广西平果沉积型铝土矿成矿物质来源及沉积环境:稀土元素地球化学制约

Ore-forming Material Source and Sedimentary Environment of Sedimentary Bauxite Deposits in Pingguo,Guangxi:Constraints of REE Geochemistry

广西平果沉积型铝土矿产出于上二叠统合山组底部,上覆于中二叠统茅口组灰岩之上。本文对广西平果教美、太平、那豆沉积型铝土矿和茅口组灰岩、领薅组沉凝灰岩进行地球化学分析,研究其稀土地球化学特征,探索铝土矿的物质来源及沉积环境。结果表明广西平果上二叠统沉积型铝土矿稀土元素地球化学配分模式与中二叠统茅口组灰岩和上二叠统合山组凝灰岩趋势一致,均具有ΣREE富集、LREE与HREE分异且LREE相对更加富集、Eu负异常等显著特征,沉积型铝土矿下部的Ce异常特征与茅口组灰岩一致,均表现为负异常,沉积型铝土矿上部的Ce正异常则与凝灰岩一致,认为平果下部铝土矿来源于底板茅口组灰岩风化,上部铝土矿物质来源与凝灰岩相同,为火山灰风化沉积的产物。平果沉积型铝土矿显示出被动大陆边缘典型特征,沉积环境逐渐由海相向海陆过渡相转变,氧化还原环境由弱还原环境向氧化环境转变。

The sedimentary bauxite deposits in Pingguo,Guangxi are confined to the bottom of the Upper Permian Heshan Formation and unconformably overlie on the limestone of the Middle Permian Maokou Formation.This paper has a discussion on REE geochemistry of the bauxite ore,the limestone of the Maokou Formation and tuffite of the Linghao Formation in Jiaomei,Taiping and Nadou in order to make an approach to ore-forming material source and sedimentary environment of the bauxite deposits.The results show that REE distribution pattern of the bauxite ore consistent with that of the limestone and tuffite with LREE enrichment and negative Eu anomaly.The negativeδCe values for the ore in the lower part are similar to those of the limestone of the Maokou Formation and positiveδCe values for the ore in the upper part are similar to those of the tuffite which indicate ore-forming material for the bauxite ore in the lower part derived from the limestone of the Maokou Formation,while ore-forming material for the bauxite ore in the upper part arine facies to marine continental transitional facies on the typical passive continental margin.