中文摘要：

桂西地区铝土矿为典型喀斯特型,包括二叠系沉积型和第四系堆积型两亚类。堆积型铝土矿是沉积型铝土矿经抬升、破碎、风化,最后堆积于喀斯特洼地中形成。以平果教美铝土矿为研究对象,探索堆积型铝土矿形成过程中矿物的变化与元素迁移。沉积型矿石的矿物组成包括硬水铝石、鲕绿泥石、锐钛矿及少量针铁矿、金红石和高岭石;堆积型矿石的矿物组成主要为硬水铝石、锐钛矿、高岭石及少量三水铝石和鲕绿泥石。转化过程中堆积型矿石中的硬水铝石含量明显增加,鲕绿泥石含量明显减少。沉积型铝土矿的主要化学组成为Al2O3、Si O2、Fe O和Ti O2;堆积型为Al2O3、Si O2、Ti O2和Fe2O3。两类矿石中元素Zr、Ba、Nb、V含量均较高,稀土总量变化大,富集轻稀土。质量平衡计算表明堆积型铝土矿形成过程中Al、Ba、Sr、Y等元素增加,而Si、Fe、Ti、Nb、V、Ce等元素减少,其余元素变化不明显。

英文摘要：

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 depres-sion 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 dia-spore,anatase and kaolinite,with subordinant gibbsite and chamosite.During the forming processes of the ac-cumulated bauxite,the amount of diaspora increase significantly,while for chamosite,it decrease sharply. Al2 O3 ,SiO2 ,FeO and TiO2 are main major elements for the sedimentary bauxite,and for the accumulated bauxite,they are Al2 O3 ,SiO2 ,TiO2 and Fe2 O3 .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.