobismutite, hessite and goldfieldite and they are associated with epithermal vein mineralization (pyrite, chalcopyrite, sphalerite, tennantite-tetrahedrite, quartz, vivianite). The presence of tellurium indicates the transition between porphyry-style mineralization to epithermal vein mineralization. Acknowledgements: This work was supported by the strategic grant POSDRU/89/1.5/S58852, Project "Postdoctoral program for training scientific researches" co-financed by the European Social Found within the Sectorial Operational Program Human Resources Development 2007-2013".

Bleaching response of coral species in the context of assemblage response

NASA Astrophysics Data System (ADS)

Swain, Timothy D.; DuBois, Emily; Goldberg, Scott J.; Backman, Vadim; Marcelino, Luisa A.

2017-06-01

Caribbean coral reefs are declining due to a mosaic of local and global stresses, including climate change-induced thermal stress. Species and assemblage responses differ due to factors that are not easily identifiable or quantifiable. We calculated a novel species-specific metric of coral bleaching response, taxon- α and - β, which relates the response of a species to that of its assemblages for 16 species over 18 assemblages. By contextualizing species responses within the response of their assemblages, the effects of environmental factors are removed and intrinsic differences among taxa are revealed. Most corals experience either a saturation response, overly sensitive to weak stress ( α > 0) but under-responsive compared to assemblage bleaching ( β < 1), or a threshold response, insensitive to weak stress ( α < 0) but over-responsive compared to assemblage bleaching ( β > 1). This metric may help reveal key factors of bleaching susceptibility and identify species as targets for conservation.

Bleaching response of coral species in the context of assemblage response.

PubMed

Swain, Timothy D; DuBois, Emily; Goldberg, Scott J; Backman, Vadim; Marcelino, Luisa A

2017-06-01

Caribbean coral reefs are declining due to a mosaic of local and global stresses, including climate change-induced thermal stress. Species and assemblage responses differ due to factors that are not easily identifiable or quantifiable. We calculated a novel species-specific metric of coral bleaching response, taxon-α and -β, which relates the response of a species to that of its assemblages for 16 species over 18 assemblages. By contextualizing species responses within the response of their assemblages, the effects of environmental factors are removed and intrinsic differences among taxa are revealed. Most corals experience either a saturation response, overly-sensitive to weak stress (α > 0) but under-responsive compared to assemblage bleaching (β < 1), or a threshold response, insensitive to weak stress (α < 0) but over-responsive compared to assemblage bleaching (β > 1). This metric may help reveal key factors of bleaching susceptibility and identify species as targets for conservation.

Hydrous metasomatism of oceanic sub-arc mantle, Lihir, Papua New Guinea. Part 2. Trace element characteristics of slab-derived fluids

NASA Astrophysics Data System (ADS)

Grégoire, Michel; McInnes, Brent I. A.; O'Reilly, Suzanne Y.

2001-11-01

Spinel peridotite xenoliths recovered from the Tubaf and Edison volcanoes, south of Lihir Island in the Tabar-Lihir-Tanga-Feni island arc in Papua New Guinea, are predominantly fresh, refractory harzburgites. Many of the harzburgite xenoliths have cross-cutting vein networks and show evidence of modal metasomatism. These metasomatic veins contain a secondary mineral assemblage consisting of fibrous, radiating orthopyroxene and fine-grained Fe-Ni sulfide with minor olivine, clinopyroxene, phlogopite, amphibole and magnetite. Adjacent to the veins, primary clinopyroxene is cloudy while orthopyroxene exhibits replacement by secondary fibrous orthopyroxene, similar in habit to orthopyroxene occurring in the veins. The mineralogical and geochemical characteristics of the Tubaf mantle xenoliths are the product of two major processes: an early partial melting depletion event that was overprinted by oxidation and alkali enrichment related to percolation of slab-derived, hydrous melts. HREE and MREE concentrations in clinopyroxene from the least metasomatised harzburgites indicate that they are the residues from a 15% to 25% partial melting event, consistent with formation in a MOR setting. The secondary vein assemblages show strong enrichment in the LILE (primarily Sr, Ba, Rb, Th, U and Pb) and the REE (primarily La, Ce, Nd, Sm, Eu and Gd), while the HFSE (Nb, Ta, Zr, Hf, and Ti) are neither enriched nor depleted. The mineral precipitates in the vein assemblages have high LREE/HFSE and LILE/HFSE, and reflect the relative solubility of these elements in hydrous melts. These trace element characteristics are similar to those of the Tabar-Lihir-Tanga-Feni arc lavas, and display the commonly observed HFSE depletion of arc magmatism. These findings support the hypothesis that this so-called "arc signature" is primarily dependent on the relative solubility of elements in slab-derived, hydrous melts, and the enrichment of these soluble elements in metasomatised mantle regions that are prone to preferential partial melting.

Petrology of gabbroic xenoliths in 1960 Kilauea basalt: crystalline remnants of prior (1955) magmatism

USGS Publications Warehouse

Fodor, R.V.; Moore, R.B.

1994-01-01

The 1960 Kapoho lavas of Kilauea's east rift zone contain 1-10 cm xenoliths of olivine gabbro, olivine gabbro-norite, and gabbro norite. Textures are poikilitic (ol+sp+cpx in pl) and intergranular (cpx+pl??ol??opx). Poikilitic xenoliths, which we interpret as cumulates, have the most primitive mineral compositions, Fo82.5, cpx Mg# 86.5, and An80.5. Many granular xenoliths (ol and noritic gabbro) contain abundant vesicular glass that gives them intersertal, hyaloophitic, and overall 'open' textures to suggest that they represent 'mush' and 'crust' of a magma crystallization environment. Their phase compositions are more evolved (Fo80-70, cpx Mg# 82-75, and An73-63) than those of the poikilitic xenoliths. Associated glass is basaltic, but evolved (MgO 5 wt%; TiO2 3.7-5.8 wt%). The gabbroic xenolith mineral compositions fit existing fractional crystallization models that relate the origins of various Kilauea lavas to one another. FeO/MgO crystal-liquid partitioning is consistent with the poikilitic ol-gabbro assemblage forming as a crystallization product from Kilauea summit magma with ???8 wt% MgO that was parental to evolved lavas on the east rift zone. For example, least squares calculations link summit magmas to early 1955 rift-zone lavas (???5 wt% MgO) through ???28-34% crystallization of the ol+sp+cpx+pl that comprise the poikilitic ol-gabbros. The other ol-gabbro assemblages and the olivine gabbro-norite assemblages crystallized from evolved liquids, such as represented by the early 1955 and late 1955 lavas (???6.5 wt% MgO) of the east rift zone. The eruption of 1960 Kapoho magmas, then, scoured the rift-zone reservoir system to entrain portions of cumulate and solidification zones that had coated reservoir margins during crystallization of prior east rift-zone magmas. ?? 1994 Springer-Verlag.

Multilocus genotyping of Giardia duodenalis in Brazilian children.

PubMed

Scalia, Luana A M; Fava, Natália M N; Soares, Rodrigo M; Limongi, Jean E; da Cunha, Maria Júlia R; Pena, Isabella F; Kalapothakis, Evanguedes; Cury, Márcia C

2016-06-01

Giardia duodenalis is a parasite of several mammalian species, including humans, distributed worldwide. This research aimed to identify the molecular assemblages/sub-assemblages of G. duodenalis and to determine the intra-assemblage genetic variation of the different genes of assemblages A and B in pre-school children in the cities of Araguari and Uberlândia, Minas Gerais, Brazil. The molecular characterization followed β-giardin (bg), glutamate dehydrogenase (gdh) and triose phosphate isomerase (tpi) protocols. Of 226 stool samples, G. duodenalis cysts were found in 45 (19.9%). The tpi gene was amplified in 34 samples: 16 assemblage A, 14 B and four mixed samples A/B. The gdh gene was amplified in 32 samples, including 14 A, 16 B and two A/B. For the bg gene, 19 samples were sequenced: nine assemblage A, five B, three E, and two mixed, A/E and B/E. Animal-specific assemblage E were identified by bg, but were not confirmed for other genes. Twelve samples were characterized by full agreement of the three genes. Two new multilocus genotyping (MLGs) for assemblage A and two new MLGs for assemblage B were also described. These findings substantiate the importance of using more than one gene protocol since the sensitivity and genetic variability changes with the locus used.Access numbers: The GenBank access numbers for the nucleotide sequences reported in this article are: JQ794877-JQ794890, JX033113-JX033118. © The Author 2016. Published by Oxford University Press on behalf of Royal Society of Tropical Medicine and Hygiene. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Gossan Hill, Victoria Island, Northwest Territories: An analogue for mine waste reactions within permafrost and implication for the subsurface mineralogy of Mars

NASA Astrophysics Data System (ADS)

Peterson, Ronald C.; Williamson, Marie-Claude; Rainbird, Robert H.

2014-08-01

Gossan Hill is located within the Minto Inlier in central Victoria Island, Northwest Territories (N 71.36697°, W 114.95155°). A study of the mineralogical associations and geological setting of this deposit indicates that it is an arrested hydrothermal system frozen in permafrost. From above, the hill stands out because of the topographic relief of 75 m and the orange-brown color of the surficial material. The surface of the hill is marked by areas of concentric color zonation up to 3 m across, with light gray centers surrounded by a yellow-orange ring that is surrounded by an orange-brown color that covers the rest of the surface of the hill. Trenches dug into these areas reveal that the central zone contains quartz and pyrite +/- native sulfur in a loose aggregate of sand-sized grains. This central area is surrounded by a zone dominated by gypsum and quartz with some jarosite. Beyond this, the surrounding surface consists of quartz, hematite, and amorphous iron oxides. The radial arrangement of the mineral assemblage indicates an increase in oxidation of sulfur from the center outward. Analysis of isotopic composition of the sulfur indicates the source of sulfur could be the underlying strata. The hill is underlain by inter-bedded carbonate and sulfate-evaporite sedimentary rocks of the Kilian formation in the upper part of the Neoproterozoic Shaler Super group. The sedimentary rocks were intruded by diabase sills of the 720 Ma Franklin igneous event, which crop out 2 km to the south of Gossan Hill. The soft friable nature of the deposit and the topographic relief of the hill indicate a post-glacial (Pleistocene) age of formation. Permafrost has maintained the disequilibrium mineral assemblage since the cessation of fluid flow. Extraction of the permafrost ice from the central zone yields a liquid with a pH of 2.3. The observed long-term persistence of pyrite encased within the acidic permafrost indicates that oxidation and dissolution reactions common in mine waste are slowed, if not stopped, in such an environment. The predicted rise of Arctic temperatures will cause the active layer to move deeper and result in the release of the acidic solutions frozen in the permafrost. Water ice or frozen CO2 just below the Martian surface would also preserve such mineral disequilibrium for very long periods of time. No region exists on Earth where ice has existed continuously for millions of years, but the Gossan Hill deposit is an excellent terrestrial analogue. On Mars, the subsurface ice may be very old. Ancient reactive Martian mineral assemblages and the fluids associated with them will reflect conditions that existed in the past.

The evolution of volcano-hosted geothermal systems based on deep wells from Karaha-Telaga Bodas, Indonesia

USGS Publications Warehouse

Moore, J.N.; Allis, R.G.; Nemcok, M.; Powell, T.S.; Bruton, C.J.; Wannamaker, P.E.; Raharjo, I.B.; Norman, D.I.

2008-01-01

Temperature and pressure surveys, fluid samples, and petrologic analyses of rock samples from deep drill holes at the Karaha - Telaga Bodas geothermal field on the volcanic ridge extending northward from Galunggung Volcano, West Java, have provided a unique opportunity to characterize the evolution of an active volcano-hosted geothermal system. Wells up to 3 km in depth have encountered temperatures as high as 353??C and a weakly altered granodiorite that intruded to within 2 to 3 km of the surface. The intrusion is shallowest beneath the southern end of the field where an acid lake overlies a nearly vertical low resistivity structure (<10 ohm-m) defined by magnetotelluric measurements. This structure is interpreted to represent a vapor-dominated chimney that provides a pathway to the surface for magmatic gases. Four distinct hydrothermal mineral assemblages document the evolution of the geothermal system and the transition from liquid- to vapor-dominated conditions. The earliest assemblage represents the initial liquid-dominated system generated during emplacement of the granodiorite between 5910 ?? 76 and 4200 ?? 150 y BP. Tourmaline, biotite, actinolite, epidote and clay minerals were deposited contemporaneously at progressively greater distances from the intrusive contact (assemblage 1). At 4200 ?? 150 y BP, flank collapse and the formation of the volcano's crater, Kawah Galunggung, resulted in catastrophic decompression and boiling of the hydrothermal fluids. This event initiated development of the modern vapor-dominated regime. Chalcedony and then quartz were deposited as the early low salinity liquids boiled (assemblage 2). Both vapor- and liquid-rich fluid inclusions were trapped in the quartz crystals. Liquid-rich fluid inclusions from the southern part of the field record salinities ranging from 0 to 26 weight percent NaCl- CaCl2 equivalent and locally contain fluorite daughter crystals. We suggest, based on temperature-salinity relationships and evidence of boiling, that these fluids were progressively concentrated as steam was lost from the system. However, mixing with fluids derived from the underlying intrusion or generated during the formation of acid SO4 water on the vapor-dominated chimney margins could have contributed to the observed salinities. As pressures declined, CO2- and SO4-rich steam-heated water drained downward, depositing anhydrite and calcite (assemblage 3) in the fractures, limiting further recharge. Fluid inclusions with salinities up to 31 weight percent NaCl equivalent were trapped in these minerals as the descending water vaporized. The final assemblage is represented by precipitates of NaCl, KCl and FeClx deposited on rock surfaces in portions of the vapor-dominated zone that boiled dry. Vapor-dominated conditions extend over a distance of at least 10 km and to depths below sea level. Deep wells drilled into the underlying liquid-dominated reservoir in the northern and central part of the volcanic ridge produce low salinity fluids representing recent recharge of meteoric and steam-heated water. The evolution of volcanic-hosted vapor-dominated geothermal systems can be described by a five stage model. Stage 1 involves the formation of an over-pressured liquid-dominated geothermal system soon after magmatic intrusion. In Stages 2 and 3, pressures progressively decrease, and a curtain of steam-heated water surrounding a magmatic vapor-dominated chimney at 350??C and 14 ?? 2 MPa develops. The relatively low pressure near the base of the chimney causes liquid inflow adjacent to the intrusion and the development of a secondary marginal vapor-dominated zone. In Stage 4, the magmatic vapor discharge from the intrusion becomes small, vapor pressure declines, and the secondary vapor-dominated zone expands above the intrusion. In Stage 5, the vapor-dominated zone floods because heat from the intrusion is insufficient to boil all liquid inflow. A more common, liquid-dominated volcanic-hosted system the

Mineralogy of Sediments on a Cold and Icy Early Mars

NASA Astrophysics Data System (ADS)

Rampe, E. B.; Horgan, B. H. N.; Smith, R.; Scudder, N.; Rutledge, A. M.; Bamber, E.; Morris, R. V.

2017-12-01

The water-related minerals discovered in ancient martian terrains suggest liquid water was abundant on the surface and/or near subsurface during Mars' early history. The debate remains, however, whether these minerals are indicative of a warm and wet or cold and icy climate. To characterize mineral assemblages of cold and icy mafic terrains, we analyzed pro- and supraglacial rocks and sediments from the Collier and Diller glacial valleys in Three Sisters, Oregon. We identified primary and secondary phases using X-ray diffraction (XRD), scanning and transmission electron microscopies with energy dispersive spectroscopy (SEM, TEM, EDS), and visible/short-wave-infrared (VSWIR) and thermal-infrared (TIR) spectroscopies. Samples from both glacial valleys are dominated by primary igneous minerals (i.e., plagioclase and pyroxene). Sediments in the Collier glacial valley contain minor to trace amounts of phyllosilicates and zeolites, but these phases are likely detrital and sourced from hydrothermally altered units on North Sister. We find that the authigenic phases in cold and icy mafic terrains are poorly crystalline and/or amorphous. TEM-EDS analyses of the <2 um size fraction of glacial flour shows the presence of many different nanophase materials, including iron oxides, devitrified volcanic glass, and Fe-Si-Al (e.g., proto-clay) phases. A variety of primary and secondary amorphous materials (e.g., volcanic glass, leached glass, allophane) have been suggested from orbital IR data from Mars, and the CheMin XRD on the Curiosity rover has identified X-ray amorphous materials in all rocks and soils measured to date. The compositions of the Gale Crater amorphous components cannot be explained by primary volcanic glass alone and likely include secondary silicates, iron oxides, and sulfates. We suggest that the prevalence of amorphous materials on the martian surface and the variety of amorphous components may be a signature of a cold and icy climate on Early Mars.

Glaucophane chloritoid-bearing assemblages from NE Oman: petrologic significance and a petrogenetic grid for high P metapelites

NASA Astrophysics Data System (ADS)

El-Shazly, A. K.; Liou, J. G.

1991-04-01

Pelitic layers and lenses interbedded with blueschists and eclogites in Saih Hatat, NE Oman contain chloritoid- and sodic amphibole-bearing mineral assemblages that are useful for reconstructing the P-T history of the area. Textural and mineral chemical relations suggest that coexisting glaucophane (Gln) and chloritoid (Ctd) formed at the expense of chlorite (Chl)+paragonite (Pg) and later broke down to garnet (Gt)+Pg during prograde metamorphism according to the reaction: Gln+Ctd+Qz=Gt+Pg+H2O. During retrogression, Gln and Chl first formed at the expense of Gt and Pg, followed by the breakdown of Ctd and Gt to Chl. The final stages of retrogression are marked by the breakdown of Gln to an aggregate of Chl+albite (Ab). A projection from quartz (Qz), H2O and phengite (Ph) on the (Al2O3+Fe2O3)-(FeO+MgO)-Na2O plane in the system NFMASH is best suited for the representation of the phase relations in high P metapelites. Petrogenetic grids for the model systems NMASH and NFASH were calculated using program GEO-CALC (Berman et al. 1987) and its database (Berman 1988) after the retrieval of S{i/o}and ΔH{f/o}for Gln and Ctd by mathematical programming and calculating all possible reactions among Gln, Ctd, Chl, jadeite (Jd), Ab, Gt, Pg, talc (Tc), pyrophyllite (Prl) and kyanite (Ky). The calculated petrogenetic grid for the system NFASH shows that Fe-Ctd and ferroglaucophane coexist at P>6.5 kbar and T<525°C, whereas the assemblage: Ct-Gln-Pg is stable between 435 and 630°C and P>6 kbar. This grid is consistent with the P-T estimates for high P metapelites from Oman, New Caledonia, Seward Peninsula, Ile de Groix, Sifnos and Peloponnese, where Gln+Ctd bearing units are interbedded with cofacial mafic blueschists and eclogites. The grid also explains the observed textural relations in the metapelites of Oman, and is consistent with the “clockwise” P-T path proposed for this area, but differs from the grids of Guiraud et al. (1990) in showing a larger stability field for Gln+Ctd that overlaps with the stability fields of Jd+Qz as well as Ab. The petrogenetic grid calculated for the system NMASH shows that Mg-Ctd+Gln-bearing assemblages require unusually low geothermal gradients to form in metapelites. It also shows that Mg-rich Ctd+Tc coexist at high pressures over a wider P-T range than predicted by Guiraud et al. (1990). This grid can therefore be applied to high P metamorphic assemblages from the eastern and western Alps.

Preliminary study on the L ate Cretaceous ostracods from continental scientific drilling SK1 in the Songliao Basin, NE China

NASA Astrophysics Data System (ADS)

Xi, Dangpeng; Qu, Haiying; Shi, Zhongye; Wan, Xiaoqiao

2017-04-01

Songliao Basin is one of the biggest lacustrine systems in Asia during Cretaceous age. Widespread deposits in the basin are mainly composed of clastic sediments which contain abundant fossils including gastropod, bivalves, ostracods, vertebrates and others. These well preserved ostracod fossils provide us valuable information about past climate changes and biotic responses in a greenhouse environment.The Cretaceous Continental Scientific Drilling in the Songliao Basin (SK1) offers a rare opportunity to study Late Cretaceous non-marine ostracod. The SK1 was drilled separately in two boreholes: the lower 959.55-meter-thick south core (SK1(s)), and the upper 1636.72-meter-thick north core (SK1 (n)), containing the Upper Quantou, Qingshankou, Yaojia, Nenjiang Formation, Sifangtai, Mingshui and lower Taikang formations. Here we establish high-resolution non-marine ostracod biostratigraphy based on SK1. 80 species belonging to 12 genera in the SK1(S) and 45 species assigned to 20 genera in the SK1(n) have been recovered. Nineteen ostracod assemblage zones have been recognized: 1. Mongolocypris longicaudata-Cypridea Assemblage Zone, 2.Triangulicypris torsuosus-Triangulicypris torsuosus. nota Assemblage Zone, 3. Cypridea dekhoinensis-Cypridea gibbosa Assemblage Zone, 4.Cypridea nota-Sunliavia tumida Assemblage Zone, 5.Cypridea edentula-Lycopterocypris grandis Assemblage Zone, 6.Cypridea fuyuensis-Triangulicypris symmetrica Assemblage Zone, 7.Triangulicypris vestilus-Triangulicypris fusiformis-Triangulicypris pumilis Assemblage Zone, 8.Cypridea panda-Mongolocypris obscura Assemblage Zone, 9. Cypridea exornata-Cypridea dongfangensis Assemblage Zone, 10.Cypridea favosa-Mongolocypris tabulata Assemblage Zone, 11.Cypridea formosa-Cypridea sunghuajiangensis Assemblage Zone, 12. Cypridea anonyma-Candona fabiforma Assemblage Zone, 13.Cypridea gracila-Cypridea gunsulinensis Assemblage Zone, 14.Mongolocypris magna-Mongolocypris heiluntszianensis Assemblage Zone, 15.Cypridea liaukhenensis-Cypridea stellata Assemblage Zone, 16. Ilyocyprimorpha-Limnocypridea sunliaonensis-Periacanthella Assemblage Zone, 17. Strumosia inandita Asemblage-Zone, 18.Talicypridea amoena-Metacypris kaitunensis-Ziziphocypris simakovi Assemblage Zone, 19.Ilyocypris Assemblage Zone. Assemblage Zone 1 to 18 are belong to late Cretaceous, but 19 might constrained to the Latest Maastrichtian to the Earliset Danian.

Mineralogical diversity (spectral reflectance and Moessbauer data) in compositionally similar impact melt rocks from Manicouagan Crater, Canada

NASA Technical Reports Server (NTRS)

Morris, R. V.; Bell, J. F., III; Golden, D. C.; Lauer, H. V., Jr.

1993-01-01

Meteoritic impacts under oxidizing surface conditions occur on both earth and Mars. Oxidative alteration of impact melt sheets is reported at several terrestrial impact structures including Manicouagan, West Clearwater Lake, and the Ries Basin. A number of studies have advocated that a significant fraction of Martian soil may consist of erosional products of oxidatively altered impact melt sheets. If so, the signature of the Fe-bearing mineralogies formed by the process may be present in visible and near infrared reflectivity data for the Martian surface. Of concern is what mineral assemblages form in impact melt sheets produced under oxidizing conditions and what their spectral signatures are. Spectral and Moessbauer data for 19 powder samples of impact melt rock from Manicouagan Crater are reported. Results show for naturally occurring materials that composite hematite-pyroxene bands have minima in the 910-nm region. Thus many of the anomalous Phobos-2 spectra, characterized by a shallow band minimum in the near-IR whose position varies between approximately 850 and 1000 nm, can be explained by assemblages whose endmembers (hematite and pyroxene) are accepted to be present on Mars. Furthermore, results show that a mineralogically diverse suite of rocks can be generated at essentially constant composition, which implies that variations in Martian surface mineralogy do not necessarily imply variations in chemical composition.

Remote detection of fluid-related diagenetic mineralogical variations in the Wingate Sandstone at different spatial and spectral resolutions

NASA Astrophysics Data System (ADS)

Okyay, Unal; Khan, Shuhab D.

2016-02-01

Well-exposed eolian units of the Jurassic system on the Colorado Plateau including the Wingate Sandstone, show prominent color variations throughout southeastern Utah due to diagenetic changes that include precipitation and/or removal of iron oxide, clay, and carbonate cement. Spatially variable characteristic diagenetic changes suggest fluid-rock interactions through the sandstone. Distinctive spectral signatures of diagenetic minerals can be used to map diagenetic mineral variability and possibly fluid-flow pathways. The main objective of this work was to identify characteristic diagenetic minerals, and map their spatial variability from regional to outcrop scale in Wingate Sandstone exposures of Lisbon Valley, Utah. Laboratory reflectance spectroscopy analysis of the samples facilitated identification of diagnostic spectral characteristics of the common diagenetic minerals and their relative abundances between altered and unaltered Wingate Sandstone. Comparison of reflectance spectroscopy with satellite, airborne, and ground-based imaging spectroscopy data provided a method for mapping and evaluating spatial variations of diagenetic minerals. The Feature-oriented Principal Component Selection method was used on Advanced Spaceborne Thermal Emission and Reflection Radiometer data so as to map common mineral groups throughout the broader Wingate Sandstone exposure in the area. The Minimum Noise Fraction and Spectral Angle Mapper methods were applied on airborne HyMap and ground-based hyperspectral imaging data to identify and map mineralogical changes. The satellite and airborne data showed that out of 25.55 km2 total exposure of Wingate Sandstone in Lisbon Valley, unaltered sandstone cover 12.55 km2, and altered sandstone cover 8.90 km2 in the northwest flank and 5.09 km2 in the southern flank of the anticline. The ground-based hyperspectral data demonstrated the ability to identify and map mineral assemblages with two-dimensional lateral continuity on near-vertical rock faces. The results showed that 39.71% of the scanned outcrop is bleached and 20.60% is unbleached while 6.33% remain unclassified, and 33.36% is masked-out as vegetation. The bleached and unbleached areas are alternating throughout the vertical face of the outcrop. The relative hematite abundance observed in the unbleached areas are somewhat symmetrical. This indicates fairly similar reaction intensities along the upper and lower reaction fronts observed in the vertical section. The distribution geometry and relative abundances of diagenetic minerals not only suggest multiple paths of fluid-flow in Wingate Sandstone but also provides some insight about relative direction of past fluid-flow.

Differences in composition of shallow-water marine benthic communities associated with two ophiolitic rock substrata

NASA Astrophysics Data System (ADS)

Bavestrello, Giorgio; Bo, Marzia; Betti, Federico; Canessa, Martina; Gaggero, Laura; Rindi, Fabio; Cattaneo-Vietti, Riccardo

2018-01-01

On marine rocky shores, several physical, chemical and biological processes operate to maintain the benthic assemblages' heterogeneity, but among the abiotic factors, the composition and texture of the rocky substrata have been only sporadically considered. However, biomineralogical studies have demonstrated an unsuspected ability of the benthic organisms to interact at different levels with rocky substrata. Therefore, the mineralogy of the substratum can affect the structure of benthic communities. To evaluate this hypothesis, the macrobenthic assemblages developed on two different ophiolitic rocks (serpentinites and metagabbros) in contact at a restricted stretch of the western Ligurian Riviera (western Mediterranean Sea), with identical environmental and climatic conditions, were analysed. Samplings were carried out at four bathymetric levels (+1m, 0m, -1m, and -3m respect to the mean sea level) and the analysis of the data evidenced differences in terms of species distribution and percent coverage. Algal communities growing on metagabbros were poorer in species richness and showed a much simpler structure when compared to the assemblages occurring on the serpentinites. The most widely distributed animal organism, the barnacle Chthamalus stellatus, was dominant on serpentinites, and virtually absent on metagabbros. Our results suggest a complex pattern of interactions between lithology and benthic organisms operating through processes of inhibition/facilitation related to the mineral properties of the substratum.

Clastic dikes of the Hatrurim basin (western flank of the Dead Sea) as natural analogues of alkaline concretes: Mineralogy, solution chemistry, and durability

NASA Astrophysics Data System (ADS)

Sokol, E. V.; Gaskova, O. L.; Kozmenko, O. A.; Kokh, S. N.; Vapnik, E. A.; Novikova, S. A.; Nigmatulina, E. N.

2014-11-01

This study shows that the mineral assemblages from clastic dikes in areas adjacent to the Dead Sea graben may be considered as natural analogues of alkaline concretes. The main infilling material of the clastic dikes is composed of well-sorted and well-rounded quartz sand. The cement of these hard rocks contains hydroxylapophyllite, tacharanite, calcium silicate hydrates, opal, calcite, and zeolite-like phases, which is indicative of a similarity of the natural cementation processes and industrial alkaline concrete production from quartz sands and industrial alkaline cements. The quartz grains exhibit a variety of reaction textures reflecting the interaction with alkaline solutions (opal and calcium hydrosilicate overgrowths; full replacement with apophyllite or thomsonite + apophyllite). The physicochemical analysis and reconstruction of the chemical composition of peralkaline Ca, Na, and K solutions that formed these assemblages reveal that the solutions evolved toward a more stable composition of zeolite-like phases, which are more resistant to long-term chemical weathering and atmospheric corrosion. The 40Ar/39Ar age of 6.2 ± 0.7 Ma obtained for apophyllite provides conclusive evidence for the high corrosion resistance of the assemblages consisting of apophyllite and zeolite-like phases.

Study on Gold and base metal occurrence in Uluwai Prospect, Western Latimojong Mountain, South Sulawesi

NASA Astrophysics Data System (ADS)

Maulana, Adi; Jaya, Asri; Imai, Akira

2018-02-01

Uluwai Prospect is located in the northern part of South Arm of Sulawesi along the eastern part of the Kalosi Fold Belt and Latimojong Mountain. The area is generally characterized by moderate to rugged topography area with elevation in the range of 700 to 1400 m above sea level in the mountainous complex called Latimojong Mountain Complex. The mineralization is characterized by a relatively simple sulphide ore mineral assemblage consists of pyrite, sphalerite and chalcopyrite. Samples were collected in areas showing abundant sulphide minerals where younger faults cut the bedding and foliation of country rocks. A number of silicified zones have been observed, as well as float material containing disseminated pyrite, chalcopyrite, and sphalerite with hematite, goethite and limonite. Some alteration types have been observed including sericitization, albitization, carbonatization and silisification. The samples collected indicated that the mineralisation is contained within metasedimentary (sandstone to mudstone) and greenschist. Geochemical analyses from 16 samples including 5 stream sediment samples indicated that the most promising mineralization occur in the prospect area are copper (Cu) and zinc (Zn). This is also supported by the abundance of chalcopyrite and sphalerite in some highly altered samples. Assaying of the collected samples revealed most of samples contain relatively low gold (Au) concentration. However, two samples contain 0.007 and 0.01 ppm of Au. In the mineralized area, Zn concentrations are up to 134 ppm, Cu up to 120 ppm and Pb up to 18 ppm and As up to 70 ppm. There is no clear relationship that exists between Au and the base metals except that one of the samples with highest Au values tend to have high Zn and As. This unclear pattern also shown by Cu, Pb and Zn. Base metal concentration in stream sediment samples show a relatively stable pattern than in rock samples. Arsenic tends to be elevated in base metal rich samples. Sb and Mo are relatively low in all sample type. However, Mo values will be high in the samples which contain highest Cu and Zn.

Le volcanisme cambrien du Maroc central : implications géodynamiquesThe Central Morocco Cambrian volcanism: geodynamic implications

NASA Astrophysics Data System (ADS)

Ouali, Houssa; Briand, Bernard; Bouchardon, Jean-Luc; Capiez, Paul

2003-05-01

In southeastern Central Morocco, the Bou-Acila volcanic complex is considered of Cambrian age. In spite of low-grade metamorphic effect, initial volcanic texture and mineralogy can be recognized and volcanic rocks are dominated by dolerites and porphyric dolerites. The initial mineralogy is composed of plagioclases, pyroxenes and dark minerals. A secondary mineral assemblage is composed of albite, epidote, chlorite and calcite. According to their immobile elements compositions, the southeastern central Morocco metavolcanites are of within-plate continental tholeiites. This volcanism and those recognized in many other areas in Morocco confirm a Cambrian extensive episode within the Gondwana supercontinent. To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003).To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003).

The formation of phosphoran olivine and stanfieldite from the pyrometamorphic breakdown of apatite in slags from a prehistoric ritual immolation site (Goldbichl, Igls, Tyrol, Austria)

NASA Astrophysics Data System (ADS)

Schneider, Philipp; Tropper, Peter; Kaindl, Reinhard

2013-04-01

In this study we report P-rich olivine and the tric-calcium phosphate (TCP) stanfieldite in partially molten quartzphyllites from the ritual immolation site at the Goldbichl, near Innsbruck in the Tyrol, Austria. During partial melting, foamy patches of dark glassy material formed at the surface of the rocks and also as layers within the rocks. The pyrometamorphic rocks contain mostly the mineral assemblage olivine + orthopyroxene + plagioclase + spinel + glass. During the investigation of slag samples from this prehistoric ritual immolation site, extremely P-rich, apatite-bearing micro-domains were found. In these domains phosphoran olivine was found whose P contents are approaching the maximum P contents in olivine according to the experimental investigations of Boesenberg and Hewins (Geochim Cosmochim Acta 74:1923-1941, 2010). The textures within these domains indicate strongly disequilibrium conditions. The phosphoran olivines formed due to reactions involving apatite and the mineral assemblage of the quartzphyllites, and coexist with plagioclase and a tri-calcium phosphate phase (TCP) showing stanfieldite Ca4(Mg, Fe2+, Mn2+)5(PO4)6 composition. In terms of its chemical composition, olivine shows a wide range in composition with P ranging from 0.3 to 0.54 a.p.f.u, which corresponds to maximal 23 wt.% P2O5. These are the highest P-contents in olivine reported from rocks so far. The incorporation of P correlates with decreasing Si contents according to the charge balancing scheme 2{{P}^{5+ }}+□{{M}_{1,2 }}=2S{{i}^{4+ }}+{{( {Mg,Fe} )}^{2+ }}{{M}_{1,2 }} . Therefore P can only be incorporated in combination with a vacancy on the M1,2 position. Micro-Raman spectroscopy of phosphoran olivines indicates that these olivines can easily be identified with this method due to the strong signals of the SiO4 and PO4 vibrations. The external vibrations of the M1,2 sites at low wave-numbers are more complex than for P-free olivine. This might be due to the effect of P5+ on the M1 2+ and M2 2+ positions and the formation of vacancies on these sites. Since micro-Raman investigations of the TCP phase yielded no conclusive match with a known Raman spectrum of a phosphate mineral so far, therefore it is most likely that the TCP phase is stanfieldite, whose Raman spectrum has not been obtained yet. Schematical Schreinemakers analysis in the system CaO-Al2O3-FeO-SiO2-P2O5-H2O shows that P-rich olivine (fayalite-sarcopside solid solution) can form from mineral reactions involving chlorite, apatite and quartz and show that the occurrence of P-rich Fe-olivines spans a large T-range but is restricted to domains with high aSiO2. The mineral assemblage in the P-rich micro-domains shows that the formation of phosphoran olivine is not only restricted to the interaction between bone material and rocks in slags from ritual immolation sites as suggested by Tropper et al. (Eur J Mineral 16:631-640, 2004) from the immolation site in Oetz but can form locally due to the pyrometamorphic breakdown of a P-rich accessory precursor phase such as apatite.

Bimodal Silurian and Lower Devonian volcanic rock assemblages in the Machias-Eastport area, Maine

USGS Publications Warehouse

Gates, Olcott; Moench, R.H.

1981-01-01

Exposed in the Machias-Eastport area of southeastern Maine is the thickest (at least 8,000 m), best exposed, best dated, and most nearly complete succession of Silurian and Lower Devonian volcanic strata in the coastal volcanic belt, remnants of which crop out along the coasts of southern New Brunswick, Canada, and southeastern New England in the United States. The volcanics were erupted through the 600-700-million-year-old Avalonian sialic basement. To test the possibility that this volcanic belt was a magmatic arc above a subduction zone prior to presumed Acadian continental collision, samples representing the entire section in the Machias-Eastport area of Maine were chemically analyzed. Three strongly bimodal assemblages of volcanic rocks and associated intrusives are recognized, herein called the Silurian, older Devonian, and younger Devonian assemblages. The Silurian assemblage contains typically nonporphyritic high-alumina tholeiitic basalts, basaltic andesites, and diabase of continental characterand calc-alkalic rhyolites, silicic dacites, and one known dike of andesite. These rocks are associated with fossiliferous, predominantly marine strata of the Quoddy, Dennys, and Edmunds Formations, and the Leighton Formation of the Pembroke Group (the stratigraphic rank of both is revised herein for the Machias-Eastport area), all of Silurian age. The shallow marine Hersey Formation (stratigraphic rank also revised herein) of the Pembroke Group, of latest Silurian age (and possibly earliest Devonian, as suggested by an ostracode fauna), contains no known volcanics; and it evidently was deposited during a volcanic hiatus that immediately preceded emergence of the coastal volcanic belt and the eruption of the older Devonian assemblage. The older Devonian assemblage, in the lagoonal to subaerial Lower Devonian Eastport Formation, contains tholeiitic basalts and basaltic andesites, typically with abundant plagioclase phenocrysts and typically richer in iron and titanium and poorer in magnesium and nickel than the Silurian basalts; and the Eastport Formation has rhyolites and silicic dacites that have higher average SiO2 and K2O contents and higher ratios of FeO* to MgO than the Silurian ones. The younger Devonian assemblage is represented by one sample of basalt from a flow in red beds of the post-Acadian Upper Devonian Perry Formation, and by three samples from pre-Acadian diabases that intrude the Leighton and Hersey Formations. These rocks are even richer in titanium and iron and poorer in magnesium and nickel than the older Devonian basalts. Post-Acadian granitic plutons exposed along the coastal belt for which analyses are available are tentatively included in the younger Devonian assemblage. The most conspicuous features of the coastal volcanics and associated intrusives are the preponderance of rocks of basaltic composition ( < 52 percent SiO2 ) in the Silurian assemblage, and the near absence in all assemblages of intermediate rocks having 57-67 percent SiO2 (calculated without volatiles). All the rocks are variably altered spilites and keratophyres. The basaltic types are adequately defined, however, by eight samples of least altered basalts having calcic plagioclase, clinopyroxene, and 0.5 percent or less CO2 , The more altered basalts are variably enriched or depleted in Na2O, K2O, and CaO relative to the least altered ones. In the silicic rocks no primary ferromagnesian minerals are preserved. The Na2O and K2O contents of the silicic rocks are erratic; they are approximately reciprocal, possibly owing to alkali exchange while the rocks were still glassy. We propose that the coastal volcanic belt extended along an axis of thermal swelling in the Earth's mantle and upward intrusion of partially melted mantle into the sialic Avalonian crust. These processes were accompanied by shoaling and emergence of the belt, and they produced the bimodal volcanism. Tholeiitic basaltic melts segregated from mantle material

Ichthyoplankton assemblage structure of springs in the Yangtze Estuary revealed by biological and environmental visions.

PubMed

Zhang, Hui; Xian, Weiwei; Liu, Shude

2015-01-01

The ichthyoplankton assemblage structure in the Yangtze Estuary was analyzed based on four springs in 1999, 2001, 2004 and 2007 in order to provide detailed characterizations of the ichthyoplankton assemblage in springs, examine the long-term dynamics of spring ichthyoplankton assemblages, and evaluate the influence of environmental factors on the spatial distribution and inter-annual variations of ichthyoplankton assemblages associated with the Yangtze Estuary. Forty-two ichthyoplankton species belonging to 23 families were collected. Engraulidae was the most abundant family, including six species and comprising 67.91% of the total catch. Only four species (Coilia mystus, Engraulis japonicus, Trachidermis fasciatus and Allanetta bleekeri) could be considered dominant, accounting for 88.70% of total abundance. The structure of the ichthyoplankton spring assemblage persisted on an annual basis, with the dominant species reappearing consistently even though their abundance fluctuated from year to year. This inter-annual variation probably reflects variable environmental conditions influenced by jellyfish blooms, declining river flow, and overfishing. Canonical correspondence analysis indicated aspatial structure of the ichthyoplankton assemblage in three areas: (1) an inner assemblage dominated by C. mystus; (2) a central assemblage dominated by A. bleekeri and T. fasciatus; and (3) a shelf assemblage featuring E. japonicus. The observed ichthyoplankton assemblage structure appears to be strongly influenced by depth, salinity and suspended particulate matter gradients.

Ichthyoplankton assemblage structure of springs in the Yangtze Estuary revealed by biological and environmental visions

PubMed Central

Zhang, Hui; Liu, Shude

2015-01-01

The ichthyoplankton assemblage structure in the Yangtze Estuary was analyzed based on four springs in 1999, 2001, 2004 and 2007 in order to provide detailed characterizations of the ichthyoplankton assemblage in springs, examine the long-term dynamics of spring ichthyoplankton assemblages, and evaluate the influence of environmental factors on the spatial distribution and inter-annual variations of ichthyoplankton assemblages associated with the Yangtze Estuary. Forty-two ichthyoplankton species belonging to 23 families were collected. Engraulidae was the most abundant family, including six species and comprising 67.91% of the total catch. Only four species (Coilia mystus, Engraulis japonicus, Trachidermis fasciatus and Allanetta bleekeri) could be considered dominant, accounting for 88.70% of total abundance. The structure of the ichthyoplankton spring assemblage persisted on an annual basis, with the dominant species reappearing consistently even though their abundance fluctuated from year to year. This inter-annual variation probably reflects variable environmental conditions influenced by jellyfish blooms, declining river flow, and overfishing. Canonical correspondence analysis indicated aspatial structure of the ichthyoplankton assemblage in three areas: (1) an inner assemblage dominated by C. mystus; (2) a central assemblage dominated by A. bleekeri and T. fasciatus; and (3) a shelf assemblage featuring E. japonicus. The observed ichthyoplankton assemblage structure appears to be strongly influenced by depth, salinity and suspended particulate matter gradients. PMID:26312180

Visible Wavelength Spectroscopy of Ferric Minerals: A Key Tool for Identification of Ancient Martian Aqueous Environments

NASA Technical Reports Server (NTRS)

Murchie, Scott L.; Bell, J. F., III; Morris, Richard V.

2000-01-01

The mineralogic signatures of past aqueous alteration of a basaltic Martian crust may include iron oxides and oxyhydroxides, zeolites, carbonates, phyllosilicates, and silica. The identities, relative abundances, and crystallinities of the phases formed in a particular environment depend on physicochemical conditions. At one extreme, hot spring environments may be characterized by smectite-chlorite to talc-kaolinite silicate assemblages, plus crystalline ferric oxides dominated by hematite. However, most environments, including cold springs, pedogenic layers, and ponded surface water, are expected to deposit iron oxides and oxyhydroxides, carbonates, and smectite-dominated phyllosilicates. A substantial fraction of the ferric iron is expected to occur in nanophase form, with the exact mineralogy strongly influenced by Eh-pH conditions. Detection of these phases has been an objective of a large body of terrestrial telescopic, Mars orbital, and landed spectral investigations and in situ compositional measurements. However, clear identifications of many of these phases is lacking. Neither carbonate nor silica has been unequivocally detected by any method. Although phyllosilicates may occur near the limit of detection by remote sensing, in general they appear to occur in only poorly crystalline form. In contrast, compelling evidence for ferric iron minerals has been gathered by recent telescopic investigations, the Imager for Mars Pathfinder (IMP), and the Thermal Emission Spectrometer (TES) on the Mars Global Surveyor (MGS). These data yield two crucial findings: (1) In the global, high spatial resolution TES data set, highly crystalline ferric iron (as coarse-grained 'gray' hematite) has been recognized but with only very limited spatial occurrence and (2) Low-resolution telescopic reflectance spectroscopy, very limited orbital reflectance spectroscopy, and landed multispectral imaging provide strong indications that at least two broad classes of ferric iron minerals are commonplace in non-dust covered regions.

Geodynamics map of northeast Asia

USGS Publications Warehouse

Parfenov, Leonid M.; Khanchuk, Alexander I.; Badarch, Gombosuren; Miller, Robert J.; Naumova, Vera V.; Nokleberg, Warren J.; Ogasawara, Masatsugu; Prokopiev, Andrei V.; Yan, Hongquan

2013-01-01

This map portrays the geodynamics of Northeast Asia at a scale of 1:5,000,000 using the concepts of plate tectonics and analysis of terranes and overlap assemblages. The map is the result of a detailed compilation and synthesis at 5 million scale and is part of a major international collaborative study of the mineral resources, metallogenesis, and tectonics of northeast Asia conducted from 1997 through 2002 by geologists from earth science agencies and universities in Russia, Mongolia, northeastern China, South Korea, Japan, and the USA.

A More Reduced Mantle Source for Enriched Shergottites; Insights from the Olivine-Phyric Shergottite Lar 06319

NASA Technical Reports Server (NTRS)

Peslier, A. H.; Hnatyshin, D.; Herd, C. D. K.; Walton, E. L.; Brandon, A. D.; Lapen, T. J.; Shafer, J.

2010-01-01

A detailed petrographic study of melt inclusions and Cr-Fe-Ti oxides of LAR 06319 leads to two main conclusions: 1) this enriched oxidized olivine- phyric shergottite represents nearly continuous crystallization of a basaltic shergottite melt, 2) the melt became more oxidized during differentiation. The first crystallized mineral assemblages record the oxygen fugacity which is closest to that of the melt s mantle source, and which is lower than generally attributed to the enriched shergottite group.

Metamorphic conditions during formation of a metapelitic sillimanite-garnet gneiss from Clemence Massif, Prince Charles Mountains, East Antarctica

USGS Publications Warehouse

Corvino, A.F.; Boger, S.D.; Wilson, C.J.L.

2007-01-01

SiO2–H2O–TiO2–Fe2O3 (MnNCKFMASHTO). Calculated mineral equilibria for the appropriate bulk composition predict that the observed assemblage, of K-feldspar–garnet–quartz–sillimanite–biotite–ilmenite–rutile, stabilised at approximately 8–9 kbar and 760–790ºC. Reaction microstructures are rare, but the preservation of relic spinel inclusions in garnet indicates an earlier low-P, high-T component and possible anticlockwise path.

Mantle-derived peridotites in southwestern Oregon: relation to plate tectonics.

PubMed

Medaris, L G; Dott, R H

1970-09-04

A group of peridotites in southwestern Oregon contains high-pressure mineral assemblages reflecting recrystallization at high temperatures (1100 degrees to 1200 degrees C) over a range of pressure decreasing from 19 to 5 kilobars. It is proposed that the peridotites represent upper-mantle material brought from depth along the ancestral Gorda-Juan de Fuca ridge system, transported eastward by the spreading Gorda lithosphere plate, and then emplaced by thrust-faulting in the western margin of the Cordillera during late Mesozoic time.

Biodegradation and mineralization of isotopically labeled TNT and RDX in anaerobic marine sediments.

PubMed

Ariyarathna, Thivanka; Vlahos, Penny; Smith, Richard W; Fallis, Stephen; Groshens, Thomas; Tobias, Craig

2017-05-01

The lack of knowledge on the fate of explosive compounds 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), particularly in marine ecosystems, constrains the application of bioremediation techniques in explosive-contaminated coastal sites. The authors present a comparative study on anaerobic biodegradation and mineralization of 15 N-nitro group isotopically labeled TNT and RDX in organic carbon-rich, fine-grained marine sediment with native microbial assemblages. Separate sediment slurry experiments were carried out for TNT and RDX at 23°C for 16 d. Dissolved and sediment-sorbed fractions of parent and transformation products, isotopic compositions of sediment, and mineralization products of the dissolved inorganic N pool ( 15 NH 4 + , 15 NO 3 - , 15 NO 2 - , and 15 N 2 ) were measured. The rate of TNT removal from the aqueous phase was faster (0.75 h -1 ) than that of RDX (0.37 h -1 ), and 15 N accumulation in sediment was higher in the TNT (13%) than the RDX (2%) microcosms. Mono-amino-dinitrotoluenes were identified as intermediate biodegradation products of TNT. Two percent of the total spiked TNT-N is mineralized to dissolved inorganic N through 2 different pathways: denitration as well as deamination and formation of NH 4 + , facilitated by iron and sulfate reducing bacteria in the sediments. The majority of the spiked TNT-N (85%) is in unidentified pools by day 16. Hexahydro-1,3,5-trinitro-1,3,5-triazine (10%) biodegrades to nitroso derivatives, whereas 13% of RDX-N in nitro groups is mineralized to dissolved inorganic N anaerobically by the end of the experiment. The primary identified mineralization end product of RDX (40%) is NH 4 + , generated through either deamination or mono-denitration, followed by ring breakdown. A reasonable production of N 2 gas (13%) was seen in the RDX system but not in the TNT system. Sixty-eight percent of the total spiked RDX-N is in an unidentified pool by day 16 and may include unquantified mineralization products dissolved in water. Environ Toxicol Chem 2017;36:1170-1180. © 2016 SETAC. © 2016 SETAC.

Preliminary metallogenic belt and mineral deposit maps for northeast Asia

USGS Publications Warehouse

Obolenskiy, Alexander A.; Rodionov, Sergey M.; Dejidmaa, Gunchin; Gerel, Ochir; Hwang, Duk-Hwan; Distanov, Elimir G.; Badarch, Gombosuren; Khanchuk, Alexander I.; Ogasawara, Masatsugu; Nokleberg, Warren J.; Parfenov, Leonid M.; Prokopiev, Andrei V.; Seminskiy, Zhan V.; Smelov, Alexander P.; Yan, Hongquan; Birul'kin, Gennandiy V.; Davydov, Yuriy V.V.; Fridovskiy, Valeriy Yu.; Gamyanin, Gennandiy N.; Kostin, Alexei V.; Letunov, Sergey A.; Li, Xujun; Nikitin, Valeriy M.; Sotnikov, Sadahisa; Sudo, Vitaly I.; Spiridonov, Alexander V.; Stepanov, Vitaly A.; Sun, Fengyue; Sun, Jiapeng; Sun, Weizhi; Supletsov, Valeriy M.; Timofeev, Vladimir F.; Tyan, Oleg A.; Vetluzhskikh, Valeriy G.; Wakita, Koji; Yakovlev, Yakov V.; Zorina, Lydia M.

2003-01-01

The metallogenic belts and locations of major mineral deposits of Northeast Asia are portrayed on Sheets 1-4. Sheet 1 portrays the location of significant lode deposits and placer districts at a scale of 1:7,500,000. Sheets 2-4 portray the metallogenic belts of the region in a series of 12 time-slices from the Archean through the Quaternary at a scale of 1:15,000,000. For all four map sheets, a generalized geodynamics base map, derived from a more detailed map by Parfenov and others (2003), is used as an underlay for the metallogenic belt maps. This geodynamics map underlay permits depicts the major host geologic units and structures that host metallogenic belts. Four tables are included in this report. A hierarchial ranking of mineral deposit models is listed in Table 1. And summary features of lode deposits, placer districts, and metallogenic belts are described in Tables 2, 3, and 4, respectively. The metallogenic belts for Northeast Asia are synthesized, compiled, described, and interpreted with the use of modern concepts of plate tectonics, analysis of terranes and overlap assemblages, and synthesis of mineral deposit models. The data supporting the compilation are: (1) comprehensive descriptions of mineral deposits; (2) compilation and synthesis of a regional geodynamics map the region at 5 million scale with detailed explanations and cited references; and (3) compilation and synthesis of metallogenic belt maps at 15 million scale with detailed explanations and cited references. These studies are part of a major international collaborative study of the Mineral Resources, Metallogenesis, and Tectonics of Northeast Asia that is being conducted from 1997 through 2002 by geologists from earth science agencies and universities in Russia, Mongolia, Northeastern China, South Korea, Japan, and the USA. Companion studies and previous publications are: (1) a detailed geodynamics map of Northeast Asia (Parfenov and 2003); (2) a compilation of major mineral deposit models (Rodionov and Nokleberg, 2000; Rodionov and others, 2000; Obolenskiy and others, 2003); and (3) a database on significant metalliferous and selected nonmetalliferous lode deposits, and selected placer districts (Ariunbileg and others, 2003).

A Comparison of Microbial Communities from Deep Igneous Crust

NASA Astrophysics Data System (ADS)

Smith, A. R.; Flores, G. E.; Fisk, M. R.; Colwell, F. S.; Thurber, A. R.; Mason, O. U.; Popa, R.

2013-12-01

Recent investigations of life in Earth's crust have revealed common themes in organism function, taxonomy, and diversity. Capacities for hydrogen oxidation, carbon fixation, methanogenesis and methanotrophy, iron and sulfur metabolisms, and hydrocarbon degradation often predominate in deep life communities, and crustal mineralogy has been hypothesized as a driving force for determining deep life community assemblages. Recently, we found that minerals characteristic of the igneous crust harbored unique communities when incubated in the Juan de Fuca Ridge flank borehole IODP 1301A. Here we present attached mineral biofilm morphologies and a comparison of our mineral communities to those from a variety of locations, contamination states, and igneous crustal or mineralogical types. We found that differences in borehole mineral communities were reflected in biofilm morphologies. Olivine biofilms were thick, carbon-rich films with embedded cells of uniform size and shape and often contained secondary minerals. Encrusted cells, spherical and rod-shaped cells, and tubes were indicative of glass surfaces. We also found that the attached communities from incubated borehole minerals were taxonomically more similar to native, attached communities from marine and continental crust than to communities from the aquifer water that seeded it. Our findings further support the hypothesis that mineralogy selects for microbial communities that have distinct phylogenetic, morphological, and potentially functional, signatures. This has important implications for resolving ecosystem function and microbial distributions in igneous crust, the largest deep habitat on Earth.

The effect of scale on the interpretation of geochemical anomalies

USGS Publications Warehouse

Theobald, P.K.; Eppinger, R.G.; Turner, R.L.; Shiquan, S.

1991-01-01

The purpose of geochemical surveys changes with scale. Regional surveys identify areas where mineral deposits are most likely to occur, whereas intermediate surveys identify and prioritize specific targets. At detailed scales specific deposit models may be applied and deposits delineated. The interpretation of regional geochemical surveys must take into account scale-dependent difference in the nature and objectives of this type of survey. Overinterpretation of regional data should be resisted, as should recommendations to restrict intermediate or detailed follow-up surveys to the search for specific deposit types or to a too limited suite of elements. Regional surveys identify metallogenic provinces within which a variety of deposit types and metals are most likely to be found. At intermediate scale, these regional provinces often dissipate into discrete clusters of anomalous areas. At detailed scale, individual anomalous areas reflect local conditions of mineralization and may seem unrelated to each other. Four examples from arid environments illustrate the dramatic change in patterns of anomalies between regional and more detailed surveys. On the Arabian Shield, a broad regional anomaly reflects the distribution of highly differentiated anorogenic granites. A particularly prominent part of the regional anomaly includes, in addition to the usual elements related to the granites, the assemblage of Mo, W and Sn. Initial interpretation suggested potential for granite-related, stockwork Mo deposits. Detailed work identified three separate sources for the anomaly: a metal-rich granite, a silicified and stockwork-veined area with scheelite and molybdenite, and scheelite/powellite concentrations in skarn deposits adjacent to a ring-dike complex. Regional geochemical, geophysical and remote-sensing data in the Sonoran Desert, Mexico, define a series of linear features interpreted to reflect fundamental, northeast-trending fractures in the crust that served as the prime conduits for mineralizing fluids. At a larger scale, the linear, northeast-trending anomalies can be shown to result from a series of discrete mineralized systems with different ages and mineral assemblages. The linear pattern of anomalies disintegrates. A regional geochemical survey in the Sonoran Desert in southwestern Arizona displays a cluster of samples anomalous in Pb, Mo, Bi and W. In detail, the original regional anomaly separates into four discrete anomalous areas, each with its own distinctive suite of elements, geographic distribution and age of mineralization. A prominent regional gold anomaly in the Gobi Desert, Xinjiang, Peoples Republic of China, extends southeastward for 30 km from known lode gold deposits. Because the anomaly cuts both lithologic units and the structural grain, and because it parallels the prevailing direction of high-velocity winds, it was originally attributed to eolian dispersion. In detail, the regional anomaly consists of several east-west-trending anomalies, parallel to local lithology and structure that most likely reflect independent sources of lode gold. The regional anomaly results from smoothing of an en-echelon set of local anomalies. These examples emphasize that interpretation of regional anomalies must be tempered to consider regional-sized geologic features. Attempts to overinterpret anomalies by assigning deposit-scale attributes to regional anomalies can lead to confusion and incorrect interpretations. Potential targets that can be readily resolved only at intermediate or detailed scales of study may be overlooked. ?? 1991.

The Mt. Ochi melange (South Evvia Island, Greece): a case study for HP metamorphism and syn-convergent exhumation.

NASA Astrophysics Data System (ADS)

Moustaka, Eleni; Soukis, Konstantinos; Huet, Benjamin; Lozios, Stylianos; Magganas, Andreas

2014-05-01

The Attic-Cycladic complex (central Aegean Sea, Greece) experienced profound extension since at least the Oligo-Miocene boundary during which the previously thickened crust was reworked by a series of detachments forming the NE directed North Cycladic Detachment System (NCDS) and the SSW directed West Cycladic Detachment System (WCDS). South Evvia Island is located at the northwestern part of the Attic Cycladic complex linking the highly thinned and polymetamorphosed central part of the complex with mainland Greece. Furthermore, greenschists-facies retrograde metamorphism has only partially overprinted the HP mineral assemblages. Consequently, it is an ideal area to study tectonic processes associated with subduction, HP metamorphism and subsequent exhumation from eclogitic depths to the surface. Geological mapping in 1:2:000 scale revealed that the tectonostratigraphy of Mt. Ochi includes three distinct units all metamorphosed in HP conditions followed by greenschist facies overprint. These units are from top to bottom a) the Ochi Unit, a thick metavolcanosedimentary sequence with some intensely folded cipoline marble intercalations and isolated occurrences of metabasic rocks b) the ophiolitic mélange (metagabbros, metawherlites, peridotites, metabasites within a metasedimentary+serpentinite matrix) and c) the lowermost Styra Unit, a cipoline marble-dominated unit with thin mica schists and rare quartzitic layers often boudinaged. The thrust fault that was responsible for the juxtaposition of these three units acted in an early stage during HP metamorphism and it was isoclinally folded and sheared by the following syn-metamorphic deformation events. Detailed structural study in meso- and microscopic scale combined with petrological and geochemical analyses of the Mt Ochi rocks led to the distinction of at least three syn-metamorphic and two post-metamorphic deformation episodes that affected all units. The oldest structure identified is a relic foliation formed by the mineral assemblage Na-amphibole + lawsonite seen as inclusion in epidote porphyroblasts within the melange. It could represent a structure of the prograde path but it could also have formed during the peak HP event. This is followed by successive folding episodes that are related to axial plane foliations and a ~E-W intersection/stretching lineation formed by typical blueschist- to epidote-blueschist facies mineral assemblages. The main foliation that can be observed in all three units is a greenschist-facies axial plane foliation accompanied by a ~ENE-WSW stretching lineation. The shear sense during the prograde path is constantly towards the WSW. In the greenschists-facies an unambiguous top-to ENE can be observed mostly in mylonitic rocks. The following deformation episodes include semi-brittle to brittle structures (shear bands brittle open folds, crenulation cleavage, and faults with increasingly higher-angle) that are not as penetrative and record the passage of the units through the brittle-ductile transitions and to higher structural levels. The kinematics of these late episodes is also towards the NE. Based on the above, the Mt Ochi HP units exhibit a common tectonometamorphic evolution since at least the early stages of the prograde path. The Ochi Unit/Styra Unit contact is a structure that formed prior to or during peak HP metamorphism and therefore it couldn't have served as the normal fault to an extrusion wedge.

Aquatic assemblages of the highly urbanized Santa Ana River Basin, California

USGS Publications Warehouse

Brown, Larry R.; Burton, Carmen; Belitz, Kenneth

2005-01-01

We assessed the structure of periphyton, benthic macroinvertebrate, and fish assemblages and their associations with environmental variables at 17 sites on streams of the highly urbanized Santa Ana River basin in Southern California. All assemblages exhibited strong differences between highly urbanized sites in the valley and the least-impacted sites at the transition between the valley and undeveloped mountains. Results within the urbanized area differed among taxa. Periphyton assemblages were dominated by diatoms (>75% of total taxa). Periphyton assemblages within the urbanized area were not associated with any of the measured environmental variables, suggesting that structure of urban periphyton assemblages might be highly dependent on colonization dynamics. The number of Ephemeroptera, Trichoptera, and Plecoptera (EPT) taxa included in macroinvertebrate assemblages ranged from 0 to 6 at urbanized sites. Benthic macroinvertebrate assemblages had significant correlations with several environmental variables within the urban area, suggesting that stream size and permanence were important determinants of distribution among the species able to survive conditions in urban streams. Only 4 of 16 fish species collected were native to the drainage. Fish assemblages of urbanized sites included two native species, arroyo chub Gila orcuttii and Santa Ana sucker Catostomus santaanae, at sites that were intermediate in coefficient of variation of bank-full width, depth, bed substrate, and water temperature. Alien species dominated urbanized sites with lesser or greater values for these variables. These results suggest that urban streams can be structured to enhance populations of native fishes. Continued study of urban streams in the Santa Ana River basin and elsewhere will contribute to the basic understanding of ecological principles and help preserve the maximum ecological value of streams in highly urbanized areas.

Comparison between epiphyte assemblages of leaves and rhizomes of the seagrass Posidonia oceanica subjected to different levels of anthropogenic eutrophication

NASA Astrophysics Data System (ADS)

Balata, David; Bertocci, Iacopo; Piazzi, Luigi; Nesti, Ugo

2008-09-01

This paper aimed to compare epiphyte assemblages of leaves and rhizomes of Posidonia oceanica exposed to different levels of concentration of nutrients. The same design including a potentially impacted meadow and two reference meadows was used in each of two locations, characterized by the presence of a city or of suspended cages of a fish farm, respectively. This allowed to test for the consistency of responses of epiphytic assemblages to different sources of eutrophication. In both studies, results documented differences in patterns of composition and abundance of epiphytic assemblages on leaves between disturbed and reference meadows, while assemblages on rhizomes did not appear sensitive to this kind of disturbance. Moreover, in potentially impacted meadows, both assemblages showed different patterns of spatial variability compared to reference assemblages. Species composition and abundance of epiphyte assemblages seemed suitable for detecting moderate nutrient increases, even if adequate sampling designs are needed to separate patterns related to the large natural spatial variability of these systems from those related to changes in environmental conditions.

Mineral Mapping with AVIRIS and EO-1 Hyperion

NASA Technical Reports Server (NTRS)

Kruse, Fred A.

2004-01-01

Imaging Spectrometry data or Hyperspectral Imagery (HSI) acquired using airborne systems have been used in the geologic community since the early 1980 s and represent a mature technology (Goetz et al., 1985; Kruse et al., 1999). The solar spectral range, 0.4 to 2.5 m, provides abundant information about many important Earth-surface minerals (Clark et al., 1990). In particular, the 2.0 to 2.5 m (SWIR) spectral range covers spectral features of hydroxyl-bearing minerals, sulfates, and carbonates common to many geologic units and hydrothermal alteration assemblages. Previous research has proven the ability of airborne and spaceborne hyperspectral systems to uniquely identify and map these and other minerals, even in sub-pixel abundances (Kruse and Lefkoff, 1993; Boardman and Kruse, 1994; Boardman et al., 1995; Kruse, et al., 1999). This paper describes a case history for a site in northern Death Valley, California and Nevada along with selected SNR calculations/results for other sites around the world. Various hyperspectral mineral mapping results for this site have previously been presented and published (Kruse, 1988; Kruse et al., 1993, 1999, 2001, 2002, 2003), however, this paper presents a condensed summary of key details for hyperspectral data from 2000 and 2001 and the results of accuracy assessment for satellite hyperspectral data compared to airborne hyperspectral data used as ground truth.

Estimating mineral abundances of clay and gypsum mixtures using radiative transfer models applied to visible-near infrared reflectance spectra

NASA Astrophysics Data System (ADS)

Robertson, K. M.; Milliken, R. E.; Li, S.

2016-10-01

Quantitative mineral abundances of lab derived clay-gypsum mixtures were estimated using a revised Hapke VIS-NIR and Shkuratov radiative transfer model. Montmorillonite-gypsum mixtures were used to test the effectiveness of the model in distinguishing between subtle differences in minor absorption features that are diagnostic of mineralogy in the presence of strong H2O absorptions that are not always diagnostic of distinct phases or mineral abundance. The optical constants (k-values) for both endmembers were determined from bi-directional reflectance spectra measured in RELAB as well as on an ASD FieldSpec3 in a controlled laboratory setting. Multiple size fractions were measured in order to derive a single k-value from optimization of the optical path length in the radiative transfer models. It is shown that with careful experimental conditions, optical constants can be accurately determined from powdered samples using a field spectrometer, consistent with previous studies. Variability in the montmorillonite hydration level increased the uncertainties in the derived k-values, but estimated modal abundances for the mixtures were still within 5% of the measured values. Results suggest that the Hapke model works well in distinguishing between hydrated phases that have overlapping H2O absorptions and it is able to detect gypsum and montmorillonite in these simple mixtures where they are present at levels of ∼10%. Care must be taken however to derive k-values from a sample with appropriate H2O content relative to the modeled spectra. These initial results are promising for the potential quantitative analysis of orbital remote sensing data of hydrated minerals, including more complex clay and sulfate assemblages such as mudstones examined by the Curiosity rover in Gale crater.

Geodiversity of hydrothermal processes along the Mid-Atlantic Ridge and ultramafic-hosted mineralization: A new type of oceanic Cu-Zn-Co-Au volcanogenic massive sulfide deposit

NASA Astrophysics Data System (ADS)

Fouquet, Yves; Cambon, Pierre; Etoubleau, Joël; Charlou, Jean Luc; Ondréas, Hélène; Barriga, Fernando J. A. S.; Cherkashov, Georgy; Semkova, Tatiana; Poroshina, Irina; Bohn, M.; Donval, Jean Pierre; Henry, Katell; Murphy, Pamela; Rouxel, Olivier

Several hydrothermal deposits associated with ultramafic rocks have recently been found along slow spreading ridges with a low magmatic budget. Three preferential settings are identified: (1) rift valley walls near the amagmatic ends of ridge segments; (2) nontransform offsets; and (3) ultramafic domes at inside corners of ridge transform-fault intersections. The exposed mantle at these sites is often interpreted to be a detachment fault. Hydrothermal cells in ultramafic rocks may be driven by regional heat flow, cooling gabbroic intrusions, and exothermic heat produced during serpentinization. Along the Mid-Atlantic Ridge (MAR), hydrothermal deposits in ultramafic rocks include the following: (1) sulfide mounds related to high-temperature low-pH fluids (Logatchev, Rainbow, and Ashadze); (2) carbonate chimneys related to low-temperature, high-pH fluids (Lost City); (3) low-temperature diffuse venting and high-methane discharge associated with silica, minor sulfides, manganese oxides, and pervasive alteration (Saldanha); and (4) stockwork quartz veins with sulfides at the base of detachment faults (15°05'N). These settings are closely linked to preferential circulation of fluid along permeable detachment faults. Compared to mineralization in basaltic environments, sulfide deposits associated with ultramafic rocks are enriched in Cu, Zn, Co, Au, and Ni. Gold has a bimodal distribution in low-temperature Zn-rich and in high-temperature Cu-rich mineral assemblages. The Cu-Zn-Co-Au deposits along the MAR seem to be more abundant than in ophiolites on land. This may be because ultramafic-hosted volcanogenic massive sulfide deposits on slow spreading ridges are usually not accreted to continental margins during obduction and may constitute a specific marine type of mineralization.

Mineralogy of the epithermal precious and base metal deposit Banská Hodruša at the Rozália Mine (Slovakia)

NASA Astrophysics Data System (ADS)

Kubač, Alexander; Chovan, Martin; Koděra, Peter; Kyle, J. Richard; Žitňan, Peter; Lexa, Jaroslav; Vojtko, Rastislav

2018-03-01

The Au-Ag-Pb-Zn-Cu epithermal deposit Banská Hodruša of intermediate-sulphidation type is located in the Middle Miocene Štiavnica stratovolcano on the inner side of the Carpathian arc in Slovakia. This deposit represents an unusual subhorizontal multi-stage vein system, related to processes of underground cauldron subsidence and exhumation of a subvolcanic granodiorite pluton. Veins are developed on a low-angle normal shear zone, possibly representing a detachment zone in andesitic wall rocks that formed during emplacement and exhumation of the granodiorite pluton. The deposit consists of two parts, separated by a thick sill of quartz-diorite porphyry. The eastern part is currently mined, and the western part has already been depleted. The Banská Hodruša mineralization was formed during four stages: (1) low-grade silicified breccia at subhorizontal structures at the base of the deposit; (2) stockwork of steep veins with rhodonite-rhodochrosite, quartz-sulphide-carbonate and quartz-gold assemblages; (3) thin quartz-gold veins with medium dip in tension cracks inside the shear zone and complementary detachment hosted quartz-base metals-gold veins; (4) Post-ore veins. Gold and electrum (920-730) occur as intergrowths with base metal sulphides or hosted in quartz and carbonates, accompanied by Au-Ag tellurides (hessite, petzite). Rare Te-polybasite and Cu-cervelleite result from re-equilibration of early Te-bearing minerals during cooling. Sulphide minerals include low Fe sphalerite ( 1.25 wt%), galena, chalcopyrite, and pyrite. The wall rock alteration is represented mostly by adularia, illite, chlorite, quartz, calcite and pyrite. Precipitation of gold, Au-Ag tellurides, Mn-bearing minerals and adularia resulted from boiling of fluids due to hydraulic fracturing, as well as opening of dilatational structures within the shear zone.

FTIR reflectance of selected minerals and their mixtures: implications for ground temperature-sensor monitoring on Mars surface environment (NASA/MSL-Rover Environmental Monitoring Station).

PubMed

Martín-Redondo, M Paz; Martínez, Eduardo Sebastian; Sampedro, M Teresa Fernández; Armiens, Carlos; Gómez-Elvira, Javier; Martinez-Frias, Jesus

2009-07-01

The Rover Environmental Monitoring Station (REMS) is one of NASA/MSL's instruments, which has been designed for measuring ambient pressure, humidity, wind speed and direction, UV radiation, and air and ground temperature (GT). The GT-sensor is dedicated to measure the real temperature of the Martian surface, integrating the IR energy coming from the ground. The existing IR spectral data of Martian dust, rocks and sediments allow for comparing the Martian spectra with the spectra of different terrestrial minerals and lithologies, and those of their alteration and weathering products. The FTIR reflectance of a set of selected astrobiologically significant minerals (including oxides, oxi/hydroxides, sulfates, chlorides, opal and clays) and basalt (as the main and most widespread volcanic Martian rock) was measured, considering different mixing amounts, and covering the specific working wavelength range of the REMS' GT-sensor. The results obtained show important percentage increases or decreases of reflectance in the entire wavelength range (e.g. basalt-hematite vs. basalt-magnetite) and specific variations limited to some spectral bands (e.g. basalt-smectite vs. basalt-jasper). The basalt reflectance percentage increases or decreases, even up to 100%, depending on the mixing of the different minerals. This unequivocally confirms the need for considering the chemical-mineralogical assemblages (and their textures) for any investigation and interpretation of Mars surface environment. Some complementary applications of this research on our planet, either in relation to the specific performances and characteristics of the GT-sensor autonomous recalibration system, or those oriented to carrying out similar studies on different types of terrestrial environmental settings, are also described.

Application of gold compositional analyses to mineral exploration in the United States

USGS Publications Warehouse

Antweiler, J.C.; Campbell, W.L.

1977-01-01

Native gold is a mineral composed of Au, Ag and Cu in solid solution and it usually contains one or more trace metals as lattice impurities, as mineral inclusions, in grain boundaries or in surface coatings. Alloy proportions of Au, Ag and Cu, together with certain other elements, can be thought of as constituting a gold "signature". Gold is associated with a great variety of ore deposits and has characteristic signatures for each of several types of ore deposits. Signatures for gold derived from igneous-metamorphic, hypothermal, mesothermal and epithermal deposits reflect conditions of ore formation by their content of Ag, Cu and characteristic associated elements. At higher temperatures of ore formation, gold has low Ag and high Cu content, and Bi and Pb are the most abundant trace elements. But at lower temperatures of ore formation, Ag is high, Cu is low, and Pb is the most abundant trace element. The same trend in gold signatures is observable in gold mining districts, such as Central City, Colorado, where zoning as shown by mineral assemblages indicates ore deposition at progressively lower temperatures as the distance from a central high-temperature zone increases. The signatures of gold may be useful in searching for porphyry Cu deposits. Signatures from Butte (Montana), Mineral Park (Arizona) and Cala Abajo (Puerto Rico), on the basis of limited sampling, are similar and distinctive. They are characterized by a similar assemblage of trace elements and are relatively high in both Ag and Cu. Another application of gold compositional data is in tracing placer gold to its bedrock source. For example, the Ag content of placer gold in the Tarryall district of Colorado differed from that of nearly all of the bedrock sources of gold found by early prospectors. However, one lightly prospected area peripheral to the Tertiary quartz monzonite stock at Montgomery Gulch contains gold with a Ag content similar to that of the placer gold. This area is the most likely source of the gold in the productive placers and may be a potential exploration target. Gold signatures may be useful in prospecting for metals other than gold. Several metals of low crustal abundance - notably Sn, W, Mo and the Pt group metals - are detected in analyses of some gold samples and may indicate economic deposits of these metals. ?? 1977.

Modification of the magnetic mineralogy in basalts due to fluid-rock interactions in a high-temperature geothermal system (Krafla, Iceland)

NASA Astrophysics Data System (ADS)

Oliva-Urcia, Belén; Kontny, Agnes; Vahle, Carsten; Schleicher, Anja M.

2011-07-01

Active high-temperature (>150 °C) geothermal areas like the Krafla caldera, NE-Iceland, often show distinct magnetic lows in aeromagnetic anomaly maps suggesting a destruction of magnetic minerals by hydrothermal activity. The main alteration processes in such an environment are low-temperature oxidation (<350 °C, maghemitization) and fluid-rock interactions. We investigated the rock magnetic properties [natural remanent magnetization (NRM) magnetic susceptibility and their temperature and field variation] and the mineralogy, using X-ray diffraction, microscopic methods and electron microprobe analyses, of two drill cores (KH1 and KH3) from the rim of the Krafla caldera. The drill cores have distinctly lower NRM values (average <3 A m-1) compared to younger surface basalts (average 20 A m-1) along with a large variation in magnetic susceptibility (1.3 × 10-7- 4.9 × 10-5 m3 kg-1). The secondary mineral assemblage (sulphides, sphene, rutile and chlorite) indicates an alteration within the chlorite-smectite zone for both cores without depth zoning. Optical miscroscopy in combination with the Bitter technique and backscatter electron microscopy along with the thermomagnetic analyses allow distinguishing two different magnetomineralogical groups of titanomaghemite: (1) titanomaghemite with intermediate titanium concentration and probably high vacancy concentration, and (2) titanomaghemite with low titanium concentration and low vacancy concentration. The mineral assemblages, textures and magnetic properties deduced from the mentioned magnetic measurements indicate two-stage transformation mechanism: (1) Dissolution of titanium at low pH under oxidizing conditions. The ulvöspinel component of titanomagnetite and ilmenite forms rutile or sphene, and Fe2 + migrates out of the spinel lattice forming titanomaghemite. (2) Formation of pyrite and dissolution of remaining titanomaghemite under reducing and acidic conditions. The latter mechanism produces ghost textures (all titanomaghemite is transformed and only their former grain shapes are preserved), with only paramagnetic minerals left and ferrimagnetic minerals nearly dissolved. This mechanism could explain the significant magnetization loss, which is seen in many local magnetic anomaly lows within the oceanic crust and volcanic islands like Iceland or Hawaii. The production of nanoporous textures in titanomaghemites is suggested as a mechanism for the enhancement of the magnetic susceptibility values related to the hydrothermal alteration of Krafla.

Assemblage Organization in Stream Fishes: Effects of Enviromental Variation and Interspecific Interactions

Treesearch

Gary D. Grossman; Robert E. Ratajczak; Maurice Crawford; Mary C. Freeman

1998-01-01

We assessed the relative importance of environmental variation, interspecific competition for space, and predator abundance on assemblage structure and microhabitat use in a stream fish assemblage inhabiting Coweeta Creek, North Carolina, USA. Our study encompassed a l0-yr time span (1983-1992) and included some of the highest and lowest flows in the last 58 years. We...

Assembly rules for functional groups of North American shrews: effects of geographic range and habitat partitioning

Treesearch

Timothy S. McCay; Matthew J. Lovallo; W. Mark Ford; Michael A. Menzel; Michael A. Menzel

2004-01-01

We examined the representation of shrew species within assemblages at 197 sites in the southern Appalachian Mountains, USA. Assemblages were classified according to representation of functional groups, including fossorial, small epigeal, and large epigeal. Average (9?SD) species richness was 2.99?1.0 and assemblages averaged 0.8 species in the fossorial and large...

[X-ray diffraction and infrared spectrum analysis of fault gouge in Wenchuan seismic belt].

PubMed

Wang, Zheng-Yang; Cao, Jian-Jin; Luo, Song-Ying; Liao, Yi-Peng

2014-05-01

Wenchuan earthquake produced a series of co-seismic surface ruptures in Leigu and Zhaojiagou, and we collected samples of co-seismic fault gouge in the surface ruptures as well as the old gouge in the fault of Nanba. Testing The new and old fault gouge was tested with X-ray diffraction and infrared absorption spectra, and its characteristics such as mineral compositions, clay mineral contents and combinations were comprehensively analyzed. The results display obvious differences between the new and old fault gouge, showing that the old fault gouge is mainly composed of wall rock debris or milled powders, while the main components of new fault gouge are clay minerals. The assemblage of clay minerals composition shows that the environment of the fault activity was mainly warm and humid, and the clay minerals were mainly transformed by low temperature and low pressure dynamic metamorphism. And this also partly indicates that the latest way of the fault activity in this area may be a creeping. However the previous researches on the fault gouge of Wenchuan earthquake fault zone are mainly focused on its mechanical properties as well as its texture and structure, the research in this paper is to determine the physical and chemical environment of fault activity through the mineral compositions and clay mineral contents in the fault gouge characteristics, and this research has important scientific significance to the researches on the evolution of the fault environment and the activity mechanism of the earthquake.

Tin in granitic melts: The role of melting temperature and protolith composition

NASA Astrophysics Data System (ADS)

Wolf, Mathias; Romer, Rolf L.; Franz, Leander; López-Moro, Francisco Javier

2018-06-01

Granite bound tin mineralization typically is seen as the result of extreme magmatic fractionation and late exsolution of magmatic fluids. Mineralization, however, also could be obtained at considerably less fractionation if initial melts already had enhanced Sn contents. We present chemical data and results from phase diagram modeling that illustrate the dominant roles of protolith composition, melting conditions, and melt extraction/evolution for the distribution of Sn between melt and restite and, thus, the Sn content of melts. We compare the element partitioning between leucosome and restite of low-temperature and high-temperature migmatites. During low-temperature melting, trace elements partition preferentially into the restite with the possible exception of Sr, Cd, Bi, and Pb, that may be enriched in the melt. In high-temperature melts, Ga, Y, Cd, Sn, REE, Pb, Bi, and U partition preferentially into the melt whereas Sc, V, Cr, Co, Ni, Mo, and Ba stay in the restite. This contrasting behavior is attributed to the stability of trace element sequestering minerals during melt generation. In particular muscovite, biotite, titanite, and rutile act as host phases for Sn and, therefore prevent Sn enrichment in the melt as long as they are stable phases in the restite. As protolith composition controls both the mineral assemblage and modal contents of the various minerals, protolith composition eventually also controls the fertility of a rock during anatexis, restite mineralogy, and partitioning behavior of trace metals. If a particular trace element is sequestered in a phase that is stable during partial melting, the resulting melt is depleted in this element whereas the restite becomes enriched. Melt generation at high temperature may release Sn when Sn-hosts become unstable. If melt has not been lost before the breakdown of Sn-hosts, Sn contents in the melt will increase but never will be high. In contrast, if melt has been lost before the decomposition of Sn-hosts, the small volume of the high-temperature melt will not be diluted by low-temperature, low-Sn melts and, therefore, could have high Sn-contents. The combination of multiple melt extractions and Sn-mobilization at high temperature results in strong Sn enrichment in late, high-temperature melts. Metal enrichment during partial melting becomes particularly efficient, if the sedimentary protolith had experienced intense chemical alteration as the loss of Na and Ca together with a relative enrichment of K favors muscovite-rich metamorphic mineral assemblages that produce large amounts of melt during muscovite dehydration melting.

Ore-fluid evolution at the Getchell Carlin-type gold deposit, Nevada, USA

USGS Publications Warehouse

Cline, J.S.; Hofstra, A.A.

2000-01-01

Minerals and fluid-inclusion populations were examined using petrography, microthermometry, quadrupole mass-spectrometer gas analyses and stable-isotope studies to characterize fluids responsible for gold mineralization at the Getchell Carlin-type gold deposit. The gold-ore assemblage at Getchell is superimposed on quartz-pyrite vein mineralization associated with a Late-Cretaceous granodiorite stock that intruded Lower-Paleozoic sedimentary rocks. The ore assemblage, of mid-Tertiary age, consists of disseminated arsenian pyrite that contains submicrometer gold, jasperoid quartz, and later fluorite and orpiment that fill fractures and vugs. Late ore-stage realgar and calcite enclose ore-stage minerals. Pre-ore quartz trapped fluids with a wide range of salinities (1 to 21 wt.% NaCl equivalent), gas compositions (H2O, CO2, and CH4), and temperatures (120 to >360??C). Oxygen- and hydrogen-isotope ratios indicate that pre-ore fluids likely had a magmatic source, and were associated with intrusion of the granodiorite stock and related dikes. Ore-stage jasperoid contains moderate salinity, aqueous fluid inclusions trapped at 180 to 220??C. Ore fluids contain minor CO2 and trace H2S that allowed the fluid to react with limestone host rocks and transport gold, respectively. Aqueous inclusions in fluorite indicate that fluid temperatures declined to ~175??C by the end of ore-stage mineralization. As the hydrothermal system collapsed, fluid temperatures declined to 155 to 115??C and realgar and calcite precipitated. Inclusion fluids in ore-stage minerals have high ??D(H2O) and ??18O(H2O) values that indicate that the fluid had a deep source, and had a metamorphic or magmatic origin, or both. Late ore-stage fluids extend to lower ??D(H2O) values, and have a wider range of ??18O(H2O) values suggesting dilution by variably exchanged meteoric waters. Results show that deeply sourced ore fluids rose along the Getchell fault system, where they dissolved carbonate wall rocks and deposited gold-enriched pyrite and jasperoid quartz. Gold and pyrite precipitated together as H2S in the ore fluids reacted with iron in the host rocks. As ore fluids mixed with local aquifer fluids, ore fluids became cooler and more dilute. Cooling caused precipitation of ore-stage fluorite and orpiment, and late ore-stage realgar. Phase separation and/or neutralization of the ore fluid during the waning stages of the hydrothermal ore system led to deposition of late ore-stage calcite.

Lithologic Control on Secondary Clay Mineral Formation in the Valles Caldera, New Mexico

NASA Astrophysics Data System (ADS)

Caylor, E.; Rasmussen, C.; Dhakal, P.

2015-12-01

Understanding the transformation of rock to soil is central to landscape evolution and ecosystem function. The objective of this study was to examine controls on secondary mineral formation in a forested catchment in the Catalina-Jemez CZO. We hypothesized landscape position controls the type of secondary minerals formed in that well-drained hillslopes favor Si-poor secondary phases such as kaolinite, whereas poorly drained portions of the landscape that collect solutes from surrounding areas favor formation of Si-rich secondary phases such as smectite. The study focused on a catchment in Valles Caldera in northern New Mexico where soils are derived from a mix of rhyolitic volcanic material, vegetation includes a mixed conifer forest, and climate is characterized by a mean annual precipitation of ~800 mm yr-1 and mean annual temperature of 4.5°C. Soils were collected at the soil-saprolite boundary from three landscape positions, classified as well drained hillslope, poorly drained convergent area, and poorly drained hill slope. Clay fractions were isolated and analyzed using a combination of quantitative and qualitative x-ray diffraction (XRD) analyses and thermal analysis. Quantitative XRD of random powder mounts indicated the presence of both primary phases such as quartz, and alkali and plagioclase feldspars, and secondary phases that include illite, Fe-oxyhydroxides including both goethite and hematite, kaolinite, and smectite. The clay fractions were dominated by smectite ranging from 36-42%, illite ranging from 21-35%, and kaolinite ranging from 1-8%. Qualitative XRD of oriented mounts confirmed the presence of smectite in all samples, with varying degrees of interlayering and interstratification. In contrast to our hypothesis, results indicated that secondary mineral assemblage was not strongly controlled by landscape position, but rather varied with underlying variation in lithology. The catchment is underlain by a combination of porphorytic rhyolite and hydrothermally altered rhyolitic tuff, with an intrusion of Paleozoic sandstone. Smectite content was generally greater in areas underlain by the tuff and likely represent a combination of both diagenic smectite formed by hydrothermal alteration of volcanic glass and authigenic smectites formed in the soils via chemical weathering.

High-pressure granulites in the Fuping Complex of the central North China Craton: Metamorphic P-T-t evolution and tectonic implications

NASA Astrophysics Data System (ADS)

Qian, Jiahui; Yin, Changqing; Zhang, Jian; Ma, Li; Wang, Luojuan

2018-04-01

Mafic granulites in the Fuping Complex occur as lenses or boudins within high-grade TTG (Trondhjemite-Tonalite-Granodiorite) gneisses. Petrographic observations reveal four generations of mineral assemblage in the granulites: an inclusion assemblage of hornblende + plagioclase + ilmenite + quartz within garnet core; an inferred peak assemblage composed of garnet ± hornblende + plagioclase + clinopyroxene + rutile/ilmenite + quartz; a decompression assemblage characterized by symplectites of clinopyroxene ± orthopyroxene + plagioclase, coronae of plagioclase ± clinopyroxene ± hornblende around embayed garnet porphyroblasts or a two-pyroxene association; and a late amphibolite-facies retrogressive assemblage. Two representative samples were used for pseudosection modeling in NCFMASHTO model system to determine their metamorphic evolution. The results show that these granulites experienced a high-pressure stage of metamorphism with peak P-T conditions of 12-13 kbar and 760-800 °C (Pmax) and a post-peak history under P-T conditions of ∼9.0 kbar and 805-835 °C (Tmax), indicating a nearly isothermal decompression process (ITD) with a slight heating. Metamorphic evolution from the Pmax to the Tmax is predicted to be dominated by garnet breakdown through continuous metamorphic reactions of garnet + quartz ± diopside = hornblende + plagioclase + liquid and garnet + quartz + hornblende = plagioclase + diopside + liquid + orthopyroxene. Further metamorphic evolution after the Tmax is dominated by cooling, suggesting that high-pressure (HP) granulites may also exist in the Fuping Complex. Metamorphic zircons in the Fuping HP mafic granulites have left inclined REE patterns, Ti contents of 1.68-6.88 ppm and crystallization temperatures of 602-712 °C. SIMS zircon U-Pb dating on these zircons yields 207Pb/206Pb ages of 1891 ± 14 Ma and 1849 ± 6 Ma, interpreted to represent the cooling stage of metamorphism. The P-T-t evolution of the Fuping HP mafic granulites records well the protracted Paleoproterozoic orogenic event occurred in the central North China Craton.

Metamorphism and gold mineralization in the Blue Ridge, Southernmost Appalachians

USGS Publications Warehouse

Stowell, H.H.; Lesher, C.M.; Green, N.L.; Sha, P.; Guthrie, G.M.; Sinha, A.K.

1996-01-01

Lode gold mineralization in the Blue Ridge of the southernmost Appalachians is hosted by metavolcanic rocks (e.g., Anna Howe mine, AL; Royal Vindicator mine, GA), metaplutonic rocks (e.g., Hog Mountain mine, AL), and metasedimentary rocks (e.g., Lowe, Tallapoosa, and Jones Vein mines, AL). Most gold occurs in synkinematic quartz ?? plagioclase ?? pyrite ?? pyrrhotite ?? chlorite veins localized along polydeformational faults that juxtapose rocks with significantly different peak metamorphic mineral assemblages. Mineralogy, chemistry, and O and H isotope studies suggest that the three types of host rocks have undergone differing amounts and types of alteration during mineralization. Limited wall-rock alteration in metavolcanic- and metasediment-hosted deposits, and relatively extensive wall-rock alteration in granitoid-hosted deposits, suggests that most deposits formed from fluids that were close to equilibrium with metavolcanic and metasedimentary rocks. Stable isotope compositions of the fluids calculated from vein minerals and vein selvages are consistent with a predominantly metasedimentary fluid source, but vary from deposit to deposit (-22 to -47??? ??D, 4-5??? ??18O, and 5-7??? ??34S at Anna Howe and Royal Vindicator; -48 to -50??? ??D, 9-13??? ??18O, and ca. 19??? ??34S at Lowe and Jones Vein; and -22 to -23??? ??D, 8-11??? ??18O, 9-10??? ??34S, and -6 ??13C at Hog Mountain). Silicate mineral thermobarometry of vein, vein selvage, and wall-rock mineral assemblages indicate that mineralization and regional metamorphism occured at greenschist to amphibolite facies (480?? ?? 75??C at Anna Howe, 535?? ?? 50??C at 6.4 ?? 1 kbars at Lowe, 530?? ?? 50??C at 6.9 ?? 1 kbars at Tallapoosa, and 460?? ?? 50??C at 5.5 ?? 1 kbars at Hog Mountain). Oxygen isotope fractionation between vein minerals and selvage minerals consistently records equilibration temperatures that are similar to or slightly lower than those estimated from silicate thermometry. Auriferous veins contain numerous fluid inclusions that were emplaced in several stages and can be subdivided into five compositional types based on salt and CO2 concentrations. Fluid inclusion isochores for early formed inclusions from these veins intercept the pressure and temperature conditions estimated from silicate mineral thermobarometry and stable isotope thermometry, and are compatible with entrapment at those conditions. These fluids exhibit significant variation in salinity (XNaClequiv = 0.0-0.2) and CO2 (XCO2 = 0.0-0.2), suggesting variation in fluid-wall-rock interaction that accompanied gold deposition during declining temperatures. Less abundant and later fluids within the veins are dominantly CO2. The association of gold mineralization with structurally controlled concordant and discordant quartz sulfide veins, and the temperatures and pressures of wall-rock alteration and regional metamorphism indicate that the present distribution of gold is a result of metamorphism during progressive D2-D3 deformation. Isotopic data for alteration envelopes date this event as Alleghanian: 279 ?? 14 Ma (K-Ar whole rock) and 343 ?? 18 Ma (K-Ar biotite) at Lowe; and 315 ?? 18 Ma (Rb-Sr whole-rock isochron; 87Sr/86Sr, = 0.7061 ?? 0.0008) and 294 ?? 16 Ma (K-Ar whole-rock) at Hog Mountain. Available data are compatible with development of the lodes during early Alleghanian overthrusting of allochthons over sedimentary rocks of the autochthonous North American margin. The implication is that the fluids were derived from metasedimentary and/or metavolcanic formations in the lower parts of the crystalline thrust stack (or possibly from underlying autochthonous sedimentary formations), ascended along permeable fault zones, and were emplaced as veins into dilatent areas in and adjacent to the fault zones.

Evolution of the blueschist and greenschist facies rocks of Sifnos, Cyclades, Greece

NASA Astrophysics Data System (ADS)

Matthews, Alan; Schliestedt, Manfred

1984-11-01

The metamorphism on the island of Sifnos is characterized by the Eocene development of a coherent highpressure blueschist terrane and an early Miocene greenschist facies overprint. This study documents the metamorphic evolution of the blueschist assemblages, still preserved in the northern parts of the island, and their subsequent transformation into greenschists in the central and southern parts. The oxygen isotope geothermometry is based on calibrations for quartz, pyroxenes and magnetite (Matthews et al. 1983a) augmented by revised calibrations for the minerals muscovite ( Δ Qz-Mu=1.55×106 T -2), epidote ( δ Qz-Ep= 1.56+1.92 Δ ps)106 T -2), and rutile ( Δ Qz-Ru=4.54×106 T -2). Oxygen isotope analyses of minerals from the Blueschist unit of northern Sifnos give consistent fractionations which are independent of rock type. An average temperature of 455° C was obtained, although the scatter in temperatures deduced from the various geothermometers suggests that equilibration occurs under slightly changing physicochemical conditions. Analyses of minerals and whole rocks shows that pervasive equilibration in the presence of a common metamorphic fluid has not occurred. The minerals and whole rocks of the greenschists of central Sifnos are systematically enriched in 18O relative to the blueschist assemblages. Chemical data indicate that the greenschist overprint was accompanied by a metasomatic enrichment of Ca2+ and CO2. The petrologic, isotopic and chemical evidence favour a metamorphism governed by the infiltration of 18O-CO2 enriched aqueous solutions. It is reasonable to assume that this is connected with the Miocene magmatic activity observed throughout the Cyclades. The marbles separating the Blueschist from the Greenschist unit probably acted as barriers to fluid infiltration into the blueschists and were responsible for their preservation. The pressure of the blueschist metamorphism is estimated at 14±2 kbar, corresponding to a depth of ca. 50 km. The structural style and stratigraphy of Sifnos are suggestive of the subduction of a continental margin sequence. It is clear that the considerable tectonic depression may be associated with continental collision and underthrusting.

Sulphur-Rich Melt At Upper Crustal Levels At Cerro La Torta, Central Andes: Evidence From Melt Inclusions Assemblages.

NASA Astrophysics Data System (ADS)

Cannatelli, C.; Godoy, B.; Alvear, B.; Moncada, D.

2016-12-01

Central Andes present some of the biggest and most important porphyry copper ore deposits in the world. Porphyry copper ore formation is related to precipitation of ore minerals from sulphur and chlorine-rich fluids. Genesis of these deposits occurred 4 km below surface, while mineralized fluids are released by magmatic melts located between 5 and 15 km depth (Sillitoe, 2010). Cerro La Torta is part of a cluster of <105 ka rhyodacitic domes related to the waning stage of the Altiplano-Puna Volcanic Complex at Central Andes (Tierney et al., 2016). These domes reflect a crystal-rich mush layer at the upper crust - named Altiplano-Puna Magma Body (APMB) - which is proposed to be a voluminous partially molten body locate at shallow depth (4-25 km), with a thickness up to 11 km (Ward et al., 2014). Cerro La Torta is a crystal-rich ( 40% vol.) dacitic flow with plagioclase, amphibole, biotite, and quartz phenocrysts on a glassy (up to 50% vol.) groundmass. During detailed petrographic observation, two types of Melt Inclusions Assemblages (MIAs) were observed in the plagioclase. Group I is found in the core of crystals, and contains sulphide, pyrite ± bubbles. Group II of bubble-bearing MIAs is observed at the rim of the phenocrysts, with no associated sulphide mineral present. Melt Inclusions size ranges from 10-40 µm, suggesting an intermediate cooling rate (Roedder 1979). Out hypothesis is that during cooling, Group I MIA is trapped as result of a metal sulfur-rich event, leading to the suggestion that sulphide-bearing MIAs from Cerro La Torta are the evidence of mineralized magmas ponding at shallow crustal levels. Furthermore, the presence of MIAs in the mush-type magmas related to the APMB implies that such systems are suitable to porphyry copper ore generation. Roedder, 1979. The Evolution of the Igneous Rocks. 15-57 Sillitoe, 2010. Econ. Geol. 105:3-41 Tierney et al., 2016. Geology 44:683-686. doi:10.1130/G37968.1Ward et al., 2014. Earth Planet Sci Letters 404:43-54

Alteration mineral mapping for iron prospecting using ETM+ data, Tonkolili iron field, northern Sierra Leone

NASA Astrophysics Data System (ADS)

Mansaray, Lamin R.; Liu, Lei; Zhou, Jun; Ma, Zhimin

2013-10-01

The Tonkolili iron field in northern Sierra Leone has the largest known iron ore deposit in Africa. It occurs in a greenstone belt in an Achaean granitic basement. This study focused mainly on mapping areas with iron-oxide and hydroxyl bearing minerals, and identifying potential areas for haematite mineralization and banded iron formations (BIFs) in Tonkolili. The predominant mineral assemblage at the surface (laterite duricrust) of this iron field is haematitegoethite- limonite ±magnetite. The mineralization occurs in quartzitic banded ironstones, layered amphibolites, granites, schists and hornblendites. In this study, Crosta techniques were applied on Enhanced Thematic Mapper (ETM+) data to enhance areas with alteration minerals and target potential areas of haematite and BIF units in the Tonkolili iron field. Synthetic analysis shows that alteration zones mapped herein are consistent with the already discovered magnetite BIFs in Tonkolili. Based on the overlaps of the simplified geological map and the remote sensing-based alteration mineral maps obtained in this study, three new haematite prospects were inferred within, and one new haematite prospect was inferred outside the tenement boundary of the Tonkolili exploration license. As the primary iron mineral in Tonkolili is magnetite, the study concludes that, these haematite prospects could also be underlain by magnetite BIFs. This study also concludes that, the application of Crosta techniques on ETM+ data is effective not only in mapping iron-oxide and hydroxyl alterations but can also provide a basis for inferring areas of potential iron resources in Algoma-type banded iron formations (BIFs), such as those in the Tonkolili field.

The graphite deposit at Borrowdale (UK): A catastrophic mineralizing event associated with Ordovician magmatism

NASA Astrophysics Data System (ADS)

Ortega, L.; Millward, D.; Luque, F. J.; Barrenechea, J. F.; Beyssac, O.; Huizenga, J.-M.; Rodas, M.; Clarke, S. M.

2010-04-01

The volcanic-hosted graphite deposit at Borrowdale in Cumbria, UK, was formed through precipitation from C-O-H fluids. The δ 13C data indicate that carbon was incorporated into the mineralizing fluids by assimilation of carbonaceous metapelites of the Skiddaw Group by andesite magmas of the Borrowdale Volcanic Group. The graphite mineralization occurred as the fluids migrated upwards through normal conjugate fractures forming the main subvertical pipe-like bodies. The mineralizing fluids evolved from CO 2-CH 4-H 2O mixtures (XCO 2 = 0.6-0.8) to CH 4-H 2O mixtures. Coevally with graphite deposition, the andesite and dioritic wall rocks adjacent to the veins were intensely hydrothermally altered to a propylitic assemblage. The initial graphite precipitation was probably triggered by the earliest hydration reactions in the volcanic host rocks. During the main mineralization stage, graphite precipitated along the pipe-like bodies due to CO 2 → C + O 2. This agrees with the isotopic data which indicate that the first graphite morphologies crystallizing from the fluid (cryptocrystalline aggregates) are isotopically lighter than those crystallizing later (flakes). Late chlorite-graphite veins were formed from CH 4-enriched fluids following the reaction CH 4 + O 2 → C + 2H 2O, producing the successive precipitation of isotopically lighter graphite morphologies. Thus, as mineralization proceeded, water-generating reactions were involved in graphite precipitation, further favouring the propylitic alteration. The structural features of the pipe-like mineralized bodies as well as the isotopic homogeneity of graphite suggest that the mineralization occurred in a very short period of time.

Last glacial to Holocene productivity and oxygen changes based on benthic foraminiferal assemblages from the western Alboran Sea

NASA Astrophysics Data System (ADS)

Pérez-Asensio, José N.; Cacho, Isabel; Frigola, Jaime; Pena, Leopoldo D.; Asioli, Alessandra; Kuhlmann, Jannis; Huhn, Katrin

2016-04-01

Late glacial to Holocene productivity and oxygen changes in the Alboran Sea were investigated analyzing benthic foraminiferal assemblages from the marine sediment core HER-GC-UB06. This 255 cm-long core was recovered at 946 m water depth in the Alboran Sea (western Mediterranean Sea) and includes homogeneous greyish clays from the last 23 ka. Nowadays, the core site is bathed by the Western Mediterranean Deep Water (WMDW) and near the overlying Levantine Intermediate Water (LIW). Benthic foraminifera from the size fraction >63 μm were identified at species level and counted until reaching at least 300 individuals. Q-mode principal component analyses (PCA) was performed to establish benthic foraminiferal assemblages. In addition, benthic foraminifera were classified according to their microhabitat preferences. Diversity was assessed with several diversity indices. Four benthic foraminiferal assemblages have been identified along the core. The distribution of these assemblages records changes in productivity and oxygen conditions during the last 23 ka. The last glacial and deglaciation interval, 23-12.5 ka, shows low diversity and is characterized by the Nonionella iridea assemblage, which includes Cassidulina laevigata, Bolivina dilatata, Nonionoides turgida and Cibicides pachyderma as secondary taxa. This assemblage can be interpreted as a moderately oxygenated mesotrophic environment with episodic pulses of fresh organic matter. Although general mesotrophic conditions prevail, the Last Glacial Maximum shows a more oligotrophic and better oxygenated setting as suggested by higher abundance of epifaunal-shallow infaunal taxa. In contrast, along the Bølling-Allerød eutrophic conditions with higher productivity and lower oxygenation are recorded by a deep infaunal taxa maximum. During the Younger Dryas (YD) and the earliest Holocene (12.5-10.5 ka), the Bolivina dilatata assemblage dominates coinciding with a lower diversity, especially during the YD. This species and the additional taxa of the assemblage (Bolivina spathulata, Bolivina subspinescens, Bulimina marginata, Bolivina variabilis and Uvigerina peregrina) also thrive in mesotrophic environments with fresh organic matter supply and moderate oxygen content. The lower part of the early Holocene (10.5-7.3 ka) is dominated by the Cassidulina obtusa assemblage including Bolivina subspinescens, Bolivina variabilis, Bulimina marginata, Gyroidina altiformis, Nonionella iridea and Quinqueloculina sp. as associated taxa. A highly diverse mesotrophic setting with slightly higher oxygenation can be inferred for this assemblage. This is supported by the higher abundance of epifaunal-shallow infaunal taxa and the presence of G. altiformis and Quinqueloculina sp. Finally, the highly diverse Alabaminella weddellensis assemblage occurs along the upper part of the core (7.3-0 ka) encompassing the upper early Holocene and late Holocene. Additional species of this assemblages are Uvigerina mediterranea, Melonis barleeanus, Cassidulina laevigata, Cassidulina obtusa and Uvigerina peregrina. This assemblage suggests mesotrophic conditions with a more continuous organic matter supply as pointed out by the occurrence of U. mediterranea and the intermediate infaunal M. barleeanus that can feed from more degraded organic matter. The onset of this assemblage around 7.3 ka might be related to the establishment of the semi-permanent productive 'Malaga cell" dated at 7.7 ka.

Preliminary geologic map and digital database of the San Bernardino 30' x 60' quadrangle, California

USGS Publications Warehouse

Morton, Douglas M.; Miller, Fred K.

2003-01-01

The San Bernardino 30'x60' quadrangle, southern California, is diagonally bisected by the San Andreas Fault Zone, separating the San Gabriel and San Bernardino Mountains, major elements of California's east-oriented Transverse Ranges Province. Included in the southern part of the quadrangle is the northern part of the Peninsular Ranges Province and the northeastern part of the oil-producing Los Angeles basin. The northern part of the quadrangle includes the southern part of the Mojave Desert Province. Pre-Quaternary rocks within the San Bernardino quadrangle consist of three extensive, well-defined basement rock assemblages, the San Gabriel Mountains, San Bernardino Mountains, and the Peninsular Ranges assemblages, and a fourth assemblage restricted to a narrow block bounded by the active San Andreas Fault and the Mill Creek Fault. Each of these basement rock assemblages is characterized by a relatively unique suite of rocks that was amalgamated by the end of the Cretaceous and (or) early Cenozoic. Some Tertiary sedimentary and volcanic rocks are unique to specific assemblages, and some overlap adjacent assemblages. A few Miocene and Pliocene units cross the boundaries of adjacent assemblages, but are dominant in only one. Tectonic events directly and indirectly related to the San Andreas Fault system have partly dismembered the basement rocks during the Neogene, forming the modern-day physiographic provinces. Rocks of the four basement rock assemblages are divisible into an older suite of Late Cretaceous and older rocks and a younger suite of post-Late Cretaceous rocks. The age span of the older suite varies considerably from assemblage to assemblage, and the point in time that separates the two suites varies slightly. In the Peninsular Ranges, the older rocks were formed from the Paleozoic to the end of Late Cretaceous plutonism, and in the Transverse Ranges over a longer period of time extending from the Proterozoic to metamorphism at the end of the Cretaceous. Within the Peninsular Ranges a profound diachronous unconformity marks the pre-Late Cretaceous-post-Late Cretaceous subdivision, but within the Transverse Ranges the division appears to be slightly younger, perhaps coinciding with the end of the Cretaceous or extending into the early Cenozoic. Initial docking of Peninsular Ranges rocks with Transverse Ranges rocks appears to have occurred at the terminus of plutonism within the Peninsular Ranges. During the Paleogene there was apparently discontinuous but widespread deposition on the basement rocks and little tectonic disruption of the amalgamated older rocks. Dismemberment of these Paleogene and older rocks by strike-slip, thrust, and reverse faulting began in the Neogene and is ongoing. The Peninsular Ranges basement rock assemblage is made up of the Peninsular Ranges batholith and a variety of metasedimentary rocks. Most of the plutonic rocks of the batholith are granodiorite and tonalite in composition; primary foliation is common, mainly in the eastern part. Tertiary sedimentary rocks of the Los Angeles Basin crop out in the Puente and San Jose Hills along with the spatially associated Glendora Volcanics; both units span the boundary between the Peninsular Ranges and San Gabriel Mountains basement rock assemblages. The San Gabriel Mountains basement rock assemblage includes two discrete areas, the high standing San Gabriel Mountains and the relatively low San Bernardino basin east of the San Jacinto Fault. The basement rock assemblage is characterized by a unique suite of rocks that include anorthosite, Proterozoic and Paleozoic gneiss and schist, the Triassic

Mineralization, alteration, and hydrothermal metamorphism of the ophiolite-hosted Turner-Albright sulfide deposit, southwestern Oregon

USGS Publications Warehouse

Zierenberg, R.A.; Shanks, Wayne C.; Seyfried, W.E.; Koski, R.A.; Strickler, M.D.

1988-01-01

The Turner-Albright sulfide deposit, part of the Josephine ophiolite, formed on and below the seafloor during Late Jurassic volcanism at a back arc spreading center. Ore fluids were probably localized by faults which were active on the seafloor at the time of sulfide deposition. The uppermost massive sulfide formed on the seafloor at hydrothermal vents. The bulk of the sulfide mineralization formed below the seafloor within olivine basalt hyaloclastite erupted near the time of mineralization. Infiltration of hydrothermal fluid into the hyaloclastite altered the rock. The fluid responsible for the hydrothermal alteration was evolved seawater with low pH and Mg and high Fe. The average value of sulfide and the difference between sulfide and contemporaneous seawater sulfate values are similar to ophiolite-hosted sulfide deposits in Cyprus. Mudstone and clinopyroxene basalt above the sulfide horizons were not altered by the ore-transporting hydrothermal fluid, but these rocks were hydrothermally metamorphosed by altered seawater heated by deep circulation into hot oceanic crust. This subseafloor metamorphism produced a mineral assemblage typical of prehnite-pumpellyite facies metamorphism. Exchange with altered seawater increased the whole-rock ??18O of the basalts to values of 9.4-11.2%. -from Authors

Fish assemblage structure in an Oklahoma Ozark stream before and after rainbow trout introduction

USGS Publications Warehouse

Walsh, M.G.; Winkelman, D.L.

2005-01-01

Rainbow trout Oncorhynchus mykiss have been widely stocked throughout the United States as a popular sport fish. Our study was initiated to evaluate potential effects of rainbow trout introduction on native fishes to inform future decisions about trout stocking in northeastern Oklahoma streams. We sampled fish assemblages in pools, glides, and riffles in Brush Creek, Delaware County, Oklahoma, from February 2000 to September 2002, and experimentally stocked rainbow trout into the stream from November 2000 to March 2001 and November 2001 to March 2002. We used a combination of multivariate analyses to evaluate seasonal and habitat effects on native fish assemblages and to compare assemblage structure between prestocking, the first year of stocking, and the second year of stocking. Mesohabitat type significantly affected assemblage structure among years, whereas we did not detect an effect of season. We did not detect differences in assemblage structure among years in glide or riffle habitats. Native fish assemblage structure in pool habitats before rainbow trout introduction differed from assemblage structure in both the first and second year of stocking. Declines in seven species, including two native game fish (smallmouth bass Micropterus dolomieu and bluegill Lepomis machrochirus), contributed to assemblage dissimilarity in pool habitats between prestocking conditions and the second year of stocking. Our results indicate that stocking rainbow trout may cause local disruption in assemblage structure in pool habitats. ?? 2004 by the American Fisheries Society.

Diatoms and stratigraphically significant silicoflagellates from the Atlantic Margin Coring Project and other Atlantic margin sites

USGS Publications Warehouse

Abbott, W.H.

1980-01-01

In 1976, 19 sites were cored along the U.S. Atlantic Continental Shelf and Slope by the Oceanographic Branch of the U.S. Geological Survey aboard the Glomar Conception. Only 6 sites contained siliceous microfossil assemblages of sufficient quantity and quality for biostratigraphic study. Two of the sites, AMCOR (Atlantic Margin Coring Project) 6002 and AMCOR 6011, contained good Miocene assemblages: a small Pleistocene assemblage occurred at the top of AMCOR 6002. A Late Miocene to Early Pliocene assemblage was encountered in AMCOR 6007B. AMCOR 6013, 6019, and 6021 contained Pleistocene assemblages. In addition to the AMCOR cores, 3 additional Atlantic Margin cores were studied. These were the JOIDES 1 (Caldrill) core, and Atlantic Slope Project (ASP) cores 10 and 22. JOIDES 1 contains a Middle Miocene assemblage similar to AMCOR 6002. ASP 10 contains a Lower Pliocene assemblage and ASP 22 contains a Middle to Late Oligocene and a Pleistocene assemblage. Siliceous assemblages at all sites consisted mainly of shallow shelf species, including brackish and marine benthics and occasionally freshwater forms. Although planktonic forms were present, they were few and most were extant cosmopolitan species. This makes it difficult to correlate the biostratigraphy of the sediments with siliceous microfossil zonations from other oceans. The only biostratigraphic zonations for Atlantic Shelf diatom assemblages are for the Miocene.

Preliminary Report on the White Canyon Area, San Juan County, Utah

USGS Publications Warehouse

Benson, William Edward Barnes; Trites, A.F.; Beroni, E.P.; Feeger, J.A.

1952-01-01

The White Canyon area in San Juan County, Utah, contains known deposits of copper-uranium ore and is currently being mapped and studied by the Geological Survey. To date, approximately 75 square miles, or about 20 percent of the area, has been mapped on a scale 1 inch=1 mile. The White Canyon area is underlain by more than 2,000 feet of sedimentary rocks, Carboniferous to Jurassic(?) in age. The area is on the flank of the Elk Ridge anticline, and the strata have a regional dip of 1 deg to 2 deg SW. The Shinarump conglomerate of Late Triassic age is the principal ore-bearing formation. The Shinarump consists of lenticular beds of sandstone, conglomeratic sandstone, clay, and siltstone, and ranges in thickness from a feather edge to as much as 75 feet. Locally the sandstones contain silicified and carbonized wood and fragments of charcoal. These vegetal remains are especially common in channel-fill deposits. Jointing is prominent in the western part of the area, and apparently affects all formations. Adjacent to the joints some of the redbeds in the sequence are bleached. Deposits of copper-uranium minerals have been found in the Moenkopi, Shinarump, and Chinle formations, but the only production of ore has been from the Shinarump conglomerate. The largest concentration of these minerals is in the lower third of the Shinarump, and the deposits seem to be controlled in part by ancient channel fills and in part by fractures. Locally precipitation of the copper and uranium minerals apparently has been aided by charcoal and clays. Visible uranium minerals include both hard and soft pitchblende and secondary hydrosulfates, phosphates, and silicates. In addition, unidentified uranium compounds are present in carbonized wood and charcoal, and in veinlets of hydrocarbons. Base-metal sulfides have been identified in all prospects that extend beyond the oxidized zone. Secondary copper minerals in the oxidized zone include the hydrous sulfates and carbonates, and possibly chrysocolla. The principal gangue minerals are quartz, clay minerals, chlorite, oxides of iron and manganese, alunite, calcite, gypsum, pyrite, allophane, gibbsite, opal, and chalcedony. The origin of the copper-uranium ores has not been determined, but the association of many deposits with fractures, the mineralogic assemblage, and a lead-uranium age determination of 50 to 60 million years for the pitchblende in the Happy Jack mine favor the hypothesis that the ores are of hydrothermal origin and were deposited in early Tertiary time. Criteria believed to be the most useful in prospecting for new deposits are (1) visible uranium minerals; (2) visible copper minerals; (3) alunite; (4) hydrocarbons; and (5) bleaching of the underlying Moenkopi formation.

Impact of tsunami on texture and mineralogy of a major placer deposit in southwest coast of India

NASA Astrophysics Data System (ADS)

Babu, N.; Babu, D. S. Suresh; Das, P. N. Mohan

2007-03-01

The great Indonesian earth quake (26 December 2004) triggered a tsunami wave across the Bay of Bengal and Indian Ocean basins and has brought a major havoc in several countries including India. The coastal segment between Thotapalli and Valiazhikal in Kerala state of southwest India, where considerably rich beach placer deposit with ilmenite percentage of more than 70% is concentrated, has been investigated to understand the impact of tsunami on coastal sediments. The grain size analysis flashes out the significant differences between the pre- and post-tsunami littoral environments. While the mineral grains collected during pre-tsunami period show well-sorted nature, the post-tsunami samples represent moderately to poorly sorted nature. Similarly, unimodal and bimodal distributions of the sediments have been recorded for pre- and post-tsunami sediments, respectively. Further, mineral assemblages corresponding to before and after this major wave activity clearly indicate the large-scale redistribution of sediments. The post-tsunami sediments register increasing trends of garnet, sillimanite and rutile. The total heavy mineral percentage of the post-tsunami sediment also shows an improved concentration, perhaps due to the large-scale transport of lighter fraction. Magnetite percentage of post-tsunami samples reflects higher concentration compared to the pre-tsunami samples, indicating the intensity of reworking process. X-ray diffraction patterns of ilmenite grains have confirmed the increased presence of pseduorutile, and pseudobrookite in post-tsunami samples, which could be due to the mixing of more altered grains. SEM examination of grains also confirms the significant alteration patterns on the ubiquitous mineral of placer body, the ilmenite. The reason for these textural, mineralogical and micromorphological changes in heavy minerals particularly in ilmenite, could be due to the churning action on the deeper sediments of onshore region or on the sediments entrapped in the near shelf region of the area, by the ˜ 6 m high tsunami waves.

Provenance of sediments from Sumatra, Indonesia - Insights from detrital U-Pb zircon geochronology, heavy mineral analyses and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Liebermann, C.; Hall, R.; Gough, A.

2017-12-01

The island of Sumatra is situated at the southwestern margin of the Indonesian archipelago. Although it is the sixth largest island in the world, the geology of the Sumatra sedimentary basins and their underlying basement is relatively poorly understood in terms of their provenance. This work is a multi-proxy provenance study utilizing U-Pb detrital zircon dating by LA-ICP-MS combined with optical and Raman spectroscopy-based heavy mineral analysis. It will help to unravel the stratigraphy of Sumatra, contribute to paleogeographic reconstruction of western SE Asia, and aid a wider understanding of Sumatran petroleum plays. Thin section analyses, heavy mineral assemblages, and >3500 concordant U-Pb zircon ages, from samples acquired during two fieldwork seasons indicate a mixed provenance for Cenozoic sedimentary formations, including both local igneous sources and mature basement rocks. Characteristic Precambrian zircon age spectra are found in all analysed Cenozoic sedimentary strata. These can be correlated with zircon age populations found in Sumatran basement rocks; Neoproterozoic and Mesoproterozoic age groups are dominant (c. 500-600 Ma, c. 850-1000 Ma, c. 1050-1200 Ma). Paleoproterozoic to Archaean zircons occur as minor populations. The Phanerozoic age spectra of the Cenozoic formations are characterised by distinct Carboniferous, Permo-Triassic, and Jurassic-Cretaceous zircon populations. Permo-Triassic zircons are interpreted to come from granitoids in the Malay peninsula or Sumatra itself. Eocene to Lower Miocene strata are characterised by ultrastable heavy minerals such as zircon, tourmaline, and rutile, which together with garnet, suggest the principal sources were igneous and metamorphic basement rocks. Cenozoic zircons appear only from the Middle Miocene onwards. This change is interpreted to indicate a new contribution from a local volcanic arc, and is supported by the occurrence of unstable heavy minerals such as apatite and clinopyroxene, and the presence of volcanic quartz. The absence of an earlier volcanic contribution is surprising since subduction is widely considered to have been active from the Eocene.

Study of Hydrothermal Mineralization in 2013 Drill Core from Hawaii Island

NASA Astrophysics Data System (ADS)

Lautze, N. C.; Calvin, W. M.; Moore, J.; Haskins, E.; Thomas, D. M.

2014-12-01

The Humu'ula Groundwater Research Project (HGRP) drilled a continuously-cored hole to nearly 2 km depth near the Saddle Road between Mauna Loa and Mauna Kea volcanoes on Hawaii Island in March of 2013. Temperatures at the bottom of the hole were unexpectedly high and reached over 100 C. A study is underway to characterize hydrothermal (secondary) mineralization in the core at depths below ~ 1 km. Secondary mineralization can indicate the presence, chemistry, and temperature of hydrothermal fluids, therein helping to characterize a present and/or past geothermal system. To date, the study is two pronged. In collaboration with University Nevada Reno (UNR) we used an Analytical Spectral Devices (ASD) FieldSpec instrument to obtain nearly 800 spectra from core depths spanning 3190 to 5785 feet. This device has a 2 cm contact probe that measures from 0.4 to 2.5 mm, and has been used successfully by UNR to identify depth-associated changes in alteration mineralogy and zoning in drill core from other pilot studies. The spectra indicate that rocks above a depth of ~1 km are only weakly altered. At greater depths to the base of the well, chlorite, possibly with some mica, and zeolites are common. The majority of zeolites are spectrally similar to each other at these wavelengths, however analcime and natrolite are uniquely identified in some sections. Epidote was not observed. The secondary mineral assemblages suggest that the alteration was produced by moderate temperature neutral pH fluids. Here, we used the spectral data as a survey tool to help identify and select over 20 sections of core for sampling and more detailed mineralogical analysis using traditional X-Ray Diffraction (XRD) and petrographic techniques, conducted in collaboration with University of Utah. This presentation will include mineral maps with depth and results of the petrographic analyses.

Downstream impacts of dams: shifts in benthic invertivorous fish assemblages

USGS Publications Warehouse

Granzotti, Rafaela Vendrametto; Miranda, Leandro E.; Agostinho, Angelo A.; Gomes, Luiz Carlos

2018-01-01

Impoundments alter connectivity, sediment transport and water discharge in rivers and floodplains, affecting recruitment, habitat and resource availability for fish including benthic invertivorous fish, which represent an important link between primary producers and higher trophic levels in tropical aquatic ecosystems. We investigated long-term changes to water regime, water quality, and invertivorous fish assemblages pre and post impoundment in three rivers downstream of Porto Primavera Reservoir in south Brazil: Paraná, Baía and Ivinhema rivers. Impacts were distinct in the Paraná River, which is fully obstructed by the dam, less evident in the Baía River which is partially obstructed by the dam, but absent in the unimpounded Ivinhema River. Changes in water regime were reflected mainly as changes in water-level fluctuation with little effect on timing. Water transparency increased in the Paraná River post impoundment but did not change in the Baía and Ivinhema rivers. Changes in fish assemblages included a decrease in benthic invertivorous fish in the Paraná River and a shift in invertivorous fish assemblage structure in the Baía and Paraná rivers but not in the unimpounded Ivinhema River. Changes in water regime and water transparency, caused by impoundment, directly or indirectly impacted invertivorous fish assemblages. Alterations of fish assemblages following environmental changes have consequences over the entire ecosystem, including a potential decrease in the diversity of mechanisms for energy flow. We suggest that keeping existing unimpounded tributaries free of dams, engineering artificial floods, and intensive management of fish habitat within the floodplain may preserve native fish assemblages and help maintain functionality and ecosystem services in highly impounded rivers.

Lions as Bone Accumulators? Paleontological and Ecological Implications of a Modern Bone Assemblage from Olduvai Gorge.

PubMed

Arriaza, Mari Carmen; Domínguez-Rodrigo, Manuel; Yravedra, José; Baquedano, Enrique

2016-01-01

Analytic models have been developed to reconstruct early hominin behaviour, especially their subsistence patterns, revealed mainly through taphonomic analyses of archaeofaunal assemblages. Taphonomic research is used to discern which agents (carnivores, humans or both) generate the bone assemblages recovered at archaeological sites. Taphonomic frameworks developed during the last decades show that the only large-sized carnivores in African biomes able to create bone assemblages are leopards and hyenas. A carnivore-made bone assemblage located in the short-grassland ecological unit of the Serengeti (within Olduvai Gorge) was studied. Taphonomic analyses of this assemblage including skeletal part representation, bone density, breakage patterns and anatomical distribution of tooth marks, along with an ecological approach to the prey selection made by large carnivores of the Serengeti, were carried out. The results show that this bone assemblage may be the first lion-accumulated assemblage documented, although other carnivores (namely spotted hyenas) may have also intervened through postdepositional ravaging. This first faunal assemblage potentially created by lions constitutes a new framework for neotaphonomic studies. Since lions may accumulate carcasses under exceptional circumstances, such as those documented at the site reported here, this finding may have important consequences for interpretations of early archaeological and paleontological sites, which provide key information about human evolution.

Lions as Bone Accumulators? Paleontological and Ecological Implications of a Modern Bone Assemblage from Olduvai Gorge

PubMed Central

Arriaza, Mari Carmen; Domínguez-Rodrigo, Manuel; Yravedra, José; Baquedano, Enrique

2016-01-01

Analytic models have been developed to reconstruct early hominin behaviour, especially their subsistence patterns, revealed mainly through taphonomic analyses of archaeofaunal assemblages. Taphonomic research is used to discern which agents (carnivores, humans or both) generate the bone assemblages recovered at archaeological sites. Taphonomic frameworks developed during the last decades show that the only large-sized carnivores in African biomes able to create bone assemblages are leopards and hyenas. A carnivore-made bone assemblage located in the short-grassland ecological unit of the Serengeti (within Olduvai Gorge) was studied. Taphonomic analyses of this assemblage including skeletal part representation, bone density, breakage patterns and anatomical distribution of tooth marks, along with an ecological approach to the prey selection made by large carnivores of the Serengeti, were carried out. The results show that this bone assemblage may be the first lion-accumulated assemblage documented, although other carnivores (namely spotted hyenas) may have also intervened through postdepositional ravaging. This first faunal assemblage potentially created by lions constitutes a new framework for neotaphonomic studies. Since lions may accumulate carcasses under exceptional circumstances, such as those documented at the site reported here, this finding may have important consequences for interpretations of early archaeological and paleontological sites, which provide key information about human evolution. PMID:27144649

Utilization of GIS modeling in geoenvironmental studies of Qaroun Lake, El Fayoum Depression, Egypt

NASA Astrophysics Data System (ADS)

Attia, Abdelaal H.; El-Sayed, Salah Abdelwahab; El-Sabagh, Moustafa E.

2018-02-01

Qaroun Lake, the study area, is a natural protectorate located at the northern part of El Fayoum Depression, Egypt. An integrated approach including hydrochemistry, mineralogy of sediments and GIS analysis and modeling was conducted in order to determine the different geoenvironmental parameters affecting the lake environmental system. Forty two environmental water and sediment samples were collected from the lake and relevant drains in 2013. The water samples were analyzed for major ions and trace elements and the sediment ones were analyzed for clay and non-clay minerals. This study showed that the saline water of the lake (31490 < TDS < 45100 mg/l) typically is Na-Cl-SO4 water possessing primary salinity properties dominated by alkalies and strong acids. The order of ionic dominance was Na+ > Mg2+ > Ca2+ > K+ - Cl- > SO42- > HCO3- > CO32-. The water salt assemblages were KCl - NaCl - Na2SO4 - MgSO4 - CaSO4 - Ca(HCO3)2 reflecting a mixed water type. The contents of NaCl, Na2SO4 and MgSO4 salts were found to be fully controlled with the lake depths. The hydrogeochemical investigations revealed that the evaporation concentration is the primary process of the lake water evolution. The presence of trace elements in the lake water is essentially of allochtonous origin. The GIS-based maps indicated that the concentrations of Zn, Co, Mo, Pb, F and Cd elements in water had increased in the eastern part of the lake; meanwhile, the contents of NO3- ions had increased in the southwestern part indicating that these parts were the most vulnerable to the potential pollution with such elements. The XRD analysis revealed the existence of different mineral assemblages (quartz, kaolinite, goethite, calcite, halite, hematite, feldspar, gypsum, dolomite and saponite) in bottom sediments. The mineral concentrations varied greatly from place to another place along the lake and their distributions were asymmetric. The dominant minerals were the quartz and calcite. The mineralogical compositions of sediments were highly affected by the natural and man-mad activities. The most effective processes were the type of the water and solid materials coming from the northern geologic formations (by the northern winds) and from the eastern and southern drains. The land coverage change detection maps indicated the positive and negative changes in the lake area and its surroundings during the period of 1987-2000. The positive change in the area of the lake was about 12.63 km2 along the northern part of the lake, while the negative one was about 4.56 km2 in the southern parts. Based on the obtained results, some recommendations were presented to avoid the detrimental effects originated from the natural and human activities.

Dust fluxes linked to intensification of Prevailing Westerlies and Trade Winds stimulated Ethmodiscus rex giant diatom blooms in the southern Mariana Trench, western tropical Pacific at onset of the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Chen, D.; Luo, M.; Algeo, T. J.; Chen, L.

2017-12-01

The strontium (Sr) and neodymium (Nd) isotope compositions and clay-mineral assemblages of the detrital fraction of sediments in the southern Mariana Trench together with major- and trace-elements concentrations of bulk sediments have been determined to trace the sediment provenance and investigate the relationship between Asian dust input and blooms of the giant diatom Ethmodiscus rex. Enrichment of barium (Ba) in relative to upper continental crust (UCC) and low average Rb/K ratios in all study cores point to both hydrothermal and volcaniclastic inputs to the sediments. Both the Sr-Nd isotope compositions and the clay-mineral assemblages of the detrital fraction reflect a two-component mixing system consisting of Mariana arc volcaniclastics and eolian Asian dust. A decrease in smectite content and an increase in illite content just before formation of laminated diatom mats (LDMs) suggest a change in the source of the eolian dust from eastern Asian deserts (EADs) to central Asian deserts (CADs) at the onset of the Last Glacial Maximum (LGM). This observation suggests a causal linkage between atmospheric circulation patterns, the sources of eolian Asian dust, and marine productivity in the western Pacific region. We postulate that the shift to CAD-sourced dust may have played a greater role in promoting biological productivity in the oligotrophic western Pacific Ocean during the LGM than previously realized.

Changing Abundance of Magnetofossil Morphologies in Pelagic Red Clay Around Minamitorishima, Western North Pacific

NASA Astrophysics Data System (ADS)

Usui, Yoichi; Yamazaki, Toshitsugu; Saitoh, Masafumi

2017-12-01

Recent investigations have discovered an unexpected abundance of magnetofossils in oxic pelagic red clays. These have potential to serve as paleoenvironmental tracers in otherwise nonfossiliferous sediments. Here, we report on variations in the abundance and morphology of magnetofossils in red clay from the western North Pacific. Magnetic measurements revealed that magnetofossils dominate the magnetic mineral assemblage of the sediments. An endmember analysis of isothermal remanent magnetization acquisition curves, supplemented by an analysis of S ratios, indicates that the magnetic assemblage can be unmixed into three endmembers, two corresponding to magnetofossils and one to terrigenous magnetic minerals. Direct counting of magnetofossil morphologies under a transmission electron microscope shows that the two magnetofossil endmembers differentiate equant magnetofossils and bullet-shaped magnetofossils, respectively. The stratigraphic variation of the endmember contributions revealed that the equant magnetofossils are dominant for the most part, while an interval at around 7 m in core depth shows higher abundance of the bullet-shaped magnetofossils. This may reflect enhanced organic carbon flux to the sediments. The organic carbon content is low throughout the sediments, and it does not show any change corresponding to the increase of bullet-shaped magnetofossils, pointing at extensive remineralization of the organic carbon. On the basis of lithostratigraphic correlation to nearby drilling sites, we tentatively estimate the age of the bullet-shaped magnetofossil increase as sometime between ˜75 and 25 Ma. These results suggest that environmental information can be obtained from magnetofossils in pelagic red clay.

Oxygen Fugacity of Mare Basalts and the Lunar Mantle Application of a New Microscale Oxybarometer Based on the Valence State of Vanadium

NASA Technical Reports Server (NTRS)

Shearer, C. K.; Karner, J.; Papike, J. J.; Sutton, S. R.

2004-01-01

The ability to estimate oxygen fugacities for mare basalts and to extend these observations to the lunar mantle is limited using bulk analysis techniques based on buffering assemblages or the valence state of iron. These limitations are due to reequilibration of mineral assemblages at subsolidus conditions, deviations of mineral compositions from thermodynamic ideality, size requirements, and the limits of the iron valence at very low fO2. Still, these approaches have been helpful and indicate that mare basalts crystallized at fO2 between the iron-w stite buffer (IW) and the ilmenite breakdown reaction (ilmenite = rutile + iron). It has also been inferred from these estimates that the lunar mantle is also highly reduced lying at conditions below IW. Generally, these data cannot be used to determine if the mare basalts become increasingly reduced during transport from their mantle source and eruption at the lunar surface and if there are differences in fO2 among mare basalts or mantle sources. One promising approach to determining the fO2 of mare basalts is using the mean valence of vanadium (2+, 3+, 4+, 5+) determined on spots of a few micrometers in diameter using synchrotron x-ray absorption fine structure (XAFS) spectroscopy. The average valence state of V in basaltic glasses is a function of fO2, temperature, V coordination, and melt composition. Here, we report the initial results of this approach applied to lunar pyroclastic glasses.

Magma storage constrains by compositional zoning of plagioclase from dacites of the caldera forming eruptions of Vetrovoy Isthmus and Lvinaya Past’ Bay (Iturup Island, Kurile Islands)

NASA Astrophysics Data System (ADS)

Maksimovich, I. A.; Smirnov, S. Z.; Kotov, A. A.; Timina, T. Yu; Shevko, A. V.

2017-12-01

The Vetrovoy Isthmus and the Lvinaya Past’ Bay on the Iturup island (Kuril island arc) are the results of large Plinian eruptions of compositionally similar dacitic magmas. This study is devoted to a comparative analysis of the storage and crystallization conditions for magma reservoirs, which were a source of large-scale explosive eruptions. The plagioclase is most informative mineral in studying of the melt evolution. The studied plagioclases possess a complex zoning patterns, which are not typical for silicic rocks in island-arc systems. It was shown that increase of Ca in the plagioclase up to unusually high An95 is related to increase of H2O pressure in both volcanic magma chambers. The study revealed that minerals of the Vetrovoy Isthmus and Lvinaya Past’ crystallized from compositionally similar melts. Despite the compositional similarity of the melts, the phenocryst assemblage of the Lvinaya Past’ differs from the Vetrovoy Isthmus by the presence of the amphibole, which indicates that the pressure in the magmatic chamber exceeded 1-2 kbar at a 4-6 wt. % of H2O in the melt. The rocks of the Vetrovoy Isthmus do not contain amphibole phenocrysts, but melt and fluid inclusions assemblages in plagioclase demonstrate that the magma degassed in the course of evolution. This is an indication that the pressure did not exceed significantly 1-2 kbar.

Mineral-solution equilibria—III. The system Na 2OAl 2O 3SiO 2H 2OHCl

NASA Astrophysics Data System (ADS)

Popp, Robert K.; Frantz, John D.

1980-07-01

Chemical equilibrium between sodium-aluminum silicate minerals and chloride bearing fluid has been experimentally determined in the range 500-700°C at 1 kbar, using rapid-quench hydrothermal methods and two modifications of the Ag + AgCl acid buffer technique. The temperature dependence of the thermodynamic equilibrium constant ( K) for the reaction NaAlSi 3O 8 + HCl o = NaCl o + 1/2Al 2SiO 5, + 5/2SiO 2 + 1/2H 2O Albite Andalusite Qtz. K = (a NaCl o) /(a H 2O ) 1/2/(a HCl o) can be described by the following equation: log k = -4.437 + 5205.6/ T( K) The data from this study are consistent with experimental results reported by MONTOYA and HEMLEY (1975) for lower temperature equilibria defined by the assemblages albite + paragonite + quartz + fluid and paragonite + andalusite + quartz + fluid. Values of the equilibrium constants for the above reactions were used to estimate the difference in Gibbs free energy of formation between NaCl o and HCl o in the range 400-700°C and 1-2 kbar. Similar calculations using data from phase equilibrium studies reported in the literature were made to determine the difference in Gibbs free energy of formation between KCl o and HCl o. These data permit modelling of the chemical interaction between muscovite + kspar + paragonite + albite + quartz assemblages and chloride-bearing hydrothermal fluids.

Earthquakes as Precursors of Ductile Shear Zones in the Dry and Strong Lower Crust

NASA Astrophysics Data System (ADS)

Menegon, L.; Pennacchioni, G.; Malaspina, N.; Harris, K.; Wood, E.

2017-12-01

The rheology and the conditions for viscous flow of the dry granulite facies lower crust are still poorly understood. Viscous shearing in the dry and strong lower crust commonly localizes in pseudotachylyte veins, but the deformation mechanisms responsible for the weakening and viscous shear localization in pseudotachylytes are yet to be explored. We investigated examples of pristine and mylonitized pseudotachylytes in anorthosites from Nusfjord (Lofoten, Norway). Mutual overprinting relationships indicate that pristine and mylonitized pseudotachylytes are coeval and resulted from the cyclical interplay between brittle and viscous deformation. The stable mineral assemblage in the mylonitized pseudotachylytes consists of plagioclase, amphibole, clinopyroxene, quartz, biotite, ± garnet ± K-feldspar. Amphibole-plagioclase geothermobarometry and thermodynamic modeling indicate that pristine and mylonitized pseudotachylytes formed at 650-750°C and 0.7-0.8 GPa. Thermodynamic modeling indicates that a limited amount of H2O infiltration (0.20-0.40 wt. %) was necessary to stabilize the mineral assemblage in the mylonite. Diffusion creep is identified as the main deformation mechanisms in the mylonitized pseudotachylytes based on the lack of crystallographic preferred orientation in plagioclase, the high degree of phase mixing, and the synkinematic nucleation of amphiboles in dilatant sites. Extrapolation of flow laws to natural conditions indicates that mylonitized pseudotachylytes are up to 3 orders of magnitude weaker than anorthosites deforming by dislocation creep, thus highlighting the fundamental role of lower crustal earthquakes as agents of weakening in strong granulites.

ASTER, ALI and Hyperion sensors data for lithological mapping and ore minerals exploration.

PubMed

Beiranvand Pour, Amin; Hashim, Mazlan

2014-01-01

This paper provides a review of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Advanced Land Imager (ALI), and Hyperion data and applications of the data as a tool for ore minerals exploration, lithological and structural mapping. Spectral information extraction from ASTER, ALI, and Hyperion data has great ability to assist geologists in all disciplines to map the distribution and detect the rock units exposed at the earth's surface. The near coincidence of Earth Observing System (EOS)/Terra and Earth Observing One (EO-1) platforms allows acquiring ASTER, ALI, and Hyperion imagery of the same ground areas, resulting accurate information for geological mapping applications especially in the reconnaissance stages of hydrothermal copper and gold exploration, chromite, magnetite, massive sulfide and uranium ore deposits, mineral components of soils and structural interpretation at both regional and district scales. Shortwave length infrared and thermal infrared bands of ASTER have sufficient spectral resolution to map fundamental absorptions of hydroxyl mineral groups and silica and carbonate minerals for regional mapping purposes. Ferric-iron bearing minerals can be discriminated using six unique wavelength bands of ALI spanning the visible and near infrared. Hyperion visible and near infrared bands (0.4 to 1.0 μm) and shortwave infrared bands (0.9 to 2.5 μm) allowed to produce image maps of iron oxide minerals, hydroxyl-bearing minerals, sulfates and carbonates in association with hydrothermal alteration assemblages, respectively. The techniques and achievements reviewed in the present paper can further introduce the efficacy of ASTER, ALI, and Hyperion data for future mineral and lithological mapping and exploration of the porphyry copper, epithermal gold, chromite, magnetite, massive sulfide and uranium ore deposits especially in arid and semi-arid territory.

MN Carbonates in the Martian Meteorite Nakhla: Possible Evidence of Brine Evaporation

NASA Technical Reports Server (NTRS)

Bailey, J. V.; McKay, D. S.; Wentworth, S. J.

2003-01-01

The importance of secondary phases in martian meteorites lies in their potential to provide clues about the martian environments responsible for their formation. During this study, we analyzed a number of carbonate-bearing fracture surfaces from the Nakhla meteorite. Here we describe the physical and chemical properties of several manganese-calcium-rich siderites. Additionally, we describe a potential model for the formation and alteration of these carbonates, and we suggest constraints on the conditions responsible for their precipitation. Nakhla is an olivine-bearing clinopyroxenite with minor amounts of feldspar, FeS, and Fe oxides. Secondary mineral assemblages include vein filling clay with embedded iron oxides, a calcium sulfate, amorphous silica, chlorapatite, halite and carbonates. Bridges and Grady suggested that the carbonates in Nakhla formed from brine evaporation. Isotope studies of the Mn rich siderite are also consistent with formation from hydrothermal fluids with an upper T constraint of 170 C.

The theory of granular packings for coarse soils

NASA Astrophysics Data System (ADS)

Yanqui, Calixtro

2013-06-01

Coarse soils are substances made of grains of different shape, size and orientation. In this paper, new massive-measurable grain indexes are defined to develop a simple and systematic theory for the ideal packing of grains. First, a linear relationship between an assemblage of monodisperse spheres and an assemblage of polydisperse grains is deduced. Then, a general formula for the porosity of linearly ordered packings of spheres in contact is settled down by the appropriated choosing of eight neighboring spheres located at the vertices of the unit parallelepiped. The porosity of axisymmetric packings of grains, related to sand piles and axisymmetric compression tests, is proposed to be determined averaging the respective linear parameters. Since they can be tested experimentally, porosities of the densest state and the loosest state of a granular soil can be used to verify the accuracy of the present theory. Diagrams for these extreme quantities show a good agreement between the theoretical lines and the experimental data, no matter the dependency on the protocols and mineral composition.

Asteroid surface materials - Mineralogical characterizations and cosmological implications

NASA Technical Reports Server (NTRS)

Gaffey, M. J.; Mccord, T. B.

1977-01-01

The theoretical basis for the interpretation of diagnostic spectral features is examined and previous characterizations of asteroid surface materials are considered. A summary is provided of results reported by Gaffey and McCord (1977) who have utilized the most sophisticated interpretive techniques available to interpret the spectral reflectance data of about 65 asteroids for mineralogic and petrologic information. Cosmological implications related to the study of asteroid surface materials are also considered, taking into account source bodies for the meteorites, postaccretionary thermal history, significant factors of asteroid thermal history, and the Apollo and Amor asteroids. It is found that the asteroids exhibit surface materials made up of assemblages of meteoritic minerals. The relative abundance of meteorite types reaching the earth's surface is very different from the population of mineralogic types on asteroid surfaces. The earth-crossing or -approaching asteroids apparently derive from a restricted source region or population which is very strongly depleted in the C2-like assemblages that dominate the belt as a whole.

Fluid-Evaporation Records Preserved in Meridiani Rocks

NASA Technical Reports Server (NTRS)

Rao, M. N.; Nyquist, Laurence E.; Sutton, S. R.

2009-01-01

We have shown earlier that the high SO3/Cl ratios found in secondary mineral assemblages in shergottite GRIM glasses (Gas-Rich Impact-Melt) likely resulted from interactions of regolith materials with sulfate-rich (and Cl-poor) solutions. The low SO3/Cl ratios determined in secondary salts in nakhalite fracture-fillings presumably formed by rock interactions with chloride-rich (and SO4-poor) solutions near Mars surface. The SO3 and Cl abundances determined by APXS in abraded rocks (RAT) from Endurance, Fram and Eagle craters indicate that these salt assemblages likely formed by evaporative concentration of brine fluids at Meridiani. The SO3/Cl ratios in the abraded rocks are examined here, instead of their absolute abundances, because the abundance ratios might provide better guide-lines for tracking the evolution of evaporating fluids at Meridiani. The SO3/Cl ratios in these samples, in turn, might provide clues for the mobile element ratios of the altering fluids that infiltrated into the Meridiani rocks.

Coordinated mineralogical and isotopic analyses of a cosmic symplectite discovered in a comet 81P/Wild 2 sample

NASA Astrophysics Data System (ADS)

Nguyen, Ann N.; Berger, Eve L.; Nakamura-Messenger, Keiko; Messenger, Scott; Keller, Lindsay P.

2017-09-01

We have discovered in a Stardust mission terminal particle a unique mineralogical assemblage of symplectically intergrown pentlandite ((Fe,Ni)9S8) and nanocrystalline maghemite (γ-Fe2O3). Mineralogically similar cosmic symplectites (COS) have only been found in the primitive carbonaceous chondrite Acfer 094 and are believed to have formed by aqueous alteration. The O and S isotopic compositions of the Wild 2 COS are indistinguishable from terrestrial values. The metal and sulfide precursors were thus oxidized by an isotopically equilibrated aqueous reservoir either inside the snow line, in the Wild 2 comet, or in a larger Kuiper Belt object. Close association of the Stardust COS with a Kool mineral assemblage (kosmochloric Ca-rich pyroxene, FeO-rich olivine, and albite) that likely originated in the solar nebula suggests the COS precursors also had a nebular origin and were transported from the inner solar system to the comet-forming region after they were altered.