黔北务正道地区沉积型铝土矿富集成矿主控因素分析

黔北务正道地区铝土矿是我国超大型铝土矿矿床，该矿床为沉积型铝土矿，其成矿过程主要受到沉积相和海平面变化的影响。通过对研究区铝土矿含矿岩系岩性和地球化学分析，认为该区铝土矿主要形成于湖泊相滨浅湖亚相，即铝土矿形成于淡水环境，含矿岩系的绿泥石黏土岩和铝土岩形成于扇三角洲和潮坪相。水动力条件和沉积分异作用控制着铝土矿类型:颗粒状铝土矿形成于滨湖等水动力较强的区域，而土状铝土矿形成与水动力较弱的浅湖区。海平面上升旋回以绿泥石岩和铝土岩沉积为主，而海平面下降旋回以铝土矿沉积为主。海平面下降旋回的跨时远大于海平面上升旋回，这也说明铝土矿的形成是漫长的风化过程。研究区铝土矿含矿岩系最多可识别出3个海平面升降旋回，这3个旋回与研究区周缘同期的碳酸盐岩和碎屑岩沉积旋回具有一致性和可对比性。

Effect of Sea Level Change on Enrichment and Mineralization of Bauxite:Taking Qianbei bauxite for example

Bauxite deposit in Wuzhengdao of Qianbei,which is the biggest bauxite deposit of China, is sedimentary type bauxite,which is affected by facies and change of sea level.Based on analysis of lithology and geochemistry of bauxite-bearing rock series in the study area,the bauxite is formed in shore lake and shallow lake.So the bauxite is deposited in fresh water.The chlorite rock and bauxite rock are deposited in fan delta and tidal flat facies.The hydro-dynamic condition determines types and grade of bauxite.Grain bauxite is formed in strong hydrodynamic condition, soil type bauxite is formed in weak hydrodynamic condition.The chlorite rock and bauxite rock are deposited during rise of sea level,and bauxite is deposited during drop of sea level.The span of drop period is much greater than rise period,which explains why forming of bauxite is a long weathering progress.Up to three cycles can be identified dur-ing deposit of bauxite-bearing rock series,and the three cycles are consistent with corresponding period deposit of car-bonate rock and clastic rock in adjacent area.