西藏邦铺钼多金属矿床矽卡岩矿物学特征及其地质意义

Mineralogical characteristics of skarn in the Bangpu Mo polymetallic deposit,Tibet,and their geological significance

西藏邦铺超大型钼多金属矿床中矽卡岩铅锌矿体赋存于下二叠统洛巴堆组矽卡岩和大理岩中,矿体呈似层状、透镜状产出,矽卡岩矿物较为发育。为进一步查明矿床矽卡岩矿物种属及矽卡岩类型,剖析矽卡岩形成环境及其与矿化类型之间的关系,基于对矽卡岩矿物系统地显微镜下观测,利用电子探针对矿床主要矽卡岩矿物化学成分进行了系统分析。结果表明,石榴子石端员组分以钙铁榴石为主,含少量锰铝榴石和钙铝榴石;单斜辉石主要为透辉石-钙铁辉石系列,含少量锰钙辉石;似辉石为铁钙蔷薇辉石;角闪石主要为钙质阳起石;绿帘石贫Fe、Mg。矽卡岩矿物组合特征表明,矿床矽卡岩兼具钙矽卡岩和锰质矽卡岩特征;早期矽卡岩形成于较强的氧化环境,成矿岩浆流体亦具有较高氧逸度。邦铺首次发现锰质矽卡岩矿物组合,表明矿区具有银矿找矿潜力,为下一步找矿工作提供了理论支撑。

The skarn type Pb-Zn ore body of the Bangpu superlarge Mo polymetallic ore deposit is hosted in the skarn and marble of the Lower Permian Luobadui Formation.The orebodies occur as stratoids or lenses,and lots of skarn minerals are developed in the ore deposit.In order to further clarify the species of skarn minerals and types of the skarn and analyze the forming environment of skarn and its relationship with the mineralization types,the authors studied the chemical composition of the main skarn minerals by using electron microprobe technology based on the systematic microscope observation.Electron microprobe analyses show that the end member of garnet is mainly andradite with a small amount of spessartite and grossularite.Pyroxene comprises mainly diopside and hedenbergite with a certain amount of johannsenite.Pyroxenoids consist mainly of ferrobustamite,and the end member of amphiboles is dominated by calcium actinolite.Fe and Mg content of epidote is very low.Skarn mineral assemblages show that the skarn of the Bangpu deposit has characteristics of both calcic skarn and manganoan skarn.The skarn of the early stage formed in a strong oxidizing environment,so did the ore-forming magmatic fluid.The discovery of manganoan skam mineral assemblages indicates that the prospecting potential of Ag in the Bangpu polymetallic ore deposit is promising,and this study provides some theoretical support for the next step prospecting work.