Science.gov

Sample records for hydrothermally altered zones

  1. Hydrothermal alteration in the Valles caldera ring fracture zone and core hole VC-1: evidence for multiple hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Woldegabriel, Giday

    1990-02-01

    Two types of hydrothermal mineral assemblages, kaolinite-alunite and sericite-chlorite were recognized in outcrop and core samples from the Jemez volcanic field, New Mexico. Active and fossil acid-sulfate hydrothermal activity, producing kaolinite-alunite alteration occurs along the caldera ring fracture and within the resurgent dome, whereas alterations of the chlorite-sericite type are mostly confined to subsurface rocks. K/Ar dates on illitic clays (<2 μm, 2-0.25 μm and <0.25 μm) separated from hydrothermally altered samples are used to document hydrothermal episodes in pre-caldera rocks of the Jemez volcanic field. The clay separates are illitic (75-95% illite layers) with K 2O contents of 8.24-8.95% in the core samples and 4.22-6.67% in the outcrops. Three episodes of hydrothermal alteration are now recognized in the Jemez Mountains region based on K/Ar age dates of illites. The earliest event (≤17-11 Ma, n=4) occurred within altered and illite-rich (≥90% illite layers) lowermost Paleozoic rocks in core hole VC-1 and may correlate with the inception of volcanism in the Jemez region (≤16.5 Ma). Illitic clays from altered andesite and rhyolite from the topographic rim of the Valles caldera were dated at 8.2 and 6.96 Ma, suggesting that a hydrothermal event related to the waning stages of the Keres Group volcanism (13-5.8 Ma) was responsible for the alteration. These dates overlap minimum ages obtained on slightly altered basalt (8.05 Ma) and andesite lava (7.07 Ma) from the southern and northwestern topographic rim of the Valles caldera, respectively. Ages of 1.21 and 1.34 Ma from illite-rich (≥90% illite layers), hydrothermally altered Paleozoic sandstone at a depth of 479 m in VC-1 suggest hydrothermal activity contemporaneous with the formation of the Toledo (1.45 Ma) and Valles (1.12 Ma) calderas. Ore minerals of sphalerite, chalcopyrite, galena, barite, and molybdenite mineralization occur in the lower half of VC-1 and are related to the Toledo

  2. Transient Hydrothermal Alteration in Fault Zones Cutting the Lower Oceanic Crust, Hess Deep Rift

    NASA Astrophysics Data System (ADS)

    McCaig, Andrew; Titarenko, Sofya; Cliff, Robert; Ivan, Savov; Adrian, Boyce

    2015-04-01

    IODP Expedition 345 drilled the first holes in the lower plutonic crust at a fast-spreading ridge, recovering primitive layered gabbros [1]. Alteration occurred as: 1) a largely static pseudomorphic alteration, predominantly in the greenschist and sub-greenschist facies with mainly talc and serpentine replacing olivine, and prehnite replacing plagioclase. Talc sometimes overprints serpentine mesh texture. 2) an overprinting metasomatic alteration, spatially related to cataclastic fault zones and macroscopic veins, dominated by prehnite and chlorite. Secondary clinopyroxene and epidote locally overprint the prehnite-chlorite assemblage, but the last events are veins of prehnite and zeolite. Metamorphosed dykes show chilled margins within the cataclasites, and are themselves affected by cataclastic deformation. Faults, dykes and overprinting alteration are all inferred to be related to the westward propagation of Cocos-Nazca spreading forming Hess Deep. 87Sr/86Sr ratios of small whole rock samples of cataclasites and dyke rocks are in the range 0.7037 - 0.7048, indicating alteration by seawater at moderate integrated fluxes. The highest values were in cataclasites overprinted by prehnite. Sampling of individual minerals has been undertaken using a microscope mounted drill, and shows that alteration is mainly affecting secondary minerals, with late prehnite veins ranging up to Sr isotope ratios of 0.7054. δ18O values range from +1 to + 6 per mil. Combined with metamorphic data this indicates alteration at temperatures between 200 and 400 °C. Secondary clinopyroxene and talc replacing serpentine are interpreted to indicate transient prograde hydrothermal events. Preliminary modelling using Comsol Multiphysics suggests that the temperatures of the overprinting alteration, as well as transient prograde events, could be achieved in a permeable fault slot cutting through crust 0.5 to 1 m.y. old. The prehnite-chlorite assemblage is predicted to be important in off

  3. Transient Hydrothermal Alteration In Fault Zones Cutting The Lower Oceanic Crust, Hess Deep Rift

    NASA Astrophysics Data System (ADS)

    McCaig, A. M.; Titarenko, S.; Cliff, R. A.; Savov, I. P.; Boyce, A.; Dutt, R.

    2014-12-01

    IODP Expedition 345 drilled the first holes in the lower plutonic crust at a fast-spreading ridge, recovering primitive layered gabbros [1]. Alteration occurred as: 1) a largely static pseudomorphic alteration, predominantly in the greenschist and sub-greenschist facies with mainly talc and serpentine replacing olivine, and prehnite replacing plagioclase. Talc sometimes overprints serpentine mesh texture. 2) an overprinting metasomatic alteration, spatially related to cataclastic fault zones and macroscopic veins, dominated by prehnite and chlorite. Secondary clinopyroxene and epidote locally overprint the prehnite-chlorite assemblage, but the last events are veins of prehnite and zeolite. Metamorphosed dykes show chilled margins within the cataclasites, and are themselves affected by cataclastic deformation. Faults, dykes and overprinting alteration are inferred to be related to the westward propagation of Cocos-Nazca spreading forming Hess Deep. 87Sr/86Sr ratios of small whole rock samples of cataclasites and dyke rocks are in the range 0.7037 - 0.7048, indicating alteration by seawater at moderate integrated fluxes. The highest values were in cataclasites overprinted by prehnite. Sampling of individual minerals has been undertaken using a microscope mounted drill, and shows that alteration is mainly affecting secondary minerals, with late prehnite veins ranging up to 0.7054. δ18O values range from +1 to + 6 per mil. Combined with metamorphic data this indicates alteration at temperatures between 200 and 400 °C. Secondary clinopyroxene and talc replacing serpentine are interpreted to indicate transient prograde hydrothermal events. Preliminary modelling using Comsol Multiphysics suggests that the temperatures of the overprinting alteration, as well as transient prograde events, could be achieved in a permeable fault slot cutting through crust 0.5 to 1 m.y. old. The prehnite-chlorite assemblage is predicted to be important in off-axis alteration, common in any

  4. A study on the prediction of ARD generation in the hydrothermal alteration zone, in Korea

    NASA Astrophysics Data System (ADS)

    Yim, G.; Cheong, Y.; Ji, S.; Park, S.

    2006-05-01

    The aim of this study was to predict acid rock drainage (ARD) generation in the hydrothermal alteration zone in the vicinity of the Busan, Korea. Recently serious water quality problems have been happening at the large- scale construction areas including the hydrothermal alteration zone. Therefore, it is important to predict the ARD vulnerability for sustainable development. To decrease the potential hazard due to the ARD in the proposed development areas, it is necessary to secure the database for the ARD in the potential vulnerable areas and to develop the most suitable ARD reduction technologies. The eighty-three samples were collected based on the grid net which was divided at a regular interval on the geological map to minimize spatial bias in the sampling process. The mineralogical analysis for the study area revealed that pyrite was present in the several areas of pyrophylite mineralization and andesite. Then samples were treated by static test such as Acid Base Accounting (ABA) and etc. pH1:2 and EC1:2 ranged from 2.27 to 7.9 and 1.89 to 648 ¥ìS/cm, respectively. The Maximum Potential Acidity (MPA) of samples ranged from 0.0009 to 71.298 kg H2SO4/t. Through the plot result of NAPP versus NAGpH, rock samples could be classified into two categories; Potential Acid Forming (PAF) rock and Non-Acid Forming (NAF) rock. Seven samples (eight percent of those tested) were classified as the PAF. Samples of rocks with high Sulfur content display the Net Acid Generation (NAGpH) values below 4.5. Results of the ABA tests indicated that the MPA value reached up to 71.30kg H2SO4/t and maximum Acid Neutralising Capacity (ANC) was 106.4kg H2SO4/t. The plot result of total Sulfur content and the ANC data, collected at the residential area, showed the possibility of the ARD occurrence in this area. The results of this study are expected to provide a fundamental and useful database to the future researches and actions related to the preservation of water quality and the

  5. Aerogeophysical measurements of collapse-prone hydrothermally altered zones at Mount Rainier volcano

    USGS Publications Warehouse

    Finn, C.A.; Sisson, T.W.; Deszcz-Pan, M.

    2001-01-01

    Hydrothermally altered rocks can weaken volcanoes, increasing the potential for catastrophic sector collapses that can lead to destructive debris flows1. Evaluating the hazards associated with such alteration is difficult because alteration has been mapped on few active volcanoes1-4 and the distribution and severity of subsurface alteration is largely unknown on any active volcano. At Mount Rainier volcano (Washington, USA), collapses of hydrothermally altered edifice flanks have generated numerous extensive debris flows5,6 and future collapses could threaten areas that are now densely populated7. Preliminary geological mapping and remote-sensing data indicated that exposed alteration is contained in a dyke-controlled belt trending east-west that passes through the volcano's summit3-5,8. But here we present helicopter-borne electromagnetic and magnetic data, combined with detailed geological mapping, to show that appreciable thicknesses of mostly buried hydrothermally altered rock lie mainly in the upper west flank of Mount Rainier. We identify this as the likely source for future large debris flows. But as negligible amounts of highly altered rock lie in the volcano's core, this might impede collapse retrogression and so limit the volumes and inundation areas of future debris flows. Our results demonstrate that high-resolution geophysical and geological observations can yield unprecedented views of the three-dimensional distribution of altered rock.

  6. Chapter C: Hydrothermal Enrichment of Gallium in Zones of Advanced Argillic Alteration-Examples from the Paradise Peak and McDermitt Ore Deposits, Nevada

    USGS Publications Warehouse

    Rytuba, James J.; John, David A.; Foster, Andrea; Ludington, Steven D.; Kotlyar, Boris

    2003-01-01

    Gallium is produced as a byproduct from bauxite and zinc sulfide ores and rarely from primary Ga ores. High Ga contents (>60 ppm) can occur in zones of advanced argillic alteration consisting of alunite+kaolinite+quartz associated with quartz-alunite (high sulfidation Au-Ag) deposits. In a magmatic-hydrothermal environment, the zones of advanced argillic alteration associated with quartz-alunite (high sulfidation) Au-Ag deposits have the highest Ga contents (max 120 ppm). In these Au deposits, Ga is enriched in the zone of alunite+kaolinite alteration and depleted in the zone of quartz-rich alteration within acid-leached rocks. Peripheral zones of argillic alteration have Ga contents and Al/Ga ratios similar to those in unaltered volcanic rocks. The zones of advanced argillic alteration that formed in a steam-heated environment in association with hot-spring-type Hg-Au deposits are not Ga enriched, and residual silicified zones have very low Ga contents. The McDermitt Hg and Paradise Peak Au-Hg deposits, Nev., have zones of advanced argillic alteration that are Ga enriched. At the Paradise Peak Au-Hg deposits, Ga is enriched in the zone of alunite+jarosite alteration that formed in a magmatic-hydrothermal environment. Ga is depleted in the zone of opal+alunite alteration formed in a steam-heated environment, in residual silicified zones formed in a magmatic-hydrothermal environment, and in zones of supergene jarosite alteration. At the McDermitt Hg deposit, Ga is enriched in the zone of alunite+kaolinite alteration below the zone of adularia-quartz alteration that coincides with the Hg ore body. The spatial relation of Ga enrichment to alunite-kaolinite alteration suggests that formation in a magmatic-hydrothermal environment. X-ray-absorption spectra of Ga-enriched samples from the McDermitt Hg deposit are similar to that of gallium sulfate and support the association of Ga enrichment with alunite alteration.

  7. Mineral types of hydrothermal alteration zones in the Dukat ore field and their relationships to leucogranite and epithermal gold-silver ore, northeastern Russia

    NASA Astrophysics Data System (ADS)

    Filimonova, L. G.; Trubkin, N. V.; Chugaev, A. V.

    2014-05-01

    The paper considers the localization of potassic and propylitic hydrothermal alteration zones in the domal volcanic-plutonic structure controlling the position of the Dukat ore field with the eponymous unique epithermal Au-Ag deposit. Comprehensive mineralogical and geochemical data on rocks and minerals in hydrothermal alteration zones and associated intrusions have shown that quartz-jarosite-sericite, quartz-pyrite-sericite, and quartz-adularia-chlorite alterations were formed with the participation of fluid flows related to a fingerlike projection of a high-K leucogranite porphyry intrusion with large phenocrysts. These hydrothermal alterations developed in the rifted graben under conditions of divergent plate boundaries, whereas quartz-clinozoisite-calcite, epidote-chlorite, and garnet-calcite-chlorite alterations were linked to K-Na leucogranite intrusive bodies and developed under conditions of convergent plate boundaries reactivated as a result of formation of the marginal Okhotsk-Chukotka volcanic belt. Phase separation and coagulation of specific portions of ascending fluids resulted in the formation and stabilization of small-sized particles of native silver and other ore components, which enabled involvement in flows of secondary geothermal solutions and ore-forming fluids. The Sr, Nd, and Pb isotopic compositions of rocks and minerals from the hydrothermal alteration zones, associated intrusions, and economic orebodies at the Dukat deposit indicate that their components have been derived from the juvenile continental crust, which was altered in pre-Cretaceous periods of endogenic activity. The components of gangue minerals of potassic and propylitic hydrothertmal alterations and associated intrusions have been taken from deep sources differing in 87Sr/86Sr and 143Nd/144Nd at similar U/Pb and Th/Pb ratios. Chalcophile lead in products of hydrothermal activity and melanocratic inclusions in leucogranite has been taken from regions with elevated U/Pb and

  8. Use of wireline logs at Cerro Prieto in identification of the distribution of hydrothermally altered zones and dike locations, and their correlation with reservoir temperatures

    SciTech Connect

    Seamount, D.T. Jr.; Elders, W.A.

    1981-01-01

    Downhole electrical and gamma-gamma density logs from nine wells weere studed and these wireline log parameters with petrologic, temperature, and petrophysical data were correlated. Here, wells M-43, T-366, and M-107 are discussed in detail as typical cases. Log data for shales show good correlation with four zones of hydrothermal alteration previously recognized on the basis of characteristic mineral assemblages and temperatures. These zones are the unaltered montmorillonite zone (< 150/sup 0/C), the illite zone (150/sup 0/C to 230/sup 0/C to 245/sup 0/C), the chlorite zone (235/sup 0/C to 300/sup 0/C, equivalent to the calc-silicate I zone in sands), and the feldspar zone (> 300/sup 0/C, equivalent to the calc-silicate II zone in sands),

  9. 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., Jr.; 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.

  10. Identification and characterization of hydrothermally altered zones in granite by combining synthetic clay content logs with magnetic mineralogical investigations of drilled rock cuttings

    NASA Astrophysics Data System (ADS)

    Meller, Carola; Kontny, Agnes; Kohl, Thomas

    2014-10-01

    Clay minerals as products of hydrothermal alteration significantly influence the hydraulic and mechanical properties of crystalline rock. Therefore, the localization and characterization of alteration zones by downhole measurements is a great challenge for the development of geothermal reservoirs. The magnetite bearing granite of the geothermal site in Soultz-sous-Forêts (France) experienced hydrothermal alteration during several tectonic events and clay mineral formation is especially observed in alteration halos around fracture zones. During the formation of clay minerals, magnetite was oxidized into hematite, which significantly reduces the magnetic susceptibility of the granite from ferrimagnetic to mostly paramagnetic values. The aim of this study was to find out if there exists a correlation between synthetic clay content logs (SCCLs) and measurements of magnetic susceptibility on cuttings in the granite in order to characterize their alteration mineralogy. Such a correlation has been proven for core samples of the EPS1 reference well. SCCLs were created from gamma ray and fracture density logs using a neural network. These logs can localize altered fracture zones in the GPK1-4 wells, where no core material is available. Mass susceptibility from 261 cutting samples of the wells GPK1-GPK4 was compared with the neural network derived synthetic logs. We applied a combination of temperature dependent magnetic susceptibility measurements with optical and electron microscopy, and energy dispersive X-ray spectroscopy to discriminate different stages of alteration. We found, that also in the granite cuttings an increasing alteration grade is characterized by an advancing oxidation of magnetite into hematite and a reduction of magnetic susceptibility. A challenge to face for the interpretation of magnetic susceptibility data from cuttings material is that extreme alteration grades can also display increased susceptibilities due to the formation of secondary magnetite

  11. Gamma ray spectrometry for recognition of hydrothermal alteration zones related to a low sulfidation epithermal gold mineralization (eastern Pontides, NE Türkiye)

    NASA Astrophysics Data System (ADS)

    Maden, Nafiz; Akaryalı, Enver

    2015-11-01

    This study presents an interpretation of radiospectrometric and magnetic data of Arzular mineralization site, which is one of the best examples for epithermal gold deposits located in the southern zone of the Eastern Pontides (NE Türkiye). Potassium is generally the most useful pathfinder element for gold mineralization zones because of its high level in altered rock surrounding the deposits. Where gold is hosted within quartz veins, typically the vein is low in the radioelements, but the hydrothermally altered host rocks will usually have a distinct radioelement signature useful for exploration. In this study, magnetic, susceptibility and radiospectrometric survey data radiometric signatures associated with the host rocks favorable for the mineralization, enhancing techniques such as the ratio maps as well as potassium (%K), equivalent thorium (eTh ppm) and equivalent uranium (eU ppm) maps were utilized. Our analysis showed that the gold mineralization associated with the alteration is significantly related to increase in potassium, due to adularia, a low T K-feldspar, and decreases in uranium and thorium due to the hydrothermal alteration and magmatic intrusion processes during the regional tectonic activities.

  12. The hydrothermal alteration of cooling lava domes

    NASA Astrophysics Data System (ADS)

    Ball, Jessica L.; Stauffer, Philip H.; Calder, Eliza S.; Valentine, Greg A.

    2015-12-01

    Hydrothermal alteration is a recognized cause of volcanic instability and edifice collapse, including that of lava domes or dome complexes. Alteration by percolating fluids transforms primary minerals in dome lavas to weaker secondary products such as clay minerals; moreover, secondary mineral precipitation can affect the porosity and permeability of dome lithologies. The location and intensity of alteration in a dome depend heavily on fluid pathways and availability in conjunction with heat supply. Here we investigate postemplacement lava dome weakening by hydrothermal alteration using a finite element numerical model of water migration in simplified dome geometries. This is combined with the rock alteration index (RAI) to predict zones of alteration and secondary mineral precipitation. Our results show that alteration potential is highest at the interface between the hot core of a lava dome and its clastic talus carapace. The longest lived alteration potential fields occur in domes with persistent heat sources and permeabilities that allow sufficient infiltration of water for alteration processes, but not so much that domes cool quickly. This leads us to conclude that alteration-induced collapses are most likely to be shallow seated and originate in the talus or talus/core interface in domes which have a sustained supply of magmatic heat. Mineral precipitation at these zones of permeability contrast could create barriers to fluid flow, potentially causing gas pressurization which might promote deeper seated and larger volume collapses. This study contributes to our knowledge of how hydrothermal alteration can affect lava domes and provides constraints on potential sites for alteration-related collapses, which can be used to target hazard monitoring.

  13. The use of high resolution ground and airborne magnetic surveys to evaluate the geometry of hydrothermal alteration zones over volcanic provinces (Invited)

    NASA Astrophysics Data System (ADS)

    Bouligand, C.; Glen, J. M.

    2013-12-01

    Geophysical methods can provide critical constraints on the distribution and volume of hydrothermal alteration, important parameters in understanding the evolution of geothermal systems. Because hydrothermal alteration modifies the magnetic properties of the volcanic substratum, magnetic surveys can be used to provide constraints on the distribution of hydrothermal alteration at depth. Using Yellowstone caldera as an example, we show that both ground and airborne magnetic surveys can be used to map and assess the volume of hydrothermal alteration. Ground magnetic surveys over unaltered volcanic terranes display high-amplitude, short-wavelength anomalies, in contrast to smooth, subdued magnetic anomalies over volcanic substrata demagnetized by hydrothermal alteration. We use this contrast to map areas of hydrothermal alteration in detail. Inverse methods applied to high-resolution airborne and ground magnetic data can be used to create three-dimensional models of the distribution of magnetization and thus illuminate the geometry of hydrothermal alteration. Because of the non-uniqueness of potential fields, the construction of inverse models requires simplifying assumptions on the distribution of magnetization, knowledge of induced and remanent magnetization of fresh and altered geological units, and detailed geological and geophysical data. Within the three hydrothermal sites that we investigated in Yellowstone National Park, subdued short-wavelength signal indicates pervasive demagnetization (alteration) of the shallow substratum that extends over larger areas than initially mapped by geology. These data also reveal that the largest degree of demagnetization (alteration) and maximum thicknesses of demagnetized (altered) substratum, reaching a few hundred meters, are associated with hydrothermal vents and with superficial hydrothermal alteration. Our three dimensional models of magnetization provide estimates of the volume of buried hydrothermal alteration ranging

  14. Complex hydrothermal alteration and illite K-Ar ages in Upper Visean molasse sediments and magmatic rocks of the Variscan Badenweiler-Lenzkirch suture zone, Black Forest, Germany

    NASA Astrophysics Data System (ADS)

    Brockamp, Olaf; Schlegel, Andreas; Wemmer, Klaus

    2015-04-01

    Post-collisional Upper Visean molasse sediments and magmatic rocks of the Badenweiler-Lenzkirch Zone reveal by microscopy of thin sections different degrees of hydrothermal illitization of feldspar and mica particles, and XRD, IR and XRF data of the <2 µm fractions show illitic material as the dominant clay mineral consisting of a mixture of 1M and 2M1 polytypes. Moreover, small amounts of illite/smectite mixed-layer minerals of R1-ordering are proved in the granites. In the separates, two illite mixing lines with different Fe + Mg contents are verified between authigenic illite from feldspar alteration and detrital illite in the molasse sediments, as well as between authigenic illite from feldspar alteration and altered mica flakes in the granites. Fe-rich detrital chlorite is present within the molasse sediments, while mixtures of high aluminous Fe-poor dioctahedral/di-trioctahedral chlorite with randomly interstratified chlorite/smectite mixed-layer minerals are formed from feldspar alteration in the granites. Illite K-Ar dating of the <2 and <0.63 µm fractions yields hydrothermal illitization of feldspar and partial resetting of the K-Ar system of detrital illite and mica flakes in the molasse sediments at ≥200 °C during Upper Permian to Middle Triassic times, while the granites in the eastern part of the study area were not altered contemporaneously. In contrast, hydrothermal activity at ≤200 °C during Upper Jurassic to Lower Cretaceous times occurred in the granites, whereas these temperatures were too low for resetting the older `Permo-Triassic' illite K-Ar ages in the molasse rocks. Within both K-Ar age clusters, the data are seen to decrease with grain size and portion of illite 2M1 polytype. The alteration phenomena indicate multiple hydrothermal episodes in the study area, and they match those from the Central and Western European crust as fluid supply was controlled geodynamically by episodic break up of Pangea.

  15. Hydrothermal alteration in oceanic ridge volcanics: A detailed study at the Galapagos Fossil Hydrothermal Field

    SciTech Connect

    Ridley, W.I.; Perfit, M.R.; Smith, M.F.; Jonasson, I.R.

    1994-06-01

    The Galapagos Fossil Hydrothermal Field is composed of altered oceanic crust and extinct hydrothermal vents within the eastern Galapagos Rift between 85{degree}49 feet W and 85{degree} 55 feet W. The discharge zone of the hydrothermal system is revealed along scarps, thus providing an opportunity to examine the uppermost mineralized, and highly altered interior parts of the crust. Altered rocks collected in situ by the submersible ALVIN show complex concentric alteration zones. Microsamples of individual zones have been analysed for major/minor, trace elements, and strontium isotopes in order to describe the complex compositional details of the hydrothermal alteration. Interlayered chlorite-smectite and chlorite with disequilibrium compositions dominate the secondary mineralogy as replacement phases of primary glass and acicular pyroxene. Phenocrysts and matrix grains of plagioclase are unaffected during alteration. Using a modification of the Gresens` equation we demonstrate that the trivalent rare earth elements (REEs) are relatively immobile, and calculate degrees of enrichment and depletion in other elements. Strontium isotopic ratios increase as Sr concentrations decrease from least-altered cores to most-altered rims and cross-cutting veins in individual samples, and can be modeled by open system behaviour under low fluid-rock ratio (<10) conditions following a period of lower-temperature weathering of volcanics within the rift zone. The complex patterns of element enrichment and depletion and strontium isotope variations indicate mixing between pristine seawater and ascending hot fluids to produce a compositional spectrum of fluids. If, as suggested here, the discharge zone alteration occurred under relatively low fluid-rock ratios, then this shallow region must play an important role in determining the exit composition of vent fluids in marine hydrothermal systems. 50 refs., 10 figs., 4 tabs.

  16. Hydrothermal alteration in oceanic ridge volcanics: A detailed study at the Galapagos Fossil Hydrothermal Field

    USGS Publications Warehouse

    Ridley, W.I.; Perfit, M.R.; Josnasson, I.R.; Smith, M.F.

    1994-01-01

    The Galapagos Fossil Hydrothermal Field is composed of altered oceanic crust and extinct hydrothermal vents within the eastern Galapagos Rift between 85??49???W and 85??55???W. The discharge zone of the hydrothermal system is revealed along scarps, thus providing an opportunity to examine the uppermost mineralized, and highly altered interior parts of the crust. Altered rocks collected in situ by the submersible ALVIN show complex concentric alteration zones. Microsamples of individual zones have been analysed for major/minor, trace elements, and strontium isotopes in order to describe the complex compositional details of the hydrothermal alteration. Interlayered chlorite-smectite and chlorite with disequilibrium compositions dominate the secondary mineralogy as replacement phases of primary glass and acicular pyroxene. Phenocrysts and matrix grains of plagioclase are unaffected during alteration. Using a modification of the Gresens' equation we demonstrate that the trivalent rare earth elements (REEs) are relatively immobile, and calculate degrees of enrichment and depletion in other elements. Strontium isotopic ratios increase as Sr concentrations decrease from least-altered cores to most-altered rims and cross-cutting veins in individual samples, and can be modeled by open system behaviour under low fluid-rock ratio (< 10) conditions following a period of lower-temperature weathering of volcanics within the rift zone. The complex patterns of element enrichment and depletion and strontium isotope variations indicate mixing between pristine seawater and ascending hot fluids to produce a compositional spectrum of fluids. The precipitation of base-metal sulfides beneath the seafloor is probably a result of fluid mixing and cooling. If, as suggested here, the discharge zone alteration occurred under relatively low fluid-rock ratios, then this shallow region must play an important role in determining the exit composition of vent fluids in marine hydrothermal systems

  17. Hydrothermal alteration of a rhyolitic hyaloclastite from Ponza Island, Italy

    NASA Astrophysics Data System (ADS)

    Ylagan, Robert F.; Altaner, Stephen P.; Pozzuoli, Antonio

    1996-12-01

    A rhyolitic hyaloclastite from Ponza island, Italy, has been hydrothermally altered producing four distinct alteration zones based on XRD and field textures: (1) non-pervasive argillic zone; (2) propylitic zone; (3) silicic zone; and (4) sericitic zone. The unaltered hyaloclastite is a volcanic breccia with clasts of vesiculated obsidian in a matrix of predominantly pumice lapilli. Incomplete alteration of the hyaloclastite resulted in the non pervasive argillic zone, characterized by smectite and disordered opal-CT. Obsidian clasts, some pumice lapilli, and pyrogenic plagioclase and biotite are unaltered. Smectite has an irregular flakey morphology, although euhedral particles are occasionally observed. The propylitic zone is characterized by mixed-layer illite/smectite (I/S) with 10 to 85% illite (I), mordenite, opal-C and authigenic K-feldspar (akspar). The matrix of the hyaloclastite is completely altered and obsidian clasts are silicified; however, plagioclase and biotite phenocrysts remain unaltered. Flakey I/S replaces pumice, and mordenite, akspar and silica line and fill pores. I/S particles are composed predominantly of subequant plates and euhedral laths. The silicic zone is characterized by highly illitic I/S with ≥ 90% I, quartz, akspar and occasional albite. In this zone the matrix and clasts are completely altered, and pyrogenic plagioclase shows significant alteration. Illitic I/S has a euhedral lath-like morphology. In the sericitic zone the hyaloclastite altered primarily to illitic I/S with ≥ 66% I, quartz, and minor akspar and pyrite. Clay minerals completely replace pyrogenic feldspars and little evidence remains of the original hyaloclastite texture. Unlike other zones, illitic I/S is fibrous and pure illite samples are composed of euhedral laths and hexagonal plates. The temperatures of hydrothermal alteration likely ranged from 30 to 90 °C for the argillic zone, from 110 to 160 °C for the propylitic zone, from 160 to 270 °C for the

  18. Precipitation of uraninite in chlorite-bearing veins of the hydrothermal alteration zone (argile de pile) of the natural nuclear reactor at Bangombe, Republic of Gabon

    SciTech Connect

    Eberly, P.; Ewing, R.; Janeczek, J.

    1995-12-31

    This paper describes the mineralogy of a phyllosilicate/uraninite/galena-bearing vein located within the hydrothermal alteration halo associated with the Bangombe reactor. Phyllosilicates within the vein include a trioctahedral Al-Mg-Fe chlorite (ripidolite), Al-rich clay (kaolinite and/or donbassite) and illite. Textural relations obtained by backscattered-electron imaging suggest that ripidolite crystallized first among the sheet silicates. Uraninite is spatially associated with ripidolite and probably precipitated at a later time. While energy-dispersive X-ray analyses suggest that the uranium phase is predominantly uraninite, coffinite or other phases may also be present.

  19. Evidence for hydrothermal alteration in the Hellas ejecta

    NASA Astrophysics Data System (ADS)

    Noe Dobrea, E. Z.; Swayze, G. A.

    2011-12-01

    We have analyzed data from MRO/CRISM, HiRISE, and CTX to study the massifs in the NW Hellas region. The Hellas basin is thought to have formed during the late heavy bombardment [Acuña et al. 1999] as a consequence of a massive impact. The impact not only excavated rocks from the deep stratigraphy, but it also deposited enough energy into the ejecta to support hydrothermal conditions [Newsom 1980]. Spectral observations of the mineralogy of the martian highlands north of Hellas suggest that the region was experiencing aqueous activity during that era [Pelkey et al. 2007]. Therefore, spectroscopic studies of the well-preserved massifs that form the rim and ejecta in northwest Hellas have the potential to reveal zones of hydrothermal alteration. Additionally, studies of the deep crustal rocks excavated as part of the ejecta are of particular relevance in light of recent discoveries of carbonate-bearing rocks exposed in complex craters on Mars [Michalski and Niles 2010; Wray et al. 2011]. Our analyses reveal outcrops in the massifs where evidence for products of hydrothermal alteration are observed. In particular, we find evidence for smectites, prehnite, chlorite, and illite exposed in these outcrops (Fig 1). The spectra of these altered units also exhibit a strong, broad concave-up absorption in the 1-1.5 μm region, consistent with the presence of Fe2+ in olivine, suggesting that only partial alteration has occurred. The mineralogy of hydrothermal alteration products is a function of the original composition of the host rock; the temperature, chemistry, and pH of the water; and the overburden pressure [DeRudder and. Beck 1963; Morris et al. 2001; 2003; Brown et al. 2010; Inoue et al. 2010]. On Earth, prehnite can form via low-grade metamorphism, where it occurs as part of the prehnite-pumpellyite metamorphic facies [Blatt and Tracy 1995], or as a product of the low-temperature (100-350°C) hydrothermal alteration of mafic rocks [Freedman et al. 2009; Marks et al

  20. Aluminum speeds up the hydrothermal alteration of olivine

    NASA Astrophysics Data System (ADS)

    Andreani, Muriel; Daniel, Isabelle; Pollet-Villard, Marion

    2014-05-01

    The reactivity of ultramafic rocks toward hydrothermal fluids controls chemical fluxes at the interface between the internal and external reservoirs of silicate planets. On Earth, hydration of ultramafic rocks is ubiquitous and operates from deep subduction zones to shallow lithospheric environments where it considerably affects the physical and chemical properties of rocks and can interact with the biosphere. This process also has key emerging societal implications, such as the production of hydrogen as a source of carbon-free energy. To date, the chemical model systems used to reproduce olivine hydrothermal alteration lead to the formation of serpentine with sluggish reaction rates. Although aluminum is common in geological environments and in hydrothermal systems in particular, its role in serpentinization or olivine dissolution has not been investigated under hydrothermal conditions. Nevertheless, abundant Al supply is expected in fluids released from dehydration of metapelites in subduction zones as well as during the hydrothermal alteration of gabbros at mid-ocean ridges. Aluminum was also abundant in primitive environments of both the Earth and Mars, stored in either Al-rich minerals like plagioclase or Al-enriched ultramafic lavas. We have investigated the role of Al on the hydrothermal alteration of olivine in a series of experiments performed in a low-pressure diamond anvil cell while following the reaction progress in situ by optical imaging and Raman spectroscopy. Experiments were run for 4.5 to 7.5 days with two olivine grains reacted in saline water (0.5 molal NaCl) at 200°C and 300°C, and P=200 MPa. After two days, olivine crystals were fully transformed to an aluminous serpentine, also enriched in iron. The presence of Al in the hydrothermal fluid increases the rate of olivine serpentinization by more than one order of magnitude by enhancing olivine solubility and serpentine precipitation. The mechanism responsible for this increased solubility

  1. Biogeochemistry of hydrothermally and adjacent non-altered soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    As a field/lab project, students in the Soil Biogeochemistry class of the University of Nevada, Reno described and characterized seven pedons, developed in hydrothermally and adjacent non-hydrothermally altered andesitic parent material near Reno, NV. Hydrothermally altered soils had considerably lo...

  2. Distribution of buried hydrothermal alteration deduced from high-resolution magnetic surveys in Yellowstone National Park

    NASA Astrophysics Data System (ADS)

    Bouligand, Claire; Glen, Jonathan M. G.; Blakely, Richard J.

    2014-04-01

    Yellowstone National Park (YNP) displays numerous and extensive hydrothermal features. Although hydrothermal alteration in YNP has been extensively studied, the volume, geometry, and type of rock alteration at depth remain poorly constrained. In this study, we use high-resolution airborne and ground magnetic surveys and measurements of remanent and induced magnetization of field and drill core samples to provide constraints on the geometry of hydrothermal alteration within the subsurface of three thermal areas in YNP (Firehole River, Smoke Jumper Hot Springs, and Norris Geyser Basin). We observe that hydrothermal zones from both liquid- and vapor-dominated systems coincide with magnetic lows observed in aeromagnetic surveys and with a decrease of the amplitude of short-wavelength anomalies seen in ground magnetic surveys. This suggests a strong demagnetization of both the shallow and deep substratum within these areas associated with the removal of magnetic minerals by hydrothermal alteration processes. Such demagnetization is confirmed by measurements of rock samples from hydrothermal areas which display significantly decreased total magnetization. A pronounced negative anomaly is observed over the Lone Star Geyser and suggests a significant demagnetization of the substratum associated with areas displaying large-scale fluid flow. The ground and airborne magnetic surveys are used to evaluate the distribution of magnetization in the subsurface. This study shows that significant demagnetization occurs over a thickness of at least a few hundred meters in hydrothermal areas at YNP and that the maximum degree or maximum thickness of demagnetization correlates closely with the location of hydrothermal activity and mapped alteration.

  3. Hydraulic characterization of hydrothermally altered Nopal tuff

    SciTech Connect

    Green, R.T.; Meyer-James, K.A.; Rice, G.

    1995-07-01

    Understanding the mechanics of variably saturated flow in fractured-porous media is of fundamental importance to evaluating the isolation performance of the proposed high-level radioactive waste repository for the Yucca Mountain site. Developing that understanding must be founded on the analysis and interpretation of laboratory and field data. This report presents an analysis of the unsaturated hydraulic properties of tuff cores from the Pena Blanca natural analog site in Mexico. The basic intent of the analysis was to examine possible trends and relationships between the hydraulic properties and the degree of hydrothermal alteration exhibited by the tuff samples. These data were used in flow simulations to evaluate the significance of a particular conceptual (composite) model and of distinct hydraulic properties on the rate and nature of water flow.

  4. 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

    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.

  5. Application of hyperspectral infrared analysis of hydrothermal alteration on Earth and Mars.

    PubMed

    Thomas, Matilda; Walter, Malcolm R

    2002-01-01

    An integrated analysis of both airborne and field short-wave infrared hyperspectral measurements was used in conjunction with conventional field mapping techniques to map hydrothermal alteration in the central portion of the Mount Painter Inlier in the Flinders Ranges, South Australia. The airborne hyperspectral data show the spatial distribution of spectrally distinct minerals occurring as primary minerals and as weathering and alteration products. Field spectral measurements, taken with a portable infrared mineral analyzer spectrometer and supported by thin-section analyses, were used to verify the mineral maps and enhance the level of information obtainable from the airborne data. Hydrothermal alteration zones were identified and mapped separately from the background weathering signals. A main zone of alteration, coinciding with the Paralana Fault zone, was recognized, and found to contain kaolinite, muscovite, biotite, and K-feldspar. A small spectral variation associated with a ring-like feature around Mount Painter was tentatively determined to be halloysite and interpreted to represent a separate hydrothermal fluid and fluid source, and probably a separate system. The older parts of the alteration system are tentatively dated as Permo-Carboniferous. The remote sensing of alteration at Mount Painter confirms that hyperspectral imaging techniques can produce accurate mineralogical maps with significant details that can be used to identify and map hydrothermal activity. Application of hyperspectral surveys such as that conducted at Mount Painter would be likely to provide similar detail about putative hydrothermal deposits on Mars. PMID:12530243

  6. Conodont color and textural alteration: an index to regional metamorphism, contact metamorphism, and hydrothermal alteration.

    USGS Publications Warehouse

    Rejebian, V.A.; Harris, A.G.; Huebner, J.S.

    1987-01-01

    Experimental and field data are used to extend the utility of conodonts as semi-quantitative thermal indices into the regimes of regional and contact metamorphism, as well as hydrothermal alteration. These experiments approximate the type of Colour Alteration Indices mixture characteristically found in conodonts recovered from hydrothermally altered rocks. These data indicate that CAI values of 6 to 8 cannot be used to assess precise temperatures of hydrothermally altered rocks but may serve as useful indicators of potential mineralization. - from Authors

  7. Lithology and hydrothermal alteration determination from well logs for the Cerro Prieto Wells, Mexico

    SciTech Connect

    Ershaghi, I.; Ghaemian, S.; Abdassah, D.

    1981-10-01

    The purpose of this study is to examine the characteristics of geophysical well logs against the sand-shale series of the sedimentary column of the Cerro Prieto Geothermal Field, Mexico. The study shows that the changes in mineralogy of the rocks because of hydrothermal alteration are not easily detectable on the existing logs. However, if the behavior of clay minerals alone is monitored, the onset of the hydrothermally altered zones may be estimated from the well logs. The effective concentration of clay-exchange cations, Q/sub v/, is computed using the data available from conventional well logs. Zones indicating the disappearance of low-temperature clays are considered hydrothermally altered formations with moderate to high-permeability and temperature, and suitable for completion purposes.

  8. A Palaeoproterozoic multi-stage hydrothermal alteration system at Nalunaq gold deposit, South Greenland

    NASA Astrophysics Data System (ADS)

    Bell, Robin-Marie; Kolb, Jochen; Waight, Tod Earle; Bagas, Leon; Thomsen, Tonny B.

    2016-07-01

    Nalunaq is an orogenic, high gold grade deposit situated on the Nanortalik Peninsula, South Greenland. Mineralisation is hosted in shear zone-controlled quartz veins, located in fine- and medium-grained amphibolite. The deposit was the site of Greenland's only operating metalliferous mine until its closure in 2014, having produced 10.67 t of gold. This study uses a combination of field investigation, petrography and U/Pb zircon and titanite geochronology to define a multi-stage hydrothermal alteration system at Nalunaq. A clinopyroxene-plagioclase-garnet(-sulphide) alteration zone (CPGZ) developed in the Nanortalik Peninsula, close to regional peak metamorphism and prior to gold-quartz vein formation. The ca. 1783-1762-Ma gold-quartz veins are hosted in reactivated shear zones with a hydrothermal alteration halo of biotite-arsenopyrite-sericite-actinolite-pyrrhotite(-chlorite-plagioclase-löllingite-tourmaline-titanite), which is best developed in areas of exceptionally high gold grades. Aplite dykes dated to ca. 1762 Ma cross-cut the gold-quartz veins, providing a minimum age for mineralisation. A hydrothermal calcite-titanite alteration assemblage is dated to ca. 1766 Ma; however, this alteration is highly isolated, and as a result, its field relationships are poorly constrained. The hydrothermal alteration and mineralisation is cut by several generations of ca. 1745-Ma biotite granodiorite accompanied by brittle deformation. A ca. 1745-Ma lower greenschist facies hydrothermal epidote-calcite-zoisite alteration assemblage with numerous accessory minerals forms halos surrounding the late-stage fractures. The contrasting hydrothermal alteration styles at Nalunaq indicate a complex history of exhumation from amphibolite facies conditions to lower greenschist facies conditions in an orogenic belt which resembles modern Phanerozoic orogens.

  9. Hydrothermal Alteration at Lonar Crater, India and Elemental Variations in Impact Crater Clays

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; Nelson, M. J.; Shearer, C. K.; Misra, S.; Narasimham, V.

    2005-01-01

    The role of hydrothermal alteration and chemical transport involving impact craters could have occurred on Mars, the poles of Mercury and the Moon, and other small bodies. We are studying terrestrial craters of various sizes in different environments to better understand aqueous alteration and chemical transport processes. The Lonar crater in India (1.8 km diameter) is particularly interesting being the only impact crater in basalt. In January of 2004, during fieldwork in the ejecta blanket around the rim of the Lonar crater we discovered alteration zones not previously described at this crater. The alteration of the ejecta blanket could represent evidence of localized hydrothermal activity. Such activity is consistent with the presence of large amounts of impact melt in the ejecta blanket. Map of one area on the north rim of the crater containing highly altered zones at least 3 m deep is shown.

  10. Environmental effects of hydrothermal alteration and historical mining on water and sediment quality in Central Colorado

    USGS Publications Warehouse

    Church, S.E.; Fey, D. L.; Klein, T.L.; Schmidt, T.S.; Wanty, R.B.; deWitt, E.H.; Rockwell, B.W.; San, Juan C.A.

    2009-01-01

    The U.S. Geological Survey conducted an environmental assessment of 198 catchments in a 54,000-km2 area of central Colorado, much of which is on Federal land. The Colorado Mineral Belt, a northeast-trending zone of historical base- and precious-metal mining, cuts diagonally across the study area. The investigation was intended to test the hypothesis that degraded water and sediment quality are restricted to catchments in which historical mining has occurred. Water, streambed sediment, and aquatic insects were collected from (1) catchments underlain by single lithogeochemical units, some of which were hydrothermally altered, that had not been prospected or mined; (2) catchments that contained evidence of prospecting, most of which contain hydrothermally altered rock, but no historical mining; and (3) catchments, all of which contain hydrothermally altered rock, where historical but now inactive mines occur. Geochemical data determined from catchments that did not contain hydrothermal alteration or historical mines met water quality criteria and sediment quality guidelines. Base-metal concentrations from these types of catchments showed small geochemical variations that reflect host lithology. Hydrothermal alteration and mineralization typically are associated with igneous rocks that have intruded older bedrock in a catchment. This alteration was regionally mapped and characterized primarily through the analysis of remote sensing data acquired by the ASTER satellite sensor. Base-metal concentrations among unaltered rock types showed small geochemical variations that reflect host lithology. Base-metal concentrations were elevated in sediment from catchments underlain by hydrothermally altered rock. Classification of catchments on the basis of mineral deposit types proved to be an efficient and accurate method for discriminating catchments that have degraded water and sediment quality. Only about 4.5 percent of the study area has been affected by historical mining

  11. The formation of alteration rims in basaltic lava flows upon hydrothermal circulation

    NASA Astrophysics Data System (ADS)

    Thien, Bruno; Driesner, Thomas; Kosakowski, Georg; Kulik, Dmitrii

    2016-04-01

    We investigated fossil hydrothermal systems in the North of the Reykjavik peninsula (Iceland), in order to better understand water-rock interactions occurring during hydrothermal fluid circulation. The observation of a lava flow formation showed that the basalt is practically not altered, except in zones of a few cm thickness around the largest fractures (i.e. alteration rims). XRD analysis and observations of polished thin sections by optical microscope evidenced a severe alteration of the protolith in the alteration rim. Secondary minerals mostly consist in pyrite, calcite and chlorite, indicating a temperature of 250°C during the hydrothermal event. The presence of pyrite and calcite in the alteration rim and their absence in the rest of the rock suggest that the fluid contained significant amount of volcanic gasses H2S and CO2 and probably followed an ascending path. Most of the calcite is located in fractures that have been formed after the precipitation of the other secondary minerals. This observation, coupled with fluid inclusions analysis, indicates a second hydrothermal event that happened at lower temperature and pressure. We reproduced those observations by using a geochemical reactive transport model (OpenGeoSys-GEM code). The purpose was to decipher how diffusion and mineral reaction kinetics (protolith dissolution and secondary minerals precipitation) influence the alteration, and to establish the time duration of the hydrothermal circulation.

  12. Contact zones and hydrothermal systems as analogues to repository conditions

    SciTech Connect

    Wollenberg, H.A.; Flexser, S.

    1984-10-01

    Radioactive waste isolation efforts in the US are currently focused on examining basalt, tuff, salt, and crystalline rock as candidate rock types to encompass waste repositories. As analogues to near-field conditions, the distributions of radio- and trace-elements have been examined across contacts between these rocks and dikes and stocks that have intruded them. The intensive study of the Stripa quartz monzonite has also offered the opportunity to observe the distribution of uranium and its daughters in groundwater and its relationship to U associated with fracture-filling and alteration minerals. Investigations of intrusive contact zones to date have included (1) a tertiary stock into Precambrian gneiss, (2) a stock into ash flow tuff, (3) a rhyodacite dike into Columbia River basalt, and (4) a kimberlite dike into salt. With respect to temperature and pressure, these contact zones may be considered "worst-case scenario" analogues. Results indicate that there has been no appreciable migration of radioelements from the more radioactive intrusives into the less radioactive country rocks, either in response to the intrusions or in the fracture-controlled hydrological systems that developed following emplacement. In many cases, the radioelements are locked up in accessory minerals, suggesting that artificial analogues to these would make ideal waste forms. Emphasis should now shift to examination of active hydrothermal systems, studying the distribution of key elements in water, fractures, and alteration minerals under pressure and temperature conditions most similar to those expected in the near-field environment of a repository. 14 refs.

  13. Tularosa Basin Play Fairway Analysis: Hydrothermal Alteration Map

    DOE Data Explorer

    Adam Brandt

    2015-11-15

    This is a hydrothermal alteration map of the Tularosa Basin area, New Mexico and Texas that was created using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) multispectral data band ratios based upon diagnostic features of clay, calcite, silica, gypsum, ferric iron, and ferrous iron. Mesoproterozoic granite in the San Andreas Range often appeared altered, but this may be from clays produced by weathering or, locally, by hydrothermal alteration. However, no field checking was done. This work was done under U.S. D.O.E. Contract #DE-EE0006730

  14. Hydrothermal alteration facies within the intrusive-hosted Salave gold prospect, NW Spain

    SciTech Connect

    Harris, M.

    1985-01-01

    The Salave gold prospect occurs within an Hercynian granodioritic complex intruding Cambro-Ordovician metasediments and a heterogeneous gabbroic body. Mineralization consists mostly of disseminated and veinlet pyrite, arsenopyrite, molybdenite, stibnite, and lesser sphalerite associated with a zoned sequence of hydrothermal alteration. Gold occurs as free particles and/or intergrown with the sulfides. Mathematical appraisal of analytical data suggests that the hydrothermal alteration resulted from largely isochemical redistribution processes imposed on the mineralogy of the host granodiorite by influxes of sporadically boiling fluids rich in CO/sub 2/. Hydrothermal alteration is described in terms of a zonal sequence inward from unaltered host rock through (1) chlorite-sericite alteration-(2) propylitic to advanced propylitic alterations-(3)albitites-(4) an auriferous (greater than or equal to 1g/t Au) sericite-carbonate-albite-(+/-)quartz-sulfide cataclastic facies. The zonation corresponds to increasing carbonatization, sericitization, albitization, desilification, and destruction of the original igneous texture. Aventurine alteration is common and is thought to be the product of late stage hydrothermal oxidizing conditions. Potassic alteration in the form of K-feldspar or biotite was occasionally observed.

  15. Field guide to hydrothermal alteration in the White River altered area and in the Osceola Mudflow, Washington

    USGS Publications Warehouse

    John, David A.; Rytuba, James J.; Ashley, Roger P.; Blakely, Richard J.; Vallance, James W.; Newport, Grant R.; Heinemeyer, Gary R.

    2003-01-01

    . The morning of the trip will examine the White River altered area, which includes high-level alteration related to a large, early Miocene magmatic-hydrothermal system exposed about 10 km east of Enumclaw, Washington. Here, vuggy silica alteration is being quarried for silica and advanced argillic alteration has been prospected for alunite. Clay-filled fractures and sulfide-rich, fine-grained sedimentary rocks of hydrothermal origin locally are enriched in precious metals. Many hydrothermal features common in high-sulfidation gold-silver deposits and in advanced argillic alteration zones overlying porphyry copper deposits (for example, Gustafson and Hunt, 1975; Hedenquist and others, 2000; Sillitoe, 2000) are exposed, although no economic base or precious metal mineralized rock has been discovered to date. The afternoon will be spent examining two exposures of the Osceola Mudflow along the White River. The Osceola Mudflow contains abundant clasts of altered Quaternary rocks from Mount Rainier that show various types of hydrothermal alteration and hydrothermal features. The mudflow matrix contains abundant hydrothermal clay minerals that added cohesiveness to the debris flow and helped allow it to travel much farther down valley than other, noncohesive debris flows from Mount Rainier (Crandell, 1971; Vallance and Scott, 1997). The White River altered area is the subject of ongoing studies by geoscientists from Weyerhaeuser Company and the U.S. Geological Survey (USGS). The generalized descriptions of the geology, geophysics, alteration, and mineralization presented here represent the preliminary results of this study (Ashley and others, 2003). Additional field, geochemical, geochronologic, and geophysical studies are underway. The Osceola Mudflow and other Holocene debris flows from Mount Rainier also are the subject of ongoing studies by the USGS (for example, Breit and others, 2003; John and others, 2003; Plumlee and others, 2003, Sisson and others, 2003; Vallance and

  16. Hydrothermal alteration favoring phreatic eruption processes at Solfatara (Campi Flegrei)

    NASA Astrophysics Data System (ADS)

    Mayer, Klaus; Scheu, Bettina; Montanaro, Cristian; Aßbichler, Donjá; Isaia, Roberto; Dingwell, Donald B.

    2015-04-01

    Solfatara and Pisciarelli fumaroles are the main surface manifestations of the strong hydrothermal activity within the Campi Flegrei caldera system and pointing to a significant risk for phreatic eruptions in this densely populated area. Phreatic eruptions, triggered by various processes are hardly predictable in occurrence time and size. Despite their hazard potential, these eruptions, as well as the influence of hydrothermal alteration on their likelihood, magnitude and style, have so far been largely overlooked in experimental volcanology. The physical properties and the mechanical behavior of volcanic rocks are highly dependent on their original magmatic microstructure and on any eventual alteration of those microstructures due to hydrothermal reactions. We have therefore investigated the potential effects of hydrothermal alteration on rock microstructure and, as a consequence, on fragmentation dynamics. Rock samples from the vicinity of the Solfatara and Pisciarelli fumaroles have been characterized 1) geochemically (X-ray fluorescence, X-ray diffraction), 2) physically (density, porosity, permeability and elastic wave velocity) and 3) mechanically (uniaxial compressive strength, tensile strength). We furthermore have investigated the effects of hydrothermal alteration on fragmentation processes using a shock-tube apparatus, operating with Argon gas, water vapor and superheated water at temperatures up to 400°C and maximum pressures of 20 MPa. Fragmentation and ejection dynamics in the presence of three different energy sources within the pores have been investigated: overpressure by 1) Argon gas; or 2) water vapor and due to 3) steam flashing of superheated water. Fragmentation speed, fragmentation efficiency and fragmented particle ejection velocity were measured. Our results indicate on the one hand, that steam flashing provides the highest energy - resulting in increased fragmentation speed and particle ejection velocity and also a significant higher

  17. Isotope geochemistry of hydrothermal alteration in East of Esfahan, Central Iran

    NASA Astrophysics Data System (ADS)

    Taghipour, Sedigheh; Taghipour, Batoul

    2010-05-01

    In the Cenozoic magmatic belt of Central Iran, the Eocene volcanics and pyroclastics from the East of Esfahan underwent extensive hydrothermal alteration. The Eocene volcanics composed mostly of andesite lava and tuffs have been altered. The survey area is laterally zoned from an inner quartz-sericite alteration zone to an outer propylitic zone. Quartz-sericite alteration is predominant (>95%), but smaller zones of alunite-jarosite and silicified zones are present and superimposed onto a quartz-sericite alteration. In the quartz-sericite zone all altered rocks are light grayish to whitish in color and porphyritic with aphanitic groundmass. Concentrations of alunite and jarosite veinlets and stockworks are dispersed irregularly in this zone. Alunite and jarosite occur also as coatings on fractured rocks. All types of alunite occurrences are brick-red, cream, white and buff in colors, while jarosite is brown to rusty in colors. To verify, chemical composition of alunite and jarosite were identified by X-ray diffraction in mineral assemblages. Major alteration zones show inclusions of propylite, quartz sericite, advanced argillic and silicified zones. These alunites are mainly porcelaneous and their compositions show a solid solution between alunite and jarosite. In alteration zones, the mineral assemblage is characterized by alunite-jarosite + quartz + sericite + alkali feldspars + chlorite ± turquoise ± barite ± iron oxides. There are numerous alunite and jarosite occurrences, mainly as veinlets, in parts of the advanced argillic zone. Alunite δ18O and δ D values range from -1.76 to 8.81‰ and from -52.86 to -129.26‰ respectively. Field observations, mineralogical evidence and results from light element stable isotope data (δ18O, δ D and δ34S); indicate that in this area alunitization is supergene in origin.

  18. Geothermometry, geochronology, and mass transfer associated with hydrothermal alteration of a rhyolitic hyaloclastite from Ponza Island, Italy

    NASA Astrophysics Data System (ADS)

    Altaner, Stephen P.; Ylagan, Robert F.; Savin, Samuel M.; Aronson, James L.; Belkin, Harvey E.; Pozzuoli, Antonio

    2003-01-01

    A rhyolitic hyaloclastite from Ponza Island, Italy, was hydrothermally altered, producing four distinct alteration zones based on X-ray diffraction mineralogy and field textures: (1) nonpervasive argillic zone; (2) propylitic zone; (3) silicic zone; and (4) sericitic zone. The unaltered hyaloclastite is volcanic breccia with clasts of vesiculated obsidian in a matrix of predominantly pumice lapilli. Incomplete alteration of the hyaloclastite resulted in the nonpervasive argillic zone, characterized by smectite and disordered opal-CT. The other three zones exhibit more complete alteration of the hyaloclastite. The propylitic zone is characterized by mixed-layer illite-smectite (I-S) with 10 to 85% I, mordenite, opal-C, and authigenic K-feldspar (akspar). The silicic zone is characterized by I-S with ≥90% I, pure illite, quartz, akspar, and occasional albite. The sericitic zone consists primarily of I-S with ≥66% I, pure illite, quartz, and minor akspar and pyrite. K/Ar dates of I-S indicate hydrothermal alteration occurred at 3.38 ± 0.08 Ma. Oxygen isotope compositions of I-S systematically decrease from zones 1 to 4. In the argillic zone, smectite has δ 18O values of 21.7 to 22.0‰ and I-S from the propylitic, silicic, and sericitic zones ranges from 14.5 to 16.3‰, 12.5 to 14.0‰, and 8.6 to 11.9‰, respectively. δ 18O values for quartz from the silicic and sericitic zones range from 12.6 to 15.9‰. By use of isotope fractionation equations and data from authigenic quartz-hosted primary fluid inclusions, alteration temperatures ranged from 50 to 65°C for the argillic zone, 85 to 125°C for the propylitic zone, 110 to 210°C for the silicic zone, and 145 to 225°C for the sericitic zone. Fluid inclusion data and calculated δ 18O water values indicate that hydrothermal fluids were seawater dominated. Mass-transfer calculations indicate that hydrothermal alteration proceeded in a relatively open chemical system and alteration in the sericitic zone

  19. Comparison of techniques for discriminating hydrothermal alteration minerals with Airborne Imaging Spectrometer data

    NASA Technical Reports Server (NTRS)

    Feldman, Sandra C.; Taranik, James V.

    1988-01-01

    Hydrothermal alteration mineralogy in the Tybo mining district of Nevada has been mapped on the basis of high spectral and spatial resolution Airborne Imaging Spectrometer (AIS) data, using band ratios, principal component analysis, and a signature-matching algorithm to delineate the alteration zones and limestone foundations. The signature-matching algorithm is found to be the most effective method of discriminating alteration minerals, and is noted to be able to identify mineralogy by matching AIS image spectra with library reference spectra. AIS bands in the 2048-2337-nm portion of the spectrum accounted for the greatest amount of variance.

  20. Hydrothermal Alteration in the Logatchev Hydrothermal Field: Implications From Secondary Mineral Assemblages and Mineral Chemistry

    NASA Astrophysics Data System (ADS)

    Lackschewitz, K. S.; Augustin, N.; Devey, C. W.; Eisenhauer, A.; Garbe-Schoenberg, D.; James, R.

    2005-12-01

    We present new data on secondary mineral assemblages, clay and whole rock chemistry and clay mineral strontium and lithium isotopic compositions of altered rocks and sediments from the active, ultramafic-hosted Logatchev hydrothermal field reflecting various alteration conditions (e.g. fluid mixing, water-rock interaction). The altered ultramafic rocks are mainly consist of lizardite, chrysotile whereas magnetite and pyrite are minor minerals. Chlorite, chlorite-smectite mixed-layer (e.g., corrensite), smectite and talc are additional common phases in the clay fraction of most of these samples.Iron-hydroxides and iron sulfides are the main components of the hydrothermal crusts, with some amounts of pyroxene, chlorite, illite and pyrite. The hydrothermal sediments beneath the crusts are characterized by quartz, smectite and chlorite as main minerals. Analyses of clay separates representing a variety of alteration styles demonstrates that significant and characteristic changes in the bulk rock chemical composition are associated with various alteration conditions. The elements Cr, Cu, Pb and U appears to have a general enrichment in the lizardite and chlorite concentrates in comparison to a depleted mantle. 87Sr/86Sr ratios of clay concentrates vary between 0.7083 and 0.7096 suggesting that the clays either formed as a result of seawater alteration or hydrothermal alteration with various portions of seawater. The strontium isotopic ratio of a chlorite sample from hydrothermal sediments beneath the hydrothermal crust is much lower than the isotopic data reported for the lizardites suggesting precipitation from fluid with lower seawater content. The Li isotopic composition (δ7Li) of the clay separates varies between -5.4 and +6.4‰. Thus, the clays are enriched in 6Li relative to both seawater (~31‰) and hydrothermal vent fluids from the Logatchev field (~6‰) suggesting that 6Li is preferentially retained in alteration products. When considered together with the

  1. Hydrothermal alteration of impact melt sheets with implications for Mars

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.

    1980-01-01

    A model of the interaction of water with an impact melt sheet is constructed to explain the presence of hydrothermal alteration, fluid flow channels, and the redistribution of volatile elements in terrestrial melt sheets. A calculation of the amount of water vaporized beneath a melt sheet with a large fraction of melt results in a maximum total steam/melt sheet ratio of 23% by weight. The model also applies to Martian impact melt sheets, which have a total volume greater than a global layer 60 m thick. Hydrothermal circulation of steam in Martian melt sheets may have produced iron-rich alteration clays, ferric hydroxides, and near-surface accumulations of salts. The ability of vapor-dominated hydrothermal systems to concentrate sulfate relative to chloride is consistent with the high sulfate to chloride ratio found in the Martian soil by the Viking landers. A major fraction of the Martian soil may consist of the erosion products of hydrothermally altered impact melt sheets.

  2. Hydrothermal Zoning of Rift Zones Inferred From Magnetic Susceptibility Variations: Implications for the Collapse of Hawaiian Shield Volcanoes, and for Ore-genesis Processes.

    NASA Astrophysics Data System (ADS)

    Cañòn-Tapia, E.; Herrero-Bervera, E.

    2009-05-01

    Hawaiian shield volcanoes have experienced large scale landslides throughout their history. These collapses are due in part to the failure of the surrounding sea floor to support the weight of the spreading volcano as it grows. Nevertheless, these collapses also might be promoted by the weakening of the volcanic edifice due to the injection of dykes within rift zones, and by the alteration of the rock due to hydrothermal activity along these zones. In turn, hydrothermal alteration modifies the rock bulk magnetic susceptibility, and such relationship provides a good opportunity to estimate the zoning of alteration by completing measurements of magnetic susceptibility. In this work we show preliminary evidence suggesting that a hydrothermal zoning can be inferred to have existed in the Hawaiian Shield volcanoes, probably reflecting the variation of the optimum temperature for alteration as a function of distance from the magma center. The mechanical destabilization of the volcanic edifice due to dyke injection and that related to alteration of the rocks seems to have been inversely related, therefore resulting in an average destabilization of approximately equal magnitude along the whole extension of the rift zone. Such uniform destabilization seemingly favors the collapse of large sectors of the volcanic shield once a critical mass is achieved. In the context of ore-genesis, zoning is known to be related to paleogeography and temperature variations among other factors. Actually, different patterns of orebody zoning are known to take place depending on the conditions prevalent in each region, and it is of interest to determine the details of zoning of the deposit to understand its genesis. Despite the fact that Hawaiian volcanoes are not the most economically important places to study ore-genesis processes, the better understanding of the processes of hydrothermal alteration gained in these settings should contribute to gain a better knowledge of the distribution of

  3. Geology and hydrothermal alteration at the Madh adh Dhahab epithermal precious-metal deposit, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Doebrich, J.L.; LeAnderson, J.P.

    1984-01-01

    Vein-related alteration consisting of quartz-sericite-pyrite, chloritic, argillic, and silicic halos was superimposed on broad zones of pervasive silicic, potassic, and argillic alteration that surrounds the rhyolite intrusive body. Quartz-sericite-pyrite alteration associated with the earliest stage of mineralization was followed by broad, pervasive, stratigraphically controlled potassic alteration. Subsequent mineralization was accompanied by quartz-sericitepyrite alteration and was followed by the main stage of mineralization that formed strong chloritic alteration halos. Development of broad zones and halos of argillic alteration also may have been related to the main stage of mineralization. Development of silicic halos was characteristic of the late stages of mineralization. Broad, pervasive propylitic alteration was then superimposed on all alteration types and represents cooling and inward encroachment of the hydrothermal system. All alteration, except the early silicic alteration is interpreted to have been related to circulating meteoric fluids heated by the rhyolite.

  4. Hydrothermal Alteration Mapping Studies for Geothermal Energy Exploration

    NASA Astrophysics Data System (ADS)

    Calvin, W. M.; Kratt, C.; Littlefield, E. F.; Lamb, A. K.

    2011-12-01

    We use a combination of satellite and aerial surveys at varying spatial resolutions to obtain regional information on hydrothermal alteration patterns and to target more expensive, but also more detailed, airborne spectral data collects. In the past decade we have performed numerous site assessments to characterize mineral, vegetation, and thermal properties as surface identifiers of geothermal resources. Our work has included the satellite sensors Landsat, ASTER, and ALI and airborne sensors MASTER, HyMap, ProSpecTIR, AVIRIS and SEBASS. As part of our validation process we collect data in the field to confirm remote identifications and we also collect samples for later laboratory analysis. These field and lab measurements corroborate our detections and help to define confidence limits in refining regions where alteration minerals are found. Validation work includes the use of an ASD field spectrometer for measurement from 0.4 to 2.5 μm in both field and lab configurations. We have a Thermo/Nicolet Nexus 6700 FTIR spectrometer and shared use of a Designs and Prototypes FTIR field instrument for validation in the thermal infrared spectral range. We usually follow remote sensing work with shallow (2m) ground probe temperature measurements. Past work has identified sinter, tufa, various argillic and propyllitic alteration zones, vegetation concentration near small surface seeps or springs, and thermal anomalies as indicative of resource potential and structural controls on fluid pathways. Playa evaporites have also been used as diagnostic indicators of geothermal systems, where thermal springs discharge into closed basins. Mapped imagery is geo-rectified to standard projections and integrated into GIS databases so that mineral maps can be readily included in regional and site specific assessments. The presentation will describe common and unique features in our surveys of geothermal fields in Nevada as outlined in the table.
    Surveyed Geothermal Sites in Nevada

  5. Mineralogy and stable isotope geochemistry of hydrothermally altered oceanic rocks

    USGS Publications Warehouse

    Stakes, D.S.; O'Neil, J.R.

    1982-01-01

    Mineralogical and isotopic variations observed in altered glassy and crystalline rocks from the East Pacific Rise and the Mid-Atlantic Ridge provide information about the temperatures of alteration and seawater/rock ratios for various hydrothermal regimes within the oceanic crust. A systematic increase in alteration temperature is evident for the glassy rocks in the sequence: (1) nontronite and celadonite vesicle fillings (35??C), (2) saponite-rich pillow breccias (130-170??C), (3) calcite-rich greenstone breccias and epidote-rich greenstone (200-350??C). These results include the highest temperatures thus far reported for saponite formation. The "seawater-dominated" hydrothermal alteration process that formed the saponite-rich pillow breccias is characterized by high water/rock ratios (>50:1), low to moderate temperatures, a seawater origin of most of the carbon in vein calcites (??13 C ??? 0) and the predominance of Fe-rich saponite and calcite as secondary phases. Greenstones (chlorite-quartz-epidote) and greenstone breccias (chlorite-quartz-albite-calcite) are altered in a "rock-dominated" system with lower water/rock ratios (50:1 to < 1:1), higher temperatures, and vein calcites with carbon that is principally of magmatic origin (??13 C ??? -4). The crystalline rocks (diabase, gabrro, and metagabbro) are affected to varying degrees by pervasive high-temperature seawater interactions that commence soon after solidification, producing varying proportions of fine-grained secondary minerals including talc, smectite, chlorite, vermiculite, actinolite, and sodic plagioclase. Hydrothermal solutions, derived from alteration of the crystalline rocks, are of the appropriate temperature and isotopic composition to alter the overlying glassy rocks to the observed mineralogies as well as being the source of metal-rich deposits associated with the oceanic spreading centers. ?? 1982.

  6. Geochemical behavior of rare earth elements of the hydrothermal alterations within the Tepeoba porphyry Cu-Mo-Au deposits at Balikesir, NW Turkey

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    This work reports the geochemical characteristics and behavior of the rare earth elements (REE) of the hydrothermal alteration of the Tepeoba porphyry Cu-Mo-Au deposit located in the Anatolian tectonic belt at Biga peninsula (Locally Balikesir province), NW Turkey. The Cu-Mo-Au mineralization at this deposit hosted in the hornfels rocks and related to the silicic to intermediate intrusion of Eybek pluton. It locally formed with brecciated zones and quartz vein stockworks, as well as the brittle fracture zones associated with intense hydrothermal alteration. Three main alteration zones with gradual boundaries formed in the mine area in the hornfels rock that represents the host rock, along that contact the Eybek pluton; potassic, propylitic and phyllic alteration zones. The potassic alteration zone that formed at the center having high amount of Cu-sulfide minerals contains biotite, muscovite, and sericite with less amount of K-feldspar and associated with tourmalinization alteration. The propylitic alteration surrounds the potassic alteration having high amount of Mo and Au and contains chlorite, albite, epidote, calcite and pyrite. The phyllic alteration zone also surrounds the potassic alteration containing quartz, sericite and pyrite minerals. Based on the REE characteristics and content and when we correlate the Alteration index (AI) with the light REEs and heavy REEs of each alteration zone, it concluded that the light REEs decrease and heavy REEs increase during the alteration processes. The relationships between K2O index with Eu/Eu* and Sr/Sr* reveals a positive correlation in the potassic and phyllic alteration zones and a negative correlation in the propylitic alteration zone. This refers to the hydrothermal solution which is responsible for the studied porphyry deposits and associated potassic and phyllic alterations has a positive Eu and Sr anomaly as well as these elements were added to the altered rock from the hydrothermal solution. Keywords: Rare

  7. Crystallization process of zircon and fergusonite during hydrothermal alteration in Nechalacho REE deposit, Thor Lake, Canada

    NASA Astrophysics Data System (ADS)

    Hoshino, M.; Watanabe, Y.; Murakami, H.; Kon, Y.; Tsunematsu, M.

    2012-04-01

    The core samples of two drill holes, which penetrate sub-horizontal mineralized horizons at Nechalacho REE deposit in the Proterozoic Thor Lake syenite, Canada, were studied in order to clarify magmatic and hydrothermal processes that enriched HFSE (e.g. Zr, Nb, Y and REE). Zircon is the most common REE minerals in Nechalacho REE deposit. The zircon is divided into five types as follows: Type-1 zircon occurs as single grain in phlogopite and the chondrite-normalized REE pattern is characterized by a steeply-rising slope from the LREE to the HREE with a positive Ce-anomaly and negative Eu-anomaly. This chemical characteristic is similar to that of igneous zircon. Type-2 zircon consists of HREE-rich magmatic porous core and LREE-Nb-F-rich hydrothermal rim. This type zircon is mostly included in phlogopite and fluorite, and occasionally in microcline. Type-3 zircon is characterized by euhedral to anhedral crystal, occurring in a complex intergrowth with REE fluorocarbonates. Type-3 zircons have high contents of REE, Nb and fluorine. Type-4 zircon consists of porous-core and -rim zones, but their chemical compositions are similar to each other. This type zircon is a subhedral crystal rimmed by fergusonite. Type-5 zircon is characterized by smaller, porous and subhedral to anhedral crystals. The interstices between small zircons are filled by fergusonite. Type-4 and -5 zircons show low REE and Nb contents. Occurrences of these five types of zircon are different according to the depth and degree of the alteration by hydrothermal solutions rich in F- and CO3 of the two drill holes, which permit a model for evolution of the zircon crystallization in Nechalacho REE deposit as follows: (1) type-1 (single magmatic zircon) is formed in miaskitic syenite. (2) LREE-Nb-F-rich hydrothermal zircon formed around HREE-rich magmatic zircon (type-2 zircon); (3) type-3 zircon crystallized thorough F and CO3-rich hydrothermal alteration of type-2 zircon which formed the complex

  8. Late Hesperian hydrothermal alteration at Majuro crater, Mars

    NASA Astrophysics Data System (ADS)

    Mangold, N.; Carter, J.; Poulet, F.; Dehouck, E.; Ansan, V.; Loizeau, D.

    2012-04-01

    Impact craters cover a large portion of the surface of Mars and could constitute a significant exobiology research target as their formation provided heat sources for aqueous processes. To date, only rare examples of hydrothermal alteration in craters have been reported on Mars while many studies have focused on modeling their effect. Using data from the Mars Reconnaissance Orbiter and Mars Express probes, we report the presence of hydrated minerals, mainly Fe/Mg phyllosilicates, with vermiculite as best-fit, that are found in an alluvial fan. This fan is located inside a crater located in NE Hellas region and dated to the Late Hesperian by crater counts and crosscutting relationships. The stratigraphic position of the hydrated minerals and presence of small domes interpreted as hydrothermal vents indicate that the alteration occurred in the lower level of the alluvial fan and was triggered by bottom-up alteration. These observations are best explained by a combination of snow deposition and subsequent melting eroding crater rims and forming the fan, with impact warming, which triggered the alteration at the base of the fan. This example shows that phyllosilicates are able to form late in the Martian history, especially in local niches of strong exobiological interest. It also suggests that a similar process was possible in alluvial fans of other large impact craters including those at Gale crater.

  9. Hydrothermal alteration in the Mount Hood Area, Oregon. Bulletin

    SciTech Connect

    Bargar, K.E.; Keith, T.E.C.; Beeson, M.H.

    1993-01-01

    The report describes the hydrothermal alteration of numerous outcrop samples collected in the vicinity of Mount Hood, as well as drill cuttings from 13 of the geothermal drill holes for which the authors were able to obtain sample splits. The study is also an outgrowth of a geologic and mineral survey of the Mount Hood Wilderness area in compliance with the Wilderness Act which requires that the U.S. Geological Survey and the U.S. Bureau of Mines evaluate the mineral resource potential of certain specified parcels of government-owned land.

  10. Lithium isotopes in hydrothermally altered basalts from Hengill (SW Iceland)

    NASA Astrophysics Data System (ADS)

    Verney-Carron, A.; Vigier, N.; Millot, R.; Hardarson, B. S.

    2015-02-01

    The Li isotope signatures of hydrothermal fluids are remarkably constant (δ7Li = 8.0 ± 1.9 ‰) irrespective of the water/rock ratio (W / R), permeability, temperature or fluid involved (seawater or meteoric). High temperature hydrothermal fluids represent the second most significant source of Li to the ocean, yet the homogeneity of the Li isotopic signatures of this source remains to be explained and in this context, the lack of data for the corresponding altered phases is problematic. We measured Li contents and Li isotope signatures (as well as mineralogy, composition and local fluid temperature) in hyaloclastites collected from a borehole in the Hellisheidi geothermal system (Iceland) which have been altered by high temperature aqueous fluids (from 170 to 300 °C). Li is more enriched in the solid phases than the other alkali metals, highlighting its greater ability to be incorporated into secondary phases, especially at high temperatures (>250 °C). Mass balance calculations show that the low Li concentrations in hydrothermal fluids are best explained by a high water/rock ratio and a high permeability of this system. The Li isotopic signature of the altered hyaloclastites (δ7Li between +1.9 and + 4.0 ‰) remains close to the fresh basalt at deep levels and high temperatures (290-300 °C) (as measured δ7Li range between +3.7 and + 4.0 ‰), and decreases at shallower depths and lower temperatures (150-270 °C) (δ7Li between +1.9 and + 3.1 ‰). A mass balance model involving basalt dissolution, secondary phase formation, and successive isotope equilibrium during the migration and the cooling of the percolating fluid was developed. The corresponding apparent mineral-fluid Li isotope fractionation factors resulting from precipitation of secondary phases (ΔLi7minerals-fluid) range between 0‰ at 300 °C and - 8.5 ‰ at 170 °C and highlight a key role of chlorite. Applying the same approach to mid-ridge oceanic hydrothermal systems allows the relatively

  11. Hydrothermal phonolite alteration in the Kaiserstuhl Volcanic Complex, Germany

    NASA Astrophysics Data System (ADS)

    Weisenberger, T. B.; Spürgin, S.

    2013-12-01

    The subvolcanic Fohberg and Endhale phonolitic intrusions in the Kaiserstuhl volcanic complex in SW Germany are economic zeolite deposits, formed by hydrothermal alteration of primary magmatic minerals. Due to the high (>40 wt%) zeolite content, which accounts for the remarkable zeolitic physicochemical properties of the ground rock, the zeolitized phonolites are in economic interest. New mineralogical and geochemical studies are carried out a) to evaluate the manifestation of hydrothermal alteration of the Fohberg and Endhale phonolitic intrusions, and b) to constrain the physical and chemical properties of the fluids, which promoted hydrothermal replacement of primary igneous minerals. The alkaline intrusive bodies are characterized by the primary mineralogy: feldspathoid mineral, K-feldspar, aegirine-augite, wollastonite, and andradite. The REE-phase götzenite is formed during late stage magmatic crystallization. Fluid-induced re-equilibration of feldspathoid minerals and wollastonite caused breakdown to a set of secondary phases. Feldspathoid minerals are totally replaced by secondary phases including various zeolite species, calcite, and barite. Wollastonite breakdown results in the formation of various zeolites, calcite, pectolite, sepiolite, and quartz. The large variability of secondary minerals indicates a heterogenic fluid composition throughout the phonolitic intrusions and through time. Zeolites formed during sub-solidus hydrothermal alteration under alkaline conditions and completely replacefeldspathoid minerals in the matrix of the rock. A sequence of Ca-Na dominated zeolite species (gonnardite, thomsonite, mesolite) is followed by pure sodium endmember species. The sequence reflects an increase in log[aNa+)/(aH+)] of the precipitating fluid. Low radiogenic 87Sr/86Sr values of secondary calcite indicate a local origin of Ca and elements necessary for secondary mineral formation most probably derived from primary igneous phases. The Fohberg phonolite

  12. Assessing the role of upwelling hydrothermal fluids in altering the upper ocean crust

    NASA Astrophysics Data System (ADS)

    Gillis, K. M.; Coogan, L. A.

    2008-12-01

    Hydrothermal alteration patterns developed at mid-ocean ridges are traditionally interpreted to form within recharge zones, with little or no alteration occurring as chemically modified fluids rise towards the seafloor. Evaluation of mineralogical and chemical data for sheeted dike complexes exposed at Pito and Hess Deeps, and drilled at Hole 504B shows that fluid-rock exchange took place at temperatures ~ 250 to >400° C throughout the sheeted dikes, with no systematic change with depth. The higher temperatures found in many dikes at all depths are indicated by metal depletion and the presence of aluminous amphibole. Thermal arguments show that high temperatures in the shallow dikes could not have been achieved in recharge zones. This is because the downward flow of seawater would act to depress temperatures in recharge zones, producing concave upwards isotherms and thus low temperatures in the shallow dikes. Thermal constraints [1] show that hot upwelling fluids have the capacity to heat and alter the sheeted dikes on viable timescales, producing the observed alteration patterns. This suggests that seawater migrating downwards through lavas and dikes is not significantly heated until it reaches the lower third of the sheeted dike complex, where heat is conducted from an underlying (hornfelsic) thermal boundary layer. The spatial distribution of upflow controls what proportion of the upper dikes are held at elevated temperatures for long enough to alter. Dikes recovered by submersible from the regionally extensive exposures at Pito and Hess Deeps show that discharge was not spatially restricted to narrow zones, but rather was focused in broad zones of upwelling [2]. Lateral variation in the mineralogical and chemical expression of discharge suggests that broad zones of upwelling migrated along the ridge axes with time. [1] Coogan, L.A. [2008] Reconciling temperatures of metamorphism, fluid fluxes, and heat transport in the upper crust at intermediate to fast

  13. Hydrothermal surface alteration in the Copahue Geothermal Field (Argentina)

    SciTech Connect

    Mas, Graciela R.; Mas, Luis C.; Bengochea, Leandro

    1996-01-24

    In the area of the Copahue Geothermal Field, there are five active geothermal manifestations, which mainly consist of fumaroles, hot springs and mud pots. Four of these manifestations are located in Argentina: Las Máquinas, Termas de Copahue, Las Maquinitas and El Anfiteatro, and the fifth on the Chilean side: Chancho Co. All of them present a strong acid sulfate country rock alteration, characterized by the assemblage alunite + kaolinite + quartz + cristobalite + pyrite + sulfur + jarosite, as the result of the base leaching by fluids concentrated in H2SO4 by atmospheric oxidation at the water table in a steam heated environment of H2S released by deeper boiling fluids. Another alteration zone in this area, called COP-2, is a fossil geothermal manifestation which shows characteristics of neutral to alkaline alteration represented mainly by the siliceous sinter superimposed over the acid alteration. The mineralogy and zoning of these alteration zones, and their relation with the hidrothermal solutions and the major structures of the area are analized.

  14. The Magmatic-Hydrothermal Transition of The Taupo Volcanic Zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Chambefort, I. S.; Dilles, J. H.; Heinrich, C. A.; Wälle, M.

    2015-12-01

    The Taupo Volcanic Zone (TVZ), New Zealand is a rifting arc that produced over the last 2 My over 6000 km3 of caldera-associated volcanic products. About four times as much magma is estimated to be trapped at depth below the central TVZ than is erupted, feeding heat, volatiles and chemicals into 23 geothermal systems with a total of ca. 4.2 GW thermal energy release. We present here a combined study linking melt, hypersaline and dilute fluid inclusion chemistry, surface and reservoir fluid chemistry and whole rock lithochemistry and discuss the magmatic-hydrothermal chemical zoning in large silicic systems. New dataset of full lithogeochemistry in active geothermal systems of the TVZ refine the zoned chemical footprint left by both dilute meteoric-dominated and magmatic-hydrothermal fluids. Altered whole rock trace elements content (including precious metals and volatiles) shows major variation with depth, due to the influence of past hydrothermal activity, magmatic degassing, natural variability of the reservoir rocks, and current active fluid-rock interactions. The concentrations of Li, Cs, Tl, Bi, Sn, Ag, Se, Te, as well as Au, generally increase upward toward the paleosurface, where they are 10-100 times greater than near known or potentially 'active' intrusions. New direct in-situ analyses of trapped fluid inclusions in phenocrysts and hydrothermal veins associated with magmatic subsolidus crystallization are compared with liquid-dominated dilute fluid inclusions and geothermal fluids Li, Cs, B, Na, Cl, K content (and precious metals) providing a unique direct assessment of the role of each component (magma, rock, fluids) in New Zealand's world known geothermal systems.

  15. An assessment of AVIRIS data for hydrothermal alteration mapping in the Goldfield Mining District, Nevada

    NASA Technical Reports Server (NTRS)

    Carrere, Veronique; Abrams, Michael J.

    1988-01-01

    Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) data were acquired over the Goldfield Mining District, Nevada, in September 1987. Goldfield is one of the group of large epithermal precious metal deposits in Tertiary volcanic rocks, associated with silicic volcanism and caldera formation. Hydrothermal alteration consists of silicification along fractures, advanced agrillic and argillic zones further away from veins and more widespread propylitic zones. An evaluation of AVIRIS data quality was performed. Faults in the data, related to engineering problems and a different behavior of the instrument while on-board the U2, were encountered. Consequently, a decision was made to use raw data and correct them only for dark current variations and detector read-out-delays. New software was written to that effect. Atmospheric correction was performed using the flat field correction technique. Analysis of the data was then performed to extract spectral information, mainly concentrating on the 2 to 2.45 micron window, as the alteration minerals of interest have their distinctive spectral reflectance features in this region. Principally kaolinite and alunite spectra were clearly obtained. Mapping of the different minerals and alteration zones was attempted using ratios and clustering techniques. Poor signal-to-noise performance of the instrument and the lack of appropriate software prevented the production of an alteration map of the area. Spectra extracted locally from the AVIRIS data were checked in the field by collecting representative samples of the outcrops.

  16. Hydrothermal minerals and microstructures in the Silangkitang geothermal field along the Great Sumatran fault zone, Sumatra, Indonesia

    USGS Publications Warehouse

    Moore, Diane E.; Hickman, S.; Lockner, D.A.; Dobson, P.F.

    2001-01-01

    Detailed study of core samples of silicic tuff recovered from three geothermal wells along the strike-slip Great Sumatran fault zone near Silangkitang, North Sumatra, supports a model for enhanced hydrothermal circulation adjacent to this major plate-boundary fault. Two wells (A and C) were drilled nearly vertically ??1 km southwest of the eastern (i.e., the principal) fault trace, and the third, directional well (B) was drilled eastward from the site of well A to within ??100 m of the principal fault trace. The examined core samples come from depths of 1650-2120 m at measured well temperatures of 180-320 ??C. The samples collected near the principal fault trace have the highest temperatures, the largest amount of secondary pore space that correlates with high secondary permeability, and the most extensive hydrothermal mineral development. Secondary permeability and the degree of hydrothermal alteration decrease toward the southwestern margin of the fault zone. These features indicate episodic, localized flow of hot, possibly CO2-rich fluids within the fault zone. The microstructure populations identified in the core samples correlate to the subsidiary fault patterns typical of strike-slip faults. The geothermal reservoir appears to be centered on the fault zone, with the principal fault strands and adjoining, highly fractured and hydrothermally altered rock serving as the main conduits for vertical fluid flow and advective heat transport from deeper magmatic sources.

  17. Characterization and modeling of illite crystal particles and growth mechanisms in a zoned hydrothermal deposit, Lake City, Colorado

    USGS Publications Warehouse

    Bove, D.J.; Eberl, D.D.; McCarty, D.K.; Meeker, G.P.

    2002-01-01

    Mean thickness measurements and crystal-thickness distributions (CTDs) of illite particles vary systematically with changes in hydrothermal alteration type, fracture density, and attendant mineralization in a large acid-sulfate/Mo-porphyry hydrothermal system at Red Mountain, near Lake City, Colorado. The hydrothermal illites characterize an extensive zone of quartz-sericite-pyrite alteration beneath two deeply rooted bodies of magmatic-related, quartz-alunite altered rock. Nineteen illites from a 3000 ft vertical drill hole were analyzed by XRD using the PVP-10 intercalation method and the computer program MudMaster (Bertaut-Warren-Averbach technique). Mean crystallite thicknesses, as determined from 001 reflections, range from 5-7 nanometers (nm) at depths from 0-1700 ft, then sharply increase to 10-16 nm at depths between 1800-2100 ft, and decrease again to 4-5 nm below this level. The interval of largest particle thickness correlates strongly with the zone of most intense quartz-sericite-pyrite alteration (QSP) and attendant high-density stockwork fracturing, and with the highest concentrations of Mo within the drill core. CTD shapes for the illite particles fall into two main categories: asymptotic and lognormal. The shapes of the CTDs are dependent on conditions of illite formation. The asymptotic CTDs correspond to a nucleation and growth mechanism, whereas surface-controlled growth was the dominant mechanism for the lognormal CTDs. Lognormal CTDs coincide with major through-going fractures or stockwork zones, whereas asymptotic CTDs are present in wallrock distal to these intense fracture zones. The increase in illite particle size and the associated zone of intense QSP alteration and stockwork veining was related by proximity to the dacitic magma(s), which supplied both reactants and heat to the hydrothermal system. However, no changes in illite polytype, which in other studies reflect temperature transitions, were observed within this interval.

  18. The tin zone: sediment-hosted hydrothermal tin mineralization at Rooiberg, South Africa

    NASA Astrophysics Data System (ADS)

    Rozendaal, A.; Misiewicz, J. E.; Scheepers, R.

    1995-04-01

    The Rooiberg tin field, also known as the Rooiberg Fragment, is located within the western lobe of the Bushveld Complex. The fragment is triangular-shaped, consists of early Proterozoic Transvaal Sequence volcano-sedimentary rocks, and is surrounded by granitoid intrusives of the Lebowa Granite Suite. Practically all the significant tin deposits are hosted by arkoses, located towards the transition with shaly arkoses at the stratigraphic top of the Boschoffsberg Quartzite Member. This stratabound distribution of individual deposits gave rise to the concept of a regionally developed continuous stanniferous zone. On regional scale, the individual deposits are broadly similar and are collectively classified as replacement and open space-filling type. Particular styles of mineralization such as tourmaline pockets/orbicules, disseminated cassiterite, steep and flat dipping sulphidic fractures and hydrothermal carbonate breccias appear to dominate each mine. Petrological and geochemical investigations of four mineralized centres, indicated the presence of a 500 600 m thick stratified zone of pervasively altered clastic sedimentary rocks of possible arkosic precursor composition. Alteration displays a distinct zonal distribution consisting of a grey-green sodic (albitized) foot wall, an approximately 80 m transitional sericitized-tourmalinized sulphidic tin zone and red hematitic potassic hanging wall. The observed zonal pattern and localization of economically significant cassiterite, is explained by the evolutionary path of magmatic stanniferous hydrothermal fluids genetically related to the surrounding acid phase of the Bushveld Complex. Areas of high fracture density, the tectonic focal points, acted as conduits for the ascending reactive fluids. Factors such as fluid-lithostatic pressure equilibration, limited fracture evolution and/or impermeable shaly arkose retarded this ascent. As a result accumulation, lateral spreading of fluid and pervasive alteration occurred

  19. Geothermal potential of Caledonian granites in Ireland and the Isle of Man: Implications from hydrothermal alteration

    NASA Astrophysics Data System (ADS)

    Fritschle, Tobias; Daly, J. Stephen; Whitehouse, Martin J.; Buhre, Stephan; McConnell, Brian; The Iretherm Team

    2015-04-01

    Ordovician to Devonian (Caledonian) granites are common in the Iapetus Suture Zone (ISZ) in Ireland and Britain. Some of these, e.g., the buried Kentstown and Glenamaddy granites, are situated beneath Upper Palaeozoic sedimentary basins, and hence are potential geothermal targets. Numerous granites of similar age and related origin (Fritschle et al., 2014) are exposed astride the ISZ. They are considered to be analogous to the buried ones, and their geochemical characteristics are used as a proxy for the buried granites as samples from deep drilling are naturally limited. The whole-rock geochemistry of nine granite intrusions (71 samples, including both hydrothermally altered and unaltered samples) varies significantly, but with no obvious geographical control. The granites are S- and I-Types with ASI (Aluminium Saturation Index) between 0.7 - 1.4. Average heat production rates range from 1.4 μW/m³ for the Leinster Granite to 4.9 μW/m³ for the Drogheda Granite (Fritschle et al., 2015). The heat-producing elements uranium (U), thorium (Th) and potassium (K) and calculated heat production rates generally correlate positively with niobium and rubidium concentrations. However, S-Type compared to I-Type granites show elevated abundances in rubidium (>130 ppm) and usually have a lower Th/U ratio. Altered samples tend to have a higher Th/U ratio compared to unaltered ones. Within individual plutons trends of decreasing heat production rates with increasing Th/U ratios were observed. This trend is attributed to the hydrothermal redistribution of the mobile heat-producing element uranium. This is also implied by uranium-enrichment in hydrothermally generated Ca and Si-veinlets. Metasomatic processes such as hydrothermal alteration appear capable of significantly redistributing mobile elements such as uranium. Hence, these processes may act as a major mechanism controlling the granite's heat production budget, often shaping a pluton's geothermal exploitation potential

  20. Hydrothermal Convection and Aqueous Alteration in Carbonaceous Chondrite Parent Bodies

    NASA Astrophysics Data System (ADS)

    Palguta, Jennifer; Travis, B. J.; Schubert, G.

    2006-09-01

    Carbonaceous chondrites (CCs) are derived from undifferentiated icy planetesimals and are the most primitive meteorites. The information that we can derive from CCs depends largely on our understanding the effects of water in carbonaceous chondrite parent bodies (CCPBs). The way water influenced the parent bodies’ evolution depends partly on the flow rates and patterns of the water circulation. The first quantitative models for the thermal evolution of CCPBs were based on parameterized hydrothermal convection and homogeneous alteration. Recent work has presented full models of hydrothermal convection in an internally heated, self-gravitating porous sphere. These results illustrate that the convective patterns in CCPBs are not uniform. Some regions of the body experience little to no pore water flow while other regions experience hundreds of pore volumes. It has long been held that CC meteorites of different chemical groups come from distinct parent bodies. Simulations showing heterogeneous patterns of fluid flow in CCPBs have led to the suggestion that parent bodies could be heterogeneously altered and, consequently, one parent body could be a source for multiple groups of CC meteorites. Previously, no numerical convection simulations of CCPBs have included water-rock reactions. We have coupled the computer code MAGHNUM with the reaction package PHREEQC. We use MAGHNUM to simulate the dynamic freezing, thawing and flow of water in a radiogenically-heated, self-gravitating body. The accompanying water-rock interactions are modeled with PHREEQC. Flow and chemistry are coupled through, for example, reaction rates and temperature. This work was supported by a grant from the Institute of Geophysics and Planetary Physics at Los Alamos National Laboratory.

  1. Postimpact hydrothermal alteration of the Manson impact structure

    NASA Astrophysics Data System (ADS)

    McCarville, P.; Crossey, L. J.

    1994-07-01

    Core materials from the Manson impact structure (MIS), Manson, Iowa, are examined in order to evaluate postimpact alteration processes. Interpretation of the high-temperature postimpact hydrothermal system is based on mineralogic investigation. MIS rocks from the M1, M7, M8, and M10 cores obtained by the continental scientific drilling project (CSDP) in 1991 and 1992 are used in this study. All lithologies, including the sedimentary clast breccias (SCB), crystalline clast breccias (CCB), and central peak crystalline peaks (CPC), have been described previously. Emphasis is placed on fluid conduits that cross-cut all these lithologies. Analytical techniques include petrography, Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). The minerals are grouped according to their temperatures of occurrence in modern geothermal systems. The highest temperatures in the MIS are represented by a garnet and ferroactinolite assemblage (assemblage I). Assemblage II contains epidote, prehnite, and wollastonite, which represents slightly lower temperatures in the system. The existence of laumontite, quartz, and adularia defines a third assemblage. Assemblage IV is defined by calcite and clays, and represents the lowest alteration temperature at the MIS. These temperature-sensitive calc-silicates serve to constrain the fluid temperatures of the MIS hydrothermal system. Assemblage I suggests that the system reached over 300 C. Successively decreasing temperatures through time, approaching ambient temperatures, are suggested by the lower temperature assemblages II, III, and IV. A model for the cooling history of the MIS is reported elsewhere. The distribution of these high-temperature minerals points to the central uplift, not the melt sheet, as being the heat source for the system.

  2. The partitioning of uranium and neptunium onto hydrothermally altered concrete

    SciTech Connect

    Zhao, P.; Allen, P.G.; Sylwester, E.R.; Viani, B.E.

    1999-10-14

    Cementitious materials that are used to construct the ground support for high-level repositories have a high probability of interacting with radionuclide-bearing fluids derived from failed waste packages. Cementitious materials provide a highly alkaline environment; pore fluids in concrete can have pH {gt} 10 for thousands to hundreds of thousands of years. Studies have shown that fresh concrete and cement phases strongly retard or immobilize certain actinides. Consequently, cementitious materials may serve as a barrier to the release of the radionuclides to the far field. However, the effect of thermal alteration of these materials, which may occur in high-level repositories, on their interaction with radionuclides has not been addressed. In contrast to retardation, colloidal silica-enriched particles that are abundant in the pore fluids of cementitious materials may facilitate radionuclide migration through the near-field into the adjacent geological environment. Due to the uncertainties of these two opposite effects, it is important to investigate the interaction of actinides with cementitious materials under varying conditions. It is expected that cementitious materials in high-level waste repositories will be subjected to and altered by hot dry and/or humid conditions forhundreds to thousands of years by the time they interact with radionuclide-bearing fluids. After alteration, the chemical and mineralogical properties of these materials will be significantly different from that of the as-placed or fresh concrete. To assess the effect that this alteration would have on radionuclide interactions, samples of hardened concrete (untreated concrete) were hydrothermally heated at 200 C for 8 months (treated concrete). The concrete used in the experiments consisted of portland cement with an aggregate of dolomitic limestone. X-ray diffraction analysis has shown that portlandite and amorphous calcium silicate hydrate gels were converted to the crystalline calcium

  3. Hydrothermal Alteration in the PACMANUS Hydrothermal Field: Implications From Secondary Mineral Assemblages and Mineral Chemistry, OPD Leg 193

    NASA Astrophysics Data System (ADS)

    Lackschewitz, K. S.; Kummetz, M.; Kummetz, M.; Ackermand, D.; Botz, R.; Devey, C. W.; Singer, A.; Stoffers, P.

    2001-12-01

    Leg 193 of the Ocean Drilling Program investigated the subsurface nature of the active PACMANUS hydrothermal field in the Manus backarc basin near Papua New Guinea. Drilling in different areas on the felsic neovolcanic Pual Ridge, including the high-temperature black smoker complex of Roman Ruins and the low-temperature Snowcap site with diffusive discharge yielded a complex alteration history with a regional primary alteration being overprinted by a secondary mineralogy. The intense hydrothermal alteration at both sites shows significant differences in the secondary mineralogy. At Roman Ruins, the upper 25 m of hydrothermally altered rocks are characterized by a rapid change from secondary cristobalite to quartz, implying a high temperature gradient. From 10 to 120 mbsf the clay mineralogy is dominated by illite and chlorite. The chlorite formation temperature calculated from oxygen isotope data lies at 250° C in 116 mbsf which is similar to the present fluid outflow temperatures of 240-250° C (Douville et al., 1999, Geochim. Cosmochim. Acta, 63, 627-643). Drilling in the Snowcap field recovered evidence for several stages of hydrothermal alteration. Between 50 and 150 mbsf, cristobalite and chlorite are the most abundant alteration minerals while hydrothermal pyrophyllite becomes abundant in some places At 67 mbsf, the isotopic composition of pyrophyllite gives a temperature for ist formation at 260° C whereas at 77 and 116 mbsf the pyrophyllite displays the highest temperatures of formation (>300° C). These temperatures are close to the maximum measured borehole temperatures of 313° C. The appearance of assemblages of chlorite, chlorite-vermiculite, chlorite-vermiculite-smectite and illite-smectite as well as the local development of corrensite below 150 mbsf suggests that the alteration at Snowcap may be more complex than that beneath Roman Ruins. Detailed geochemical studies of the authigenic clay mineral phases will provide further insights into the

  4. Mg Isotope Fractionation During Hydrothermal Ultramafic Rock Alteration

    NASA Astrophysics Data System (ADS)

    Beinlich, A.; Mavromatis, V.; Austrheim, H.; Oelkers, E. H.

    2013-12-01

    Both riverine and ocean waters are enriched in 24Mg compared to the homogenous chondritic Mg isotopic composition of the Earth's mantle requiring a fractionation step that is generally attributed to low temperature continental crust weathering [1,2,3]. Here we present new observations on the Mg isotope fractionation during hydrothermal alteration of ultramafic rocks from three different localities in Norway, the Linnajavri Ultramafic Complex (LUC), the Feragen Ultramafic Body (FUB), and the Solund Sedimentary Basin (SSB). Mineral separates of coexisting olivine and serpentine from serpentinized peridotite samples from the FUB and SSB exhibit invariant Mg isotope ratios suggesting that serpentinization does not fractionate Mg isotopes. In contrast, antigorite carbonation at the LUC resulted in significant inter-mineral Mg isotope fractionation among the antigorite, magnesite, and talc. The carbonation of the natural samples is constrained by O isotope thermometry at ~275 °C [4] and hence closes the temperature gap between previous investigations of the natural distribution of Mg isotopes during surface weathering and magmatic processes. Textures, mass-balance, and reaction path considerations indicate that antigorite carbonation conserved Mg and Si. The precursor antigorite has an isotopic composition of δ26Mg (DSM3)=-0.11×0.05 ‰, whereas the talc is enriched in 26Mg with mean δ26Mg=0.17×0.08 ‰ and the magnesite is depleted in 26Mg with mean δ26Mg=-0.95×0.15 ‰. This hydrothermal fractionation has significant implications for the Mg isotopic compositions of natural surface waters. Our results suggest that carbonation reactions beneath off-axis low temperature hydrothermal vent sites may exert an important control on the Mg isotope ratio in ocean water. As carbonate minerals dissolve significantly faster than silicate minerals [5,6], the chemical weathering of carbonated ultramafic and by analogy mafic rocks on the continents will yield isotopically

  5. Hydrothermal alteration as a trigger mechanism for earthquake swarms: the Vogtland/NW Bohemia region as a case study

    NASA Astrophysics Data System (ADS)

    Heinicke, J.; Fischer, T.; Gaupp, R.; Götze, J.; Koch, U.; Konietzky, H.; Stanek, K.-P.

    2009-07-01

    Earthquake swarms occur mostly in regions with CO2-enriched pore fluids. It is generally accepted that both geodynamic stress accumulation and critical pore fluid pressures act as a triggering mechanism for most seismic events. The new thesis presented here is that hydrothermal alteration processes in fault zones help facilitate the shear failure propagation due to mechanical weakening and dissolution of the wall rock, in addition to the normal shear stress and fluid overpressure. The basic idea that stress corrosion cracking results from chemical weakening and comminution has been discussed for many years. However, it has not yet been applied to explain the earthquake swarm phenomenon. Studies of extensive alteration as well as the latest investigations of CO2 sequestration give evidence that these high dissolution rates of wall rock in contact with an acid fluid phase exist in seismogenic fault zones. Several indications support the assumption that in the Vogtland/NW Bohemia region, the weakening of stressed fault zones by hydrothermal alteration could take place at seismogenic depths and could generate earthquake swarms. Investigations of quartz samples from the fracture zones by means of cathodoluminescence as well as spatiotemporal analysis of seismicity and numerical modelling of alteration-induced earthquake swarms support this hypothesis.

  6. Spectral reflectance analysis of hydrothermal alteration in drill chips from two geothermal fields, Nevada

    NASA Astrophysics Data System (ADS)

    Lamb, A. K.; Calvin, W. M.

    2010-12-01

    We surveyed drill chips with a lab spectrometer in the visible-near infrared (VNIR) and short-wave infrared (SWIR) regions, 0.35-2.5 μm, to evaluate hydrothermal alteration mineralogy of samples from two known geothermal fields in western Nevada. Rock is fractured into small pieces or “chips” during drilling and stored in trays by depth interval. The drill chips are used to determine subsurface properties such as lithology, structure, and alteration. Accurately determining alteration mineralogy in the geothermal reservoir is important for indicating thermal fluids (usually associated with fluid pathways such as faults) and the highest temperature of alteration. Hydrothermal minerals, including carbonates, iron oxides, hydroxides, sheet silicates, and sulfates, are especially diagnostic in the VNIR-SWIR region.. The strength of reflectance spectroscopy is that it is rapid and accurate for differentiating temperature-sensitive minerals that are not visually unique. We examined drill chips from two western Nevada geothermal fields: Hawthorne (two wells) and Steamboat Springs (three wells) using an ASD lab spectrometer with very high resolution. The Steamboat Hills geothermal field has produced electricity since 1988 and is well studied, and is believed to be a combination of extensional tectonics and magmatic origin. Bedrocks are Cretaceous granodiorite intruding into older metasediments. Hot springs and other surface expressions occur over an area of about 2.6 km2. In contrast, the Hawthorne geothermal reservoir is a ‘blind’ system with no surface expressions such as hot springs or geysers. The geothermal field is situated in a range front fault zone in an extensional area, and is contained in Mesozoic mixed granite and meta-volcanics. We collected spectra at each interval in the chip trays. Interval length varied between 10’ and 30’. - Endmember analysis and mineral identification were performed -using standard analysis approaches used to map mineralogy

  7. Hydrothermal alteration in research drill hole Y-2, Lower Geyser Basin, Yellowstone National Park, Wyoming

    SciTech Connect

    Bargar, K.E.; Beeson, M.H.

    1981-05-01

    Y-2, a US Geological Survey research diamond-drill hole in Lower Geyser Basin, Yellowstone National Park, was drilled to a depth of 157.4 meters. The hole penetrated interbedded siliceous sinter and travertine to 10.2 m, glacial sediments of the Pinedale Glaciation interlayered with pumiceous tuff from 10.2 to 31.7 m, and rhyolitic lavas of the Elephant Back flow of the Central Plateau Member and the Mallard Lake Member of the Pleistocene Plateau Rhyolite from 31.7 to 157.4 m. Hydrothermal alteration is pervasive in most of the nearly continuous drill core. Rhyolitic glass has been extensively altered to clay and zeolite minerals (intermediate heulandite, clinoptilolite, mordenite, montmorillonite, mixed-layer illite-montmorillonite, and illite) in addition to quartz and adularia. Numerous veins, vugs, and fractures in the core contain these and other minerals: silica minerals (opal, ..beta..-cristobalite, ..cap alpha..-cristobalite, and chalcedony), zeolites (analcime, wairakite, dachiardite, laumontite, and yugawaralite), carbonates (calcite and siderite), clay (kaolinite and chlorite), oxides (hematite, goethite, manganite, cryptomelane, pyrolusite, and groutite), and sulfides (pyrhotite and pyrite) along with minor aegirine, fluorite, truscottite, and portlandite. Interbedded travertine and siliceous sinter in the upper part of the drill core indicate that two distinct types of thermal water are responsible for precipitation of the surficial deposits, and further that the water regime has alternated between the two thermal waters more than once since the end of the Pinedale Glaciation (approx. 10,000 years B.P.). Alternation of zones of calcium-rich and sodium- and potassium-rich hydrothermal minerals also suggests that the calcium-rich and sodium- and potassium-rich hydrothermal minerals also suggests that the water chemistry in this drill hole varies with depth.

  8. Soil-plant-microbial relations in hydrothermally altered soils of Northern California

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soils developed on relict hydrothermally altered soils throughout the Western United States present unique opportunities to study the role of geology on above and belowground biotic activity and composition. Soil and vegetation samples were taken at three unaltered andesite and three hydrothermally ...

  9. Central Remnant Craters on Mars - Localization of Hydrothermal Alteration at the Edge of Crater Floors?

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.

    2001-01-01

    Localized erosion at the edge of crater floors may be caused by hydrothermal alteration due to focusing of fluid flow around an impact melt sheet following crater formation, coupled with hydrothermal self-sealing under the center of the crater. Additional information is contained in the original extended abstract.

  10. The origin of massive hydrothermal alterations: what drives fluid flow?

    NASA Astrophysics Data System (ADS)

    Gomez-Rivas, Enrique; Bons, Paul D.; Martín-Martín, Juan-Diego; Corbella, Mercè; Stafford, Sherry L.; Griera, Albert; Teixell, Antonio; Salas, Ramón; Travé, Anna

    2014-05-01

    Hydrothermal alterations form when fluids warmer than the host rocks flow through them dissolving and precipitating minerals. These fluids typically flow upwards from deeper geologic units using faults as major conduits. In some cases, hydrothermal alterations affect large (km-scale) rock volumes. One example of such process is the massive high-temperature dolostones that crop out at the Benicàssim outcrop analogue (Maestrat Basin, E Spain). In this area, seismic-scale fault-controlled stratabound dolostone bodies extend over several kilometres away from large-scale faults, replacing Lower Cretaceous limestones. The fluid responsible for such alteration is a seawater-derived brine that interacted with underlying Permian-Triassic and Paleozoic basement rocks. The estimated volume of fluid required to produce the Benicàssim dolomitization is huge, with fluid-rock ratios in the order of several tens to a few hundreds, depending on composition and reaction temperature (Gomez-Rivas et al., 2014). An open key question is what brought this warm fluid (80 - 150 ºC) upwards to a depth of less than 1 km, where the dolomitization reaction took place. The driving forces should have been able not only to provide sufficient fluid volumes at shallow depths but also to heat up the whole host rock, including the non-replaced limestones. There are two hyphoteses for driving a warm fluid upwards in the Maestrat Basin: (a) rapid release through faults of overpressured solutions in recurrent pulses and (b) thermal convection. We present a series of heat and fluid flow numerical simulations to constrain the dolomitization conditions under these two end-member cases. The results indicate that in a pulsating model the fluid must flow upwards at velocities higher than cm/s to keep their elevated temperature. Otherwise they cool down quickly, and the host rocks cannot be heated. Such velocities can be reached if the fluid flow velocity equals that of fracture propagation, as in mobile

  11. Petrology and Geochemistry of Hydrothermally Altered Volcanic Rocks in the Iheya North Hydrothermal Field, Middle Okinawa Trough

    NASA Astrophysics Data System (ADS)

    Yamasaki, T.

    2015-12-01

    The Iheya North hydrothermal field is located in the middle Okinawa Trough, a young and actively spreading back-arc basin extending behind the Ryukyu arc-trench system in the southeastern margin of the East China Sea. In this hydrothermal field, two scientific drilling expeditions (IODP Exp 331 and SIP CK14-04) were conducted using a deep-sea drilling vessel "Chikyu," and samples from a total of 27 holes were taken. Through these expeditions, Kuroko-type volcanogenic massive sulfide deposits (VMS), hydrothermally altered volcanic rocks, and pumiceous and pelagic sediments were recovered. The recovered core provided important information about the relationship between hydrothermal activity, alteration, and ore mineralization. Whole-rock major element composition and trace element (TE) patterns of pumices were very similar to those of rhyolites in the middle Okinawa Trough (RMO). However, pumices were relatively enriched in chalcophile elements Sr and Nb, which suggest incipient mineralization. Volcanic rock generally demonstrated strong silicification and was greenish pale gray in color. Regardless of severe alteration, some rock displayed major element composition broadly similar to the RMO. Alteration was evidenced by an increase in the content of SiO2 and MgO, and decrease in Al2O3, Na2O, and K2O content. The most striking geochemical feature of altered volcanic rock was the discordance between texture and the degree of modification of TEs. Some samples showed decussate texture occupied by petal-like quartz with severe silicification, but no prominent disturbance of concentration and patterns of TEs were observed. In contrast, samples with well-preserved igneous porphyritic texture showed very low TE content and modification of TE patterns. These results suggest that the modification of texture and composition of TEs, as well as silicification, do not occur by a uniform process, but several processes. This may reflect the differences in temperature and the

  12. Hydrothermal alteration of cementitious materials, Part II: second and third batch of samples

    SciTech Connect

    Meike, A.; Myers, K. B. L.

    1997-10-25

    This report describes experiments designed to provide data for a quick engineering assessment of the microstructural, mineralogical, and mechanical changes in hydrothermally altered concrete and changes in associated water chemistry.

  13. Impact of hydrothermal alteration on lava dome stability: a numerical modelling approach

    NASA Astrophysics Data System (ADS)

    Detienne, Marie; Delmelle, Pierre

    2016-04-01

    Lava domes are a common feature of many volcanoes worldwide. They represent a serious volcanic hazard as they are prone to repeated collapses, generating devastating debris avalanches and pyroclastic flows. While it has long been known that hydrothermal alteration degrades rock properties and weakens rock mass cohesion and strength, there is still little quantitative information allowing the description of this effect and its consequences for assessing the stability of a volcanic rock mass such as a lava dome. In this study, we use the finite difference numerical model FLAC 3D to investigate the impact of hydrothermal alteration on the stability of a volcanic dome lying on a flat surface. Different hydrothermal alteration distributions were tested to encompass the variability observed in natural lava domes. Rock shear strength parameters (minimum, maximum and mean cohesion "c" and friction angle "φ" values) representative of various degrees of hydrothermal rock alteration were used in the simulations. The model predicts that reduction of the basement rock's shear strength decreases the factor of safety significantly. A similar result is found by increasing the vertical and horizontal extension of hydrothermal alteration in the basement rocks. In addition, pervasive hydrothermal alteration within the lava dome is predicted to exert a strong negative influence on the factor of safety. Through reduction of rock porosity and permeability, hydrothermal alteration may also affect pore fluid pressure within a lava dome. The results of new FLAC 3D runs which simulate the effect of hydrothermal alteration-induced pore pressure changes on lava dome stability will be presented.

  14. Mapping of hydrothermal alternation zones and regional rock types using computer enhanced ERTS MSS images. [Nevada

    NASA Technical Reports Server (NTRS)

    Rowan, L. C.; Wetlaufer, P. H.; Billingsley, F. C.; Goetz, A. F. H.

    1974-01-01

    A combination of digital computer processing and color compositing of ERTS MSS images has been used to map hydrothermal alternation zones and regional rock types in south-central Nevada. The technique is based on enhancement of subtle visible and near infrared reflectivity differences between mineralogically dissimilar rocks, especially unaltered and altered rocks. MSS spectral bands are ratioed, pixel by pixel, in the computer and subsequently stretched. These ratio values are used to produce a new black and white image which shows the subtle spectral reflectivity differences. Additional enhancement is achieved by preparing color composites of two or more stretched ratio images. The choice of MSS bands for rationing depends on the spectral reflectance properties of the rocks to be discriminated. Although this technique is in the initial stage of development and is untested in other areas, it already appears to have considerable potential for targeting mineral prospects and for regional geologic mapping.

  15. Application of graphite as a geothermometer in hydrothermally altered metamorphic rocks of the Merelani-Lelatema area, Mozambique Belt, northeastern Tanzania

    NASA Astrophysics Data System (ADS)

    Malisa, Elias Pausen

    1998-02-01

    Upper Precambrian pelitic and psammitic gneisses in the Mozambique Belt are usually graphite rich. The determination of crystallisation temperatures around and in the hydrothermally altered rocks of the Merelani-Lelatema mining areas, northeastern Tanzania, were made by studying the lattice parameter C of graphite. In this way, the migration of the chromophore elements giving colour to the gemstones, e.g. tanzanite, green garnet and green tourmaline in the area, can be studied. Within the hydrothermally altered zone graphite gives temperatures that range from 523°C to 880°C. These temperatures are much higher than the 390-440°C obtained through fluid inclusion studies of tanzanite, which indicates that the graphite was not hydrothermally introduced. Furthermore the hydrothermal solutions are post-metamorphic.

  16. Tourmaline nodules: indicators of hydrothermal alteration and SnZn(W) mineralization in the Cape Granite Suite, South Africa

    NASA Astrophysics Data System (ADS)

    Rozendaal, A.; Bruwer, L.

    1995-07-01

    Tourmaline and quartz-tourmaline nodular aggregates are common in S-type granitoids of the Cape Granite Suite in the Tygerberg terrane of the Neoproterozoic Saldania belt, South Africa. Most of the aggregates occur within the 200 km long Yzerfontein-Helderberg linear zone, which hosts a diversity of exo- and endomagmatic base and precious metal deposits. The conspicuous dark spherical nodules, with diameters of up to 40 cm, are surrounded by a leucocratic halo and consist mainly of tourmaline (schorl) and quartz. Spatial and temporal relationships indicate that the nodules are features of post-magmatic replacement related to the hydrothermal alteration of crystallized granite. Their distribution is possibly controlled by fluid movement along micro-fractures and diffusion along grain boundaries. Nodule composition suggests that the hydrothermal fluids that formed them were oxidizing and chemically simple, mainly B-(F)-rich and consequently acidic with anomalously high concentrations of Zn, Sn and Ga. Where proximal to Sn-Zn-(W) quartz-vein deposits, spatial relations show that nodule formation is more widespread than and preceded the vein mineralization. This relationship, coupled with the similar metal association of the nodules and veins, suggests a common hydrothermal fluid source. It also allows the use of tourmaline nodules as regional indicators of hydrothermal alteration and of late-stage vein deposits of similar metal association.

  17. Hydrothermal Alteration Constrained by Mineral Assemblages on Mars: Evidence from Craters Near Syrtis Major

    NASA Astrophysics Data System (ADS)

    Mustard, J. F.; Ehlmann, B. L.; Murchie, S. L.

    2009-12-01

    contains small breccia blocks, perhaps emplaced as breccia dikes. The formation of prehnite is constrained to < 3 kbar and 200-350°C. The key question that we are pursuing is does the aqueous alteration pre-date crater formation or is it a consequence of post-impact hydrothermal activity? We will present detailed mapping of lithologic units, their mineral assemblages, and the geologic relationships to assess if the diagnostic mineral assemblages are associated with zones of alteration predicted by hydrothermal models for impact craters. Ehlmann, B. L., et al., 2008. Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract P34A-04. Ehlmann, B. L., et al., 2009. (in press) JGR-Planets. Marzo, G. A., et al., 2008. Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract P53A-1438. Mustard, J.F. et al., 2008. Nature 454, 305-309.

  18. Evolving hydrothermal systems in the Islas Orcadas fracture zone

    SciTech Connect

    Kimball, K.L.; Spear, F.S.; Gerlach, D.G.

    1985-01-01

    Petrographic and isotopic evidence suggest that the chemical and isotopic composition of fluids responsible for alteration of ultramafic rocks from the Islas Orcadas Fracture Zone evolve with time. Reaction space analyses of high T alterations indicate these reactions release small amounts of Mg, Fe and Si to the fluid. Calculations of equilibrium fluid compositions indicate fluids concentrated in metallic chloride species, suggesting 1) low water/rock ratios (<<1) or 2) reaction of the fluid with other rocks prior to its reaction with the ultramafics. Reaction space analyses of low T alterations show production of larger quantities of metallic species and are compatible with calculated fluid compositions at water/rock=1. In vein mineral separates, high T minerals have lower 87/86Sr and higher Sr than later, lower T minerals, suggesting MORB contamination of the early fluids and more seawater component in late fluids. In samples containing multiple generations of a mineral in one vein, earlier minerals have lower 87/86Sr than later minerals (more seawater at approx. 709.). Oxygen isotopes show MORB affinites.

  19. The mineral chemistry of hydrothermally altered and metamorphosed wall-rocks at the Stollberg Fe-Pb-Zn-Mn(-Ag) deposit, Bergslagen, Sweden

    NASA Astrophysics Data System (ADS)

    Ripa, M.

    1994-06-01

    The c. 1.9 Ga old Stollberg sulphide and Mnrich skarn iron ores and sulphide ores in Bergslagen, south-central Sweden are hosted by hydrothermally altered and metamorphosed felsic volcanic and volcaniclastic rocks. The ores are underlain by comformable alteration zones characterized by albite-gedrite-quartz and biotite-muscovite-plagioclase-K-feldspar-quartz +/- garnet assemblages. The present mineralogies are interpreted as medium-grade metamorphic equivalents to the original alteration mineral assemblages. PT-conditions during prograde regional metamorphism are semiquantatively determined to be 510 to 560 °C at approximately 3 kbar. With increasing modal content of gedrite and biotite in the alteration zones, the Mg/Fe ratios and XMg's in octahedral positions of these minerals also increase. In the gedrite-bearing strata, whole-rock Mg/Fe ratios remain constant, whereas in the biotite-rich unit the wholerock Mg/Fe trend is parallel to that of the biotites. The trends in the metamorphic mineral composition are interpreted to be a product of original changes in fluid composition during the evolution of a sub-seafloor hydrothermal system. During the initial stage of alteration, Fe-Mn-rich fluids altered the rocks, and during a later stage, the fluids became more Mg-rich, possibly due to entrainment of fresh seawater, and the alteration zones became relatively more Mg-rich. Sulphide precipitation was contemperaneous with Mg metasomatism, suggesting base metal precipitation was a function of the mixing of cool seawater with hydrothermal fluid. It is proposed that early hydrothermal alteration was associated with the deposition of areally extensive Fe-oxide formation, and that Mg metasomatism defines a second stage of hydrothermal activity during which sulphide mineralization overprinted the earlier formed Fe-oxide deposit.

  20. Geochemical element mobility during the hydrothermal alteration in the Tepeoba porphyry Cu-Mo-Au deposits at Balikesir, NW Turkey

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    The Tepeoba porphyry Cu-Mo-Au deposit represents one of the important copper source and mineral deposits in the Anatolian tectonic belt at Balikesir province, NW Turkey. It considered as a vein-type deposit locally associated with intense hydrothermal alteration within the brecciation, quartz stockwork veining, and brittle fracture zones in the main host rock that represented by hornfels, as well as generally related to the shallow intermediate to silicic intrusive Eybek pluton. Based on the field and geologic relationships and types of ore mineral assemblages and the accompanied alteration types, there are two mineralization zones; hypogene (primary) and oxidation/supergene zones are observed associated with three alteration zones; potassic, phyllic, and propylitic zones related to this porphyry deposit. The phyllic and propylitic alterations locally surrounded the potassic alteration. The ore minerals related to the hypogene zone represented by mostly chalcopyrite, Molybdenite, and pyrite with subordinate amount of marcasite, enargite, and gold. On the other hand they include mainly cuprite with chalcopyrite, pyrite and gold as well as hematite and goethite at the oxidation/supergene zone. This study deals with the quantitative calculations of the mass/volume changes (gains and losses) of the major and trace elements during the different episodes of alteration in this porphyry deposit. These mass balance data reveal that the potassic alteration zone that the main Cu- and Mo-enriched zone, has enrichment of K, Si, Fe, and Mg, and depletion of Na referring to replacement of plagioclase and amphibole by K-feldspar, sericite and biotite. While the propylitic alteration that is the main Mo- and Au-enriched zone is accompanied with K and Na depletion with enrichment of Si, Fe, Mg, and Ca forming chlorite, epidote, carbonate and pyrite. On the other hand the phyllic alteration that occurred in the outer part around the potassic alteration, characterized by less amount

  1. 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

  2. Near-field/altered-zone models report

    SciTech Connect

    Hardin, E. L., LLNL

    1998-03-01

    lithophysal units. These units are made up of moderately to densely welded, devitrified, fractured tuff. The rock's chemical composition is comparable to that of typical granite, but has textural features and mineralogical characteristics of large-scale, silicic volcanism. Because the repository horizon will be approximately 300 m below the ground surface and 200 m above the water table, the repository will be partially saturated. The welded tuff matrix in the host units is highly impermeable, but water and gas flow readily through fractures. The degree of fracturing in these units is highly variable, and the hydrologic significance of fracturing is an important aspect of site investigation. This report describes the characterization and modeling of a region around the potential repository--the altered zone--a region in which the temperature will be increased significantly by waste-generated heat. Numerical simulation has shown that, depending on the boundary conditions, rock properties, and repository design features incorporated in the models, the altered zone (AZ) may extend from the water table to the ground surface. This report also describes models of the near field, the region comprising the repository emplacement drifts and the surrounding rock, which are critical to the performance of engineered components. Investigations of near-field and altered-zone (NF/AZ) processes support the design of underground repository facilities and engineered barriers and also provide constraint data for probabilistic calculations of waste-isolation performance (i.e., performance assessment). The approach to investigation, which is an iterative process involving hypothesis testing and experimentation, has relied on conceptualizing engineered barriers and on performance analysis. This report is a collection, emphasizing conceptual and numerical models, of the recent results contributed from studies of NF/AZ processes and of quantitative measures of NF/AZ performance. The selection and

  3. 3D modelling of hydrothermal alteration associated with VHMS deposits in the Kristineberg area, Skellefte district, northern Sweden

    NASA Astrophysics Data System (ADS)

    Chmielowski, Riia M.; Jansson, Nils; Persson, Mac Fjellerad; Fagerström, Pia

    2016-01-01

    This contribution presents a 3D assessment of metamorphosed and deformed, hydrothermally altered volcanic rocks, hosting the massive sulphide deposits of the Kristineberg area in the 1.9 Ga Skellefte mining district in northern Sweden, using six calculated alteration parameters: the Ishikawa alteration index, the chlorite-carbonate-pyrite index and calculated net mass changes in MgO, SiO2, Na2O and Ba. The results, which are also available as film clips in the Supplementary data, confirm inferences from geological mapping; namely that the sericite- and chlorite-rich alteration zones have complex and cross-cutting geometries and that most of these zones are semi-regional in extent and range continuously from surface to over a kilometre deep. The major known massive sulphide deposits occur proximal to zones characterised by coincidence of high values for the alteration index and chlorite-carbonate-pyrite index and large MgO gains, which corresponds to zones rich in magnesian silicates. These zones are interpreted as the original chlorite-rich, proximal parts the alteration systems, and form anomalies extending up to 400 m away from the sulphide lenses. In addition, the stratigraphically highest VHMS are hosted by rocks rich in tremolite, talc, chlorite and dolomite with lesser clinozoisite, which have high chlorite-carbonate-pyrite index and low-medium alteration index values, reflecting a greater importance of some chlorite-carbonate alteration at this stratigraphic level. Vectoring towards massive sulphide deposits in this area can be improved by combining the AI and CCPI indexes with calculated mass changes for key mobile elements. Of the ones modelled in this study, MgO and SiO2 appear to be the most useful.

  4. Correlation of wireline log characteristics with hydrothermal alteration and other reservoir properties of the Salton Sea and Westmorland geothermal fields, Imperial Valley, California, USA

    SciTech Connect

    Muramoto, F.S.; Elders, W.A.

    1984-05-01

    A detailed study of wireline logs from 11 wells in the Salton Sea and Westmorland geothermal systems was undertaken in order to determine the effects of hydrothermal alteration on the response of electrical and gamma-gamma density well logs. For the Salton Sea geothermal field, definite correspondence between log responses and hydrothermal mineralogy is evident, which in turn is related to the physical properties of the rocks. Three hydrothermal and one unaltered zone can be identified from log data on shales. These are: (1) the unaltered montmorillonite zone (<100/sup 0/ to 190/sup 0/C); (2) the illite zone (100/sup 0/ to 190/sup 0/C to 230/sup 0/ to 250/sup 0/C); (3) the chlorite zone (230/sup 0/ to 250/sup 0/C to 290/sup 0/ to 300/sup 0/C); and (4) the feldspar zone (>290/sup 0/ to 300/sup 0/C). The characteristic responses on well logs by which these zones are identified result primarily from changes in clay mineralogy of the shales and increases in density with progressive hydrothermal metamorphism. In the Westmorland geothermal field, differentiating mineral zones from log responses was only partially successful. However, analyses of both well log and petrologic data for wells Landers 1 and Kalin Farms 1 suggest that the former is heating up and the latter is cooling.

  5. Hydrothermal, deuteric and acidic basalt alteration at the Skouriotissa Mine, Cyprus: relevance for Mars.

    NASA Astrophysics Data System (ADS)

    Bost, N.; Westall, F.; Ramboz, C.; Fontaine, C.; Meunier, A.; Foucher, F.

    2012-04-01

    Basalts are the prevalent rock type on Mars and the products of aqueously altered basalts and hydrated minerals associated with basalts are of particular interest as possible tracers of a past, slightly more clement climate on the planet and/or magmatic processes [1,2]. Study of alteration processes of basalts on Earth that show some similarities to surface and subsurface processes occurring on Mars will help understand and interpret martian features. The Skouriotissa mine in Cyprus is an open pit copper mine (consisting of a very massive sulphide deposit, VMS) exposing the upper pillow basalt formation in the Troodos ophiolitic zone. The basalt has been altered by (1) hydrothermal and deuteritic processes and (2) acidic water (pH <5) associated with the mining working. We have analysed the mineralogical evolution of the basalt through different alteration facies (phyllosilicates, including Mg-smectite, vermiculite, nontronite, and zeolites), depending on the type of alteration. Similar mineralogical associations have been described on Noachian/early Hesperian Mars (e.g. [1,2.3]) and may have been formed by the same kinds of processes. These suites of rocks form part of the collection of Mars analogue rocks that is being prepared at the CNRS/Observatoire des Sciences de l'Univers en région Centre (OSUC) in Orléans to help calibrate present and future flight instruments (e.g. MSL, the international Mars- 2018 in situ mission). This collection is named International Space Analogue Rockstore (ISAR) and the relevant information is contained in the website: http://www.isar.cnars-orleans.fr [4,5]. [1] Bibring et al., 2006, Science 312; [2] Ehlmann et al., 2011, Nature 479; [3] Meunier et al., in prep. ; [4] Bost N. et al., in review (Icarus).[5] Bost N. et al., This Conference, abstract 1403.

  6. Hydrothermal circulation, serpentinization, and degassing at a rift valley-fracture zone intersection: Mid-Atlantic Ridge near 15[degree]N, 45[degree]W

    SciTech Connect

    Rona, P.A.; Nelson, T.A. ); Bougault, H.; Charlou, J.L.; Needham, H.D. ); Appriou, P. ); Trefry, J.H. ); Eberhart, G.L.; Barone, A. )

    1992-09-01

    A hydrothermal system characterized by high ratios of methane to both manganese and suspended particulate matter was detected in seawater sampled at the eastern intersection of the rift valley of the Mid-Atlantic Ridge with the Fifteen-Twenty Fracture Zone. This finding contrasts with low ratios in black smoker-type hydrothermal systems that occur within spreading segments. Near-bottom water sampling coordinated with SeaBeam bathymetry and camera-temperature tows detected the highest concentrations of methane at fault zones in rocks with the appearance of altered ultramafic units in a large dome that forms part of the inside corner high at the intersection. The distinct chemical signatures of the two types of hydrothermal systems are inferred to be controlled by different circulation pathways related to reaction of seawater primarily with ultramafic rocks at intersections of spreading segments with fracture zones but with mafic rocks within spreading segments.

  7. Castro ring zone: a 4,500-km2 fossil hydrothermal system in the Challis volcanic field, central Idaho.

    USGS Publications Warehouse

    Criss, R.E.; Ekren, E.B.; Hardyman, R.F.

    1984-01-01

    The largest fossil hydrothermal system occupying a 4500 km2 area in central Idaho is revealed by delta 18O studies. The remains of this meteoric-hydrothermal system are preserved within a sharply bounded, 15 km wide, 70-km-diameter annulus of low delta 18O rock (+2.0 to -8.8per mille) termed the Castro ring zone. The zone is centred on a less depleted (+4.5) core zone consisting of granitic rocks of the Castro pluton. This 700-km2 Eocene subvolcanic batholith has intruded, domed, and hydrothermally metamorphosed a thick sequence of Challis Volcanics, the stratigraphically low rocks in the 2000-km2 Van Horn Peak and the 1000-km2 Thunder Mountain cauldron complexes being most strongly altered. Less extreme 18O depletions occur in the youngest major ash-flow sheets of these complexes, indicating a vertical 18O gradient. Water/rock ratios of geothermal systems are surprisingly insensitive to the circulation scale.-L.-di H.

  8. Geochemistry of Phosphorus and Nitrogen in Volcanic Rocks Altered by Submarine Hydrothermal Activities at the Suiyo Seamount in Japan

    NASA Astrophysics Data System (ADS)

    Noda, M.; Kakegawa, T.; Naraoka, H.; Marumo, K.; Urabe, T.

    2002-12-01

    Phosphorus and nitrogen are essential major elements for all microorganisms. In order to understand the ecological conditions of subvent microorganisms and thermophilic microorganisms on ocean floor, it is necessary to understand the behavior of bio-essential elements not only in hydrothermal fluids but also in the subvent environment. Nine sites of hydrothermal discharging area were drilled in the Suiyo volcanic caldera, Izu-Ogasawara (Bonin) island-arc, western Pacific. Approximately 2 to 10 m deep drill core samples were recovered in the last two years. Chemical compositions and hydrothermal mineral assemblages in the drilled core samples were determined by XRF, ICP-MS, and XRD. Morphology of phosphorous-bearing minerals and their chemistry were examined by electron microprobe. Nitrogen isotopes were measured by the EA-IRMS system. Primary igneous-rock texture (such as euhedral plagioclase phenocryst) is found in the less altered rocks. They often associated with montmorillonite. Highly altered rocks are divided into two groups. First group is characterized by extensive (up to 90%) replacement of primary igneous mineral assemblage by chlorite, mica and sulfide. Second group is cemented with large amounts of sulfates with sulfide (mainly pyrite). It is found in a few drill core sections that hydrothermal hydrous silicate minerals change with depth from montmorillonite to chlorite and mica through mixed layer of chlorite/montmorillonite. This may suggest the more extensive and higher temperature alteration in deeper zones in a certain area. Electron microprobe analyses and bulk chemical composition indicate that the depletion of phosphorous in altered rocks (below 0.1 wt%) but enrichment of phosphorous in sulfide zones. This suggests that phosphorous was easily dissolved from igneous rocks by hydrothermal process, but readily precipitated with sulfides. The reason for co-precipitation of phosphates with sulfides is not certain, but such co-precipitation mechanism

  9. Hydrothermally altered impact melt rock and breccia - Contributions to the soil of Mars

    NASA Technical Reports Server (NTRS)

    Allen, C. C.; Keil, K.; Gooding, J. L.

    1982-01-01

    An examination is made of samples of melt rock and breccia from 12 terrestrial impact craters to identify alteration minerals and their conditions of formation. It is found that in most cases the dominant assemblage is clay-silica-K feldspar-zeolite, suggesting hydrothermal alteration at low pressures and temperatures of 100-300 C. The clays are in the main Fe-chlorites and smectites, in most cases depleted in Al and enriched in Fe and Mg relative to their source rocks. The alteration of impact glass is found often to be complete, whereas the alteration of crystalline melt rock is limited to a few percent of the rock volume. Impact breccia is altered to only a slight extent compared with the alteration of glass. It is believed that impact-induced hydrothermal alteration is to be expected at Martian impact sites if significant quantities of ground ice and/or water are present.

  10. Distribution of hydrothermally altered rocks in the Reko Diq, Pakistan mineralized area based on spectral analysis of ASTER data

    USGS Publications Warehouse

    Rowan, L.C.; Schmidt, R.G.; Mars, J.C.

    2006-01-01

    The Reko Diq, Pakistan mineralized study area, approximately 10??km in diameter, is underlain by a central zone of hydrothermally altered rocks associated with Cu-Au mineralization. The surrounding country rocks are a variable mixture of unaltered volcanic rocks, fluvial deposits, and eolian quartz sand. Analysis of 15-band Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data of the study area, aided by laboratory spectral reflectance and spectral emittance measurements of field samples, shows that phyllically altered rocks are laterally extensive, and contain localized areas of argillically altered rocks. In the visible through shortwave-infrared (VNIR + SWIR) phyllically altered rocks are characterized by Al-OH absorption in ASTER band 6 because of molecular vibrations in muscovite, whereas argillically altered rocks have an absorption feature in band 5 resulting from alunite. Propylitically altered rocks form a peripheral zone and are present in scattered exposures within the main altered area. Chlorite and muscovite cause distinctive absorption features at 2.33 and 2.20????m, respectively, although less intense 2.33????m absorption is also present in image spectra of country rocks. Important complementary lithologic information was derived by analysis of the spectral emittance data in the 5 thermal-infrared (TIR) bands. Silicified rocks were not distinguished in the 9 VNIR + SWIR bands because of the lack of diagnostic spectral absorption features in quartz in this wavelength region. Quartz-bearing surficial deposits, as well as hydrothermally silicified rocks, were mapped in the TIR bands by using a band 13/band 12 ratio image, which is sensitive to the intensity of the quartz reststrahlen feature. Improved distinction between the quartzose surficial deposits and silicified bedrock was achieved by using matched-filter processing with TIR image spectra for reference. ?? 2006 Elsevier Inc. All rights reserved.

  11. Geochemical results of a hydrothermally altered area at Baker Creek, Blaine County, Idaho

    USGS Publications Warehouse

    Erdman, James A.; Moye, Falma J.; Theobald, Paul K.; McCafferty, Anne E.; Larsen, Richard K.

    2001-01-01

    The area immediately east of Baker Creek, Blaine County, Idaho, is underlain by a thick section of mafic to intermediate lava flows of the Eocene Challis Volcanic Group. Widespread propylitic alteration surrounds a zone of argillic alteration and an inner core of phyllic alteration. Silicified breccia is present along an east-trending fault within the zone of phyllic alteration. As part of a reconnaissance geochemical survey, soils and plants were sampled. Several species of plants (Douglas-fir [ Pseudotsuga menziesii ], mountain big sagebrush [ Artemisia tridentata ssp. vaseyana ], and elk sedge [ Carex geyerii ]) were collected from 10 upland localities and stream sediments, panned concentrates, and aquatic mosses were collected from 16 drainage basin localities all of which were generally within the area of alteration. Geochemical results yielded anomalous concentrations of molybenum, zinc, silver, and lead in at least half of the seven different sample media and of gold, thallium, arsenic, antimony, manganese, boron, cadmium, bismuth, copper, and beryllium in from one to four of the various media. Part of this suite of elements? silver, gold, arsenic, antimony, thallium, and manganese? suggests that the mineralization in the area is epithermal. Barite and pyrite (commonly botryoidal-framboidal) are widespread throughout the area sampled. Visible gold and pyromorphite (a secondary lead mineral) were identified in only one small drainage basin, but high levels of gold were detected in aquatic mosses over a larger area. Data from the upland and stream sampling indicate two possible mineralized areas. The first mineralized area was identified by a grab sample from an outcrop of quartz stockwork that contained 50 ppb Au, 1.5 ppm Ag, and 50 ppm Mo. Although the soil and plant species that were sampled in the area indicated mineralized bedrock, the Douglas-fir samples were the best indicators of the silver anomaly. The second possible mineralized area centers on the

  12. 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

  13. Influence of hydrothermal alteration on phreatic eruption processes in Solfatara (Campi Flegrei)

    NASA Astrophysics Data System (ADS)

    Mayer, K.; Scheu, B.; Montanaro, C.; Isaia, R.; Dingwell, D. B.

    2014-12-01

    The strong hydrothermal activity exhibited at Campi Flegrei by the Solfatara and Pisciarelli fumaroles points to a significant risk for phreatic eruptions in this densely populated area. Phreatic eruptions, triggered by various processes are hardly predictable in occurrence time and size. Despite their hazard potential, these eruptions, as well as the influence of hydrothermal alteration on their likelihood, magnitude and style, have so far been largely overlooked in experimental volcanology. The physical properties and the mechanical behavior of volcanic rocks are highly dependent on their original magmatic microstructure and on any eventual alteration of those microstructures due to hydrothermal reactions. We have therefore investigated the potential effects of hydrothermal alteration on rock microstructure and, as a consequence, on fragmentation dynamics. Rock samples from the vicinity of the Solfatara fumaroles have been characterized 1) geochemically (X-ray fluorescence, X-ray diffraction), 2) physically (density, porosity, permeability and elastic wave velocity) and 3) mechanically (uniaxial compressive strength, tensile strength). We have investigated the effects of hydrothermal alteration on fragmentation processes using a shock-tube apparatus, operating with Argon gas, water vapor and superheated water at temperatures up to 400°C and maximum pressures of 20 MPa. The three different energy sources within the pores initiating fragmentation, have been investigated: overpressure by 1) Argon gas; or 2) water vapor and due to 3) steam flashing of water. Fragmentation speed, fragmentation efficiency and fragmented particle ejection velocity were measured. Our results indicate, that steam flashing provides the highest energy - resulting in increased particle ejection velocity and higher fragmentation efficiency. Based on our results, we aim to constrain the influence of hydrothermal alteration on the dynamics of phreatic explosions and the effect on the amount of

  14. Anomaly Detection and Comparative Analysis of Hydrothermal Alteration Materials Trough Hyperspectral Multisensor Data in the Turrialba Volcano

    NASA Astrophysics Data System (ADS)

    Rejas, J. G.; Martínez-Frías, J.; Bonatti, J.; Martínez, R.; Marchamalo, M.

    2012-07-01

    The aim of this work is the comparative study of the presence of hydrothermal alteration materials in the Turrialba volcano (Costa Rica) in relation with computed spectral anomalies from multitemporal and multisensor data adquired in spectral ranges of the visible (VIS), short wave infrared (SWIR) and thermal infrared (TIR). We used for this purposes hyperspectral and multispectral images from the HyMAP and MASTER airborne sensors, and ASTER and Hyperion scenes in a period between 2002 and 2010. Field radiometry was applied in order to remove the atmospheric contribution in an empirical line method. HyMAP and MASTER images were georeferenced directly thanks to positioning and orientation data that were measured at the same time in the acquisition campaign from an inertial system based on GPS/IMU. These two important steps were allowed the identification of spectral diagnostic bands of hydrothermal alteration minerals and the accuracy spatial correlation. Enviromental impact of the volcano activity has been studied through different vegetation indexes and soil patterns. Have been mapped hydrothermal materials in the crater of the volcano, in fact currently active, and their surrounding carrying out a principal components analysis differentiated for a high and low absorption bands to characterize accumulations of kaolinite, illite, alunite and kaolinite+smectite, delimitating zones with the presence of these minerals. Spectral anomalies have been calculated on a comparative study of methods pixel and subpixel focused in thermal bands fused with high-resolution images. Results are presented as an approach based on expert whose main interest lies in the automated identification of patterns of hydrothermal altered materials without prior knowledge or poor information on the area.

  15. Mapping hydrothermally altered rocks in the Northern Grapevine Mountains, Nevada and California with the airborne imaging spectrometer

    NASA Technical Reports Server (NTRS)

    Kruse, Fred A.

    1987-01-01

    Seven flightlines of Airborne Imaging Spectrometer (AIS) data were analyzed for an area of hydrothermally altered rocks. The data were reduced to reflectance relative to an average spectrum, and an automated procedure was used to produce a color coded image displaying absorption band information. Individual spectra were extracted from the AIS images to determine the detailed mineralogy. Two alteration types were mapped based upon mineralogy identified using the AIS data. The primary alteration type is quartz sericite pyrite alteration which occurs in northwest-trending zones in quartz monzonite porphyry. The AIS data allow identification of sericite (muscovite) based upon a strong absorption feature near 2.21 micron and weaker absorption features near 2.35 and 2.45 micron. The second alteration type occurs as a zone of argillic alteration associated with a granitic intrusion. Montmorillonite was identified based on a weak to moderate absorption feature near 2.2 micron and the absence of the two absorption features at longer wavelengths characteristic of sericite. Montmorillonite could be identified only where concentrations of sericite did not mask the montmorillonite spectrum.

  16. Hydrothermal alteration and the chemistry of ore-forming fluids in an unconformity-type uranium deposit

    SciTech Connect

    Komninou, A.; Sverjensky, D.A.

    1995-07-01

    Compositions of hydrothermal chlorite and fine-grained white mica from the inner and outer alteration halos in the Koongarra U deposit were analyzed by electron microprobe and analytical electron microscopy. Analyses show that although chlorite and white mica compositions vary considerably outside the main ore zone, they are uniform inside the ore zone. Ore-zone chlorite has a ratio of Fe/(Fe + Mg) of 0.25 and low octahedral occupancy (average 5.5 per formula unit), which may represent a mixture of di- and trioctahedral chlorite. White mica has a typical K + Na atomic content of 0.85 per formula unit. These compositions were used to calculate the activity ratios a{sub Fe{sup +2}}/a{sub H{sup +}}{sup 2}, a{sub Mg{sup +2}}/a{sub H{sup +}}{sup 2}, a{sub K{sup +}}/a{sub H{sup +}}, and a{sub Na{sup +}}/a{sub H{sup +}} for the hydrothermal fluids associated with deposition of uraninite. Hydrothermal apatite analyses in conjunction with salinities suggested from fluid inclusion studies were used to calculate the pH of the fluids during the pre-ore alteration. The calculated pH values range from 4.8 to 6.0. Finally, the coexistence of chlorite with quartz and hematite was used to calculate oxygen fugacities. The calculated values are about 2 log units higher than for the hematite-magnetite buffer at 200{degrees}C. Consequently, the oxidation state of the fluid lay in the hematite field and U was probably transported as uranyl complexes.

  17. Hydrothermal alteration in metasedimentary rock-hosted orogenic gold deposits, Reefton goldfield, South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Christie, Anthony B.; Brathwaite, Robert L.

    2003-01-01

    Orogenic or mesothermal quartz lodes in lower Palaeozoic Greenland Group metasedimentary rocks of the Reefton area have produced 67 tonnes (t) of gold prior to 1951, and recent exploration has identified new gold resources in several deposits, including the largest past producers, Blackwater and Globe-Progress. The metasedimentary rocks consist of alternating sandstone and mudstone beds that were metamorphosed to lower greenschist facies prior to being hydrothermally altered adjacent to the quartz lodes. The sandstones are feldspathic litharenites averaging Q65-F10-R25, with detrital grains of quartz, rock fragments, muscovite, and plagioclase and biotite that were altered to albite and chlorite, respectively, during metamorphism. Accessory minerals are graphite, apatite, zircon, tourmaline and titanite. Hydrothermal alteration of the sandstones has developed a mineral assemblage of K-mica, carbonate (dolomite, ankerite, ferroan magnesite and magnesian siderite), chlorite, pyrite and arsenopyrite. The abundance of hydrothermal chlorite is greater at Blackwater than at the other prospects studied. Hydrothermal alteration associated with the quartz lodes is marked by bleaching, magnesian siderite spots, disseminated arsenopyrite and pyrite and thin carbonate, quartz and sulphide veins. These trends are accompanied by increasing concentrations of S, As and Sb and decreasing Na, and a decrease of Fe and Mg in K-mica. The alkali alteration indices 3K/Al (representing K-mica) and Na/Al (representing albite) generally show antipathetic trends, with 3K/Al increasing near the lodes and Na/Al decreasing. These trends reflect the replacement of albite by K-mica. Carbonate alteration indices CO2/(Ca + Mg +Fe) and CO2/[Ca + Mg + Fe -0.5(S + As)] quantify the abundance of hydrothermal carbonates, but they show variable correlation with the lodes. They increase the width of the alteration halo in the hanging wall of the lodes at the Globe-Progress and General Gordon prospects

  18. Minerals produced during cooling and hydrothermal alteration of ash flow tuff from Yellowstone drill hole Y-5

    USGS Publications Warehouse

    Keith, T.E.C.; Muffler, L.J.P.

    1978-01-01

    A rhyolitic ash-flow tuff in a hydrothermally active area within the Yellowstone caldera was drilled in 1967, and cores were studied to determine the nature and distribution of primary and secondary mineral phases. The rocks have undergone a complex history of crystallization and hydrothermal alteration since their emplacement 600,000 years ago. During cooling from magmatic temperatures, the glassy groundmass underwent either devitrification to alkali feldspar + ??-cristobalite ?? tridymite or granophyric crystallization to alkali feldspar + quartz. Associated with the zones of granophyric crystallization are prismatic quartz crystals in cavities similar to those termed miarolitic in plutonic rocks. Vapor-phase alkali feldspar, tridymite, magnetite, and sporadic ??-cristobalite were deposited in cavities and in void spaces of pumice fragments. Subsequently, some of the vapor-phase alkali feldspar crystals were replaced by microcrystalline quartz, and the vapor-phase minerals were frosted by a coating of saccharoidal quartz. Hydrothermal minerals occur primarily as linings and fillings of cavities and fractures and as altered mafic phenocrysts. Chalcedony is the dominant mineral related to the present hydrothermal regime and occurs as microcrystalline material mixed with various amounts of hematite and goethite. The chalcedony displays intricate layering and was apparently deposited as opal from silica-rich water. Hematite and goethite also replace both mafic phenocrysts and vapor-phase magnetite. Other conspicuous hydrothermal minerals include montmorillonite, pyrite, mordenite, calcite, and fluorite. Clinoptilolite, erionite, illite, kaolinite, and manganese oxides are sporadic. The hydrothermal minerals show little correlation with temperature, but bladed calcite is restricted to a zone of boiling in the tuff and clearly was deposited when CO2 was lost during boiling. Fractures and breccias filled with chalcedony are common throughout Y-5 and may have been

  19. Hydrothermal alteration, ore fluid characteristics, and gold depositional processes along a trondhjemite-komatiite contact at Tarmoola, Western Australia

    USGS Publications Warehouse

    Duuring, P.; Hagemann, S.G.; Cassidy, K.F.; Johnson, C.A.

    2004-01-01

    studies and stage II mineral equilibria, gold deposited from a homogeneous, neutral to slightly alkaline (pH 5.1-5.5), reduced, low-salinity (<5.5 wt % NaCl equiv) fluid that had a bulk composition of 78 mole percent H2O and 21 mole percent CO2, and trace amounts of CH4, C2H6, H2, Ar, H2S, and He. Gold deposition occurred at 300?? ?? 50??C and 0.5 to 3.0 kbars. Assuming lithostatic fluid pressures, gold precipitated at a 2- to 10-km depth. Stage II gray quartz ??18Ofluid values range from 5.9 to 7.5 per mil, whereas ??Dfluid values calculated from the dehydration of muscovite grains and measured directly from bulk fluid inclusion analyses of stage II gray quartz have ranges of -9 to -35 and -27 to -28 per mil, respectively. Hydrothermal ore fluids were transported from greater crustal depths to the site of gold deposition during the district-scale D3 event by shallowly W dipping, reverse brittle-ductile shear zones in supracrustal rock and along the steeply east dipping trondhjemite contact. Associated subhorizontal east-west shortening caused the reactivation of the eastern trondhjemite margin and subparallel foliation, which facilitated the transport of hydrothermal fluids and the generation of gold-bearing veins and hydrothermal alteration zones in komatiite. East-west-striking fractures in trondhjemite aided the lateral migration of ore fluids away from trondhjemite margins and the formation of east-west-striking gold-bearing veins and broad alteration zones. Gold was most likely transported in the stage II fluid as bisulfide complexes. The sulfidation of trondhjemite and komatiite wall rock by the stage II fluid caused the destabilization of An bisulfide complexes and gold deposition. Potassium, Ca, and CO2 metasomatism of komatiite wall rock may have enhanced gold deposition via the acidification of the stage II fluid. The physicochemical characteristics of the Tarmoola ore fluid and relative timing of gold mineralization are consistent with the Yilgarn-wide,

  20. Mesozoic hydrothermal alteration associated with gold mineralization in the Mercur district, Utah

    SciTech Connect

    Wilson, P.N.; Parry, W.T. )

    1990-09-01

    K/Ar dates and chemical data show that a Mesozoic gold-bearing hydrothermal system altered black shales of the Mississippian Great Blue Limestone throughout an area encompassing the Mercur gold district, Utah. K/Ar dates of illite veins and illite-rich, clay-sized separates of altered shales that are enriched in Au, As, Hg, Sc, and other heavy metals indicate that hydrothermal activity occurred from 193 to 122 Ma. Several ages from within the Mercur district cluster near 160 Ma and may date the minimum age of gold mineralization.

  1. Hydrothermal processes at seafloor spreading centers,

    SciTech Connect

    Sleep, N.H.

    1983-01-01

    This chapter discusses the initial entry of hydrothermal seawater into deep levels of the oceanic crust, the effectiveness of hydrothermal circulation in cooling the crust, the geometry of hydrothermal circulation, the relationship between the hydrothermal circulation and the magma chamber, the reaction of the oceanic crust with the seawater, and the identification of the hydrothermal fluid which alters a rock sample. Topics considered include the crack front, observation relevant to the crack front, the limitations of the crack front hypothesis, the observed pattern of hydrothermal alteration, the nature of the hydrothermal fluid, the physics of large scale convection, and convection through crack zones. Knowledge of hydrothermal circulation at the ridge axis is based on sampling of the hydrothermal fluid, indirect geophysical measurements of the oceanic crust, and studies of rocks which are believed to have undergone hydrothermal alteration at the ridge axis. Includes 2 drawings.

  2. Mapping Hydrothermal Alterations in the Muteh Gold Mining Area in Iran by using ASTER satellite Imagery data

    NASA Astrophysics Data System (ADS)

    Asadi Haroni, Hooshang; Hassan Tabatabaei, Seyed

    2016-04-01

    Muteh gold mining area is located in 160 km NW of Isfahan town. Gold mineralization is meso-thermal type and associated with silisic, seresitic and carbonate alterations as well as with hematite and goethite. Image processing and interpretation were applied on the ASTER satellite imagery data of about 400 km2 at the Muteh gold mining area to identify hydrothermal alterations and iron oxides associated with gold mineralization. After applying preprocessing methods such as radiometric and geometric corrections, image processing methods of Principal Components Analysis (PCA), Least Square Fit (Ls-Fit) and Spectral Angle Mapper (SAM) were applied on the ASTER data to identify hydrothermal alterations and iron oxides. In this research reference spectra of minerals such as chlorite, hematite, clay minerals and phengite identified from laboratory spectral analysis of collected samples were used to map the hydrothermal alterations. Finally, identified hydrothermal alteration and iron oxides were validated by visiting and sampling some of the mapped hydrothermal alterations.

  3. Formation Sequences of Iron Minerals in the Acidic Alteration Products and Variation of Hydrothermal Fluid Conditions

    NASA Astrophysics Data System (ADS)

    Isobe, H.; Yoshizawa, M.

    2008-12-01

    Iron minerals have important role in environmental issues not only on the Earth but also other terrestrial planets. Iron mineral species related to alteration products of primary minerals with surface or subsurface fluids are characterized by temperature, acidity and redox conditions of the fluids. We can see various iron- bearing alteration products in alteration products around fumaroles in geothermal/volcanic areas. In this study, zonal structures of iron minerals in alteration products of the geothermal area are observed to elucidate temporal and spatial variation of hydrothermal fluids. Alteration of the pyroxene-amphibole andesite of Garan-dake volcano, Oita, Japan occurs by the acidic hydrothermal fluid to form cristobalite leaching out elements other than Si. Hand specimens with unaltered or weakly altered core and cristobalite crust show various sequences of layers. XRD analysis revealed that the alteration degree is represented by abundance of cristobalite. Intermediately altered layers are characterized by occurrence including alunite, pyrite, kaolinite, goethite and hematite. A specimen with reddish brown core surrounded by cristobalite-rich white crust has brown colored layers at the boundary of core and the crust. Reddish core is characterized by occurrence of crystalline hematite by XRD. Another hand specimen has light gray core, which represents reduced conditions, and white cristobalite crust with light brown and reddish brown layers of ferric iron minerals between the core and the crust. On the other hand, hornblende crystals, typical ferrous iron-bearing mineral of the host rock, are well preserved in some samples with strongly decolorized cristobalite-rich groundmass. Hydrothermal alteration experiments of iron-rich basaltic material shows iron mineral species depend on acidity and temperature of the fluid. Oxidation states of the iron-bearing mineral species are strongly influenced by the acidity and redox conditions. Variations of alteration

  4. Signature of hydrothermal alteration in ground-magnetic surveys at Yellowstone National Park

    NASA Astrophysics Data System (ADS)

    Bouligand, C.; Glen, J. M.; McPhee, D. K.

    2011-12-01

    Yellowstone National Park (YNP) hosts a very large hydrothermal system with over 10,000 thermal features. Although hydrothermal alteration in YNP has been extensively studied with field observations, remote-sensing imagery, and core drilling, the volume and geometry of hydrothermal systems at depth remain poorly constrained. Magnetic surveys can help to investigate buried hydrothermal alteration as demonstrated by the high-resolution aeromagnetic survey of YNP (Finn and Morgan, J. Volcanol. Geotherm. Res., 115, 207-231, 2002). Results of this survey show that magnetic lows extend over and beyond areas of hydrothermal activity. This suggests large volumes of buried demagnetized rocks due to hydrothermal alteration of the volcanic substratum. Although the interpretation of magnetic anomalies is non-unique, Finn and Morgan (2002) used these magnetic lows to estimate a minimum volume of buried altered rock assuming complete demagnetization of the substratum. This aeromagnetic survey was of relatively high resolution (flight line spacing < 500 m and flight elevation <350 m above ground), but it was insufficient for detailed mapping of individual thermal areas. In order to obtain a closer look at several areas, we performed ground-based magnetic surveys within YNP using a cesium-vapor magnetometer along 4-5 km long transects crossing four thermal areas (Norris Geyser Basin, Lower Geyser Basin, Lone Star Geyser Basin, and Smoke Jumper Hot-springs). We also performed a detailed survey over an area of about 800 m x 500 m around Lone Star Geyser. We also collected gravity data to help characterize the subsurface geologic structures and performed magnetic susceptibility, magnetic remanence, and density measurements on rock samples collected in the field and from drill cores collected in 1967-1968 to characterize physical properties of fresh and altered geologic units. The long magnetic transects show that magnetic anomalies are damped in altered areas suggesting a significant

  5. Textures of Secondary Alteration Zones in Nakhla

    NASA Technical Reports Server (NTRS)

    McKay, D. S.; Wentworth, S. J.; Longazo, T. G.; Thomas-Keprta, K.; Gibson, E. K.

    2001-01-01

    Textures of secondary minerals in cracks in Nakhla are described and illustrated with high resolution Scanning Electron Microscopy (SEM) and BSE. Some Nakhla textures resemble alteration textures of glass in seafloor basalts. Criteria for inorganic vs. biogenic alteration are discussed. Additional information is contained in the original extended abstract.

  6. Recent massive sulfide deposits of the Semenov ore district, Mid-Atlantic Ridge, 13°31' N: Associated rocks of the oceanic core complex and their hydrothermal alteration

    NASA Astrophysics Data System (ADS)

    Pertsev, A. N.; Bortnikov, N. S.; Vlasov, E. A.; Beltenev, V. E.; Dobretsova, I. G.; Ageeva, O. A.

    2012-09-01

    The oceanic core complexes and large-offset detachment faults characteristic of the slow-spreading Mid-Atlantic Ridge are crucial for the structural control of large hydrothermal systems, including those forming sub-seafloor polymetallic sulfide mineralization. The structural-geological, petrographic, and mineralogical data are considered for the oceanic core complex enclosing the Semenov-1, -2, -3, -4, and -5 inactive hydrothermal sulfide fields recently discovered on the Mid-Oceanic Ridge at 13°31' N. The oceanic core complex is composed of serpentinized and talc-replaced peridotites and sporadic gabbroic rocks, however, all hydrothermal fields reveal compositional indications of basaltic substrate. The volcanic structures superposed on the oceanic core complex are marked by outcrops of pillow lavas with fresh quenched glass. Dolerites regarded as volcanic conduits seem to represent separate dike swarms. The superposed volcanic structures develop largely along the near-latitudinal high-angle tectonic zone controlling the Semenov-1, -2, -5, and -3 hydrothermal sulfide fields. The manifestations of hydrothermal metasomatic alteration are diverse. The widespread talcose rocks with pyrrhotite-pyrite mineralization after serpentinite, as well as finding of talc-chlorite metabasalt are interpreted as products of hydrothermal activity in the permeable zone of detachment fault. Chloritization and brecciation of basalts with superposed quartz or opal, barite, and pyrite or chalcopyrite mineralization directly related to the sub-seafloor sulfide deposition. The native copper mineralization in almost unaltered basalts at the Semenov-4 field is suggested to precipitate from ore-forming fluids before they reach the level of sub-seafloor sulfide deposition. Amphibolites with plagiogranite veinlets are interpreted as tectonic fragments of the highest-temperature portions of hydrothermal systems, where partial melting of basic rocks in the presence of aqueous fluid with

  7. Hydrothermal alteration in the Bosumtwi impact structure: Evidence from 2M1-muscovite, alteration veins, and fracture fillings

    NASA Astrophysics Data System (ADS)

    Petersen, Michael T.; Newsom, Horton E.; Nelson, Melissa J.; Moore, Duane M.

    Drill-core samples from the Bosumtwi impact structure (1.07 Myr old and 10.5 km in diameter) in Ghana exhibit mineralogical evidence for post-impact hydrothermal alteration. Nine samples of drill core obtained through the 2004 International Continental Scientific Drilling Project (ICDP) were studied, including an uppermost fallback layer overlying impactite breccias, and partly deformed massive meta-graywacke bedrock. The petrographic study revealed alteration veins containing secondary sericitic muscovite (comparable to 2M1-muscovite) crosscutting original bedding in meta-graywacke and forming a matrix between clasts in impactite breccias. X-ray diffraction (XRD) shows that these impactite samples are rich in 2M1-muscovite, consistent with post-impact fluid deposition and alteration. Optical analysis indicates the presence of a pre-impact stratiform chlorite in meta-graywacke samples and a secondary alteration chlorite occurring in all samples. Secondary illite was detected in upper impactites of drill core LB-08A and samples containing accretionary lapilli. The lower temperature constraint for the hydrothermal event is given by 2M1-muscovite, secondary chlorite, and illite, all of which form at temperatures greater than 280 °C. An absence of recrystallization of quartz and feldspar indicates an upper temperature constraint below 900 °C. The presence of alteration materials associated with fractures and veins in the uppermost impactites of drill cores LB-07A and LB-08A indicates that a post-impact hydrothermal system was present in and adjacent to the central uplift portion of the Bosumtwi impact structure. A sample containing accretionary lapilli obtained from drill core LB-05A exhibits limited evidence that hydrothermal processes were more widespread within the impactites on the crater floor.

  8. Seismic properties and effects of hydrothermal alteration on Volcanogenic Massive Sulfide (VMS) deposits at the Lalor Lake in Manitoba, Canada

    NASA Astrophysics Data System (ADS)

    Miah, Khalid H.; Bellefleur, Gilles; Schetselaar, Ernst; Potter, David K.

    2015-12-01

    Borehole sonic and density logs are essential for mineral exploration at depth, but its limited availability to link rock properties of different ore forming geologic structure is a hindrance to seismic data interpretations. In situ density and velocity logs provide first order control on the reflectivity of various lithologic units. We analyzed borehole logs from 12 drill holes over and around the Lalor VMS deposits geographically located in the northern Manitoba, Canada, in an attempt to characterize lithologic units based on its seismic properties. The Lalor Lake deposit is part of the Paleoproterozoic Flin Flon Belt, and associated with an extensive hydrothermal alteration system. Volcanogenic Massive Sulfide (VMS) zones are distributed in several ore lenses with relatively shallower facies comprise solid to solid sulfides, tend to be disseminated or Stringer sulfides, while deeper lenses are gold and silver enriched and occurred in the highly altered footwall region. Our analysis suggests that massive sulfide and diorite have higher acoustic impedance than other rock units, and can produce useful reflection signatures in seismic data. Bivariate distributions of P-wave velocity, density, acoustic impedance and Poisson's ratio in end-member mineral cones were used for qualitative assessment of the extent of alteration of various lithologic units. It can be inferred that hydrothermal alteration has considerably increased P-wave velocity and density of altered argillite and felsic volcanic rocks in comparison to their corresponding unaltered facies. Amphibole, garnet, kyanite, pyrite, sphalerite and staurolite are the dominant end-member alteration minerals affecting seismic rock properties at the VMS site.

  9. Hydrothermal alteration in Oregon's Newberry Volcano No. 2: fluid chemistry and secondary-mineral distribution

    SciTech Connect

    Keith, T.E.C.; Mariner, R.H.; Bargar, K.E.; Evans, W.C.; Presser, T.S.

    1984-04-01

    Newberry 2 was drilled in the caldera floor of Newberry Volcano, Oregon, by the US Geological Survey during 1979-81. The maximum temperature measured was 265C at the bottom of the hole, 932 m below the surface. Rocks recovered fr9om the drill hole are divided into three intervals on the basis of hydrothermal alteration and mineral deposition: (1) 0-290 m consists of unaltered, largely glassy volcanic material, with present temperatures ranging from 20 to 40C; (2) 290-700 m consists of permeable tuff layers, tuff breccia units, and brecciated and fractured rhyodacitic to dacitic lava flows, with temperatures ranging from 40 to 100C; (3) 700-932 m consists of impermeable andesitic to basaltic lava flows that generally show little effect of alteration, interlayered with permeable hydrothermally altered flow breccia, with temperatures gradually increasing from 100 at 700 m to 265C at 932 m. Hydrothermal alteration throughout the system is controlled by rock permeability, temperature, composition of geothermal fluids, and composition and crystallinity of host rocks. Rock alteration consists mainly of replacement of glass by clay minerals and, locally, zeolites, partial replacement of plagioclase phenocrysts by calcite +/- epidote +/- illite, and whole-rock leaching adjacent to fluids channels. Open-space deposition of hydrothermal minerals in fractures, vesicles, and interbreccia pore space is far more abundant than replacement. A cooling shallow convection system in the upper 700 m is indicated by the occurrence of hydrothermal minerals that were deposited in a slightly higher temperature environment than presently exists. Below 700 m, the heat flow is conductive, and fluid flow is controlled by horizontal lava flows. Homogenization temperatures of secondary quartz fluid inclusions were as high as 370C.

  10. Mapping of hydrothermally altered rocks using airborne multispectral scanner data, Marysvale, Utah, mining district

    USGS Publications Warehouse

    Podwysocki, M.H.; Segal, D.B.; Jones, O.D.

    1983-01-01

    Multispectral data covering an area near Marysvale, Utah, collected with the airborne National Aeronautics and Space Administration (NASA) 24-channel Bendix multispectral scanner, were analyzed to detect areas of hydrothermally altered, potentially mineralized rocks. Spectral bands were selected for analysis that approximate those of the Landsat 4 Thematic Mapper and which are diagnostic of the presence of hydrothermally derived products. Hydrothermally altered rocks, particularly volcanic rocks affected by solutions rich in sulfuric acid, are commonly characterized by concentrations of argillic minerals such as alunite and kaolinite. These minerals are important for identifying hydrothermally altered rocks in multispectral images because they have intense absorption bands centered near a wavelength of 2.2 ??m. Unaltered volcanic rocks commonly do not contain these minerals and hence do not have the absorption bands. A color-composite image was constructed using the following spectral band ratios: 1.6??m/2.2??m, 1.6??m/0.48??m, and 0.67??m/1.0??m. The particular bands were chosen to emphasize the spectral contrasts that exist for argillic versus non-argillic rocks, limonitic versus nonlimonitic rocks, and rocks versus vegetation, respectively. The color-ratio composite successfully distinguished most types of altered rocks from unaltered rocks. Some previously unrecognized areas of hydrothermal alteration were mapped. The altered rocks included those having high alunite and/or kaolinite content, siliceous rocks containing some kaolinite, and ash-fall tuffs containing zeolitic minerals. The color-ratio-composite image allowed further division of these rocks into limonitic and nonlimonitic phases. The image did not allow separation of highly siliceous or hematitically altered rocks containing no clays or alunite from unaltered rocks. A color-coded density slice image of the 1.6??m/2.2??m band ratio allowed further discrimination among the altered units. Areas

  11. Linear stability analysis for hydrothermal alteration of kimberlitic rocks

    NASA Astrophysics Data System (ADS)

    Afanasyev, Andrey; Belyaeva, Ekaterina

    2016-04-01

    The influx of groundwater into hot kimberlite deposits results in the reaction of water with olivine-rich rocks. The products of the reaction are serpentine and release of latent heat. The rise of temperature due to the heat release increases the rate of the reaction. Under certain conditions, this self-speeding up of the reaction can result in instabilities associated with a significantly higher final serpentinisation in slightly warmer regions of the kimberlite deposit. We conduct linear stability analysis of serpentinisation in an isolated volume of porous kimberlitic rocks saturated with water and an inert gas. There is a counteracting interplay between the heat release tending to destabilise the uniform distribution of parameters and the heat conduction tending to stabilise it by smoothing out temperature perturbations. We determine the critical spatial scale separating the parameters where one phenomenon dominates over another. The perturbations of longer-than-critical length grow, whereas the perturbations of shorter-than-critical length fade. The analytical results of the linear stability analysis are supported by direct numerical simulations using a full nonlinear model. Keywords: Hydrothermal systems, volcaniclastic deposits, phase transitions, instability analysis, numerical solutions

  12. Mineral and whole-rock compositions of seawater-dominated hydrothermal alteration at the Arctic volcanogenic massive sulfide prospect, Alaska

    USGS Publications Warehouse

    Schmidt, J.M.

    1988-01-01

    The Arctic volcanogenic massive sulfide prospect, located in the Ambler mineral district of northwestern Alaska, includes three types of hydrothermally altered rocks overlying, underlying, and interlayered with semimassive sulfide mineralization. Hydrothermal alteration of wall rocks and deposition of sulfide and gangue minerals were contemporaneous with Late Devonian of Early Mississippian basalt-rhyolite volcanism. Alteration developed asymmetrically around a linear fissure, suggesting fracture control of ore fluids rather than a point source. Microprobe analyses of phyllosilicates from the Arctic area indicate two discrete mineral populations. These differences in mineral chemistry are the result of differences in protolith composition caused by hydrothermal alteration-metasomatism. -from Author

  13. Mineralogical, geochemical and isotopic characteristics of hydrothermal alteration processes in the active, submarine, felsic-hosted PACMANUS field, Manus Basin, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Lackschewitz, K. S.; Devey, C. W.; Stoffers, P.; Botz, R.; Eisenhauer, A.; Kummetz, M.; Schmidt, M.; Singer, A.

    2004-11-01

    During ODP Leg 193, 4 sites were drilled in the active PACMANUS hydrothermal field on the crest of the felsic Pual Ridge to examine the vertical and lateral variations in mineralization and alteration patterns. We present new data on clay mineral assemblages, clay and whole rock chemistry and clay mineral strontium and oxygen isotopic compositions of altered rocks from a site of diffuse low-temperature venting (Snowcap, Site 1188) and a site of high-temperature venting (Roman Ruins, Site 1189) in order to investigate the water-rock reactions and associated elemental exchanges. The volcanic succession at Snowcap has been hydrothermally altered, producing five alteration zones: (1) chlorite ± illite-cristobalite-plagioclase alteration apparently overprinted locally by pyrophyllite bleaching at temperatures of 260-310°C; (2) chlorite ± mixed-layer clay alteration at temperatures of 230°C; (3) chlorite and illite alteration; (4) illite and chlorite ± illite mixed-layer alteration at temperatures of 250-260°C; and (5) illite ± chlorite alteration at 290-300°C. Felsic rocks recovered from two holes (1189A and 1189B) at Roman Ruins, although very close together, show differing alteration features. Hole 1189A is characterized by a uniform chlorite-illite alteration formed at ˜250°C, overprinted by quartz veining at 350°C. In contrast, four alteration zones occur in Hole 1189B: (1) illite ± chlorite alteration formed at ˜300°C; (2) chlorite ± illite alteration at 235°C; (3) chlorite ± illite and mixed layer clay alteration; and (4) chlorite ± illite alteration at 220°C. Mass balance calculations indicate that the chloritization, illitization and bleaching (silica-pyrophyllite assemblages) alteration stages are accompanied by different chemical changes relative to a calculated pristine precursor lava. The element Cr appears to have a general enrichment in the altered samples from PACMANUS. The clay concentrate data show that Cr and Cu are predominantly

  14. 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.

  15. Impact Hydrothermal Alteration of Terrestrial Basalts: Explaining the Rock Component of the Martian Soil

    NASA Technical Reports Server (NTRS)

    Nelson, M. J.; Newsom, H. E.

    2003-01-01

    The large energy in terrestrial impacts can create hydrothermal systems and consequently produce hydrothermal alteration materials. In this study we consider the chemistry of impact and volcanic hydrothermal alteration under relatively low water/rock ratios in basaltic or a somewhat more evolved protolith. Our work on the Lonar and Mistastin craters suggests that Fe-rich clays, including Fe-rich saponite can be produced. We postulate that similar alteration materials are produced on Mars and could be a component of the martian soil or regolith, contrary to some earlier studies. The martian regolith is a globally homogenized product of various weathering processes. The soil [1] is thought to consist of a rock component, with lesser amounts of mobile elements (Ca, Na, and K) than a presumed protolith, and a salt or mobile element component enriched in sulfur and chlorine [2, 3]. In this study we consider the contributions of impacts and consequent hydrothermal processes to the rock component of the martian soil.

  16. Evaluation of LANDSAT MSS vs TM simulated data for distinguishing hydrothermal alteration

    NASA Technical Reports Server (NTRS)

    Abrams, M. J.; Kahle, A. B.; Madura, D. P.; Soha, J. M.

    1978-01-01

    The LANDSAT Follow-On (LFO) data was simulated to demonstrate the mineral exploration capability of this system for segregating different types of hydrothermal alteration and to compare this capability with that of the existing LANDSAT system. Multispectral data were acquired for several test sites with the Bendix 24-channel MSDS scanner. Contrast enhancements, band ratioing, and principal component transformations were used to process the simulated LFO data for analysis. For Red Mountain, Arizona, the LFO data allowed identification of silicified areas, not identifiable with LANDSAT 1 and 2 data. The improved LFO resolution allowed detection of small silicic outcrops and of a narrow silicified dike. For Cuprite - Ralston, Nevada, the LFO spectral bands allowed discrimination of argillic and opalized altered areas; these could not be spectrally discriminated using LANDSAT 1 and 2 data. Addition of data from the 1.3- and 2.2- micrometer regions allowed better discriminations of hydrothermal alteration types.

  17. Hydrothermal Quartz Oxygen Isotope Ratios in Altered Post-Collapse Rhyolite at Sevenmile Hole, Grand Canyon of the Yellowstone River, Yellowstone National Park, WY

    NASA Astrophysics Data System (ADS)

    Phillips, A. R.; Larson, P. B.; John, D. A.; Pauley, B. M.

    2008-12-01

    The Grand Canyon of the Yellowstone River, Yellowstone National Park, Wyoming, displays regions of pervasively hydrothermally altered rock formed in the shallow, epithermal portions of a hydrothermal system. Hydrothermal fluid circulation causing the alteration is driven by magmatism related to the Yellowstone Caldera thermal anomaly. The protolith, the Tuff of Sulfur Creek, is a 480 ka high silica, low δ18O rhyolitic tuff that erupted after the Yellowstone caldera collapse at 640 ka. Incision of the canyon has exposed 350 vertical meters in the Sevenmile Hole vicinity. Hydrothermal mineralogy determined by standard XRD powder techniques and PIMA on over 90 samples shows both vertical and lateral variation. A vertical transition occurs from kaolinite at depths less than about 100 meters below the present day canyon rim, to illite in deeper exposures. This transition may correspond to a temperature of 150°C, based on a similar transition in the active Yellowstone hydrothermal system. A lateral variation of mineral assemblages in the altered tuff suggests temperatures that may range up to 330°C. Alteration was most likely caused by a liquid due to the presence of pyrite throughout. Local zones of suspected hydrothermal fluid upwelling correspond to the most intense silicification and highest temperature mineral assemblages. This alteration includes quartz + illite ± hyalophane, slawsonite, and buddingtonite. At similar depths outside inferred fluid upwelling zones, lower temperature assemblages are quartz + illite/smectite ± alunite and buddingtonite. At shallow depths, the lowest temperatures are suggested by the presence of quartz + kaolinite ± alunite and opal. Dickite, a kaolinite polymorph, may indicate locally higher temperatures in the shallow kaolinite zones. Oxygen isotope ratios of silica phases were measured for approximately 50 samples using laser fluorination techniques with an error of ±0.2‰. Hydrothermal quartz displays δ18O signatures more

  18. Hydrothermal alteration in the 3.5 b.y. old Onverwacht Group of South Africa

    NASA Technical Reports Server (NTRS)

    Hart, R.; Dewit, M. J.

    1985-01-01

    K-Ar studies of authigenic and alteration phases from the 3.5 b.y. old Onverwacht group of South Africa delineate hydrothermal metamorphism that ended 3.3 b.y. years ago. A whole rock K-Ar errochron from analysis of barite, dolomite, chert, and serpentinite (komatiite) gives an age of 3.3 b.y. with an intercept of 1,678 + or - 103. The 3.3. b.y. age for the metamorphism in the Onverwacht was confirmed by the Argon isotopes stepwise heating experiments of komatiites and basaltic komatiites from the Onverwacht Group. In addition, the errochron suggests all the phase studied equilibrated with a reservoir of hydrothermal argon with relatively uniform isotopic composition. The concept of hydrothermal activity in the Onverwacht Group is discussed and illustrated with photographs.

  19. Hydrothermal alteration of sediments associated with surface emissions from the Cerro Prieto geothermal field

    SciTech Connect

    Valette-Silver, J.N.; Esquer P., I.; Elders, W.A.; Collier, P.C.; Hoagland, J.R.

    1981-01-01

    A study of the mineralogical changes associated with these hydrothermal vents was initiated with the aim of developing possible exploration tools for geothermal resources. The Cerro Prieto reservoir has already been explored by extensive deep drilling so that relationships between surface manifestations and deeper hydrothermal processes could be established directly. Approximately 120 samples of surface sediments were collected both inside and outside of the vents. The mineralogy of the altered sediments studied appears to be controlled by the type of emission. A comparison between the changes in mineralogy due to low temperature hydrothermal activity in the reservoir, seen in samples from boreholes, and mineralogical changes in the surface emission samples shows similar general trends below 180 C: increase of quartz, feldspar and illite, with subsequent disappearance of kaolinite, montmorillonite, calcite and dolomite. These mineral assemblages seem to be characteristic products of the discharge from high intensity geothermal fields.

  20. Tectonic record, magmatic history and hydrothermal alteration in the Hercynian Guérande leucogranite, Armorican Massif, France

    NASA Astrophysics Data System (ADS)

    Ballouard, C.; Boulvais, P.; Poujol, M.; Gapais, D.; Yamato, P.; Tartèse, R.; Cuney, M.

    2015-04-01

    The Guérande peraluminous leucogranite was emplaced at the end of the Carboniferous in the southern part of the Armorican Massif. At the scale of the intrusion, this granite displays structural heterogeneities with a weak deformation in the southwestern part, whereas the northwestern part is marked by the occurrence of S/C and mylonitic extensional fabrics. Quartz veins and pegmatite dykes orientations as well as lineations directions in the granite and its country rocks demonstrate both E-W and N-S stretching. Therefore, during its emplacement in an extensional tectonic regime, the syntectonic Guérande granite has probably experienced some partitioning of the deformation. The southwestern part is characterized by a muscovite-biotite assemblage, the presence of restites and migmatitic enclaves, and a low abundance of quartz veins compared to pegmatite dykes. In contrast, the northwestern part is characterized by a muscovite-tourmaline assemblage, evidence of albitization and gresenization and a larger amount of quartz veins. The southwestern part is thus interpreted as the feeding zone of the intrusion whereas the northwestern part corresponds to its apical zone. The granite samples display continuous compositional evolutions in the range of 69.8-75.3 wt.% SiO2. High initial 87Sr/86Sr ratios and low εNd(T) values suggest that the peraluminous Guérande granite (A/CNK > 1.1) was formed by partial melting of metasedimentary formations. Magmatic evolution was controlled primarily by fractional crystallization of K-feldspar, biotite and plagioclase (An20). The samples from the apical zone show evidence of secondary muscovitization. They are also characterized by a high content in incompatible elements such as Cs and Sn, as well as low Nb/Ta and K/Rb ratios. The apical zone of the Guérande granite underwent a pervasive hydrothermal alteration during or soon after its emplacement. U-Th-Pb dating on zircon and monazite revealed that the Guérande granite was emplaced

  1. Selective concentration of cesium in analcime during hydrothermal alteration, Yellowstone National Park, Wyoming

    USGS Publications Warehouse

    Keith, T.E.C.; Thompson, J.M.; Mays, R.E.

    1983-01-01

    Chemical and mineralogical studies of fresh and hydrothermally altered rhyolitic material in Upper and Lower Geyser Basins, Yellowstone National Park, show that all the altered rocks are enriched in Cs and that Cs is selectively concentrated in analcime. The Cs content of unaltered rhyolite lava flows, including those from which the altered sediments are derived, ranges from 2.5 to 7.6 ppm. The Cs content of analcime-bearing altered sedimentary rocks is as high as 3000 ppm, and in clinoptilolite-bearing altered sedimentary rocks Cs content is as high as 180 ppm. Altered rhyolite lava flows which were initially vitrophyres, now contain up to 250 ppm Cs, and those which were crystallized prior to hydrothermal alteration contain up to 14 ppm. Mineral concentrates of analcime contain as much as 4700 ppm Cs. The Cs must have been incorporated into the analcime structure during crystallization, rather than by later cation substitution, because analcime does not readily exchange Cs. The Cs Cl of the fluids circulating through the hydrothermal system varies, suggesting that Cs is not always a conservative ion and that Cs is lost from upflowing thermal waters due to water-rock interaction resulting in crystallization of Cs-bearing analcime. The source of Cs for Cs enrichment of the altered rocks is from leaching of rhyolitic rocks underlying the geyser basins, and from the top of the silicic magma chamber that underlies the area. Analcime is an important natural Cs sink, and the high Cs concentrations reported here may prove to be an important indicator of the environment of analcime crystallization. ?? 1983.

  2. Present-day submarine hydrothermal activity in the Taupo-Rotorua Zone (Bay of Plenty, New Zealand)

    SciTech Connect

    Osipenko, A.B.; Egorov, Yu.O.; Fazlullin, S.M.; Gavrilenko, G.M.; Shul`kin, V.I.; Chertkova, L.V.

    1994-09-01

    We made detailed descriptions of the structure and material composition of sedimentary and water columns in the vicinity of active submarine hydrothermal activity in the southern part of the Bay of Plenty (North Island, New Zealand). Geophysical methods revealed that the hydrothermal system is confined to a tectonically distinct zone with a sedimentary cover characterized by complex structure. Chemical and mineralogical investigations confirmed that the activity of underwater vents exerts no substantial regional influence on the composition and features of ore mineralization in these formations. It is shown that essentially hydrothermal formations distinguishable within areas of otherwise monotypic sediments directly coincide with zones of hydrothermal discharge in the ocean floor. The absence of pronounced hydrothermal anomalies, together with the presence of {open_quotes}tongues{close_quotes} of anomalous concentrations of water-soluble gases suggests that the discharges are primarily hydrothermal in character.

  3. Effect of Hydrothermal Alteration on Rock Properties in Active Geothermal Setting

    NASA Astrophysics Data System (ADS)

    Mikisek, P.; Bignall, G.; Sepulveda, F.; Sass, I.

    2012-04-01

    Hydrothermal alteration records the physical-chemical changes of rock and mineral phases caused by the interaction of hot fluids and wall rock, which can impact effective permeability, porosity, thermal parameters, rock strength and other rock properties. In this project, an experimental approach has been used to investigate the effects of hydrothermal alteration on rock properties. A rock property database of contrastingly altered rock types and intensities has been established. The database details horizontal and vertical permeability, porosity, density, thermal conductivity and thermal heat capacity for ~300 drill core samples from wells THM12, THM13, THM14, THM17, THM18, THM22 and TH18 in the Wairakei-Tauhara geothermal system (New Zealand), which has been compared with observed hydrothermal alteration type, rank and intensity obtained from XRD analysis and optical microscopy. Samples were selected from clay-altered tuff and intercalated siltstones of the Huka Falls Formation, which acts as a cap rock at Wairakei-Tauhara, and tuffaceous sandstones of the Waiora Formation, which is a primary reservoir-hosting unit for lateral and vertical fluid flows in the geothermal system. The Huka Falls Formation exhibits argillic-type alteration of varying intensity, while underlying Waiora Formations exhibits argillic- and propylithic-type alteration. We plan to use a tempered triaxial test cell at hydrothermal temperatures (up to 200°C) and pressures typical of geothermal conditions, to simulate hot (thermal) fluid percolation through the rock matrix of an inferred "reservoir". Compressibility data will be obtained under a range of operating (simulation reservoir) conditions, in a series of multiple week to month-long experiments that will monitor change in permeability and rock strength accompanying advancing hydrothermal alteration intensity caused by the hot brine interacting with the rock matrix. We suggest, our work will provide new baseline information concerning

  4. Hydrothermal alteration and sulfide mineralization in gabbroids of the Markov Deep (Mid-Atlantic Ridge, 6° N)

    NASA Astrophysics Data System (ADS)

    Sharkov, E. V.; Abramov, S. S.; Simonov, V. A.; Krinov, D. I.; Skolotnev, S. G.; Bel'Tenev, V. E.; Bortnikov, N. S.

    2007-12-01

    A new type of sulfide occurrence related to metasomatically altered brecciated gabbroids has been studied at the Sierra Leone site situated in the axial rift valley of the Mid-Atlantic Ridge (Markov Deep, 6° N). Two associations of plutonic, subvolcanic, and volcanic rocks were dredged: (1) mid-ocean ridge basalts (MORB) and their intrusive analogues and (2) rocks of the silicic Fe-Ti-oxide series with dominating gabbronorites and sporadic trondhjemites. Almost all igneous rocks at the Sierra Leone site are enriched in Pb, Cu, U, Ga, Ta, Nb, Cs, and Rb and depleted in Zr, Th, and Hf. The rocks of the Fe-Ti-oxide series are enriched in Zn, Sn, and Mo and depleted in Ni and Cr. The main ore-bearing zone is situated at the foot of the eastern wall of the deep, where it is hosted in cataclastic hornblende gabbro and gabbronorite of the Fe-Ti-oxide series. Ore mineralization in metasomatically altered rocks is composed of quartz-sulfide and prehnite-sulfide veinlets, disseminated sulfide, and veined copper sulfide ore. The ore consists of pyrite, chalcopyrite, sphalerite, pyrrhotite, bornite, chalcocite, and digenite. The δ34S value of sulfides varies from 3.0 to 15.3‰. At the foot of the eastern wall of the Markov Deep, directly downslope from the ore-bearing zone, loose sediments contain grains of native Cu, Pb, Zn, and Sn and intermetallic compounds (isoferroplatinum, tetraferroplatinum, and brass) apparently derived from the ore. Mineral assemblages of ore-bearing metasomatic rocks and fluid inclusions therein were studied. Ore metasomatism developed under a low oxygen potential within a temperature interval from 400 to 160°C, though initial hydrothermal alteration of rocks proceeded at temperatures of 800-450°C. The temperature of stringer-disseminated ore mineralization is estimated at 170-280°C. The hydrothermal fluids are considered to be of magmatic origin; as the hydrothermal system evolved, they became diluted with seawater that was contained in

  5. Progressive hydrothermal alteration of feldspars from the Comstock Lode Region, Nevada: Submicron elemental imaging by Time of Flight-SIMS

    NASA Astrophysics Data System (ADS)

    Handler, M. R.; Vicenzi, E. P.; Sorensen, S. S.

    2002-05-01

    Time of Flight-Secondary Ionization Mass Spectrometry (ToF-SIMS) allows elemental mapping and depth profiling at lateral and depth resolutions of several hundred nanometers, with near-simultaneous acquisition of the entire elemental mass range and extending to larger hydrocarbon molecules. ToF-SIMS has been greatly utilized by surface scientists, but has rarely been used in terrestrial geosciences (e.g. [1]). Essentially a surface imaging technique, with shallow depth profiling abilities, it is ideal for investigating the distribution of elements and molecules (e.g. OH) on mineral surfaces, thin films [1], around fluid inclusions, and to trace chemical changes during weathering or hydrothermal alteration. To illustrate the potential of this analytical technique we highlight the progressive hydrothermal alteration of feldspars in the host andesites of the Comstock Lode paleohydrothermal system, Nevada. The Miocene Comstock Lode and related Ag-Au deposits are hosted mainly within Miocene Alta andesites, which were extensively sampled in the 1880s by G.F. Becker[2]. A sub-suite of these samples from the Sutro Tunnel document progressive hydrothermal alteration, with whole rock δ 18O values progressing from ~ +6 ‰ in distal andesites to -1.5 ‰ at the Coryell Lode [3]. The andesites are porphyritic with up to 50% feldspar phenocrysts, and minor mafic phases. Feldspar phenocrysts show systematic progression of alteration and replacement textures with decreasing whole rock δ 18O values and increasing proximity to the Coryell Lode. Relatively fresh igneous zoned phenocrysts (An35-55) grade into grains with fluid inclusions, crosscutting calcite +/- quartz veins, and increasingly complex reaction rims. Chemical alteration of feldspar progresses along cracks filled with fluid inclusions. Within 400 m of the Coryell Lode, feldspar phenocrysts have fully recrystallized, following crystallographic controls: Ab98-90 + An58-68, +/- sericite +/- calcite. A combination of BSE

  6. Identification of hydrothermal alteration assemblages using airborne imaging spectrometer data

    NASA Technical Reports Server (NTRS)

    Feldman, S. C.; Taranik, J. V.

    1986-01-01

    Airborne Imaging Spectrometer (AIS) data, field and laboratory spectra and samples for X-ray diffraction analysis were collected in argillically altered Tertiary volcanic rocks in the Hot Creek Range, Nevada. From laboratory and field spectral measurements in the 2.0 to 2.4 micron range and using a spectroradiometer with a 4 nm sampling interval, the absorption band centers for kaolinite were loacted at 2.172 and 2.215 microns, for montmorillonite at 2.214 micron and for illite at 2.205. Based on these values and the criteria for resolution and separtion of spectral features, a spectral sampling interval of less than 4 nm is necessary to separate the clays. With an AIS spectral sampling interval of 9.3 nm, a spectral matching algorithm is more effective for separating kaolinite, montmorillonite, ad illite in Hot Creek Range than using the location of absorption minima alone.

  7. Trace element behavior in hydrothermal experiments: Implications for fluid processes at shallow depths in subduction zones

    NASA Astrophysics Data System (ADS)

    You, C.-F.; Castillo, P. R.; Gieskes, J. M.; Chan, L. H.; Spivack, A. J.

    1996-05-01

    Chemical evaluation of fluids affected during progressive water-sediment interactions provides critical information regarding the role of slab dehydration and/or crustal recycling in subduction zones. To place some constraints on geochemical processes during sediment subduction, reactions between décollement sediments and synthetic NaCl-CaCl 2 solutions at 25-350°C and 800 bar were monitored in laboratory hydrothermal experiments using an autoclave apparatus. This is the first attempt in a single set of experiments to investigate the relative mobilities of many subduction zone volatiles and trace elements but, because of difficulties in conducting hydrothermal experiments on sediments at high P-T conditions, the experiments could only be designed for a shallow (˜ 10 km) depth. The experimental results demonstrate mobilization of volatiles (B and NH 4) and incompatible elements (As, Be, Cs, Li, Pb, Rb) in hydrothermal fluids at relatively low temperatures (˜ 300°C). In addition, a limited fractionation of light from heavy rare earth elements (REEs) occurs under hydrothermal conditions. On the other hand, the high field strength elements (HFSEs) Cr, Hf, Nb, Ta, Ti, and Zr are not mobile in the reacted fluids. The observed behavior of volatiles and trace elements in hydrothermal fluids is similar to the observed enrichment in As, B, Cs, Li, Pb, Rb, and light REEs and depletion in HFSEs in arc magmas relative to magmas derived directly from the upper mantle. Thus, our work suggests a link between relative mobilities of trace elements in hydrothermal fluids and deep arc magma generation in subduction zones. The experimental results are highly consistent with the proposal that the addition of subduction zone hydrous fluids to the subarc mantle, which has been depleted by previous melting events, can produce the unique characteristics of arc magmas. Moreover, the results suggest that deeply subducted sediments may no longer have the composition necessary to generate

  8. Comparison of hydrothermal alteration of carboniferous carbonate and siliclastic rocks in the Valles caldera with outcrops from the Socorro caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Armstrong, Augustus K.; Renault, Jacques R.; Oscarson, Robert L.

    1995-08-01

    Continental Scientific Drilling Program (CSDP) drill hole VC-2B [total depth 1761.7 m (5780 ft); maximum temperature 295 °C] was continuously cored through the Sulphur Springs hydrothermal system in the western ring-fracture zone of the 1.14 Ma Valles caldera. Among other units, the hole penetrated 760.2 m (2494.1 ft) of Paleozoic carbonate and siliciclastic strata underlying caldera fill and precaldera volcanic and epiclastic rocks. Comparison of the VC-2B Paleozoic rocks with corresponding lithologies within and around the 32.1 Ma Socorro caldera, 192 km ( 119 miles) to the south-southwest, provides insight into the variability of alteration responses to similar caldera-related hydrothermal regimes. The Pennsylvanian Madera Limestone and Sandia Formation from VC-2B preserve many of the sedimentological and diagenetic features observed in these units on a regional basis and where unaffected by high temperatures or hydrothermal activity. Micrites in these formations in VC-2B are generally altered and mineralized only where fractured or brecciated, that is, where hydrothermal solutions could invade carbonate rocks which were otherwise essentially impermeable. Alteration intensity (and correspondingly inferred paleopermeability) is only slightly higher in carbonate packstones and grainstones, low to intermediate in siltstones and claystones, and high in poorly cemented sandstones. Hydrothermal fracture-filling phases in these rocks comprise sericite (and phengite), chlorite, allanite, apatite, an unidentified zeolite and sphene in various combinations, locally with sphalerite, galena, pyrite and chalcopyrite. Terrigenous feldspars and clays are commonly altered to chlorite and seriate, and euhedral anhydrite "porphyroblasts" with minor chlorite occur in Sandia Formation siltstone. Fossils are typically unaltered, but the walls of some colonial bryozoans in the Madera Limestone are altered to the assemblage chlorite-sericite-epidote-allanite. La, Ce and Nd are

  9. IODP Expedition 345: Hydrothermal Alteration of Fast-Spreading EPR Lower Crust

    NASA Astrophysics Data System (ADS)

    Marks, N.; Faak, K.; Gillis, K. M.; McCaig, A. M.; Nozaka, T.; Python, M.

    2013-12-01

    Integrated Ocean Drilling Program (IODP) Expedition 345 sampled lower crustal primitive gabbroic rocks that formed at the fast-spreading East Pacific Rise (EPR) and are exposed at the Hess Deep Rift. Site U1415 is located along the southern slope of the intrarift ridge at ~ 4850 m water depth. The primary science results were obtained from coring of two ~110 m deep reentry holes (U1415J and U1415P) and one 35-m-deep single-bit hole (U1415I), all co-located within an ~200-m-wide area. The metamorphic mineral assemblages in the rocks recovered at Site U1415 record the cooling of primitive gabbroic lithologies from magmatic (>1000°C) to zeolite facies conditions (<200°C) associated with EPR spreading, Cocos-Nazca rifting and exposure onto the seafloor. Amphibolite facies alteration (including rare brown amphibole, secondary clinopyroxene and tremolite-chlorite corona textures between olivine and plagioclase) is sparsely developed in the core, and is intense in only a few samples. Lower grade greenschist (<400°C) and subgreenschist facies (<200°C) alteration of olivine to talc, serpentine, or clay minerals is more pervasive, and is commonly accompanied by prehnite microveins in plagioclase. The intensity of alteration varies with igneous lithology, in particular, the modal abundance of olivine, as well as proximity to zones of brittle fracturing and cataclasis. Mesh textured serpentinization is the most common alteration after olivine, although tremolite-chlorite corona textures are variably developed in all of the olivine-bearing gabbroic lithologies recovered at Site U1415. The freshest lithologies at Site U1415 are found in the Layered Series (Unit II) of Holes U1415I and J and Multi-textured Layered Olivine Gabbro Series (Unit II) in Hole U1415P. The Troctolite Series in Holes U1415J (Unit III) and U1415P (Unit III) are more pervasively altered than the gabbroic series, with U1415J troctolites being more altered (~80%) than in Hole U1415P (~65%). This likely

  10. Geochemical Evidence for Recent Hydrothermal Alteration of Marine Sediments in Mid-Okinawa Trough, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Tanaka, A.; Abe, G.; Yamaguchi, K. E.

    2014-12-01

    Recent studies have shown that submarine hydrothermal system supports diverse microbial life. Bio-essential metals supporting such microbial communities were released from basalts by high-temperature water-rock interaction in deeper part of the oceanic crust and carried by submarine fluid flow. Its total quantity in global hydrothermal settings has been estimated to be on the order of ~1019 g/yr, which is surprisingly on the same order of the total river flows (Urabe et al., 2011). Therefore, it is important to explore how submarine river system works, i.e., to understand mechanism and extent of elemental transport, which should lead to understanding of the roles of hydrothermal circulation in oceanic crust in controlling elemental budget in the global ocean and geochemical conditions to support deep hot biosphere.  We performed REE analysis of marine sediments influenced by submarine hydrothermal activity in Mid-Okinawa Trough. The sediment samples used in this study are from IODP site at Iheya North region and JADE site at Izena region. The samples show alternation between volcanic and clastic sediments. Hydrothermal fluids of this area contain elevated concentrations of volatile components such as H2, CO2, CH4, NH4+, and H2S, supporting diverse chemoautotrophic microbial community (Nakagawa et al., 2005). The purpose of this study is to examine the effect of hydrothermal activity on the REE signature of the sediments. Chondrite-normalized REE patterns of the samples show relative enrichment of light over heavy REEs, weak positive Ce anomalies, and variable degrees of negative Eu anomalies. The REE patterns suggest the sediments source was mainly basalt, suggesting insignificant input of continental materials. Negative Eu anomalies found in the IODP site become more pronounced with increasing depth, suggesting progressive increase of hydrothermal alteration where Eu was reductively dissolved into fluids by decomposition of feldspars. Contrary, at the JADE site

  11. Hydrothermal Alteration Mineral Mapping Using Hyperspectral Imagery in Dixie Valley, Nevada

    SciTech Connect

    Kennedy-Bowdoin, T; Martini, B A; Silver, E A; Pickles, W L

    2004-04-02

    Hyperspectral (HyMap) data was used to map the location of outcrops of high temperature, hydrothermally alterated minerals (including alunite, pyrophyllite, and hematite) along a 15 km swath of the eastern front of the Stillwater Mountain Range in Dixie Valley, Nevada. Analysis of this data set reveals that several outcrops of these altered minerals exist in the area, and that one outcrop, roughly 1 square kilometer in area, shows abundant high temperature alteration. Structural analysis of the altered region using a Digital Elevation Model (DEM) suggests that this outcrop is bounded on all sides by a set of cross-cutting faults. This fault set lies within the Dixie Valley Fault system (Caskey et al. 1996). Both the intense alteration in this area and the presence of cross-cutting faults indicate a high probability of recent hot fluid escape.

  12. Finite element analysis of heat transport in a hydrothermal zone

    SciTech Connect

    Bixler, N.E.; Carrigan, C.R.

    1987-01-01

    Two-phase heat transport in the vicinity of a heated, subsurface zone is important for evaluation of nuclear waste repository design and estimation of geothermal energy recovery, as well as prediction of magma solidification rates. Finite element analyses of steady, two-phase, heat and mass transport have been performed to determine the relative importance of conduction and convection in a permeable medium adjacent to a hot, impermeable, vertical surface. The model includes the effects of liquid flow due to capillarity and buoyancy and vapor flow due to pressure gradients. Change of phase, with its associated latent heat effects, is also modeled. The mechanism of capillarity allows for the presence of two-phase zones, where both liquid and vapor can coexist, which has not been considered in previous investigations. The numerical method employs the standard Galerkin/finite element method, using eight-node, subparametric or isoparametric quadrilateral elements. In order to handle the extreme nonlinearities inherent in two-phase, nonisothermal, porous-flow problems, steady-state results are computed by integrating transients out to a long time (a method that is highly robust).

  13. The hydrothermal system associated with the Kilauea East Rift Zone, Hawaii

    SciTech Connect

    Thomas, D.M.; Conrad, M.E.

    1997-12-31

    During the last twenty years drilling and fluid production on the Kilauea East Rift Zone (KERZ) has shown that an active hydrothermal system is associated with much of the rift. Well logging and fluid geochemistry indicate that reservoir temperatures exceed 360 C but are highly variable. Although neither well testing nor pressure decline data have clearly demonstrated the lateral limits of the reservoir, divergent fluid compositions over short distances suggest that the larger hydrothermal system is strongly compartmentalized across the rift zone. The chemical compositions of production fluids indicate that recharge is derived from ocean water and meteoric recharge and isotopic data suggest that the latter may be derived from subsurface inflow from the flanks of Mauna Loa.

  14. Mineralogy, paragenesis and textures associated with metasomatic- hydrothermal processes, Qatruyeh area, Sanandaj- Sirjan zone, SW Iran

    NASA Astrophysics Data System (ADS)

    Asadi, S.; Rajabzadeh, M. A.

    2009-04-01

    The Qatruyeh area is located at about 40 Km northeastern of Neyriz region, in the eastern edge of the high P- Low T metamorphic Zagros orogenic belt. The studied area principally includes outcrops of green schist facies metamorphic rocks that are thrusted over the Neotethyan ophiolites. Hydrothermal activities occurred episodically in the Mesozoic era . The textural relationships, mineral assemblages and X- Ray diffractions have recognized two different stages of hydrothermal alteration during mineralization. The Mineralization was largely controlled by striking faults and host rock layers. Three different types of magnetite are distinguished in microscopic investigation. The First is euhedral to subhedral, partly replacement by martite with exsolved ilmenites. The Second reveals myrmekite like textures and the last type includes layered magnetite. All of the types are related to replacement textures such as psedomorphism, widening of a fracture filling, irregulare or vermicular intergrowths, islands of unreplaced host rock, cusp or caries, nonmatching walls or borders of a fracture and rims of one mineral penetrating another along its crystallographic direction. X- Ray analyses indicate oxide minerals (Magnetite, Hematite, Maghemite, Specularite, Goethite, Limonite and Ilmenite), Silicate minerals (Tourmaline-shorl and dravite-, Epidote, Chlorite, Actinolite, Titanite, Paragonite, Talc, Muscovite and Quartz), Carbonate minerals (Siderite and Malachite) and Sulfide minerals (Pyrite and Chalcopyrite-minor-) as major phases. The mineral paragenesis and textures show two different stages of metasomatic- hydrothermal alteration. The first stage alteration (Sodic- Calsic) accompanying with mineral paragenesis of Magnetite+ Tourmaline+ Titanite+ Paragonite and the second stage of alteration (Solfidation- Oxidation) follows with Magnetite+ Hematite+ Quartz

  15. Hydrothermal alteration of the Ediacaran Doushantuo Formation in the Yangtze Gorges area (South China)

    NASA Astrophysics Data System (ADS)

    Derkowski, Arkadiusz; Bristow, Thomas F.; Wampler, J. M.; Środoń, Jan; Marynowski, Leszek; Elliott, W. Crawford; Chamberlain, C. Page

    2013-04-01

    The geochemical and fossil record preserved in the Ediacaran age (635-551 Ma) Doushantuo Formation of South China has been extensively examined to explore the impact of changing climate and the oxidation state of the oceans on the development and distribution of early multicellular life. In the Yangtze Gorges area, this formation shows many of the geochemical trends and features thought to typify global ocean chemistry in the Ediacaran Period, but there are indications that post-sedimentary processes modified these signals. This study of clay minerals and organic matter builds a more detailed picture of the type and degree of post-sedimentary alteration at different stratigraphic levels of the formation and focuses on how this alteration influenced stable carbon and oxygen isotope records. In the cratonward Jiulongwan and Huajipo sections of the Doushantuo Formation, its lower part (Members 1 and 2) consists largely of dolomitic shale, rich in authigenic saponite that crystallized in an alkaline sedimentary basin. Saponite has been altered to chlorite via corrensite across tens of meters of strata in lower Member 2, with increased alteration downward toward the cap dolostone. The greater chloritization is accompanied by lower δ18O and higher δD values of trioctahedral clays. This pattern of alteration of trioctahedral clays is likely due to hydrothermal fluid activity in the underlying, relatively permeable Nantuo Formation and cap dolostone. A concomitant increase of solid bitumen reflectance toward the base of the formation supports this idea. In the uppermost part of the formation in the Yangtze Gorges area (Member 4), a typical open water marine dolomitic shale rich in illite and organic matter, increases in the methylphenanthrenes ratio index and solid bitumen reflectance correlate with decrease of the bulk rock K/Al ratio upward, providing evidence for hot fluid migration above the nearly impermeable shale. Clay from the upper part of the formation is

  16. Hydrothermal alteration in research drill hole Y-3, Lower Geyser Basin, Yellowstone National Park, Wyoming

    USGS Publications Warehouse

    Bargar, Keith E.; Beeson, Melvin H.

    1985-01-01

    Y-3, a U.S. Geological Survey research diamond-drill hole in Lower Geyser Basin, Yellowstone National Park, Wyoming, reached a depth of 156.7 m. The recovered drill core consists of 42.2 m of surficial (mostly glacial) sediments and two rhyolite flows (Nez Perce Creek flow and an older, unnamed rhyolite flow) of the Central Plateau Member of the Pleistocene Plateau Rhyolite. Hydrothermal alteration is fairly extensive in most of the drill core. The surficial deposits are largely cemented by silica and zeolite minerals; and the two rhyolite flows are, in part, bleached by thermal water that deposited numerous hydrothermal minerals in cavities and fractures. Hydrothermal minerals containing sodium as a dominant cation (analcime, clinoptilolite, mordenite, Na-smectite, and aegirine) are more abundant than calcium-bearing minerals (calcite, fluorite, Ca-smectite, and pectolite) in the sedimentary section of the drill core. In the volcanic section of drill core Y-3, calcium-rich minerals (dachiardite, laumontite, yugawaralite, calcite, fluorite, Ca-smectite, pectolite, and truscottite) are predominant over sodium-bearing minerals (aegirine, mordenite, and Na-smectite). Hydrothermal minerals that contain significant amounts of potassium (alunite and lepidolite in the sediments and illitesmectite in the rhyolite flows) are found in the two drill-core intervals. Drill core y:.3 also contains hydrothermal silica minerals (opal, [3-cristobalite, chalcedony, and quartz), other clay minerals (allophane, halloysite, kaolinite, and chlorite), gypsum, pyrite, and hematite. The dominance of calcium-bearing hydrothermal minerals in the lower rhyolitic section of the y:.3 drill core appears to be due to loss of calcium, along with potassium, during adiabatic cooling of an ascending boiling water.

  17. Diffuse-flow hydrothermal field in an oceanic fracture zone setting, Northeast Pacific: Deposit composition

    USGS Publications Warehouse

    Hein, J.R.; Koski, R.A.; Embley, R.W.; Reid, J.; Chang, S.-W.

    1999-01-01

    This is the first reported occurrence of an active hydrothermal field in an oceanic fracture zone setting. The hydrothermal field occurs in a pull-apart basin within the Blanco Fracture Zone (BFZ), which has four distinct mineral deposit types: (1) barite mounds and chimneys, (2) barite stockwork breccia, (3) silica-barite beds, and (4) silica, barite, and Fe-Mn oxyhydroxide in sediments. All deposit types contain minor amounts of sulfides. In barite stockwork, silica-barite beds, and mineralized sediment, Ba, Ph, Ag, S, Au, Zn, Cu, Hg, TI, As, Mo, Sb, U, Cd, and Cu are enriched relative to unmineralized rocks and sediments of the BFZ. Fe and Mn are not enriched in the barite stockwork or silica-barite beds, but along with P, Co, and Mg are enriched in the mineralized sediments. Silver contents in deposits of the hydrothermal field range up to 86 ppm, gold to 0.7 ppm, zinc to 3.2%, copper to 0.8%, and barium to 22%. Mineralization occurred by diffuse, low to intermediate temperature (mostly <250??C) discharge of hydrothermal fluids through pillow lavas and ponds of mixed volcaniclastic and biosiliceous sediments. Bacterial mats were mineralized by silica, barite, and minor Fe hydroxides, or less commonly, by Mn oxyhydroxides. Pervasive mineralization of bacterial mats resulted in formation of silica-barite beds. Silica precipitated from hydrothermal fluids by conductive cooling and mixing with seawater. Sulfate, U, and rare earth elements (REEs) in barite were derived from seawater, whereas the REE content of hydrothermal silica deposits and mineralized sediments is associated with the aluminosilicate detrital fraction. Fe-, Zn-, Cu-, Pb-, and Hg-sulfide minerals, Ba in barite, and Eu in all mineralized deposits were derived from hydrothermal fluids. Manganese oxides and associated elements (Co, Sb, Mo, W, Cl, and Cu) and Fe oxides and associated elements (Be, B, P, and Mo) precipitated as the result of mixing of hydrothermal fluids with seawater. ?? 2001 Canadian

  18. Hydrothermal alteration and diagenesis of terrestrial lacustrine pillow basalts: Coordination of hyperspectral imaging with laboratory measurements

    USGS Publications Warehouse

    Greenberger, Rebecca N; Mustard, John F; Cloutis, Edward A; Mann, Paul; Wilson, Janette H.; Flemming, Roberta L; Robertson, Kevin; Salvatore, Mark R; Edwards, Christopher

    2015-01-01

    The phases identified in the sample are albite, large iron oxides, and titanite throughout; calcite in vesicles; calcic clinopyroxene, aegirine, and Fe/Mg-bearing clay in the rind; and fine-grained hematite and pyroxenes in the interior. Using imaging spectroscopy, the chemistry and mineralogy results extend to the hand sample and larger outcrop. From all of the analyses, we suggest that the pillow basalts were altered initially after emplacement, either by heated lake water or magmatic fluids, at temperatures of at least 400-600°C, and the calcic clinopyroxenes and aegirine identified in the rind are a preserved record of that alteration. As the hydrothermal system cooled to slightly lower temperatures, clays formed in the rind, and, during this alteration, the sample oxidized to form hematite in the matrix of the interior and Fe3+ in the pyroxenes in the rind. During the waning stages of the hydrothermal system, calcite precipitated in vesicles within the rind. Later, diagenetic processes albitized the sample, with albite replacing plagioclase, lining vesicles, and accreting onto the exterior of the sample. This albitization or Na-metasomatism occurred when the lake within the Hartford Basin evaporated during a drier past climatic era, resulting in Na-rich brines. As Ca-rich plagioclase altered to albite, Ca was released into solution, eventually precipitating as calcite in previously-unfilled vesicles, dominantly in the interior of the pillow. Coordinated analyses of this sample permit identification of the alteration phases and help synthesize the aqueous history of pillow lavas of the Talcott formation. These results are also relevant to Mars, where volcanically-resurfaced open basin lakes have been found, and this Hartford Basin outcrop may be a valuable analog for any potential volcano-lacustrine interactions. The results can also help to inform the utility and optimization of potentially complementary, synergistic, and uniquely-suited techniques for

  19. 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

  20. Mineral associations produced by sodic-calcic hydrothermal alteration in the Buffalo Mountain pluton, north-central Nevada

    SciTech Connect

    McBride, D. . Dept. of Geology and Geography)

    1993-03-01

    Sodic-calcic (Na-Ca) hydrothermal alteration is prevalent throughout Mesozoic-age arc igneous rocks in the western US. The middle Jurassic Buffalo Mountain pluton, located in north-central Nevada, contains particularly well developed Na-Ca metasomatism. The Buffalo Mountain pluton is composed of porphyritic syenite, quartz monzonite, small bordering stocks (which account for less than 1% of the pluton), and an extensive felsic dike swarm. Quartz monzonite intruded syenite and constitutes the majority of the surface area. Unaltered porphyritic syenite is composed of perthite, plagioclase, quartz, augite, hornblende, biotite, olivine, magnetite, and other minerals accounting for less than 1% of the rock. Unaltered quartz monzonite is an aggregate of K-feldspar, plagioclase, quartz, biotite, hornblende, and accessory minerals accounting for less than 1% of the rock. The dikes cut both phases of the total intrusive rock body and are closely related in space to zones of Na-Ca alteration. Alteration variably affects all igneous rock types and exists as both fracture-controlled and pervasive Na-Ca alteration. Sodic-calcic alteration resulted in the following mineral reactions: K-feldspar is replaced by chalky-colored plagioclase, and primary mafic minerals react to form pale green diopside or, less commonly, actinolite. Garnet, scapolite, and epidote are often spatially associated with Na-Ca altered rocks. The fact that Na-Ca alteration occurs most commonly in and around dikes suggests that they might have been the source of channel for fluid entry into the surrounding igneous rocks. Further study will seek to constrain the origins and pathways of Na-Ca fluids.

  1. Hydrothermal Alteration on Basaltic Mauna Kea Volcano as a Template for Identification of Hydrothermal Alteration on Basaltic Mars

    NASA Technical Reports Server (NTRS)

    Morris, R. V.; Graff, T. G.; Ming, D. W.; Mertzman, S. A.; Bell, J. F., III

    2003-01-01

    Certain samples of palagonitic tephra from Mauna Kea Volcano (Hawaii) are spectral analogues for bright martian surface materials at visible and near-IR wavelengths because both are characterized by a ferric absorption edge extending from about 400 to 750 nm and relatively constant reflectivity extending from about 750 nm to beyond 2000 nm. Palagonite is a yellow or orange isotropic mineraloid formed by hydration and devitrification of basaltic glass. For Mars-analogue palagonite, the pigment is nanometersized ferric oxide particles (np-Ox) dispersed throughout an allophane-like hydrated basaltic glass matrix. Crystalline phyllosilicates are not generally detected, and the hydration state of the is not known. The poorly crystalline nature of glass alteration products implies relatively low temperature formation pathways. We report here x-ray diffraction, major element, Mossbauer, and VNIR data for 9 basaltic tephras. Thermal emission spectra are reported in a separate abstract. Our multidisciplinary approach both tightly constrains mineralogical interpretations and maximizes overlap with datasets available for the martian surface available now and in the future.

  2. Hydrothermal alteration and mass exchange in the hornblende latite porphyry, Rico, Colorado

    NASA Astrophysics Data System (ADS)

    Larson, Peter B.; Cunningham, Charles G.; Naeser, Charles W.

    1994-03-01

    The Rico paleothermal anomaly, southwestern Colorado, records the effects of a large hydrothermal system that was active at 4 Ma. This hydrothermal system produced the deep Silver Creek stockwork Mo deposit, which formed above the anomaly's heat source, and shallower base and precious-metal vein and replacement deposits. A 65 Ma hornblende latite porphyry is present as widespread sills throughout the area and provided a homogenous material that recorded the effects of the hydrothermal system up to 8 km from the center. Hydrothermal alteration in the latite can be divided into a proximal facies which consists of two assemblages, quartz-illite-calcite and chlorite-epidote, and a distal facies which consists of a distinct propylitic assemblage. Temperatures were gradational vertically and laterally in the anomaly, and decreased away from the centra heat source. A convective hydrothermal plume, 3 km wide and at least 2 km high, was present above the stock-work molybdenum deposit and consisted of upwelling, high-temperature fluids that produced the proximal alteration facies. Distal facies alteration was produced by shallower cooler fluids. The most important shallow base and precious-metal vein deposits in the Rico district are at or close to the boundary of the thermal plume. Latite within the plume had a large loss of Na2O, large addition of CaO, and variable SiO2 exchante. Distal propylitized latite samples lost small amounts of Na2O and CaO and exchanged minor variable amounts of SiO2. The edge of the plume is marked by steep Na2O exchange gradients. Na2O exchange throughout the paleothermal anomaly was controlled by the reaction of the albite components in primary plagioclase and alkali feldspars. Initial feldspar alteration in the distal facies was dominated by reaction of the plagioclase, and the initial molar ratio of reactants (alkali feldspar albite component to plagioclase albite component) was 0.35. This ratio of the moles of plagioclase to alkali feldspar

  3. Hydrothermal alteration and zeolitization of the Fohberg phonolite, Kaiserstuhl Volcanic Complex, Germany

    NASA Astrophysics Data System (ADS)

    Weisenberger, Tobias Björn; Spürgin, Simon; Lahaye, Yann

    2014-11-01

    The subvolcanic Fohberg phonolite (Kaiserstuhl Volcanic Complex, Germany) is an economic zeolite deposit, formed by hydrothermal alteration of primary magmatic minerals. It is mined due to the high (>40 wt%) zeolite content, which accounts for the remarkable zeolitic physicochemical properties of the ground rock. New mineralogical and geochemical studies are carried out (a) to evaluate the manifestation of hydrothermal alteration, and (b) to constrain the physical and chemical properties of the fluids, which promoted hydrothermal replacement. The alkaline intrusion is characterized by the primary mineralogy: feldspathoid minerals, K-feldspar, aegirine-augite, wollastonite, and andradite. The rare-earth elements-phase götzenite is formed during the late-stage magmatic crystallization. Fluid-induced re-equilibration of feldspathoid minerals and wollastonite caused breakdown to a set of secondary phases. Feldspathoid minerals are totally replaced by various zeolite species, calcite, and barite. Wollastonite breakdown results in the formation of various zeolites, calcite, pectolite, sepiolite, and quartz. Zeolites are formed during subsolidus hydrothermal alteration (<150 °C) under alkaline conditions. A sequence of Ca-Na-dominated zeolite species (gonnardite, thomsonite, mesolite) is followed by natrolite. The sequence reflects an increase in and decrease in of the precipitating fluid. Low radiogenic 87Sr/86Sr values indicate a local origin of the elements necessary for secondary mineral formation from primary igneous phases. In addition, fractures cut the intrusive body, which contain zeolites, followed by calcite and a variety of other silicates, carbonates, and sulfates as younger generations. Stable isotope analysis of late-fracture calcite indicates very late circulation of meteoric fluids and mobilization of organic matter from surrounding sedimentary units.

  4. Molecular alteration of marine dissolved organic matter under experimental hydrothermal conditions

    NASA Astrophysics Data System (ADS)

    Hawkes, Jeffrey A.; Hansen, Christian T.; Goldhammer, Tobias; Bach, Wolfgang; Dittmar, Thorsten

    2016-02-01

    Marine dissolved organic matter (DOM) is a large (660 Pg) pool of reduced carbon that is subject to thermal alteration in hydrothermal systems and sedimentary basins. In natural high-temperature hydrothermal systems, DOM is almost completely removed, but the mechanism and temperature dependence of this removal have not been studied to date. We investigated molecular-level changes to DOM that was solid-phase extracted (SPE-DOM) from the deep ocean of the North Pacific Ocean. This complex molecular mixture was experimentally exposed to temperatures between 100 and 380 °C over the course of two weeks in artificial seawater, and was then characterised on a molecular level via ultrahigh-resolution Fourier-transform ion cyclotron mass spectrometry (FT-ICR-MS). Almost 93% of SPE-DOM was removed by the treatment at 380 °C, and this removal was accompanied by a consistent pattern of SPE-DOM alteration across the temperatures studied. Higher molecular weight and more oxygen rich compounds were preferentially removed, suggesting that decarboxylation and dehydration of carboxylic acid and alcohol groups are the most rapid degradation mechanisms. Nitrogen containing compounds followed the same overall trends as those containing just C, H and O up to 300 °C. Above this temperature, the most highly altered samples contained very little of the original character of marine DOM, instead being mainly composed of very low intensity N- and S- containing molecules with a high H/C ratio (>1.5). Our results suggest that abiotic hydrothermal alteration of SPE-DOM may already occur at temperatures above 68 °C. Our experiments were conducted without a sedimentary or mineral phase, and demonstrate that profound molecular alteration and almost complete removal of marine SPE-DOM requires nothing more than heating in a seawater matrix.

  5. Detection of hydrothermal alteration at Virginia City, Nevada using Airborne Imaging Spectrometry (AIS)

    NASA Technical Reports Server (NTRS)

    Hutsinpiller, A.; Taranik, J. V.

    1986-01-01

    Airborne Imaging Spectrometer (AIS) data were collected over Virginia City, Nevada; an area of gold and silver mineralization with extensive surface exposures of altered volcanic rocks. The data were corrected for atmospheric effects by a flat-field method, and compared to library spectra of various alteration minerals using a spectral analysis program SPAM. Areas of strong clay alteration were identified on the AIS images that were mapped as kaolinitic, illitic, and sericitic alterations zones. Kaolinitic alteration is distinguishable in the 2.1 to 2.4 and 1.2 to 1.5 micrometer wavelength regions. Montmorillonite, illite, and sericite have absorption features similar to each other at 2.2 micrometer wavelength. Montnorillonite and illite also may be present in varying proportions within one Ground Instantaneous Field of View (GIFOV). In general AIS data is useful in identifying alteration zones that are associated with or lie above precious metal mineralization at Virginia City.

  6. Geology, mineralization, and hydrothermal alteration and relationships to acidic and metal-bearing surface waters in the Palmetto Gulch area, southwestern Colorado

    USGS Publications Warehouse

    Bove, Dana J.; Kurtz, Jeffrey P.; Wright, Winfield G.

    2002-01-01

    The Palmetto Gulch area is affected by low pH and metal-bearing drainage from abandoned mines, and perhaps, from natural weathering around vein zones. To investigate these anthropogenic and potential natural sources of acidity and metals, we mapped the geology, veins, and hydrothermally altered areas; conducted mine dump leachate studies; and collected reconnaissance water quality data. Several small abandoned mines are present in the Palmetto Gulch area that produced small amounts of relatively high-grade silver ore from fault-controlled polymetallic vein deposits. These veins are hosted in lavas, breccias, and related volcaniclastic sediments that ponded within the 28 Ma San Juan-Uncompahgre caldera complex. These rock units generally have conformable contacts and have shallow dips to the northwest. Lava flows of pyroxene andesite, which host the Roy-Pray mine, are massive near their base and typically grade upward into tightly jointed rock with 2-15 cm joint spacing. In general, most hydrothermally altered rock within the Palmetto Gulch area is restricted to envelopes surrounding the mineralized veins and faults. Composite zones of vein-related alteration vary from about 50 to 80 m wide along the high ridgelines and narrow to less than 10 to 15 m beneath an elevation of about 5,462 m. Where unaffected by surficial oxidation, these altered zones contain as much as 7 to 10 volume percent finely-disseminated pyrite. The majority of rocks in the area were affected by regional and vein-related propylitic alteration. These greenish-colored rocks have alteration products consisting of chlorite, illite, and calcite; and feldspars are typically weakly altered. Most of these rocks have detectable amounts of calcite, while as much as 11 percent by weight was detected in samples collected during this study. The Palmetto Gulch area is affected by low pH and metal-bearing drainage from abandoned mines, and perhaps, from natural weathering around vein zones. To investigate

  7. Mapping Weak, Altered Zones and Perched Water With Aerogeophysical Measurements at Mount Adams, Washington: Implications for Volcanic Instability

    NASA Astrophysics Data System (ADS)

    Finn, C. A.; Deszcz-Pan, M.; Anderson, E. D.; Horton, R.

    2006-12-01

    Hydrothermally altered rocks, particularly if water saturated, can weaken stratovolcanoes. This increases the potential for catastrophic sector collapses that can lead to destructive debris flows. Evaluating the hazards associated with such alteration is difficult, because alteration has been mapped on few active volcanoes and the distribution and intensity of subsurface alteration and location of perched water tables are largely unknown on any active volcano. At Mount Adams, some Holocene debris flows contain abundant hydrothermal minerals derived from collapse of an altered edifice. Intense hydrothermal alteration can significantly reduce the resistivity (from hundreds to tens ohm-m) and magnetization of volcanic rocks. These changes can be identified with helicopter electromagnetic and magnetic measurements and visualized in 3D. 100 m is the greatest depth that the lowest frequency electromagnetic data could penetrate into the low resistivity, altered zones; outside the altered zones, the depth of penetration was up to 300 m. Total-field magnetic data can detect magnetization variations to several thousand meters depth. Electromagnetic and magnetic data, combined with geological mapping and rock property measurements, indicate the presence of appreciable thicknesses of hydrothermally altered rock in the central core of Mount Adams north of the summit. We identify steep cliffs at the western edge of this zone as the likely source for future large debris flows. Water, and perhaps melted ice, is needed as a lubricant to transform debris avalanches into lahars. Therefore, knowing the distribution of both is important for hazard assessments. Over the low resistivity summit, the electromagnetic data detected ice with a thickness of 0 to about 80 m and an estimated volume of up to 0.1 km3. Over resistive ridges ice thicknesses could not be determined. The electromagnetic data also identified perched water tables in the brecciated core of the upper 300 m of the volcano

  8. Hydrothermal alteration in basalts from Vargeão impact structure, south Brazil, and implications for recognition of impact-induced hydrothermalism on Mars

    NASA Astrophysics Data System (ADS)

    Yokoyama, Elder; Nédélec, Anne; Baratoux, David; Trindade, Ricardo I. F.; Fabre, Sébastien; Berger, Gilles

    2015-05-01

    The 12-km-wide Vargeão impact structure was formed 123 Myr ago in the Paraná basaltic province (southern Brazil). At this time the province region had a dry climate, although a large brackish aquifer had been formed in the underlying sandstones. It is therefore one of the best terrestrial analogs for studying impact-related products on a dry martian surface environment with preserved ice-rich ground. The basalts within the impact structure display cm-sized breccia veins filled with lithic clasts, glassy remnants, newly formed Fe-oxyhydroxides and secondary phases, such as calcite, phyllosilicates and, subordinately quartz and zeolite. The textural and mineralogical study of these phases demonstrate their hydrothermal origin. Although the very center of the structure has experienced the highest pressures and temperatures, the most developed hydrothermal changes are recognized in an inner collar surrounding the central depression. This inner collar is also the location of major modifications of the rock magnetic properties. These magnetic signatures are related to the distribution of impact-related faults and to the formation of new iron oxides. Geochemical modeling indicate that hydrothermal phases formation required low water/rock ratios. Our observations therefore suggest that hydrothermal alteration took place following the perturbation of the aquifer by the impact, but evidence for hydrothermal circulation is limited in comparison with other impact-related hydrothermal systems. This situation may be explained by the presence of the aquifer below the heat source, such a setting being exceptional for the Earth, but common on Mars. However, the spectroscopic signatures in visible/near infrared images suggest that this kind of impact-related hydrothermal alteration may be still indentified in large impact craters on Mars by orbital instruments. These results does not exclude the possibility that more developed alteration took place in breccias that are today

  9. Low-temperature zircon growth related to hydrothermal alteration of siderite concretions in Mississippian shales, Scotland

    NASA Astrophysics Data System (ADS)

    Bojanowski, Maciej J.; Bagiński, Bogusław; Clarkson, Euan; Macdonald, Ray; Marynowski, Leszek

    2012-08-01

    Zircon occurs in voids and cracks in phosphatic coprolites enclosed in siderite concretions in Mississippian shales near Edinburgh, Scotland. The zircon formed during hydrothermal alteration of early-diagenetic concretions and occurs as spherical aggregates of prismatic crystals, sometimes radiating. Vitrinite reflectance measurements indicate temperatures of ~270°C for the zircon-bearing concretions and the host shales. Molecular parameter values based on dibenzothiophene and phenanthrene distribution and occurrence of di- and tetra-hydro-products of polycyclic aromatic compounds suggest that the rocks experienced relatively high-temperature aqueous conditions related to hydrothermal fluids, perhaps associated with neighboring mafic intrusions. The zircon was dissolved from the concretions, transported in fluids, and reprecipitated in voids. This is the first record of the precipitation of authigenic zircon in sedimentary rock as a new phase, not as outgrowths.

  10. Regional patterns of hydrothermal alteration of sediments as interpreted from seafloor reflection coefficients, Middle Valley, Juan De Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Rohr, Kristin M. M.; Schmidt, Ulrike; Groschel-Becker, Henrike

    1993-09-01

    Reflection coefficients of the seafloor have been calculated from three multi-channel seismic reflection profiles across Middle Valley of the Juan de Fuca ridge. Seafloor reflection coefficients in this sedimented rift valley are high over an active hydrothermal vent and adjacent to major offset faults. Comparison of our measurements to drilling results from Leg 139 shows that high reflection coefficients over an active vent mound are produced by cemented sediments. Large reflection coefficients adjacent to major faults may have a similar origin and indicate that ongoing faulting creates pathways for hydrothermal fluids which alter the sediments and result in higher densities and velocities. Since 30 Hz seismic energy responds to the top 50 m of sediments, we are looking at the integrated response of hydrothermal alteration over tens of thousands of years. This is the first time seafloor reflection coefficients have been used to identify highly altered sediments in a region of deep-water hydrothermal activity.

  11. 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

  12. A reduced crustal magnetization zone near the first observed active hydrothermal vent field on the Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Zhu, Jian; Lin, Jian; Chen, Yongshun J.; Tao, Chunhui; German, Christopher R.; Yoerger, Dana R.; Tivey, Maurice A.

    2010-09-01

    Inversion of near-bottom magnetic data reveals a well-defined low crustal magnetization zone (LMZ) near a local topographic high (37°47‧S, 49°39‧E) on the ultraslow-spreading Southwest Indian Ridge (SWIR). The magnetic data were collected by the autonomous underwater vehicle ABE on board R/V DaYangYiHao in February-March 2007. The first active hydrothermal vent field observed on the SWIR is located in Area A within and adjacent to the LMZ at the local topographic high, implying that this LMZ may be the result of hydrothermal alteration of magnetic minerals. The maximum reduction in crustal magnetization is 3 A/M. The spatial extent of the LMZ is estimated to be at least 6.7 × 104 m2, which is larger than that of the LMZs at the TAG vent field on the Mid-Atlantic Ridge (MAR), as well as the Relict Field, Bastille, Dante-Grotto, and New Field vent-sites on the Juan de Fuca Ridge (JdF). The calculated magnetic moment, i.e., the product of the spatial extent and amplitude of crustal magnetization reduction is at least -3 × 107 Am2 for the LMZ on the SWIR, while that for the TAG field on the MAR is -8 × 107 Am2 and that for the four individual vent fields on the JdF range from -5 × 107 to -3 × 107 Am2. Together these results indicate that crustal demagnetization is a common feature of basalt-hosted hydrothermal vent fields at mid-ocean ridges of all spreading rates. Furthermore, the crustal demagnetization of the Area A on the ultraslow-spreading SWIR is comparable in strength to that of the TAG area on the slow-spreading MAR.

  13. Hydrothermal Alteration Minerals of the Geysers Steam Field, California and their Potential Use in Exploration

    SciTech Connect

    Moore, Diane

    1980-12-16

    Little information has been published on the hydrothermal alteration minerals occurring at depth in the Geysers steam field, California. Steiner (1958) reported the occurrence of wairakite from a well; McNitt (1964) identified pyrite, sericite, calcite, quartz, siderite, apatite and chlorite in cores of Franciscan graywacke and greenstone. Recently, Union Oil Geothermal Division furnished a set of well cores from the cap rock overlying the steam reservoir for geophysical studies (Lockner -e t -a l . , 1980). Cores of metagraywacke and greenstone from 4 wells were compared to unaltered Franciscan metagraywacke from surface exposures. Several previously unreported alteration minerals were found in the cored rocks, including epidote, tremolite-actinolite, prehnite and tourmaline. This note describes the observed alteration minerals and some of the factors that controlled their growth.

  14. Evidence for low-grade metamorphism, hydrothermal alteration, and diagenesis on mars from phyllosilicate mineral assemblages

    USGS Publications Warehouse

    Ehlmann, B.L.; Mustard, J.F.; Clark, R.N.; Swayze, G.A.; Murchie, S.L.

    2011-01-01

    The enhanced spatial and spectral resolution provided by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter (MRO) has led to the discovery of numerous hydrated silicate minerals on Mars, particularly in the ancient, cratered crust comprising the southern highlands. Phases recently identified using visible/near-infrared spectra include: smectite, chlorite, prehnite, high-charge phyllosilicates (illite or muscovite), the zeolite analcime, opaline silica, and serpentine. Some mineral assemblages represent the products of aqueous alteration at elevated temperatures. Geologic occurrences of these mineral assemblages are described using examples from west of the Isidis basin near the Nili Fossae and with reference to differences in implied temperature, fluid composition, and starting materials during alteration. The alteration minerals are not distributed homogeneously. Rather, certain craters host distinctive alteration assemblages: (1) prehnite-chlorite-silica, (2) analcime-silica-Fe,Mg-smectite-chlorite, (3) chlorite-illite (muscovite), and (4) serpentine, which furthermore has been found in bedrock units. These assemblages contrast with the prevalence of solely Fe,Mg-smectites in most phyllosilicate-bearing terrains on Mars, and they represent materials altered at depth then exposed by cratering. Of the minerals found to date, prehnite provides the clearest evidence for subsurface, hydrothermal/metamorphic alteration, as it forms only under highly restricted conditions (T = 200 400??C). Multiple mechanisms exist for forming the other individual minerals; however, the most likely formation mechanisms for the characteristic mineralogic assemblages observed are, for (1) and (2), low- grade metamorphism or hydrothermal (400??C has not been found.

  15. Hydrothermal alteration in well Baca 22, Baca geothermal area, Valles Caldera, New Mexico

    SciTech Connect

    Fox, D.J.

    1984-01-01

    A number of exploration wells were drilled to supply steam for a proposed electric generating plant. Drill cuttings from one of these wells, Baca 22, were studied with a petrographic microscope and by x-ray diffraction to determine the nature of the original rocks and of the hydrothermal alteration. The hydrothermal alteration is used to determine the temperatures of alteration which can then be compared with borehole temperatures to determine if the mineral assemblages are compatible with present day temperatures. It is shown that there is evidence indicating that the upper 2000 feet of borehole is cooler now than it has been in the past. Sample sizes were limited in this study (usually less than 5 grams). In most cases, one quarter of the sample was used to make the thin section while the remainder was reserved for x-ray analysis. Samples were mounted in epoxy and cut to a thickness of 30 microns for petrographic study. X-ray diffraction patterns were obtained using a Debye-Scherrer camera and Fek..cap alpha.. radiation.

  16. Mineral formation and redox-sensitive trace elements in a near-surface hydrothermal alteration system

    SciTech Connect

    Gehring, A.U.; Schosseler, P.M.; Weidler, P.G.

    1999-07-01

    A recent hydrothermal mudpool at the southwestern slope of the Rincon de la Vieja volcano in Northwest Costa Rica exhibits an argillic alteration system formed by intense interaction of sulfuric acidic fluids with wall rock materials. Detailed mineralogical analysis revealed an assemblage with kaolinite, alunite, and opal-C as the major mineral phases. Electron paramagnetic resonance spectroscopy (EPR) showed 3 different redox-sensitive cations associated with the mineral phases, Cu{sup +} is structure-bound in opal-C, whereas VO{sup 2+} and Fe{sup 3+} are located in the kaolinite structure. The location of the redox-sensitive cations in different minerals of the assemblage is indicative of different chemical conditions. The formation of the alteration products can be described schematically as a 2-step process. In a first step alunite and opal-C were precipitated in a fluid with slightly reducing conditions and a low chloride availability. The second step is characterized by a decrease in K{sup +} activity and subsequent formation of kaolinite under weakly oxidizing to oxidizing redox conditions as indicated by structure-bound VO{sup 2+} and Fe{sup 3+}. The detection of paramagnetic trace elements structure-bound in mineral phases by EPR provide direct information about the prevailing redox conditions during alteration and can, therefore, be used as additional insight into the genesis of the hydrothermal, near-surface system.

  17. Constraints on transport and kinetics in hydrothermal systems from zoned garnet crystals.

    PubMed

    Jamtveit, B; Hervig, R L

    1994-01-28

    Zonation of oxygen isotope ratios, fluorine, and rare earth element abundances across garnet crystals from the Permian Oslo Rift reflect temporal variation of the hydrothermal system in which the garnets grew. A sharp rimward decrease in the (18)O/(16)O ratio (of 5 per mil) across the interface between aluminum-rich garnet cores and iron-rich rims indicates influx of meteoric fluids to a system initially dominated by magmatic fluids. This influx may record the transition from ductile to brittle deformation of the hydrothermally altered rocks. In contrast, fluorine and light rare earth element concentrations increase at the core-rim interface. These data may reflect enhanced advective transport and notable kinetic control on trace element uptake by the garnets during brittle deformation. PMID:17754883

  18. Hydrothermal alteration experiments: tracking the path from interstellar to chondrites organics

    NASA Astrophysics Data System (ADS)

    Vinogradoff, V.; Bernard, S.; Le Guillou, C.; Jaber, M.; Remusat, L.

    2015-10-01

    Organic molecules are detected in primitive carbonaceous chondrites. The origin of these organics, whether formed prior the accretion phase, or in-situ on the parent body, is still a matter of debate. We have investigated experimentally the chemical evolution of interstellar organic molecules submitted to hydrothermal conditions, mimicking asteroidal alteration (T<200°C). In particular, we want to assess the potential catalytic role of clays minerals in the polymerization/degradation of organics. Hexamethylenetetramine (HMT, compound of C-N bonds) is used as a plausible interstellar precursors from icy grains. Experimental products reveal a large diversity of molecules, including nitrogen organic molecules similar to those found in chondrites.

  19. Hydrothermal alteration mapping of Siberian gold-ore fields based on satellite spectroscopy data

    NASA Astrophysics Data System (ADS)

    Ananyev, Yu S.; Maskov, A. A.; Abramova, R. N.

    2015-11-01

    The mapping of the hydrothermal alterations in Urjahskoe and Fedorov-Kedrov gold-ore fields was conducted by applying channel relationship method (band ratio) based on ASTER spectral-zonal satellite image data. It was determined that the calculated mineral indices in ore-bearing structures are zonal. Outer ore-bearing structures revealed increased ferric mineral index values, while inner - high epidote- chlorite- calcite and muscovite- siderite mineral index values. Detected regularities could be used in identifying potential gold-ore bearing areas within identical fields based on remote sensing survey data.

  20. Hydrothermal alteration products and stable isotope ratios of the Sulfur Creek Tuff; a window into the subsurface environment of the Yellowstone caldera in Yellowstone National Park, WY

    NASA Astrophysics Data System (ADS)

    Lonero, A.; Larson, P. B.

    2013-12-01

    The Yellowstone Caldera in northwest Wyoming is the site of active hydrothermal alteration. Hydrothermal activity relating to the Yellowstone hotspot has resulted in the alteration of rhyolites within the caldera. Specifically, the Seven Mile Hole area of the Grand Canyon of Yellowstone River provides an ideal location and opportunity to investigate the nature of the ongoing hydrothermal alteration. Here, erosion by the river has exposed a sequence of rocks which are host to hydrothermal fluids and are themselves significantly altered. Analyses of clay minerals and other alteration products, such as opal, has been undertaken in order to characterize and distinguish different zones of alteration. Hydrogen isotope ratios have been measured for the altered rock units within the Seven-Mile Hole area, and they range from -84.6 ‰ to -185.1 ‰ (VSMOW). Samples from this area commonly contain minerals such as kaolinite, illite, alunite, or buddingtonite, and the deuterium / hydrogen (D/H) ratios of these mineral phases are shown to vary considerably with respect to their location and elevation in the canyon. Additionally, oxygen isotope ratios have been measured on some samples in order to compare the samples' isotope values to the local meteoric water line. Plotting these samples in δD - δ18O space has shown that some values lie in a region trending away from the meteoric water line and along a "kaolinite line." This area is parallel to the array of Yellowstone hot spring fluids and a broad range of values are possible here depending on temperature of alteration. Furthermore, these data support a model where hydrothermal fluids flow upward through faults related to caldera collapse that are present in the sulfur creek tuff. This research may also show that the unique coloration patterns visible on the slopes of the Grand Canyon of Yellowstone can be, in part, explained as the result of both surface oxidation and hydrothermal alteration processes. Major element XRF

  1. EVALUATION OF LOW-SUN ILLUMINATED LANDSAT-4 THEMATIC MAPPER DATA FOR MAPPING HYDROTHERMALLY ALTERED ROCKS IN SOUTHERN NEVADA.

    USGS Publications Warehouse

    Podwysocki, Melvin H.; Power, Marty S.; Salisbury, Jack; Jones, O.D.

    1984-01-01

    Landsat-4 Thematic Mapper (TM) data of southern Nevada collected under conditions of low-angle solar illumination were digitally processed to identify hydroxyl-bearing minerals commonly associated with hydrothermal alteration in volcanic terrains. Digital masking procedures were used to exclude shadow areas and vegetation and thus to produce a CRC image suitable for testing the new TM bands as a means to map hydrothermally altered rocks. Field examination of a masked CRC image revealed that several different types of altered rocks displayed hues associated with spectral characteristics common to hydroxyl-bearing minerals. Several types of unaltered rocks also displayed similar hues.

  2. Hydrothermal alteration and diagenesis of terrestrial lacustrine pillow basalts: Coordination of hyperspectral imaging with laboratory measurements

    NASA Astrophysics Data System (ADS)

    Greenberger, Rebecca N.; Mustard, John F.; Cloutis, Edward A.; Mann, Paul; Wilson, Janette H.; Flemming, Roberta L.; Robertson, Kevin M.; Salvatore, Mark R.; Edwards, Christopher S.

    2015-12-01

    We investigate an outcrop of ∼187 Ma lacustrine pillow basalts of the Talcott Formation exposed in Meriden, Connecticut, USA, focusing on coordinated analyses of one pillow lava to characterize the aqueous history of these basalts in the Hartford Basin. This work uses a suite of multidisciplinary measurements, including hyperspectral imaging, other spectroscopic techniques, and chemical and mineralogical analyses, from the microscopic scale up to the scale of an outcrop. The phases identified in the sample are albite, large iron oxides, and titanite throughout; calcite in vesicles; calcic clinopyroxene, aegirine, and Fe/Mg-bearing clay in the rind; and fine-grained hematite and pyroxenes in the interior. Using imaging spectroscopy, the chemistry and mineralogy results extend to the hand sample and larger outcrop. From all of the analyses, we suggest that the pillow basalts were altered initially after emplacement, either by heated lake water or magmatic fluids, at temperatures of at least 400-600 °C, and the calcic clinopyroxenes and aegirine identified in the rind are a preserved record of that alteration. As the hydrothermal system cooled to slightly lower temperatures, clays formed in the rind, and, during this alteration, the sample oxidized to form hematite in the matrix of the interior and Fe3+ in the pyroxenes in the rind. During the waning stages of the hydrothermal system, calcite precipitated in vesicles within the rind. Later, diagenetic processes albitized the sample, with albite replacing plagioclase, lining vesicles, and accreting onto the exterior of the sample. This albitization or Na-metasomatism occurred when the lake within the Hartford Basin evaporated during a drier past climatic era, resulting in Na-rich brines. As Ca-rich plagioclase altered to albite, Ca was released into solution, eventually precipitating as calcite in previously-unfilled vesicles, dominantly in the interior of the pillow. Coordinated analyses of this sample permit

  3. Precursors predicted by artificial neural networks for mass balance calculations: Quantifying hydrothermal alteration in volcanic rocks

    NASA Astrophysics Data System (ADS)

    Trépanier, Sylvain; Mathieu, Lucie; Daigneault, Réal; Faure, Stéphane

    2016-04-01

    This study proposes an artificial neural networks-based method for predicting the unaltered (precursor) chemical compositions of hydrothermally altered volcanic rock. The method aims at predicting precursor's major components contents (SiO2, FeOT, MgO, CaO, Na2O, and K2O). The prediction is based on ratios of elements generally immobile during alteration processes; i.e. Zr, TiO2, Al2O3, Y, Nb, Th, and Cr, which are provided as inputs to the neural networks. Multi-layer perceptron neural networks were trained on a large dataset of least-altered volcanic rock samples that document a wide range of volcanic rock types, tectonic settings and ages. The precursors thus predicted are then used to perform mass balance calculations. Various statistics were calculated to validate the predictions of precursors' major components, which indicate that, overall, the predictions are precise and accurate. For example, rank-based correlation coefficients were calculated to compare predicted and analysed values from a least-altered test dataset that had not been used to train the networks. Coefficients over 0.87 were obtained for all components, except for Na2O (0.77), indicating that predictions for alkali might be less performant. Also, predictions are performant for most volcanic rock compositions, except for ultra-K rocks. The proposed method provides an easy and rapid solution to the often difficult task of determining appropriate volcanic precursor compositions to rocks modified by hydrothermal alteration. It is intended for large volcanic rock databases and is most useful, for example, to mineral exploration performed in complex or poorly known volcanic settings. The method is implemented as a simple C++ console program.

  4. Alteration zones around Kupferschiefer-type base metal mineralization in West Germany

    NASA Astrophysics Data System (ADS)

    Schmidt, F.-P.

    1987-07-01

    Several occurrences of red-colored rocks, which represent an unusual species within the lower Zechstein sediments as well as siderite ribbons and kaolinization have been reported from the West German lower Zechstein sequence. The red-colored rocks had been classified into two types, i.e., the stratiform red layers (SRL) and the Rote Fäule (RF). With regard to the gray beds, both types are characterized by enrichments and depletions of certain elements. As a result, ore-related Rote Fäule could be distinguished from insignificant stratiform red layers. Whereas Rote Fäule, which represents the alteration zone around diagenetic Kupferschiefer-type deposits, is chiefly characterized by apparent red coloring and enrichment in sulfate S, both the siderite ribbons and kaolinization of feldspars refer to formation of Cu-As sulfides and arsenides due to a hydrothermal, epigenetic process. Formation under more oxidizing, synsedimentary conditions is presumed for the stratiform red layers.

  5. Magma-hydrothermal contact zone of the Stromboli volcano (Italy): evidence from buchite xenoliths

    NASA Astrophysics Data System (ADS)

    Renzulli, A.; Serri, G.; Tribaudino, M.; Santi, P.; Salvioli-Mariani, E.

    2003-04-01

    orthorhombic symmetry. On the basis of mineralogical, geochemical and textural data we conclude that the buchites are the result of high-T, low-P contact metamorphism of hydrothermally altered ("intermediate argillic") volcanic rocks, induced by basaltic magmas analogous to those of the present-day activity of Stromboli. The argillaceous protoliths could have suffered intense thermal metamorphism/partial melting, either as in situ wall-rocks or as blocks stoped in the subvolcanic magma feeding system.

  6. 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.

  7. Mineralization, alteration, and hydrothermal metamorphism of the ophiolite-hosted Turner-Albright sulfide deposit, southwestern Oregon

    USGS Publications Warehouse

    Zierenberg, R.A.; Shanks, Wayne C., III; Seyfried, W.E., Jr.; 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

  8. Hydrothermal alteration experiments of olivine with varying Fe contents: An attempt to simulate aqueous alteration of the carbonaceous chondrites

    NASA Technical Reports Server (NTRS)

    Takatori, Koichi; Tomeoka, Kazushige; Tsukimura, Katsuhiro; Takeda, Hiroshi

    1993-01-01

    Hydrothermal alteration experiments of olivine powder with several Fe/Mg ratios were carried out under acidic and neutral conditions, and transition electron microscopy (TEM) observations were made on the run products. Well-developed tubular crystals of serpentine (chrysotile) were synthesized from Fo100 under both acidic and neutral conditions, and from Fo92 and Fo80 under acidic condition. Abundance and size of chrysotile apparenlty dependent on the Fe contents of olivine, i.e. with increasing Fe contents, less and smaller chrysotile was formed. Acidity of the solution plays an important role for the formation of chrysotile. Platy and fibrous crystals of phyllosilicate, probably serpentine, were obtained from Fo50 and Fo20 treated under acidic condition, which are most similar to the phyllosilicates in the CI and CM chondrites. Framboidal aggregates of Fe-rich grains (presumably Fe-hydroxide) were formed from Fa100 and Fo20, but no phyllosilicate was formed from Fa100.

  9. Hydrothermal Alteration Mineralogy Characterized Through Multiple Analytical Methods: Implications for Mars

    NASA Astrophysics Data System (ADS)

    Black, S.; Hynek, B. M.; Kierein-Young, K. S.; Avard, G.; Alvarado-Induni, G.

    2015-12-01

    Proper characterization of mineralogy is an essential part of geologic interpretation. This process becomes even more critical when attempting to interpret the history of a region remotely, via satellites and/or landed spacecraft. Orbiters and landed missions to Mars carry with them a wide range of analytical tools to aid in the interpretation of Mars' geologic history. However, many instruments make a single type of measurement (e.g., APXS: elemental chemistry; XRD: mineralogy), and multiple data sets must be utilized to develop a comprehensive understanding of a sample. Hydrothermal alteration products often exist in intimate mixtures, and vary widely across a site due to changing pH, temperature, and fluid/gas chemistries. These characteristics require that we develop a detailed understanding regarding the possible mineral mixtures that may exist, and their detectability in different instrument data sets. This comparative analysis study utilized several analytical methods on existing or planned Mars rovers (XRD Raman, LIBS, Mössbauer, and APXS) combined with additional characterization (thin section, VNIR, XRF, SEM-EMP) to develop a comprehensive suite of data for hydrothermal alteration products collected from Poás and Turrialba volcanoes in Costa Rica. Analyzing the same samples across a wide range of instruments allows for direct comparisons of results, and identification of instrumentation "blind spots." This provides insight into the ability of in-situ analyses to comprehensively characterize sites on Mars exhibiting putative hydrothermal characteristics, such as the silica and sulfate deposits at Gusev crater [eg: Squyres et al., 2008], as well as valuable information for future mission planning and data interpretation. References: Squyres et al. (2008), Detection of Silica-Rich Deposits on Mars, Science, 320, 1063-1067, doi:10.1126/science.1155429.

  10. Evidence for Impact-induced Hydrothermal Alteration at the Lonar Crater, India, and Mistastin Lake, Canada

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; Hagerty, J. J.

    2003-01-01

    The 50,000 year old, 1.8km diameter Lonar crater is located in Maharashtra, India. This relatively small crater is of particular interest because of its unique morphological and mineralogical properties, which make it a valid analogue for similar craters on the surface of Mars. We show that even in this relatively small crater, substantial hydrothermal alteration of shocked breccias in the floor of the crater has occurred, probably due to the thermal effects of the impact event. The 38 my old, 28 km diameter, Mistastin crater contains an 80 m thick impact melt sheet. We have also documented the presence of alteration phases in the material from this larger crater.

  11. High-temperature hydrothermal alteration of tje Boehls Butte anorthosite: Origin of a bimodal plagioclase assemblage

    SciTech Connect

    Mora, Claudia I; Riciputi, Lee R; Cole, David; Walker, Karen

    2008-01-01

    The Boehls Butte anorthosite consists predominantly of an unusual bimodal assemblage of andesine and bytownite anorthite. Oxygen isotope compositions of the anorthosite were profoundly altered by high temperature, retrograde interaction with meteorichydrothermal fluids that varied in composition from isotopically evolved to nearly pristine meteoric water. Oxygen isotope ratios of bulk plagioclase separates are in the range ?7.0 to -6.2% V-SMOW, however, secondary ion mass spectrometry indicates spot-sized isotope values as low as -16%. Typical inter- and intra-plagioclase grain variability is 3 6%, and extreme heterogeneity of up to 20%is noted in a few samples. High-temperature hydrothermal alteration of intermediate plagioclase is proposed to explain the origin of bytownite anorthite in the anorthosite and creation of its unusual bimodal plagioclase assemblage. The anorthite-forming reaction created retrograde reaction-enhanced permeability which, together with rapid decompression, extension, and unroofing of the anorthosite complex, helped to accommodated influx of significant volumes of meteoric-hydrothermal fluids into the anorthosite.

  12. Effect of hydrothermal circulation on slab dehydration for the subduction zone of Costa Rica and Nicaragua

    NASA Astrophysics Data System (ADS)

    Rosas, Juan Carlos; Currie, Claire A.; Harris, Robert N.; He, Jiangheng

    2016-06-01

    Dehydration of subducting oceanic plates is associated with mantle wedge melting, arc volcanism, intraslab earthquakes through dehydration embrittlement, and the flux of water into the mantle. In this study, we present two-dimensional thermal models of the Costa Rica-Nicaragua subduction zone to investigate dehydration reactions within the subducting Cocos plate. Seismic and geochemical observations indicate that the mantle wedge below Nicaragua is more hydrated than that below Costa Rica. These trends have been hypothesized to be due to a variation in either the thermal state or the hydration state of the subducting slab. Despite only small variations in plate age along strike, heat flow measurements near the deformation front reveal significantly lower heat flow offshore Nicaragua than offshore Costa Rica. These measurements are interpreted to reflect an along-strike change in the efficiency of hydrothermal circulation in the oceanic crust. We parameterize thermal models in terms of efficient and inefficient hydrothermal circulation and explore their impact on slab temperature in the context of dehydration models. Relative to models without fluid flow, efficient hydrothermal circulation reduces slab temperature by as much at 60 °C to depths of ∼75 km and increases the predicted depth of eclogitization by ∼15 km. Inefficient hydrothermal circulation has a commensurately smaller influence on slab temperatures and the depth of eclogitization. For both regions, the change in eclogitization depth better fits the observed intraslab crustal seismicity, but there is not a strong contrast in the slab thermal structure or location of the main dehydration reactions. Consistent with other studies, these results suggest that observed along-strike differences in mantle wedge hydration may be better explained by a northwestward increase in the hydration state of the Cocos plate before it is subducted.

  13. Evolution of a dynamic paleo-hydrothermal system at Mangatete, Taupo Volcanic Zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Drake, Bryan D.; Campbell, Kathleen A.; Rowland, Julie V.; Guido, Diego M.; Browne, Patrick R. L.; Rae, Andrew

    2014-08-01

    Recent quarrying and active faulting at Mangatete, Taupo Volcanic Zone (TVZ), New Zealand, illuminate a rare spatial and temporal window on a dynamic Late Quaternary geothermal system. Detailed geological mapping, stratigraphic logging, AMS 14C dating, and textural and mineralogical analyses were used to construct a complex history of hydrothermal, volcanological and tectonic activity from ~ 36 to 2 ka. Extinct, surface hydrothermal manifestations occur over a ~ 2 km2 area, and include in situ siliceous sinters distributed on normal fault terraces, an inferred hydrothermal eruption breccia (HEB) containing acid-etched sinter blocks, another probable HEB that was bathed in silicifying thermal fluids, and sinter clasts that were entrained in a debris flow associated with a volcanic ash event. Preserved sinter textures typical of near-neutral pH, alkali chloride spring discharge channels, aprons, terraces and affiliated marshes comprise plant-rich, palisade, tufted bubble mat, and domal stromatolitic fabrics. In addition, a packed fragmental sinter facies is shown herein to constitute silicified microbial mats that were broken, transported and deposited as point bar deposits in thermal spring-fed streams. Moreover, four unusual siliceous sinter fabrics-vuggy, globular spongy, scalloped, and arcuate wavy layered-are interpreted to have formed from local acid-sulfate-chloride thermal springs, possibly associated with paleo-fumaroles. The reconstructed history of paleo-hydrothermal activity indicates that the oldest sinters (~ 36 ka) at Mangatete developed in alkali chloride hot springs, but then underwent post-depositional alterion/overprinting by acid-sulfate steam condensate and were dismembered, possibly by a hydrothermal eruption. Low pH hot-spring discharges forming the unusual, inferred acid sinter fabrics were localized in the same area. A shift in paleo-hydrology is evidenced by unaltered, alkali chloride sinters dated between ~ 22 and 3 ka. A cluster of sinter

  14. Hydrothermal brecciation in the Jemez Fault zone, Valles Caldera, New Mexico: Results from CSDP (Continental Scientific Drilling Program) corehole VC-1

    SciTech Connect

    Hulen, J.B.; Nielson, D.L.

    1987-06-01

    Paleozoic and Precambrian rocks intersected deep in Continental Scientific Drilling Program corehole VC-1, adjacent to the late Cenozoic Valles caldera complex, have been disrupted to form a spectacular breccia sequence. The breccias are of both tectonic and hydrothermal origin, and probably formed in the Jemez fault zone, a major regional structure with only normal displacement since mid-Miocene. Tectonic breccias are contorted, crushed, sheared, and granulated; slickensides are commmon. Hydrothermal breccias, by contrast, lack these frictional textures, but arej commonly characterized by fluidized matrix foliation and prominent clast rounding. Fluid inclusions in the hydrothermal breccias are dominantly two-phase, liquid-rich at room temperature, principally secondary, and form two distinctly different compositional groups. Older inclusions, unrelated to brecciation, are highly saline and homogenize to the liquid phase in the temperature range 189 to 246/sup 0/C. Younger inclusions, in part of interbreccia origin, are low-salinity and homogenize (also to liquid) in the range 230 to 283/sup 0/C. Vapor-rich inclusions locally trapped along with these dilute liquid-rich inclusions document periodic boiling. These fluid-inclusion data, together with alteration assemblages and textures as well as the local geologic history, have been combined to model hydrothermal brecciation at the VC-1 site.

  15. Silica and Iron Oxide Minerals in Acidic Hydrothermal Alteration Products at Volcanic Fumaroles - Crystallinity of Cristobalite and Morphology of Hematite

    NASA Astrophysics Data System (ADS)

    Isobe, H.; Korenaga, Y.

    2010-12-01

    Cristobalite is a common alteration product occured in highly acidic hydrothermal environment around fumaroles in geothermal/volcanic areas. In the terrestrial environment, iron mineral species and morphology in the alteration products relate to temperature, acidity and redox conditions of surface or subsurface fluids. These silica and iron minerals show various textures and crystallographic characteristics depending on geochemical conditions. Severe acidic hydrothermal alteration of the pyroxene-amphibole andesite occurs at Garan-dake volcano, Oita, Japan. We carried out petrologic observation and powder XRD analysis of the hydrothermal alteration products with various color, composition and textures. XRD analysis revealed that the alteration degree is represented by abundance of cristobalite. Intermediately altered layers are characterized by various occurrence of alunite, pyrite, kaolinite, goethite and hematite. Detailed powder XRD analysis show that the primary diffraction peak of cristobalite composed with two or three phases with different d-spacing and FWHM by peak profile fitting analysis. Most samples contain well-crystallized, shorter d-spacing and narrow FWHM cristobalite and less-crystallized, longer d-spacing and wide FWHM cristobalite with various ratio. Samples with silica phases resembled to agate, and reddish samples with spheroidal hematite of several micron meters in diameter contain the least-cryatallized, largest d-spacing and very wide FWHM cristobalite phase in addition to the well and low-crystallized phases. The granular hematite grains show quite similar texture with hydrothermal alteration experimental products of iron-rich basalt with sulfuric acid solution possible hydrothermal alteration in the Martian volcano. Occurence of poorly crystalline cristobalite and fine grained spheroidal hematite may have essential constraint to understand acidic hydrotermal alteration processes in the volcanic provinces on the terrestrial planets.

  16. Shallow hydrothermal alteration and permeability changes in pyroclastic deposits: a case study at La Fossa cone (Vulcano island, Italy):

    NASA Astrophysics Data System (ADS)

    Cangemi, Marianna; Madonia, Paolo; Speziale, Sergio; Oliveri, Ygor

    2016-04-01

    La Fossa cone at Vulcano, the southernmost island of the Aeolian volcanic archipelago (Italy), has been characterized by an intense fumarolic activity since its last eruption dated 1888-90. Mineralogical alteration induced by shallow hydrothermal circulation has significantly reduced the permeability of the volcanic products, causing important feedbacks on the circulation of fluids in the shallowest portion of the volcanic edifice. The summit area of the cone is sealed by a quite continuous coating surface, fostering the condensation of hydrothermal fluids inside the volcanic edifice. The combination of fractures and volcano-stratigraphic discontinuities, conveying hydrothermal fluids, makes significant rock volumes prone to slide seaward, as occurred in 1988 during the main unrest experienced by Vulcano island since its last eruption. Similar instability conditions are found over the Forgia Vecchia crater rim area, formed by phreatic activity on the NE flank of the cone, where tensile fracturing and hydrothermal circulation interacts with mutual negative feedbacks. In the behalf of the DPC-INGV V3 Project 2012-15 we investigated the mineralogical composition and the hydraulic conductivity (under saturated conditions) of volcanic deposits potentially prone to hydrothermal fluid circulation, for evaluating their ability in retaining water, creating favourable conditions for gravitational instability. We also measured rainfall rate and volumetric soil moisture content in two automated stations located in different areas, with and without active hydrothermal circulation. We found that hydrothermal alteration transforms volcanic products into clay minerals, significantly reducing permeability of volcanic deposits. Argillified volcanic materials show background water contents, modulated by impulsive increments following rainfalls, higher than unaltered pyroclastic deposits, due to the combination of lower permeability and direct condensation of hydrothermal vapour. The

  17. Fluid chemistry and evolution of hydrothermal fluids in an Archaean transcrustal fault zone network: The case of the Cadillac Tectonic Zone, Abitibi greenstone belt, Canada

    USGS Publications Warehouse

    Neumayr, P.; Hagemann, S.G.; Banks, D.A.; Yardley, B.W.D.; Couture, J.-F.; Landis, G.P.; Rye, R.

    2007-01-01

    Detailed fluid geochemistry studies on hydrothermal quartz veins from the Rouyn-Noranda and Val-d'Or areas along the transcrustal Cadillac Tectonic Zone (CTZ) indicate that unmineralized (with respect to gold) sections of the CTZ contained a distinct CO2-dominated, H2S-poor hydrothermal fluid. In contrast, both gold mineralized sections of the CTZ (e.g., at Orenada #2) and associated higher order shear zones have a H2O-CO2 ?? CH4-NaCl hydrothermal fluid. Their CO2/H2S ratios indicate H2S-rich compositions. The Br/Cl compositions in fluid inclusions trapped in these veins indicate that hydrothermal fluids have been equilibrated with the crust. Oxygen isotope ratios from hydrothermal quartz veins in the CTZ are consistently 2??? more enriched than those of associated higher order shear zones, which are interpreted to be a function of greater fluid/rock ratios in the CTZ and lower fluid/rock ratios, and more efficient equilibration of the hydrothermal fluid with the wall rock, in higher order shear zones. An implication from this study is that the lower metal endowment of the transcrustal CTZ, when compared with the higher metal endowment in higher order shear zones (ratio of about 1 : 1000), may be the result of the lack of significant amounts of H2O-H2S rich fluids in most of the CTZ. In contrast, gold mineralization in the higher order shear zones appear to be controlled by the high H2S activity of the aqueous fluids, because gold was likely transported in a bisulfide complex and was deposited during sulfidation reactions in the wall rock and phase separation in the quartz veins. ?? 2007 NRC Canada.

  18. Discrimination of hydrothermally altered rocks along the Battle Mountain-Eureka, Nevada, mineral belt using Landsat images

    USGS Publications Warehouse

    Krohn, M. Dennis; Abrams, Michael J.; Rowan, Lawrence C.

    1978-01-01

    Landsat Multispectral Scanner (MSS) images of the northwestern part of the Battle Mountain-Eureki, Nevada mineral belt were evaluated for distinguishing hydrothermally altered rocks associated with porphyry copper and disseminated gold deposits. Detection of altered rocks from Landsat is based on the distinctive spectral reflectance of limonite present at coatings on weathered surfaces Some altered rocks are visible as bleached areas in individual MSS bands; however, they cannot be consistently distinguished from unaltered rocks with high albedo nor from bright areas resulting .from topographic slope. Black-and-white ratio images were generated to subdue .topographic effects, and three ratio images were composited in color to portray spectral radiance differences, forming an image known as a color-ratio composite (CRC). The optimum CRC image for this area has MSS 4/5 as blue, MSS 4/6 as yellow, and MSS 6/7 as magenta, and differs in two respects from most CRC images of arid areas. First, as a result of the increased vegetation cover in the study area, MSS 5/6 was replaced by MSS 4/6 as the yellow layer. Second, 70 mm positive transparencies were replaced by large format images (64 cm), thereby improving the internal registration of the CRC image and the effective spatial resolution. The pattern of limonitic rocks depicted in the CRC closely agrees with the mapped pattern of the alteration zones at the Copper Canyon and Copper Basin porphyry copper deposits. Certain west-facing topographic slopes in the altered areas are depicted as unaltered in the CRC, apparently due to atmospheric scattering, and illustrate the need for atmospheric correction. The disseminated gold deposits at Gold Acres and Tenabo are poorly represented in the CRC because of the general absence of limonite on these deposits. The presence of unaltered limonitic sedimentary and volcanic rocks is the largest obstacle to discriminating altered areas within the mineral belt. Reflectance spectra, made

  19. The changing microstructural arrangement of graphite during deformation and hydrothermal alteration of amphibolite-facies mylonite, Alpine Fault, New Zealand.

    NASA Astrophysics Data System (ADS)

    Kirilova, M.; Toy, V.; Timms, N.; Craw, D.; Little, T. A.; Halfpenny, A.; Beyssac, O.

    2015-12-01

    Graphitisation in a convergent plate boundary setting, such as the Alpine Fault, New Zealand, is associated both with fault weakening and orogenic gold mineralisation. Previously, these processes have been investigated in rocks that experienced mineralisation at maximum of greenschist-facies conditions. However, metals are most mobile at upper greenschist- to amphibolite-facies. We examine the microstructural record of mobilisation of graphite at these conditions due to dislocation and diffusion creep in the Alpine Fault zone and as a function of varying shear strain magnitude. We have mapped graphite distribution across a strain gradient in samples, recovered from Deep Fault Drilling Project (DFDP) boreholes, by using reflected light and scanning electron microscopy. Raman spectrometry was used to determine the degree of maturity of the carbonaceous material. In the schists and protomylonites, graphite occurs as very fine (1-5μm), dusty grains, dispersed as inclusions in the main mineral phases (quartz, anorthite, muscovite, biotite). Further into the mylonite zone, the modal proportion of graphite increases and it forms clusters and trains, aligned with the foliation. In the brittlely-deformed rocks (cataclasites and gouges on or near the fault principal slip zone) graphite is most abundant (<50%), occurring as clusters and shear plane parallel trains. We infer shear deformation under both ductile and brittle conditions concentrates the graphite. Independent evidence demonstrates fluid transport and consequent alteration was most important in the brittlely deformed rocks (Sutherland et al., 2012, Geology 40, 1143; Schleicher et al., in press. N.Z.J.Geol&Geophys). We thus infer hydrothermal enrichment caused graphite remobilization, re-deposition, and enrichment in structurally controlled microstructural sites. We will discuss implications of these microstructural and mineralogical changes for strain localisation and deformation-induced permeability.

  20. Rare earth elements as indicators of hydrothermal processes within the East Scotia subduction zone system

    NASA Astrophysics Data System (ADS)

    Cole, Catherine S.; James, Rachael H.; Connelly, Douglas P.; Hathorne, Ed C.

    2014-09-01

    The East Scotia subduction zone, located in the Atlantic sector of the Southern Ocean, hosts a number of hydrothermal sites in both back-arc and island-arc settings. High temperature (>348 °C) ‘black smoker’ vents have been sampled at three locations along segments E2 and E9 of the East Scotia back-arc spreading ridge, as well as ‘white smoker’ (<212 °C) and diffuse (<28 °C) hydrothermal fluids from within the caldera of the Kemp submarine volcano. The composition of the endmember fluids (Mg = 0 mmol/kg) is markedly different, with pH ranging from <1 to 3.4, [Cl-] from ∼90 to 536 mM, [H2S] from 6.7 to ∼200 mM and [F-] from 35 to ∼1000 μM. All of the vent sites are basalt- to basaltic andesite-hosted, providing an ideal opportunity for investigating the geochemical controls on rare earth element (REE) behaviour. Endmember hydrothermal fluids from E2 and E9 have total REE concentrations ranging from 7.3 to 123 nmol/kg, and chondrite-normalised distribution patterns are either light REE-enriched (LaCN/YbCN = 12.8-30.0) with a positive europium anomaly (EuCN/Eu∗CN = 3.45-59.5), or mid REE-enriched (LaCN/NdCN = 0.61) with a negative Eu anomaly (EuCN/Eu∗CN = 0.59). By contrast, fluids from the Kemp Caldera have almost flat REE patterns (LaCN/YbCN = 2.1-2.2; EuCN/Eu∗CN = 1.2-2.2). We demonstrate that the REE geochemistry of fluids from the East Scotia back-arc spreading ridge is variably influenced by ion exchange with host minerals, phase separation, competitive complexation with ligands, and anhydrite deposition, whereas fluids from the Kemp submarine volcano are also affected by the injection of magmatic volatiles which enhances the solubility of all the REEs. We also show that the REE patterns of anhydrite deposits from Kemp differ from those of the present-day fluids, potentially providing critical information about the nature of hydrothermal activity in the past, where access to hydrothermal fluids is precluded.

  1. Hydrothermal cooling along the Eastern Lau Spreading Center: No evidence for discharge beyond the neovolcanic zone

    NASA Astrophysics Data System (ADS)

    Baker, Edward T.; Martinez, Fernando; Resing, Joseph A.; Walker, Sharon L.; Buck, Nathaniel J.; Edwards, Margo H.

    2010-08-01

    Heat transported from the mantle beneath spreading centers creates an astonishingly narrow ribbon of convective heat discharge at plate boundaries, as apparently demonstrated by exhaustive exploration for hydrothermal discharge sites over the last three decades. Recent observations and models are now challenging this assumption of exclusively axis-centric high-temperature venting. One example is the proposal that intense cooling along the vertical boundaries of a broad low-velocity volume (LVV) of hot crust could generate high-temperature fluids several kilometers off axis. To test the hypothesis that substantial hydrothermal discharge might occur beyond the LVV, we conducted a dense survey grid of the ridge and surrounding seafloor (up to ±5 km) along 175 km of the Eastern Lau Spreading Center and Valu Fa Ridge (˜1800 km of track line). Our sampling array extended from ˜50 to 400 m above bottom and included light-scattering, oxidation-reduction potential, and hydrographic sensors attached to the tow line and beneath the IMI120 sonar mapping system. The surveys successfully mapped plumes from several vent fields in the neovolcanic zone (˜±1.5 km about the axis) but did not detect evidence of significant discharge anywhere farther off-axis. At a few locations on the Valu Fa Ridge, however, we did record oxidation-reduction potential anomalies with hydrographic density signatures that imply low-temperature hydrothermal sources on the axial flank. Although these sites are hundreds of meters deeper than the adjacent crest, they are above, not beyond, the previously mapped LVV. Our results thus do not support a simple picture of high-temperature fluids ascending undiluted through the crust to the seafloor several kilometers off-axis. However, we cannot exclude the possibilities that the largely unmapped LVV is narrower here than seen on other ridges, that hydrothermal fluids formed beyond the LVV are channeled to the axis, or that discharge beyond the neovolcanic

  2. Mineralogical, IR-spectral and geochemical monitoring of hydrothermal alteration in a deformed and metamorphosed Jurassic VMS deposit at Arroyo Rojo, Tierra del Fuego, Argentina

    NASA Astrophysics Data System (ADS)

    Biel, C.; Subías, I.; Acevedo, R. D.; Yusta, I.; Velasco, F.

    2012-04-01

    The Arroyo Rojo Zn-Pb-Cu volcanogenic massive sulfide deposit is the main deposit of the Fin del Mundo District in the Fuegian Andes, Argentina. This deposit is hosted by a Middle Jurassic volcanic and volcanoclastic sequence forming the Lemaire Formation. The latter consists, from the base up, of the following: rhyolitic and dacitic porphyritic rocks, ignimbrite, tuff, and flow. It is underlain by a pre-Jurassic basement and overlain by the hyaloclastic andesites of the Yahgán Formation. The Arroyo Rojo consists of stacked lenticular lenses that are associated with disseminated mineralization in both the footwall and the hanging wall. The internal structure of the ore lenses is marked by the occurrence of massive, semi-massive and banded facies, along with stringer and brecciated zones and minor ore disseminations. The mineral assemblage comprises mainly pyrite and sphalerite, with minor amounts of galena and chalcopyrite and rare pyrrhotite, arsenopyrite, tetrahedrite and bournonite. The ores and the volcanic host rocks have metamorphosed to greenschist facies and were overprinted by a penetrative tectonic foliation, which led to the development of mylonitic, and cataclastic textures, recrystallization and remobilization. Primary depositional characteristics and regional and hydrothermal alteration patterns were preserved despite deformation and metamorphism. Therefore, primary banding was preserved between facies boundaries. In addition, some remnants of magmatic origin are recognizable in preserved phenocrysts and volcaniclastic phenoclasts. Most of the volcanic and volcaniclastic rocks of the host sequence show a rhyolitic to rhyo-dacitic composition. Regional seafloor alteration, characterized by the presence of clinozoisite, Fe-chlorite and titanite, along with quartz and albite, is partially obliterated by hydrothermal alteration. The hydrothermal alteration is stratabound with the following assemblages, which developed from the base to top: (1) Quartz

  3. Hydrothermal alteration maps of the central and southern Basin and Range province of the United States compiled from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data

    USGS Publications Warehouse

    Mars, John L.

    2013-01-01

    Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and Interactive Data Language (IDL) logical operator algorithms were used to map hydrothermally altered rocks in the central and southern parts of the Basin and Range province of the United States. The hydrothermally altered rocks mapped in this study include (1) hydrothermal silica-rich rocks (hydrous quartz, chalcedony, opal, and amorphous silica), (2) propylitic rocks (calcite-dolomite and epidote-chlorite mapped as separate mineral groups), (3) argillic rocks (alunite-pyrophyllite-kaolinite), and (4) phyllic rocks (sericite-muscovite). A series of hydrothermal alteration maps, which identify the potential locations of hydrothermal silica-rich, propylitic, argillic, and phyllic rocks on Landsat Thematic Mapper (TM) band 7 orthorectified images, and geographic information systems shape files of hydrothermal alteration units are provided in this study.

  4. Systematics of hydrothermal alteration at the volcanic-hosted Falun Zn-Pb-Cu-(Au-Ag) deposit - implications for ore genesis, structure and exploration in a 1.9 Ga ore district, Fennoscandian Shield, Sweden

    NASA Astrophysics Data System (ADS)

    Kampmann, Tobias C.; Jansson, Nils J.; Stephens, Michael B.; Majka, Jarosław

    2016-04-01

    The Palaeoproterozoic, volcanic-hosted Falun Zn-Pb-Cu-(Au-Ag) sulphide deposit was mined for base and precious metals during several centuries, until its closure in 1992. The deposit is located in a 1.9 Ga ore district in the Bergslagen lithotectonic unit, Fennoscandian Shield, south-central Sweden. Both the ores and their host rock underwent polyphase ductile deformation, and metamorphism under amphibolite facies and later retrograde conditions at 1.9-1.8 Ga (Svecokarelian orogenic system). This study has the following aims: (i) Classify styles and intensities of alteration in the hydrothermally altered zone at Falun; (ii) identify precursor rocks to hydrothermally altered rocks and their spatial distribution at the deposit; (iii) evaluate the chemical changes resulting from hydrothermal alteration using mass change calculations; and (iv) assess the pre-metamorphic alteration assemblages accounting for the observed metamorphic mineral associations in the altered rocks at Falun. Results will have implications for both the ore-genetic and structural understanding of the deposit, as well as for local and regional exploration. Metamorphic mineral associations in the altered rocks include biotite-quartz-cordierite-(anthophyllite) and, more proximally, quartz-anthophyllite-(biotite-cordierite/almandine), biotite-cordierite-(anthophyllite) and biotite-almandine-(anthophyllite). The proximal hydrothermally altered zone corresponds to intense chlorite-style alteration. Subordinate dolomite or calcite marble, as well as calc-silicate (tremolite, diopside) rocks are also present at the deposit. Metavolcanic rocks around the deposit are unaltered, weakly sericitized or sodic-altered. Immobile-element (e.g. Zr, TiO2, Al2O3, REE) systematics of the silicate-rich samples at and around the deposit suggest that the precursors to the hydrothermally altered rocks at Falun were predominantly rhyolitic in composition, dacitic rocks being subordinate and mafic-intermediate rocks

  5. IODP Expedition 345: Characterizing Hydrothermal Alteration of Fast-Spreading EPR Lower Crust using O, Sr and Nd isotopics

    NASA Astrophysics Data System (ADS)

    Marks, N.; Gillis, K. M.; Lindvall, R. E.; Schorzman, K.

    2014-12-01

    The Integrated Ocean Drilling Program (IODP) Expedition 345 sampled lower crustal primitive gabbroic rocks that formed at the fast-spreading East Pacific Rise (EPR) and are exposed at the Hess Deep Rift. The metamorphic mineral assemblages in the rocks recovered at Site U1415 record the cooling of primitive gabbroic lithologies from magmatic (>1000°C) to zeolite facies conditions (<200°C) associated with EPR spreading, Cocos-Nazca rifting and exposure onto the seafloor. The dominant alteration assemblage is characterized by lower grade greenschist (<400°C) and subgreenschist facies (<200°C) alteration of olivine to talc, serpentine, or clay minerals, and is commonly accompanied by prehnite microveins in plagioclase. The intensity of alteration varies with igneous lithology, in particular, the modal abundance of olivine, as well as proximity to zones of brittle fracturing and cataclasis. We have attempted to characterize the nature and extent of isotopic exchange associated alteration and cooling and present a record of variations in O, Sr, and Nd isotopic compositions in altered rocks from the lower plutonic crust at Hess Deep. The Rb-Sr and 18O/16O systems exhibit sensitivity to hydrothermal interactions with seawater; whereas the Sm-Nd system appears essentially undisturbed by the minimal alteration experienced by the rocks drilled at Site U1415. The 87Sr/86Sr isotopic compositions of olivine gabbros (Mg# 0.81-0.89) range from 0.702536-0.703950 (±0.000008). Higher 87Sr/86Sr ratios are strongly correlated with percentage of hydrous minerals, and are higher in samples with a greater modal abundance of olivine. These rocks have somewhat higher 87Sr/86Sr ratios than upper plutonic rocks from the Northern Escarpment at Hess Deep (Kirchner and Gillis, 2012), although their percentage of hydrous phases is apparently similar. The d18O in these rocks ranges from 0.23‰ to 4.65‰ (±0.67); troctolites have systematically lower d18O than the gabbro and gabbronorites

  6. A paleomagnetic and stable isotope study of the pluton at Rio Hondo near Questa, New Mexico: implications for CRM related to hydrothermal alteration

    USGS Publications Warehouse

    Hagstrum, J.T.; Johnson, C.M.

    1986-01-01

    Paleomagnetic and rock magnetic data combined with stable isotope data from the middle Tertiary pluton along the Rio Hondo in northern New Mexico suggest that its magnetic remanence has both thermal (TRM) and high-temperature chemical (CRM) components. Oxygen isotope temperatures indicate that magnetite associated with the more rapidly cooled higher levels of the pluton, and with mafic inclusions and cogenetic rhyolitic dikes sampled at lower levels of exposure, ceased subsolidus recrystallization and isotopic exchange above its Curie temperature (580??C) in the presence of a magmatic fluid. Continued cooling imparted a TRM to these portions of the pluton. The more slowly cooled granodiorite at lower levels has quartz-magnetite isotopic temperatures that are below the Curie temperature of magnetite implying that its magnetization is high-temperature CRM. Sub-Curie isotopic temperatures for other granitic plutons in the western U.S.A. suggest that CRM may be commonly derived from subsolidus interactions between magnetite and magmatic fluids in plutonic rocks. A meteoric-hydrothermal system generated by the cooling Rio Hondo pluton, and not by younger adjacent intrusions, resulted in limited alteration along zones of high permeability near the southern margin of the Rio Hondo pluton, and in more prevasive alteration of the pluton to the north. The meteoric-hydrothermal alteration occurred at relatively high temperatures (> 350??C) and, with the exception of local chloritization, caused little visible alteration of the rocks. The isotopic ratios indicate that little of the magnetite could have grown from or exchanged with a meteoric-hydrothermal fluid. ?? 1986.

  7. Water making hot rocks soft: How hydrothermal alteration affects volcano stability

    NASA Astrophysics Data System (ADS)

    Ball, J. L.

    2015-12-01

    My research involves using numerical models of groundwater flow and slope stability to determine how long-term hydrothermal alteration in stratovolcanoes can cause increases in pore fluid pressure that lead to edifice collapse. Or in simpler terms: We can use computers to figure out how and why water that moves through hot rocks changes them into softer rocks that want to fall down. It's important to pay attention to the soft rocks even if they look safe because this can happen a long time after the stuff that makes them hot goes away or becomes cool. Wet soft rocks can go very far from high places and run over people in their way. I want show where the soft wet rocks are and how they might fall down so people will be safer.

  8. Fate of copper complexes in hydrothermally altered deep-sea sediments from the Central Indian Ocean Basin.

    PubMed

    Chakraborty, Parthasarathi; Sander, Sylvia G; Jayachandran, Saranya; Nath, B Nagender; Nagaraju, G; Chennuri, Kartheek; Vudamala, Krushna; Lathika, N; Mascarenhas-Pereira, Maria Brenda L

    2014-11-01

    The current study aims to understand the speciation and fate of Cu complexes in hydrothermally altered sediments from the Central Indian Ocean Basin and assess the probable impacts of deep-sea mining on speciation of Cu complexes and assess the Cu flux from this sediment to the water column in this area. This study suggests that most of the Cu was strongly associated with different binding sites in Fe-oxide phases of the hydrothermally altered sediments with stabilities higher than that of Cu-EDTA complexes. The speciation of Cu indicates that hydrothermally influenced deep-sea sediments from Central Indian Ocean Basin may not significantly contribute to the global Cu flux. However, increasing lability of Cu-sediment complexes with increasing depth of sediment may increase bioavailability and Cu flux to the global ocean during deep-sea mining. PMID:25108489

  9. Controls on thallium uptake during hydrothermal alteration of the upper ocean crust

    NASA Astrophysics Data System (ADS)

    Coggon, Rosalind M.; Rehkämper, Mark; Atteck, Charlotte; Teagle, Damon A. H.; Alt, Jeffrey C.; Cooper, Matthew J.

    2014-11-01

    Hydrothermal circulation is a fundamental component of global biogeochemical cycles. However, the magnitude of the high temperature axial hydrothermal fluid flux remains disputed, and the lower temperature ridge flank fluid flux is difficult to quantify. Thallium (Tl) isotopes behave differently in axial compared to ridge flank systems, with Tl near-quantitatively stripped from the intrusive crust by high temperature hydrothermal reactions, but added to the lavas during low temperature reaction with seawater. This contrasting behavior provides a unique approach to determine the fluid fluxes associated with axial and ridge flank environments. Unfortunately, our understanding of the Tl isotopic mass balance is hindered by poor knowledge of the mineralogical, physical and chemical controls on Tl-uptake by the ocean crust. Here we use analyses of basaltic volcanic upper crust from Integrated Ocean Drilling Program Hole U1301B on the Juan de Fuca Ridge flank, combined with published analyses of dredged seafloor basalts and upper crustal basalts from Holes 504B and 896A, to investigate the controls on Tl-uptake by mid-ocean ridge basalts and evaluate when in the evolution of the ridge flank hydrothermal system Tl-uptake occurs. Seafloor basalts indicate an association between basaltic uptake of Tl from cold seawater and uptake of Cs and Rb, which are known to partition into K-rich phases. Although there is no clear relationship between Tl and K contents of seafloor basalts, the data do not rule out the incorporation of at least some Tl into the same minerals as the alkali elements. In contrast, we find no relationship between the Tl content and either the abundance of secondary phyllosilicate minerals, or the K, Cs or Rb contents in upper crustal basalts. We conclude that the uptake of Tl and alkali elements during hydrothermal alteration of the upper crust involves different processes and/or mineral phases compared to those that govern seafloor weathering. Furthermore

  10. Biogeochemistry of hydrothermal vent mussel communities: the deep-sea analogue to the intertidal zone

    NASA Astrophysics Data System (ADS)

    Johnson, Kenneth S.; Childress, James J.; Beehler, Carl L.; Sakamoto, Carole M.

    1994-07-01

    Continuous measurements of sulfide, silicate and temperature were made in situ from the submersible Alvin in the Rose Garden and New Vent hydrothermal fields of the Galapagos Spreading Center. Continuous measurements of temperature also were made for an 18 day period in the Rose Garden field. The results demonstrate several adaptations that appear to have contributed to the success of the vent mussel Bathymodiolus thermophilus in the Rose Garden. Dense clusters of B. thermophilus can disperse the hydrothermal fluids laterally for distances of several meters. This results in a large increase in the area of the redox transition zone, where both dissolved oxygen and hydrogen sulfide are available. As a result, the animal communities can grow to occupy areas that would not otherwise provide adequate reduced substrates. Measurements of the temperature demonstrate a distinct tidal periodicity. This periodicity will result in a large range of environmental conditions within the vent community. The mussel can tolerate these wide ranges in condition because of its ability to accept long periods of anoxia and to filter feed.

  11. The mechanism of the hydrothermal alteration of cerium- and plutonium-doped zirconolite

    NASA Astrophysics Data System (ADS)

    Pöml, P.; Geisler, T.; Cobos-Sabaté, J.; Wiss, T.; Raison, P. E.; Schmid-Beurmann, P.; Deschanels, X.; Jégou, C.; Heimink, J.; Putnis, A.

    2011-03-01

    A comprehensive study on the aqueous stability of Ce- and Pu-doped zirconolite has been performed. Four series of hydrothermal experiments were carried out with Ce-doped zirconolite powders: (1) a solution series (1 M HCl, 2 M NaCl, 1 M NaOH, 1 M NH 3, pure H 2O), (2) a temperature series ( T = 100-300 °C), (3) a surface area-to-fluid volume ratio series, and (4) a series using different reactor materials (Teflon ©, Ni, and Ag). In addition, experiments on 238Pu- and 239Pu-doped zirconolite ceramics in a 1 M HCl solution have been performed. The 238Pu-doped zirconolite had already accumulated significant radiation damage and was X-ray amorphous, while the 239Pu-doped zirconolite was still well-crystalline. The results of the different experimental series can be summarized as follows: (1) After 14 days the degree of alteration is insignificant for all solutions other than 1 M HCl, which was therefore used for all other experimental series; (2) TiO 2 and m-ZrO 2 replaced the zirconolite grains to varying degrees in the 1 M HCl solution, i.e., zirconolite dissolution is incongruent; (3) the degree of alteration increases only slightly with increasing temperature; (4) the alteration rate is independent on the surface to volume ratio; (5) Ag dissolved from the silver reactors dramatically increases the reaction rate, while Ni from the Ni reactors reduces the solubility of Ti and Zr in the HCl solution, indicating that background electrolytes have a strong effect on the alteration rate. From the experiment with the Pu-doped samples at 200 °C in a 1 M HCl solution it was found that the amorphous 238Pu-doped zirconolite was altered to a significantly greater extent than the crystalline counterparts. The results suggest a coupled dissolution-reprecipitation mechanism, which is discussed in detail.

  12. Laboratory simulated hydrothermal alteration of sedimentary organic matter from Guaymas Basin, Gulf of California. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Leif, Roald N.

    1993-01-01

    High temperature alteration of sedimentary organic matter associated with marine hydrothermal systems involves complex physical and chemical processes that are not easily measured in most natural systems. Many of these processes can be evaluated indirectly by examining the geochemistry of the hydrothermal system in the laboratory. In this investigation, an experimental organic geochemical approach to studying pyrolysis of sedimentary organic matter is applied to the hydrothermal system in the Guaymas Basin, Gulf of California. A general survey of hydrothermal oils and extractable organic matter (bitumen) in hydrothermally altered sediments identified several homologous series of alkanones associated with a high temperature hydrothermal origin. The alkanones range in carbon number from C11 to C30 with no carbon number preference. Alkan-2-ones are in highest concentrations, with lower amounts of 3-, 4-, 5- (and higher) homologs. The alkanones appear to be pyrolysis products synthesized under extreme hydrothermal conditions. Hydrous pyrolysis and confinement pyrolysis experiments were performed to simulate thermally enhanced diagenetic and catagenetic changes in the immature sedimentary organic matter. The extent of alteration was measured by monitoring the n-alkanes, acyclic isoprenoids, steroid and triterpenoid biomarkers, polycyclic aromatic hydrocarbons and alkanones. The results were compared to bitumen extracts from sediments which have been naturally altered by a sill intrusion and accompanied hydrothermal fluid flow. These pyrolysis experiments duplicated many of the organic matter transformations observed in the natural system. Full hopane and sterane maturation occurred after 48 hr in experiments at 330 deg C with low water/rock mass ratios (0.29). A variety of radical and ionic reactions are responsible for the organic compound conversions which occur under extreme hydrothermal conditions. Short duration pyrolysis experiments revealed that a portion of the

  13. Behavior of nuclear waste elements during hydrothermal alteration of glassy rhyolite in an active geothermal system: Yellowstone National Park, Wyoming

    SciTech Connect

    Sturchio, N.C.; Seitz, M.G.

    1984-12-31

    The behavior of a group of nuclear waste elements (U, Th, Sr, Zr, Sb, Cs, Ba, and Sm) during hydrothermal alteration of glassy rhyolite is investigated through geochemical analyses of whole rocks, glass and mineral separates, and thermal waters. Significant enrichments of U, Sr, Sb, Cs, and Ba are found in altered rock relative to unaltered rock. Excess Sr, Cs, and Ba are concentrated in zeolites in altered rock. Excess U is associated with titanomagnetite surfaces. Th, Zr, and Sm are relatively immobile during alteration, and are strongly concentrated in celadonite. 19 refs., 2 figs., 2 tabs.

  14. Zones of life in the subsurface of hydrothermal vents: A synthesis

    NASA Astrophysics Data System (ADS)

    Larson, B. I.; Houghton, J.; Meile, C. D.

    2011-12-01

    Subsurface microbial communities in Mid-ocean Ridge (MOR) hydrothermal systems host a wide array of unique metabolic strategies, but the spatial distribution of biogeochemical transformations is poorly constrained. Here we present an approach that reexamines chemical measurements from diffuse fluids with models of convective transport to delineate likely reaction zones. Chemical data have been compiled from bare basalt surfaces at a wide array of mid-ocean ridge systems, including 9°N, East Pacific Rise, Axial Seamount, Juan de Fuca, and Lucky Strike, Mid-Atlantic Ridge. Co-sampled end-member fluid from Ty (EPR) was used to constrain reaction path models that define diffuse fluid compositions as a function of temperature. The degree of mixing between hot vent fluid (350 deg. C) and seawater (2 deg. C) governs fluid temperature, Fe-oxide mineral precipitation is suppressed, and aqueous redox reactions are prevented from equilibrating, consistent with sluggish kinetics. Quartz and pyrite are predicted to precipitate, consistent with field observations. Most reported samples of diffuse fluids from EPR and Axial Seamount fall along the same predicted mixing line only when pyrite precipitation is suppressed, but Lucky Strike fluids do not follow the same trend. The predicted fluid composition as a function of temperature is then used to calculate the free energy available to autotrophic microorganisms for a variety of catabolic strategies in the subsurface. Finally, the relationships between temperature and free energy is combined with modeled temperature fields (Lowell et al., 2007 Geochem. Geophys., Geosys.) over a 500 m x 500 m region extending downward from the seafloor and outward from the high temperature focused hydrothermal flow to define areas that are energetically most favorable for a given metabolic process as well as below the upper temperature limit for life (~120 deg. C). In this way, we can expand the relevance of geochemical model predictions of

  15. Mapping hydrothermally altered rocks at Cuprite, Nevada, using the advanced spaceborne thermal emission and reflection radiometer (Aster), a new satellite-imaging system

    USGS Publications Warehouse

    Rowan, L.C.; Hook, S.J.; Abrams, M.J.; Mars, J.C.

    2003-01-01

    The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a 14-band multispectral instrument on board the Earth Observing System (EOS), TERRA. The three bands between 0.52 and 0.86 ??m and the six bands from 1.60 and 2.43 ??m, which have 15- and 30-m spatial resolution, respectively, were selected primarily for making remote mineralogical determinations. The Cuprite, Nevada, mining district comprises two hydrothermal alteration centers where Tertiary volcanic rocks have been hydrothermally altered mainly to bleached silicified rocks and opalized rocks, with a marginal zone of limonitic argilized rocks. Country rocks are mainly Cambrian phyllitic siltstone and limestone. Evaluation of an ASTER image of the Cuprite district shows that spectral reflectance differences in the nine bands in the 0.52 to 2.43 ??m region provide a basis for identifying and mapping mineralogical components which characterize the main hydrothermal alteration zones: opal is the spectrally dominant mineral in the silicified zone; whereas, alunite and kaolinite are dominant in the opalized zone. In addition, the distribution of unaltered country rocks was mapped because of the presence of spectrally dominant muscovite in the siltstone and calcite in limestone, and the tuffaceous rocks and playa deposits were distinguishable due to their relatively flat spectra and weak absorption features at 2.33 and 2.20 ??m, respectively. An Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) image of the study area was processed using a similar methodology used with the ASTER data. Comparison of the ASTER and AVIRIS results shows that the results are generally similar, but the higher spectral resolution of AVIRIS (224 bands) permits identification of more individual minerals, including certain polymorphs. However, ASTER has recorded images of more than 90 percent of the Earth's land surface with less than 20 percent cloud cover, and these data are available at nominal or no cost

  16. High-resolution water column survey to identify active sublacustrine hydrothermal discharge zones within Lake Rotomahana, North Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Walker, Sharon L.; de Ronde, Cornel E. J.; Fornari, Daniel; Tivey, Maurice A.; Stucker, Valerie K.

    2016-03-01

    Autonomous underwater vehicles were used to conduct a high-resolution water column survey of Lake Rotomahana using temperature, pH, turbidity, and oxidation-reduction potential (ORP) to identify active hydrothermal discharge zones within the lake. Five areas with active sublacustrine venting were identified: (1) the area of the historic Pink Terraces; (2) adjacent to the western shoreline subaerial "Steaming Cliffs," boiling springs and geyser; (3) along the northern shoreline to the east of the Pink Terrace site; (4) the newly discovered Patiti hydrothermal system along the south margin of the 1886 Tarawera eruption rift zone; and (5) a location in the east basin (northeast of Patiti Island). The Pink Terrace hydrothermal system was active prior to the 1886 eruption of Mount Tarawera, but venting along the western shoreline, in the east basin, and the Patiti hydrothermal system appear to have been initiated in the aftermath of the eruption, similar to Waimangu Valley to the southwest. Different combinations of turbidity, pH anomalies (both positive and negative), and ORP responses suggest vent fluid compositions vary over short distances within the lake. The seasonal period of stratification limits vertical transport of heat to the surface layer and the hypolimnion temperature of Lake Rotomahana consequently increases with an average warming rate of ~ 0.010 °C/day due to both convective hydrothermal discharge and conductive geothermal heating. A sudden temperature increase occurred during our 2011 survey and was likely the response to an earthquake swarm just 11 days prior.

  17. An unusual spectral unit in West Candor Chasma: Evidence for hydrothermal or aqueous alteration?

    NASA Technical Reports Server (NTRS)

    Geissler, P. E.; Singer, R. B.

    1992-01-01

    A spectrally distinctive unit on the floor of W. Candor Chasma (6 S, 76 W) in the central Valles Marineris may be a likely candidate for hydrothermal or aqueous alteration. This unusual material is noticeably redder than nearby plains and canyon floor-covering deposits of similar brightness in several Viking Orbiter color composite images calibrated using PICS Level I procedures. The surrounding plains and canyon floor units have colors that are typical for much of the weathered soil on Mars. Relative to adjacent materials, the West Candor unit has lower green-filter reflectance and higher red-filter reflectance. While subtle, these spectral characteristics were observed for this unit in a number of multi-spectral images acquired at different seasons and phase angles. When the color image data are transformed to hue, saturation, and value coordinates, the West Candor material stands out prominently among the rocks and soils of Coprates Quadrangle as a spatially coherent unit with a unique hue. Physically, this means that the unit is compositionally distinct (unlike most of the bright materials in the region), since its spectral reflectance cannot be obtained through simple multiplicative scaling of the reflectance of the surrounding bright materials or by altering the spectral reflectance of the surrounding materials with an additive constant that is independent of wavelength. Recent studies of the directional reflectance properties of the surface in this region indicate that the photometric phase function of the unit is similar to that of surrounding bright materials (isotropic to slightly back scattering).

  18. Unravelling the deep fluid composition in the Taupo Volcanic Zone: insight into the magmatic-hydrothermal transition

    NASA Astrophysics Data System (ADS)

    Chambefort, I. S.; Lewis, B.; Boseley, C.; Begue, F.; Rae, A.

    2012-12-01

    The Ngatamariki Geothermal Field represents the only location in the Taupo Volcanic Zone where geothermal well drilling has intercepted intrusive rocks with a high temperature alteration halo. Thus it presents the perfect opportunity to study the magmatic-hydrothermal transition in the TVZ by characterising the nature of the deep magmatic fluids inferred to be linked to the geothermal heat source. In addition to the calc-alkaline Ngatamariki diorite (encountered in a 1985 drillhole; Wood, 1986), recent (2012) geothermal drilling encountered a quartz-phyric tonalite. After emplacement, these intrusions cooled, degassed, and produced a high temperature alteration halo, associated with intense quartz-illite/muscovite-pyrite alteration and pervasive quartz replacement of the overlying tuff-breccia. This alteration zone contains abundant high temperature quartz veins, similar to quartz veining stockwork characteristic of Porphyry Cu (±Au-Mo) systems. The recently encountered quartz-phyric tonalite contains common phenocrysts of quartz and pseudomorphs of plagioclase and minor ferromagnesian minerals (predominantly amphiboles) in a medium-grained, magnetite-bearing felsic groundmass. Quartz phenocrysts are generally rounded and embayed quartz eyes (≤1 cm diam.), or skeletal crystals. SEM-CL imaging was used to map the crystallisation history of the phenocrystic quartz in the tonalite and the quartz veins cross-cutting the diorite and overlying pyroclastic rocks. The quartz eyes show a complex growth history with zones of dissolution and recrystallisation. Skeletal quartz crystals also have complex zoning and are outlined by myrmekitic textures and/or dendritic overgrowths with the groundmass (granophyric textures). These features form in granites due to undercooling during shallow magmatic emplacement and are often associated with the exsolution of a volatile phase. Cathodoluminescence indicates that the edges of the quartz veins are lined by euhedral crystals

  19. Evolution of a dynamic paleo-hydrothermal system at Mangatete, Taupo Volcanic Zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Drake, Bryan D.; Campbell, Kathleen A.; Rowland, Julie V.; Guido, Diego M.; Browne, Patrick R. L.; Rae, Andrew

    2014-08-01

    Recent quarrying and active faulting at Mangatete, Taupo Volcanic Zone (TVZ), New Zealand, illuminate a rare spatial and temporal window on a dynamic Late Quaternary geothermal system. Detailed geological mapping, stratigraphic logging, AMS 14C dating, and textural and mineralogical analyses were used to construct a complex history of hydrothermal, volcanological and tectonic activity from ~ 36 to 2 ka. Extinct, surface hydrothermal manifestations occur over a ~ 2 km2 area, and include in situ siliceous sinters distributed on normal fault terraces, an inferred hydrothermal eruption breccia (HEB) containing acid-etched sinter blocks, another probable HEB that was bathed in silicifying thermal fluids, and sinter clasts that were entrained in a debris flow associated with a volcanic ash event. Preserved sinter textures typical of near-neutral pH, alkali chloride spring discharge channels, aprons, terraces and affiliated marshes comprise plant-rich, palisade, tufted bubble mat, and domal stromatolitic fabrics. In addition, a packed fragmental sinter facies is shown herein to constitute silicified microbial mats that were broken, transported and deposited as point bar deposits in thermal spring-fed streams. Moreover, four unusual siliceous sinter fabrics-vuggy, globular spongy, scalloped, and arcuate wavy layered-are interpreted to have formed from local acid-sulfate-chloride thermal springs, possibly associated with paleo-fumaroles. The reconstructed history of paleo-hydrothermal activity indicates that the oldest sinters (~ 36 ka) at Mangatete developed in alkali chloride hot springs, but then underwent post-depositional alterion/overprinting by acid-sulfate steam condensate and were dismembered, possibly by a hydrothermal eruption. Low pH hot-spring discharges forming the unusual, inferred acid sinter fabrics were localized in the same area. A shift in paleo-hydrology is evidenced by unaltered, alkali chloride sinters dated between ~ 22 and 3 ka. A cluster of sinter

  20. Mineralogical-geochemical features of travertines of the modern continental hydrotherms: A G-1 well, Tunka depression, Baikal rift zone

    NASA Astrophysics Data System (ADS)

    Soktoev, B. R.; Rikhvanov, L. P.; Ilenok, S. S.; Baranovskaya, N. V.; Taisaev, T. T.

    2015-07-01

    The mineral and chemical composition of travertines is studied in the modern discharge zone of the hydrothermal fluids of the Tunka depression, Baikal rift zone. The matrix of travertines is mostly made up of aragonite and calcite, which host about 20 mineral phases of Ag, Au, Pb, Cu, Sb, Sn, Fe, and other chemical elements. Similar rocks have previously been found in areas of modern submarine ore formation and tectonically active structures of the crust (New Zealand, the Cheleken Peninsula and others). Our materials confirm the opinion of some researchers who study modern hydrothermal ore formation in spreading zones that the formation of hydrothermal deposits requires favorable geochemical barriers rather than significant contents of metals in thermal waters. It is shown that microbial communities, concentrating chemical elements playing an important role in formation of ore mineralization in the discharge zones of thermal waters may be these barriers. According to our data, at the territory of the Tunka depression, thermal carbonic waters with endogenic components are delivered to the upper crustal horizons, involved in the existing hydrogeological systems, mixed with waters of active water exchange, and contribute to their chemical composition. This is manifested in the specific elemental and micromineral (Au, Ag, etc.) composition of the limescale of drinking water. In this local discharge zone, an effect of radioactive orphans has been found, which is similar to that established in barite chimneys from the Juan-de-Fuca Ridge.

  1. Mapping hydrothermally altered rocks on Mount Rainier, Washington, with Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data

    USGS Publications Warehouse

    Crowley, J.K.; Zimbelman, D.R.

    1997-01-01

    Mount Rainier has produced numerous Holocene debris flows, the largest of which contain clays and other minerals derived from hydrothermally altered rocks on the volcano's edifice. Imagery from an advanced airborne sensor was used to map altered rocks at Mount Rainier and demonstrates their distinctly nonuniform distribution. The mapping of altered rocks helps to identify edifice failure surfaces and to recognize the source areas for the largest debris flow events. Remote sensing methods like those used at Mount Rainier can enhance ground-based mapping efforts and should prove useful for rapidly identifying hazardous sectors at other volcanoes.

  2. Fluidization and hydrothermal alteration of the suevite deposit at the Ries Crater, West Germany, and implications for Mars

    NASA Technical Reports Server (NTRS)

    Newsom, Horton E.; Sewards, Terry; Keil, Klaus; Graup, Guenther

    1986-01-01

    The emplacement, cooling, and alteration of the suevite at the Ries Crater are discussed. The clay mineralogy of the suevite is examined in terms of the cooling of the suevite and the importance of hydrothermal alteration. It is observed that the suevite contains large number of chimneylike degassing pipes, and that the suevite outside of the crater rim contains about 15 wt pct clay. The vertical channels or degassing pipes related to the fall-out of suevite are described. The relationship between the formation of the impact deposits on earth and Mars and the origin of Martian soil, and the emplacement and alteration of impact ejecta is studied.

  3. Field Trip Guide to Serpentinite, Silica-Carbonate Alteration, and Related Hydrothermal Activity in the Clear Lake Region, California

    SciTech Connect

    Fraser Goff; George Guthrie

    1999-06-01

    This guide is designed to familiarize scientists with the geology, structure, alteration, and fluids typical of California serpentinites for purposes of carbon dioxide sequestration (Lackner et al., 1995). Goff et al. (1997) and Goff and Lackner (1998) describe the geology and geochemistry of some of the serpentinites from this area. Mechanisms of silica-carbonate alteration were outlined by Barnes et al. (1973). Donnelly-Nolan et al. (1993) most recently reviewed relations between regional hydrothermal alteration and Quarternary volcanic activity. Stanley et al. (1998) summarized geophysical characteristics of the region.

  4. Natural alteration in the cooling Topopah Spring tuff, Yucca Mountain, Nevada, as an analog to a waste-repository hydrothermal regime

    SciTech Connect

    Levy, S.; Valentine, G.

    1993-11-01

    Studies of natural hydrothermal alteration in the cooling Topopah Spring tuff suggest a useful ``self-analog`` predictor of fluid-rock interactions within the thermal regime imposed by a potential nuclear waste repository at Yucca Mountain. This tuff has the advantages of representative rock types and appropriate spatial distribution of lithologic features. The cooling history of the tuff spanned the temperature range for any proposed repository thermal load, and the unsaturated-zone hydrologic conditions of the natural alteration would have been similar to existing conditions. A site at northeastern Yucca Mountain, with a prominent vertical fracture zone, has been selected for natural analog studies. The cooling of the tuff and the movement of water in the fracture zone and adjacent matrix will be modeled with the finite element code FEHNM, capable of simulating flow through porous and fractured media using a dual porosity-dual permeability continuum model, with heat transfer and two-phase (vapor and liquid) processes fully accounted for.

  5. The contribution of hydrothermally altered ocean crust to the mantle halogen and noble gas cycles

    NASA Astrophysics Data System (ADS)

    Chavrit, Déborah; Burgess, Ray; Sumino, Hirochika; Teagle, Damon A. H.; Droop, Giles; Shimizu, Aya; Ballentine, Chris J.

    2016-06-01

    Recent studies suggest that seawater-derived noble gases and halogens are recycled into the deep mantle by the subduction of oceanic crust. To understand the processes controlling the availability of halogens and noble gases for subduction, we determined the noble gas elemental and isotopic ratios and halogen (Cl, Br, I) concentrations in 28 igneous samples from the altered oceanic crust (AOC) from 5 ODP sites in the Eastern and Western Pacific Ocean. Crushing followed by heating experiments enabled determination of noble gases and halogens in fluid inclusions and mineral phases respectively. Except for He and Ar, Ne, Kr and Xe isotopic ratios were all air-like suggesting that primary MORB signatures have been completely overprinted by air and/or seawater interaction. In contrast, 3He/4He ratios obtained by crushing indicate that a mantle helium component is still preserved, and 40Ar/36Ar values are affected by radiogenic decay in the mineral phases. The 130Xe/36Ar and 84Kr/36Ar ratios are respectively up to 15 times and 5 times higher than those of seawater and the highest ratios are found in samples affected by low temperature alteration (shallower than 800-900 m sub-basement). We consider three possible processes: (i) adsorption onto the clays present in the samples; (ii) fluid inclusions with a marine pore fluid composition; and (iii) fractionation of seawater through phase separation caused by boiling. Ninety percent of the Cl, Br and I were released during the heating experiments, showing that halogens are dominantly held in mineral phases prior to subduction. I/Cl ratios vary by 4 orders of magnitude, from 3 × 10-6 to 2 × 10-2. The mean Br/Cl ratio is 30% lower than in MORB and seawater. I/Cl ratios lower than MORB values are attributed to Cl-rich amphibole formation caused by hydrothermal alteration at depths greater than 800-900 m sub-basement together with different extents of I loss during low and high temperature alteration. At shallower depths, I

  6. Hydrogen and oxygen isotope constraints on hydrothermal alteration of the Trinity peridotite, Klamath Mountains, California

    USGS Publications Warehouse

    Liakhovitch, V.; Quick, J.E.; Gregory, R.T.

    2005-01-01

    The Trinity peridotite represents a rare opportunity to examine a relatively fertile plagioclase peridotite that was exhumed and later subjected to intrusive events in a seafloor environment, followed by its emplacement and incorporation into a continent. Over 250 stable isotopic determinations on whole rocks and minerals elucidate the hydrothermal evolution of the Trinity complex. All three serpentine polymorphs are present in the Trinity peridotite; these separate on the basis of their ??D values: antigorite, -46 < ??D < -82??? and lizardite and chrysotile, -90 < ??D < -106 and -110 < ??D < -136???, respectively. Antigorite coexists with chlorite, talc, and tremolite in contact aureole assemblages associated with Silurian/Devonian gabbroic plutons. Lizardite and chrysotile alteration carries a meteoric signature, which suggests association with post-emplacement serpentinization, or overprinting of earlier low-temperature seafloor serpentinization. Regionally, contours of ??D values exhibit bull's-eye patterns associated with the gabbroic plutons, with ??D maxima coinciding with the blackwall alteration at the margins on the plutons. In contrast to the hydrogen isotope behavior, oxygen isotope values of the three polymorphs are indistinguishable, spanning the range 5.3 < ??18O< 7.5, and suggesting low integrated fluid fluxes and strongly 18O-shifted fluids. Inferred primary ?? 18O values for peridotite, gabbro, and late Mesozoic granodiorite indicate a progressive 18O enrichment with time for the source regions of the rocks. These isotopic signatures are consistent with the geology, petrochemistry, and geochronology of the Trinity massif, which indicate the following history: (1) lithospheric emplacement and cooling of the peridotite in an oceanic environment ??? 472 Ma; (2) intrusion of gabbroic plutons into cold peridotite in an arc environment between 435 and 404 Ma; and finally (3) intrusion of felsic plutons between 171 and 127 Ma, long after the peridotite

  7. Constraints on microbial biogeography in Guaymas Basin hydrothermal sediments: energetic limits, thermal stress, and upward compression of metabolic zones

    NASA Astrophysics Data System (ADS)

    Mckay, L. J.; Klokman, V.; Teske, A. P.

    2012-12-01

    Subsurface hydrothermal temperatures and flow cause upward compression of geochemical and metabolic zones in Guaymas Basin seafloor sediments. The Guaymas hydrothermal system can be viewed as an accessible seafloor analog to deep, geothermally heated sedimentary microbial ecosystems. Using push core samples collected by the Alvin submersible (Cruises AT15-40 and 56 in 2008 and 2009) we are investigating thermal limits and substrate concentration ranges and their influence on microbial biogeography. Hydrothermally active sediments at Guaymas Basin host a wide range of shallow subsurface temperatures: from 3°C to 200°C in the upper 45 centimeters. A combination of extreme temperatures and compressed geochemical zonation limits the depth range of microbial colonization in Guaymas sediments. Microbial abundance is relatively high in Guaymas surface sediments, peaking around 10^10 cells/ml and decreasing to below detection at very hot temperatures. Our data describe how the biogeography of physiological modes—in particular anaerobic oxidation of methane (AOM) —is shaped by localized physicochemical conditions in Guaymas Basin hydrothermal sediments. Microbial oxidation changes the δ13C signature of porewater methane (CH4) from its baseline value of -43‰ (Welhan, 1988; Pearson et al., 2005) towards heavier values within a temperature window up to ca. 80°C; at higher temperatures, no CH4 oxidation imprint can be detected. δ13C values for dissolved inorganic carbon (DIC) indicate that bacterial remineralization of organic carbon may occur up to 100°C. 13C depleted DIC correlates well with 13C enriched CH4 in situ pinpointing zones of AOM between, for example, 20 and 40 cm below seafloor and 30°C and 50°C. 16S rDNA clone libraries support these suggested zones with the regular occurrence of (AN)aerobic (ME)thanotrophic Archaea. Given its high temperature tolerance, AOM can occur widely in the geothermally and hydrothermally heated subsurface.

  8. Crustal magmatism under a hydrothermal system, and the imprints of assimilation of hydrothermally altered protolith: an investigation of geochemical signatures in rhyolitic magmas at Yellowstone caldera

    NASA Astrophysics Data System (ADS)

    Girard, G.

    2014-12-01

    Yellowstone caldera, Wyoming, hosts one of the largest hydrothermal systems on Earth, fueled by heat and volatiles released from hotspot-derived basalt magmas that stall in the crust. Prolonged hydrothermal activity has pervasively altered the subsurface and such altered material is presumed to have acted as a source for magmas erupted after the two largest caldera eruptions, as evidenced by low-δ18O signatures in these magmas. This study focuses on the youngest Yellowstone volcanic units, the ~ 255 ka to ~ 70 ka large volume (~ 360 km3) Central Plateau Member (CPM) rhyolites. New laser-ablation ICP-MS whole rock, glass and mineral trace element data were obtained in order to refine existing constraints on CPM petrogenesis. Small temporal increases in elements such as As (3.1-4.1 ppm), Rb (170-200 ppm), Cs (3.6-4.3 ppm), Pb (26-31 ppm), Th (23-27 ppm) and U (5.4-6.8 ppm) contrast with increases of ~ 40-50 % in HFSE and REE in the same samples. The highest observed temporal increase is that of Zn, from 65 to 105 ppm. Caesium is highly incompatible with mineral/glass partition coefficients KD < 0.05 measured in all investigated mineral phases. Rubidium is also incompatible but its sanidine/glass KD ~ 0.4 results in a larger bulk distribution coefficient DRb ~ 0.2. For Pb, sanidine/glass KD ~ 0.8 leads to DPb > 0.4. Zinc is observed to be compatible in clinopyroxene, fayalite, zircon, chevkinite (KD ~ 5-12), and Fe-Ti oxides (KD ~ 40), such that DZn may approach 1. Fractional crystallization or partial melting processes alone cannot explain the same small increase rate of elements with diverse degrees of incompatibility (Rb, Cs and Pb), nor a larger increase rate in nearly compatible Zn. Assimilation by the juvenile CPM magmas of a crustal material of distinct composition appears to be required, and hydrothermally altered rhyolites, comprising much of the Yellowstone subsurface represent the most likely assimilant. Lower Rb, Cs, Pb (perhaps also As and U) and higher

  9. SIMS Investigations on Growth and Sector Zoning in Natural Hydrothermal Quartz: Isotopic and Trace Element Analyses

    NASA Astrophysics Data System (ADS)

    May, E.; Vennemann, T. W.; Baumgartner, L. P.; Meisser, N.

    2014-12-01

    Quartz is the most abundant mineral in the Earth's crust and is found in virtually every geological context. Despite its ubiquity and the detailed studies on the conditions of quartz crystallization, some questions concerning its growth and sector zoning with regard to trace element incorporation and oxygen isotope fractionations and the implications thereof for interpretations on the conditions of formation remain (e.g., Jourdan et al., 2009). This study presents new in-situ measurements of trace element and oxygen isotope ratios on natural hydrothermal quartz from an extensional gold-bearing quartz vein in the western Swiss Alps. The temperature of formation of the veins is estimated by quartz-hematite oxygen isotope thermometry to be about 360°C. A detailed SEM-CL study of this sample shows cyclic lamellar growth, alternating with phases of dissolution that are directly followed by macro-mosaic growth of the quartz, before returning to a cyclic lamellar growth again. Trace element concentrations (measured for Na, K, Li, Al, and Ti) notably showed Al/Si variations of three orders of magnitude and coupled Al and Li variations, likely substituting for Si in different growth zones with lower values in macro-mosaic zones precipitating after the period of dissolution. The oxygen isotope composition of the crystal, in contrast, is homogeneous through all growth zones (δ18O values between 15.6‰ and 16.2‰) indicating that the fluid must have been buffered by the host-rock and/or the source of the fluid remained the same despite the period of quartz dissolution. Furthermore, the temperature during crystallization of the quartz crystal has likely also remained similar. The fact that no variations are measured in oxygen isotope compositions but some variations in trace element contents may suggest that changes in pressure were important during the formation of this quartz crystal. Give the pressure effects on the solubility of quartz (Fournier and Potter, 1982), both

  10. Hydrothermal alteration of surficial rocks at Solfatara (Campi Flegrei): Petrophysical properties and implications for phreatic eruption processes

    NASA Astrophysics Data System (ADS)

    Mayer, Klaus; Scheu, Bettina; Montanaro, Cristian; Yilmaz, Tim I.; Isaia, Roberto; Aßbichler, Donjá; Dingwell, Donald B.

    2016-06-01

    Solfatara crater is located within the Campi Flegrei caldera to the west of Naples (Italy). It is one of the largest fumarolic manifestations known, and the rocks hosting the hydrothermal system are affected by intense hydrothermal alteration. Alteration can result in changes of degassing behavior, and in the formation of a cap rock thereby increasing the probability of phreatic eruptions. Here, we investigate the effects of alunitic (solfataric) alteration on the mineralogy, the physical properties (porosity, density, permeability) and the mechanical properties (strength) of the rocks involved, as well as its influence on fragmentation and ejection behavior. Our results show that the pristine mineralogy of deposits from the vicinity of the Solfatara cryptodome and from Pisciarelli is almost completely replaced by amorphous silica and alunite. The differences in the degree of alteration among the samples series are reflected in the investigated properties and behavior as well as in the analysis of the experimentally generated particles. Alunitic alteration increases porosity and permeability, whereas it reduces density, elastic wave velocity and strength leading to higher fragmentation and ejection speeds for the sample series examined in this study. Our results also show that alteration results in the generation of a high fraction of fines (particle sizes < 10 μm) during fragmentation, mainly composed of alunite crystals. Due to their potential for inducing chronic disease, dispersion of such material should represent a serious health hazard on a local scale and the evaluation of precautions should be considered.

  11. Behavior of nuclear waste elements during hydrothermal alteration of glassy rhyolite in an active geothermal system: Yellowstone National Park, Wyoming

    SciTech Connect

    Sturchio, N.C.; Seitz, M.G.

    1984-12-31

    The behavior of a group of nuclear waste elements (U, Th, Sr, Zr, Sb, Cs, Ba, and Sm) during hydrothermal alteration of glassy rhyolite is investigated through detailed geochemical analyses of whole rocks, glass and mineral separates, and thermal waters. Significant mobility of U, Sr, Sb, Cs, and Ba is found, and the role of sorption processes in their observed behavior is identified. Th, Zr, and Sm are relatively immobile, except on a microscopic scale. 9 references, 2 figures, 2 tables.

  12. Chromium Redox Equilibria in Fluids and Minerals under Hydrothermal and Subduction-zone Conditions

    NASA Astrophysics Data System (ADS)

    Hao, J.; Sverjensky, D. A.; Hazen, R. M.

    2015-12-01

    Chromium mobility and isotopic variations have been reported from a variety of high-temperature environments from hydrothermal to diamond-forming at elevated temperatures and pressures [1, 2, 3]. In addition, experiments under upper mantle conditions reported Cr-rich fluids in equilibrium with chromium oxide (Cr3+2O3) [4]. These studies suggest the need for theoretical models of the aqueous speciation of chromium in fluids and the stabilities of Cr minerals under deep crustal and upper mantle conditions. We estimated the thermodynamic properties of aqueous Cr2+, Cr3+, HCrO4-, CrO42-, and Cr2O72- using published data [5, 6] and the Deep Earth Water Model [7] to predict the different oxidation states of aqueous Cr to 1,000 °C and 5.0 GPa. We show that Cr(II) becomes the major redox state of Cr in hydrothermal fluids at 100 to 400 °C, with log fO2,g at magnetite/hematite over a wide range of pH values. In subduction zones, with log fO2,g at QFM to QFM - 2, a range of Cr redox states (II, III, and VI) may exist at 600 °C and 5 GPa depending on the pH. However, at higher temperatures (1000 °C), aqueous Cr(III) disappears and Cr(II) is favored relative to Cr(VI), again depending on the pH. Our predicted stability of Cr(II) in aqueous fluids at high temperatures suggests new mechanisms for redox/pH dependent Cr isotopic fractionation. We also estimated the thermodynamic properties of Cr(II)- and Cr(III)-garnets with the Sverjensky-Molling equation [8] to investigate the stability of Cr-garnet-fluid equilibria at elevated pressures and temperatures. References: [1] Schoenberg et al., 2008, Chem Geol 249, 294-306; [2] Farkaš et al., 2013, GCA 123, 74-92; [3] Stachel & Harris, 2008, Ore Geol. Rev, 34, 5-32; [4] Klein-BenDavid et al., 2011, Lithos 125, 122-130; [5] Ball & Nordstrom, 1998, J Chem Eng Data 43, 895-918; [6] Johnson & Nelson, 2012, Inorg Chem 51, 6116-6128; [7] Sverjensky et al. 2014, GCA 129, 125-145; [8] Sverjensky & Molling, 1992, Nature 356, 231-234.

  13. Continuous country rock contamination and hydrothermal alteration of the Ni-Cu-PGE sulphide-bearing (ultra-)basic Uitkomst Complex, South Africa

    NASA Astrophysics Data System (ADS)

    Gauert, Christoph; Globig, Jan

    2014-05-01

    This mineralized ultrabasic to basic igneous complex of Bushveld Complex age (De Waal et al., 2001) and with affinity to a Bushveld complex primary magma composition Gauert, 1998) deserves further investigation, since new drill core material became available. An intersection of the downdip extension of the complex of constant thickness reveals upper gabbronoritic units which are geochemically evolved and strongly contaminated with quartz by assimilation of country rocks. Hydrothermal, partly deuteric alteration is widespread over the complex, but pronounced in its lower and upper zones. Selective, connate to meteoric fluid ingress, controlled by contact metamorphism (Sarkar et al., 2008) and structure (Joubert, 2013), led to significant deuteric alteration. Highly talc-carbonate altered chromitiferous peridotite sections show formation of cube-shaped spinels, probably indicating auto-metamorphic conditions. Autometamorphism of the ultrabasic rocks produced a wide range of non-sulfide assemblages, despite the relatively restricted compositional range within each rock type; a crucial variable is the XCO2 of the metamorphic fluid. The sulphide mineralogy of the ultramafic-hosted deposit is influenced by the temperature and composition of the hydrothermal fluid. Reduction reactions associated with the serpentinization fronts in the dunitic adcumulates gave rise to Ni-Fe alloy and native Cu bearing assemblages. Greenschist facies hydration gave rise to serpentinites, hosting assemblages rich in pentlandite and in some cases violarite and marcasite, mackinawite, millerite, and valleriite. Oxidized fluids associated with low temperature talc-carbonate alteration in the chromitiferous peridotite formed Ni-sulphide minerals coexisting with pyrite and hematite. Both the sulfide and nickel components in the ore may contain substantial proportions of the total nickel budget. Low temperature alteration effectively redistributed the sulfide elements in serpentinites, leading to

  14. Implications of an ultramafic body in a basalt-dominated oceanic hydrothermal system on the vent fluid composition and on processes within sediments overlying a hydrothermal discharge zone: results of reactive-transport modeling

    NASA Astrophysics Data System (ADS)

    Alt-Epping, P.; Diamond, L. W.

    2009-04-01

    We use 2D reactive transport simulations to assess the hydraulic, thermal and chemical implications of an ultramafic body of lherzolitic composition within a basalt-dominated oceanic hydrothermal system. The simulations are fully coupled and hence account for the progressive serpentinization and the associated porosity/permeability reduction of the model lherzolite over time. We focus on the chemical fingerprints that reveal the presence of the ultramafic body at depth and that may be detected by direct seafloor exploration. These are the vent fluid composition and the porewater and mineral alteration within the rock column overlying a hydrothermal discharge zone. We compare ocean crust sections with and without sedimentary cover. Simulations suggest that the boundary between the basalt and the lherzolite constitutes a sharp reaction front. The type and distribution of alteration phases that form at the reaction front are a result of fluid flow across the basalt-lherzolite interface and thus are determined by the geometry and rate of hydrothermal fluid flow. Consequently, observations of the occurrence and extent of alteration phases, such as Fe-rich chlorite in the lherzolite or of rodingitization of the basalt, may be interpreted in terms of the reactive-transport model to reconstruct paleo-fluid flow in the permeable oceanic basement. The alteration of the lherzolite produces a fluid that is strongly reducing and depleted in silica. The most important chemical indicator of this rock-water interaction is an elevated H2 concentration. Under reducing (i.e. SO4-2 and CO2 free) conditions the enrichment in H2 is proportional to the extent of reaction between the fluid and the ultramafic rock. Under these conditions H2 behaves conservatively and the fluid remains enriched in H2 even though the concentration of all other major aqueous species is quickly buffered to new values when the fluid subsequently passes through basalt. This produces a vent fluid which is

  15. Seafloor hydrothermal clay alteration at Jade in the back-arc Okinawa Trough: Mineralogy, geochemistry and isotope characteristics

    SciTech Connect

    Marumo, Katsumi; Hattori, K.H.

    1999-09-01

    Seafloor hydrothermal activity at Jade has resulted in extensive alteration of the host epiclastic sediments and pumiceous tuffs, forming mica, kaolins (kaolinite and halloysite), Mg-rich chlorite, talc, montmorillonite, and a mixed-layer mineral of dioctahedral chlorite and montmorillonite (Chl/Mont). Clay mineral assemblages show a vertical variation, which reflects variable amounts of cold seawater incorporated into hot hydrothermal fluids in subsurface sediments and tuff. However, mixing alone cannot explain the occurrence of abundant kaolin minerals at Jade. The formation of kaolin minerals requires much more acidic fluid than expected from simple mixing of hydrothermal fluids and cold seawater. Low pH values are likely attained by oxidation of H{sub 2}S either dissolved in the hydrothermal fluid or released from the fluid during decompression. The fluid reaching the seafloor is discharged into cold seawater, which caused precipitation of sulfides close to vents and native sulfur and barite at the margins of the vent areas. Halloysite, barite and anhydrite show Sr isotope compositions similar to marine Sr, indicating the derivation of marine Sr directly from seawater or by the dissolution of calcareous nannoplanktons. At Jade, there is only one black smoker actively discharging high temperature ({approximately}320 C) fluid, but there are many fossil sulfide chimneys and mounds in the area. The mineralogy and high Au and Cu in these precipitates suggest highly metalliferous hydrothermal activity in the past. These activities likely resulted in discharge of hydrothermal plumes and fall-outs of sulfides and sulfates on the seafloor. These fall-outs were incorporated in sediments far from the vent areas. They are now recorded as high metal contents in sediments with no petrographic and mineralogical evidence of in-situ hydrothermal activity. Some are high as 8,100 ppm for Cu, 12,500 ppm for Zn, 1,000 ppm for As, 100 ppm for Ag and 21,000 ppm for Pb. Detrital

  16. Physical, chemical and mineralogical evolution of the Tolhuaca geothermal system, southern Andes, Chile: Insights into the interplay between hydrothermal alteration and brittle deformation

    NASA Astrophysics Data System (ADS)

    Sanchez-Alfaro, Pablo; Reich, Martin; Arancibia, Gloria; Pérez-Flores, Pamela; Cembrano, José; Driesner, Thomas; Lizama, Martin; Rowland, Julie; Morata, Diego; Heinrich, Christoph A.; Tardani, Daniele; Campos, Eduardo

    2016-09-01

    In this study, we unravel the physical, chemical and mineralogical evolution of the active Tolhuaca geothermal system in the Andes of southern Chile. We used temperature measurements in the deep wells and geochemical analyses of borehole fluid samples to constrain present-day fluid conditions. In addition, we reconstructed the paleo-fluid temperatures and chemistry from microthermometry and LA-ICP-MS analysis of fluid inclusions taken from well-constrained parageneses in vein samples retrieved from a ~ 1000 m borehole core. Based on core logging, mineralogical observations and fluid inclusions data we identify four stages (S1-S4) of progressive hydrothermal alteration. An early heating event (S1) was followed by the formation of a clay-rich cap in the upper zone (< 670 m) and the development of a propylitic alteration assemblage at greater depth (S2). Boiling, flashing and brecciation occurred later (S3), followed by a final phase of fluid mixing and boiling (S4). The evolution of hydrothermal alteration at Tolhuaca has produced a mineralogical, hydrological and structural vertical segmentation of the system through the development of a low-permeability, low-cohesion clay-rich cap at shallow depth. The quantitative chemical analyses of fluid inclusions and borehole fluids reveal a significant change in chemical conditions during the evolution of Tolhuaca. Whereas borehole (present-day) fluids are rich in Au, B and As, but Cu-poor (B/Na ~ 100.5, As/Na ~ 10- 1.1, Cu/Na ~ 10- 4.2), the paleofluids trapped in fluid inclusions are Cu-rich but poor in B and As (B/Na ~ 10- 1, As/Na ~ 10- 2.5, Cu/Na ~ 10- 2.5 in average). We interpret the fluctuations in fluid chemistry at Tolhuaca as the result of transient supply of metal-rich, magmatically derived fluids where As, Au and Cu are geochemically decoupled. Since these fluctuating physical and chemical conditions at the reservoir produced a mineralogical vertical segmentation of the system that affects the mechanical and

  17. An assessment of hydrothermal alteration in the Santiaguito lava dome complex, Guatemala: implications for dome collapse hazards

    USGS Publications Warehouse

    Ball, Jessica L.; Calder, Eliza S.; Hubbard, Bernard E.; Bernstein, Marc L.

    2013-01-01

    A combination of field mapping, geochemistry, and remote sensing methods has been employed to determine the extent of hydrothermal alteration and assess the potential for failure at the Santiaguito lava dome complex, Guatemala. The 90-year-old complex of four lava domes has only experienced relatively small and infrequent dome collapses in the past, which were associated with lava extrusion. However, existing evidence of an active hydrothermal system coupled with intense seasonal precipitation also presents ideal conditions for instability related to weakened clay-rich edifice rocks. Mapping of the Santiaguito dome complex identified structural features related to dome growth dynamics, potential areas of weakness related to erosion, and locations of fumarole fields. X-ray diffraction and backscattered electron images taken with scanning electron microscopy of dacite and ash samples collected from around fumaroles revealed only minor clay films, and little evidence of alteration. Mineral mapping using ASTER and Hyperion satellite images, however, suggest low-temperature (<150 °C) silicic alteration on erosional surfaces of the domes, but not the type of pervasive acid-sulfate alteration implicated in collapses of other altered edifices. To evaluate the possibility of internal alteration, we re-examined existing aqueous geochemical data from dome-fed hot springs. The data indicate significant water–rock interaction, but the Na–Mg–K geoindicator suggests only a short water residence time, and δ18O/δD ratios show only minor shifts from the meteoric water line with little precipitation of secondary (alteration) minerals. Based on available data, hydrothermal alteration on the dome complex appears to be restricted to surficial deposits of hydrous silica, but the study has highlighted, importantly, that the 1902 eruption crater headwall of Santa María does show more advanced argillic alteration. We also cannot rule out the possibility of advanced alteration

  18. Holocene and Paleogene arkoses of the Massif Central, France: Mineralogy, chemistry, provenance, and hydrothermal alteration of the type arkose

    SciTech Connect

    Kamp, P.C. van de ); Helmold, K.P. ); Leake, B.E. . Dept. of Geology and Applied Geology)

    1994-01-01

    Paleogene arkoses of the Auvergne region of France represent the type arkose originally described by Brongniart (1826). They are alluvial-fan and fluvial deposits including traction-current sandstones (arenites) and matrix-rich debris-flow deposits (wackes). Locally, they have been extensively altered by geothermal waters related to nearby Tertiary-Holocene volcanic activity. The alteration is typified by leaching of detrital grains and precipitation of ubiquitous chert cement. The average Gazzi-Dickinson composition of unaltered arenites is Q[sub 40]F[sub 60]L[sub 0], with K/F (potash feldspar/total feldspar) = 0.63. Altered arenites have an average composition of Q[sub 55]F[sub 43]L[sub 2], with K/F = 0.73, reflecting loss of plagioclase due to intense alteration. Chemical analyses of 130 sand and rock samples demonstrate original sediment compositions and changes due to hydrothermal alteration. Holocene sands and unaltered Paleogene clastics are compositionally similar and show variation trends similar to feldspathic clastics derived from granitic basement in other basins. Silica enrichment in the altered sandstones causes dilution of all other elements as an effect of constant summation. Consequently, most element abundances decline proportionately with silica dilution. Na and Rb, however, are reduced below the levels predicted by dilution due to plagioclase and biotite destruction. As a result, K/Rb ratios are higher in the altered sandstones. Ba, S, SO[sub 4], As, and Sb are enriched in the altered rocks by precipitation from hydrothermal solutions. Barium is in barite as fracture-filling veins and scattered patches in sandstone matrix.

  19. Hydrothermal alteration products of gabbros help accommodate exhumation-related deformation in mantle-derived ultramafics exposed at the Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Picazo, S.; Cannat, M.; Escartin, J.; Gibert, B.; Delacour, A.; Silantyev, S.

    2011-12-01

    Outcrops of deeply-derived ultramafic rocks and gabbros are widespread along slow spreading ridges but the rheology and dynamics of the exhumation faults and of their uplifted footwalls are still poorly known. Previous studies of samples collected within meters of exposed exhumation fault surfaces in the Atlantic have shown that a gabbroic component was added to the primarily ultramafic material in the fault zone, allowing for the growth of abundant amphibole, chlorite and talc. The nature of this component (altered magmatic intrusions or metasomatic hydrothermal fluids) could not, however, be ascertained in the pervasively sheared fault material. In this abstract we report on a set of 474 samples collected at the Mid-Atlantic Ridge (MAR) during the Serpentine cruise (2007; RV Pourquoi Pas? PI Y. Fouquet) next to the ultramafic-hosted Ashadze (13°N) and Logatchev (14°45'N) vent fields. Most of these 474 samples are weakly to moderately deformed and are interpreted as representing the upper few hundred meters below their respective exhumation fault zone, rather than the fault zone itself. The large number of samples, and their overall moderate degree of deformation gives us a chance to propose a semi-statistical study of plastic, brittle-plastic and brittle deformation in ultramafic rocks next to a MAR exhumation system, in relation with the magmatic and hydrothermal history. Our primary finding is that significant brittle-plastic deformation systematically involves amphibole±chlorite±talc-bearing ultramafic lithologies. Serpentine is commonly present in these deformed assemblages, but we did not find serpentine-only shear zones. Amphibole (in successive generations ranging from hornblende to tremolite) and chlorite occur in veins, many of which also contain zircon and some relict plagioclase, indicating a magmatic origin. Relicts of primary peridotite minerals in the most amphibole-rich samples indicate that magmatic injection followed on an episode of

  20. Paleoproterozoic volcanic centers of the São Félix do Xingu region, Amazonian craton, Brazil: Hydrothermal alteration and metallogenetic potential

    NASA Astrophysics Data System (ADS)

    da Cruz, Raquel Souza; Fernandes, Carlos Marcello Dias; Villas, Raimundo Netuno Nobre; Juliani, Caetano; Monteiro, Lena Virgínia Soares; Lagler, Bruno; Misas, Carlos Mario Echeverri

    2016-06-01

    Geological, petrographic, scanning electron microscopy, and X-ray diffraction studies revealed hydrothermalized lithotypes evidenced by overprinted zones of potassic, propylitic, sericitic, and intermediate argillic alterations types, with pervasive and fracture-controlled styles, in Paleoproterozoic volcano-plutonic units of the São Félix do Xingu region, Amazonian craton, northern Brazil. The Sobreiro Formation presents propylitic (epidote + chlorite + carbonate + clinozoisite + sericite + quartz ± albite ± hematite ± pyrite), sericitic (sericite + quartz + carbonate), and potassic (potassic feldspar + hematite) alterations. The prehnite-pumpellyite pair that is common in geothermal fields also occurs in this unit. The Santa Rosa Formation shows mainly potassic (biotite + microcline ± magnetite), sericitic (sericite + quartz + carbonate ± chlorite ± gold), and intermediate argillic (montmorillonite + kaolinite/halloysite + illite) alterations. These findings strongly suggest the involvement of magma-sourced and meteoric fluids and draw attention to the metallogenetic potential of these volcanic units for Paleoproterozoic epithermal and rare and base metal porphyry-type mineralizations, similar to those already identified in other portions of the Amazonian craton.

  1. A study of the hydrothermal alteration in Paleoproterozoic volcanic centers, São Félix do Xingu region, Amazonian Craton, Brazil, using short-wave infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    da Cruz, Raquel Souza; Fernandes, Carlos Marcello Dias; Villas, Raimundo Netuno Nobre; Juliani, Caetano; Monteiro, Lena Virgínia Soares; de Almeida, Teodoro Isnard Ribeiro; Lagler, Bruno; de Carvalho Carneiro, Cleyton; Misas, Carlos Mario Echeverri

    2015-10-01

    Hypogene hydrothermal minerals have been identified by short-wave infrared spectroscopy in hydrothermally altered rocks from the Sobreiro and Santa Rosa formations, which belong to a Paleoproterozoic volcano-plutonic system in Amazonian craton. Three clay minerals are spectrally recognized: montmorillonite, kaolinite, and illite. The integration of these data with those available in the literature, including gold occurrences, suggests that those rocks are hydrothermal products of both volcanic thermal sources and later crustal intrusions, as evidenced by variable styles of propylitic, sericitic, potassic, and intermediate argillic alteration. The influence of meteoric fluids is emphasized. This low cost exploratory technique, which can be applied to hand samples, seems to be promising in the separation of hydrothermally altered volcano-plutonic centers in regions submitted to severe weathering conditions, in addition to aid elaborating models for prospecting mineral deposits.

  2. Reaction Weakening of Dunite in Friction Experiments at Hydrothermal Conditions and Its Relevance to Subduction Zones

    NASA Astrophysics Data System (ADS)

    Moore, D. E.; Lockner, D. A.

    2014-12-01

    To improve our understanding of processes occurring in the mantle wedge near the downdip limit of seismicity in subduction zones, we conducted triaxial friction tests on dunite gouge at temperatures in the range 200-350°C, 50 MPa fluid pressure and 100 MPa effective normal stress. Dunite, quartzite, and granite forcing blocks were used respectively to approximate changing rock/fluid chemistry with decreasing distance above the subduction thrust. All experiments were characterized by an initial increase in frictional strength to a peak value, followed by a decrease associated with shearing-enhanced alteration of the dunite gouge. Reaction products and the extent of weakening varied with the chemical environment. In the dunite-block experiments, strength gradually declined from the peak value to a coefficient of friction, µ ~ 0.5-0.6, consistent with the frictional strength of serpentine that formed on the shear surfaces from alteration of the gouge. Interaction of dunite gouge with quartzite and granite driving blocks resulted in significantly greater weakening, to μ ~ 0.3, at temperatures of 250°C and higher. Talc and serpentine partly replaced dunite gouge sheared between quartzite blocks, and metastable saponitic smectite clays crystallized in dunite sheared between granite blocks, as a result of fluid-assisted chemical exchange with the minerals in the wall rocks. These results suggest that rapid and substantial weakening can occur in the mantle wedge immediately overlying the subducting slab. Whichever the chemical environment, attainment of peak strength typically was accompanied by oscillatory slip with small stress drops that gradually was replaced by stable slip with increasing displacement. This oscillatory behavior in some ways resembles the tremor events that have been reported near the forearc mantle corner in subduction zones, and it may indicate the possible involvement of mineral reactions in some instances of tremor.

  3. CO2- and Ca-rich Fluids Drive Dolomite Formation During Hydrothermal Alteration of Peridotite

    NASA Astrophysics Data System (ADS)

    Grozeva, N. G.; Klein, F.; Seewald, J.; Sylva, S.

    2014-12-01

    We present an experimental study investigating reaction pathways during the interaction of CO2-rich aqueous fluids with mantle peridotite, which have major implications for geochemical budgets and microbial life in oceanic lithosphere. Powdered harzburgite was reacted with a Ca-enriched fluid in a flexible-cell hydrothermal apparatus at 300°C and 35 MPa for 1.7 years. A CO2-rich fluid was subsequently injected and allowed to react for 8 months to examine the formation of carbonates under reducing conditions. Fluids were sampled throughout the experiment to monitor changes in fluid chemistry, and the secondary mineralogy was analyzed at the end of the experiment. Fluid speciation and mineral analyses suggest that initial serpentinization of harzburgite led to the precipitation of serpentine, brucite, magnetite, chlorite, calcite and Ni-sulfides. Fluids during this stage were characterized by low concentrations of dissolved Si, Mg and CO2, alkaline pH(25°C), and high concentrations of dissolved Ca, consistent with buffering by serpentine-brucite-diopside-calcite equilibria. H2(aq) concentrations increased during the first 10 months of reaction (due to magnetite formation), but subsequently plateaued, suggesting that serpentinization approached completion prior to CO2 injection. The introduction of CO2 resulted in acidic pH(25°C), substantial decreases in H2(aq) concentrations, and increases in dissolved SiO2 and Mg2+ concentrations. Dolomite and high-Mg calcite appear to have formed at the expense of olivine, calcite and likely brucite. However, petrographic observations suggest that Mg-calcite was only a transient phase and was ultimately destabilized in favor of dolomite. Replacement textures with carbonate in mesh centers are strikingly similar to those found in dolomite-altered abyssal serpentinites from the Atlantis Massif. While magnesite precipitation seems possible in ridge environments, high CO2(aq) and Ca2+ activities in serpentinization systems appear

  4. Multifractal magnetic susceptibility distribution models of hydrothermally altered rocks in the Needle Creek Igneous Center of the Absaroka Mountains, Wyoming

    USGS Publications Warehouse

    Gettings, M.E.

    2005-01-01

    Magnetic susceptibility was measured for 700 samples of drill core from thirteen drill holes in the porphyry copper-molybdenum deposit of the Stinkingwater mining district in the Absaroka Mountains, Wyoming. The magnetic susceptibility measurements, chemical analyses, and alteration class provided a database for study of magnetic susceptibility in these altered rocks. The distribution of the magnetic susceptibilities for all samples is multi-modal, with overlapping peaked distributions for samples in the propylitic and phyllic alteration class, a tail of higher susceptibilities for potassic alteration, and an approximately uniform distribution over a narrow range at the highest susceptibilities for unaltered rocks. Samples from all alteration and mineralization classes show susceptibilities across a wide range of values. Samples with secondary (supergene) alteration due to oxidation or enrichment show lower susceptibilities than primary (hypogene) alteration rock. Observed magnetic susceptibility variations and the monolithological character of the host rock suggest that the variations are due to varying degrees of alteration of blocks of rock between fractures that conducted hydrothermal fluids. Alteration of rock from the fractures inward progressively reduces the bulk magnetic susceptibility of the rock. The model introduced in this paper consists of a simulation of the fracture pattern and a simulation of the alteration of the rock between fractures. A multifractal model generated from multiplicative cascades with unequal ratios produces distributions statistically similar to the observed distributions. The reduction in susceptibility in the altered rocks was modelled as a diffusion process operating on the fracture distribution support. The average magnetic susceptibility was then computed for each block. For the purpose of comparing the model results with observation, the simulated magnetic susceptibilities were then averaged over the same interval as the

  5. Structural evolution of the Mount Wall region in the Hamersley province, Western Australia and its control on hydrothermal alteration and formation of high-grade iron deposits

    NASA Astrophysics Data System (ADS)

    Dalstra, Hilke J.

    2014-10-01

    The discovery of two relatively small but high-grade iron ore deposits near Mt Wall, an intensely faulted part of the southwestern Hamersley province provides unique insights into the structural control on ore formation in this region. The deposits have many geological features typical of the high grade microplaty hematite group which also contains the much larger Mt Tom Price, Paraburdoo and Mt Whaleback deposits. The deposits are structurally controlled along early normal faults and contain abundant microplaty hematite and martite, and are largely confined to the Dales Gorge member of the Brockman Iron Formation. In addition to the microplaty hematite-martite ore, there are martite-goethite ores and rare magnetite-goethite or magnetite-hematite ores. Below the modern weathering surface, hydrothermally altered zones in wallrock BIF from the Lower Dales Gorge member contain magnetite, hematite and carbonate/talc bearing mineral assemblages. A staged ore genesis model involving early extension and fluid circulation along normal faults, hypogene silica leaching and carbonate alteration, followed by deep meteoric oxidation with microplaty hematite formation and finally weathering can explain most features of the Mt Wall deposits. The role of deformation was to provide pathways for mineralising fluids and initiate the seed points for the mineralised systems. High grade iron in the Wellthandalthaluna deposit is situated between the NW to NNW trending Boolgeeda Creek fault and a synthetic joining splay, the Northern fault. Both are high angle normal faults and formed during early extension in this part of the province. Faults are characterised by localised small scale deformation and brecciation, deep carbonate alteration and oxidation. Recent weathering has penetrated deeply into the fault zones, converting the carbonate-rich assemblages into goethite. Mineralisation in the Arochar deposit is situated in the overlap or relay zone between two segments of the Mt Wall

  6. Hydrothermal alteration of sediments associated with surface emissions from the Cerro Prieto geothermal field, Baja, California, Mexico

    SciTech Connect

    Valette-Silver, J.N.; Esquer-Patino, I.; Elders, W.A.; Collier, P.C.; Hoagland, J.R.

    1981-01-01

    Surface emissions from the Cerro Prieto geothermal reservoir are restricted to a 100 km/sup 2/ area on the western side of the field, near the volcano Cerro Prieto and the lake Laguna Vulcano. Some 57 surface emissions, explored in 1979, were classified into hot springs, mud pots, pools, fumaroles and geysers (Valette and Esquer-Patino, 1979). A study of the mineralogical changes associated with these hydrothermal vents was initiated with the aim of developing possible exploration tools for geothermal resources. The Cerro Prieto reservoir has already been explored by extensive deep drilling so that relationships between surface manifestations and deeper hydrothermal processes could be established directly. Approximately 120 samples of surface sediments were collected both inside and outside of the vents. The mineralogy of the altered sediments studied appears to be controlled by the type of emission. A comparison between the changes in mineralogy due to low temperature hydrothermal activity in the reservoir, seen in samples from boreholes, and mineralogical changes in the surface emission samples shows similar general trends below 180/sup 0/C: increase of quartz, feldspar and illite, with subsequent disappearance of kaolinite, montmorillonite, calcite and dolomite. These mineral assemblages seem to be characteristics of the discharge from high intensity geothermal fields.

  7. State of stress and relationship of mechanical properties to hydrothermal alteration at Valles caldera core hole 1, New Mexico

    SciTech Connect

    Dey, T.N.; Kranz, R.L.

    1988-06-10

    We measured the densities, total and microcrack porosities, and ultrasonic velocities of a number of core samples from an 856-m-deep core hole near the Banco Bonito vent at Valles Caldera, New Mexico. Reductions in porosity with depth define a zone from about 600 m down where hydrothermal mineralization and recrystallization have been most active. This zone is also reflected in a large decrease in the anisotropy of acoustic velocities. Stress orientation estimates based on microcrack orientations at the 812-m depth as determined by differential strain curve analysis, as well as anelastic strain recovery measurements on a sample from 472-m depth, show a horizontal E-W minimum compression direction and a maximum compression inclined about 30/sup 0/ from vertical.

  8. Chlorine isotope geochemistry of hydrothermally altered oceanic crust: Mineralogical controls and experimental constraints

    NASA Astrophysics Data System (ADS)

    Cisneros, M.; Barnes, J.; Jenkins, D. M.; Gardner, J. E.

    2012-12-01

    Chlorine stable isotopes (37Cl and 35Cl) can provide an important fingerprint for geochemical recycling of subducted oceanic lithosphere and fluid-rock interaction due to chlorine's high solubility in aqueous phases. To implement Cl isotopes as a tracer of volatile element recycling, we must constrain the δ37Cl value of potential Cl reservoirs and determine fractionation factors between Cl-bearing phases. δ37Cl and Cl concentrations of hydrothermally altered oceanic crust (AOC) samples from seven IODP/ODP/DSDP drill sites have been measured on bulk rock samples (n = 50). For ease of comparing results, samples are categorized into three lithologies: 1) extrusive lavas, 2) sheeted dikes, and 3) gabbros. Extrusive lava Cl concentrations vary from <0.01 wt% to 0.03 wt% (avg = 95 ppm Cl; n= 20) and δ37Cl values range from -1.4 to +1.0‰ (avg = 0.0 ± 0.6‰). Chlorine concentrations of the sheeted dikes range from < 0.01 wt% to 0.05 wt% (avg = 163 ppm Cl; n = 11) and δ37Cl values of dikes range from - 0.4 to + 1.4‰ (avg = 0.1 ± 0.3‰). Bulk chlorine concentrations of the gabbros range from < 0.01 wt% to 0.09 wt% (avg = 244 ppm Cl; n = 19). δ37Cl values of gabbros range from - 0.6 to + 1.8‰ (avg = 0.6 ± 0.6‰). Three general conclusions can be derived from these AOC bulk rock results: 1) δ37Cl values and Cl concentrations increase with increasing total amphibole content. 2) Based on re-calculations of mass balance equations using updated AOC Cl concentrations (~3 times higher than previous estimates, this study), the total amount of Cl recycled into the mantle is higher than previously estimated. 3) [Cl] and δ37Cl values can provide a crude estimate of metamorphic grade in AOC samples. Amphibole-water Cl isotope fractionation experiments are necessary for quantifying the magnitude of Cl fractionation and to aid in interpreting the range of natural Cl isotope variation. Determination of equilibrium fractionation factors between hydrous minerals and co

  9. Mapping hydrothermal alteration using aircraft VNIR scanners at the Rosemont porphyry copper deposit. [Visible-Near Infrared

    NASA Technical Reports Server (NTRS)

    Sadowski, R. M.; Abrams, M. J.

    1983-01-01

    Two Visible-Near Infrared (VNIR) scanners, the NS-001 and the M2S, were flown over the Rosemont porphyry copper deposit as part of the NASA/JPL/GEOSAT test site program. This program was established to determine the feasibility and limitations of mapping hydrothermal alteration with multispectral scanners. Data from the NS-001 at 0.83 and 2.2 microns were used to identify Fe(3+) and OH enriched outcrops. These areas were then correlated with three alteration assemblages. The first correlation, hematite-epidote, was the most obvious and appeared as a strong ferric iron signature associated with hematite stained Cretaceous arkoses and andesites. The second correlation, qtz-sericite, showed a combined ferric-hydroxyl signature for a phyllicly altered quartz monzonite. The third correlation, skarn, was identified only after a review of calc-silicate mineral VNIR spectra. Altered limestones that outcrop west of the deposit have a similar ferric iron-hydroxyl signature as the quartz-sericite altered quartz monzonite. This skarn signature has been interpreted to indicate the presence of andradite, hydro-grossularite and idocrase. Data from the second scanner, M2S, was used to search for variation in ferric iron mineral type. Resulting imagery data indicated that hematite was the dominant ferric iron mineral present in the Rosemont area.

  10. Quantification of diagenetic overprint processes deduced from fossil carbonate shells and laboratory-based hydrothermal alteration experiments

    NASA Astrophysics Data System (ADS)

    Griesshaber, Erika; Casella, Laura; Mavromatis, Vasileios; Dietzel, Martin; Immenhauser, Adrian; Schmahl, Wolfgang

    2016-04-01

    Benthic and nektonic marine biogenic carbonate archives represent the foundation of numerous studies aiming at reconstructions of past climate dynamics and environmental change. However, living organisms are not in thermodynamic equilibrium and create local chemical environments where physiologic processes such as biomineralization takes place. After the death of the organism the former physiologic disequilibrium conditions are not sustained any more and all biological tissues are altered by equilibration according to the surrounding environment: diagenesis. With increasing diagenetic alteration, the biogenic structure and fingerprint fades away and is replaced by inorganic features. Thus, recrystallization of organism-specific microstructure is a clear indicator for diagenetic overprint. Microstructural data, which mirror recrystallization, are of great value for interpreting geochemical proxies for paleo-environment reconstruction. Despite more than a century of research dealing with carbonate diagenesis, many of the controlling processes and factors are only understood in a qualitative manner. One of the main issues is that diagenetically altered carbonates are usually present as the product of a complex preceding diagenetic pathway with an unknown number of intermediate steps. In this contribution we present and discuss laboratory based alteration experiments with the aim to investigate time-series data sets in a controlled manner. We conducted hydrothermal alteration experiments with modern Arctica islandica (bivalvia) and Notosaria nigricans (brachiopoda) in order to mimic diagenetic overprint. We explore first the potential of electron backscattered diffraction (EBSD) measurements together with statistical data evaluation as a tool to quantify diagenetic alteration of carbonate skeletons. Subsequently, we compare microstructural patterns obtained from experimentally altered shell material with those of fossil specimens that have undergone variable degrees of

  11. Characterization of Active Hydrothermal Fluid Discharge and Recharge Zones in the Endeavour Axial Valley, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Salmi, M.; Hutnak, M.; Hearn, C.; Tivey, M.; Bjorklund, T.; Johnson, H. P.

    2012-12-01

    Sites where warm hydrothermal fluid vents at mid-ocean spreading centers are important for understanding a wide range of critical oceanic processes, but discharge zones represent a very limited portion of crustal fluid circulation pathways. Mapping the distribution of both fluid recharge and discharge sites within the axial valley provides wider insight into the larger scale features of hydrothermal circulation. Our 2011 survey consisted of 180 conductive heat flow stations within the Endeavour axial valley in roughly a 400 m by 1000 m grid, extending across the entire axial valley from the outer flank of the western boundary ridge to the eastern wall. Data acquisition used thermal blankets which measured conductive heat flow without requiring substantial sediment cover. A surprising result from this survey was zones of high heat flow extending across-strike, from the summit of the west valley wall across the entire axial valley floor. This trend was correlated with anomalously low seafloor magnetization from a near-bottom survey with the ROV JASON. Unexpectedly, over half of the axial valley floor was anomalously low at <50 mW m-2, while a small portion of the sites within the 'warm zone' had heat flow values >1 W m-2. The areas of extremely low heat flow values are interpreted as being directly influenced by recharge zones. Based on MCS estimates of partial melt depth below the axial valley and the assumption of no fluid advection, the purely conductive heat flow for this region should be on the order of 1 W m-2.The observation that conductive heat flux is suppressed over large portions of the axial valley floor suggests that heat transfer within the crustal sub-surface fluid reservoir is widespread, and impacts a large portion of our survey area. The largely bi-modal distribution of high and low conductive heat flow, coupled with geophysical and video observations, suggest current Endeavour axial valley crustal fluid circulation models need to be re-evaluated.

  12. Halogens and noble gases in Mathematician Ridge meta-gabbros, NE Pacific: implications for oceanic hydrothermal root zones and global volatile cycles

    NASA Astrophysics Data System (ADS)

    Kendrick, Mark A.; Honda, Masahiko; Vanko, David A.

    2015-12-01

    Six variably amphibolitised meta-gabbros cut by quartz-epidote veins containing high-salinity brine, and vapour fluid inclusions were investigated for halogen (Cl, Br, I) and noble gas (He, Ne, Ar, Kr, Xe) concentrations. The primary aims were to investigate fluid sources and interactions in hydrothermal root zones and determine the concentrations and behaviours of these elements in altered oceanic crust, which is poorly known, but has important implications for global volatile (re)cycling. Amphiboles in each sample have average concentrations of 0.1-0.5 wt% Cl, 0.5-3 ppm Br and 5-68 ppb I. Amphibole has Br/Cl of ~0.0004 that is about ten times lower than coexisting fluid inclusions and seawater, and I/Cl of 2-44 × 10-6 that is 3-5 times lower than coexisting fluid inclusions but higher than seawater. The amphibole and fluid compositions are attributed to mixing halogens introduced by seawater with a large halogen component remobilised from mafic lithologies in the crust and fractionation of halogens between fluids and metamorphic amphibole formed at low water-rock ratios. The metamorphic amphibole and hydrothermal quartz are dominated by seawater-derived atmospheric Ne, Ar, Kr and Xe and mantle-derived He, with 3He/4He of ~9 R/Ra (Ra = atmospheric ratio). The amphibole and quartz preserve high 4He concentrations that are similar to MORB glasses and have noble gas abundance ratios with high 4He/36Ar and 22Ne/36Ar that are greater than seawater and air. These characteristics result from the high solubility of light noble gases in amphibole and suggest that all the noble gases can behave similarly to `excess 40Ar' in metamorphic hydrothermal root zones. All noble gases are therefore trapped in hydrous minerals to some extent and can be inefficiently lost during metamorphism implying that even the lightest noble gases (He and Ne) can potentially be subducted into the Earth's mantle.

  13. Alteration mapping at Goldfield, Nevada, by cluster and discriminant analysis of Landsat digital data. [mapping of hydrothermally altered volcanic rocks

    NASA Technical Reports Server (NTRS)

    Ballew, G.

    1977-01-01

    The ability of Landsat multispectral digital data to differentiate among 62 combinations of rock and alteration types at the Goldfield mining district of Western Nevada was investigated by using statistical techniques of cluster and discriminant analysis. Multivariate discriminant analysis was not effective in classifying each of the 62 groups, with classification results essentially the same whether data of four channels alone or combined with six ratios of channels were used. Bivariate plots of group means revealed a cluster of three groups including mill tailings, basalt and all other rock and alteration types. Automatic hierarchical clustering based on the fourth dimensional Mahalanobis distance between group means of 30 groups having five or more samples was performed using Johnson's HICLUS program. The results of the cluster analysis revealed hierarchies of mill tailings vs. natural materials, basalt vs. non-basalt, highly reflectant rocks vs. other rocks and exclusively unaltered rocks vs. predominantly altered rocks. The hierarchies were used to determine the order in which sets of multiple discriminant analyses were to be performed and the resulting discriminant functions were used to produce a map of geology and alteration which has an overall accuracy of 70 percent for discriminating exclusively altered rocks from predominantly altered rocks.

  14. Towards the kinetics of diagenetic overprint processes deduced from laboratory-based hydrothermal alteration of modern Arctica islandica shell material

    NASA Astrophysics Data System (ADS)

    Casella, Laura A.; Griesshaber, Erika; Mavromatis, Vasileios; Dietzel, Martin; Immenhauser, Adrian; Schmahl, Wolfgang W.

    2016-04-01

    Benthic and nektonic marine biogenic carbonate archives represent the foundation of numerous studies aiming at paleo-environment reconstructions. However, living organisms are not in thermodynamic equilibrium as they form local chemical environments for physiologic processes such as biological mineralization of their hard tissues. This disequilibrium is not sustained after death and all biological tissues are altered by equilibration with the surrounding environment: diagenesis. To understand transformation during diagenesis we performed laboratory-based hydrothermal alteration experiments on Arctica islandica shells at four different temperatures between 100 °C and 175 °C treated in simulated meteoric and burial waters, respectively. We investigated, relative to unaltered shells, the kinetics of Arctica islandica bioaragonite to calcite transition as well as microstructural- and nanostructural characteristics of the altered shells with X-ray diffraction, micro-Raman, high-resolution SEM and EBSD. At hydrothermal treatment at 100 °C bioaragonite - although metastable at 1 bar - does not transform to calcite, even in meteoric fluids and over a time period of 28 days. We noted a drastic recrystallization from the initial fine-grained fractal microstructure and pronounced axial texture to a new and still fine-grained microstructure with an almost randomized orientation distribution. At 175 °C the transformation to coarse-grained calcite is complete after 8 days. Calcite formation starts after a passive incubation period of 4 days; after 6 days the aragonite is almost completely transformed. In solutions simulating meteoric water the grain size of the newly formed calcite reaches 100-150 μm, while in burial fluids the calcite reaches sizes in the 1mm range during 28 days of alteration. Phase transformation proceeds where the hydrothermal fluid is in contact with the aragonite: at shell surfaces, around pores and in growth lines. Our observations lead us to the

  15. Hydrothermal Concentration of Zr, Y + HREE in the Lake Zone of the Thor Lake Rare Metal Deposit, Northwest Territories

    NASA Astrophysics Data System (ADS)

    Sheard, E. R.; Heiligmann, M.; Williams-Jones, A. E.

    2009-05-01

    The Thor Lake rare-metal (Zr, Y, REE, Nb, Ta, Be, Ga) deposit in Northwest Territories contains Canada's largest resource of Zr, Y and HREE and is one of the largest resources of these elements on the planet. Much of the mineralization was clearly concentrated by hydrothermal processes, providing compelling evidence for Zr mobility. Geologically, the deposit is situated at the southern edge of the Slave Province of the Canadian Shield, within the 2150 Ma alkaline to peralkaline Blachford Lake complex consisting of an early suite of gabbro, quartz syenite and granite, which was intruded by the Grace Lake granite and, in turn, by the Thor Lake syenite [1]. A layered alkaline intrusion dominated by nepheline syenite occurs below the Thor Lake syenite and is thought to represent the youngest phase of the complex. This intrusion comprises numerous sub- horizontal layers of sodalite syenite, alkali syenite and lujavrite. Evidence of cumulate and adcumulus textures, cyclic magmatic differentiation and rhythmic layering of mafic and felsic units on scales ranging from tens of centimetres to several metres indicate a complex history of pulsed injection of magma and magmatic differentiation. The upper part of the layered intrusion and the overlying Thor Lake syenite contain the bulk of the rare metal mineralization, with Zr hosted primarily by zircon, Nb primarily by ferrocolumbite and fergusonite, and Y + HREE by fergusonite and zircon. The LREE are hosted by monazite, allanite, bastnaesite and synchisite/parisite. The precursor rocks to the ore were pervasively altered by Fe- and K-rich hydrothermal fluids, which replaced much of the primary mineralogy by magnetite, biotite and K-feldspar and redistributed/concentrated the rare metals including Zr (as secondary zircon). This alteration was overprinted locally by intense sodic alteration. In other rare-metal-rich alkaline complexes such as Strange Lake, Ilimaussaq and Lovozero, the Zr, Nb, Y + REE mineralization has been

  16. Element redistribution during hydrothermal alteration of rhyolite in an active geothermal system: Yellowstone drill cores Y-7 and Y-8

    NASA Astrophysics Data System (ADS)

    Sturchio, Neil C.; Muehlenbachs, Karlis; Seitz, Martin G.

    1986-08-01

    Hydrothermal alteration of the 0.54 Ma Biscuit Basin rhyolite flow in Yellowstone drill cores Y-7 and Y-8 has involved significant changes in Ti-normalized whole rock concentrations of Li, Mg, Ca, Na, K, Mn, Rb, Sr, Sb, Cs, Ba, and U, whereas such changes have generally not occurred for Al, Fe, Sc, Co, Y, Zr, REE, Hf, Ta, and Th. The relatively mobile elements have been redistributed over distances from 2-5 cm to more than 10-100 m, and are associated mainly with zeolites and clays, in thoroughly altered samples; average whole rock changes in Ti-normalized mass range from about 0.5-17 g/Kg (9-49%) for major elements and 0.1-280 mg/Kg (19-4260%) for minor and trace elements. Compositional changes correlate with hydrothermal mineralogy. The relatively immobile elements have been redistributed over a distance of at least 10-100 μm but less than 2-5 cm, and are associated mainly with clays, in thoroughly altered samples. Addition of SiO 2 ranges from 110-890 g/Kg in samples where porosity has been thoroughly sealed by silica deposition. Thermal water is not in oxygen isotopic equilibrium with any primary or secondary phases analyzed except calcite. Modest depletions of 18O (1-2%) due to exchange with thermal water apparently have occurred in Y-8 plagioclase and obsidian. Oxygen isotope ratios in obsidian-replacing smectite and in veinlet celadonite and β-cristobalite suggest that these phases precipitated from water locally enriched in 18O (up to ~8% heavier than present thermal water). The minimum integrated water/rock mass ratio in Y-7 and Y-8 is 10 3-10 4 (assuming advective transport).

  17. Remote detection of past habitability at Mars-analogue hydrothermal alteration terrains using an ExoMars Panoramic Camera emulator

    NASA Astrophysics Data System (ADS)

    Harris, J. K.; Cousins, C. R.; Gunn, M.; Grindrod, P. M.; Barnes, D.; Crawford, I. A.; Cross, R. E.; Coates, A. J.

    2015-05-01

    A major scientific goal of the European Space Agency's ExoMars 2018 rover is to identify evidence of life within the martian rock record. Key to this objective is the remote detection of geological substrates that are indicative of past habitable environments, which will rely on visual (stereo wide-angle, and high resolution images) and multispectral (440-1000 nm) data produced by the Panoramic Camera (PanCam) instrument. We deployed a PanCam emulator at four hydrothermal sites in the Námafjall volcanic region of Iceland, a Mars-analogue hydrothermal alteration terrain. At these sites, sustained acidic-neutral aqueous interaction with basaltic substrates (crystalline and sedimentary) has produced phyllosilicate, ferric oxide, and sulfate-rich alteration soils, and secondary mineral deposits including gypsum veins and zeolite amygdales. PanCam emulator datasets from these sites were complemented with (i) NERC Airborne Research and Survey Facility aerial hyperspectral images of the study area; (ii) in situ reflectance spectroscopy (400-1000 nm) of PanCam spectral targets; (iii) laboratory X-ray Diffraction, and (iv) laboratory VNIR (350-2500 nm) spectroscopy of target samples to identify their bulk mineralogy and spectral properties. The mineral assemblages and palaeoenvironments characterised here are analogous to neutral-acidic alteration terrains on Mars, such as at Mawrth Vallis and Gusev Crater. Combined multispectral and High Resolution Camera datasets were found to be effective at capturing features of astrobiological importance, such as secondary gypsum and zeolite mineral veins, and phyllosilicate-rich substrates. Our field observations with the PanCam emulator also uncovered stray light problems which are most significant in the NIR wavelengths and investigations are being undertaken to ensure that the flight model PanCam cameras are not similarly affected.

  18. Discrimination of hydrothermally altered rocks along the Battle Mountain-Eureka, Nevada mineral belt using LANDSAT images

    NASA Technical Reports Server (NTRS)

    Krohn, M. D.; Abrams, M. J.; Rowan, L. C. (Principal Investigator)

    1979-01-01

    The author has identified the following significant results. Limonitic alteration halos associated with two copper prophyry deposits were successfully mapped at Battle Mountain. Alteration halos from both a hypogene system at Copper Canyon and a supergene system at Copper Basin are recognizable in the composite. Both copper porphyry deposits are located in sedimentary rock units that commonly have ferruginous coatings; yet, in most cases, the hydrothermally derived limonite was distinguishable in the CRC from sedimentary limonite. Large format playback images with pixel sizes from 200 to 400 micron m provided details of spatial resolution and color separation unachievable on enlargements from 70 mm film chips. Details of the alteration halos could be resolved only in the large format images. Two aspects of the alteration halos of the porphyry copper deposits were not mapped on the CRC. The optimum CRC image for the area studied consists of MSS 4/5 as blue, MSS 4/6 as yellow, and MSS 6/7 as magenta using diazo films. The disseminated gold deposits at Gold Acres are not depicted in the CRC image.

  19. Geology, alteration, and magmatic-hydrothermal history of The Geysers felsite -- potential applications for exploration and development

    SciTech Connect

    Hulen, J.B.; Nielson, D.L. )

    1993-01-01

    The [open quotes]felsite[close quotes] is a shallow, young, granitic intrusive body centrally located within and beneath. The Geysers steam field. The field and the felsite are coaxial, and hydrothermal alteration effected by hot-water dominated geothermal systems antedating the modern steam reservoir shows systematic vertical zonation with respect to the pluton. The research summarized in this communication was undertaken both to clarify the role of the pluton in reservoir evolution, and to characterize critical felsite-specific controls on the fields's deep porosity and permeability. The felsite comprises at least three major intrusive phases. Two are high-silica granites probably older than 1.3 Ma. The third is granodiorite (1 Ma), temporally and chemically equivalent to overlying extrusive dacites of the Clear Lake volcanic field. All three intrusive phases are too old to be heat sources for the modern steam field, but probably were the heat engines for the prior liquid-dominant systems. Younger, deeper magmatic heat sources are strongly implied for the current vapor-dominated regime. Porosity in the felsite is provided by: (1) Extensively mineralized fractures and breccias, probably of both tectonic and high-temperature hydrothermal origin; and (2) miarolitic cavities in the upper levels of the pluton. The latter could be analogous to calcite-dissolution cavities in overlying metagraywacke -- they could serve as storage sites for the fields's liquid water reserves. Porosity in these fractures, breccias, and vugs in partially occluded by hydrothermal vein minerals deposited in prior hotwater-dominated systems --tourmaline, ferroaxinite, quartz, potassium feldspar, epidote, actinolite, prehnite, and many others. Such secondary mineralization conceptually could serve as an excellent exploration guide to potentially productive portions of the felsite beyond the field's present boundaries.

  20. Formation of Complex Amino Acid Precursors in Simulated Primitive Atmosphere and Their Alteration under Simulated Submarine Hydrothermal Conditions

    NASA Astrophysics Data System (ADS)

    Kobayashi, Kensei; Kurihara, Hironari; Hirako, Tomoaki; Obayashi, Yumiko; Kaneko, Takeo; Takano, Yoshinori; Yoshimura, Yoshitaka

    Since late 1970's a great number of submarine hydrothermal systems (SHSs) has been dis-covered, and they are considered possible sites of chemical evolution and generation of life on the Earth since their discovery in late 1970s. A number of experiments simulating the con-ditions of SHSs were conducted, and abiotic production and polymerization of amino acids were reported. Free amino acids were frequently used as starting materials to examine possible organic reactions in the simulation experiments. In our early studies, not free amino acids but complex amino acids precursors with large molecular weights were formed abiotically from simulated primitive Earth atmosphere (a mixture of CO, N2 and H2 O) (Takano et al., 2004). Such complex organics (hereafter referred as to CNWs) should have been delivered to SHSs in Primitive Ocean, where they were subjected to further alteration. We examined possible alteration of the complex organics in high-temperature high-pressure environments by the su-percritical water flow reactor (SCWFR) (Islam et al.. 2003) and an autoclave. CNWs were quite hydrophilic compounds whose molecular weights were ca. 3000. After heating 573 K for 2 min in the SCWFR, aggregates of organics were formed, which were separated from aque-ous solution with a Nucleopore filter (pore size: 200 nm). We propose the following scenario of chemical evolution: (1) Complex organics including amino acid precursors were formed in primitive atmosphere and/or extraterrestrial environments, (ii) they were delivered to primor-dial SHSs, (iii) hydrothermal alteration occurred in SHSs to give organic aggregates, (iv) quite primitive molecular systems with subtle biological functions were generated in the competition among such aggregates. References: Islam, Md. N., Kaneko, T., and Kobayashi, K (2003). Reactions of Amino Acids with a Newly ConstructedSupercritical Water Flow Reactor Simulating Submarine Hydrothermal Systems. Bull. Chem. Soc. Jpn., 76, 1171. Takano, Y

  1. Variability of low temperature hydrothermal alteration in upper ocean crust: Juan de Fuca Ridge and North Pond, Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Rutter, J.; Harris, M.; Coggon, R. M.; Alt, J.; Teagle, D. A. H.

    2014-12-01

    Over 2/3 of the global hydrothermal heat flux occurs at low temperatures (< 150°) on the ridge flanks carried by fluid volumes comparable to riverine discharge. Understanding ridge flank hydrothermal exchange is important to quantify global geochemical cycles. Hydrothermal chemical pathways are complex and the effects of water-rock reactions remain poorly constrained. Factors controlling fluid flow include volcanic structure, sediment thickness, and basement topography. This study compares the effects of low temperature alteration in two locations with contrasting hydrogeological regimes. The intermediate spreading Juan de Fuca ridge flank (JdF) in the northeast Pacific sports a thick sediment blanket. Rare basement outcrops are sites of fluid recharge and discharge. The average alteration extent (~10% secondary minerals), oxidation ratio (Fe3+/FeTOT=34%), and alteration character (orange, green, grey halos) of basement is constant with crustal age and depth along a 0.97-3.6 m.yr transect of ODP basement holes. However, vesicle fills record an increasingly complex history of successive alteration with age. In contrast, North Pond, a ~8 m.yr-old sediment-filled basin at 22N on the slow spreading Mid Atlantic Ridge, hosts rapid, relatively cool SE to NW basinal fluid flow. Average alteration extent (~10%) and oxidation ratio (33%) of Hole 395A basalts are similar to JdF. However, 395A cores are dominated by orange alteration halos, lack celadonite, but have abundant zeolite. Vesicle fill combinations are highly variable, but the most common fill progression is from oxidising to less oxidising secondary assemblages. The comparable extent of alteration between these two sites and the absence of an age relationship on the JdF suggests that the alteration extent of the upper crust is uniform and mostly established by 1 Myr. However, the variable alteration character reflects the influence of regional hydrology on hydrothermal alteration.

  2. Use of multispectral scanner images for assessment of hydrothermal alteration in the Marysvale, Utah, mining area.

    USGS Publications Warehouse

    Podwysocki, M.H.; Segal, D.B.; Abrams, M.J.

    1983-01-01

    Airborne multispectral scanner. A color composite image was constructed using the following spectral band ratios: 1.6/2.2 mu m, 1.6/0.48 mu m, and 0.67/1.0 mu m. The color ratio composite successfully distinguished most types of altered rocks from unaltered rocks; further division of altered rocks into ferric oxide-rich and -poor types.

  3. Identification of hydrothermal alterations associated with Copper (Cu) mineralization in Sidi flah-Bouskour inlier, Moroccon Anti Atlas

    NASA Astrophysics Data System (ADS)

    Adiri, Zakaria; El Harti, Abderrazak; Jellouli, Amine; Bachaoui, El Mostafa; El Ghmari, Abderrahmène

    2016-04-01

    The massive of Saghro at the Moroccan Anti Atlas is known by the abundance of economically important deposits. Among others, the Copper (Cu) deposit in Sidi flah-Bouskour inlier. With its high potential in terms of production, this deposit is considered among the most important and most promising at national scale. The objective of this work is to evaluate the potential of multispectral Terra ASTER and Landsat 8 OLI data in mapping hydrothermal alterations associated with this copper mineralization. The methodology was based on Mixture Tuned Matched Filtering (MTMF) and the Spectral Angle Mapper (SAM) classifications. The application of these techniques on the Visible-Near (VNIR), Shortwave Infrared (SWIR) and Thermal Infrared (TIR) spectral regions gave satisfactory results in comparison to the pre-existing geological studies and the ground truth. Therefore, the methodology used can be generalized to the Moroccan Anti Atlas for mineral exploration.

  4. Hydrothermal alteration of CM carbonaceous chondrites: Implications of the identification of tochilinite as one type of meteoritic PCP

    NASA Technical Reports Server (NTRS)

    Zolensky, M. E.

    1984-01-01

    Poorly characterized phases (PCP's) constitute up to 30 volume percent of some CM carbonaceous chondrites, and are therefore an important key to an understanding of the physico-chemical conditions attending matrix evolution. An iron rich form of the terrestrial phase tochilinite was recently identified as a common type of PCP. Tochilinite has the general formula 6Fe(0.9)S.5(Mg,Fe)(OH)2 and consists of alternating machinawite (FeS) and brucite ((Mg,Fe)(OH)2) sheets, with iron vacancies in the sulfide sheets. In iron rich tochilinite, ferrous hydroxide, called amakinite, replaces brucite. If CM carbonaceous kchondrites have underdone hydrothermal alteration, iron rich tochilinite, at least, probably grew from aqueous solutions characterized by low FO2, high FS2, pH 10 to 12, and at a temperature at or below 170 C.

  5. Impact Lithologies and Post-Impact Hydrothermal Alteration Exposed by the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico

    NASA Technical Reports Server (NTRS)

    Kring, David A.; Zurcher, Lukas; Horz, Friedrich

    2003-01-01

    The Chicxulub Scientific Drilling Project recovered a continuous core from the Yaxcopoil-1 (YAX-1) borehole, which is approx.60-65 km from the center of the Chicxulub structure, approx.15 km beyond the limit of the estimated approx.50 km radius transient crater (excavation cavity), but within the rim of the estimated approx.90 km radius final crater. Approximately approx.100 m of melt-bearing impactites were recoverd from a depth of 794 to 895 m, above approx.600 m of underlying megablocks of Cretaceous target sediments, before bottoming at 1511 m. Compared to lithologies at impact craters like the Ries, the YAX-1 impactite sequence is incredibly rich in impact melts of unusual textural variety and complexity. The impactite sequence has also been altered by hydrothermal activity that may have largely been produced by the impact event.

  6. The Martian Soil as a Geochemical Sink for Hydrothermally Altered Crustal Rocks and Mobile Elements: Implications of Early MER Results

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; Nelson, M. J.; Shearer, C. K.; Draper, D. S.

    2005-01-01

    Hydrothermal and aqueous alteration can explain some of the exciting results from the MER team s analyses of the martian soil, including the major elements, mobile elements, and the nickel enrichment. Published results from the five lander missions lead to the following conclusions: 1) The soil appears to be globally mixed and basaltic with only small local variations in chemistry. Relative to martian basaltic meteorites and Gusev rocks the soils are depleted in the fluid-mobile element calcium, but only slightly enriched to somewhat depleted in iron oxide. 2) The presence of olivine in the soils based on M ssbauer data argues that the soil is only partly weathered and is more akin to a lunar regolith than a terrestrial soil. 3) The presence of bromine along with sulfur and chlorine in the soils is consistent with addition of a mobile element component to the soil.

  7. Geothermal Frontier: Penetrate a boundary between hydrothermal convection and heat conduction zones to create 'Beyond Brittle Geothermal Reservoir'

    NASA Astrophysics Data System (ADS)

    Tsuchiya, N.; Asanuma, H.; Sakaguchi, K.; Okamoto, A.; Hirano, N.; Watanabe, N.; Kizaki, A.

    2013-12-01

    EGS has been highlightened as a most promising method of geothermal development recently because of applicability to sites which have been considered to be unsuitable for geothermal development. Meanwhile, some critical problems have been experimentally identified, such as low recovery of injected water, difficulties to establish universal design/development methodology, and occurrence of large induced seismicity. Future geothermal target is supercritical and superheated geothermal fluids in and around ductile rock bodies under high temperatures. Ductile regime which is estimated beyond brittle zone is target region for future geothermal development due to high enthalpy fluids and relatively weak water-rock interaction. It is very difficult to determine exact depth of Brittle-Ductile boundary due to strong dependence of temperature (geotherm) and strain rate, however, ductile zone is considered to be developed above 400C and below 3 km in geothermal fields in Tohoku District. Hydrothermal experiments associated with additional advanced technology will be conducting to understand ';Beyond brittle World' and to develop deeper and hotter geothermal reservoir. We propose a new concept of the engineered geothermal development where reservoirs are created in ductile basement, expecting the following advantages: (a)simpler design and control the reservoir, (b)nearly full recovery of injected water, (c)sustainable production, (d)cost reduction by development of relatively shallower ductile zone in compression tectonic zones, (e)large quantity of energy extraction from widely distributed ductile zones, (f)establishment of universal and conceptual design/development methodology, and (g) suppression of felt earthquakes from/around the reservoirs. In ductile regime, Mesh-like fracture cloud has great potential for heat extraction between injection and production wells in spite of single and simple mega-fracture. Based on field observation and high performance hydrothermal

  8. Hydrothermal alteration and its effects on the magnetic properties of Los Pelambres, a large multistage porphyry copper deposit

    NASA Astrophysics Data System (ADS)

    Tapia, Joseline; Townley, Brian; Córdova, Loreto; Poblete, Fernando; Arriagada, César

    2016-09-01

    The Los Pelambres porphyry copper deposit is located 190 km north of Santiago, Chile. A paleomagnetic and mineralogical study was conducted at this deposit to determine the effects of hydrothermal alteration on the magnetic properties and minerals of rocks within the deposit when compared to the surrounding country rock. In the Los Pelambres deposit, magnetic properties of rocks are carried by titano-hematite and titano-magnetite solid solution minerals, where the former commonly indicates the exsolution of rutile. Magnetic minerals of intrusive rocks from the greater Los Pelambres region show that magmatic titano-magnetites and magnetites are the main magnetization carriers. The hydrothermal fluid associated with rutile exsolution textures could have played an important role in the mineralization of Cu in this deposit. The paleomagnetic properties in the Los Pelambres deposit can be divided in three main groups: (i) HMRG (high magnetic remanence group), (ii) HMSG (high magnetic susceptibility group), and (iii) LMSG (low magnetic susceptibility/remanence group). In-situ magnetic properties of the HMSG and LMSG are similar to the formations and units present regionally, however HRMG samples clearly differ from the country rocks. The high variability of in-situ magnetic properties presented in the Los Pelambres deposit has also been characteristic of other porphyry copper deposits in Chile (e.g., Chuquicamata and El Teniente). Regarding the field of exploration geophysics and porphyry copper deposits, this study suggests that phyllic, chloritic, and potassic alterations are related to low, intermediate, and high in-situ NRM, respectively, suggesting that geophysical methods must target a noisy magnetic signal depending on the scale of the study. The knowledge and results obtained are especially meaningful because magnetic surveys conducted for exploration do not commonly allow for the detection of ore mineralization.

  9. In-Situ pH Measurements in Mid-Ocean Ridge Hydrothermal Vent Fluids: Constraints on Subseafloor Alteration Processes at Crustal Depths

    NASA Astrophysics Data System (ADS)

    Schaen, A. T.; Ding, K.; Seyfried, W. E.

    2013-12-01

    Developments in electrochemistry and material science have facilitated the construction of ceramic (YSZ) based chemical sensor systems that can be used to measure and monitor pH and redox in aqueous fluids at elevated temperatures and pressures. In recent years, these sensor systems have been deployed to acquire real-time and time series in-situ data for high-temperature hydrothermal vent fluids at the Main Endeavour Field (Juan de Fuca Ridge), 9oN (East Pacific Rise), and at the ultramafic-hosted Rainbow field (36oN, Mid-Atlantic Ridge). Here we review in-situ pH data measured at these sites and apply these data to estimate the pH of fluids ascending to the seafloor from hydrothermal alteration zones deeper in the crust. In general, in-situ pH measured at virtually all vent sites is well in excess of that measured shipboard owing to the effects of temperature on the distribution of aqueous species and the solubility of metal sulfides, especially Cu and Zn, originally dissolved in the vent fluids. In situ pH measurements determined at MEF (Sully vent) and EPR 9oN (P-vent) in 2005 and 2008 were 4.4 ×0.02 and 5.05×0.05, respectively. The temperature and pressure (seafloor) of the vent fluids at each of the respective sites were 356oC and 220 bar, and 380oC and 250 bar. Plotting these data with respect to fluid density reveals that the in-situ pH of each vent fluid is approximately 1.5 pH units below neutrality. The density-pH (in-situ) correlation, however, is important because it provides a means from which the vent fluids were derived. Using dissolved silica and chloride from fluid samples at the MEF (Sully) suggest T/P conditions of approximately 435oC, 380 bar, based on quartz-fluid and NaCl-H2O systems. At the fluid density calculated for these conditions, pH (in-situ) is predicted to be ~6.2. Attempts are presently underway to assess the effect of the calculated pH on metal sulfide and silicate (e.g., plagioclase, chlorite) solubility in comparison with

  10. Modeling Heat Transfer, Fluid Circulation and Permeability Alteration in Hydrothermal Systems with Loose Coupling to Magmatic Intrusion Modeling in the Lower Crust

    NASA Astrophysics Data System (ADS)

    Taron, J.; Karakas, O.; Mangan, M.; Dufek, J.; Ingebritsen, S.; Hickman, S. H.; Williams, C. F.

    2014-12-01

    The evolution of large scale hydrothermal systems entails spatially and temporally evolving permeability fields. During hydrothermal circulation, thermo-elastic stress and fluid pressure changes act upon partially open or hydrothermally altered fracture sets to modify permeability within the system, thereby shifting the patterns of circulation. To explore these interactions we are developing a thermo-hydromechanical (THM) simulator capable of coupling the dominant physics of the hydrothermal system and allowing flexibility in the use of monolithic or staggered numerical schemes. Permeability is allowed to evolve under several constitutive models tailored to both porous media and fractures, considering the influence of thermo-hydromechanical stress, creep, and elasto-plastic shear and dilation in a ubiquitously fractured medium. To expand our understanding of the long-term evolution of these systems, simulations incorporate information gleaned from the modeling of magmatic processes in the lower crust, where characteristics of the heat source are crucial in defining hydrothermal evolution. Results of a stochastic dike intrusion model are fed into the hydrothermal simulator to explore sensitivity relative to characteristics of the magmatic source. This is a first step to examining feedback mechanisms between heat transfer within geothermal fields and heat supply from the lower crust in a rigorous manner. We compare several simulations that elucidate the relative importance of magma intrusion rate and spatial distribution on overall heat transfer characteristics.

  11. U-Pb and Ar-Ar geochronology of the Fujiawu porphyry Cu-Mo deposit, Dexing district, Southeast China: Implications for magmatism, hydrothermal alteration, and mineralization

    NASA Astrophysics Data System (ADS)

    Li, Xiaofeng; Hu, Ruizhong; Rusk, Brian; Xiao, Rong; Wang, Cuiyun; Yang, Feng

    2013-09-01

    The Fujiawu porphyry Cu-Mo deposit is one of several porphyry Cu-Mo deposits in the Dexing district, Jiangxi Province, Southeast China. New zircon SHRIMP U-Pb data yield a weighted mean 206Pb/238U age of 172.0 ± 2.1 and 168.5 ± 1.4 Ma from weakly altered granodiorite porphyry and quartz diorite porphyry, respectively. Two hydrothermal biotites from granodiorite porphyry give an Ar-Ar step-heating plateau age of 169.9 ± 1.8 and 168.7 ± 1.8 Ma. Hydrothermal apatite exsolved from altered biotite yields an isotope dilution thermal ionization mass spectrometry isochron age of 164.4 ± 0.9 Ma. The apatite age is similar to the ages obtained from hydrothermal rutile (165.0 ± 1.1 and 164.8 ± 1.6 Ma) and indicates that the magmatism and hydrothermal activity in the Fujiawu deposit occurred in the Middle Jurassic. Hydrothermal fluid circulation related to multiple stages of magma emplacement resulted in Cu-Mo mineralization in the Fujiawu porphyry deposit. The zircon SHRIMP U-Pb ages and the published molybdenite Re-Os age (170.9 ± 1.5 Ma) represent the timing of magma crystallization and Mo mineralization, whereas the rutile and apatite U-Pb ages reflect the timing of Cu mineralization following quartz diorite emplacement. The data suggest slow cooling after emplacement of the quartz diorite porphyry.

  12. Preferential Radionuclide Transport in a Tuff with Altered Zones: Micro-scale Mapping

    NASA Astrophysics Data System (ADS)

    Hu, Q.; Liu, X.; Zuo, R.

    2009-12-01

    Understanding radionuclide transport in fractured rock is important for performance assessment of proposed radioactive waste disposal sites. We performed laboratory tests to study water imbibition and radionuclide transport into initially dry tuff by contacting one end of a sample with water containing a mixture of tracers (Re, 99Tc, Sr, Cs, 235U, 237Np, and 242Pu). The tuff sample, collected from Yucca Mountain, Nevada, is a cube 1-cm on each side and has a 1-mm thick altered gray zone embedded within the tuff matrix. Such gray zones are observed to be adjacent to lithophysae and fractures, are primarily quartz and tridymite, and have different hydraulic and chemical properties from the rock matrix. Capillary-driven imbibition transports tracer chemicals away from the imbibing face, causing separation of non-sorbing and sorbing tracers in tuff. Using a micro-scale profiling technique of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), we directly mapped the distribution of radionuclides along the altered zone (as well as transverse to the unaltered matrix). We found that the altered zone shows higher permeability, and less retardation of sorbing radionuclides, than the unaltered matrix, leading to preferential transport along the altered zone. Transverse profiling of the unaltered matrix indicated only limited penetration of strongly sorbing radionuclides, such as Pu.

  13. Mineral identification and mapping of hydrothermal alteration zones using high-spectral resolution images (AVIRIS)

    NASA Technical Reports Server (NTRS)

    Van Der Meer, Freek D.

    1994-01-01

    High-spectral resolution images (AVIRIS) of the cuprite mining area were used to evaluate atmospheric calibration algorithms and test several mineral mapping techniques. Four scene normalization techniques were used: (1) the flat-field method, (2) the internal average reflectance method, (3) the empirical line method, and (4) the atmospheric absorption removal method (ATREM). The algorithms were evaluated in terms of their spectral interpret- ability and their ability to remove both solar irradiance and atmospheric absorption features, noise, and artifacts. Noise was quantified by calculating the coefficient of variation of the spectra, and spectral interpretability was quantified by calcu- lating a difference spectrum (eg, laboratory spectrum minus pixel spectrum) for areas with known occurrences of clay minerals. These difference spectra were useful in evaluating the degree of removal of atmospheric features. The empirical line method produced the best calibration results. Mineral mapping as done using (1) color-composites of bands on the shoulders and centers of expected absorption features, (2) color-coded spectra, and (3) spectral angle mapping.

  14. What causes low magnetization at basalt-hosted hydrothermal sites? Insights from inactive site Krasnov (MAR 16°38'N)

    NASA Astrophysics Data System (ADS)

    Szitkar, Florent; Dyment, Jérôme; Choi, Yujin; Fouquet, Yves

    2014-04-01

    magnetic surveys acquired near the seafloor show that active basalt-hosted hydrothermal sites are associated with zones of lower magnetization. This observation may reflect the thermal demagnetization of a hot hydrothermal zone, the alteration of basalt affected by hydrothermal circulation, and/or the presence of thick, nonmagnetic hydrothermal deposits. In order to discriminate among these inferences, we acquired vector magnetic data 50 m above inactive hydrothermal site Krasnov using the Remotely Operated Vehicle (ROV) Victor. This deep hydrothermal site, located 7 km east of the Mid-Atlantic Ridge (MAR) axis at 16°38'N, is dissected by major normal faults and shows no evidence of recent hydrothermal activity. It is therefore a perfect target for investigating the magnetic signature of an inactive basalt-hosted hydrothermal site. Krasnov exhibits a strong negative magnetic anomaly, which implies that the lower magnetization observed at basalt-hosted hydrothermal sites is not a transient effect associated with hydrothermal activity, but remains after activity ceases. Thermal demagnetization plays only a secondary role, if any, in the observed magnetic low. Forward models suggest that both the nonmagnetic hydrothermal deposits and an altered zone of demagnetized basalt are required to account for the observed magnetic low. The permanence of this magnetic signature makes it a useful tool to explore midocean ridges and detect inactive hydrothermal sites.

  15. 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

  16. Report on static hydrothermal alteration studies of Topopah Spring tuff waters in J-13 water at 150{sup 0}C

    SciTech Connect

    Knauss, K.G.; Beiriger, W.B.

    1984-08-31

    This report presents the results of preliminary experimental work done to define the package environment in a potential nuclear waste repository in the Topopah Spring Member of the Paintbrush Tuff. The work is supported by the Nevada Nuclear Waste Storage Investigations (NNWSI) Project as a part of the Waste Package task to design a package suitable for waste storage within volcanic units at the Nevada Test Site. Static hydrothermal alteration experiments were run for 4 months using polished wafers either fully submerged in an appropriate natural ground water or exposed to water-saturated air with enough excess water to allow refluxing. The aqueous results agreed favorably with similar experiments run using crushed tuff, and the use of solid polished wafers allowed us to directly evaluate the effects of reaction on the tuff. The results are preliminary in the sense that these experiments were run in Teflon-lined, static autoclaves, whereas subsequent experiments have been run in Dickson-type gold-cell rocking autoclaves. The results predict relatively minor changes in water chemistry, very minor alteration of the host rock, and the production of slight amounts of secondary minerals, when liquid water could return to the rock pores following the temperature maximum during the thermal period. 7 references, 16 figures, 10 tables.

  17. Cathodoluminescence microscopy and spectroscopy of forsterite from Kaba meteorite: An application to the study of hydrothermal alteration of parent body

    NASA Astrophysics Data System (ADS)

    Gucsik, Arnold; Endo, Taro; Nishido, Hirotsugu; Ninagawa, Kiyotaka; Kayama, Masahiro; Bérczi, Szaniszló; Nagy, Szabolcs; Ábrahám, Péter; Kimura, Yuki; Miura, Hitoshi; Gyollai, Ildikó; Simonia, Irakli; Rózsa, Péter; Posta, József; Apai, Dániel; Mihályi, Krisztián; Nagy, Mihály; Ott, Ulrich

    2013-12-01

    Highly forsteritic olivine (Fo: 99.2-99.7) in the Kaba meteorite emits bright cathodoluminescence (CL). CL spectra of red luminescent forsterite grains have two broad emission bands at approximately 630 nm (impurity center of divalent Mn ions) in the red region and above 700 nm (trivalent Cr ions) in the red-IR region. The cores of the grains show CL blue luminescence giving a characteristic broad band emission at 400 nm, also associated with minor red emissions related to Mn and Cr ions. CL color variation of Kaba forsterite is attributed to structural defects. Electron probe microanalyzer (EPMA) analysis shows concentrations of Ca, Al, and Ti in the center of the forsterite grain. The migration of diffusible ions of Mn, Cr, and Fe to the rim of the Kaba meteoritic forsterite was controlled by the hydrothermal alteration at relatively low temperature (estimated at about 250 °C), while Ca and Al ions might still lie in the core. A very unusual phase of FeO (wüstite) was also observed, which may be a terrestrial alteration product of FeNi-metal.

  18. Analysis of Fracture Alignment and Hydrothermal Flow in Accommodation Zones That Link Facing Half-Grabens, Oregon Basalt Plateau

    NASA Astrophysics Data System (ADS)

    Osterloo, M. M.; Brumby, S. P.; Douglas, B. J.; Finkelstein, D. B.; Funsten, H. O.; Pratt, L. L.

    2005-05-01

    The Warner Valley, located in the southern Oregon portion of the Basin and Range Province, is composed of igneous units originating from the Steens Mountains volcanism. Normal faults associated with two opposing half grabens which define the valley are linked by a fractured accommodation zone. Within the valley are a series of shallow dilute to evaporatively concentrated hypersaline alkaline lakes that are being investigated as an analog to evaporative paleo-lakes on Mars. Little precipitation falls during the summer months and most of the surface water originates as runoff from snow pack in the winter and early spring. One additional recharge mechanism for the lakes is infill from fracture-controlled springs. Several of these springs are hydrothermal in nature with temperatures ranging from 18° C to 70° C. Integration of remote sensing datasets with field-based data provides a unique opportunity to combine medium to high spatial resolution imaging with ground truth measurements. This permits identification and correlation of the fault and spring locations and verification of the fracture control on the distribution of springs based on a larger data set than is available from field work alone. Landsat and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) data, as well as digital elevation models, are used in the analysis. Gradients and absolute values from digital elevation models are used to define the trends of the faults and fractures as well as the fault offsets. Many of the springs are marked by highly vegetated riparian zones that are identified via spectral and textural signatures present in these types of multispectral visible/infrared imagery. A majority of the hot springs are located within the accommodation zone of the opposing half-grabens; this highly fractured area is investigated in the datasets. Maps of vegetation variations within the valley coupled with thermal anomalies, derived from the imagery, serve to verify locations

  19. Seismic properties of rocks affected by hydrothermal alteration: a case study from the Lalor Lake VMS mining camp

    NASA Astrophysics Data System (ADS)

    Miah, K.; Bellefleur, G.; Schetselaar, E.

    2013-12-01

    Global demand of base metals, uranium, diamonds, and precious metals has been pushing technological barrier to find and extract minerals at higher depth, which was not feasible in just a few decades ago. Seismic properties of rocks containing and surrounding ore bodies have been useful in characterizing and modeling geologic structures, and mapping high-resolution images of ore bodies. Although seismic surveys and drill hole sonic and density logs are essential for mineral exploration at depth, limited availability of seismic logs to link rock properties of different ore forming geologic structure is a hindrance to seismic interpretations. Volcanogenic Massive Sulphides (VMS) are rich in minerals and of primary interests among geologists and mining industries alike. VMS deposits occur due to focused discharge of metal-enriched fluids associated in the hydrothermal alteration process, and are rich in Zn, Cu, Pb, Ag, Au, etc. Alteration halos surrounding ore deposits can be widespread, and their locations are easier to determine than the deposits within them. Physical rock properties affected by alteration can provide clues on type and potentially size of ore deposits in the surrounding area. In this context, variations in seismic properties of rocks due to hydrothermal alteration near the deposits can help in improving modeling accuracy, and better interpretation of seismic data for economic mineral exploration. While reflection seismic techniques can resolve ore bodies at higher depths than other conventional geophysical techniques, they are relatively expensive both in terms of field data acquisition and post-processing, especially for high-resolution 3D surveys. Acoustic impedance contrasts of ore lenses with their hosting rock environment; geometry, size and spatial location relative to the surface affect their detection with seismic data. Therefore, apriori knowledge of seismic rock properties from drill hole logs and core samples in the potential survey area

  20. Hydrothermal alteration of graywacke and basalt by 4 molal NaCl.

    USGS Publications Warehouse

    Rosenbauer, R.J.; Bischoff, J.L.; Radtke, A.S.

    1983-01-01

    Rock-water interaction experiments were carried out at 350oC and 500 bar at a 1/10 rock/fluid ratio using 4 molal NaCl brine. Reaction of brine and greywacke lead to the conversion of illite, dolomite and quartz to albite and smectite. In the process, the rock gained Na and released Ca, K, heavy metals and CO2 to solution. Metal mobilization was found to primarily depend on acidity which was produced by Na metasomatism and by dedolomitization. Reaction of brine and basalt produced only minor alteration in which some smectite and little albite formed. No significant acidity was produced nor did metals become mobilized. Production of acidity during albitization depends entirely on the phase being altered. Albitization of greywacke produces H+ whereas the albitization of basalt apparently consumes this ion. -J.E.S.

  1. Fluid inclusions and preliminary studies of hydrothermal alteration in core hole PLTG-1, Platanares geothermal area, Honduras

    USGS Publications Warehouse

    Bargar, K.E.

    1991-01-01

    The Platanares geothermal area in western Honduras consists of more than 100 hot springs that issue from numerous hot-spring groups along the banks or within the streambed of the Quebrada de Agua Caliente (brook of hot water). Evaluation of this geothermal area included drilling a 650-m deep PLTG-1 drill hole which penetrated a surface mantling of stream terrace deposits, about 550 m of Tertiary andesitic lava flows, and Cretaceous to lower Tertiary sedimentary rocks in the lower 90 m of the drill core. Fractures and cavities in the drill core are partly to completely filled by hydrothermal minerals that include quartz, kaolinite, mixed-layer illite-smectite, barite, fluorite, chlorite, calcite, laumontite, biotite, hematite, marcasite, pyrite, arsenopyrite, stibnite, and sphalerite; the most common open-space fillings are calcite and quartz. Biotite from 138.9-m depth, dated at 37.41 Ma by replicate 40Ar/39 Ar analyses using a continuous laser system, is the earliest hydrothermal mineral deposited in the PLTG-1 drill core. This mid-Tertiary age indicates that at least some of the hydrothermal alteration encountered in the PLTG-1 drill core occured in the distant past and is unrelated to the present geothermal system. Furthermore, homogenization temperatures (Th) and melting-point temperatures (Tm) for fluid inclusions in two of the later-formed hydrothermal minerals, calcite and barite, suggest that the temperatures and concentration of dissolved solids of the fluids present at the time these fluid inclusions formed were very different from the present temperatures and fluid chemistry measured in the drill hole. Liquid-rich secondary fluid inclusions in barite and caicite from drill hole PLTG-1 have Th values that range from about 20??C less than the present measured temperature curve at 590.1-m depth to as much as 90??C higher than the temperature curve at 46.75-m depth. Many of the barite Th measurements (ranging between 114?? and 265??C) plot above the

  2. Oxygen and Hydrogen Isotope Values for Unaltered and Hydrothermally Altered Samples from the Cretaceous Linga Plutonic Complex of the Peruvian Coastal Batholith near Ica.

    NASA Astrophysics Data System (ADS)

    Gonzalez, L. U.; Holk, G. J.; Clausen, B. L.; Poma Porras, O. A.

    2015-12-01

    A portion of the Peruvian Coastal Batholith near Ica, Peru is being studied using stable isotopes to determine the source of hydrothermal fluids that caused propylitic, phyllic, and potassic alteration in the mineralized Linga plutonic complex. Sources of hydrothermal fluids and water/rock ratios are estimated to understand the role of such fluids in alteration during cooling. A set of 64 mineral analysis from 18 igneous samples, 7 unaltered and 11 altered, were analyzed for D/H and 18O/16O isotopes. The δ18O values for whole rocks with no apparent alteration vary from +6.8‰ to +7.9‰, with sets of δ18O mineral values indicating isotopic equilibrium at closure temperatures from 571°C to 651°C, and no interaction with meteoric water. This conclusion is bolstered by hornblende (-87‰ to -64‰) and biotite (-81‰ to -74‰) δD values Most δ18O values for samples with hydrothermal alteration suggest that alteration results from magmatic fluids; however, several analyses indicate interaction with other fluids. The high δ18O values for plagioclase (+9.3‰) and hornblende (+6.3‰) from a metamorphic aureole in volcanic host rock near a plutonic intrusion may be due to interaction with metamorphic or low temperature magmatic fluids. Plagioclase (+2.6‰) and biotite (+0.1‰) δ18O values in a sample from the Jurassic volcanic envelope indicate a significant effect from meteoric-hydrothermal fluids. An altered monzonite yielded δ18O values for quartz (+5.5‰), K-spar (+5.6‰), and magnetite (+0.4‰), also suggesting interaction with meteoric fluids. A diorite from an area with strong epidotization produced an epidote δD value of -25.8‰ and a monzonite from a highly veined area has an epidote δD value of -36.1‰ suggesting interaction with sea water. This new data indicate that the Linga complex was primarily influenced by magmatic hydrothermal fluids, but metamorphic, meteoric, and sea water may have had some influence in producing alteration

  3. Relation of Carlin-type gold mineralization to lithology, structure and alteration: Screamer zone, Betze-Post deposit, Nevada

    NASA Astrophysics Data System (ADS)

    Ye, Zaojun; Kesler, Stephen E.; Essene, Eric J.; Zohar, Pamela B.; Borhauer, Jeffrey L.

    2003-01-01

    An evaluation of the relation between geologic features and gold grade has been undertaken in the Screamer zone of the Betze-Post deposit, the largest Carlin-type gold deposit in the world. Screamer, which forms the western end of Betze-Post, is a stratiform ore zone that is hosted almost entirely by the wispy member of the Popovich Formation. The wispy member is overlain by the planar member of the same formation and underlain by the Roberts Mountains Formation, both of which contain much smaller amounts of gold mineralization in the Screamer zone. Geologic features recognized at Screamer reflect the long history of events that have affected the area since mid-Paleozoic time. The two earliest events at Screamer were probably sulfidation and formation of flat fractures, and the two latest events were pyritization and formation of kaolinite-filled fractures, which took place at least partly during gold mineralization. Gold mineralization at Screamer shows ambiguous relations to most lithologic, alteration and structural features. For instance, gold grades in the wispy member of the Popovich Formation are slightly higher in rock units that contain the largest proportion of debris flow material, but this relation does not account for most ore. The correlation of gold grades with fracture density is also generally poor, but gold grades are slightly higher in samples containing vertical and/or kaolinite-bearing fractures, particularly those with a northeasterly trend. Most early veins at Screamer are horizontal and most later veins are vertical, suggesting that the long-term trend of fluid pressures in the area has been from lithostatic to hydrostatic. Finally, gold grades correlate poorly with silicification and decarbonatization, and although some gold appears to be associated with rock containing kaolinite, much is not. The only rock feature that shows a direct relation to gold grade is pyrite. Some pyrite formed by sulfidation of the original rock, but much of it

  4. Pb-isotope systematics of a fossil hydrothermal system from the Troodos ophiolite, Cyprus: Evidence for a polyphased alteration history

    NASA Astrophysics Data System (ADS)

    Booij, Ernst; Bettison-Varga, Lori; Farthing, Dori; Staudigel, Hubert

    2000-10-01

    Pb-isotopic ratios have been determined on massive sulphides from the Troodos ophiolite and their inferred source rocks: epidosites and greenschist altered dikes. The latter have distinctly higher Pb-isotope ratios than the sulphides. The high 207Pb/ 204Pb ratios for the whole rocks indicate the involvement of an old (sedimentary) Pb-component. Extensive leaching of three epidosite samples shows that the radiogenic Pb can be removed and the resulting trend for the leached samples is consistent with a Pb-Pb age of ˜95 Ma for these rocks. Inferred initial Pb isotope ratios are similar to those of the sulphides (this study) and fresh glasses from the Akaki Canyon in Cyprus. Therefore the Pb incorporated in the massive sulphides may originate from these greenschist facies hydrothermally altered rocks. The isotopic composition of the leachate Pb points toward a sedimentary origin. Calculation of the Pb-isotopic ratios for 90 Ma old "average" Troodos sediment shows that the "foreign" Pb in the epidosites may very well be derived from this source. This Pb probably does not reside within the mineral lattices of these metamorphic rocks, but rather is adsorbed on mineral surfaces or is present in microscopic particulate matter that may have been filtered from the circulating seawater. Unmodified seawater is considered an unlikely Pb source because of the extremely small dissolved Pb contents of seawater. Furthermore, no seawater or sedimentary signature is evident in the sulphides. Several models of Pb transport from different sources into these rocks may be envisaged, such as dissolution of Miocene evaporites and brine formation, equilibration of pore waters to the Pb isotope ratios of host sediments, and direct infiltration of deep sea particulate matter from the nepheloid layer. With the limited amount of data presently available it is impossible to critically determine the most likely processes of Pb transport.

  5. 76 FR 64818 - Safety Zone; Truman-Hobbs Alteration of the Elgin Joliet & Eastern Railroad Drawbridge, Morris, IL

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-19

    ... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone; Truman-Hobbs Alteration of the Elgin Joliet.... This zone is intended to restrict vessels from a portion of the Illinois River due to the Truman-Hobbs... and contrary to the public interest. Background and Purpose The Truman-Hobbs alteration of the...

  6. Surface heat flow and CO2 emissions within the Ohaaki hydrothermal field, Taupo Volcanic Zone, New Zealand

    USGS Publications Warehouse

    Rissmann, C.; Christenson, B.; Werner, C.; Leybourne, M.; Cole, J.; Gravley, D.

    2012-01-01

    Carbon dioxide emissions and heat flow have been determined from the Ohaaki hydrothermal field, Taupo Volcanic Zone (TVZ), New Zealand following 20a of production (116MW e). Soil CO2 degassing was quantified with 2663 CO2 flux measurements using the accumulation chamber method, and 2563 soil temperatures were measured and converted to equivalent heat flow (Wm -2) using published soil temperature heat flow functions. Both CO2 flux and heat flow were analysed statistically and then modelled using 500 sequential Gaussian simulations. Forty subsoil CO 2 gas samples were also analysed for stable C isotopes. Following 20a of production, current CO2 emissions equated to 111??6.7T/d. Observed heat flow was 70??6.4MW, compared with a pre-production value of 122MW. This 52MW reduction in surface heat flow is due to production-induced drying up of all alkali-Cl outflows (61.5MW) and steam-heated pools (8.6MW) within the Ohaaki West thermal area (OHW). The drying up of all alkali-Cl outflows at Ohaaki means that the soil zone is now the major natural pathway of heat release from the high-temperature reservoir. On the other hand, a net gain in thermal ground heat flow of 18MW (from 25MW to 43.3??5MW) at OHW is associated with permeability increases resulting from surface unit fracturing by production-induced ground subsidence. The Ohaaki East (OHE) thermal area showed no change in distribution of shallow and deep soil temperature contours despite 20a of production, with an observed heat flow of 26.7??3MW and a CO 2 emission rate of 39??3T/d. The negligible change in the thermal status of the OHE thermal area is attributed to the low permeability of the reservoir beneath this area, which has limited production (mass extraction) and sheltered the area from the pressure decline within the main reservoir. Chemistry suggests that although alkali-Cl outflows once contributed significantly to the natural surface heat flow (~50%) they contributed little (<1%) to pre-production CO 2

  7. A hybrid zone between Bathymodiolus mussel lineages from eastern Pacific hydrothermal vents

    PubMed Central

    2013-01-01

    Background The inhabitants of deep-sea hydrothermal vents occupy ephemeral island-like habitats distributed sporadically along tectonic spreading-centers, back-arc basins, and volcanically active seamounts. The majority of vent taxa undergo a pelagic larval phase, and thus varying degrees of geographical subdivision, ranging from no impedance of dispersal to complete isolation, often exist among taxa that span common geomorphological boundaries. Two lineages of Bathymodiolus mussels segregate on either side of the Easter Microplate, a boundary that separates the East Pacific Rise from spreading centers connected to the Pacific-Antarctic Ridge. Results A recent sample from the northwest flank of the Easter Microplate contained an admixture of northern and southern mitochondrial haplotypes and corresponding alleles at five nuclear gene loci. Genotypic frequencies in this sample did not fit random mating expectation. Significant heterozygote deficiencies at nuclear loci and gametic disequilibria between loci suggested that this transitional region might be a ‘Tension Zone’ maintained by immigration of parental types and possibly hybrid unfitness. An analysis of recombination history in the nuclear genes suggests a prolonged history of parapatric contact between the two mussel lineages. We hereby elevate the southern lineage to species status as Bathymodiolus antarcticus n. sp. and restrict the use of Bathymodiolus thermophilus to the northern lineage. Conclusions Because B. thermophilus s.s. exhibits no evidence for subdivision or isolation-by-distance across its 4000 km range along the EPR axis and Galápagos Rift, partial isolation of B. antarcticus n. sp. requires explanation. The time needed to produce the observed degree of mitochondrial differentiation is consistent with the age of the Easter Microplate (2.5 to 5.3 million years). The complex geomorphology of the Easter Microplate region forces strong cross-axis currents that might disrupt self

  8. Distribution of Potential Hydrothermally Altered Rocks in Central Colorado Derived From Landsat Thematic Mapper Data: A Geographic Information System Data Set

    USGS Publications Warehouse

    Knepper, Daniel H.

    2010-01-01

    As part of the Central Colorado Mineral Resource Assessment Project, the digital image data for four Landsat Thematic Mapper scenes covering central Colorado between Wyoming and New Mexico were acquired and band ratios were calculated after masking pixels dominated by vegetation, snow, and terrain shadows. Ratio values were visually enhanced by contrast stretching, revealing only those areas with strong responses (high ratio values). A color-ratio composite mosaic was prepared for the four scenes so that the distribution of potentially hydrothermally altered rocks could be visually evaluated. To provide a more useful input to a Geographic Information System-based mineral resource assessment, the information contained in the color-ratio composite raster image mosaic was converted to vector-based polygons after thresholding to isolate the strongest ratio responses and spatial filtering to reduce vector complexity and isolate the largest occurrences of potentially hydrothermally altered rocks.

  9. Mapping advanced argillic alteration zones with ASTER and Hyperion data in the Andes Mountains of Peru

    NASA Astrophysics Data System (ADS)

    Ramos, Yuddy; Goïta, Kalifa; Péloquin, Stéphane

    2016-04-01

    This study evaluates Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Hyperion hyperspectral sensor datasets to detect advanced argillic minerals. The spectral signatures of some alteration clay minerals, such as dickite and alunite, have similar absorption features; thus separating them using multispectral satellite images is a complex challenge. However, Hyperion with its fine spectral bands has potential for good separability of features. The Spectral Angle Mapper algorithm was used in this study to map three advanced argillic alteration minerals (alunite, kaolinite, and dickite) in a known alteration zone in the Peruvian Andes. The results from ASTER and Hyperion were analyzed, compared, and validated using a Portable Infrared Mineral Analyzer field spectrometer. The alterations corresponding to kaolinite and alunite were detected with both ASTER and Hyperion (80% to 84% accuracy). However, the dickite mineral was identified only with Hyperion (82% accuracy).

  10. Nickeliferous pyrite tracks pervasive hydrothermal alteration in Martian regolith breccia: A study in NWA 7533

    NASA Astrophysics Data System (ADS)

    Lorand, Jean-Pierre; Hewins, Roger H.; Remusat, Laurent; Zanda, Brigitte; Pont, Sylvain; Leroux, Hugues; Marinova, Maya; Jacob, Damien; Humayun, Munir; Nemchin, Alexander; Grange, Marion; Kennedy, Allen; Göpel, Christa

    2015-11-01

    Martian regolith breccia NWA 7533 (and the seven paired samples) is unique among Martian meteorites in showing accessory pyrite (up to 1% by weight). Pyrite is a late mineral, crystallized after the final assembly of the breccia. It is present in all of the lithologies, i.e., the fine-grained matrix (ICM), clast-laden impact melt rocks (CLIMR), melt spherules, microbasalts, lithic clasts, and mineral clasts, all lacking magmatic sulfides due to degassing. Pyrite crystals show combinations of cubes, truncated cubes, and octahedra. Polycrystalline clusters can reach 200 μm in maximum dimensions. Regardless of their shape, pyrite crystals display evidence of very weak shock metamorphism such as planar features, fracture networks, and disruption into subgrains. The late fracture systems acted as preferential pathways for partial replacement of pyrite by iron oxyhydroxides interpreted as resulting from hot desert terrestrial alteration. The distribution and shape of pyrite crystals argue for growth at moderate to low growth rate from just-saturated near neutral (6 < pH<10), H2S-HS-rich fluids at minimum log fO2 of >FMQ + 2 log units. It is inferred from the maximum Ni contents (4.5 wt%) that pyrite started crystallizing at 400-500 °C, during or shortly after a short-duration, relatively low temperature, thermal event that lithified and sintered the regolith breccias, 1.4 Ga ago as deduced from disturbance in several isotope systematics.

  11. A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

    PubMed Central

    Haigh, Sarah; Lyon, Ian

    2014-01-01

    Abstract A conspicuous biomorphic ovoid structure has been discovered in the Nakhla martian meteorite, made of nanocrystalline iron-rich saponitic clay and amorphous material. The ovoid is indigenous to Nakhla and occurs within a late-formed amorphous mesostasis region of rhyolitic composition that is interstitial to two clinopyroxene grains with Al-rich rims, and contains acicular apatite crystals, olivine, sulfides, Ti-rich magnetite, and a new mineral of the rhoenite group. To infer the origin of the ovoid, a large set of analytical tools was employed, including scanning electron microscopy and backscattered electron imaging, wavelength-dispersive X-ray analysis, X-ray mapping, Raman spectroscopy, time-of-flight secondary ion mass spectrometry analysis, high-resolution transmission electron microscope imaging, and atomic force microscope topographic mapping. The concentric wall of the ovoid surrounds an originally hollow volume and exhibits internal layering of contrasting nanotextures but uniform chemical composition, and likely inherited its overall shape from a preexisting vesicle in the mesostasis glass. A final fibrous layer of Fe-rich phases blankets the interior surfaces of the ovoid wall structure. There is evidence that the parent rock of Nakhla has undergone a shock event from a nearby bolide impact that melted the rims of pyroxene and the interstitial matter and initiated an igneous hydrothermal system of rapidly cooling fluids, which were progressively mixed with fluids from the melted permafrost. Sharp temperature gradients were responsible for the crystallization of Al-rich clinopyroxene rims, rhoenite, acicular apatites, and the quenching of the mesostasis glass and the vesicle. During the formation of the ovoid structure, episodic fluid infiltration events resulted in the precipitation of saponite rinds around the vesicle walls, altered pyrrhotite to marcasite, and then isolated the ovoid wall structure from the rest of the system by depositing a

  12. Formation of Hematite fine crystals by hydrothermal alteration of synthetic Martian basalt, static and fluid flow experiments

    NASA Astrophysics Data System (ADS)

    Kobayashi, K.; Isobe, H.

    2011-12-01

    Exploration made by Martian rovers and probes provided enormous information on the composition of the Martian surface materials. Origin and formation processes of the Martian surface materials should be various depending on topography and history of the Martian crust. Especially, iron minerals in the Martian soil should have essential role to characterize surface environment of the "red planet". In the present study, experimental reproduction of the Martian soil was carried out by hydrothermal alteration of the synthetic iron-rich basaltic rock. Experimental conditions for temperature and fluid composition followed Isobe and Yoshizawa (2010). Static alteration experiments are carried out at 100 °C and 150 °C, and mass ratio of the starting material to the pH1.0 sulfuric acid solution is 1:50. Run durations are 1, 2, 4 or 8 weeks. Appropriate mass of dry ice was sealed in the experimental vessels to expel atmospheric oxygen with CO2. For the static experiments, powdered starting materials were charged in PFA vial to keep textures of the run products. For the fluid flow experiments, we constructed closed loop with Teflon tube inclined approximately 45°. One of the vertical tube is charged with crushed synthetic basalt and heated approximately 150°C by aluminum block with ribbon heater. Surlfuric acid solution flows through the tube from bottom to top and cooled at the end of the aluminum block. Cooled solution returns to the bottom of the heated tube through another vertical tube without heating block. In the static condition run products, characteristic iron mineral particles are formed for 100°C and 150°C concordant with Isobe and Yoshizawa (2010). These iron minerals distributed not only inside the starting material powder but also on the surface of the reaction vessel and the PFA vial in the reactive solution. The surface of the reaction vessel shows orange and reddish color on 100°C and 150°C run products, respectively. By SEM observation, dissolution of

  13. Gas geochemistry of a shallow submarine hydrothermal vent associated with the El Requesón fault zone, Bahía Concepción, Baja California Sur, México

    USGS Publications Warehouse

    Forrest, Matthew J.; Ledesma-Vazquez, Jorge; Ussler, William, III; Kulongoski, Justin T.; Hilton, David R.; Greene, H. Gary

    2005-01-01

    We investigated hydrothermal gas venting associated with a coastal fault zone along the western margin of Bahía Concepción, B.C.S., México. Copious discharge of geothermal liquid (≈ 90 °C) and gas is occurring in the intertidal and shallow subtidal zones (to a depth of 13 m) through soft sediments and fractures in rocks along a ∼750 m linear trend generally sub-parallel to an onshore fault near Punta Santa Barbara. Hydrothermal activity shows negative correlation with tidal height; temperatures in the area of hydrothermal activity were up to 11.3 °C higher at low tide than at high tide (measured tidal range ≈ 120 cm). Gas samples were collected using SCUBA and analyzed for chemical composition and stable isotope values. The main components of the gas are N2 (≈ 53%; 534 mmol/mol), CO2 (≈ 43%; 435 mmol/mol), and CH4 (≈ 2.2%; 22 mmol/mol). The δ13C values of the CH4 (mean = − 34.3‰), and the ratios of CH4 to C2H6(mean = 89), indicate that the gas is thermogenic in origin. The carbon stable isotopes and the δ15N of the N2 in the gas (mean = 1.7‰) suggest it may be partially derived from the thermal alteration of algal material in immature sedimentary organic matter. The He isotope ratios (3He / 4He = 1.32 RA) indicate a significant mantle component (16.3%) in the gas. Here, we suggest the name El Requesón fault zone for the faults that likely formed as a result of extension in the region during the late Miocene, and are currently serving as conduits for the observed hydrothermal activity.

  14. Evaluation of 0.46- to 2.36-micrometre multispectral scanner images of the East Tintic mining district, Utah, for mapping hydrothermally altered rocks.

    USGS Publications Warehouse

    Rowan, L.C.; Kahle, A.B.

    1982-01-01

    Airborne multispectral scanner images recorded in the 0.46 to 2.36 micrometre region for the E Tintic mining district, Utah, were evaluated to determine their usefulness for distinguishing six types of hydrothermally altered rocks from a wide range of sedimentary and igneous rock types. The laboratory and field evaluation of a color ratio composite image, supported by in situ spectral reflectance measurements and an alteration map compiled from a published map, shows that silicified, argillized, and pyritized rocks can be mapped in detail utilizing an intense OH absorption band centered near 2.2 micrometre. This absorption band is absent or weak in most of the unaltered rocks. -from Authors

  15. Application of MAC-Europe AVIRIS data to the analysis of various alteration stages in the Landdmannalauger Hydrothermal Area (South Iceland)

    NASA Technical Reports Server (NTRS)

    Sommer, S.; Loercher, G.; Endres, S.

    1993-01-01

    In June 1991 extensive airborne remote sensing data-sets have been acquired over Iceland in the framework of the joint NASA/ESA Multisensor Airborne Campaign Europe (MAC-Europe). The study area is located within the Torfajokull central volcanic complex in South Iceland. This complex is composed by anomalously abundant rhyolitic acid volcanics, which underwent intensive hydrothermal alteration. Detailed studies of surface alteration of rhyolitic rocks in the area showed that all the major elements are leached as the rock is affected by complex mineralogical changes. Montmorillonite appears during the earliest stages of alteration. In the ultimate alteration product montmorillonite is absent and the rock consists mostly of amorphous silica, anatase, up to a volume of 50% kaolinite and variable amounts of native sulphur and pyrite. The case study presented shall endeavor to assess the potential of MAC-Europe AVIRIS and TMS data in determining a possible zonation of hydrothermal alteration in relationship to the active geo-thermal fields and structural features. To this end, the airborne data is analysed in comparison with laboratory spectral measurements of characteristics rock, soil, and vegetation samples collected in the study areaduring the summer of 1992. Various spectral mapping algorithms as well as unmixing approaches are tested and evaluated. Detailed geological and structural mapping as well as geochemical analysis of the main rock and soil types were performed to underpin the analysis of the airborne data.

  16. Alteration zone Mapping in the Meiduk and Sar Cheshmeh Porphyry Copper Mining Districts of Iran using Advanced Land Imager (ALI) Satellite Data

    NASA Astrophysics Data System (ADS)

    Beiranvand Pour, A.; Hashim, M.

    2015-10-01

    This study evaluates the capability of Earth Observing-1 (EO1) Advanced Land Imager (ALI) data for hydrothermal alteration mapping in the Meiduk and Sar Cheshmeh porphyry copper mining districts, SE Iran. Feature-oriented principal components selection, 4/2, 8/9, 5/4 band ratioing were applied to ALI data for enhancing the hydrothermally altered rocks associated with porphyry copper mineralization, lithological units and vegetation. Mixture-tuned matched-filtering (MTMF) was tested to discriminate the hydrothermal alteration areas of porphyry copper mineralization from surrounding environment using the shortwave infrared bands of ALI. Results indicate that the tested methods are able to yield spectral information for identifying vegetation, iron oxide/hydroxide and clay minerals, lithological units and the discrimination of hydrothermally altered rocks from unaltered rocks using ALI data.

  17. Episodic intrusion, internal differentiation, and hydrothermal alteration of the miocene tatoosh intrusive suite south of Mount Rainier, Washington

    USGS Publications Warehouse

    du Bray, E.A.; Bacon, C.R.; John, D.A.; Wooden, J.L.; Mazdab, F.K.

    2011-01-01

    The Miocene Tatoosh intrusive suite south of Mount Rainier is composed of three broadly granodioritic plutons that are manifestations of ancestral Cascades arc magmatism. Tatoosh intrusive suite plutons have individually diagnostic characteristics, including texture, mineralogy, and geochemistry, and apparently lack internal contacts. New ion-microprobe U-Pb zircon ages indicate crystallization of the Stevens pluton ca. 19.2 Ma, Reflection-Pyramid pluton ca. 18.5 Ma, and Nisqually pluton ca. 17.5 Ma. The Stevens pluton includes rare, statistically distinct ca. 20.1 Ma zircon antecrysts. Wide-ranging zircon rare earth element (REE), Hf, U, and Th concentrations suggest late crystallization from variably evolved residual liquids. Zircon Eu/Eu*-Hf covariation is distinct for each of the Reflection-Pyramid, Nisqually, and Stevens plutons. Although most Tatoosh intrusive suite rocks have been affected by weak hydrothermal alteration, and sparse mineralized veins cut some of these rocks, significant base or precious metal mineralization is absent. At the time of shallow emplacement, each of these magma bodies was largely homogeneous in bulk composition and petrographic features, but, prior to final solidification, each of the Tatoosh intrusive suite plutons developed internal compositional variation. Geochemical and petrographic trends within each pluton are most consistent with differential loss of residual melt, possibly represented by late aplite dikes or erupted as rhyolite, from crystal-rich magma. Crystal-rich magma that formed each pluton evidently accumulated in reservoirs below the present level of exposure and then intruded to a shallow depth. Assembled by episodic intrusion, the Tatoosh intrusive suite may be representative of midsized composite plutonic complexes beneath arc volcanoes. ?? 2011 Geological Society of America.

  18. Listvenite from the Oman Ophiolite: complete carbonation of peridotite during hydrothermal alteration by CO2-rich fluids

    NASA Astrophysics Data System (ADS)

    Streit, E.; Kelemen, P. B.; Eiler, J. M.; Goldstein, S. L.

    2012-12-01

    Hydrothermal alteration of peridotite in the Oman Ophiolite has resulted in the formation of listvenite, characterized by complete carbonatization, in which all of the Mg and Ca and much of the Fe has been incorporated into carbonate minerals. Here we examine chemical and isotopic evidence for the temperatures, timing, and fluid composition involved in the formation of this listvenite. Listvenites occur within 500m of the basal thrust of the ophiolite, frequently along the contact with underlying metasediments, but also as tabular bodies or bands, ~5-100m thick, within partially serpentinized peridotite. The listvenites are composed primarily of magnesite (and/or dolomite) + quartz + relict Cr-spinel. Clumped isotope data from magnesite and dolomite suggest that carbonate phases within the listvenite formed at peak temperatures ~150-170C. At these temperatures, thermodynamic stability of the magnesite + quartz assemblage (relative to talc + magnesite) requires that these minerals formed at relatively high PCO2. These CO2-rich fluids were likely derived from metamorphic dehydration of the underlying sediment during emplacement of the ophiolite. Carbon and oxygen stable isotopes are fairly uniform between listvenite samples and are consistent with values in some of the underlying metasediments. Initial 87Sr/86Sr values in the listvenite vary from 0.7085 to 0.7135, mostly significantly higher than seawater values, and are consistent with values within the underlying metasediments, suggesting mass-transfer. Trace and major element patterns are also suggestive of mass-transfer from underlying clastic sediments and limestones. Although the major mineral assemblages do not vary much between samples, bulk composition indicates that some listwanites have undergone significant silicification in addition to carbonation, while others have undergone very little mass transfer beyond the addition of CO2.

  19. Modeled temperatures and fluid source distributions for the Mexican subduction zone: Effects of hydrothermal circulation and implications for plate boundary seismic processes

    NASA Astrophysics Data System (ADS)

    Perry, Matthew; Spinelli, Glenn A.; Wada, Ikuko; He, Jiangheng

    2016-02-01

    In subduction zones, spatial variations in pore fluid pressure are hypothesized to control the sliding behavior of the plate boundary fault. The pressure-temperature paths for subducting material control the distributions of dehydration reactions, a primary control on the pore fluid pressure distribution. Thus, constraining subduction zone temperatures are required to understand the seismic processes along the plate interface. We present thermal models for three margin-perpendicular transects in the Mexican subduction zone. We examine the potential thermal effects of vigorous fluid circulation in a high-permeability aquifer within the basaltic basement of the oceanic crust and compare the results with models that invoke extremely high pore fluid pressures to reduce frictional heating along the megathrust. We combine thermal model results with petrological models to determine the spatial distribution of fluid release from the subducting slab and compare dewatering locations with the locations of seismicity, nonvolcanic tremor, slow-slip events, and low-frequency earthquakes. Simulations including hydrothermal circulation are most consistent with surface heat flux measurements. Hydrothermal circulation has a maximum cooling effect of 180°C. Hydrothermally cooled crust carries water deeper into the subduction zone; fluid release distributions in these models are most consistent with existing geophysical data. Our models predict focused fluid release, which could generate overpressures, coincident with an observed ultraslow layer (USL) and a region of nonvolcanic tremor. Landward of USLs, a downdip decrease in fluid source magnitude could result in the dissipation in overpressure in the oceanic crust without requiring a downdip increase in fault zone permeability, as posited in previous studies.

  20. Modeled Temperatures and Fluid Source Distributions for the Mexico Subduction Zone: Effects of Hydrothermal Cooling and Implications for Plate Boundary Seismic Processes

    NASA Astrophysics Data System (ADS)

    Perry, M. R.; Spinelli, G. A.; Wada, I.

    2014-12-01

    In subduction zones, spatial variations in pore fluid pressure are hypothesized to control the distribution and nature of slip behavior (e.g., "normal" earthquakes, slow slip events, non-volcanic tremor, very low frequency earthquakes) on the plate boundary fault. A primary control on the pore fluid pressure distribution in subduction zones is the distribution of fluid release from hydrous minerals in the subducting sediment and rock. The distributions of these diagenetic and metamorphic fluid sources are controlled by the pressure-temperature paths that the subducting material follows. Thus, constraining subduction zone thermal structure is required to inform conceptual models of seismic behavior. Here, we present results of thermal models for the Mexico subduction zone, a system that has received recent attention due to observations of slow-slip events and non-volcanic tremor. We model temperatures in five margin-perpendicular transects from 96 ˚W to 104 ˚W. In each transect, we examine the potential thermal effects of vigorous fluid circulation in a high permeability aquifer within the basaltic basement of the oceanic crust. In the transect at 100˚W, hydrothermal circulation cools the subducting material by up to 140 ˚C, shifting peak slab dehydration landward by ~100 km relative to previous estimates from models that do not include the effects of fluid circulation. The age of the subducting plate in the trench increases from ~3 Ma at 104 ˚W to ~18 Ma at 96 ˚W; hydrothermal circulation redistributes the most heat (and cools the system the most) where the subducting plate is youngest. For systems with <20 Ma subducting lithosphere, hydrothermal circulation in oceanic crust should be considered in estimating subduction zone temperatures and fluid source distributions.

  1. Depth-dependent permeability of hydrothermal discharge zones: measurements through tidal modulation and implications for mid-ocean ridge heat budgets

    NASA Astrophysics Data System (ADS)

    Barreyre, T.; Crone, T. J.; Olive, J. A. L.

    2015-12-01

    The efficiency of hydrothermal circulation as a heat and mass exchanger is strongly modulated by the permeability structure of newly formed oceanic crust, which is known to vary spatially and temporally. Here we use the modulation of discharge temperatures by oscillatory tidal loading to estimate permeability vs. depth profiles beneath hydrothermal discharge zones at three basalt-hosted hydrothermal fields. Phase lags between fluctuations in discharge temperature and seafloor tidal loading have previously been inverted for the permeability of the underlying discharge zone using the poroelastic modulation model of Jupp and Schulz [2004]. This has yielded a wide range of permeability estimates ranging from 10-13­-10-9 m2. Here we extend the model to a stratified medium comprising a top layer (2A) of permeability k2A overlying a bottom layer (2B) of permeability k2B. We apply it to three basalt-hosted hydrothermal fields on a slow- (Lucky Strike), intermediate- (Main Endeavour Field), and fast-spreading (East Pacific Rise, EPR-9ºN) ridge, where stratification is well known from seismic studies. We estimate a layer 2A permeability of ~10-10 m2 at Lucky Strike, in sharp contrast with EPR-9ºN, where k2A ~ 10-13 m2. At the Main Endeavour field, two different sites located above different distinct discharge zones (as indicated by magnetic studies) yield a high and a low permeability. The permeability of layer 2B is not as well constrained as that of layer 2A, with possible values ranging from 10-14-10-12 m2. We note, however, that the variability in measured phase lags across hydrothermal fields is compatible with a uniform layer 2B permeability of ~10-13 m2. Using theoretical scalings for high-Rayleigh porous convection, we demonstrate that the permeability of layer 2B sets the "effective permeability" of the entire convective system, and therefore the efficiency of heat extraction through young oceanic crust. A uniform layer 2B permeability would thus reconcile the

  2. 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.

  3. Are the alteration halos of massive sulfide deposits syngenetic Evidence from U-Pb dating of hydrothermal rutile at the Kidd volcanic center, Abitibi subprovince, Canada

    SciTech Connect

    Schandl, E.S.; Davis, D.W.; Krogh, T.E. )

    1990-06-01

    The Kidd volcanic complex is composed of felsic volcanic and subvolcanic rocks of Archean age. Metasomatic events affecting the lithology of the Kidd volcanic complex include silicification, extensive CO{sub 2} metasomatism (carbonate), K-metasomatism (sericite-fuchsite), and chlorite and minor carbonate alterations. Petrographic evidence, supported by stable isotope and fluid inclusion studies, suggests that silicification and early carbonate alteration were synvolcanic, and therefore related to ore deposition. During subsequent extensive K-metasomatism, sericite precipitated in the rhyolite, and fuschsite precipitated in the ultramafic rocks. Although chlorite postdates K-metasomatism, the micas and chlorite are both found in anastomosing microfissures, commonly occupying the same set of fractures. Hydrothermal rutile formed by the breakdown of magnetite-ilmenite during K-metasomatism and chlorite alteration gives an age of 2624 {plus minus} 62 Ma (95% confidence level). It is therefore approximately 100 m.y. younger than syngenetic massive sulfide mineralization (2712 {plus minus} 2 Ma). Sulfide stringers within sericite and chlorite veins suggest some remobilization of the ores during these later events. This alteration assemblage, is identical to that found associated with many lode-gold deposits in the Superior province. Recent dating of micas and rutile associated with gold deposits in the Abitibi subprovince gives comparable ages to the rutile in the Kidd volcanic complex, which must therefore record a widespread, late hydrothermal event affecting mineralized rocks.

  4. Reactive transport modeling of hydrothermal circulation in oceanic crust: effect of anhydrite precipitation on the dynamics of submarine hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Yang, J.

    2009-12-01

    Hydrothermal fluid circulation represents an extremely efficient mechanism for the exchange of heat and matter between seawater and oceanic crust. Precipitation and dissolution of minerals associated with hydrothermal flow at ridge axes can alter the crustal porosity and permeability and hence influence the dynamics of hydrothermal systems. In this study, a fully coupled fluid flow, heat transfer and reactive mass transport model was developed using TOUGHREACT to evaluate the role of mineral precipitation and dissolution on the evolution of hydrothermal flow systems, with a particular attention focused on anhydrite precipitation upon heating of seawater in recharge zones and the resultant change in the crustal porosity and permeability. A series of numerical case studies were carried out to assess the effect of temperature and aqueous phase inflow concentrations on the reactive geochemical system. The impact of chemically induced porosity and permeability changes on the dynamics of hydrothermal systems was also addressed.

  5. Hydrothermal alteration related to a deep mantle source controlled by a Cambrian intracontinental strike-slip fault: Evidence for the Meruoca felsic intrusion associated with the Transbraziliano Lineament, Northeastern Brazil

    NASA Astrophysics Data System (ADS)

    Santos, Roberto Ventura; Oliveira, Claudinei Gouveia de; Parente, Clóvis Vaz; Garcia, Maria da Glória Motta; Dantas, Elton Luis

    2013-04-01

    One of the most prominent geological structures in Borborema Province, northeast Brazil, is the Transbraziliano Lineament that crosscuts most of the South American Platform and was active at least until the Devonian. This continental structure is responsible for the formation of rift and pull-apart basins in Northeastern Brazil, most of which filled with volcanic and continental sedimentary rocks (Parente et al., 2004). In the region of Sobral, Ceará State, this same continental structure controlled the intrusion of the Meruoca pluton and the formation of the Jaibaras Basin, which is bounded by strike-slip shear zones. Hydrothermal alterations seem to have been pervasive in Meruoca, as indicated by disturbances in both the Rb-Sr and U-Pb systems (Sial et al., 1981; Fetter, 1999) and by the large dispersion of anisotropic magnetic susceptibility (AMS) (Archanjo et al., 2009). In this paper, we address the origin of the hydrothermal fluids that affected the borders of the Meruoca batholith and their relationship with the activity of the Transbraziliano Lineament. These fluids were responsible for carbonate veins and Fe-Cu mineral concentrations that are commonly found associated with hydrothermally altered breccias. The carbon and oxygen isotope composition of these carbonate veins suggest that they may be related to CO2-bearing mantle-derived fluids that were channelized by the Transbraziliano Lineament. Based on oxygen isotopes, we argue that Fe-Cu concentrations may have formed in isotope equilibrium with the rhyolitic rocks at temperatures between 500 and 560 °C. This scenario points to magmatism as the main process in the formation of these rocks. We also report a K-Ar age of 530 ± 12 Ma for muscovite associated with the last ductile event that affected the Sobral-Pedro II Shear Zone and a U-Pb age of 540.8 ± 5.1 Ma for the Meruoca pluton. We further suggest that this granite is a late-kinematic intrusion that is most likely associated with the Parapu

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

    USGS Publications Warehouse

    Berger, B.R.; Henley, R.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. ?? 2010.

  7. Element distribution is altered in a zone surrounding human glioblastoma multiforme.

    PubMed

    Dehnhardt, Markus; Zoriy, Myroslav V; Khan, Zahidul; Reifenberger, Guido; Ekström, Tomas J; Sabine Becker, J; Zilles, Karl; Bauer, Andreas

    2008-01-01

    Recent data indicate that A(1) adenosine receptor (A(1)AR) density is increased in a zone surrounding human and experimental gliomas. On the contrary, tumor tissue and adjacent brain tissue show low to intermediate A(1)AR densities. In order to assess whether changes in A(1)AR expression are indicating further processes of a chemical reorganization of the peritumoral zone, we investigated element concentrations and distribution patterns of copper and zinc in six human glioblastoma multiforme (GBM) specimens by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Uranium and lead were used as external standards. Copper and zinc levels were increased in a peritumoral zone corresponding to the region of elevated A(1)AR density. They showed a lower density in the solid tumor in comparison to surrounding brain tissue, although the cellular density was higher within GBM. Our findings suggest that the immediate vicinity of GBM is characterized by increased levels of copper and zinc supporting the view that higher A(1)AR density surrounding GBM is not an isolated alteration of peritumoral tissue but an indicator of complex changes in the vicinity of infiltrative tumors. Further research is needed to explore the pathophysiological consequences of altered peritumoral element distribution. PMID:18319136

  8. Thermo-physical rock properties and the impact of advancing hydrothermal alteration - A case study from the Tauhara geothermal field, New Zealand

    NASA Astrophysics Data System (ADS)

    Mielke, Philipp; Nehler, Mathias; Bignall, Greg; Sass, Ingo

    2015-08-01

    The thermo-physical rock properties density, porosity, matrix permeability, thermal conductivity and specific heat capacity of 418 orientated rock plugs cut from 233 cores recovered from geothermal investigation wells THM12, THM13, THM14, THM17, THM18, THM19, and TH18 at the Tauhara geothermal field, New Zealand were measured and a statistical database was set up. The lithotype of each sample was classified, and the hydrothermal alteration rank and intensity was determined by optical microscopy. The hydrothermal clays (typically smectite, smectite-illite, illite) were analysed by the methylene blue dye adsorption test and short wave infrared spectroscopy. Investigated stratigraphic units are the Huka Falls Formation with its sub members upper, middle and lower Huka Falls Formation, the Wairora Formation, Spa Andesite and its associated breccias, and Racetrack rhyolite and its associated breccias. Lithotypes are clay-altered tuff and intercalated mudstone/siltstone (cap rock for the Tauhara geothermal system); tuffaceous sandstones, sedimentary and pyroclastic breccias and pumiceous ash tuff (reservoir-hosting units); and rhyolitic and andesitic lavas, and their associated breccias. The obtained rock property data indicate a common porosity range of 30% to 45% for sediments, volcaniclastics and lava breccias, an average of 10% for andesite lava, and 39% for rhyolite lava. Matrix permeability of mudstone, siltstone, breccias and lavas is commonly < 1 mD, while sandstone, tuff and brecciated lavas have two to three orders of magnitude higher permeabilities. Both porosity and permeability decrease with depth. Thermal conductivity decreases with increasing porosity, and is similar for most lithotypes (0.7 W m- 1 K- 1 to 1 W m- 1 K- 1), while lavas have higher values (0.9 W m- 1 K- 1 to 1.4 W m- 1 K- 1). Specific heat capacity is similar for all lithotypes (0.6 kJ kg- 1 K- 1 to 0.8 kJ kg- 1 K- 1). Advancing hydrothermal alteration decreases the porosity of sandstone and

  9. A conspicuous clay ovoid in Nakhla: evidence for subsurface hydrothermal alteration on Mars with implications for astrobiology.

    PubMed

    Chatzitheodoridis, Elias; Haigh, Sarah; Lyon, Ian

    2014-08-01

    Abstract A conspicuous biomorphic ovoid structure has been discovered in the Nakhla martian meteorite, made of nanocrystalline iron-rich saponitic clay and amorphous material. The ovoid is indigenous to Nakhla and occurs within a late-formed amorphous mesostasis region of rhyolitic composition that is interstitial to two clinopyroxene grains with Al-rich rims, and contains acicular apatite crystals, olivine, sulfides, Ti-rich magnetite, and a new mineral of the rhoenite group. To infer the origin of the ovoid, a large set of analytical tools was employed, including scanning electron microscopy and backscattered electron imaging, wavelength-dispersive X-ray analysis, X-ray mapping, Raman spectroscopy, time-of-flight secondary ion mass spectrometry analysis, high-resolution transmission electron microscope imaging, and atomic force microscope topographic mapping. The concentric wall of the ovoid surrounds an originally hollow volume and exhibits internal layering of contrasting nanotextures but uniform chemical composition, and likely inherited its overall shape from a preexisting vesicle in the mesostasis glass. A final fibrous layer of Fe-rich phases blankets the interior surfaces of the ovoid wall structure. There is evidence that the parent rock of Nakhla has undergone a shock event from a nearby bolide impact that melted the rims of pyroxene and the interstitial matter and initiated an igneous hydrothermal system of rapidly cooling fluids, which were progressively mixed with fluids from the melted permafrost. Sharp temperature gradients were responsible for the crystallization of Al-rich clinopyroxene rims, rhoenite, acicular apatites, and the quenching of the mesostasis glass and the vesicle. During the formation of the ovoid structure, episodic fluid infiltration events resulted in the precipitation of saponite rinds around the vesicle walls, altered pyrrhotite to marcasite, and then isolated the ovoid wall structure from the rest of the system by depositing a

  10. The Yatela gold deposit in Mali, West Africa: The final product of a long-lived history of hydrothermal alteration and weathering

    NASA Astrophysics Data System (ADS)

    Masurel, Quentin; Miller, John; Hein, Kim A. A.; Hanssen, Eric; Thébaud, Nicolas; Ulrich, Stanislav; Kaisin, Jean; Tessougue, Samuel

    2016-01-01

    The Yatela gold deposit is located in the Kédougou-Kénieba inlier (KKI), a window of ca. 2200-2050 Ma rocks that are exposed in eastern Senegal and western Mali. The geology of the KKI differs from other Paleoproterozoic granite-greenstone belts and sedimentary basins by the abundance of carbonate rocks. The Yatela deposit occurs within 8 km of the regional-scale Senegal-Mali Shear Zone. Country rocks in the Yatela region have been subjected to polycyclic deformation and regional greenschist-facies metamorphism. A syn-kinematic diorite stock has intruded the metasedimentary sequences in the open pit and is associated with a hornblende-hornfels contact aureole. Field relationships and micro-textural data indicate that the primary gold mineralisation is shear-hosted. The similar relative timing and structural setting between the Yatela primary gold mineralisation and other world-class deposits in the region (e.g., Loulo, Lawrence et al., 2013a; Massawa, Treloar et al., 2014; Sadiola Hill, Masurel et al., in press) suggest that regional orogenic gold mineralisation occurred during a period of transcurrent tectonics, after the cessation of regional compressional deformation. The primary gold mineralisation at Yatela, however, is low-grade and sub-economic. It is hosted by marbles and, to a lesser extent, diorite. The primary ore is pyrite-rich, with abundant chalcopyrite, minor arsenopyrite and accessory Zn-Pb-Sb-Fe-Ag-Co-Ni-bearing mineral species. Post-Birimian surficial dissolution of hydrothermally altered and mineralised host marbles resulted in the creation of troughs, which were draped and infilled with a ferruginous dissolution residue enriched in gold. This auriferous residuum formed the economic resource mined at Yatela until decommissioning in 2013. The Yatela gold deposit is unique with respect to mineralisation types encountered in West Africa because an auriferous residuum of economic interest (>1 Moz) derives from an underlying sub-economic Birimian

  11. Hydrothermal alteration and tectonic setting of intrusive rocks from East Brawley, Imperial Valley: an application of petrology to geothermal reservoir analysis

    SciTech Connect

    Keskinen, M.; Sternfeld, J.

    1982-01-01

    A geothermal well near East Brawley intersected a series of thin (3 to 35m) diabasic to dioritic intrusives. The petrology and chemistry of these meta-igneous rocks can provide insight into the thermal and fluid chemical characteristics of the reservoir and into the processes of magma generation at depth. A description of the rock types and their hydrothermal alteration is presented in order to increase the petrologic data base relating to this important facet of the geothermal potential of the Salton Trough and to provide a case study illustrating how detailed petrologic examination of well cuttings can provide important input in the construction of a geothermal reservoir model.

  12. Detection and mapping of hydrothermally altered rocks in the vicinity of the Comstock Lode, Virginia Range, Nevada, using enhanced Landsat images

    USGS Publications Warehouse

    Ashley, Roger P.; Goetz, A.F.H.; Rowan, L.C.; Abrams, M.J.

    1979-01-01

    The Virginia Range, immediately southeast of Reno, Nev., consists mainly of flows, breccias, and turfs of Miocene age. Most of these volcanic rocks are of intermediate composition; rhyodacite is the most common rock type. Basalt, rhyolite and rhyolite tuff, and tuffaceous sedimentary rocks of Miocene and Pliocene age also cover substantial areas in the range. Pre-Tertiary metasedimentary, metavolcanic, and granitic rocks are exposed in scattered inliers, mostly along the southern and eastern margins of the range. Several large areas and many small areas within the volcanic pile were subjected to hydrothermal alteration during and after the period of intermediate volcanic activity. Economic precious metal mineralization is spatially and temporally associated with the hydrothermal alteration in several areas. The most important deposit is the Comstock Lode, which produced 192 million troy ounces of silver and 8.3 million troy ounces of gold from epithermal veins (Bonham, 1969). The hydrothermally altered rocks include silicified, advanced argillic, montmorillonite-bearing argillic, and propylitic types. The first three types typically contain pyrite, and some propylitic rocks contain pyrite as well. Supergene oxidation of these pyritic rocks produces limonitic bleached rocks. The term 'limonite,' as used here, refers to any combination of the minerals hematite, goethite, and Jarosite. Where vegetation cover is sparse to moderate, these limonitic rocks are readily identified on Landsat images enhanced by the color-ratio composite technique developed by Rowan and others (1974), so the altered areas can be mapped. About 30 percent tree cover (here mainly pinyon pine) is sufficient to change the spectral signature of individual picture elements (pixels) enough so that limonitic materials can no longer be uniquely identified. As in all other areas where this technique has been applied, limonitic unaltered rocks with intermediate to high albedos have the same appearance on

  13. Metalliferous sediments from Eolo Seamount (Tyrrhenian Sea): Hydrothermal deposition and re-deposition in a zone of oxygen depletion

    USGS Publications Warehouse

    Dekov, V.M.; Kamenov, George D.; Savelli, C.; Stummeyer, Jens; Thiry, M.; Shanks, Wayne C.; Willingham, A.L.; Boycheva, T.B.; Rochette, P.; Kuzmann, E.; Fortin, D.; Vertes, A.

    2009-01-01

    A sediment core taken from the south-east slope of the Eolo Seamount is composed of alternating red-brown and light-brown to bluish-grey layers with signs of re-deposition in the middle-upper section. The red-brown layers are Fe-rich metalliferous sediments formed as a result of low-temperature (??? 77????C) hydrothermal discharge, whereas the bluish-grey layers most probably originated from background sedimentation of Al-rich detrital material. The metalliferous layers are composed mainly of Si-rich goethite containing some Al. Co-precipitation of hydrothermally released SiO44- and Fe2+ as amorphous or poorly crystalline Fe-Si-oxyhydroxides explains the high Si concentration in goethite. The elevated Al content of the goethite is fairly unusual, but reflects the extremely high background Al content of the Tyrrhenian seawater due to the high eolian terrigenous flux from the Sahara desert. The Sr and Nd isotope data suggest that the Eolo metalliferous sediments are the product of a 3-component mixture: hydrothermal fluid, seawater, and detrital material (Saharan dust and Aeolian Arc material). The enrichment in Fe, P, As, Mo, Cd, Be, Sb, W, Y, V, depletion in REE and transition elements (Cu, Co, Ni, Zn) and the REE distribution patterns support the low-temperature hydrothermal deposition of the metalliferous layers. The hydrothermal field is located in a seawater layer of relative O2 depletion, which led to a significant fractionation of the hydrothermally emitted Fe and Mn. Fe-oxyhydroxides precipitated immediately around the vents whereas Mn stayed in solution longer and the Mn-oxides precipitated higher up on the seamount slope in seawater with relatively higher O2 levels. High seismic activity led to sediment re-deposition and slumping of the Mn-rich layers down slope and mixing with the Fe-rich layers. ?? 2009 Elsevier B.V. All rights reserved.

  14. Generation of felsic melts within fast-spreading oceanic crust: Experimental partial melting of hydrothermally altered sheeted dike

    NASA Astrophysics Data System (ADS)

    Fischer, L. A.; Erdmann, M.; France, L.; Deloule, E.; Koepke, J.

    2013-12-01

    In recent oceanic crust and in ophiolites, felsic lithologies are observed. Different processes, like fractional crystallization of MORB and partial melting of mafic rocks are discussed to form these lithologies. Partial melting is expected as a major process in forming felsic lithologies at the base of the sheeted dike complex of fast-spreading ridges, where the axial melt lens is assumed to be located directly beneath the sheeted dikes.It is widely accepted that this melt lens has the potential to trigger partial melting of mafic lithologies at the gabbro/dike transition zone. In this experimental study, the influence of partial melting on the generation of felsic lithologies is examined. Therefore, partial melting experiments at a pressure of 100 MPa were performed. As starting material, a natural basalt from the IODP (Integrated Ocean Drilling Program) drilling at Site 1256 (equatorial East Pacific Rise) was chosen, which is representative for the lower sheeted dike complex. It is characterized as a moderately altered dolerite containing plagioclase (An50-57), clinopyroxene (Mg# 0.55-0.60) and quartz, with chlorite as secondary phase; sulfides and Fe-Ti-oxides are present as accessory minerals. The partial melting experiments were conducted in an H2-controlled IHPV at the Institute of Mineralogy in Hanover, Germany. To investigate the evolution of the partial melts, different experiments were performed at temperatures between 1030°C and 910°C and a constant pressure of 100 MPa. All experiments were water saturated leading to a fO2 corresponding to QFM +1 (QFM = quartz-fayalite-magnetite oxygen buffer). This is slightly more oxidized than MORB crystallization due to the influence of a hydrous fluid which generally increases the oxygen activity. The experimental products were analyzed using electron microprobe for major elements, and a SIMS (CRPG Nancy, France) for trace elements. We present here our first results on phase relations and mineral compositions

  15. An experimental study on felsic rock artificial seawater interaction: implications for hydrothermal alteration and sulfate formation in the Kuroko mining area of Japan

    NASA Astrophysics Data System (ADS)

    Ogawa, Yasumasa; Shikazono, Naotatsu; Ishiyama, Daizo; Sato, Hinako; Mizuta, Toshio

    2005-03-01

    Experimental studies on the interactions between artificial seawater (ASW) and fresh rhyolite, perlite and weakly altered dacitic tuff containing a small amount of smectite suggest changing cation transfer during smectite-forming processes. Initially, dissolution of K from the rocks accompanies incorporation of Mg and Ca from ASW during both earlier (devitrification stage) and later smectite formation, whereas Ca incorporated with early smectite formation redissolves with progressive reaction. Barium mobility increases toward the later smectite-forming reactions. Therefore, the large amounts of barite, anhydrite and gypsum in Kuroko ore deposits are considered to have precipitated from hydrothermal solutions derived from the interaction with previously altered felsic rocks during late smectite formation, rather than by the reaction with fresh felsic rocks.

  16. The hydrothermal alteration and contact metamorphism on the tonalite and volcanics of the Komahashi-Daini Seamount, northern Kyushu-Palau Ridge

    NASA Astrophysics Data System (ADS)

    Haraguchi, S.; Ishii, T.; Li, Y.; Kato, Y.

    2011-12-01

    , albite and quartz in the altered plutonic rocks indicate alteration under 150 to 200°C or higher than this temperature. We considered this alteration was caused by hydrothermal circulation between intrusive rock and host rocks. We also considered that the volcanic rocks had effected under contact metamorphism because these volcanics exhibits prominent re-crystallization. The mineral assemblage of epidote, chlorite and albite in the altered volcanic rocks indicate alteration under higher temperature of plutonic rocks. We considered that this secondary mineralization is the effect of contact metamorphism by intrusion of tonalitic magma. Volcanics were also affected under hydrothermal alteration by fluid circulation between intrusion and host rock. Therefore, we considered that these volcanics are the products of arc volcanism before rifting activity, assumed to earliest stage volcanics of the KPR. The earliest stage of arc volcanism in the KPR was only reported from the Palau Islands. Therefore, this volcanics is important to indicate the environment of early stage arc volcanism in the KPR.

  17. Quantitative impact of hydrothermal alteration on electrical resistivity in geothermal systems from a joint analysis of laboratory measurements and borehole data in Krafla area, N-E Iceland

    NASA Astrophysics Data System (ADS)

    Lévy, Léa; Páll Hersir, Gylfi; Flóvenz, Ólafur; Gibert, Benoit; Pézard, Philippe; Sigmundsson, Freysteinn; Briole, Pierre

    2016-04-01

    Rock permeability and fluid temperature are the two most decisive factors for a successful geothermal drilling. While those parameters are only measured from drilling, they might be estimated on the basis of their impact on electrical resistivity that might be imaged from surface soundings, for example through TEM (Transient Electro Magnetic) down to one km depth. The electrical conductivity of reservoir rocks is the sum of a volume term depending on fluid parameters and a surface term related to rock alteration. Understanding the link between electrical resistivity and geothermal key parameters requires the knowledge of hydrothermal alteration and its petrophysical signature with the Cation Exchange Capacity (CEC). Fluid-rock interactions related to hydrothermal circulation trigger the precipitation of alteration minerals, which are both witnesses of the temperature at the time of reaction and new paths for the electrical current. Alteration minerals include zeolites, smectites, chlorites, epidotes and amphiboles among which low temperatures parageneses are often the most conductive. The CEC of these mineral phases contributes to account for surface conductivity occuring at the water-rock interface. In cooling geothermal systems, these minerals constitute in petrophysical terms and from surface electrical conduction a memory of the equilibrium phase revealed from electrical probing at all scales. The qualitative impact of alteration minerals on resistivity structure has been studied over the years in the Icelandic geothermal context. In this work, the CEC impact on pore surfaces electrical conductivity is studied quantitatively at the borehole scale, where several types of volcanic rocks are mixed together, with various degrees of alteration and porosity. Five boreholes located within a few km at the Krafla volcano, Northeast Iceland, constitute the basis for this study. The deepest and reference hole, KJ-18, provides cuttings of rock and logging data down to 2215

  18. Description and validation of an automated methodology for mapping mineralogy, vegetation, and hydrothermal alteration type from ASTER satellite imagery with examples from the San Juan Mountains, Colorado

    USGS Publications Warehouse

    Rockwell, Barnaby W.

    2012-01-01

    The efficacy of airborne spectroscopic, or "hyperspectral," remote sensing for geoenvironmental watershed evaluations and deposit-scale mapping of exposed mineral deposits has been demonstrated. However, the acquisition, processing, and analysis of such airborne data at regional and national scales can be time and cost prohibitive. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor carried by the NASA Earth Observing System Terra satellite was designed for mineral mapping and the acquired data can be efficiently used to generate uniform mineral maps over very large areas. Multispectral remote sensing data acquired by the ASTER sensor were analyzed to identify and map minerals, mineral groups, hydrothermal alteration types, and vegetation groups in the western San Juan Mountains, Colorado, including the Silverton and Lake City calderas. This mapping was performed in support of multidisciplinary studies involving the predictive modeling of surface water geochemistry at watershed and regional scales. Detailed maps of minerals, vegetation groups, and water were produced from an ASTER scene using spectroscopic, expert system-based analysis techniques which have been previously described. New methodologies are presented for the modeling of hydrothermal alteration type based on the Boolean combination of the detailed mineral maps, and for the entirely automated mapping of alteration types, mineral groups, and green vegetation. Results of these methodologies are compared with the more detailed maps and with previously published mineral mapping results derived from analysis of high-resolution spectroscopic data acquired by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) sensor. Such comparisons are also presented for other mineralized and (or) altered areas including the Goldfield and Cuprite mining districts, Nevada and the central Marysvale volcanic field, Wah Wah Mountains, and San Francisco Mountains, Utah. The automated

  19. Can Low Water/Rock Hydrothermal Alteration of Impact Materials Explain the Rock Component of the Martian Soil?

    NASA Technical Reports Server (NTRS)

    Nelson, M. J.; Newsom, H. E.

    2003-01-01

    The martian regolith is a globally homogenized product of chemical and aeolian weathering processes. The soil is thought to consist of a rock component, with lesser amounts of mobile elements (Ca, Na, and K) than a presumed protolith, and a salt or mobile element component enriched in sulfur and chlorine. In this study we consider the contributions of hydrothermal processes to the origin of the rock component of the martian soil.

  20. Remote sensing detection of gold related alteration zones in Um Rus area, Central Eastern Desert of Egypt

    NASA Astrophysics Data System (ADS)

    Amer, Reda; Kusky, Timothy; El Mezayen, Ahmed

    2012-01-01

    Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Phased Array L-band Synthetic Aperture Radar (PALSAR) images covering the Um Rus area in the Central Eastern Desert of Egypt were evaluated for mapping geologic structure, lithology, and gold-related alteration zones. The study area is covered by Pan-African basement rocks including gabbro and granodiorite intruded into a variable mixture of metavolcanics and metasediments. The first three principal component analyses (PCA1, PCA2, PCA3) in a Red-Green-Blue (RGB) of the visible through shortwave-infrared (VNIR + SWIR) ASTER bands enabled the discrimination between lithological units. The results show that ASTER band ratios ((2 + 4)/3, (5 + 7)/6, (7 + 9)/8) in RGB identifies the lithological units and discriminates the granodiorite very well from the adjacent rock units.The granodiorites are dissected by gold-bearing quartz veins surrounded by alteration zones. The microscopic examination of samples collected from the alteration zones shows sericitic and argillic alteration zones. The Spectral Angle Mapper (SAM) and Spectral Information Divergence (SID) supervised classification methods were applied using the reference spectra of the USGS spectral library. The results show that these classification methods are capable of mapping the alteration zones as indicated by field verification work. The PALSAR image was enhanced for fracture mapping using the second moment co-occurrence filter. Overlying extracted faults and alteration zone classification images show that the N30E and N-S fractures represent potential zones for gold exploration. It is concluded that the proposed methods can be used as a powerful tool for ore deposit exploration.

  1. Petrochemistry and hydrothermal alteration within the Tyrone Igneous Complex, Northern Ireland: implications for VMS mineralization in the British and Irish Caledonides

    NASA Astrophysics Data System (ADS)

    Hollis, Steven P.; Roberts, Stephen; Earls, Garth; Herrington, Richard; Cooper, Mark R.; Piercey, Stephen J.; Archibald, Sandy M.; Moloney, Martin

    2014-06-01

    Although volcanogenic massive sulfide (VMS) deposits can form within a wide variety of rift-related tectonic environments, most are preserved within suprasubduction affinity crust related to ocean closure. In stark contrast to the VMS-rich Appalachian sector of the Grampian-Taconic orogeny, VMS mineralization is rare in the peri-Laurentian British and Irish Caledonides. Economic peri-Gondwanan affinity deposits are limited to Avoca and Parys Mountain. The Tyrone Igneous Complex of Northern Ireland represents a ca. 484-464 Ma peri-Laurentian affinity arc-ophiolite complex and a possible broad correlative of the Buchans-Robert's Arm belt of Newfoundland, host to some of the most metal-rich VMS deposits globally. Stratigraphic horizons prospective for VMS mineralization in the Tyrone Igneous Complex are associated with rift-related magmatism, hydrothermal alteration, synvolcanic faults, and high-level subvolcanic intrusions (gabbro, diorite, and/or tonalite). Locally intense hydrothermal alteration is characterized by Na-depletion, elevated SiO2, MgO, Ba/Sr, Bi, Sb, chlorite-carbonate-pyrite alteration index (CCPI) and Hashimoto alteration index (AI) values. Rift-related mafic lavas typically occur in the hanging wall sequences to base and precious metal mineralization, closely associated with ironstones and/or argillaceous sedimentary rocks representing low temperature hydrothermal venting and volcanic quiescence. In the ca. 475 Ma pre-collisional, calc-alkaline lower Tyrone Volcanic Group rift-related magmatism is characterized by abundant non-arc type Fe-Ti-rich eMORB, island-arc tholeiite, and low-Zr tholeiitic rhyolite breccias. These petrochemical characteristics are typical of units associated with VMS mineralization in bimodal mafic, primitive post-Archean arc terranes. Following arc-accretion at ca. 470 Ma, late rifting in the ensialic upper Tyrone Volcanic Group is dominated by OIB-like, subalkaline to alkali basalt and A-type, high-Zr rhyolites. These units

  2. Isotopically-diverse rhyolites coeval with the Columbia River Basalts Large Igneous Province: evidence for widespread mantle-plume driven hydrothermal alteration and remelting of the crust

    NASA Astrophysics Data System (ADS)

    Colon, D.; Bindeman, I. N.; Stern, R. A.; Fisher, C. M.

    2014-12-01

    The formation of the most recent flood basalt province on Earth, the Columbia River Flood Basalts (CRBs) of the northwestern USA, was accompanied by eruptions of several thousand km3 of rhyolite in a short time window from 16.7 to 15 Ma. These rhyolites span from low (+1‰) to high (+11‰) in δ18O values as recorded by major phenocrysts, and alteration-resistant zircons within each rhyolite commonly display diversity of up to 6‰ δ18O, indicative of batch assembly prior to eruption. Significant variation in ɛHf also exists in zircons, ranging from -39 to 0 in rhyolites erupted through the North American cratonic crust, and from -1 to +9 in rhyolites erupted through accreted oceanic terranes to the east of the Sr87/86Sr = 0.706 line. This isotopic diversity cannot be accounted for by fractionation of a CRB-like parent magma, demonstrating that the syn-CRB rhyolites must have been derived from melting of the crust. Abundant low-δ18Omelt values among syn-CRB rhyolites further constrains this crustal melting to shallow depths of 5-10 km, due to the shallow depths of the necessary hydrothermal alteration of the protolith. By contrast, high-δ18O rhyolites must have been formed by remelting of sedimentary or metasedimentary rocks. Low-δ18O rhyolites are also most common in the vicinity of the crustal suture between the thick lithosphere of the Archean craton and the thin lithosphere of the accreted terranes. Thermomechanical modeling suggests that this contrast concentrates crustal heating and deformation, creating pathways for meteoric water to penetrate the crust and cause extensive hydrothermal alteration less than 1 Ma before those same rocks remelt to form low-δ18O rhyolites. Finally, we suggest that this extensive crustal hydrothermal alteration and melting may be typical of continental flood basalt provinces world wide, and particularly when there is syn-volcanic extension.

  3. Progressive Dehydration and Re-equilibration of Slab Lithologies During Subduction: Mechanism For Recycling of Heavy, Hydrothermally-Altered Crust and Mantle Derived Stable Isotopic Signatures into the Deep Mantle

    NASA Astrophysics Data System (ADS)

    Dixon, J. E.; Simons, K.; Kingsley, R. H.; le Roux, P. J.; Ryan, J. G.

    2012-12-01

    , previously-dehydrated materials to wedge-like values as the slab is subducted. Slab-derived materials, be they direct samples of the slab, shallowly-released slab fluids entrained in subduction channel serpentines, or incipient melts of slab lithologies formed below the zone of major dehydration, will preserve heavy isotopic values derived ultimately from hydrothermally-altered crust and mantle. We present a model linking the initial volatile content of the slab, the conditions and extent of dehydration, and the amount of continental material transported below the zone of arc magma generation to the thermal parameters of the slab.

  4. Deoxygenation alters bacterial diversity and community composition in the ocean’s largest oxygen minimum zone

    NASA Astrophysics Data System (ADS)

    Beman, J. Michael; Carolan, Molly T.

    2013-10-01

    Oceanic oxygen minimum zones (OMZs) have a central role in biogeochemical cycles and are expanding as a consequence of climate change, yet how deoxygenation will affect the microbial communities that control these cycles is unclear. Here we sample across dissolved oxygen gradients in the oceans’ largest OMZ and show that bacterial richness displays a unimodal pattern with decreasing dissolved oxygen, reaching maximum values on the edge of the OMZ and decreasing within it. Rare groups on the OMZ margin are abundant at lower dissolved oxygen concentrations, including sulphur-cycling Chromatiales, for which 16S rRNA was amplified from extracted RNA. Microbial species distribution models accurately replicate community patterns based on multivariate environmental data, demonstrate likely changes in distributions and diversity in the eastern tropical North Pacific Ocean, and highlight the sensitivity of key bacterial groups to deoxygenation. Through these mechanisms, OMZ expansion may alter microbial composition, competition, diversity and function, all of which have implications for biogeochemical cycling in OMZs.

  5. A Geochemical and Mineralogical Model for Formation of Layered Sulfate Deposits at Meridiani Planum by Hydrothermal Acid-sulfate Alteration of Pyroclastic Basalt

    NASA Astrophysics Data System (ADS)

    McCollom, T. M.; Hynek, B. M.

    2012-12-01

    The Mars Exploration Rover (MER) Opportunity has extensively characterized sulfate-rich, hematite-bearing bedrock exposed at Meridiani Planum, Mars. Based on various measurements, the mineral composition of the bedrocks has been interpreted to include: amorphous silica/glass/phyllosilicates, Mg-, Ca-, and Fe-bearing sulfates including jarosite, minor amounts of igneous phases including plagioclase, pyroxene, olivine, and magnetite, and hematite [1,2]. Chemically, the bedrocks closely resemble the composition of pristine martian basalt with addition of S and O, and minor variations of Mg and Cl with depth [3,4]. Based on these and other observations, the MER team has proposed that the bedrocks represent chemically altered siliciclastic sediments combined with sulfate salts formed by evaporation of sulfate-bearing fluids, modified by transport and multiple stages of infiltrating groundwater [3,5]. Several alternative scenarios have been proposed for the origin of the rocks including large impacts [6], evaporating glacial deposits [7], acid-fog alteration [8], and hydrothermal acid-sulfate alteration of basalt [4]. In order to further evaluate the potential contribution of hydrothermal proceeses to the deposits, we performed numerical geochemical models of acid-sulfate alteration of martian basalt based on constraints provided by recent laboratory experiments. Experimental studies of alteration of basalt conducted in our lab [9] indicate that the initial stages of acid-sulfate alteration of pyroclastic basalt are characterized by rapid decomposition of igneous crystalline phases including plagioclase, pyroxene, and olivine, while the glass (and igneous phases protected within the glass) remain unreactive. Elements released by dissolving minerals are precipitated primarily as amorphous silica and Ca-, Al-, Fe- and Mg-bearing sulfates, while precipitation of phyllosilicates and Fe-oxides/oxyhydroxides (FeOx) is kinetically inhibited. Based on these constraints, models

  6. 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. PMID:20624060

  7. Subglacial Hydrothermal Alteration Minerals in Jökulhlaup Deposits of Southern Iceland, with Implications for Detecting Past or Present Habitable Environments on Mars

    NASA Astrophysics Data System (ADS)

    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 (< μm 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°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.

  8. Alteration of chaotic advection in blood flow around partial blockage zone: Role of hematocrit concentration

    NASA Astrophysics Data System (ADS)

    Maiti, Soumyabrata; Chaudhury, Kaustav; DasGupta, Debabrata; Chakraborty, Suman

    2013-01-01

    Spatial distributions of particles carried by blood exhibit complex filamentary pattern under the combined effects of geometrical irregularities of the blood vessels and pulsating pumping by the heart. This signifies the existence of so called chaotic advection. In the present article, we argue that the understanding of such pathologically triggered chaotic advection is incomplete without giving due consideration to a major constituent of blood: abundant presence of red blood cells quantified by the hematocrit (HCT) concentration. We show that the hematocrit concentration in blood cells can alter the filamentary structures of the spatial distribution of advected particles in an intriguing manner. Our results reveal that there primarily are two major impacts of HCT concentrations towards dictating the chaotic dynamics of blood flow: changing the zone of influence of chaotic mixing and determining the enhancement of residence time of the advected particles away from the wall. This, in turn, may alter the extent of activation of platelets or other reactive biological entities, bearing immense consequence towards dictating the biophysical mechanisms behind possible life-threatening diseases originating in the circulatory system.

  9. Vent fluid chemistry of the Rainbow hydrothermal system (36°N, MAR): Phase equilibria and in situ pH controls on subseafloor alteration processes

    NASA Astrophysics Data System (ADS)

    Seyfried, W. E., Jr.; Pester, Nicholas J.; Ding, Kang; Rough, Mikaella

    2011-03-01

    -fluid equilibria. Indeed, the predicted correlation between dissolved silica and H 2 defines a trend that is in good agreement with vent fluid data from Rainbow and other high-temperature ultramafic-hosted hydrothermal systems. We speculate that the moderate concentrations of dissolved silica in vent fluids from these systems result from hydrothermal alteration of plagioclase and olivine in the form of subsurface gabbroic intrusions, which, in turn are variably replaced by chlorite + magnetite + talc ± tremolite, with important implications for pH lowering, dissolved sulfide concentrations, and metal mobility.

  10. Surface hydrothermal minerals and their distribution in the Tengchong geothermal area, China

    SciTech Connect

    Meixiang, Z.; Wei, T.

    1987-01-01

    In the active hydrothermal areas of Tengchong there is widespread evidence that hydrothermal minerals are deposited directly from the geothermal fluid or from water-rock interactions. X-ray powder diffraction, electron microprobe analyses and classical optical methods were used to identify these hydrothermal minerals. Sulfates (gypsum, alunite, alunogen, halotrichite, etc.), carbonates (calcite, trona, thermonatrite, etc.), clay minerals (kaolinite, illite-smectite mixed layer mineral, etc.) and silica minerals (opal, chalcedony, etc.) are the dominant phases. Native sulfur, pyrite, marcasite and aragonite are next in order of abundance. Some chabazite, analcime, pitchblende, coffinite, hematite, thenardite, rozenite, coquimbite, manganocalcite and rhodochrosite is also present. Although travertine and efflorescences, along with carbonates and simple sulfates, are widespread in the low-temperature hydrothermal areas, siliceous sinters and hydrothermal altered minerals, such as clay minerals, zeolites and efflorescences with complex sulfates containing Fe, Al, are only found in a few high-temperature hydrothermal areas, such as in the Hot Sea and the Ruidian hydrothermal areas. Most of the wall rock was intensely altered by geothermal fluid in the Hot Sea and Ruidian, zoning in the characteristic feature of the altered minerals within the Hot Sea. Pitchblende, coffinite, pyrite, marcasite and hematite, which are all of hydrothermal genesis, as well as the sulfate with Al and Fe, seem to be the result of water-rock interaction.

  11. Use of airborne imaging spectrometer data to map minerals associated with hydrothermally altered rocks in the northern grapevine mountains, Nevada, and California

    USGS Publications Warehouse

    Kruse, F.A.

    1988-01-01

    Three flightlines of Airborne Imaging Spectrometer (AIS) data, acquired over the northern Grapevine Mountains, Nevada, and California, were used to map minerals associated with hydrothermally altered rocks. The data were processed to remove vertical striping, normalized using an equal area normalization, and reduced to reflectance relative to an average spectrum derived from the data. An algorithm was developed to automatically calculate the absorption band parameters band position, band depth, and band width for the strongest absorption feature in each pixel. These parameters were mapped into an intensity, hue, saturation (IHS) color system to produce a single color image that summarized the absorption band information, This image was used to map areas of potential alteration based upon the predicted relationships between the color image and mineral absorption band. Individual AIS spectra for these areas were then examined to identify specific minerals. Two types of alteration were mapped with the AIS data. Areas of quartz-sericite-pyrite alteration were identified based upon a strong absorption feature near 2.21 ??m, a weak shoulder near 2.25 ??m, and a weak absorption band near 2.35 ??m caused by sericite (fine-grained muscovite). Areas of argillic alteration were defined based on the presence of montmorillonite, identified by a weak to moderate absorption feature near 2.21 ??m and the absence of the 2.35 ??m band. Montmorillonite could not be identified in mineral mixtures. Calcite and dolomite were identified based on sharp absorption features near 2.34 and 2.32 ??m, respectively. Areas of alteration identified using the AIS data corresponded well with areas mapped using field mapping, field reflectance spectra, and laboratory spectral measurements. ?? 1988.

  12. Rhyolite genesis at the Picabo Volcanic Center of the Snake River Plain: Progressive recycling of hydrothermally altered rhyolites revealed by high resolution analysis of individual zircons

    NASA Astrophysics Data System (ADS)

    Drew, D.; Bindeman, I. N.; Watts, K. E.; Schmitt, A. K.; McCurry, M. O.

    2012-12-01

    The Picabo eruptive center of the Snake River Plain (SRP) produced a series of normal and low δ18O rhyolites from 10.44 Ma to 6.62 Ma, providing the first evidence of progressive recycling of hydrothermally altered rhyolites during the formation of a caldera complex. In this study we present a characterization of ignimbrites and associated lavas based on U-Pb ages and δ18O compositions of individual zircon cores measured by ion microprobe, phenocryst δ18O values measured by laser fluorination, whole rock 87Sr/86Sr and 143Nd/144Nd compositions, and whole rock geochemistry. Our data define rhyolite genesis at the Picabo volcanic center through time and have implications for the transition between volcanic centers. Caldera complex evolution at Picabo began with eruption of the 10.44 ± 0.27 Ma Tuff of Arbon Valley (TAV), a chemically zoned unit with a normal δ18Omelt value (8.15‰), very high 87Sr/86Sr (up to 0.734430) and very low ɛNd (-18). Eruptions continued with the ~9.1 Ma Two-and-a-Half-Mile Rhyolite (Kellogg et al., 1988), a unit significant in that it has an even lower ɛNd than the TAV and a normal δ18Omelt value (8.10‰). This low ɛNd of -23, of the Two-and-a-Half-Mile Rhyolite, reveals that greater than 40% of Archean crust was assimilated. These normal δ18O eruptions were followed by a series of lower δ18O eruptions distinguishable by Sr and Nd isotopes and whole rock chemistry. The 8.25 ± 0.26 Ma Rhyolite of West Pocatello has the lowest δ18Omelt value (3.34‰) of these eruptions, and based on nearly identical age, 87Sr/86Sr, 143Nd/144Nd, and whole rock chemistry, we correlate it to a 1,000 m thick intracaldera tuff (present in the INEL drillcore). Along with a distinct decrease in δ18O, from the TAV to the Rhyolite of West Pocatello, there is a corresponding increase in δ18Ozircon heterogeneity from the TAV (1‰ variation) to the low δ18O units with the greatest δ18Ozircon diversity (up to 5‰). Although morphological evidence for

  13. Cu-Mn-Fe alloys and Mn-rich amphiboles in ancient copper slags from the Jabal Samran area, Saudi Arabia: With synopsis on chemistry of Fe-Mn(III) oxyhydroxides in alteration zones

    NASA Astrophysics Data System (ADS)

    Surour, Adel A.

    2015-01-01

    In the Jabal Samran area (western Saudi Arabia), secondary copper mineralization in a NE-trending shear zone in which the arc metavolcanic host rocks (dacite-rhyodacite) show conjugate fractures and extensive hydrothermal alteration and bleaching. The zones contain frequent Fe-Mn(III) oxyhydroxides (FeOH-MnOH) that resulted from oxidation of pyrite and Mn-bearing silicates. In the bleached part, the groundmass is represented by Fe-bearing interstratified illite-smectite with up to 4.02 wt% FeOt. FeOH-MnOH are pre-weathering phases formed by hydrothermal alteration in a submarine environment prior to uplifting. Five varieties of FeOH are distinguished, four of them are exclusively hydrothermal with ∼20 wt% H2O whereas the fifth contains ∼31-33 wt% H2O and might represent reworking of earlier hydrothermal FeOH phases by weathering. FeOH fills thin fractures in the form of veinlets and crenulated laminae or as a pseudomorph for pyrite, goethite and finally ferrihydrite, and this oxyhydroxide is characterized by positive correlation of Fe2O3 with SiO2 and Al2O3. On the other hand, MOH shows positive correlation between MnO2 and Al2O3 whereas it is negative between Fe2O3 and SiO2. Paratacamite is the most common secondary copper mineral that fills fractures and post-dates FeOH and MnOH. It is believed that Cl- in the structure of paratacamite represents inherited marine storage rather than from surfacial evaporates or meteoric water. The mineralogy of slags suggests a complicated mineral assemblage that includes native Cu prills, synthetic spinifixed Mn-rich amphiboles with 16.73 wt% MnO, brown glass and Ca-Mn-Fe phase close to the olivine structure. EMPA indicate that the some Cu prills have either grey discontinuous boarder zone of S-rich Mn-Cu alloy (with up to 21.95 wt% S and 19.45 wt% Mn) or grey Cu-Mn-Fe alloy (with up to 15.9 wt% Cu, 39. 12 wt% Mn and 61.64 wt% Fe). Mn in the Cu prills is expelled inward as Cu-Mn-Fe alloy inclusions whereas S is expelled

  14. A Model for Generation of Martian Surface Dust, Soil and Rock Coatings: Physical vs. Chemical Interactions, and Palagonitic Plus Hydrothermal Alteration

    NASA Technical Reports Server (NTRS)

    Bishop, J. L.; Murchie, S.; Pieters, C.; Zent, A.

    1999-01-01

    This model is one of many possible scenarios to explain the generation of the current surface material on Mars using chemical, magnetic and spectroscopic data from Mars and geologic analogs from terrestrial sites. One basic premise is that there are physical and chemical interactions of the atmospheric dust particles and that these two processes create distinctly different results. Physical processes distribute dust particles on rocks, forming physical rock coatings, and on the surface between rocks forming soil units; these are reversible processes. Chemical reactions of the dust/soil particles create alteration rinds on rock surfaces or duricrust surface units, both of which are relatively permanent materials. According to this model the mineral components of the dust/soil particles are derived from a combination of "typical" palagonitic weathering of volcanic ash and hydrothermally altered components, primarily from steam vents or fumeroles. Both of these altered materials are composed of tiny particles, about 1 micron or smaller, that are aggregates of silicates and iron oxide/oxyhydroxide/sulfate phases. Additional information is contained in the original extended abstract.

  15. Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits

    NASA Astrophysics Data System (ADS)

    Patten, Clifford G. C.; Pitcairn, Iain K.; Teagle, Damon A. H.; Harris, Michelle

    2016-02-01

    Volcanogenic massive sulphide (VMS) deposits are commonly enriched in Cu, Zn and Pb and can also be variably enriched in Au, As, Sb, Se and Te. The behaviour of these elements during hydrothermal alteration of the oceanic crust is not well known. Ocean Drilling Program (ODP) Hole 1256D penetrates a complete in situ section of the upper oceanic crust, providing a unique sample suite to investigate the behaviour of metals during hydrothermal alteration. A representative suite of samples was analysed for Au, As, Sb, Se and Te using low detection limit methods, and a mass balance of metal mobility has been carried out through comparison with a fresh Mid-Oceanic Ridge Basalt (MORB) glass database. The mass balance shows that Au, As, Se, Sb, S, Cu, Zn and Pb are depleted in the sheeted dyke and plutonic complexes by -46 ± 12, -27 ± 5, -2.5 ± 0.5, -27 ± 6, -8.4 ± 0.7, -9.6 ± 1.6, -7.9 ± 0.5 and -44 ± 6 %, respectively. Arsenic and Sb are enriched in the volcanic section due to seawater-derived fluid circulation. Calculations suggest that large quantities of metal are mobilised from the oceanic crust but only a small proportion is eventually trapped as VMS mineralisation. The quantity of Au mobilised and the ratio of Au to base metals are similar to those of mafic VMS, and ten times enrichment of Au would be needed to form a Au-rich VMS. The Cu-rich affinity of mafic VMS deposits could be explained by base metal fractionation both in the upper sheeted dykes and during VMS deposit formation.

  16. Hydrothermal systematics, alteration, and mineralization in the Grant Canyon, Bacon Flat, and Blackburn Oil Fields, Nevada - Intriguing Parallels with Carlin-Type gold deposits

    SciTech Connect

    Hulen, J.B.; Nielson, D.L. )

    1993-08-01

    Nevada's three known thermally active oil reservoirs-Blackburn, Bacon Flat, and Grand Canyon-share a surprisingly long list of essential attributes with the Carlin-type, low-grade, sediment-hosted gold deposits, particularly those of the Alligator Ridge mining district. Like these rich precious-metal ore bodies, the three fields (1) are hosted by Paleozoic carbonate and calcareous silici-clastic strata; (2) occur in structural or structural/stratigraphic traps sealed beneath shales or hydrothermally argillized and silicified tuffs and epiclastic debris, (3) have undergone intense fracturing and brecciation, as well as massive hydrothermal decalcification as major porosity-creating processes; (4) occupy rocks partly altered to or veined by the secondary-mineral assemblage quartz-kaolin-barite-pyrite-marcasite; (5) have a direct geothermal connection; (6) are enriched in the elements arsenic, antimony, mercury, thallium, and even contain significant traces of gold-up 50 ppb in altered Mississippian Chainmain Shale in the Blackburn field. Moreover, measured temperatures, as well as late-stage, fluid-inclusion homogenization temperatures (T[sub h]) at the fields-all in the range 100-135[degrees]C-fall within the fluid-inclusion T[sub h] span of 90-165[degrees]C recorded for multiple Alligator Ridge deposits. Fracture-controlled live oil and oil-bearing fluid inclusions in some of the Alligator Ridge ores provide further evidence of genetic similarities with the oil reservoirs. The authors suggest that the three oil fields could represent either weakly mineralized analogs of the gold deposits or an incipient phase in their evolution ultimately leading to ore mineralization.

  17. Mineralogy of iron sulfides in CM1 and CI1 lithologies of the Kaidun breccia: Records of extreme to intense hydrothermal alteration

    NASA Astrophysics Data System (ADS)

    Harries, Dennis; Zolensky, Michael E.

    2016-06-01

    The polymict Kaidun microbreccia contains lithologies of C-type chondrites with euhedral iron sulfide crystals of hydrothermal origin. Our FIB-TEM study reveals that acicular sulfides in a CM1 lithology are composed of Fe-rich pyrrhotite with nonintegral vacancy superstructures (NC-pyrrhotite), troilite, and pentlandite, all showing distinct exsolution textures. Based on phase relations in the Fe-Ni-S system, we constrain the temperature of formation of the originally homogeneous monosulfide solid solution to the range of 100-300 °C. In some crystals the exsolution of pentlandite and the microtextural equilibration was incomplete, probably due to rapid cooling. We use thermodynamic modeling to constrain the physicochemical conditions of the extreme hydrothermal alteration in this lithology. Unless the CM1 lithology was sourced from a large depth in the parent body (internal pressure >85 bar) or the temperatures were in the lower range of the interval determined, the water was likely present as vapor. Previously described light δ34S compositions of sulfides in Kaidun's CM1 lithology are likely due to the loss of 34S-enriched H2S during boiling. Platy sulfide crystals in an adjacent, intensely altered CI1 lithology are composed of Fe-poor, monoclinic 4C-pyrrhotite and NC-pyrrhotite and probably formed at lower temperatures and higher fS2 relative to the CM1 lithology. However, a better understanding of the stability of Fe-poor pyrrhotites at temperatures below 300 °C is required to better constrain these conditions.

  18. Mineralogy of iron sulfides in CM1 and CI1 lithologies of the Kaidun breccia: Records of extreme to intense hydrothermal alteration

    NASA Astrophysics Data System (ADS)

    Harries, Dennis; Zolensky, Michael E.

    2016-05-01

    The polymict Kaidun microbreccia contains lithologies of C-type chondrites with euhedral iron sulfide crystals of hydrothermal origin. Our FIB-TEM study reveals that acicular sulfides in a CM1 lithology are composed of Fe-rich pyrrhotite with nonintegral vacancy superstructures (NC-pyrrhotite), troilite, and pentlandite, all showing distinct exsolution textures. Based on phase relations in the Fe-Ni-S system, we constrain the temperature of formation of the originally homogeneous monosulfide solid solution to the range of 100-300 °C. In some crystals the exsolution of pentlandite and the microtextural equilibration was incomplete, probably due to rapid cooling. We use thermodynamic modeling to constrain the physicochemical conditions of the extreme hydrothermal alteration in this lithology. Unless the CM1 lithology was sourced from a large depth in the parent body (internal pressure >85 bar) or the temperatures were in the lower range of the interval determined, the water was likely present as vapor. Previously described light δ34S compositions of sulfides in Kaidun's CM1 lithology are likely due to the loss of 34S-enriched H2S during boiling. Platy sulfide crystals in an adjacent, intensely altered CI1 lithology are composed of Fe-poor, monoclinic 4C-pyrrhotite and NC-pyrrhotite and probably formed at lower temperatures and higher fS2 relative to the CM1 lithology. However, a better understanding of the stability of Fe-poor pyrrhotites at temperatures below 300 °C is required to better constrain these conditions.

  19. Hydrothermal alteration, fluid inclusions and stable isotope systematics of the Alvo 118 iron oxide-copper-gold deposit, Carajás Mineral Province (Brazil): Implications for ore genesis

    NASA Astrophysics Data System (ADS)

    Torresi, Ignacio; Xavier, Roberto Perez; Bortholoto, Diego F. A.; Monteiro, Lena V. S.

    2012-03-01

    The Alvo 118 iron oxide-copper-gold (IOCG) deposit (170 Mt at 1.0 wt.% Cu, 0.3 g/t Au) lies in the southern sector of the Itacaúnas Shear Belt, Carajás Mineral Province, along a WNW-ESE-striking, 60-km-long shear zone, close to the contact of the ~2.76-Ga metavolcano-sedimentary Itacaiúnas Supergroup and the basement (~3.0 Ga Xingu Complex). The Alvo 118 deposit is hosted by mafic and felsic metavolcanic rocks and crosscutting granitoid and gabbro intrusions that have been subjected to the following hydrothermal alteration sequence towards the ore zones: (1) poorly developed sodic alteration (albite and scapolite); (2) potassic alteration (biotite or K-feldspar) accompanied by magnetite formation and silicification; (3) widespread, pervasive chlorite alteration spatially associated with quartz-carbonate-sulphide infill ore breccia and vein stockworks; and (4) local post-ore quartz-sericite alteration. The ore assemblage is dominated by chalcopyrite (~60%), bornite (~10%), hematite (~20%), magnetite (10%) and subordinate chalcocite, native gold, Au-Ag tellurides, galena, cassiterite, F-rich apatite, xenotime, monazite, britholite-(Y) and a gadolinite-group mineral. Fluid inclusion studies in quartz point to a fluid regime composed of two distinct fluid types that may have probably coexisted within the timeframe of the Cu-Au mineralizing episode: a hot (>200°C) saline (32.8‰ to 40.6 wt.% NaCl eq.) solution, represented by salt-bearing aqueous inclusions, and a lower temperature (<200°C), low to intermediate salinity (<15 wt.% NaCl eq.) aqueous fluid defined by two-phase (LH2O + VH2O) fluid inclusions. This trend is very similar to those defined for other IOCG systems of the Carajás Mineral Province. δ 18OH2O values in equilibrium with calcite (-1.0‰ to 7.5‰ at 277°C to 344°C) overlap the lower range for primary magmatic waters, but the more 18O-depleted values also point to the involvement of externally derived fluids, possibly of meteoric origin

  20. Comparing the deformation and hydrothermal alteration record of tectonic exhumation of mantle-derived ultramafic rocks from the Mid-Atlantic Ridge and from Ocean Continent Transitions (Central Alps and Western Iberia Margin)

    NASA Astrophysics Data System (ADS)

    Picazo, S. M.; Cannat, M.; Manatschal, G.

    2012-12-01

    that deformation localized in tremolite-bearing, or in talc-bearing shear zones. Tremolite-bearing shear zones localized deformation in the ultramafic rocks prior to serpentinization. Tremolites appear to have formed as hydrothermal alteration products after evolved gabbroic rocks intruded into the peridotites. Talc-bearing shear zones developed after serpentinization. Talc crystallized due to hydrothermal alteration of serpentine by Si-rich fluids (probably due to an interaction with mafic rocks). It therefore appears that the rheology of detachments at the MAR is largely influenced by the injection of magma near the fault. By contrast, strain localization in OCT detachments would be mostly due to the weak rheology of serpentine. Finally we note a systematic difference in the late to post deformation alteration record of MAR and OCT ultramafic samples: OCT samples have recorded extensive static carbonatation of serpentinite, after their emplacement in the paleo-seafloor. By contrast, samples from the MAR show limited carbonatation, in the form of angular carbonate veins that formed in a fracture network at the end of the exhumation process.

  1. (238)U/(235)U isotope ratios of crustal material, rivers and products of hydrothermal alteration: new insights on the oceanic U isotope mass balance.

    PubMed

    Noordmann, Janine; Weyer, Stefan; Georg, R Bastian; Jöns, Svenja; Sharma, Mukul

    2016-01-01

    In this study, the U isotope composition, n((238)U)/n((235)U), of major components of the upper continental crust, including granitic rocks of different age and post-Archaean shales, as well as that of rivers (the major U source to the oceans) was investigated. Furthermore, U isotope fractionation during the removal of U at mid-ocean ridges, an important sink for U from the oceans, was investigated by the analyses of hydrothermal water samples (including low- and high-temperature fluids), low-temperature altered basalts and calcium carbonate veins. All analysed rock samples from the continental crust fall into a limited range of δ(238)U between -0.45 and -0.21 ‰ (relative to NBL CRM 112-A), with an average of -0.30 ± 0.15 ‰ (2 SD, N = 11). Despite differences in catchment lithologies, all major rivers define a relatively narrow range between -0.31 and -0.13 ‰, with a weighted mean isotope composition of -0.27 ‰, which is indistinguishable from the estimate for the upper continental crust (-0.30 ‰). Only some tributary rivers from the Swiss Alps display a slightly larger range in δ(238)U (-0.29 to +0.01 ‰) and lower U concentrations (0.87-3.08 nmol/kg) compared to the investigated major rivers (5.19-11.69 nmol/kg). These findings indicate that only minor net U isotope fractionation occurs during weathering and transport of material from the continental crust to the oceans. Altered basalts display moderately enriched U concentrations (by a factor of 3-18) compared to those typically observed for normal mid-ocean ridge basalts. These, and carbonate veins within altered basalts, show large U isotope fractionation towards both heavy and light U isotope compositions (ranging from -0.63 to +0.27 ‰). Hydrothermal water samples display low U concentrations (0.3-1 nmol/kg) and only limited variations in their U isotope composition (-0.43 ± 0.25 ‰) around the seawater value. Nevertheless, two of the investigated fluids display

  2. The boron isotope geochemistry of tourmaline-rich alteration in the IOCG systems of northern Chile: implications for a magmatic-hydrothermal origin

    NASA Astrophysics Data System (ADS)

    Tornos, Fernando; Wiedenbeck, Michael; Velasco, Francisco

    2012-06-01

    Hydrothermal tourmaline is common in the iron oxide-copper-gold (IOCG) deposits of the Coastal Cordillera of Chile where it occurs as large crystals in the groundmass of magmatic-hydrothermal breccias, such as in the Silvita or Tropezón ore bodies, or as small grains in replacive bodies or breccia cement in the ore-bearing andesite, as seen at the Candelaria or Carola deposits. Tourmaline shows strong chemical zoning and has a composition of schorl-dravite with significant povondraite and uvite components. The observed boron isotope composition is fairly variable, between -10.4‰ and +6.0‰ with no major differences among the different deposits, suggesting a common genetic mechanism. The δ11B values are significantly lower than those of seawater or marine evaporites and very similar to those of younger porphyry copper deposits and volcanic rocks in the region, indicating that the boron has a common, likely magmatic, origin. The predominant boron source was ultimately dewatering of the subducting slab with a significant contribution derived from the overlying continental basement. The range of δ11B values is between those of the porphyry copper deposits and the porphyry tin deposits of the Andes, suggesting that the IOCG mineralization might be genetically related to fluids having more crustal contamination than the porphyry copper deposits; such an interpretation is at odds with current models that propose that the Andean IOCG deposits are related to juvenile melts or to the circulation of basinal brines. Furthermore, the obtained δ11B data are markedly different from those of the tourmaline in the Carajás IOCG district (Brazil), suggesting that IOCGs do not form by a unique mechanism involving only one type of fluids.

  3. Experimental Hydrous Partial Melting of Natural Pristine and Altered MORB Beneath Subduction Zones

    NASA Astrophysics Data System (ADS)

    Carter, L. B.; Skora, S. E.; Blundy, J.

    2012-12-01

    ). Textural evidence further suggests that the K-composition of the starting material likely contributes to the location of the elusive second critical endpoint. Textural evidence implies the presence of 2 immiscible fluids at 850°C in the pristine MORB sample (in agreement with the location of the second critical endpoint of Kessel et al. 2005, using K-free MORB). This is in contrast to AOC which appears to have had only a single fluid phase (in agreement with the conclusion of Klimm et al. 2008, simulating a synthetic AOC composition). Accessory phases, apart from rutile, were not yet positively identified in our run products. Instead, we will use trace element data combined with a mass balance approach and fractionation of key trace element ratios (e.g. U/Th; La/Th, etc.) to evaluate whether accessory phases are present or not. Our study suggests that subducted MORB may behave heterogeneously during partial melting in subduction zone environments, owing to significant chemical variations in the K2O content of pristine versus altered oceanic crust. Geochemical analysis of the resulting mineralogy and melt composition of this study will further assist in the understanding of element transfer from the subducted slab to the overriding mantle wedge.

  4. The Hydrothermal System at Home Plate in Gusev Crater, Mars: Formation of High Silica Material by Acid-Sulfate Alteration of Basalt

    NASA Technical Reports Server (NTRS)

    Morris, R. V.; Ming, D. W.; Gellert, R.; Yen, A.; Clark, B. C.; Gnaff, T. G.; Arvidson, R. E.; Squyres, S. W.

    2008-01-01

    The Alpha Particle X-ray Spectrometer (APXS) instrument on the Mars Exploration Rover (MER) Spirit measured three targets on or adjacent to Home Plate in Gusev Crater that have unusually high SiO2 concentrations (68% to 91%), unusually low FeO concentrations (1% to 7%, with total Fe as FeO), and unusually high TiO2/FeO ratios (0.2 to 1.2 by weight) [1]. Two targets (Kenosha Comets and Lefty Ganote) are located on high albedo soil (Gertrude Weise) that was exposed by the rover wheels, and one target is a float rock called Fuzzy Smith. Kenosha Comets has the highest SiO2 concentration, lowest FeO concentration, and highest TiO2/FeO ratio. Mineralogical evidence from the MER Miniature Thermal Emission Spectrometer (Mini-TES) suggests that the SiO2 is present as amorphous (noncrystalline) SiO2 at Gertrude Weise and nearby targets [2,3]. Mini-TES data were not acquired for Fuzzy Smith. Home Plate is considered to have an explosive volcanic origin, resulting when basaltic magma came into contact with ground water or ice [4]. Within 50 m to 1 km of Home Plate are sulfate rich soil deposits (Paso Robles class soils with 22-35% SO3) which are considered to be probable fumarolic and/or hydrothermal deposits associated with the volcanism [5]. We develop the model here, suggested by [5], that the high-silica materials are another manifestation of acid-sulfate processes associated with fumarolic and hydrothermal activity at Home Plate. This is done by analogy with basaltic materials altered by acid sulfate processes on the Island of Hawaii.

  5. Fluid-rock interactions in the Rhine Graben: A thermodynamic model of the hydrothermal alteration observed in deep drilling

    NASA Astrophysics Data System (ADS)

    Komninou, A.; Yardley, B. W. D.

    1997-02-01

    Deep drilling at Soultz-sous-Forêts, France, on the western flanks of the Rhine Graben, has penetrated Hercynian granite underlying Mesozoic sediments. Veins are present throughout the drilled granite, and there are flows of warm water localized in fractures within the granite. Detailed mineralogical study of core material from the research drillhole EPS 1 has been carried out in order to assess the alteration history of the Soultz granite, part of the crystalline basement of the Rhine Graben. The results of the study have been used, in conjunction with analyses of present-day fluids from deep drilling in the Rhine Graben reported in the literature, to model thermodynamically the alteration process, and in particular to evaluate if it is likely to be continuing today. Reaction-path calculations show that if deep basinal brines, such as are known from sediments of the central Rhine Graben, react with Hercynian granite, they will form different alteration assemblages depending on both the path that the fluid follows (e.g., descending through sediments or through granite) and the extent of preexisting alteration of the granite. The calculations suggest that fluid now sampled from granite in EPS-1 achieved its peak temperature, c. 200°C, while within Permo-Triassic sandstone. The modeling also indicates that present-day fluids from the Rhine Graben system are capable of producing the vein quartz and possibly also the baryte veins, seen in the EPS 1 core. Much of the alteration present in the granite in the vicinity of veins and fractures may have been produced by a flow regime similar to that prevailing today.

  6. Fluid-rock interactions in the Rhine Graben: A thermodynamic model of the hydrothermal alteration observed in deep drilling

    SciTech Connect

    Komninou, A.; Yardley, B.W.D.

    1997-02-01

    Deep drilling at Soultz-sous-Forets, France, on the western flanks of the Rhine Graben, has penetrated Hercynian granite underlying Mesozoic sediments. Veins are present throughout the drilled granite, and there are flows of warm water localized in fractures within the granite. Detailed mineralogical study of core material from the research drillhole EPSI has been carried out in order to assess the alteration history of the Soultz granite, part of the crystalline basement of the Rhine Graben. The results of the study have been used, in conjunction with analyses of present-day fluids from deep drilling in the Rhine Graben reported in the literature, to model thermodynamically the alteration process, and in particular to evaluate if it is likely to be continuing today. Reaction-path calculations show that if deep basinal brines, such as are known from sediments of the central Rhine Graben, react with Hercynian granite, they will form different alteration assemblages depending on both the path that the fluid follows (e.g., descending through sediments or through granite) and the extent of preexisting alteration of the granite. The calculations suggest that fluid now sampled from granite in EPS-1 achieved its peak temperature, c. 200{degrees}C while within Permo-Triassic sandstone. The modeling also indicates that present-day fluids from the Rhine Graben system are capable of producing the vein quartz and possibly also the baryte veins, seen in the EPSI core. Much of the alteration present in the granite in the vicinity of veins and fractures may have been produced by a flow regime similar to that prevailing today. 48 refs., 15 figs., 4 tabs.

  7. Prenatal cocaine exposure alters progenitor cell markers in the subventricular zone of the adult rat brain

    PubMed Central

    Patel, Dhyanesh Arvind; Booze, Rosemarie M.; Mactutus, Charles F.

    2013-01-01

    Long-term consequences of early developmental exposure to drugs of abuse may have deleterious effects on the proliferative plasticity of the brain. The purpose of this study was to examine the long-term effects of prenatal exposure to cocaine, using the IV route of administration and doses that mimic the peak arterial levels of cocaine use in humans, on the proliferative cell types of the subventricular zones (SVZ) in the adult (180 days-old) rat brain. Employing immunocytochemistry, the expression of GFAP+ (type B cells) and nestin+(GFAP−) (Type C and A cells) staining was quantified in the subcallosal area of the SVZ. GFAP+ expression was significantly different between the prenatal cocaine treated group and the vehicle (saline) control group. The prenatal cocaine treated group possessed significantly lower GFAP+ expression relative to the vehicle control group, suggesting that prenatal cocaine exposure significantly reduced the expression of type B neural stem cells of the SVZ. In addition, there was a significant sex difference in nestin+ expression with females showing approximately 8–13% higher nestin+ expression compared to the males. More importantly, a significant prenatal treatment condition (prenatal cocaine, control) by sex interaction in nestin+ expression was confirmed, indicating different effects of cocaine based on sex of the animal. Specifically, prenatal cocaine exposure eliminated the basal difference between the sexes. Collectively, the present findings suggest that prenatal exposure to cocaine, when delivered via a protocol designed to capture prominent features of recreational usage, can selectively alter the major proliferative cell types in the subcallosal area of the SVZ in an adult rat brain, and does so differently for males and females. PMID:22119286

  8. The Ajo Mining District, Pima County, Arizona--Evidence for Middle Cenozoic Detachment Faulting, Plutonism, Volcanism, and Hydrothermal Alteration

    USGS Publications Warehouse

    Cox, Dennis P.; Force, Eric R.; Wilkinson, William H.; More, Syver W.; Rivera, John S.; Wooden, Joseph L.

    2006-01-01

    Introduction: The Ajo porphyry copper deposit and surrounding Upper Cretaceous rocks have been separated from their plutonic source and rotated by detachment faulting. Overlying middle Cenozoic sedimentary and volcanic rocks have been tilted and show evidence for two periods of rotation. Following these rotations, a granitic stock (23.7?0.2 Ma) intruded basement rocks west of the Ajo deposit. This stock was uplifted 2.5 km to expose deep-seated Na-Ca alteration.

  9. Opaque assemblages in CR2 Graves Nunataks (GRA) 06100 as indicators of shock-driven hydrothermal alteration in the CR chondrite parent body

    NASA Astrophysics Data System (ADS)

    Abreu, Neyda M.; Bullock, Emma S.

    2013-12-01

    We have studied the petrologic characteristics of sulfide-metal lodes, polymineralic Fe-Ni nodules, and opaque assemblages in the CR2 chondrite Graves Nunataks (GRA) 06100, one of the most altered CR chondrites. Unlike low petrologic type CR chondrites, alteration of metal appears to have played a central role in the formation of secondary minerals in GRA 06100. Differences in the mineralogy and chemical compositions of materials in GRA 06100 suggest that it experienced higher temperatures than other CR2 chondrites. Mineralogic features indicative of high temperature include: (1) exsolution of Ni-poor and Ni-rich metal from nebular kamacite; (2) formation of sulfides, oxides, and phosphates; (3) changes in the Co/Ni ratios; and (4) carbidization of Fe-Ni metal. The conspicuous absence of pentlandite may indicate that peak temperatures exceeded 600 °C. Opaques appear to have been affected by the action of aqueous fluids that resulted in the formation of abundant oxides, Fe-rich carbonates, including endmember ankerite, and the sulfide-silicate-phosphate scorzalite. We suggest that these materials formed via impact-driven metamorphism. Mineralogic features indicative of impact metamorphism include (1) the presence of sulfide-metal lodes; (2) the abundance of polymineralic opaque assemblages with mosaic-like textures; and (3) the presence of suessite. Initial shock metamorphism probably resulted in replacement of nebular Fe-Ni metal in chondrules and in matrix by Ni-rich, Co-rich Fe metal, Al-Ti-Cr-rich alloys, and Fe sulfides, while subsequent hydrothermal alteration produced accessory oxides, phosphates, and Fe carbonates. An extensive network of sulfide-metal veins permitted effective exchange of siderophile elements from pre-existing metal nodules with adjacent chondrules and matrix, resulting in unusually high Fe contents in these objects.

  10. Ohaaki reservoir chemistry: characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Christenson, B. W.; Mroczek, E. K.; Kennedy, B. M.; van Soest, M. C.; Stewart, M. K.; Lyon, G.

    2002-06-01

    Situated along the eastern margin of the Taupo Volcanic Zone (TVZ), the high-gas and high-enthalpy production fluids from the Ohaaki geothermal field are chemically similar to other arc-type volcanic systems found along this part of the TVZ. Two thermal upwellings can be distinguished within the field, each apparently emanating from fault structures in the Mesozoic basement greywackes. Although both plumes have similar salinities and appear to be fully equilibrated with the reservoir rocks containing them, fluids associated with the eastern upflow zone are enriched in B and F compared to those in the western upflow zone. δ 2H and δ 18O signatures for water suggest that up to 20% of the water in the discharges may derive from a magmatic source, and a δ 2H-Cl trend established by the East-Bank fluids indicate end-member mixing between a high-Cl fluid and Cl-deficient steam containing as much as 40% arc-type vapour. Gas signatures in fluids from the two production fields show compositional differences that cannot be explained by physical reservoir processes. The eastern fluids have higher N 2/Ar and CO 2/He ratios, and consistently higher CH 4-CO 213C fractionation temperatures than those in the western upflow zone. In addition, stark differences in 3He/ 4He and 40Ar/ 36Ar ratios for the two production fields suggest two-component mixing for the respective source components, with the eastern fluids having a significantly larger radiogenic gas content than those to the west. Collectively, these signatures suggest the presence of a relatively young and shallowly seated degassing intrusive beneath the eastern upflow zone, perhaps as shallow as 4 km beneath the surface.

  11. Hydrothermal Processes

    NASA Astrophysics Data System (ADS)

    German, C. R.; von Damm, K. L.

    2003-12-01

    (after C. A. Stein and S. Stein, 1994). The first geochemical evidence for the existence of hydrothermal vents on the ocean floor came in the mid-1960s when investigations in the Red Sea revealed deep basins filled with hot, salty water (40-60 °C) and underlain by thick layers of metal-rich sediment (Degens and Ross, 1969). Because the Red Sea represents a young, rifting, ocean basin it was speculated that the phenomena observed there might also prevail along other young MOR spreading centers. An analysis of core-top sediments from throughout the world's oceans ( Figure 2) revealed that such metalliferous sediments did, indeed, appear to be concentrated along the newly recognized global ridge crest (Boström et al., 1969). Another early indication of hydrothermal activity came from the detection of plumes of excess 3He in the Pacific Ocean Basin (Clarke et al., 1969) - notably the >2,000 km wide section in the South Pacific ( Lupton and Craig, 1981) - because 3He present in the deep ocean could only be sourced through some form of active degassing of the Earth's interior, at the seafloor. (62K)Figure 2. Global map of the (Al+Fe+Mn):Al ratio for surficial marine sediments. Highest ratios mimic the trend of the global MOR axis (after Boström et al., 1969). One area where early heat-flow studies suggested hydrothermal activity was likely to occur was along the Galapagos Spreading Center in the eastern equatorial Pacific Ocean (Anderson and Hobart, 1976). In 1977, scientists diving at this location found hydrothermal fluids discharging chemically altered seawater from young volcanic seafloor at elevated temperatures up to 17 °C ( Edmond et al., 1979). Two years later, the first high-temperature (380±30 °C) vent fluids were found at 21° N on the East Pacific Rise (EPR) (Spiess et al., 1980) - with fluid compositions remarkably close to those predicted from the lower-temperature Galapagos findings ( Edmond et al., 1979). Since that time, hydrothermal activity has been

  12. 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

  13. Hydrothermal Processing

    SciTech Connect

    Elliott, Douglas C.

    2011-03-11

    This chapter is a contribution to a book on Thermochemical Conversion of Biomass being edited by Prof. Robert Brown of Iowa State University. It describes both hydrothermal liquefaction and hydrothermal gasification of biomass to fuels.

  14. Genesis of the hydrothermal gold deposits in the Canan area, Lepaguare District, Honduras

    NASA Astrophysics Data System (ADS)

    Mattioli, Michele; Menichetti, Marco; Renzulli, Alberto; Toscani, Lorenzo; Salvioli-Mariani, Emma; Suarez, Pedro; Murroni, Alessandro

    2014-04-01

    The Canan area (Honduras) is characterized by a gold-bearing ore deposit that is associated with quartz-veined shear zones. Gold mineralization occurs in low-to medium-grade metamorphic host-rocks (graphitic and sericitic schists). Hydrothermal fluids, which are associated with the emplacement of Cretaceous-Tertiary granodioritic intrusions, are responsible for the formation of quartz veins and the hydrothermal alteration of wall-rocks. Three main altered zones have been detected in the wall-rocks as far as 150 cm from the quartz veins. The distal zone (up to 50-cm thick) contains quartz, chlorite and illite. The intermediate zone is the thickest (up to 80 cm) and is marked by quartz, muscovite, sulphides, kaolinite and native elements such as Au and Ag. The proximal zone, which is close to the quartz veins, is rather thin (up to 25 cm) and contains clay minerals, Al-oxides-hydroxides and sulphides. The transition from the distal to the proximal zone is accompanied by the enrichment of SiO2 and the depletion of all other major elements, except for Fe2O3(tot). Precious metals occur in the highest concentrations in the intermediate zone (Au up to 7.6 ppm and Ag up to 11 ppm). We suggest that gold was transported as a reduced sulphur complex and was precipitated from the hydrothermal solution by the reaction of the sulphur complexes with Fe2+ from the alteration of the mafic minerals of the host-rock. Fluid-wall-rock interactions seem to be the main cause of gold mineralization. Genetic relationships with a strike-slip fault system, hydrothermal alteration zones within the metamorphic wall-rocks, and an entire set of geochemical anomalies are consistent with orogenic-type gold deposits of the epizonal class.

  15. Effective use of principal component analysis with high resolution remote sensing data to delineate hydrothermal alteration and carbonate rocks

    NASA Technical Reports Server (NTRS)

    Feldman, Sandra C.

    1987-01-01

    Methods of applying principal component (PC) analysis to high resolution remote sensing imagery were examined. Using Airborne Imaging Spectrometer (AIS) data, PC analysis was found to be useful for removing the effects of albedo and noise and for isolating the significant information on argillic alteration, zeolite, and carbonate minerals. An effective technique for using PC analysis using an input the first 16 AIS bands, 7 intermediate bands, and the last 16 AIS bands from the 32 flat field corrected bands between 2048 and 2337 nm. Most of the significant mineralogical information resided in the second PC. PC color composites and density sliced images provided a good mineralogical separation when applied to a AIS data set. Although computer intensive, the advantage of PC analysis is that it employs algorithms which already exist on most image processing systems.

  16. Stable isotope (S, O, H and C) studies of the phyllic and potassic phyllic alteration zones of the porphyry copper deposit at Sungun, East Azarbaidjan, Iran

    NASA Astrophysics Data System (ADS)

    Calagari, Ali Asghar

    2003-05-01

    The porphyry copper deposit (PCD) at Sungun is located in East Azarbaidjan, NW of Iran. The magmatic suites in the Sungun area are a part of the NW-SE trending Cenozoic magmatic belt of Iran. The Sungun porphyries occur as stocks and dikes. The stocks are divided into two groups, I and II. Porphyry Stock II, ranging in composition from quartz monzonite through granodiorite to granite, hosts the Sungun PCD. Four distinct types of hypogene alterations were recognized at Sungun: (1) potassic; (2) potassic-phyllic; (3) phyllic; and (4) propylitic. Stable isotope (S, O, H, and C) studies were restricted to within the phyllic and potassic-phyllic alteration zones, where numerous cross-cutting quartz, sulfides, carbonates, and sulfate veinlets are present. The objective of these studies was to determine the origin of the ore-forming solutions, and their important components (e.g. sulfur and carbon). Twenty sulfide and four sulfate samples were taken from sulfide and gypsum veinlets within Porphyry Stock II and the associated skarn zone for sulfur isotopic analyses. The δ34S values of sulfides (pyrite, chalcopyrite, molybdenite, galena, sphalerite) and sulfate (gypsum) range from -4.6 to -0.2‰ (mean of -1.5‰) and from 10.9 to 14.4‰ (mean of 12.9‰), respectively. These values are almost analogous to those from El Salvador (Chile) and Ajo (Arizona), and Twin Buttes (Arizona), and strongly suggest a magmatic source for the sulfur at Sungun. Twenty-eight fluid inclusion-rich quartz samples from quartz veinlets beneath the supergene zones of the Porphyry Stock II were chosen for O and H isotopic analyses. The δ18O (of quartz) and δD (of fluid inclusions in quartz) values range from 8.3 to 10.2‰ (mean of 9.2‰) and -58 to -75‰ (mean of -66‰) relative to Standard Mean Ocean Water (SMOW), respectively. The calculated δ18O values of the fluids range from 4.4‰ (T=375 ° C) to 7.6‰ (T=570 ° C) with a mean of 6.4‰. The δ18O and δD values of the fluids lie

  17. Evaluation of AIS-2 (1986) data over hydrothermally altered granitoid rocks of the Singatse Range (Yerington) Nevada and comparison with 1985 AIS-1 data

    NASA Technical Reports Server (NTRS)

    Lyon, R. J. P.

    1987-01-01

    The Airborne Imaging Spectrometer-2 (AIS-2) flights along 2 subparallel lines (bearing 013) were designed to traverse 3 major rock assemblages - the Triassic sedimentary sequence; the granitoid rocks of the Yerington batholith and the Tertiary ignimbritic ash flow and ash fall tuffs. The first 2 sites are hydrothermally altered to a quartz-sericite-tourmaline mineralogy. The first AIS-2 data set showed numerous line dropouts and a considerable number of randomly distributed dark pixels. A second decommutation reduced the dropout essentially to near zero and the dark pixels by about 75 percent. Vertical striping was removed by histogram matching, column by column. A log residual spectrum was calculated which showed the departure of a 2 x 2 pixel area from the spatially and spectrally averaged scene. A 1:1 correlation was found with the log residual AIS-2 data and a large open pit area of gypsum. An area with known sericite agreed with the overflight data, and an area known to be free of any significant amount of O-H bearing materials showed no evidence of any in the AIS-2 log residuals.

  18. The sulphur springs geothermal field, St. Lucia, lesser Antilles: Hydrothermal mineralogy of wells SL-1 and SL-2

    NASA Astrophysics Data System (ADS)

    Battaglia, S.; Gianelli, G.; Rossi, R.; Cavarretta, G.

    Two wells have been drilled to depths of 1413 and 2213 meters in the geothermal field of Sulphur Springs, St. Lucia, and reveal a complex volcanic sequence characterized by collapse episodes followed by the emplacement of dacite domes. The geothermal reservoir consists of fractured volcanic rocks and produces superheated steam. Well-bottom temperatures are around 270-290°C. The hydrothermal alteration found in both the productive SL-2 well and the non-productive SL-1 is strongly reminiscent of that of porphyry copper deposits, with (1) an inner, high-temperature potassic zone characterized by the occurrence of dravitic tourmaline, quartz, and biotite, (2) an outer propylitic alteration zone that is partly superimposed on (3) a potassic alteration zone. The alteration mineral assemblages indicate that the hydrothermal system has cooled at the levels sampled.

  19. Acid sulfate alteration of fluorapatite, basaltic glass and olivine by hydrothermal vapors and fluids: Implications for fumarolic activity and secondary phosphate phases in sulfate-rich Paso Robles soil at Gusev Crater, Mars

    NASA Astrophysics Data System (ADS)

    Hausrath, E. M.; Golden, D. C.; Morris, R. V.; Agresti, D. G.; Ming, D. W.

    2013-01-01

    Phosphate-rich rocks and a nearby phosphate-rich soil, Paso Robles, were analyzed in Gusev Crater, Mars, by the Mars Exploration Rover Spirit and interpreted to be highly altered, possibly by hydrothermal or fumarolic alteration of primary, phosphate-rich material. To test mineral phases resulting from such alteration, we performed hydrothermal acid-vapor and acid-fluid experiments on olivine (Ol), fluorapatite (Ap), and basaltic glass (Gl) as single phases and a mixture of phases. Minerals formed include Ca-, Al-, Fe- and Mg-sulfates with different hydration states (anhydrite, bassanite, gypsum; alunogen; hexahydrite, and pentahydrite). Phosphate-bearing minerals formed included monocalcium phosphate monohydrate (MCP) (acid-vapor and acid-fluid alteration of fluorapatite only) and ferrian giniite (acid-fluid alteration of the Ol + Gl + Ap mixture). MCP is likely present in Paso Robles if primary Ca-phosphate minerals reacted with sulfuric acid with little transport of phosphate. Under fluid:rock ratios allowing transport of phosphate, a ferric phosphate phase such as ferrian giniite might form instead. Mössbauer measurements of ferrian giniite-bearing alteration products and synthetic ferrian giniite are consistent with Spirit's Mössbauer measurements of the ferric-bearing phase in Paso Robes soil, but are also consistent with ferric sulfate phases in the low-P soil Arad_Samra. Therefore, Mössbauer data alone do not constrain the fluid:rock ratio. However, the excess iron (hematite) in Paso Robles soil, which implies aqueous transport, combined with our laboratory experiments, suggest acid-sulfate alteration in a hydrothermal (fumarolic) environment at fluid:rock ratios sufficient to allow dissolution, transport, and precipitation of secondary chemical components including a ferric phosphate such as ferrian giniite.

  20. Surface water data and geographic relation to Tertiary age intrusions and hydrothermal alteration in the Grand Mesa, Uncompahgre, and Gunnison National Forests (GMUG) and intervening Bureau of Land Management (BLM) lands

    USGS Publications Warehouse

    Bove, Dana J.; Knepper, Daniel H.

    2000-01-01

    This data set covering the western part of Colorado includes water quality data from eight different sources (points), nine U.S. Geological Survey Digital Raster Graph (DRG) files for topographic bases, a compilation of Tertiary age intrusions (polygons and lines), and two geotiff files showing areas of hydrothermally altered rock. These data were compiled for use with an ongoing mineral resource assessment of theGrand Mesa, Uncompahgre, and Gunnison National Forests (GMUG) and intervening Bureau of Land Management(BLM) lands. This compilation was assembled to give federal land managers a preliminary view of water within sub-basinal areas, and to show possible relationships to Tertiary age intrusion and areas of hydrothermal alteration.

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

    NASA Astrophysics Data System (ADS)

    Getahun, Aberra; Reed, Mark H.; Symonds, Robert

    1996-05-01

    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 (FeCl 3) 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

  2. Long-term hydrocephalus alters the cytoarchitecture of the adult subventricular zone.

    PubMed

    Campos-Ordoñez, Tania; Herranz-Pérez, Vicente; Chaichana, Kaisorn L; Rincon-Torroella, Jordina; Rigamonti, Daniele; García-Verdugo, Jose M; Quiñones-Hinojosa, Alfredo; Gonzalez-Perez, Oscar

    2014-11-01

    Hydrocephalus can develop secondarily to a disturbance in production, flow and/or absorption of cerebrospinal fluid. Experimental models of hydrocephalus, especially subacute and chronic hydrocephalus, are few and limited, and the effects of hydrocephalus on the subventricular zone are unclear. The aim of this study was to analyze the effects of long-term obstructive hydrocephalus on the subventricular zone, which is the neurogenic niche lining the lateral ventricles. We developed a new method to induce hydrocephalus by obstructing the aqueduct of Sylvius in the mouse brain, thus simulating aqueductal stenosis in humans. In 120-day-old rodents (n=18 per group), the degree of ventricular dilatation and cellular composition of the subventricular zone were studied by immunofluorescence and transmission electron microscopy. In adult patients (age>18years), the sizes of the subventricular zone, corpus callosum, and internal capsule were analyzed by magnetic resonance images obtained from patients with and without aqueductal stenosis (n=25 per group). Mice with 60-day hydrocephalus had a reduced number of Ki67+ and doublecortin+cells on immunofluorescence, as well as decreased number of neural progenitors and neuroblasts in the subventricular zone on electron microscopy analysis as compared to non-hydrocephalic mice. Remarkably, a number of extracellular matrix structures (fractones) contacting the ventricular lumen and blood vessels were also observed around the subventricular zone in mice with hydrocephalus. In humans, the widths of the subventricular zone, corpus callosum, and internal capsule in patients with aqueductal stenosis were significantly smaller than age and gender-matched patients without aqueductal stenosis. In summary, supratentorial hydrocephalus reduces the proliferation rate of neural progenitors and modifies the cytoarchitecture and extracellular matrix compounds of the subventricular zone. In humans, this similar process reduces the subventricular

  3. Long-term hydrocephalus alters the cytoarchitecture of the adult subventricular zone

    PubMed Central

    Campos-Ordoñez, Tania; Herranz-Pérez, Vicente; Chaichana, Kaisorn L.; Rincon-Torroella, Jordina; Rigamonti, Daniele; García-Verdugo, Jose M.; Quiñones-Hinojosa, Alfredo; Gonzalez-Perez, Oscar

    2014-01-01

    Hydrocephalus can develop secondarily to a disturbance in production, flow and/or absorption of cerebrospinal fluid. Experimental models of hydrocephalus, especially subacute and chronic hydrocephalus, are few and limited, and the effects of hydrocephalus on the subventricular zone are unclear. The aim of this study was to analyze the effects of long-term obstructive hydrocephalus on the subventricular zone, which is the neurogenic niche lining the lateral ventricles. We developed a new method to induce hydrocephalus by obstructing the aqueduct of Sylvius in the mouse brain, thus simulating aqueductal stenosis in humans. In 120-day-old rodents (n = 18 per group), the degree of ventricular dilatation and cellular composition of the subventricular zone were studied by immunofluorescence and transmission electron microscopy. In adult patients (age > 18 years), the sizes of the subventricular zone, corpus callosum, and internal capsule were analyzed by magnetic resonance images obtained from patients with and without aqueductal stenosis (n=25 per group). Mice with 60-day hydrocephalus had a reduced number of Ki67+ and doublecortin+ cells on immunofluorescence, as well as decreased number of neural progenitors and neuroblasts in the subventricular zone on electron microscopy analysis as compared to non-hydrocephalic mice. Remarkably, a number of extracellular matrix structures (fractones) contacting the ventricular lumen and blood vessels were also observed around the subventricular zone in mice with hydrocephalus. In humans, the widths of the subventricular zone, corpus callosum, and internal capsule in patients with aqueductal stenosis were significantly smaller than age and gender-matched patients without aqueductal stenosis. In summary, supratentorial hydrocephalus reduces the proliferation rate of neural progenitors and modifies the cytoarchitecture and extracellular matrix compounds of the subventricular zone. In humans, this similar process reduces the

  4. Criteria for recognition of localization and timing of multiple events of hydrothermal alteration in sandstones illustrated by petrographic, fluid inclusion, and isotopic analysis of the Tera Group, Northern Spain

    NASA Astrophysics Data System (ADS)

    González-Acebrón, Laura; Goldstein, R. H.; Mas, Ramón; Arribas, José

    2011-11-01

    Stratigraphic relations, detailed petrography, microthermometry of fluid inclusions, and fine-scale isotopic analysis of diagenetic phases indicate a complex thermal history in Tithonian fluvial sandstones and lacustrine limestones of the Tera Group (North Spain). Two different thermal events have been recognized and characterized, which are likely associated with hydrothermal events that affected the Cameros Basin during the mid-Cretaceous and the Eocene. Multiple stages of quartz cementation were identified using scanning electron microscope cathodoluminescence on sandstones and fracture fills. Primary fluid inclusions reveal homogenization temperatures (Th) from 195 to 350°C in the quartz cements of extensional fracture fillings. The high variability of Th data in each particular fluid inclusion assemblage is related to natural reequilibration of the fluid inclusions, probably due to Cretaceous hydrothermal metamorphism. Some secondary fluid inclusion assemblages show very consistent data (Th = 281-305°C) and are considered not to have reequilibrated. They are likely related to an Eocene hydrothermal event or to a retrograde stage of the Cretaceous hydrothermalism. This approach shows how multiple thermal events can be discriminated. A very steep thermal gradient of 97-214°C/km can be deduced from δ18O values of ferroan calcites (δ18O -14.2/-11.8‰ V-PDB) that postdate quartz cements in fracture fillings. Furthermore, illite crystallinity data (anchizone-epizone boundary) are out of equilibrium with high fluid inclusion Th. These observations are consistent with heat-flux related to short-lived events of hydrothermal alteration focused by permeability contrasts, rather than to regional heat-flux associated with dynamo-thermal metamorphism. These results illustrate how thermal data from fracture systems can yield thermal histories markedly different from host-rock values, a finding indicative of hydrothermal fluid flow.

  5. Anhydrite precipitation in seafloor hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Theissen-Krah, Sonja; Rüpke, Lars H.

    2016-04-01

    The composition and metal concentration of hydrothermal fluids venting at the seafloor is strongly temperature-dependent and fluids above 300°C are required to transport metals to the seafloor (Hannington et al. 2010). Ore-forming hydrothermal systems and high temperature vents in general are often associated with faults and fracture zones, i.e. zones of enhanced permeabilities that act as channels for the uprising hydrothermal fluid (Heinrich & Candela, 2014). Previous numerical models (Jupp and Schultz, 2000; Andersen et al. 2015) however have shown that high permeabilities tend to decrease fluid flow temperatures due to mixing with cold seawater and the resulting high fluid fluxes that lead to short residence times of the fluid near the heat source. A possible mechanism to reduce the permeability and thereby to focus high temperature fluid flow are mineral precipitation reactions that clog the pore space. Anhydrite for example precipitates from seawater if it is heated to temperatures above ~150°C or due to mixing of seawater with hydrothermal fluids that usually have high Calcium concentrations. We have implemented anhydrite reactions (precipitation and dissolution) in our finite element numerical models of hydrothermal circulation. The initial results show that the precipitation of anhydrite efficiently alters the permeability field, which affects the hydrothermal flow field as well as the resulting vent temperatures. C. Andersen et al. (2015), Fault geometry and permeability contrast control vent temperatures at the Logatchev 1 hydrothermal field, Mid-Atlantic Ridge, Geology, 43(1), 51-54. M. D. Hannington et al. (2010), Modern Sea-Floor Massive Sulfides and Base Metal Resources: Toward an Estimate of Global Sea-Floor Massive Sulfide Potential, in The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries, edited by R. J. Goldfarb, E. E. Marsh and T. Monecke, pp. 317-338, Society of Economic Geologists

  6. Geochemical variability of hydrothermal emissions between three Pacific volcanic arc systems: Alaskan-Aleutian and Cascadian, North America and Taupo Volcanic Zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Blackstock, J. M.; Horton, T. W.; Gravley, D. M.; Deering, C. D.

    2013-12-01

    Knowledge of the source, transport, and fate of hydrothermal fluids in the upper crust informs our understanding and interpretation of ore-forming processes, volcanogenic hazards, geothermal resources, and volatile cycling. Co-variation between fluid inclusion CO2/CH4 and N2/Ar ratios is an established tracer of magmatic, meteoric, and crustal fluid end-members. Yet, this tracer has had limited application to macroscopic fluid reservoirs accessible via geothermal wells and hydrothermal features (e.g. pools). In this study, we compared the covariance CO2/CH4 and N2/Ar ratios of gases collected throughout the Taupo Volcanic Zone, New Zealand (TVZ), the Alaska-Aleutian Volcanic Arc, USA (AAVA), and the Cascadian Volcanic Arc, USA (CVA) with corresponding δ13C and 3He/4He values. Our findings show that there is good agreement between these proxies for different end-member contributions at coarse scales. However, some samples classified as meteoric water according to the CO2/CH4 and N2/Ar ratios also show more positive δ13C values (~ -7.0 per mil) and relatively higher 3He/4He ratios indicative of magmatic input from primarily mantle sources. This unexpected result may be related to magmatic fluids, CO2 in particular, mixing with predominantly meteoric derived waters. The potential to identify magmatic CO2 in groundwater samples overlying geothermal systems in differing volcanic arc settings using simple and cost-effective gas ratios is a promising step forward in the search for ';surface blind' but developable geothermal systems and volcanic monitoring. 3He/4He anomalies also support this inference and underscore the potential decoupling of thermal anomalies and magmatic-derived fluids in the Earth's crust. The general agreement between the co-variation of CO2/CH4 and N2/Ar ratios with other isotope and geochemical proxies for magmatic, meteoric, and crustal end-members is encouraging to employ expanded use of these ratios for both the exploration and monitoring of

  7. Preliminary report on the use of LANDSAT-1 (ERTS-1) reflectance data in locating alteration zones associated with uranium mineralization near Cameron, Arizona

    USGS Publications Warehouse

    Spirakis, Charles S.; Condit, Christopher D.

    1975-01-01

    LANDSAT-I (ERTS-I) multispectral reflectance data were used to enhance the detection of alteration around uranium deposits near Cameron, Ariz. The technique involved stretching and ratioing computer-enhanced data from which electronic noise and atmospheric haze had been removed. Using present techniques, the work proves that LANDSAT-I data are useful in detecting alteration around uranium deposits, but the method may still be improved. Bluish-gray mudstone in the target area could not be differentiated from the altered zones on the ratioed images. Further experiments involving combinations of ratioed and nonratioed data will be required to uniquely define the altered zones.

  8. The Rožná uranium deposit (Bohemian Massif, Czech Republic): shear zone-hosted, late Variscan and post-Variscan hydrothermal mineralization

    NASA Astrophysics Data System (ADS)

    Kříbek, Bohdan; Žák, Karel; Dobeš, Petr; Leichmann, Jaromír; Pudilová, Marta; René, Miloš; Scharm, Bohdan; Scharmová, Marta; Hájek, Antonín; Holeczy, Daniel; Hein, Ulrich F.; Lehmann, Bernd

    2009-01-01

    Three major mineralization events are recorded at the Rožná uranium deposit (total mine production of 23,000 t U, average grade of 0.24% U): (1) pre-uranium quartz-sulfide and carbonate-sulfide mineralization, (2) uranium, and (3) post-uranium quartz-carbonate-sulfide mineralization. (1) K-Ar ages for white mica from wall rock alteration of the pre-uranium mineralization style range from 304.5 ± 5.8 to 307.6 ± 6.0 Ma coinciding with the post-orogenic exhumation of the Moldanubian orogenic root and retrograde-metamorphic equilibration of the high-grade metamorphic host rocks. The fluid inclusion record consists of low-salinity aqueous inclusions, together with H2O-CO2-CH4, CO2-CH4, and pure CH4 inclusions. The fluid inclusion, paragenetic, and isotope data suggest that the pre-uranium mineralization formed from a reduced low-salinity aqueous fluid at temperatures close to 300°C. (2) The uraniferous hydrothermal event is subdivided into the pre-ore, ore, and post-ore substages. K-Ar ages of pre-ore authigenic K-feldspar range from 296.3 ± 7.5 to 281.0 ± 5.4 Ma and coincide with the transcurrent reorganization of crustal blocks of the Bohemian Massif and with Late Stephanian to Early Permian rifting. Massive hematitization, albitization, and desilicification of the pre-ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the Moldanubian domain. The wide range of salinities of fluid inclusions is interpreted as a result of the large-scale mixing of basinal brines with meteoric water. The cationic composition of these fluids indicates extensive interaction with crystalline rocks. Chlorite thermometry yielded temperatures of 260°C to 310°C. During this substage, uranium was probably leached from the Moldanubian crystalline rocks. The hydrothermal alteration of the ore substage followed, or partly overlapped in time, the pre-ore substage alteration. K-Ar ages of illite from ore substage alteration range from 277.2 ± 5.5 to

  9. Sulfur and oxygen isotope study of the Vermont copper belt: evidence of seawater hydrothermal alteration and sulfate reduction in a high-grade metamorphic terrane

    SciTech Connect

    Shanks, W.C. III; Woodruff, L.G.; Slack, J.F.

    1985-01-01

    Massive sulfide deposits of the Orange County copper district, in east-central Vermont, consist of stratiform lenses of pyrrhotite, chalcopyrite, and minor sphalerite within amphibolite-facies rocks of Early Devonian (.) age. The deposits occur at several different stratigraphic levels. The two largest, Elizabeth and Ely, are in quartz-mica schists of the Gile Mountain Formation; the Pike Hill deposit occurs in calcareous quartz-mica schist of the underlying Waits River Formation. Two small deposits (Orange and Gove) are within the Standing Pond Volcanics, a thin tholeiitic amphibolite near the Gile Mountain-Waits River contact. The Elizabeth deposit in particularly distinctive, and contains a suite of unusual wall rocks rich in quartz, carbonate, muscovite, amphibole, phlogopite, tourmaline, spessartine, and sodic plagioclase. Sulfur isotope values at Elizabeth and Ely of 5.1 to 9.1 per thousands contrast with values for Gove (1.9 to 4.2) and Pike Hill (1.5 to 4.6). Disseminated sulfides in amphibolites of the Standing Pond Volcanics have sulfur isotope values in the range -0.1 to 1.7 per thousands, typical of MORB. These data require sulfur contributions to massive sulfide deposits both from basalt and from contemporaneous seawater sulfate sources. Whole-rock (carbonate free) oxygen isotope analyses of host lithologies range from 7.9 per thousands (Standing Pond Volcanics) to 19.9 per thousands (Waits River Formation). Detailed sampling of Elizabeth wall rocks (including those high in B, Na, Mg, Al, Si, Mn) yields a narrow range of oxygen isotope values (11.1 to 14.1); heavier values correlate with higher silica contents. Isotopically light wallrock lithologies are probably due to premetamorphic seawater hydrothermal alteration.

  10. 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

  11. The Lac Des Iles Palladium Deposit, Ontario, Canada part I. The effect of variable alteration on the Offset Zone

    NASA Astrophysics Data System (ADS)

    Boudreau, Alan; Djon, Lionnel; Tchalikian, Arnaud; Corkery, John

    2014-06-01

    The recently discovered Offset Zone of the Mine Block Intrusion of the Lac des Iles Complex hosts palladium mineralization with unusually high Pd/Pt and Pd/Ir ratios in rocks that range from relatively unaltered norite to amphibolites and chlorite-actinolite-talc schist. Quantitative assessment of the effect of progressive alteration using mineral modes was done using total silicate H2O as a monitor of reaction progress ( ξ = moles H2O added to form alteration minerals per 100 g of rock). Major mineral modal variations define three reaction regions: (1) ξ = 0.00-0.03, characterized by epidote/clinozoisite formation and some amphibole; (2) ξ = 0.03-0.23, characterized by formation of chlorite, amphibole, quartz muscovite/sericite, and calcite after plagioclase + pyroxene; and (3) ξ = 0.23-0.28, characterized by the formation of talc after earlier formed amphibole. Epidote occurs as an incongruent product from the destruction of plagioclase that is itself lost as the reaction proceeds. Pyroxene is altered at about twice the rate of plagioclase, resulting in pyroxene-rich protoliths to be more altered than those relatively enriched in plagioclase. Major elements variations largely reflect variations in the plagioclase/pyroxene ratio of the protolith, but compositional trends suggest a loss of Na with reaction progress. The base metal sulfides chalcopyrite, pyrrhotite, and pentlandite show decreasing abundance with reaction progress, forming pyrite (± magnetite) as an intermediate reaction product that also is lost as the reaction proceeds. Millerite is overall low but increases slightly. A more limited data set on the platinum-group minerals suggests that platinum-group element (PGE)-arsenides increase whereas PGE-sulfides and PGE-Bi-tellurides decrease with reaction progress. Assuming ore element concentrations in the protolith were constant and similar to relatively fresh norites, Pd increases modestly, by 5 %, whereas Pt decreases by about 65 % in the most

  12. Cyclic development of igneous features and their relationship to high-temperature hydrothermal features in the Henderson porphyry molybdenum deposit, Colorado

    USGS Publications Warehouse

    Carten, R.B.; Geraghty, E.P.; Walker, B.M.

    1988-01-01

    The Henderson porphyry molybdenum deposit was formed by the superposition of coupled alteration and mineralization events, of varying intensity and size, that were associated with each of at least 11 intrusions. Deposition of molybdenite was accompanied by time-equivalent silicic and potassic alteration. High-temperature alteration and mineralization are spatially and temporally linked to the crystallization of compositionally zoned magma in the apex of stocks. Differences in hydrothermal features associated with each intrusion (e.g., mass of ore, orientation and type of veins, density of veins, and intensity of alteration) correlate with differences in primary igneous features (e.g., composition, texture, morphology, and size). The systematic relations between hydrothermal and magmatic features suggest that primary magma compositions, including volatile contents, largely control the geometry, volume, level of emplacement, and mechanisms of crystallization of stocks. These elements in turn govern the orientations and densities of fractures, which ultimately determine the distribution patterns of hydrothermal alteration and mineralization. -from Authors

  13. Geologic evolution of the Lost City Hydrothermal Field

    NASA Astrophysics Data System (ADS)

    Denny, Alden R.; Kelley, Deborah S.; Früh-Green, Gretchen L.

    2016-02-01

    The Lost City Hydrothermal Field (LCHF) is a novel serpentinite-hosted vent field located on the Atlantis Massif southern wall. Results of 2 m resolution bathymetry, side scan, and video and still imagery, integrated with direct submersible observations provide the first high-resolution geologic map of the LCHF. These data form the foundation for an evolutionary model for the vent system over the past >120,000 years. The field is located on a down-dropped bench 70 m below the summit of the massif. The bench is capped by breccia and pelagic carbonate deposits underlain by variably deformed and altered serpentinite and gabbroic rocks. Hydrothermal activity is focused at the 60 m tall, 100 m across, massive carbonate edifice "Poseidon," which is venting 91°C fluid. Hydrothermal activity declines south and west of the Poseidon complex and dies off completely at distances greater than 200 m. East of Poseidon, the most recent stage of hydrothermal flow is characterized by egress of diffuse fluids from narrow fissures within a low-angle, anastomosing mylonite zone. South of the area of current hydrothermal activity, there is evidence of two discrete previously unrecognized relict fields. Active venting sites defined by carbonate-filled fissures that cut the carbonate cap rock at the summit of the massif mark the present-day northernmost extent of venting. These spatial relationships reflect multiple stages of field development, the northward migration of venting over time, and the likely development of a nascent field at the massif summit.

  14. The Effect of Variable Greenschist Alteration on the Offset Zone of the Lac Des Iles Pd Deposit, Ontario, Canada

    NASA Astrophysics Data System (ADS)

    Boudreau, A. E.

    2013-12-01

    The recently discovered Offset zone of the Mine Block Intrusion of the Lac des Iles Complex hosts Pd deposits with unusually high Pd/Pt and Pd/Ir ratios in rocks that range from relatively unaltered mineralized norite to chlorite-actinolite-talc schist. Questions remain as to the degree the deposit is magmatic or has been upgraded by later fluid activity. Quantitative assessment of the effect of progressive alteration using mineral modes was done using total silicate H2O as a monitor of reaction progress (ξ = moles H2O added to form alteration minerals). Major mineral modal variations define three reaction regions: (1) ξ = 0.00 - 0.03, characterized by epidote/clinozoisite formation and some amphibole, (2) ξ = 0.03 - 0.23, characterized by precipitation of chlorite, amphibole, quartz muscovite/sericite and calcite after plagioclase + pyroxene and (3) ξ = 0.23 - 0.28, characterized by the production of talc after earlier formed amphibole. Epidote occurs as an incongruent product from the destruction of plagioclase that is itself lost as the reaction proceeds. Pyroxene is altered at about twice the rate of plagioclase, resulting in pyroxene-rich protoliths to be more altered than those relatively enriched in plagioclase. Major elements variations largely reflect variations in the plagioclase/pyroxene ratio of the protolith but suggest mainly a loss of Na with reaction progress. Base metal sulfides chalcopyrite, pyrrhotite and pentlandite show decreasing abundance with reaction progress, dissolving incongruently to pyrite and magnetite as intermediate reaction products. Millerite is overall low but increase slightly. A more limited data set on the platinum-group minerals suggests that PGE-arsenides increase whereas PGE-sulfides and PGE-Bi-tellurides decrease with reaction progress. Assuming ore element concentrations in the protolith were constant and similar to relatively fresh norites, Pd increases modestly, by 5%, whereas Pt decreases by about 65% in the most

  15. Exploration of gold occurrences in alteration zones at Dungash district, Southeastern Desert of Egypt using ASTER data and geochemical analyses

    NASA Astrophysics Data System (ADS)

    Salem, S. M.; El Sharkawi, M.; El-Alfy, Z.; Soliman, N. M.; Ahmed, S. E.

    2016-05-01

    The present study aims at exploration of new gold occurrences in the alteration zones at Dungash district. Processed ASTER images band ratios 7/6 × 4/6 and (7 + 9/8), field geology and mineralogical and geochemical data help characterize three types of alterations in three areas 1 to 3 that may be targeted for Au exploration. Area1 confined to the metavolcanics located in the SE of Dungash gold mine and revealed silicified and sericitized type alterations, composed of quartz, epidote, chlorite, biotite and opaque minerals mainly pyrite and chalcopyrite. Area2 occurs in the gabbro-diorite rocks at Abu Meraiwa area NE of Dungash gold mine, which are rich in kaolinite, illite, sericite, pyrite, arsenopyrite and chalcopyrite that record kaolinitized alteration. Area3 is hosted in carbonaceous listwaenized serpentinite thus indicating the role of listwaenitization type alteration in ore genesis. It is composed of calcite, chromite, pyrite, arsenopyrite, chalcopyrite and Ni-bearing sulphides. Au contents in area 1 range between 0.12 and 14.91 ppm, and between 6.1 and 16.3 ppm in area 2, while gold values in area 3 vary from <0.01 to 0.03 ppm. Dungash district is comprised of Pan-African assemblages of ophiolitic ultramafics thrusted over the island arc metavolcanics of dacitic- andesite composition. Gabbro-diorite rocks are intruded in the ultramafics and the acidic metavolcanics as well as diorite-quartz diorite suite intruded in the intermediate metavolcanics. Several acidic dykes, granitic dykes and quartz veins cut through the different rocks types.

  16. Distributions of Irritative Zones Are Related to Individual Alterations of Resting-State Networks in Focal Epilepsy

    PubMed Central

    Song, Yinchen; Sanganahalli, Basavaraju G.; Hyder, Fahmeed; Lin, Wei-Chiang; Riera, Jorge J.

    2015-01-01

    Alterations in the connectivity patterns of the fMRI-based resting-state networks (RSNs) have been reported in several types of epilepsies. Evidence pointed out these alterations might be associated with the genesis and propagation of interictal epileptiform discharges (IEDs). IEDs also evoke blood-oxygen-level dependent (BOLD) responses, which have been used to delineate irritative zones during preoperative work-up. Therefore, one may expect a relationship between the topology of the IED-evoked BOLD response network and the altered spatial patterns of the RSNs. In this study, we used EEG recordings and fMRI data obtained simultaneously from a chronic model of focal epilepsy in Wistar rats to verify our hypothesis. We found that IED-evoked BOLD response networks comprise both cortical and subcortical structures with a rat-dependent topology. In all rats, IEDs evoke both activation and deactivation types of BOLD responses. Using a Granger causality method, we found that in many cases areas with BOLD deactivation have directed influences on areas with activation (p<0.05). We were able to predict topological properties (i.e., focal/diffused, unilateral/bilateral) of the IED-evoked BOLD response network by performing hierarchical clustering analysis on major spatial features of the RSNs. All these results suggest that IEDs and disruptions in the RSNs found previously in humans may be different manifestations of the same transient events, probably reflecting altered consciousness. In our opinion, the shutdown of specific nodes of the default mode network may cause uncontrollable excitability in other functionally connected brain areas. We conclude that IED-evoked BOLD responses (i.e., activation and deactivation) and alterations of RSNs are intrinsically related, and speculate that an understanding of their interplay is necessary to discriminate focal epileptogenesis and network propagation phenomena across different brain modules via hub-based connectivity. PMID

  17. Exploration of gold occurrences in alteration zones at Dungash district, Southeastern Desert of Egypt using ASTER data and geochemical analyses

    NASA Astrophysics Data System (ADS)

    Salem, S. M.; El Sharkawi, M.; El-Alfy, Z.; Soliman, N. M.; Ahmed, S. E.

    2016-05-01

    The present study aims at exploration of new gold occurrences in the alteration zones at Dungash district. Processed ASTER images band ratios 7/6 × 4/6 and (7 + 9/8), field geology and mineralogical and geochemical data help characterize three types of alterations in three areas 1 to 3 that may be targeted for Au exploration. Area1 confined to the metavolcanics located in the SE of Dungash gold mine and revealed silicified and sericitized type alterations, composed of quartz, epidote, chlorite, biotite and opaque minerals mainly pyrite and chalcopyrite. Area2 occurs in the gabbro-diorite rocks at Abu Meraiwa area NE of Dungash gold mine, which are rich in kaolinite, illite, sericite, pyrite, arsenopyrite and chalcopyrite that record kaolinitized alteration. Area3 is hosted in carbonaceous listwaenized serpentinite thus indicating the role of listwaenitization type alteration in ore genesis. It is composed of calcite, chromite, pyrite, arsenopyrite, chalcopyrite and Ni-bearing sulphides. Au contents in area 1 range between 0.12 and 14.91 ppm, and between 6.1 and 16.3 ppm in area 2, while gold values in area 3 vary from <0.01 to 0.03 ppm. Dungash district is comprised of Pan-African assemblages of ophiolitic ultramafics thrusted over the island arc metavolcanics of dacitic- andesite composition. Gabbro-diorite rocks are intruded in the ultramafics and the acidic metavolcanics as well as diorite-quartz diorite suite intruded in the intermediate metavolcanics. Several acidic dykes, granitic dykes and quartz veins cut through the different rocks types.

  18. Distributions of Irritative Zones Are Related to Individual Alterations of Resting-State Networks in Focal Epilepsy.

    PubMed

    Song, Yinchen; Sanganahalli, Basavaraju G; Hyder, Fahmeed; Lin, Wei-Chiang; Riera, Jorge J

    2015-01-01

    Alterations in the connectivity patterns of the fMRI-based resting-state networks (RSNs) have been reported in several types of epilepsies. Evidence pointed out these alterations might be associated with the genesis and propagation of interictal epileptiform discharges (IEDs). IEDs also evoke blood-oxygen-level dependent (BOLD) responses, which have been used to delineate irritative zones during preoperative work-up. Therefore, one may expect a relationship between the topology of the IED-evoked BOLD response network and the altered spatial patterns of the RSNs. In this study, we used EEG recordings and fMRI data obtained simultaneously from a chronic model of focal epilepsy in Wistar rats to verify our hypothesis. We found that IED-evoked BOLD response networks comprise both cortical and subcortical structures with a rat-dependent topology. In all rats, IEDs evoke both activation and deactivation types of BOLD responses. Using a Granger causality method, we found that in many cases areas with BOLD deactivation have directed influences on areas with activation (p<0.05). We were able to predict topological properties (i.e., focal/diffused, unilateral/bilateral) of the IED-evoked BOLD response network by performing hierarchical clustering analysis on major spatial features of the RSNs. All these results suggest that IEDs and disruptions in the RSNs found previously in humans may be different manifestations of the same transient events, probably reflecting altered consciousness. In our opinion, the shutdown of specific nodes of the default mode network may cause uncontrollable excitability in other functionally connected brain areas. We conclude that IED-evoked BOLD responses (i.e., activation and deactivation) and alterations of RSNs are intrinsically related, and speculate that an understanding of their interplay is necessary to discriminate focal epileptogenesis and network propagation phenomena across different brain modules via hub-based connectivity. PMID

  19. Altered speeds and trajectories of neurons migrating in the ventricular and subventricular zones of the reeler neocortex.

    PubMed

    Britto, Joanne M; Tait, Karen J; Johnston, Leigh A; Hammond, Vicki E; Kalloniatis, Michael; Tan, Seong-Seng

    2011-05-01

    The Reelin signaling pathway is essential for proper cortical development, but it is unclear to whether Reelin function is primarily important for cortical layering or neuron migration. It has been proposed that Reelin is perhaps required only for somal translocation but not glial-dependent locomotion. This implies that the location of neurons responding to Reelin is restricted to the outer regions of the cortical plate (CP). To determine whether Reelin is required for migration outside of the CP, we used time-lapse imaging to track the behavior of cells undergoing locomotion in the germinal zones. We focused on the migratory activity in the ventricular/subventricular zones where the first transition of bipolar to multipolar migration occurs and where functional Reelin receptors are known to be expressed. Despite Reelin loss, neurons had no difficulty in undergoing radial migration and indeed displayed greater migratory speed. Additionally, compared with the wild-type, reeler neurons displayed altered trajectories with greater deviation from a radial path. These results suggest that Reelin loss has early consequences for migration in the germinal zones that are portrayed as defective radial trajectories and migratory speeds. Together, these abnormalities can give rise to the increased cell dispersion observed in the reeler cortex. PMID:20847150

  20. Fracture zones in the Mid Atlantic Ridge lead to alterations in prokaryotic and viral parameters in deep-water masses.

    PubMed

    Muck, Simone; Griessler, Thomas; Köstner, Nicole; Klimiuk, Adam; Winter, Christian; Herndl, Gerhard J

    2014-01-01

    We hypothesized that mixing zones of deep-water masses act as ecotones leading to alterations in microbial diversity and activity due to changes in the biogeochemical characteristics of these boundary systems. We determined the changes in prokaryotic and viral abundance and production in the Vema Fracture Zone (VFZ) of the subtropical North Atlantic Ocean, where North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) are funneled through this narrow canyon and therefore, are subjected to intense vertical mixing. Consequently, salinity, potential temperature, oxygen, PO4, SiO4, NO3 were altered in the NADW inside the VFZ as compared to the NADW outside of the VFZ. Also, viral abundance, lytic viral production (VP) and the virus-to-prokaryote ratio (VPR) were elevated in the NADW in the VFZ as compared to the NADW outside the VFZ. In contrast to lytic VP, lysogenic VP and both the frequency of lytically (FIC) and lysogenically infected cells (FLC) did not significantly differ between in- and outside the VFZ. Generally, FIC was higher than FLC throughout the water column. Prokaryotic (determined by T-RFLP) and viral (determined by RAPD-PCR) community composition was depth-stratified inside and outside the VFZ. The viral community was more modified both with depth and over distance inside the VFZ as compared to the northern section and to the prokaryotic communities. However, no clusters of prokaryotic and viral communities characteristic for the VFZ were identified. Based on our observations, we conclude that turbulent mixing of the deep water masses impacts not only the physico-chemical parameters of the mixing zone but also the interaction between viruses and prokaryotes due to a stimulation of the overall activity. However, only minor effects of deep water mixing were observed on the community composition of the dominant prokaryotes and viruses. PMID:24917857

  1. Indications of mineral zoning in a fossil hydrothermal system at the Meager Creek geothermal prospect, British Columbia, Canada, from induced polarization studies

    SciTech Connect

    Ward, S.H.; Zhao, J.X.; Groenwald, J.; Moore, J.N.

    1985-05-01

    By measuring the induced-polarization parameters m (chargeability) and tau (time-constant) we have found evidence that the center of a presumed fossil hydrothermal system at Meager Creek, British Columbia, lies south of the main manifestation of the present-day convective hydrothermal system. What implication this finding has for development of the present-day system is unknown. However, some of the fractures formed during the development of the fossil hydrothermal system may serve as conduits for fluids of the present-day system. The analysis is limited by the lack of availability of a good subsurface distribution of core samples. Nevertheless, a surface induced-polarization survey is expected to yield information about the geometry of the fossil system. Such knowledge would have implications not only for Meager Creek but for other hydrothermal systems of Cascades volcano type. 16 refs., 15 figs., 1 tab.

  2. Near-Seafloor Magnetic Exploration of Submarine Hydrothermal Systems in the Kermadec Arc

    NASA Astrophysics Data System (ADS)

    Caratori Tontini, F.; de Ronde, C. E. J.; Tivey, M.; Kinsey, J. C.

    2014-12-01

    Magnetic data can provide important information about hydrothermal systems because hydrothermal alteration can drastically reduce the magnetization of the host volcanic rocks. Near-seafloor data (≤70 m altitude) are required to map hydrothermal systems in detail; Autonomous Underwater Vehicles (AUVs) are the ideal platform to provide this level of resolution. Here, we show the results of high-resolution magnetic surveys by the ABE and Sentry AUVs for selected submarine volcanoes of the Kermadec arc. 3-D magnetization models derived from the inversion of magnetic data, when combined with high resolution seafloor bathymetry derived from multibeam surveys, provide important constraints on the subseafloor geometry of hydrothermal upflow zones and the structural control on the development of seafloor hydrothermal vent sites as well as being a tool for the discovery of previously unknown hydrothermal sites. Significant differences exist between the magnetic expressions of hydrothermal sites at caldera volcanoes ("donut" pattern) and cones ("Swiss cheese" pattern), respectively. Subseafloor 3-D magnetization models also highlight structural differences between focused and diffuse vent sites.

  3. An oxygen isotope and geochemical study of meteoric-hydrothermal systems at Pilot Mountain and selected other localities, Carolina slate belt

    USGS Publications Warehouse

    Klein, T.L.; Criss, R.E.

    1988-01-01

    Several epigenetic mineral deposits in the Carolina slate belt are intimately related to meteoric-hydrothermal systems of late Precambrian and early Paleozoic age. At Pilot Mountain, low 18O rocks correlate well with zones of strong silicic alteration and alkali leaching accompanied by high alumina minerals (sericite, pyrophyllite, andalusite ?? topaz) and anomalous concentrations of Cu, Mo, Sn, B, and Au. A magmatic source for much of the sulfur and metal is likely, and a subordinate magmatic water component in the fluid of the central zone is possible. This central zone is surrounded by a >30 km2 peripheral zone of low 18O sericite schists, chlorite-sericite schists, and andesitic volcanic rocks. Reconnaissance studies of other alteration zones in the Carolina slate belt have so far disclosed the involvement of meteoric-hydrothermal fluids at the Snow Camp pyrophyllite deposit, at the Hoover Hill and Sawyer Au mines, and probably at the Haile and Brewer Au mines. -from Authors

  4. The chemistry of hydrothermal magnetite: a review

    USGS Publications Warehouse

    Nadoll, Patrick; Angerer, Thomas; Mauk, Jeffrey L.; French, David; Walshe, John

    2014-01-01

    Magnetite (Fe3O4) is a well-recognized petrogenetic indicator and is a common accessory mineral in many ore deposits and their host rocks. Recent years have seen an increased interest in the use of hydrothermal magnetite for provenance studies and as a pathfinder for mineral exploration. A number of studies have investigated how specific formation conditions are reflected in the composition of the respective magnetite. Two fundamental questions underlie these efforts — (i) How can the composition of igneous and, more importantly, hydrothermal magnetite be used to discriminate mineralized areas from barren host rocks, and (ii) how can this assist exploration geologists to target ore deposits at greater and greater distances from the main mineralization? Similar to igneous magnetite, the most important factors that govern compositional variations in hydrothermal magnetite are (A) temperature, (B) fluid composition — element availability, (C) oxygen and sulfur fugacity, (D) silicate and sulfide activity, (E) host rock buffering, (F) re-equilibration processes, and (G) intrinsic crystallographic controls such as ionic radius and charge balance. We discuss how specific formation conditions are reflected in the composition of magnetite and review studies that investigate the chemistry of hydrothermal and igneous magnetite from various mineral deposits and their host rocks. Furthermore, we discuss the redox-related alteration of magnetite (martitization and mushketovitization) and mineral inclusions in magnetite and their effect on chemical analyses. Our database includes published and previously unpublished magnetite minor and trace element data for magnetite from (1) banded iron formations (BIF) and related high-grade iron ore deposits in Western Australia, India, and Brazil, (2) Ag–Pb–Zn veins of the Coeur d'Alene district, United States, (3) porphyry Cu–(Au)–(Mo) deposits and associated (4) calcic and magnesian skarn deposits in the southwestern United

  5. The Mantos Blancos copper deposit: an upper Jurassic breccia-style hydrothermal system in the Coastal Range of Northern Chile

    NASA Astrophysics Data System (ADS)

    Ramírez, L. E.; Palacios, C.; Townley, B.; Parada, M. A.; Sial, A. N.; Fernandez-Turiel, J. L.; Gimeno, D.; Garcia-Valles, M.; Lehmann, B.

    2006-06-01

    The Upper Jurassic Mantos Blancos copper deposit (500 Mt at 1.0% Cu), located in the Coastal Range of northern Chile, displays two superimposed hydrothermal events. An older phyllic alteration probably related to felsic magmatic-hydrothermal brecciation at ˜155 Ma, and younger (141-142 Ma) potassic, propylitic, and sodic alterations, coeval with dioritic and granodioritic stocks and sills, and dioritic dikes. Main ore formation is genetically related to the second hydrothermal event, and consists of hydrothermal breccias, disseminations and stockwork-style mineralization, associated with sodic alteration. Hypogene sulfide assemblages show distinctive vertical and lateral zoning, centered on magmatic and hydrothermal breccia bodies, which constitute the feeders to mineralization. A barren pyrite root zone is overlain by pyrite-chalcopyrite, and followed upwards and laterally by chalcopyrite-digenite or chalcopyrite-bornite. The assemblage digenite-supergene chalcocite characterizes the central portions of high-grade mineralization in the breccia bodies. Fluid inclusions show evidence of boiling during the potassic and sodic alteration events, which occurred at temperatures around 450-460°C and 350-410°C, and salinities between 3-53 and 13-45 wt% NaCl eq., respectively. The hydrothermal events occurred during episodic decompression due to fluid overpressuring, hydrofracturing, and sharp changes from lithostatic to hydrostatic conditions. Sulfur isotope results of hypogene sulfide minerals fall in a narrow range around 0 per mil, suggesting a dominance of magmatic sulfur. Carbon and oxygen isotopic data of calcites from propylitic alteration suggest a mantle-derived carbon and oxygen isotope fractionation due to low-temperature alteration.

  6. Exploring an active hydrothermal system - An analogue study from the Swiss Alps

    NASA Astrophysics Data System (ADS)

    Egli, Daniel; Herwegh, Marco; Berger, Alfons; Baron, Ludovic

    2016-04-01

    Understanding the detailed flow paths in hydrothermal reservoirs is crucial for successful exploration of naturally porous and permeable rock masses for energy production. However, due to the common inaccessibility of active hydrothermal systems of suitable depth, e.g. in the northern Alpine foreland of the European Alps, direct observations are normally impossible and the knowledge about such systems is still insufficient. For that reason, a known fault-bound hydrothermal system in the crystalline basement of the Aar Massif serves as an analogue for potential geothermal reservoirs in the deep crystalline subsurface of the northern Alpine foreland. During summer 2015, a 125 m hole has been drilled across this active hydrothermal zone on the Grimsel Pass for in-situ characterization of its structural, petrophysical, mechanical as well as geophysical parameters. With this information, this project aims at improving the knowledge of natural hydrothermal systems as a potentially exploitable energy source. The investigated system is characterized by a central breccia zone surrounded by different types of cataclasites and localized high strain zones. The surrounding includes different altered and deformed granitoid host rocks. In this study, we focus on the ductile and brittle deformation (shear zones, fractures, joints) that provides the main fluid pathways. Their spatial distribution around a central water-bearing breccia zone as well as their continuity and permeability provide constraints on the water flow paths in such structurally controlled hydrothermal systems. The aim will be the connection of detailed structural data with petrophysical parameters such as porosities and permeabilities. The drillcore shows the high variability of deformation structures and related fluid pathways at different scales (millimeter-decameter) demonstrating the urgent need for an improved understanding of the link between mechanical evolution, associated deformation structures as well

  7. Crustal magnetization and the subseafloor structure of the ASHES vent field, Axial Seamount, Juan de Fuca Ridge: Implications for the investigation of hydrothermal sites

    NASA Astrophysics Data System (ADS)

    Caratori Tontini, Fabio; Crone, Timothy J.; Ronde, Cornel E. J.; Fornari, Daniel J.; Kinsey, James C.; Mittelstaedt, Eric; Tivey, Maurice

    2016-06-01

    High-resolution geophysical data have been collected using the Autonomous Underwater Vehicle (AUV) Sentry over the ASHES (Axial Seamount Hydrothermal Emission Study) high-temperature (~348°C) vent field at Axial Seamount, on the Juan de Fuca Ridge. Multiple surveys were performed on a 3-D grid at different altitudes above the seafloor, providing an unprecedented view of magnetic data resolution as a function of altitude above the seafloor. Magnetic data derived near the seafloor show that the ASHES field is characterized by a zone of low magnetization, which can be explained by hydrothermal alteration of the host volcanic rocks. Surface manifestations of hydrothermal activity at the ASHES vent field are likely controlled by a combination of local faults and fractures and different lava morphologies near the seafloor. Three-dimensional inversion of the magnetic data provides evidence of a vertical, pipe-like upflow zone of the hydrothermal fluids with a vertical extent of ~100 m.

  8. Root-Zone Salinity Alters Raffinose Oligosaccharide Metabolism and Transport in Coleus.

    PubMed Central

    Gilbert, G. A.; Wilson, C.; Madore, M. A.

    1997-01-01

    Exposure of variegated coleus (Coleus blumei Benth.) plants to a saline root-zone environment (60 mM NaCl:12 mM CaCl2) resulted in a significant decline in elongation growth rate over the 30-d experimental period. During the initial 5 to 10 d of exposure, mature source leaves showed strongly diminished rates of photosynthesis, which gradually recovered to close to the control rates by the end of the experiment. In green leaf tissues, starch levels showed the same transient decline and recovery pattern. Low starch levels were accompanied by the appearance of several novel carbohydrates, including high-molecular-weight raffinose family oligosaccharides (RFOs) with a degree of polymerization (DP) of 5 to 8, and an O-methylated inositol (OMI). New enzyme activities, including galactan:galactan galactosyltransferase, for the synthesis of high-DP RFOs and myo-inositol 6-O-methyltransferase for O-methylation of myo-inositol, were induced by salinity stress. Phloem-sap analysis showed that in the stressed condition substantially more sucrose than RFO was exported, as was the OMI. In white sink tissues these phloem sugars were used to synthesize high-DP RFOs but not OMIs. In sink tissues galactan:galactan galactosyltransferase but not myo-inositol 6-O-methyltransferase was induced by salinity stress. Models reflecting the changes in carbohydrate metabolism in source and sink tissues in response to salinity stress are presented. PMID:12223871

  9. Retinoic Acid and Environmental Enrichment Alter Subventricular Zone and Striatal Neurogenesis after Stroke

    PubMed Central

    Plane, Jennifer M.; Whitney, Justin T.; Schallert, Tim; Parent, Jack M.

    2010-01-01

    Neurogenesis increases in the adult rodent forebrain subventricular zone (SVZ) after experimental stroke. Newborn neurons migrate to the injured striatum, but few survive long-term and little evidence exists to suggest that they integrate or contribute to functional recovery. One potential strategy to improve stroke recovery is to stimulate neurogenesis and integration of adult-born neurons by using treatments that enhance neurogenesis. We examined the influence of retinoic acid (RA), which stimulates neonatal SVZ and adult hippocampal neurogenesis, and environmental enrichment (EE), which enhances survival of adult-born hippocampal neurons. We hypothesized that the combination of RA and EE would promote survival of adult-generated SVZ-derived neurons and improve functional recovery after stroke. Adult rats underwent middle cerebral artery occlusion, received BrdU on days 5–11 after stroke and were treated with RA/EE, RA alone, EE/vehicle or vehicle alone and were killed 61 days after stroke. Rats underwent repeated MRI and behavioral testing. We found that RA/EE treatment preserved striatal and hemisphere tissue and increased SVZ neurogenesis as demonstrated by Ki67 and doublecortin (DCx) immunolabeling. All treatments influenced the location of BrdU- and DCx-positive cells in the post-stroke striatum. RA/EE increased the number of BrdU/NeuN-positive cells in the injured striatum but did not lead to improvements in behavioral function. These results demonstrate that combined pharmacotherapy and behavioral manipulation enhances post-stroke striatal neurogenesis and decreases infarct volume without promoting detectable functional recovery. Further study of the integration of adult-born neurons in the ischemic striatum is necessary to determine their restorative potential. PMID:18778705

  10. Diagenetic alteration of iron and phosphorus records below the sulfate-methane-transition-zone in Black Sea sediments

    NASA Astrophysics Data System (ADS)

    Egger, Matthias; Kraal, Peter; Jilbert, Tom; Sulu-Gambari, Fatimah; Slomp, Caroline

    2016-04-01

    The sediments of the Black Sea are characterized by vast deposits of iron oxide-rich lake sediments below the current marine sediments. The lake sediments were deposited until ca. 9000 years ago when the former giant lake became connected to the Mediterranean Sea through post-glacial sea level rise. The subsequent downward diffusion of marine sulfate into the methane-bearing lake sediments has led to a multitude of diagenetic reactions in the sulfate-methane-transition zone (SMTZ), including anaerobic oxidation of methane (AOM) with sulfate. While the cycles of sulfur, methane and iron in the SMTZ have been extensively studied (e.g. Jorgensen et al., 2004), relatively little is known about the diagenetic alterations of the sediment record occurring directly below the SMTZ. Here, we combine detailed geochemical analyses of the sediment and pore water with multicomponent diagenetic modeling to study the diagenetic alterations below the SMTZ at two sites in the Black Sea. We focus on the dynamics of iron and phosphorus and demonstrate that downward sulfidization leads to dissolution of Fe-oxide bound P, Fe-carbonate and vivianite in the lake sediments. Below the sulfidization front, downward diffusing phosphate is bound again in vivianite. Trends in total sediment P with depth are significantly altered highlighting that diagenesis may strongly overprint burial records of P below a lake-marine transition. We also demonstrate that cryptic sulfur cycling cannot explain the observed release of dissolved Fe below the SMTZ. Instead, we suggest that organoclastic Fe-oxide reduction and/or AOM coupled to the reduction of Fe-oxides are the key processes explaining the high concentrations of dissolved Fe at depth in the sediment. Reference Jørgensen, B. B., Böttcher, M. E., Lüschen, H., Neretin, L. N. and Volkov, I. I.: Anaerobic methane oxidation and a deep H2S sink generate isotopically heavy sulfides in Black Sea sediments, Geochim. Cosmochim. Acta, 68(9), 2095-2118, 2004.

  11. Hydrothermal processes above the Yellowstone magma chamber: Large hydrothermal systems and large hydrothermal explosions

    USGS Publications Warehouse

    Morgan, L.A.; Shanks, W.C. Pat, III; Pierce, K.L.

    2009-01-01

    Hydrothermal explosions are violent and dramatic events resulting in the rapid ejection of boiling water, steam, mud, and rock fragments from source craters that range from a few meters up to more than 2 km in diameter; associated breccia can be emplaced as much as 3 to 4 km from the largest craters. Hydrothermal explosions occur where shallow interconnected reservoirs of steam- and liquid-saturated fluids with temperatures at or near the boiling curve underlie thermal fields. Sudden reduction in confi ning pressure causes fluids to fl ash to steam, resulting in signifi cant expansion, rock fragmentation, and debris ejection. In Yellowstone, hydrothermal explosions are a potentially signifi cant hazard for visitors and facilities and can damage or even destroy thermal features. The breccia deposits and associated craters formed from hydrothermal explosions are mapped as mostly Holocene (the Mary Bay deposit is older) units throughout Yellowstone National Park (YNP) and are spatially related to within the 0.64-Ma Yellowstone caldera and along the active Norris-Mammoth tectonic corridor. In Yellowstone, at least 20 large (>100 m in diameter) hydrothermal explosion craters have been identifi ed; the scale of the individual associated events dwarfs similar features in geothermal areas elsewhere in the world. Large hydrothermal explosions in Yellowstone have occurred over the past 16 ka averaging ??1 every 700 yr; similar events are likely in the future. Our studies of large hydrothermal explosion events indicate: (1) none are directly associated with eruptive volcanic or shallow intrusive events; (2) several historical explosions have been triggered by seismic events; (3) lithic clasts and comingled matrix material that form hydrothermal explosion deposits are extensively altered, indicating that explosions occur in areas subjected to intense hydrothermal processes; (4) many lithic clasts contained in explosion breccia deposits preserve evidence of repeated fracturing

  12. Falling phytoplankton: altered access to the photic zone over 60 years of warming in Lake Baikal, Siberia

    NASA Astrophysics Data System (ADS)

    Hampton, S. E.; Izmest'eva, L. R.; Moore, M.; Katz, S. L.

    2011-12-01

    Vertical stratification of aquatic ecosystems can be strongly reinforced by long-term warming, altering access to suitable habitat differentially across plankton taxa. Surface waters in the world's most voluminous freshwater lake - Lake Baikal in Siberia - are warming at an average rate of 2.01°C century-1, with more dramatic warming in the summer (3.78°C century-1). This long-term warming trend occurs within seasonal cycles of freezing and thawing, and against the larger backdrop of shorter-term climate dynamics, such as those associated with the Pacific Decadal Oscillation and Arctic Oscillation, with which shifting Siberian weather patterns affect the timing of seasonal changes (e.g., stratification) at the lake. While the increasing temperature difference between surface and deeper waters implies stronger stratification in the summer in general, the available long-term temperature data are not sufficiently fine-scaled across depth to further resolve stratification patterns. However, analysis of long-term vertical phytoplankton distributions may give perspectives on the dynamics of the physical environment that plankton experience. For example, many of Lake Baikal's endemic, cold-adapted phytoplankton species are large and heavy diatoms that require strong mixing to remain suspended, a process that is suppressed by stronger summer stratification. Observed vertical patterns of algal distribution are consistent with the predictions of increased warming and intensified stratification with diatoms present in summer increasingly sinking far beyond the photic zone. Specifically, the average depth of diatoms in August, the most reliably stratified month at Lake Baikal, has increased from depths roughly aligned with photic zone (0.1% light penetration) limits (ca. 40 m) in the 1970s to average depths approximately 48 m below the photic zone by the end of the century. Concurrently, smaller motile algae such as cryptomonads have maintained or increased their presence in

  13. Mechanical and transport properties of rocks at high temperatures and pressures. Task II: fracture permeability of crystalline rocks as a function of temperature, pressure, and hydrothermal alteration

    SciTech Connect

    Not Available

    1981-01-01

    The primary objective is to measure and understand the variation of the fracture permeability of quartzite subjected to hydrothermal conditions. Pore fluids will consist of distilled water and aqueous Na/sub 2/CO/sub 3/ solutions at temperatures to 250/sup 0/C, fluid pressures to 20 MPa and effective normal stresses to 70 MPa. Fluid flow rates will be controllable to rates at least as small as 0.2 ml/day (approx. 4 fracture volumes). Experiments are designed to assess what role, if any, pressure solution may play at time scales of those of the experiments (less than or equal to 2 weeks). Secondary objectives are: (1) continue simulated fracture studies, incorporating inelastic deformation into model and characterize the nature of inelastic deformation occurring on loaded tensile fractures in quartzite; (2) continue dissolution experiment, with emphasis on dissolution modification of tensile fracture surfaces on quartzite; and (3) study natural fractures in a quartzite exhibiting hydrothermal dissolution features.

  14. Hydrothermal ore-forming processes in the light of studies in rock- buffered systems: II. Some general geologic applications

    USGS Publications Warehouse

    Hemley, J.J.; Hunt, J.P.

    1992-01-01

    The experimental metal solubilities for rock-buffered hydrothermal systems provide important insights into the acquisition, transport, and deposition of metals in real hydrothermal systems that produced base metal ore deposits. Water-rock reactions that determine pH, together with total chloride and changes in temperature and fluid pressure, play significant roles in controlling the solubility of metals and determining where metals are fixed to form ore deposits. Deposition of metals in hydrothermal systems occurs where changes such as cooling, pH increase due to rock alteration, boiling, or fluid mixing cause the aqueous metal concentration to exceed saturation. Metal zoning results from deposition occurring at successive saturation surfaces. Zoning is not a reflection simply of relative solubility but of the manner of intersection of transport concentration paths with those surfaces. Saturation surfaces will tend to migrate outward and inward in prograde and retrograde time, respectively, controlled by either temperature or chemical variables. -from Authors

  15. Oxygen isotope mapping of the Archean Sturgeon Lake caldera complex and VMS-related hydrothermal system, Northwestern Ontario, Canada

    NASA Astrophysics Data System (ADS)

    Holk, Gregory J.; Taylor, Bruce E.; Galley, Alan G.

    2008-08-01

    The hydrothermal and magmatic evolution of the Sturgeon Lake caldera complex is graphically documented by a regional-scale (525 km2) analysis of oxygen isotopes. Spatial variations in whole-rock oxygen isotope compositions provide a thermal map of the cumulative effects of multiple stages of hydrothermal metasomatism before, during, and after volcanogenic massive sulfide (VMS) mineralization. There is a progressive, upward increase in δ18O from less than 2‰ to greater than 15‰ through a 5-km-thick section above the Biedelman Bay subvolcanic intrusive complex. This isotopic trend makes it clear that at least the earlier phases of this intrusive complex were coeval with the overlying VMS-hosting cauldron succession and provided thermal energy to drive a convective hydrothermal circulation system. The sharp contrast in δ18O values between late stage phases of the Biedelman Bay intrusion and immediate hanging wall strata indicates that the main phase of VMS-related hydrothermal activity took place before late-stage resurgence in the cauldron-related magmatic activity. Mineralogical and isotopic evidence indicates the presence of both syn- and postmineralization hydrothermal activity defined by the presence of widespread semiconformable and more restricted discordant alteration zones that affect the pre- and syncauldron strata. The semiconformable alteration zones formed during early stages of hydrothermal circulation and are defined by widespread silicification and carbonatization in association with relatively high δ18O values. The discordant alteration assemblages, containing Al-silicate minerals with chloritoid and/or Fe-rich carbonate or chlorite, centered on synvolcanic faults represent restricted zones of both seawater inflow and hydrothermal fluid upflow. A rapid increase in δ18O values (˜7-9‰) over a short distance (<200 m) suggests marked cooling of hydrothermal fluid from ˜350°C to less than 130°C either just before or during discharge onto the

  16. Mineralogy at the magma-hydrothermal system interface in andesite volcanoes, New Zealand

    NASA Astrophysics Data System (ADS)

    Wood, C. Peter

    1994-01-01

    Ejecta from phreatomagmatic eruptions of Ruapehu and White Island andesite volcanoes in New Zealand provide insight into the mineralogical reactions that occur when magma invades a vent-hosted hydrothermal system. At the surface and in ejected blocks from shallow depths, hydrothermal alteration mineralogies are dominated by silica polymorphs, anhydrite, natroalunite, and pyrite. Blocks from greater depths are composed mainly of cristobalite, anhydrite, halite, and magnetite. Where altered material was heated to magmatic temperatures, thermal decomposition reactions produced mullite, wollastonite, and indialite. Some ejected breccias contain osumilite, cordierite, sanidine, and hypersthene, indicative of reactions occurring near the osumilite-cordierite phase boundary at >800 °C and water pressure <0.2 kbar. Hedenbergite, wollastonite, andradite, and magnetite are found in rare skarn fragments, possibly formed by metasomatism of silica-poor, sulfate-rich hydrothermal deposits. High- temperature parageneses of these types have not been reported before in shallow, acidic volcano-hydrothermal systems. However, they may be typical of the magma- hydrothermal contact zone at many andesite volcanoes.

  17. Gold-silver mining districts, alteration zones, and paleolandforms in the Miocene Bodie Hills Volcanic Field, California and Nevada

    USGS Publications Warehouse

    Vikre, Peter G.; John, David A.; du Bray, Edward A.; Fleck, Robert J.

    2015-01-01

      Based on volcanic stratigraphy, geochronology, remnant paleosurfaces, and paleopotentiometric surfaces in mining districts and alteration zones, present landforms in the Bodie Hills volcanic field reflect incremental construction of stratovolcanoes and large- to small-volume flow-domes, magmatic inflation, and fault displacements. Landform evolution began with construction of the 15–13 Ma Masonic and 13–12 Ma Aurora volcanic centers in the northwestern and northeastern parts of the field, respectively. Smaller volcanoes erupted at ~11–10 Ma in, between, and south of these centers as erosional detritus accumulated north of the field in Fletcher Valley. Distally sourced, 9.7–9.3 Ma Eureka Valley Tuff filled drainages and depressions among older volcanoes and was partly covered by nearly synchronous eruptives during construction of four large 10–8 Ma volcanoes, in the southern part of the field. The lack of significant internal fault displacement, distribution of Eureka Valley Tuff, and elevation estimates derived from floras, suggest that the Bodie Hills volcanic field attained present elevations mostly through volcano construction and magmatic inflation, and that maximum paleoelevations (>8,500 ft) at the end of large volume eruptions at ~8 Ma are similar to present elevations.

  18. Modeling changes in mineral assemblages and sorptive capacity within the altered zone: analytical data for flow-through experiment

    SciTech Connect

    DeLoach, L., LLNL

    1997-10-01

    Mineral changes that may occur within the altered zone (AZ) will develop in response to complex interactions among condensate, pore waters, fracture mineralogy, and the mineralogy of the in situ rocks. At the Yucca Mountain site, the mineralogy of the in situ rock varies from one lithologic unit to another, reflecting different initial bulk rock chemistries and different degrees of devitrification and welding. To account for these variations when describing the possible changes the potential repository block will experience during heating and fluid movement, a credible database of experimental results describing the chemical and mineralogical consequences of rock-water interaction must be available; against this, modeling capabilities are compared. Once the capability is established to accurately simulate the time-dependent evolution of rock-water systems at elevated temperatures, confidence can be placed in models of the mineral changes expected within the AZ. This report describes experiments and modeling that consider the effects of different starting materials on mineral evolution and on the rates of mineral formation. Bounds are placed on the kinetics of the controlling dissolution-rate constants, which are the fundamental parameters that influence secondary mineral development. The sensitivity of the results to different secondary minerals is considered in the simulations. The most significant parameters affecting the results are shown to be the effective surface areas of the phases involved, the rate constants for the phases, and, for the case of vitric material, the model used for glass dissolution.

  19. Radiation damage-controlled localization of alteration haloes in albite: implications for alteration types and patterns vis-à-vis mineralization and element mobilization

    NASA Astrophysics Data System (ADS)

    Pal, D. C.; Chaudhuri, T.

    2016-07-01

    Uraninite, besides occurring in other modes, occurs as inclusions in albite in feldspathic schist in the Bagjata uranium deposits, Singhbhum shear zone, India. The feldspathic schist, considered the product of Na-metasomatism, witnessed multiple hydrothermal events, the signatures of which are preserved in the alteration halo in albite surrounding uraninite. Here we report radiation damage-controlled localization of alteration halo in albite and its various geological implications. Microscopic observation and SRIM/TRIM simulations reveal that the dimension of the alteration halo is dependent collectively on the zone of maximum cumulative α dose that albite was subjected to and by the extent of dissolution of uraninite during alteration. In well-preserved alteration haloes, from uraninite to the unaltered part of albite, the alteration minerals are systematically distributed in different zones; zone-1: K-feldspar; zone-2: chlorite; zone-3: LREE-phase/pyrite/U-Y-silicate. Based on textures of alteration minerals in the alteration microdomain, we propose a generalized Na+➔K+➔H+ alteration sequence, which is in agreement with the regional-scale alteration pattern. Integrating distribution of ore and alteration minerals in the alteration zone and their geochemistry, we further propose multiple events of U, REE, and sulfide mineralization/mobilization in the Bagjata deposit. The alteration process also involved interaction of the hydrothermal fluid with uraninite inclusions resulting in resorption of uraninite, redistribution of elements, including U and Pb, and resetting of isotopic clock. Thus, our study demonstrates that alteration halo is a miniature scale-model of the regional hydrothermal alteration types and patterns vis-à-vis mineralization/mobilization. This study further demonstrates that albite is vulnerable to radiation damage and damage-controlled fluid-assisted alteration, which may redistribute metals, including actinides, from radioactive minerals

  20. Distribution of Hydrothermal Mineral Assemblages in the Sevenmile Hole Area, Grand Canyon of the Yellowstone River, Yellowstone National Park, Wyoming

    NASA Astrophysics Data System (ADS)

    Phillips, A.; Larson, P.; John, D.; Cosca, M.; Pauley, B.; Manion, J.; Pritchard, C.; Andersen, A.

    2007-12-01

    Incision of the Grand Canyon of the Yellowstone River in Yellowstone National Park has exposed approximately 350 vertical meters of hydrothermally altered rhyolites. This older alteration formed in the shallow portion of a hydrothermal system that was most likely similar to the modern Yellowstone hydrothermal environment. Hydrothermal fluid circulation is related to the ongoing rhyolitic magmatism that produced the Yellowstone caldera at 640 ka. The rhyolitic magmatism and hydrothermal system are shallow expressions of deeper mantle- derived basalts. The older alteration is well exposed in the Sevenmile Hole area, near the northeastern margin of the caldera. Here, the alteration protolith is the high silica, low-18O, rhyolitic Tuff of Sulfur Creek. The tuff erupted at about 480 ka after resurgent doming associated with the third cycle collapse of the Yellowstone caldera. The tuff is a rheomorphically deformed densely welded agglutinate fallout ash that was deposited along the caldera wall. It contains phenocrysts of quartz, sodic plagioclase, and potassium feldspar. The tuff is exposed from the rim of the canyon, which is very close to the pre-alteration paleosurface, to the river bottom where it is covered by detrital sediments and actively forming hot spring deposits. Rocks exposed within the field area are pervasively hydrothermally altered. Mineral phases in approximately 90 samples were determined in the field using a Portable Infrared Mineral Analyser (PIMA). Subsequently, more precise mineral determinations were made using standard petrographic and powder XRD techniques. The alteration mineralogy consists of variable assemblages that include zones of kaolinite + opal; kaolinite + alunite with local dickite and typically high opal and/or quartz concentrations; highly silicified zones containing illite with or without smectite; and weakly silicified zones containing mostly illite. Minor (less than 1 percent) fine-grained disseminated pyrite is ubiquitous. The

  1. Fossil Magmatic-Hydrothermal Systems in Pleistocene Brokeoff Volcano, Lassen Volcanic National Park, California

    NASA Astrophysics Data System (ADS)

    John, D. A.; Breit, G. N.; Lee, R. G.; Dilles, J. H.; Muffler, L. P.; Clynne, M. A.

    2006-12-01

    The mineralogy, distribution, and isotopic composition of altered rocks exposed in the core of Brokeoff Volcano are attributed to two fossil magmatic-hydrothermal systems that are partly masked by younger alteration related to modern hot springs. Brokeoff Volcano was a large andesitic volcano (~600 to 400 ka) that preceded formation of Lassen Peak and the Lassen dome field. The two centers of fossil hydrothermal activity are about 1 km apart and are identified here as the Brokeoff Mountain (BM) and Mt. Diller (MD) systems. The BM system, centered about 1 km NE of Brokeoff Mountain, covers about 1.5 km2 extending 2.5 km west from Diamond Peak, through Sulphur Works, to west of the ridge between Brokeoff Mountain and Mt. Diller. Alteration affected mostly andesite lavas and breccias of the Mill Canyon sequence (~600-475 ka). Core alteration extends westward and upward from an altered andesite plug exposed west of Sulphur Works. It consists of narrow, west-trending, brecciated vuggy silica ledges as long as 600 m surrounded by zones of variable thickness (<1 to 30 m) composed of alunite, kaolinite, pyrophyllite, dickite, topaz, pyrite, and a range of silica minerals. Farther outward from the advanced argillic alteration are broader zones of propylitic (chlorite-calcite-illite-pyrite) and smectite-pyrite alteration. Initial S-O isotopic data indicate that alunite formed by high-temperature disproportionation of magmatic SO2. The ~3 km2 MD system, centered about 1 km SE of Mt. Diller, extends 3 km ESE to near Bumpass Hell. Lavas and breccias of the Mill Canyon sequence and the Mt. Diller sequence (ca. 400 ka) have been hydrothermally altered. Although the center of the MD system is largely obscured by landslides and by superimposed steam-heated acid leaching related to present-day hydrothermal activity, recognized core alteration consists of pyrite-rich quartz-dickite and quartz-kaolinite breccias; pyrite content locally exceeds 50%. Only minor amounts of alunite and

  2. Rb-Sr and oxygen isotopic study of alkalic rocks from the Trans-Pecos magmatic province, Texas: Implications for the petrogenesis and hydrothermal alteration of continental alkalic rocks

    SciTech Connect

    Lambert, D.D.; Malek, D.J.; Dahl, D.A. )

    1988-10-01

    Rb-Sr and O isotopic data for mid-Tertiary alkalic rocks from the Trans-Pecos magmatic province of west Texas demonstrate that hydrothermal alteration and fluid/rock (cation exchange) interactions have affected the isotope geochemistry of these rocks. Strontium and O isotopic data for late-stage minerals in an alkali basalt (hawaiite) still record two episodes of fluid/rock interactions. These data suggest that later meteoric fluids introduced Sr with a Cretaceous marine {sup 87}Sr/{sup 86}Sr ratio into minerals with significant cation exchange capacity. Dilute HCl leaching experiments demonstrate the removal of this labile or exchangeable Sr from the alkali basalt. Rb-Sr isotopic data for the leached alkali basalt and handpicked calcite record a crystallization age of 42 Ma, consistent with K-Ar data for an unaltered alkali basalt (hawaiite) dike from the same area (42.6 {plus minus} 1.3 Ma). Leaching experiments on one phonolite suggest the Sr isotopic variability in unleached phonolite and nepheline trachyte samples may be attributed to Sr in secondary calcite and zeolites, which have an upper Cretaceous marine {sup 87}Sr/{sup 86}Sr ratio. Rb-Sr isotopic data for leached phonolite and sanidine separate yield an age of 36.5 {plus minus} 0.8 Ma, within analytical uncertainty of a K-Ar biotite age (36.0 {plus minus} 1.1 Ma) of another phonolite. These leaching experiments demonstrate that the Rb-Sr isotopic systematics of hydrothermally-altered continental alkalic rocks may be significantly improved, providing more reliable geochronologic and isotopic tracer information necessary in constructing precise models of mantle sources.

  3. Recrystallization and hydrothermal growth of high U-Th zircon in the Weondong deposit, Korea: Record of post-magmatic alteration

    NASA Astrophysics Data System (ADS)

    Park, Changyun; Song, Yungoo; Chung, Donghoon; Kang, Il-Mo; Khulganakhuu, Chuluunbaatar; Yi, Keewook

    2016-09-01

    In this study, we investigate zircons with high U and Th contents of 12,000-24,000 and 11,000-40,000 ppm, respectively, from leucocratic granite in the Weondong region of South Korea. Hydrothermally epitaxial growth textures are observed in addition to four distinct textures with different backscattered electron (BSE) intensities within single zircon crystals. We describe the internal textures of the zircon crystals and define the chemical characteristics of each textural domain. The zircon crystals show internally recrystallized and externally crystallized textures, supporting the concept of post-magmatic fluid control. After crystallization of the primary zircon by late magmatism, four types of secondary textures were developed. The type-I domain shows patchy forms within the primary domain due to the structural and chemical recrystallization of self-irradiated zircon by a fluid-dominated diffusion reaction process. The type-II domain is characterized by a pure zircon composition, mineral inclusions (mainly thorite), and micropores due to chemical recrystallization by a coupled dissolution-reprecipitation process during interaction with aqueous fluids. The type-III domain is the purest zircon, is interconnected with type-II, and formed by a second coupled dissolution-reprecipitation process. The type-IV domain is the hydrothermal recrystallization/overgrowth texture formed by the direct crystallization process from fluorine-enriched, zircon-saturated aqueous fluid. These results indicate that the zircon crystals were formed sequentially or intermittently through multi-genetic processes by post-magmatic fluids. Furthermore, we conclude that F-enriched post-magmatic fluid migrated large amounts of zirconium, resulting in the typical overgrowth texture of zircon.

  4. Microbial and Mineral Descriptions of the Interior Habitable Zones of Active Hydrothermal Chimneys from the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Holden, J. F.; Lin, T.; Ver Eecke, H. C.; Breves, E.; Dyar, M. D.; Jamieson, J. W.; Hannington, M. D.; Butterfield, D. A.; Bishop, J. L.; Lane, M. D.

    2013-12-01

    Actively venting hydrothermal chimneys and their associated hydrothermal fluids were collected from the Endeavour Segment, Juan de Fuca Ridge to determine the mineralogy, chemistry and microbial community composition of their interiors. To characterize the mineralogy, Mössbauer, FTIR, VNIR and thermal emission spectroscopies were used for the first time on this type of sample in addition to thin-section petrography, x-ray diffraction and elemental analyses. A chimney from the Bastille edifice was Fe-sulfide rich and composed primarily of chalcopyrite, marcasite-sphalerite, and pyrrhotite while chimneys from the Dante and Hot Harold edifices were Fe-sulfide poor and composed primarily of anhydrite. The bulk emissivity and reflectance spectroscopies corroborated well with the petrography and XRD analyses. The microbial community in the interior of Bastille was most closely related to mesophilic-to-thermophilic anaerobes of the deltaproteobacteria and hyperthermophilic archaea while those in the interiors of Dante and Hot Harold were most closely related to mesophilic-to-thermophilic aerobes of the beta-, gamma- and epsilonproteobacteria. The fluid temperatures (282-321°C) and chemistries of the three chimneys were very similar suggesting that differences in mineralogy and microbial community compositions were more dependent on fluid flow characteristics and paragenesis within the chimney. Thin-section petrography of the interior of another hydrothermal chimney collected from the Dante edifice (emitting 336°C fluid) shows a thin coat of Fe3+ oxide associated with amorphous silica on the exposed outer surfaces of pyrrhotite, sphalerite and chalcopyrite in pore spaces, along with anhydrite precipitation in the pores that is indicative of seawater ingress. The Fe-sulfide minerals were likely oxidized to ferrihydrite with increasing pH and Eh due to cooling and seawater exposure, providing reactants for bioreduction. Culture-based most-probable-number estimates of

  5. [In Situ Analysis of Element Geochemistry in Submarine Basalt in Hydrothermal Areas from Ultraslow Spreading Southwest Indian Ridge].

    PubMed

    Wang, Yan; Sun, Xiao-ming; Xu, Li; Liang, Ye-heng; Wu, Zhong-wei; Fu, Yu; Huang, Yi

    2015-03-01

    In this study, we analyze element geochemistry of submarine basalt in situ, which is sampled in hydrothermal areas from ultraslow spreading Southwest Indian Ridge, including the fresh basalt rocks (B19-9, B15-13) and altered basalt (B5-2). And we can confirm that altered mineral in B5-2 is celadonite by microscope and Raman Spectrum. Furthermore, amygdaloidal celadonites are analyzed by electron microprobe (EPMA) and EDS-line scanning. The results show that K-contents decrease and Na-contents increase from the core to the edge in these altered minerals, indicating the transition from celadonite to saponite. Celadonite is an altered minerals, forming in low temperature (< 50 degrees C) and oxidizing condition, while saponite form in low water/rock and more reducing condition. As a result, the transition from celadonite to saponite suggests environment change from oxidizing to reducing condition. Using the result of EPMA as internal standard, we can analyze rare earth elements (REE) in altered mineral in situ. Most of result show positive Eu anomaly (Δ(Eu)), indicating hydrothermal fluid transform from oxidizing to reducing, and reducing fluid rework on the early altered minerals. Comparison with REE in matrix feldspar both in altered and unaltered zoning, we find that reducing fluid can leach REE from the matrix feldspar, leading to lower total REE concentrations and positive Eu anomaly. So leaching process play an important role in hydrothermal system. PMID:26117900

  6. Untangling Magmatic Processes and Hydrothermal Alteration of in situ Superfast Spreading Ocean Crust at ODP/IODP Site 1256 with Fuzzy c-means Cluster Analysis of Rock Magnetic Properties

    NASA Astrophysics Data System (ADS)

    Dekkers, M. J.; Heslop, D.; Herrero-Bervera, E.; Acton, G.; Krasa, D.

    2014-12-01

    Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6.44.1' N, 91.56.1' W) on the Cocos Plate occurs in 15.2 Ma oceanic crust generated by superfast seafloor spreading. Presently, it is the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Here we interpret down-hole trends in several rock-magnetic parameters with fuzzy c-means cluster analysis, a multivariate statistical technique. The parameters include the magnetization ratio, the coercivity ratio, the coercive force, the low-field susceptibility, and the Curie temperature. By their combined, multivariate, analysis the effects of magmatic and hydrothermal processes can be evaluated. The optimal number of clusters - a key point in the analysis because there is no a priori information on this - was determined through a combination of approaches: by calculation of several cluster validity indices, by testing for coherent cluster distributions on non-linear-map plots, and importantly by testing for stability of the cluster solution from all possible starting points. Here, we consider a solution robust if the cluster allocation is independent of the starting configuration. The five-cluster solution appeared to be robust. Three clusters are distinguished in the extrusive segment of the Hole that express increasing hydrothermal alteration of the lavas. The sheeted dike and gabbro portions are characterized by two clusters, both with higher coercivities than in lava samples. Extensive alteration, however, can obliterate magnetic property differences between lavas, dikes, and gabbros. The imprint of thermochemical alteration on the iron-titanium oxides is only partially related to the porosity of the rocks. All clusters display rock magnetic characteristics in line with a stable NRM. This implies that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Determination of the absolute paleointensity with thermal techniques is

  7. High-resolution near-bottom vector magnetic anomalies over Raven Hydrothermal Field, Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Tivey, Maurice A.; Johnson, H. Paul; Salmi, Marie S.; Hutnak, Michael

    2014-10-01

    High-resolution, near-bottom vector magnetic data were collected by remotely operated vehicle Jason over the Raven hydrothermal vent field (47°57.3'N 129°5.75'W) located north of Main Endeavour vent field on the Endeavour segment of the Juan de Fuca Ridge. The survey was part of a comprehensive heat flow study of the Raven site using innovative thermal blanket technology to map the heat flux and crustal fluid pathways around a solitary hydrothermal vent field. Raven hydrothermal activity is presently located along the western axial valley wall, while additional inactive hydrothermal deposits are found to the NW on the upper rift valley wall. Magnetic inversion results show discrete areas of reduced magnetization associated with both active and inactive hydrothermal vent deposits that also show high conductive heat flow. Higher spatial variability in the heat flow patterns compared to the magnetization is consistent with the heat flow reflecting the currently active but ephemeral thermal environment of fluid flow, while crustal magnetization is representative of the static time-averaged effect of hydrothermal alteration. A general NW to SE trend in reduced magnetization across the Raven area correlates closely with the distribution of hydrothermal deposits and heat flux patterns and suggests that the fluid circulation system at depth is likely controlled by local crustal structure and magma chamber geometry. Magnetic gradient tensor components computed from vector magnetic data improve the resolution of the magnetic anomaly source and indicate that the hydrothermally altered zone directly beneath the Raven site is approximately 15 × 106 m3 in volume.

  8. Hydrothermal alteration and melting of the crust during the Columbia River Basalt-Snake River Plain transition and the origin of low-δ18O rhyolites of the central Snake River Plain

    NASA Astrophysics Data System (ADS)

    Colón, Dylan P.; Bindeman, Ilya N.; Ellis, Ben S.; Schmitt, Axel K.; Fisher, Christopher M.

    2015-05-01

    We present compelling isotopic evidence from ~15 Ma rhyolites that erupted coeval with the Columbia River Basalts in southwest Idaho's J-P Desert and the Jarbidge Mountains of northern Nevada at that suggests that the Yellowstone mantle plume caused hydrothermal alteration and remelting of diverse compositions of shallow crust in the area where they erupted. These rhyolites also constitute the earliest known Miocene volcanism in the vicinity of the Bruneau-Jarbidge and Twin Falls (BJTF) volcanic complexes, a major center of voluminous (103-104 km3) low-δ18O rhyolitic volcanism that was previously defined as being active from 13 to 6 Ma. The Jarbidge Rhyolite has above-mantle δ18O (δ18O of +7.9‰ SMOW) and extremely unradiogenic εHf (- 34.7) and εNd (- 24.0). By contrast, the J-P Desert units are lower in δ18O (+4.5 to 5.8‰), and have more moderately unradiogenic whole-rock εHf (- 20.3 to - 8.9) and εNd (- 13.4 to - 7.7). The J-P Desert rhyolites are geochemically and petrologically similar to the younger rhyolites of the BJTF center (the one exception being their high δ18O values), suggesting a common origin for J-P Desert and BJTF rhyolites. The presence of low-δ18O values and unradiogenic Nd and Hf isotopic compositions, both of which differ greatly from the composition of a mantle differentiate, indicate that some of these melts may be 50% or more melted crust by volume. Individual J-P Desert units have isotopically diverse zircons, with one lava containing zircons ranging from - 0.6‰ to + 6.5‰ in δ18O and from - 29.5 to - 2.8 in εHf. Despite this diversity, zircons all have Miocene U/Pb ages. The range of zircon compositions fingerprints the diversity of their source melts, which in turn allow us to determine the compositions of two crustal end-members which melted to form these rhyolites. These end-members are: 1) Archean basement with normal to high-δ18O and unradiogenic εHf and 2) hydrothermally altered, shallow, young crust with low

  9. Formation of Intermediate Carbon Phases in Hydrothermal Abiotic Organic Synthesis

    NASA Astrophysics Data System (ADS)

    Fu, Q.; Foustoukos, D. I.; Seyfried, W. E.

    2005-12-01

    With high dissolved concentrations of methane and other hydrocarbon species revealed at the Rainbow and Logatchev vent systems on the Mid-Atlantic Ridge, it is essential to better understand reaction pathways of abiotic organic synthesis in hydrothermal systems. Thus, we performed a hydrothermal carbon reduction experiment with 13C labeled carbon source at temperature and pressure conditions that approximate those inferred for ultramafic-hosted hydrothermal systems. Pentlandite, a common alteration mineral phase in subseafloor reaction zones, acted as a potential catalyst. Surface analysis techniques (XPS and ToF-SIMS) were used to characterize intermediate carbon species within this process. Time series dissolved H2 and H2S concentrations indicated thermodynamic equilibrium. Dissolved H2 and H2S concentrations of 13 and 2 mmol/kg, respectively, are approximately equivalent to measured values in Rainbow and Logatchev hydrothermal systems. Isotopically pure 13C methane and other alkane species (C2H6 and C3H8) were observed throughout the experiment, and attained steady state conditions. XPS analysis on mineral product surface indicated carbon enrichment on mineral surface following reaction. The majority of surface carbon involves species containing C-C or C-H bonds, such as alkyl or methylene groups. Alcohol and carboxyl groups in fewer amounts were also observed. ToF-SIMS analysis, which can offer isotope identification with high mass resolution, showed that most of these carbon species were 13C-labeled. Unlike gas phase Fischer-Tropsch synthesis, no carbide was observed on mineral product surface during the experiment. Therefore, a reaction pathway is proposed for formation of dissolved linear alkane species in hydrothermal abiotic organic synthesis, where oxygen-bearing organic compounds are expected to form in aqueous products by way of alcohol and carboxyl groups on mineral catalyst surface.

  10. Oxygen isotope exchange kinetics of mineral pairs in closed and open systems: Applications to problems of hydrothermal alteration of igneous rocks and Precambrian iron formations

    USGS Publications Warehouse

    Gregory, R.T.; Criss, R.E.; Taylor, H.P., Jr.

    1989-01-01

    The systematics of stable-isotope exchange between minerals and fluids are examined in the context of modal mineralogical variations and mass-balance considerations, both in closed and in open systems. On mineral-pair ??18O plots, samples from terranes that have exchanged with large amounts of fluid typically map out steep positively-sloped non-equilibrium arrays. Analytical models are derived to explain these effects; these models allow for different exchange rates between the various minerals and the external fluids, as well as different fluid fluxes. The steep arrays are adequately modelled by calculated isochron lines that involve the whole family of possible exchange trajectories. These isochrons have initially-steep near-vertical positive slopes that rotate toward a 45?? equilibrium slope as the exchange process proceeds to completion. The actual data-point array is thus analogous to the hand of an "isotopic clock" that measures the duration of the hydrothermal episode. The dimensionless ratio of the volumetric fluid flux to the kinetic rate parameter ( u k) determines the shape of each individual exchange trajectory. In a fluid-buffered system ( u k ??? 1), the solutions to the equations: (1) are independent of the mole fractions of the solid phases; (2) correspond to Taylor's open-system water/rock equation; and (3) yield straight-line isochrons that have slopes that approach 1 f, where f is the fraction reacted of the more sluggishly exchanging mineral. The isochrons for this simple exchange model are closely congruent with the isochrons calculated for all of the more complex models, thereby simplifying the application of theory to actual hydrothermal systems in nature. In all of the models an order of magnitude of time (in units of kt) separates steep non-equilibrium arrays (e.g., slope ??? 10) from arrays approaching an equilibrium slope of unity on a ??-?? diagram. Because we know the approximate lifetimes of many hydrothermal systems from geologic and

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

    USGS Publications Warehouse

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

    1996-01-01

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

  12. Analysis of the Magmatic - Hydrothermal volcanic field of Tacora Volcano, northern Chile, using passive seismic tomography

    NASA Astrophysics Data System (ADS)

    Pavez Orrego, Claudia; Comte, Diana; Gutierrez, Francisco; Gaytan, Diego

    2016-04-01

    The results of a passive seismic tomography developed in the Tacora Volcano, northern Chile, are presented. In this area, the main thermal manifestations are fumarolic fields mainly distributed in the western flank of the volcano. Around the volcanic area were installed 17 short period seismic stations, between August and December, 2014. Using the P and S wave arrival times of the seismicity record, a 3D velocity model was determined through a passive seismic tomography. For a better visualization of low and high velocity anomalies, the Leapfrog Viewer Software has been used. The areas of high Vp /Vs values, located directly under the volcanic chain, are interpreted as fluid-saturated areas, corresponding to the recharge zone of the hydrothermal system. Meanwhile, low Vp /Vs values represent the location of a magmatic reservoir and circulation networks of magmatic-hydrothermal fluids. The final model it was contrasted with available geochemical information showing a match between the low Vp/Vs areas (magma reservoirs / hydrothermal fluids), fumarolic fields and surface hydrothermal alteration. Finally, we present a cluster analysis using the percentage variation of %dVp, with which we have found a method for the identification of clay level areas related with the intermediate values of Vp/Vs (1.70 - 1.75) and the degassification zones.

  13. Lessons from studies of impact crater hydrothermal processes in terrestrial analogs and their implications for impact craters on Mars

    NASA Astrophysics Data System (ADS)

    Newsom, H. E.

    2011-12-01

    ), producing alteration zones that are spatially limited. For Mars therefore, where will evidence of impact hydrothermal processes be found? A) Extensive hydrothermal alteration requires large craters (>20 km diam.), with heat from basement uplift, and the presence of shocked and melted material in crater fill and ejecta. B) Assuming water is available from precipitation, ice, or groundwater, hydrothermal fluids can be generated in impact melt sheets, melt-bearing ejecta, and central uplifts. C) Hydrothermal fluids can contribute to the formation of impact crater lakes with accompanying precipitation of evaporites and alteration of materials on the lake floors. D) Hydrothermal fluids derived from hot central uplifts and melt sheets may also migrate into porous megabreccias and faulted rocks associated with crater walls and central uplifts leading to formation or precipitation of alteration minerals. C) Outside of large craters or basins, alteration of melt-bearing ejecta can occur if the ejecta is relatively thick (> 100 m), and water is available. In conclusion, based on terrestrial analog studies, impact hydrothermal processes are a plausible explanation for the alteration phases observed in association with Martian craters.

  14. Hydrothermal Alteration of Glass from Underground Nuclear Tests: Formation and Transport of Pu-clay Colloids at the Nevada National Security Site

    SciTech Connect

    Zavarin, M.; Zhao, P.; Joseph, C.; Begg, J.; Boggs, M.; Dai, Z.; Kersting, A. B.

    2015-05-27

    across a range of temperatures (25-200 °C) that represent hydrothermal conditions representative of the underground nuclear test cavities (when groundwater has re-saturated the nuclear melt glass and glass dissolution occurs). Colloid loads and Pu concentrations were monitored along with the mineralogy of both the colloids and the secondary mineral phases. The intent was to establish an upper limit for Pu concentrations at the NNSS, provide context regarding the Pu concentrations observed at the NNSS to date and the Pu concentrations that may be observed in the future. The results provide a conceptual model for the risks posed by Pu migration at the NNSS.

  15. Chemical reaction path modeling of hydrothermal processes on Mars: Preliminary results

    NASA Technical Reports Server (NTRS)

    Plumlee, Geoffrey S.; Ridley, W. Ian

    1992-01-01

    Hydrothermal processes are thought to have had significant roles in the development of surficial mineralogies and morphological features on Mars. For example, a significant proportion of the Martian soil could consist of the erosional products of hydrothermally altered impact melt sheets. In this model, impact-driven, vapor-dominated hydrothermal systems hydrothermally altered the surrounding rocks and transported volatiles such as S and Cl to the surface. Further support for impact-driven hydrothermal alteration on Mars was provided by studies of the Ries crater, Germany, where suevite deposits were extensively altered to montmorillonite clays by inferred low-temperature (100-130 C) hydrothermal fluids. It was also suggested that surface outflow from both impact-driven and volcano-driven hydrothermal systems could generate the valley networks, thereby eliminating the need for an early warm wet climate. We use computer-driven chemical reaction path calculation to model chemical processes which were likely associated with postulated Martian hydrothermal systems.

  16. Chemical and physical studies of type 3 chondrites. IX. Thermoluminescence and hydrothermal annealing experiments and their relationship to metamorphism and aqueous alteration in type < 3. 3 ordinary chondrites

    SciTech Connect

    Guimon, R.K.; Lofgren, G.E.; Sears, D.W.G.

    1988-01-01

    Samples of four type 3 chondrites have been annealed at 400-850/sup 0/C and 0.77-1 kbar for 10-500 h in the presence of various amounts of water (0-10 wt.%) and sodium disilicate (0-2 molal) and their thermoluminescence properties measured. After annealing for > 20 h at temperatures > 600/sup 0/C, the TL sensitivity of the samples increased by factors of up to 40. After annealing at < 600/sup 0/C for 10-500 h, or relatively short periods at high temperatures (e.g., less than or equal to 20 h at 850/sup 0/C), the TL sensitivity of the samples decreased by up to 2 orders of magnitude (depending on the original value). The TL peak temperatures observed in the present experiments are consistent with a low form of feldspar (the TL phosphor) being produced at < 800/sup 0/C and a high form being produced at > 800/sup 0/C. When both high and low forms were present originally, the low-form was destroyed preferentially. The authors suggest that these data are consistent with the TL-metamorphism trends observed in type > 3.2 chondrites, being due to the formation of feldspar by the devitrification of chondrule glass during metamorphism. For types < 3.2, the TL data are equally consistent with these types experiencing lower levels of metamorphism than the higher types, or with type 3.0 being produced from higher types by aqueous alteration. The presence of water with non-terrestrial D/H ratios, and petrographic evidence for aqueous alteration in Semarkona, lead to favoring the aqueous alteration hypothesis.

  17. Reconstructing Magmatic-Hydrothermal Systems via Geologic Mapping of the Tilted, Cross-sectional Exposures of the Yerington District, Nevada

    NASA Astrophysics Data System (ADS)

    Dilles, J. H.; Proffett, J. M.

    2011-12-01

    The Jurassic Yerington batholith was cut by Miocene to recent normal faults and tilted ~90° west (Proffett, 1977). Exposures range from the volcanic environment to ~6 km depth in the batholith. Magmatic-hydrothermal fluids derived from the Luhr Hill granite and associated porphyry dikes produced characteristic porphyry copper mineralization and rock alteration (K-silicate, sericitic, and advanced argillic) in near-vertical columnar zones above cupolas on the deep granite. In addition, saline brines derived from the early Mesozoic volcanic and sedimentary section intruded by the batholith were heated and circulated through the batholith producing voluminous sodic-calcic and propylitic alteration. The magnetite-copper ore body at Pumpkin Hollow is hosted in early Mesozoic sedimentary rocks in the contact aureole of the batholith, and appears to be an IOCG type deposit produced where the sedimentary brines exited the batholith. Although many advances in understanding of Yerington have been made by lab-based geochronology and geochemistry studies, the first order igneous and hydrothermal features were recognized first in the 1960s and 1970s and are best documented by geological mapping at a variety of scales ranging from 1:500 to 1:24,000. The Anaconda technique of mapping mine benches, trenches, and drill cores was perfected here (Einaudi, 1997), and other techniques were used for surface exposures. The geologic and hydrothermal alteration maps establish that hydrothermal alteration accompanied each of several porphyry dike intrusions, and affected more than 100 km3 of rock. Both zonation in alteration mineralogy and vein orientations allow reconstruction of source areas and >5 km-long flow-paths of hydrothermal fluids through the batholith and contact aureole.

  18. A preliminary study of older hot spring alteration in Sevenmile Hole, Grand Canyon of the Yellowstone River, Yellowstone Caldera, Wyoming

    USGS Publications Warehouse

    Larson, P.B.; Phillips, A.; John, D.; Cosca, M.; Pritchard, C.; Andersen, A.; Manion, J.

    2009-01-01

    Erosion in the Grand Canyon of the Yellowstone River, Yellowstone Caldera (640??ka), Wyoming, has exposed a cross section of older hydrothermal alteration in the canyon walls. The altered outcrops of the post-collapse tuff of Sulphur Creek (480??ka) extend from the canyon rim to more than 300??m beneath it. The hydrothermal minerals are zoned, with an advanced argillic alteration consisting of an association of quartz (opal) + kaolinite ?? alunite ?? dickite, and an argillic or potassic alteration association with quartz + illite ?? adularia. Disseminated fine-grained pyrite or marcasite is ubiquitous in both alteration types. These alteration associations are characteristic products of shallow volcanic epithermal environments. The contact between the two alteration types is about 100??m beneath the rim. By analogy to other active geothermal systems including active hydrothermal springs in the Yellowstone Caldera, the transition from kaolinite to illite occurred at temperatures in the range 150 to 170????C. An 40Ar/39Ar age on alunite of 154,000 ?? 16,000??years suggests that hydrothermal activity has been ongoing since at least that time. A northwest-trending linear array of extinct and active hot spring centers in the Sevenmile Hole area implies a deeper structural control for the upflowing hydrothermal fluids. We interpret this deeper structure to be the Yellowstone Caldera ring fault that is covered by the younger tuff of Sulphur Creek. The Sevenmile Hole altered area lies at the eastern end of a band of hydrothermal centers that may mark the buried extension of the Yellowstone Caldera ring fault across the northern part of the Caldera. ?? 2009 Elsevier B.V.

  19. A preliminary study of older hot spring alteration in Sevenmile Hole, Grand Canyon of the Yellowstone River, Yellowstone Caldera, Wyoming

    NASA Astrophysics Data System (ADS)

    Larson, Peter B.; Phillips, Allison; John, David; Cosca, Michael; Pritchard, Chad; Andersen, Allen; Manion, Jennifer

    2009-11-01

    Erosion in the Grand Canyon of the Yellowstone River, Yellowstone Caldera (640 ka), Wyoming, has exposed a cross section of older hydrothermal alteration in the canyon walls. The altered outcrops of the post-collapse tuff of Sulphur Creek (480 ka) extend from the canyon rim to more than 300 m beneath it. The hydrothermal minerals are zoned, with an advanced argillic alteration consisting of an association of quartz (opal) + kaolinite ± alunite ± dickite, and an argillic or potassic alteration association with quartz + illite ± adularia. Disseminated fine-grained pyrite or marcasite is ubiquitous in both alteration types. These alteration associations are characteristic products of shallow volcanic epithermal environments. The contact between the two alteration types is about 100 m beneath the rim. By analogy to other active geothermal systems including active hydrothermal springs in the Yellowstone Caldera, the transition from kaolinite to illite occurred at temperatures in the range 150 to 170 °C. An 40Ar/ 39Ar age on alunite of 154,000 ± 16,000 years suggests that hydrothermal activity has been ongoing since at least that time. A northwest-trending linear array of extinct and active hot spring centers in the Sevenmile Hole area implies a deeper structural control for the upflowing hydrothermal fluids. We interpret this deeper structure to be the Yellowstone Caldera ring fault that is covered by the younger tuff of Sulphur Creek. The Sevenmile Hole altered area lies at the eastern end of a band of hydrothermal centers that may mark the buried extension of the Yellowstone Caldera ring fault across the northern part of the Caldera.

  20. Near-infrared reflectance of zunyite: implications for field mapping and remote-sensing detection of hydrothermally altered high alumina rocks.

    USGS Publications Warehouse

    Crowley, J.K.

    1984-01-01

    Several hydroxyl-bearing minerals have diagnostic absorption bands in the 2.0-2.4 mu m wave length range, and can be identified with an orbital radiometer and with high-resolution airborne and field portable spectrometers. Among such minerals, zunyite, 143Al13Si5O20(OH,F)18Cl, has distinctive spectral absorption characteristics and is notably restricted to, and thus an indicator mineral of, advanced argillic alteration. Although seldom noted because it visually resembles quartz, zunyite is probably not as rare as generally believed. Laboratory measurements and general considerations underlie suggestions favouring the feasibility of detecting zunyite, alone and in mixtures with other Al-OH minerals, using field portable spectrometers.-G.J.N.

  1. Detection and mapping of hydrothermally altered rocks in the vicinity of the comstock lode, Virginia Range, Nevada, using enhanced LANDSAT images

    NASA Technical Reports Server (NTRS)

    Ashley, R. P. (Principal Investigator); Goetz, A. F. H.; Rowan, L. C.; Abrams, M. J.

    1979-01-01

    The author has identified the following significant results. LANDSAT images enhanced by the band-ratioing method can be used for reconnaissance alteration mapping in moderately heavily vegetated semiarid terrain as well as in sparsely vegetated to semiarid terrain where the technique was originally developed. Significant vegetation cover in a scene, however, requires the use of MSS ratios 4/5, 4/6, and 6/7 rather than 4/5, 5/6, and 6/7, and requires careful interpretation of the results. Supplemental information suitable to vegetation identification and cover estimates, such as standard LANDSAT false-color composites and low altitude aerial photographs of selected areas is desirable.

  2. Thermal Models of the Costa Rica - Nicaragua Subduction Zone: the Effect of a Three-Dimensional Oceanic Plate Structure and Hydrothermal Circulation in the Temperature Distribution and Mantle Wedge Dynamics

    NASA Astrophysics Data System (ADS)

    Rosas, J. C.; Currie, C. A.; He, J.

    2014-12-01

    Over the last years several 2D thermo-mechanical models of the Costa Rica - Nicaragua Subduction Zone (CNSZ) have studied the thermal distribution of sections of the fault. Such investigations allow us to understand temperature-related aspects of subduction zones, like volcanism and megathrust earthquake locations. However, certain features of the CNSZ limit the range of applicability of 2D models. In the CNSZ, geochemical trends and seismic anisotropy studies reveal a 3D mantle wedge flow that departs from the 2D corner flow. The origin of this flow are dip variations (20o to 25o between Nicaragua and Costa Rica) and the presence of a slab window in Panama that allows material to flow into the mantle wedge. Also, the Central America trench has abrupt variations in surface heat flux that contrasts with steady changes in plate age and convergence rate. These variations have been attributed to hydrothermal circulation (HC), which effectively removes heat from the oceanic crust.In this project we analyze the thermal structure of the CNSZ. The objective is to study dehydration and metamorphic reactions, as well as the length of the megathrust seismogenic zone. We created 3D finite-element models that employ a dislocation creep rheology for the mantle wedge. Two aspects make our models different from previous studies: an up-to-date 3D slab geometry, and an implementation of HC by introducing a conductive proxy in the subducting aquifer, allowing us to model convective heat transport without the complex, high-Rayleigh number calculations. A 3D oceanic boundary condition that resembles the along-strike changes in surface heat flux is also employed. Results show a maximum mantle wedge flow rate of 4.69 cm/yr in the along-strike direction, representing more than 50% of the slab convergence rate. With respect to 2D models, analysis shows this flow changes temperatures by ~100 C in the mantle wedge near areas of strong slab curvature. Along the subducting interface, there is

  3. Phyllosilicate minerals in the hydrothermal mafic-ultramafic-hosted massive-sulfide deposit of Ivanovka (southern Urals): comparison with modern ocean seafloor analogues

    NASA Astrophysics Data System (ADS)

    Nimis, Paolo; Tesalina, Svetlana G.; Omenetto, Paolo; Tartarotti, Paola; Lerouge, Catherine

    We have studied textural relationships and compositions of phyllosilicate minerals in the mafic-ultramafic-hosted massive-sulfide deposit of Ivanovka (Main Uralian Fault Zone, southern Urals). The main hydrothermal phyllosilicate minerals are Mg-rich chlorite, variably ferroan talc, (Mg, Si)-rich and (Ca, Na, K)-poor saponite (stevensite), and serpentine. These minerals occur both as alteration products after mafic volcanics and ultramafic protoliths and, except serpentine, as hydrothermal vein and seafloor mound-like precipitates associated with variable amounts of (Ca, Mg, Fe)-carbonates, quartz and Fe and Cu (Co, Ni) sulfides. Brecciated mafic lithologies underwent pervasive chloritization, while interlayered gabbro sills underwent partial alteration to chlorite + illite +/- actinolite +/- saponite +/- talc-bearing assemblages and later localized deeper alteration to chlorite +/- saponite. Ultramafic and mixed ultramafic-mafic breccias were altered to talc-rich rocks with variable amounts of chlorite, carbonate and quartz. Chloritization, locally accompanied by formation of disseminated sulfides, required a high contribution of Mg-rich seawater to the hydrothermal fluid, which could be achieved in a highly permeable, breccia-dominated seafloor. More evolved hydrothermal fluids produced addition of silica, carbonates and further sulfides, and led to local development of saponite after chlorite and widespread replacement of serpentine by talc. The Ivanovka deposit shows many similarities with active and fossil hydrothermal sites on some modern oceanic spreading centers characterized by highly permeable upflow zones. However, given the arc signature of the ore host rocks, the most probable setting for the observed alteration-mineralization patterns is in an early-arc or forearc seafloor-subseafloor environment, characterized by the presence of abundant mafic-ultramafic breccias of tectonic and/or sedimentary origin.

  4. Tracing fluid pathways in Archean hydrothermal systems with imaging spectroscopy

    NASA Astrophysics Data System (ADS)

    von Ruitenbeek, F. J. A.; Cudahy, T.; Hale, M.; van der Werff, H. M. A.; van der Meer, F. D.

    2008-09-01

    Abstract Fossil submarine hydrothermal systems in Archean greenstone belts and other geologic terranes are important because of their relationship with volcanic massive sulfide (VMS) mineral deposits and their association with environments that are favorable for early forms of life. Interpretation and reconstruction of these systems is difficult because of their geologic complexity. Airborne imaging spectroscopy provides information about the presence, abundance, and composition of near-infrared active minerals at continuous spatial coverage and high spatial resolution, and can therefore be used to obtain new geologic insights into of the Archean hydrothermal systems. It was applied to the Panorama VMS-district in the Soanesville greenstone belt, Western Australia. Results from the analyses of 189 hand specimen showed that the wavelength position of the main absorption feature of white micas, a proxy for their Al content, varied between 2195 nm and 2225 nm. These wavelength variations and the relative abundance of white micas were used to reconstruct fossil fluid pathways from low-temperature recharge to hightemperature discharge zones. Results also showed that the absorption-wavelength variations of white micas could be mapped from airborne imaging spectroscopy using a stochastic method where the presence of white mica minerals and their absorption wavelengths in field measurements were predicted from hyperspectral band ratios. Analysis of the spatial patterns in segmented images, covering 52 km2, of white mica probability and their absorption wavelengths and their comparison with field data resulted in the identification of regional scale hydrothermal fluid pathways, a regional-scale K alteration event, and differences in hydrothermal regime between the northern and southern parts of the test area.

  5. Three-dimensional geophysical mapping of rock alteration and water content at Mount Adams, Washington: Implications for lahar hazards

    USGS Publications Warehouse

    Finn, C.A.; Deszcz-Pan, M.; Anderson, E.D.; John, D.A.

    2007-01-01

    Hydrothermally altered rocks, particularly if water saturated, can weaken stratovolcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-traveled, destructive debris flows. Evaluating the hazards associated with such alteration is difficult because alteration has been mapped on few active volcanoes and the distribution and intensity of subsurface alteration are largely unknown on any active volcano. At Mount Adams, some Holocene debris flows contain abundant hydrothermal minerals derived from collapse of the altered, edifice. Intense hydrothermal alteration significantly reduces the resistivity and magnetization of volcanic rock, and therefore hydrothermally altered rocks can be identified with helicopter electromagnetic and magnetic measurements. Electromagnetic and magnetic data, combined with geological mapping and rock property measurements, indicate the presence of appreciable thicknesses of hydrothermally altered rock in the central core of Mount Adams north of the summit. We identify steep cliffs at the western edge of this zone as the likely source for future large debris flows. In addition, the electromagnetic data identified water in the brecciated core of the upper 100-200 m of the volcano. Water helps alter the rocks, reduces the effective stress, thereby increasing the potential for slope failure, and acts, with entrained melting ice, as a lubricant to transform debris avalanches into lahars. Therefore knowing the distribution of water is also important for hazard assessments. Our results demonstrate that high-resolution geophysical and geological observations can yield unprecedented views of the three-dimensional distribution of altered rock and shallow pore water aiding evaluation of the debris avalanche hazard.

  6. Hydrothermal evolution of the Sar-Cheshmeh porphyry Cu Mo deposit, Iran: Evidence from fluid inclusions

    NASA Astrophysics Data System (ADS)

    Hezarkhani, Ardeshir

    2006-12-01

    The Sar-Cheshmeh porphyry Cu-Mo deposit is located in Southwestern Iran (˜65 km southwest of Kerman City) and is associated with a composite Miocene stock, ranging in composition from diorite through granodiorite to quartz-monzonite. Field observations and petrographic studies demonstrate that the emplacement of the Sar-Cheshmeh stock took place in several pulses, each with associated hydrothermal activity. Molybdenum was concentrated at a very early stage in the evolution of the hydrothermal system and copper was concentrated later. Four main vein Groups have been identified: (I) quartz+molybdenite+anhydrite±K-feldspar with minor pyrite, chalcopyrite and bornite; (II) quartz+chalcopyrite+pyrite±molybdenite±calcite; (III) quartz+pyrite+calcite±chalcopyrite±anhydrite (gypsum)±molybdenite; (IV) quartz±calcite±gypsum±pyrite±dolomite. Early hydrothermal alteration produced a potassic assemblage (orthoclase-biotite) in the central part of the stock, propylitic alteration occurred in the peripheral parts of the stock, contemporaneously with potassic alteration, and phyllic alteration occurred later, overprinting earlier alteration. The early hydrothermal fluids are represented by high temperature (350-520 °C), high salinity (up to 61 wt% NaCl equivalent) liquid-rich fluid inclusions, and high temperature (340-570 °C), low-salinity, vapor-rich inclusions. These fluids are interpreted to represent an orthomagmatic fluid, which cooled episodically; the brines are interpreted to have caused potassic alteration and deposition of Group I and II quartz veins containing molybdenite and chalcopyrite. Propylitic alteration is attributed to a liquid-rich, lower temperature (220-310 °C), Ca-rich, evolved meteoric fluid. Influx of meteoric water into the central part of the system and mixing with magmatic fluid produced albitization at depth and shallow phyllic alteration. This influx also caused the dissolution of early-formed copper sulphides and the remobilization of

  7. 76 FR 72839 - Safety Zone; Truman-Hobbs Alteration of the Elgin Joliet & Eastern Railroad Drawbridge; Illinois...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-28

    ... removal of the Elgin Joliet & Eastern Railroad Drawbridge's old bridge piers and pier protection cells...-Hobbs alteration of the Elgin Joliet & Eastern Railroad Drawbridge, which consists of the removal of the.... However, it has fallen behind schedule and will now go until December 9, 2011. The falling...

  8. Hydrothermal mineralogy and fluid inclusions chemistry to understand the roots of active geothermal systems

    NASA Astrophysics Data System (ADS)

    Chambefort, I. S.; Dilles, J. H.; Heinrich, C.

    2013-12-01

    An integrated study to link magmatic textures, magmatic mineral compositions, hydrothermal alteration zoning, hydrothermal mineral chemistry, and fluid inclusion compositions has been undertaken to link an intrusive complex and its degassing alteration halo with their surface equivalent in an active geothermal system. Ngatamariki geothermal system, New Zealand, presents a unique feature in the Taupo Volcanic Zone (TVZ). Drilling intercepted an intrusive complex with a high temperature alteration halo similarly to what is observed in magmatic-derived ore deposits. Thus it presents the perfect opportunity to study the magmatic-hydrothermal transition of the TVZ by characterizing the nature of the deep magmatic fluids link to the heat source of the world known geothermal fields. The record of magmatic-hydrothermal fluid-rock interactions preserved at Ngatamariki may be analogous of processes presently occurring at depth beneath TVZ geothermal systems. The intrusive complex consists of over 5 km3 of tonalite, diorite, basalt and aplitic dykes. Evidence of undercooling subsolidus magmatic textures such as myrmekite and skeletal overgrowth are commonly observed and often linked to volatile loss. The fluids released during the crystallization of the intrusive complex are interpreted to be at the origin of the surrounding high temperature alteration halo. Advanced argillic to potassic alteration and high temperature acidic assemblage is associated with high-temperature quartz veining at depth and vuggy silica at the paleo-surface. Major element compositions of the white micas associated with the high temperature halo show a transition from, muscovite to phengite, muscovitic illite away from the intrusion, with a transition to pyrophyllite and/ or topaz, and andalusite characteristic of more acidic conditions. Abundant high-density (up to 59 wt% NaCl eq and homogenization temperatures of 550 degree Celsius and above) coexist with low-density vapor fluid inclusions. This

  9. Geochronology and Nd isotope geochemistry of the Gameleira Cu-Au deposit, Serra dos Carajás, Brazil: 1.8-1.7 Ga hydrothermal alteration and mineralization

    NASA Astrophysics Data System (ADS)

    Pimentel, Márcio M.; Lindenmayer, Zara G.; Laux, Jorge H.; Armstrong, Richard; de Araújo, Janice Caldas

    2003-01-01

    The Gameleira deposit is one of several important Cu-Au deposits associated with the late Archean (ca. 2.7 Ga) volcanic rocks of the Itacaiúnas supergroup in the Carajás mineral province, southeastern Pará. It comprises mainly biotite- and sulphide-rich veins and quartz-grunerite-biotite-gold hydrothermal veins that cut andesitic rocks. It is interpreted as representative of the Fe oxide Cu-Au class of deposit. Sm-Nd isotopic data indicate an age of 2719±80 Ma (MSWD=3.0) and ɛNd( T) of -1.4 for the host meta-andesites. Metavolcanic rocks and cogenetic gabbros give an age of 2757±81 Ma (1 σ) with ɛNd( T) of -0.8. This is considered the best estimate for the crystallization age of the Gameleira volcanic and subvolcanic rocks. Negative ɛNd( T) and Archean TDM model ages (mostly between 2.8 and 3.1 Ga) suggest some contamination with older crustal material. The andesitic/gabbroic rocks are cut by two generations of granite dykes. The older has striking petrographic and geochemical similarities to the ca. 1.87 Ga alkali-rich Pojuca granite, which is exposed a few kilometers to the northwest of the deposit. The younger is a leucogranite with a U-Pb SHRIMP age of 1583+9/-7 Ma. Neodymium isotopic analyses of the two generations of granites indicate a strong crustal affinity and possible derivation from reworking of the Archean crust. The quartz-grunerite-gold hydrothermal vein yields a Sm-Nd isochron (MSWD=.83) age of 1839±15 Ma (1 σ) with ɛNd( T) of -9.2. Pervasive potassic alteration, represented by the widespread formation of biotite in the country rocks, is dated by Ar-Ar at 1734±8 Ma, and a similar age of 1700±31 Ma (1 σ) is indicated by the Sm-Nd isochron for the biotite-sulphide veins. Similar to that for the quartz-grunerite vein, the ɛNd( T) value for the sulphide-rich veins is strongly negative (-8.2), thereby suggesting that the original fluids percolated through, leached, or were derived from igneous rocks with an Archaean Nd isotopic signature

  10. Numerical Modeling of the Impact-Induced Hydrothermal System at Sudbury Crater

    NASA Astrophysics Data System (ADS)

    Abramov, O.; Kring, D. A.

    2003-12-01

    An understanding of impact-generated hydrothermal systems is crucial for deciphering the environment on early Earth and Mars, as well as predicting promising locations for finding evidence of past life on Mars. Impact events and early life may be tightly connected -- a sudden increase in the number of impact events which occurred at ˜3.9 Ga coincides remarkably well with the earliest isotopic evidence of life on Earth at ˜3.85 Ga, and hydrothermal systems generated by impact events can provide a habitable environment for thermophilic organisms. Several hydrothermal systems associated with terrestrial impact craters have been identified on the basis of mineralogical evidence. Examples of known systems include the 35 km Manson crater, the 80 km Puchezh-Katunki crater, and the 250 km Sudbury crater. In order to better constrain the expected lifetimes of these systems and further understand their mechanics, a finite-difference computer simulation is used to evaluate the effects of convective cooling by circulating water and steam. In this work we present modeling results of water and heat transport shortly after the formation of the Sudbury impact crater in present-day Ontario, Canada. Our model predicts that an impact-induced hydrothermal system associated with a Sudbury-sized impact crater can remain active for at least 105 - 106 years. While the location and volume of the habitable zone within the crater changes as the crater undergoes cooling, it is sufficiently long-lived for an ecosystem to develop. The insight into the mechanics of these systems gained from this model can help locate hydrothermal vents and hydrothermally altered minerals at Martian impact craters.

  11. Chemical equilibrium and mass balance relationships associated with the Long Valley hydrothermal system, California, U.S.A.

    USGS Publications Warehouse

    White, A.F.; Peterson, M.L.

    1991-01-01

    Recent drilling and sampling of hydrothermal fluids from Long Valley permit an accurate characterization of chemical concentrations and equilibrium conditions in the hydrothermal reservoir. Hydrothermal fluids are thermodynamically saturated with secondary quartz, calcite, and pyrite but are in disequilibrium with respect to aqueous sulfide-sulfate speciation. Hydrothermal fluids are enriched in 18O by approximately 1??? relative to recharge waters. 18O and Cl concentrations in well cuttings and core from high-temperature zones of the reservoir are extensively depleted relative to fresh rhyolitic tuff compositions. Approximately 80% of the Li and 50% of the B are retained in the altered reservoir rock. Cl mass balance and open-system 18O fractionation models produce similar water-rock ratios of between 1.0 and 2.5 kg kg-1. These water-rock ratios coupled with estimates of reservoir porosity and density produce a minimum fluid residence time of 1.3 ka. The low fluid Cl concentrations in Long Valley correlate with corresponding low rock concentrations. Mass balance calculations indicate that leaching of these reservoir rocks accounts for Cl losses during hydrothermal activity over the last 40 ka. ?? 1991.

  12. RhoE deficiency alters postnatal subventricular zone development and the number of calbindin-expressing neurons in the olfactory bulb of mouse.

    PubMed

    Ballester-Lurbe, Begoña; González-Granero, Susana; Mocholí, Enric; Poch, Enric; García-Manzanares, María; Dierssen, Mara; Pérez-Roger, Ignacio; García-Verdugo, José M; Guasch, Rosa M; Terrado, José

    2015-11-01

    The subventricular zone represents an important reservoir of progenitor cells in the adult brain. Cells from the subventricular zone migrate along the rostral migratory stream and reach the olfactory bulb, where they originate different types of interneurons. In this work, we have analyzed the role of the small GTPase RhoE/Rnd3 in subventricular zone cell development using mice-lacking RhoE expression. Our results show that RhoE null mice display a remarkable postnatal broadening of the subventricular zone and caudal rostral migratory stream. This broadening was caused by an increase in progenitor proliferation, observed in the second postnatal week but not before, and by an altered migration of the cells, which appeared in disorganized cell arrangements that impaired the appropriate contact between cells in the rostral migratory stream. In addition, the thickness of the granule cell layer in the olfactory bulb was reduced, although the density of granule cells did not differ between wild-type and RhoE null mice. Finally, the lack of RhoE expression affected the olfactory glomeruli inducing a severe reduction of calbindin-expressing interneurons in the periglomerular layer. This was already evident in the newborns and even more pronounced 15 days later when R