滇东南荒田钨矿床成矿流体来源及演化:来自白钨矿地球化学特征的约束  

Source and evolution of ore-forming fluids in the Huangtian tungsten deposit in southeastern Yunnan:Constraints from geochemistry characteristics of scheelite

作　　者：周瑞辉 林木森 吴久芳 易友根 朱律运 王中良 ZHOU Ruihui;LIN Musen;WU Jiufang;YI Yougen;ZHU Lyuyun;WANG Zhongliang(Zijin School of Geology and Mining,Fuzhou University,Fuzhou 350108,Fujian,China;Western Geological Party of Fujian,Xiamen 361000,Fujian,China)

机构地区：[1]福州大学紫金地质与矿业学院,福建福州350108 [2]福建省闽西地质大队,福建厦门361000

出　　处：《地质通报》2023年第10期1728-1744,共17页Geological Bulletin of China

基　　金：福建省教育厅2021年度中青年教师教育科研项目《滇东南文山州香坪山矿区钨矿成因研究》(编号:JAT210031)。

摘　　要：荒田钨矿床位于滇东南老君山多金属成矿区北缘,是近年来新发现的一处大型白钨矿床。白钨矿从早到晚共划分为2个阶段:白钨矿-萤石-石英阶段(白钨矿Ⅰ)、白钨矿-碳酸盐阶段(白钨矿Ⅱ);根据产状又分为4种类型:白钨矿Ⅰ-a、白钨矿Ⅰ-b、白钨矿Ⅱ-a、白钨矿Ⅱ-b。白钨矿Ⅰ-b、Ⅱ发育明显的振荡环带。为确定成矿流体来源及演化,在详细的钻孔岩心编录和矿物显微组构研究的基础上,利用LA-ICP-MS分析了不同阶段白钨矿中的微量及稀土元素。结果显示:白钨矿的稀土元素主要受3Ca^(2+)=2REE^(3+)+□Ca(此处“□”指Ca的空位)的替换机制控制,稀土元素在白钨矿中的分布存在明显的不均一现象,但均为LREE富集型,与老君山花岗岩的球粒陨石配分模式类似,白钨矿LREE-MREE-HREE图解及Sm/Nd值显示,其与老君山花岗岩密切相关。除早期白钨矿Ⅰ-a部分测试点显示负Eu异常外,其余测试点均显示正Eu异常,Eu的价态也由Eu^(3+)为主转变为Eu^(2+)为主。白钨矿中Mo含量逐渐降低,表明成矿流体从早期到晚期氧逸度逐渐降低。此外,白钨矿中Sr含量(36.6×10^(-6)~619×10^(-6),平均值206.25×10^(-6))较高,矿床围岩主要为海相沉积碳酸盐岩,推测水岩反应为成矿流体提供了大量的Sr和Ca。The Huangtian tungsten deposit is located in the northern margin of the Laojunshan polymetallic metallogenic zone in southeastern Yunnan.It is a newly discovered large-scale scheelite deposit in recent years.Scheelite is divided into two stages from early to late:scheelite-fluorite-quartz stage(scheeliteⅠ),scheelite-carbonate stage(scheeliteⅡ);Four types:scheeliteⅠ-a,scheeliteⅠ-b,scheeliteⅡ-a,scheeliteⅡ-b.The scheeliteⅠ-b andⅡhave obvious oscillating rings.In order to determine the source and evolution of its ore-forming fluids,based on the detailed borehole core cataloging and the study of mineral microfabrication,LA-ICP-MS was used to analyze the trace and rare earth elements in scheelite at different stages.Our data show that the rare earth elements in scheelite are mainly controlled by the substitution mechanism of 3Ca^(2+)=2REE^(3+)+□Ca,the distribution of rare earth elements in scheelite is obviously inhomogeneous,but they are all LREE-enriched types,similar to the chondrite partition pattern of the Laojunshan granite.The LREE-MREE-HREE diagram of scheelite and the Sm/Nd ratio show that it is closely related to the Laojunshan granite.Except for some test points of early scheelite I-a,which showed negative Eu anomaly,the rest of the test points showed positive Eu anomaly,Eu also changes from the Eu^(3+)dominated to Eu^(2+)dominated.and the content of Mo in scheelite also changed.It gradually decreases,indicating that the oxygen fugacity of the ore-forming fluid decreases gradually from the early stage to the late stage.In addition,the Sr content(36.6×10^(-6)~619×10^(-6),average 206.25×10^(-6))in scheelite is relatively high,and the surrounding rocks of the deposit are mainly marine sedimentary carbonate rocks.It is speculated that the water-rock reaction is as follows:Ore-forming fluids provide a large amount of Sr and Ca.

关 键 词：滇东南 白钨矿 成矿流体 LA-ICP-MS 微量元素 稀土元素 

分 类 号：P595[天文地球—地球化学] P618.67[天文地球—地质学]