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Liu X.,China University of Geosciences | Wang Q.,China University of Geosciences | Zhang Q.,The Bureau of Geo exploration Guangxi and Mineral Development | Yang S.,China University of Geosciences | And 3 more authors.
Mineralium Deposita | Year: 2017

More than 0.5 billion tons of late Permian bauxite overlies the karstic topography of the Maokou Formation of western Guangxi in China. Here, we provide new mineralogical, geochemical, Sr–Nd–Pb isotopic, and pyrite S isotope and trace element compositional data for the Pingguo bauxite deposit, aiming to further our understanding of the genesis of Permian bauxite. The Pingguo bauxite contains three distinct layers: a lower layer dominated by ferric clay or weathered iron ore, a middle layer of cryptocrystalline and oolitic bauxite ore, and an upper layer dominated by argillaceous bauxite. The bauxite ore is mainly diaspore, pyrite, chamosite, and anatase, whereas the argillaceous bauxite contains diaspore, kaolinite, pyrophyllite, pyrite, and anatase. Two types of pyrite have been identified within the bauxite: fine-grained and framboidal pyrite (Py1) occurring in aggregates and coarse-grained and euhedral pyrite (Py2). Py1 is enriched in trace elements and is thought to have a diagenetic origin, whereas Py2 is deficient in trace elements and is considered to have formed by later recrystallization. The S isotopic composition of pyrite (−34.11 to −18.91‰) and visible ovoid microorganisms within the bauxite provide evidences of microbial activity during bauxite formation. The Sr–Nd–Pb isotopic composition of the bauxite indicates that these ores were generated by the weathering of basalts belonging to the Emeishan Large Igneous Province (LIP) and limestones of the Maokou Formation. Microorganisms were likely to have enhanced the dissolution and weathering of the parent rock and facilitated the precipitation of diaspore under near-surface conditions. © 2017 Springer-Verlag Berlin Heidelberg

Wang Q.,China University of Geosciences | Wang Q.,Beijing University of Technology | Deng J.,China University of Geosciences | Deng J.,Beijing University of Technology | And 8 more authors.
Journal of Asian Earth Sciences | Year: 2010

Most of the karstic bauxite deposits in China are enriched in REE, and the REE has commonly been considered to be adsorbed on the surface of clay or diaspore minerals as ion state. However, occurrence of REE minerals in the bauxite deposits has not been reported by far. In the Quyang bauxite deposit from Guangxi province, we find REE minerals. The minerals are parisite and churchite. Parisite is widely distributed in the ooids and matrix, inducing positive Ce anomaly of the ores; whereas, churchite is rare and occurred in the core of ooid. The compositions of the REE minerals show the Eu anomaly can change gently during the weathering, and the Eu anomaly analyses suggest that the REE in the ores are mostly derived from the underlying carbonates. The parisite is formed in an alkaline condition, while churchite in an acidic situation; the co-existence of the two minerals in the ores suggests the Permian environment for bauxite formation is complex with great change of pH value. Moreover, parisite is inferred to be formed earlier than the churchite. © 2010 Elsevier Ltd.

Liu X.,China University of Geosciences | Wang Q.,China University of Geosciences | Zhang Q.,The Bureau of Geo exploration Guangxi and Mineral Development | Zhang Y.,China University of Geosciences | Li Y.,China University of Geosciences
Ore Geology Reviews | Year: 2016

Karstic bauxites in western Guangxi, China, comprise two subtypes: Permian bauxite and Quaternary bauxite. The Quaternary bauxite originated from the breaking up, rolling, and accumulating of Permian bauxite in karstic depressions in Quaternary. Various types of rare earth element (REE) minerals were discovered during the formation of the Permian and Quaternary bauxites from the Xinxu, Longhe, and Tianyang bauxite deposits in this study. Five types of REE minerals, including bastnäsite, parisite, cerianite, rhabdophane, and churchite, were identified. Bastnäsite and parisite are the most abundant, and they are widely developed in the Permian ore and also present in the Quaternary ore. Obvious variations in bastnäsite and parisite REE compositions were observed, which is ascribed to distinctions in the source materials in the primary weathering profile from different areas. The mode of occurrence of bastnäsite and parisite suggests they were mainly precipitated under alkaline and reducing conditions during the Permian bauxite-forming stage and underwent intensive corrosion in the Quaternary. Churchite was formed during the Permian weathering stage under acidic condition. Both cerianite and rhabdophane occur in fractures within the Permian bauxite ore, indicating that both formed during the Quaternary weathering stage. It is considered that the rhabdophane enriched in Ce have formed locally, in the process of that the Ce3+, released from bastnäsite rapidly, entered the rhabdophane lattice before being oxidized to Ce4+. Cerianite was mainly found in association with Mn-Al hydroxides, suggesting that the released Ce3+ was oxidized into Ce4+ and precipitated cerianite in fractures within the Permian bauxite ore. Mass balance equations reveal a depletion in nearly all REEs during the transformation from the Permian to the Quaternary bauxite ore, mainly caused by the dissolution of bastnäsite and parisite. The genesis of the REE minerals, together with the occurrence of other minerals, indicates that intensively acidic and oxidizing conditions developed before the formation of the Permian bauxite ore. Towards the end of the Permian, the conditions became reducing and alkaline, favorable for the large-scale bauxitization. The Quaternary bauxite-forming stage was characterized by variable pH and Eh conditions, with acidic (pH=4-6) and oxidizing (Eh>2) conditions at the surface of the exposed Permian bauxite ore. © 2015 Elsevier B.V.

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