46 results on '"Christophe Renac"'
Search Results
2. Stable isotope study of rainfall, river drainage and hot springs of the kerguelen archipelago, SW Indian Ocean
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Christophe, Renac, Bertrand, Moine, Jean-Pierre, Goudour, Marc, LeRomancer, and Chantal, Perrache
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- 2020
- Full Text
- View/download PDF
3. P-T-X reconstruction for ore deposits using petroleum-rich fluid inclusions in fluorite: A case study in the Bou Jaber diapir-related Ba–Pb–Zn–F deposit, Northern Tunisia
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Abidi, Riadh, Marignac, Christian, Slim-Shimi, Najet, Pironon, Jacques, Gasquet, Dominique, Somarin, Alireza K., Christophe, Renac, and Hibsch, Christian
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- 2019
- Full Text
- View/download PDF
4. The microbial controls on the deposition of <scp>Pb‐Zn</scp> minerals in carbonate‐hosted Tunisian ore deposits
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Riadh Abidi, Najet Slim‐Shimi, Christan Marignac, Alireza K. Somarin, Christophe Renac, Etienne Deloule, Nouri Hatira, and Dominique Gasquet
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Geochemistry and Petrology ,Geology - Published
- 2022
5. Ecological risk assessment linked to potentially toxic elements (PTE) in a Mexican complex hydrological system (Tobari coastal lagoon, Sonora, México)
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Beatriz Gonzalez_Perez, María Vicenta Esteller-Alberich, Sofia E. Garrido Hoyos, Carlos Diaz Delgado, Martin E. Jara Marini, Christophe Renac, and Aurélie Barats
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- 2022
6. 40Ar/39Ar dating of high temperature geothermal systems: First attempt on hydrothermally altered pyroxenes from the Saintes archipelago (Lesser Antilles arc, Guadeloupe)
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Philippe Münch, Alexiane Favier, Jean-Marc Lardeaux, Christophe Renac, Chrystèle Verati, François Orange, Michel Corsini, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS), and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])
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White mica ,010504 meteorology & atmospheric sciences ,Meta-pyroxene ,Geochemistry ,[SDU.STU.PE]Sciences of the Universe [physics]/Earth Sciences/Petrography ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Hydrothermal circulation ,40Ar/39Ar dating ,Geochemistry and Petrology ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,[SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology ,[SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology ,Geothermal gradient ,[SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,[SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics ,geography ,geography.geographical_feature_category ,Plateau ,Muscovite ,Geology ,Volcano ,Hydrothermal reaction ,Back-arc basin ,[SDU]Sciences of the Universe [physics] ,Illite ,Archipelago ,[SDE]Environmental Sciences ,engineering ,Fossil geothermal system ,[SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy - Abstract
International audience; We investigate the potential of 40Ar-39Ar systematics in secondary K-bearing minerals developed at the expense of hydrothermally altered volcanic pyroxenes from a fossil geothermal system located in the Saintes archipelago (Lesser Antilles magmatic arc).Our work reports the first example of dating hydrothermal muscovite crystallization developed during pseudomorphic transformation of pyroxenes within altered rhyodacites at temperatures above 300 °C. The white micas display a well-defined Ar/Ar plateau age of 2.59 ± 0.12 Ma, interpreted as the best age estimate for high temperature fluid circulation in the Saintes geothermal paleo-reservoir. A model of muscovite substitution by illite during cooling supports the interpretation that illitization perturbs the K-Ar and the Ar-Ar ages only when muscovite is highly illitized and/or if illitization is significantly younger than muscovite crystallization. The whole temporal dataset implies a fast cooling rate (>150 °C/200 ka) and a maximal lifetime of 650 ka for the Saintes hydrothermal system.
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- 2021
7. Mass balance and origin of fluids associated to smectite and chlorite/smectite alteration in Seival Mine Cu–Mineralization – Camaquã Basin – Brazil (Part II)
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Eduardo Fontana, Andre Sampaio Mexias, Rodrigo W. Lopes, Marie-Christine Gerbe, Christophe Renac, Lauro Valentim Stoll Nardi, Aurélie Barats, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Univ Fed Rio Grande do Sul, Inst Geociencias, BR-91501970 Porto Alegre, RS, Brazil, Univ Fed Rio Grande do Sul, Fac Agron, Dept Solos, Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Institut national des sciences de l'Univers (INSU - CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)
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010504 meteorology & atmospheric sciences ,Geochemistry ,Copper deposits in volcano–sedimentary ,Mass balance ,High–temperature copper deposits ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Chlorite–smectite ,chemistry.chemical_compound ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,Geochemistry and Petrology ,Argillic alteration ,Chlorite ,0105 earth and related environmental sciences ,Labradorite ,Calcite ,geography ,geography.geographical_feature_category ,Andesine ,Volcanic rock ,chemistry ,13. Climate action ,engineering ,sequences ,Meteoric–hydrothermal alteration ,Carbonate ,Economic Geology ,Clay minerals - Abstract
International audience; The Seival Mine, located in the Camaquã Basin, hosts several small Cu and Ag ore deposits in volcano–sedimentary sequence surrounding the Lavras do Sul Intrusive Complex. Alteration minerals consist of calcite, sulfate, smectite and chlorite/smectite associated with Cu–rich sulfides. The mass balance calculations from less altered to altered volcanic rocks show large chemical changes with the mobility of mettallic elements in major or trace amounts. Mass balance calculations for similar volcanic protoliths, with different degrees of alteration or textural variations, indicate that increasing proportions of clay minerals reflects higher degrees of alteration. This alteration did not mobilize Si, Al, Fe, and Mg and had a small effect on other metallic elements such as Cu, Zn, Ni, and Au. Consequently, fluids associated with propylitic to argillic alteration with chlorite–smectite precipitation did not participate in the transport of base metals and ore deposition. Interpretations of oxygen stable–isotopes for magmatic, late magmatic and hydrothermal minerals show decreasing proportion magmatic fluid (δ18Ofluid of andesine labradorite ca. 5 to 7‰), toward a predominance of meteoric fluid (δ18Ofluid of quartz and calcite) between −12 and 0‰ for the low–temperature alteration (250 to 80 °C). Carbon stable isotopes result suggest a mixture of inorganic carbon ca. −7 to −5‰ from volcanic CO2 with late carbonate precipitation with atmospheric signatures ca. −4 to −1‰. These mass balance and stable isotopes interpretations suggest that high–temperature late–magmatic fluid/rock interaction (650 to 350 °C) has promoted the base metal enrichment.
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- 2019
8. Au Cu Ag mineralization controlled by brittle structures in Lavras do Sul Mining District and Seival Mine deposits, Camaquã Basin, southern Brazil
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E. Fontana, Rodrigo W. Lopes, Andre Sampaio Mexias, Everton Marques Bongiolo, Marcos Müller Bicca, Christophe Renac, and Ruy Paulo Philipp
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Dike ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Geochemistry ,Geology ,010502 geochemistry & geophysics ,01 natural sciences ,Tectonics ,Sinistral and dextral ,Shear (geology) ,Geochronology ,Magmatism ,Shear zone ,Structural geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
The mineralization of the Lavras do Sul Mining District and Seival Mine are controlled by brittle structures associated with the emplacement of the volcanogenic rocks and granitoids located in Lavras do Sul region, southernmost Brazil. This magmatism is associated with the evolution of the Camaqua Basin, an Ediacaran basin generated during the post–collisional stage of development of the Dom Feliciano Belt. The regional tectonic process has led to the activation of a large–scale high–angle shear zones and intense fracturing in the brittle to brittle–ductile regime. The relative chronology of structures and stress–field variations were recognized through remote sensing and structural data. The ore–deposits are controlled by extensional fractures and normal fault systems with a N70°W/70–85°NE direction in Lavras do Sul and a N40–60°E/70–88°NW direction in Seival and are disseminated or occur associated with quartz and calcite veins, respectively. We made a comparison of structures going from regional scale to smaller mineralized areas. The structural analysis of remote sensing and geophysical images (aeromagnetometry and aerogamma–spectrometry) integrated with structural data allowed us to reconstruct the paleostress tensor that generated the main fault systems and associated fractures of the host rock, which enabled the hydrothermal fluid circulation and the ore deposition. The integration of structural data such as fault slip planes, slickenlines, shear fractures systems, extensional fractures and kinematic indicators with the stratigraphic data allowed us to reconstruct the main directions of the tectonic efforts associated with the emplacement of the mineralizing magmas. The mineralization is associated with the sinistral N70°W/80–88°NE oriented Palma–Jacques Fault in the Lavras do Sul Mining District as well as the sinistral N50°E/80–88°SE oriented Cabritos–Perau Fault and the sinistral N20°E/80–88°SW oriented Segredo Fault in Seival Mine region. Their maximum compressional stresses are subhorizontal and NW–SE oriented, while a late subhorizontal and NE–SW oriented compressional stress affected only the rocks of the Seival Mine. These two main compressive stresses are associated with the development of a transcurrent (escape) tectonics during the final evolution of the Dom Feliciano Belt, constrained by U Pb zircon geochronology between 600 and 580 Ma. Transcurrent and normal NE–SW oriented faults are more expressive in volcanogenic rocks of the Seival Mine area, while extensional vein–type NW–SE oriented fractures are the most important structures in the Lavras do Sul area. We suggested that N70°W/70–88°NE oriented monzonitic dikes in Lavras do Sul and N50°E/70–88°NW oriented andesitic to trachyandesitic dikes in Seival area are probably the source of the mineralization.
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- 2018
9. Interplay of magmatic and diapiric environments in the Djebel El Hamra Pb-Zn-Hg ore district, northern Tunisia
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Christophe Renac, Dominique Gasquet, Christian Marignac, Christian Hibsch, Etienne Deloule, Nouri Hatira, Najet Slim-Shimi, Riadh Abidi, Alireza K. Somarin, Environnements, Dynamiques et Territoires de la Montagne (EDYTEM), and Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])
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Dolostone ,010504 meteorology & atmospheric sciences ,Evaporite ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,El Hamra ore deposits . Tortonian-Messinian . TSR and BSR . Hydrothermal system ,chemistry.chemical_compound ,Geophysics ,Sphalerite ,δ34S ,chemistry ,13. Climate action ,Geochemistry and Petrology ,Galena ,[SDE]Environmental Sciences ,engineering ,Economic Geology ,Sedimentary rock ,Sulfate ,Deposition (chemistry) ,Geology ,0105 earth and related environmental sciences - Abstract
International audience; The Djebel El Hamra Pb-Zn-Ba-Sr (Hg) deposits in northern Tunisia are hosted in a post-nappe anticline with a core of a Triassicevaporite diapir affected by the NE–SW-trending Ghardimaou-Cap Serrat lineament. Three stages of mineralization occurred inthe Triassic dolostone: stages I and II caused alternating deposition of sulfate (Ba, Sr) and sulfide (sphalerite, galena) minerals;stage III formed late-stage calcite-marcasite-cinnabar. Zebra textures record the syntectonic transition from compression toextension in the Late Tortonian-Messinian interval. Two fluid end-members were involved in sulfate deposition: one lowsalinity(L1, ~3 wt% eq. NaCl) fluid, probably from a meteoric origin, and a Na-Ca-Cl brine (L2, ~22 wt% eq. NaCl) solutionwhich originated from the Triassic diapiric source. A third end-member fluid (L3) with long residence time in the basement wasalso involved in the Pb-Zn deposition. The δ34S values froma cluster of sulfates around +16‰, show a Triassic evaporate source.The sulfur in sphalerite resulted from bacterial sulfate reduction (BSR); however, crystallization in a closed system resulted in arange of δ34S between +1.6 and +26.5‰. The δ34S values in galena (−28.4 to +8.2‰) are consistent with a BSR and thermochemicalsulfate reduction (TSR) origin of the sulfur. Secondary ion mass spectrometry (SIMS) lead isotope data in galena(207Pb/204Pb: 15.595 to 16.193, 206Pb/204Pb: 18.673 to 18.939, 208Pb/204Pb: 38.330 to 40.572) point to local contributions(sedimentary and Cenozoic magmatic rocks) to the main source from the Precambrian basement. Ore deposition occurred at adepth of about 2 km at temperatures between 80 and 250 °C. A shallow magmatic heat source was the cause of these thermalfluctuations.
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- 2021
10. Oxic and post-oxic chemical changes related to eogenesis and mesogenesis in a Miocene paleolake
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Aurélie Barats, Andre Sampaio Mexias, Marie-Christine Gerbe, Martina Rozmaric, Jérôme Barriere, Christophe Renac, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Univ Fed Rio Grande do Sul, Inst Geociencias, BR-91501970 Porto Alegre, RS, Brazil, Univ Fed Rio Grande do Sul, Inst Geociencias, Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Marine Environment Laboratories [Monaco] (IAEA-MEL), International Atomic Energy Agency [Vienna] (IAEA), Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Institut national des sciences de l'Univers (INSU - CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)
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0106 biological sciences ,010506 paleontology ,Dolomite ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Aquatic Science ,engineering.material ,01 natural sciences ,chemistry.chemical_compound ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,[SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology ,Ankerite ,Dissolution ,[SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,Earth-Surface Processes ,Calcite ,Chemistry ,010604 marine biology & hydrobiology ,Authigenic ,13. Climate action ,[SDU]Sciences of the Universe [physics] ,[SDE]Environmental Sciences ,engineering ,Carbonate ,Pyrite ,Deposition (chemistry) - Abstract
In the Forez Basin of the French Massif Central, clay-rich alluvial deposits include a series of red- and green-colored sediments and carbonate cement that record evaporation and oxidizing/reducing conditions related to intra-continental climate during the Early to Middle Miocene. The mineralogy, chemistry and relative chronology of authigenic calcite-ankerite, ferroan dolomite, pyrite, and analcite-clinoptilolite in clay-rich sediment enabled reconstruction of a series of processes related to deposition, eogenesis, and mesogenesis. The low-Mg calcite, ankerite, and ferroan-dolomite cement, systematically associated with zeolites (analcite and clinoptilolite), represent eogenetic precipitation associated with oxic to post-oxic water with Ca–Fe–Mg carbonic, then Na–Al–Si(OH)4-rich water. Occurrence of framboidal and cubic pyrites with low-Mg calcite and analcite is related to post-oxic conditions associated with deposition, eogenesis and times of early mesogenesis. Changes in the morphology, size, and chemistry of framboidal and cubic pyrite grains were related to reducing-oxidizing cycles and to the growth of grains. Sulfur isotope measures on framboidal and cubic pyrite suggest that both morphologies are related to bacterial reduction of SO42− to H2S and HS−1. With the exception of some sample depths (0–40 m below surface), similar chemical contents (trace elements [TE], rare earth elements [REE] and platinoids) suggest a similar, constant reservoir of metal and metalloids associated with the clayey sediment and volcanic fragments. Moreover, the TE and REE chemistry of cubic pyrite, in contrast to carbonates, indicates growth of pyrite during eogenesis to mesogenesis stages. The mineralogical and chemical changes are interpreted as reflecting dissolution of iron oxyhydroxides, rather than ankerite and ferroan-dolomite. Chemical elements from dissolution of iron oxyhydroxides would have mixed with hydrogen monosulfide and contributed to the growth of cubic pyrite. The crystal size distributions of pyrite grains suggest a closed system with surface-controlled growth. Assuming those conditions, the growth time of framboidal to cubic pyrite, based on diffusion of HS−1 in the clay-rich sediments, was estimated to have been from several days to a few years, to as much as 500 years (mm-scale pyrite).
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- 2020
11. Implication of 40Ar/39Ar–petrochronology in the Buracão orogenic gold deposit for tectonic and low-temperature evolution of the northern Brasília Fold Belt, Brazil
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S. Gallet, Reiner Neumann, Gustavo Luiz Campos Pires, Christophe Renac, and Everton Marques Bongiolo
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Phyllite ,Greenschist ,Metamorphic rock ,Muscovite ,Geochemistry ,Geology ,Gold deposit ,Fold (geology) ,engineering.material ,Tectonics ,engineering ,Biotite ,Earth-Surface Processes - Abstract
The 40Ar/39Ar ages (muscovite and biotite) and P-T estimations presented here allow us to reconstruct the Pressure–Temperature–time (P–T–t) path from the metamorphic peak to the generation of the orogenic Au (As, Bi, Ag) mineralization in the Buracao area. The application of software-based pseudosections for bulk phyllite composition allows us to better recognize three main stages in the P-T-t path. Rocks from the study area evolved from (i) syn-D1a greenschist metamorphic peak (T = 480–550 °C and P
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- 2021
12. Mineral assemblages and temperature associated with Cu enrichment in the Seival area (Neoproterozoic Camaquã Basin of Southern Brazil)
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Lauro Valentim Stoll Nardi, Andre Sampaio Mexias, Marcia Elisa Boscato Gomes, Eduardo Fontana, Christophe Renac, Rodrigo W. Lopes, Aurélie Barats, Universidade Federal do Rio Grande do Sul [Porto Alegre] (UFRGS), Géoazur (GEOAZUR 7329), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Univ Fed Rio Grande do Sul, Inst Geociencias, BR-91501970 Porto Alegre, RS, Brazil, Univ Fed Rio Grande do Sul, Fac Agron, Dept Solos, Universidade Federal dos Vales do Jequitinhonha e Mucuri = Federal University of Jequitinhonha and Mucuri Vallays (UFJMV), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), and Universidade Federal dos Vales do Jequitinhonha e Mucuri - UFVJM
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geography ,Mineral ,geography.geographical_feature_category ,Lava ,Andesite ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,010501 environmental sciences ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Lapilli ,Volcanic rock ,chemistry.chemical_compound ,Albite ,chemistry ,Geochemistry and Petrology ,Titanite ,engineering ,Economic Geology ,Chlorite ,Geology ,0105 earth and related environmental sciences - Abstract
International audience; The Neoproterozoic sequence of volcanic rocks in the Camaquã Basin included in the Lavras do Sul Shoshonitic Association hosts disseminated Cu deposits. The volcanic sequence in the Seival Mine area includes andesitic lava flows, lapilli tuff, volcanic agglomerate and andesitic dikes with pervasive alteration. The hydrothermal alteration is interpreted to be a product of late–magmatic fluids or the mixing of magmatic with meteoric fluids or basinal brines. The late–magmatic hydrothermal system started after volatile oversaturation and degassing in a magmatic system, which was partially segregated into vesicles. The similar REE contents in the andesine–labradorite and albite indicate that the fluid temperatures ranged from 600 to 250 °C. The crystallization of titanite and Fe–clinochlore to Mg–chamosite followed the albitization process. The temperature range associated with the chloritization process was estimated using a chlorite geothermometer and varied from 251 ± 56 to 183 ± 39 °C. The precipitation of Mg–saponite and smectite–rich chlorite/smectite mixed–layers in some andesitic lava flows and the precipitation of quartz, calcite, barite and hematite in fractures suggest fluid circulation with temperatures lower than the chloritization process. The alteration minerals are represented by chlorite and albite associated with pyrite–chalcopyrite, while chlorite/smectite mixed–layers and barite or hematite are associated with bornite–chalcocite–covellite. Thermodynamic calculations confirm the potential coprecipitation of pyrite–chalcopyrite with chlorite and albite. The occurrence of bornite–chalcocite–covellite and barite seems to be favored by low–temperature chlorite/smectite with neutral to mildly acidic water influx. Consequently, albitization and the process of chloritization at high temperatures (>ca. 251 ± 56 °C) can be used as an exploration guide for primary pyrite–chalcopyrite enrichment, and chlorite/smectite at low temperatures (ca. 250 to 50 °C) can be related to bornite–chalcocite–covellite or the process of Cu enrichment.
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- 2019
13. P–T–X conditions on the genesis of orogenic Au (As, Bi, Ag) deposit in metasedimentary rocks of the Buracão Area, Araí Group, Brasília Fold Belt, Brazil
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A. Barats, Everton Marques Bongiolo, Reiner Neumann, Gustavo Luiz Campos Pires, Christophe Renac, insituto de geociencias, universidade federal do rio de janeiro, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), Centro de Tecnologia Mineral, Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])
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Mineralization (geology) ,020209 energy ,Metamorphic rock ,Geochemistry ,Metamorphism ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Geology ,02 engineering and technology ,Fold (geology) ,15. Life on land ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Ore genesis ,Geochemistry and Petrology ,0202 electrical engineering, electronic engineering, information engineering ,engineering ,Carbonate rock ,Economic Geology ,Pyrite ,Pyrrhotite ,0105 earth and related environmental sciences - Abstract
International audience; The orogenic Au (As, Bi, Ag) mineralization (up to 31 g/t) of the Buracão area is hosted in the metasedimentary Paleo–Mesoproterozoic Traíras Formation, Araí Group, Brasília Fold Belt, Brazil. In order to discuss the P–T–X conditions that generated this mineralization, we present mineralogical, geochemical and fluid inclusion data of veins, gold and wall rocks. Coupled with previous structural data these additional data allow us to link metamorphism and deformation with fluid migration and ore genesis. The integration of fluid inclusion microthermometry with mineral geothermobarometers and structures show that rocks of the study area evolved from: (i) syn–D1a metamorphic peak (400–560 °C
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- 2019
14. First assessment on trace elements in sediment cores from Namibian coast and pollution sources evaluation
- Author
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Martina Rozmaric, Sabine Schmidt, Emilia Vassileva, Anna Maria Orani, M. O. Angelidis, Deon C. Louw, Christophe Renac, Marine Environment Laboratories [Monaco] (IAEA-MEL), International Atomic Energy Agency [Vienna] (IAEA), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)
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Pollution ,[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,Provenance ,Environmental Engineering ,010504 meteorology & atmospheric sciences ,Stable isotope ratio ,media_common.quotation_subject ,Anomaly (natural sciences) ,Geochemistry ,Sediment ,010501 environmental sciences ,Contamination ,01 natural sciences ,13. Climate action ,Environmental Chemistry ,Environmental science ,Enrichment factor ,Waste Management and Disposal ,Bay ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,media_common - Abstract
Trace elements (TEs), Rare Earth Elements (REEs) and Pb isotope ratios were determined in six small cores sampled along the Namibian coast and different indices, such as Enrichment Factor, Geo-accumulation Index and Pollution load index, were calculated to evaluate possible metal contamination in the area. Concentrations of Pb, Cu, As and Cd were strongly enhanced at the upper 7 cm of core C5, which is located at Walvis Bay, at the major harbor and urban/industrial center of Namibia, indicating the impact from the recent anthropogenic activities. Principal Component Analysis was applied to the data set indicating possible common sources of the contaminants. Pb stable isotope ratios, combined with the dating of core C5 at Walvis Bay, further confirmed the anthropogenic provenance of Pb sources in the recent sediment deposits, which occurred after 1945, when the anthropogenic activities in the area began to increase. REEs profiles were also determined, showing enrichment in REEs for some of the samples, typical for the minerals present in the area. Ce anomaly was detected in one of the cores but the REEs profile did not reveal anomalies ascribable to anthropogenic influence.
- Published
- 2018
15. Gossan mineralogy, textures, and gold enrichment over the Au (As, Bi, Ag) deposit in the Buracão Area (Brasília Fold Belt, Brazil): Implications for gold prospecting in weathering profiles
- Author
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Reiner Neumann, Christophe Renac, Gustavo Luiz Campos Pires, Everton Marques Bongiolo, insituto de geociencias, universidade federal do rio de janeiro, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])
- Subjects
Mineralization (geology) ,Hypogene ,Depósitos minerais ,Fineness ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Mineralogy ,Weathering ,010501 environmental sciences ,010502 geochemistry & geophysics ,01 natural sciences ,Brasilia Fold Belt ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,Mineralização aurífera ,Geochemistry and Petrology ,Prospecting ,[SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology ,[SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology ,Dissolution ,ComputingMilieux_MISCELLANEOUS ,Gossan ,0105 earth and related environmental sciences ,Fold (geology) ,15. Life on land ,[SDU]Sciences of the Universe [physics] ,[SDE]Environmental Sciences ,Economic Geology ,Geology - Abstract
The orogenic pyrite–rich Au (As, Bi, Ag) mineralization (up to 31 g/t) of the Buracao area is one of several orogenic deposits in the Brasilia Fold Belt (BFB; Central Brazil), exposed to tropical weathering that shows extensive oxidized profiles. The distribution and thickness of these gossan profiles lead to variable gold enrichments and uncertainties to gold prospecting in this region. In order to investigate physicochemical processes related to the evolution of the gossan cover and the supergene gold enrichment, we present mineralogical, textural and geochemical data from each zone of twenty gossan profiles in the Buracao area. These results show that the mineralogy and textures along the gossan profile reflect oxidation, hydrolysis, dissolution and precipitation processes controlled by different Eh–pH conditions, which are controlled by supergene conditions and hypogene ore composition. The geometry, distribution, and thickness of gossan profiles, as well as the style of gold occurrence, reflects textures of the hypogene orebodies, while the weathering has an important role in the gold chemical refining (i.e., increasing ca. 25% in gold fineness) and the distribution of gold grades along the profile. These points allowed us to identify that the leached spongy hematite–rich zone in the upper indigenous profile contains the higher fineness gold grades (i.e., the “bonanza level”), and Bi–minerals such as waylandite and bismutite that may be important pathfinders for high gold grades in these gossan profiles. Our results demonstrate that ore prospection in gossans over Au–As–Bi–Ag deposits should be done focusing on leached zones, different to that traditionally conducted in gossans related to base metal sulfide deposits that have focused on precipitation zones. The similarities between the hypogene mineralization of the Buracao area and many deposits in the BFB and worldwide encourage the application of this approach elsewhere, which improve gold prospecting in weathering profiles over orogenic deposits.
- Published
- 2020
16. Tracing source and mobility of arsenic and trace elements in a hydrosystem impacted by past mining activities (Morelos state, Mexico)
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Christophe Renac, M. V. Esteller, Gaël Durrieu, Sofia Esperenza Garrido Hoyos, Humberto Saint Martin, Anna Maria Orani, Aurélie Barats, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Marine Environment Laboratories [Monaco] (IAEA-MEL), International Atomic Energy Agency [Vienna] (IAEA), Université de Toulon (UTLN), Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Universidad Nacional Autónoma de México = National Autonomous University of Mexico (UNAM), Universidad Autonoma del Estado de Morelos (UAEM), Instituto Mexicano de Tecnología del Agua (IMTA), Instituto Mexicano de Tecnología del Agua - IMTA (IMTA), Universidad Nacional Autónoma de México (UNAM), Université Côte d'Azur (UCA), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), and Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS)
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Environmental Engineering ,River ecosystem ,010504 meteorology & atmospheric sciences ,media_common.quotation_subject ,chemistry.chemical_element ,Weathering ,010501 environmental sciences ,01 natural sciences ,chemistry.chemical_compound ,[CHIM]Chemical Sciences ,Environmental Chemistry ,Waste Management and Disposal ,ComputingMilieux_MISCELLANEOUS ,Arsenic ,0105 earth and related environmental sciences ,media_common ,Stable isotope ratio ,Arsenate ,Sediment ,Particulates ,Pollution ,6. Clean water ,Speciation ,chemistry ,13. Climate action ,Environmental chemistry ,[SDE]Environmental Sciences - Abstract
The Sierra Huautla (Morelos State, Mexico) is a biological reserve with historical mines of Ag and Pb. In this area, waters used by inhabitants are contaminated by arsenic (As). An integrated environmental survey was realized both in waters and sediments to better constrain the source and the mobility of As and other trace elements. Two areas of interest were selected: (1) the Nexpa River ecosystem to determine the local geochemical background, and (2) the Huautla area, affected by past mining activities. This study allowed the definition of the local geochemical baseline in sediments or in waters, demonstrated uncontaminated by TE in the Nexpa area, except for As in the dissolved phase or for Cd in Suspended Particulate Matters (SPM). In the Huautla area, TE contents in water were higher than the World Health Organization (WHO) limits for Al, As and Mn in unfiltered waters, and only for As in the dissolved phase. Speciation analyses revealed arsenic to be present only as the toxic-inorganic arsenate species, As(+V). In SPM, Ag, As, Cd and Zn concentrations were higher than Sediment Quality Guidelines (SQG). The different geochemical indice (EF: 5, PLI: 3, EF: Igeo: 5–3) demonstrated that SPM were significantly contaminated and consistute an health risk for Huautla inhabitants exposed to As-contaminated waters and TE-rich SPM. The combination of mineralogy, chemistry, C and S stable isotopes with thermodynamic modeling indicate dissolutions of minerals from local geological formations, sorption-desorption phenomena from clays and oxy-hydroxides, and the weathering responsible for the transport of the TE-rich SPM (1.8 wt% for 17% of the total TE concentration). Moreover, the past mining activity would be a source of the contamination only for As in waters from flooded mines.
- Published
- 2020
17. Metallogenesis of the Paleoproterozoic Piaba orogenic gold deposit, São Luís cratonic fragment, Brazil
- Author
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Fernando Rodrigo dos Anjos Lucas, Fred Jourdan, Marco Antonio Galarza, Richard Armstrong, Evandro Luiz Klein, Joana D.S. Queiroz, Saney Cecílio Ferreira de Freitas, Christophe Renac, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), Western Australian Argon Isotope Facility, Department of Applied Geology & JdL-CMS, Austalian National University, Australian National University (ANU), Brazilian Geological Survey - CPRM, GPGE (GPGE), Conj. Satélite Tv, Programa de Pós-Graduação em Geologia e Geoquímica, Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Western Australian Argon Isotope Facility (WAAIF), The Institute for Geoscience Research [Perth] (TIGeR), School of Earth and Planetary Science [Perth - Curtin university], Curtin University [Perth], Planning and Transport Research Centre (PATREC)-Planning and Transport Research Centre (PATREC)-Curtin University [Perth], Planning and Transport Research Centre (PATREC)-Planning and Transport Research Centre (PATREC)-School of Earth and Planetary Science [Perth - Curtin university], and Planning and Transport Research Centre (PATREC)-Planning and Transport Research Centre (PATREC)
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Felsic ,010504 meteorology & atmospheric sciences ,Andesite ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Geology ,engineering.material ,010502 geochemistry & geophysics ,Sericite ,01 natural sciences ,Brésil ,Geochemistry and Petrology ,Ultramafic rock ,Rhyacian ,Breccia ,engineering ,GEODYNAMIQUE ,Economic Geology ,Fluid inclusions ,Pyrite ,0105 earth and related environmental sciences - Abstract
International audience; Piaba is an orogenic gold deposit (~ 3.5 Moz) of the São Luís cratonic fragment in north-northeastern Brazil. The deposit is epizonal–mesozonal and associated with the development of a subvertical strike–slip fault that cut across Rhyacian metavolcano-sedimentary rocks and granitoids. The metavolcano-sedimentary sequence comprises carbon-bearing schists, andesite/dacite, ultramafic rocks and felsic tuffs formed at 2240 ± 5 Ma to 2227 ± 33 Ma that were intruded at 2214 ± 3 Ma by fine-grained, subvolcanic granophyric granodiorite. Whole-rock geochemistry indicates that the hosting metavolcano-sedimentary sequence formed in a subduction-related (arc, back-arc?) setting, which has previously been interpreted as the early-arc stage of an accretionary orogen (2240–2214 Ma) that was followed by voluminous subduction-related calc-alkaline arc magmatism (2168–2145 Ma) and by a collisional phase (2100 ± 15 Ma) that produced several bodies of peraluminous granites. The hydrothermal alteration of the host rocks produced early, distal carbonization and hematitization and proximal, ore-related chlorite–sericite–carbonate–sulfide alteration. Two styles of mineralization, occurring in association, are present: (1) a network of thin quartz ± sulfide veinlets and subordinate narrow breccia veins with refractory- to free-milling gold dissemination in hydrothermally-altered host rocks, and (2) subordinate low-sulfide Au-quartz veins with free-milling gold. Fluid inclusions and stable isotopes characterize the mineralizing solution as a relatively reduced (log fO2 = − 30 to − 35), neutral to slightly alkaline (pH 5 to 6.2), low-salinity (average 5% NaCl), aqueous-carbonic (XCO2 = 5 to 59 mol%, XH2O = 40 to 93 mol%, XN2 and XCH4 < 1 mol%) metamorphic fluid (δ18OH2O = + 5.5 to + 8.9‰, δDH2O = − 8 to − 69‰), and suggest that gold mineralization occurred at 250° to 330 °C and 1.25 to 2.8 kbar in response to phase separation and fluid–rock interactions that produced sulfidation and minor carbonatization. Sulfur (δ34S = − 2.7 to − 3.8‰) is from an undetermined source, probably magmatic (oxidized) or sedimentary. Lead isotope compositions of gold, ore-related pyrite and K-feldspar from regional rocks suggest that collision-related granitoids of ca. 2100 ± 15 Ma are the most likely sources for Pb in the ore, although mantle and lower crustal sources are also observed. 40Ar/39Ar in hydrothermal sericite yielded a plateau age of 1980 ± 13 Ma, which is similar to the Pb–Pb model age of gold of 1959 Ma. These are considered the minimum age for gold mineralization, whereas the maximum age of 2009 ± 11 Ma is given by a small gold-hosting intrusion in the same region.
- Published
- 2015
18. Hydrothermal alteration of volcanic rocks in Seival Mine Cu–mineralization – Camaquã Basin – Brazil (part I): Chloritization process and geochemical dispersion in alteration halos
- Author
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Marcia Elisa Boscato Gomes, Eduardo Fontana, Rodrigo W. Lopes, Andre Sampaio Mexias, Aurélie Barats, Christophe Renac, Lauro Valentim Stoll Nardi, Univ Fed Rio Grande do Sul, Inst Geociencias, BR-91501970 Porto Alegre, RS, Brazil, Univ Fed Rio Grande do Sul, Fac Agron, Dept Solos, Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
geography ,Chalcocite ,geography.geographical_feature_category ,Geochemistry ,Mineralogy ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,engineering.material ,Covellite ,010502 geochemistry & geophysics ,01 natural sciences ,Hydrothermal circulation ,Volcanic rock ,Petrography ,Geochemistry and Petrology ,visual_art ,engineering ,Bornite ,visual_art.visual_art_medium ,Economic Geology ,Pyrite ,010503 geology ,Clay minerals ,Geology ,0105 earth and related environmental sciences - Abstract
International audience; The Seival Mines are situated in the NE portion of the Lavras do Sul mining district, southernmost Brazil. They are hosted by volcanic and sub-volcanic rocks of Neoproterozoic age, which are part of the post–collisonal Camaquã Basin volcano–sedimentary sequence. The mineralization occurs in shoshonitic volcanic and sub–volcanic rocks of the Lavras do Sul Shoshonitic Association. They are of intermediate composition and exhibit widespread hydrothermal alteration. The mineralization occurs primarily in the form of bornite, chalcocite, covellite, pyrite, and in supergene phases as malachite. Mineral occurrence is always controlled by fractures. Ore is associated with chloritization processes, which produced smectite, chlorite/smectite and corrensite clay minerals and gangue of carbonate, mostly calcite, and barite. In this study field mapping and drill core sampling, petrography with optical microscopy and electron microscopy, X–ray diffraction for clay size fraction characterization and whole–rock geochemistry are used to understand the spatial distribution and relative chronology of hydrothermal alteration products of different lithology in the mineralized zones. The post–magmatic fluid activity and hydrothermal lower–temperature alteration that produced smectite ➔ chlorite/smectite ➔ chlorite and corrensite ➔ carbonate have changed the major, minor, trace and rare earth element (REE) contents. Lavas and sub-volcanic rocks contain Cu–Fe sulfides. In alteration halos, Cu–sulfides with supergene influence is related to circulation of late hydrothermal fluids. The pH variations and sulfide materials are related to dispersion metals around vertical structures.
- Published
- 2017
19. New 40Ar/39Ar ages and revised 40K/40Ar* data from nephelinitic–phonolitic volcanic successions of the Trindade Island (South Atlantic Ocean)
- Author
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Christophe Renac, Mauro Cesar Geraldes, Gustavo Luiz Campos Pires, Anderson Costa dos Santos, Fred Jourdan, Reiner Neumann, Everton Marques Bongiolo, programa de pos-graduacao em geologia, insituto de geociencias, universidade federal do rio de janeiro, Universidade do Estado do Rio de Janeiro - Faculdade de Geologia, Géoazur (GEOAZUR 7329), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Western Australian Argon Isotope Facility (WAAIF), The Institute for Geoscience Research [Perth] (TIGeR), School of Earth and Planetary Science [Perth - Curtin university], Curtin University [Perth], Planning and Transport Research Centre (PATREC)-Planning and Transport Research Centre (PATREC)-Curtin University [Perth], Planning and Transport Research Centre (PATREC)-Planning and Transport Research Centre (PATREC)-School of Earth and Planetary Science [Perth - Curtin university], Planning and Transport Research Centre (PATREC)-Planning and Transport Research Centre (PATREC), Centre for Mineral Technology (CETEM), Ministère de la Science et Technologie, Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Western Australian Argon Isotope Facility, Department of Applied Geology & JdL-CMS, Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)
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geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Pleistocene ,Ephemeral key ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Volcanism ,010502 geochemistry & geophysics ,01 natural sciences ,Plume ,Paleontology ,Geophysics ,Volcano ,13. Climate action ,Geochemistry and Petrology ,South American Plate ,Period (geology) ,14. Life underwater ,Cenozoic ,Geomorphology ,Geology ,0105 earth and related environmental sciences - Abstract
International audience; The Trindade Island is located in the South Atlantic Ocean, 1170 km from the Brazilian coast and represents the eastern end of the submarine E–W Vitória–Trindade Chain. This is interpreted as the Trindade plume track beneath the South American plate during the Cenozoic. Almeida (1961) recognized five volcanogenic successions at Trindade in decreasing age: the Trindade Complex (TC) and the Desejado (DF), Morro Vermelho (MV), Valado (VF) and Paredão (PF) formations, composed of nephelinitic to phonolitic effusive-pyroclastic deposits, dykes and necks. Here, we present new 40Ar/39Ar ages and re-evaluation of available 40K/40Ar* data that, coupled with previous petrological information, allowed us to reconstruct the volcanic history of the island (i.e., 3.9–0.25 Ma) distinguishing near synchronous volcanic episodes and solving several stratigraphic uncertainties reported in the literature.The geochronological dataset show that the nephelinitic–phonolitic volcanism at Trindade was discontinuous throught time, being marked by periods of high volcanic activity and periods of quiescence, which suggests variable melt production and eruption rates. The peak of the volcanic activity occurred between 3.9 and 2.5 Ma (i.e., Lower Pliocene to Lower Pleistocene) that is represented by the TC, which correspond to the largest volume of volcanic deposits preserved in the island. The volcanic activity slows down progressively from 2.5 Ma to cease at ca. 1.6 Ma, period that is represented by the DF. This volcanism was followed by a quiescent period that lasted until the ephemeral nephelinitic volcanism of the MV (no age), VA (no age) and PF (ca. 0.25 Ma). Thus, the volcanic activity in Trindade was ceased completely at ca. 0.25 Ma, event registered in the uppermost volcanic deposits of the PF and that represents the last volcanic activity in the Brazilian territory.
- Published
- 2016
20. The origin of sulfate mineralization and the nature of the BaSO4–SrSO4 solid-solution series in the Ain Allega and El Aguiba ore deposits, Northern Tunisia
- Author
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Alirisa Soumarin, Najet Slim-Shimi, Riadh Abidi, Nouri Hatira, Dominique Gasquet, Sarah A. Gleeson, Christian Marignac, Christophe Renac, Département de géologie, Faculté des Sciences de Bizerte [Université de Carthage], Université de Carthage - University of Carthage-Université de Carthage - University of Carthage, Faculté des Sciences Mathématiques, Physiques et Naturelles de Tunis (FST), Université de Tunis El Manar (UTM), Ecole Nationale Supérieure des Mines de Nancy (ENSMN), Université de Lorraine (UL)-Institut Mines-Télécom [Paris] (IMT), Faculté des sciences de Gabes, Environnements, Dynamiques et Territoires de la Montagne (EDYTEM), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Transferts lithosphériques, Université de Géologie de l'université Jean Monnet, Department of Geology, Brandon University, Brandon University, Department of Earth and Atmospheric Sciences [Edmonton], University of Alberta, Institut Mines-Télécom [Paris] (IMT)-Université de Lorraine (UL), Environnements, Dynamiques et Territoires de Montagne (EDYTEM), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), and Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS)
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Tunisia ,010504 meteorology & atmospheric sciences ,Dolomite ,Geochemistry ,Mineralogy ,chemistry.chemical_element ,Basinal brine ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,chemistry.chemical_compound ,Geochemistry and Petrology ,Galena ,Marcasite ,Hydrothermal fluid ,0105 earth and related environmental sciences ,Strontium ,Triassic diapir ,Geology ,Sr)SO4 solid-solution ,Evaporite ,Sphalerite ,chemistry ,engineering ,Carbonate rock ,Carbonate ,Economic Geology ,(Ba ,Pyrite - Abstract
International audience; Ain Allega and El Aguiba are among the largest barite-celestite deposits attributed to the Triassic period in Tunisia. They are located in the flysch zone on the eastern edge of the Triassic diapir of Jebel Hamra. The ore body consists of dolomite intensely brecciated and surrounded by marls, clay, gypsum and dolomite which forms the hanging wall of the deposit, and rimmed by Paleocene marls. The ore the surface structure, which in turn controls the mechanism of adsorption and incorporation of minor and trace elements into the growing crystal. For a solid solution, the transitional supersaturation for different growth mechanisms can be significantly different for the two end members. One of the most interesting and intriguing phenomena observed in natural crystals of the (Ba, Sr) SO4 solid solution from this study area is the development of compositional oscillatory zoning, consisting of alternating Ba-rich and Sr-rich layers. The sulfur isotope analyses show significant variability for barite and celestite (from 16.2 to 23 ‰). These values are interpreted as the result of the mixing of two sulfur end-members in the mineralizing fluids, corresponding to thermochemical sulfate reduction of Messinian seawater, together with Triassic sulfate, as sulfur sources. Fluid inclusion studies of celestite show that the BaSO4-SrSO4 solid-solution in both deposits was precipitated from hot saline solution (Th=190±20°C; 16.37 wt. % NaCl equivalent in Ain Allega and 8.2 wt. % NaCl equivalent in El Aguiba). Consequently, the precipitation could be from mixing of basinal brines with magmatic-meteoric fluid. minerals show a cap-rock type mineralization with various forms and types, in particular impregnation in dolomite, breccia cement, replacement of carbonate caprock and open space-filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite and pyrite. Principal gangue minerals are barite, celestite, calcite, dolomite and quartz .The ore minerals are hosted by the Triassic carbonate rocks, which show hydrothermal alteration, dissolution and brecciation. The study of barite-celestite solid-solution shows a bimodal distribution in which the composition is not continuous. Some intermediate compositions are missing; 20-80% SrSO4 for El Aguiba ore deposit and 50-70% SrSO4 for the Ain Allega ore deposit. X-ray diffraction peaks in the BaSO4-SrSO4 series display considerable broadening at intermediate compositions. The unit cell volume varies from 346.97 Å3 in barite (100% BaSO4) to 308.29 Å3 in celestite (100% SrSO4). This variation in cell parameters is attributed to the degree of substitution of barium by strontium since there is less variation between ionic radii of these elements. Consequently, these substitutions caused variation in morphologies, position and d-spacing of peaks (200, 011, 113, 312,122, 112, and 111). Some barite crystals have small-scale, strontium compositional banding which suggests that the crystals responded to regular fluctuations in physiochemical conditions during deposition. The degree of supersaturation in Ba2+ and Sr2+ controls the growth mechanism and consequently
- Published
- 2012
21. Structural and lithological controls of gold–bearing veins associated with the Brasiliano–Pan African Orogeny: An example from the Buracão Area, Araí Group (Brasília Fold Belt, Brazil)
- Author
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Maurício Prado, Christophe Renac, Débora Barros Nascimento, Everton Marques Bongiolo, Gustavo Luiz Campos Pires, Programa De Pós-Graduação Em Geologia E Geoquímica, PPGG, Universidade Federal do Rio de Janeiro (UFRJ), Instituto de Geociências, Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Paringa Mineração Limitada, Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
010504 meteorology & atmospheric sciences ,Greenschist ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Geology ,Orogeny ,Fold (geology) ,engineering.material ,010502 geochemistry & geophysics ,Sericite ,01 natural sciences ,Statherian ,Shear (geology) ,engineering ,Vein (geology) ,Geomorphology ,Biotite ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
International audience; The Buracão area, Central Brazil, comprises a group of structurally–controlled vein–type gold prospects, hosted in the metasedimentary Traíras Fm. of the Araí Group. This group records all tectonic stages of the Statherian taphrogenesis in Central Brazil and represents part of the Brasília Fold Belt (BFB) developed during the Neoproterozoic Brasiliano Orogeny. Three lithostratigraphic units were identified at the study area: two phyllitic and one composed of intercalation of quartzite and carbonaceous/sericite phyllites that hosted the Au mineralized vein systems. These units were metamorphosed to the biotite zone, greenschist facies. The high–grade mineralization (up to 31 g/t) occurs as subvertical zoned or massive veins with quartz, white mica, Fe–sulfides and Fe–oxides oriented in four main directions (i.e. N50°E; N°20E; N–S and E–W). Two deformational phases, each subdivided in two stages (D1a, D1b, D2a and D2b) were recognized in the study area. These deformational phases comprise different sets of structures, such as foliations, folds, faults, fractures and veins that represent regional deformational events on subordinated scale. The D1a and D1b stages represent the regional N–S trending thrust fronts and propagation folding developed during the evolution of W–E shortening, respectively. The D2a and D2b were correlated to the development and reactivation of regional–scale N– and NE–trending transpressive shear systems at different crustal levels, respectively. The gold–bearing quartz veins were developed during D2a stage as a complex shear fracture set according to a Riedel system, representing subordinated structures of the regional transpressive system. The structurally–controlled gold occurrences of the Buracão area is an example of orogenic vein–type gold mineralization developed during the Brasiliano–Pan African Orogeny at the BFB in Central Brazil. Our work suggests that this poorly studied part of BFB has good potential for additional high-grade orogenic gold deposits.
- Published
- 2016
22. Origin of pegmatites and fluids at Ponta Negra (RJ, Brazil) during late- to post-collisional stages of the Gondwana Assembly
- Author
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Andre Sampaio Mexias, Renata da Silva Schmitt, Everton Marques Bongiolo, Christophe Renac, Patricia d'Almeida de Toledo Piza, Instituto de Geociências, Universidade Federal do Rio de Janeiro (UFRJ), Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Universidade Federal do Rio Grande do Sul [Porto Alegre] (UFRGS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Nice Sophia Antipolis (... - 2019) (UNS), and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
010504 meteorology & atmospheric sciences ,Partial melting ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Geology ,Skarn ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Gondwana ,13. Climate action ,Geochemistry and Petrology ,engineering ,Fluid inclusions ,Syenogranite ,Pegmatite ,Biotite ,0105 earth and related environmental sciences ,Zircon - Abstract
International audience; The Ponta Negra Pegmatites (PNP), part of a pegmatitic province in Rio de Janeiro State, Brazil, crop out along an intensely deformed, medium- to high-grade metamorphic area that is proximal to a crustal-scale thrust zone developed during the Brasiliano/Pan–African Orogeny. Fieldwork shows that the pegmatites formed in two distinct stages: (i) syn-collisional leucosome veins (Group I) conformable with the tectonic foliation of the gneissic host rocks and (ii) late- to post-collisional dykes (Group II) that cross-cut the same tectonic foliation at a high angle.In this paper, we use geochemistry of whole-rock and mineral separates (alkali–feldspar and biotite), fluid inclusion microthermometry and stable isotopic (δ18O, δD, δ13C) determinations on minerals (quartz, alkali–feldspar, biotite and magnetite) and fluid inclusions to provide insights into the composition of the pegmatite-forming melts, associated fluids, and their geotectonic significance. U–Pb SHRIMP dating of the Cajú syenogranite was performed to evaluate and compare the timing of magmatic events along the Cabo Frio Tectonic Domain as this is the closest post-collisional pluton to the studied pegmatites.The calculated temperature for the Group I syn-collisional veins (740 °C) is similar to previous estimates for the peak metamorphic conditions in the study area. Variations in the temperature of the Group II pegmatite dykes obtained from stable isotopes (380 to 720 °C), and microthermometric data from primary fluid inclusions with traces of N2 (Th = 280 to 360 °C), may reflect the thermodynamics of the pegmatite crystallization, exsolution textures and isotopic exchange. The composition of fluids in equilibrium within the pegmatite dykes consists of magmatic and metamorphic components. The minimum pressures calculated for the emplacement of the pegmatites are equivalent to a shallow crustal depth between 1.7 and 3.5 km, which corresponds to the exhumation of the orogen since the emplacement of the pegmatites. A linear trend of decreasing CO2 content and δ13CCO2 is consistent with mixtures between (i) carbon derived from organic matter or volatilization of skarns and (ii) inorganic carbon (carbonate).Based on the data obtained, we propose that the pegmatites of Ponta Negra are close to an LCT-type geochemical signature (highly peraluminous magmas with normative corundum), and originated by partial melting of the metasedimentary Palmital succession at depth, during the waning stages of the Búzios Orogeny. The primary melts of the PNP cross-cut both the Neoproterozoic supracrustals and the Paleoproterozoic orthogneissic basement during its ascent and emplacement at higher crustal levels. Variable melt sources explain the slight differences in geochemical compositions among the studied rocks within the metasedimentary succession, which probably include Mn-bearing exhalites, as well as differentiation processes.The 454 ± 5 Ma U–Pb (zircon) age of the Cajú syenogranite overlaps previous geochronological data of 440 ± 11 Ma obtained on a pegmatite dyke at Ponta Negra, bracketing and extending the time interval for the Gondwana assembly collapse magmatism in the region. The heat that triggered this magmatic event could still be a consequence of the collisional orogeny, increasing contents of heat-producing elements, or, a large intraplate extension that followed the Gondwana amalgamation and initiated the formation of Paleozoic basins.
- Published
- 2016
23. Hydrothermal fluid interaction in basaltic lava units, Kerguelen Archipelago (SW Indian Ocean)
- Author
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Peter Bowden, Kurtis Kyser, Jean-Yves Cottin, Bertrand Moine, Christophe Renac, Laboratoire de Transferts Lithosphériques (LTL), Université Jean Monnet [Saint-Étienne] (UJM), Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Department of Geological Sciences and Geological Engineering, Queen's University [Kingston, Canada], Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), and Université Jean Monnet - Saint-Étienne (UJM)
- Subjects
010504 meteorology & atmospheric sciences ,[SDE.MCG]Environmental Sciences/Global Changes ,Carbonate minerals ,Geochemistry ,stable isotopes ,interaction ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Peralkaline rock ,Hydrothermal circulation ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,Geochemistry and Petrology ,Fluid inclusions ,14. Life underwater ,meteoric-hydrothermal alteration ,[SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology ,Kerguelen basalt ,[SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,Basalt ,Igneous rock ,fluid inclusions ,[SDU]Sciences of the Universe [physics] ,[SDE]Environmental Sciences ,Meteoric water ,engineering ,Celadonite ,fluid–rock ,Geology - Abstract
Hydrothermally altered basaltic lava-units in the northern Kerguelen Archipelago contain a wide variety of secondary silicate and carbonate minerals, including zeolites, hydrothermal calcite, dolomite and magnesite, as well as celadonite, orthoclase (adularia) and quartz. Petrography, fluid-inclusion microthermometry, trace-elements geochemistry, Sr isotopes and stable-isotope compositions indicate hydrothermal fluid cells derived from meteoric water interacting with basalts and Rb-rich subvolcanic peralkaline rocks at temperatures ranging from 50 to 200 °C associated with the cooling of the lava pile. The calculated δ 18 O values of meteoric-hydrothermal waters in fossil hydrothermal systems are identical to those in present-day hot springs, suggesting that meteoric recharge was continuous throughout the igneous cooling cycles of the 28–23 Ma older host basalts and the younger 15–5 Ma old peralkaline intrusions. The Kerguelen northern coastline hydrothermal system in the basaltic pile demonstrates that much of the silicate mineralogy and almost all carbonate secondary minerals in altered basalts were derived from meteoric-hydrothermal fluids, rather than products of seawater interaction, or even magmatic-hydrothermal fluids associated with peralkaline intrusions.
- Published
- 2010
24. Formation of non-expandable 7 Å halloysite during Eocene–Miocene continental weathering at Djebel Debbagh, Algeria: A geochemical and stable-isotope study
- Author
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F. Assassi and Christophe Renac
- Subjects
Supergene (geology) ,Aptian ,Stratigraphy ,Geochemistry ,Geology ,Weathering ,engineering.material ,Halloysite ,Isotopes of oxygen ,Diagenesis ,Paleontology ,Meteoric water ,engineering ,Alpine orogeny - Abstract
In north-eastern Algeria, autochthonous limestone units at Djebel Debbagh varying in age from Aptian to Cenomanian underwent burial diagenesis followed by deformation during the Alpine orogeny. Karst windows formed during Oligocene to Miocene times, and are now filled with clay minerals, which currently help to sustain a local mineral industry. The largest karst window at Djebel Debbagh contains substantial volumes of 7 A halloysite ore. Mineralogical investigations on the 7 A halloysite indicate a non-expandable material, with measured water contents varying from 14.1 to 15.5 wt.% H2O. Non-expandable 7 A halloysite showed limited hydrogen-exchange capacity during a 24-month laboratory experiment, suggesting that hydrogen and oxygen isotopes had not exchanged since equilibrium at the time of halloysite formation. Therefore, stable-isotope data were used to calculate reliable temperature profiles and to determine fluid composition. It is suggested on the basis of geochemical and mineralogical data that 7 A halloysite formed between 25 °C and 40 °C in equilibrium with meteoric water during Eocene to Miocene times. Estimates of supergene temperatures and calculated stable-isotope values for rainfall correspond to continental climate conditions during Miocene times, coeval with the closure of the Liguro oceanic basin.
- Published
- 2009
25. Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil
- Author
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Christophe Renac, André Giret, Kazuo Fuzikawa, Candido Augusto Veloso Moura, Evandro Luiz Klein, and Chris Harris
- Subjects
Stable isotope ratio ,Metamorphic rock ,Geochemistry ,Schist ,Mineralogy ,Isotopes of oxygen ,chemistry.chemical_compound ,Geophysics ,chemistry ,Geochemistry and Petrology ,Mineral redox buffer ,Carbonate ,Economic Geology ,Fluid inclusions ,Quartz ,Geology - Abstract
The Serrinha gold deposit of the Gurupi Belt, northern Brazil, belongs to the class of orogenic gold deposits. The deposit is hosted in highly strained graphitic schist belonging to a Paleoproterozoic (∼2,160 Ma) metavolcano-sedimentary sequence. The ore-zones are up to 11 m thick, parallel to the regional NW-SE schistosity, and characterized by quartz-carbonate-sulfide veinlets and minor disseminations. Textural and structural data indicate that mineralization was syn- to late-tectonic and post- metamorphic. Fluid inclusion studies identified early CO2 (CH4-N2) and CO2 (CH4-N2)-H2O-NaCl inclusions that show highly variable phase ratios, CO2 homogenization, and total homogenization temperatures both to liquid and vapor, interpreted as the product of fluid immiscibility under fluctuating pressure conditions, more or less asso- ciated with postentrapment modifications. The ore-bearing fluid typically has 18-33mol% of CO2, up to 4mol% of N2, and less than 2mol% of CH4 and displays moderate to high densities with salinity around 4.5wt% NaCl equiv. Mineralization occurred around 310 to 335°C and 1.3 to 3.0 kbar, based on fluid inclusion homogenization temperatures and oxygen isotope thermometry with estimated oxygen fugacity indicating relatively reduced conditions. Stable isotope data on quartz, carbonate, and fluid inclusions suggest that veins formed from fluids with δ 18 OH2O and δDH2O (310-335°C) values of +6.2 to +8.4‰
- Published
- 2006
26. Carbonatite melt in oceanic upper mantle beneath the Kerguelen Archipelago
- Author
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Jean-Pierre Lorand, Christophe Renac, André Giret, Michel Grégoire, Guillaume Delpech, Simon M.F. Sheppard, Jean-Yves Cottin, Bertrand Moine, and Suzanne Y. O'Reilly
- Subjects
Calcite ,Dolomite ,Geochemistry ,Geology ,Silicate ,chemistry.chemical_compound ,chemistry ,Geochemistry and Petrology ,Silicate minerals ,Carbonatite ,Carbonate ,Metasomatism ,Mafic - Abstract
Some mantle-derived Kerguelen harzburgite and dunite xenoliths have bulk-rock and mineral trace element compositions that provide evidence of carbonatitic metasomatism similar to that described in some continental and other oceanic settings. Rare xenoliths contain carbonates that are highly enriched in rare earth elements (REE), interpreted to be quenched, evolved carbonatitic melts. One amphibole-bearing dunite mantle wall-rock containing carbonates in small interstitial pockets (100–500 μm across) has been studied in detail. Mg-bearing calcite (MgO
- Published
- 2004
27. Isotopic fluid changes in a Neoproterozoic porphyry-epithermal system: The Uruguay mine, southern Brazil
- Author
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Marcia Elisa Boscato Gomes, Andre Sampaio Mexias, Jorge Henrique Laux, Christophe Renac, L. V. S. Nardi, Luiz Henrique Ronchi, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), Instituto de Geociências, Universidade Federal do Rio Grande do Sul [Porto Alegre] (UFRGS), Universidade Federal de Pelotas = Federal University of Pelotas (UFPel), Brazilian Geological Survey - CPRM, Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)
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chemistry.chemical_classification ,Sulfide ,Stable isotope ratio ,Chalcopyrite ,δ18O ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Geology ,Context (language use) ,engineering.material ,chemistry ,Geochemistry and Petrology ,visual_art ,visual_art.visual_art_medium ,engineering ,Economic Geology ,Sedimentary rock ,Pyrite ,Clay minerals - Abstract
International audience; Identifying the source, origin and time of emplacement of copper and gold deposits in the Neoproterozoic volcano-sedimentary and plutonic series of southern Brazil is a longstanding research goal. In this geological context, the Camaquã and Lavras do Sul areas are reported to be a post-collisional domain related to the Braziliano-Pan-African Orogenic Cycle. This study focused on the Uruguay open-pit mine through a detailed assessment of the mineralogy, geochemistry and (S, O, H and C) stable isotopes of pyrite, chalcopyrite, clay minerals and carbonates as veins or disseminated sulfides in sedimentary rocks. The results indicate that the Camaquã mine is a low-sulfidation epithermal-type deposit with sulfide precipitations related to a mixture of magmatic (δ34S = 1 to 4‰; δ18O: 3 to 9‰) and meteoric waters (δ18O = − 4 to − 12‰) and a temperature varying from 350 to 80 °C. Ore precipitation is associated with sequential sulfide crystallization exhausting the S magmatic source.
- Published
- 2014
28. Role of compressive tectonics on gas charging into the Ordovician sandstone reservoirs in the Sbaa Basin, Algeria: constrained by fluid inclusions and mineralogical data
- Author
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Gomes, Marcia E.B., Barats, Aurélie, Gerbe, Marie, Lopes, Rodrigo, Nardi, Lauro V.S., Lopes, R.W., Mexias, A.S., Philipp, R.P., Bicca, M.M., Fontana, Eduardo, Pires, G.L.C., Bongiolo, E.M., Geraldes, M.C., Santos, A.C., Jourdan, F., Neumann, R., Pires, Gustavo Luiz Campos, Nascimento, Débora Barros, Prado, Maurício, Bongiolo, Everton Marques, Piza, Patricia d'Almeida de Toledo, Schmitt, Renata da Silva, Mexias, André Sampaio, Mohammed, Tabeliouna, Jean-Yves, Cottin, Peter, Bowden, Christophe, Renac, Mexias, Andre, Louni-Hacini, Amina, Brouillet, Stéphanie, Cottin, Jean-Yves, Wazir, I., Pagel, M., Tournier, F., Portier, E., Renac, C., Univ Fed Rio Grande do Sul, Inst Geociencias, BR-91501970 Porto Alegre, RS, Brazil, Univ Fed Rio Grande do Sul, Fac Agron, Dept Solos, Laboratoire de Chimie Analytique Bio-Inorganique et Environnement (LCABIE), Université de Pau et des Pays de l'Adour (UPPA)-Centre National de la Recherche Scientifique (CNRS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Instituto de Geociências, Universidade Federal do Rio Grande do Sul [Porto Alegre] (UFRGS), Instituto de Geociencias, JRC Institute for Transuranium Elements [Karlsruhe] (ITU ), European Commission - Joint Research Centre [Karlsruhe] (JRC), insituto de geociencias, universidade federal do rio de janeiro, Instituto de Biofísica e Biomatemática, Universidade de Coimbra [Coimbra], Helmholtz zentrum für Schwerionenforschung GmbH (GSI), Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Univ Fed Rio Grande do Sul, Inst Geociencias, Université des Sciences et de la Technologie Houari Boumediene = University of Sciences and Technology Houari Boumediene [Alger] (USTHB), Cité de la céramique - Sèvres et Limoges, Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Interactions et dynamique des environnements de surface (IDES), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Géosciences Paris Sud (GEOPS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Gaz de France Suez (GDF Suez), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement et la société-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Université Jean Monnet [Saint-Étienne] (UJM), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), USTBH, Alger, Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)
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010504 meteorology & atmospheric sciences ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Siderite ,chemistry.chemical_compound ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,Fluid inclusions ,[SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology ,Quartz ,[SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,Calcite ,Cementation (geology) ,Diagenesis ,chemistry ,13. Climate action ,[SDU]Sciences of the Universe [physics] ,[SDE]Environmental Sciences ,engineering ,General Earth and Planetary Sciences ,Carbonate ,Geology ,Dickite - Abstract
Structure- and tectonic-related gas migration into Ordovician sandstone reservoirs and its impact on diagenesis history were reconstructed in two fields in the Sbaa Basin, in SW Algeria. This was accomplished by petrographical observations, fluid inclusion microthermometry and stable isotope geochemistry on quartz, dickite and carbonate cements and veins. Two successive phases of quartz cementation (CQ1 and CQ2) occurred in the reservoirs. Two- phase aqueous inclusions show an increase in temperatures and salinities from the first CQ1 diagenetic phase toward CQ2 in both fields. Microthermometric data on gas inclusions in quartz veins reveal the presence of an average of 92 ± 5 mole% of CH4 considering a CH4-CO2 system, which is similar to the present-day gas composition in the reservoirs. The presence of primary methane inclusions in early quartz overgrowths and in quartz and calcite veins suggests that hydrocarbon migration into the reservoir occurred synchronically with early quartz cementation in the sandstones located near the contact with the Silurian gas source rock at 100-140°C during the Late Carboniferous period and the late Hercynian episode fracturing at temperatures between 117 and 185°C, which increased in the NW-direction of the basin. During the fracture filling, three main types of fluids were identified with different salinities and formation temperatures. A supplementary phase of higher fluid temperature (up to 226°C) recorded in late quartz, and calcite veins is related to a Jurassic thermal event. The occurrence of dickite cements close to the Silurian base near the main fault areas in both fields is mainly correlated with the sandstones where the early gas was charged. It implies that dickite precipitation is related to acidic influx. Late carbonate cements and veins (calcite - siderite - ankerite and strontianite) occurred at the same depths resulting from the same groundwater precipitation. The absence o
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- 2014
29. Rhyolite petrogenesis and meteoric–hydrothermal alteration at the Maghnia volcanic massif, Northwest Algeria
- Author
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Amina Louni-Hacini, Jean-Yves Cottin, Christophe Renac, Stéphanie Brouillet, Andre Sampaio Mexias, Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Universidade Federal do Rio Grande do Sul [Porto Alegre] (UFRGS), Université des Sciences et de la Technologie Houari Boumediene = University of Sciences and Technology Houari Boumediene [Alger] (USTHB), UFR Sciences de l'Université Jean Monnet, Laboratoire Magmas et Volcans (LMV), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Université des Sciences et de la Technologie Houari Boumediene [Alger] (USTHB), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), and Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Rhyolite ,010504 meteorology & atmospheric sciences ,Western Mediterranean–Algeria ,Geochemistry ,010502 geochemistry & geophysics ,Feldspar ,01 natural sciences ,Isotopes of oxygen ,Petrography ,Geochemistry and Petrology ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,Petrogenesis ,Petrology ,0105 earth and related environmental sciences ,geography ,geography.geographical_feature_category ,Fractional crystallization (geology) ,Element mobility ,Volcanic rock ,visual_art ,Meteoric water ,visual_art.visual_art_medium ,Meteoric–hydrothermal alteration ,Smectite formation ,Economic Geology ,Geology - Abstract
International audience; Volcanic rocks from the Maghnia region of northwest Algeria consist of fresh to altered rhyolitic units that were emplaced during late Miocene time. Petrographic observations and geochemical data indicate that rhyolitic rocks were derived from a hybridized peraluminous magma. Petrogenetic modeling, REE contents and oxygen isotope data of quartz and feldspar and spessartine-rich garnet allows the reconstruction of the fractional crystallization between 680 and 780 °C and pressure of less than 0.5 GPa. Rhyolitic units are partially weathered and form an economic deposit of montmorillonite. Spectroscopic data and stable isotopes (O, H) of glass and montmorillonite indicate that the residual glass was partially hydrated by meteoric water at temperatures between 31 and 54 °C. The chemical mass balance indicates that rhyolitic rocks were altered to montmorillonite by meteoric water enriched in Ca, Mg and Sr. The combination of the chemical mass balance and the 87Sr/86Sr initial ratios of rhyolite and montmorillonite indicate that continental water/rock interaction was related to the surrounding Miocene lacustrine limestone.
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- 2014
30. Intracontinental Miocene: Reconstruction of hydrology and paleoclimate change in the Forez Basin, France (Part II)
- Author
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Christophe Renac, Frédérick Gal, Anne-Marie Bodergat, Marie-Christine Gerbe, Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement [Lyon] (LGL-TPE), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Metrol. Monitoring & Anal Div, Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)
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Delta ,010506 paleontology ,Stratigraphy ,Dolomite ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Late Miocene ,010502 geochemistry & geophysics ,01 natural sciences ,Diagenesis ,Sedimentary depositional environment ,Paleontology ,chemistry.chemical_compound ,0105 earth and related environmental sciences ,Stable isotopes ,Calcite ,Intracontinental basin ,Geology ,Authigenic ,Miocene ,15. Life on land ,chemistry ,13. Climate action ,Eogenesis ,Sedimentary rock - Abstract
International audience; Sedimentary successions of palustrine deposits from the Forez Graben recorded changes in depositional and hydrological conditions throughout the Middle to Late Miocene of France. Paleontological, mineralogical and geochemical data combined with mass-balance calculation allowed the identification of modern, diagenetic and eogenetic stages of authigenic precipitation within the sedimentary pile. Stratigraphic log contains six clay- and sand-rich sequences, some associated with freshwater ostracods. delta C-13, delta O-18 values and Sr isotopic ratios of whole-rock samples and ostracods indicate that the Montrond-les-Bains upper sequence (8 to 175 mbs) is a continental lake system that recorded continental weather condition (15 to 25 degrees C) during the upper Miocene time. Geochemical changes permit the estimation of variations of evaporation-inflow changes (E/I: 8 to 75% and delta O-18(rainfall) -6 to -8 parts per thousand) associated with two sequences. delta O-18 and E/I progressive changes were related to runoff to colder climate conditions. large E/I values in below 100 mbs are associated with the appearance of authigenic calcite and dolomite precipitation. Euhedral dolomite seems to be related to desiccation period that induced capillary pumping of water undersaturated with respect to calcite but saturated for dolomite. The lower part of the Middle Miocene sedimentary series (175 to 300 mbs) hosts continental deposits with scarce fossil, a larger proportion of dolomite and massive pyrite levels related to mixed eogenetic and diagenetic precipitation. Scarce preserved "eogenetic levels" with unrealistic E/I ratios suggest either delta O-18 values similar to the upper section but with temperature lower than 15 C, or a similar temperature but very low delta O-18(rainfall). Calculated delta O-18(H2O) values have to be as low as -15 parts per thousand. delta O-18(H2O) values are similar to present-day melted snow. This stable isotope suggests episodes of regional warming melting surrounding snow, and able to mobilize as well as deposit thick sand levels. Eogenetic to diagenetic calcite, dolomite and pyrite precipitation involves Sand Mg-fluid influxes associated with methanogenic process (eogenesis) mixed with recrystallized pyrite and dolomite with diagenetic fluid circulation.
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- 2013
31. Intracontinental Miocene: Climate and paleolake volumes in the Forez Basin, France (Part I)
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Marie-Christine Gerbe, H. Gonord, G. Michon, Christophe Renac, Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Magmas et Volcans (LMV-ENSMSE), École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-SPIN-Centre National de la Recherche Scientifique (CNRS)-Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS), Laboratoire Magmas et Volcans (LMV), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Calcite ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Stratigraphy ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Geology ,Continental climate ,Late Miocene ,Structural basin ,Sedimentary basin ,010502 geochemistry & geophysics ,01 natural sciences ,Graben ,Paleontology ,chemistry.chemical_compound ,chemistry ,13. Climate action ,Temperate climate ,Precipitation ,0105 earth and related environmental sciences - Abstract
International audience; European Tertiary sedimentary basins as the Forez Graben, France, are potential records of continental paleoclimates. The Forez Basin hosts deposited and precipitated sediments of Oligocene to Miocene age. Geochemical data of carbonates indicate strictly continental origin starting at Eocene-Oligocene with tropical to temperate climate conditions, then during the Middle Miocene a temperate continental climate prevails. Combining volume of calcite deposits and their geochemical data, volumes of large lakes and evaporation/inflow ratios were reconstructed. The Late Miocene in the Forez Graben has been affected by dissolution and secondary precipitation of calcite, barite, which is the result of wetter and colder climate conditions. These lake volume calculations represent the first estimation of large lakes volumes in Western Europe during the Miocene.
- Published
- 2013
32. Metallogenic Model of the Trepca Pb-Zn-Ag Skarn Deposit, Kosovo: Evidence from Fluid Inclusions, Rare Earth Elements, and Stable Isotope Data
- Author
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Sabina Strmić Palinkaš, Christophe Renac, Ferenc Molnár, Jorge E. Spangenberg, Ladislav Palinkaš, Volker Lüders, Gani Maliqi, Institute of Mineralogy and Petrography, Géoazur (GEOAZUR 7329), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Institute of Mineralogy and Geochemistry, Université de Lausanne (UNIL), German Research Centre for Geosciences - Helmholtz-Centre Potsdam (GFZ), Geological Survey of Finland, Faculty of Mines and Metallurgy, Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)
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Mineralization (geology) ,010504 meteorology & atmospheric sciences ,Geochemistry ,Mineralogy ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Skarn ,550 - Earth sciences ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Siderite ,chemistry.chemical_compound ,Geochemistry and Petrology ,Galena ,Marcasite ,Fluid inclusions ,10. No inequality ,0105 earth and related environmental sciences ,Arsenopyrite ,Geology ,Geophysics ,Sphalerite ,chemistry ,visual_art ,skarn ,hydrothermal ,fluid inclusions ,stable isotopes ,phreatomagmatic breccia ,visual_art.visual_art_medium ,engineering ,Economic Geology - Abstract
International audience; The Trepča Pb-Zn-Ag skarn deposit (29 Mt of ore at 3.45% Pb, 2.30% Zn, and 80 g/t Ag) is located in the Kopaonik block of the western Vardar zone, Kosovo. The mineralization, hosted by recrystallized limestone of Upper Triassic age, was structurally and lithologically controlled. Ore deposition is spatially and temporally related with the postcollisional magmatism of Oligocene age (23-26 Ma). The deposit was formed during two distinct mineralization stages: an early prograde closed-system and a later retrograde open-system stage. The prograde mineralization consisting mainly of pyroxenes (Hd54-100Jo0-45Di0-45) resulted from the interaction of magmatic fluids associated with Oligocene (23-26 Ma) postcollisional magmatism. Whereas there is no direct contact between magmatic rocks and the mineralization, the deposit is classified as a distal Pb-Zn-Ag skarn. Abundant pyroxene reflects low oxygen fugacity (
- Published
- 2013
33. Evidence of Ediacaran glaciation in southernmost Brazil through magmatic to meteoric fluid circulation in the porphyry-epithermal Au-Cu deposits of Lavras do Sul
- Author
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Luiz Henrique Ronchi, Andre Sampaio Mexias, Everton Marques Bongiolo, Marcia Elisa Boscato Gomes, Christophe Renac, Patricia Patrier-Mas, Instituto de Geociências, Universidade Federal do Rio de Janeiro (UFRJ), Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Géoazur (GEOAZUR 6526), Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Universidade Federal do Rio Grande do Sul [Porto Alegre] (UFRGS), Universidade Federal de Pelotas = Federal University of Pelotas (UFPel), HydrASA (Hydrogéologie, argiles, sols et altérations), Université de Poitiers-Centre National de la Recherche Scientifique (CNRS), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Stable isotope ratio ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Geology ,010502 geochemistry & geophysics ,01 natural sciences ,Hydrothermal circulation ,Craton ,13. Climate action ,Geochemistry and Petrology ,Meteoric water ,Argillic alteration ,Glacial period ,Clay minerals ,Quartz ,0105 earth and related environmental sciences - Abstract
International audience; The Lavras do Sul Au-Cu mining district, southern Brazil, hosts an Ediacaran plutonic-volcanic association with hydrothermal alteration. This association is interpreted as a ca. 600-580 Ma tilted porphyry-epithermal system, where the main ore occurs in phyllic and intermediate argillic halos around quartz veins. In this paper we used detailed field mapping, fluid inclusion microthermometry, oxygen and hydrogen isotope measurements of whole-rocks, feldspars, clay minerals and quartz from propylitic, phyllic and intermediate argillic alteration to reconstruct the hydrothermal fluid temperatures and compositions. The results showed that the deeper zones of the hydrothermal system were predominantly influenced by magmatic fluid and its shallower zones by meteoric water with very negative δ18O compositions. Our data support a model of mixing between magmatic-derived fluids with meteoric waters of glacial origin. Based on stable isotope data we propose indirect evidence of high latitude position for the study area during Brasiliano/Pan-African convergence of the Kalahari and Rio de La Plata cratons.
- Published
- 2011
34. Type I eclogites from Roberts Victor kimberlites: Products of extensive mantle metasomatism
- Author
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Christophe Renac, Yoann Gréau, Olivier Alard, Jin Xiang Huang, William L. Griffin, Suzanne Y. O'Reilly, Géosciences Montpellier, Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC), Macquarie University, ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS), Manteau et Interfaces, and Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
010504 meteorology & atmospheric sciences ,Geochemistry ,[SDU.STU.PE]Sciences of the Universe [physics]/Earth Sciences/Petrography ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle (geology) ,Isotopes of oxygen ,South Africa ,xenoliths ,Geochemistry and Petrology ,kimberlites ,Fluid inclusions ,Xenolith ,eclogites ,Eclogite ,Metasomatism ,Kimberlite ,Protolith ,Geology ,0105 earth and related environmental sciences - Abstract
International audience; Type I and Type II eclogite xenoliths from the Roberts Victor kimberlite (South Africa) show marked differences in terms of microstructures, mineralogy, major-and trace-element compositions and oxygen-isotope compositions. The unequilibrated microstructures of Type I eclogites, their typical accessory assemblages (phologopite, diamond, sulphides, fluid inclusions) and the ubiquitous presence of "melt pockets" in garnets provide strong evidence of metasomatism. Type II eclogites systematically lack such features and are microstructurally more equilibrated. Type I eclogites are more magnesium-rich than most Type II (mean Mg# = 0.56 vs. 0.46), while Type II eclogites are generally more Ca-rich (mean CaO = 9 vs. 12 wt%) and Fe-rich (mean FeO = 10 vs. 12 wt%). Type I eclogites are systematically enriched in LREE, Sr, Ba, alkali elements, HFSE, Th and U compared to the more depleted Type II eclogites. Calculated trace-element patterns of fluids in equilibrium with Type I eclogites are closely similar to those of volatile-rich small-volume mantle melts in the carbonatite-kimberlite spectrum commonly inferred to be responsible for mantle metasomatism. Although oxygen isotopes are often used to argue for a subduction origin of mantle eclogites, correlations between delta O-18 of garnet and typical metasomatic tracers suggest that the metasomatic process also has shifted the oxygen-isotope compositions of the Type I eclogites toward heavier values. Roberts Victor Type I eclogites thus carry the imprint of a metasomatic process that strongly modified their major-element, trace-element and isotopic compositions, while the more pristine Type II eclogites escaped this modification. Therefore, attempts to constrain the origin of Roberts Victor eclogites should not be based on the much more abundant Type I eclogites, which retain little geochemical memory of their protoliths. The most suitable materials for such investigations may be the less metasomatised, but more rare, Type II eclogites.
- Published
- 2011
35. Reconstruction of groundwater flows and chemical water evolution in an amagmatic hydrothermal system (La Léchère, French Alps)
- Author
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Dominique Gasquet, Christophe Renac, Marc Dzikowski, Emilie Thiébaud, Laboratoire Magmas et Volcans (LMV), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Environnements, Dynamiques et Territoires de Montagne (EDYTEM), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Centre d'Electronique et de Micro-optoélectronique de Montpellier (CEM2), Université Montpellier 2 - Sciences et Techniques (UM2)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Transferts Lithosphériques (LTL), Université Jean Monnet [Saint-Étienne] (UJM), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Environnements, Dynamiques et Territoires de la Montagne (EDYTEM), Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry]), and Foray, Charlotte
- Subjects
Metamorphic rock ,[SDE.MCG]Environmental Sciences/Global Changes ,Dolomite ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Aquifer ,010501 environmental sciences ,010502 geochemistry & geophysics ,01 natural sciences ,chemistry.chemical_compound ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,[SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology ,[SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology ,Geomorphology ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,Water Science and Technology ,geography ,geography.geographical_feature_category ,La Léchère ,Stable isotope ratio ,Hydrochemistry ,Alps ,Schist ,6. Clean water ,Orogenic setting ,[SDE.MCG] Environmental Sciences/Global Changes ,chemistry ,[SDU]Sciences of the Universe [physics] ,13. Climate action ,[SDE]Environmental Sciences ,Facies ,Thermal conditions ,Carbonate ,Groundwater ,Geology - Abstract
Summary A detailed picture of the hydrogeochemistry of an alpine thermal area (La Lechere, French Alps) was drawn up from new and complete analyses of shallow and deep groundwater, including major and trace elements, gases, and stable (δ 18 O, δD, δ 13 C, δ 34 S) and radiogenic isotopes ( 14 C), combined with data on the trace and stable isotope (δ 18 O, δ 34 S) contents of the aquifer rocks. Three different groundwater facies were recognized: (1) the shallow groundwater in the carbonate and crystalline rocks presents a poorly mineralized Ca–HCO 3 facies; (2) the shallow groundwater from the evaporitic fault zone presents a mineralized Ca–Mg–SO 4 facies; (3) and the deep thermal water presents a highly-mineralized Ca–Na–SO 4 facies. The evolution from facies 2 to facies 3 is controlled by three phenomena: (i) the presence or absence of evaporitic deposits along the fault, which governs whether or not the water can interact with carbonates and dolomites, (ii) interactions with micaschists and Permo-Carboniferous rocks, which lead to Ca–Na exchanges and enrichment in some trace elements and gases (CO 2 , CH 4 and H 2 S), and (iii) the long residence time (several thousand years) and high temperature (90 °C) of the thermal water.
- Published
- 2010
36. Identification of different groundwater flowpaths within volcanic aquifers using natural tracers for the evaluation of the influence of lava flows morphology (Argnat basin, Chaîne des Puys, France)
- Author
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Frédéric Huneau, Hélène Celle-Jeanton, Christophe Renac, Guillaume Bertrand, Sébastien Loock, Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Géosciences hydrosciences matériaux constructions (Ghymac), Université Sciences et Technologies - Bordeaux 1, Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), and Université Sciences et Technologies - Bordeaux 1 (UB)
- Subjects
010504 meteorology & atmospheric sciences ,Groundwater flow ,Lava ,[SDE.MCG]Environmental Sciences/Global Changes ,0207 environmental engineering ,Geochemistry ,stable isotopes ,Aquifer ,02 engineering and technology ,01 natural sciences ,unsaturated zone ,hydrochemistry ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,Vadose zone ,media_common.cataloged_instance ,European union ,020701 environmental engineering ,Geomorphology ,ComputingMilieux_MISCELLANEOUS ,A'a flows ,0105 earth and related environmental sciences ,Water Science and Technology ,media_common ,geography ,geography.geographical_feature_category ,basalt aquifer ,Groundwater recharge ,6. Clean water ,Volcanic rock ,13. Climate action ,Groundwater ,Geology - Abstract
Hydrochemical and stable isotopic (2H, 18O) data were used to characterize the groundwater flow and major chemical features within a complex fractured volcanic aquifer system, the Argnat basin, which is located in the Chaine des Puys (French Massif Central). From 10 sampling points, the study of the transfer into the saturated zone from upstream to downstream, given the geological context and topography, allows to estimate the role of supply from high and low altitudes to the recharge processes. This work shows the existence of different types of supply between pahoehoe and a’a flows. Therefore, the morphology of volcanic flows impacts the chemical and isotopic signatures of groundwater, enhancing or reducing the influence of the unsaturated zone on the pathways of infiltrated water. Pahoehoe flows imply horizontal water flows of low discharge at the top of the lava whereas a’a flows seems to be much more heterogeneous and locally able to promote the existence of perched water bodies and further vertical circulations. Taking into account these two types of behaviour, a conceptual scheme of the functioning of this heterogeneous environment is proposed, which will help towards a sustainable management of volcanic aquifers in relation with the European Union Groundwater Directive (2006/118/CE) (2006).
- Published
- 2010
37. Fractionation of oxygen and iron isotopes by partial melting processes: Implications for the interpretation of stable isotope signatures in mafic rocks
- Author
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Fanus Viljoen, Alex N. Halliday, Christophe Renac, Catherine McCammon, Helen M. Williams, Suzanne Y. O'Reilly, Jeffrey C. Alt, Norman J. Pearson, Sune G. Nielsen, William L. Griffin, Laboratoire Magmas et Volcans (LMV), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Department of Earth and Planetary Sciences [Sydney], Macquarie University, ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC), Bayerisches Geoinstitut (BGI), Universität Bayreuth, Department of Earth Sciences [Oxford], University of Oxford, Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), and University of Oxford [Oxford]
- Subjects
melting ,010504 meteorology & atmospheric sciences ,Subduction ,Stable isotope ratio ,oxygen isotopes ,Partial melting ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,iron isotopes ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle plume ,Mantle (geology) ,Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,Oceanic crust ,Lithosphere ,Earth and Planetary Sciences (miscellaneous) ,14. Life underwater ,Eclogite ,Geology ,ComputingMilieux_MISCELLANEOUS ,mantle ,0105 earth and related environmental sciences - Abstract
Recycling of oceanic crust into the deep mantle via subduction is a widely accepted mechanism for creating compositional heterogeneity in the upper mantle and for explaining the distinct geochemistry of mantle plumes. The oxygen isotope ratios (δ18O) of some ocean island basalts (OIB) span values both above and below that of unmetasomatised upper mantle (5.5 ± 0.4‰) and provide support for this hypothesis, as it is widely assumed that most variations in δ18O are produced by near-surface low-temperature processes. Here we show a significant linear relationship between δ18O and stable iron isotope ratios (δ57Fe) in a suite of pristine eclogite xenoliths. The δ18O values of both bulk samples and garnets range from values within error of normal mantle to significantly lighter values. The observed range and correlation between δ18O and δ57Fe is unlikely to be inherited from oceanic crust, as δ57Fe values determined for samples of hydrothermally altered oceanic crust do not differ significantly from the mantle value and show no correlation with δ18O. It is proposed that the correlated δ57Fe and δ18O variations in this particular eclogite suite are predominantly related to isotopic fractionation by disequilibrium partial melting although modification by melt percolation processes cannot be ruled out. Fractionation of Fe and O isotopes by removal of partial melt enriched in isotopically heavy Fe and O is supported by negative correlations between bulk sample δ57Fe and Cr content and bulk sample and garnet δ18O and Sc contents, as Cr and Sc are elements that become enriched in garnet- and pyroxene-bearing melt residues. Melt extraction could take place either during subduction, where the eclogites represent the residues of melted oceanic lithosphere, or could take place during long-term residence within the lithospheric mantle, in which case the protoliths of the eclogites could be of either crustal or mantle origin. This modification of both δ57Fe and δ18O by melting processes and specifically the production of low-δ18O signatures in mafic rocks implies that some of the isotopically light δ18O values observed in OIB and eclogite xenoliths may not necessarily reflect near-surface processes or components. © 2009 Elsevier B.V. All rights reserved.
- Published
- 2009
38. Mean recharge times and chemical modelling transfers from shallow groundwater to mineralized thermal waters at Montrond-les-Bains, Eastern Massif Central, France
- Author
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Patrice Squarcioni, Frédérick Gal, René-Pierre Ménot, Christophe Renac, Ch. Perrache, Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), HydroInvest, Société HydroInvest, Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Geochemistry ,Elements and isotopes geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Aquifer ,Groundwater recharge ,Bicarbonate-rich water ,010502 geochemistry & geophysics ,01 natural sciences ,6. Clean water ,Mixing models ,Isotopic signature ,Basement (geology) ,Isotope geochemistry ,Clastic rock ,Sedimentary rock ,French Massif Central ,Geomorphology ,Groundwater ,Geology ,Palaeo-hydrology ,0105 earth and related environmental sciences ,Water Science and Technology - Abstract
Summary A re-appraisal of interactions between basinal waters and hydrothermal fluids within the silici-clastic series of the intracontinental Cenozoic Forez Basin is proposed using major element and isotope geochemistry together with thermodynamic models. Recharge processes and shallow sedimentary units in the Forez Basin were compared using major elements and isotopic data ( 87 Sr/ 86 Sr, δ 18 O, δ 2 H, δ 13 C, Tritium and 14 C) for waters, sedimentary carbonates and Hercynian basement rocks. Waters derived from Late Pleistocene to Early Holocene surface recharge followed by mixing and chemical evolution through percolation into deep groundwater horizons are investigated. Isotopic ratios and chemical speciation computed for deeper waters from 0 to 200 m depth indicate that mineralised waters were produced by initial surficial dissolution of calcite in calcareous-mudstone providing its Sr isotopic signature. At about 200 m depth, Na–H 3 O + cation-exchange with clayey-sand rich levels provides additional Ca, Na, and OH contents, for carbonate-saturated water. Na–H 3 O + cation exchange can not contribute large Na–HCO 3 concentrations. Geochemical changes such as increasing δ 13 C DIC values observed from 200 to 500 m depth were modelled by addition of thermal water and geogenic CO 2 in increasing proportions with depth (500 mbs). Thermodynamic calculations of mineral proportions indicate water–rock interactions with primary minerals in the metamorphic basement and secondary minerals observed in the basin. Water temperature and its meteoric origin suggest a basin-wide recharge system with water–rock interaction driven by heat flow rather than through deep crustal fractures.
- Published
- 2009
39. Characterization of the metasomatic agent in mantle xenoliths from Devès, Massif Central (France) using coupled in situ trace-element and O, Sr and Nd isotopic compositions
- Author
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Stephanie Touron, William L. Griffin, Jean-Yves Cottin, Christophe Renac, Sue O'Reilly, Laboratoire Magmas et Volcans (LMV), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
In situ ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Trace element ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Geology ,Ocean Engineering ,Massif ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle xenoliths ,Characterization (materials science) ,Metasomatism ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,Water Science and Technology - Abstract
International audience
- Published
- 2008
40. Caracterização petrográfica e geoquímica da sequência magmática da Mina do Seival, Formação Hilário (Bacia do Camaquã – Neoproterozoico), Rio Grande do Sul, Brasil
- Author
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Rodrigo W. Lopes, Andre Sampaio Mexias, Eduardo Fontana, Marcia Elisa Boscato Gomes, Lauro Valentim Stoll Nardi, Christophe Renac, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)
- Subjects
Mina do Seival, Alteração hidrotermal, Petrografia, Magmatismo Shoshonítico, Depósitos de Cobre, Geoquímica, Bacia do Camaquã ,13. Climate action ,Seival Mine, Hydrothermal alteration, Shoshonitic magmatism, Petrography, Copper deposits, Geochemistry, Camaquã Basin ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,General Earth and Planetary Sciences ,010501 environmental sciences ,010502 geochemistry & geophysics ,01 natural sciences ,0105 earth and related environmental sciences - Abstract
A Mina do Seival é constituída por rochas vulcânicas e diques de composição andesítica e traqui-andesítica, dispostas em duas sequências. A sequência I inclui rochas piroclásticas e efusivas, e a sequência II é representada pelos diques de composição andesítica. Ambas são incluídas na Associação Shoshonítica de Lavras do Sul. Este magmatismo é relacionado ao estágio pós-colisional do ciclo Brasiliano/Pan-Africano, situando-se estratigraficamente no Alogrupo Bom Jardim, pertencendo à Formação Hilário na Bacia do Camaquã (Neoproterozoico). A área possui intensa alteração hidrotermal e mineralizações de Cu. A mineralização e o magmatismo da Sequência II são controlados por estruturas tectônicas orientadas segundo N/NE e NO, que são relacionadas à distensão regional no período pós-colisional da Orogênese Brasiliano/Pan-Africana. Processos hidrotermais em diferentes temperaturas atuaram sobre estas rochas originando produtos de alteração pervasiva, principalmente clorita, corrensita e esmectita, com veios preenchidos por quartzo, carbonato, barita e minerais de cobre. Em ambas as sequências encaixantes da Mina do Seival é possível identificar a afinidade shoshonítica das rochas. Os elevados teores de Cu, Zn e Ni nos diques em relação às rochas piroclásticas e às efusivas, mesmo nas mais hidrotermalizadas, sugerem que as principais ocorrências de mineralização de Cu têm origem magmática. Os dados químicos de rocha total indicam que o enriquecimento dos elementos componentes da mineralização, Ag, Au, Cu e Zn, está relacionado aos diques da Sequência II. Os teores de Au e Cu são mais elevados nas amostras com menores concentrações de carbonatos, sugerindo que a carbonatação não tem relação com a deposição dos minérios., The Seival Mine consists of andesitic volcanic and trachy-andesitic volcanic and hipabissal rocks grouped into two volcanic sequences. The Sequence I is composed of pyroclastic rocks and effusive rocks, and sequence II by andesite dikes. The area shows intense hydrothermal alteration and Cu mineralization. This magmatism is related to the post-collisional stage of the cycle Brasiliano/Pan-African, and it is stratigraphically positioned in the Bom Jardim Allogroup, Hilário Formation, which is part of the Neoproterozoic Camaquã Basin. Sequence II magmatism and mineralization are controlled by tectonic structures with N/NE and NW orientation, which are related to regional extension during the post-collisional stage of Brasiliano/Pan-African Orogeny. Processes involving different temperatures caused pervasive alteration products, with generation of chlorite, corrensite and smectite, with veins filled by quartz, carbonate, barite and copper minerals. In both sequences of Seival Mine is possible to identify the shoshonitic affinity of host sequences, as pointed out by geochemical data. The higher contents of Cu, Zn, and Ni in andesite dikes in relation to pyroclastic and effusive rocks, even in the hydrothermally altered types, suggest that the main Cu mineralizations have magmatic origin. The Au and Cu contents are higher in samples with lower carbonate concentrations, which suggests than carbonate alteration have no relation with ore deposition.
- Published
- 2014
41. Thermal History Constraints from Studies of Organic Matter, Clay Minerals, Fluid inclusions, and Apatite Fission Tracks at the Ardeche Paleo-margin (BA1 Drill Hole, GPF Program), France
- Author
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Maurice Pagel, Luis Martinez, Christophe Renac, Jean-Jacques Braun, Guy Vasseur, and Jean Robert Disnar
- Subjects
Anhydrite ,Dolomite ,Geochemistry ,Mineralogy ,Geology ,engineering.material ,chemistry.chemical_compound ,chemistry ,Illite ,engineering ,Carbonate rock ,Carbonate ,Sedimentary rock ,Fluid inclusions ,Quartz - Abstract
The thermal history of the Ardeche paleo-margin (southeastern France) has been reconstructed using various analytical data from minerals and organic matter and conventional interpretation. These methods comprise Tmax and vitrinite reflectance measurements on organic matter, determination of the smectite content in mixed-layer illite/smectite, fluid-inclusion microthermometry in quartz, barite, dolomite, and anhydrite, and fission-track analyses in apatite. The Balazuc (BA1) drill hole, 1730 m deep, intersects mainly Jurassic carbonate rocks, Triassic sandstones, and sulfate-rich claystones and ends in Carboniferous rocks. The present bottom-hole temperature is 70°C. Other drill holes, less than 6 km away, were studied when necessary. One of the main objectives of this paper is to ssess the agreement between the different geothermometric methods, and to check their limitations and convergence when used on carbonate- and sandstone-dominated reservoirs. In the Triassic sandstones, primary aqueous inclusions in anhydrite cement and at the boundary between the detrital quartz grain and the quartz overgrowth are one-phase brine inclusions entrapped below 70°C. The homogenization temperature determined on the later barite cement is about 100°C. Aqueous two-phase inclusions in healed microfractures in anhydrite are present at the base of the drill core near major faults. Temperatures as high as 210°C recorded for these fluid inclusions could be associated with episodic fluid injections from below through the fault zones during the Early Jurassic. The fluid inclusions in dolomite, most of them reequilibrated during burial, indicate a trapping temperature of 130-145°C at 1600 m and a temperature decrease towards the surface. This value is in good agreement with the MPTB (maximum paleotemperature of burial) method on organic matter, which converges to a maximum burial temperature of 130°C at the same depth. The apatite fission-track data agree with these temperatures and indicate that the temperature decreased below 120 ± 10°C during the Eocene. These paleotemperatures, much higher than the present ones, can be explained by the erosion of 1900 m of mainly Cretaceous sediments. This interpretation implies a high average sedimentation rate during the Cretaceous, in agreement with data determined on a regional scale. A time-temperature evolution is proposed for the formations present in the Balazuc drill hole and the eroded sedimentary rocks. The application of the dual reaction model of the transformation of smectite to illite (Velde and Vasseur 1992) shows that the data are in good agreement with the kinetic model. However, the vitrinite reflectance variation trend with depth, predicted from the Burnham and Sweeney model (1989), is different from the data variation. No definitive explanation can be proposed for the failure of aturity assessment through vitrinite reflectance in the BA1 drill hole.
- Published
- 1997
42. Estudo da evolução dos processos de alteração supergênica de rocha granítica - Granito Independência - Morro do IPA, Porto Alegre, RS
- Author
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Andre Sampaio Mexias, Marcia Elisa Boscato Gomes, Christophe Renac, Alberto Vasconcellos Inda, Laurent Caner, Marcelo Henrique Neumann, Elissa F. Ramos, and Maria Lidia Vignol-Lelarge
- Subjects
010506 paleontology ,Supergene (geology) ,Geochemistry ,Context (language use) ,engineering.material ,010502 geochemistry & geophysics ,Feldspar ,01 natural sciences ,Petrography ,visual_art ,Illite ,engineering ,visual_art.visual_art_medium ,General Earth and Planetary Sciences ,Kaolinite ,Quartz ,Geology ,Biotite ,0105 earth and related environmental sciences - Abstract
As rochas da superfície terrestre estão permanentemente expostas à ação de agentes naturais, como a água, as variações de temperatura, os gases atmosféricos e a ação dos seres vivos. Dentre a ação dos seres vivos, nos centros urbanos destaca-se a ação antrópica, que por vezes acaba por degradar os recursos naturais. Nesse contexto, entender os processos de transformação das rochas, para que se possa compreender a gênese e evolução dos solos, e assim, aperfeiçoar métodos para sua recuperação, torna-se imprescindível. Este estudo foi desenvolvido em um perfil de alteração de rocha granítica localizado na área urbana de Porto Alegre, onde foram coletadas oito amostras representativas dos diferentes níveis, da rocha ao solo. As amostras foram analisadas por difratometria de raios X (DRX), pelo método do pó na rocha total e na fração < 4 μm. A composição química foi determinada por fluorescência de raios X (FRX). Fragmentos das amostras foram observados no microscópio eletrônico de varredura (elétrons secundários) e no microscópio ótico. Os estudos mineralógicos e petrográficos mostraram a existência de pequena variação composicional vertical no perfil, essencialmente composto por quartzo, feldspato alcalino e caolinita, identificados em todos os horizontes, e ilita/biotita identificadas nos horizontes saprolíticos. As análises através de imagens de elétrons secundários permitiram identificar ainda a presença de haloisita. A exsudação de ferro pelas lamelas da biotita observada no microscópio óptico marca o início da alteração supergênica no granito. Os dados de FRX mostram que a escolha do elemento imóvel de referência para verificar a existência ou não de enriquecimento dos elementos ao longo do perfil é muito importante, pois neste trabalho verificou-se que o alumínio tem um comportamento móvel, provavelmente associado às condições de acidez do solo.
- Published
- 2012
43. A cloritização na Mina Uruguai, Minas do Camaquã, RS, Brasil
- Author
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Guilherme TROIAN, André MEXIAS, Márcia GOMES, Denise CANARIM, Patricia PATRIER-MAS, and Christophe RENAC
- Subjects
Mineralization (geology) ,geography ,Chamosite ,geography.geographical_feature_category ,Chemistry ,Geochemistry ,Hydrothermal circulation ,Petrography ,Volcanic rock ,chemistry.chemical_compound ,Clastic rock ,General Earth and Planetary Sciences ,Clay minerals ,Chlorite - Abstract
A região das Minas do Camaquã é a parte constituinte da Bacia do Camaquã, a qual possui direção NE-NW e é preenchida por sedimentos siliciclásticos intercalados com rochas vulcânicas. A clorita é o argilomineral mais abundante da área, ocorrendo em grande quantidade nos halos de alteração hidrotermal presentes nas rochas encaixantes nas mineralizações na Mina Uruguai. Este trabalho consiste na caracterização petrológica, química e estrutural das cloritas, que fornece importante informações sobre diferentes processos e condições de formação do ambiente hidrotermal. Para isso se realizou petrografia óptica, difratometria de raios X, modelamento dos difratogramas através do programa Reynolds Newmod © e microscopia eletrônica de varredura (elétrons secundários e micro-análises por EDS) em amostras representativas de diferentes zonas de alteração hidrotermal identificadas. As cloritas se apresentam com três diferentes tendências: a Clorita I ocorre com aspecto pervasivo sobre matriz das rochas localizadas próximos aos filões mineralizados; é classificada como Fe-clinocloro, apresenta na fração ˂1 µm predominância do politipo IIb e um enriquecimento em Mg2+ e na fração ˂10 µm predominância do politipo Ib (90°) e enriquecimento em Fetotal . A Clorita II ocorre com veios preenchendo pequenas fraturas; é classificada como Chamosita e apresenta politipo estrutural IIb. A Clorita III ocorre alterando minerais detríticos sendo classificada como Mg-Chamosita. A variação na quantidade de ferro das cloritas geradas por processos hidrotermais ( Clorita I ˂10 µm e Clorita II) fornece indícios da ocorrência de pelo menos dois pulsos no processo de alteração hidrotermal: um responsável pela intensa alteração da matriz e dos clastos das rochas e outro responsável pela geração de veios tardios. A variação na quantidade Fetotal dos dois diferentes fluidos responsáveis pela cristalização das cloritas fica evidenciada pela associação de co-genecidade da Clorita II com a hematita, mostrando que o fluido final foi muito mais enriquecido em ferro que o fluido precoce cristalizou a Clorita I ˂10 µm.
- Published
- 2010
44. Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil.
- Author
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Evandro Klein, Chris Harris, Christophe Renac, André Giret, Candido Moura, and Kazuo Fuzikawa
- Abstract
The Serrinha gold deposit of the Gurupi Belt, northern Brazil, belongs to the class of orogenic gold deposits. The deposit is hosted in highly strained graphitic schist belonging to a Paleoproterozoic (∼2,160 Ma) metavolcano-sedimentary sequence. The ore-zones are up to 11 m thick, parallel to the regional NW–SE schistosity, and characterized by quartz-carbonate-sulfide veinlets and minor disseminations. Textural and structural data indicate that mineralization was syn- to late-tectonic and postmetamorphic. Fluid inclusion studies identified early CO
2 (CH4 -N2 ) and CO2 (CH4 -N2 )-H2 O-NaCl inclusions that show highly variable phase ratios, CO2 homogenization, and total homogenization temperatures both to liquid and vapor, interpreted as the product of fluid immiscibility under fluctuating pressure conditions, more or less associated with postentrapment modifications. The ore-bearing fluid typically has 18–33mol% of CO2 , up to 4mol% of N2 , and less than 2mol% of CH4 and displays moderate to high densities with salinity around 4.5wt% NaCl equiv. Mineralization occurred around 310 to 335°C and 1.3 to 3.0 kbar, based on fluid inclusion homogenization temperatures and oxygen isotope thermometry with estimated oxygen fugacity indicating relatively reduced conditions. Stable isotope data on quartz, carbonate, and fluid inclusions suggest that veins formed from fluids with δ18 OH2O and δDH2O (310–335°C) values of +6.2 to +8.4‰ and −19 to −80‰, respectively, which might be metamorphic and/or magmatic and/or mantle-derived. The carbon isotope composition (δ13 C) varies from −14.2 to −15.7‰ in carbonates; it is −17.6‰ in fluid inclusion CO2 and −23.6‰ in graphite from the host rock. The δ34 S values of pyrite are −2.6 to −7.9‰. The strongly to moderately negative carbon isotope composition of the carbonates and inclusion fluid CO2 reflects variable contribution of organic carbon to an originally heavier fluid (magmatic, metamorphic, or mantle-derived) at the site of deposition and sulfur isotopes indicate some oxidation of the originally reduced fluid. The deposition of gold is interpreted to have occurred mainly in response to phase separation and fluid-rock interactions such as CO2 removal and desulfidation reactions that provoked variations in the fluid pH and redox conditions. [ABSTRACT FROM AUTHOR]- Published
- 2006
- Full Text
- View/download PDF
45. Characterisation of the metasomatic agent in mantle xenoliths from Deves, massif central (France) using oupled in-situ trace element and o, SR, ND isotopic compositions
- Author
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Christophe Renac, Stephanie Touron, Jean-Yves Cottin, Suzanne Y O'Reilly, and Griffin, William L.
46. Fractionation of Fe and O isotopes in the mantle
- Author
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Helen Williams, Sune Nielsen, Christophe Renac, Mccammon, C. A., Griffin, William L., and Suzanne Y O'Reilly
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