黔北务正道地区新民铝土矿形成过程中的REE迁移与富集  

The migration and enrichment of REE in the formation process of the Xinmin bauxite deposit in the Wuchuan-Zheng’anDaozhen area,Northern Guizhou,China

作　　者：王洪 谷静[1] 黄智龙[1] 赵浪叶 WANG Hong;GU Jing;HUANG Zhi-long;ZHAO Lang-ye(State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵州贵阳550081 [2]中国科学院大学,北京100049

出　　处：《矿物学报》2021年第4期439-453,共15页Acta Mineralogica Sinica

基　　金：贵州省科技支撑项目(编号:黔科合支撑[2019]2859号);矿床地球化学国家重点实验室领域前沿项目(编号:SKLODG-2018-01)。

摘　　要：新民铝土矿床是近年来黔北务正道地区新发现的大型铝土矿床,为古风化壳沉积型,其含矿岩系为二叠系下统梁山组,该组底部稀土元素异常富集。为研究其铝土矿化过程中稀土元素地球化学行为,采集了2个钻孔剖面、一个露头剖面的铝质岩系以及相关地层的样品,进行了主、微量元素分析。结果显示,铝质岩系与下伏地层韩家店组具有相似的Ti/Nb、Nb/Ta组成,说明韩家店组可能为铝质岩系和稀土元素的主要源区。ΣREE、稀土元素活动迁移系数Kjw值和δCe等稀土特征的剖面变化表明,稀土元素的异常富集发生在铝质岩系沉积前的古风化壳阶段,但厚度较薄,而铝质岩系的再风化阶段稀土元素发生一定量的迁移,但不具稀土矿化意义;铝土矿化过程中,从轻稀土到重稀土,元素活动性逐渐减弱;古风化壳阶段富铁绿泥石在弱碱性、弱还原环境下沉淀,同时下伏碳酸盐岩地层促进了稀土元素在富铁绿泥石层中的富集,而铝质岩系的沉积和再风化阶段均为酸性、氧化环境。The Xinmin bauxite deposit is an newly discovered large bauxite deposit in recent years in the Wuchuan-Zheng’an-Daozhen area,Northern Guizhou.It belongs to the paleo-weathering crust sedimentary deposit,with host rocks of the Lower Permian Liangshan Formation.Rare earth elements are extreamly enriched in the bottom part of the Liangshan Formation.In order to investigate the geochemical behavior of rare earth elements during the bauxite mineralization,in this study,we have analyzed compositions of major and trace elements in samples of bauxite-bearing rocks in the Liangshan Formation and adjacent formations from two borehole profiles and one outcrop profile.Our new data show that the bauxite-bearing rock series have Ti/Nb and Nb/Ta ratios similar to those of rocks in the underlying Hanjiadian Formation,suggesting that the Hanjiadian Formation could be the main source of the bauxite and REEs in the bauxite-bearing rocks.The variations ofΣREE contents,REE mobility coefficients(Kjw),andδCe values in samples of the weathering profiles indicate the abnormal enrichment of rare earth elements occurred in the stage of paleo-weathering crust before the deposition of bauxite-bearing rocks,though the thickness of paleo-weathering crust is relatively thin.In the stage of re-weathering of bauxite-bearing rocks,a certain amount of REEs was migrated but the REE migration has no significance to the REE mineralization.During the process of bauxite mineralization,the mobilities of REEs were gradually decreased from LREE to HREE.The Fe-rich chlorite of the bauxite-bearing rocks was deposited under weakly alkaline and weakly reduced conditions in the paleo-weathering crust.The underlying carbonate of the Huanglong Formation,meanwhile,promoted the enrichment of REEs in Fe-rich chlorite layers.The deposition and re-weathering of bauxite-bearing rocks occurred under acidic and oxidized conditions.

关 键 词：务正道地区 铝土矿 稀土元素地球化学 元素迁移与富集 

分 类 号：P595[天文地球—地球化学] P618.7[天文地球—地质学]