Characteristics of sulfur isotope geochemistry of Xitieshan lead-zinc deposit,Qinghai:The mixing of sulfurs from hydrothermal and seawater

Xietieshan lead-zinc deposit is located in the north margin of Qaidam basin,Qinghai Province. It has been recognized as the integrated exhalative sediment (SEDEX) system that includes breccias pipes,local vent and distal vent. The lead-zinc ore-bodies are divided into three types:Unbedded,bedded and a few reformed veins. The study on the sulfur isotope composition of sulfide minerals from different parts of the SEDEX system shows that regular changing of the δ34S values from breccias pipes,local vent to distal vent. For example,results from the analysis of pyrite show that the δ34S value of pyrite of stockwork quartz-albite rock (breccias pipes) is 0.8‰,that of sulfide veins (feeding zone) is 2.95‰,the unbedded ore-body 4.48‰,bedded ore-body 3.25‰,carbon schist 6.26‰,and the reformed vein 2.93‰. The sulfur of stockwork rock (breccias pipes) is of a δ34S value of magmatic resources,and the value of the carbon schist deposit on bedded or marble represents of the reduction of the seawater sulfate. The δ34S value of the ore-body is between the two of them,which suggests that the sulfur of the ore is a mixture of hydrothermal source and seawater. Seawater sulfate may ultimately be the source of sulfur for the Xitieshan deposit probably by bacteria sulfate reduction (BSR). A stratigraphic upward decrease in δ34S was observed,which suggests and the mixing of hydrothermal sulfur with magnitude H2S from onsite reduction of ambient sulfate in the ore forming process.