广西扶绥第四系萨伦托型铝土矿淋滤成矿过程

Leaching-Metallogenic Process of Quaternary Salento-type Bauxite in Fusui Area, Guangxi

位于广西扶绥地区的铝土矿资源主要存在二叠系合山组原生岩溶型铝土矿层与第四系萨伦托型(岩溶堆积型)铝土矿床两种赋存形式,前者覆盖在中二叠统茅口组与上二叠统合山组的不整合面上,后者属于第四系松散堆积物,是原生铝土矿层被改造的产物。本文通过对广西扶绥铝土矿区内不同类型矿石样品的矿物学与地球化学分析,力图恢复从二叠系原生铝土矿的形成到最终成为萨伦托型铝土矿的矿石演化过程。不同采样点所代表的矿石可能经历的环境类型如下:ZK15108代表未受现代地下水改造的深埋状态;ZK4353代表受到现代地下水改造的浅埋状态;剖面MY代表暴露地表的原生矿层;剖面KL代表典型的萨伦托型矿床剖面。在该过程中,矿石内以高岭石与绿泥石为代表的黏土矿物有向一水软铝石及一水硬铝石等铝矿物转化的趋势。所有矿床均显示易迁移元素如碱金属与碱土金属等几乎全部流失,而Ti与Al呈现显著正相关关系,这些是红土化及铝土矿化过程中强烈的化学风化作用导致的结果。质量变化计算结果显示,在原始的铝土矿层剖面中,所有元素均呈现亏损,但Al因亏损程度较小因此呈现相对富集。当矿层接受现代地下水系统改造时,矿层内元素的迁移特征出现分异。而当进入到地表淋滤状态时,杂质元素被带走而Al出现富集。在广西原生铝土矿向萨伦托型铝土矿转变的过程中,淋滤作用的强度及地下水排泄通畅程度是控制矿石质量的最主要的两个因素。

The bauxite in the Fusui area, Guangxi, includes two kinds of deposits： the primitive bauxite in the Permian Heshan Formation and the Quaternary Salento-type（karstic accumulational） bauxite. The former is limited to the unconformity between the Middle Permian Maokou Formation and the Upper Permian Heshan Formation, the latter is composed of the Quaternary incompact sediments which transformed from the Permian primitive bauxite. Based on mineralogical and geochemical analyses on the bauxite samples taken from different sites in Fusui, the ore forming process from the Permian primitive bauxite to the Quaternary Salento-type bauxite has been reconstructed. Each sample site represents a possible environment that ores may undergo during the metallogenic process： drilling core ZK15108 has not been influenced by the modern groundwater for its deep buried depth, so it can be seen as the initial state of the original bauxite. Shallowly buried drilling core ZK 4353 is reworked by the groundwater system. The profile MY is an exposed original bauxite profile in the surface environment. The profile KL is a typical Salento-type profile. During the ore forming process, the clay minerals（kaolinite and chamosite） in ores transform to aluminum minerals（boehmite and diaspore）. Alkali metals and alkali earth metals are mostly leached from the bauxite deposit and Ti is positively correlated with Al due to the intense chemical weathering during lateritization and bauxitization. Results from the mass change calculations indicate that all elements in the primitive bauxite profile are depleted whereas aluminum is relatively enriched. When the bauxite deposit is reworked by the modern groundwater system, the elements in the deposit display varied mobility. After the profiles exposing in the surface environment, impurities are removed from the profiles and the aluminum is enriched. The intensity of the leaching process and the drainage condition are crucial factors controlling the ore quality of the Salento-type bauxite.