Interaction between karst terrain and bauxites: evidence from Quaternary orebody distribution in Guangxi SW China

摘要

Most bauxite in China is located upon the karst surface, yet the relation between karstification process and bauxite formation is barely known. Here we discuss how the relation affects the karst and bauxite evolution through analyzing distributions of orebody parameters from 9,007 exploration wells (434 orebodies) in western Guangxi, South China block. In high-elevation karst terrain dominated by peaks, orebodies have greater average thickness, lower Al2O3 and higher Fe2O3 ^T than those in low-elevation region dominated by depressions. Principal component and multifractal analyses show that the Al2O3, Fe2O3 ^T and LOI and the orebody thickness, determined by depression geometry, have more even distributions in high-elevation terrain. This explains that the interaction between the oxidized, alkaline water in karst surface and the ferrous clay minerals that released H⁺ during bauxite secondary weathering was more intensive in high-elevation terrain than in low-elevation one. The interaction with self-organized nature is considered responsible for the even development of karstic depressions and bauxite orebody thicknesses in high-elevation terrain. In comparison, SiO2 distribution is more even in low-elevation terrain, where connected depressions near the phreatic zone facilitated SiO2 mobilization and even distribution.