Ore-Forming Material Sources Of Dashui Gold-Field,West Qinling Belt,China

The Dashui gold-field is located at the western margin of the Mianlue suture zone of the west Qinling mountains.It belongs to the central gold metallogenic belt?the Bailongjiang metallogenic belt?of west Qinling and consists of three gold deposits,Ge'erke,Gongbei and Ge'ertuo.The gold ore bodies are mainly buried in the triassic crystalline limestone with shallow green schist facies metamorphism,situated in second-order structures within geometrical complexities and major jogs along the crustal-scale sinistral Mianlue Suture The deposits in the Dashui gold-field are deeply weathered to depths of up to 400 m,with secondary Fe-oxides having replaced pyrite and other sulfides.The mineral symbiosis can be divided into four stages:?.Strawberry pyrite of diagenetic stage Py₀,with lower Fe and S total amount and higher Bi and As.?-1.Early metallogenic stage pyrite Py₁,which symbiotic with quartz and calcite,accompanied by a small amount of chalcopyrite,galena and arsenopyrite,with higher Fe and S total amount and lower trace elements.?-2.Marcasite of late metallogenic stage Mrc₂,which also symbiotic with quartz and calcite,with higher Fe and S total amount and lower trace elements than Py₁.?.The supergene oxidation stage hematite Hem,related to natural gold.The content of trace elements in hematite shows the inheritance of metallogenic stage sulfide.Synthetically analysis of the published S isotopic composition of sulfides shows Py₀ has a?³⁴S?9.93‰S isotope value,which is lower than S isotopic composition of triassic sea water(?³⁴S is from 11‰to 13‰),but is similar with the theoretical value of sulfide which from sediments formed at the end of closed Mianlue Ocean's evolution.The?³⁴S value of Py₁ and Mrc₂ are very concentrated at about 1.63‰,which shows intense homogenization of sulfur source?s?in ore-forming fluid.Au,S and other metallogenic materials may be derived from metamorphic rocks at the deep greenschist-amphibolite facies metamorphic interface.We'd like to classified the deposits of Dashui gold-field as deep oxidized epizonal orogenic gold deposit.