Sample records for ankerite

  1. Fluid Inclusions and Daughter Minerals of Taibai Gold Deposit, ShaanXi Province, China

    Institute of Scientific and Technical Information of China (English)


    A discovery of daughter minerals in fluid inclusions of Taibai gold deposit, Shaanxi province has been focused on, which is a unique breccia-cemented gold-bearing system. The breccia zone strikes NWW-SEE, occurring in Devonian strata of Southern Qinling Mountains. The cement is mainly composed of ankerite, pyrite, calcite and quartz, which may be divided into four main tectonic-mineralizing stages. Gold mainly occurs in pyrite and ankerite of stage II and IV. It is found that three types of fluid inclusions can be distinguished: (1) aqueous inclusions (type B); (2) CO2-rich inclusions (type C); (3) daughter minerals-containing inclusions (type A). LRM (Laser Raman Micro-probe) analyses shows that the content of CO2 occupies 54.4-70.7% (mole fraction, so as the follows) in vapor phases of different type fluid inclusions. CH4 (5.2%-7.3%) and H2S (6.0%-12.7%) exist in both vapor and liquid phases. Many daughter minerals in fluid inclusions of ankerite and quartz have been found. Several kinds of daughter minerals, including ankerite, pyrite, arsenopyrite and halite, were determined by using SEM (scanning electron microscope) / EDS (energy dispersive spectrometer) technique. EPMA (electron probe micro-analysis) technique was also applied to study the daughter minerals exposed to the surface of polis hed thin sections.

  2. Origin of REE-rich ferrocarbonatites in southern Siberia (Russia): implications based on melt and fluid inclusions (United States)

    Prokopyev, Ilya R.; Borisenko, Alexander S.; Borovikov, Andrey A.; Pavlova, Galina G.


    Fe-rich carbonatites with a mineral assemblage of ankerite-calcite or siderite are widespread in southern Siberia, Russia. The siderite carbonatites are associated with F-Ba-Sr-REE mineralization and have a 40Ar/39Ar age of 117.2 ± 1.3 Ma. Melt and fluid inclusions suggest that the carbonatites formed from volatile-rich alkali- and chloride-bearing carbonate melts. Ankerite-calcite carbonatites formed from carbonatite melt at a temperature of more than 790 °C. The ferrocarbonatites (the second phase of carbonatite intrusion) formed from a sulfate-carbonate-chloride fluid phase (brine-melt) at >650 °C and ≥360 MPa. The brine-melt fluid phase had high concentrations of Fe and LREEs. A subsequent hydrothermal overprint contributed to the formation of economically important barite-Sr-fluorite-REE mineralization in polymict siderite breccia.

  3. The CO2 consumption potential during gray shale weathering: Insights from the evolution of carbon isotopes in the Susquehanna Shale Hills critical zone observatory (United States)

    Jin, Lixin; Ogrinc, Nives; Yesavage, Tiffany; Hasenmueller, Elizabeth A.; Ma, Lin; Sullivan, Pamela L.; Kaye, Jason; Duffy, Christopher; Brantley, Susan L.


    Shale covers about 25% of the land surface, and is therefore an important rock type that consumes CO2 during weathering. We evaluated the potential of gray shale to take up CO2 from the atmosphere by investigating the evolution of dissolved inorganic carbon (DIC) concentrations and its carbon isotopic ratio (δ13CDIC) along water flow paths in a well-characterized critical zone observatory (Susquehanna Shale Hills catchment). In this catchment, chemical weathering in shallow soils is dominated by clay transformation as no carbonates are present, and soil pore waters are characterized by low DIC and pH. In shallow soil porewaters, the DIC, dominated by dissolved CO2, is in chemical and isotopic equilibrium with CO2 in the soil atmosphere where pCO2 varies seasonally to as high as 40 times that of the atmosphere. The degradation of ancient organic matter is negligible in contributing to soil CO2. The chemistry of groundwater varies along different flowpaths as soil pore water recharges to the water table and then dissolves ankerite or secondary calcite under the valley floor. Weathering of carbonate leads to much higher concentrations of DIC (∼2500 μmol/L) and divalent cations (Ca2+ and Mg2+) in groundwaters than soil waters. The depth to the ankerite weathering front is hypothesized to be roughly coincident with the water table but it varies due to heterogeneities in the protolith composition. Groundwater chemistry therefore shows different saturation indices with respect to ankerite depending upon location along the valley. The δ13CDIC values of these groundwaters document mixing between the ankerite and soil CO2. The major element concentrations, DIC, and δ13CDIC in the first-order stream incising the valley of the catchment are derived from groundwater and soil waters in proportions that vary both spatially and temporally. The CO2 degassed slightly in the stream but little evidence of C isotopic equilibration with the atmosphere is observed, due to the short

  4. Carbonatite magmatism of the southern Siberian Craton 1 Ga ago: Evidence for the beginning of breakup of Laurasia in the early Neoproterozoic (United States)

    Savelieva, V. B.; Danilova, Yu. V.; Bazarova, E. P.; Ivanov, A. V.; Kamenetsky, V. S.


    Apatite and biotite from dolomite‒ankerite and calcite‒dolomite carbonatite dikes emplaced into the Paleoproterozoic metamorphic rock complex in the southern part of the Siberian Craton are dated by the U-Pb (LA-ICP-MS) and 40Ar-39Ar methods, respectively. Proceeding from the lower intercept of discordia with concordia, the age of apatite from calcite‒dolomite carbonatite is estimated to be 972 ± 21 Ma and that for apatite from dolomite‒ankerite carbonatite, as 929 ± 37 Ma. Values derived from their upper intercept have no geological sense. The ages obtained for biotite by the 40Ar-39Ar method are 965 ± 9 and 975 ± 14 Ma. It means that the formation of carbonatites reflects the earliest phases of the Neoproterozoic stage in extension of the continental lithosphere.

  5. Thermodynamic Simulation of Carbonate Cements-Water-Carbon Dioxide Equilibrium in Sandstone for Prediction of Precipitation/Dissolution of Carbonate Cements


    Duan, Yiping; Feng, Mingshi; Zhong, Xinyan; Shang, Ruishu; Huang, Lihong


    Carbonate cements, such as calcite, dolomite, ferrocalcite and ankerite, play important roles in the formation of pores in sandstones: precipitation of carbonate cements modifies pores and inhibits compaction, while dissolution creates secondary pores. This work proposed a precipitation-dissolution model for carbonate cements-CO2-H2O system by means of ion equilibrium concentration ([M2+], M = Ca, Mg, Fe or Mn) with different factors, such as temperature, depth, pH, P CO 2 , variable rock com...

  6. Exhalites Associated with Pb-Zn Mineralization in Devonian System and Their Prospecting Implications,Qinling,China

    Institute of Scientific and Technical Information of China (English)


    The exhalation origin of the ankerite-siliceous rocks associated with Pb-Zn mineralizations in the Devonian system of Qinling is discussed in the light of geologic setting,sedimentary-tectonic environment,lithological and chemical characteristics.On this basis,criteria for distinguishing them and their potential role as an indicator in prospecting are described.Ankerite-siliceous rocks are developed in the strata-bound Pb-Zn polymetallic belt in the Devonian system of Qinling.They are microcrystalline,dark grey and compact in appearance and are commonly carbonaceous,As a persistent ore-bearing horizon in the region,their genetic relation to the Pb-Zn deposits in generally accepted.However,a consensus has yet to be reached among geologists concerning their origein as a product of hydrothermal metasomtism at the late stage of sedimentation or as exhalite resulting from submarine exhalation.Accumulating evidence from direct observations on modern submarine hydrothermal systems strongly indicates that seafloor exhalation is a much more common geologic process than previously thought nd its metallogenic implications have long been overlooked.Characteristics of the ankerite-siliceous rocks as a product of exhalation and their significance as a guide in prospecting are described on the basis or geological setting,lithology,lithochemistry,REE,and isotopic and trace element features.

  7. Multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks (United States)

    Bernard, Sylvain; Benzerara, Karim; Beyssac, Olivier; Brown, Gordon E., Jr.


    Pyritized plant tissues with well-preserved morphology were studied in rocks from Vanoise (western Alps, France) that experienced high-pressure, low-temperature metamorphic conditions in the blueschist facies during the Alpine orogeny. Organic and inorganic phases composing these fossils were characterized down to the nanometer scale by Raman microspectroscopy, scanning transmission X-ray microscopy and transmission electron microscopy. The graphitic but disordered organic matter composing these fossils is chemically and structurally homogeneous and mostly contains aromatic functional groups. Its original chemistry remains undefined likely because it was significantly transformed by diagenetic processes and/or thermal degradation during metamorphism. Various mineral phases are closely associated with this organic matter, including sulphides such as pyrite and pyrrhotite, carbonates such as ankerite and calcite, and iron oxides. A tentative time sequence of formation of these diverse mineral phases relative to organic matter decay is proposed. The absence of traces of organic matter sulphurization, the pervasive pyritization of the vascular tissues and the presence of ankerite suggest that the depositional/diagenetic environment of these metasediments was likely rich in reactive iron. Fe-sulphides and ankerite likely precipitated early and might have promoted the preservation of the fossilized biological soft tissues by providing mechanical resistance to compaction during diagenesis and subsequent metamorphism. In contrast, iron oxides which form rims of 100-nm in thickness at the interface between organic matter and Fe-sulphides may result from metamorphic processes. This study illustrates that it may be possible in some instances to deconvolve metamorphic from diagenetic imprints and opens new avenues to better constrain processes that may allow the preservation of organic fossils during diagenesis and metamorphism.

  8. High resolution cathodoluminescence spectroscopy of carbonate cementation in Khurmala Formation (Paleocene-L. Eocene) from Iraqi Kurdistan Region, Northern Iraq (United States)

    Omer, Muhamed F.; Omer, Dilshad; Zebari, Bahroz Gh.


    A combination of high resolution cathodoluminsecnce-spectroscopy (HRS-CL) with spatial electron microprobe analysis and optical microscopy is used to determine paragenesis and history of cementation in the limestones and dolostones of Khurmala Formation which is exposed in many parts of Northern Iraq. Khurmala Formation was subjected to different diagenetic processes such as micritization, compaction, dissolution, neomorphism, pyritization and cementation that occurred during marine to shallow burial stages and culminated during intermediate to deep burial later stages. Five dolomite textures are recognized and classified according to crystal size distribution and crystal-boundary shape. Dolomitization is closely associated with the development of secondary porosity that pre-and postdates dissolution and corrosion; meanwhile such porosity was not noticed in the associated limestones. Microprobe analysis revealed three types of cement, calcite, dolomite and ankerite which range in their luminescence from dull to bright. Cathodoluminescence study indicated four main texture generations. These are (1) unzoned microdolomite of planar and subhedral shape, with syntaxial rim cement of echinoderm that show dull to red luminescence, (2) equant calcite cements filling interparticle pores which shows dull luminescence and weak zonal growth, (3.1) homogenous intrinsic blue stoichiometric calcite with dull luminescence and without activators, (3.2) coarse blocky calcite cement with strong oscillatory zoning and bright orange luminescence which postdates other calcite cements, (4) ankerite cement with red to orange, non-luminescence growth zonation which is the last formed cement.

  9. Mineral identification in Colombian coals using Moessbauer spectroscopy and X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Fajardo, M. [Universidad del Valle, A.A, Departamento de Fisica (Colombia); Mojica, J. [Instituto Nacional de Investigaciones en Geociencia, Mineria y Quimica (INGEOMINAS) (Colombia); Barraza, J. [Universidad del Valle, A.A, Departamento de Procesos Quimicos, Facultad de Ingenieria (Colombia); Perez Alcazar, G.A.; Tabares, J.A. [Universidad del Valle, A.A, Departamento de Fisica (Colombia)


    Minerals were identified in three Colombian coal samples from the Southwest of the country using Moessbauer spectroscopy and X-ray diffraction. Original and sink separated coal fractions of specific gravity 1.40 and 1.60 with particle size less than 600 {mu}m were used in the study. Using Moessbauer spectroscopy, the minerals identified in the original coal samples were pyrite jarosite, ankerite, illite and ferrous sulfate, whereas by means of X-ray diffraction, minerals identified were kaolinite, quartz, pyrite, and jarosite. Differences in mineral composition were found in the original and sink separated fractions using both techniques. Moessbauer spectra show that the mineral phases in low concentrations such as illite, ankerite and ferrous sulfate do not always appear in the spectra of sink coals, despite of those minerals occurring in the original coal, due to the fact that they are associated with the organic matter and not liberated in the grinding process. X-ray results show that the peak intensity grows as the specific gravity is increased indicating that the density separation method could be an effective process to clean coal.

  10. Predicting cement distribution in geothermal sandstone reservoirs based on estimates of precipitation temperatures (United States)

    Olivarius, Mette; Weibel, Rikke; Whitehouse, Martin; Kristensen, Lars; Hjuler, Morten L.; Mathiesen, Anders; Boyce, Adrian J.; Nielsen, Lars H.


    Exploitation of geothermal sandstone reservoirs is challenged by pore-cementing minerals since they reduce the fluid flow through the sandstones. Geothermal exploration aims at finding sandstone bodies located at depths that are adequate for sufficiently warm water to be extracted, but without being too cemented for warm water production. The amount of cement is highly variable in the Danish geothermal reservoirs which mainly comprise the Bunter Sandstone, Skagerrak and Gassum formations. The present study involves bulk and in situ stable isotope analyses of calcite, dolomite, ankerite, siderite and quartz in order to estimate at what depth they were formed and enable prediction of where they can be found. The δ18O values measured in the carbonate minerals and quartz overgrowths are related to depth since they are a result of the temperatures of the pore fluid. Thus the values indicate the precipitation temperatures and they fit the relative diagenetic timing identified by petrographical observations. The sandstones deposited during arid climatic conditions contain calcite and dolomite cement that formed during early diagenesis. These carbonate minerals precipitated as a response to different processes, and precipitation of macro-quartz took over at deeper burial. Siderite was the first carbonate mineral that formed in the sandstones that were deposited in a humid climate. Calcite began precipitating at increased burial depth and ankerite formed during deep burial and replaced some of the other phases. Ankerite and quartz formed in the same temperature interval so constrains on the isotopic composition of the pore fluid can be achieved. Differences in δ13C values exist between the sandstones that were deposited in arid versus humid environments, which suggest that different kinds of processes were active. The estimated precipitation temperatures of the different cement types are used to predict which of them are present in geothermal sandstone reservoirs in

  11. Diagenesis and Fluid Flow History in Sandstones of the Upper Permian Black Jack Formation, Gunnedah Basin, Eastern Australia

    Institute of Scientific and Technical Information of China (English)

    BAI Guoping; John B. KEENE


    The fluid flow history during diagenesis of sandstones in the Upper Permian Black Jack Formation of the Gunnedah Basin has been investigated through integrated petrographic observations, fluid inclusion investigations and stable isotope analyses. The early precipitation of mixed-layer illite/smectite, siderite, calcite, ankerite and kaolin proceeded at the presence of Late Permian connate meteoric waters at temperatures of up to 60℃. These evolved connate pore waters were also parental to quartz, which formed at temperatures of up to 87℃. The phase of maximum burial was characterized by development of filamentous illite and late calcite at temperatures of up to ~90℃. Subsequent uplifting and cooling led to deep meteoric influx from surface, which in turn resulted in dissolution of labile grains and carbonate cements, and formation of second generation of kaolin. Dawsonite was the last diagenetic mineral precipitated and its formation is genetically related to deep-seated mamagtic sourced CO2.

  12. Phase transformations of siderite ore by the thermomagnetic analysis data (United States)

    Ponomar, V. P.; Dudchenko, N. O.; Brik, A. B.


    Thermal decomposition of Bakal siderite ore (that consists of magnesium siderite and ankerite traces) was investigated by thermomagnetic analysis. Thermomagnetic analysis was carried-out using laboratory-built facility that allows automatic registration of sample magnetization with the temperature (heating/cooling rate was 65°/min, maximum temperature 650 °C) at low- and high-oxygen content. Curie temperature gradually decreases with each next cycles of heating/cooling at low-oxygen content. Curie temperature decrease after 2nd cycle of heating/cooling at high-oxygen content and do not change with next cycles. Final Curie temperature for both modes was 320 °C. Saturation magnetization of obtained samples increases up to 20 Am2/kg. The final product of phase transformation at both modes was magnesioferrite. It was shown that intermediate phase of thermal decomposition of Bakal siderite ore was magnesiowustite.

  13. Microstructural characterization of material used as supporter in pre hispanic paints; Caracterizacion microestructural de material utilizado como soporte en pinturas prehispanicas

    Energy Technology Data Exchange (ETDEWEB)

    Silva V, Y. [FIME-UANL, San Nicolas de los Garza, Nuevo Leon (Mexico); Zorrilla, C.; Canetas, J.; Hernandez, R.; Aguilar F, M.; Arenas A, J. [IFUNAM, 04510 Mexico D.F. (Mexico); Martinez, G. [INAH, 04000 Mexico D.F. (Mexico)


    The aim of this work is to show the characterization of pre hispanic paintings mainly of the materials that support the pigments. The samples come from three different archaeological sites, Palenque-Chiapas (two specimens), Teotihuacan-Estado de Mexico (one specimen) and Mitla-Oaxaca (one specimen); Mayan, Teotihuacan and Mixtec-Zapotec culture respectively. The samples were analyzed by Sem, EDS, Tem, XRD and IR. The results show calcite as common phase for all the samples, however exist other phases identified depending on the site as dolomite, ankerite, calcium silicon chloride, etc. The origin of the red color of the analyzed pigments were cinnabar (HgS) by a sample of Palenque and hematite (Fe{sub 2}O{sub 3}) by the other specimen, this last crystalline phase also present in the Mitla and Teotihuacan samples. By IR were identified some organic compounds in all the samples, but not copal. (Author)

  14. Exhalative Lead-Zinc Deposits in Shallow Sea, Southern Xicheng Belt, Gansu Province

    Institute of Scientific and Technical Information of China (English)

    ZHU Xinyou; WANG Dongbo; WEI Zhiguo; QIU Xiaoping; WANG Ruiting


    SEDEX-type lead-zinc deposits in the southern belt of the Xicheng Devonian basin, GansuProvince has been already identified. However, the sedimentary environment of the limestone andphilite of the Xihanshui Group within which the lead-zinc deposits occur is littoral and shallow sea.This is different from those in the northern belt such as the Changba-Lijiagou lead-zinc deposits, whichwere formed in deep sea. The reef and bioclastic limestone are widespread in the southern belt.Particularly they are associated with lead-zinc ores and there are no striae and banding but massive ordisseminated structures. It is discovered that the black chimney consists of sphalerite, ankerite, pyriteand galena, in which black, coarse and radial sphalerite occurs as irregularly veins or cylindricafitywith a width of 10-40 cm in the center, and it is surround by fine ankerite and minor celestite withribbon structure. The immediate wall rock of the chimney, reef limestone, was unaltered and theoutside reef and bioclastic limestone were intensively silicified. Those silicified reef and bioclasticlimestone host disseminated lead-zinc ores of the Lnoba and Bijiashan type. It is concluded that theexhalative system occurred in a shallow sea in the Givetian of the middle Devonian. Brine is boiled dueto low pressure, and a great deal of lead and zinc was dispersed in the interface between the limestoneand phyllite and formed a source bed. In the Triassic period, meta-hydrothermai fluids leached andextracted metals from the source bed, and then moved and mineralized in open space such as archesand inverse limbs of anticlines, and formed massive and vein ores such as the Jianyagou andDengjiashan type deposits.

  15. A New Genetic Type of Gold Deposits-Meso-Epithermal Carbonate-Type Gold Deposits as Exemplified by the Baguamiao Suprlarge Gold Deposit

    Institute of Scientific and Technical Information of China (English)


    Gold deposits of the meso-epithermal carbonate type were first proposed based on the study of the Baguamiao gold deposit.This new type of gold deposits has many unique characteristics as follows:(1)Obviously strata-bound.The gold deposits are hosted in Middle Devonian turbidite formations;(2)Structrually controlled.Struc-ture is an important factor leading to metallogenesis of this type of gold deposits.The shape and distribution of orebodies are controlled by byittle-ductile shear zones;(3)Multi-stage wall-rock alteration.According to the characteristics of mineral assemblage,gold mineralization can be classified into three stages in association with various wall-rock al-terations.Wall-rock alterations closely genetically related to the gold mineralization are ankerization ,silicification,pyrrhotization and pyritization ;(4)Mineral compositions of the orebodies are mainly pyrrhotite,pyrite,marcasitolite,chalcopyrite,quartz,ankerite,and sericite.Gold mineralization is associated closely in space and time with iron sulfides;(5)Rare elements and REE in ores are low in contents relative to those of the crust.Au content varies from 1.91g/t to 11.15g/t ,averaging 5.5g/t;(6)Studies of sulfur,hydrogen,oxygen and carbon isotopes in main gangue minerals (quartz and ankerite)indicate that fluids and ore-forming materials came from deep-seated sources;(7)Three types of inclusions are recognized in terms of their composition and the vapor amounts of inclusions.The homogenization temperatures of inclusions range from 210℃to 310℃,averaging 230℃,showing that this type of gold deposits belongs to the meso-epithermal type;(8)Metallogenic age of this type of gold deposits is similar to that of the collision between the Yangtze Plate and the North China Plate,indicating that gold deposits of this type are genetically related to continental-margin plate activity.

  16. Mineral Sequestration of Carbon Dixoide in a Sandstone-Shale System

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Tianfu; Apps, John A.; Pruess, Karsten


    A conceptual model of CO2 injection in bedded sandstone-shale sequences has been developed using hydrogeologic properties and mineral compositions commonly encountered in Gulf Coast sediments. Numerical simulations were performed with the reactive fluid flow and geochemical transport code TOUGHREACT to analyze mass transfer between sandstone and shale layers and CO2 immobilization through carbonate precipitation. Results indicate that most CO2 sequestration occurs in the sandstone. The major CO2 trapping minerals are dawsonite and ankerite. The CO2 mineral-trapping capacity after 100,000 years reaches about 90 kg per cubic meter of the medium. The CO2 trapping capacity depends on primary mineral composition. Precipitation of siderite and ankerite requires Fe+2 supplied mainly by chlorite and some by hematite dissolution and reduction. Precipitation of dawsonite requires Na+ provided by oligoclase dissolution. The initial abundance of chlorite and oligoclase therefore affects the CO2 mineral trapping capacity. The sequestration time required depends on the kinetic rate of mineral dissolution and precipitation. Dawsonite reaction kinetics is not well understood, and sensitivity regarding the precipitation rate was examined. The addition of CO2 as secondary carbonates results in decreased porosity. The leaching of chemical constituents from the interior of the shale causes slightly increased porosity. The limited information currently available for the mineralogy of natural high-pressure CO2 gas reservoirs is also generally consistent with our simulation. The ''numerical experiments'' give a detailed understanding of the dynamic evolution of a sandstone-shale geochemical system.

  17. The thermal and chemical evolution of hydrothermal vent fluids in shale hosted massive sulphide (SHMS) systems from the MacMillan Pass district (Yukon, Canada) (United States)

    Magnall, J. M.; Gleeson, S. A.; Blamey, N. J. F.; Paradis, S.; Luo, Y.


    At Macmillan Pass (YT, Canada), the hydrothermal vent complexes beneath two shale-hosted massive sulphide (SHMS) deposits (Tom, Jason) are well preserved within Late Devonian strata. These deposits provide a unique opportunity to constrain key geochemical parameters (temperature, salinity, pH, fO2, ΣS) that are critical for metal transport and deposition in SHMS systems, and to evaluate the interaction between hydrothermal fluids and the mudstone host rock. This has been achieved using a combination of detailed petrography, isotopic techniques (δ34S, δ13C and δ18O values), carbonate rare earth element analysis (LA-ICP-MS), fluid inclusion analysis (microthermometry, gas analysis via incremental crush fast scan mass spectrometry), and thermodynamic modelling. Two main paragenetic stages are preserved in both vent complexes: Stage 1 comprises pervasive ankerite alteration of the organic-rich mudstone host rock and crosscutting stockwork ankerite veining (±pyrobitumen, pyrite and quartz) and; Stage 2 consists of main stage massive sulphide (galena-pyrrhotite-pyrite ± chalcopyrite-sphalerite) and siderite (±quartz and barytocalcite) mineralisation. Co-variation of δ18O and δ13C values in ankerite can be described by temperature dependent fractionation and fluid rock interaction. Together with fluid inclusion microthermometry, this provides evidence of a steep thermal gradient (from 300 to ∼100 °C) over approximately 15 m stratigraphic depth, temporally and spatially constrained within the paragenesis of both vent complexes and developed under shallow lithostatic (28), characteristic of diagenetic fluids, are coupled with positive europium anomalies and variable light REE depletion, which are more consistent with chloride complexation in hot (>250 °C) hydrothermal fluids. In this shallow sub-seafloor setting, thermal alteration of organic carbon in the immature, chemically reactive mudstones also had an important role in the evolution of fluid chemistry

  18. Diagenesis and reservoir quality evolution of palaeocene deep-water, marine sandstones, the Shetland-Faroes Basin, British continental shelf

    Energy Technology Data Exchange (ETDEWEB)

    Mansurbeg, H. [Department of Earth Sciences, Uppsala University, Villavaegen 16, SE 752 36 Uppsala (Sweden); Morad, S. [Department of Earth Sciences, Uppsala University, Villavaegen 16, SE 752 36 Uppsala (Sweden); Department of Petroleum Geosciences, The Petroleum Institute, P.O. Box 2533, Abu Dhabi (United Arab Emirates); Salem, A. [Faculty of Education at Kafr El-Sheikh, Tanta University, Kafr El-Sheikh (Egypt); Marfil, R.; Caja, M.A. [Departmento Petrologia y Geoquimica, Facultad de Geologia, UCM, 28040 Madrid (Spain); El-ghali, M.A.K. (Geology Department, Al-Fateh University, P.O. Box 13696, Libya); Nystuen, J.P. [Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, NO-0316 Oslo (Norway); Amorosi, A. [Department of Earth Sciences, University of Bologna, Via Zamboni 67, 40127 Bologna (Italy); Garcia, D. [Centre SPIN, Department GENERIC, Ecole Nationale Superieure des Mines de Saint Etienne 158, Cours Fauriel 42023, Saint-Etienne (France); La Iglesia, A. [Instituto de Geologia Economica (CSIC-UCM), Facultad de Geologia, UCM, 28040 Madrid (Spain)


    The Palaeocene, deep-water marine sandstones recovered from six wells in the Shetland-Faroes Basin represent lowstand, transgressive and highstand systems tract turbiditic sediments. Mineralogic, petrographic, and geochemical analyses of these siliciclastics are used to decipher and discuss the diagenetic alterations and subsequent reservoir quality evolution. The Middle-Upper Palaeocene sandstones (subarkoses to arkoses) from the Shetland-Faroes Basin, British continental shelf are submarine turbiditic deposits that are cemented predominantly by carbonates, quartz and clay minerals. Carbonate cements (intergranular and grain replacive calcite, siderite, ferroan dolomite and ankerite) are of eogenetic and mesogenetic origins. The eogenetic alterations have been mediated by marine, meteoric and mixed marine/meteoric porewaters and resulted mainly in the precipitation of calcite ({delta}{sup 18}O{sub V-PDB}=-10.9 permille and -3.8 permille), trace amounts of non-ferroan dolomite, siderite ({delta}{sup 18}O{sub V-PDB}=-14.4 permille to -0.6 permille), as well as smectite and kaolinite in the lowstand systems tract (LST) and highstand systems tract (HST) turbiditic sandstone below the sequence boundary. Minor eogenetic siderite has precipitated between expanded and kaolinitized micas, primarily biotite. The mesogenetic alterations are interpreted to have been mediated by evolved marine porewaters and resulted in the precipitation of calcite ({delta}{sup 18}O{sub V-PDB}=-12.9 permille to -7.8 permille) and Fe-dolomite/ankerite ({delta}{sup 18}O{sub V-PDB}=-12.1 permille to -6.3 permille) at temperatures of 50-140 and 60-140 C, respectively. Quartz overgrowths and outgrowth, which post- and pre-date the mesogenetic carbonate cements is more common in the LST and TST of distal turbiditic sandstone. Discrete quartz cement, which is closely associated with illite and chlorite, is the final diagenetic phase. The clay minerals include intergranular and grain replacive

  19. Geochemistry of Precambrian carbonates: II. Archean greenstone belts and Archean sea water. (United States)

    Veizer, J; Hoefs, J; Lowe, D R; Thurston, P C


    Carbonate rocks with geological attributes of marine sediments are a minor component of the Archean greenstone belts. Despite their relative scarcity, these rocks are important because they record chemical and isotopic properties of coeval oceans. The greenstones containing such carbonates appear to cluster at approximately 2.8 +/- 0.2 and approximately 3.5 +/- 0.1 Ga ago. The samples for the younger group are from the Abitibi, Yellowknife, Wabigoon (Steep Rock Lake), Michipicoten and Uchi greenstone belts of Canada and the "Upper Greenstones" of Zimbabwe. The older group includes the Swaziland Supergroup of South Africa, Warrawoona Group of Australia and the Sargur marbles of India. Mineralogically, the carbonates of the younger greenstones are mostly limestones and of the older ones, ferroan dolomites (ankerites); the latter with some affinities to hydrothermal carbonates. In mineralized areas with iron ores, the carbonate minerals are siderite +/- ankerite, irrespective of the age of the greenstones. Iron-poor dolomites represent a later phase of carbonate generation, related to post-depositional tectonic faulting. The original mineralogy of limestone sequences appears to have been an Sr-rich aragonite. The Archean carbonates yield near-mantle Sr isotopic values, with (87Sr/86Sr)o of 0.7025 +/- 0.0015 and 0.7031 +/- 0.0008 for younger and older greenstones, respectively. The best preserved samples give delta 13C of +1.5 +/- 1.5% PDB, comparable to their Phanerozoic counterparts. In contrast, the best estimate for delta 18O is -7% PDB. Archean limestones, compared to Phanerozoic examples, are enriched in 16O as well as in Mn2+ and Fe2+, and these differences are not a consequence of post-depositional alteration phenomena. The mineralogical and chemical attributes of Archean carbonates (hence sea water) are consistent with the proposition that the composition of the coeval oceans may have been buffered by a pervasive interaction with the "mantle", that is, with

  20. Fluid evolution and mineralogy of Mn-Fe-barite-fluorite mineralizations at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in Germany (United States)

    Majzlan, Juraj; Brey-Funke, Maria; Malz, Alexander; Donndorf, Stefan; Milovský, Rastislav


    Numerous small deposits and occurrences of Mn-Fe-fluorite-barite mineralization have developed at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in central Germany. The studied mineralizations comprise the assemblages siderite+ankerite-calcite-fluorite-barite and hematite-Mn oxides-calcite-barite, with the precipitation sequence in that order within each assemblage. A structural geological analysis places the origin of the barite veins between the Middle Jurassic and Early Cretaceous. Primary fluid inclusions contain water vapour and an aqueous phase with NaCl and CaCl2 as the main solutes, with salinities mostly between 24-27 mass. % CaCl2 eq. Th measurements range between 85 °C and 160 °C in barite, between 139 °C and 163 °C in siderite, and between 80 °C and 130 °C in fluorite and calcite. Stable isotopes (S, O) point to the evaporitic source of sulphur in the observed mineralizations. The S,C,O isotopic compositions suggest that barite and calcite could not have precipitated from the same fluid. The isotopic composition of the fluid that precipitated barite is close to the sea water in the entire Permo-Mesozoic time span whereas calcite is isotopically distinctly heavier, as if the fluids were affected by evaporation. The fluid evolution in the siliciclastic/volcanic Rotliegend sediments (as determined by a number of earlier petrological and geochemical studies) can be correlated with the deposition sequence of the ore minerals. In particular, the bleaching of the sediments by reduced Rotliegend fluids (basinal brines) could be the event that mobilized Fe and Mn. These elements were deposited as siderite+ankerite within the Zechstein carbonate rocks and as hematite+Mn oxides within the oxidizing environment of the Permian volcanic and volcanoclastic rocks. A Middle-Jurassic illitization event delivered Ca, Na, Ba, and Pb from the feldspars into the basinal brines. Of these elements, Ba was deposited as massive barite

  1. Magnetic Properties of Oil-gas-bearing Rocks of The Central Part of Dniper-donetsk Trough (United States)

    Kuderavets, R.; Maksymchuk, V.; Gorodisky, Y.

    Small amplitude positive local delta F anomalies were revealed by the results of high- accuracy magnetic prospecting in the Dniper-Donets trought over a series of oil-gas- bearing structures. Their nature can be explained by lithofacial and epigenetic rock magnetic variations in the oxidized-reduced zones of carbon deposits. Though, there is no trustable experimental data on magnetic properties of rocks in these zones. To study peculiarities of lateral and vertical magnetic perceptability, mineral rock com- position distribution within oil-gas-bearing areas in Dniper-Donetsk trough a series of investigations of these characteristics have been conducted for productive and un- productive holes. In general, the magnetic perceptability of core from 19 holes, near oil-gas deposits and far from theirs as well were determined. A statistic analysis of the obfained cappa values was done, rock mineral composition in some holes was de- termined. The results make it possible to conclude: 1. The cut is composed mainly of terrigenous rocks and is characterized by a slight differentiation by the magnetic perceptability (0-150x10E-5Si) 2. Small values of rock magnetic perceptability (1- 3x10E-5Si) and dispersion for low Visean substage of low carbon with which oil-gas- bearing of the region under study is closely connected were determined. 3. Statistic analysis proved the existence of some types of cappa distribution within the hole in particular it differs within productive and unproductive formations. 4. Larger values of cappa and their dispersion in comparison with analogical deposits in productive formations, were revealed. 5. A series of secondary epigenic minerals: quartz, kaoli- nite, aragonite, ankerite, dolomite, pirite, hematite, siderite was determined in the de- posit zone and out of it. The largest amount of ironminerals (ankerite, pirite, hematite, siderite) was found in terrigeneous rocks (argillite) located over and under carbon de- posits. The analysis of the

  2. A high-pyrite semianthracite of Late Permian age in the Songzao Coalfield, southwestern China: Mineralogical and geochemical relations with underlying mafic tuffs

    Energy Technology Data Exchange (ETDEWEB)

    Dai, Shifeng; Wang, Xibo; Chen, Wenmei [State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing 100083, (China); Li, Dahua [Research Center of State Key Laboratory of Coal Resources and Safe Mining, Chongqing 400042, (China); Chou, Chen-Lin [Illinois State Geological Survey (Emeritus), 615 East Peabody Drive, Champaign, IL 61820, (United States); Zhou, Yiping [Yunnan Institute of Coal Geology Prospection, Kunming 650218, (China); Zhu, Changsheng; Li, Hang [Research Center of State Key Laboratory of Coal Resources and Safe Mining, Chongqing 400042, (China); Zhu, Xingwei; Xing, Yunwei; Zhang, Weiguo; Zou, Jianhua [State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing 100083, (China)


    The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis. The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe-Mg-rich fluids during early diagenesis. The high pyrite (S{sub p,d} 8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids. Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO{sub 2}/Al{sub 2}O{sub 3} (1.13) but a higher Al{sub 2}O{sub 3}/Na{sub 2}O (80.1) value and is significantly enriched in trace elements including Sc (13.5 {mu}g/g), V (121 {mu}g/g), Cr (33.6 {mu}g/g), Co (27.2 {mu}g/g), Ni (83.5 {mu}g/g), Cu (48.5 {mu}g/g), Ga (17.3 {mu}g/g), Y (68.3 {mu}g/g), Zr (444 {mu}g/g), Nb (23.8 {mu}g/g), and REE (392 {mu}g/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO{sub 2}/Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}/Na{sub 2}O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for

  3. Petrography and geochemistry of Oligocene bituminous coal from the Jiu Valley, Petrosani basin (southern Carpathian Mountains), Romania

    Energy Technology Data Exchange (ETDEWEB)

    Belkin, Harvey E.; Tewalt, Susan J. [U.S. Geological Survey, 956 National Center, Reston, VA 20192 (United States); Hower, James C. [University of Kentucky Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511 (United States); Stucker, J.D. [University of Kentucky Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511 (United States); University of Kentucky Department of Earth and Environmental Sciences, Lexington, KY 40506 (United States); O' Keefe, Jennifer M.K. [Morehead State University, Morehead, KY, 40351 (United States); Tatu, Calin A. [University of Medicine and Pharmacy, Department of Immunology, Clinical Laboratory No. 1, Pta. E. Murgu No. 2, RO-1900 Timisoara (Romania); Buia, Grigore [University of Petrosani, Department of Geology, University St. 20, RO-2675 Petrosani (Romania)


    Belt samples of Oligocene (Chattian) bituminous coal from 10 underground mines located in the Jiu Valley, Hunedoara County, Petrosani basin, Romania, have been examined and analyzed for proximate and ultimate analysis, major-, minor- and trace-element chemistry, organic petrography, and vitrinite reflectance. The mineral chemistry and mode of occurrence of trace elements also have been investigated using SEM and electron microprobe techniques. Twenty coal beds occur in the Jiu Valley and most of the samples are from bed no. 3, the most productive bed of the Dilja-Uricani Formation of Oligocene age. The Petrosani basin, oriented SW-NE, is 48-km long, 10-km wide at the eastern part and 2-km wide at the western part. The coal mines are distributed along the center of the valley generally following the Jiu de Vest River. Reflectance measurements indicate that the rank of the coals ranges from high-volatile B to high-volatile A bituminous. Overall, rank decreases from the southwest to the northeast. In bed no. 3, R{sub max} varies from 0.75% in the northeast to 0.93% in the southwest. Although, most Oligocene coals in Romania and adjacent countries are lignite in rank, the Jiu Valley bituminous coals have been affected by regional metamorphism and attending hydrothermal fluids related to the Alpine orogenic event. The coals are all dominated by vitrinite; resinite and funginite are important minor macerals in most of the coals. Pyrite and carbonate generally dominate the mineral assemblages with carbonate more abundant in the northwest. Siderite occurs as nodules and masses within the macerals (generally vitrinite). Dolomite and calcite occur as fracture fillings, plant-cell fillings, and in other authigenic forms. Late-stage fracture fillings are siderite, dolomite, calcite, and ankerite. In one instance, two populations of siderite ({proportional_to} 35 and {proportional_to} 45 wt.% FeO) plus ankerite fill a large fracture. Late-stage pyrite framboid alteration is Ni

  4. A high-pyrite semianthracite of Late Permian age in the Songzao Coalfield, southwestern China: Mineralogical and geochemical relations with underlying mafic tuffs (United States)

    Dai, S.; Wang, X.; Chen, W.; Li, D.; Chou, C.-L.; Zhou, Y.; Zhu, Chen; Li, H.; Zhu, Xudong; Xing, Y.; Zhang, W.; Zou, J.


    The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis.The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe-Mg-rich fluids during early diagenesis. The high pyrite (Sp,d=8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids.Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO2/Al2O3 (1.13) but a higher Al2O3/Na2O (80.1) value and is significantly enriched in trace elements including Sc (13.5??g/g), V (121??g/g), Cr (33.6??g/g), Co (27.2??g/g), Ni (83.5??g/g), Cu (48.5??g/g), Ga (17.3??g/g), Y (68.3??g/g), Zr (444??g/g), Nb (23.8??g/g), and REE (392??g/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO2/Al2O3 and Al2O3/Na2O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for incompatible elements and chondrite-normalized diagram for rare earth elements) of coal and tuff, indicated that

  5. Fluid evolution and mineralogy of Mn-Fe-barite-fluorite mineralizations at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in Germany

    Directory of Open Access Journals (Sweden)

    Majzlan Juraj


    Full Text Available Numerous small deposits and occurrences of Mn-Fe-fluorite-barite mineralization have developed at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in central Germany. The studied mineralizations comprise the assemblages siderite+ankerite-calcite-fluorite-barite and hematite-Mn oxides-calcite-barite, with the precipitation sequence in that order within each assemblage. A structural geological analysis places the origin of the barite veins between the Middle Jurassic and Early Cretaceous. Primary fluid inclusions contain water vapour and an aqueous phase with NaCl and CaCl2 as the main solutes, with salinities mostly between 24–27 mass. % CaCl2 eq. Th measurements range between 85 °C and 160 °C in barite, between 139 °C and 163 °C in siderite, and between 80 °C and 130 °C in fluorite and calcite. Stable isotopes (S, O point to the evaporitic source of sulphur in the observed mineralizations. The S,C,O isotopic compositions suggest that barite and calcite could not have precipitated from the same fluid. The isotopic composition of the fluid that precipitated barite is close to the sea water in the entire Permo–Mesozoic time span whereas calcite is isotopically distinctly heavier, as if the fluids were affected by evaporation. The fluid evolution in the siliciclastic/volcanic Rotliegend sediments (as determined by a number of earlier petrological and geochemical studies can be correlated with the deposition sequence of the ore minerals. In particular, the bleaching of the sediments by reduced Rotliegend fluids (basinal brines could be the event that mobilized Fe and Mn. These elements were deposited as siderite+ankerite within the Zechstein carbonate rocks and as hematite+Mn oxides within the oxidizing environment of the Permian volcanic and volcanoclastic rocks. A Middle-Jurassic illitization event delivered Ca, Na, Ba, and Pb from the feldspars into the basinal brines. Of these elements, Ba was

  6. A salt diapir-related Mississippi Valley-type deposit: the Bou Jaber Pb-Zn-Ba-F deposit, Tunisia: fluid inclusion and isotope study (United States)

    Bouhlel, Salah; Leach, David L.; Johnson, Craig A.; Marsh, Erin; Salmi-Laouar, Sihem; Banks, David A.


    The Bou Jaber Ba-F-Pb-Zn deposit is located at the edge of the Bou Jaber Triassic salt diapir in the Tunisia Salt Diapir Province. The ores are unconformity and fault-controlled and occur as subvertical column-shaped bodies developed in dissolution-collapse breccias and in cavities within the Late Aptian platform carbonate rocks, which are covered unconformably by impermeable shales and marls of the Fahdene Formation (Late Albian-Cenomanian age). The host rock is hydrothermally altered to ankerite proximal to and within the ore bodies. Quartz, as fine-grained bipyramidal crystals, formed during hydrothermal alteration of the host rocks. The ore mineral assemblage is composed of barite, fluorite, sphalerite, and galena in decreasing abundance. The ore zones outline distinct depositional events: sphalerite-galena, barite-ankerite, and fluorite. Fluid inclusions, commonly oil-rich, have distinct fluid salinities and homogenization temperatures for each of these events: sphalerite-galena (17 to 24 wt% NaCl eq., and Th from 112 to 136 °C); ankerite-barite (11 to 17 wt% NaCl eq., and Th from 100 to 130 °C); fluorite (19 to 21 wt% NaCl eq., Th from 140 to 165 °C). The mean temperature of the ore fluids decreased from sphalerite (125 °C) to barite (115 °C) and increased during fluorite deposition (152 °C); then decreased to ˜110 °C during late calcite precipitation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of fluid inclusions in fluorite are metal rich (hundreds to thousands ppm Pb, Zn, Cu, Fe) but the inclusions in barite are deficient in Pb, Zn, Cu, Fe. Inclusions in fluorite have Cl/Br and Na/Br ratios of several thousand, consistent with dissolution of halite while the inclusions analysed in barite have values lower than seawater which are indicative of a Br-enriched brine derived from evaporation plus a component of halite dissolution. The salinity of the barite-hosted fluid inclusions is less than obtained simply by the

  7. CO 2 degassing and trapping during hydrothermal cycles related to Gondwana rifting in eastern Australia (United States)

    Uysal, I. Tonguç; Golding, Suzanne D.; Bolhar, Robert; Zhao, Jian-xin; Feng, Yue-xing; Baublys, Kim A.; Greig, Alan


    Intensive carbonate and clay mineral authigenesis took place throughout the Late Permian Bowen-Gunnedah-Sydney basin system in eastern Australia. We conducted isotopic and trace element analyses of carbonate and clay minerals from clastic sedimentary rocks of the Gunnedah Basin and the Denison Trough in the Bowen Basin. Rb-Sr isochron age data of the illitic clays are consistent with episodic hydrothermal fluid flow events that occurred in association with Gondwana rifting accompanied by alkaline magmatism at ˜85 Ma and ˜95 Ma. Stable isotope data of carbonate and clay minerals from the Gunnedah Basin are indicative of meteoric waters from a high-latitude environment as the main fluid source, whereas trace element, Sr and Nd isotope data highlight mixing of meteoric fluids with magmatic and/or crustal components, with a possible input from marine carbonates for some samples. Trace metals, oxygen and strontium isotopes of dawsonites from the Denison Trough are interpreted to have been mobilised by fluids that interacted with evolved clastic sedimentary and marine carbonate end members. According to the carbon isotope data, CO 2 for calcite and ankerite precipitation was sourced mainly from thermal degradation of organic matter and magmatism, whereas the CO 2 used for dawsonite formation is inferred to have been derived from magmatic and marine sources. In the low permeability environments (particularly in coal seams), the increasing accumulation and oversaturation of CO 2 particularly promote the precipitation of dawsonite.

  8. Catalytic decarboxylations of fatty acids in immature oil source rocks

    Institute of Scientific and Technical Information of China (English)

    李哲; 张再龙; 孙燕华; 劳永新; 蔺五正; 吴卫芳


    Catalytic decarboxylations of fatty acids in immature oil source rock samples were examined in this study. The rock samples were obtained from seven oil fields in China. In order to clarify the effect of each mineral matter in the rock samples, both the Fe M?ssbauer effect and the X-ray diffraction (XRD) were used to determine the relative content of each mineral in the rock samples, and the catalytic activities of several minerals like clays, carbonates and pyrite were determined. The Fe M?ssbauer effect and the XRD studies show that clays are the main mineral components in the rock samples except for the samples from Biyang and Jianghan in which the main mineral component is ankerite. The other mineral components include calcite, plagioclase, quartz, feldspar, siderite, aragonite, pyrite, analcime, pyroxene and anhydrite. The studies of the catalytic decarboxylations of fatty acids suggest that carbonates and pyrite can make much greater contributions to the catalytic activities of the rock samples than clays. It is found that the overall catalytic activities of the rock samples are well related to the relative contents and the catalytic activities of clays, carbonates and pyrite in the rock samples.

  9. Mineralogy of Iza Cave (Rodnei Mountains, N. Romania

    Directory of Open Access Journals (Sweden)

    Tamas Tudor


    Full Text Available The secondary minerals from Iza Cave result from the interactions of karst water and/or cave atmosphere with a variety of sedimentaryand metamorphic rocks. The cave passages expose at various extents Eocene limestones and conglomerates, Oligocene blackshales, Upper Precambrian micaschists, marble and dolomitic marble and associated ore deposits. Twelve secondary mineralsidentified in the cave (carbonates, sulfates, phosphates, oxides and hydroxides, and silicates are presented in this study. Calcite,aragonite, gypsum, brushite and hydroxylapatite are the components of common speleothems in the limestone, dolomite andconglomerate areas of the cave. Ankerite crusts are related to areas with pyrite mineralization within the metamorphic carbonaterocks. Goethite, jarosite, hematite and gypsum form various speleothems in the sectors within micaschists and conglomerates. Largeweathering deposits occurring in passage areas developed within micaschists consist of illite, kaolinite, jarosite, goethite, gypsumand alunite. The extent of the weathering deposits occurring on non-karst rocks in the underground environment makes this cave aparticularly interesting site for studies of water-rock interactions.

  10. Study of phyllosilicates and carbonates from the Capri Chasma region of Valles Marineris on Mars based on Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars (MRO-CRISM) observations (United States)

    Jain, Nirmala; Chauhan, Prakash


    Spectral reflectance data from the MRO-CRISM (Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars) of Capri Chasma, a large canyon within Valles Marineris on Mars, have been studied. Results of this analysis reveal the presence of minerals, such as, phyllosilicates (illite, smectite (montmorillonite)) and carbonates (ankerite and manganocalcite). These minerals hint of the aqueous history of Noachian time on Mars. Phyllosilicates are products of chemical weathering of igneous rocks, whereas carbonates could have formed from local aqueous alteration of olivine and other igneous minerals. Four different locations within the Capri Chasma region were studied for spectral reflectance based mineral detection. The study area also shows the spectral signatures of iron-bearing minerals, e.g. olivine with carbonate, indicating partial weathering of parent rocks primarily rich in ferrous mineral. The present study shows that the minerals of Capri Chasma are characterized by the presence of prominent spectral absorption features at 2.31 μm, 2.33 μm, 2.22 μm, 2.48 μm and 2.52 μm wavelength regions, indicating the existence of hydrous minerals, i.e., carbonates and phyllosilicates. The occurrence of carbonates and phyllosilicates in the study area suggests the presence of alkaline environment during the period of their formation. Results of the study are important to understand the formation processes of these mineral assemblages on Mars, which may help in understanding the evolutionary history of the planet.

  11. Mineralogy, geochemistry and pyrite content of Bulgarian subbituminous coals, Pernik Basin

    Energy Technology Data Exchange (ETDEWEB)

    Kostova, I.; Petrov, O.; Kortenski, J. [Bulgarian Academy of Sciences, Sofia (Bulgaria). Inst. of Applied Mineralogy


    The mineralogy and geochemistry of Pernik subbituminous coals (coal bed A) and some genetic peculiarities related to the mineral formation were studied. The mineral matter of the coal consists chiefly of pyrite, kaolinite, siderite, quartz and calcite. Other minerals (dolomite, ankerite, plagioclase and some sulphates) are present in minor amounts, some occurring as accessory single crystals. Pyrite is them main mineral in these coals and exhibits a large array of textures and morphology. Isolated and clustered euhedral, bacterial and inorganic framboidal, cluster-like, homogeneous and microconcretional massive, infilling and replacing anhedral, and cleat-filling and fracture-filling infiltrational pyrite types were observed. Four stages of mineralization were distinguished: pyrite-kaolinite, pyrite, pyrte-siderite and sulphate stages. The amount of pyrite present in two sections of coal bed A was determined by quantitative powder X-ray diffraction analysis. The concentrations of 37 trace elements were determined. As, Cu, Co, Ni, Zn, Pb, V, Ti, Mo Rb, Cr and Mn are typomorphic for this coal. On the basis of their relation to organic or inorganic matter, four groups of trace elements were subdivided; and on the basis of cluster analysis four associations were differentiated. 19 refs., 31 figs., 2 tabs.

  12. Typomorpic Characteristics of the Major Minerals in the Puziwan Gold Deposit, Datong, Shanxi, China

    Institute of Scientific and Technical Information of China (English)

    QING Min; NIU Cuiyi; LEI Shibin


    Utilizing theories of minerageny and prospecting mineralogy, the authors studied theattitude, morphotype and chemical composition of metallic minerals of pyrite, gold, chalcopyrite,galena and sphalerite, non-metallic minerals of quartz, carbonate, dolomite and rutile in the Puziwangold deposit. The study shows the following results. (1) The mineral assemblage is complex and thespecies of sulfide are abundant with occurrences of sulfosalt minerals. (2) The composition in theminerals is complex and there rich micro elements, including As, Sb, Bi, Se, Te, Au, Ag, Cu, Pb, Zn, andCr, Ni, V. The typomorphic characteristics of the association of the elements and their specific valuesuggest that gold mineralization is associated with shallow magmatic hydrothermai activity, the ore-forming fluid is the mixture of abundant rising alkali magmatic water originating from the mantle orthe lower crust and the descending acid atmospheric water. (3) Ankerite, Fe-rich sphalerite, granularTi-rich rutile are widely distributed, which indicate great denudation depths, high mineralizationtemperature. The deposit is found in the middle and shallow positions of the porphyry series. The deeplayers are not favorable for gold mineralization. (4) Copper minerals are rich in the ores and sulfideshave high content of copper, suggesting possible porphyry-type Cu (Au) mineralization in deeppositions and the surrounding areas.

  13. Formation mechanism of carbonate cemented zones adjacent to the top overpressured surface in the central Junggar Basin,NW China

    Institute of Scientific and Technical Information of China (English)


    Carbonate cemented zones are normally adjacent to the top overpressured surface in the central Junggar Basin,NW China.Stable carbon and oxygen isotopic compositions and petrological investigations of carbonate cements in the carbonate cemented zones indicate that:(1) carbonate cements are composed dominantly of ferrocalcite,ferroan dolomite,and ankerite;(2) carbonate cements are formed under a high temperature circumstance in the subsurface,and organic fluid migration has an important effect on the formation of them;and(3) carbon and oxygen ions in the carbonate cements migrate from the underlying overpressured system.This suggests that the occurrence of carbonate cemented zones in this region results from multiple phases of organic fluid expulsion out of the overpressure compartment through geological time.This study provides a plausible mechanism of the formation of carbonate cemented zones adjacent to the top overpressured surface in the clastic sedimentary basins,and has an important implication for understanding the internal correlation between the formation of carbonate cemented zones adjacent to top overpressured surface and geofluids expulsion out of overpressured system.

  14. Field Validation of Supercritical CO 2 Reactivity with Basalts

    Energy Technology Data Exchange (ETDEWEB)

    McGrail, B. Peter; Schaef, Herbert T.; Spane, Frank A.; Cliff, John B.; Qafoku, Odeta; Horner, Jake A.; Thompson, Christopher J.; Owen, Antoinette T.; Sullivan, Charlotte E.


    Continued global use of fossil fuels places a premium on developing technology solutions to minimize increases in atmospheric CO2 levels. CO2 storage in reactive basalts might be one of these solutions by permanently converting injected gaseous CO2 into solid carbonates. Herein we report results from a field demonstration where ~1000 MT of CO2 was injected into a natural basalt formation in Eastern Washington State. Following two years of post-injection monitoring, cores were obtained from within the injection zone and subjected to detailed physical and chemical analysis. Nodules found in vesicles throughout the cores were identified as the carbonate mineral, ankerite Ca[Fe, Mg, Mn](CO3)2. Carbon isotope analysis showed the nodules are chemically distinct as compared with natural carbonates present in the basalt and clear correlation with the isotopic signature of the injected CO2. These findings provide field validation of rapid mineralization rates observed from years of laboratory testing with basalts.

  15. Forms of Iron in the Phosphorites of Abu-Tartur Area, Egypt

    Institute of Scientific and Technical Information of China (English)



    The Campanian-Maastrichtian phosphatic deposits in Egypt, called the Duwi Formation, comprise a part of the extensive Middle East to North African phosphogenic province of Late Cretaceous to Paleogene age. The province holds the greatest accumulation of phosphorites in the geological history, possibly in excess of 70 billion metric tons. The phosphate resources in Egypt alone exceed 3 billion metric tons. Two-third of these three billions occur only in the Abu-Tartur area. Among the phosphorite deposits in Egypt, the phosphorites of the Abu-Tartur area are characterized by high contents of iron ranging from 3 % to 7% with an average of 5 %. The detailed mineralogical and geochemical studies on the Abu-Tartur phosphorites revealed that iron is found in the form of pyrite, ankerite, clay minerals, microinclusions, and iron oxide.Pyrite, which is the major fraction, occurs as filling cement and partial to complete replacement of phosphatic grains and confined to the fresh phosphorites while iron oxide occurs as cryptocrystalline aggregates of red to brown particles and is confined to the weathered outcrops. Exclusive relations between pyrite in the fresh phosphorite samples inside the Abu-Tartur mine and iron oxide in the equivalent horizon of the weathered exposure indicated that iron oxide was formed by the oxidation of pyrite as a result of weathering. All of these forms harm the quality of ore, manufacturing processes, and the produced phosphoric acid and fertilizers.

  16. Mineralogy and source rock evaluation of the marine Oligo-Miocene sediments in some wells in the Nile Delta and North Sinai, Egypt (United States)

    El sheikh, Hassan; Faris, Mahmoud; Shaker, Fatma; Kumral, Mustafa


    This paper aims to study the mineralogical composition and determine the petroleum potential of source rocks of the Oligocene-Miocene sequence in the Nile Delta and North Sinai districts. The studied interval in the five wells can be divided into five rock units arranged from the top to base; Qawasim, Sidi Salem, Kareem, Rudeis, and Qantara formations. The bulk rock mineralogy of the samples was investigated using X-Ray Diffraction technique (XRD). The results showed that the sediments of the Nile Delta area are characterized by the abundance of quartz and kaolinite with subordinate amounts of feldspars, calcite, gypsum, dolomite, and muscovite. On the other hand, the data of the bulk rock analysis at the North Sinai wells showed that kaolinite, quartz, feldspar and calcite are the main constituents associated with minor amounts of dolomite, gypsum, mica, zeolite, and ankerite. Based on the organic geochemical investigations (TOC and Rock-Eval pyrolysis analyses), all studied formations in both areas are thermally immature but in the Nile delta area, Qawasim, Sidi Salem and Qantara formations (El-Temsah-2 Well) are organically-rich and have a good petroleum potential (kerogen Type II-oil-prone), while Rudeis Formation is a poor petroleum potential source rock (kerogen Type III-gas-prone). In the North Sinai area, Qantara Formation has a poor petroleum potential (kerogen Type III-gas-prone) and Sidi Salem Formation (Bardawil-1 Well) is a good petroleum potential source rock (kerogen Type II-oil-prone).

  17. Mineralization Zoning in Yindongzi—Daxigou Barite—Siderite,Silver—Polymetallic Deposits in the Qinling Orogen,China

    Institute of Scientific and Technical Information of China (English)

    方维萱; 胡瑞忠; 等


    The Yindongzi-Daxigou strata-bound barite-siderite,silver-polymetallic deposits discovered in the Qinling orogen are hosted within flysch facies in a deep-water fault-controlled basin on the passive northern margin of the Qinling microplate.The orebodies occur in a series of hydrothermal depositonal rocks.Mineralization zoning is characterized by Fe-Ba←Ba-Cu←Pb-Ab→Cu-Ag→Pb→Au.This is obviously a gradational transition mineralization from ventproximal mineralization to more distal mineralization.In this gradational transition between Chefanggou and Yindongzi,vent-proximal mineralization consists of silver-polymetallic orebodies(Pb-Ag),which is the center of hydrothermal mineralization.The Chefanggou Ba-Cu ore district in the west and the Yindongzi Cu-Ag ore district in the east represent vent lateral mineralization.Distal mineralization in the west is represented by the Daxigou Fe-Ba ore district while distal mineralization in te east is represented by the Pb ore district.Thick massive,laminated barren albite chert and jasperite,sometimes with minor silver-ploymetallic mineralization of commercial importance,and pyritization in rocks feature more distal mineralization.Geochemical anomalies of Au-As associations are found in ankerite phyllite and muddy sandstone.Actually,Au deposits are dominantly controlled by the late brittle-ductile shear zone.

  18. Mineralization Zoning in Yindongzi-Daxigou Barite-Siderite, Silver-Polymetallic Deposits in the Qinling Orogen, China

    Institute of Scientific and Technical Information of China (English)

    方维萱; 胡瑞忠; 黄转莹


    The Yindongzi-Daxigou strata-bound barite-siderite, silver-polymetallic deposits discovered in the Qinling orogen are hosted within flysch facies in a deep-water fault-controlled basin on the passive northern margin of the Qinling microplate. The orebodies occur in a series of hydrothermal depositional rocks. Mineralization zoning is characterized by Fe-Ba←Ba-Cu←Pb-Ag→Cu-Ag→Pb→Au. This is obviously a gradational transition mineralization from ventproximal mineralization to more distal mineralization. In this gradational transition between Chefanggou and Yindongzi, vent-proximal mineralization consists of silver-polymetallic orebodies (Pb-Ag), which is the center of hydrothermal mineralization. The Chefanggou Ba-Cu ore district in the west and the Yindongzi Cu-Ag ore district in the east represent vent lateral mineralization. Distal mineralization in the west is represented by the Daxigou Fe-Ba ore district while distal mineralization in the east is represented by the Pb ore district. Thick massive, laminated barren albite chert and jasperite, sometimes with minor silver-ploymetallic mineralization of commercial importance, and pyritization in rocks feature more distal mineralization. Geochemical anomalies of Au-As associations are found in ankerite phyllite and muddy sandstone.Actually, Au deposits are dominantly controlled by the late brittle-ductile shear zone.

  19. A salt diapir-related Mississippi Valley-type deposit: The Bou Jaber Pb-Zn-Ba-F deposit, Tunisia: Fluid inclusion and isotope study (United States)

    Bouhlel, Salah; Leach, David; Johnson, Craig A.; Marsh, Erin; Salmi-Laouar, Sihem; Banks, David A.


    The Bou Jaber Ba-F-Pb-Zn deposit is located at the edge of the Bou Jaber Triassic salt diapir in the Tunisia Salt Diapir Province. The ores are unconformity and fault-controlled and occur as subvertical column-shaped bodies developed in dissolution-collapse breccias and in cavities within the Late Aptian platform carbonate rocks, which are covered unconformably by impermeable shales and marls of the Fahdene Formation (Late Albian–Cenomanian age). The host rock is hydrothermally altered to ankerite proximal to and within the ore bodies. Quartz, as fine-grained bipyramidal crystals, formed during hydrothermal alteration of the host rocks. The ore mineral assemblage is composed of barite, fluorite, sphalerite, and galena in decreasing abundance. The ore zones outline distinct depositional events: sphalerite-galena, barite-ankerite, and fluorite. Fluid inclusions, commonly oil-rich, have distinct fluid salinities and homogenization temperatures for each of these events: sphalerite-galena (17 to 24 wt% NaCl eq., and Th from 112 to 136 °C); ankerite-barite (11 to 17 wt% NaCl eq., and Th from 100 to 130 °C); fluorite (19 to 21 wt% NaCl eq., Th from 140 to 165 °C). The mean temperature of the ore fluids decreased from sphalerite (125 °C) to barite (115 °C) and increased during fluorite deposition (152 °C); then decreased to ∼110 °C during late calcite precipitation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of fluid inclusions in fluorite are metal rich (hundreds to thousands ppm Pb, Zn, Cu, Fe) but the inclusions in barite are deficient in Pb, Zn, Cu, Fe. Inclusions in fluorite have Cl/Br and Na/Br ratios of several thousand, consistent with dissolution of halite while the inclusions analysed in barite have values lower than seawater which are indicative of a Br-enriched brine derived from evaporation plus a component of halite dissolution. The salinity of the barite-hosted fluid inclusions is less than obtained

  20. Mineralisation footprints and regional timing of the world-class Siguiri orogenic gold district (Guinea, West Africa) (United States)

    Lebrun, Erwann; Thébaud, Nicolas; Miller, John; Roberts, Malcolm; Evans, Noreen


    Siguiri is a world-class orogenic gold district hosted in the weakly metamorphosed Upper Birimian to Lower Tarkwa Group sedimentary rocks of the Siguiri Basin (Guinea). The district is characterised by a protracted deformation history associated with four main deformation events: D1S is a N-S compression; D2S is an E-W compression progressively evolving into an early-D3S transpression and then into a late-D3S NNW-SSE transtension and D4S is a NE-SW compression. Field observations, petrography and geochemistry at three key deposits of the Siguiri district (Bidini, Sintroko PB1 and Kosise) suggest a polyphase hydrothermal history that can be subdivided into four hydrothermal events. The first hydrothermal event was associated with the development of barren bedding-parallel and en-echelon V2S quartz-dominated-(pyrite) veins. The second hydrothermal event is characterised by the development of V3A pyrite-ankerite veins late during D3S. Laser ablation-ICP-MS data show that this vein set contains high gold contents of up to 43.3 ppm, in substitution in pyrite crystal lattice, representing a minor first gold mineralisation event. The third and most prominently developed hydrothermal event is late D3S and represents the second and principal gold mineralisation event. This mineralisation event led to two distinct mineralisation textures. The first texture is best exposed in the Kosise deposit and is characterised by gold-bearing quartz-ankerite-arsenopyrite conjugate V3B veins. Although the bulk of the gold is hosted in native gold grains in V3B veins, LA-ICP-MS analyses show that gold also substitutes in the arsenopyrite crystal lattice (up to 55.5 ppm). The second mineralisation texture is best expressed in the Sanu Tinti deposit and consists of disseminated barren pyrite hosted in a polymict conglomerate. The second and third hydrothermal events are both structurally controlled by a series of early-D3S N-S, NE-SW, WNW-ESE and E-W sub-vertical incipient structures

  1. Authigenic layer silicate minerals in borehole Elmore 1, Salton Sea Geothermal Field, California, USA (United States)

    McDowell, S. Douglas; Elders, Wilfred A.


    A combined petrographic/X-ray/electron microprobe and energy dispersive system investigation of sandstone cuttings from borehole Elmore # 1 near the center of the Salton Sea Geothermal Field has revealed numerous regular variations in the composition, texture, mineralogy and proportions of the authigenic layer silicate minerals in the temperature interval 185° C (411.5 m depth) to 361° C (2,169 m). At temperatures near 190° C, dolomite/ankerite+calcite-bearing sandstones contain an illite/mixed layer phase with 10% expandable layers (dolomite/ankerite zone). In shale, the percentage of expandable layers in the mixed layer phase changes from 10 15% at 185° C to 5% at 210° C (494 m). In the interval 250° C (620 m) to 325° C (1,135 m), the calcite+pyrite+epidote-bearing sandstones contain a layer silicate assemblage of chlorite and illite (chlorite-calcite zone). In the shallower portions of this metamorphic zone, the illite contains 0 5% expandable layers, while at depths greater than 725 m (275° C) it is completely free of expandable layers. On increasing temperature, the white mica shows regular decreases in SiIV, Mg and Fe, and increase in AlIV, AlVI, and interlayer occupancy, as it changes gradually from fine-grained illite (=textural sericite) to coarse-grained recrystallized phengitic white mica. In the same interval, chlorite shows decreases in AlVI and octahedral vacancies and an increase in total Mg+Fe. The sandstones range from relatively unmodified detrital-textured rocks with porosities up to 20% and high contents of illite near 250° C to relatively dense hornfelsic-textured rocks with trace amounts of chlorite and phengite and porosities near 5% at 325° C. Numerous complex reactions among detrital (allogenic) biotite, chlorite, and muscovite, and authigenic illite and chlorite, occur in the chlorite-calcite zone. Biotite appears, and calcite disappears, at a temperature near 325° C and a depth of 1,135m. The biotite zone so produced persists

  2. Carbon and oxygen isotopic composition of carbonate cements of different phases in terrigenous siliciclastic reservoirs and significance for their origin: A case study from sandstones of the Triassic Yanchang Formation, southwestern Ordos Basin,China

    Institute of Scientific and Technical Information of China (English)

    WANG Qi; ZHUO Xizhun; CHEN Guojun; LI Xiaoyan


    Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope (their δ18O values range from -0.3‰-0.1‰) and lighter oxygen isotope (their ‰18O values range from -22.1‰--19.5‰). Generally, they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water. This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones, preserving intragranular volume and providing the mass basis for later dissolution caused by acidic fluid flow to produce secondary porosity. Ferriferous calcites are characterized by relatively light carbon isotope with δ13C values ranging from -8.02‰ to -3.23‰, and lighter oxygen isotope with δ18O values ranging from -22.9‰ to -19.7‰, which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis. As the mid-late diagenetic products, ferriferous calcites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir. The late ankerite is relatively heavy in carbon isotope with δ13C values ranging from -1.92‰ to -0.84‰, and shows a wide range of variations in oxygen isotopic composition, with δ18O values ranging from -20.5‰ to -12.6‰. They are believed to have nothing to do with decarboxylation, but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation, and the alkaline diagenetic environment at the mid-late stage would promote this process.

  3. Carbonate cements and grains in submarine fan sandstones—the Cergowa Beds (Oligocene, Carpathians of Poland) recorded by cathodoluminescence (United States)

    Pszonka, Joanna; Wendorff, Marek


    The cathodoluminescence (CL) observations with cold cathode, supplemented by reconnaissance scanning electron microscope analyses, bring new data on petrology, provenance and diagenesis of the Oligocene-age Cergowa sandstones from the Outer Carpathians (SE Poland). The sandstones represent a variety of mass gravity flow sediments deposited on a submarine fan, which now forms a lenticular lithosome—a part of the Menilite Beds-Krosno Beds suite important for the hydrocarbons industry. The most common components of the Cergowa sandstones observed under the CL are carbonates—cement and grains that are mainly represented by lithoclasts. Carbonate cement is represented by five generations: brown (Cb), orange (Co), yellow (Cy), zoned (Cz) and black (Ck). Pore-filling Cb and Co calcite cements are interpreted as genetically related to eo- and mesodiagenetic phases. The mesodiagenetic phase is characterised by randomly distributed relatively large monocrystalline-zoned rhombs of dolomite cement (Cz) and ankerite/ferroan dolomite (Ck). The telodiagenetic phase is represented by pore-filling yellow calcite (Cy) that crystallised under the influence of suboxic meteoric waters. Lithoclasts represent six microfacies of carbonate rocks eroded in the source area, i.e. microbreccia, tectonised immature calcarenite/wacke, microsparite, sparite, biomicrosparite/packstone and dolostone. Pronounced indentations of terrigenous sand grains into intraclasts of packstone/biomicrosparite, coupled with commonly present similar packstone-type matrix, suggest that a significant part of matrix resulted from compaction of soft biomicrosparite grains. Terrigenous grains bound by calcite cement are commonly corroded by acidic diagenetic fluids, and partial or even complete replacement of silicates by calcite and clay minerals is illustrated here by feldspar grains. Substantial carbonate cementation has resulted in both the significant hardness and abrasion resistance of the Cergowa sandstones

  4. Evolution of pores and fractures in an unconventional Upper Carboniferous reservoir analogue, Westphalian D, W-Germany

    Energy Technology Data Exchange (ETDEWEB)

    Hoehne, M.; Schurk, K.; Hilgers, C. [RWTH Aachen Univ. (Germany). Reservoir-Petrology, Energy and Mineral Resources Group (EMR); Koehrer, B. [Wintershall Holding GmbH, Barnstorf (Germany); Bertier, P. [RWTH Aachen Univ. (Germany). Inst. of Clay and Interface Mineralogy


    Uncertainties in reservoir characterization of tight gas sandstones can be significantly reduced by using quantitative data from outcrops. The active Piesberg quarry near Osnabrueck exposes Upper Carboniferous strata and therefore provides a reservoir outcrop analog to the gas-bearing tight gas fields in NW-Germany. This study focused on variations of sedimentary facies, porosity, diagenesis and structural inventory in the quarry. The Westphalian D strata at Piesberg consist of siliciclastic, coarse- to fine-grained sandstones with a strong cementation, intercalated with coal seams, siltstones and mudstones. Petrography shows shale-, mudstone and clay rip-up fragments squeezed into primary porosity during eodiagenesis. Sandstone types commonly show low porosities (<10 %) and very low permeabilities (<0.01 mD) mainly due to intense quartz cementation. Scarce authigenic carbonates are euhedral ankerites formed during burial. Secondary porosity resulted mostly from detrital carbonate leaching and limited dissolution of feldspars. Within a zone of up to several meters around faults, porosity is much higher. Feldspars are almost completely altered to illite and locally to kaolinite. Partly dissolved detrital carbonates show Fe-oxide margins around intragranular pores, indicative of Fe-rich compositions formed during telo-diagenesis. Both joints and faults were mapped throughout the quarry and strike, slip and throw of the latter were documented. Cemented fractures prevail around faults and may thus be associated with the structural and diagenetic evolution of the Upper Carboniferous of the Piesberg area. This study is embedded into a larger outcrop analog study of RWTH Aachen in cooperation with Wintershall. Its aim is to unravel the impact of structural diagenesis on the alteration and evolution of pore space and thus reservoir quality. Results can be used to develop datadriven exploration strategies and improved development options for analogous subsurface tight gas

  5. Petrology And Geochemistry Of Barite Mineralisation Around Azara North Central Nigeria

    Directory of Open Access Journals (Sweden)



    Full Text Available ABSTRACT The Azara barite deposits formed parts of Middle Benue Trough which is located in an elongated rift or faulted-bounded mega structural depression trending NE-SW to a length of over 1000 km and a width of 100 km.Petrological and geochemical investigations of Azrara barite deposits were carried out. Eight 8 selected samples of barites were collected from the veins four from known veins V1V3V17 and V 18 and four from new veins VAVBVCand VD werecarried out with the aim of determining their mineralisation potentials using petrographic studies and gravimetric method of analyses. The Petrographic studies of some of the thin section of the samples conducted using a polarizing microscope to determine the contents distributions and textures of the various veins Table 1. The weight percentage composition of barite in the samples are V1 86.39 VC82.61 V1881.48 V3 81.17 V17 79.82 VA78.94 VB76.82 and VD 70.55 respectively. It is deduced from this work that the chemical weathering of the carbonates resulted in two distinct types of barites Barite associated with mainly quartz SiO2 and limonite FeOOH.nH2O as major gangue and barite with siderite Ferrous Carbonate with high amount of Mg ankerite Ca Fe Mg CO3 and Calcite CaCO3. The outcomes were compared with the barite specification of Weigal1937 of 95.00 and were found to be good for making drilling mud for use in the oil industry paints and other chemicals

  6. SHRIMP U-Pb ages of xenotime and monazite from the Spar Lake red bed-associated Cu-Ag deposit, western Montana: Implications for ore genesis (United States)

    Aleinikoff, John N.; Hayes, Timothy S.; Evans, Karl V.; Mazdab, Frank K.; Pillers, Renee M.; Fanning, C. Mark


    Xenotime occurs as epitaxial overgrowths on detrital zircons in the Mesoproterozoic Revett Formation (Belt Supergroup) at the Spar Lake red bed-associated Cu-Ag deposit, western Montana. The deposit formed during diagenesis of Revett strata, where oxidizing metal-bearing hydrothermal fluids encountered a reducing zone. Samples for geochronology were collected from several mineral zones. Xenotime overgrowths (1–30 μm wide) were found in polished thin sections from five ore and near-ore zones (chalcocite-chlorite, bornite-calcite, galena-calcite, chalcopyrite-ankerite, and pyrite-calcite), but not in more distant zones across the region. Thirty-two in situ SHRIMP U-Pb analyses on xenotime overgrowths yield a weighted average of 207Pb/206Pb ages of 1409 ± 8 Ma, interpreted as the time of mineralization. This age is about 40 to 60 m.y. after deposition of the Revett Formation. Six other xenotime overgrowths formed during a younger event at 1304 ± 19 Ma. Several isolated grains of xenotime have 207Pb/206Pb ages in the range of 1.67 to 1.51 Ga, and thus are considered detrital in origin. Trace element data can distinguish Spar Lake xenotimes of different origins. Based on in situ SHRIMP analysis, detrital xenotime has heavy rare earth elements-enriched patterns similar to those of igneous xenotime, whereas xenotime overgrowths of inferred hydrothermal origin have hump-shaped (i.e., middle rare earth elements-enriched) patterns. The two ages of hydrothermal xenotime can be distinguished by slightly different rare earth elements patterns. In addition, 1409 Ma xenotime overgrowths have higher Eu and Gd contents than the 1304 Ma overgrowths. Most xenotime overgrowths from the Spar Lake deposit have elevated As concentrations, further suggesting a genetic relationship between the xenotime formation and Cu-Ag mineralization.

  7. Phase relations and dehydration behaviour of calcareous sediments at P-T conditions of accretionary wedge systems (United States)

    Massonne, H.-J.


    In a recent paper (Eur. J. Mineral. 20), Massonne and Willner (2008) presented P-T pseudosections for common rocks involved in accretionary wedge systems and argued that the dehydration of psammopelitic rocks could be an essential process for the formation of these systems. These authors assumed that this dehydration process leads to softening of the sedimentary cover of oceanic crust during early subduction so that this material can be scraped off the basic crust. Since many accretionary wedge systems contain metamorphosed calcareous sediments it was tested which influence carbonates, ignored by Massonne and Willner (2008), could have on the dehydration behaviour of these sediments. For this purpose, P-T pseudosections were calculated for a calcareous greywacke and a marly limestone in the system Na-Ca-K-Fe-Mn-Mg-Al-Si-Ti-C-O-H with the PERPLEX software package (Connolly, 2005) for the pressure-temperature range 1-25 kbar and 150-450°C. In addition to the thermodynamic data and solid solution models already used by Massonne and Willner (2008), a newly created quaternary (Ca-Mn-Mg-Fe2+) solid solution model was applied to carbonate with calcite structure together with an existing dolomite-ankerite model. Aragonite was considered as a pure phase. The Mn end-member was added to the previously used stilpnomelane model in order to calculate the P-T conditions of garnet formation at high pressure. Along a low geotherm of 10-12°C/km, the dehydration behaviour of a calcareous greywacke resembles that of the previously studied psammopelite. However, the relevant dehydration event (release of about 1 wt% H2O) occurs in the temperature interval 270-330°C and, thus, at temperatures about 30°C higher than in an ordinary psammopelite. The calculated compositions of fluids generated at low geotherms (

  8. Mineralogical and geochemical characteristics of Miocene pelitic sedimentary rocks from the south-western part of the Pannonian Basin System (Croatia: Implications for provenance studies

    Directory of Open Access Journals (Sweden)

    Anita Grizelj


    Full Text Available Fifty-two samples of Miocene pelitic sedimentary rock from outcrops on Medvednica, Moslavačka Gora and Psunj Mts., and boreholes in the Sava Depression and the Požega Sub-depression were investigated. These sediments formed in different marine (with normal and reduced salinity, brackish, and freshwater environments, depending on the development stage of the Pannonian Basin System. Carbonate minerals, clay minerals and quartz are the main constituents of all pelitic sedimentary rocks, except in those from Moslavačka Gora Mt in which carbonate minerals are not present. Feldspars, pyrite, opal-CT, and hematite are present as minor constituents in some rocks. Besides calcite, dependent on the sedimentary environment and diagenetic changes, high-magnesium calcite, aragonite, dolomite and ankerite/Ca-dolomite are also present. Smectite or illite-smectite is the main clay minerals in the samples. Minor constituents, present in almost all samples, are detrital illite and kaolinite. In some samples chlorite is also present in a low amount. Major elements, trace elements and rare earth elements patterns used in provenance analysis show that all analysed samples have a composition similar to the values of the upper continental crust (UCC. The contents of major and trace elements as well as SiO2/Al2O3, K2O/Al2O3, Na2O/K2O, Eu/Eu*, La/Sc, Th/Sc, La/Co Th/Co, Th/Cr, Ce/Ce* and LREE/HREE ratios, show that the analysed pelitic sedimentary rocks were formed by weathering of different types of mostly acidic (silicic, i.e. felsic rocks.

  9. Tourmaline from the Archean G.R.Halli gold deposit, Chitradurga greenstone belt, Dharwar craton (India):Implications for the gold metallogeny

    Institute of Scientific and Technical Information of China (English)

    Susmita Gupta; M. Jayananda; Fareeduddin


    Tourmaline occurs as a minor but important mineral in the alteration zone of the Archean orogenic gold deposit of Guddadarangavanahalli (G.R.Halli) in the Chitradurga greenstone belt of the western Dharwar craton, southern India. It occurs in the distal alteration halo of the G.R.Halli gold deposit as (a) clusters of very fine grained aggregates which form a minor constituent in the matrix of the altered metabasalt (AMB tourmaline) and (b) in quartz-carbonate veins (vein tourmaline). The vein tourmaline, based upon the association of specific carbonate minerals, is further grouped as (i) albite-tourmaline-ankerite-quartz veins (vein-1 tourmaline) and (ii) albite-tourmaline-calcite-quartz veins (vein-2 tourmaline). Both the AMB tourmaline and the vein tourmalines (vein-1 and vein-2) belong to the alkali group and are clas-sified under schorl-dravite series. Tourmalines occurring in the veins are zoned while the AMB tour-malines are unzoned. Mineral chemistry and discrimination diagrams reveal that cores and rims of the vein tourmalines are distinctly different. Core composition of the vein tourmalines is similar to the composition of the AMB tourmaline. The formation of the AMB tourmaline and cores of the vein tour-malines are proposed to be related to the regional D1 deformational event associated with the emplacement of the adjoining ca. 2.61 Ga Chitradurga granite whilst rims of the vein tourmalines vis-à-vis gold mineralization is spatially linked to the juvenile magmatic accretion (2.56e2.50 Ga) east of the studied area in the western part of the eastern Dharwar craton.

  10. Mobilization of Ag, heavy metals and Eu from the waste deposit of the Las Herrerias mine (Almería, SE Spain) (United States)

    Navarro, A.; Cardellach, E.


    We studied the mobility of silver, heavy metals and europium in waste from the Las Herrerías mine in Almería (SE Spain). The most abundant primary mineral phases in the mine wastes are hematite, hydrohematite, barite, quartz, muscovite, anorthite, calcite and phillipsite. The minor phase consisted of primary minerals including ankerite, cinnabar, digenite, magnesite, stannite, siderite and jamesonite, and secondary minerals such as glauberite, szomolnokite, thenardite and uklonscovite. The soils show high concentrations of Ag (mean 21.6 mg kg-1), Ba (mean 2.5%), Fe (mean 114,000 mg kg-1), Sb (mean 342.5 mg kg-1), Pb (mean 1,229.8 mg kg-1), Zn (mean 493 mg kg-1), Mn (mean 4,321.1 mg kg-1), Cd (mean 1.2 mg kg-1) and Eu (mean 4.0 mg kg-1). The column experiments showed mobilization of Ag, Al, Ba, Cu, Cd, Eu, Fe, Mn, Ni, Sb, Pb and Zn, and the inverse modelling showed that the dissolution of hematite, hausmannite, pyrolusite and anglesite can largely account for the mobilization of Fe, Mn and Pb in the leaching experiment. The mobility of silver may be caused by the presence of kongsbergite and chlorargyrite in the waste, while the mobility of Eu seems to be determined by Eu(OH)3, which controls the solubility of Eu in the pH-Eh conditions of the experiments. The mineralogy, pH, Eh and geochemical composition of the mine wastes may explain the possible mobilization of heavy metals and metalloids. However, the absence of contaminants in the groundwater may be caused by the carbonate-rich environment of “host-rocks” that limits their mobility.

  11. Origin of carbonate concretions from mud mounds in the Gulf of Cadiz (SW Iberian Peninsula); Origen de las concreciones carbonatadas de los monticulos de fango en el Golfo de Cadiz (SO Peninsula Iberica)

    Energy Technology Data Exchange (ETDEWEB)

    Rejas, M.; Taberner, C.; Pueyo, J. J.; Giralt, S.; Mata, M. P.; Gibert, J. M. de; Diaz del Rio, V.


    The Gulf of Cadiz displays a number of structures that are associated with fluid circulation (mud volcanoes, mud mounds and pockmarks).This area has been used as natural laboratory for the sedimentological, bio- logical and biogeochemical studies of these environments. Analysis of the associated authigenic carbonates has been widely used as a proxy to yield insights into the circulation and chemical composition of these flu- ids. A study of carbonate concretions from the Iberico, Cornide and Arcos mud mounds in the Diasom Field was undertaken to better understand the origin and type of fluids from which these concretions precipitated. The concretions display varying morphologies, some of which correspond to bioturbation traces. X-ray dif- fractions revealed that these carbonate concretions are mainly composed of dolomite, Fe-rich dolomite, high magnesium calcite (HMC) and ankerite. The δ{sup 1}3 C values of carbonate minerals ranged between -48.3 and-10.9 V-PDB, which suggests that the main processes involved in their genesis are organic matter oxidation, bac- terial sulphate-reduction (BSR) and anaerobic methane oxidation (AOM). The origin of the methane is main- ly thermogenic, and only few concretions yielded δ{sup 1}3C values lower than -40 V-PDB, suggesting oxidation of microbial methane. Fluids involved in the carbonate precipitation are interpreted as being related to gas hydrate destabilisation (δ{sup 18}O fluid-V-SMOW values higher than +2%) and, to a lesser extent, modified seawater enriched in {sup 18}O due to rock-water interaction. Nevertheless, the highest δ{sup 1}8O fluid-V-SMOW values suggest that the influence of other deep-seated fluids due to clay-mineral dehydration cannot be ruled out. (Author)

  12. Mineralogy and geochemistry of Bobov Dol coals, Bulgaria

    Energy Technology Data Exchange (ETDEWEB)

    Vassilev, S.V.; Yossifova, M.G.; Vassileva, C.G. (Bulgarian Academy of Sciences, Sofia (Bulgaria). Inst. of Applied Mineralogy)


    The mineralogy, elemental composition and modes of occurrence of 49 elements in nine composite samples of Bobov Dol high-ash coals were studied by optical microscopy, scanning and transmission electron microscopy, X-ray diffractometry and chemical analysis. The major minerals were quartz, kaolinite, illite, plagioclase and K-feldspar and the minor minerals and phases were pyrite, marcasite, siderite, calcite, dolomite, gypsum, muscovite, montmorillonite and volcanic glass. The accessory minerals include a wide variety of minerals, such as galena, pyrrhotite, magnetite, hematite, goethite, chromite, rutile, anatase, corundum, gibbsite, biotite, chlorite, zircon, enstatite, garnet, jarosite, alunite, barite, polyhalite, aragonite, ankerite, witherite, apatite, halite and sylvite. The modes of occurrence and some genetic peculiarities of the above-mentioned minerals are described. Thirty-three elements occurred in concentrations higher than the respective Clarke values; especially S, Rb, Nb, Hf, Zn, Cu, Pb, Mn, Ti and U. The concentration trends and modes of occurrence of the trace elements are also discussed. In decreasing order of significance, the trace elements probably occur as element-organic compounds, as impurities in the mineral constituents, as major components in the minerals, as major and impurity components in the inorganic amorphous constituents, and in the fluid constituents. The Bobov Dol coals have undergone complex syngetenic, diagenetic and epigenetic mineralization processes associated with hydrothermal and volcanic activities. These processes were also accompanied by intensive tectonic movements, and possibly, by a later change from continental to marine sedimentation in the area after burial of the coal. 38 refs., 1 fig., 6 tabs., 5 plates.

  13. Mineralogy of the sulfate-sulfide mineralizations at the Garus District; NW of Iran Mineralogía de las mineralizaciones sulfato-sulfurosas del Distrito Garus, NW de Irán

    Directory of Open Access Journals (Sweden)

    Bahram Vusuq


    Full Text Available There are some vein type sediment hosted sulfate-sulfide mineralizations in Garus district, NW of Iran. They occur in a (shale host rock of Precambrian age and they show evidence of some deformation. The field, microscopic, XRD and SEM-EDS techniques were used in this investigation. Mineralogical, the veins are composed of barite (Sulfate phase, galena, chalcopyrite, covellite (main sulfide minerals and dolomite, ankerite, quartz, cerussite, anglesites’, calcite, goethite as gangues. Microscopic and XRD investigations indicated the presence of more than 15 minerals at Garus. The SEM-EDS assessments show some probable minor phases present in the investigated galenas. Field and microscopic investigations show barite formed earlier than the sulphide mineralization. The objective of this research is to reveal the new horizons in the mineral exploration in NW of Iran.Existen sedimentos que albergan venas con mineralizaciones de sulfatos y sulfuros en el distrito Garus, en el noroeste de Irán. Estas mineralizaciones ocurren en rocas calizas (esquistos precámbricas con evidencias de deformación. Se utilizaron en este estudio datos de campo, microscópicos, DRX y técnicas de SEM_EDS. Mineralógicamente las venas están compuestas de barita (fase de sulfatos, galena, calcopirita, covelina (principales sulfuros y dolomita, ankerita, cuarzo, cerustira, anglesita, calcita y goethita como ganga. La microscopía y la DRX indicaron más de 15 minerales en el distrito de Garus. Las valoraciones de SEM-EDS muestran probables fases menores en las galenas estudiadas. Las investigaciones de campo y a nivel microscópico muestran que las baritas se formaron antes que la mineralización de sulfuros. El objetivo de este artículo es revelar nuevos horizontes de exploración para la exploración minera en el NW de Irán.

  14. River water quality in weathered limestone: A case study in upper Mahanadi basin, India

    Indian Academy of Sciences (India)

    B K Panigrahy; B C Raymahashay


    Stromatolitic limestone and calcareous shale belonging to Chattisgarh Supergroup of Proterozoic age dominate the upper part of the Mahanadi river basin.X-ray diffractogram (XRD)of limestone rocks show presence of a significant amount of calcite,dolomite and ankerite.Shales of various colours contain calcite and dolomite.It is observed that congruent dissolution of carbonate minerals in the Charmuria pure limestone has given rise to a typical karst topography.On the other hand, limestones are also seen to support red and black soil pro files.This indicates that the limestone bedrock undergoes a parallel incongruent weathering,which leaves a residue of decomposed rock. The XRD analyses reveal that the limestone soils thus formed contain an assemblage of quartz,clays and Fe-oxides.It is likely that the silicate component trapped during deposition of the stromatolitic limestone weathers incongruently resulting in diverse soil profiles.Carbonate and silicate mineral weathering schemes have been worked out to explain the soil formation,fixation of Al in clay minerals, and Fe in goethite.The water quality parameters such as Ca, Mg and HCO3 in the river water suggest under saturation with respect to calcite and dolomite.The mineral stability diagrams indicate that kaolinite and Ca-smectite are stable in the river water environment,hence they occur in suspended sediments and soils.The dominant influence of carbonate weathering on the water quality is observed even in the downstream part of the river outside the limestone terrain.

  15. Mineralogical and chemical analyses of ancient glass beads from Taiwan and their implications (United States)

    Liou, Y. S.; Liu, Y. C.


    Large numbers of monochrome glass beads with different colors, shapes, and stylistics excavated from the archaeological sites of Taiwan, which were dated mainly from the 2nd century AD to the early Historical Period of Taiwan. Archaeologically, these glass beads were more prevalent in eastern and northern Taiwan and were generally believed to be non-native, as well as were brought into Taiwan through the maritime exchange and/or trade activities between Taiwan and Southeast Asia/China since the Neolithic Age. Nevertheless, ancient glass beads have been little studies in Taiwan, aspects of these glass beads are not well detailed. In this work, non-destructive micro-Raman spectroscopy and μXRF are used in combination to examine 56 ancient glass beads excavated from six archaeological sites, eastern Taiwan, to unravel the mineralogical and chemical compositions and to help decipher the raw materials used and the provenance of beads. Micro-Raman measurements indicate the presence of hematite, zincite, siderite, sphalerite, lead tin yellow type II, adularia, chalcedony, anatase, rutite, ankerite, graphite, calcite, etc. Hematite, zincite, siderite, sphalerite, lead tin yellow type II, and rutile were found to be colorants/opacifiers. Among these crystalline phases, lead tin yellow type II was first detected in the ancient glass bead unearthed from Taiwan, which is accordant with results of chemical analysis. The chemical results obtained by μXRF show SiO2, Al2O3, Na2O, K2O, MgO, CaO, and PbO as the most abundant oxides. It is found that Na2O, Na2O, K2O, Al2O3, and MgO are the main/minor fluxes. According to the results, the three most frequent types are mineral soda alumina glass, soda plant ash glass, and lead silicate glass. The provenance of ancient beads unearthed from archaeological sites of Taiwan is possibility of multiple sources.

  16. Diagenesis and reservoir quality of the Lower Cretaceous Quantou Formation tight sandstones in the southern Songliao Basin, China (United States)

    Xi, Kelai; Cao, Yingchang; Jahren, Jens; Zhu, Rukai; Bjørlykke, Knut; Haile, Beyene Girma; Zheng, Lijing; Hellevang, Helge


    The Lower Cretaceous Quantou Formation in the southern Songliao Basin is the typical tight oil sandstone in China. For effective exploration, appraisal and production from such a tight oil sandstone, the diagenesis and reservoir quality must be thoroughly studied first. The tight oil sandstone has been examined by a variety of methods, including core and thin section observation, XRD, SEM, CL, fluorescence, electron probing analysis, fluid inclusion and isotope testing and quantitative determination of reservoir properties. The sandstones are mostly lithic arkoses and feldspathic litharenites with fine to medium grain size and moderate to good sorting. The sandstones are dominated by feldspar, quartz, and volcanic rock fragments showing various stages of disintegration. The reservoir properties are quite poor, with low porosity (average 8.54%) and permeability (average 0.493 mD), small pore-throat radius (average 0.206 μm) and high displacement pressure (mostly higher than 1 MPa). The tight sandstone reservoirs have undergone significant diagenetic alterations such as compaction, feldspar dissolution, quartz cementation, carbonate cementation (mainly ferrocalcite and ankerite) and clay mineral alteration. As to the onset time, the oil emplacement was prior to the carbonate cementation but posterior to the quartz cementation and feldspar dissolution. The smectite to illite reaction and pressure solution at stylolites provide a most important silica sources for quartz cementation. Carbonate cements increase towards interbedded mudstones. Mechanical compaction has played a more important role than cementation in destroying the reservoir quality of the K1q4 sandstone reservoirs. Mixed-layer illite/smectite and illite reduced the porosity and permeability significantly, while chlorite preserved the porosity and permeability since it tends to be oil wet so that later carbonate cementation can be inhibited to some extent. It is likely that the oil emplacement occurred

  17. Oscillation of mineral compositions in Core SG-1b, western Qaidam Basin, NE Tibetan Plateau (United States)

    Fang, Xiaomin; Li, Minghui; Wang, Zhengrong; Wang, Jiuyi; Li, Jiao; Liu, Xiaoming; Zan, Jinbo


    Uplift of the Tibetan Plateau since the Late Miocene has greatly affected the nature of sediments deposited in the Qaidam Basin. However, due to the scarcity of continuously dated sediment records, we know little about how minerals responded to this uplift. In order to understand this response, we here present results from the high-resolution mineral profile from a borehole (7.3–1.6 Ma) in the Basin, which shows systematic oscillations of various evaporite and clay minerals that can be linked to the variation of regional climate and tectonic history. In particular, x-ray diffraction (XRD) analyses show that carbonate minerals consist mainly of calcite and aragonite, with minor ankerite and dolomite. Evaporates consist of gypsum, celesite and halite. Clay minerals are principally Fe-Mg illite, mixed layers of illite/smectite and chlorite, with minor kaolinite and smectite. Following implications can be drawn from the oscillations of these minerals phases: (a) the paleolake was brackish with high salinity after 7.3 Ma, while an abrupt change in the chemical composition of paleolake water (e.g. Mg/Ca ratio, SO42‑ concentration, salinity) occurred at 3.3 Ma; (b) the three changes at ~6.0 Ma, 4.5–4.1 Ma and 3.3 Ma were in response to rapid erosions/uplift of the basin; (c) pore water or fluid was Fe/Mg-rich in 7.3–6.0 Ma, Mg-rich in 6.0–4.5 Ma, and K-rich in 4.1–1.6 Ma and (d) evaporation rates were high, but weaker than today’s.

  18. Forms of Iron in the Phosphorites of Abu—Tartur Area,Egypt

    Institute of Scientific and Technical Information of China (English)



    The Campanian-Maastrichtian phosphatic deposits in Egypt,called the Duwi Forma-tion,comprise a part of the extensive Middle East to North African phosphogenic province of Late Cretaceous to Paleogene age.The province holds the greatest accumulation of phosphorites in the geological history,possibly in excess of 70 billion metric tons.The phosphate resources in Egypt alone exceed 3 billion metric tons.Two-third of these three billions occur only in the Abu-Tartur area.Among the phosphorite deposits in Egypt,the phosphorites of the Abu-Tartur area are characterized by high contents of iron ranging from 3% to 7% with an average of 5%.The detailed mineralogical and geochemical studies on the Abu-Tartur phosphorites revealed that iron is found in the form of pyrite,ankerite,clay minerals,microinclusions,and iron oxide.Pyrite,which is the major fraction,occurs as filling cement and partial to complete teplacement of phosphatic grains and confined to the fresh phosphorites while iron oxide occurs as cryp-tocrystalline aggregates of red to brown particles and is confined to the weathered outcrops.Ex-clusive relations between pyrite in the fresh phosphorite samples inside the Abu-Tartur mine and iron oxide in the equivalent horizon of the weathered exposure indicated that iron oxide was formed by the oxidation of pyrite as a result of weathering.All of these forms harm the quality of ore,manufacturing processes,and the produced phosphoric acid and fertilizers.

  19. Mineral matter in coals and their reactions during coking

    Energy Technology Data Exchange (ETDEWEB)

    Grigore, Mihaela; French, David [The Commonwealth Scientific and Industrial Research Organisation (CSIRO) - Energy Technology, Lucas Heights, NSW 2234 (Australia); Sakurovs, Richard [The Commonwealth Scientific and Industrial Research Organisation (CSIRO) - Energy Technology, Newcastle, NSW 2300 (Australia); Sahajwalla, Veena [School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052 (Australia)


    Degradation of coke in the blast furnace is influenced by its inherent mineral matter, the formation of which is itself dependent upon the nature of the coal mineral matter. To date few studies have been made of coke mineralogy and its relationship to the mineralogy of the parent coal. In this study the effect of carbonisation on coal mineral matter has been investigated by a detailed quantitative mineralogical examination of nine cokes and their parent coals. The quantitative analysis was performed on X-ray diffraction patterns of the mineral matter of cokes and coals, using SIROQUANT {sup trademark}. Coke mineralogy and its composition varied strongly between cokes, more strongly than variations in elemental composition of the ash. The mineral matter in the studied cokes consisted of crystalline mineral phases and also significant levels of amorphous phase (ranging between 44 and 75%). Decomposition of clays such as kaolinite, montmorillonite, illite and chamosite produced the amorphous phase and some of the crystalline mineral phases such as mullite, {gamma}-alumina, spinel, cristobalite and leucite. The type of association of mineral matter in coals had an important role in how the clays decomposed. For example, association of kaolinite with silica-bearing minerals in intimate intermixture favoured formation of mullite over {gamma}-alumina. Akermanite and diopside result from reaction of kaolinite with associated calcium bearing minerals (calcite, dolomite or ankerite). Quartz, fluorapatite and the three polymorphs of TiO{sub 2} (anatase, brookite and rutile) were the coal minerals that were least affected during carbonisation, as they were also found in the cokes, yet even they were affected in some cases. (author)

  20. Palaeoredox indicators from the organic-rich Messinian early post-evaporitic deposits of the Apennines (Central Italy) (United States)

    Sampalmieri, G.; Iadanza, A.; Cipollari, P.; Cosentino, D.; Lo Mastro, S.


    barren laminated sediments, hasn't been thoroughly clarified yet. The aim of the present study, dealing with messinian p-ev1 deposits from Marche and Maiella successions, is to provide more details in the definition of the environment developed during the early post-evaporitic phase. Since the lamination and the absence of benthic fauna suggest the occurrence of anoxic conditions, the following indirect proxies for the detection of organic matter have been investigated: 1) sedimentary fabric and microfacies; 2) framboidal pyrite size distribution; 3) natural radioactivity (authigenic uranium values, Th/U ratios). Natural radioactivity has been achieved through gamma spectrometry, with field and laboratory specific techniques. In the Maccarone section (Marche region), p-ev1 deposits are constituted by: barren greyish shales; laminated black shales interbedded with calcitic and ankeritic horizons; thin intercalations of sandstones. Organic-matter and framboidal pyrite commonly occur. Size analysis of framboids populations yielded a mean diameter of 4÷8 m, typical of disaerobic facies. Microfacies analysis yielded also the presence of crystals aggregates of barite, up to 50 m in size, and of isolated detrital (silicilastic) crystals. Without considering γ-ray values of the volcaniclastic layer (52-65 Cps) occurring within the p-ev1 interval, black shales horizons revealed the maximum natural radioactivity (NRD of about 50 Cps) recorded inthe studied section. Lower γ-activity characterizes the calcitic layers (i.e. "Colombacci") and the ankerites. Field NRD spectra acquired on different lithologies, showed variable contributions of 238U, 232Th and 40K. Both the blue-greyish shales and the black shales are characterized by total NRD related to the three main radioelements: 40K is associated to abundant 238U content (Thppm/Uppm 1). The 238U content is primarily referable to processes of organic matter enrichment (authigenic uranium) and secondarily to the input of


    Institute of Scientific and Technical Information of China (English)

    蒋宜勤; 文华国; 祁利祺; 张锡新; 李云


    二叠系风城组为准噶尔盆地乌尔禾地区重要的勘探层系,也是成因非常特殊的深湖相含盐火山-沉积建造.通过14口钻井岩心观察,296片薄片鉴定,30块扫描电镜和28件X衍射等分析技术手段,较为详细地研究了风城组盐类矿物及伴生矿物的各项特征,识别出硅硼钠石、碳酸钠钙石、白云石等主要盐类矿物和硬石膏、石膏、玉髓、黄铁矿和蒙脱石等伴生矿物,确定风城组深湖相含盐火山-沉积建造与同期相间发生的火山喷发和湖底热液喷流活动有关,其成因可与酒西盆地下沟组湖相喷流岩和东非裂谷坦噶尼喀湖现代深湖底热液喷流沉积作用相类比,提出“深水湖盆热液喷流含盐火山-沉积建造模式”.%In the Urho area of Junggar Basin,the Permian Fengcheng Formation is an important exploration stratam characterized by very special deep lake salt-bearing volcanic-sedimentary for-mation. Based on the core observation,thin section identification,scanning electron microscopy, X-ray diffraction and chemical analysis,a more detailed study was made on the characteristics of the salt minerals and their associated minerals in the Fengcheng Formation. Salt minerals in the Fengcheng Formation consist of reedmergnerite,shortite, trona,ankerite and associated with an-hydrite, gypsum,chalcedony,pyrite and smectite. It was indicated that the Fengcheng Formation were related to the interphase volcanic eruption and lake hydrothermal exhalative activities in the same period. Their characters and genesis can be compared with the lacustrine exhalative rocks of Xiagou Formation in Jiuxi Basin and the modern deep lacustrine hydrothermal exhalative deposi-tion in Tanga Nika Lake, East African rift Valley. Accordingly,a hydrothermal exhalative salt-bearing volcano-sedimentary mode in the deep lake basin was proposed in the paper.

  2. Thermodynamic Simulation of Carbonate Cements-Water-Carbon Dioxide Equilibrium in Sandstone for Prediction of Precipitation/Dissolution of Carbonate Cements. (United States)

    Duan, Yiping; Feng, Mingshi; Zhong, Xinyan; Shang, Ruishu; Huang, Lihong


    Carbonate cements, such as calcite, dolomite, ferrocalcite and ankerite, play important roles in the formation of pores in sandstones: precipitation of carbonate cements modifies pores and inhibits compaction, while dissolution creates secondary pores. This work proposed a precipitation-dissolution model for carbonate cements-CO2-H2O system by means of ion equilibrium concentration ([M2+], M = Ca, Mg, Fe or Mn) with different factors, such as temperature, depth, pH, [Formula: see text], variable rock composition and overpressure. Precipitation-dissolution reaction routes were also analyzed by minimization of the total Gibbs free energy (ΔG). Δ[M2+], the variation of [Ca2+], [Fe2+], [Mg2+] or [Mn2+] for every 100 m of burial depths, is used to predict precipitation or dissolution. The calculation results indicate that the increasing temperature results in decrease of equilibrium constant of reactions, while the increasing pressure results in a relatively smaller increase of equilibrium constant; As a result, with increasing burial depth, which brings about increase of both temperature and pressure, carbonate cements dissolve firstly and produces the maximal dissolved amounts, and then precipitation happens with further increasing depth; For example, calcite is dissolving from 0.0 km to 3.0 km with a maximal value of [Ca2+] at depth of 0.8 km, and then precipitates with depth deeper than 3.0 km. Meanwhile, with an increasing CO2 mole fraction in the gaseous phase from 0.1% to 10.0% in carbonate systems, the aqueous concentration of metal ions increases, e.g., dissolved amount of CaFe0.7Mg0.3(CO3)2 increases and reaches maximum of 1.78 mmol·L-1 and 8.26 mmol·L-1 at burial depth of 0.7 km with CO2 mole fraction of 0.1% and 10.0%, respectively. For the influence of overpressure in the calcite system, with overpressure ranging from 36 MPa to 83 MPa, pH reaches a minimum of 6.8 at overpressure of 51 MPa; meanwhile, Δ[Ca2+] increases slightly from -2.24 mmol·L-1 to

  3. In situ Sr isotope analysis of apatite by LA-MC-ICPMS: constraints on the evolution of ore fluids of the Yinachang Fe-Cu-REE deposit, Southwest China (United States)

    Zhao, Xin-Fu; Zhou, Mei-Fu; Gao, Jian-Feng; Li, Xiao-Chun; Li, Jian-Wei


    Apatite is a ubiquitous accessory mineral in a variety of rocks and hydrothermal ores. Strontium isotopes of apatite are well known to retain petrogenetic information and have been widely used to investigate the origin of igneous rocks, but such attempts have rarely been made to constrain ore-forming processes of hydrothermal systems. We here report in situ LA-MC-ICPMS Sr isotope data of apatite from the ~1660-Ma Yinachang Fe-Cu-REE deposit, Southwest China. The formation of this deposit was coeval to the emplacement of regionally distributed doleritic intrusions within a continental-rift setting. The deposit has a paragenetic sequence consisting of sodic alteration (stage I), magnetite mineralization (stage II), Cu sulfide and REE mineralization (stage III), and final barren calcite veining (stage IV). The stage II and III assemblages contain abundant apatite, allowing to investigate the temporal evolution of the Sr isotopic composition of the ore fluids. Apatite of stage II (Apt II) is associated with fluorite, magnetite, and siderite, whereas apatite from stage III (Apt III) occurs intimately intergrown with ankerite and Cu sulfides. Apt II has 87Sr/86Sr ratios varying from 0.70377 to 0.71074, broadly compatible with the coeval doleritic intrusions (0.70592 to 0.70692), indicating that ore-forming fluids responsible for stage II magnetite mineralization were largely equilibrated with mantle-derived mafic rocks. In contrast, Apt III has distinctly higher 87Sr/86Sr ratios from 0.71021 to 0.72114, which are interpreted to reflect external radiogenic Sr, likely derived from the Paleoproterozoic strata. Some Apt III crystals have undergone extensive metasomatism indicated by abundant monazite inclusions. The metasomatized apatite has much higher 87Sr/86Sr ratios up to 0.73721, which is consistent with bulk-rock Rb-Sr isotope analyses of Cu ores with 87Sr/86Sri from 0.71906 to 0.74632. The elevated 87Sr/86Sr values of metasomatized apatite and bulk Cu ores indicate

  4. Reactive Transport Models with Geomechanics to Mitigate Risks of CO2 Utilization and Storage

    Energy Technology Data Exchange (ETDEWEB)

    Deo, Milind [Univ. of Utah, Salt Lake City, UT (United States); Huang, Hai [Univ. of Utah, Salt Lake City, UT (United States); Kweon, Hyukmin [Univ. of Utah, Salt Lake City, UT (United States); Guo, Luanjing [Univ. of Utah, Salt Lake City, UT (United States)


    Reactivity of carbon dioxide (CO2), rocks and brine is important in a number of practical situations in carbon dioxide sequestration. Injectivity of CO2 will be affected by near wellbore dissolution or precipitation. Natural fractures or faults containing specific minerals may reactivate leading to induced seismicity. In this project, we first examined if the reactions between CO2, brine and rocks affect the nature of the porous medium and properties including petrophysical properties in the timeframe of the injection operations. This was done by carrying out experiments at sequestration conditions (2000 psi for corefloods and 2400 psi for batch experiments, and 600°C) with three different types of rocks – sandstone, limestone and dolomite. Experiments were performed in batch mode and corefloods were conducted over a two-week period. Batch experiments were performed with samples of differing surface area to understand the impact of surface area on overall reaction rates. Toughreact, a reactive transport model was used to interpret and understand the experimental results. The role of iron in dissolution and precipitation reactions was observed to be significant. Iron containing minerals – siderite and ankerite dissolved resulting in changes in porosity and permeability. Corefloods and batch experiments revealed similar patterns. With the right cationic balance, there is a possibility of precipitation of iron bearing carbonates. The results indicate that during injection operations mineralogical changes may lead to injectivity enhancements near the wellbore and petrophysical changes elsewhere in the system. Limestone and dolomite cores showed consistent dissolution at the entrance of the core. The dissolution led to formation of wormholes and interconnected dissolution zones. Results indicate that near wellbore dissolution in these rock-types may lead to rock failure. Micro-CT images of the cores before and after the experiments

  5. Geology and geochemistry of the shear-hosted Julie gold deposit, NW Ghana (United States)

    Amponsah, Prince Ofori; Salvi, Stefano; Béziat, Didier; Siebenaller, Luc; Baratoux, Lenka; Jessell, Mark W.


    The Leo Man Craton in West Africa is host to numerous economic gold deposits. If some regions, such as the SW of Ghana, are well known for world-class mineralizations and have been extensively studied, gold occurrences elsewhere in the craton have been discovered only in the last half a century or so, and very little is known about them. The Julie gold deposit, located in the Paleoproterozoic Birimian terrane of NW Ghana, is one such case. This deposit is hosted in a series of granitoid intrusives of TTG composition, and consists of a network of deformed, boudinaged quartz lodes (A-type veins) contained within an early DJ1 E-W trending shear zone with dextral characteristics. A conjugate set of veins (C-type) perpendicular to the A-type veins contains low grade mineralization. The main ore zone defines a lenticular corridor about 20-50 m in width and about 3.5 km along strike, trending E-W and dipping between 30 and 60°N. The corridor is strongly altered, by an assemblage of sericite + quartz + ankerite + calcite + tourmaline + pyrite. This is surrounded by a second alteration assemblage, consisting of albite + sericite + calcite + chlorite + pyrite + rutile, which marks a lateral alteration that fades into the unaltered rock. Mass balance calculations show that during alteration overall mass was conserved and elemental transfer is generally consistent with sulfidation, sericitization and carbonatization of the host TTG. Gold is closely associated with pyrite, which occurs as disseminated grains in the veins and in the host rock, within the mineralized corridor. SEM imagery and LA-ICP-MS analyses of pyrites indicate that in A-type veins gold is associated with bismuth, tellurium, lead and silver, while in C-type veins it is mostly associated with silver. Pyrites in A-type veins contain gold as inclusions and as free gold on its edges and fractures, while pyrites from C-type veins contains mostly free gold. Primary and pseudosecondary fluid inclusions from both

  6. Geochemical and mineralogical characterization of sulfur and iron in coal waste rock, Elk Valley, British Columbia, Canada. (United States)

    Essilfie-Dughan, Joseph; Hendry, M Jim; Dynes, James J; Hu, Yongfeng; Biswas, Ashis; Lee Barbour, S; Day, S


    Exposure of coal waste rock to atmospheric oxygen can result in the oxidation of sulfide minerals and the release of sulfate (SO4(2-)) and associated trace elements (e.g., Se, As, Cd, and Zn) to groundwaters and surface waters. Similarly, reduced iron minerals such as siderite, ankerite, and the sulfide, pyrite, present in the waste rock can also undergo oxidation, resulting in the formation of iron oxyhydroxides that can adsorb trace elements released from the oxidation of the sulfide minerals. Characterization and quantification of the distribution of sulfide and iron minerals, their oxidation products, as well as leaching rates are critical to assessing present-day and future impacts of SO4(2-) and associated trace elements on receiving waters. Synchrotron-based X-ray absorption near edge spectroscopic analysis of coal waste rock samples from the Elk Valley, British Columbia showed Fe present as pyrite (mean 6.0%), siderite (mean 44.3%), goethite (mean 35.4%), and lepidocrocite (mean 14.3%) with S present as sulfide (mean 26.9%), organic S (mean 58.7%), and SO4(2-) (mean 14.4%). Squeezed porewater samples from dump solids yielded mean concentrations of 0.28mg/L Fe and 1246mg/L SO4(2-). Geochemical modeling showed the porewaters in the dumps to be supersaturated with respect to Fe oxyhydroxides and undersaturated with respect to gypsum, consistent with solids analyses. Coupling Fe and S mineralogical data with long-term water quality and quantity measurements from the base of one dump suggest about 10% of the sulfides (which represent 2% of total S) in the dump were oxidized over the past 30years. The S from these oxidized sulfides was released to the receiving surface water as SO4(2-) and the majority of the Fe precipitated as secondary Fe oxyhydroxides (only 3.0×10(-5)% of the Fe was released to the receiving waters over the past 30years). Although the data suggest that the leaching of SO4(2-) from the waste rock dump could continue for about 300years

  7. Origin of alternate amphibole and quartz rich bands in amphibole bearing quartzite from North Khetri Copper Belt, Rajasthan, India (United States)

    Paul, J.; Baidya, A. S.; Pal, D. D. C.


    form new carbonate minerals which are also common in this area in the form of ankerite/dolomite veins. The probable reaction will be [(1.5+x)Fe2+ + 0.5Fe3+ + 2OH-]fluid + [(3.5-x)Mg2+ +3Ca2++ 2CO32-]cb + [7Si4+ + 2Al3+ + 22O2-]qz-ab unit = [Ca2Mg2.5Fe2+1.5Fe3+0.5Al1.5Si7O22(OH)2]amp + [Ca(Mg1-x, Fe2+x)(CO3)2]ank/dol veins

  8. Injection of CO2 with H2S and SO2 and Subsequent Mineral Trapping in Sandstone-Shale Formation

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Tianfu; Apps, John A.; Pruess, Karsten; Yamamoto, Hajime


    Carbon dioxide (CO{sub 2}) injection into deep geologic formations can potentially reduce atmospheric emissions of greenhouse gases. Sequestering less-pure CO{sub 2} waste streams (containing H{sub 2}S and/or SO{sub 2}) would be less expensive or would require less energy than separating CO{sub 2} from flue gas or a coal gasification process. The long-term interaction of these injected acid gases with shale-confining layers of a sandstone injection zone has not been well investigated. We therefore have developed a conceptual model of injection of CO{sub 2} with H{sub 2}S and/or SO{sub 2} into a sandstone-shale sequence, using hydrogeologic properties and mineral compositions commonly encountered in Gulf Coast sediments of the United States. We have performed numerical simulations of a 1-D radial well region considering sandstone alone and a 2-D model using a sandstone-shale sequence under acid-gas injection conditions. Results indicate that shale plays a limited role in mineral alteration and sequestration of gases within a sandstone horizon for short time periods (10,000 years in present simulations). The co-injection of SO{sub 2} results in different pH distribution, mineral alteration patterns, and CO{sub 2} mineral sequestration than the co-injection of H{sub 2}S or injection of CO{sub 2} alone. Simulations generate a zonal distribution of mineral alteration and formation of carbon and sulfur trapping minerals that depends on the pH distribution. The co-injection of SO{sub 2} results in a larger and stronger acidified zone close to the well. Precipitation of carbon trapping minerals occurs within the higher pH regions beyond the acidified zones. In contrast, sulfur trapping minerals are stable at low pH ranges (below 5) within the front of the acidified zone. Corrosion and well abandonment due to the co-injection of SO{sub 2} could be important issues. Significant CO{sub 2} is sequestered in ankerite and dawsonite, and some in siderite. The CO{sub 2} mineral

  9. On the potential for CO2 mineral storage in continental flood basalts – PHREEQC batch- and 1D diffusion–reaction simulations

    Directory of Open Access Journals (Sweden)

    Van Pham Thi


    Full Text Available Abstract Continental flood basalts (CFB are considered as potential CO2 storage sites because of their high reactivity and abundant divalent metal ions that can potentially trap carbon for geological timescales. Moreover, laterally extensive CFB are found in many place in the world within reasonable distances from major CO2 point emission sources. Based on the mineral and glass composition of the Columbia River Basalt (CRB we estimated the potential of CFB to store CO2 in secondary carbonates. We simulated the system using kinetic dependent dissolution of primary basalt-minerals (pyroxene, feldspar and glass and the local equilibrium assumption for secondary phases (weathering products. The simulations were divided into closed-system batch simulations at a constant CO2 pressure of 100 bar with sensitivity studies of temperature and reactive surface area, an evaluation of the reactivity of H2O in scCO2, and finally 1D reactive diffusion simulations giving reactivity at CO2 pressures varying from 0 to 100 bar. Although the uncertainty in reactive surface area and corresponding reaction rates are large, we have estimated the potential for CO2 mineral storage and identified factors that control the maximum extent of carbonation. The simulations showed that formation of carbonates from basalt at 40 C may be limited to the formation of siderite and possibly FeMg carbonates. Calcium was largely consumed by zeolite and oxide instead of forming carbonates. At higher temperatures (60 – 100 C, magnesite is suggested to form together with siderite and ankerite. The maximum potential of CO2 stored as solid carbonates, if CO2 is supplied to the reactions unlimited, is shown to depend on the availability of pore space as the hydration and carbonation reactions increase the solid volume and clog the pore space. For systems such as in the scCO2 phase with limited amount of water, the total carbonation potential is limited by the amount of water present

  10. The South African industry use of Mössbauer spectroscopy to solve operational problems (United States)

    Waanders, Frans B.; Mulaba-Bafubiandi, Antoinne F.; Lodya, Lonzeche


    South Africa is a country that is very rich in mineral resources but the use of Mössbauer spectroscopy to solve operational industrial problems is however very limited. In the Bushveld Igneous Complex the main minerals extracted from the ore are the platinum group metals and chromium, but secondary recovery of base metals such as nickel, copper and cobalt forms an integral part of the process. Losses of nickel in the slag can amount to about 4 % and subsequent a slag cleaning furnace is used to reduce the loss to less than 0.5 % nickel oxide. The Fe2+/Fe3+ ratio and mineralogy was used to determine the partial oxygen pressure in the furnaces and also the efficiency of the nickel recovery. From the Mössbauer results, augmented with XRD, SEM, EMP-WDX and MLA analyses, optimum conditions were determined to ensure minimum metal losses. The use of Mössbauer spectroscopy in the coal industry, to investigate mineral changes that occur during its use, is also of importance. The main minerals present in coal were determined with the aid of various techniques, such as Mössbauer, XRD, SEM and HR-TEM, with the major iron minerals found to be pyrite, illite, ankerite and jarosite. A large quantity of coal is used to produce syngas via gasification plants for the production of synthetic fuels. The change of the mineral matter during gasification was studied and the changes occurring during the gasification process were followed. The syngas produced, is further treated by means of the Fischer-Tropsch process where an iron catalyst is incorporated in the process. The usefulness and fouling of the catalyst is being studied with the aid of Mössbauer spectroscopy. The calibration of equipment to determine work hardening in mining equipment was also investigated and found to be a useful tool in industry. From the above few examples it is evident that, although used on a limited base, Mössbauer spectroscopy, augmented by various other spectroscopic tools, still ensures optimal

  11. Agricolaite, a new mineral of uranium from Jáchymov, Czech Republic (United States)

    Skála, Roman; Ondruš, Petr; Veselovský, František; Císařová, Ivana; Hloušek, Jan


    The new mineral agricolaite, a potassium uranyl carbonate with ideal formula K4(UO2)(CO3)3, occurs in vugs of ankerite gangue in gneisses in the abandoned Giftkiesstollen adit at Jáchymov, Czech Republic. The name is after Georgius Agricola (1494-1555), German scholar and scientist. Agricolaite occurs as isolated equant irregular translucent grains to 0.3 mm with yellow color, pale yellow streak, and vitreous luster. It is brittle with uneven fracture and displays neither cleavage nor parting. Agricolaite is non-fluorescent. Mohs hardness is ~4. It is associated with aragonite, brochantite, posnjakite, malachite, rutherfordine, and "pseudo-voglite". Experimental density is higher than 3.3, Dcalc is 3.531 g. cm-3. The mineral is monoclinic, space group C2/ c, with a 10.2380(2), b 9.1930(2), c 12.2110(3) Å, β 95.108(2)°, V 1144.71(4) Å3, Z = 4. The strongest lines in the powder X-ray diffraction pattern are d( I)( hkl): 6.061(55)(002), 5.087(57)(200), 3.740(100)(202), 3.393(43)(113), 2.281(52)(402). Average composition based on ten electron microprobe analyses corresponds to (in wt.%) UO3 48.53, K2O 31.49, CO2(calc) 22.04 which gives the empirical formula K3.98(UO2)1.01(CO3)3.00. The crystal structure was solved from single-crystal X-ray diffraction data and refined to R 1 = 0.0184 on the basis of the 1,308 unique reflections with F o > 4 σF o. The structure of agricolaite is identical to that of synthetic K4(UO2)(CO3)3 and consists of separate UO2(CO3)3 groups organized into layers parallel to (100) and two crystallographically non-equivalent sites occupied by K+ cations. Both the mineral and its name were approved by the IMA-CNMNC.

  12. Chemical and mineralogical data of the metalliferous mineralization from S. Carlo mine (Peloritani mts, Ne Sicily, Italy

    Directory of Open Access Journals (Sweden)

    Pisacane, G


    Full Text Available The mineralization processes in the Peloritani Belt (Southern Sector of the Calabria- Peloritani Arc prevalently developed during the Variscan orogenesis producing Pb, Zn, Fe, As, Sb, Cu, Ag, W, etc. polymetalliferous ore-bearing horizons. This paper focuses on the polymetalliferous mineralization recognised in the ancient S. Carlo Mine, which has already been subject of some studies and is part of an important discordant vein deposits system that are widespread in the Mandanici Unit (MaU. This Unit is characterized by a Variscan low-P, polyphasic and plurifacial metamorphic basement, exhibiting a prograde zoning, from chlorite zone of greenschist facies to oligoclase-almandine zone of amphibolite facies. The Variscan main foliation (Fv2 is irregularly cut by mineralized veins of decimetric to metric width. They are also perpendicular to the Alpine mylonitic shear zones of metric thickness developing along the sub-horizontal tectonic contacts between the tectono-stratigraphic units. These vein deposits formed along late-Alpine systems of fractures and faults, after Peloritani nappe emplacement. Minerographic study reveals a metalliferous mineral association mainly composed of tetrahedrite associated with, in order of decreasing abundance, chalcopyrite, bournonite, pentlandite, stromeyerite, arsenopyrite, scheelite, galena, sphalerite, pyrite, bismuthinite, boulangerite, jamesonite, covellite, bornite and argentite. Quartz, siderite and ankerite among non-metalliferous minerals are predominant. This work has been supported by mineralogical studies and chemical analyses carried out by Atomic Absorption and Inductively Coupled Plasma-Mass Spectrometry on powdered and separated samples of minerals. Geochemical data (major and trace elements have allowed a detailed characterization of the minerals. They have revealed that the most significant minerals with Au contents around 1 ppm are tetrahedrite, sphalerite, chalcopyrite and bournonite. The

  13. An integrated geochemical, geophysical and mineralogical study of river sediments in alpine area and soil samples near steel plant, in Austria (United States)

    Irfan, M. I.; Meisel, T.


    , ankerite, corundum (anthropogenic), garnet, chlorite, titanium oxide minerals (ilmenite, rutile, titanite) and amphibole etc. The observed significant increase in heavy metal content from the source region of the Vordernberger Bach at 1500 m above sea level to the confluence of the Vordernberger Bach with the Mur River at 540 m AMSL can be attributed to anthropogenic influence. As expected, the anthropogenic input is more pronounced in the vicinity of historic and current iron and steel production.

  14. Allogenic groundwater recharge to Erenhot Basin%外源地下水补给二连浩特盆地

    Institute of Scientific and Technical Information of China (English)

    陈建生; 王彦超; 谢飞; 徐燚; 陈亚飞; 詹泸成; 江巧宁


    In order to identify the source of groundwater recharge in Erenhot, the transforming relationships between atmospheric precipitation, surface water, soil water, and groundwater were studied through isotope geochemical analysis. Due to evaporation, the soil moisture remains lower than the maximum water holding capacity for a long period, and the infiltration of precipitation is not sufficient to change this situation. Compared with precipitation, the soil water is more depleted in deuterium and oxygen isotopes. Through comparison of deuterium and oxygen isotopes in soil water, groundwater, and local precipitation, it was found that the soil water is mainly recharged by groundwater. The isotopic composition of precipitation in the Qiangtang Basin, in Tibet, is similar to that of the groundwater in Erenhot, indicating that the groundwater in the Erenhot Basin is recharged by an allogenic water source. Ankerite, red clay, travertine, siliceous sinter, gypsum, and other minerals are widely distributed in the basalt eruption regions in the Erenhot Basin. Elements such as Fe, Mg, Ca, and Si in these minerals may come from deep-circulating groundwater. The formation of ankerite and red clay indicates that the deep-circulating groundwater goes through a high-temperature process. The allogenic water may come from the seepage of rivers and lakes in the Tibetan Plateau, and the deep-circulating groundwater recharges the groundwater of Erenhot ’ s volcanic basalt areas via volcanic lava pipes. Based on the principle of deep circulation of groundwater, four artesian wells have been drilled near the craters in Erenhot, with the flow capacity of a single well reaching 30 m3/h.%为了查明二连浩特地下水的补给来源,采用同位素地球化学分析方法,研究了二连浩特地区的大气降水、地表水、土壤水与地下水之间的转化关系。结果表明:土壤含水率在蒸发作用下长期处于亏缺状态,入渗降水不足以改变土壤含

  15. Mineralogy,fluid inclusion and C,O,Sr isotope study of the Ko(s)ice-Medvedia magnesite deposit,Western Carpathians,Slovakia%斯洛伐克西喀尔巴阡山Ko(s)ice-Medvedia菱镁矿床的矿物学、流体包裹体和碳-氧-锶同位素研究

    Institute of Scientific and Technical Information of China (English)

    Martin RADVANEC; Peter KOD(E)RA; Walter PROCHASKA


    富镁的卤水来源是上二叠纪和下三叠纪的分馏蒸发岩来源.铁质碳酸盐流体的高溴和高碘含量,说明在铁交代过程中周围黑色片岩的明显影响.菱镁矿和铁交代作用,表明交代流体中的碳和二氧化碳,主要是海洋沉积的来源.菱铁矿的"Sr/86Sr比值((0.71124~0.71140),说明锶的多来源,最初应是石炭纪和二叠纪的海水,但它被当地其它陆壳中的锶混染.%Kosice deposit is the second biggest magnesite deposit in Slovakia (150 Mt), located in the eastern part of the Gemeric unit. The main Mg-carbonate body is hosted by Carboniferous limestone and dolomitic limestone, while footwall black schists contain thin carbonate lenses replaced by Fe-carbonates. Paleozoic rocks were affected by low-grade metamorphism (chlorite zone) during Variscan orogeny (M1). Mg-replacement started with the crystallization of dolomite 1, followed by magnesite and terminating by formation of Fe-magnesite along cracks. Fe-carbonates include early ankerite-dolomite, ankerite and later siderite with calcite and quartz. Based on carbonate geothermometry dolomite 1 crystallization occurred at 300 ~ 340℃, which is supported by the M1 metamorphic mineral assemblage (chlorite, muscovite-illite). Ankerite crystallization occurred at 320 ~370℃. Minor veinlets with dolomite 2, chlorite and illite-phengite represent younger mineral assemblage of the M2 metamorphism, attributed to Alpine orogeny.Fluid inclusion (FI) study in magnesite showed the presence of brines of variable composition (mostly 21 to 42 wt% NaCl eq.)with high concentration of salts other than NaCl, and variable amount of dissolved CO2. Homogenization temperatures (Th) ranged from 164 to 217℃ in two-phase aqueous FIs and 217 to 344℃ in halite(?)-bearing FIs. CO2-rich FIs (1 ~22 wt% NaCl eq. , CO2 where they co-exist with halite-bearing inclusions. CO2 shows increased participation in fluids in later stages of Mg-replacement. Quartz associated

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

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


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

  17. Reservoir quality and petrophysical properties of Cambrian sandstones and their changes during the experimental modelling of CO2 storage in the Baltic Basin

    Directory of Open Access Journals (Sweden)

    Kazbulat Shogenov


    Full Text Available The objectives of this study were (1 to review current recommendations on storage reservoirs and classify their quality using experimental data of sandstones of the Deimena Formation of Cambrian Series 3, (2 to determine how the possible CO2 geological storage (CGS in the Deimena Formation sandstones affects their properties and reservoir quality and (3 to apply the proposed classification to the storage reservoirs and their changes during CGS in the Baltic Basin. The new classification of the reservoir quality of rocks for CGS in terms of gas permeability and porosity was proposed for the sandstones of the Deimena Formation covered by Lower Ordovician clayey and carbonate cap rocks in the Baltic sedimentary basin. Based on permeability the sandstones were divided into four groups showing their practical usability for CGS (‘very appropriate’, ‘appropriate’, ‘cautionary’ and ‘not appropriate’. According to porosity, eight reservoir quality classes were distinguished within these groups. The petrophysical, geochemical and mineralogical parameters of the sandstones from the onshore South Kandava and offshore E6 structures in Latvia and the E7 structure in Lithuania were studied before and after the CO2 injection-like alteration experiment. The greatest changes in the composition and properties were determined in the carbonate-cemented sandstones from the uppermost part of the South Kandava onshore structure. Partial dissolution of pore-filling carbonate cement (ankerite and calcite and displacement of clay cement blocking pores caused significant increase in the effective porosity of the samples, drastic increase in their permeability and decrease in grain and bulk density, P- and S-wave velocity, and weight of the dry samples. As a result of these alterations, carbonate-cemented sandstones of initially ‘very low’ reservoir quality (class VIII, ‘not appropriate’ for CGS, acquired an ‘appropriate’ for CGS

  18. Importance of micro-scale oxygen isotopic study in Gunflint cherts (1.9 Ga): new constraints on paleo-temperatures reconstructions (United States)

    Marin, J.; Chaussidon, M.; Robert, F.; Marty, B.


    Isotopic composition of sedimentary Precambrian cherts contains a record of the Precambrian environment through their oxygen isotopes (δ18O). Indeed, their δ18O values may reflect their temperature of formation, hence the temperature of the ocean provided the seawater δ18O remained constant around 0 ± 3 permil (Holmden and Muehlenbachs, 1993) during these last 3.5 Ga (Knauth and Lowe, 1978; Robert and Chaussidon , 2006). However, this temperature record can be modified by isotopic exchange with hydrothermal or metamorphic fluids. For a given age, the δ18O values of cherts show large variations (Knauth and Lowe, 2003; Perry and Lefticariu, 2003; Robert and Chaussidon, 2006) which complicates the paleo-temperatures reconstructions. To better understand the origin of these local variations, we have analyzed with SIMS, µm-scale δ18O variations in five cherts from the 1.9 Ga old Gunflint iron-formation (Canada) that stands among the least metamorphosed Precambrian cherts. Five chert samples, containing different types of silica (microcrystalline quartz, drusy quartz, megaquartz, and quartz veins), minor carbonates (siderite and ankerite), hematite and pyrite, were analysed (> 100 spots per sample) by multicollector CAMECA ims 1270 ion microprobe (CRPG-CNRS in Nancy). The external reproducibility on quartz standards was of ± 0.17 permil (1 σ, n=65). The Gunflint cherts show (i) detrital quartz with δ18O 10-12 permil lower than microcrystalline quartz, (ii) a typical 3-6 permil, δ18O range for microcrystalline quartz and (iii) quartz veins with δ18O 5-7 permil, lower than microcrystalline quartz. Variations in the proportion of the different types of silica appear to explain the isotopic heterogeneity observed the whole rock sample scale (i.e. sample 4 of 06/30/84; bulk = 22.75 ± 0.3 permil as compared with a mean δ18O calculated from the measured δ18O values of the different phases of silica = 23.18 ± 0.8 permil). Isotopic mapping of quartz veins shows

  19. Analysis of a intra-Carixian clay horizon into carbonate platform of the Ouarsenis (Algeria): composition, dynamic and paleo-climatic implication

    Energy Technology Data Exchange (ETDEWEB)

    Benhamou, M.; Salhi, A. [Oran Univ., Faculte des Sciences de la Terre et de l' Amenagement du Territoire, Dpt. de Geologie (Algeria)


    During the Late Sinemurian a carbonate platform has developed on the Ouarsenis area (external Tell o f the Algerian Alpine belt) with setting deposits of the Kef Sidi Amar Carbonate Formation. A first maximum flooding materialized by a brachiopods (Zeilleriids) layer, is occurring during the Late Carixian. The Late Carixian deepening has been followed by a sea-level fall documented by several meters incisions filled by transgressive breccia and conglomerates. After this episode, this material was sealed by a pedogenic bed (0,05 to 0,20 m) which corresponds to a yellow clay deposit containing well rounded particles interpreted as pedo-genetic globules. These corpuscles are composed of reddish and hardened clay, corroded quartz grains, rhombic and zoned dolomite crystals and ankerite, monocrystalline and xeno-morphous detrital quartz grains (1-2 mm). The observed characteristics allow to recognize a typical calcrete. They are the result of pedo-genetic diagenesis developed inside the phreatic water-table near the surface: this is an alteration profile. The mineralogic fraction has been analyzed by X-Ray which show results of association clay mineral as a predominance of illite (85%) and mixed-layer illite-montmorillonite (I-M, 10%) associated with a low ration of chlorite (5%) and kaolinite trace (1%). This mineralogic clay association indicates a shallow water (hydro-morphic zone). Among these clay minerals, the illite reveals the precious indications in a source area. In this case, it comes from the decomposition of the schist paleo-relief located in the internal domain. This rock was transformed by acid leaching (action of the sour humus) into kaolinite with the presence of the quartzification. The origin of the mixed-layer clay I-M (10%) is the result of the active pedogenesis. The simultaneous presence of the illite, chlorite, kaolinite and the mixed-layer clay I-M seems to be result from the erosion exercised on the alteration product or arenitisation of the

  20. Ancient geochemical cycling in the Earth as inferred from Fe isotope studies of banded iron formations from the Transvaal Craton (United States)

    Johnson, Clark; Beard, Brian; Beukes, Nicolas; Klein, Cornelis; O'Leary, Julie


    Variations in the isotopic composition of Fe in Late Archean to Early Proterozoic Banded Iron Formations (BIFs) from the Transvaal Supergroup, South Africa, span nearly the entire range yet measured on Earth, from -2.5 to +1.0‰ in 56Fe/54Fe ratios relative to the bulk Earth. With a current state-of-the-art precision of +/-0.05‰ for the 56Fe/54Fe ratio, this range is 70 times analytical error, demonstrating that significant Fe isotope variations can be preserved in ancient rocks. Significant variation in Fe isotope compositions of rocks and minerals appears to be restricted to chemically precipitated sediments, and the range measured for BIFs stands in marked contrast to the isotopic homogeneity of igneous rocks, which have δ56Fe=0.00+/-0.05‰, as well as the majority of modern loess, aerosols, riverine loads, marine sediments, and Proterozoic shales. The Fe isotope compositions of hematite, magnetite, Fe carbonate, and pyrite measured in BIFs appears to reflect a combination of (1) mineral-specific equilibrium isotope fractionation, (2) variations in the isotope compositions of the fluids from which they were precipitated, and (3) the effects of metabolic processing of Fe by bacteria. For minerals that may have been in isotopic equilibrium during initial precipitation or early diagenesis, the relative order of δ56Fe values appears to decrease in the order magnetite > siderite > ankerite, similar to that estimated from spectroscopic data, although the measured isotopic differences are much smaller than those predicted at low temperature. In combination with on-going experimental determinations of equilibrium Fe isotope fractionation factors, the data for BIF minerals place additional constraints on the equilibrium Fe isotope fractionation factors for the system Fe(III)-Fe(II)-hematite-magnetite-Fe carbonate. δ56Fe values for pyrite are the lowest yet measured for natural minerals, and stand in marked contrast to the high δ56Fe values that are predicted from

  1. An experimental study on mineral sequestration of CO{sub 2} in basics and ultra basics rocks; Etude experimentale des reactions de carbonatation minerale du CO{sub 2} dans les roches basiques et ultrabasiques

    Energy Technology Data Exchange (ETDEWEB)

    Dufaud, F


    percents per hour in high temperature experiments. In all cases, carbonation is shown to proceed according to dissolution/precipitation mechanisms. A quasi stoichiometric coupling is evidenced between carbonation and (proto) serpentinization in high-temperature experiments. Newly formed carbonates are mostly magnesite MgCO{sub 3} with Fe and Ca in solid solution. In low temperature samples, the silicates are covered with a thin silica layer and with carbonate spherules consisting of ankerite CaFe(CO{sub 3}){sub 2} - dolomite CaMg(CO{sub 3}){sub 2} - siderite cores surrounded by magnesite overgrowth. In CO{sub 2}-saturated water, peridotites are more reactive than serpentinite and basalts, in accordance with thermodynamic modelling whereas serpentinites are the most reactive in the supercritical CO{sub 2} phase, showing stronger reactivities in this latter phase than in CO{sub 2}-saturated water. In high temperature experiments, the rate of mineral storage is larger at 400 C than at 500 C, in agreement with thermodynamic modelling of the system. High water fugacities and high fluid salinities are shown to have a positive effect on mineral storage rates. Isotopic mass balance of carbon have evidenced that about 15% of the mineral storage consist of a reduced carbon phase, also identified by transmission electron microscopy as an ill-organized graphite phase. (author)

  2. Organic petrology and geochemistry of mudrocks from the lacustrine Lucaogou Formation, Santanghu Basin, northwest China: Application to lake basin evolution (United States)

    Hackley, Paul C.; Fishman, Neil; Wu, Tao; Baugher, Gregory


    inertinite is present in the upper section, indicating greater terrestrial influx and consistent with higher quartz and plagioclase content (dominantly authigenic chalcedony and albite). Laminated mudstones in the upper section indicate anoxia prevented bioturbation from benthic grazing, also indicating stratified water column conditions. A decrease upsection in authigenic dolomite with reciprocal increase of ankerite/siderite is consistent with decreasing salinity, as is an overall decrease in gammacerane index values. These observations suggest evolution from a shallow, stratified evaporative (saline) setting to a deeper, stratified freshwater basin with higher water input during Lucaogou deposition. The evolution from an under-filled to balance-filled lake in Santanghu Basin is similar to Lucaogou deposition in Junggar Basin, suggesting similar tectonic and climatic controls. Paleoclimate interpretations from other researchers in this area suggested an evolution from semi-arid to humid conditions during the Roadian; we interpret that the evolution from an under-filled to balanced-filled lake seen in our data is in response to climate change, and may represent increased groundwater delivery to the Santanghu Basin.

  3. Solid-Fluid Interaction in Glutenite Reservoirs of the Upper Submember, Fourth Member,Shahejie Formation in Northern Slope of Dongying Sag%东营凹陷北部陡坡带沙四上亚段砂砾岩储层固体-流体相互作用研究

    Institute of Scientific and Technical Information of China (English)

    董果果; 黄文辉; 万欢; 王华军


    fluid and solid is characterized by quartz dissolution, feldspar overgrowth and the precipitation of ferrocalcite,ankerite and anhydrite,which largely infill pores and destroy the reservoirs.There are two hydrocarbon expulsion episodes,namely,the deposition period from the second member of Shahejie Formation to Dongying Formation,and the latest one of Guantao Formation.These two events are in correspondence with the development of two secondary pore zones.

  4. Geology and Geochemistry of the Early Proterozoic Kortejärvi and Laivajoki Carbonatites, Central Fennoscandian Shield, Finland

    Directory of Open Access Journals (Sweden)

    Nykänen, J.


    Full Text Available This paper provides for the first time extensive petrological, mineralogical and geochemical data on the early Proterozoic Kortejärvi and Laivajoki carbonatites, northern Finland, which form metamorphosed and highly strained bodies 2 and 4 km long within a Svecokarelian shear zone in central Fennoscandian Shield. They are not exposed, but have been penetrated by a couple of deep drill holes. In terms of modal mineralogy, both intrusions contain calcite carbonatite and dolomite-calcite carbonatite as their main rock types, but Kortejärvi also contains dolomite carbonatite and calcite-dolomite carbonatite, some glimmerite and olivine-magnetite rock and Laivajärvi tremolite-calcite carbonatite, tremolite-dolomite carbonatite, serpentine-talc-dolomite rock and glimmerite. The main country rock is an amphibolite which is not fenitized. No alkaline rocks have been detected in these intrusions. Calcite is most common mineral in both occurrences. Other carbonate minerals include dolomite with minor ankerite and occassional siderite. In addition to low-Ti phlogopite, tetraferriphlogopite is also encountered. Fresh olivine is rare, and its alteration products include titaniferous clinohumite. The amphiboles are mainly calcic amphiboles, including actinolite, tremolite and edenite. The only sodic-calcic amphibole is accessory richterite. Other essential minerals are Ti-poor magnetite with ilmenite exsolutions, fluorapatite (3.95-4.89 wt. % F, monazite, and allanite-(Ce. Geochemically, the Kortejärvi rocks are mostly magnesiocarbonatites, whereas those of Laivajärvi, due to their higher magnetite content, are ferrocarbonatites. Of the trace elements, Nb is much lower (8-30 ppm in proper carbonatites than the average for carbonatites and U and Th (<0.9 ppm and<2.4 pm, respectively lower than average. Sr is typical, but not high (1830-3480 ppm, and Ba is rather low (27-348 ppm. The REEs are hosted by allanite and monazite and their concentrations in the

  5. Numerical modeling of injection and mineral trapping of CO2 withH2S and SO2 in a Sandstone Formation

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Tianfu; Apps, John A.; Pruess, Karsten; Yamamoto, Hajime


    Carbon dioxide (CO{sub 2}) injection into deep geologic formations could decrease the atmospheric accumulation of this gas from anthropogenic sources. Furthermore, by co-injecting H{sub 2}S or SO{sub 2}, the products respectively of coal gasification or combustion, with captured CO{sub 2}, problems associated with surface disposal would be mitigated. We developed models that simulate the co-injection of H{sub 2}S or SO{sub 2} with CO{sub 2} into an arkose formation at a depth of about 2 km and 75 C. The hydrogeology and mineralogy of the injected formation are typical of those encountered in Gulf Coast aquifers of the United States. Six numerical simulations of a simplified 1-D radial region surrounding the injection well were performed. The injection of CO{sub 2} alone or co-injection with SO{sub 2} or H{sub 2}S results in a concentrically zoned distribution of secondary minerals surrounding a leached and acidified region adjacent to the injection well. Co-injection of SO{sub 2} with CO{sub 2} results in a larger and more strongly acidified zone, and alteration differs substantially from that caused by the co-injection of H{sub 2}S or injection of CO{sub 2} alone. Precipitation of carbonates occurs within a higher pH (pH > 5) peripheral zone. Significant quantities of CO{sub 2} are sequestered by ankerite, dawsonite, and lesser siderite. The CO{sub 2} mineral-trapping capacity of the formation can attain 40-50 kg/m{sup 3} medium for the selected arkose. In contrast, secondary sulfates precipitate at lower pH (pH < 5) within the acidified zone. Most of the injected SO{sub 2} is transformed and immobilized through alunite precipitation with lesser amounts of anhydrite and minor quantities of pyrite. The dissolved CO{sub 2} increases with time (enhanced solubility trapping). The mineral alteration induced by injection of CO{sub 2} with either SO{sub 2} or H{sub 2}S leads to corresponding changes in porosity. Significant increases in porosity occur in the acidified

  6. Investigations using Laboratory Testbeds to Interpret Flight Instrument Datasets from Mars Robotic Missions (United States)

    Ming, D. W.; Morris, R. V.; Sutter, B.; Archer, P. D., Jr.; Achilles, C.


    high (725-820 °C) temperature and an endothermic reaction in concert with the high temperature release. The high-temperature thermal decomposition is consistent with calcite, dolomite, or ankerite, (3-6 wt.%) or any combination of these phase based upon laboratory testbed experiments. Recent laboratory experiments suggest that the low temperature CO2 release was caused by a reaction between calcium carbonate and hydrated magnesium perchlorate; although, CO2 release by the oxidation of organic materials and Fe-/Mg-rich carbonates cannot be ruled out. MSL landed in Gale crater on August 5, 2012. Although numerous analog samples have been analyzed on the JSC laboratory testbeds, no SAM, CheMin, or ChemCam analyses have been acquired by MSL to date. The JSC SAM laboratory testbed consists of a thermal analyzer coupled with a MS configured to operate under total pressure (30 mbar), heating rate (35 °C/min), and purge gas composition (He) analogous to the flight SAM. The CheMin and ChemCam laboratory testbeds were developed and built by inXitu, Inc. and Los Alamos National Laboratory, respectively, to acquire datasets relevant to the MSL CheMin and ChemCam flight instruments.

  7. Assessing Biogenecity of Stromatolites: Return to the Facies (United States)

    Shapiro, R. S.; Jameson, S.; Rutter, A.; McCarthy, K.; Planavsky, N. J.; Severson, M.


    The discovery of richly microfossiliferous cherty stromatolites near Schreiber and Kakabeka Falls, Ontario, in the 1.9 Ga Gunflint Iron Formation, firmly established the field of pre-Cambrian paleontology. In the half-century since this discovery, paradigm shifts in the ecology of the microfossils as well as the utility of stromatolites as biological markers has caused a re-evaluation of our understanding of the pre-Cambrian fossil record. This research summarizes facies evaluation of the two stromatolite marker beds in the Gunflint-correlative Biwabik Iron Formation of Minnesota. The centimeter-scale microstratigraphy of cores drilled through the central and eastern Mesabi Iron Range was coupled with field descriptions of outcrops and mines in both the Biwabik and Gunflint iron formations. Eight lithologic facies associated with the stromatolites are identified: A) Pebble conglomerate clasts ranging in size of 0.5-3 cm, syneresis cracks, and septarian nodules with medium to coarse grain matrix; B) siltstone with subparallel sub-mm to 5 cm magnetitic and non-magnetic bands; C) stromatolitic boundstone comprising stratiform, pseudocolumnar, domal, undulatory, flat-laminated, dendritic, columnar, and mico-digitate forms and oncoids 0.5 to 2 cm diameter; D) grainstone with medium to coarse siliceous and carbonate ooids and peloids; E) massive green crystalline beds with bands of magnetite, quartz, calcite, disseminated pyrite and localized ankerite; F) autobreccicated fabric of 0.3 to 10 mm clasts; G) medium to coarse sandstone; H) quartzite. Correlation between 11 cores near Hoyt Lakes and 9 cores through the basal stromatolite layer at the MinnTac Mine near Virginia revealed that stromatolites formed both on conglomerate and medium quartz sandstone. Multiple forms of stromatolite may occur in a vertical succession (flat-laminated to undulatory to psuedocolumnar to columnar) or a core may be dominated by one type, typically columnar-stratiform. Where stromatolites do

  8. 湖南醴陵肖家山金矿地质特征及成矿条件研究%Geological characteristics and metallogenic conditions of Xiaoj iashan gold deposit in Liling of Hunan

    Institute of Scientific and Technical Information of China (English)

    陶诗龙; 赖健清; 宋维国; 查道函


    肖家山金矿属于醴陵金矿田的一个典型金矿床。矿区主要出露的地层为中元古界冷家溪群,系一套巨厚的绿片岩相浅变质碎屑岩,为矿床的矿源层。区域岩浆活动强烈,主要出露中生代的花岗岩,为成矿提供了热源和动力。矿区褶皱、断裂构造发育,其中三斗田脆-韧性剪切带和雁林寺韧性剪切带为矿区主要的控矿容矿构造。矿脉主要产于断裂中,呈似脉状。矿床以热液成矿作用为主,成矿期可分为石英―黄铁矿阶段,含金石英―硫化物阶段,石英―铁白云石阶;矿区流体包裹体均为富液相的气液两相包裹体,流体均一温度介于180℃~360℃之间,盐度为3.12%~9.84%(wt%NaCl equiv),流体的密度介于0.67 g/cm3~0.92g/cm3。综合分析矿床是一中高温热液叠加改造型金矿床。%Xiaojiashan gold deposit was a typical gold deposit in Liling gold ore field.The main outcropped strata in the mining area were Mesoproterozoic Lengjiaxi Group,which was a set of thick green schist facies epimetamorphic clastic rock and was the ore source bed of the deposit.With the intensive magmatic activities in this area,mainly outcropped Mesozoic granite provided heat source and dynamic force for mineralization. Among the developed folds and faulted structures,Sandoutian brittle-ductile shear zone and Yanlinsi ductile shear zone were the primary ore-controlling and host structures in the mining area.Vein ores mainly oc-curred in the fractures in veinlike form.The deposit was mainly formed by hydatogenesis,and the minerali-zation periods included quartz-pyrite phase,gold-bearing quartz-sulfide phase and quartz-ankerite phase.The liquid inclusions in the mining area were rich-liquid phase gas-liquid inclusions,while the homogenization temperature of fluid ranged between 180℃ and 360℃ and the salinity ranged between 3.12% and 9.84%(wt%NaCl equiv)and the density of fluid ranged between 0.67g/cm3 and 0

  9. Ore features and gold occurrence in Yinwagou Gold Deposit,Gansu Province%甘肃阴洼沟金矿床矿石特征及金的赋存状态研究

    Institute of Scientific and Technical Information of China (English)

    赵民; 郭月琴; 赵国斌; 温志亮; 杨鹏飞; 李普涛; 吴天娇


    Characteristics of gold minerals and the occurrence of gold have been determined in Yinwagou Gold Deposit ,on the basis of systematic laboratory study ,such as electron microscope observation ,multi-element analysis ,e-lectronic microprobe energy spectrum analysis , electronic microprobe wavelength spectrum analysis , mineral phase a-nalysis .The result shows the gold ores mainly have three different mineralogical types ,that is low sulphide altered rock type gold ore,low sulphide cataclastic quartz-vein type gold ore and low sulphide ankerite -albite-quartz-vein type gold ore ,and Au is the only one industrially valuable element;the metallic mineral content in the ore is low and they are mainly limonite ,hematite and pyrite;non-metallic minerals are mainly quartz ,followed by sericite ,carbonate min-erals,feldspar,chlorite and kaolinite; gold minerals are native gold,and the average fineness of native gold is 975;The main type of dissemination is fissure gold ,followed by inclusion gold ,few in the form of the intergranular gold;grain size of native gold is dominated by fine visible gold ,followed by microgranular gold .Native gold is primarily visi-ble gold,followed by microscopic gold .%为了查清阴洼沟金矿床矿石特征及金的赋存状态,采用电子显微镜、多元素分析、电子探针能谱分析、电子探针波谱分析、物相分析等技术方法,对阴洼沟金矿床的金矿石、金矿物进行了系统的研究.研究结果表明:金矿石工艺类型主要有少硫化物蚀变岩型金矿石、少硫化物碎裂石英脉型金矿石和少硫化物铁白云石-钠长石-石英脉型3种,且有工业价值的元素只有Au;矿石中金属矿物含量较低,主要是褐铁矿、赤铁矿及黄铁矿,非金属矿物主要是石英,其次是绢云母、碳酸盐矿物、长石、绿泥石及高岭石;金矿物为自然金,金成色平均为975;金的嵌布类型以裂隙金为主,其次为包裹金,粒间金含量较少;自然金以细

  10. Quantitative mineral proxies of fluid chemistry and geothermal gradients in the Kumano Transect, Nankai Trough, Japan (United States)

    Sample, James; Weeks, Sarah; Fisher, Andrew; Defliese, Will; Tripati, Aradhna; IOPD Expedition 348 Science Party


    The Nankai Trough subduction margin is capable of generating tsunamigenic earthquakes with M>8. The physical properties of materials involved in faulting and the magnitude of fluid overpressures exert important controls on the nature of seismicity. We present data from diagenetic carbonates constraining the temperature and chemistry of fluids passing through the accretionary system during deformation. Reference drill sites C0011 and C0012 sampled the sedimentary section and part of basaltic crust. Both sites comprise hemipelagic mud, silty and sandy turbidites with significant ash and volcaniclastic sediment. Carbonates are dominantly calcite or ankerite with varying substitutions of primarily Mn and Fe for Ca. The minimum δ18O values of carbonate samples show a steady trend of decreasing values with depth, and although multiple factors contribute to isotope signatures, at a first order the isotopes are consistent with recent carbonate formation at temperatures following along a geotherm. Temperatures of carbonate formation determined from carbon clumped geothermometry at both sites confirm formation in equilibrium with the modern geothermal gradients, although showing some scatter, consistent with recent and active cementation. Cuttings and cores from Site C0002 in the Kumano Basin, from depths up to ~3 km, suggest increased faulting and carbonate formation with depth. Sample below 2100 mbsf include numerous carbonate slickenfibers. Carbonates are dominantly calcite or low-Mn calcite, with minor Fe substitution. Veined samples show a steady of trend of decreasing δ18O values with depth that could be attributed to vein formation at increasing burial temperatures. No temperature measurements are available from this interval and temperatures have to be estimated by extrapolation of measurements from the shallow Kumano Basin, and using thermal conductivity measurements of well cuttings. The preliminary clumped isotope temperature estimates, mainly from a cored fault

  11. Sulfide-Sulfate Mineralizations in Verzino Area (Crotone Basin, Southern Italy): New insights on localized hydrothermal fluid circulations and their relationship with tectonics. (United States)

    Berardi, Gabriele; Lucci, Federico; Cozzupoli, Domenico; Pizzino, Luca; Cantucci, Barbara; Quattrocchi, Fedora


    In this early stage of the work we present a preliminary study of hydrothermal mineralizations found in Verzino locality, Crotone Basin, Southern Appennines, (Calabria, Italy). Both geochemical and petrographic investigations were developed with the aim of understanding the genesis of the sulfide-sulfate associations present in the "Argille Marnose del Ponda" formation, deepening their relationship with fluids circulation. These mineralizations have been recognized only in two "Calanchi" morphostructures - Badlands like morphology developed by the differential erosional pattern of the "Argille Marnose del Ponda" fm. - and constituting the northwestern flank of a little valley evolved in the Miocene sedimentary sequence from "Conglomerato di S.Nicola" fm. to "Evaporiti Superiori" fm. The mineralizations are distributed along isooriented centimetric veins (with mean direction of N120) and in nodules diffused close to the veins. These hydrothermal mineralizations are constituted by an associations of Pyrite spherical nodules (millimetric to centimetric in radius with occurrences of well developed octahedral habit single crystals), sulphate crystals (Gypsum, Jarosite, NatroJarosite), Oxides (Goethite mainly), millimetric veins of Barite and micrometric Ankerite specimens. The data (mineral habits, semiquantitative compositions and x-Ray spectra), obtained by an integration of S.E.M and XRD investigations, permit us, at the current stage of the study, to hypothesize a possible hydrothermal origin (whose temperature range estimate needs further investigations) for the sulfide-sulfate mineral phases. At the moment, we exclude their primary or secondary sedimentary provenance. The comparison of our results with the previous scientific literature focused on hydrothermal sulfide-sulfate systems (Vinogradov and Stephanov, 1964; Kostov, 1968; Plummer 1971; Boles, 1978; Ferrini and Moretti 1998) allows us to propose a possible "thermal window" ranging in the interval 50°C-230

  12. Origins of chromite and magnetite in sedimentary rocks deposited in a shallow water environment in the 3.2 Ga Moodies Group, South Africa (United States)

    Otake, T.; Sakamoto, Y.; Itoh, S.; Yurimoto, H.; Kakegawa, T.


    *Otake, T. Div. of Sustainable Resources Engineering, Hokkaido Univ., Sapporo, Japan Sakamoto, Y. Dep. of Earth Science, Tohoku Univ., Sendai, Japan Itoh, S. Dep. of Natural History Sciences, Hokkaido Univ., Sapporo, Japan Yurimoto. H. Dep. of Natural History Sciences, Hokkaido Univ., Sapporo, Japan Kakegawa, T. Dep. of Earth Science, Tohoku Univ., Sendai, Japan Geochemical data from ferruginous chemical sedimentary rocks (e.g., Banded Iron Formation: BIF) have been used to reconstruct the surface environments of early Earth. However, only a few studies have investigated the geochemical characteristics of BIFs deposited in a shallow water environment during the Archean, which may have differed from those deposited in a deep water environment. Therefore, we investigated geological, petrographic and geochemical characteristics of ferruginous rocks deposited in a shallow water environment in the Moodies group, in the Barberton Greenstone Belt, South Africa. We obtained ferruginous rock samples in the Moodies group from both an outcrop and underground gold mine, and compared the characteristics of these samples. The 70 sedimentary rock samples were divided into groups based on the dominant Fe minerals they contain: Hematite-rich jaspilite (HM group), Magnetite-rich iron formation/shale/sandstone (MT group), and Siderite-rich sandstone (SD group). Samples in the HM group are predominantly composed of fine-grained quartz (< 20 μm) and hematite (< 5 μm), which are interpreted to be chemical precipitates. Samples in the MT group contain quartz, magnetite, siderite, ankerite, chlorite, biotite and chromite. The grain size of magnetite is much larger (20-150 μm) than that of hematite in the HM group. The magnetite is interpreted as a secondary mineral transformed from hematite during early diagenesis. Results of in situ oxygen isotope analysis by

  13. Mass transfer and fluid evolution in late-metamorphic veins, Rhenish Massif (Germany): insight from alteration geochemistry and fluid-mineral equilibria modeling (United States)

    Marsala, Achille; Wagner, Thomas


    Element mobility and fluid-rock interaction related to the formation of late-metamorphic quartz veins have been studied by combination of mineral chemistry, whole-rock geochemistry, mass balance analysis and fluid-mineral equilibria modeling. The quartz veins are hosted by very low-grade metasedimentary rocks of the fold-and-thrust belt of the Rhenish Massif (Germany). The veins record two stages of evolution, a massive vein filling assemblage with elongate-blocky quartz, chlorite, apatite and albite, and a later open space filling assemblage with euhedral crystals of quartz, ankerite-dolomite and minor calcite and sulfides. Detailed mass balance analysis of an alteration profile adjacent to a representative quartz vein demonstrates that element mobility is restricted to the proximal zone. The most important element changes are gain of Ca, Fe, Mg, Mn, P and CO2, and loss of Si, K and Na. The data demonstrate that wall-rock carbonation is one of the main alteration features, whereas mobility of Si, K and Na are related to dissolution of quartz and destruction of detrital feldspar and muscovite. The whole-rock geochemical data, in conjunction with fluid composition data and pressure-temperature estimates, were used as input for fluid-mineral equilibria modeling in the system Si-Al-Fe-Mg-Ca-Na-K-C-S-O-H-B-F-Cl. Modeling involved calculation of rock-buffered fluid compositions over the temperature interval 100-500 °C, and reaction-path simulations where a rock-buffered high-temperature fluid reacts with fresh host-rocks at temperatures of 400, 300 and 200 °C. Calculated rock-buffered fluid compositions demonstrate that retrograde silica solubility is a strong driving force for quartz leaching in the temperature-pressure window of 380-450 °C and 0.5 kbar. These conditions overlap with the estimated temperatures for the initial stage of vein formation. Reaction-path models show that high-temperature alteration can produce the observed silica leaching, suggesting that

  14. 鄂尔多斯盆地陇东地区延长组砂岩成岩作用及孔隙演化%Diagenesis and porosity evolution of sandstones in Longdong Area, Ordos Basin

    Institute of Scientific and Technical Information of China (English)

    钟大康; 祝海华; 孙海涛; 蔡超; 姚泾利; 刘显阳; 邓秀芹; 罗安湘


    Researches based on the pore casting thin sections, scanning electron microscopy (SEM) and X-ray diffraction, combined with the analysis of physical properties, have shown that the types of the sandstone reservoirs of Triassic Yanchang Formation in Longdong Area, Ordos Basin, are lithic arkose sandstone, feldspathic lithic sandstone and arkose with low compositional and low structural maturities. The high quality reservoirs were mainly developed in some coarse grained sandstones rich in rigid grains. The primitive porosity of this sandstone is approximately 39% from some empirical formula. During burring, its porosity decreased to 18. 5% due to the fast burial and richness in the shale, slate and phyllite debris. Afterwards, the porosity continually decreased in some extent (3. 5%) as a result of the overgrowth of quartz and chlorite cementation. Constantly, the calcite and dolomite cementation contributed a porosity loss of about 5%. Afterwards, the dissolutions of carbonate cement, feldspar and debris made a contribution to the increase of porosity by about 4%-8%. Finally, the dissolution pores and some primary pores were infilled by ferrocalcite and ankerite cement.%大量岩石薄片、孔隙铸体薄片、扫描电镜与X衍 射以及常规物性等分析资料研究表明,鄂尔多斯盆地陇东地区三叠系延长组砂岩主要为成分成熟度及结构成熟度较低的长石质岩屑砂岩、岩屑砂岩和长石砂岩.优质储层主要发育于粗粒富含刚性颗粒的砂岩中,这类砂岩在埋藏过程中由于早期快速埋藏加之泥岩、板岩及千枚岩岩屑含量高,经历了强烈的压实作用,使其由原始孔隙度大约为39%降低至18.5%;此后发生石英颗粒次生加大及绿泥石胶结,使孔隙有一定程度的损失(大约3.5%);紧随其后的是方解石及白云石碳酸盐胶结,损失孔隙度5%;后来出现碳酸盐胶结物与长石及岩屑的溶蚀作用,新增加孔隙度4%~8%,

  15. 河南淅川木变石宝石学研究(上)%Gemological Research of Wood Theyndrite in Xichuan

    Institute of Scientific and Technical Information of China (English)

    王亚军; 周燕萍; 石斌; 袁心强


    以中国河南淅川木变石为对象,利用现代测试技术对其宝石学特征进行研究。首先对其进行常规测试,矿片镜下分析得出样品里面主要的矿物成分是石英和钠闪石;通过 X 射线粉末衍射得出灰蓝色样品的主要成分是石英、方解石、白云石和重晶石,黄色样品的主要成分是石英、钠闪石和铁白云石;拉曼光谱测试结果显示灰蓝色样品因为其具有显著的466 cm-1特征拉曼峰所以可以判断其属于二氧化硅类,褐黄色样品的拉曼谱峰,因为其具有显著的467 cm-1特征拉曼峰所以可以判断其属于二氧化硅类即石英[4],其中1089 cm-1代表了闪石类矿物的 Si-O 伸缩振动,所以黄色基底部分主要的物质应是二氧化硅,此外还有闪石类矿物红外吸收光谱显示样品具有相同的反射谱峰1158 cm-1、816 cm-1、704 cm-1、565 cm-1和520 cm-1,结果显示这些谱峰均属石英,表明样品主要是由石英组成;通过激光诱导离解光谱分析出样品的主要元素是 Si、Na、Mg、Ca 等,次要元素是 Be、Cu、Ag、Pd、Ca、Al、Pb 等,而致色元素则是Fe。%In this article,the gemological characteristic of wood theyndrite in Xichuan, Henan provence,China has been studied through modern testing technology.Firstly,the wood theyndrite has been tested by conventional technique.The microscopic analysis of the thin section of ore sample shows that the main mineral compositions are quartz and riebeckite;main compositions of the dusty blue samples are confirmed by X-Ray Powder Diffraction,namely,quartz,calcite,dolomite and barite,and for the yellow sample,the main composition are quartz,riebeckite and ankerite;Raman spectroscopy test shows sig-nificant Raman spectrum peak of 466 cm-1 characteristic in the dusty blue sample,hence it can be concluded that it belongs to silicon dioxide.The isabellinus sample has signifi-cant Raman spectrum peak of 467 cm-1 characteristic which indicates it belongs

  16. 饱和CO2地层水驱过程中的水-岩相互作用实验%An experimental study on water-rock interaction during water flooding in formations saturated with CO2

    Institute of Scientific and Technical Information of China (English)

    于志超; 杨思玉; 刘立; 李实; 杨永智


    , followed by dawsonite, while ankerite the weakest. The concentration of K+ in the reaction solution varies mainly due to the dissolution of detrital K-feldspar grains. A small amount of kaolinite and intermediate products were generated after the experiment. The composition of intermediate products is mainly composed of C, O, Na, Cl, Al and Si, which have a trend to change into carbonate minerals. New minerals (Kaolinite and intermediate products) and the particles released by the dissolution of the carbonate cement were moved to pore throats and blocked the path of pore, which was the main reason that caused the core permeability reduction. The experiment results have reproduced the short-term process of corrosion of feldspar and dissolution of carbonate minerals as well as precipitation of new minerals after CO, injection, revealed reasons of permeability variation, and provided geochem-ical evidence for CO2 trapping mechanisms underground.

  17. Cockade-textured cataclasite and silica gel from damage zone in carbonated ultramafics: markers of cycles of seismic activity? (United States)

    Scarsi, Marco; Crispini, Laura; Garofalo, Paolo; Capponi, Giovanni


    Shallow crustal processes occurring during seismic slips and generating fracture networks are of great interest due to their complex interplay with a spectrum of other geological processes . Our study focuses on faults with peculiar core textures, similar to those of "cockade breccia" (Genna et al., 1996) and "clast cortex grains" (Rempe et al., 2014), and on their relation with syntectonic hydrothermal alteration linked with Au bearing-quartz and chalcedony veins. Our work aims to study the enviromental conditions for the formation of such peculiar texture, their relation with the hydrothermal vein system and their potential as shallow seismic indicators. We present field, microstructural and petrochemical data of a peculiar damage zone of fault rocks located in carbonated peridotites and serpentinites of the Ligurian Alps (Voltri Massif, Italy). These are mainly reverse faults, which are coeval with syntectonic Au-bearing quartz veins and chalcedony veins (Giorza et al., 2010), in which lherzolites occupy the hangingwall of the faults and serpentinites the footwall. The fault rocks show evidence for carbonation, as olivine and serpentine are clearly transformed into an assemblage made of magnesite, dolomite and minor ankerite. The damage zones of the faults are serpentinite-rich and about 10 m in thickness, while the cataclasite cores are carbonate-rich and ca. 1 m thick. The top of the fault core shows the occurrence of a chalcedony shear veins with chatter marks and slikenlines on the surface. The "cockade breccia" is made of spherical aggregates of Fe-Mg carbonates and are 1 mm to 3 cm in size. These aggregates show cores of microcrystalline Fe-Mg carbonates, and concentric outer layers of relatively coarser Fe-Mg carbonates with radial or laminated texture. In some cases, these aggregates show evidence for rotation along secondary slip zones. We interpret all these features as the products of chemical interaction between the olivine and serpentine initially

  18. The Main Geological Events of the Kangdian Proterozoic Eon and Response from to the La-La IOCG Deposit%康滇地轴元古代重大地质事件与拉拉IOCG矿床成矿响应

    Institute of Scientific and Technical Information of China (English)

    王奖臻; 李泽琴; 黄从俊


    Precambrian deposits are the dominant members of the IOCG group in terms of both copper and gold resources.These giant IOCG deposits are located in intracratonic settings within about 100 km of the margins of Archean or Paleoproterozoic cratons or other lithospheric boundaries.Their tectonic setting at formation was most likely anorogenic,with magmatism and associated hydrothermal activity driven by mantle underplating and/or plumes.Based on a review of isotopic dating data from the Kangdian Proterozoic rocks/minerals,three major geological events are suggested: the formation of the Kangdian basement of the Yangtze craton,2486-1884 Ma,which would be as a part of Kenorland supercontinent;the Kangdian Continental Rifting located along the west margin of Yangtz craton,1725-1466 Ma,which happened during the anorogenic period of Columbia supercontinent;metamorphism-magmatism events(1100-721 Ma) were the response to assembling and rifting of Rodinia supercontinent.The La-La IOCG deposit is hosted by the Kangdian basement of the western margin of Yangtze craton.The host rocks of the deposits are Proterozoic metamorphic rocks,Hekou Group,the protolith of which was the products of the Kangdian Rifting during 1712-1680 Ma,which contributed Stage I meneralization of the Lala IOCG deposit: Iron-P-REE.StageII(1000-900 Ma),with chalcopyrite(I) + magnetite(II) + molybdenite+purple fluorite + ankerite ± pyrite ± cobaltite ± quartz ±biotite(II) ± garnet(II) ± sericite,and StageIII(~850 Ma),with dolomite/calcite+chalcopyrite±quartz,followed assembling of Rodinia supercontinent.%有关IOCG最新研究成果建议,将IOCG矿床限定于资源量大于1 Mt的大型/超大型矿床。对世界上已知的大型/超大型IOCG矿床的成矿背景和成矿作用进行分析对比,发现前寒纪大型/超大型IOCG矿床均位于前寒纪超大陆的边缘、形成于非造山期,与壳幔相互作用有关,与板底垫托、地幔柱等相关的重大地质事件关系密切。

  19. Dark Clasts in the ACFER 059/El Djouf 001 Meteorite (CR) from the Sahara: Implications for their Origins (United States)

    Endress, M.; Keil, K.; Bischoff, A.


    Introduction: Dark clasts (DC) occur in almost all known chondrite groups. They have been interpreted mostly as matrix or C1 and C2 chondritic material. Weisberg et al. (1991) recently described DCs in six samples of the CR2 chondrite group. Here we focus on DCs in the paired samples of the Acfer/El Djouf meteorite (Bischoff et al., 1992). Thirty-six DCs in 12 polished thin sections were studied. Results: DCs occur in all investigated thin sections with an average of 50 DCs in each and make up 2.4 to 3.7 vol%. DCs are mostly irregularly shaped and up to 2.4 mm in maximum dimension, with most ranging between 200 and 400 micrometers. They have sharp boundaries to the surrounding matrix of the host meteorite in reflected light as well as in backscatter images of an SEM. Some DCs are light to dark brownish, others are opaque in transmitted light. Both types are heavily fractured and contain only a negligible abundance of weathering products. DCs have abundant fine-grained matrix including chondrule fragments, mineral fragments and, frequently, phyllosilicate clusters. The abundances of these components vary greatly among the DC. Only one CAI and two microchondrules in DCs were detected. Chondrule fragments are mostly relics of former porphyritic chondrules (PO, POP, PP); olivine and pyroxene compositions are Fa1-47 and Fs3-25, respectively. Some olivines show high MnO contents up to 3 wt%. Major components in the matrix of DCs are magnetite, pyrrhotite and pentlandite. Magnetite grains are up to 25 micrometers in size and show the typical features of magnetite from CI chondrites: spherules, framboids and platelets. The sulfides constitute an average of 1 vol% and occur mostly as large laths up to 50 micrometers long. Accessory phases throughout the matrix in DCs are spinel, carbonate (ankerite-like), phosphate, ilmenite, schreibersite and Fe, Ni. Two Os,Mo,Ir-rich particles were detected. The bulk compositions of individual DCs vary, probably due to different

  20. Mg replacement at the Gemerská Poloma talc-magnesite deposit,Western Carpathians,Slovakia%斯洛伐克西喀尔巴阡山脉Gemerská Poloma滑石-菱镁矿矿床中镁的交代作用

    Institute of Scientific and Technical Information of China (English)

    Martin RADVANEC; Peter KOD(E)RA; Walter PROCHASKA


    Gemerska Poloma deposit is an important talc deposit (20 Mt of talc), located in the Gemeric unit within Western Carpathians. The partly steatizated Mg-carbonatic carbonate body was formed inside Early Paleozoic volcano-sedimentary complexes (black schist, metapelite) , regionally metamorphosed during Variscan metamorphic event (M1) in chlorite-biotite zone. The body,originally limestone, consists of white-grey and/or grey-black coarse-grained magnesite and dolomite 1 that is cut by veins of younger dolomite 2 and talc. Several successive mineral assemblages within two major metamorphic events M1 and M2 have been recognized.Earliest assemblage consists of ankerite, Mg-siderite and siderite (accompanied by schorl, Fe-chlorite, apatite and illite-muscovite) ,occurring as very small relicts in magnesite and dolomite 1 and probably preceding the peak of M1 metamorphism. The peak of the M1 is represented by the assemblage F-rich phlogopite, Mg-chlorite 1, dravite (the rim of schorl) and quartz. During retrograde part of the M1 successive Mg replacement occurred starting with the crystallisation of dolomite 1, followed by magnesite and terminating by formation of Fe-magnesite along cracks. Based on carbonate geothermometry, the peak of M1 occurred at 460 ~490℃, which is supported by metamorphic mineral assemblage. The M2 metamorphism, related to the younger Alpine orogeny, was responsible for the formation of talc, dolomite 2 and Mg-chlorite 2 along the faults in the host Mg carbonate body.Fluid inclusion study in magnesite showed the presence of fluids with very complex composition, probably MgCl2 dominated brines of evolved evaporitic origin. In primary brine inclusions the salinity reached up to ~35 wt% MgCl2 eq. and homogenisation temperature (Th) occurred in the range 216 to 235 ℃. Fluid inclusion in quartz showed also the presence of MgCl2 dominated brines of similar composition, however, with a higher range of Th values (248 to 313℃). If assuming that