Material source analysis and element geochemical research about two types of representative bauxite deposits and terra rossa in western Guangxi, southern China

摘要

In this study, geologic field observations and geochemical indicators of the types of representative bauxite deposits, terra rossa and underlying carbonate rocks in western Guangxi, southern China, were investigated. Their interrelations, material sources, formation and evolution processes were discussed. The results show an inherited relationship between terra rossa and its underlying limestone. The relevant parameter diagrams of trace and rare earth elements suggest that the two types of bauxite deposits probably possess identical material sources. Both bauxite deposits and terra rossa have close affinities with each other, implying that carbonate rocks similar to the underlying limestone might be a major material source for their formation. However, the eolian component represented by Chinese loess and igneous rock genesis with respect to Emeishan basalt plume may not contribute so much to the material source of bauxite deposits and terra rossa. In the process of leaching and pedogenesis, the mobile elements, such as Ca, Mg and Na, were preferentially dissolved and removed from parent rocks, and the less mobile elements Al, Fe, Ti and Si were accumulated and enriched. During the period of diagenesis and bauxitization, elements K and Si were largely removed from the system. Especially, in transformation from primary bauxite to secondary bauxite deposit, the contents of many "less mobile" elements, such as Fe and Ti, decreased. This finding is possibly due to the strongly acidic environment caused by decomposition of pyrite in primary sedimentation-type bauxite deposit. This study systematically analyzed the inherited relations and evolution processes among carbonate rock, terra rossa, and two types of bauxite deposits, and gave a guide for the bauxite deposit prospecting in western Guangxi.