西藏浦桑果矽卡岩型铜多金属矿床富Co机制研究

The Pusangguo deposit is the only one skarn Cu-polymetallic deposit in which the associated element of cobalt has reached the industrial grade in the Gangdese metallogenic belt by far. However, the reason for Co enrichment in the Pusangguo deposit has not yet been studied. Based on detailed works in field and lab, three aspects of researches in this project will be carried out to reveal the mechanism of Co enrichment in the Pusangguo deposit. One is ascertain the occurrence of cobalt in the deposit by using microscopic observation, scanning electron microscope and electron probe. The second is tracing the sources of cobalt through comparative study on major elements, trace elements and rare earth elements among the intrusive rocks, the strata and ores. The third is carrying out in situ trace elements determination of cobalt-bearing metal sulfides and analyzing physicochemical conditions and component of fluid inclusions to dissect the nature and evolution of ore-forming fluid and find out factors controlling the precipitation and enrichment of Co in the Pusangguo deposit. The project has significant values in deeply understanding relationships between Co and Cu-Pb-Zn mineralization, in delineating industrial cobalt ore bodies, in comprehensive utilization of ores, as well as in further ore prospecting in the Pusangguo deposit.

浦桑果是冈底斯成矿带上目前仅有的伴生钴品位达到工业指标的矽卡岩型铜多金属矿床，然而矿床富钴的缘由尚未揭晓。本项目在详尽的野外和室内工作基础上，拟开展如下三方面的工作，从而揭示矿床的富钴机制。一是利用显微镜观察、扫描电镜及电子探针分析，查明钴的赋存状态；二是通过对比矿区侵入岩、地层及矿石的主量、微量、稀土元素组成，追踪钴的成矿物质来源地质体；三是借助载钴金属硫化物原位微区微量元素测试、流体包裹体物理化学条件及成分分析，剖析成矿流体性质与演化对钴沉淀并发生富集的控制因素。该项研究对于深入把握矿床Co与Cu、Pb、Zn矿化之间关系，圈定钴的工业矿体、矿石综合利用及矿区下一步找矿预测具有重要价值。

西藏浦桑果铜多金属矿床位于冈底斯成矿带西段，是目前冈底斯成矿带发现的首例富钴矽卡岩型铜多金属矿床，具较高经济价值。矿床的剥蚀程度低，保存较完整，Cu+Pb+Zn金属资源量大于50万吨（331+332+333），钴金属量大于300吨，钴平均品位为140g/t。通过详细的野外地质调查和室内工作发现，钴主要与铜、铅、锌等金属元素共伴生，构成富钴Cu(-Pb-Zn)矿体，但钴的赋存状态和富集机制不清。本次研究以此为重点科学问题，以地质编录和镜下鉴定为基础，利用电子探针、LA-ICP-MS等分析技术，主要对矿物学、年代学展开系统研究，结合同位素、流体包裹体分析结果，对钴的富集机制及矿床成因进行探讨。主要获得了以下几方面的研究成果：1）电子探针及LA-ICP-MS微区分析表明，矿区高品位钴主要以独立钴矿物和类质同象形式赋存，独立钴矿物为辉砷镍钴矿，发育于黄铜矿颗粒中；类质同象Co主要替代闪锌矿或黄铁矿中的Fe元素。2）LA-ICP-MS锆石U-Pb、闪锌矿Rb-Sr同位素年代学结果表明，矿区侵入岩体侵位和矿化时代均为中新世，与冈底斯斑岩-矽卡岩铜多金属成矿带内大多矿床的成岩成矿时代相吻合。3）流体包裹体、H-O-S-Pb同位素分析表明，矿区硫具岩浆硫特征，Pb、Zn等金属元素主要来自于上地壳物质，主成矿期成矿流体具中高温低盐度特征且混有后期的大气降水。4）岩石地球化学及锆石Hf同位素特征表明，矿区辉长岩较黑云母花岗闪长岩和闪长玢岩富集Co、Ni等金属元素，其初始岩浆可能起源于壳幔混染物质；黑云母花岗闪长岩和闪长玢岩主要起源于地壳物质，且提供了矿区主要的含Cu、Pb、Zn等矿化元素成矿流体，向上运移过程中混有来自辉长岩体的富钴流体加入，随着温度、压力等物理化学条件的改变，在有利构造和接触带构造部位沉淀富集。