川西冕宁-德昌稀土成矿带壳源混染促进稀土成矿作用  

REE Mineralization Promoted by Crustal Contamination in Mianning-Dechang REE Metallogenic Belt,the Western Sichuan,China

作　　者：司渊龙 赵云[1,2] 王瑞 周利敏[4] 孙英才 王俊达 朱志敏[5] SI Yuan-long;ZHAO Yun;WANG Rui;ZHOU Li-min;SUN Ying-cai;WANG Jun-da;ZHU Zhi-min(School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;Institute of Earth Sciences,China University of Geosciences,Beijing 100083,China;National Research Center for Geoanalysis,Beijing 100037,China;Institute of Multipurpose Utilization of Mineral Resources,Chinese Academy of Geological Sciences,Chengdu 610041,Sichuan,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质大学(北京)地质过程与矿产资源国家重点实验室,北京100083 [3]中国地质大学(北京)科学研究院,北京100083 [4]国家地质实验测试中心,北京100037 [5]中国地质科学院矿产综合利用研究所,四川成都610041

出　　处：《地球科学与环境学报》2024年第5期636-650,共15页Journal of Earth Sciences and Environment

基　　金：国家重点研发计划项目(2022YFF0800902);四川省科技计划项目(2023NSFSC0272)。

摘　　要：川西冕宁-德昌稀土成矿带是我国重要的稀土成矿带之一,然而壳源混染与稀土成矿之间的关系尚缺乏有效制约。辉钼矿Re-Os同位素体系已发展成为示踪壳源混染作用的灵敏指示剂。为了揭示壳源混染在川西碳酸岩型稀土成矿中的作用,对牦牛坪和木落寨稀土矿床开展了辉钼矿Re-Os同位素研究。岩相学特征表明,辉钼矿在岩浆期产出于方解石间隙中,在伟晶岩期产出于石英间隙中,在热液期与热液矿物、硫化物共生。牦牛坪稀土矿床2件辉钼矿样品Re-Os模式年龄分别为25.93和26.05 Ma,Re含量(质量分数,下同)分别为44.933×10^(-6)和28.678×10^(-6);木落寨稀土矿床的辉钼矿样品Re-Os模式年龄为28.90 Ma,Re含量为38.765×10^(-6)。辉钼矿形成年龄与稀土矿床成岩成矿年龄一致,说明辉钼矿沉淀与稀土成矿同期,3件辉钼矿样品Re含量均为10-5数量级,表示其成矿物质具有壳幔混合特征。壳源混染中和了稀土成矿流体pH值,使稀土-氯化物和稀土-硫酸盐失稳,富CO 2含钼流体的混合促进了成矿流体中CO^(2-)_(3)与稀土元素结合,导致氟碳铈矿的沉淀。The Mianning-Dechang REE metallogenic belt in the western Sichuan is the most important REE belts in China.Nevertheless,the relationship between crustal contamination and REE mineralization remains elusive.The Re-Os isotopic signatures of molybdenite have been widely applied for tracing crustal contamination.In order to reveal the influence of crustal contamination on carbonatite-related REE mineralization,the Re-Os isotopic composition of molybdenite was studied in Maoniuping and Muluozhai REE deposits.Molybdenite occurs in calcite interstice in magmatic stage,or occurs in quartz interstice in pegmatite stage,or intergrows with hydrothermal minerals(fluorite,barite,bastn site)and sulfide(pyrite,galena)in hydrothermal stage.The Re-Os model ages of molybdenite in Maoniuping REE deposit are dated at 25.93 and 26.05 Ma,and the Re contents are 44.933×10^(-6)and 28.678×10^(-6),respectively.The Re-Os model age of molybdenite in Muluozhai REE deposit is dated at 28.90 Ma,and the Re content is 38.765×10^(-6).The formation age of molybdenite is consistent with the diagenesis and mineralization age of REE deposit,indicating that molybdenite precipitation and REE mineralization occur simultaneously.The Re content of three molybdenite samples are in the level of 10-5,indicating a crust-mantle mixing affinity.The contamination neutralizes the pH of REE-bearing fluid,which lead to the instability of REE-chloride and REE-sulfate.The mixing of molybdenum-bearing fluid increases the concentration of CO^(2-)_(3) in the fluid and promotes the precipitation of bastn site.

关 键 词：碳酸岩型稀土矿床 RE-OS同位素 成矿时代 壳源混染 沉淀机制 冕宁-德昌稀土成矿带 四川 

分 类 号：P618.7[天文地球—矿床学] P597[天文地球—地质学]