Abstract:

The bauxite ores in Western Gaungxi, China, mainly belong to the karstic type, and can be further divided into two subclasses, the Permian sedimentary and the Quaternary accumulated bauxites. The Permian bauxite ores were formed by uplifting, breaking-up and weathering, and then accumulated in the karstic depression area at the end. Based on the studies on the Jiaomei bauxite deposit, in this paper the authors investigated the evolution of mineral composition and elemental migration during formation of the accumulated bauxite. By employing the techniques of X-ray fluorescence,mass spectrometry,X-ray diffraction,differential thermal analysis and thermogravimetric analysis, we well understood their mineralogical and geochemical signatures. The studies show that ore minerals in the sedimentary bauxite deposits mainly include diaspore, chamosite,anatase and small amount of goethite,rutile and kaolinite.For the accumulated bauxite the major ore minerals are diaspore, anatase and kaolinite, with subordinant gibbsite and chamosite.During the forming processes of the accumulated bauxite, the amount of diaspora increase significantly, while for chamosite, it decrease sharply. Al₂O₃, SiO₂, FeO and TiO₂ are main major elements for the sedimentary bauxite, and for the accumulated bauxite, they are Al₂O₃, SiO₂, TiO₂ and Fe₂O₃. Both of the two types of bauxites have a very high content of Zr, Ba, Nb, V, unstable ∑REE and enrichment of LREE. Mass change calculation indicates that during the forming processes, Al,Ba, Sr and Y increased, while Si, Fe, Ti, Nb, V and Ce reduced.

Key words: Jiaomei bauxite deposit, mineral evolution, element migration, Western Guangx