贵州丹寨老东寨铅锌矿床稀土元素和硫同位素地球化学特征

老东寨铅锌矿床是黔东南地区近年来新发现的中型铅锌矿床,主矿体赋存于震旦系陡山沱组中,该矿床尚未有地球化学等方面的研究报道,导致对其成因机制知之甚少。本研究在系统分析矿床地质的基础上,对该矿床开展硫化物和围岩稀土元素及硫化物S同位素地球化学研究,为厘清其成因机制提供地球化学依据。结果表明硫化物稀土元素含量较低(ΣREE=4.31×10^?6~39.9×10^?6,均值21.1×10^?6),与容矿白云岩REE含量(13.9×10^?6)相当,但低于围岩地层(10820×10^?6)。闪锌矿均具有弱的Ce负异常(δCe=0.62~0.89),Eu出现了负异常(δEu=0.45~0.86)和正异常(1.22~4.47)。金属硫化物(闪锌矿、方铅矿)δ³⁴S值介于9.99‰~17.31‰之间,低于震旦纪–寒武纪海水的δ³⁴S值(20‰~35‰),揭示成矿流体中的硫可能主要来源于海相硫酸盐热化学还原作用(TSR)。结合区域铅锌矿床研究认为,老东寨铅锌矿床属于构造–岩性控制的后生热液矿床,铅锌等金属元素来源与赋矿地层关系密切,结合矿石REE地球化学特征及重晶石的产出及分布情况,推测该矿床成矿环境经历了从氧化到还原的过程。

Geochemical characteristics of REE and S isotopes for the Laodongzhai Pb-Zn deposit in Danzhai,Guizhou Province,China

The Laodongzhai Pb-Zn deposit is a representative medium-sized Pb-Zn deposit in SE Guizhou.Orebodies of the Laodongzhai Pb-Zn deposit occurred in silty dolostone of the Sinian Doushantuo Formation.So far,no report on its geochemistry has been presented.Thus,little is known about its genetic mechanism.Based on the systematic geological study,Rare Earth Elements(REE)and S isotope geochemical study of sulfides and wall rocks in this deposit has been undertaken in order to provide a geochemical basis for understanding its formation mechanism.The results show that the sulfides have low total REE contents(ΣREE=4.31×10^?6-39.9×10^?6,average 21.1×10^?6)with negative Ce anomalies(δCe=0.62-0.89),but obvious Eu anomalies from positive to negative(from 0.45-0.86 to 1.22-4.47).The δ³⁴ S values of sulfides,varying from 9.99‰ to 17.31‰,are lower than those of the Sinian-Cambrian seawater sulfate(20‰ to 35‰).It can be seen that reduced S of the Laodongzhai Pb-Zn deposit could be produced by the marine sulfate thermochemical reduction(TSR).With the regional geological and geochemical researches,it is believed that the Laodongzhai Pb-Zn deposit belongs to an epigenetic hydrothermal deposit that is controlled by structure and lithology,and its S was mainly sourced from the marine sulfate. It is believed that the ore-forming process experienced the transformation from oxidized to reduced environments.