桂西沉积型铝土矿床成矿规律及成矿模式

桂西沉积型铝土矿床是以陆地风化成因为主的矿床,其成矿模式为:地壳隆升→火山尘沉积→风化淋滤成矿→海侵保存→海相改造→成岩变质→沉积铝土矿床。成矿期为259~253 Ma前的晚二叠世吴家坪期,赋矿层位为上二叠统合山组底部吴家坪阶地层。在成矿期的陆地区域,全球性火山喷发产生的中酸性火山尘覆盖层经风化淋滤成矿作用形成三水铝矿床,在紧接着发生的大海侵事件中沉入海底而保存下来,经海相改造和成岩变质作用,最终形成了沉积型铝土矿床。浅水沼泽和台缘浅滩区风化淋滤脱硅作用较弱,火山尘沉积层转变为高硅的铁铝岩或硫铁矿;较深水的台缘斜坡区和盆地相区因没有风化淋滤成矿作用,成矿物质沉积层基本保持着原岩结构和成分。

Metallogenic regularity and model of sedimentary bauxite deposits in western Guangxi

The sedimentary bauxite deposit in western Guangxi is a kind of polygenesis deposits mainly of weathering leaching action in land area. Its metallogenic model is: crust uplift→volcanic dust deposit→weathering-leaching mineralization→sea transgression preservation→marine transformation→diagenesis metamorphism→sedimentary bauxite deposits. The metallogenic epoch is 259-253 Ma ago in the Permian Wujiapingian. The bauxite deposits are hosted in the Wujiapingian stage located in the bottom of the upper Permian Heshan formation. Medium-acid volcanic dust layers from global volcanic eruption were transformed into gibbsite deposits in the land areas,and sank into sea to be preserved in the immediately following transgression of sea. Underwent marine transformation and diagenesis metamorphism,they were transferred into sedimentary bauxite deposits. The volcanic dust layers were transferred into high silicon Fe-Al rock or pyrite deposits with a weaker weathering-leaching desilication in shallow water marsh and shoal,while it remains its original structure and components in the deeper water basins without weathering-leaching mineralization.