Study on Mineral Assemblage Differences of Bauxite Deposits in Southeast Yunnan under Ancient Environmental Control

Southeastern Yunnan bauxite deposits are generally characterized by karst-type bauxite features, yet distinct variations in ore-forming geological conditions and mineral assemblages are observed across different deposits, with their genesis remaining unclear. This study focuses on the Hongsheke and Tiechang bauxite deposits in southeastern Yunnan. Using sedimentary facies analysis and multiple mineralogical techniques, we delineate the stratigraphic evolution of the ore-bearing successions and characterize their mineral assemblages. We further evaluate how paleoenvironmental conditions control bauxite mineral assemblages and metallogenic types. Results indicate that the Hongsheke deposit predominantly contains boehmite, kaolinite, hematite, and limonite, formed under oxidizing and weakly acidic conditions proximal to the weathering crust, exhibiting typical autochthonous bauxite features. The Tiechang deposit, conversely, is dominated by diaspore, chlorite, and goethite, representing allochthonous bauxite formed in a restricted shallow marine environment with reducing and weakly alkaline conditions. Differences in oolitic textures and Fe–Al mineral assemblages between the two deposits reflect variations in paleoenvironmental and climatic conditions. Overall, the Hongsheke deposit was located in a paleogeographic transitional zone between marine and terrestrial environments, while the Tiechang deposit formed in a relatively restricted shallow marine setting. Sea-level fluctuations are identified as critical factors controlling the zonal distribution of bauxite mineral assemblages and metallogenic types.