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Georges Calas - One of the best experts on this subject based on the ideXlab platform.
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Luminescence of uranium-bearing Opals: Origin and use as a pH record
Chemical Geology, 2016Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Mostafa Fayek, Thomas Vercouter, Georges CalasAbstract:Fluorescence of minerals has been long used for U exploration. It is proposed here that Opal fluorescence can be used as a probe of the pH of the formation solution, bringing constraints for modeling U speciation and sequestration at the Earth's surface. We present a study of fluorescence spectroscopy of U in Opals resulting from low-temperature (29 degre) alteration of mineralized rhyolitic lavas (NOpal I U deposit, Sierra Peña Blanca, Mexico). These Opals show green fluorescence with a concentric distribution at microscopic scale, which is unambiguously assigned to uranyl groups (oxidized form of U). Spectra appear typical of uranyl in Opal as reported in literature for other localities according to peak positions. When considering also the lifetime of fluorescence spectra (with time resolved laser fluorescence spectroscopy), fingerprinting indicates that uranyl occurs either as phosphate or hydroxo-polynuclear complexes trapped onto the Opal internal surface. Data are indicative of a pH of Opal formation around 8, as derived from both conditions of laboratory experiments and reference to calculated diagrams of speciation. This pH value is consistent with the NOpal geological formations that were potentially in contact with the aquifer involved in the hydrothermal process. In addition, the microscopic zoning of U suggests that the speciation has been stable since Opal formation more than 50 ka ago, which allows the record of pH that prevailed at that time.
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Evidence for nanocrystals of vorlanite, a rare uranate mineral, in the NOpal I low-temperature uranium deposit (Sierra Peña Blanca, Mexico)
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (
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evidence for nanocrystals of vorlanite a rare uranate mineral in the nOpal i low temperature uranium deposit sierra pena blanca mexico
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (<50 °C) temperature. The presence of nanoscale uranate crystals in an environment largely dominated by uranyl silicates indicates that uranates may play a role in uranium scavenging at low temperature. In addition, the occurrence of vorlanite in the crystal shape consistent with its structure provides unique information on its conditions of formation.
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alteration geochemistry of the nOpal i uranium deposit sierra pena blanca mexico a natural analogue for a radioactive waste repository in volcanic tuffs
Terra Nova, 2008Co-Authors: Georges Calas, Thierry Allard, Pierre Agrinier, Philippe IldefonseAbstract:Natural analogues provide an approach to characterize and test the long-term modelling of a repository performance. This article presents geochemical information about the alteration conditions of the NOpal I uranium deposit, Mexico, an analogue for the proposed Yucca Mountain radioactive waste repository. Mineralization and hydrothermal alteration of volcanic tuffs are contemporaneous, according to petrographic observations. Trace element geochemistry (U, Th, REE) provides evidence for local mobilization of uranium under oxidizing conditions and further precipitation under reducing conditions. O- and H-isotope geochemistry of kaolinite, smectite, Opal and calcite suggests that argillic alteration proceeded at shallow depth with meteoric water at 25–75 °C, a low-temperature context, unusual for volcanic-hosted uranium deposits. This temperature range is compatible with some post-closure evolution models of the proposed Yucca Mountain repository.
Guillaume Othmane - One of the best experts on this subject based on the ideXlab platform.
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Luminescence of uranium-bearing Opals: Origin and use as a pH record
Chemical Geology, 2016Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Mostafa Fayek, Thomas Vercouter, Georges CalasAbstract:Fluorescence of minerals has been long used for U exploration. It is proposed here that Opal fluorescence can be used as a probe of the pH of the formation solution, bringing constraints for modeling U speciation and sequestration at the Earth's surface. We present a study of fluorescence spectroscopy of U in Opals resulting from low-temperature (29 degre) alteration of mineralized rhyolitic lavas (NOpal I U deposit, Sierra Peña Blanca, Mexico). These Opals show green fluorescence with a concentric distribution at microscopic scale, which is unambiguously assigned to uranyl groups (oxidized form of U). Spectra appear typical of uranyl in Opal as reported in literature for other localities according to peak positions. When considering also the lifetime of fluorescence spectra (with time resolved laser fluorescence spectroscopy), fingerprinting indicates that uranyl occurs either as phosphate or hydroxo-polynuclear complexes trapped onto the Opal internal surface. Data are indicative of a pH of Opal formation around 8, as derived from both conditions of laboratory experiments and reference to calculated diagrams of speciation. This pH value is consistent with the NOpal geological formations that were potentially in contact with the aquifer involved in the hydrothermal process. In addition, the microscopic zoning of U suggests that the speciation has been stable since Opal formation more than 50 ka ago, which allows the record of pH that prevailed at that time.
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Evidence for nanocrystals of vorlanite, a rare uranate mineral, in the NOpal I low-temperature uranium deposit (Sierra Peña Blanca, Mexico)
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (
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evidence for nanocrystals of vorlanite a rare uranate mineral in the nOpal i low temperature uranium deposit sierra pena blanca mexico
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (<50 °C) temperature. The presence of nanoscale uranate crystals in an environment largely dominated by uranyl silicates indicates that uranates may play a role in uranium scavenging at low temperature. In addition, the occurrence of vorlanite in the crystal shape consistent with its structure provides unique information on its conditions of formation.
Thierry Allard - One of the best experts on this subject based on the ideXlab platform.
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Luminescence of uranium-bearing Opals: Origin and use as a pH record
Chemical Geology, 2016Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Mostafa Fayek, Thomas Vercouter, Georges CalasAbstract:Fluorescence of minerals has been long used for U exploration. It is proposed here that Opal fluorescence can be used as a probe of the pH of the formation solution, bringing constraints for modeling U speciation and sequestration at the Earth's surface. We present a study of fluorescence spectroscopy of U in Opals resulting from low-temperature (29 degre) alteration of mineralized rhyolitic lavas (NOpal I U deposit, Sierra Peña Blanca, Mexico). These Opals show green fluorescence with a concentric distribution at microscopic scale, which is unambiguously assigned to uranyl groups (oxidized form of U). Spectra appear typical of uranyl in Opal as reported in literature for other localities according to peak positions. When considering also the lifetime of fluorescence spectra (with time resolved laser fluorescence spectroscopy), fingerprinting indicates that uranyl occurs either as phosphate or hydroxo-polynuclear complexes trapped onto the Opal internal surface. Data are indicative of a pH of Opal formation around 8, as derived from both conditions of laboratory experiments and reference to calculated diagrams of speciation. This pH value is consistent with the NOpal geological formations that were potentially in contact with the aquifer involved in the hydrothermal process. In addition, the microscopic zoning of U suggests that the speciation has been stable since Opal formation more than 50 ka ago, which allows the record of pH that prevailed at that time.
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Evidence for nanocrystals of vorlanite, a rare uranate mineral, in the NOpal I low-temperature uranium deposit (Sierra Peña Blanca, Mexico)
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (
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evidence for nanocrystals of vorlanite a rare uranate mineral in the nOpal i low temperature uranium deposit sierra pena blanca mexico
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (<50 °C) temperature. The presence of nanoscale uranate crystals in an environment largely dominated by uranyl silicates indicates that uranates may play a role in uranium scavenging at low temperature. In addition, the occurrence of vorlanite in the crystal shape consistent with its structure provides unique information on its conditions of formation.
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alteration geochemistry of the nOpal i uranium deposit sierra pena blanca mexico a natural analogue for a radioactive waste repository in volcanic tuffs
Terra Nova, 2008Co-Authors: Georges Calas, Thierry Allard, Pierre Agrinier, Philippe IldefonseAbstract:Natural analogues provide an approach to characterize and test the long-term modelling of a repository performance. This article presents geochemical information about the alteration conditions of the NOpal I uranium deposit, Mexico, an analogue for the proposed Yucca Mountain radioactive waste repository. Mineralization and hydrothermal alteration of volcanic tuffs are contemporaneous, according to petrographic observations. Trace element geochemistry (U, Th, REE) provides evidence for local mobilization of uranium under oxidizing conditions and further precipitation under reducing conditions. O- and H-isotope geochemistry of kaolinite, smectite, Opal and calcite suggests that argillic alteration proceeded at shallow depth with meteoric water at 25–75 °C, a low-temperature context, unusual for volcanic-hosted uranium deposits. This temperature range is compatible with some post-closure evolution models of the proposed Yucca Mountain repository.
Guillaume Morin - One of the best experts on this subject based on the ideXlab platform.
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Luminescence of uranium-bearing Opals: Origin and use as a pH record
Chemical Geology, 2016Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Mostafa Fayek, Thomas Vercouter, Georges CalasAbstract:Fluorescence of minerals has been long used for U exploration. It is proposed here that Opal fluorescence can be used as a probe of the pH of the formation solution, bringing constraints for modeling U speciation and sequestration at the Earth's surface. We present a study of fluorescence spectroscopy of U in Opals resulting from low-temperature (29 degre) alteration of mineralized rhyolitic lavas (NOpal I U deposit, Sierra Peña Blanca, Mexico). These Opals show green fluorescence with a concentric distribution at microscopic scale, which is unambiguously assigned to uranyl groups (oxidized form of U). Spectra appear typical of uranyl in Opal as reported in literature for other localities according to peak positions. When considering also the lifetime of fluorescence spectra (with time resolved laser fluorescence spectroscopy), fingerprinting indicates that uranyl occurs either as phosphate or hydroxo-polynuclear complexes trapped onto the Opal internal surface. Data are indicative of a pH of Opal formation around 8, as derived from both conditions of laboratory experiments and reference to calculated diagrams of speciation. This pH value is consistent with the NOpal geological formations that were potentially in contact with the aquifer involved in the hydrothermal process. In addition, the microscopic zoning of U suggests that the speciation has been stable since Opal formation more than 50 ka ago, which allows the record of pH that prevailed at that time.
-
Evidence for nanocrystals of vorlanite, a rare uranate mineral, in the NOpal I low-temperature uranium deposit (Sierra Peña Blanca, Mexico)
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (
-
evidence for nanocrystals of vorlanite a rare uranate mineral in the nOpal i low temperature uranium deposit sierra pena blanca mexico
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (<50 °C) temperature. The presence of nanoscale uranate crystals in an environment largely dominated by uranyl silicates indicates that uranates may play a role in uranium scavenging at low temperature. In addition, the occurrence of vorlanite in the crystal shape consistent with its structure provides unique information on its conditions of formation.
Mostafa Fayek - One of the best experts on this subject based on the ideXlab platform.
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Luminescence of uranium-bearing Opals: Origin and use as a pH record
Chemical Geology, 2016Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Mostafa Fayek, Thomas Vercouter, Georges CalasAbstract:Fluorescence of minerals has been long used for U exploration. It is proposed here that Opal fluorescence can be used as a probe of the pH of the formation solution, bringing constraints for modeling U speciation and sequestration at the Earth's surface. We present a study of fluorescence spectroscopy of U in Opals resulting from low-temperature (29 degre) alteration of mineralized rhyolitic lavas (NOpal I U deposit, Sierra Peña Blanca, Mexico). These Opals show green fluorescence with a concentric distribution at microscopic scale, which is unambiguously assigned to uranyl groups (oxidized form of U). Spectra appear typical of uranyl in Opal as reported in literature for other localities according to peak positions. When considering also the lifetime of fluorescence spectra (with time resolved laser fluorescence spectroscopy), fingerprinting indicates that uranyl occurs either as phosphate or hydroxo-polynuclear complexes trapped onto the Opal internal surface. Data are indicative of a pH of Opal formation around 8, as derived from both conditions of laboratory experiments and reference to calculated diagrams of speciation. This pH value is consistent with the NOpal geological formations that were potentially in contact with the aquifer involved in the hydrothermal process. In addition, the microscopic zoning of U suggests that the speciation has been stable since Opal formation more than 50 ka ago, which allows the record of pH that prevailed at that time.
-
Evidence for nanocrystals of vorlanite, a rare uranate mineral, in the NOpal I low-temperature uranium deposit (Sierra Peña Blanca, Mexico)
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (
-
evidence for nanocrystals of vorlanite a rare uranate mineral in the nOpal i low temperature uranium deposit sierra pena blanca mexico
American Mineralogist, 2013Co-Authors: Guillaume Othmane, Thierry Allard, Guillaume Morin, Imène Esteve, Mostafa Fayek, Nicolas Menguy, Georges CalasAbstract:The occurrence of vorlanite, cubic CaUO4, is reported in the NOpal I uranium deposit (Sierra Pena Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing Opal, with a Ca/U ratio of ∼1. Association with Opal suggests that vorlanite formed at NOpal during late-stage U-mobilization under oxidizing conditions and low (<50 °C) temperature. The presence of nanoscale uranate crystals in an environment largely dominated by uranyl silicates indicates that uranates may play a role in uranium scavenging at low temperature. In addition, the occurrence of vorlanite in the crystal shape consistent with its structure provides unique information on its conditions of formation.
