Geological characteristics and occurrence state of silver in the Tongkeng Ag-Zn polymetallic deposit in Dachang,Guangxi
The Tongkeng deposit,situated at the northeastern edge of the Youjiang Basin,constitutes an important part of the Dachang ore field.In recent years,multiple Ag-Zn polymetallic ore(mineralization)bodies have been discovered within the mining area.Nevertheless,the understanding of the occurrence state of silver and the enrichment and mineralization regularity of silver-polymetallic deposits remains extremely limited.Through field investigations and mineralogical research,the Tongkeng silver-zinc deposit is divided into four stages:the cassiterite-quartz stage(Ⅰ),the cassiterite-sulfide stage(Ⅱ),the silver-bearing-galena stage(Ⅲ),and the quartz-calcite stage(Ⅳ).It is determined that silver mineralization primarily occurs in the silver-bearing-galena stage.By utilizing analysis methods such as BSE-EDS and EPMA,in-depth studies are carried out on the characteristics of ore minerals and the occurrence state of silver.This enables the exploration of the output characteristics and enrichment regularity of silver and the analysis of the key factors restricting the output and enrichment of silver.The results indicate that in the Tongkeng Ag-Zn deposit,silver is mainly visible silver(>1 μm),and there is a small amount of invisible silver(<1 μm).The visible silver is mainly composed of diaphorite and owyheeite.Diaphorite is distributed in galena in the form of inclusions at the middle section of 405.At the middle section of 455,it is distributed in galena in the forms of inclusions,bone needle-like,and orthogonal grid-like,or occurs irregularly in the gaps and edges of galena.Owyheeite only occurs at the edges and gaps of galena at the middle section of 455.Invisible silver is mainly present in galena and some tin-bearing sulfosalts in the form of isomorphism or submicroscopic inclusions.As an important silver-bearing mineral,both Cu+and Sb3+have an impact on the entry of Ag+into galena.Cu+will combine with Ag+and precipitate in early tetrahedrite rather than in galena.Sb enables Ag to enter the galena lattice through the equation Ag++Sb3+=2Pb2+,thus forming silver-bearing sulfosalts in the late stage of mineralization.
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