Combined tectonic and paleogeographic controls on the genesis of bauxite in the Early Carboniferous to Permian Central Yangtze Island

Abstract

Two bauxite horizons, with a total reserve of 1.29 Bt, occur in the Lower Carboniferous and Lower Permian in the central South China Block. Different from other intracontinental bauxites in China, which are genetically linked to the orogenesis along the continental margin, these bauxites were generated in the absence of marginal orogenesis. The genesis of these bauxites were studied based on tectonic, paleogeographic, and paleoclimatic controls. The orebody in Huofengchong (HFC) region is hosted within the Lower Carboniferous, which overlies upon the Cambrian dolomite unconformably. The orebody in the regions of Yanfengba (YFB) and Baiyantou (BYT) occurs in Lower Permian, which overlies upon the Silurian shale or Devonian dolomite unconformably. The mineral assemblages in the Carboniferous HFC bauxite consist of diaspore, illite, anatase, and in Permian YFB and BYT bauxite, the minerals are diaspore, anatase, illite, clinochlore, and kaolinite. The data from the U-Pb isotope measurements of detrital zircons from these bauxites provide two main ages: (1) a maximum U-Pb age peak of ca. 800 Ma from the Carboniferous HFC and (2) a maximum age peak of ca. 1100 Ma for the Permian BYT and YFB. The ca. 800 Ma detrital zircons from the Carboniferous bauxite are dominating in the Paleozoic sedimentary units, which likely derive from the erosion of the Mid- to Neo-proterozoic felsic volcanic and intrusive rocks (Panxi-Hannan arc) occurring in the western margin of the South China Block. By contrast, the zircons with ages of ca. 1100 Ma are prevalent in the Paleozoic sediments from the center of the block. The above results indicate that the Lower Carboniferous and Lower Permian bauxites are sourced from the sedimentary rocks in the western and central parts of the South China Block, respectively. Despite the difference in the provenance, these two episodes of deposits were both deposited in a tidal flat-restricted platform attached to an EW-trending Yangtze island, occupies the western to central parts of the South China block. This indicates that the shift from a marginal to central uplift within the paleo-island from Early Carboniferous to Early Permian has induced the transition in the provenance of the source material. In addition, the weathered materials from the two provenances both accumulated in the coastal region receiving further bauxitization. The bauxitization was boosted by the persistent preferable tepid and humid paleoclimate, defined by the equatorial position of South China block and the drop of global temperature during the metallogenic period.