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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. [ABSTRACT FROM AUTHOR]

Abstract: The Guangou bauxite deposit in western Henan, China, is located in the North China Block and to the north of the North Qinling orogenic belt. The orebody is hosted within the lower member of the Carboniferous Benxi Formation, which overlies unconformably upon the Ordovician Majiagou Formation. In the lower member of the Benxi Formation, the bauxite orebody (with a diaspore–illite–anatase mineral assemblage) is sandwiched between underlying ferric clay (illite–hematite–goethite) and overlying top clay (kaolinite–quartz–goethite). According to field observations and geochemical evidence including trace- and rare-earth-element (REE) compositions, especially Zr/Hf ratios, the ferric clays were weathered from the underlying argillaceous limestones in the Majiagou Formation. During this weathering process, trace elements S, Zn, Ni, Cr, V, Sc, F, Ba, and Be are depleted; Li, Rb, and B are enriched; and Zr, Hf, Bi, Ta, Ga, Nb, and Th are relatively immobile. REEs exhibit evident differentiation with enrichment of La, Ce, Pr, and Nd and depletion of Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The bauxite formed in weak reducing, slightly basic water conditions according to the geneses of coexisting diaspore and anatase, and it was altered during the epigenetic and second exposure periods, forming kaolinite and goethite, respectively. Interelemental relationship analyses of the ores suggest that the elemental behaviors of trace elements and REEs in the bauxitization process are mainly controlled by the mineral compositions in bauxite ore and chemical properties of the elements. For instance, zircon, rutile, and anatase contain Zr, Hf, Nb, Ta, W, and U. Based on geochemical evidence, together with age data and chemical compositions of the detrital minerals, both distant igneous rocks in the plate margin and Paleozoic carbonates and Precambrian rocks inside North China Block provide the miscellaneous material for the bauxite ore and the top clay. [Copyright &y& Elsevier]