黔东北地区金亮萤石矿床稀土元素地球化学特征与成矿物质来源

Ceochemical characteristics of rare earth elements and the source of ore-forming materials in the Jinliang fluorite deposit in the northeastern Guizhou

黔东北-渝东南一带分布有大量的萤石矿床(点),这些矿床(点)主要分布在北东向区域性断裂两盘的奥陶系下统桐梓组和红花园组灰岩中NW、NNW向张性断裂内,矿体呈脉状或透镜状产出,深部至奥陶系下统桐梓组逐渐尖灭,关于该区萤石矿成因及物质来源长期存在较大争议。金亮萤石矿床是黔东北沿河地区代表性小型萤石矿床,本文对该矿床中萤石开展稀土元素地球化学研究。结果表明,萤石ΣREE为67.4×10^(-6)~90.55×10^(-6),LREE/HREE值为43.98~78.78,δEu值为77.07~94.71,δCe值为0.39~0.42。矿床萤石稀土分布模式呈明显右倾曲线,为轻稀土相对富集型,以Eu正异常和Ce负异常明显为特征。结合矿床地质特征,认为该萤石矿床为热液成因的产物,萤石为同源同期热液流体在氧化环境成矿。萤石成矿作用与沉积岩关系密切,其中成矿物质Ca主要来源于下奥陶统红花园组灰岩,可能部分来源于深部碳酸盐岩,而成矿物质F主要来源于深部上震旦统陡山沱组至下寒武统明心寺组高氟地层。

A large number of fluorite deposits(occurrences)are distributed in the northeastern Guizhou and southeastern Chongqing.These deposits(occurrences)are mainly distributed in the NW-and NNW-trending extensional faults within limestone beds of the lower Ordovician Tongzi and Honghuayuan formations in two sides of the NE-trending regional faults.Their orebodies occurred mainly in forms of vein or lens.They are gradually pinched out in the deeply distributed lower Ordovician Tongzi Formation.The origins and material sources of fluorite deposits in this area have been controversially debated for a long time.The Jinliang fluorite deposit is a representative small-scale fluorite deposit in the Yanhe area in the northeastern Guizhou.In this paper,we have conducted REE geochemical research of fluorites in this deposit.The results show that fluorite samples haveΣREE contents,LREE/HREE,δEu andδCe values ranging from 67.4×10^(-6) to 90.55×10^(-6),from 43.98 to 78.78,from 77.07 to 94.71,and from 0.39 to 0.42 respectively.The REE distribution patterns of fluorites in the deposit are characterized with obviously right-declined curves,relatively LREE enriched patterns,obvious Eu positive and Ce negative anomalies.Combined with geological characteristics of the deposit,it is believed that the Jinliang fluorite deposit is a product of hydrothermal genesis,and its fluorite was formed by the homologous and contemporaneous hydrothermal fluid in an oxidized environment.The mineralization of fluorite could be closely related to sedimentary rocks.It is believed that the Ca could be mainly sourced from the limestone of the Lower Ordovician Honghuayuan Formation,and could be partially sourced from carbonate rocks in the depth,while the F could be mainly sourced from the high-fluorine strata of the Upper Sinian Doushantuo Formation and the Lower Cambrian Mingxinsi Formation.