西藏冈底斯中段雄村铜金矿床成矿流体特征与成因探讨  

Ore_forming fluid characteristics and genesis of Xiongcun copper-gold deposit in central Gangdese, Tibet

作　　者：徐文艺[1] 曲晓明[1] 侯增谦[2] 杨丹[1] 杨竹森[1] 崔艳合[1] 陈伟十[1] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]中国地质科学院地质研究所,北京100037

出　　处：《矿床地质》2006年第3期243-251,共9页Mineral Deposits

基　　金：国家自然科学基金项目(40303008);科技部"973"计划项目(2002CB412605)的联合资助

摘　　要：雄村铜金矿是在西藏冈底斯中段新发现的一个矿床,流体包裹体组成分析揭示该矿床成矿流体为富含CO2、N2和有机气体的Na+_K+_Ca2+_Cl-_SO2-4_HS-_CO2-3体系,Na/K、Na/Ca和Cl-/SO2-4摩尔比值分别为1.5～7.1、0.2～2.1和1.0～29.3。氢、氧同位素分析显示,成矿流体δ18O值范围为-4.7‰～+2.2‰,δD值范围为-104‰～-82‰,表明成矿流体以大气水为主,但岩浆流体可能也对矿床的形成起了重要作用。硫化物硫同位素组成也显示硫主要来自深源岩浆,雄村矿床高盐度流体的形成可能与岩浆流体的低压不混溶密切相关。高盐度流体是雄村贱金属元素活化、迁移的重要介质;地下水中高的有机质还原SO2是诱发贱金属沉淀成矿的重要机制。有机质还原SO2也为Au的活化、迁移提供了介质和有利的还原环境。雄村矿床的形成与岩浆流体和循环地下水共同作用有关,浅部稳定的热体制和高的有机质还原SO2机制是形成雄村矿床特殊蚀变矿化样式的重要原因。GC and IC analyses of the fluid inclusions reveal that the ore-forming fluids of the Xiongcun copper-gold deposit are of the CO2, N2, and organic gas-rich Na^＋-K^＋ -Ca^2＋ -Cl^--SO4^2--HS^--CO3^2- system with Na/K molar ratios 1.5--7.1, Na/Ca molar ratios 0.2--2.1 and Cl^-/SO4^24- molar ratios 1.0--29.3. Oxygen and hydrogen isotopic analyses of the vein quartz show that δ^18H2O and δ^DH2O values range from - 4.7%o to ＋ 2.2%o and from - 104%o to - 82%o, respectively, which indicates that the ore-forming fluids of the Xiongcun deposit are dominated by meteoric water, with the probable participation of magmaic water. The highly saline fluids may be related to the immiscibility of magmatic water, and are the important media for the base metals transportation in the Xiongcun deposit. The ore-forming fluids of the Xiongcun deposit are characterized by high organic gas contents, which constitute an important factor responsible for copper and gold mineralization. The reduction of SO2 by organic gas leads to the precipitation of the base metals and provides gold mineralization with activation and transportation media and a stable reduction environment. The Xiongcun deposit is different from the typical high-sulfidation and low-sulfidation epithermal deposits, which are formed in a stable shallow high-temperature regime and related to meteoric and magmatic water. It is the reduction of SO2 by organic gas rather than the SO2 disproportion that produces lots of HS^- which are necessary for the precipitation of base metals and transportation of gold in the ore-forming process of this type of epithermal deposits.

关 键 词：地球化学 成矿流体 流体组成 氢氧同位素 浅成热液矿床 雄村 西藏 

分 类 号：P618.41[天文地球—矿床学] P618.51[天文地球—地质学]