Mineralogical and geochemical characteristics of the Nanchuan-Wulong bauxite deposit in Chongqing

The Nanchuan-Wulong bauxite deposit in Chongqing are ascribed to the karst bauxite deposit hosted in southern Chongqing-northern Guizhou bauxite belt. The mineralogical analysis on the basis of microscopic examination,X-ray power diffraction patterns,MAL and SEM-EDS has revealed that diaspore,kaolinite and chlorite are the major minerals in the bauxite ores with the minor minerals such as illite,boehmite,gibbsite, chamosite,siderite,hematite,goethite,pyrite,anatase,rutile,apatite,quartz zircon,calcite,feldspar and small amounts of rare-earth minerals. The ore fabrics and mineral assemblages indicate that the Nanchuan-Wulong bauxite deposit were formed in the depositional-diagenetic environments close to the phreatic zone. Both the ore textures and morphology of zircon grains also indicate that much of bauxitic soils were once transported in a short distance. Geochemically,the major chemical compositions in the bauxite ores consist of Al₂O₃,TFeO,SiO₂ and TiO₂. The elements REE,Zr,Hf,Nb,Ta,Th,Sc,Li and Ga are enriched as well in the bauxitization processes. The underlying shale,carbonate rocks and acidic volcanic rocks are believed to contribute the mother materials to the formation of the bauxite deposits. In addition,the formation of the bauxite deposits may have something to do with microorganisms.