Abstract:Abstract The Wuchuan-Zhen′an-Daozhen Al metallogenic district, north Guizhou province, located in southern Chongqing-central Guizhou bauxite metallogenic belt, is one of the major bauxite belts in Guizhou province. The bauxite-bearing rock series is the Middle Permian Liangshan Formation and the ore genesis of the bauxite belongs to paleo-weathering crust sedimentary type. The results of the chemical compositions analysis show that the Al2O3 contents and Ai/Si ratios of the earthy, clastic bauxite is higher than those of the oolitic, dense massive bauxite. Based on the microscopic observation, powder diffraction and electron microprobe analysis, the major minerals of bauxite ores are the diaspore, boehmite, and clay minerals, of which the diaspore is aggregated distribution and shows a short column, subhedral-euhedral crystal form, the clay mineral is mainly kaolinite and shows present island and residual cyclic occurrences, the other clay minerals include illite, montmorillonite and chlorite. Other minerals consist of pyrite minerals, magnetite, feldspar, quartz, rutile, zircon, anatase, calcite and dolomite. The main minerals in bauxite rocks are clay minerals, which are mainly kaolinite, and other minerals are similar with the bauxite. The content of Al2O3, SiO2, TiFe2O3 and TiO2 in bauxite ores is greater than 83% and the content of the loss on ignition is less than 14%, while the content of Al2O3, SiO2, TiFe2O3 and TiO2 in bauxite rocks is less than 80% and the content of loss on ignition is greater than 15%. This indicates that the bauxite ores is significantly different from bauxite rocks. Combined with previous studies, this paper suggests the formation process of bauxite ores is that under the suitable climatic conditions, the sandshale of the Hanjiadian Formation (the ore-forming mother rocks) was weathering and leaching, then formed weathering residues and clay minerals (mainly kaolinite) which enriched in Al, Ti and other inert elements. After migrated to lakes basin environment, the clay minerals continually lost silicon and iron, enriched in aluminum and formed bauxite rocks. Finally, under the processes of deep buried compaction, diagenesis and mineralization, these clay minerals further lost silicon and iron, enriched in aluminum, the industrial bauxite ores formed in the Middle Permian.