Geological features of the Xiasai silver-polymetallic deposit in West Sichuan,China

The Xiasai silver-polymetallic deposit lies in the exometamorphic zone of the late Yanshanian granite body in the Yidun island arc orogenic belt in West Sichuan.It is a super-large hydrothermal vein type silver-polymetallic deposit.A research on the geologic characteristics,ore mineralogy,fluid inclusions and stable isotope geochemistry indicates that the deposit occurs in the sandstone,siltstone and slate of the Upper Triassic Quegasi Formation and suffered epimetamorphism.The orebodies are mainly veinlike,lenticular and disseminated and controlled strictly by fractured zones.The ore minerals are mainly pyrite,galena,sphalerite,chalcopyrite,Ag sulfosalts and sulfosalts etc.The vein minerals are mainly quartz,calcite,sericitolite and chlorite etc.The ore-forming process can be divided into three phases consisting of four stages.The integrated geological,microelement and isotopic geochemical studies show that silver and other metal elements mainly come from the country rock and granite.The origin of the deposit is genetically an epithermal hydrothermal filling and metasomatic deposit formed by the late magmatic hydrothermal ore-forming fluids.Based on the geological features,the ore-forming regularities and prospecting target for the deposit in this region are discussed.The discovery of the Xiasai silver-polymetallic deposit provides a new idea and an important foundation for prospecting for the similar type of deposits in West Sichuan and the Qinghai-Xizang(Tibet) plateau.