利用绿帘石化学成分及原位Sr同位素指示成矿流体特征:以东天山地区多头山铁铜矿床为例  

Discriminating characteristics of hydrothermal fluids using epidote mineral chemistry and strontium isotopes:A case study of the Duotoushan Fe-Cu deposit,eastern Tianshan

作　　者：张维峰[1] 陈华勇[2,3] 邓新[1] 金鑫镖 刘舒展 谭娟娟[1] ZHANG Weifeng;CHEN Huayong;DENG Xin;JIN Xinbiao;LIU Shuzhan;TAN Juanjuan(Wuhan Center of Geological Survey,China Geological Survey,Wuhan 430205,China;CAS Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;Center of Excellence for Deep Earth Sciences,Chinese Academy of Sciences,Guangzhou 510640,China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430205 [2]中国科学院广州地球化学研究所中国科学院矿物学与成矿学重点实验室,广东广州510640 [3]中国科学院深地科学卓越中心,广东广州510640

出　　处：《地学前缘》2023年第2期384-400,共17页Earth Science Frontiers

基　　金：国家自然科学基金项目(41702099);中国地质调查局项目(DD20190050,DD20190374)。

摘　　要：绿帘石族矿物是热液矿床中常见的Ca-Al硅酸盐矿物,常具有较高的微量元素含量,其化学成分和Sr同位素能够指示成矿流体的物理化学条件和来源。本文以东天山地区的多头山矿床为例,对主成矿期磁铁矿阶段大量分布的绿帘石族矿物展开研究。矿物化学结果表明,其分子式中Al原子数较高(1.95~2.24),富含Fe^(3+)而贫Fe^(2+),稀土总量较低[(21.53~63.52)×10^(-6)],属于绿帘石端员;同时样品富集中稀土元素,强烈亏损轻稀土元素,具中等Eu负异常,暗示稀土元素的分馏与中-碱性条件下硬酸离子的络合作用有关。元素的线性关系研究表明,REE主要通过类质同象替代的机制进入矿物晶格。多头山绿帘石与石英-榍石-磁铁矿等共生,具有明显的Ce负异常(0.64~0.91)和较高的U/Th比值,指示成矿流体的氧逸度较高。绿帘石的初始Sr/Sr值为0.704 62~0.704 95,介于百灵山花岗杂岩与围岩或石炭纪海水之间,表明成矿流体来源于岩浆水,并且在与围岩发生交互作用的同时伴随有外来盆地卤水的加入。本文研究进一步表明绿帘石可以作为揭示多种类型岩浆-热液矿床流体性质与演化过程的良好指示矿物。Epidote,a common Ca-Al-bearing silicate mineral in many types of hydrothermal deposits,usually has high concentrations of trace elements,thus its mineral chemistry as well as Sr isotopic characteristics can reveal the physico-chemical conditions and sources of the ore-forming fluid.In this contribution we present a study on the epidote-group minerals precipitated during Fe mineralization at the Duotoushan deposit.With high Al-coordination numbers(1.95-2.24),and enriched in Fe^(3+) but depleted in Fe^(2+) and rare earth elements(REE),the studied mineral grains are identified as the epidote end member.The mineral grains are further characterized by MREE enrichment and LREE depletion with moderate negative Eu anomalies,suggesting the complexation of hard acids at neutral to basic pH may have caused the REE fractionation.Correlation analysis indicates REEs are mainly incorporated into the Duotoushan epidote through isomorphous substitution.At Duotoushan,the epidote-group minerals coexist with quartz,titanite and magnetite,exhibit negative Ce anomalies(0.64-0.91),and have high U/Th ratios,indicating they are formed under relatively high oxygen fugacity.Since the in-situ(^(87)Sr/^(86)Sr)_(i) ratios(0.70462-0.70495)lie between the Bailingshan granitic complex and hosted rocks or Carboniferous seawater,we propose that the initial fluids are magmatic in origin and external basinal fluid may have added into the hydrothermal system during water-rock interaction.Furthermore,our study indicates that epidote is a robust indicator for tracing fluid evolution in magmatic hydrothermal deposits.

关 键 词：绿帘石 矿物化学 SR同位素 成矿流体演化 东天山 

分 类 号：P611.1[天文地球—矿床学] P578.956[天文地球—地质学] P574.2