赣北石门寺钨多金属矿床成矿流体演化过程:白钨矿微区成分限定  

Evolution of ore-forming fluids in Shimensi tungsten polymetallic deposit of northern Jiangxi:Constraints from in situ trace element analysis of scheelite

作　　者：陈长发 高剑峰[2] 张清清 闵康 CHEN ChangFa;GAO JianFeng;ZHANG QingQing;MIN Kang(School of Earth Science and Resources,Chang’an University,Xi’an 710054,Shaanxi,China;State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,Guizhou China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]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 [3]中国科学院大学,北京100049

出　　处：《矿床地质》2021年第2期293-310,共18页Mineral Deposits

基　　金：国家重点研发计划(编号:2016YFC0600207);国家杰出青年科学基金(编号:42025301)联合资助。

摘　　要：大湖塘钨矿地处江南造山带中段,为一大型钨-钼-铜多金属矿田,由4个矿床组成,其中石门寺矿床规模最大。文章利用LA-ICP-MS对石门寺矿床石英脉型钨矿中的白钨矿进行单矿物原位微区分析,以揭示成矿流体演化过程。研究表明,石英脉中的白钨矿可划分为2期,其中,早期白钨矿与黑钨矿、黑云母及石英共生,而晚期白钨矿在石英大脉中仅与石英共生。前者表现为右倾型稀土元素配分模式,而后者则显示平坦型稀土元素配分模式,两者均具Eu正异常。此外,早期白钨矿较晚期白钨矿具有较高的ΣREE、Mo、Sn、Nb、Ta、Y含量,但Sr含量较低。早期白钨矿表现出LREE富集型和较高的ΣREE、Nb、Ta含量,说明成矿流体来源于岩浆热液,从早期到晚期成矿流体中Eu由Eu^(2+)为主转变为Eu^(3+)为主,表明流体演化过程中氧逸度升高,暗示成矿晚期有氧化性大气降水加入。早期高LREE、Sn、Nb、Ta含量的白钨矿的沉淀以及辉钼矿结晶显著改变成矿流体的组成,导致晚期白钨矿具平坦型REE配分模式和低Mo、Sn、Nb、Ta的特征。此外,在流体演化过程中,新元古代花岗闪长岩中斜长石因为蚀变分解持续为成矿热液提供Eu和Sr,造成白钨矿Eu正异常和晚期白钨矿中Sr含量的升高。Located in the middle of the Jiangnan Orogenic Belt,the world-class Dahutang W-Mo-Cu orefield is composed of four deposits,of which the Shimensi deposit is the largest one.In order to reveal the evolution process of ore-forming fluids,the authors carried out in-situ LA-ICP-MS trace element analysis of scheelite from quartzvein type mineralization in the Shimensi deposit.Studies have shown that scheelite has two generations.The early generation of scheelite in the quartz-vein is associated with wolframite,biotite and quartz,whereas the late generation only coexists with quartz.The former shows a right-leaning REE partition pattern,while the latter one shows flat REE partition curve,with both of them having Eu positive anomalies.In addition,early generation has higherΣREE,Mo,Sn,Nb,Ta and Y but lower Sr content than late generation.LREE-enrichment and highΣREE,Nb and Ta content of early generation indicate that the ore-forming fluids were dominantly derived from magmatic hydrothermal fluids.Eu in the early and late ore-forming fluids were dominated by Eu^(2+)and Eu^(3+),respectively,suggesting that oxygen fugacity increased during the evolution of ore-forming fluids and recycled meteoric water might have been added into the fluids in the later stage.The precipitation of molybdenite and early scheelite with high LREE,Sn,Nb and Ta had significantly lower REE,Sn,Nb,Ta and Mo in evolved fluids,leading to flat REE partition curve and low Mo,Sn,Nb and Ta characteristics in later generation.In addition,the Eu normal anomaly and increasing Sr content in scheelite in late stage may have resulted from the decomposition of plagioclase in Neoproterozoic granodiorite.

关 键 词：地球化学 白钨矿 成矿流体演化 微量元素 稀土元素 石门寺钨多金属矿床 

分 类 号：P618.67[天文地球—矿床学]