石榴子石U-Pb精确测年对斑岩-矽卡岩型铜矿床成岩时限的制约——以西藏桑日铜矿为例  

Constraints on the geochronology of porphyry-skarn copper deposit from U-Pb dating of garnet:a case study of the Sangri copper deposit,Tibet

作　　者：林彬[1,2] 陈蕾 刘振宇 唐菊兴[1] 邹兵[2] 贺文 LIN Bin;CHEN Lei;LIU Zhenyu;TANG Juxing;ZOU bin;HE Wen(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing,100037;Université Laval,Quebec,G1V0A6,Canada;Geological Survey Institute of Jilin Province,Changchun,130102)

机构地区：[1]中国地质科学院矿产资源研究所自然资源部深地资源成矿作用与矿产预测重点实验室,北京100037 [2]拉瓦尔大学,加拿大魁北克G1V0A6 [3]吉林省地质调查院,长春130102

出　　处：《地质学报》2020年第10期2883-2892,共10页Acta Geologica Sinica

基　　金：中国地质科学院基本科研业务费专项经费项目(编号SYSCR2019-02);国家自然科学基金项目(编号41902097);国家重点研发计划-深地专项(编号2018YFC0604101);西藏自治区科技计划项目(编号XZ201901-GB-24)联合资助。

摘　　要：矽卡岩型矿床是全球最具经济价值且研究最为深入的矿床类型之一。其矿物分带、金属矿化机制、流体演化特征均已获得共识性的结论,但其矽卡岩的成岩作用时限一致是困扰成矿作用机理研究的难题。桑日铜矿是青藏高原班公湖-怒江成矿带中段新发现的重要斑岩-矽卡岩型矿床。金属矿物主要为黄铜矿、黄铁矿和少量辉钼矿,呈细脉状、块状、浸染状产于斑岩和矽卡岩中。文章以西藏班戈县桑日铜矿为实例,利用飞秒激光剥蚀系统高分辨率电感耦合等离子体质谱仪,对矿区内矽卡岩中的石榴子石进行U-Pb精确定年,获得其结晶时代为83.2±2.3Ma(MSWD=1.2,n=26),有效限定矽卡岩成岩作用时代为晚白垩世。同时,将其与含矿斑岩锆石U-Pb年龄和辉钼矿Re-Os年龄对比,发现三者在误差范围内基本一致,说明三者属于同一成岩成矿作用事件的产物。因此,石榴子石U-Pb精确测年能够有效厘定矽卡岩矿床或斑岩-矽卡岩成矿系统中矽卡岩成岩作用时限,也为诸多矽卡岩矿床成矿机理研究提供了新的测试手段和数据支撑,具有良好的应用前景。Skarn deposits,as one of the most economically viable and highly studied deposits,is famous and commonly identified by its mineral zone,metal mineralization,and ore-forming fluid evolution.However,determining the diagenesis age of skarn is a challenge for the mineralization study of skarn deposit in the past decades.The Sangri copper deposit is a newly discovered porphyry-skarn deposit in the middle of the Bangong Co-Nujiang metallogenic belt,located in the Qinghai-Tibet Plateau.Chalcopyrite,pyrite,and molybdenite are the common metal minerals,occurring as veinlet,massive,and disseminated in the porphyry and skarn.The U-Pb age of garnet in the skarn dated by femtosecond laser erosion system with high-resolution inductively coupled plasma mass spectrometer is 83.2±2.3 Ma(MSWD=1.2,n=26),from the Sangri copper deposit in the Bangion county,Tibet.These data showed that diagenesis age of skarn was late Cretaceous.At the same time,compared with the U-Pb age of zircon from the ore-bearing porphyry and the Re-Os age of molybdenite,U-Pb age of garnet was consistent with them within the error range,indicating that they were the products of the same mineralization event.Therefore,the accurate U-Pb dating of garnet can effectively confirm the diagenesis age of skarn deposit or porphyry-skarn deposit.It is a new geochronology method and provides useful support for the metallogenic mechanism study of skarn deposits.

关 键 词：石榴子石 U-PB测年 矽卡岩矿床 斑岩成矿系统 桑日 西藏 

分 类 号：P618.41[天文地球—矿床学] P597.3[天文地球—地质学]