西藏雄村铜金矿床流体包裹体显微测温与特征元素测定

Microthermometry and characteristic element determination of fluid inclusions from Xiongcun copper-gold deposit in Tibet

雄村斑岩型铜金矿床作为冈底斯成矿带西段一个重要的大型铜金矿床的代表,对其成矿流体方面的研究还较为薄弱。文章在野外地质观察的基础上,对岩体的石英斑晶和不同期次的石英脉体中的流体包裹体进行了岩相学观察、显微测温、拉曼光谱分析以及同步辐射X射线荧光微探针分析。岩相学观察显示,石英脉中流体包裹体主要为气液两相水溶液包裹体、含CO_2三相包裹体和含子晶三相包裹体。显微测温结果显示,早期石英硫化物脉体中流体包裹体均一温度范围为100~500℃,盐度w(Na Cleq)为0.35%~53.39%,晚期石英硫化物脉中流体包裹体均一温度范围为120~440℃,盐度w(Na Cleq)为1.39%~22.67%。拉曼光谱分析结果显示,矿化石英脉中流体包裹体发育CO_2、CH_4、N_2,有利于促进流体的相分离,不混溶气体的分离也有利于金属元素的沉淀。同步辐射X射线荧光微探针分析结果表明,石英闪长斑岩流体包裹体中富含成矿元素Cu和Au,在流体包裹体气相中,Mo、S、Fe、Mn、Hg、Ni、Tl、Cr、K等元素无一例外地相对富集,Zn、Pb、Rb、As、Br则优先进入液相。高温热液流体不混溶相分离过程中,成矿元素选择性迁移,在各相中进行不均匀分配。因此,雄村矿床成矿流体是直接从岩浆熔体中出溶的高温、高氧化性、高盐度的富含Cu、Au、Mo、Fe等元素的岩浆流体,成矿元素在流体出溶和分离各相中的不均匀分配是成矿元素最终富集成矿的关键因素。

The Xiongcun porphyry copper-gold deposit is an important representative of the large copper-gold deposits along the western Gangdise metallogenic belt; nevertheless, the study of the ore-forming fluid remains relatively insufficient. On the basis of field geological observation, the authors carried out petrographic observation, microthermometric measurement, laser Raman microprobe analysis and SRXRF analysis of the fluid inclusions in quartz phenocrysts and different stages of quartz veins. Petrographic observation reveals that fluid inclusions in both kinds of vein quartz are mainly two-phase aqueous inclusions, three-phase CO2-aqueous inclusions, and three-phase solid fluid inclusions. Microthermometry shows that early stage quartz veins have Th of 160 ~ 500℃, and salinity w（ NaCleq） of 5. 09% ~ 53. 39%, whereas late stage quartz veins have Th of 160 ~ 440℃, and salinity w（ Na Cleq） of1. 39% ~ 22. 67%. Laser Raman test shows that CO2, CH4, N2 exist in fluid inclusions, and these components are favorable for the phase separation of the fluid, and the separation of immiscible gas is also conducive to the precipitation of metal elements. Synchrotron radiation X-ray fluorescence microprobe analysis results show that the fluid inclusions in quartz diorite porphyrite are rich in ore-forming elements Cu and Au. Mo, S, Fe, Mn, Hg, Ni, Tl, K elements are rich in the gas phase of fluid inclusions without exception, the elements such as Zn, Pb, Rb, As and Br have the priority of entering the liquid phase. In the separation process of high temperature immiscible hydrothermal fluid, the ore-forming elements migrate selectively and are distributed unevenly in various phases. Therefore, the ore-forming fluids of the Xiongcun porphyry copper-gold deposit are high temperature, high oxidation and high salinity magmatic fluids rich in Cu, Au, Mo, Fe elements exsolved directly from magmatic melt. In the process of exsolution, the uneven distribution of ore-forming elements in each phase is the key factor for the enrichment of ore-forming elements.