Mineralogy, geochemistry, and genesis of lateritic bauxite deposits in the Wuchuan-Zheng'an-Daozhen area, Northern Guizhou Province, China

摘要

The lateritic bauxite deposits in the Wuchuan-Zheng'an-Daozhen area, Northern Guizhou Province, are hosted by the Liangshan Formation which unconformably overlies the Lower-Middle Silurian mud-shale and the Upper Carboniferous limestone and underlies the Middle Permian limestone. From the bottom upward, the deposits are generally composed of brick-red, yellow-brown, and gray bauxite horizons. Diaspore, boehmite, kaolinite, smectite and hematite are the major mineral components in the bauxite ores with small amounts of gibbsite, illite, goethite, pyrite, anatase, zircon, quartz and feldspar. The textural features of ores suggest that the bauxite has an authigenic origin but locally underwent transportation and re-deposition. Geochemical investigations indicate that the immobile elements like Al, Ti, Zr, Cr, Hf, Nb, Ta and Th were obviously enriched during bauxitization. Factors such as the type of parent rock, pH variation in weathering solutions, adsorption processes, groundwater chemical characteristics, Fe concentration variation in the weathering profiles, leaching degree of minerals, and geochemistry of elements have played a significant role in the distribution of trace and rare earth elements during weathering of the lateritic bauxite. The bauxites may have a close genetic relationship with the Hanjiadian mud shale and the Huanglong limestone in view of their similar chondrite-normalized REE patterns, Zr/Hf and Nb/Ta ratios. However, field observations and geochemical data suggest that the precursors of bauxites are complex and the main components of precursors are basic igneous rocks possibly from the Neoproterozoic basic igneous rocks and the Mesoproterozoic basic-ultrabasic intrusions in the Yangtze Block.