石榴子石矽卡岩与钨矿化关系研究:以湖北大冶铜山口铜钼钨矿床为例  

Relationship between garnet skarn and W mineralization:A case study from the Tongshankou Cu-Mo-W deposit,Daye,Hubei

作　　者：朱乔乔[1] 谢桂青[1,2] 纪云昊 李新昊 汪方跃[3] ZHU QiaoQiao;XIE GuiQing;JI YunHao;LI XinHao;WANG FangYue(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;MNR Key Laboratory for Exploration Theory&Technology of Critical Mineral Resources,School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;School of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,China)

机构地区：[1]中国地质科学院矿产资源研究所,自然资源部成矿作用与资源评价重点实验室,北京100037 [2]中国地质大学(北京),自然资源部战略性金属矿产找矿理论与技术重点实验室,北京100083 [3]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《岩石学报》2023年第6期1600-1618,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41925011、92162217);中央级公益性科研院所基本科研业务费专项资金(KK2122)联合资助。

摘　　要：石榴子石是矽卡岩型矿床的标志性矿物之一,其结构和成分特征被广泛用来示踪早期成矿流体性质的变化,但其生长过程与金属元素富集过程的关系还不清楚。本文对长江中下游成矿带最西端鄂东矿集区内的铜山口铜钼钨矿床中的石榴子石开展了显微结构和电子探针主量元素、LA-ICP-MS微量元素点分析和面扫描分析。结果显示,铜山口矿床中的石榴子石端元成分以钙铁榴石-钙铝榴石为主,普遍含有一定量的W,特别是在钙铁榴石端元比例高的石榴子石中(可达3898×10-6),且W与Mo、As、Sn存在明显的正相关关系、与Ti存在一定的负相关关系,指示W以类质同象的方式进入石榴子石晶格。石榴子石可包裹结构简单的白钨矿或被具复杂结构的白钨矿交代,指示石榴子石记录了白钨矿形成前和形成过程中流体性质(氧逸度和W含量等)的变化。铜山口矿床中钙铁榴石的大量结晶,导致成矿早期W的大量分散,不利于高品位和大规模钨矿的形成,仅在这些钙铁榴石遭受强烈的退化蚀变时,释放的W在一定程度能够提高矿石的品位,这可能是氧化性矽卡岩型钨矿通常比还原性矽卡岩型钨矿品位低、规模小的重要原因。石榴子石的成分特征(如W、Sn等元素含量和W/Sn、W/Mo和W/As等比值)可以作为判断矽卡岩的氧化还原性和钨矿床的品位及规模的依据,并具有成为W、Mo和Sn等矿床的找矿勘查指示矿物的潜力。Garnet is one of the definition minerals of skarn deposit,its textural and compositional characteristics have proven useful in tracking the features of ore-forming fluids at early stage.However,the relationship between garnet growth and the enrichment process of economic metal remains unclear.In this paper,texture and geochemistry of garnet from the Tongshankou Cu-Mo-W deposit,Edong district,were studied by electron probe microanalysis and LA-ICP-MS.Results show that the majority of garnet grains belong to andradite-grossular series with a certain amount of W,especially in garnets with high proportions of andradite(up to 3898×10-6).Tungsten has strong positive correlations with Mo and As,as well as a certain negative correlation with Ti,indicating that W was incorporated into the garnet lattice by isomorphic substitution.Garnet can either includes scheelite grains with simple texture or be replaced by scheelite grains with complex textures,suggesting garnet recorded the evolution of hydrothermal fluids features(e.g.,f O2 and W contents)from pre-to co-precipitation of scheelite.The deposit of massive andradite at Tongshankou is expected to widely dispersion of W in the early stage of mineralization,resulting in low grade and small scale of W deposit.The W host by garnet is likely to release and improve the grade of the ore to a certain extent only when these garnets experience extensive replacement during retrograde alteration,which is probably the critical reason that why oxidized W skarn commonly has lower grade and smaller scale than reduced W skarn.This research highlights that the compositional features(e.g.,W,Sn contents or W/Sn,W/Mo and W/As ratios)of garnet can be used as indicators for the redox properties of skarn and the grade and scale of W deposits.Garnet also serves as a potential prospecting and exploration indicator mineral for W,Mo,and Sn deposits.

关 键 词：石榴子石矽卡岩 钨矿 赋存状态 LA-ICP-MS 面扫描 找矿勘查指示矿物 铜山口 

分 类 号：P618.2[天文地球—矿床学]