西藏雄村铜金矿床石英闪长斑岩中单个流体包裹体的SRXRF研究及其意义

Synchrotron Radiation X-Ray Fluorescence Microprobe Analysis of the Fluid Inclusions in Quartz Diorite Porphyrite from the Xiongcun Copper-Gold Deposit in Tibet

雄村铜金矿床是近年来西藏冈底斯成矿带内发现的一处超大型铜金矿床,该矿床位于冈底斯造山带中段南缘。对石英闪长斑岩的石英斑晶和晚期石英脉体中的流体包裹体进行了岩相学观察和同步辐射X射线荧光微探针分析。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等元素的含量无一例外地相对富集,Zn、Pb、Rb、As、Br则优先进入流体液相。高温热液流体在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,温压等物理化学条件的变化会影响成矿元素迁移分配的地球化学行为。因此,雄村矿床成矿流体是直接从岩浆熔体中出溶的富含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。

Xiongcun copper-gold deposit, a large-size copper-gold deposit discovered along Gangdise metal- logenic belt, is located in the middle of the southern margin of Gangdise orogenic belt. The study of its ore- forming fluid is still weak relatively. On the basis of field geological observations, this paper presents the petrography observation, synchrotron radiation X-ray fluorescence microprobe analysis and the analysis of the fluid inclusions in quartz phenocryst and late stage quartz veins. Synchrotron radiation X-ray fluores- cence 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, and Cr elements are rich in the gas phase of fluid inclusions without exception, while the elements such as Zn, Pb, Rb, As and Br have the priority to enter into the liquid phase. In the separation process of high temperature immiscible hydrothermal fluid, the ore-forming elements migrate selectively and distribute non-uniform in various phases. The change of temperature, pressure and other physical and chemical conditions can affect the migration and distribution geochemical behavior of the ore-forming elements. Therefore, the ore-forming fluid of Xiongcun porphyry copper-gold deposit is magmatic fluid rich in Cu, Au, Mo, and Fe 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 ore-forming elements enrichment.