Genesis of karst bauxite-bearing sequences in Baofeng, Henan (China), and the distribution of critical metals

摘要

Bauxite-bearing sequences are not only the main economic sources of Aluminum, but also of many critical metals. The distribution of critical metals was determined from six bauxite profiles in Baofeng, and an evolution model was proposed for the formation of bauxite-bearing sequences. Following a terrestrial deposition of the lower pisolitic bauxite horizon and the underlying clayey layer, transportation and redeposition of bauxitic materials during submergence led to the formation of the upper bauxite horizon presenting finely-clastic and oolitic textures, as well as the intercalated clayey layers. Both bauxite ores and clay samples contain highly elevated contents of Li, B, Sc, V, Ga, Zr, Nb, W and total REEs. Li contents are extremely low in high-grade bauxite ores (10.92-44.77 ppm), compared to highly elevated values in low-grade bauxite ores (35.81-1601 ppm) and clay samples (38.54-1965 ppm), enlightening a new potential resource for Li, the bauxite-bearing sequences resting on karstified carbonate. The distribution pattern of Ga is similar to that of Li, and the correlation analysis indicates that Ga is primarily associated with silicates, i.e. clay minerals. The vertical distribution of Li, B, V, Cr and Ga shares the same pattern, similar to that of K2O and SiO2, being highly enriched in clayey layers relative to bauxite horizons. Both Sc and total REEs are also highly enriched in Baofeng bauxite profiles, highlighting a potential Sc and REEs resource.