川西冕宁木落寨碳酸岩型稀土矿床流体演化对成矿的制约:来自包裹体和稳定同位素的证据  

The evolution of ore-forming fluid constraints on mineralization of the Muluozhai carbonatite-related REE deposit in western Sichuan: Evidence from fluid inclusions and stable isotopes

作　　者：郑旭 刘琰[2] 欧阳怀 付浩邦 贾玉衡[3] 丁岩 ZHENG Xu;LIU Yan;OUYANG Huai;FU HaoBang;JIA YuHeng;DING Yan(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;MNR Key Laboratory of Deep-Earth Dynamics,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;College of Earth Science,Guilin University of Technology,Guilin 541004,China;The Wankaifeng Rare Earth Energy Company,Mianning 615600,China)

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室(北京),北京100083 [2]自然资源部深地动力学重点实验室中国地质科学院地质研究所,北京100037 [3]桂林理工大学地球科学学院,桂林541004 [4]四川万凯丰稀土能源有限公司,冕宁615600

出　　处：《岩石学报》2019年第5期1389-1406,共18页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划"973"项目(2015CB452600);国家自然科学基金重大研究计划(9185527)和面上项目(41772044);中国地质科学院基本科研业务费(YYWF201705);自然资源部中国地质调查局地质调查项目(DD20190060);高等学校学科创新引智计划(B07011)联合资助

摘　　要：木落寨稀土矿床位于青藏高原东部,扬子克拉通西南缘,属于典型的碳酸岩型稀土矿床。与其他成矿过程复杂的碳酸岩型稀土矿床相比,该矿床具有完整而连续的流体演化过程,且几乎不受热液蚀变和后期构造-岩浆事件的影响,因此是研究碳酸岩型稀土矿床成矿过程的理想对象。本次研究结合详细的1∶5000矿区岩性-构造-蚀变-矿化野外地质调查和流体包裹体研究,将矿床形成过程划分为三期,即岩浆期、热液期和表生期。热液期作为主要的成矿期,又可细分为热液早阶段、热液中阶段和热液晚阶段三个阶段。对热液不同阶段的重晶石、萤石、石英和氟碳铈矿的流体包裹体研究表明,主要分为以下6类:(1)熔体(M类)包裹体;(2)熔流包裹体;(3)富CO_2包裹体(WC类);(4)含子矿物富CO_2包裹体(SC类);(5)含子矿物水溶液三相包裹体(S类);(6)气液两相包裹体(W类)。热液早阶段为岩浆-热液过渡阶段,以粗粒萤石和重晶石为特征,发育熔融和熔流包裹体,指示成矿流体来自岩浆出溶。WC、SC和S类包裹体主要在热液中阶段石英和萤石中而W类包裹体大部分存在于热液晚阶段氟碳铈矿中。WC类包裹体具有不同的CO_2充填度,表明热液中阶段成矿流体发生不混溶作用。结合WC类包裹体端元组成的显微测温结果和等容线法,模拟计算出不混溶作用发生的温度为280～320℃之间,压力为120～180MPa,盐度范围较大,为2. 4%～42. 4%Na Cleqv。热液成矿期晚阶段氟碳铈矿中的W类包裹体具有稳定的气液比,说明成矿环境较均匀,其测温结果显示大规模稀土矿化主要发生在200～260℃之间,压力<200bars,盐度为6. 5%～11. 2%Na Cleqv。激光拉曼结果显示SC和S类包裹体中的子晶主要为重晶石、天青石和无水芒硝等硫酸盐,指示成矿流体富集Na^+、Ca^(2+)、K^+、Sr^(2+)、Ba^(2+)、SO_4^(2-)、F^-和Cl^-离子。成矿流体δD和δ^(18)O同位素组成分�The Muluozhai rare earth element(REE) deposit located in eastern Tibetan Plateau and southwestern Yangtze,is the typical carbonatite-related REE deposit.Compared with other carbonatite-related REE deposits with complicated mineralization processes,the Muluozhai REE deposit has a completed and continuous fluid evolution process and is almost unaffected by hydrothermal alteration and late tectono-magmatic events.Therefore,it is an ideal target for understanding the mineralization process of REE deposits.Based on the detail geological investigation of the 1∶5000 petrology-structure-alteration-mineralization mapping and the study of fluid inclusions,three periods are recognized,namely:(1) magmatic period;(2) hydrothermal period and(3) supergene period.The hydrothermal period is the main mineralization period with divided into early,middle and late stages.The results of study on fluid inclusions in fluorite,quartz and bastnsite from different hydrothermal stages show that six types are recognized,as followed:(1)melt inclusion(M type);(2) melt-fluid inclusion(ML type);(3) CO2-rich aqueous fluid inclusion(WC type);(4) solid-bearing CO2-rich fluid inclusion(SC type);(5) solid-bearing aqueous fluid inclusion(S type);and(6) aqueous-rich fluid inclusion(W type).The early hydrothermal stage is transition from magmatic to hydrothermal process.This stage is characterized by coarse-grained fluorite and barite and host M and ML types inclusions,implying that the ore-forming fluid exsolved from magma.WC,SC and S types inclusions are dominant in the fluorite and quartz from the middle hydrothermal stage whereas the W type inclusions are abundant in bastnsite from the late hydrothermal stage.Generally,the WC type inclusions with various carbonic filling degrees are interpreted as the immiscibility took place in the middle hydrothermal stage.Based on the microthermometric and isochoric results of end members of WC type inclusions,immiscibility is constrained at the temperature of 280~320℃,pressure of 120~180 MPa and salini

关 键 词：流体包裹体 稳定同位素 木落寨 碳酸岩型稀土矿床 

分 类 号：P597.2[天文地球—地球化学] P618.7[天文地球—地质学]