云南兰坪盆地西缘脉状铜矿床富CO_2流体来源的He和Ar同位素证据  

Origin of CO_2-rich ore-forming fluids in the vein-type Cu deposits in western Lanping Basin, Yunnan: Evidence from He and Ar isotopes

作　　者：张锦让[1,2] 温汉捷[2] 邹志超[3] 杜胜江[2] 

机构地区：[1]成都地质矿产研究所资源评价与矿床研究室,四川成都610081 [2]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵州贵阳550002 [3]成都理工大学地球科学学院,四川成都610059

出　　处：《地球化学》2015年第2期167-177,共11页Geochimica

基　　金：国家青年科学基金(41403038);国家重点基础研究发展计划(2009CB421005);中国地质调查局综合研究项目(12120113094400)

摘　　要：兰坪盆地西缘广泛发育大量沉积岩容矿脉状铜矿床, 这些脉状铜矿床的成矿流体以普遍存在大量富CO2 流体包裹体为特征, 这在整个兰坪盆地是十分罕见的, 显著区别于盆地流体成矿系统主导成矿的Pb-Zn 矿床.为探明这种富CO2 流体的来源, 本文首次报道了盆地西缘2 个代表性脉状铜矿床（连城、金满）主成矿阶段形成的黄铜矿、黄铁矿的He 和Ar 同位素组成的研究结果.结果表明, 2 个矿床不同样品流体包裹体中3He/4He 比值变化较小, 介于0.01-0.07 Ra 之间, 明显区别于幔源氦的3He/4He 特征值（6-9 Ra）, 而与壳源氦的3He/4He 特征值（0.01-0.05 Ra）极其-致; 40Ar/36Ar 比值变化较大, 介于305-1142 之间, 明显高于大气中的40Ar/36Ar 比值（295.5）.结合矿床地质、流体包裹体及H、O 同位素地球化学特征, 认为兰坪盆地西缘脉状铜矿床中富CO2 的成矿流体以混有少量饱和大气水的地壳流体为主, 没有明显的幔源流体参与.A series of vein-type Cu deposits occur in western Lanping Basin in Yunnan Province of China. The ore-forming fluids responsible for these vein-type Cu deposits are characterized by abundant CO2-rich fluid inclusions, which are significantly different from those of basinal fluid systems that are responsible for the Pb-Zn deposits in other parts of the Lanping Basin. In order to better understand the sources of the CO2-rich fluids, the authors report new results of helium and argon isotopic compositions of the fluid inclusions in pyrite and chalcopyrite formed at the main mineralizing stage for two vein-type copper deposits in western Lanping Basin. The analytical results show that the 3He/4He ratios of all samples range from 0.01 to 0.07 Ra, which are all significantly lower than the mantle values, but are consistent with the typical crustal values (0.01~0.05). The measured 40Ar/36Ar values range from 305 to 1142, which are greatly higher than the atmospheric value of 295.5. Based on the results of geology, fluid inclusions and H, O isotopic geochemistry, we suggest that the CO2-rich fluids are mainly derived from the crustal fluids, with no considerable involvement of mantle-derived fluids. It may have been mixed with some amount of air-saturated water, which can reduce the 40Ar/36Ar ratio for hydrothermal fluid, but has little effect on the R/Ra ratio.

关 键 词：富CO2流体 HE-AR同位素 地壳流体 脉状铜矿床 兰坪盆地西缘 云南 

分 类 号：P597[天文地球—地球化学] P618[天文地球—地质学]