滇西河西锶矿床的陆相热水沉积成因——天青石矿物化学和Sr-S同位素证据  

Continental hydrothermal sedimentary origin of the Hexi strontium deposit in western Yunnan Province,SW China:Evidence from elemental and Sr-S isotopic compositions of celestines

作　　者：邓邹斌 薛传东[1,2] 王维 张佳慧 邓杨 李政桥 DENG Zou-bin;XUE Chuan-dong;WANG Wei;ZHANG Jia-hui;DENG Yang;LI Zheng-qiao(Department of Earth Sciences,Kunming University of Science and Technology,Kunming 650093,China;Observation and Research Station of Basinal Brine and Petroliferous Fluid Coupling and Metallogeny at the Jinding Zinc-Lead Deposit in Lanping,Yunnan,Lanping 671400,China;Sichuan Mineral Resources Exploration Group Co.,Ltd.,Chengdu 610051,China)

机构地区：[1]昆明理工大学地球科学系,云南昆明650093 [2]兰坪金顶铅锌矿盆地-油气流体成矿云南省野外科学观测研究站,云南兰坪671400 [3]四川省矿产资源勘查集团有限责任公司,四川成都610051

出　　处：《岩石矿物学杂志》2024年第6期1411-1430,共20页Acta Petrologica et Mineralogica

基　　金：第二次青藏高原综合科学考察研究(2021QZKK0301);国家自然科学基金项目(421630077,41373049);云南省新一轮找矿战略行动计划项目(Y202405)。

摘　　要：滇西河西大型锶矿床产于青藏高原东南缘兰坪中-新生代盆地北部,矿体主要赋存于上三叠统三合洞组碳酸盐岩中,且中新统金顶群含石膏砂泥质岩石中也多有产出,受成矿期近S-N向逆断层和近E-W向走滑断层控制。本文通过天青石岩相学观察和矿物化学分析,将热液期天青石分为Cls1、Cls2和Cls3三个世代,Cls1主要为他形粒状结构,Cls2和Cls3为自形柱状或板条状结构。其中,Cls2以发育Sr-Ba固溶体震荡环带为特点,指示矿石沉淀经历了快速到缓慢的结晶转换过程。Sr-S同位素示踪结果显示,天青石具有较均一的^(87)Sr/^(86)Sr值(0.707695~0.707792,均值为0.707740),与区域三合洞组灰岩及晚三叠世海水的Sr同位素组成一致;天青石的δ^(34)S值(17.26‰~17.49‰,均值为17.36‰)略高于金顶群石膏岩的δ^(34)S值(12.5‰~15.0‰)。分析认为,富Sr流体的形成可能与三合洞组灰岩受重力压实及深部热源导致的高压脱水作用有关,这些含矿热液早期聚集在三合洞组有利的构造圈闭空间内。在印度-欧亚大陆碰撞导致的构造应力变化和深部热源驱动下,含矿热液沿深切盆地基底的近S-N向逆冲构造上升运移,最后在浅表部与金顶群沉积期的氧化性湖相盆地卤水发生混合,导致三合洞组热液充填交代和金顶群热水沉积成矿作用近于同步发生。因此,河西锶矿床是一类兼具陆相热水沉积成矿特点的后生热液充填型矿床。The Hexi large strontium deposit in western Yunnan Province is located in the northern part of the Meso-Cenozoic Lanping Basin,southeast margin of the Qinghai-Tibet Plateau.The ore bodies mainly occur in the carbonate rocks of the Upper Triassic Sanhedong Formation,and are also abundant in the gypsum-bearing sand-mudstones of the Miocene Jinding Group.They are controlled by the near S-N-extending reverse fault and the near E-W-exten-ding strike-slip fault during the metallogenic stage.After the petrography observation and mineral chemical compositions analysis,the hydrothermal celestine can be divided into three generations of Cls1,Cls2 and Cls3,respectively.Cls1 mainly has an heteromorphic granular structure,while Cls2 and Cls3 exhibit an idiomorphic columnar or lamellar structure,and Cls2 is characterized by Sr-Ba solid solution oscillating rings,revealing that the ore precipitation had undergone a rapid to slow crystallization process.The Sr and S isotopic tracing results show that the celestine has an uniform ^(87)Sr/^(86)Sr value of 0.707695~0.707792,with an average value of 0.707740,which is consistent with the Sr isotopic compositions of adjacent Sanhedong Formation limestones and the Late Triassic seawaters.Theδ^(34)S value of celestine(17.26‰~17.49‰,with an average value of 17.36‰)is slightly higher than that of the Jinding Group gypsum(12.5‰~15.0‰).This indicates that the formation of Sr-rich fluid may be related to the high-pressure dehydration of the Sanhedong Formation limestone caused by gravity compaction and deep source heat flow,and the ore-bearing hydrothermal fluid concentrated at the favorable structural traps in the Sanhedong Formation during the early stage.Influenced by the regional tectonic stress changes and deep heat effect driven by the India-Eurasia collision process,these ore-bearing hydrothermal fluid migrated upward along the near S-N-extending reverse structure and mixed with the oxidizing lacustrine basin brine of the Jinding Group at the shallow surface.The hydrotherma

关 键 词：天青石 矿物化学 Sr-S同位素 后生热液充填型矿床 陆相热水沉积成因 河西锶矿床 兰坪盆地 

分 类 号：P611[天文地球—矿床学] P616[天文地球—地质学]