Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG Deposits
Uranium mineralization is commonly accompanied by enrichment of fluorite and other F-bearing minerals, leading to the hypothesis that fluoride may play a key role in the hydrothermal transport of U. In this paper, we review the thermodynamics of U(IV) and U(VI) complexing in chloride- and fluoride-b...
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Wiley
2018-01-01
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| Series: | Geofluids |
| Online Access: | http://dx.doi.org/10.1155/2018/6835346 |
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| author | Yanlu Xing Yuan Mei Barbara Etschmann Weihua Liu Joël Brugger |
| author_facet | Yanlu Xing Yuan Mei Barbara Etschmann Weihua Liu Joël Brugger |
| author_sort | Yanlu Xing |
| collection | DOAJ |
| description | Uranium mineralization is commonly accompanied by enrichment of fluorite and other F-bearing minerals, leading to the hypothesis that fluoride may play a key role in the hydrothermal transport of U. In this paper, we review the thermodynamics of U(IV) and U(VI) complexing in chloride- and fluoride-bearing hydrothermal fluids and perform mineral solubility and reactive transport calculations to assess equilibrium controls on the association of F and U. Calculations of uraninite and U3O8(s) solubility in acidic F-rich (Cl : F = 100 [ppm-based]) hydrothermal fluids at 25–450°C, 600 bar, show that U(IV)-F complexes (reducing conditions) and uranyl-F complexes (oxidizing conditions) predominate at low temperature (T<~200°C), while above ~250°C, chloride complexes predominate in acidic solutions. In the case of uraninite, solubility is predicted to decrease dramatically as U(IV)Cl22+ becomes the predominant U species at T>260°C. In contrast, the solubility of U3O8(s) increases with increasing temperatures. We evaluated the potential of low-temperature fluids to upgrade U and F concentrations in magnetite-chalcopyrite ores. In our model, an oxidized (hematite-rich) granite is the primary source of F and has elevated U concentration. Hydrothermal fluids (15 wt.% NaCl equiv.) equilibrated with this granite at 200°C react with low-grade magnetite-chalcopyrite ores. The results show that extensive alteration by these oxidized fluids is an effective mechanism for forming ore-grade Cu-U mineralization, which is accompanied by the coenrichment of fluorite. Fluorite concentrations are continuously upgraded at the magnetite-hematite transformation boundary and in the hematite ores with increasing fluid : rock (F/R) ratio. Overall, the model indicates that the coenrichment of F and U in IOCG ores reflects mainly the source of the ore-forming fluids, rather than an active role of F in controlling the metal endowment of these deposits. Our calculations also show that the common geochemical features of hematite-dominated IOCG deposits can be related to a two-phase process, whereby a magnetite-hematite-rich orebody (formed via a number of processes/tectonic settings) is enriched in Cu ± U and F during a second stage (low temperature, oxidized) of hydrothermal circulation. |
| format | Article |
| id | doaj-art-68d51257ed9b4ed2be3653f7945f13e9 |
| institution | OA Journals |
| issn | 1468-8115 1468-8123 |
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| spelling | doaj-art-68d51257ed9b4ed2be3653f7945f13e92025-08-20T02:35:25ZengWileyGeofluids1468-81151468-81232018-01-01201810.1155/2018/68353466835346Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG DepositsYanlu Xing0Yuan Mei1Barbara Etschmann2Weihua Liu3Joël Brugger4School of Earth, Atmosphere and the Environment, Monash University, Clayton, VIC 3800, AustraliaSchool of Earth, Atmosphere and the Environment, Monash University, Clayton, VIC 3800, AustraliaSchool of Earth, Atmosphere and the Environment, Monash University, Clayton, VIC 3800, AustraliaCSIRO Mineral Resources Flagship, Clayton, VIC 3168, AustraliaSchool of Earth, Atmosphere and the Environment, Monash University, Clayton, VIC 3800, AustraliaUranium mineralization is commonly accompanied by enrichment of fluorite and other F-bearing minerals, leading to the hypothesis that fluoride may play a key role in the hydrothermal transport of U. In this paper, we review the thermodynamics of U(IV) and U(VI) complexing in chloride- and fluoride-bearing hydrothermal fluids and perform mineral solubility and reactive transport calculations to assess equilibrium controls on the association of F and U. Calculations of uraninite and U3O8(s) solubility in acidic F-rich (Cl : F = 100 [ppm-based]) hydrothermal fluids at 25–450°C, 600 bar, show that U(IV)-F complexes (reducing conditions) and uranyl-F complexes (oxidizing conditions) predominate at low temperature (T<~200°C), while above ~250°C, chloride complexes predominate in acidic solutions. In the case of uraninite, solubility is predicted to decrease dramatically as U(IV)Cl22+ becomes the predominant U species at T>260°C. In contrast, the solubility of U3O8(s) increases with increasing temperatures. We evaluated the potential of low-temperature fluids to upgrade U and F concentrations in magnetite-chalcopyrite ores. In our model, an oxidized (hematite-rich) granite is the primary source of F and has elevated U concentration. Hydrothermal fluids (15 wt.% NaCl equiv.) equilibrated with this granite at 200°C react with low-grade magnetite-chalcopyrite ores. The results show that extensive alteration by these oxidized fluids is an effective mechanism for forming ore-grade Cu-U mineralization, which is accompanied by the coenrichment of fluorite. Fluorite concentrations are continuously upgraded at the magnetite-hematite transformation boundary and in the hematite ores with increasing fluid : rock (F/R) ratio. Overall, the model indicates that the coenrichment of F and U in IOCG ores reflects mainly the source of the ore-forming fluids, rather than an active role of F in controlling the metal endowment of these deposits. Our calculations also show that the common geochemical features of hematite-dominated IOCG deposits can be related to a two-phase process, whereby a magnetite-hematite-rich orebody (formed via a number of processes/tectonic settings) is enriched in Cu ± U and F during a second stage (low temperature, oxidized) of hydrothermal circulation.http://dx.doi.org/10.1155/2018/6835346 |
| spellingShingle | Yanlu Xing Yuan Mei Barbara Etschmann Weihua Liu Joël Brugger Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG Deposits Geofluids |
| title | Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG Deposits |
| title_full | Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG Deposits |
| title_fullStr | Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG Deposits |
| title_full_unstemmed | Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG Deposits |
| title_short | Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG Deposits |
| title_sort | uranium transport in f cl bearing fluids and hydrothermal upgrading of u cu ores in iocg deposits |
| url | http://dx.doi.org/10.1155/2018/6835346 |
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