Fluid unmixing/immiscibility as an ore-forming process in the giant REE–Nb–Fe deposit, Inner Mongolian, China: Evidence from fluid inclusions |
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| Authors: | Hong-Rui Fan Fang-Fang Hu Kui-Feng Yang Kai-Yi Wang |
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| Institution: | Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China |
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| Abstract: | The giant Bayan Obo REE–Nb–Fe deposit consists of replacement bodies hosted in dolomite marble made up of magnetite, REE fluorocarbonates, fluorite, aegirine, amphibole, calcite and barite. Two or three phase CO2-rich, three phase hypersaline liquid–vapor–solid, and two phase liquid-rich inclusions have been recognized in mineralized fluorite and quartz samples. Microthermometry measurements indicate that the carbonic phase in CO2-rich inclusions is nearly pure CO2. Fluids involving in REE–Nb–Fe mineralization at Bayan Obo might be mainly of H2O–CO2–NaCl–(F–REE) system. Coexistences of brine inclusions and CO2-rich inclusions with similar homogenization temperatures give evidence that immiscibility happened during REE mineralization. An unmixing of an original H2O–CO2–NaCl fluid probably derived from carbonatitic magma. The presence of REE-carbonates as an abundant solid in fluid inclusions shows that the original ore-forming fluids are very rich in REE, and therefore, have the potential to produce economic REE ores at Bayan Obo. |
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| Keywords: | Fluid inclusion Fluid unmixing/immiscibility REE mineralization Bayan Obo |
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