贵州务—正—道地区铝土矿含铝岩系中稀土元素富集规律及赋存形式

Enrichment regularities and occurrence forms of rare earth elements in bauxite ore-bearing rocks in the Wuchuan-Zheng’an-Daozhen area,Guizhou Province

务川-正安-道真(务-正-道)地区是贵州省重要的铝土矿集区,提交铝土矿石资源储量超过7亿吨。区内铝土矿含铝岩系为下二叠统大竹园组,其中广泛富集稀土元素,由于这类稀土元素富集规律和赋存形式尚存在较大争议,综合利用和地质勘探依然缺少实际理论依据。本文通过对该区铝土矿含铝岩系的地质特征及其中伴生稀土元素研究,以总结分析稀土元素地球化学特征和富集规律,并讨论其赋存形式。研究结果表明,务-正-道地区含铝岩系中稀土元素基本呈右倾的配分模式,LREE表现为明显富集,Eu负异常明显。该套含铝岩系中上部样品普遍具有Ce正异常,而底部绿泥石泥岩则为Ce负异常。总体而言,稀土元素在研究区北西部和南东部向斜中的含量相对较高,而在中部向斜含铝岩系中相对较低。稀土元素主要赋存在底部的绿泥石泥岩中。其赋存形式可能主要以离子吸附或类质同象置换的形式赋存于铝矿物和黏土矿物表面或晶格中,也存在稀土元素的独立矿物。本研究为该类资源地质勘探和综合利用提供地质地球化学依据。

The Wuchuan-Zheng’an-Daozhen area is an important bauxite deposit concentration area in Guizhou Province,with over 700 million tons of submitted bauxite reserve.The bauxite ore in the area is hosted in the Lower Permian Dazhuyuan Formation,in which REE is widely enriched.Due to the significant controversy over the enrichment patterns and occurrence states of rare earth elements in those bauxite-bearing rocks,it is still lack of practical theoretical basis for comprehensive utilization and geological exploration of REE resources.Based on the study of the geological characteristics of the bauxite ore-bearing rocks in this area and the geochemistry of associated REE in those rocks,we have summarized and analyzed geochemical characteristics and enrichment laws of the REE in the bauxite ore-bearing rocks and discussed occurrence forms of the REE in those rocks.The research results indicate that the bauxite ore-bearing rocks in the Wuchuan-Zheng’an-Daozhen area have basically right declined REE distribution patterns with obviously enriched LREE and obviously negative Eu anomalies.There are positive Ce anomalies for samples in the upper and middle parts of this set of bauxite ore-bearing rocks,while there are negative Ce anomalies for chlorite mudstone samples in the bottom part.In general,REE contents of bauxite ore-bearing rocks in the northwestern and southeastern parts of the syncline in the study area are relatively high,while those of samples in the central part of the syncline are relatively low.The REE mainly occurred in the chlorite mudstone at the bottom.The REE in the bauxite ore-bearing rocks could occur mainly in forms of ion adsorption on the surface or isomorphic replacement in the lattice of aluminum minerals and clay minerals.In addition,the REE also could occur in the form of independent mineral.This study provides geological and geochemical basis for the geological exploration and comprehensive utilization of the REE resources in bauxite ore-bearing rocks.