贵州铝土矿成矿作用的实验研究及其成因分析

THE EXPERIMENTAL STUDY OF BAUXITE MINERALIZATION IN GUIZHOU AND ANALYSIS ON THEIR ORIGIN

通过对与贵州铝土矿成矿作用有关的水云母粘土岩、铝土岩和铝铁岩等在不同Eh和pH条件下铝、硅、铁溶解作用的实验研究,结合理论分析和野外实际,本文认为,贵州铝土矿之红矿是在水动力条件良好的地表氧化条件下淋滤水云母粘土岩的结果;其白矿是由红矿在富有机酸的还原体系的沼泽相中经脱铁、脱硅作用而形成的。红矿是贵州铝土矿的物质基础,铝土矿质量的优劣和储量的多少,取决于沼泽化前红矿质量的优劣和堆积聚积的规模与厚度;而沼泽化造成的水体系的物化环境是红矿变白的必要条件。氧化条件下成矿(三水铝石),还原条件下除杂,是白矿形成的必经步骤。

Tests of dissolution of Al_2O_3, SiO_2 and Fe_2O_3 of hydromica claystone (containing muscovite claystone and illite claystone), aluminous claystone(kaoltnite claystone) and ferralites relative to mineralization of bauxite in Guizhou of China under different pH and Eh Conditions of the CO_2-H_2O systems have been made. Results show that: (1)The dissolution of SiO_2 in above four kinds of rock is stronger than that of Al_2O_3 in solutions with different pH values of the CO_2-H_2O systems under oxidizing conditions and thus their desiliconization is stronger too, but they do not show deferridization at pH≥4. (2) Deferridization of the above four kinds of rock is pronounced, and the alumino-ferric rock at pH 4-8 and aluminous rock at pH 5-8 exhibit also striking desiliconization, but hydromica claystone do not exhibit desiliconization in the solutions with different pH values in the reducing CO_2-H_2O systems rich in organic acids. on the basis of the experimenntal results and through combining theoretical analysis with field work, the author assumes that red bauxite i. e. lateritic bauxite, in Guizhou is the product of weathering and leaching of ore-forming mother materials (hydromica clastone)in oxidizing conditions on the earth's surface; while white bauxite was formed by deferridization and desiliconization of the red bauxite in the swamp environments and under reducing conditions rich in organic acids. Lateritic bauxite is the material basis of this type of bauxite. The quality and reserves of the bauxite depend on the quality and size and thickness of accumulation of the red bauxite before swamping. The reducing environment rich in organic acids in the swamp is the necessary condition of deferridization, desiliconization, enrichment and transformation of lean red bauxite into enriched white bauxite. In general, gibbsite is the product of weathering and leaching on the earth's surface. The mother materials of the bauxite, i. e. muscovite, illite, feldspar and kaolinite, can not be transformed into gibbsite in the swamp environment where water flow was sluggish. Therefore, mineralization under the oxidizing conditions and impurities discarding under the reducing conditions seem to be the only way for forming white bauxite.