A study of the modes of occurrence of silver and gold and the characteristics of silver minerals in the Anji polymetallic deposit of Zhejiang Province

There exists a lead-zinc-copper polymetallic deposit of hydrothermal type in the Anji mining area.The ore samples from prospecting trenches and bore holes were analyzed and tested,and the results indicate that all kinds of ores contain high grade of silver,and hence the silver ore body can be distinguished from other ore bodies.Based on microscopic examination,SEM/EDS and EPMA analysis,the authors found that Cu,Pb and Zn occur respectively in chalcopyrite,galena and sphalerite,and silver may be closely coexistent with Pb-Zn-Cu sulfides.Based on studying tens of typical thin sections by using microscopic examination,SEM/EDS and EPMA,the authors also found that in most lead-zinc and copper ores,gold and silver exist as isomorphism in galena,chalcopyrite,sphalerite and pyrite,with the content of 0.03%～0.57% and 0.02%～3% respectively.In the hydrothermal filling type lead-zinc ores,silver exists mainly in the form of independent silver-bearing minerals,such as Ag-tetrahedrite and polybasite,which carry small amounts of isomorphic gold and occur mainly in galena as micro-inclusions in the subhedral crystal,short prismatic,blade,lath-shaped,dendritic and irregular forms.Actually,single particle sizes of Ag-tetrahedrite and polybasite are generally in the range of 10～60 μm,with only a few grains reaching 100 μm.In addition,the silver mineral aggregates canl be up to 200 μm in size.The silver and gold in the independent silver-bearing minerals can reach 10.98%～69.12% and 0.14%～0.35% respectively.The results obtained show that galena is a very important silver-carrying mineral,and the ores with rich galena are especially likely to contain independent silver-bearing minerals.