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

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 skarn 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.