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阿尔金西段库木塔什萤石矿床成因:磷灰石U-Pb年龄、原位Sr-Nd同位素、地球化学约束

Genesis of Kumutashi Fluorite Deposit in the West Altyn-Tagh Orogen,NW China:Constraints from Apatite In-Situ U-Pb Dating,Sr-Nd Isotope and Chemistry
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摘要 近年来,阿尔金西段取得萤石找矿重大突破,相继发现卡尔恰尔和库木塔什等矿床,但成矿时代和成矿机制研究薄弱。笔者选取库木塔什矿床与萤石密切共生磷灰石为研究对象,开展原位U-Pb定年、Sr-Nd同位素及地球化学分析,以探讨萤石矿成矿时代及矿床成因。磷灰石常呈自形-半自形结构,表面均匀,单偏光下近乎透明,主要与萤石、方解石、带云母、氟碳铈矿等矿物共生。结果显示,磷灰石U-Pb同位素年龄为(448±27)Ma,成矿作用与碱长花岗岩侵入活动密切相关,均为晚奥陶世构造-岩浆活动产物。磷灰石中F含量为4.20%~5.12%,Cl含量小于0.02%,极低的Cl含量表明出溶的流体Cl含量较低。磷灰石稀土元素含量较高(908×10^(-6)~2164×10^(-6)),稀土配分曲线显示强烈Eu负异常和Ce正异常,且与萤石、方解石、碱长花岗岩有明显的一致性,推测与岩浆-热液阶段大量流体出溶密切相关。磷灰石的^(87)Sr/^(86)Sr值为0.70913~0.71047,^(143)Nd/^(144)Nd值为0.51138~0.51153,εNd(t)值为-13.3~-10.3,表明成矿物质具有壳幔混合特征。综合研究表明,阿尔金西段萤石成矿时代为奥陶纪,与同期碱长花岗岩密切相关,形成于后碰撞伸展阶段,成矿流体来源于碱长花岗岩的熔体-流体演化,为岩浆热液充填型矿床。 In recent years,significant breakthroughs in fluorite prospecting have been made in the western Altyn-Tagh Terrane,and Kaerqiaer,Kumutashi and other deposits have been discovered successively,however,the research on metallogenic epoch and ore-forming processes are still unclear.In this paper,the closely symbiotic apatite with fluorite were selected as the research object to carry out the main microanalysis of apatite,U-Pb dating and in situ Sr-Nd isotopic test analysis,so as to explore the metallogenic epoch and the genesis of deposit.The apatite often has a self-semi-automorphic structure with uniform surface and nearly transparent under monopolarized light,mainly symbiotic with fluorite,calcite,tainiolite,bastnaesite and other minerals.The study shows that the U-Pb isotope age of apatite microregion is(448±27)Ma,and the fluorite mineralization is closely related to the invasive activity of alkali feldspar granite,all of which are the products of the late Ordovician tectonic-magmatic activity.The F content of apatite is 4.20%to 5.12%;the Cl content is less than 0.02%,and the very low Cl content indicates a low dissolved fluid Cl content.The content of rare earth elements is high(908×10^(-6)~2164×10^(-6)),and the partition curve of rare earth shows strong Eu negative anomaly and positive Ce negative anomaly.This anomaly is obviously consistent with its associated fluorite,calcite and alkali feldspar granite,which may be closely related to the dissolution of massive fluid in the magma-hydrothermal stage.The ratio of ^(87)Sr/^(86)Sr of apatite is from 0.70913 to 0.71047,the ratio of ^(143)Nd/^(144)Nd is from 0.51138 to 0.51153,andεNd(t)is from-13.27 to-10.26,reflecting that the ore-forming materials have the characteristics of crust-mantle mixing.Comprehensive studies show that the ore-forming age of fluorite in the western Altyn-Tagh Terrane is Ordovician,closely related to the same period alkali feldspar granite,formed in the post-collision extension stage,the ore-forming fluid may be derived from the melt-fluid evolution of alkali feldspar granite,and it is a magmatic hydrothermal filling type deposit.
作者 高永宝 陈康 王亮 赵辛敏 李艳广 刘明 张龙 王元伟 张毅 刘基 GAO Yongbao;CHEN Kang;WANG Liang;ZHAO Xinmin;LI Yanguang;LIU Ming;ZHANG Long;WANG Yuanwei;ZHANG Yi;LIU Ji(Technology Innovation Center for Gold Ore Exploration,China Geological Survey,Xi’an 710100,Shaanxi,China;Xi'an Center of Mineral Resources Survey,China Geological Survey,Xi’an 710100,Shaanxi,China;State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,Shaanxi,China;Xi’an Center of China Geological Survey,Xi’an 710119,Shaanxi,China;School of Earth Sciences and Resources,Chang’an University,Xi’an 710054,Shaanxi,China)
出处 《西北地质》 CAS CSCD 北大核心 2024年第4期1-20,I0002,共21页 Northwestern Geology
基金 陕西省自然科学基础研究计划项目“阿尔金卡尔恰尔超大型萤石矿带高氟岩浆-热液演化与成矿机制研究”(2023-JC-YB-241) 中国地质调查局自然资源综合调查指挥中心科技创新基金项目“阿尔金卡尔恰尔地区超大型萤石成矿带成矿流体性质研究”(KC20230011) 中国地质调查局项目“西昆仑大红柳滩-甜水海地区大型矿产资源基地综合调查”(DD20190143) “新疆若羌县帕夏拉依档一带萤石、锂矿产调查评价”(DD20243309) “阿尔金伊里奇曼-红柳沟地区萤石、金铜矿产调查评价”(DD20211551)联合资助。
关键词 地球化学特征 磷灰石 萤石矿床 库木塔什 阿尔金西段 geochemical characteristics apatite fluorite deposit the Kumutashi deposit West Altyn-Tagh Orogen
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