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Sample records for hydrothermally altered zones

  1. Oxygen isotope, aeromagnetic, and gravity anomalies associated with hydrothermally altered zones in the Yankee Fork mining district, Custer County, Idaho.

    USGS Publications Warehouse

    Criss, R.E.; Champion, D.E.; McIntyre, D.H.

    1985-01-01

    Anomalous geochemical and geophysical properties correlate spatially with epithermal Ag-Au deposits in altered volcanic rocks. Areas of low 18O, low magnetic susceptibilities, low remanent magnetizations and relatively high rock densities are much larger than the zones of obvious (not shown) hydrothermal alteration. Low aeromagnetic intensities and positive Bouguer anomalies are also associated with the altered rock, as which has delta 18O <6per mille. The altering and mineralizing fluids were Tertiary meteoric waters.-G.J.N.

  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. 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.

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

    PubMed

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

    2001-02-01

    Hydrothermally altered rocks can weaken volcanoes, increasing 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 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 flows and future collapses could threaten areas that are now densely populated. 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 summit. 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. Use of radiogenic heat for demarcation of hydrothermal alteration zones in the Pernambuco-Brazil

    NASA Astrophysics Data System (ADS)

    Cunha, Leandro O.; Dutra, Alanna C.; Costa, Alexandre B.

    2017-10-01

    In this paper, we identify hydrothermal alteration zones that are located at the eastern extreme of Borborema Province, Pernambuco State, using radiogenic heat, in combination with magnetic and radioelement data collected both from the air and on the ground. The use of these methods enabled the mapping of geological lineaments based on total magnetic intensity maps, radioelement concentration maps, ternary maps and the F factor, as well as physical properties provided by ground data (thermal conductivity, density, and magnetic susceptibility). The data integration was based on low values of radiogenic heat and high K concentrations, as well as high F factors, amplitudes of the analytic signal, and K/eTh and eU/eTh values. These characteristics occur within the Pernambuco lineament and within other features to the southeast, a short distance south of the lineaments, which are made up of units including a migmatitic gneiss complex, as well as the Modern, Itaporanga and Sierra Passira Intrusive Suites. In these areas, elongated sources that are consistent with lineaments were identified. These sources were assigned depths of up to 3 km and are 5-10 km long, with the most significant extending SE-NW. These areas are favorable for the mineralization of iron, titanium and nickel. As the results are satisfactory, such areas can be studied in detail in the future.

  7. Identification of hydrothermal alteration zones of the Baogutu porphyry copper deposits in northwest China using ASTER data

    NASA Astrophysics Data System (ADS)

    Zhang, Nannan; Zhou, Kefa

    2017-01-01

    Remote sensing technology plays a vital role in the initial stages of ore deposits exploration, with special significance in arid and semiarid regions. Advanced spaceborne thermal emission and reflection radiometer (ASTER) creates opportunities for geologists and many researchers to study the extraction of hydrothermal alterations of the porphyry copper and epithermal gold deposits. ASTER data were used to map distribution of hydrothermal alteration of deposits in the Baogutu region which is located in western Junggar, Xinjiang, China, including Baogutu II and Baogutu V deposits. Band ratio logical operator (BRLO), principal component analysis (PCA), mixture-tuned matched-filtering (MTMF), and constrained energy minimization (CEM) techniques were used for detailed hydrothermal alteration mapping. The alteration zones were identified using BRLO and PCA. The minerals subject to alteration were extracted by MTMF and CEM. The results were validated through field observation, spectral measurements, and petrographic studies. By comparing the extraction results and accuracy rates of four methods, CEM boasts the highest accuracy and identifies the altered minerals corresponding to three types of alterations at accuracy of over 80%. The identifying result of CEM method indicates that the prospect areas that were located in the southeast part of the Baogutu II rocks and in the southwest part of the Baogutu V rocks are valuable for further exploration.

  8. Identification of Hydrothermal Alteration Zones Based on Geochemical and Mineralogical Data, Northwest Turkey

    NASA Astrophysics Data System (ADS)

    Unal Ercan, H.; Schroeder, P.; Ece, I.

    2013-12-01

    The Saribeyli - Sigirli and Bodurlar kaolin deposits (Çanakkale) are hosted by andesitic tuffs of the Oligocene volcanic rocks. Mineralogical composition of these deposits shows the similarities and differences because they are exposed to different physical and chemical conditions at different. The Saribeyli kaolin deposit shows the following mineral zonation from the fault zone to the outer; i) quartz, ii) alunite + quartz × kaolinite × dickite, iii) kaolinite + dickite × alunite × quartz, iv) kaolinite + feldspar × montmorillonite, respectively. The Bodurlu kaolin deposits shows the following mineral zonation from the fault zone to outer; i) quartz, ii) Qquartz + kaolinite + quartz × illite × alunite, iii) kaolinite + quartz + illite × jarosite × halloysite, iv) kaolinite + halloysite + illite + quartz + montmorillonite. The two N30°W trending faults pass through the north and south boundaries of the Saribeyli kaolin quarry. Fault zones which pass through inside the Bodurlu kaolin quarry, exhibit a group of six parallel fracture systems and kaolinazitation occurred between and in the vicinity of these fracture systems. Based on FE-SEM studies, micromorphologic features of kaolinite crystals show that kaolinite occurs as hexagonal blocky and book-shaped kaolinite which forms ordered and disordered crystals. Halloysite crystals form parallel and randomly non-parallel sticks. The Saribeyli alunites occur pseudo-hexagonal and alunite crystals have a small hole on the crystals. The δ34 isotopic values of the Saribeyli deposit range from +4.1 to +2.4 ‰ and these values reflect its formation from magmatic-hydrothermal derived sulfur. The O- and H- isotopic values in these deposit range from δ18O +6.7 to +12.7 ‰ and δD -61 to -97‰, which are very close the area of primitive magmatic water. Isotope data suggest that original geothermal waters were the mixture of magmatic and meteoric waters. The O- and H- isotopic values of the Bodurlu kaolin deposit

  9. 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.

  10. The study of hydrothermal alteration zones in Kahang exploration area (north eastern of Isfahan, central of Iran) using microscopy studies and TM and Aster satellite data

    NASA Astrophysics Data System (ADS)

    Zahra Afshooni, Seyedeh; Esmaeily, Dariush

    2010-05-01

    Kahang ore deposit located in 73 km to the northeast of Isfahan city and 10 km to the east of Zefreh town, covering an area about 18.6 km2. This ore deposit is a part of Uromieh-Dokhtar volcanopolotonic belt. The rocks of the area included Andesite, Porphyritic Andesite, Dacite, Porphyritic, Rhyodacite, Diorite, Quartz Monzonite and Porphyry Micro Granite. In plutons, there is a trend from basic to acid features along with decreasing of age from margin to center of massive. Kahang region is an alteration and breccia zone. The occurrence of alteration zones and iron oxides were confirmed by satellite images processing. Generally, more than 90% of rocks of this region have been affected by hydrothermal fluids. Remote sensing refers to detection and measurement from a distance. For the first time, this exploration area was studied using satellite images processing (TM) and primary results showed that is suitable place for resources of Copper (Cu) and Molybdenum (Mo). Hydrothermal alteration commonly occurs in geothermal areas in association with ore deposits producing alteration assemblages typically dominated by silicates, sulfides, sulfates and carbonates. In the alteration zones studies the subject discussed is the study of existing minerals in such zones and study of chemical specifications of altering fluids. Four alteration zones Based on observations derived from the study of thin sections, XRD analysis and deep remote sensing using TM and Aster satellite images studies could be identified in this area: propylitic alteration zone with chlorite, epidot, calcite; argillic alteration zone with clay minerals; phyllic (qartz-sericite) alteration zone with quartz, sericite and pyrite and silicic alteration zone with abundant quartz.

  11. A directed matched filtering algorithm (DMF) for discriminating hydrothermal alteration zones using the ASTER remote sensing data

    NASA Astrophysics Data System (ADS)

    Fereydooni, H.; Mojeddifar, S.

    2017-09-01

    This study introduced a different procedure to implement matched filtering algorithm (MF) on the ASTER images to obtain the distribution map of alteration minerals in the northwestern part of the Kerman Cenozoic Magmatic Arc (KCMA). This region contains many areas with porphyry copper mineralization such as Meiduk, Abdar, Kader, Godekolvari, Iju, Serenu, Chahfiroozeh and Parkam. Also argillization, sericitization and propylitization are the most common types of hydrothermal alteration in the area. Matched filtering results were provided for alteration minerals with a matched filtering score, called MF image. To identify the pixels which contain only one material (endmember), an appropriate threshold value should be used to the MF image. The chosen threshold classifies a MF image into background and target pixels. This article argues that the current thresholding process (the choice of a threshold) shows misclassification for MF image. To address the issue, this paper introduced the directed matched filtering (DMF) algorithm in which a spectral signature-based filter (SSF) was used instead of the thresholding process. SSF is a user-defined rule package which contains numeral descriptions about the spectral reflectance of alteration minerals. On the other hand, the spectral bands are defined by an upper and lower limit in SSF filter for each alteration minerals. SSF was developed for chlorite, kaolinite, alunite, and muscovite minerals to map alteration zones. The validation proved that, at first: selecting a contiguous range of MF values could not identify desirable results, second: unexpectedly, considerable frequency of pure pixels was observed in the MF scores less than threshold value. Also, the comparison between DMF results and field studies showed an accuracy of 88.51%.

  12. 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

  13. 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),

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

    USGS Publications Warehouse

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

    2008-01-01

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

  15. Integration of remote sensing and aeromagnetic data for mapping structural features and hydrothermal alteration zones in Wadi Allaqi area, South Eastern Desert of Egypt

    NASA Astrophysics Data System (ADS)

    Eldosouky, Ahmed M.; Abdelkareem, Mohamed; Elkhateeb, Sayed O.

    2017-06-01

    Remote sensing and aeromagnetic data provided significant information for detecting potential areas of mineralization in Wadi Allaqi in the South Eastern Desert of Egypt. Application of band ratios and Crosta technique of Principal Component Analysis (PCA) using Landsat-8 successfully highlighted the hydrothermal alteration zones and the structural elements represented by lithologic contacts and faults/fracture zones. Structural lineaments were also successfully extracted using remote sensing and aeromagnetic data. Center for Exploration Targeting (CET) Grid analysis and CET Porphyry Analysis techniques were applied for constructing the structural complexity heat map and probable near circular features of porphyry intrusions respectively. Combining data of lineaments, alteration zones and porphyry intrusions after obtaining a consequence of each map allowed predicting and mapping areas of probable high mineral resources. Overlaying the present sites of mineralization on the final map validated the prepared mineral predictive map. Overall results clearly revealed that areas of high structural complexity, fractures/faults density are in agreement with the detected areas of hydrothermal alterations which also matched with the known mineralization mines in the study area.

  16. 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

  17. 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

  18. U-Pb dating of zircon in subsurface, hydrothermally altered pyroclastic deposits and implications for subsidence in a magmatically active rift: Taupo Volcanic Zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Wilson, C. J. N.; Charlier, B. L. A.; Rowland, J. V.; Browne, P. R. L.

    2010-03-01

    Recognising and correlating hydrothermally altered rock units within buried volcanic sequences in the Taupo Volcanic Zone (TVZ) in New Zealand is difficult. This is because of broad similarities in the lithologies of many major ignimbrite units, and the destruction by hydrothermal alteration of distinctive chemical and mineralogical characteristics. However, magmatic zircons are commonly present, are highly resistant to hydrothermal alteration and yield crystallisation ages in intensely altered rocks. Crystallisation-age spectra have been obtained by SIMS techniques (SHRIMP-RG) on zircons extracted from cores from altered ignimbrites penetrated by drillholes at the Waiotapu, Te Kopia and Orakei Korako geothermal fields in the central TVZ. At Waiotapu, the thick (up to 350 m) densely welded Waiotapu Ignimbrite returned a zircon age spectrum with a probability density function (pdf) peak of 0.79 Ma, consistent with an eruption age (from 40Ar/ 39Ar techniques) of 0.71 ± 0.06 (1 s.d.) Ma. Three older ignimbrite sheets yielded age spectra that were consistent stratigraphically. The shallowest of the three yielded sparse zircons that gave a pdf peak of 1.24 Ma and it may correlate with the 1.18 ± 0.02 Ma Ahuroa ignimbrite. The middle sheet, although 220 m thick, yielded an age spectrum identical to that obtained from pumice in the widespread 1.21 ± 0.04 Ma Ongatiti ignimbrite, extending earlier estimates of the likely volume of this large deposit. The deepest sheet has a spectrum consistent with an eruption age of 1.45 ± 0.05 Ma; it has no surficial correlative, but its likely coeruptive ash forms part of a concentrated group of primary or secondary tephra in sediments on the ocean floor east of New Zealand and in sedimentary basins across the North Island. These three ignimbrites were previously correlated with either major ignimbrites exposed on the Paeroa Fault scarp, 10 km to the west, or the Akatarewa Ignimbrite that occurs in drillholes at Te Kopia and Orakei

  19. 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

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. Pore Pressure Distribution and Flank Instability in Hydrothermally Altered Stratovolcanoes

    NASA Astrophysics Data System (ADS)

    Ball, J. L.; Taron, J.; Hurwitz, S.; Reid, M. E.

    2015-12-01

    Field and geophysical investigations of stratovolcanoes with long-lived hydrothermal systems commonly reveal that initially permeable regions (such as brecciated layers of pyroclastic material) can become both altered and water-bearing. Hydrothermal alteration in these regions, including clay formation, can turn them into low-permeability barriers to fluid flow, which could increase pore fluid pressures resulting in flank slope instability. We examined elevated pore pressure conditions using numerical models of hydrothermal flow in stratovolcanoes, informed by geophysical data about internal structures and deposits. Idealized radially symmetric meshes were developed based on cross-sectional profiles and alteration/permeability structures of Cascade Range stratovolcanoes. We used the OpenGeoSys model to simulate variably saturated conditions in volcanoes heated only by regional heat fluxes, as well as 650°C intrusions at two km depth below the surface. Meteoric recharge was estimated from precipitation rates in the Cascade Range. Preliminary results indicate zones of elevated pore pressures form: 1) where slopes are underlain by continuous low-permeability altered layers, or 2) when the edifice has an altered core with saturated, less permeable limbs. The first scenario might control shallow collapses on the slopes above the altered layers. The second could promote deeper flank collapses that are initially limited to the summit and upper slopes, but could progress to the core of an edifice. In both scenarios, pore pressures can be further elevated by shallow intrusions, or evolve over longer time scales under forcing from regional heat flux. Geometries without confining low-permeability layers do not show these pressure effects. Our initial scenarios use radially symmetric models, but we are also simulating hydrothermal flow under real 3D geometries with asymmetric subsurface structures (Mount Adams). Simulation results will be used to inform 3D slope

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    geophysical data, as well as analog fossil hydrothermal systems in volcanoes elsewhere, constrain hydrothermal alteration geometry on the pre-Osceola-collapse edifice of Mount Rainier. Relatively narrow zones of acid magmatic-hydrothermal alteration in the central core of the volcano grade to more widely distributed smectite-pyrite alteration farther out on the upper flanks, capped by steam-heated alteration with a large component of alteration resulting from condensation of fumarolic vapor above the water table. Alteration was polygenetic in zones formed episodically, and was strongly controlled by fluxes of heat and magmatic fluid and by local permeability.

  6. Biogeochemistry of hydrothermally and adjacent non-altered soils

    USDA-ARS?s Scientific Manuscript database

    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...

  7. Hydrothermal Alteration of the Mt Unzen Conduit (Shimabara/Japan)

    NASA Astrophysics Data System (ADS)

    Yilmaz, T. I.; Mayer, K.; Hess, K. U.; Janots, E.; Gilg, H. A.; Dingwell, D. B.

    2016-12-01

    Investigations were carried out on hydrothermally altered coherent dacitic dykes samples from (USDP-4) drill core at Mt Unzen stratovolcano (Shimabara/Japan). XRF, XRD, EMPA, and C-O-isotope analysis led to insights concerning chemistry, mineralogy, and intensity of alteration as well as the origin of carbonate-precipitating fluids. Additionally a textural characterization of the occurring replacement features in the magma conduit zone was performed. The occurrence of the main secondary phases such as chlorite, pyrite, carbonates, and R1 (Reichweite parameter) illite-smectite indicate a weak to moderate propylitic to phyllic hydrothermal alteration. The dacitic samples of the dykes show different hydrothermal alteration features: (i) carbonate pseudomorphs after hornblende as well as core and zonal textures due to replacement of plagioclase by R1 illite-smectite, (ii) colloform banded fracture fillings and fillings in dissolution vugs, and (iii) chlorite and R1 illite-smectite in the groundmass. Carbonates in fractures comprise iron-rich dolomite solid solutions ("ankerite") and calcite. Isotopic values of d13Cvpdb = -4.59 ± 0.6‰ and d18Ovpdb = -21.73 ± 0.5‰ indicate a hydrothermal-magmatic origin for the carbonate formation. The chlorite-carbonate-pyrite index (CCPI) and the Ishikawa alteration index (AI), applied to the investigated samples show significant differences (CCPI=52.7-57.8; AI=36.1-40.6) indicating their different degree of alteration. According to Nakada et al., 2005, the C13 to C16 dykes represent the feeder dyke from the latest eruption (1991-1995) whereas C8 represents an earlier dyke feeder dyke from an older eruption. Weakest conduit alteration, which was obtained in samples C16-1-5 and C13-2-5, correlates with the alteration degree of the pristine dome rocks. Highest CCPI value was determined for sample C14-1-5 and the highest AI value was determined for sample C15-2-6. The degrees of alteration do not indicate highest alteration of the

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Influence of aluminum on the hydrothermal alteration rate of olivine

    NASA Astrophysics Data System (ADS)

    Andreani, M.; Daniel, I.; Pollet-Villard, M.

    2013-12-01

    The reactivity of ultramafic rocks under hydrothermal conditions 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 by confocal 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 very fast precipitation of serpentine may inhibit magnetite nucleation here. However, this does not rule out an H2 production since serpentines classically incorporate non negligible amount of ferric iron in their structure. The

  13. 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

  14. 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.

  15. 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.

    2017-03-01

    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.

  16. 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.

  17. Spectroscopic Analysis of Hydrothermal Alteration in Geothermal Drill Core

    NASA Astrophysics Data System (ADS)

    Calvin, W. M.; Littlefield, E. F.

    2012-12-01

    Water geochemistry can vary with depth and location within a geothermal reservoir, owing to natural factors such as changing rock type, gas content, fluid source and temperature. The interaction of these variable fluids with the host rock will cause changes in the host rock and create a variety of alteration minerals and precipitates. These alteration products can suggest regions of past fluid flow in the subsurface and their mineralogy can be used to determine fluid temperature. Infrared spectroscopy is particularly good at identifying a wide variety of hydrothermal alteration minerals, requires no sample preparation, and is especially helpful in discrimination among clay minerals. We have applied traditional remote sensing hyperspectral techniques in several pilot studies of geothermal drill core and chip analysis. We have surveyed a variety of samples, including drill chip boards, boxed core, and drill cuttings from envelopes and chip trays. Alteration mineralogy can indicate both the presence of thermal fluids and the hottest fluid temperature. These preliminary studies have established reliable methods for core/chip surveys that can rapidly measure samples with high depth resolution and show the efficiency of the technique to sample continuously and provide alteration logs similar to geophysical logs. We have successfully identified a wide variety of phyllosilicates, zeolites, opal, calcite, and iron oxides and hydroxides in drill core and cuttings from geothermal wells. In high vertical resolution measurements (every 10') we note depth-associated changes in alteration minerals, patterns or zones. Temperature dependent mineral assemblages are found, both gradational with depth and as narrow zones associated with vein or fracture fill. Amorphous silica is clearly identified and seen only in the highest temperature wells. We can readily identify montmorillonite/illite transitions that may be associated with Na/Ca/K variation and may eventually be used for

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. Tularosa Basin Play Fairway Analysis: Hydrothermal Alteration Map

    SciTech Connect

    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

  4. 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.

  5. Hydrothermal alteration in the Baca Geothermal System, Redondo Dome, Valles Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Hulen, Jeffrey B.; Nielson, Dennis L.

    1986-02-01

    Thermal fluids circulating in the active hydrothermal system of the resurgent Redondo dome of the Valles caldera have interacted with their diverse host rocks to produce well-zoned alteration assemblages, which not only help locate permeable fluid channels but also provide insight into the system's thermal history. The alteration shows that fluid flow has been confined principally to steeply dipping normal faults and subsidiary fractures as well as thin stratigraphic aquifers. Permeability along many of these channels has been reduced or locally eliminated by hydrothermal self-sealing. Alteration from the surface through the base of the Miocene Paliza Canyon Formation is of three distinctive types: argillic, propylitic, and phyllic. Argillic alteration forms a blanket above the deep water table in formerly permeable nonwelded tuffs. Beneath the argillic zone, pervasive propylitic alteration is weakly developed in felsic host rocks but locally intense in deep intermediate composition volcanics. Strong phyllic alteration is commonly but not invariably associated with major active thermal fluid channels. Phyllic zones yielding no fluid were clearly once permeable but now are hydrothermally sealed. High-temperature alteration phases at Baca are presently found at much lower temperatures. We suggest either that isotherms have collapsed due to gradual cooling of the system, that they have retreated without overall heat loss due to uplift of the Redondo dome, that the system has shifted laterally, or that it has contracted due to a drop in the water table. The deepest Well (B-12, 3423 m) in the dome may have penetrated through the base of the active hydrothermal system. Below a depth of 2440 m in this well, hydrothermal veining largely disappears, and the rocks resemble those developed by isochemical thermal metamorphism. The transition is reflected by temperature logs, which show a conductive thermal gradient below 2440 m. This depth may mark the dome's neutral plane

  6. Textural and mineralogical changes associated with the incipient hydrothermal alteration of glassy dacite at the submarine PACMANUS hydrothermal system, eastern Manus Basin

    NASA Astrophysics Data System (ADS)

    Monecke, T.; Giorgetti, G.; Scholtysek, O.; Kleeberg, R.; Götze, J.; Hannington, M. D.; Petersen, S.

    2007-02-01

    temperatures below 150 °C in an environment that allowed the development of steep temperature gradients. Comparison of the new data to the findings of deep drilling during ODP Leg 193 suggests that the smectite-rich alteration in the immediate subsurface of the PACMANUS hydrothermal vent field represents the low-temperature equivalent of illite- and chlorite-rich alteration associations forming in the upflow zones of the hydrothermal fluids in the deeper portion of the volcanic sequence.

  7. 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.

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

    USGS Publications Warehouse

    Altaner, S.P.; Ylagan, R.F.; Savin, S.M.; Aronson, J.L.; Belkin, H.E.; Pozzuoli, A.

    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 ??18 O 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. ??18 O 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 ??18 O 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

  9. 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.

  10. Hydrothermal fault zones in the lower oceanic crust: An example from the Samail ophiolite, Oman

    NASA Astrophysics Data System (ADS)

    Zihlmann, Barbara; Müller, Samuel; Koepke, Juergen; Teagle, Damon

    2017-04-01

    Hydrothermal circulation is a key process for the exchange of chemical elements between the oceans and the solid Earth and particularly for the extraction of heat from newly accreted crust at mid-ocean ridges. However, due to a dearth of samples from intact oceanic crust, or continuous samples from ophiolites, there remain major short comings in our understanding of hydrothermal circulation in the oceanic crust, especially in the deeper part. In particular, it is unknown whether fluid recharge and discharge occurs pervasively or if it is mainly channeled onto discrete zones such as faults. Here, we present a description of a hydrothermal fault zone that crops out in the layered gabbro section, of Wadi Gideah in the Samail ophiolite in Oman, which might be a channel of enhanced fluid flow. Field observations reveal an approximately one meter-thick chlorite - epidote normal fault with heavily altered gabbro clasts in the center. In places there is copper mineralization within the chlorite - epidote zone. In both, the hanging and the footwall the gabbro is heavily altered and veined, mainly with amphibole, epidote, prehnite and zeolite veins. Even though the fault zone is within the layered gabbro section, and perhaps only 1 km above the crust-mantle boundary, the gabbro around the fault zone shows highly variable textures. Preliminary strontium isotope whole rock data yield 87Sr/86Sr ratios of ˜ 0.7046, which are considerably more radiogenic than "fresh" gabbro from the Oman ophiolite (87Sr/86Sr = 0.7026 - 0.7030), and similar to black smoker hydrothermal signatures based on epidote, measured elsewhere in the ophiolite.

  11. LANDSAT detection of hydrothermal alteration in the Nogal Canyon Cauldron, New Mexico

    NASA Technical Reports Server (NTRS)

    Vincent, R. K.; Rouse, G.

    1977-01-01

    In 1974 a circular-shaped iron oxide anomaly was observed in an image of a LANDSAT frame centered near Truth or Consequences, New Mexico. Field examination of the anomaly has shown that it coincides with a zone of hydrothermal alteration on the northern edge of the Nogal Canyon Cauldron. The altered area contains clay minerals ranging in colors from white to vivid red, the latter presumably resulting from hematite staining. In situ gas measurements showed no evidence of active hydrogen sulfide seepage. Preliminary geochemical analyses of grab samples have detected no significant amounts of mineralization. Whereas this area does not at present appear to be economically important, it provides an example of how LANDSAT can be utilized in reconnaissance mapping for cauldrons, calderas, and other volcanic features which display hydrothermal alteration.

  12. 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.

  13. Stable isotopes in seafloor hydrothermal systems: Vent fluids, hydrothermal deposits, hydrothermal alteration, and microbial processes

    USGS Publications Warehouse

    Shanks, Wayne C.

    2001-01-01

    The recognition of abundant and widespread hydrothermal activity and associated unique life-forms on the ocean floor is one of the great scientific discoveries of the latter half of the twentieth century. Studies of seafloor hydrothermal processes have led to revolutions in understanding fluid convection and the cooling of the ocean crust, the chemical and isotopic mass balance of the oceans, the origin of stratiform and statabound massive-sulfide ore-deposits, the origin of greenstones and serpentinites, and the potential importance of the subseafloor biosphere. Stable isotope geochemistry has been a critical and definitive tool from the very beginning of the modern era of seafloor exploration.

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

  15. K isotopes as a tracer of seafloor hydrothermal alteration

    PubMed Central

    Parendo, Christopher A.; Jacobsen, Stein B.

    2017-01-01

    At ocean spreading ridges, circulation of seawater through rock at elevated temperatures alters the chemical and isotopic composition of oceanic crust. Samples obtained from drilling into ocean floor and from ophiolites have demonstrated that certain isotope systems, such as 18O/16O and 87Sr/86Sr, are systematically modified in hydrothermally altered oceanic crust. Although K is known to be mobile during hydrothermal alteration, there have not yet been any K-isotope analyses of altered oceanic crustal materials. Moreover, the 41K/39K of seawater was recently found to be significantly higher than that of igneous rocks, so the addition of seawater K to oceanic crust would be expected to generate 41K/39K variations in affected rocks. Here, we report high-precision 41K/39K measurements for samples from the Bay of Islands ophiolite, and we document large variations in 41K/39K, covarying with previous determinations of 87Sr/86Sr. Our data indicate that analytically resolvable 41K/39K effects arise in oceanic crust as a result of hydrothermal alteration. This finding raises the possibility that 41K/39K can be used as an effective tracer of oceanic crust recycled into the mantle, as a diagnostic criterion by which to identify ancient fragments of oceanic crust, and as a constraint on the flux of K between oceanic crust and seawater. PMID:28174267

  16. K isotopes as a tracer of seafloor hydrothermal alteration.

    PubMed

    Parendo, Christopher A; Jacobsen, Stein B; Wang, Kun

    2017-02-21

    At ocean spreading ridges, circulation of seawater through rock at elevated temperatures alters the chemical and isotopic composition of oceanic crust. Samples obtained from drilling into ocean floor and from ophiolites have demonstrated that certain isotope systems, such as (18)O/(16)O and (87)Sr/(86)Sr, are systematically modified in hydrothermally altered oceanic crust. Although K is known to be mobile during hydrothermal alteration, there have not yet been any K-isotope analyses of altered oceanic crustal materials. Moreover, the (41)K/(39)K of seawater was recently found to be significantly higher than that of igneous rocks, so the addition of seawater K to oceanic crust would be expected to generate (41)K/(39)K variations in affected rocks. Here, we report high-precision (41)K/(39)K measurements for samples from the Bay of Islands ophiolite, and we document large variations in (41)K/(39)K, covarying with previous determinations of (87)Sr/(86)Sr. Our data indicate that analytically resolvable (41)K/(39)K effects arise in oceanic crust as a result of hydrothermal alteration. This finding raises the possibility that (41)K/(39)K can be used as an effective tracer of oceanic crust recycled into the mantle, as a diagnostic criterion by which to identify ancient fragments of oceanic crust, and as a constraint on the flux of K between oceanic crust and seawater.

  17. Experimental study on hydrothermal alteration of dacite collected from the Hatoma knoll, Okinawa Trough, Japan

    NASA Astrophysics Data System (ADS)

    Masaki, Y.; Shibuya, T.; Yoshizaki, M.; Nozaki, T.; Suzuki, K.; Takai, K.

    2012-12-01

    The Okinawa Trough is a back-arc basin located between the southern part of Japan offshore and Taiwan North. Hemipelagic sediments supplied from the continents covered at the bottom of the trough. Vigorous hydrothermal activity exists with rifting. The Hatoma Knoll (the depth 1500 m) is one of the active hydrothermal fields located in the southern part of the trough. The measured highest temperature of the vent fluid was 301 °C. The rocks were sampled by manned research submersible ship "Shinkai 2000" in 2000. During the dive program, 25 hydrothermal fluid samples were collected and their chemical compositions were analyzed (Nakano et al., 2001). As a result, it was revealed that the compositions of the hydrothermal vent fluids are strongly influenced by the dacitic rock presumably in a reaction zone. In this presentation, we will show the results of experimental study on hydrothermal alteration dacite sample collected from the Hatoma Knoll. The sample was obtained near the hydrothermal area with ROV "Hyper-Dolphin" during the NT11-20 cruise in 2011. The experiment simulating water/rock reaction was conducted at 300 °C and 325 bars for more than 2,200 hours using the dacite sample and synthetic seawater. The reaction cell is made of a gold tube with a titanium head, which is pressurized in an autoclave. The chemical components of reacted fluid and altered dacite were measured with pH meter, ion chromatograph, ICP-AES, gas chromatograph, and XRD. We also observed thin section of the samples before and after the experiment under microscope. The major element concentrations of the reacted fluid were comparable with those of the natural hydrothermal fluids in the Hatoma Knoll in an order of magnitude except for Mn. As a result of XRD analysis, there was no significant difference in mineral assemblage between the starting material and the experimental product.

  18. Magnetic properties related to hydrothermal alteration processes at the Escondida porphyry copper deposit, northern Chile

    NASA Astrophysics Data System (ADS)

    Riveros, K.; Veloso, E.; Campos, E.; Menzies, A.; Véliz, W.

    2014-08-01

    Fluid-rock interaction related to the circulation of hydrothermal fluids can strongly modify the physicochemical properties of wall rocks in porphyry Cu deposits. These processes can also produce compositional and textural changes in ferromagnetic minerals, which can be quantified using magnetic methods. In the Escondida porphyry Cu deposit of northern Chile, each hydrothermally altered lithology is characterized by a discrete assemblage of Fe-Ti oxide minerals. These minerals have distinctive bulk magnetic susceptibility ( K bulk), temperature-dependent magnetic susceptibility, and magnetic hysteresis parameters. Selectively altered rocks (i.e., potassic and chloritic alteration types) exhibit the highest K bulk values (>3.93 × 10-3 SI units), and their hysteresis parameters indicate multidomain magnetic mineral behavior. This suggests that these rocks are composed of the coarsest magnetic grain sizes within the deposit. Optical analyses and susceptibility-temperature curves confirm that the magnetic signals in selectively altered rocks are mainly carried by secondary magnetite. In contrast, pervasively altered rocks (i.e., quartz-sericite and argillic alteration types) exhibit low K bulk values (<1.93 × 10-4 SI units) and contain smaller pseudo-single domain magnetic grain assemblages. This is consistent with the destruction and/or reduction in size of magnetite under acidic conditions. The results therefore demonstrate a genetic relationship between the hydrothermal alteration processes, Fe-Ti oxide minerals, and magnetic properties of the wall rock in the Escondida deposit. These magnetic methods can be considered a sensitive and efficient petrophysical tool for the identification and semi-quantification of alteration assemblages, and facilitating the recognition and mapping of discrete hydrothermal zones during exploration and operation of porphyry Cu deposits.

  19. Uranium (VI) and Neptunium (V) Transport Fractured, Hydrothermally Altered Concrete

    SciTech Connect

    Matzen, S.L.; Beiriger, J.M.; Torretto, P.C.; Zhao, P.

    1999-11-04

    In a high level waste repository in which temperatures are elevated due to waste decay, concrete structures will be subjected to hydrothermal conditions that will alter their physical and chemical properties. Virtually no studies have examined the interaction of hydrothermally altered concrete with radionuclides. We present the results of experiments in which soluble and colloid-associated actinides, uranium (U) and neptunium (Np), were eluted into a fractured, hydrothermally altered concrete core. Although the fluid residence time in the fracture was estimated to be on the order of 1 minute, U and Np were below detection (10{sup -9}-10{sup -8} M) in the effluent from the core, for both soluble and colloid-associated species. Inorganic colloids and latex microspheres were similarly immobilized within the core. Post-test analysis of the core identified the immobilized U and Np at or near the fracture surface, with a spatial distribution similar to that of the latex microspheres. Because hydrothermal alteration followed fracturing, the growth of crystalline calcium silicate hydrate and clay mineral alteration products on, and possibly across the fracture, resulted in a highly reactive fracture that was effective at capturing both soluble and colloidal radionuclides. Comparison of results from batch experiments [1] with these experiments indicate that partitioning of U and Np to the solid phase, and equilibration of the incoming fluid with the concrete, occurs rapidly in the fractured system. Transport of U through the concrete may be solubility and/or sorption limited; transport of Np appears to be limited primarily by sorption.

  20. 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.

  1. Effects Of Hydrothermal Alteration On Magnetic Properties And Magnetic Signatures - Implications For Predictive Magnetic Exploration Models

    NASA Astrophysics Data System (ADS)

    Clark, D.

    2012-12-01

    Magnetics is the most widely used geophysical method in hard rock exploration and magnetic surveys are an integral part of exploration programs for many types of mineral deposit, including porphyry Cu, intrusive-related gold, volcanic-hosted epithermal Au, IOCG, VMS, and Ni sulfide deposits. However, the magnetic signatures of ore deposits and their associated mineralized systems are extremely variable and exploration that is based simply on searching for signatures that resemble those of known deposits and systems is rarely successful. Predictive magnetic exploration models are based upon well-established geological models, combined with magnetic property measurements and geological information from well-studied deposits, and guided by magnetic petrological understanding of the processes that create, destroy and modify magnetic minerals in rocks. These models are designed to guide exploration by predicting magnetic signatures that are appropriate to specific geological settings, taking into account factors such as tectonic province; protolith composition; post-formation tilting/faulting/ burial/ exhumation and partial erosion; and metamorphism. Patterns of zoned hydrothermal alteration are important indicators of potentially mineralized systems and, if properly interpreted, can provided vectors to ore. Magnetic signatures associated with these patterns at a range of scales can provide valuable information on prospectivity and can guide drilling, provided they are correctly interpreted in geological terms. This presentation reviews effects of the important types of hydrothermal alteration on magnetic properties within mineralized systems, with particular reference to porphyry copper and IOCG deposits. For example, an unmodified gold-rich porphyry copper system, emplaced into mafic-intermediate volcanic host rocks (such as Bajo de la Alumbrera, Argentina) exhibits an inner potassic zone that is strongly mineralized and magnetite-rich, which is surrounded by an outer

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. Hydrothermal fault zone mapping using seismic and electrical measurements

    NASA Astrophysics Data System (ADS)

    Onacha, Stephen Alumasa

    This dissertation presents a new method of using earthquakes and resistivity data to characterize permeable hydrothermal reservoirs. The method is applied to field examples from Casa Diablo in the Long Valley Caldera, California; Mt. Longonot, Kenya; and Krafla, Iceland. The new method has significant practical value in the exploration and production of geothermal energy. The method uses P- and S-wave velocity, S-wave polarization and splitting magnitude, resistivity and magnetotelluric (MT) strike directions to determine fracture-porosity and orientation. The conceptual model used to characterize the buried, fluid-circulating fault zones in hydrothermal systems is based on geological and fracture models. The method has been tested with field earthquake and resistivity data; core samples; temperature measurements; and, for the case of Krafla, with a drilled well. The use of resistivity and microearthquake measurements is based on theoretical formulation of shared porosity, anisotropy and polarization. The relation of resistivity and a double porosity-operator is solved using a basis function. The porosity-operator is used to generate a correlation function between P-wave velocity and resistivity. This correlation is then used to generate P-wave velocity from 2-D resistivity models. The resistivity models are generated from magnetotelluric (MT) by using the Non-Linear Conjugate Gradient (NLCG) inversion method. The seismic and electrical measurements used come from portable, multi station microearthquake (MEQ) monitoring networks and multi-profile, MT and transient electromagnetic (TEM) observation campaigns. The main conclusions in this dissertation are listed below: (1) Strong evidence exists for correlation between MT strike direction and anisotropy and MEQ S-wave splitting at sites close to fluid-filled fracture zones. (2) A porosity operator generated from a double porosity model has been used to generate valid P-wave velocity models from resistivity data. This

  7. 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.

  8. 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.

  9. 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

  10. Petrology of hydrothermal alteration in the Vargeão basaltic impact structure (South Brazil)

    NASA Astrophysics Data System (ADS)

    Yokoyama, E.; Nédélec, A.; Trindade, R. I.; Baratoux, D.; Berger, G.

    2011-12-01

    Impact cratering process is of primary importance in the evolution of solid bodies of the Solar System. But craters on basaltic rocks, which are the best analog for the surface of other planets and satellites, are rare on Earth. Most studies to date were done in the Lonar crater, a simple crater 1.8 km in diameter, formed on the basaltic flows of the Deccan Province (India). Recently, one medium-size complex crater was identified on volcanic rocks of the Paraná basin (south Brazil) and may provide additional analog to the craters of most rocky planets and satellites. The 12 km wide Vargeão is a very well-preserved impact structure formed on basaltic and subordinately rhyodacites flows of the Serra Geral Formation (about 133-131 Ma), which are locally intertrapped by eolian-sandstones of Botucatu Formation. The impact-related features are represented by shatter cones, breccia-veins and planar deformation features in quartz (few occurrence in the sandstones). This work is focused on the petrogenesis of the centimeter breccia-veins that are found in all lithologies. We conducted a detailed petrological study (petrography, microprobe, SEM, Raman spectroscopy, Spectroscopy of reflectance and XRD) on these veins and their host-rocks. Our results show that the veins were strongly affected by the post-impact hydrothermal fluids. The hydrothermal alteration varies geographically in the structure. On the rim area this alteration consists of total or partial substitution of the melt matrix by quartz, calcite, iron oxides and clay minerals. At the central area, the alteration mineral assembly is composed of quartz, iron oxides, zeolites, clay minerals and rarely calcite. Usually, the alteration shows a zoned setting, which also varies locally. The nature of occurrence of second mineral identified in the context of post-impact hydrothermal alteration of impact craters on basalt represent a critical interpretation to interpret alteration signature of impact craters and the old

  11. 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.

  12. 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.

  13. Identification of hydrothermal alteration minerals for exploring of porphyry copper deposit using ASTER data, SE Iran

    NASA Astrophysics Data System (ADS)

    Pour, Amin Beiranvnd; Hashim, Mazlan

    2011-11-01

    The NW-SE trending Central Iranian Volcanic Belt hosts many well-known porphyry copper deposits in Iran. It becomes an interesting area for remote sensing investigations to explore the new prospects of porphyry copper and vein type epithermal gold mineralization. Two copper mining districts in southeastern segment of the volcanic belt, including Meiduk and Sarcheshmeh have been selected in the present study. The performance of Principal Component Analysis, band ratio and Minimum Noise Fraction transformation has been evaluated for the visible and near infrared (VNIR) and, shortwave infrared (SWIR) subsystems of ASTER data. The image processing techniques indicated the distribution of iron oxides and vegetation in the VNIR subsystem. Hydrothermal alteration mineral zones associated with porphyry copper mineralization identified and discriminated based on distinctive shortwave infrared (SWIR) properties of the ASTER data in a regional scale. These techniques identified new prospects of porphyry copper mineralization in the study areas. The spatial distribution of hydrothermal alteration zones has been verified by in situ inspection, X-ray diffraction (XRD) analysis, and spectral reflectance measurements. Results indicated that the integration of the image processing techniques has a great ability to obtain significant and comprehensive information for the reconnaissance stages of porphyry copper exploration in a regional scale. The results of this research can assist exploration geologists to find new prospects of porphyry copper and gold deposits in the other virgin regions before costly detailed ground investigations. Consequently, the introduced image processing techniques can create an optimum idea about possible location of the new prospects.

  14. Impact-Facilitated Hydrothermal Alteration in the Rim of Endeavour Crater, Mars

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, D. W.; Schroeder, C.; Farrand, W. H.; Crumpler, L. S.; Yen, A. S.

    2017-01-01

    Endeavour crater, a Noachian-aged, 22 km diameter impact structure on Meridiani Planum, Mars, has been investigated by the Mars Exploration Rover Opportunuity for over 2000 sols (Mars days). The rocks of the western rim region (oldest to youngest) are: (i) the pre-impact Matijevic fm.; (ii) rim-forming Shoemaker fm. polymict impact breccias; (iii) Grasberg fm., fine-grained sediments draping the lower slopes; and (iv) Burns fm., sulfate-rich sandstones that onlap the Grasberg fm. The rim is segmented and transected by radial fracture zones. Evidence for fluid-mediated alteration includes m-scale detections of phyllosilicates from orbit, and cm-scale variations in rock/soil composition/mineralogy documented by the Opportunity instrument suite. The m-scale phyllosilicate detections include Fe(3+)-Mg and aluminous smectites that occur in patches in the Matijevic and Shoemaker fms. Rock compositions do not reveal substantial differences for smectite-bearing compared to smectite-free rocks. Interpretation: large-scale hydrothermal alteration powered by impact-deposited heat acting on limited water supplies engendered mineralogic transfomations under low water/rock, near-isochemical conditions. The cm-scale alterations, localized in fracture zones, occurred at higher water/rock as evidenced by enhanced Si and Al contents through leaching of more soluble elements, and deposition of Mg, Ni and Mn sulphates and halogen salts in soils. Visible/near infrared reflectance of narrow curvilinear red zones indicate higher nanophase ferric oxide contents and possibly hydration compared to surrounding outcrops. Broad fracture zones on the rim have reflectance features consistent with development of ferric oxide minerals. Interpretation: water fluxing through the fractures in a hydrothermal system resulting from the impact engendered alteration and leaching under high water/rock conditions. Late, localized alteration is documented by Ca-sulfate-rich veins that are not confined to

  15. 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

  16. Chemistry, mineralogy and alteration intensity of hydrothermal altered Mt Unzen conduit rocks (Shimabara/Japan)

    NASA Astrophysics Data System (ADS)

    Hess, Kai-Uwe; Yilmaz, Tim; Gilg, H. Albert; Janots, Emilie; Mayer, Klaus; Nakada, Setsuya; Dingwell, Donald

    2017-04-01

    Investigations were carried out on hydrothermally altered coherent dacitic dykes samples from (USDP-4) drill core at Mt Unzen stratovolcano (Shimabara/Japan). XRF, XRD, EMPA, C-O-isotope, hot-cathode CL and SEM analysis led to insights concerning chemistry, mineralogy, and intensity and type of alteration as well as the origin of carbonate-precipitating fluids. Additionally a textural characterization of the occurring replacement features in the volcanic conduit rocks was performed. The occurrence of the main secondary phases such as chlorite, pyrite, carbonates, and R1 (Reichweite parameter) illite-smectite and kaolinite group minerals indicate a weak to moderate propylitic to phyllic hydrothermal alteration. The dacitic samples of the dykes show different hydrothermal alteration features: (i) carbonate and chlorite pseudomorphs after hornblende as well as core and zonal textures due to replacement of plagioclase by R1 illite-smectite as well as kaolinite group minerals, (ii) colloform banded fracture fillings and fillings in dissolution vugs, and (iii) chlorite, R1 illite-smectite as well as kaolinite group minerals in the groundmass. Late chlorite veins crosscut precipitates of R1 illite-smectite as well as kaolinite group minerals. Carbonates in fractures and in pseudomorphs after hornblende comprise iron-rich dolomite solid solutions ("ankerite") and calcite. Isotopic values indicate a hydrothermal-magmatic origin for the carbonate formation. The chlorite-carbonate-pyrite index (CCPI) and the Ishikawa alteration index (AI), applied to the investigated samples show significant differences (CCPI=52.7-57.8; AI=36.1-40.6) indicating their different degree of alteration. According to Nakada et al., 2005, the C13 to C16 dykes represent the feeder dyke from the latest eruption (1991-1995) whereas C8 represents an earlier dyke feeder dyke from an older eruption. Weakest alteration, which was obtained in samples C16-1-5 and C13-2-5, correlates with the alteration

  17. 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.

  18. Preliminary map of limonitic hydrothermal alteration for portions of the Needles 1° x 2° quadrangle, Arizona and California

    USGS Publications Warehouse

    Raines, Gary L.

    1983-01-01

    The map shows areas of limonitic hydrothermal alteration but does not show hydrothermally altered areas lacking limonitic materials. Table 1 lists, for each hydrothermally altered area detected, the type of alteration and the anomalous trace-element geochemical suite found in that area.

  19. 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

  20. Mineral-chemical studies of metamorphosed hydrothermal alteration in the Kristineberg volcanogenic massive sulfide district, Sweden

    NASA Astrophysics Data System (ADS)

    Hannington, Mark D.; Kjarsgaard, Ingrid M.; Galley, Alan G.; Taylor, Bruce

    2003-06-01

    The massive sulfide deposits of the Kristineberg area, Sweden, occur within a 2- to 3-km-thick succession of felsic volcaniclastic rocks belonging to the Skellefte Group. The volcanic pile is intruded by a synvolcanic Jorn-type granitoid (Viterliden intrusive complex) and is overlain by a thick sequence of metasedimentary rocks (Vargfors Group). Mineralization occurs at two main stratigraphic levels, at the base of the felsic volcanic succession and at the contact with the metasedimentary rocks of the Vargfors Group. The Kristineberg Cu-Zn mine is the largest deposit (approximately 21 Mt) and occurs at the base of the volcanic pile, close to the contact with the Viterliden intrusive complex. Four smaller deposits (Ravliden, Ravlidmyran, Horntrask and Nyliden) occur along the upper ore horizon. These deposits are thought to be related to a late intrusive phase of the Viterliden complex which cuts the altered volcanic rocks at the Kristineberg deposit. Within an area of about 50 km2 surrounding the Kristineberg deposit, felsic volcanic rocks between the two ore horizons are affected by extensive albite-destructive alteration (sodium depletion) and development of chlorite and muscovite (strong co-enrichment in magnesium and potassium). The Kristineberg deposit is enveloped by a large and partly transposed quartz-chlorite alteration zone, approximately 2 km in diameter, and a distal but coherent pyrite-quartz-muscovite alteration zone extending as far as 4 km from the deposit. Chlorite(±talc) in the mine area is notably magnesium-rich and contains anomalous F, Ba, Zn and Mn. High fluorine is also present in coexisting muscovite and phlogopite. The magnesium-rich chlorite alteration contrasts sharply with the iron enrichment observed in many other felsic, volcanic-hosted Precambrian massive sulfide deposits. This may indicate fixation of iron by large amounts of pyrite in the section or entrainment of large amounts of seawater in the hydrothermal upflow zones. Kyanite

  1. Composition-volume changes during hydrothermal alteration of andesite at Buttercup Hill, Noranda District, Quebec

    NASA Astrophysics Data System (ADS)

    Lesher, C. M.; Gibson, H. L.; Campbell, I. H.

    1986-12-01

    Hydrothermally altered andesites in the upper member of the Amulet formation at Buttercup Hill, Noranda, Quebec represent part of the aquifer and cap of a self-sealing geothermal system that focussed the discharge of hydrothermal fluids during the formation of massive Cu-Zn sulfide deposits. Five alteration facies are recognized pervasive greenschist faciés regional metamorphism (least-altered andesite) epidotization-silicification albitization-silicification chloritization sericitization-silicification. Alteration is localized on permeable zones such as amygdules, fractures, flow tops, discordant breccia dikes, and conformable breccia horizons. Epidotized-silicified andesite is enriched in Ca-Sr-Eu and depleted in Mg and first transition series metals (FTSM) relative to least-altered andesite. Albitized-silicified andesite is significantly enriched in Na and depleted in most FTSM relative to least-altered andesite. The abundances and inter-element ratios of the rare-earth elements (REE) and most high field-strength elements (HFS: Y, Zr, Th, U, Hf, Ta) are similar in least-altered, epidotized-silicified and albitized-silicified andesites. The most silicified andesites are strongly enriched in Na-Si, strongly depleted in Mg and divalent FTSM and slightly but systematically depleted in REE and most HFS elements. Serialized andesites were previously silicified; they are very strongly enriched in K-Rb-Cs-Ba, very strongly depleted in Na-Ca-Sr-Eu and slightly depleted in light REE relative to silicified andesite. Chloritized andesitic rocks exhibit heavy REE and HFS element ratios similar to those of leastaltered andesite, but are relatively strongly enriched in Mg and divalent FTSM, strongly depleted in Si and large ion lithophile (LIL) elements and slightly depleted in light REE. The coupled behavior of the heavy REE and most HFS elements during epidotization, albitization, silicification, chloritization and serialization suggests that they were inert during

  2. Contrasted monazite hydrothermal alteration mechanisms and their geochemical implications

    NASA Astrophysics Data System (ADS)

    Poitrasson, Franck; Chenery, Simon; Bland, David J.

    1996-12-01

    In spite of the major importance of monazite as a repository for the rare earths and Th in the continental crust, for U-Th-Pb geochronology, and as a possible form for high-level nuclear waste, very little work has been carried out so far on the behaviour of this mineral during fluid-rock events. This contribution describes two contrasting examples of the hydrothermal alteration of monazite. The first case comes from a sample of the Carnmenellis granite (Cornwall, Southwest England), chloritized at 284 ± 16°C, whereas the other occurs in the Skiddaw granite (Lake District, Northwest England), which underwent greisenization at 200 ± 30°C. An integrated study involving backscattered scanning electron microscopy, electron microprobe analyses, and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) reveals that the chloritization event was characterized by the coupled substitution 2REE 3+ ⇌ Th 4+ + Ca 2+ in the altered parts of the monazite, thus leaving the P-O framework of the crystal untouched. In contrast, greisenization led to the coupled substitution REE 3+ + P 5+ ⇌ Th 4+ + Si 4+, and therefore involved a partial destruction of the phosphate framework. The resulting rare earth element patterns are quite different for these two examples, with a maximum depletion for Dy and Er in the altered parts of the Carnmenellis monazite, whereas the Skiddaw monazite shows a light rare earth depletion but an Yb and Er enrichment during alteration. This latter enrichment, accompanied by an increase in U but roughly unchanged Pb concentrations, probably resulted from a decrease in the size of the 9-coordinated site in monazite, thereby favouring the smaller rare earths. These contrasted styles of monazite alteration show that the conditions of fluid-rock interaction will not only affect the aqueous geochemistry of the lanthanides, actinides and lead, and the relative stability of the different minerals holding these elements. Variations in these

  3. Contrasted monazite and allanite crystalline lattice responses under hydrothermal alteration

    NASA Astrophysics Data System (ADS)

    Poitrasson, F.

    2004-05-01

    Various cases of monazite and allanite hydrothermal alteration have been studied using micro-imaging (BSE-SEM), in situ spectroscopic (micro-Raman) and in situ chemical approaches (electron microprobe and LA-ICP-MS). These data, combined with literature results lead to the conclusion that monazite displays much more variable responses to fluid-mineral interactions than allanite despite a much simpler crystallographic structure. Depending on the fluid-rock conditions, monazite alteration can translate into cationic substitutions, monoclinic to hexagonal structure transition, dissolution and replacement by allanite, selective thorium removal and replacement by pyrite or dissolution-reprecipitation. In contrast, allanite responses to alteration are rather limited since they consist mostly in the substitution leading to epidote or to the leaching of the A-crystallographic sites prior to mineral dissolution. These results are surprising since monazite has only on cationic site besides that of phosphorous, whereas allanite has six different types of crystallographic sites, and can thus potentially display more variable chemical exchanges with fluids than monazite. This finding can be put in perspective with the tendency of minerals to occur in the metamict state in nature. Silicates, like zircon and allanite are frequently found in such a state, whereas metamict phosphates, like monazite and apatite are rare. It has been shown that this results mostly from the very low annealing temperature, below 200oC, of monazite and apatite, compared to allanite and zircon which need temperatures in excess to 700oC to fully restore their crystal lattice from the amorphous state. Apatite, like monazite, can also show a lot of different cationic substitutions. All these properties can be summarised as a much greater flexibility of the phosphate crystalline lattices compared to the silicate ones and this has important implications for geochronology, fluid-mineral chemical exchanges and

  4. 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.

  5. 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.

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

    USDA-ARS?s Scientific Manuscript database

    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 ...

  8. 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.

  9. Localization of magma injections, hydrothermal alteration, and deformation in a volcanic detachment (Piton des Neiges, La Réunion)

    NASA Astrophysics Data System (ADS)

    Famin, Vincent; Berthod, Carole; Michon, Laurent; Eychenne, Julia; Brothelande, Elodie; Mahabot, Marie-Myriam; Chaput, Marie

    2016-11-01

    This contribution aims at understanding how magmatism, hydrothermal alteration, and deformation may have interacted to localize a detachment (a low-angle normal fault) in a basaltic volcano. Piton des Neiges, an inactive volcano of La Réunion Island, has been deeply cut by erosion, allowing its inner structure to be investigated. The deepest unit observed in the edifice is a kilometer-scale plutonic complex, the top of which is intruded by multiple sills. This zone of repeated sill intrusions has been interpreted as a detachment because it displays evidence of hydrothermal alteration in the greenschist facies linked to a brittle-ductile shear deformation. Deformation begins with cataclasis and is followed by mylonitization and chlorite crystallization, then by hydrofracturing and pumpellyite crystallization. Subsequent and post-deformation calcite crystallization occurs in voids such as fractures and vacuoles. Aluminium substitutions in chlorite suggest that the syn-deformation hydrothermal alteration did not exceed 250 °C and peaked in the deformation zone. Comparison of bulk-rock major element analyses of fresh, altered and deformed rocks shows that the zone of sill intrusion and deformation localized increased concentrations of P and K otherwise depleted in the footwall and hangingwall rocks, suggesting that the detachment acted as a trap for fluids. In contradiction with proposed models of volcano spreading, it is apparent that the portion of Piton des Neiges accessible to observation did not deform by creep of a large hydrothermal system or a plutonic complex below its solidus. Instead, the interface between the already cooled plutonic complex and the host rock acted as a brittle failure zone and was repeatedly intruded by magma injections. This localized heat source promoted hydrothermal alteration and low temperature creep in and around the discontinuity. The same process of magmatism-related weakening might occur on active volcanoes; it may, for instance

  10. The role of prokaryotes in supergene alteration of submarine hydrothermal sulfides

    NASA Astrophysics Data System (ADS)

    Glynn, S.; Mills, R. A.; Palmer, M. R.; Pancost, R. D.; Severmann, S.; Boyce, A. J.

    2006-04-01

    We combine mineralogical, stable isotope and organic biomarker data to understand the role of prokaryote activity in supergene reactions within submarine hydrothermal sulfidic sediments. Data are presented for two adjacent cores from the periphery of the inactive Alvin hydrothermal mound. The limit of oxygenated seawater penetration into the sulfidic sediments is expressed as a sharp peak in solid phase Cu (atacamite and secondary Cu sulfides) associated with supergene alteration of the sulfide pile. Total prokaryote numbers are low throughout the upper few metres of sediment relative to published data for deep-sea sites. However, there is a statistically significant enrichment of prokaryote numbers at the redox front that coincides with abundant Fe-oxide filaments and a unique distribution of microbial biomarkers. The dominance of quaternary-branched alkanes in the oxidized transition zone immediately above the redox front (and their absence below) suggests a significant role of the source organisms in iron or sulfide oxidation under the more circumneutral conditions associated with the redox transition zone. The morphology of the Fe-oxide filaments preserved within late stage silica and gypsum mineralization is consistent with a biogenic origin of the filaments. Gypsum sulfur isotopes are in equilibrium with fluids that are derived from quantitative sulfide oxidation and gypsum nucleation is inferred to be biologically induced. These new data suggest that supergene alteration of sulfidic sediments generates sharp redox and pH gradients that stimulate prokaryotic activity, in particular iron and sulfide oxidisers, which in turn govern the distribution of secondary mineral phases and the abundance of redox sensitive trace metals.

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. Hydrothermal alteration in the EPF replacement wells, Olkaria Geothermal field, Kenya

    SciTech Connect

    Mungania, J.

    1996-12-31

    Olkaria Geothermal area is located in the central sector of the Kenya, Rift Valley. A 45MW Geothermal power station has been operational at Olkaria since 1985 supplied by 22 of the 26 wells drilled in the Eastern production field (EPF). Between 1988 and 1993, eight more wells referred to as {open_quote}replacement wells{close_quote} were drilled in the same field to boost steam supply to the station. Petrographic analyses of the drill cuttings is usually done to determine detail stratigraphy of the field, extends of hydrothermal activity, subsurface structures and other parameters which may influence production potential of a well. Analyses of the drill cuttings from the EPF wells show that: Variations in the whole rock alteration intensities correlate with differences in rocktypes. Permeable horizons, especially the productive feeder zones are well marked by enhanced hydrothermal minerals depositions, mainly quartz, calcite, pyrite and epidote. Other aspects of state of reservoir like boiling are signified by presence of bladed calcite.

  17. 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.

  18. 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.

  19. Role Of Hydrothermal System At Shallower Depth In 2.77 Ga Alteration Of Mt. Roe Basalt, Pilbara, Western Australia

    NASA Astrophysics Data System (ADS)

    Nedachi, Y.; Nedachi, M.; Taguchi, S.; Ohmoto, H.

    2004-12-01

    The sericite-chlorite alteration zone of the 2.77 Ga Mt. Roe basalt near Whim Creek, Pilbara, Western Australia, has been attracting attention if it is paleo-weathering profile (paleosol) formed under anoxic atmosphere or if it is hydrothermally altered zone by reduced fluid. It is also interesting in the standpoint of biological activity at late-Archean era, as it has been reported that the black veins in alteration zone and the sediment above it are characterized by the organic carbons with d13C values of methanogen and methanotroph. A fresh and consecutive core of Mt Roe basalt including alteration zones, which was drilled by ABDP (Archean Biosphere Drilling Project) in July 2003, gives new and more detailed insight into this concern. The core is ca. 300 m long, and is composed of amygdaloidal/massive basaltic lavas and tuffs with clastic sediments interbedded. About seventy selected samples were studied mineralogically using microscope, XRD, XGT and EPMA, and were analyzed chemically for major and trace elements using XRF and ICP-mass. The results show that (1) the core is composed of at least three lava/tuff units with different Ti/Zr and Zr/Hf ratios which are separated by thick sedimentary units, (2) the sedimentary units are comprised of sandstone, siltstone and shale, all of which are black-colored and rich in organic carbon, (3) the strongly sericitized horizons of several meters were recognized just below these sedimentary units, (4) thin sericitized layers are interbetted in amygdaloidal basalt and tuff horizons, the major part of which is associated with the fine-grained, black and organic carbon-rich quartz vein, (5) in some parts of sericitized zone, sulfide, Zn-rich and Ti-REE veins were observed, (6) all of the sericitized zone is characterizes by the depletion of Fe, Mg, Ca, Na and P and the enrichment of K, (7) several other kinds of veins, such as quartz, calcite, and chlorite, distribute across the basalt horizon, (8) organic carbons in black

  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. A Hydrothermally Altered, Mn-incrusted Marine Sediment as an Analogue for Martian Deposits?

    NASA Astrophysics Data System (ADS)

    Gross, C.; Bishop, J. L.; Maturilli, A.; D'Amore, M.; Helbert, J.

    2015-12-01

    The investigated sample was dredged in the Kahouanne basin during the research cruise SO-154 (RV Sonne) in the Lesser Antilles Island Arc between the islands of Guadeloupe and Montserrat (Halbach et al., 2002). The Kahouanne basin represents the southern extension of the large Kallinago intra-arc basin and has a length of approximately 40 km and a width of 15 km. The western margin of the basin is dominated by the Shoe-Rock-Spur fault zone. Previous research cruises found indications for low-temperature hydrothermal fluid-flow along the fault zone (Polyak et al., 1992). The sample 18CD is a sediment with grain- sizes of 0.25-0.63 mm, cemented by a Nontronite-Manganese matrix, partly displaying layer-like texture. The groundmass is composed of feldspar, pyroxenes, glass- and rhyodacitic fragments, as well as pelagic carbonates in clasts of different size. Often, ignimbritic textures are visible, pointing to volcanic ejection products. A detailed analysis was carried out on the sample 18CD, starting with the preparation of thin-sections, followed by XRD, XRF, ICP-OES, AAS, SEM (EDX-ZAF). In addition, we analyzed the sample with bi-directional reflectance and emission measurements conducted in the Planetary Emissivity Laboratory (PEL) at the German Aerospace Center (DLR), as well as visible/near-infrared reflectance using an ASD spectrometer at the SETI Institute. The results of the spectroscopic measurements show striking similarities to Martian nontronites, detected by orbiting instruments. Furthermore, the in-depth analyses of the hydrothermally altered sediment reveals reasonable processes and products for past and present Mars. References: Halbach et al., 2002. InterRidgeNews 11(1), 18-22; Polyak et al., 1992. J. Volcanol. Geotherm. Res., 54, 81-105.

  3. Hydrothermal Alteration in Submarine Basaltic Rocks from the Reykjanes Geothermal Field, Iceland. (Invited)

    NASA Astrophysics Data System (ADS)

    Zierenberg, R. A.; Schiffman, P.; Fowler, A. P.; Marks, N.; Fridleifsson, G.; Elders, W. A.

    2013-12-01

    The Iceland Deep Drilling Project (IDDP) is preparing to drill to 4-5 km in the Reykjanes Geothermal Field to sample geothermal fluids at supercritical temperature and pressure for power generation. The Reykjanes geothermal field is the on-land extension of the Reykjanes Ridge spreading center. The upper 1-2 kilometers drilled at Reykjanes are submarine basalts and basaltic sediments, hyalloclastites, and breccias, with an increasing proportion of basaltic intrusive rocks below 2 km depth. Geothermal fluids are evolved seawater with a composition similar to mid-ocean ridge hydrothermal systems. Zn- and Cu-rich sulfide scale, locally enriched in Au and Ag, are deposited in production pipes. The sulfide deposits are compositionally and isotopically similar to seafloor massive sulfides. In anticipation of deeper drilling, we have investigated the mineralogy and geochemistry of drill cuttings from a 3 km deep well (RN-17). The depth zoning of alteration minerals is similar to that described from other Icelandic geothermal fields, and is comparable to observed seafloor metamorphic gradients in ODP drill holes and ophiolites. Chlorite-epidote alteration occurs at depths >400 m and passes downhole through epidote-actinolite alteration and into amphibole facies (hornblende-calcic plagioclase) alteration below 2.5 km. Local zones of high temperature (>800°C), granoblastic-textured, pyroxene hornfels, are interpreted to form by contact metamorphism during dike/sill emplacement. Similar granoblasically altered basalts were recovered from the base of the sheeted dikes in IODP Hole 1256D. Downhole compositional variations of drill cuttings, collected every 50 m, suggest that rocks below ~ 2 km are little altered. Whole-rock oxygen isotope profiles are consistent with low water/rock ratios, but suggest that early stages of hydrothermal alteration included meteoric water-derived fluids. Strontium isotope profiles indicate more extensive exchange with seawater-derived fluids

  4. Hydrothermal brecciation in the Jemez fault zone, Valles Caldera, New Mexico: Results from continental Scientific Drilling Program core hole VC-1

    NASA Astrophysics Data System (ADS)

    Hulen, Jeffrey B.; Nielson, Dennis L.

    1988-06-01

    An unusual breccia sequence penetrated in the lower 30 m of Continental Scientific Drilling Program core hole VC-1 (total depth 856 m) records a complex hydrothermal history culminating in hydraulic rock rupture and associated alteration at the edge of the Quaternary Valles caldera. The breccias, both tectonic and hydrothermal in origin, were formed in the Jemez fault zone, near the intersection of this major regional structure with the caldera's ring-fracture margin. Tectonic breccias in the sequence are contorted, crushed, and sheared. Coexisting hydrothermal breccias lack such frictional textures but display matrix flow foliation and prominent clast rounding, features characteristic of fluidization. These hydrothermal breccias were intensely altered, during at least five major stages, to quartz-illite-phengite-pyrite aggregates; traces of molybdenite occur locally. This assemblage indicates interaction with hydrothermal fluid at temperatures in excess of 200°C. The extrapolated present maximum temperature of 184°C in the breccia zone therefore represents considerable cooling since these phases were formed. Fluid inclusions in the breccias also preserve evidence of the prior passage of hotter fluids. The inclusions are principally two phase, liquid rich, secondary in origin, and concentrated in hydrothermal quartz. Older, high-salinity inclusions, unrelated to brecciation, homogenize in the temperature range 189°-246°C. Younger inclusions, in part of interbreccia origin, are low-salinity and homogenize in the temperature range 230°-283°C; locally coexisting liquid- and vapor-rich inclusions document periodic boiling of the dilute fluids. These fluid-inclusion data, along with the probable age of the hydrothermal breccias (<1.5 Ma), the assumed depth at which they developed (about 515 m), and the contemporaneous state of stress (extensional) can be combined to model hydrothermal brecciation at the VC-1 site. The minimum fluid pressure (Pfr) required to

  5. 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.

  6. 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

  7. 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

  8. Magnetic effects of hydrothermal alteration in porphyry copper and iron-oxide copper-gold systems: A review

    NASA Astrophysics Data System (ADS)

    Clark, David A.

    2014-06-01

    Magnetic anomaly patterns can be used as a tool for mapping lithology, metamorphic zones and hydrothermal alteration systems, as well as identifying structures that may control passage of magmas or hydrothermal fluids associated with mineralisation. Reliable geological interpretation of mineralised systems requires an understanding of the magmatic, metamorphic and hydrothermal processes that create, alter and destroy magnetic minerals in rocks. Predictive magnetic exploration models for porphyry copper and iron oxide copper-gold (IOCG) deposits can be derived from standard geological models by integrating magnetic petrological principles with petrophysical data, deposit descriptions, and modelling of observed magnetic signatures of these deposits. Even within a particular geological province, the magnetic signatures of similar deposits may differ substantially, due to differences in the local geological setting. Searching for “look-alike” signatures of a known deposit is likely to be unrewarding unless pertinent geological factors are taken into account. These factors include the tectonic setting and magma type, composition and disposition of host rocks, depth of emplacement and post-emplacement erosion level, depth of burial beneath younger cover, post-emplacement faulting and tilting, remanence effects contingent on ages of intrusion and alteration, and metamorphism. Because the effects of these factors on magnetic signatures are reasonably well understood, theoretical magnetic signatures appropriate for the local geological environment can qualitatively guide exploration and make semiquantitative predictions of anomaly amplitudes and patterns. The predictive models also allow detectability of deposit signatures to be assessed, for example when deposits are buried beneath a considerable thickness of nonmagnetic overburden, are covered by highly magnetic heterogeneous volcanic rocks, or there is a strong regional magnetic gradient. This paper reviews the

  9. Hydrothermal Alteration of Hyaloclastites Adjacent to Sill-Like Intrusives in the HSDP 3-km Core Hole.

    NASA Astrophysics Data System (ADS)

    McClain, J. S.; Schiffman, P.; Walton, A. W.; Yin, Q.; Pauly, B.

    2008-12-01

    Hyaloclastites at present depths below1880 mbsl on the submarine flanks of Mauna Kea volcano have been intruded by numerous, < 10 m-thick, sill-like bodies. The contact metamorphism of the hyaloclastites has resulted in up to 1 m-thick bleached zones, characterized by the presence of Na-and Mg-enriched alteration rinds on sideromelane clasts as well as the precipitation of drusy hydrothermal clinopyroxene (calcic augite to hedenbergite) and analcime within void spaces. The intrusive activity associated with contact metamorphism appears to have occurred early in the diagenetic history of the hylaoclastites, when they possessed porosities of 40-50%, because (1) early induration and pore-filling by hydrothermal minerals apparently strengthened them, preventing significant grain compaction during subsequent burial, (2) hydrothermal minerals have been coated or overgrown by smectite, zeolites, and palagonite during subsequent diagenesis and microbial innoculation, and (3) 87Sr/86Sr ratios of hydrothermal rinds on glass shards, averaging .7069 ± .0006, imply extensive interaction with seawater, whereas 87Sr/86Sr ratios of adjacent palagonitized glass, averaging .7042 ± .0002, imply interaction with comparatively less fluid, presumably after diagenetic pore-filling. Thermal modeling, which assumes (1) convective cooling, (2) that hydrothermal clinopyroxenes formed at minimum temperatures of 350°C, and (3) that hyaloclastite porosities approached 50% at the time of intrusion, implies that the observed contact aureoles must have been produced by mafic intrusions that maintained temperatures above the solidus rather than being rapidly cooled and frozen. This may have occurred because magma continued to flow in the intrusion conduit, consistent with the suggestion that these intrusions fed overlying pillow flows (Garcia et al., 2007). If this intrusive activity occurred at shallow depths within the edifice of Mauna Kea (Seaman et al. 2004), then hydrothermal clinopyroxene

  10. 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.

  11. Sulfur and oxygen isotopic study of Paleozoic sediment-hosted Zn-Pb(-Ag-Au-Ba-F) deposits and associated hydrothermal alteration zones in the Nome Complex, Seward Peninsula, Alaska

    USGS Publications Warehouse

    Shanks, W.C. Pat; Slack, John F.; Till, Alison B.; Thurston, Roland; Gemery-Hill, Pamela

    2014-01-01

    The stratabound Nelson deposit, and the deformed veins at the Galena and Quarry deposits, may be older than the Aurora Creek-Christophosen and Wheeler North deposits. The Nelson deposit has a lower and narrower range of δ34S values (1.9 to 10.4‰), averaging about 8‰. The Galena and Quarry veins display δ34S values that are similar to those of the stratabound Nelson deposit. Barite samples from the Aurora Creek-Christophosen, Wheeler North, and Quarry deposits have 34S-enriched δ34S values between 25 and 30‰ that are consistent with derivation of the sulfur from coeval (Paleozoic) seawater sulfate. Given their δ34S values, it is likely that the Aurora Creek-Christophosen and Wheeler North deposits formed in closed sub-basins with euxinic conditions that led to extreme Rayleigh distillation to produce the very large range and very high δ34S values. The Nelson deposit probably formed within an anoxic but not euxinic sub-basin. At Nelson, sulfide was likely derived by a subsurface thermochemical sulfate reduction (TSR) reaction, similar to reactions that are inferred to have produced the sulfides in the Galena and Quarry deposits, which are interpreted as feeder veins for the stratabound deposits. Calculations of oxygen isotope temperatures are based on the assumption that evolved seawater with δ18O of 3‰ was the mineralizing and altering fluid related to the formation of the sulfide deposits. Temperatures of aluminous alteration and sulfide mineralization were between 109 and 209 °C, determined on the basis of oxygen isotope fractionations between the mineralizing fluid and proportionate amounts of quartz and muscovite in the rocks. These temperature estimates agree well with known temperatures of SEDEX mineralization worldwide. Sulfur isotope values also are generally consistent with the known ranges in SEDEX deposits worldwide (δ34S ≈ -5 to 25‰).

  12. Strontium and oxygen isotopic profiles through 3 km of hydrothermally altered oceanic crust in the Reykjanes Geothermal System, Iceland

    NASA Astrophysics Data System (ADS)

    Marks, N. E.; Zierenberg, R. A.; Schiffman, P.

    2010-12-01

    The Iceland Deep Drilling Program well of opportunity RN-17 was drilled 3 km into a section of hydrothermally altered basaltic crust in the Reykjanes geothermal system in Iceland. The system is located on the landward extension of the Mid-Atlantic Ridge, and the circulating hydrothermal fluid is modified seawater, making Reykjanes a useful analogue for mid-oceanic ridge hydrothermal systems. Whole rock oxygen isotope ratios range from -0.13 to 3.61‰, which are significantly depleted relative to fresh MORB (5.8±0.2‰). If oxygen isotope exchange between fluid and rock proceeded under equilibrium in a closed system, the bulk of the exchange must have occurred in the presence of a meteoric- as opposed to seawater-derived fluid. The concentrations of Sr in the altered basalt range from well below to well above concentrations in fresh rock, and appear to be strongly correlated with the dominant alteration mineralogy, although there is no correlation with 87Sr/86Sr isotopic ratios. Whole rock Sr isotopic ratios ranged from 0.70329 in the least altered crystalline basalt, to 0.70609 in the most altered hyaloclastite samples; there is no correlation with depth. Sr isotopic variation in epidote grains measured by laser ablation MC-ICP-MS ranged from 0.70353 to 0.70731. Three depth intervals have distinctive isotopic signatures, at 1000 m, 1350 m, and 2000 m depth, where 87Sr/86Sr ratios are elevated (mean value >0.7050) relative to background levels (mean altered basalt value ~0.7042). These areas are proximal to feed zones, and the 1350 m interval directly overlies the transition from dominantly extrusive to intrusive lithologies. Strontium and oxygen isotope data indicate that the greenschist-altered basalts were in equilibrium with modified hydrothermal fluids at a relatively high mean water/rock mass ratios (generally in the range 1-3), and require the presence of both meteoric- and seawater-derived recharge fluids at various stages in the hydrothermal history.

  13. Strontium alteration in the Troodos ophiolite: implications for fluid fluxes and geochemical transport in mid-ocean ridge hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Bickle, Mike J.; Teagle, Damon A. H.

    1992-09-01

    New and published strontium isotope analyses from the Troodos ophiolite constrain fluid-solid exchange processes, and the magnitude and circulation paths of the hydrothermal fluids. The 87Sr/ 86Sr profile reflects alteration in the recharge zone of an evolving hydrothermal system. Fluid-rock strontium isotope exchange in the upper ˜ 1.5 km of extrusive lavas was kinetically limited and seawater-derived fluids emitted from the base of this zone were buffered to 87Sr/ 86Sr ratios between ˜ 0.7047 and 0.7059. In contrast, over the next ˜ 1 km depth interval of sheeted dykes and the uppermost plutonics, 87Sr/ 86Sr values cluster about0.7054 ± 7 (2σ) and fluid flow is inferred to have been pervasive with near-equilibrium fluid-rock exchange. Quartz-chlorite and epidosite zones, the probable pathways of the concentrated, high-temperature upwelling fluids, have identical 87Sr/ 86Sr ratios to adjacent diabase dykes. On Troodos a time-integrated fluid flux in excess of2.9 × 10 7 kg m -2 is required to transport the strontium isotope composition of ˜ 0.7054, set in the kinetically controlled exchange zone, through the ˜ 1 km of sheeted dykes and into the zones of concentrated upwelling. The uniformity of the 87Sr/ 86Sr ratios in the diabase sheeted dykes and high-temperature epidosite and quartz-chlorite rocks indicate that the strontium isotopic alteration took place during the high temperature phase of hydrothermal circulation. The inferred minimum time-integrated fluid flux of2.9 × 10 7 kg m -2 substantially exceeds that of˜ 5 × 10 6 kg m -2 inferred from thermal models of high temperature circulation, but is comparable with estimates of the hydrothermal flux from oceanic budgets of 3He, Mg and 87Sr. The high flux estimate for Troodos is consistent with the ophiolite venting fluids, with 87Sr/ 86Sr elevated significantly above rock values, which contrasts with the near-MORB 87Sr/ 86Sr ratios of fluids from active high-temperature vents at mid-ocean ridges and

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. Mauna Loa's submarine western flank: Landsliding, deep volcanic spreading, and hydrothermal alteration

    NASA Astrophysics Data System (ADS)

    Morgan, Julia K.; Clague, David A.; Borchers, Deanna C.; Davis, Alicé S.; Milliken, Kitty L.

    2007-05-01

    Four new remotely operated vehicle dives carried out by Monterey Bay Aquarium Research Institute (MBARI) reveal a heterogeneous distribution of lithologies and compositions along a transect across the submarine west flank of Mauna Loa, from the outer scarp of the frontal bench to the upper flank. The frontal bench is composed predominantly of volcaniclastic sediments, ranging from very fine-grained monomictic hyaloclastites to coarse-grained, compositionally mixed volcaniclastic breccias. The predominance of subaerially derived clasts suggests accumulations of landslide deposits, probably emplaced along a regional shear plane preserved in cataclastic breccias with local foliations and grain trails. Repeated packages of inversely graded strata are interpreted to reflect thrust imbrication of the resulting volcaniclastic apron during volcanic spreading of Mauna Loa's western flank, similar to that now documented along Kīlauea's south flank. Many of the rocks from the bench show evidence for alteration, ranging from low-grade burial diagenesis to higher-grade hydrothermal alteration, including phases never before observed in submarine Hawaiian rocks, including epidote, talc, sphene, and corrensite. Alteration is concentrated in deformed zones, denoting pathways for fluid flow into or out of the volcanic edifice. Formed at depth, the altered rocks were subsequently transported along low-angle thrust faults into the bench and exposed along high-angle fractures and faults. The upper submarine flanks are draped by subaerially erupted, submarine emplaced pillow lavas and interbedded hyaloclastites, generated by shoreline-crossing lava flows. Basalt glasses indicate Mauna Loa origin but imply earlier compositions than present-day lavas, consistent with Ar-Ar ages suggesting eruption 0.28 ± 0.10 Ma. Late stage detachment of a nearshore slump produced the 'Ālika 2 debris avalanche that broke through the frontal bench, perhaps portending the evolution of the active Hilina

  19. 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.

  20. 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

  1. 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,

  2. 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.

  3. Thermocapillary oscillatory convection in half-zone liquid bridge and hydrothermal wave

    NASA Astrophysics Data System (ADS)

    Tang, Ze Mei

    It is now generally accepted that thermocapillary convection in half-zone liquid bridge of large Prandtl number fluid transfers from axis-symmetric convection to oscillatory convection directly with the increasing temperature difference, and it may be excited by the hydrothermal wave. In present study, thermocapillary oscillatory convection in a half-zone liquid bridge has been simulated for large Prandtl number fluid (10 cSt silicon oil) in the gravity level 1x10-4 g0 . The direct numerical simulation shows that for half-zone of large Prandtl fluid, the steady axissymmetric thermocapillary convection transfers to oscillatory convection via a 3-D steady state flow with azimuthal wave number m = 2 for some parameters, for example, L/d = 0.4 and V/Vo = 0.985, as the Marangoni number is increased. It is also of interest that the flow on the free surface at the z-constant cross section is from the cold spots towards the hot spots, which is similar to the results obtained in half-zone liquid bridge of Pr = 0.01 by Levenstam et al. Moreover, the present study reports the numerical results for hydrothermal wave in a liquid layer in the gravity level 1x10-4 g0 . The amplitudes of oscillatory velocity and temperature in the liquid layer are compared with those in the half-zone liquid bridge, which show that the amplitude of hydrothermal wave in the liquid layer is much smaller than that in the liquid bridge. The information about the existence of the steady state flow m = 2 prior to the oscillatory convection in half-zone liquid bridge and the very small amplitude of hydrothermal wave in a liquid layer are useful for understanding the mechanism for transition to oscillatory convection in the half zone.

  4. Hydrothermal alteration in the Reykjanes geothermal system: Insights from Iceland deep drilling program well RN-17

    NASA Astrophysics Data System (ADS)

    Marks, Naomi; Schiffman, Peter; Zierenberg, Robert A.; Franzson, Hjalti; Fridleifsson, Gudmundur Ó.

    2010-01-01

    The Reykjanes geothermal system is a seawater-recharged hydrothermal system that appears to be analogous to seafloor hydrothermal systems in terms of host rock type and low water/rock alteration. The similarities make the Reykjanes system a useful proxy for seafloor vents. At some time during the Pleistocene, the system was dominated by meteoric water recharge, and fluid composition at Reykjanes has evolved through time as a result of changing proportions of meteoric water influx as well as differing pressure and temperature conditions. The purpose of this study is to characterize secondary mineralization, degree of metasomatic alteration, and bulk composition of cuttings from well RN-17 from the Reykjanes geothermal system. The basaltic host rock includes hyaloclastite, breccia, tuff, extrusive basalt, diabase, as well as a marine sedimentary sequence. The progressive hydrothermal alteration sequence observed with increasing depth results from reaction of geothermal fluids with the basaltic host rock. An assemblage of greenschist facies alteration minerals, including actinolite, prehnite, epidote and garnet, occurs at depths as shallow as 350 m; these minerals are commonly found in Icelandic geothermal systems at temperatures above 250 °C (Bird and Spieler, 2004). This requires hydrostatic pressures that exceed the present-day depth to boiling point curve, and therefore must record alteration at higher fluid pressures, perhaps as a result of Pleistocene glaciation. Major, minor, and trace element profiles of the cuttings indicate transitional MORB to OIB composition with limited metasomatic shifts in easily mobilized elements. Changes in MgO, K 2O and loss on ignition indicate that metasomatism is strongly correlated with protolith properties. The textures of alteration minerals reveal alteration style to be strongly dependent on protolith as well. Hyaloclastites are intensely altered with calc-silicate alteration assemblages comprising calcic hydrothermal

  5. 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.

  6. Airborne Magnetic and Electromagnetic Data map Rock Alteration and Water Content at Mount Adams, Mount Baker and Mount Rainier, Washington: Implications for Lahar Hazards and Hydrothermal Systems

    NASA Astrophysics Data System (ADS)

    Finn, C. A.; Deszcz-Pan, M.; Horton, R.; Breit, G.; John, D.

    2007-12-01

    High resolution helicopter-borne magnetic and electromagnetic (EM) data flown over the rugged, ice-covered, highly magnetic and mostly resistive volcanoes of Mount Rainier, Mount Adams and Mount Baker, along with rock property measurements, reveal the distribution of alteration, water and hydrothermal fluids that are essential to evaluating volcanic landslide hazards and understanding hydrothermal systems. 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. Intense hydrothermal alteration significantly reduces the magnetization and resistivity of volcanic rock resulting in clear recognition of altered rock by helicopter magnetic and EM measurements. Magnetic and EM data, combined with geological mapping and rock property measurements, indicate the presence of appreciable thicknesses of hydrothermally altered rock west of the modern summit of Mount Rainier in the Sunset Amphitheater region, in the central core of Mount Adams north of the summit, and in much of the central cone of Mount Baker. We identify the Sunset Amphitheater region and steep cliffs at the western edge of the central altered zone at Mount Adams as likely sources for future debris flows. In addition, the EM data identified water-saturated rocks in the upper 100-200 m of the three volcanoes. The water-saturated zone could extend deeper, but is beyond the detection limits of the EM data. Water in hydrothermal fluids reacts with the volcanic rock to produce clay minerals. The formation of clay minerals and presence of free water 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. Finally, modeling requires extremely low

  7. 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.

  8. 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

  9. 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.

  10. Hydrothermal alteration of concrete: Yucca Mountain repository analogues

    SciTech Connect

    Myers, K.B.; Meike, A.

    1997-10-01

    Concrete could comprise a major share of construction materials present in the potential Yucca Mountain high-level radioactive waste repository. Concrete and shotcrete would be used as mechanical support (precast concrete liners), or road bed (invert) in repository emplacement drifts. These drifts could reach at least 150 to 200{degrees}C for extended periods of time, possibly in the presence of fluids. This study characterizes chemical and structural transformations in concrete that may occur as a result of a repository hydrothermal cycle. The specific concrete formulation to be used in the potential Yucca Mountain repository had not been determined at the time of the experiment. Invert and Fibercrete{sup TM} materials from the Exploratory Studies Facility (ESF) were chosen for these experiments as representatives of standard construction concrete used in this setting.

  11. Chemical transport in geothermal systems in Iceland: Evidence from hydrothermal alteration

    NASA Astrophysics Data System (ADS)

    Franzson, Hjalti; Zierenberg, Robert; Schiffman, Peter

    2008-06-01

    This study focuses on the chemical changes in basaltic rocks in fossil low- and high-temperature hydrothermal systems in Iceland. The method used takes into account the amount of dilution caused by vesicle and vein fillings in the rocks. The amount of dilution allows a calculation of the primary concentration of the immobile element Zr, and by multiplying the composition of the altered rock by the ratio of Zr (protolith)/Zr (altered rock) one can compute the mass addition caused by the dilution of the void fillings, and also make a direct comparison with the likely protoliths from the same areas. The samples were divided into three groups; two from Tertiary fossil high-temperature systems (Hafnarfjall, Geitafell), and the third group from a low temperature, zeolite-altered plateau basalt succession. The results show that hydrothermally altered rocks are enriched in Si, Al, Fe, Mg and Mn, and that Na, K and Ca are mobile but show either depletion or enrichment. The elements that are immobile include Zr, Y, Nb and probably Ti. The two high-temperature systems show quite similar chemical alteration trends, an observation which may apply to Icelandic fresh water high-temperature systems in general. The geochemical data show that the major changes in the altered rocks from Icelandic geothermal systems may be attributed to addition of elements during deposition of pore-filling alteration minerals. A comparison with seawater-dominated basalt-hosted hydrothermal systems shows much greater mass flux within the seawater systems, even though both systems have similar alteration assemblages. The secondary mineral assemblages seem to be controlled predominantly by the thermal stability of the alteration phases and secondarily by the composition of the hydrothermal fluids.

  12. 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

  13. Characteristics of hydrothermal alteration mineralogy and geochemistry of igneous rocks from the epithermal Co-O mine and district, Eastern Mindanao (Philippines)

    NASA Astrophysics Data System (ADS)

    Sonntag, Iris; Hagemann, Steffen

    2010-05-01

    Detailed petrographic as well as hyperspectral analyses using PIMA (Portable Infrared Mineral Analyser) and geochemical (major, trace and rare earth elements) studies were conducted on samples of the epithermal, low sulfidation Co-O mine (47,869 ounces gold produced in 2009 with an average grade of 13.3 g/t gold) and district in Eastern Mindanao (Philippines). The aims of the study were to unravel the petrogenetic origin of the various volcanic (host rocks) and intrusive rocks (potential fluid driver) as well as their relationship and influence on the hydrothermal alteration zoning and fluid chemistry. The auriferous veins at the Co-O mine were formed during two hydrothermal stages associated with the district wide D1 and D2 deformation events. Gold in stage 1 quartz veins is in equilibrium with galena and sphalerite, whereas in stage 2 it is associated with pyrite. Auriferous quartz veins of stage 1 reflect temperatures below 250° C or strong variations in pH and fO2 at higher temperatures, due to potential involvement of acidic gas or meteoric water. Cathodoluminescense studies revealed strong zonation of quartz associated with Au, presumably related to changes in the Al content, which is influenced by the pH. Plumose textures indicate times of rapid deposition, whereas saccharoidal quartz grains are related to potential calcite replacement. The geology of the Co-O mine and district is dominated by Miocene volcanic rocks (basic to intermediate flows and pyroclastics units), which are partly covered by Pliocene volcanic rocks and late Oligocene to Miocene limestones. The Miocene units are intruded by diorite (presumably Miocene in age). The epithermal mineralization event may be related to diorite intrusions. The geochemistry of all igneous rocks in the district is defined by a sub-alkaline affinity and is low to medium K in composition. Most units are related to a Miocene subduction zone with westward subduction, whereas the younger Pliocene rocks are related to

  14. 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.

  15. 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).

  16. 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.

  17. 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.

  18. Newgres: a turbo pascal program to solve a modified version of gresens' hydrothermal alteration equation

    NASA Astrophysics Data System (ADS)

    Leitch, C. H. B.; Day, S. J.

    Chemical compositions of altered rocks cannot be compared directly to the compositions of the unaltered parent rocks because of volume changes attendant on alteration. In order to make such a comparison, the observed chemical changes must be corrected for volume changes, usually by identifying immobile elements that are conserved during alteration. Gresens' equation can be used to estimate the volume changes, and subsequently calculate the chemical changes. A modified version of Gresens' hydrothermal alteration equation has been derived that expresses metasomatic losses and gains as a ratio of component weights rather than a weight difference. The resulting equation is more applicable to comparison of the behavior of components during hydrothermal alteration. In graphical presentations loss of components can be given the same visual weight as component gain. The programs GRES (for Gresens' equation) and NEWGRES (for the modified equation) enable rapid modeling of chemical mass balance during hydrothermal alteration, with the ability to rapidly compare the outcome of selecting different parent rocks or different immobile components.

  19. 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

  20. 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

  1. Paris vs. Murchison: Impact of hydrothermal alteration on organic matter in CM chondrites

    NASA Astrophysics Data System (ADS)

    Vinogradoff, V.; Le Guillou, C.; Bernard, S.; Binet, L.; Cartigny, P.; Brearley, A. J.; Remusat, L.

    2017-09-01

    Unravelling the origin of organic compounds that were accreted into asteroids requires better constraining the impact of asteroidal hydrothermal alteration on their isotopic signatures, molecular structures, and spatial distribution. Here, we conducted a multi-scale/multi-technique comparative study of the organic matter (OM) from two CM chondrites (that originate from the same parent body or from identical parent bodies that accreted the same mixture of precursors) and underwent a different degree of hydrothermal alteration: Paris (a weakly altered CM chondrite - CM 2.8) and Murchison (a more altered one - CM 2.5). The Paris insoluble organic matter (IOM) shows a higher aliphatic/aromatic carbon ratio, a higher radical abundance and a lower oxygen content than the Murchison IOM. Analysis of the OM in situ shows that two texturally distinct populations of organic compounds are present within the Paris matrix: sub-micrometric individual OM particles and diffuse OM finely distributed within phyllosilicates and amorphous silicates. These results indicate that hydrothermal alteration on the CM parent body induced aromatization and oxidation of the IOM, as well as a decrease in radical and nitrogen contents. Some of these observations were also reported by studies of variably altered fragment of Tagish Lake (C2), although the hydrothermal alteration of the OM in Tagish Lake was apparently much more severe. Finally, comparison with data available in the literature suggests that the parent bodies of other chondrite petrologic groups could have accreted a mixture of organic precursors different from that accreted by the parent body of CMs.

  2. 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

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. A hybrid zone between hydrothermal vent mussels (Bivalvia: Mytilidae) from the Mid-Atlantic Ridge.

    PubMed

    O'Mullan, G D; Maas, P A; Lutz, R A; Vrijenhoek, R C

    2001-12-01

    This study provides the first example of a hybrid zone between animal taxa distributed along the mid-ocean ridge system. We examined the distribution and genetic structure of deep-sea hydrothermal vent mussels (Bivalvia: Mytilidae) along a 2888-km portion of the Mid-Atlantic Ridge between 37 degrees 50' N and 14 degrees 45' N latitude. Mitochondrial DNA (mtDNA), allozymes and multivariate-morphometric evidence discriminated between individuals of a northern species, Bathymodiolus azoricus, and a southern species, B. puteoserpentis, that were separated by an intermediate ridge segment almost devoid of mussels. A small sample of mussels from Broken Spur, a vent locality along this intermediate zone, revealed a mixed population with gene frequencies and morphology that were broadly intermediate to those of the northern and southern species. Multilocus clines in mtDNA and allozyme frequencies were centred over the intermediate zone. We consider intrinsic and extrinsic processes that might limit genetic exchange across this hybrid zone.

  13. K-Ar ages on intrusive and altered zones in the Chignik and Sutwik Island quadrangles: A section in The United States Geological Survey in Alaska: Accomplishments during 1979

    USGS Publications Warehouse

    Wilson, Frederic H.

    1981-01-01

    Continued K-Ar dating of intrusive rocks and hydrothermal alteration zones in the Chignik and Sutwik Island quadrangles of the Alaska Peninsula, supplemental to that by Wilson, Detterman, and Silberman (1978) and Wilson (1978), has refined our knowledge of the ages of the igneous rocks and clarified relations between altered zones and igneous events in the area.

  14. Fractal Dimension Change Point Model for Hydrothermal Alteration Anomalies in Silk Road Economic Belt, the Beishan Area, Gansu, China

    NASA Astrophysics Data System (ADS)

    Han, H. H.; Wang, Y. L.; Ren, G. L.; LI, J. Q.; Gao, T.; Yang, M.; Yang, J. L.

    2016-11-01

    Remote sensing plays an important role in mineral exploration of “One Belt One Road” plan. One of its applications is extracting and locating hydrothermal alteration zones that are related to mines. At present, the extracting method for alteration anomalies from principal component image mainly relies on the data's normal distribution, without considering the nonlinear characteristics of geological anomaly. In this study, a Fractal Dimension Change Point Model (FDCPM), calculated by the self-similarity and mutability of alteration anomalies, is employed to quantitatively acquire the critical threshold of alteration anomalies. The realization theory and access mechanism of the model are elaborated by an experiment with ASTER data in Beishan mineralization belt, also the results are compared with traditional method (De-Interfered Anomalous Principal Component Thresholding Technique, DIAPCTT). The results show that the findings produced by FDCPM are agree with well with a mounting body of evidence from different perspectives, with the extracting accuracy over 80%, indicating that FDCPM is an effective extracting method for remote sensing alteration anomalies, and could be used as an useful tool for mineral exploration in similar areas in Silk Road Economic Belt.

  15. Hydrothermal palygorskite and ferromanganese mineralization at a central California margin fracture zone

    USGS Publications Warehouse

    Gibbs, A.E.; Hein, J.R.; Lewis, S.D.; McCulloch, D.S.

    1993-01-01

    Ferromanganese oxyhydroxide crusts and nodules associated with palygorskite were recovered from the Santa Lucia Escarpment where the Morro Fracture Zone intersects the central California continental margin. Palygorskite was found in pure, high-Mg, low-Al, boxwork-textured veins, and disseminated in poorly consolidated palygorskite-rich mudstone. The purity of the palygorskite boxwork blades and the boxwork structure suggest formation by direct precipitation rather than by diagenetic or detrital processes. Interaction of hydrothermal fluids with oceanic basalt and/or deeper ultramafic rocks produced a Mg-Si enriched fluid supersaturated with respect to palygorskite that precipitated directly from the fluid at or near the seafloor. The close association of Fe-Mn crusts and nodules with both the palygorskite-rich mudstone and boxwork-vein palygorskite suggests a genetic link between the three types of mineralization. Mixed origin hydrothermal-hydrogenetic Fe-Mn crusts, with up to 50% hydrothermal input, formed contemporaneously with and subsequent to palygorskite formation. Fe-Mn nodules collected in the same dredge are of combined hydrogenetic and diagenetic origin and appear to be unrelated to hydrothermal mineralization that produced the crusts and palygorskite. The thickness of the Fe-Mn crusts and rare diatom fragments within the mudstone suggest an age of formation between 13 and 5 Ma. ?? 1993.

  16. Silicon isotopes fractionation in meteoric chemical weathering and hydrothermal alteration systems of volcanic rocks (Mayotte)

    NASA Astrophysics Data System (ADS)

    Basile-Doelsch, Isabelle; Puyraveau, Romain-Arnaud; Guihou, Abel; Haurine, Frederic; Deschamps, Pierre; rad, Setareh; Nehlig, Pierre

    2017-04-01

    Low temperature chemical weathering fractionates silicon (Si) isotopes while forming secondary silicates. The Si fractionation ranges of high temperature secondary phyllosilicates formed in hydrothermal alteration environments have not been investigated to date. Several parameters, including temperature, reaction rates, pH, ionic concentrations in solution, precipitation/dissolution series or kinetic versus equilibrium regime are not the same in hydrothermal alteration and surface weathering systems and may lead to different fractionation factors. In this work, we analyzed Si isotopes in these two types of alteration conditions in two profiles sampled on the volcanic island of Mayotte. In both profiles, Si-bearing secondary mineral was kaolinite. Both profiles showed 30Si depletion as a function of the degree of alteration but each with a distinct pattern. In the meteoric weathering profile, from the bottom to the top, a gradual decrease of the δ30Si from parent rock (-0.29 ± 0.13 ‰) towards the most weathered product (-2.05 ± 0.13 ‰) was observed. In the hydrothermal alteration profile, in which meteoric weathering was also superimposed at the top of the profile, an abrupt transition of the δ30Si was measured at the interface between parent-rock (-0.21 ± 0.11 ‰) and the altered products, with a minimum value of -3.06 ± 0.16 ‰˙ At the scale of Si-bearing secondary minerals, in the chemical weathering system, a Δ30Sikaol-parentrock of -1.9 ‰ was observed, in agreement with results in the literature. A low temperature kinetic fractionation 30ɛ of -2.29 ‰ was calculated using a simple steady state model. However, an unexpected Δ30Sikaol-parentrock of -2.85 ‰ was measured in the hydrothermal alteration site, pointing to possible mechanisms linked to dissolution/precipitation series and/or to ionic composition of the solution as the main controlling factors of fractionation in hydrothermal conditions. At the scale of the profiles, both δ30Si

  17. 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

  18. 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.

  19. Temporal evolution of the giant Salobo IOCG deposit, Carajás Province (Brazil): constraints from paragenesis of hydrothermal alteration and U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    deMelo, Gustavo H. C.; Monteiro, Lena V. S.; Xavier, Roberto P.; Moreto, Carolina P. N.; Santiago, Erika S. B.; Dufrane, S. Andrew; Aires, Benevides; Santos, Antonio F. F.

    2017-06-01

    The giant Salobo copper-gold deposit is located in the Carajás Province, Amazon Craton. Detailed drill core description, petrographical studies, and U-Pb SHRIMP IIe and LA-ICP-MS geochronology unravel its evolution regarding the host rocks, hydrothermal alteration and mineralization. Within the Cinzento Shear Zone, the deposit is hosted by orthogneisses of the Mesoarchean Xingu Complex (2950 ± 25 and 2857 ± 6.7 Ma) and of the Neoarchean Igarapé Gelado suite (2763 ± 4.4 Ma), which are crosscut by the Old Salobo granite. Remnants of the Igarapé Salobo metavolcanic-sedimentary sequence are represented by a quartz mylonite with detrital zircon populations (ca. 3.1-3.0, 2.95, 2.86, and 2.74 Ga). High-temperature calcic-sodic hydrothermal alteration (hastingsite-actinolite) was followed by silicification, iron-enrichment (almandine-grunerite-magnetite), tourmaline formation, potassic alteration with biotite, copper-gold ore formation, and later Fe-rich hydrated silicate alteration. Myrmekitic bornite-chalcocite and magnetite comprise the bulk of copper-gold ore. All these alteration assemblages have been overprinted by post-ore hematite-bearing potassic and propylitic alteration, which is also recognized in the Old Salobo granite. In the central zone of the deposit the mylonitized Igarapé Gelado suite rocks yield an age of 2701 ± 30 Ma. Zircon ages of 2547 ± 5.3 and 2535 ± 8.4 Ma were obtained for the Old Salobo granite and for the high-grade copper ore, respectively. A U-Pb LA-ICP-MS monazite age (2452 ± 14 Ma) from the copper-gold ore indicates hydrothermal activity and overprinting in the Siderian. Therefore, a protracted tectono-thermal event due to the reactivation of the Cinzento Shear Zone is proposed for the evolution of the Salobo deposit.

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

    NASA Astrophysics Data System (ADS)

    Schwenzer, Susanne P.; Kring, David A.

    2013-09-01

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

  1. 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

  2. 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.

  3. 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.

  4. Microearthquakes Beneath the Endeavour Hydrothermal Vent Fields: Insights Into Reaction Zone Processes

    NASA Astrophysics Data System (ADS)

    Wilcock, W. S.; Hooft, E. E.; McGill, P. R.; Toomey, D. R.; Barclay, A. H.; Stakes, D. S.; Ramirez, T. M.

    2007-12-01

    From 2003-2006, a novel seismic network comprising seven short-period corehole seismometers and a broadband Guralp CMG-1T OBS was deployed using remotely operated vehicles in a subseafloor configuration on the Endeavour segment of the Juan de Fuca mid-ocean ridge. The seismic monitoring array was one part of a multi-disciplinary prototype NEPTUNE experiment designed to investigate the linkages between seismic deformation, hydrothermal fluxes, and microbial productivity along oceanic plate boundaries. The seismic network recorded high-quality data that illustrate the advantages of using an ROV to deploy seismometers in well- coupled configurations that are also away from the effects of ocean currents. A preliminary analysis of the first year of Keck seismic data was undertaken during a research apprenticeship class taught in the fall of 2004 at the University of Washington's Friday Harbor Laboratories. Eight post- baccalaureate students obtained a preliminary catalog of nearly 13,000 earthquakes on the Endeavour segment. Two of the apprentices conducted a second-pass analysis to refine the locations of ~3000 earthquakes that are within or near the network. Further analysis of these proximal earthquakes has focused on the application of cross-correlation and relative relocation techniques, the determination of focal mechanisms using P-wave first motions and P- to S-wave amplitudes ratios, and improved estimates of earthquake magnitudes. The results show that the entire Endeavour segment was seismically active during 2003-2004. Within the network, the earthquakes are located in tight clusters centered at ~2 km depth in the inferred location of the hydrothermal reaction zone immediately above a crustal magma chamber imaged by seismic reflection studies. The number of earthquakes below each hydrothermal vent field correlates with the heat flux measured by other researchers and the vertical thickness of this reaction zone, inferred from the distribution of seismicity, is

  5. 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

  6. 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

  7. 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.

  8. Hydrothermal alteration of kimberlite by convective flows of external water.

    PubMed

    Afanasyev, A A; Melnik, O; Porritt, L; Schumacher, J C; Sparks, R S J

    Kimberlite volcanism involves the emplacement of olivine-rich volcaniclastic deposits into volcanic vents or pipes. Kimberlite deposits are typically pervasively serpentinised as a result of the reaction of olivine and water within a temperature range of 130-400 °C or less. We present a model for the influx of ground water into hot kimberlite deposits coupled with progressive cooling and serpentisation. Large-pressure gradients cause influx and heating of water within the pipe with horizontal convergent flow in the host rock and along pipe margins, and upward flow within the pipe centre. Complete serpentisation is predicted for wide ranges of permeability of the host rocks and kimberlite deposits. For typical pipe dimensions, cooling times are centuries to a few millennia. Excess volume of serpentine results in filling of pore spaces, eventually inhibiting fluid flow. Fresh olivine is preserved in lithofacies with initial low porosity, and at the base of the pipe where deeper-level host rocks have low permeability, and the pipe is narrower leading to faster cooling. These predictions are consistent with fresh olivine and serpentine distribution in the Diavik A418 kimberlite pipe, (NWT, Canada) and with features of kimberlites of the Yakutian province in Russia affected by influx of ground water brines. Fast reactions and increases in the volume of solid products compared to the reactants result in self-sealing and low water-rock ratios (estimated at <0.2). Such low water-rock ratios result in only small changes in stable isotope compositions; for example, δO(18) is predicted only to change slightly from mantle values. The model supports alteration of kimberlites predominantly by interactions with external non-magmatic fluids.

  9. 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

  10. 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.

  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. Normal Faulting, Fluid Upflow Pathways, and Alteration in the Subsurface of a Seafloor Ultramafic-Hosted Hydrothermal System, northern Apennines, Italy

    NASA Astrophysics Data System (ADS)

    Alt, J.; Levine, D.; Crispini, L.; Gaggero, L.; Shanks, W. C., III; Gulbransen, C.

    2016-12-01

    We document the mineralogy and geochemistry of a fault that acted as a hydrothermal upflow zone in the subsurface of a seafloor ultramafic-hosted hydrothermal system in the northern Apennines, Italy. The objectives are to understand fluid flow pathways, and the relative roles of upwelling hydrothermal fluids versus cold seawater and biological effects in such systems on the modern seafloor, which is much more difficult to access and study. Peridotites were exposed on the seafloor by detachment faulting, intruded by MORB gabbros, and are overlain by MORB lavas and pelagic sediments. North of the village of Reppia are two 1-2 m wide fault shear zones in serpentinite, oriented at a high angle to the detachment surface and extending hundreds of meters below the detachment. The host peridotite is 90-100% serpentinized, and serpentinite is highly replaced by talc plus tremolite and sulfide in the shear zones. At the paleo-seafloor, the fault offsets carbonate-cemented serpentinite breccia, talc-altered serpentinite, and serpentinite in the footwall to the west, from pillow basalts of the hanging wall on the east. Here the fault rocks consist of 90% Fe-dolomite with a few percent each of calcite, quartz, serpentine, talc, sulfides, chlorite, and trace relict Cr-spinel. The fault ends upward in massive sulfide overlain by pillow basalts and pelagic sediment. Three main alteration stages are identified. 1. Background serpentinites exhibit slight LREE enrichments and elevated d34S values (+3.9 to +5.2‰) consistent with serpentinization by upwelling hot hydrothermal fluids. 2. Talc alteration of serpentinite leads to strong LREE enrichments, negative Eu anomalies, silica metasomatism, and elevated Cu during the main hydrothermal upflow stage. 3. Carbonate alteration varies from slight veining of serpentinite to near-total replacement in the shallow fault rocks, with variable enrichments of LREE, Ca, Si, and metals. Carbonate oxygen isotope temperatures of 15-150°C and d13C

  13. Experimental hydrothermal alteration of andesite at 325 ˚C, 300 bar: Comparison with the hydrothermal fluids in the Hatoma Knoll, southern Okinawa Trough

    NASA Astrophysics Data System (ADS)

    Saitoh, Masafumi; Shibuya, Takazo; Nozaki, Tatsuo; Torimoto, Junji; Ueda, Hisahiro; Sato, Tomoki; Suzuki, Katsuhiko

    2017-04-01

    Formation processes and types of hydrothermal sulfide deposits are closely related to chemical compositions of subseafloor hydrothermal fluids. Subseafloor hydrothermal alteration of intermediate to felsic rocks is a major process that controls the fluid compositions in the arc/back-arc hydrothermal systems, although the chemical reaction process during water-rock interaction has not been examined in detail. We experimentally reacted a NaCl solution under high-pressure and -temperature conditions with fresh andesite collected from the Hatoma Knoll, southern Okinawa Trough. The concentrations of selected elements (e.g., K, Ca, and Si) in the fluid obtained by the experiment are inconsistent with those of the hydrothermal fluids in the Hatoma Knoll. The present results suggest that the inputs of magmatic volatiles derived from andesitic magma to the hydrothermal fluids may not be significant whereas hydrothermal reactions with felsic rocks (e.g., dacite and rhyolite) and/or sediments may contribute substantially to the fluid compositions in the Hatoma Knoll.

  14. 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

  15. 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

  16. 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.

  17. Potassium Isotopes as a New Tracer of Seafloor Hydrothermal Alteration: The Bay of Islands Ophiolite

    NASA Astrophysics Data System (ADS)

    Parendo, C. A.; Jacobsen, S. B.; Wang, K.

    2016-12-01

    Hydrothermal circulation at and around oceanic spreading ridges results in elemental exchange between seawater and oceanic crust, with profound implications for both the ionic composition of seawater and the elemental composition of various solid-Earth reservoirs over geological time. Potassium is among the elements known to be mobile during hydrothermal alteration. Here we investigate the isotopic character of this K exchange by obtaining high-precision 41K/39K data for 6 samples from the Bay of Islands Ophiolite, Newfoundland, Canada—a piece of ca. 485 Ma oceanic crust that was affected by seafloor hydrothermal alteration prior to being obducted. Our 41K/39K analyses are generated using an Isoprobe-P MC-ICPMS equipped with a hexapole collision and reaction cell, which essentially eliminates interferences from the K-isotope mass spectrum. The analyses have an external reproducibility of about 0.07‰ (2SD). We find that the 41K/39K ratios of the ophiolite rocks span a range of approximately 0.70‰ and covary with previously determined 87Sr/86Sr ratios. The stratigraphically deepest, least-altered sample (an olivine gabbro) has a 41K/39K ratio within error of that typically observed in common igneous rocks. The stratigraphically higher, more-altered samples (which include hornblende gabbro, plagiogranite, diabase, and basalt) have 41K/39K ratios that are markedly heavier. This variability in 41K/39K ratios is interpreted to reflect variable addition of seawater K to the rocks. A simple open-system water-rock interaction calculation shows that the covariation between 41K/39K and 87Sr/86Sr can be plausibly explained as the result of hydrothermal alteration. The simplest scenario assumes that the 41K/39K ratio of seawater at the time of interest was similar to its present-day value, in which case the calculation suggests that isotopically heavy seawater K is added to oceanic crust with little fractionation—i.e., an effective fractionation factor near 0.0‰. The

  18. 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.

  19. 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.

  20. Investigation of Icelandic rift zones reveals systematic changes in hydrothermal outflow in concert with seismic and magmatic events: Implications for investigation of Mid-Ocean Ridge hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Curewitz, D.; Karson, J. A.

    2010-12-01

    Co-registration of several generations of geological data was carried out for hydrothermal fields along active rift zones of the Iceland plate boundary zone. Significant short- and long-term changes in vent locations, flow rates and styles, and fluid characteristics over short periods take place in concert with recorded earthquakes, dike intrusions, and fissure eruptions. Higher resolution, more detailed analysis of the Icelandic hydrothermal sites will inform investigation of similar data from mid-ocean ridge hydrothermal systems along the RIDGE 2000 focus sites. Initial results from the Hengill and Krafla geothermal areas covering a time-span of nearly 40 years at ~10 year intervals reveal limited changes in the surface expression of fault populations, with the exception of local fault and fracture systems. The location and population density of individual vents and groups of vents underwent significant changes over the same time period, with either vents shifting location, or new vents opening and old vents closing. Registration of changes in vent fluid temperatures, vent field ground temperatures, fluid flow rates, and vent eruptive styles reveal changes in hydrothermal flow systematics in concert with the observed changes in vent location and vent population density. Significant local seismic and volcanological events (earthquakes, earthquake swarms, dike intrusions, eruptions, inflation/deflation) that are potential triggers for the observed changes take place in intervening years between production of successive maps. Changes in modeled stress intensities and local fracture/fault density and geometry associated with these tectono-magmatic events correspond well to inferred locations of increased or decreased shallow permeability thought to control hydrothermal outflow behavior. Recent seismic events are strongly linked to well-mapped changes in fracture/fault population and hydrothermal flow behavior in the Hveragerdi region, near Hengill, and provide higher

  1. 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.

  2. Hydrothermal alteration in Lesser Antilles volcanoes: a study of trace element and U-Th isotope redistribution in active- and paleo- hydrothermal systems of Guadeloupe and Montserrat

    NASA Astrophysics Data System (ADS)

    Salaun, Anne; Villemant, Benoît.; Gerard, Martine; Komorowski, Jean-Christophe; Manhes, Gérard

    2010-05-01

    Hydrothermally altered material have been collected in active hydrothermal systems and in debris avalanche deposits (DAD) that have sampled different region of the paleo-hydrothermal system of La Soufrière of Guadeloupe and Soufriere Hills volcanoes. A detailed analysis of the mineralogy, the trace element (REE, U, Th, 1st transition series) composition and the U-Th isotopes disequilibrium of this altered material has been performed. These results are discussed in terms of relative element mobility and associated mineralogical assemblages in function of the progressive alteration stages of the andesitic material. Andesitic products that have been affected by shallow hydrothermal alteration are complex assemblages of volcanic material (glass, phenocrysts and xenocrysts with complex magmatic histories) of different ages and lithologies. In DAD, this altered material has been more or less deeply reworked during transport. This material has eventually been exposed to later meteoritic or fumarollic alteration. Since REE and other incompatible elements (Th, U, Hf, Zr) are mainly concentrated in the groundmass of andesitic magmas, composition variations of these elements in altered material mainly traces the transformation of volcanic glass into smectite. This transformation is accompanied during the first stages of hydrothermal alteration, (1) by a massive loss of alkaline and 1st transition series elements, (2) by a large REE fractionation, characterized by a low LREE mobility and a progressive HREE depletion with alteration degree, and (3) by a large U depletion relative to Th. LREE, Hf and Zr are not significantly modified by these alteration processes except that their absolute concentrations are generally increased in altered material by mass balance effects. U is generally redistributed over relatively short distances (maximum few centimetres) and is sometimes re-concentrated by adsorption on silica polymorphs or magnetites. Meteoric and low temperatures

  3. Effects of hydrothermal alteration on Pb in the active PACMANUS hydrothermal field, ODP Leg 193, Manus Basin, Papua New Guinea: A LA-ICP-MS study

    NASA Astrophysics Data System (ADS)

    Beaudoin, Yannick; Scott, Steven D.; Gorton, Michael P.; Zajacz, Zoltan; Halter, Werner

    2007-09-01

    The conventional model of leaching volcanic rocks as a source of metals in a seafloor hydrothermal systems has been tested by examining the behavior of Pb and other trace elements during hydrothermal alteration. ODP Leg 193 drill sites 1188 (Snowcap) and 1189 (Roman Ruins) on Pual Ridge in the eastern Manus Basin offshore eastern Papua New Guinea provide a unique three-dimensional window into an active back-arc hydrothermal system. We investigate by means of a LA-ICP-MS microbeam technique the capacity of Pb to be leached from a host volcanic rock exposed to various types and intensities of alteration. Our results are in general agreement with previous studies that utilized bulk analytical techniques but provide a more detailed explanation of the processes. Fresh representative dacitic lavas from the Pual Ridge have an average whole rock Pb content of 5.2 ppm, an average interstitial glass Pb content of 5.6 ppm and an average plagioclase Pb content of 1.0 ppm. Altered matrix samples have highly variable Pb values ranging from 0 to 52.4 ppm. High Pb values in altered samples are associated with a low temperature chlorite and clay mineral assemblage, in some cases overprinted by a high temperature (up to 350 °C) silica-rich "bleaching" alteration. Only the most highly altered matrix samples have REE patterns that differ from the fresh Pual Ridge dacite. This may represent either different lava histories or alteration characteristics that have affected normally immobile REEs. Altered samples with the highest Pb values have similar REE patterns to those of the local unaltered lavas. They are compositionally similar to typical Pual Ridge dacites indicating a genetic relationship between the main regional volcanic suite and the subseafloor hydrothermally altered, Pb-enriched material. Relative loss/gain for Pb between the analyzed altered samples and a calculated precursor show a maximum relative gain of 901%. Samples with relative Pb gain from both drill sites are

  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. 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

  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. A multidisciplinary approach to quantify the permeability of the Whakaari/White Island volcanic hydrothermal system (Taupo Volcanic Zone, New Zealand)

    NASA Astrophysics Data System (ADS)

    Heap, Michael J.; Kennedy, Ben M.; Farquharson, Jamie I.; Ashworth, James; Mayer, Klaus; Letham-Brake, Mark; Reuschlé, Thierry; Gilg, H. Albert; Scheu, Bettina; Lavallée, Yan; Siratovich, Paul; Cole, Jim; Jolly, Arthur D.; Baud, Patrick; Dingwell, Donald B.

    2017-02-01

    Our multidisciplinary study aims to better understand the permeability of active volcanic hydrothermal systems, a vital prerequisite for modelling and understanding their behaviour and evolution. Whakaari/White Island volcano (an active stratovolcano at the north-eastern end of the Taupo Volcanic Zone of New Zealand) hosts a highly reactive hydrothermal system and represents an ideal natural laboratory to undertake such a study. We first gained an appreciation of the different lithologies at Whakaari and (where possible) their lateral and vertical extent through reconnaissance by land, sea, and air. The main crater, filled with tephra deposits, is shielded by a volcanic amphitheatre comprising interbedded lavas, lava breccias, and tuffs. We deployed field techniques to measure the permeability and density/porosity of (1) > 100 hand-sized sample blocks and (2) layered unlithified deposits in eight purpose-dug trenches. Our field measurements were then groundtruthed using traditional laboratory techniques on almost 150 samples. Our measurements highlight that the porosity of the materials at Whakaari varies from ∼ 0.01 to ∼ 0.7 and permeability varies by eight orders of magnitude (from ∼ 10-19 to ∼ 10-11 m2). The wide range in physical and hydraulic properties is the result of the numerous lithologies and their varied microstructures and alteration intensities, as exposed by a combination of macroscopic and microscopic (scanning electron microscopy) observations, quantitative mineralogical studies (X-ray powder diffraction), and mercury porosimetry. An understanding of the spatial distribution of lithology and alteration style/intensity is therefore important to decipher fluid flow within the Whakaari volcanic hydrothermal system. We align our field observations and porosity/permeability measurements to construct a schematic cross section of Whakaari that highlights the salient findings of our study. Taken together, the alteration typical of a volcanic

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

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

    USGS Publications Warehouse

    Blecker, S.W.; Stillings, L.L.; DeCrappeo, N.M.; Ippolito, J.A.

    2014-01-01

    Soils developed on relict hydrothermally altered soils throughout the Western USA 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 altered (acid-sulfate) sites located in and around Lassen VolcanicNational Park in northeastern California. In addition, three different types of disturbed areas (clearcut, thinned, and pipeline) were sampled in acid-sulfate altered sites. Soils were sampled (0–15 cm) in mid-summer 2010 from both under-canopy and between-canopy areas within each of the sites. Soils were analyzed for numerous physical and chemical properties along with soil enzyme assays, C and N mineralization potential, microbial biomass-C and C-substrate utilization. Field vegetation measurements consisted of canopy cover by life form (tree, shrub, forb, and grass), tree and shrub density, and above-ground net primary productivity of the understory. Overall, parameters at the clearcut sites were more similar to the unaltered sites, while parameters at the thinned and pipeline sites were more similar to the altered sites. We employed principal components analysis (PCA) to develop two soil quality indices (SQI) to help quantify the differences among the sites: one based on the correlation between soil parameters and canopy cover, and the second based on six sub-indices. Soil quality indices developed in these systems could provide a means for monitoring and identifying key relations between the vegetation, soils, and microorganisms.

  14. Volcano collapse promoted by hydrothermal alteration and edifice shape, Mount Rainier, Washington

    USGS Publications Warehouse

    Reid, M.E.; Sisson, T.W.; Brien, D.L.

    2001-01-01

    Catastrophic collapses of steep volcano flanks threaten many populated regions, and understanding factors that promote collapse could save lives and property. Large collapses of hydrothermally altered parts of Mount Rainier have generated far-traveled debris flows; future flows would threaten densely populated parts of the Puget Sound region. We evaluate edifice collapse hazards at Mount Rainier using a new three-dimensional slope stability method incorporating detailed geologic mapping and subsurface geophysical imaging to determine distributions of strong (fresh) and weak (altered) rock. Quantitative three-dimensional slope stability calculations reveal that sizeable flank collapse (>0.1 km3) is promoted by voluminous, weak, hydrothermally altered rock situated high on steep slopes. These conditions exist only on Mount Rainier's upper west slope, consistent with the Holocene debris-flow history. Widespread alteration on lower flanks or concealed in regions of gentle slope high on the edifice does not greatly facilitate collapse. Our quantitative stability assessment method can also provide useful hazard predictions using reconnaissance geologic information and is a potentially rapid and inexpensive new tool for aiding volcano hazard assessments.

  15. Volcano collapse promoted by hydrothermal alteration and edifice shape, Mount Rainier, Washington

    NASA Astrophysics Data System (ADS)

    Reid, Mark E.; Sisson, Thomas W.; Brien, Dianne L.

    2001-09-01

    Catastrophic collapses of steep volcano flanks threaten many populated regions, and understanding factors that promote collapse could save lives and property. Large collapses of hydrothermally altered parts of Mount Rainier have generated far-traveled debris flows; future flows would threaten densely populated parts of the Puget Sound region. We evaluate edifice collapse hazards at Mount Rainier using a new three-dimensional slope stability method incorporating detailed geologic mapping and subsurface geophysical imaging to determine distributions of strong (fresh) and weak (altered) rock. Quantitative three-dimensional slope stability calculations reveal that sizeable flank collapse (>0.1 km3) is promoted by voluminous, weak, hydrothermally altered rock situated high on steep slopes. These conditions exist only on Mount Rainier's upper west slope, consistent with the Holocene debris-flow history. Widespread alteration on lower flanks or concealed in regions of gentle slope high on the edifice does not greatly facilitate collapse. Our quantitative stability assessment method can also provide useful hazard predictions using reconnaissance geologic information and is a potentially rapid and inexpensive new tool for aiding volcano hazard assessments.

  16. Oxygen isotope evidence for submarine hydrothermal alteration of the Del Puerto ophiolite, California

    USGS Publications Warehouse

    Schiffman, P.; Williams, A.E.; Evarts, R.C.

    1984-01-01

    The oxygen isotope compositions and metamorphic mineral assemblages of hydrothermally altered rocks from the Del Puerto ophiolite and overlying volcaniclastic sedimentary rocks at the base of the Great Valley sequence indicate that their alteration occurred in a submarine hydrothermal system. Whole rock ??18O compositions decrease progressively down section (with increasing metamorphic grade): +22.4??? (SMOW) to +13.8 for zeolite-bearing volcaniclastic sedimentary rocks overlying the ophiolite; +19.6 to +11.6 for pumpellyite-bearing metavolcanic rocks in the upper part of the ophiolite's volcanic member; +12.3 to +8.1 for epidote-bearing metavolcanic rocks in the lower part of the volcanic member; +8.5 to +5.7 for greenschist facies rocks from the ophiolite's plutonic member; +7.6 to +5.8 for amphibolite facies or unmetamorphosed rocks from the plutonic member. Modelling of fluid-rock interaction in the Del Puerto ophiolite indicates that the observed pattern of upward enrichment in whole rock ??18O can be best explained by isotopic exchange with discharging 18O-shifted seawater at fluid/rock mass ratios near 2 and temperatures below 500??C. 18O-depleted plutonic rocks necessarily produced during hydrothermal circulation were later removed as a result of tectonism. Submarine weathering and later burial metamorphism at the base of the Great Valley sequence cannot by itself have produced the zonation of hydrothermal minerals and the corresponding variations in oxygen isotope compositions. The pervasive zeolite and prehnite-pumpellyite facies mineral assemblages found in the Del Puerto ophiolite may reflect its origin near an island arc rather than deep ocean spreading center. ?? 1984.

  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. Ridge Alterations Post-extraction in the Esthetic Zone

    PubMed Central

    Chappuis, V.; Engel, O.; Reyes, M.; Shahim, K.; Nolte, L.-P.; Buser, D.

    2013-01-01

    Dimensional alterations of the facial bone wall following tooth extractions in the esthetic zone have a profound effect on treatment outcomes. This prospective study in 39 patients is the first to investigate three-dimensional (3D) alterations of facial bone in the esthetic zone during the initial 8 wks following flapless tooth extraction. A novel 3D analysis was carried out, based on 2 consecutive cone beam computed tomographies (CBCTs). A risk zone for significant bone resorption was identified in central areas, whereas proximal areas yielded only minor changes. Correlation analysis identified a facial bone wall thickness of ≤ 1 mm as a critical factor associated with the extent of bone resorption. Thin-wall phenotypes displayed pronounced vertical bone resorption, with a median bone loss of 7.5 mm, as compared with thick-wall phenotypes, which decreased by only 1.1 mm. For the first time, 3D analysis has allowed for documentation of dimensional alterations of the facial bone wall in the esthetic zone of humans following extraction. It also characterized a risk zone prone to pronounced bone resorption in thin-wall phenotypes. Vertical bone loss was 3.5 times more severe than findings reported in the existing literature. PMID:24158340

  19. 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

  20. 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.

  1. Hydrothermal alteration features in the Vargeão basaltic impact structure (South Brazil): Implications about the presence of liquid water in Mars

    NASA Astrophysics Data System (ADS)

    Yokoyama, E.; Nédélec, A.; Baratoux, D.; Berger, G.; Trindade, R. I.

    2013-05-01

    shows a zoned setting, which also varies locally. The nature of occurrence of second minerals identified in the context of post-impact hydrothermal alteration of impact craters on basalt represent a critical interpretation to interpret alteration signature of impact craters and the old Noachian terrains of Mars. The interpretation of this signature remains controversial. It may result from the excavation of globally altered volcanic material in a warm and wet Mars, or alternatively it may result from impact-associated hydrothermal alteration. Our results at Vargeão may be used to assess these different hypotheses.

  2. Hydrothermal quartz formation during fluctuations of brittle shear-zone activity and fluid flow: grain growth and deformation structures of the Pfahl shear zone (Germany)

    NASA Astrophysics Data System (ADS)

    Yilmaz, T.; Prosser, G.; Liotta, D.; Kruhl, J. H.

    2012-12-01

    The Bavarian Pfahl shear zone is a WNW-ESE trending dextral strike-slip shear zone at the SW margin of the Bohemian Massif (Central Europe). It was discontinuously active during decreasing PT-conditions, i.e. from ductile to brittle, from the late-Carboniferous to the late-Cretaceous - Paleocene times. Triassic hydrothermal activity produced a 150 km long and 30-100 m wide quartz dyke along the main fault, surrounded by sheared basement rocks. Within a zone of >10 m metasomatism transformed the wall rocks to mostly kaolinite, chlorite and phyllosilicates. The quartz dyke exhibits a layered to lenticular and partly symmetric structure with different types of quartz masses, transected by a complex quartz vein network. This already indicates pulses of fluid flux and fragmentation during the lifetime of the shear zone. Analyses by optical microscopy, cathodoluminescence (CL) and SEM-EDX reveal at least four subsequent stages of quartz crystallization and fragmentation. (i) The oldest generation of quartz is represented by a homogeneous dark grey to reddish quartz mass made up by ~10-20 μm-sized crystals. It contains mm- to cm-sized angular wall-rock fragments, completely altered to kaolinite, indicating intense wall-rock alteration prior to the earliest event of silica precipitation. This rules out the possibility that the quartz mass developed from silicification of the wall rocks. This first type of quartz occurs as cm- to dm-large angular fragments in (ii) a light grey to pink quartz mass formed by ~10-50 μm-sized crystals. The different colours result from variable types and amounts of inclusions. Quartz of both generations shows random crystallographic orientations and complex inclusion structures. It probably developed during two fragmentation events and possibly from a silica gel precursor that crystallized after precipitation. (iii) The third quartz generation formed as a set of mm- to dm-wide veins roughly parallel to the trend of the Pfahl zone

  3. 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.

  4. 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.

  5. Boron contents and isotopic compositions of the hydrothermally altered oceanic crust from the Troodos ophiolite, Cyprus

    NASA Astrophysics Data System (ADS)

    Matsukura, S.; Yamaoka, K.; Ishikawa, T.; Kawahata, H.

    2010-12-01

    The boron contents and isotopic compositions were determined for the hydrothermally altered oceanic crust through the Troodos ophiolite. The samples were represented by the International Crustal Research Drilling Group (ICRDG) drill-Holes CY1 (479m), CY2A (689m), CY4 (2263m), and selected outcrops along the Akaki river. Hole CY1 was composed upper and lower pillow lava, CY4 constituted sheeted dike complex and gabbro section, and the samples along Akaki river formed from pillow lava to sheeted dike complex. Hole CY2A was composed pillow lava and sheeted dike, drilled near Agrokipia ‘B’ deposit a stockwork type which completely enclosed within the lower pillow lava. The goal of this study is to understand the Boron geochemistry during hydrothermal alteration of the oceanic crust including hydrothermal ore deposit as Agrokipia ‘B’. The average boron contents of each sequence from Troodos ophiolite were pillow lava (63.2ppm), sheeted dike complex (4.5ppm), gabbro section (1.6ppm). But then, those of Oman ophiolite were 7.9ppm, 5.3ppm, 1.7ppm (Yamaoka et al., 2010 submitted). Thus, both of these ophiolites, the vertical profile of boron content decreased with depth, also the boron contents were much richer than fresh-MORB (0.5ppm) (Spivack and Edmond, 1987; Chaussidon and Jambon, 1994). This indicates boron rich of the altered oceanic crust were derived from seawater. And sheeted dike complex and gabbro section were similar value relatively, but pillow lava differed widely. These results may represent the difference of length being submarine, because these ophiolites were generated in deep water of the Tethys sea about 90Ma (Late Cretaceous) (Tilton et al., 1981; Mukasa and Ludden, 1987), and Oman ophiolite was obducted about 70Ma (Lanphere, 1981) but Troodos ophiolite uplifted about 10Ma (Middle Miocene) (Robertson and Woodcock, 1979).

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  8. 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.

  9. Hydrothermal alteration of Variscan granites, southern Schwarzwald, Federal Republic of Germany

    NASA Astrophysics Data System (ADS)

    Simon, K.

    1990-03-01

    Hercynian S-type granites from the southeastern Schwarzwald granite series represent cogenetic biotite-and two-mica granites. Oxygen- and hydrogen-isotope data show that hydrothermal alteration invoking isotopically light surface waters resulted in a drastic reduction in δ18O and δ D and pronounced disequilibrium between the minerals. Effective water-rock ratios are calculated to be high, about 0.8 vol units. A shift in the18O/16O and the chemical composition of the fluid due to water-rock interaction is continuously traced from pure H2O with meteoric isotopic character in the deep-seated biotite granites to slightly saline water with rock-equilibrated isotopic composition in the two-mica granites at a shallower level. Substantial retrograde hydrometamorphism in the temperature range 500° to 200° C resulted mineralogically in high-temperature chloritization of biotite, and low-temperature muscovitization as well as feldspar alteration, respectively. Another result of the re-equilibration of cations is strong disturbance of the Rb-Sr system which affects measured ages and initial87Sr/86Sr values. Hydrothermal differentiation and alteration probably overlap to a very large extent magmatic differentiation processes.

  10. Identification and spectral characteristics of hydrothermal alteration on Landsat TM imagery of north Chile

    NASA Technical Reports Server (NTRS)

    Baker, Michael C. W.

    1987-01-01

    This study examines the application of Landsat TM data to the identification of hydrothermal alteration in the arid terrain of the El Salvador region of north Chile. Numerical reflectance values were extracted from the digital Landsat TM data for a variety of rock surfaces, including four parts of the El Salvador gossan, for each of six spectral bands. These reflectance values were analyzed statistically in order to select the three spectral bands, combined as a color composite image, that are most efficient in discriminating different varieties of alteration and for general geological interpretation. The most cost effective composite image for this area is a combination of bands 1, 4 and 7 as the blue, green and red components respectively, with simple contrast enhancement. This image is superior to some much more expensive enhancement techniques and allows unambiguous identification of areas of hydrothermal alteration larger than about 50 m. The display includes a practical guide to the use of Landsat TM imagery for volcanic gold exploration.

  11. 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.

  12. 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

  13. 238U-230Th disequilibrium in hydrothermally altered material: a tool for dating volcano flank-collapse events

    NASA Astrophysics Data System (ADS)

    Salaun, A.; Villemant, B.; Gérard, M.; Komorowski, J. C.; Louvat, P.; Manhès, G.; Michel, A.; Moureau, J.

    2009-12-01

    Flank instability has been recognized as a very common and often recurrent process in the evolution of volcanoes. Prolonged and extensive hydrothermal system activity is a major cause of volcano instability in promoting conditions of mechanical weakness in the edifice that can lead to partial edifice-collapse with emplacement of debris avalanche deposits (DAD). We report results from U-series disequilibrium analysis of altered material collected in active hydrothermal systems and in DADs that have sampled different regions of the paleo-hydrothermal systems developed prior to collapse on La Soufrière of Guadeloupe and Soufriere Hills (Montserrat) volcanoes. Significant redistribution of chemical elements occurs during hydrothermal alteration with a large fractionation between elements of the U-decay series. Indeed, samples of active hydrothermal systems show large variations in U/Th ratio at generally constant (230Th/232Th). This chemical fractionation between U and Th offers the opportunity to date hydrothermal alteration and to constrain the age of the active hydrothermal system involved in edifice collapses. The evolution of trace element compositions (REE, U, Th) are documented throughout the successive stages of andesite-dacite alteration and discussed in terms of relative element mobility and associated mineralogical assemblages. A progressive HREE depletion occurs together with significant U enrichment at low alteration degrees, followed by a final U depletion. Alteration of glass into smectite is accompanied by large U depletions relative to Th. On the contrary, U enrichment is associated with silica polymorphs. All these processes are discussed in terms of relative U behaviours during leaching, incorporation and adsorption processes. U and Th isotope contents have been determined in hydrothermally altered material contained in two distinct DADs of La Soufrière of Guadeloupe (14C ages: 7 700 yrs BP and 45 000 yrs BP) and one DAD from Soufrière Hills

  14. 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.

  15. Effect of hydrothermal alteration on rock magnetic properties from basalts in the Krafla geothermal field, Iceland

    NASA Astrophysics Data System (ADS)

    Oliva-Urcia, B.; Kontny, A.; Vahle, C.; Schleicher, A. M.

    2007-12-01

    The high-temperature Krafla geothermal field is situated within the caldera of the Krafla central volcano in NE Iceland. The last fissure eruptions (Krafla fires) occurred between 1975 and 1984. Aeromagnetic surveys from this area indicate a magnetic high corresponding to Mt. Krafla, whereas the magnetic low coincides with the caldera bottom where the Krafla geothermal field is located. The geothermal fluids are meteoric in origin and the Sudurhlídar field is boiling from depth until the surface. The permeability is higher in vertical than in horizontal profiles and the production of secondary minerals suggests a depth zonal distribution related to the temperature. The study of the magnetic properties of volcanic rocks affected by hydrothermal alteration is significant to understand magnetic anomalies related to MORB and its tectonic implications. Our study focuses in an area where the hydrothermal alteration diminishes the Ti-magnetite content of fissure subaerial lavas. The samples were taken from KH1 (200 m depth) and KH3 (400 m depth) drill cores, from the rim of the caldera. In our study we aim to correlate both, c-T curves and textural observations from the magnetic phases with the degree of hydrothermal alteration. NRM, field dependence of susceptibility (Fd) and Koenigsberg ratios (Q) from the samples are very low: NRM is < 3.1 A/m, Fd values range between 0.2 and 7.9, and Q between 0 and 6. Magnetic susceptibility varies with the magnetic mineral content. Typical textural features are shrinkage cracks from maghemitization together with exsolved textures in Ti-magnetite from high temperature oxidation. This texture is present in the deeper part of both cores (177 m in KH1 and 380 m in KH3), but KH1 samples show abundant ghost structures of Ti-magnetite, altered to a network formed by clays and Ti-oxide. A high quantity of sulphide precipitation accompanies the ghost structures. The magnetic phases strongly alter depending on the porosity of the rocks, but

  16. 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

  17. 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.

  18. Alteration and geochemical zoning in Bodie Bluff, Bodie mining district, eastern California

    USGS Publications Warehouse

    Herrera, P.A.; Closs, L.G.; Silberman, M.L.

    1993-01-01

    Banded, epithermal quartz-adularia veins have produced about 1.5 million ounces of gold and 7 million ounces of silver from the Bodie mining district, eastern California. The veins cut dacitic lava flows, pyroclastic rocks and intrusions. Sinter boulders occur in a graben structure at the top of Bodie Bluff and fragments of sinter and mineralized quartz veins occur in hydrothermal breccias nearby. Explosive venting evidently was part of the evolution of the ore-forming geothermal systems which, at one time, must had reached the paleosurface. Previous reconnaissance studies at Bodie Bluff suggested that the geometry of alteration mineral assemblages and distribution of some of the major and trace elements throughout the system correspond to those predicted by models of hot-spring, volcanic rock hosted precious metal deposits (Silberman, 1982; Silberman and Berger, 1985). The current study was undertaken to evaluate these sugestions further. About 500 samples of quartz veins and altered rocks, including sinter, collected over a vertical extent of 200 meters within Bodie Bluff were petrographically examined and chemically analyzed for trace elements by emission spectrographic and atomic absorption methods. Sixty-five samples were analyzed for major elements by X-ray fluorescence methods. The results of these analyses showed that, in general, alteration mineral assemblage and vertical geochemical zoning patterns follow those predicted for hot-spring deposits, but that geochemical zoning patterns for sinter and quartz veins (siliceous deposits), and altered wall rocks are not always similar. The predicted depth-concentration patterns for some elements, notably Au, Ag, Hg, and Tl in quartz veins, and Hg, As and Ag in wall rocks were not as expected, or were perturbed by the main ore producing zone. For both quartz veins and altered wall rocks, the main ore zone had elevated metal contents. Increased concentration of many of these elements could indicate proximity to this

  19. 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.

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

    USGS Publications Warehouse

    Zierenberg, R.A.; Shanks, Wayne C.; Seyfried, W.E.; Koski, R.A.; Strickler, M.D.

    1988-01-01

    The Turner-Albright sulfide deposit, part of the Josephine ophiolite, formed on and below the seafloor during Late Jurassic volcanism at a back arc spreading center. Ore fluids were probably localized by faults which were active on the seafloor at the time of sulfide deposition. The uppermost massive sulfide formed on the seafloor at hydrothermal vents. The bulk of the sulfide mineralization formed below the seafloor within olivine basalt hyaloclastite erupted near the time of mineralization. Infiltration of hydrothermal fluid into the hyaloclastite altered the rock. The fluid responsible for the hydrothermal alteration was evolved seawater with low pH and Mg and high Fe. The average value of sulfide and the difference between sulfide and contemporaneous seawater sulfate values are similar to ophiolite-hosted sulfide deposits in Cyprus. Mudstone and clinopyroxene basalt above the sulfide horizons were not altered by the ore-transporting hydrothermal fluid, but these rocks were hydrothermally metamorphosed by altered seawater heated by deep circulation into hot oceanic crust. This subseafloor metamorphism produced a mineral assemblage typical of prehnite-pumpellyite facies metamorphism. Exchange with altered seawater increased the whole-rock ??18O of the basalts to values of 9.4-11.2%. -from Authors

  1. Hydrothermally-altered dacite terrains in the Methana peninsula Greece: Relevance to Mars

    NASA Astrophysics Data System (ADS)

    Cloutis, Edward A.; Jonatanson, Victoria; Bandfield, Joshua L.; Amador, Elena S.; Rivera-Hernández, Frances; Mann, P.; Mertzman, Stanley A.

    2017-04-01

    Dacitic rocks, often indicative of crustal recycling on Earth, have been identified in some regions on Mars, as have possible hydrothermally/aqueously-altered dacites. To enable more robust identification of unaltered and altered dacites on Mars and other planetary bodies, we undertook a spectroscopic-structural-compositional study of altered and unaltered dacites from a dacitic volcanic region in Methana, Greece. Dacites erupted in this region range from fresh to pervasively hydrothermally altered, resulting in friable, Si-enriched products, as well as fumarolic deposition of Si and S-rich precipitates. Spectrally, fresh dacites are unremarkable in the 0.35-2.5 μm region with low, generally flat, reflectance and few, if any, absorption bands. Dacite infrared spectra exhibit Si-O absorption features in the 8-10 μm region (which are characteristic of Si-bearing rocks, in general). With increasing alteration, reflectance over the 0.35-2.5 μm range increases, absorption bands in the 1.4 and 1.9 μm region, associated with H2O/OH, and in the 2.2-2.3 μm region, associated with SiOH, become deeper, Fe3+-associated absorption bands in the 0.43 and 0.9 μm region appear, and the Christiansen feature near 8 μm moves to shorter wavelengths. Silica-rich coatings appear to be spectrally indistinguishable from Si-rich alteration. Alteration-formed sulfates may be detectable by the presence of diagnostic absorption features in the 0.35-2.5 μm region. Spectral similarities between different poorly crystalline high-Si phases make it difficult to uniquely determine the processes that formed high-Si surfaces that have been identified on Mars. However, the samples described here show a variety of spectral features that correspond to variable amounts of alteration. We find a similar range of spectral features, likely due to similar phases, on Mars, perhaps indicating a similar range of alteration environments. Comparison of laboratory spectra to Mars observational data also

  2. 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.

  3. 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.

  4. 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.

  5. 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.

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

    USGS Publications Warehouse

    Larson, P.B.; Cunningham, C.G.; Naeser, C.W.

    1994-01-01

    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

  7. Kinetically Controlled Alteration of the Chemical Record During Diagenesis: An Experimental Study on Hydrothermal Carbonate Replacement

    NASA Astrophysics Data System (ADS)

    Mueller, T.; Dohmen, R.; Jonas, L.; Immenhauser, A.

    2016-12-01

    The geological record stored in the geochemical composition of carbonates provides a direct source of information on the Earth systems. However, the robustness and accuracy of these key records can be compromised by post-depositional alteration of sediments, such as dolomitization during diagenesis or low temperature metamorphism. Hence, knowledge on the mechanisms and rates of these processes hold the key to evaluate the robustness of proxies or to evaluate the extent of geochemical alteration. Previously, we presented experimental results of hydrothermal alteration of single calcite crystals and aragonitic coral fragments leading to replacement of the original carbonate by a Ca-Mg carbonate phase of variable composition. The experiments revealed the formation of a multiphase reaction rim with multiple replacement fronts [1]. Here, the reaction rate as well as composition of the reaction products is controlled by element transport in the pore fluid. In this study we focus on the reaction path of the replacement reaction and its effect on the recorded Mg-isotope composition. XRD diffraction patterns suggest the initial precipitation of non-ordered protodolomite that is subsequently continuously recrystallizing over the duration of the experiments to form an ordered, albeit non-stoichiometric dolomite. These observations are in agreement with Mg-isotope composition measured of the bulk reaction rim showing a systematic evolution over time that cannot be explained by simple Rayleigh or equilibrium fractionation. We interpret these findings as additional, but delayed reaction fronts affecting the microstructure and chemical composition of the newly formed carbonate rim that are essentially decoupled from the initial replacement front. Our results highlight the need to quantitatively understand alteration processes during diagenesis in order to accurately interpret the preserved geochemical record stored in element and isotope ratios of carbonates. [1] Jonas L

  8. 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

  9. 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.

  10. 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

  11. From Magma Formation to Hydrothermal Alteration: an Integrated Study of the Martian Crust Using Thermodynamic Modeling of Geochemical Systems

    NASA Astrophysics Data System (ADS)

    Griffith, Laura Lee

    Hydrothermal systems have undoubtedly occurred on Mars. These systems are of interest for a number of reasons. Hydrothermal alteration of host rocks can have effects on the atmosphere of the planet, the volatile budget, local hydrologic patterns, the rheology of the rocks, their ability to resist weathering, and even lower the melting temperature of crustal rocks. In addition, there is a connection between hydrothermal systems and the origin of life on earth that raises questions about life on Mars. The approach taken used theoretical geochemical modeling techniques to model hypothetical hydrothermal systems on Mars. The initial phase of the research involved understanding terrestrial systems that were used as analogs for Martian systems. Compositions of Icelandic host rocks were used as input for extensive modeling calculations. These calculations investigated the roles of initial rock composition, fluid temperature, partial pressure of carbon dioxide in the fluid, water to rock ratio, and oxygen fugacity of the fluid on alteration assemblages. The second phase utilized the data available on the SNC meteorites (they are suspected to come from Mars) as the basis for hydrothermal system modeling. The focus of this investigation was the variability of alteration assemblages that could be produced from the SNC meteorites. The final investigation broadened the scope of possible substrates for hydrothermal systems by using theoretical geochemical modeling of igneous processes to produce likely Martial crustal rock compositions from a possible Martial mantle composition. A variety of variables (depth of initial melting, amount of initial melt, cooling rate during ascent, and depth of final emplacement) were examined to determine their effects on compositions of the calculated melts. Several rock compositions produced by the igneous modeling were used as input for hydrothermal modeling calculations. These calculations examined possible differences in alteration

  12. 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.

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  6. Distribution and mineralogy of platinum-group elements in altered chromitites of the Campo Formoso layered intrusion (Bahia State, Brazil): control by magmatic and hydrothermal processes

    NASA Astrophysics Data System (ADS)

    Garuti, G.; Proenza, J. A.; Zaccarini, F.

    2007-03-01

    Polyphase, penetrative hydrothermal metasomatism in chromitites of the Campo Formoso layered intrusion produced spectacular chromite - ferrian chromite zoning and transformed the primary intercumulus silicates into a chlorite - serpentine - carbonate - talc assemblage. Alteration did not substantially modify the composition of chromite cores and the distribution of platinum-group elements (PGE) through the sequence of chromitite layers, which still are consistent with magmatic fractionation processes. Texture and composition of laurite and Os-Ir-Ru alloys included in chromite cores indicate that these PGM were not altered, and are probably magmaticin origin. In contrast, the PGM located in the intergranular chlorite matrix (laurite, Ir-Ru-Rh sulfarsenides and Pt-Pd compounds with Sb, Bi and Te) display evidence of hydrothermal reworking. These PGM are intimately intergrown with low-temperature Ni-sulfides. The paragenesis suggests that the Ni-sulfides-PGM assemblage formed at the expenses of unknown PGM precursors, which must have been originally present in the intercumulus silicate matrix. Mechanism of formation involves a sequence of dissolution-precipitation events controlled by variation of redox conditions during chromite alteration. The presence of a secondary ore mineral assemblage consisting of galena, bismuthinite, native antimony, and various Pb-Sb compounds suggests a possible contribution of fluids derived from the adjacent granite.

  7. 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

  8. 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.

  9. 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

  10. 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.

  11. 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

  12. Fluid flow and metasomatism in a subduction zone hydrothermal system: Catalina schist terrane, California

    SciTech Connect

    Barton, M.D.; Bebout, G.E. )

    1989-11-01

    On Santa Catalina Island, southern California, bluechist to amphibolite facies metasedimentary, metamafic, and meta-ultramafic rocks show veining and alteration that reflect fluid flow and mass transfer at 25-45 km depths in an Early Cretaceous subduction zone. Synkinematic and postkinematic veins record fluid transport and metasomatism during prograde metamorphism and uplift. Vein and host-rock mineralogy and whole-rock compositions demonstrate large-scale chemical redistribution, especially of Si and alkali elements. Veins and host rocks trend toward isotopic equilibration with aqueous fluids with {delta}{sup 18}O{sub SMOW}=+13{per thousand} {plus minus} 1{per thousand}. The likely source for these fluids is in lower temperature, sediment-rich parts of the subduction zone. Carbon isotope systematics support this conclusion and indicate the influence of an organic C source. Quartz solubility relations indicate the importance of fluid-flow paths in chemical redistribution during subduction. These results document large-scale fluid flow and the complexity of possible metasomatic and mechanical mixing processes at intermediate levels of subduction zones. The record of subduction-zone mass transfer in the Catalina Schist is compatible with the record inferred for greater depths from geochemical and petrologic studies of arc magmatism.

  13. Geochemistry of hydrothermal alteration at the Roosevelt hot springs thermal area, Utah

    NASA Astrophysics Data System (ADS)

    Parry, W. T.; Ballantyne, J. M.; Bryant, N. L.; Dedolph, R. E.

    1980-01-01

    Hot spring deposits in the Roosevelt thermal area consist of opaline sinter and sintercemented alluvium. Alluvium, plutonic rocks, and amphibolite-facies gneiss have been altered by acidsulfate water to alunite and opal at the surface, and alunite, kaolinite, montmorillonite, and muscovite to a depth of 70 m. Marcasite, pyrite, chlorite, and calcite occur below the water table at about 30 m. The thermal water is dilute (ionic strength 0.1-0.2) sodium-chloride brine. The spring water now contains 10 times as much Ca, 100 times as much Mg, and up to 2.5 times as much SO 4 as the deep water. Although the present day spring temperature is 25°C, the temperature was 85°C in 1950. A model for development of the observed alteration is supported by observation and irreversible mass transfer calculations. Hydrothermal fluid convectively rises along major fractures. Water cools by conduction and steam separation, and the pH rises due to carbon dioxide escape. At the surface, hydrogen and sulfate ions are produced by oxidation of H 2S. The low pH water percolates downward and reacts with feldspar in the rocks to produce alunite, kaolinite, montmorillonite, and muscovite as hydrogen ion is consumed.

  14. 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).

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Crowley, James K.; Zimbelman, David R.

    1997-06-01

    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.

  1. 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.

  2. 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

  3. Future Edifice Collapse as a Result of Active Hydrothermal Alteration and Geologic Structure at Mt. Baker, Washington

    NASA Astrophysics Data System (ADS)

    Warren, S. N.; Watters, R. J.; Tucker, D. S.

    2006-12-01

    Hydrothermally argillic altered rocks are much weaker than their un-altered counterpart and progressive alteration deep within a volcano can lead to the catastrophic collapse of the edifice. This type of failure represents one of the most destructive and far-reaching natural hazards associated with volcanoes. Mapped Holocene debris flows containing hydrothermally altered rock in drainages around Mt. Baker and continuous hydrothermal activity in the Sherman Crater since 1975 suggest that Mt Baker is capable of producing a catastrophic collapse debris flow in the future. This research uses field data obtained from the Sherman Crater in August 2006 combined with laboratory testing and computer modeling to characterize the stability of Mt. Baker. Completed fieldwork includes the collection of in situ rock and clay samples and measurement of major discontinuities at three sites near the Sherman Crater. Additional laboratory work will include coring of rock samples to determine uniaxial and triaxial strength. Magnetic susceptibility data and previous detailed mapping of the Sherman Crater will supplement the data in order to construct a slope stability model of the upper portion of Mt. Baker. Modeling failures under different geologic uncertainties, groundwater pressure and seismic loading better constrain the possible size, direction, and run-out distances of a failure from the edifice. This information helps estimate the hazard and risk to residents and infrastructure in the vicinity.

  4. Mineralogical and chemical characteristics of newer dolerite dyke around Keonjhar, Orissa: Implication for hydrothermal activity in subduction zone setting

    NASA Astrophysics Data System (ADS)

    Sengupta, Piyali; Ray, Arijit; Pramanik, Sayantani

    2014-06-01

    The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE-SW, NW-SE and NNE-SSW trends. The mafic dykes of the present study exhibit several mineralogical changes like clouding of plagioclase feldspars, bastitisation of orthopyroxene, and development of fibrous amphibole (tremolite-actinolite) from clinopyroxene, which are all considered products of hydrothermal alterations. This alteration involves addition and subtraction of certain elements. Graphical analyses with Alteration index and elemental abundances show that elements like Rb, Ba, Th, La and K have been added during the alteration process, whereas elements like Sc, Cr, Co, Ni, Si, Al, Fe, Mg and Ca have been removed. It is observed that in spite of such chemical alteration, correlation between major and trace elements, characteristic of petrogenetic process, is still preserved. This might reflect systematic Alteration (addition or subtraction) of elements without disturbing the original element to element correlation. It has also been established by earlier workers that the evolution of newer dolerite had occurred in an arc-back arc setting which may also be true for newer dolerites of the present study. This is evident from plots of pyroxene composition and whole rock composition of newer dolerite samples in different tectonic discrimination diagrams using immobile elements. The newer dolerite dykes of the Keonjhar area may thus be considered to represent an example of hydrothermal activity on mafic rocks in an arc setting.

  5. Paleointensity estimates from oceanic gabbros: Effects of hydrothermal alteration and cooling rate

    NASA Astrophysics Data System (ADS)

    Usui, Yoichi

    2013-09-01

    Gabbros recovered by previous ocean drillings were investigated in paleointensity and rock magnetic experiments. The young ages of the samples (ca. 0.78-1.3 Ma) enable a direct comparison between the plutonic paleointensity and volcanic data. Microscopic observations revealed two kinds of magnetite: needle-shaped exsolution in plagioclase and aggregate associated with the hydrothermal alteration of olivine. In Shaw paleointensity experiments, some samples revealed reasonable estimates, while some others showed an anomalously low ratio of natural remanent magnetization (NRM) versus thermoremanent magnetization (TRM). First-order reversal curve (FORC) diagrams indicated that the reasonable NRM/TRM were from non-interacting single domain magnetite exsolved in plagioclase, while the anomalously low NRM/TRM were from secondary magnetite associated with olivine. From the paleointensity results, the mean virtual axial dipole moment (VADM) was calculated to be 8.2 ±2.1 [1022Am2]. Volcanic records in the PINT database for 0.78-1.3 Ma revealed a mean virtual dipole moment (VDM) of 6.3 ± 0.73 [1022Am2]. The difference between them is consistent with the theoretical prediction of the cooling rate effect on paleointensity. These results indicate that oceanic gabbros are reliable paleointensity recorders.

  6. 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

  7. 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

  8. 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

  9. A multi-faceted approach to characterize acid-sulfate alteration processes in volcanic hydrothermal systems on Earth and Mars

    NASA Astrophysics Data System (ADS)

    Marcucci, Emma Cordts

    Acid-sulfate alteration is a dominant weathering process in high temperature, low pH, sulfur-rich volcanic environments. Additionally, hydrothermal environments have been proposed as locations where life could have originated on Earth. Based on the extensive evidence of flowing surface water and persistent volcanism, similar locations and processes could have existed on early Mars. Globally observed alteration mineral assemblages likely represent relic Martian hydrothermal settings. Yet the limited understanding of environmental controls, limits the confidence of interpreting the paleoconditions of these hydrothermal systems and assessing their habitability to support microbial life. This thesis presents a series of laboratory experiments, geochemical models, analog fieldwork, and Martian remote sensing to characterize distinguishing features and controls of acid-sulfate alteration. The experiments and models were designed to replicate alteration is a highly acidic, sulfurous, and hot field sites. The basaltic minerals were individually reacted in both experimental and model simulations with varying initial parameters to infer the geochemical pathways of acid-sulfate alteration on Earth and Mars. It was found that for a specific starting material, secondary mineralogies were consistent. Variations in pH, temperature and duration affected the abundance, shape, and size of mineral products. Additionally evaporation played a key role in secondary deposits; therefore, both alteration and evaporitic processes need to be taken into consideration. Analog volcanic sites in Nicaragua were used to supplement this work and highlight differences between natural and simulated alteration. In situ visible near-infrared spectroscopy demonstrated that primary lithology and gas chemistry were dominant controls of alteration, with secondary effects from environmental controls, such as temperature and pH. The spectroscopic research from the field was directly related to Mars

  10. Salvaging primary remanence from hydrothermally altered oceanic gabbros in the Oman ophiolite: A selective destructive demagnetization approach

    NASA Astrophysics Data System (ADS)

    Usui, Yoichi; Yamazaki, Shusaku

    2010-07-01

    Widespread hydrothermal alteration and formation of secondary magnetite have been problems for paleomagnetic work on gabbros in the Oman ophiolite. Mechanical removal of hydrothermally altered ferromagnesian minerals from gabbro and gabbronorite in the Wadi Rajmi area revealed a cryptic remanence which could not be detected by stepwise demagnetization of bulk rock core samples. After the mechanical removal, samples consist of plagioclase and clinopyroxene. These samples exhibit remanence directions of southeast declination and shallow inclination. This direction is consistent with previously reported paleomagnetic directions at crystallization of the Oman ophiolite. In contrast, bulk rock core samples yielded north declination, resembling the younger remanence directions associated with the obduction of the ophiolite. Microscopic observation and paleomagnetic directional comparison concluded that the cryptic remanence is a primary magnetization carried by exsolved magnetite in plagioclase and clinopyroxene. Our results suggest that previous paleomagnetic data from whole rock gabbros in the Oman ophiolite as well as tectonically active ocean floor should be taken with care.

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

    NASA Astrophysics Data System (ADS)

    Marumo, Katsumi; Hattori, Kéiko 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 2S 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. The isotopic compositions of kaolinite (δ 18O = +7.4‰, δD = -23‰), Chl/Mont (δ 18O = +7.0‰, δD = -32‰), and mica (δ 18O = +5.4 to +9.9‰, δD = -30 to -26‰) suggest fluids of a heated seawater origin. The O isotopic data yielded formation temperatures of 170°C for kaolinite, 61 to 110°C for halloysite, and 145 to 238°C for mica. Barite δ 34S values (+21.0 to +22.5‰) are very similar to the marine sulfate value, confirming that the barite formation took place due to mixing of Ba-bearing hydrothermal fluids and sulfate-rich seawater. Native sulfur shows a large variation in δ 34S in one hand specimen probably because of rapid disequilibrium precipitation of S during fluid exhalation on the seafloor. Sulfur in hydrothermal fluids

  12. Iceland Deep Drilling Project: (V) Isotopic Evidence of Hydrothermal Exchange and Seawater Ingress from Alteration Minerals in the Reykjanes Geothermal System

    NASA Astrophysics Data System (ADS)

    Marks, N. E.; Zierenberg, R. A.; Schiffman, P.

    2009-12-01

    The Reykjanes geothermal system is a seawater recharged hydrothermal system located on the landward extension of the Mid-Atlantic Ridge in Iceland. Fluid compositions in the system have evolved through time as a result of changing proportions of meteoric water as well as differing pressure and temperature conditions imposed by glaciation (Sveinbjornsdottir, 1986; Fridleifsson et al., 2005; Marks et al., 2009). Samples from the deepest part of Reykjanes well RN-17 include greenschist to pyroxene hornfels facies assemblages, suggesting seawater penetration into a part of the system that is close to the high temperature reaction zone. Electron microprobe studies of drill cuttings reveal intense alteration of hyaloclastites with calc-silicate alteration assemblages comprising calcic hydrothermal plagioclase, grandite garnet, prehnite, epidote, hydrothermal clinopyroxene, and titanite. In contrast, crystalline basalts and intrusive rocks display a wide range in alteration intensity from essentially unaltered to pervasive and nearly complete replacement of feldspar and pyroxene. Epidote is widely distributed throughout the RN-17 samples and fills veins and vugs, replaces glass in hyaloclastites and the interstitial matrix of basalt samples, and is also an alteration product of primary plagioclase. 87Sr/86Sr values of individual epidote grains measured by LA-ICPMS were typically 0.7045-0.7050, but ranged as high as 0.7073 in individual grains. Anhydrite is widespread in shallow portions of the Reykjanes system to about 1500 m. 87Sr/86Sr values of anhydrite from the Reykjanes geothermal system range from 0.7044-0.7053, and gypsum values range from 0.7093 to 0.7094. The Sr isotopic ratios of alteration minerals are shifted from basaltic values (0.7030-0.7034; O’Nions and Grönvold, 1973; Sun and Jahn, 1975) toward seawater values (0.70916; Palmer and Edmond, 1989). This suggests that seawater Sr is able to penetrate deep within the geothermal system, and that seawater Sr

  13. 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.

  14. The carbonate rock-hosted epithermal gold deposit of Agdarreh, Takab geothermal field, NW Iran—hydrothermal alteration and mineralisation

    NASA Astrophysics Data System (ADS)

    Daliran, Farahnaz

    2008-06-01

    The disseminated gold deposit of Agdarreh (24.5 t at 3.7 g/t Au) is hosted in hydrothermally leached Miocene reefal limestone in the Takab geothermal field, which is part of the Cenozoic Urumieh-Dokhtar volcanic arc of NW Iran. Alteration and mineralisation are largely bedding controlled blanket-like and include: (1) pre-ore decalcification; (2) first-stage silicification associated with pyrite (early pyrite with 3-4 wt% As, late pyrite with <1-3 wt% As) and sphalerite; (3) second-stage silicification with precipitation of galena, Pb-Sb-As sulphides, sulphosalts, tellurides and native bismuth; (4) late-stage cinnabar and barite in vugs; (5) oxide ore stage and carbonate alteration (complex Mn-Fe-rich oxyhydroxides, arsenates, sulphates, APS minerals and rutile in residual leached rock and infill of karstic cavities). Gold occurs invisibly in the jasperoids and is enriched in the Mn-Fe oxyhydroxide surface cap of the jasperoids. Gold mineralisation is associated with the hydrothermal metal suite of As, Sb, Hg, Te, Se, Tl, Ba, Zn, Ag, Cd, Bi and Pb, and is characterised by very low Cu contents. Arsenian pyrite probably carried most of the primary (invisible) gold. Native gold occurs in association with the late-stage cinnabar and the oxide ore. The Agdarreh deposit shows many similarities with Carlin-type ore and is interpreted to have resulted from near-surface hydrothermal activity related to the Cenozoic arc volcanism that developed within the extensional Takab graben. The extensive oxidation at Agdarreh may be partly due to the waning stages of hydrothermal activity. Active H2S-bearing thermal springs are locally depositing extremely high contents of Au and Ag, and travertine is present over large areas, suggesting that ore-forming hydrothermal activity occurred periodically from the Miocene to Recent in the Takab geothermal field.

  15. 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.

  16. 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

  17. 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

  18. Conditions of Formation of Secondary Quartz in Hydrothermally Altered, Subsurface Dacite beneath the Deep-Sea PACMANUS Hydrothermal Field, Manus Basin, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Vanko, D. A.; Wicker, S. G.; Binns, R. A.

    2006-05-01

    New fluid inclusion (FI) data from secondary quartz within the altered felsic rocks underlying the PACMANUS hydrothermal field provide additional constraints on the thermal conditions and fluid salinities accompanying hydrothermal alteration. PACMANUS, at a water depth of about 1650 to 1700 m on the summit of the neovolcanic Pual Ridge in the eastern part of the Manus backarc basin, is an active seafloor system situated in a felsic volcanic setting at a convergent plate boundary. Two sites of active venting - Roman Ruins, with high-temperature (220-276° C) sulfide chimneys, and Snowcap, which is an area of lower-temperature (6- 65° C) diffuse flow - were cored during Ocean Drilling Program Leg 193. Drilling reached sub-seafloor depths of 387 m at Snowcap and 206 m at Roman Ruins. At both Snowcap and Roman Ruins, fresh dacite/rhyodacite is underlain by highly to completely altered rocks with clays (illite, illite-smectite, chlorite, and mixed layer clays), disseminated pyrite, silica and late stage anhydrite. At shallow depths the silica is mostly cristobalite, whereas quartz is the polymorph at depth. Secondary quartz occurs in amygdules, alone or with accessory anhydrite and pyrite; in cm-scale granular nodules; and as tiny grains forming an open mosaic with interstitial clays and pore space. Scarce FI in secondary quartz are small (10-20μ), irregular, and contain liquid (L) plus vapor. Only a few are arrayed along healed fractures, and most are interpreted as primary. FI from Snowcap homogenize to L between 290° C and 390° C. Ice melting temperatures vary between about -10° C and -0.4° C, with most ice melting near -2.0° C. Thus, while most FI have near-seawater salinities, a significant number are much more saline, while others are much less saline, approaching fresh water. FI from Roman Ruins homogenize between 257° C and 370° C, and ice melting temperatures vary from about -14° C to -1.2° C. These data are best explained if the hydrothermal

  19. 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

  20. Denitrification and environmental factors influencing nitrate removal in Guaymas Basin hydrothermally altered sediments

    PubMed Central

    Bowles, Marshall W.; Nigro, Lisa M.; Teske, Andreas P.; Joye, Samantha B.

    2012-01-01

    We measured potential nitrate removal and denitrification rates in hydrothermally altered sediments inhabited by Beggiatoa mats and adjacent brown oil stained sediments from the Guaymas Basin, Gulf of California. Sediments with Beggiatoa maintained slightly higher rates of potential denitrification than did brown sediments at 31.2 ± 12.1 versus 21.9 ± 1.4 µM N day−1, respectively. In contrast, the nitrate removal rates in brown sediments were higher than those observed in mat-hosting sediments at 418 ± 145 versus 174 ± 74 µM N day−1, respectively. Additional experiments were conducted to assess the responses of denitrifying communities to environmental factors [i.e., nitrate, sulfide, and dissolved organic carbon (DOC) concentration)]. The denitrifying community had a high affinity for nitrate (Km = 137 ± 91 µM NO3−), in comparison to other environmental communities of denitrifiers, and was capable of high maximum rates of denitrification (Vmax = 1164 ± 153 µM N day−1). The presence of sulfide resulted in significantly lower denitrification rates. Microorganisms with the potential to perform denitrification were assessed in these sediments using the bacterial 16S rRNA gene and nitrous oxide reductase (nosZ) functional gene libraries. The bacterial 16S rRNA gene clone library was dominated by Epsilonproteobacteria (38%), some of which (e.g., Sulfurimonas sp.) have a potential for sulfide-dependent denitrification. The nosZ clone library did not contain clones similar to pure culture denitrifiers; these clones were most closely associated with environmental clones. PMID:23112796

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

    PubMed

    Johnson, Shannon B; Won, Yong-Jin; Harvey, Julio Bj; Vrijenhoek, Robert C

    2013-01-24

    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. 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. 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-recruitment of mussels by removing

  2. Hydrothermal alteration in volcanic rocks, eastern part of the Lukavice Group, Železné Hory Mountains, Czech Republic

    NASA Astrophysics Data System (ADS)

    Pertold, Z.; Watkinson, D. H.; Novotný, L.

    1993-06-01

    Many rocks mapped as felsic metavolcanics in the eastern part of the Lukavice Group are shown to be altered mafic metavolcanics, similar to those in the Noranda and Flin Flon-Snow Lake mining districts, Canada. The relatively fresh rocks of the Lukavice Group are rhyolite, dacite-andesite, and andesite-basalt of calcalka-line character. Assuming no substantial volume change during alteration, Ti, P, La, Ce, Yb, Lu, Th (partly), Sc and V contents remained unchanged. Altered rocks are enriched in (Fe + Mg), K and Si and depleted in Na, Ca and Zr. Some elements show both increased and decreased contents in altered rocks (Mg, Ba, Sm, eu, Tb and Hf). Although hydrothermal alteration in the Lukavice Group is of large extent, it is of the proximal Kuroko style and not of regional ‘Amulet Rhyolite’ style. Implications for a large hydrothermal system within a volcanic pile are discussed in relation to the Ordovician Lukavice Group and its mineral deposits and to some other parts of the Bohemian Massif with volcanosedimentary sequences of the same age.

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. Weathering and hydrothermal alteration of basalts in Iceland: mineralogy from VNIR, TIR, XRD, and implications for Mars

    NASA Astrophysics Data System (ADS)

    Ehlmann, B. L.; Mustard, J. F.; Bish, D. L.

    2009-12-01

    Recent orbital investigations have revealed that aqueous alteration on early Mars took place in diverse alteration environments indicated by distinctive assemblages of minerals (Murchie et al., 2009, JGR). There is growing evidence for past diagenetic or low-temperature/pressure hydrothermal activity on Mars at neutral to alkaline pH, indicated by the presence of Fe/Mg smectites, chlorite, prehnite, serpentine, opaline silica, and zeolites such as analcime in Noachian terrains (Ehlmann et al., 2009, JGR). In recent investigations of terrestrial Mars analog sites, neutral to alkaline pH alteration of basalt, both pedogenic and hydrothermal, has been understudied in favor of sulfur-rich, acidic systems including those at the Hawaiian volcanoes and Rio Tinto, Spain. We began study of the alteration of basalt lava flows in Iceland as a geochemical analog for Noachian Mars. Because the basaltic bedrock is recently formed (<16Ma) with few localities of more highly evolved composition and has poorly formed soils and spare vegetation, the ground and surface waters are broadly similar to those which might have existed on Noachian Mars. Iceland has a variety of geothermal spring systems--low T, low S; low T, high S; and high T, high S--each of which creates distinctive mineralogic assemblages. Here we examine rocks of the Hvalfjordur peninsula, collected from basalt flows that were in some places altered at the surface by pedogenesis and in other locations were hydrothermally altered by non-sulfurous groundwater circulation (low T, low S) following the emplacement of a later hot basalt flow. Rock samples were surveyed in the field using a portable VNIR spectrometer. Altered and unaltered rocks that were typical for the locality were collected as were altered rocks whose spectra were most similar to those measured by CRISM from Mars orbit. Ten rocks were ultimately selected for detailed laboratory analyses: zeolitized basaltic rocks bearing minerals including analcime and

  8. Hydrothermal alteration and permeability changes in granitic intrusions related to Sn-W deposits : case study of Panasqueira (Portugal)

    NASA Astrophysics Data System (ADS)

    Launay, Gaetan; Sizaret, Stanislas; Guillou-Frottier, Laurent; Gloaguen, Eric; Melleton, Jérémie; Pichavant, Michel; Champallier, Rémi; Pinto, Filipe

    2017-04-01

    The Panasqueira Sn-W deposit occurs as a dense network of flat wolframite and cassiterite-bearing quartz veins concentrated in the vicinity of a hidden greisen cupola, and to a lesser extent as disseminated cassiterites in the greisen. Previous studies (Thadeu 1951; 1979) have suggested that the Panasqueira deposit is genetically related to magmatic activity for which the most part is unexposed, and being only represented by the greisen cupola. Hydrothermal fluid circulation during the final stages of granite crystallisation has probably led to the greisenisation of the cupola followed by the deposition of the mineralization in the veins system. Mineral replacement reactions that occurred during the greisenisation could affect rock properties (porosity, density and permeability) which control fluid circulation in the granite. This study aims to investigate effects of greisenisation reactions on the dynamic (time varying) permeability that ultimately leads to fluid circulation in the greisen cupola. To do so, petrological study and experimental determinations of hydrodynamic features (porosity and permeability) for different granite alteration levels and petrographic types (unaltered granite to greisen) are combined and then integrated in coupled numerical models of fluid circulation around the granitic intrusion. Greisen occurs in the apical part of the granitic body and results in the pervasive alteration of the granite along the granite-schist contact. This greisen consists mainly of quartz and muscovite formed by the replacement of feldspars and bleaching of biotites of the initial granite. Otherwise, greisen is generally vuggy which suggests a porosity increase of the granite during hydrothermal alteration processes. This porosity increase has a positive effect on the permeability of the granitic system. Indeed, experimental measurements of permeability with the Paterson press indicate that the initial granite is impermeable (10-20 m2) whereas the greisen is

  9. Crystal chemistry and oxidation state of Fe-rich prehnite from a hydrothermally altered dolerite

    NASA Astrophysics Data System (ADS)

    Nagashima, Mariko; Iwasa, Kiyoka; Akasaka, Masahide

    2017-07-01

    Fe-rich prehnite, Ca2(Al,Fe)(AlSi3)O10(OH)2, in a hydrothermally altered dolerite sill from Mitsu, Shimane Peninsula, Japan, was studied using 57Fe Mössbauer spectroscopy and X-ray Rietveld method to determine the oxidation state and distribution of Fe within the prehnite and to clarify its structural properties. Prehnite shows two modes of occurrence: a druse and vein mineral (prehnite I) associated with Fe-rich pumpellyite and laumontite and a replacement of primary plagioclase (prehnite II). The Fe contents of prehnite I and II are 0.33-0.44 and 0.01-0.46 Fe3+ atoms per formula unit, respectively. The Mössbauer spectrum of prehnite II consists of one doublet with isomer shift (IS) = 0.364 mm/s and quadrupole splitting (QS) = 0.284 mm/s assigned to Fe3+ at the octahedral M site. In contrast, the Mössbauer spectrum of prehnite I consists of two doublets assigned to Fe3+ at the M site (IS = 0.369 mm/s and QS = 0.299 mm/s) and Fe2+ at the seven coordinated A site (IS = 1.05 and QS = 2.78 mm/s). According to X-ray Rietveld refinements with Pmna and Pma2 space groups, the fitting with Pma2 gave more reduced reliability factors than those using Pmna for both specimens, implying ordering of Al and Si at the tetrahedral T2 sites. Determined T2-O bond lengths at the Al-rich and Si-rich T2 sites, 1.71-1.72 and 1.62-1.64 Å, respectively, also indicate the ordered arrangement of Al and Si at the T2 sites. Refined site occupancies at the A and M sites are represented as A (Ca0.993(9)Fe2 + 0.007) M (Al0.666(6)Fe3 + 0.334) for prehnite I, and A Ca1.0 M (Al0.865(5)Fe3 + 0.135) for prehnite II, respectively. The existence of Fe2+ in the A site filling Ca deficiency in prehnite I is consistent with the result from the Mössbauer analysis.

  10. 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

  11. 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.

  12. 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

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

    NASA Astrophysics Data System (ADS)

    Dey, Thomas N.; Kranz, Robert L.

    1988-06-01

    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° from vertical.

  14. Geochemistry of volcanic and hydrothermal fluids and volatile budget of the Kamchatka Kuril subduction zone

    NASA Astrophysics Data System (ADS)

    Taran, Yuri A.

    2009-02-01

    A data base for the composition and emission rates of more than 100 thermal manifestations including boiling geothermal systems and 23 volcanoes along the 1900 km long Kamchatka-Kuril (KK) arc is presented. These results were used to estimate mean fluxes of volatiles from the KK arc. The fluxes from the KK arc are compared with the fluxes from the best studied Central American (CA) arc and with the compiled literature data on global fluxes. The error ranges and the OUT/IN (in)balance calculations are also discussed. The estimated fluxes of volatiles from volcanic fumaroles and the observed, normalized to the Cl content, fluxes from hydrothermal systems are very close, with the higher hydrothermal flux from Kuril Islands due to a larger number of the acidic Cl-SO 4 springs on the Islands and their outflow rates. The total volcanic SO 2 flux from the whole KK arc is estimated to be higher than 3000 t/d. The measured S and C fluxes from hydrothermal systems are much lower than the volcanic output due to the loss of these components in the upper crust (mineral precipitation). The Cl/ 3He ratio is inferred to be a stable indicator of the arc setting for hydrothermal and volcanic fluids with a mean value of (2 ± 4) × 10 9. Comparison of the obtained volcano-hydrothermal fluxes with fluxes calculated from the erupted solid volcanic products at Kamchatka and Kurils during Holocene time reveals that the total estimated volatile output from the KK arc is compatible with the total magmatic output if the intruded to erupted ratio is close to 7, i.e. almost the same as assumed for the Central American arc. Calculated fluxes as well as the ratios for OUT/IN fluxes (volcanic + hydrothermal output/slab + mantle input) for CO 2, S, H 2O, Cl, N 2, 4He and 3He from the KK arc normalized to the arc length are in general close to the global estimates. The fractions of CO 2 and S in the total volatile output at KK arc derived directly from the mantle wedge are 18% and 16% (mole basis

  15. 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.

  16. 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

  17. Radiometric dating of sediment cores from a hydrothermal vent zone off Milos Island in the Aegean Sea.

    PubMed

    Ugur, Aysun; Miquel, Juan-Carlos; Fowler, Scott W; Appleby, Peter

    2003-05-20

    Sediment cores from a hydrothermal vent zone off Milos Island in the Aegean Sea were dated using the 210Pb method. The average unsupported 210Pb inventory in the cores was calculated to be 3256 Bq m(-2). The corresponding mean annual 210Pb flux of 105 Bq m(-2) year(-1) is comparable to estimates of the atmospheric flux given in the literature. 210Pb fluxes calculated from the unsupported 210Pb inventories in cores are also comparable with the 210Pb vertical fluxes determined from settling particles off the coast of Milos Island. The highest unsupported 210Pb concentrations (89 Bq kg(-1)) were measured in the sediments nearest to the hydrothermal vent area suggesting that the sedimentation rate is lowest at this site. Direct gamma measurements of 210Pb were used to date three sediment cores that are located at different distances from the vent zone: one is in the immediate vicinity of the vent; and others are outside the zone. Sedimentation rates for these cores, calculated using the CRS and CIC models, ranged from 0.088+/-0.008 cm year(-1) to 0.14+/-0.01 cm year(-1). Where both models were applicable, the results given by the two methods were in good agreement. 137Cs concentrations in all three cores generally declined with depth but showed no clear signal of either the period of maximum fallout from weapons testing or the Chernobyl accident. 210Po activities were also measured and the maximum 210Po concentration was in the sediment surface layer (166 Bq kg(-1)).

  18. Formate as an energy source for microbial metabolism in chemosynthetic zones of hydrothermal ecosystems.

    PubMed

    Windman, Todd; Zolotova, Natalya; Schwandner, Florian; Shock, Everett L

    2007-12-01

    Formate, a simple organic acid known to support chemotrophic hyperthermophiles, is found in hot springs of varying temperature and pH. However, it is not yet known how metabolic strategies that use formate could contribute to primary productivity in hydrothermal ecosystems. In an effort to provide a quantitative framework for assessing the role of formate metabolism, concentration data for dissolved formate and many other solutes in samples from Yellowstone hot springs were used, together with data for coexisting gas compositions, to evaluate the overall Gibbs energy for many reactions involving formate oxidation or reduction. The result is the first rigorous thermodynamic assessment of reactions involving formate oxidation to bicarbonate and reduction to methane coupled with various forms of iron, nitrogen, sulfur, hydrogen, and oxygen for hydrothermal ecosystems. We conclude that there are a limited number of reactions that can yield energy through formate reduction, in contrast to numerous formate oxidation reactions that can yield abundant energy for chemosynthetic microorganisms. Because the energy yields are so high, these results challenge the notion that hydrogen is the primary energy source of chemosynthetic microbes in hydrothermal ecosystems.

  19. Platinum-group minerals from the Jinbaoshan Pd-Pt deposit, SW China: evidence for magmatic origin and hydrothermal alteration

    NASA Astrophysics Data System (ADS)

    Wang, Christina Yan; Prichard, Hazel M.; Zhou, Mei-Fu; Fisher, Peter C.

    2008-09-01

    The Jinbaoshan Pt-Pd deposit in Yunnan, SW China, is hosted in a wehrlite body, which is a member of the Permian (˜260 Ma) Emeishan Large Igneous Province (ELIP). The deposit is reported to contain one million tonnes of Pt-Pd ore grading 0.21% Ni and 0.16% Cu with 3.0 g/t (Pd + Pt). Platinum-group minerals (PGM) mostly are ˜10 μm in diameter, and are commonly Te-, Sn- and As-bearing, including moncheite (PtTe2), atokite (Pd3Sn), kotulskite (PdTe), sperrylite (PtAs2), irarsite (IrAsS), cooperite (PtS), sudburyite (PdSb), and Pt-Fe alloy. Primary rock-forming minerals are olivine and clinopyroxene, with clinopyroxene forming anhedral poikilitic crystals surrounding olivine. Primary chromite occurs either as euhedral grains enclosed within olivine or as an interstitial phase to the olivine. However, the intrusion has undergone extensive hydrothermal alteration. Most olivine grains have been altered to serpentine, and interstitial clinopyroxene is often altered to actinolite/tremolite and locally biotite. Interstitial chromite grains are either partially or totally replaced by secondary magnetite. Base-metal sulfides (BMS), such as pentlandite and chalcopyrite, are usually interstitial to the altered olivine. PGM are located with the BMS and are therefore also interstitial to the serpentinized olivine grains, occurring within altered interstitial clinopyroxene and chromite, or along the edges of these minerals, which predominantly altered to actinolite/tremolite, serpentine and magnetite. Hydrothermal fluids were responsible for the release of the platinum-group elements (PGE) from the BMS to precipitate the PGM at low temperature during pervasive alteration. A sequence of alteration of the PGM has been recognized. Initially moncheite and atokite have been corroded and recrystallized during the formation of actinolite/tremolite, and then, cooperite and moncheite were altered to Pt-Fe alloy where they are in contact with serpentine. Sudburyite occurs in veins

  20. 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

  1. Spuriously shallow NRM inclinations of hydrothermally altered Juan de Fuca Ridge sediment - secondary magnetization or disruption of the sediment fabric

    NASA Astrophysics Data System (ADS)

    Urbat, M.; Brandau, A.

    2003-04-01

    The marine sediment of the active Dead Dog Vent Field in Middle Valley, Juan de Fuca Ridge (ODP Holes 1036A-C), is strongly altered due to focused hydrothermal fluid circulation. A detailed paleo- and rockmagnetic study of the sediment indicates that the magnetic signal (iron oxides and secondary iron sulfides) sensitively reflects both thermally accelerated rates of diagenesis and direct reaction with the fluids. The explanation of NRM directions, however, in some of the lithologically homogeneous intervals is not straightforward. In these hydrothermally altered intervals the paleomagnetic record displays spuriously shallow or even negative inclinations, and a detailed analysis of the AF-demagnetization behavior does not indicate a true recording of the Earth magnetic field. We explore several potential causes for the NRM directions including authigenic precipitation of new magnetic minerals or the disruption of the sedimentary fabric and concomitant distortion of the NRM record. Spuriously shallow inclinations in all three holes correspond to inclinations of the minimum axes of the AMS ellipsoid that significantly deviates from vertical (i.e. 90° as would be expected for an undisturbed marine sedimentary fabric). We discuss, whether the secondary precipitation of (non-) magnetic minerals can explain the NRM behavior, if the volume of the original minerals is changed.

  2. Identification of hydrothermal alterations using Dar-Zarouk parameters and concept of anisotropy for 2D resistivity data

    NASA Astrophysics Data System (ADS)

    Permatasari, A. O.; Supriyanto, Kuswanto, A.

    2017-07-01

    Measurement of geoelectric methods is commonly performed by using homogeneous and isotropy approaches. However, these approaches are not entirely the same due to the earth's real condition. Therefore, it needs to be measured with inhomogeneous and anisotropy approach. This approach uses the parameter of Dar-Zarouk. The parameter of Dar-Zarouk is used to calculate the values of the resistivity of media and the coefficient of anisotropy. This research is intended for identifying the hydrothermal alteration that is not uniform in the field. The inhomogeneous and anisotropy approach is very appropriate to be used and expected to give a clearer cross section of true resistivity in subsurface imaging. The results of the model using the parameter of Dar-Zarouk sharpen the anomaly, hence the existence of alteration could be more visible and easier identified.

  3. Low Temperature Weathering vs. Hydrothermal Alteration of Radiation-damaged Zircon in a Lateritic Profile From Nsimi (Cameroon)

    NASA Astrophysics Data System (ADS)

    Delattre, S.; Utsunomiya, S.; Ewing, R. C.; Balan, E.; Calas, G.

    2006-05-01

    Zircon has an exceptional chemical durability. Hence, zirconium is used as a reference for mass balance calculations of chemical weathering. However, radiation damage from the alpha-decay of U and Th increases its chemical reactivity. The impact of radiation-induced amorphization on the mobility of zirconium is still debated. Previous results obtained on zircons from sediments and soils of the Amazon basin (Brazil) have shown that highly metamict zircons do not survive to the intense weathering and erosion processes under tropical conditions, suggesting that metamict zircon could be a significant source of Zr at the Earth's surface. Here we report new results about the relations between zircon alteration and accumulated radiation damage in a laterite developed in situ from granitic rocks, ruling out any preferential mechanical abrasion of metamict zircon. SEM images of the zircons, combined with Raman microprobe measurements of the degree of cristallinity, revealed preferential alteration of damaged grains. Based on TEM analysis, there is no evidence of a reprecipitation of baddeleyite (ZrO2) or incongruent dissolution of zircon. However, the damaged areas display higher amounts of Al, Fe (up to 1 wt. %) and Ca, with significant Pb loss. TEM observations reveal the presence of abundant nano-vesicles containing some chlorine (> 5 wt. %) and to a lesser extent Na and Ca. These features are most likely related to hydrothermal alteration. This event has lead to significant chemical exchanges and partial recrystallization of metamict zircon grains, which might occur at relatively low temperature in wet environments. This study illustrates the need to establish quantitative criteria to distinguish between the hydrothermal alteration and low-temperature weathering of zircon.

  4. 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.

  5. 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

  6. 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

  7. Ion-adsorption REEs in regolith of the Liberty Hill pluton, South Carolina, USA: An effect of hydrothermal alteration

    USGS Publications Warehouse

    Bern, Carleton R.; Yesavage, Tiffany; Foley, Nora K.

    2017-01-01

    Ion-adsorbed rare earth element (REE) deposits supply the majority of world heavy REE production and substantial light REE production, but relatively little is known of their occurrence outside Southeast Asia. We examined the distribution and forms of REEs on a North American pluton located in the highly weathered and slowly eroding South Carolina Piedmont. The Hercynian Liberty Hill pluton experiences a modern climate that includes ~ 1500 mm annual rainfall and a mean annual temperature of 17 °C. The pluton is medium- to coarse-grained biotite-amphibole granite with minor biotite granite facies. REE-bearing phases are diverse and include monazite, zircon, titanite, allanite, apatite and bastnäsite. Weathered profiles were sampled up to 7 m-deep across the ~ 400 km2 pluton. In one profile, ion-adsorbed REEs plus yttrium (REE + Y) ranged up to 581 mg/kg and accounted for up to 77% of total REE + Y in saprolite. In other profiles, ion-adsorbed REE + Y ranged 12–194 mg/kg and only accounted for 3–37% of totals. The profile most enriched in ion-adsorbed REEs was located along the mapped boundary of two granite facies and contained trioctahedral smectite in the saprolite, evidence suggestive of hydrothermal alteration of biotite at that location. Post-emplacement deuteric alteration can generate easily weathered REE phases, particularly fluorocarbonates. In the case of Liberty Hill, hydrothermal alteration may have converted less soluble to more soluble REE minerals. Additionally, regolith P content was inversely correlated with the fraction ion-adsorbed REEs, and weathering related secondary REE-phosphates were found in some regolith profiles. Both patterns illustrate how low P content aids in the accumulation of ion-adsorbed REEs. The localized occurrence at Liberty Hill sheds light on conditions and processes that generate ion-adsorbed REEs.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. Coupled Porosity and Chemical Evolution of Hydrothermal Circulation: Implications for the Morphology of Vents and Recharge Zones at Mid-Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Montesi, L.; Liao, Y.; Bai, H.; Ma, Z.; Tao, R.; Syverson, D. D.; Lowell, R. P.; Fischer, T. P.

    2015-12-01

    While the clearest evidence for hydrothermal circulation resides in focused upwellings at high-temperature vents, which form chimneys, circulation also features less-understood low-temperature diffuse flow and recharge zones. Flow focusing depends on the subsurface porosity and permeability structure, which, in the reactive environment of hydrothermal circulation, is likely influenced by mineral dissolution and precipitation from hydrothermal fluids. We developed two-dimensional Finite Element models of coupled reactive flow and porosity evolution and discuss how reactions may influence flow focusing and the morphology of upwellings and downwellings. This work can also address the chemical and thermal flux provided to the ocean, and the grade and volume of metal sulfide deposition. Our coupled system (See image) considers 1) Darcy flow driven by fluid buoyancy; 2) Heat transport in a porous medium; 3) Evolution of dissolved mineral concentration; 4) Evolution of porosity and permeability in response to mineral precipitation or dissolution. We also include an "ocean" layer, which allows hot fluid to escape the system without being forced to cool dramatically as they approach the seafloor. Absent porosity evolution, hydrothermal circulation forms flame-like upwellings that bend to avoid downdrafts. The circulation varies at the time scale of decades. Assuming thermodynamic equilibrium is maintained, precipitation of amorphous silica takes place in the upwellings as they rise and cool down. When coupled with porosity and permeability evolution, silicate precipitation forces the upwellings to flatten and become diffuse. Localized recharge zones stabilize and develop an armor of low porosity rocks where high temperature fluids cooled rapidly and deposited silica as they approach the recharge zone. This morphology of localized, armored recharge zone and diffuse upwellings does not match observations at natural vent fields, which implies that a critical element of the

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Hydrothermal alteration and timing of gold mineralisation in the Rumbia Complex, Southeast Arm of Sulawesi, Indonesia

    NASA Astrophysics Data System (ADS)

    Mawaleda, Musri; Suparka, Emmy; Idham Abdullah, Chalid; Indro Basuki, Nurcahyo; Forster, Marnie; Jamal; Kaharuddin

    2017-06-01

    The Rumbia Mountains, which in this study named Rumbia schist Complex is an east-west oriented, composed by a high-pressure/low-temperature, and a medium-pressure/low-temperature metamorphic rocks. Identified as mica schist, glauchopane schist, and green schist. Rumbia complex known as the location of gold deposits prospects discovered by local communities since 2007. The results of research showed that the metamorphic rocks are as hosts. There are two phase of gold mineralization that occurs in this area, namely: 1) Associated with tectonic deformation and metamorphic rocks exhumation, and 2) gold-related hydrothermal deposits. Radiometric age dating used 40Ar/39Ar geochronology, indicate that the first of gold mineralisation in the Rumbia Complex occurred ∼23 million years ago, and the second gold mineralisation were subsequently overprinting at 7 million years ago.

  4. Buffering of potassium in seawater by alteration of basalt in low-temperature, off-axis, hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Laureijs, C. T.; Coogan, L. A.

    2016-12-01

    It is generally accepted that the composition of seawater has varied through the Phanerzoic and that the variation is linked to changes in the same global fluxes that control the long-term carbon cycle. However, K is observed to be stable at a value of 10 mmol/L despite variable river and hydrothermal fluxes [1]. Secondary K-bearing phases are widely observed in altered upper oceanic crust, suggesting that reactions between seawater and basalt in low-temperature, off-axis, oceanic hydrothermal systems could buffer the K concentration of seawater [2]. As K-feldspar is a common secondary K-bearing mineral in Cretaceous and rare in Cenozoic oceanic crust, the formation of K-feldspar by breakdown of plagioclase reacting with a model Cretaceous seawater was modeled at 15 ºC using the PhreeqC code (version 3.2) and the associated llnl.dat database. A fluid with a K-content of 11 mmol/L in equilibrium with K-feldspar and calcite was generated, consistent with K-feldspar acting as a buffer for the K-content in Cretaceous seawater and the production of alkalinity stabilizing atmospheric CO2 levels on the long-term timescales. A compilation of the K2O content of lavas from DSDP and ODP drill cores (from: http://www.earthchem.org/petdb) shows that the average K-content of altered crust was higher in the Cretaceous than the Cenozoic. This data is inconsistent with the model for the composition of seawater presented in [2], but is consistent with an updated and modified version of this model, that uses more realistic fluxes [3]. We conclude that oceanic off-axis hydrothermal systems probably do buffer the K-content of seawater. [1] Timofeeff et al. (2006), Geochim. Cosmochim. Acta. 70, 1977-1994; [2] Demicco et al. (2005), Geology 33, 877-880. [3] Coogan & Dosso (2012), Earth Planet. Sci. Lett. 323-324, 92-101.

  5. Deformation associated with the denudation of mantle-derived rocks at the Mid-Atlantic Ridge 13°-15°N: The role of magmatic injections and hydrothermal alteration

    NASA Astrophysics Data System (ADS)

    Picazo, Suzanne; Cannat, Mathilde; Delacour, AdéLie; EscartíN, Javier; RouméJon, StéPhane; Silantyev, Sergei

    2012-09-01

    Outcrops of deeply derived ultramafic rocks and gabbros are widespread along slow spreading ridges where they are exposed in the footwall of detachment faults. We report on the microstructural and petrological characteristics of a large number of samples from ultramafic exposures in the walls of the Mid-Atlantic Ridge (MAR) axial valley at three distinct locations at lat. 13°N and 14°45'N. One of these locations corresponds to the footwall beneath a corrugated paleo-fault surface. Bearing in mind that dredging and ROV sampling may not preserve the most fragile lithologies (fault gouges), this study allows us to document a sequence of deformation, and the magmatic and hydrothermal history recorded in the footwall within a few hundred meters of the axial detachment fault. At the three sampled locations, we find that tremolitic amphiboles have localized deformation in the ultramafic rocks prior to the onset of serpentinization. We interpret these tremolites as hydrothermal alteration products after evolved gabbroic rocks intruded into the peridotites. We also document two types of brittle deformation in the ultramafic rocks, which we infer could produce the sustained low magnitude seismicity recorded at ridge axis detachment faults. The first type of brittle deformation affects fresh peridotite and is associated with the injection of the evolved gabbroic melts, and the second type affects serpentinized peridotites and is associated with the injection of Si-rich hydrothermal fluids that promote talc crystallization, leading to strain localization in thin talc shear zones. We also observed chlorite + serpentine shear zones but did not identify samples with serpentine-only shear zones. Although the proportion of magmatic injections in the ultramafic rocks is variable, these characteristics are found at each investigated location and are therefore proposed as fundamental components of the deformation in the footwall of the detachment faults associated with denudation of

  6. 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.

  7. 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.

  8. Rapid structural alterations of the active zone lead to sustained changes in neurotransmitter release.

    PubMed

    Matz, Jacob; Gilyan, Andrew; Kolar, Annette; McCarvill, Terrence; Krueger, Stefan R

    2010-05-11

    The likelihood with which an action potential elicits neurotransmitter release, the release probability (p(r)), is an important component of synaptic strength. Regulatory mechanisms controlling several steps of synaptic vesicle (SV) exocytosis may affect p(r), yet their relative importance in determining p(r) and eliciting temporal changes in neurotransmitter release at individual synapses is largely unknown. We have investigated whether the size of the active zone cytomatrix is a major determinant of p(r) and whether changes in its size lead to corresponding alterations in neurotransmitter release. We have used a fluorescent sensor of SV exocytosis, synaptophysin-pHluorin, to measure p(r) at individual synapses with high accuracy and employed a fluorescently labeled cytomatrix protein, Bassoon, to quantify the amount of active zone cytomatrix present at these synapses. We find that, for synapses made by a visually identified presynaptic neuron, p(r) is indeed strongly correlated with the amount of active zone cytomatrix present at the presynaptic specialization. Intriguingly, active zone cytomatrices are frequently subject to synapse-specific changes in size on a time scale of minutes. These spontaneous alterations in active zone size are associated with corresponding changes in neurotransmitter release. Our results suggest that the size of the active zone cytomatrix has a large influence on the reliability of synaptic transmission. Furthermore, they implicate mechanisms leading to rapid structural alterations at active zones in synapse-specific forms of plasticity.

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

    PubMed

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

    2015-06-01

    In the Neoarchean (~ 2.7 Ga) contact metamorphosed charnockitic footwall of the Mesoproterosoic (1.1 Ga) South Kawishiwi intrusion of the Duluth Complex, the primary metamorphic mineral assemblage and Cu-Ni-PGE sulfide mineralization is overprinted by an actinolite + chlorite + cummingtonite + prehnite + pumpellyite + quartz + calcite hydrothermal mineral assemblage along 2-3 cm thick veins. In calcite, hosted by the hydrothermal alteration zones and in a single recrystallized quartz porphyroblast, four different fluid inclusion assemblages are documented; the composition of these fluid inclusions provide p-T conditions of the fluid flow, and helps to define the origin of the fluids and evaluate their role in the remobilization and reprecipitation of the primary metamorphic sulfide assemblage. Pure CO2 fluid inclusions were found as early inclusions in recrystallized quartz porphyroblast. These inclusions may have been trapped during the recrystallization of the quartz during the contact metamorphism of the footwall charnockite in the footwall of the SKI. The estimated trapping pressure (1.6-2.0 kbar) and temperature (810-920 °C) conditions correspond to estimates based on felsic veins in the basal zones of the South Kawishiwi intrusion. Fluid inclusion assemblages with CO2-H2O-NaCl and CH4-N2-H2O-NaCl compositions found in this study along healed microfractures in the recrystallized quartz porphyroblast establish the heterogeneous state of the fluids during entrapment. The estimated trapping pressure and temperature conditions (240-650 bar and 120-150 °C for CO2-H2O-NaCl inclusions and 315-360 bar and 145-165 °C for CH4-N2-H2O-NaCl inclusions) are significantly lower than the p-T conditions (> 700 °C and 1.6-2 kbar) during the contact metamorphism, indicating that this fluid flow might not be related to the cooling of the Duluth Complex and its contact aureole. The presence of chalcopyrite inclusions in these fluid inclusions and in

  10. 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

  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. Pervasive, high temperature hydrothermal alteration in the RN-17B drill core, Reykjanes Geothermal System-Iceland Deep Drilling Project

    NASA Astrophysics Data System (ADS)

    Zierenberg, R. A.; Schiffman, P.; Marks, N. E.; Reed, M. H.; Elders, W. A.; Fridleifsson, G. O.

    2010-12-01

    In November 2008, 9.5 m of core were recovered from Reykjanes production well RN-17B at a depth of 2800m. The core consists mainly of hyaloclastite breccias, hetrolithic breccias with clasts of crystalline basalt, and volcaniclastic sandstones/siltstones. Much of the material appears to have been transported and redeposited, but homolithic breccias and hyaloclastites, some with upright flow lobes of basalt with quenched rims, are interpreted to have erupted in situ. Fine-scale features (glass rims, quench crystals, vesicles, phenocrysts) are well preserved, but all lithologies are pervasively hydrothermally altered such that primary clinopyroxene is ubiquitously uralitized and primary plagioclase (An42-80) is replaced by albite and/or more calcic plagioclase. In contrast, cuttings of similar lithologies, recovered by rotary drilling in intervals immediately above and below the core, exhibit much lesser degrees of hydrothermal alteration and commonly contain igneous plagioclase and clinopyroxene. Vitric clasts in the core are recrystallized into aggregates of chlorite and actinolite. In some breccias, cm-scale metadomains are composed of patchy albite or actinolite/magnesiohornblende giving the core a green and white spotted appearance. Minor amounts (<1%) of disseminated pyrite occur throughout the core, but two intervals with more abundant sulfide contain chalcopyrite and sphalerite in addition to pyrite. Amygdales and vugs in the breccias, initially filled with chlorite, actinolite, epidote, and/or albite, have been partly overprinted with hornblende and anorthite. The core is cut in places by < 1 cm- wide veins composed of early epidote + actinolite + titanite and later anorthite + magnesiohornblende/pargasite. Quartz is not present in any alteration domains observed in the core, although it is reported from virtually all of the cutting intervals above and below the cored section. Seawater-basalt reaction calculations suggest that albite formed during early

  13. High-grade iron ore at Windarling, Yilgarn Craton: a product of syn-orogenic deformation, hypogene hydrothermal alteration and supergene modification in an Archean BIF-basalt lithostratigraphy

    NASA Astrophysics Data System (ADS)

    Angerer, Thomas; Hagemann, Steffen G.; Danyushevsky, Leonid

    2013-08-01

    Banded iron formation (BIF)-hosted iron ore deposits in the Windarling Range are located in the lower greenstone succession of the Marda-Diemals greenstone belt, Southern Cross domain, Yilgarn Craton and constitute a total hematite-martite-goethite ore resource of minimum 52 Mt at 60 wt.% Fe (0.07 P). Banded iron formation is interlayered with high-Mg basalts at Windarling and precipitated during episodes of volcanic quiescence. Trace element content and the rare earth element (REE) ratios Y/Ho (42 to 45), Sm/Yb (1.5), together with positive La and Gd anomalies in `least-altered' hematite-magnetite-metachert-BIF indicate the precipitation from Archean seawater that was fertilised by hydrothermal vent fluids with a basaltic HREE-Y signature. Hypogene iron ore in sub-greenschist facies metamorphosed BIF formed during three distinct stages: ore stage 1 was a syn- to post-metamorphic, syn-D1, Fe-Ca-Mg-Ni-Co-P-REE metasomatism that produced local Ni-REE-rich Fe-dolomite-magnetite alteration in BIF. Hydrothermal alteration was induced by hot fluid flow controlled by brittle-ductile reactivation of BIF-basalt margins and crosscutting D1 faults. The Ni-Co-rich content of dolomite and a shift in REE ratios in carbonate-altered BIF towards Archean mafic rock signature (Y/Ho to 31 to 40, Sm/Yb to 1 to 2 and Gd/Gd* to 1.2 to 1.4) suggest that high-Mg basalts in the Windarling Range were the primary source of introduced metals. During ore stage 2, a syn-deformational and likely acidic and oxidised fluid flow along BIF-basalt margins and within D1 faults leached carbonate and precipitated lepidoblastic and anhedral/granoblastic hematite. High-grade magnetite-hematite ore is formed during this stage. Ore stage 3 hydrothermal specular hematite (spcH)-Fe-dolomite-quartz alteration was controlled by a late-orogenic, brittle, compressional/transpressional stage (D4; the regional-scale shear-zone-related D3 is not preserved in Windarling). This minor event remobilised iron oxides

  14. 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

  15. 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

  16. Sericitic alteration at the La Crocetta deposit (Elba Island, Italy): interplay between magmatism, tectonics and hydrothermal activity

    NASA Astrophysics Data System (ADS)

    Maineri, Cinzia; Benvenuti, Marco; Costagliola, Pilar; Dini, Andrea; Lattanzi, Pierfranco; Ruggieri, Giovanni; Villa, Igor M.

    2003-01-01

    The La Crocetta mine near Porto Azzurro (Elba Island, Tuscany, Italy) is an important producer of raw material for the ceramic industry. Exploitation focuses on a pervasively sericitized porphyritic aplite of the Tuscan Magmatic Province, locally known as "eurite", which underwent significant potassium enrichment during sericitic alteration. Eurites are located along the hanging wall of the Elba Centrale Fault, a low-angle extensional lineament of regional significance. A later carbonatization stage, apparently associated with high-angle extensional tectonics, locally overprinted the sericitized facies. It is expressed by carbonate ± pyrite ± quartz veins, with adverse effects on ore quality. Sericitization was accompanied by addition of potassium, and loss of Na (± Ca, Fe). Rubidium was not enriched along with potassium during sericitization, contrary to what would be expected for interaction with late-magmatic fluids. New 40Ar-39Ar data from eurites provide an isochron age of about 6.7 Ma for the sericitization, whereas the age of the unaltered protolith is ca. 8.8 Ma. Field evidence indicates the Elba Centrale Fault to be the main channel for the hydrothermal fluids. On the other hand, the involvement of heat and/or fluids contributed by the Porto Azzurro pluton, which crops out in the La Crocetta area, is ruled out by field, geochemical and geochronological data (40Ar-39Ar age of Porto Azzurro =5.9 Ma, i.e. significantly younger than the sericitization event). Fluid inclusion studies suggest that sericitization was associated with a low-temperature (<250 °C) hydrothermal system. Fluids were locally boiling, of variable salinity (4-17 wt% NaCl equiv.), and contained some CO2 ( XCO2≤0.027). Their ultimate source is not unequivocally constrained; meteoric and/or magmatic contributions may be possible. Low-salinity (≤2.6 wt% NaCl equiv.), low-temperature (<250 °C) fluids are associated with the late carbonate veining. They are considered to be of

  17. 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.

  18. Isotopic constraints on the formation of carbonates during low-temperature hydrothermal oceanic crust alteration

    NASA Astrophysics Data System (ADS)

    Stolper, D. A.; Antonelli, M. A.; Ramos, D. S.; Bender, M. L.; Schrag, D. P.; DePaolo, D. J.; Higgins, J. A.

    2016-12-01

    Low temperature (<100°C) water-rock reactions in oceanic crust have a potentially large influence on seawater chemical compositions and atmospheric pCO2. Quantification of the conditions (e.g., temperature) of oceanic crust alteration is needed to evaluate its importance for global silicate weathering fluxes. The isotopic and chemical compositions of secondary carbonates in oceanic crust reflect the temperature and chemistry of the circulating fluid and thus are used to reconstruct past conditions of crustal alteration. For example, temperatures are calculated via carbonate δ18O thermometry using measured δ18Ocarb vs. assumed δ18Ofluid. δ18Ofluid is usually assumed to be the seawater value at the time of carbonate formation. We present measured clumped-isotope temperatures (Tclump) and δ18O, δ13C, δ44Ca, and 87Sr/86Sr values of Jurassic carbonates from altered oceanic crust (ODP Site 801). Tclump measured at Caltech ranges from 24-51°C. Calculated δ18Ofluid (based on Tclump and δ18Ocarb) ranges from -0.4‰ (±0.4, 1σ) to -3.5‰ (±0.6). Higher temperatures correlate with lower δ18Ofluid (R2 = 0.75). This suggests that at elevated temperatures, δ18Ofluid was modified away from seawater values, likely via the preferential incorporation of 18O vs. 16O into secondary minerals relative to water. This indicates that δ18Ofluid values of circulating fluids are not necessarily identical to seawater δ18O. Tclump measurements are being replicated at Harvard for further verification. Carbonates with δ13C indicating a seawater C source (δ13C > 0‰) have average δ44Ca (relative to modern seawater) of -0.84‰ (±0.08). This is indistinguishable from igneous rock δ44Ca and suggests that carbonate Ca is derived from igneous Ca released during crustal alteration. Carbonates with δ13C indicating an organic C source (δ13C < -2.5‰) have lower δ44Cacarb (< -1‰). Carbonate 87Sr/86Sr ranges from 0.70742 to 0.70656. Based on the seawater 87Sr/86Sr curve, this

  19. Geochemical investigations and Fluid inclusion studies on iron ores from Qatruyeh area, Sanandaj-Sirjan zone, SW Iran: implications for a hydrothermal-metasomatic genetic model

    NASA Astrophysics Data System (ADS)

    Asadi, Sina; Rajabzadeh, Mohammad Ali

    2010-05-01

    The Qatruyeh iron deposits are located in the eastern edge of the NW-SE trending Sanandaj-Sirjan metamorphic zone of southwestern Iran and are hosted by a Late Proterozoic to Early Paleozoic sequence dominated by metamorphosed carbonate rocks. The ores occur as layered bodies, with lesser amounts within disseminated magnetite- and hematite-bearing veins. Geochemical analyses of the high-field strength, large ion lithophile, and rare earth elements (REE) indicate that mineralization within the low-grade layered magnetite ores was related to magmatic process accompanied by Na-Ca alteration. The stage is shown by metasomatic replacement textures, gradational contact between layered magnetite and host rock and mineral assemblages of actinolite + titanite + siderite + tourmaline (dravite) + quartz + paragonite. Chemical analyses on layered magnetite show Zn, Cr, LREE and Co/Ni ratio were enriched, whereas V and HREE were depleted. Subsequent to formation, low-temperature hydrothermal activity produced hematite ores with associated propyllitic-sericitic alteration with hematite (specularite) + chlorite + epidote + muscovite + quartz assemblages. The metacarbonate host rocks are LILE-depleted and HFSE-enriched due to metasomatic alteration. REE were relatively immobile during host rock alterations. Microthermometric analyses generally, have been described and measured only on primary inclusions of two-phase liquid +vapor (type A), and two-phase vapor +liquid with (type B). Type A inclusions are dominated by more than 80 vol % of H2O at room temperature. The first ice temperature of melting (Tm) often occurs around -24.5° to -19.5° C. Salinities determined by last ice Tm were 3.5 to 15 weight percent NaCl equivalent (size of inclusions between 2.5 and 15μm) for inclusions trapped in whole quartz samples. The average of homogenization temperature (Th) values change between 300 and 345°C and Tm measurements range from -11.3° to -3.5°C. Homogenization temperature exists

  20. Application of hydrothermal alteration mineral mapping using airborne hyperspectral remote sensing: data taken in the Baixianishan region of Gansu Province as an example

    NASA Astrophysics Data System (ADS)

    Yu, Sun; Zhao, Yingjun; Zhang, Donghui; Qin, Kai; Tian, Feng

    2016-10-01

    Hyperspectral remote sensing, featured by integrated images and spectra, is now a frontier of the remote sensing. Using meticulous spectra, hyperspectral remote sensing technology can depict spectral features of objects in detail and are capable of identifying objects rather than simply discriminating them. This study took the Baixianishan region in Gansu Province as an example, and CASI/SASI airborne hyperspectral data were utilized to extract and map alteration minerals by MTMF mapping method. Six hydrothermal alteration minerals were mapped, which contained limonite, sericite and epidote. In addition, we analyzed the types, combinations and distribution of the alteration minerals and divided three stages of hydrothermal activity. It is considered that the favorable ore-forming elements for gold deposits are middle Hercynian porphyraceous granite, fracture and veined distribution of sericite and limonite. The application of CASI/SASI airborne hyperspectral remote sensing data in the Baixianishan area has achieved ideal results, indicative of their wide application potential in the geological research.

  1. 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

  2. Transformation of graphite by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Kirilova, Matina; Toy, Virginia; Timms, Nicholas; Halfpenny, Angela; Menzies, Catriona; Craw, Dave; Rooney, Jeremy; Giorgetti, Carolina

    2017-04-01

    Graphite is a material with one of the lowest frictional strengths, with coefficient of friction of 0.1 and thus in natural fault zones it may act as a natural solid lubricant. Graphitization, or the transformation of organic matter (carbonaceous material, or CM) into crystalline graphite, is induced by compositional and structural changes during diagenesis and metamorphism. The supposed irreversible nature of this process has allowed the degree of graphite crystallinity to be calibrated as an indicator of the peak temperatures reached during progressive metamorphism. We examine processes of graphite emplacement and deformation in the Alpine Fault Zone, New Zealand's active continental tectonic plate boundary. Raman spectrometry indicates that graphite in the distal, amphibolite-facies Alpine Schist, which experienced peak metamorphic temperatures up to 640 ◦C, is highly crystalline and occurs mainly along grain boundaries within quartzo-feldspathic domains. The subsequent mylonitisation in the Alpine Fault Zone resulted in progressive reworking of CM under lower temperature conditions (500◦C-600◦C) in a structurally controlled environment, resulting in spatial clustering in lower-strain protomylonites, and further foliation-alignment in higher-strain mylonites. Subsequent brittle deformation of the mylonitised schists resulted in cataclasites that contain over three-fold increase in the abundance of graphite than mylonites. Furthermore, cataclasites contain graphite with two different habits: highly-crystalline, foliated forms that are inherited mylonitic graphite; and lower-crystallinity, less mature patches of finer-grained graphite. The observed graphite enrichment and the occurrence of poorly-organised graphite in the Alpine Fault cataclasites could result from: i) hydrothermal precipitation from carbon-supersaturated fluids; and/or ii) mechanical degradation by structural disordering of mylonitic graphite combined with strain-induced graphite

  3. 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; 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.

  4. 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.

  5. 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

  6. Hydrothermal reequilibration of igneous magnetite in altered granitic plutons and its implications for magnetite classification schemes: Insights from the Handan-Xingtai iron district, North China Craton

    NASA Astrophysics Data System (ADS)

    Wen, Guang; Li, Jian-Wei; Hofstra, Albert H.; Koenig, Alan E.; Lowers, Heather A.; Adams, David

    2017-09-01

    Magnetite is a common mineral in igneous rocks and has been used as an important petrogenetic indicator as its compositions and textures reflect changing physiochemical parameters such as temperature, oxygen fugacity and melt compositions. In upper crustal settings, igneous rocks are often altered by hydrothermal fluids such that the original textures and compositions of igneous magnetite may be partly or completely obliterated, posing interpretive problems in petrological and geochemical studies. In this paper, we present textural and compositional data of magnetite from variably albitized granitoid rocks in the Handan-Xingtai district, North China Craton to characterize the hydrothermal reequilibration of igneous magnetite. Four types of magnetite have been identified in the samples studied: pristine igneous magnetite (type 1), reequilibrated porous magnetite (type 2), reequilibrated nonporous magnetite (type 3), and hydrothermal magnetite (type 4). Pristine igneous magnetite contains abundant well-developed ilmenite exsolution lamellae that are largely replaced by titanite during subsequent hydrothermal alteration. The titanite has a larger molar volume than its precursor ilmenite and thus causes micro-fractures in the host magnetite grains, facilitating dissolution and reprecipitation of magnetite. During sodic alteration, the igneous magnetite is extensively replaced by type 2 and type 3 magnetite via fluid-induced dissolution and reprecipitation. Porous type 2 magnetite is the initial replacement product of igneous magnetite and is subsequently replaced by the nonoporous type 3 variety as its surface area is reduced and compositional equilibrium with the altering fluid is achieved. Hydrothermal type 4 magnetite is generally euhedral and lacks exsolution lamellae and porosity, and is interpreted to precipitate directly from the ore-forming fluids. Hydrothermal reequilibration of igneous magnetite has led to progressive chemical purification, during which trace

  7. 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.

  8. The Effectiveness of Hydrothermal Alteration Mapping based on Hyperspectral Data in Tropical Region

    NASA Astrophysics Data System (ADS)

    Muhammad, R. R. D.; Saepuloh, A.

    2016-09-01

    Hyperspectral remote sensing could be used to characterize targets at earth's surface based on their spectra. This capability is useful for mapping and characterizing the distribution of host rocks, alteration assemblages, and minerals. Contrary to the multispectral sensors, the hyperspectral identifies targets with high spectral resolution. The Wayang Windu Geothermal field in West Java, Indonesia was selected as the study area due to the existence of surface manifestation and dense vegetation environment. Therefore, the effectiveness of hyperspectral remote sensing in tropical region was targeted as the study objective. The Spectral Angle Mapper (SAM) method was used to detect the occurrence of clay minerals spatially from Hyperion data. The SAM references of reflectance spectra were obtained from field observation at altered materials. To calculate the effectiveness of hyperspectral data, we used multispectral data from Landsat-8. The comparison method was conducted by comparing the SAM's rule images from Hyperion and Landsat-8, resulting that hyperspectral was more accurate than multispectral data. Hyperion SAM's rule images showed lower value compared to Landsat-8, the significant number derived from using Hyperion was about 24% better. This inferred that the hyperspectral remote sensing is preferable for mineral mapping even though vegetation covered study area.

  9. Microbial mediation of authigenic clays during hydrothermal alteration of basaltic tephra, Kilauea Volcano

    NASA Astrophysics Data System (ADS)

    Konhauser, Kurt O.; Schiffman, Peter; Fisher, Quentin J.

    2002-12-01

    Highly altered, glassy tephras within the active steam vents at Kilauea Volcano, Hawaii, contain subsurface bacteria characterized by small (<500 nm in diameter), epicellular grains attached directly to the cell walls. Compositionally, the grains were dominated by Si, Al, Fe, and K, in a stoichiometry similar to a dioctahedral smectite. The initial dissolution of glass, which may in part have been microbiologically mediated, served as the source for many of the elements sequestered into the biomineralized clays. Overlying the tephras are white crusts (silica and calcite) and green-colored biofilms. The biofilms comprise a filamentous, likely cyanobacterial, community coated with spherical (<100 nm in diameter) grains of amorphous silica directly attached to the sheaths. Individual precipitates can easily be resolved, but quite often they coalesce, forming a dense mineral matrix of amorphous silica. For both the clays and silica, the microbial surfaces are clearly sites for mineral nucleation and growth. These observations imply that microbial biomineralization may be a significant process in the overall alteration of primary basaltic glass in active steam vent systems.

  10. Evolution of fluid-rock interactions: fluid inclusion, isotopic, and major/minor element chemistry of hydrothermally altered volcanic rock in core RN-17B, Reykjanes, Iceland

    NASA Astrophysics Data System (ADS)

    Fowler, A. P.; Zierenberg, R. A.; Schiffman, P.; Marks, N. E.; Fridleifsson, G. O.

    2011-12-01

    The Reykjanes Peninsula, Iceland, hosts a seawater-dominated geothermal system. Previous studies indicate an evolution of the system from meteoric to seawater. The inclined 4-inch diameter RN-17B drill core was collected from 2798.5 m to 2808.5 m (~2555 m below surface) at in situ temperature of approximately 330°C. Samples for this study were obtained from the Iceland Deep Drilling Project (IDDP). The core contains hydrothermally altered rocks of basaltic composition. Hydrothermal alteration ranges from upper greenschist to lower amphibolite grade, dependent on protolith size and composition. Veins in the core grade inward from radial epidote + acicular hornblende + titanite + pyrite, to clearer equant and compositionally zoned epidote vein centers. Felted amphibole replaces hyaloclastite and smaller crystalline clasts within the core, but is absent from the centers of crystalline pillow basalt fragments. Amphibole in vein selvages and vesicle fillings is green and acicular. Electron microprobe analyses of amphibole indicate it spans a compositional range of ferrohornblende through paragasite. The pistacite component (Xps) of vein epidote ranges from 16.5 to 36.7. The Xps component shows both normal and reverse zoning within single epidote crystals across this range, and follows no distinct pattern. Vein epidote adjacent to the wall rock has a higher aluminum concentration than vein centers. This may be due to mobilization of aluminum from plagioclase in the wall rock during albitization. Solutions flowing through open fractures may have lower Al-content and thus precipitate more Fe-rich epidote than those next to the fracture walls. Primary fluid inclusions in epidote range in size from <1 to 10 μm in diameter. Secondary fluid inclusions are <1 μm in diameter and not measurable. Calculated fluid inclusion salinities range from 0.5 to 7.6 weight percent NaCl, with lower salinities adjacent to the wall rock and higher salinities in the vein centers

  11. 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

  12. Chemical Variations in the Rocks of La Primavera Geothermal Field (Mexico) Related with Hydrothermal Alteration

    SciTech Connect

    Prol-Ledesma, R.M.; Hernandez-Lombardini, S.I.; Lozano-Santa Cruz, R.

    1995-01-01

    The origin and fate of the components dissolved in the geothermal fluids are of great importance in the study of epithermal deposits, and in the environmental considerations for exploitation of geothermal fields. The chemical study of La Primavera geothermal field in Mexico has environmental importance due to the high arsenic concentration observed in the thermal water and the possible contamination of aquifers in the area. The variations in the chemistry of all altered samples with respect to unaltered samples indicates depletion of manganese, and the alkalis; and enrichment in iron and magnesium. Most samples show an enrichment in aluminum and titanium, and depletion in silica and calcium. Trace elements follow different trends at various depths: shallow depths are more favorable for deposition of the analyzed trace elements than the surface or the deep part of the reservoir.

  13. 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.

  14. 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

  15. 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

  16. Constraints on the Composition and Hydrothermal Alteration History of the Pacific Lower Crust beneath the Hawaiian Islands: Geochemical Investigation of Gabbroic Xenoliths from Hualalai Volcano

    NASA Astrophysics Data System (ADS)

    Gao, R.; Lassiter, J. C.

    2013-12-01

    Understanding the composition and hydrothermal alteration history of the lower oceanic crust (LOC) can help constrain deep hydrothermal circulation at mid-ocean ridges, which may have a substantial impact on the thermal regime and magmatic processes at spreading centers. Previous studies of LOC primarily examined ophiolites or layer-3 gabbros exposed at the seafloor through faulting. These potentially have experienced secondary hydrothermal alteration in response to faulting, uplift and exposure. We examined major and trace element and isotopic compositions of a suite of gabbroic xenoliths derived from the 1800-1801 Kapulehu flow, Hualalai, Hawaii to constrain the composition and 'primary' hydrothermal alteration history of the in situ Pacific crust beneath the Hawaiian Islands (HI). Although most Hualalai gabbros have trace element and isotopic compositions consistent with derivation from Hualalai magmas, a subset has characteristics indicative of an origin from MORB-related melts. These gabbros contain LREE-depleted clinopyroxene, have Sr-Nd-Hf isotopic compositions that overlap the range of EPR basalts, and are geochemically distinct from Hualalai-related xenoliths and lavas. Despite the limited range recorded, plagioclase and clinopyroxene oxygen isotope compositions correlate well for both MORB-related and Hualalai-related gabbroic xenoliths. This suggests clinopyroxene and plagioclase are in equilibrium. The △plag-cpx (~0.6-0.9‰) is consistent with closure temperatures of ~1170-1220 C.δ18Ocpx (+4.9-5.3‰) of the MORB-related gabbros are negatively correlated with cpx 87Sr/86Sr, but not with 143Nd/144Nd or La/Sm. In contrast, δ18Oplag does not correlate with plag 87Sr/86Sr. Cpx Sr-isotopes may be affected by seawater alteration, which is not as apparent in plag due to higher Sr concentrations. However, the MORB-related gabbros have δ18O values that are largely in the range for normal, fresh MORB (δ18Omelt/NMORB = +5.7-6.0‰, △melt-cpx~0.7‰). This

  17. 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).

  18. 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.

  19. OSCAR - Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge

    NASA Astrophysics Data System (ADS)

    Hobbs, R. W.

    2016-12-01

    The cooling of oceanic crust is the principal physical process responsible for removing heat from the solid Earth to the hydrosphere. The nature of the heat flow process has a significant effect on the creation and ageing of oceanic crust. Close to the ridge-axis seismic velocity and density increase rapidly as the permeability of recently accreted crust is reduced by chemical alteration and mineral deposition through hydrothermal circulation. The maximum depth of this circulation is poorly constrained though, especially at ridges that do not host significant axial magma chambers, which in turn has implications for crustal formation processes. In the oceans, the processes and regions involved in the heating of the cold abyssal water, necessary to close the global thermohaline circulation cycle, are in dispute. Models of ocean circulation which include spatially varying heat flux based on crustal age show that geothermal heating is an important process. Although small compared to solar heating of the ocean's surface, geothermal heating of the abyssal ocean is unidirectional and directly heats the bottom boundary layer. A combined geophysical and oceanographic experiment has been conducted in the Panama basin to constrain the effects of heat and mass flux through young ocean crust to the ocean. At a full spreading rate of 66 mm/yr, the ridge system is classed as intermediate to fast and the Carnegie and Cocos ridges form a contained basin where the heat gain by the ocean can be determined. Based on a simple cooling curve,the OSCAR data show that the geothermal contribution is over 70% to the abyssal water upwelling. This is the largest contribution yet observed in abyssal basins and is in line with a growing number of studies arguing that geothermal heating plays a significant role in this upwelling.

  20. 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.

  1. 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.

  2. Magmatic 87Sr/86Sr relicts in hydrothermally altered quartz diorites (Brabant Massif, Belgium) and the role of epidote as a Sr filter

    NASA Astrophysics Data System (ADS)

    André, Luc; Deutsch, Sarah

    1986-01-01

    The porphyritic quartz diorites of the Caledonian Brabant Massif have been totally altered. Ca, Rb, Sr, Zr, Ce, Y measurements and Sr-Nd isotopic analyses were performed on the Quenast plug and the Lessines sill, in an attempt to study the relative mobility of Sr and evaluate the extent, direction and magnitude of the 87Sr/86Sr alterations. Sr electron microprobe analyses of epidote were also carried out to assess its role in the Sr distribution. The initial 87Sr/86Sr ratio is shown to have had an unsteady behaviour during the studied water/rock interactions since it has been sometimes enhanced, sometimes depressed and occasionally not modified. The possibility and magnitude of the 87Sr contamination turn out to be strictly related to the degree of Sr accommodation in the secondary minerals. Epidote in particular has proved to be the main trap for the hydrothermal Sr and this mineral is thus regarded as the major controlling factor of 87Sr hydrothermal contamination. The epidote-poor rocks (albite+chlorite-rich rocks) seem to have been unaffected by any Sr interchange with the aqueous solutions. Therefore, as alteration quickly follows the crystallization of the magma, their initial 87Sr/ 86Sr ratio, which is deduced from an isochron, might be a primary petrogenetic feature enabling interpretation of the genesis of their parental magmas. On the other hand, in the epidote-rich rocks, this ratio has been readily altered; it could thus generally be used only to trace the origin of the hydrothermal solutions. As a consequence, these rocks should not be selected for dating an alteration event by the Rb-Sr method.

  3. Structural setting of Fimiston- and Oroya-style pyrite-telluride-gold lodes, Paringa South mine, Golden Mile, Kalgoorlie: 1. Shear zone systems, porphyry dykes and deposit-scale alteration zones

    NASA Astrophysics Data System (ADS)

    Mueller, Andreas G.

    2017-07-01

    The Golden Mile in the 2.7 Ga Eastern Goldfields Province of the Yilgarn Craton, Western Australia, has produced 385 million tonnes of ore at a head grade of 5.23 g/t gold (1893-2016). Gold-pyrite ore bodies (Fimiston Lodes) trace kilometre-scale shear zone systems centred on the D2 Golden Mile Fault, one of three northwest striking sinistral strike-slip faults segmenting upright D1 folds. The Fimiston shear zones formed as D2a Riedel systems in greenschist-facies (actinolite-albite) tholeiitic rocks, the 700-m-thick Golden Mile Dolerite (GMD) sill and the Paringa Basalt (PB), during left-lateral displacement of up to 12 km on the D2 master faults. Pre-mineralisation granodiorite dykes were emplaced into the D2 shear zones at 2674 ± 6 Ma, and syn-mineralisation diorite porphyries at 2663 ± 11 Ma. The widespread infiltration of hydrothermal fluid generated chlorite-calcite and muscovite-ankerite alteration in the Golden Mile, and paragonite-ankerite-chloritoid alteration southeast of the deposit. Fluid infiltration reactivated the D2 shear zones causing post-porphyry displacement of up to 30 m at principal Fimiston Lodes moving the southwest block down and southeast along lines pitching 20°SE. D3 reverse faulting at the southwest dipping GMD-PB contact of the D1 Kalgoorlie Anticline formed the 1.3-km-long Oroya Shoot during late gold-telluride mineralisation. Syn-mineralisation D3a reverse faulting alternated with periods of sinistral strike-slip (D2c) until ENE-WSW shortening prevailed and was accommodated by barren D3b thrusts. North-striking D4 strike-slip faults of up to 2 km dextral displacement crosscut the Fimiston Lodes and the barren thrusts, and control gold-pyrite quartz vein ore at Mt. Charlotte (2651 ± 9 Ma).

  4. Element Mobility and Mass Transfer during Serpentinization and Hydrothermal Alteration of Seafloor Rocks: Implications from the Geochemistry of Atlantis Massif (IODP Expedition 357)

    NASA Astrophysics Data System (ADS)

    Bilenker, L.; Weis, D.; Alt, J.

    2016-12-01

    IODP Expedition 357 extracted 57 meters of drill core from Atlantis Massif, located at 30°N where the Atlantis Transform Fault intersects the Mid-Atlantic Ridge. This oceanic core complex is associated with the Lost City Hydrothermal Field and is a unique place to investigate the abiotic and biotic geochemical processes that play a role in the alteration of both crustal and mantle seafloor rocks. The samples collected represent a wide range in degree of alteration (0% to 100% serpentinization, metasomatism, oxidation) and lithology (peridotite, harzburgite, gabbro, basalt, dolerite, schist). Major and trace element compositions and isotopic ratios allow us to quantify element mobility and mass transfer during serpentinization and hydrothermal alteration. We analyzed drill core from seven of the nine Expedition 357 sites. Elemental compositions of 45 samples indicate a correlation between geochemical composition and degree of alteration, lithology, and proximity to Lost City or the Mid-Atlantic Ridge (MAR). For example, in general across the sites, a higher degree of alteration is observed in mafic samples with lower SiO2, enrichment in MgO, a positive U anomaly, and high loss on ignition values (up to 14%), and samples that originate closest to the MAR have MORB-like trace element signatures. Using these data alongside isotopic ratios provides insight into the source of the lithological units and fingerprint subsequent alteration processes. Additionally, comparing our data to well-characterized samples from previous ODP Legs (147, 149, 153) in comparable settings allows for us to assess several variables of seafloor alteration that may influence stable isotope fractionation, including biological processes, water to rock ratio, temperature, and the number of phases of alteration. This study contributes to our understanding of element mobility and mass transfer during serpentinization and has implications for its role in sustaining life.

  5. 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.

  6. 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.

  7. Differing responses of zircon, chevkinite-(Ce), monazite-(Ce) and fergusonite-(Y) to hydrothermal alteration: Evidence from the Keivy alkaline province, Kola Peninsula, Russia

    NASA Astrophysics Data System (ADS)

    Macdonald, Ray; Bagiński, Bogusław; Zozulya, Dmitry

    2017-09-01

    A quartzolite from the Rova occurrence, Keivy alkali granite province, Kola Peninsula, Russia, is used to examine the differing responses of certain rare-metal minerals during interaction with hydrothermal fluids. The minerals are two silicates [chevkinite-(Ce) and zircon], a phosphate [monazite-(Ce)] and an oxide [fergusonite-(Y)]. Textural evidence is taken to show that the dominant alteration mechanism was interface-coupled dissolution-reprecipitation. Zircon was the most pervasively altered, possibly by broadening of cleavage planes or fractures; the other minerals were altered mainly on their rims and along cracks. The importance of cracks in promoting fluid access is stressed. The compositional effects of the alteration of each phase are documented. The hydrothermal fluids carried few ligands capable of transporting significant amounts of rare-earth elements (REE), high field strength elements (HFSE) and actinides; alteration is inferred to have been promoted by mildly alkaline, Ca-bearing fluids. Expansion cracks emanating from fergusonite-(Y) are filled with unidentified material containing up to 35 wt% UO2 and 25 wt% REE2O3, indicating late-stage, short-distance mobility of these elements. Electron microprobe chemical dating of monazite yielded an age of 1665 ± 22 Ma, much younger than the formation age of the Keivy province (2.65-2.67 Ga) but comparable to that of the Svecofennian metamorphic event which affected the area (1.9-1.7 Ga) or during fluid-thermal activation of the region during rapakivi granite magmatism (1.66-1.56 Ga). Dates for altered monazite range from 2592 ± 244 Ma to 773 ± 88 Ma and reflect disturbance of the U-Th-Pb system during alteration.

  8. 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.

  9. Differing responses of zircon, chevkinite-(Ce), monazite-(Ce) and fergusonite-(Y) to hydrothermal alteration: Evidence from the Keivy alkaline province, Kola Peninsula, Russia

    NASA Astrophysics Data System (ADS)

    Macdonald, Ray; Bagiński, Bogusław; Zozulya, Dmitry

    2017-03-01

    A quartzolite from the Rova occurrence, Keivy alkali granite province, Kola Peninsula, Russia, is used to examine the differing responses of certain rare-metal minerals during interaction with hydrothermal fluids. The minerals are two silicates [chevkinite-(Ce) and zircon], a phosphate [monazite-(Ce)] and an oxide [fergusonite-(Y)]. Textural evidence is taken to show that the dominant alteration mechanism was interface-coupled dissolution-reprecipitation. Zircon was the most pervasively altered, possibly by broadening of cleavage planes or fractures; the other minerals were altered mainly on their rims and along cracks. The importance of cracks in promoting fluid access is stressed. The compositional effects of the alteration of each phase are documented. The hydrothermal fluids carried few ligands capable of transporting significant amounts of rare-earth elements (REE), high field strength elements (HFSE) and actinides; alteration is inferred to have been promoted by mildly alkaline, Ca-bearing fluids. Expansion cracks emanating from fergusonite-(Y) are filled with unidentified material containing up to 35 wt% UO2 and 25 wt% REE2O3, indicating late-stage, short-distance mobility of these elements. Electron microprobe chemical dating of monazite yielded an age of 1665 ± 22 Ma, much younger than the formation age of the Keivy province (2.65-2.67 Ga) but comparable to that of the Svecofennian metamorphic event which affected the area (1.9-1.7 Ga) or during fluid-thermal activation of the region during rapakivi granite magmatism (1.66-1.56 Ga). Dates for altered monazite range from 2592 ± 244 Ma to 773 ± 88 Ma and reflect disturbance of the U-Th-Pb system during alteration.

  10. 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

  11. 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

  12. 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

  13. METEORIC-HYDROTHERMAL SYSTEMS.

    USGS Publications Warehouse

    Criss, Robert E.; Taylor, Hugh P.

    1986-01-01

    This paper summarizes the salient characteristics of meteoric-hydrothermal systems, emphasing the isotopic systematics. Discussions of permeable-medium fluid dynamics and the geology and geochemistry of modern geothermal systems are also provided, because they are essential to any understanding of hydrothermal circulation. The main focus of the paper is on regions of ancient meteoric-hydrothermal activity, which give us information about the presently inaccessible, deep-level parts of modern geothermal systems. It is shown oxygen and hydrogen isotopes provide a powerful method to discover and map fossil hydrothermal systems and to investigate diverse associated aspects of rock alteration and ore deposition.

  14. 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.

  15. 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

  16. 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

  17. New insights to the formation of dolomite and magnesite through hydrothermal alteration of Ca-carbonates: An experimental approach

    NASA Astrophysics Data System (ADS)

    Kell-Duivestein, Isaac; Dietzel, Martin; Baldermann, Andre; Mavromatis, Vasileios

    2017-04-01

    Advanced knowledge about the physicochemical conditions and reaction paths underlying Ca-Mg carbonate formation, such as dolomite and magnesite, during the advanced stage of diagenesis is a pre-requirement for the accurate interpretation of proxy signals established from carbonate-hosting sedimentary archives. In this study, hydrothermal precipitation experiments were performed in order to trace and quantify the evolution of elemental (Ca, Mg and Sr) and stable isotopic δ18O signatures during the (trans)formation of intermediate aragonite and low-Mg calcite to more stable dolomite and magnesite in the presence of Mg- and Na-chloride-rich brines. Therefore, 330 mg of inorganic CaCO3 seed material (aragonite or calcite) was reacted with 30 mL of an artificial brine solution, originally containing 0.2 M of MgCl2(aq) and 0.1 M or 0.05 M of NaHCO3, in Teflon-lined stainless steel autoclaves at temperatures of 150, 180 and 220˚ C over the course of 365 days. The evolution of reaction products and of the experimental solutions was monitored by ICP-OES, CRDS, FTIR, XRD, EMPA and SEM analyses as well as pH and alkalinity measurements. Based on the apparent solid-phase composition and reactive fluid chemistry the following sequence of mineral growth was established: aragonite and/or low-Mg calcite reacted with aqueous Mg2+ ions to form intermediate huntite, brucite and high-Mg calcite, subsequently altered to Ca-excess dolomite and Ca-rich magnesite and finally converted to nearly stoichiometric endmembers. A progressive evolution in the stoichiometry of dolomite (from 42 to 50 mol% MgCO3) and magnesite (from 80 to 98 mol% MgCO3) as well as the increase in the degree of cation order in dolomite (from 0.26 to 0.74) were observed during this reaction sequence, implying a kinetic drive towards the (thermodynamically stable) end members. The latter processes were also traced, by means of δ18O isotope exchange kinetics between fluid and precipitating solids in bulk (Δ = δ18

  18. Alteration of uranium minerals in the Koongarra deposit, Australia: Unweathered zone

    NASA Astrophysics Data System (ADS)

    Isobe, Hiroshi; Murakami, Takashi; Ewing, Rodney C.

    1992-08-01

    The alteration behavior of natural uranium minerals may be used as a natural analogue for the long-term behavior of actinide-bearing ceramic waste forms. Specifically, uraninite (UO 2+ x) has been used as a natural analogue in the study of the processes and alteration products that are important in the corrosion of the UO 2 in spent nuclear fuel. Uranium minerals from the Koongarra deposit, Northern Territory of Australia, were examined in order to understand the alteration processes of the primary ore body in the unweathered zone, which extends at depths greater than 20 m from the surface. The primary mineral is uraninite with less than 2 wt% of CaO and 10 wt% of PbO. Uraninite has been altered to uranyl-lead oxides and uranyl silicates by the ground water which contains Si (10 mg/1), Mg (25 mg/l) and PO 4 (100 μg/l) at the present time. Uraninite reacted to form sklodowskite, a uranyl-Mg silicate (MgSi 2U 2O 11 · 7H 2O). Lead in uraninite is not released to form kasolite, a uranyl-Pb silicate (PbSiUO 6 · 2H 2O), but was enriched in residual phases such as curite (Pb 3U 8O 27 · 5H 2O) and wo¨lsendorfite (PbU 2O 7 · 2H 2O). Primary uraninite contains Ca, but Ca has an apparently high mobility and was not retained in the U-Pb oxides or uranyl silicates. Kasolite is observed with Pb-free sklodowskite in the uranyl silicates region formed by the alteration of uraninite and U-Pb oxides. Kasolite crystals are euhedral and acicular. This suggests that radiogenic Pb, produced in sklodowskite, was released to form kasolite. Redistribution of Pb in uranyl silicates may take place continuously in the uranyl silicates region of the deposit.

  19. Alteration-weakening leading to localized deformation in a damage aureole adjacent to a dormant shear zone

    NASA Astrophysics Data System (ADS)

    Backeberg, Nils R.; Rowe, Christie D.; Barshi, Naomi

    2016-09-01

    Deformation adjacent to faults and shear zones is traditionally thought to correlate with slip. Inherited structures may control damage geometry, localizing fluid flow and deformation in a damage aureole around structures, even after displacement has ceased. In this paper we document a post-shearing anastomosing foliation and fracture network that developed to one side of the Mesoarchean Marmion Shear Zone. This fracture network hosts the low-grade, disseminated Hammond Reef gold deposit. The shear zone juxtaposed a greenstone belt against tonalite gneiss and was locked by an intrusion that was emplaced during the final stages of suturing. After cessation of activity, fluids channeled along fault- and intrusion-related fractures led to the pervasive sericitization of feldspars. Foliated zones resulted from flattening in the weaker sericite-rich tonalite during progressive alteration without any change in the regional NW-SE shortening direction. The anastomosing pattern may have been inherited from an earlier ductile fabric, but sericite alteration and flattening fabrics all formed post-shearing. Thus, the apparent foliated fracture network adjacent to the Marmion Shear Zone is a second-order effect of shear-related damage, distinct in time from shear activity, adjacent to an effectively dormant shear zone. This phenomenon has implications for understanding the relative timing of fault zone activity, alteration and (in this case) gold mineralization related to long-term fault zone permeability.

  20. 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.

  1. 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.

  2. Insights into magmatic processes and hydrothermal alteration of in situ superfast spreading ocean crust at ODP/IODP site 1256 from a cluster analysis of rock magnetic properties

    NASA Astrophysics Data System (ADS)

    Dekkers, Mark J.; Heslop, David; Herrero-Bervera, Emilio; Acton, Gary; Krasa, David

    2014-08-01

    analyze magnetic properties from Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6°44.1' N, 91°56.1' W) on the Cocos Plate in ˜15.2 Ma oceanic crust generated by superfast seafloor spreading, the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Fuzzy c-means cluster analysis and nonlinear mapping are utilized to study down-hole trends in the ratio of the saturation remanent magnetization and the saturation magnetization, the coercive force, the ratio of the remanent coercive force and coercive force, the low-field magnetic susceptibility, and the Curie temperature, to evaluate the effects of magmatic and hydrothermal processes on magnetic properties. A statistically robust five cluster solution separates the data predominantly into three clusters that express increasing hydrothermal alteration of the lavas, which differ from two distinct clusters mainly representing the dikes and gabbros. Extensive alteration 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. Thus, the analysis complements interpretation based on electrofacies analysis. All clusters display rock magnetic characteristics compatible with an ability to retain a stable natural remanent magnetization suggesting that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Paleointensity determination is difficult because of the propensity of oxyexsolution during laboratory heating and/or the presence of intergrowths. The upper part of the extrusive sequence, the granoblastic dikes, and moderately altered gabbros may contain a comparatively uncontaminated thermoremanent magnetization.

  3. 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

  4. 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

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

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

    PubMed

    Beman, J Michael; Carolan, Molly T

    2013-01-01

    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.

  11. 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

  12. 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.

  13. Alteration in a large, 4 Ma, mineralized hydrothermal system: Mineralogy, stable isotopes, and mass exchange in an upwelling fossil geothermal plume at Rico, Colorado

    SciTech Connect

    Larson, P.B. . Dept. of Geology)

    1993-04-01

    A large hydrothermal system at Rico, CO, produced the deep Silver Creek stockwork Mo deposit (44 million tons of 0.31 Mo drilled, geologic reserves in excess of 200 million tons), and shallower vein and replacement deposits that were the source of historic production (> 80,000 tons each of Pb and Zn, > 5,000 tons of Cu, > 14 million oz Ag, and > 83,000 oz Au from 1879 through 1968). Isotopic dating of intrusive rocks and alteration minerals has shown that the mineralization formed contemporaneously about 4 Ma from a single hydrothermal system. This system altered a large volume of rocks (the Rico Paleothermal Anomaly, or PTA) centered on the mineralized area, with a heat source at the stockwork Mo deposit. The alteration is well-displayed in the widespread sills and dikes of 65 Ma hornblende latite porphyry. Low latite [sup 18]O/[sup 16]O ratios (< 0 per mil) in the center of the PTA were produced in a large upwelling fossil geothermal plume, 3 km in diameter and now exposed for over 2 vertical km. Outside the plume, [sup 18]O/[sup 16]O ratios increase gradationally away from the center (to the initial latite value of about 9 per mil) and define a concentric bull's-eye pattern. Chlorite tetrahedral Al geothermometer T's increase gradationally toward the system's center. Mass exchange in the plume is characterized by intense Na[sup +] leaching. All these effects are gradational in the PTA and diminish to background values 8 km from the plume's center. All mineralization in the district lies within the plume's boundary.

  14. 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.

  15. Mutant IDH1 Disrupts the Mouse Subventricular Zone and Alters Brain Tumor Progression.

    PubMed

    Pirozzi, Christopher J; Carpenter, Austin B; Waitkus, Matthew S; Wang, Catherine Y; Zhu, Huishan; Hansen, Landon J; Chen, Lee H; Greer, Paula K; Feng, Jie; Wang, Yu; Bock, Cheryl B; Fan, Ping; Spasojevic, Ivan; McLendon, Roger E; Bigner, Darell D; He, Yiping; Yan, Hai

    2017-02-01

    IDH1 mutations occur in the majority of low-grade gliomas and lead to the production of the oncometabolite, D-2-hydroxyglutarate (D-2HG). To understand the effects of tumor-associated mutant IDH1 (IDH1-R132H) on both the neural stem cell (NSC) population and brain tumorigenesis, genetically faithful cell lines and mouse model systems were generated. Here, it is reported that mouse NSCs expressing Idh1-R132H displayed reduced proliferation due to p53-mediated cell cycle arrest as well as a decreased ability to undergo neuronal differentiation. In vivo, Idh1-R132H expression reduced proliferation of cells within the germinal zone of the subventricular zone (SVZ). The NSCs within this area were dispersed and disorganized in mutant animals, suggesting that Idh1-R132H perturbed the NSCs and the microenvironment from which gliomas arise. Additionally, tumor-bearing animals expressing mutant Idh1 displayed a prolonged survival and also overexpressed Olig2, features consistent with IDH1-mutated human gliomas. These data indicate that mutant Idh1 disrupts the NSC microenvironment and the candidate cell of origin for glioma; thus, altering the progression of tumorigenesis. Additionally, this study provides a mutant Idh1 brain tumor model that genetically recapitulates human disease, laying the foundation for future investigations on mutant IDH1-mediated brain tumorigenesis and targeted therapy.

  16. Effects of hydrothermal alteration on the magnetic mineralogy of mid-ocean ridge basalts, IODP Site 1301B, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Linville, L. M.; Housen, B.; Sager, W.

    2005-12-01

    <