摘要
夹皮沟矿集区发育众多石英脉型和蚀变岩型金矿床,区内的金矿床属于中温热液金矿床,并以中温低盐度流体、中侏罗世成矿、成因上与同期岩浆作用关系密切为主要特征。为了刻画同期岩浆-热液作用的过程,探讨其对金成矿的贡献,示踪区内金成矿作用过程,以区内的冰湖沟金矿床为例,开展了系统的矿床地质、岩相学,以及锆石的矿物学、年代学和地球化学研究。研究结果显示:1)金主要赋存在震碎角砾岩的胶结物中;2)根据锆石的晶体形态、内部结构、微量元素组成和U-Pb年龄,热液胶结角砾岩和角砾状矿石胶结物中锆石可划分为捕获锆石(第一组195~185 Ma)、继承锆石(第二组175~172 Ma)和热液锆石(第三组176~173 Ma),其中热液锆石(第三组)的U-Pb年龄为176~173 Ma,指示成矿作用发生在中侏罗世;3)第二、三组锆石具有较低w(Y)、高Y/Ho值,指示晚阶段花岗质熔体与富P和Ti的热液流体共存,同时它们的w(Hf)与Th/U、Yb/Gd值呈现出系统的演化趋势,指示岩浆经历了逐步的冷却和分异作用,并最终形成热液流体;4)第二组锆石与第三组锆石相比,具有较高的Ce/Ce^(*)值和Eu/Eu^(*)值,指示岩浆是高氧逸度的,而热液流体是低氧逸度的,同时锆石的不相容元素(如P、Y、LREE、Nb、Th、Pb^(*)等)的质量分数随着w(Hf)(从第二组到第三组)增加逐步增加,指示在岩浆分异及向热液演化过程中,不相容元素逐步进入热液流体相,并逐步富集。结合区域成果,由于岩浆具有高温、高氧逸度、富挥发组分,抑制了硫化物在其演化早阶段结晶,使得Au、S、Fe,以及不相容元素在晚阶段岩浆/热液流体中富集,形成初始含矿流体;在向上运移过程中,强烈的水岩反应、温压和氧逸度的降低,致使含矿流体处于不稳定状态,Au和硫化物大量沉淀,最终形成金矿床。从区域成矿背景、矿床地质、元素地球化学、成矿流体和成岩成矿年代学等角度综合分析,认为上述地质过程是夹皮沟矿集区大规模金成矿的根源。
The Jiapigou mining district(JMD)is famous in the world for its numerous quartz vein-and altered rock-type gold deposits.The gold deposits in the JMD belong to mesothermal gold deposits and are characterized by fluids with moderate temperature and low salinity,Middle Jurassic mineralization,and genesis related to synchronic magmatism.In order to depict the process of synchronic magmatism-hydrothermalism,and tace the process of Au mineralization in this region,we present the deposit geology,petrology,and mineralogy,geochronology,and geochemistry of zircon from the Binghugou gold deposit in the JMD.The results show that:1)Gold mainly occurs in cements of the shattered breccia;2)Based on the morphology,internal structure,trace element composition,and U-Pb age,the zircons in the cements of the hydrothermal breccia and breccia-type ore can be divided into the captured(GroupⅠ:195-185 Ma),inherited(GroupⅡ:175-172 Ma)and hydrothermal zircons(GroupⅢ:176-173 Ma),and the U-Pb age of the hydrothermal zircons(GroupⅢ)at 176-173 Ma indicating that Au mineralization occurred in the Middle Jurassic;3)The zircons in the GroupsⅡ-Ⅲhave low w(Y)values and high Y/Ho ratios,indicating that the late stage granitic melts coexist with the P-and Ti-rich hydrothermal fluids,and have systematic trends between w(Hf)-Th/U and w(Hf)-Yb/Gd,indicating that magma experienced gradual cooling and differentiation,and finally formed hydrothermal fluid;4)The Ce/Ce^(*)and Eu/Eu^(*)ratios of the GroupⅡzircons are obviously higher than those of the GroupⅢzircons,indicating that the magma has high oxygen fugacity,and the hydrothermal fluid has low oxygen fugacity,while the values of the incompatible elements(P,Y,LREE,Nb,Th,and Pb^(*))gradual increase with the increase of the values of w(Hf)of the zircons(from the GroupⅡtoⅢ),indicated that incompatible elements gradually entered the hydrothermal fluid phase and enriched during magmatic differentiation and magmatic-hydrothermal transition.Combined the geological observations,the magma is characterized by high temperature,high oxygen fugacity and volatile-rich components,which hindered the crystallization of sulfides in the early stage of its evolution,and promoted the enrichment of Au,S,Fe and incompatible elements in the late stage of its evolution/hydrothermal fluid,resulting in the formation of the initial ore-bearing fluids.In the process of upward migration,abundant gold and sulfides precipitated from the ore-bearing fluids due to its unstable state caused by the intense fluid-rock interaction and decrease of pressure,temperature and oxygen fugacity,resulting in the formation of gold deposit.Combined with the regional metallogenic setting,ore geology,element geochemistry,ore-bearing fluid,and chronology of magmatism and mineralization,the above geological process is likely to have resulted in the giant gold mineralization observed in the JMD.
作者
韩吉龙
孙景贵
张勇
张笑天
刘阳
王抒
褚小磊
Han Jilong;Sun Jinggui;Zhang Yong;Zhang Xiaotian;Liu Yang;Wang Shu;Chu Xiaolei(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;College of Earth Sciences,Jilin University,Changchun 130061,China;Institute of Mineral Resources,Chinese Academy of Geological Sciences/MNR Key Laboratory of Metallogeny and MineralAssessment,Beijing 100037,China;State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,China)
出处
《吉林大学学报（地球科学版）》
CAS
CSCD
北大核心
2023年第3期728-747,共20页
Journal of Jilin University：Earth Science Edition
基金
国家自然科学基金项目(42072085,42202068)
自然资源部成矿作用与资源评价重点实验室开放基金项目(ZS2102)
