投稿时间：2022-01-25
修订日期：2022-06-11
网络发布日期：2022-09-09
中文摘要:甘肃厂坝-李家沟铅锌矿床位于西秦岭多金属成矿带内的西成矿集区，为矿集区内重要的超大型铅锌矿床。矿体赋存在中泥盆统安家岔组的白云石化大理岩及石英片岩中，其成因认识一直存在争议，主要分歧集中在是同生还是后生。文章对不同成矿阶段的闪锌矿，采用多接收电感耦合等离子体质谱(MC-ICP-MS)测定Zn同位素组成、采用激光剥蚀-多接收电感耦合等离子体质谱(LA-MC-ICP-MS)原位微区分析技术测定S、Pb同位素组成，示踪成矿物质来源，并分析矿物沉淀机制，为深入理解矿床成因提供新的精细证据。研究结果显示，Ⅰ、Ⅱ、Ⅲ三个成矿阶段闪锌矿的δ66Zn分别为0.08‰~0.29‰，平均0.20‰；0.19‰~0.37‰，平均0.30‰；0.36‰~0.37‰，平均0.37‰。其中，Ⅰ阶段的闪锌矿δ34SⅠ值为20.9‰~26.1‰，平均24.4‰；Ⅱ阶段的闪锌矿δ34SⅡ值为12.2‰~21.9‰，平均19.1‰；Ⅲ阶段的闪锌矿δ34SⅢ值为18.2‰~24.7‰，平均21.5‰。3个阶段的矿石矿物Pb同位素组成变化不大，206Pb/204Pb为17.922~18.013，207Pb/204Pb为15.567~15.647，208Pb/204Pb为37.990~38.266。δ66Zn同位素值显示，成矿金属早期来源于围岩海相碳酸盐岩，由于混合了岩浆热液或者是瑞利分馏作用，在成矿作用中后期δ66Zn同位素逐渐上升。δ34S同位素值显示，早期硫源主要为地层中的硫酸盐，中后期的δ34S同位素值降低，可能是成矿流体中岩浆热液中的S2-成分逐渐增多导致，闪锌矿为硫酸盐通过TSR反应沉淀成矿。Pb同位素指示成矿物质来源于上地壳，并混入了部分古老的变质基底的成分。笔者研究发现，厂坝-李家沟铅锌矿的成矿机制为不同来源的流体混合，随着pH值、成矿流体的温度发生变化而沉淀成矿。
Abstract:Changba-Lijiagou giant Pb-Zn deposit is located in the Xicheng ore cluster, West Qingling polymetallic metallogenic belt. The deposit is hosted in Middle Devonian Anjiacha Formation dolomitic marble and quartz schist. The ore genesis has been debated for years, which is mainly about syngenetic sedimentary or epigenetic mineralization. In this study, the Zn isotopic compositions of sphalerites formed in different stages are investigated by MC-ICP-MS and in-situ S, Pb isotopic compositions of different stages sphalerites are investigated by LA-MC-ICP-MS. The results are used to determine the metal origins and precipitation mechanism of sulfides, which provide new evidence for ore genesis. The sphalerites formed in three different stages (Ⅰ, Ⅱ, Ⅲ) exhibit various Zn isotopic compositions (δ66ZnⅠ=0.08‰ to 0.29‰, on average of 0.20‰; δ66ZnⅡ=0.19‰ to 0.37‰, on average of 0.30‰; δ66ZnⅢ=0.36‰ to 0.37‰, on average of 0.37‰), and the in-situ S isotopic composition (δ34SⅠ=20.9‰ to 26.1‰, on average of 24.4‰; δ34SⅡ=12.2‰ to 21.9‰，on average of 19.1‰; δ34SⅢ=18.2‰ to 24.7‰, on ave-rage of 21.5‰). The Pb isotopic compositions of ore minerals formed in the three stages change little (206Pb/204Pb=17.922~18.013, 207Pb/204Pb=15.567~15.647, 208Pb/204Pb=37.990~38.266). The δ66Zn isotopic compositions indicate that the ore-forming metal was derived from the host rock of marine carbonate in the early stage, and the δ66Zn isotopic values gradually increased due to fluids mixing with the magmatic hydrothermal or Rayleigh distribution in the middle and late stage of mineralization. The δ34S isotope values indicate that the early sulfur source was mainly sulphate in the strata. The decrease of δ34S isotope values in the middle and late stages might be attributed to increasing of the S2- component in the magmatic hydrothermal fluid, the sphalerite is precipitated from sulfate through TSR reaction. The Pb isotope values show that the metallogenic material comes from the upper crust, mixed partly with the metamorphosed basement. This study indicates that the mineralization mechanism of the Changba-Lijiagou Pb-Zn deposit is the mixing of fluids from different sources, and the rapid change of pH and temperature of ore-forming fluids caused the precipitation of sulfides.
keywords:geochemistry sphalerite Zn isotope in-situ S isotope in-situ Pb isotope precipitation mechanism Changba-Lijiagou Pb-Zn ore deposit
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基金项目:本文得到自然资源部重点实验室基本科研业务费项目(编号:KK2104)和地质调查项目(编号:DD20190368)联合资助
引用文本：
魏然,王义天,胡乔青,黄诗康,窦平,胡文荣.2022.甘肃厂坝-李家沟超大型铅锌矿床成矿金属来源——来自闪锌矿原位S-Pb和Zn同位素证据[J].矿床地质,41(4):722~740WEI Ran,WANG YiTian,HU QiaoQing,HUANG ShiKang,DOU Ping,and HU WenRong.2022.Source of ore-forming metals in Changba-Lijiagou super-large Pb-Zn deposit, Gansu Province: Evidence from in-situ S-Pb and Zn isotopic compositions of sphalerite[J].Mineral Deposits41(4):722~740
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