西藏冈底斯成矿带鸡公村钼矿床Re超常富集机制研究

The Jigongcun Mo deposit is an extraordinary enrichment of rhenium deposit which had been discovered for the first time in the Gangdese metallogenic belt, Tibet.But the types of minerals containing rhenium and the occurrence of rhenium is not clear at present, and the sources of ore-forming materials, migration,precipitation and Enrichment mechanism of rhenium has also not yet been studied.Based on the detailed works in field and lab, We plan on studying the types of minerals containing rhenium and the occurrence of rhenium in the deposit by using microscopic observation, scanning electron microscope and electron probe.Combined with the host metal sulfides trace elements and sulfur isotope data, the comparative study on major elements, trace elements and rare earth elements among the ores, intrusive rocks and the strata,and the diagenetic and metallogenic ages will be carried out for tracing the sources of rhenium. Furthermore, geochemical study of the fluid inclusions will be used for finding out the features and evolution process of the ore-forming fluid and the factors controlling the precipitation and enrichment of Re in the Jigongcun deposit combined with the above research. This applying study on the rhenium mineralization of the Jigongcun deposit is beneficial to enriching the material about mineralogy and geochemical behavior of rhenium. In addition, it has an important guiding significance to carry out prospecting potential evaluation work about Re for the similar geological background areas.

鸡公村钼矿床是西藏冈底斯成矿带上首次发现的具有铼超常富集的钼矿床，目前含铼矿物种类、铼的赋存状态尚不清楚，铼成矿物质来源、运移、沉淀及其富集机理也尚未揭晓。因此，本项目拟在扎实的野外地质调查及室内岩矿研究基础上，通过光学显微镜、电子探针及扫描电镜分析，查明含铼矿物种类及铼的赋存状态；通过对比各类岩、矿石主微量元素组成及成岩-成矿时代追踪铼成矿物质来源相关地质体，并结合铼的寄主金属硫化物微量元素及S同位素测试限定铼的成矿物质来源；通过流体包裹地球化学研究，查明成矿流体性质，还原流体演化过程，并结合前述研究剖析铼的富集机理。本次研究对鸡公村钼矿床关于铼成矿作用的重点解剖，不仅可以丰富铼的矿物学及地球化学行为素材，而且对于区域上具有相似成矿地质背景的地区开展关于铼的找矿潜力评价工作具有重要的指导意义。

鸡公村富Re石英脉型钼矿床位于西藏冈底斯斑岩铜矿带东段，矿体呈层状或透镜状赋存于石英脉内，严格受北西向或近东西向断裂构造控制。矿床的形成具有4个热液/矿化阶段：1）成矿前阶段（阶段Ⅰ），以发育厚的无钼石英脉为特征；2)成矿早阶段（阶段Ⅱ），以发育富含Re辉钼矿的厚石英脉为显著特征，该阶段富Re辉钼矿可见有块状辉钼矿(Mo1型，Re平均值=1811ppm)和叶片状辉钼矿(Mo2型，Re平均值=1312ppm)两种类型，其它硫化物发育较少；3)成矿晚阶段（阶段Ⅲ），主要形成贫Re叶片状辉钼矿(Mo3型，Re平均值=107ppm)的石英脉，此外还发育大量方铅矿和黄铁矿；4)成矿后阶段(阶段Ⅳ),形成厚的无矿石英-方解石脉。辉钼矿电子探针及LA-ICP-MS原位微量元素分析均表明鸡公村钼矿床并没有独立Re矿物的形成，Re均以置换Mo的形式赋存于辉钼矿中。辉钼矿Re-Os同位素定年结果表明鸡公村钼矿床成矿时代为22.0±0.4Ma，表明矿床形成于早中新世，早于冈底斯斑岩铜矿带大多数斑岩铜矿床。详细的流体包裹体研究表明，成矿前阶段的流体具有相对高温(311–337℃)、高压(1300–1600bar)、低盐度(0.2–2.6%)特征，为富含CO2的岩浆热液流体。成矿早阶段发育的石英-钾长石脉中广泛共存水溶液包裹体与富含CO2包裹体，指示流体不混溶，流体温度在262–300℃之间，压力在900–1100bar之间，由于相分离造成的相对氧化条件导致该阶段沉淀了大量富Re辉钼矿。成矿晚阶段具有明显的岩浆流体与大气降水混合特征，流体温度在220–271℃之间，并沉淀了大量贫Re的辉钼矿。H-O-S同位素组成显示矿床成矿物质与成矿流体均来自深部岩浆。结合区域研究资料，本项目研究结果表明鸡公村富Re石英脉型钼矿床的形成可能与早中新世印度大陆向北俯冲有关。