Provenance and ore-forming process of Permian lithium-rich bauxite in central Yunnan, SW China

Permian lithium-rich karstic bauxites are newly discovered in central Yunnan province, western margin of the South China Block, with a reserve of 16 million tonnes, which has a great potential for aluminum and lithium exploitation. Provenance and ore-forming processes are still debatable. Mineralogical, geochemical, and geochronological analyses were conducted on two typical bauxite profiles to explore the genetic process of the Permian bauxites in central Yunnan province. Profile A contains three layers from bottom to top: clayey bauxite, claystone, pisolitic bauxite. Profile B contains five layers from bottom to top: claystone, pisolitic bauxite, claystone, pisolitic bauxite, and mottled claystone. Pisolitic bauxite mainly consists of diaspore and chamosite, with small amounts of goethite, anatase, and boehmite. Clayey bauxite dominantly consists of boehmite and kaolinite, with small amounts of diaspore and anatase. Claystone predominantly consists of kaolinite or illite. Three stages of bauxite formation are identified: (1) during weathering of regional sedimentary strata, boehmite, kaolinite, and illite were formed; (2) during bauxite deposition, diaspore, chamosite, anatase, pyrite, with small amounts of illite, kaolinite, and barite were formed; (3) during second exposure caused by paleo-uplift, goethite was formed. Correlation analyses demonstrate that kaolinite is the most likely host mineral of Li in the studied bauxites and the leaching process after bauxite deposition can significantly reduce the lithium contents. Two profiles’ differences in sequence can be attributed to their different locations in the paleokarst terrain. Topography of karst terrain controls the ore-forming conditions, thus affecting the sequence and mineralogy of bauxite profiles. In our case, during the bauxite deposition, the uplifted area was not submerged at first, then as the groundwater rose, the uplifted area was immersed. Therefore, the ore-forming conditions in uplifted areas changed from oxidizing to reducing and became more alkaline. In contrast, the karstic depression was submerged throughout the bauxite deposition. All layers in the karstic depression were formed under reducing and alkaline conditions. Data from U-Pb isotope measurements of detrital zircons from bauxites in central Yunnan province provides 3 main ages, which are 500–650 Ma, 800 Ma, and 980 Ma. There are several minor peak ages in the age spectrum, which are 288–310 Ma, 1500 Ma, 1800 Ma, 2000 Ma, and 2500 Ma. Age distribution pattern of bauxites is more similar to that of the Ordovician sedimentary units than other regional rocks in central Yunnan province, which indicates the major contribution of the eroded Ordovician sedimentary rocks to bauxites.