西藏冈底斯甲马和南木矿床流体包裹体SR-XRF研究

SR-XRF studies of fluid inclusions from the Jiama and Nanmu deposits in the Gangdise copper-polymetallic metallogenic belt of Tibet

对西藏冈底斯铜多金属成矿带中甲马和南木矿床的流体包裹体开展了系统的同步辐射X射线荧光(SR-XRF)微束原位无损分析,结果显示:甲马矿床流体包裹体中高Cr、Pb,低Ni、Fe,且存在高于地壳丰度的Pt、Ir含量异常;南木矿床流体包裹体中高Cr、Cu、Pb,低Ni、Fe、Zn,晚期有Au富集,Cu倾向于在高盐度流体中富集。甲马和南木两矿床成矿流体中元素的原始地幔标准化模式与两矿区的成矿斑岩大体类似,显示出两矿床与区内斑岩在物质来源上具有亲缘性,幔源和壳源物质共同参与了成矿。但Cr含量的差异也显示出,尽管成矿流体与斑岩岩浆可能都起源于深部,但二者在演化上是平行的。对于甲马矿床的成因,流体包裹体SR-XRF原位组成分析以及显微测温结果不支持喷流沉积成因观点。

SR-XRF microprobe was used to measure elements in fluid inclusions hosted by quartz associated intimately with Cu mineralization of the Jiama and Nanmu deposits in the Gangdise copper-polymetallic metallogenic belt of Tibet. Analyses show that fluid inclusions from Jiama are rich in Cr and Pb but poor in Fe and Ni. In addition, fluid inclusions from Jiama show Pt and Ir anomalies, with the Pt and Ir concentrations higher than those of the continental crust. Fluid inclusions from Nanmu are rich in Cr, Cu and Pb but poor in Fe, Zn and Ni. In the Nanmu deposit, copper concentrations in highly saline fluid inclusions are by far higher than those in low salinity fluid inclusions and vapor inclusions, suggesting that copper selectively entered saline fluids. SRXRF microanalysis also reveals that gold was concentrated in late-stage ore-forming fluids. Primitive mantle normalized patterns of the first transitional metal elements in fluid inclusions from Jiama and Nanmu are generally similar to those of mineralizing intrusives in the corresponding areas. These features imply that ore-forming fluids and mineralizing porphyries have similar material resources in Jiama and Nanmu districts. Both mantlederived and crust-derived materials contributed to mineralization. However, the ore-forming fluids did not originate from porphyries but evolved parallel to porphyries. SR-XRF microanalysis results of fluid inclusions fail to support submarine exhalation origin of the Jiama deposit.