广西两种三水铝石铝土矿成矿的差异性

DIFFERENCES OF MINERALIZATION OF TWO GIBBSITE BAUXITES IN GUANGXI PROVINCE

广西2种岩溶型三水铝石铝土矿都是含三水锅石和针铁矿的大型矿床，但二者成矿过程通异。平果式铝土矿是在晚白垩世至老第三纪湿热海洋性气候下，硬水锅石被泥石流搬运至异地，经受了年积温104℃，降水量近2．0m/a的强烈大气降水淋滤。生成三水锅石贵港式原地残积矿床的更新世成矿期气温和降水量均低于前者，低水活度导致铁矿物中的赤铁矿的高含量。热力学稳定性图解显示：平果式三水铝石-针铁矿组合稳定在t＝27℃，a（H2O）≥0．88的高铝体系中；贵港式针铁矿-赤铁矿组合稳定在t＝22℃，a（H2O）＝0．724的低铝体系中。均不含软水铝石。

Both of the two karstic gibbsite bauxites are in Guangxi Province of the large-scalemineral deposits consisted of gibbsite and goethite. Yet there are major differences between theirmineralization. The Pingguo type is an allochthonous bauxite. The diaspore bauxite wa transported by debris flow and leached by powerful meteoric water under the hurnid and tropical marine climate, suffering an annual accurnulative temperature of 10 000 ℃ the gibbsite formedduring Late Cretacoous to Early Tertiary while the Guigang troe is an autochthonous residualbauxite deposit. It underwent the lower temperature and the leaching of rainfall during the oreforming period in Pleistocene. The lower water activity resulted in the higher contents ofhernatite in Fe-minerals. Thermedrodric stability diagrarn may show their differences. Thegibbsite-gOethite mineral assemblage of Pinggu type is stable in the system of high aldriniurncontent at t=27℃, a (H2O)≥0. 88. The goethite-hernatite mineral assernblage of the Pingguo tgn is stable in the system of low alurniniurn content at t=22℃ a (H2O) = 0. 724. Thereare no thedrite in both of the two types.