Mineralization process of the Kafang tin-copper deposit in the Gejiu district, Yunnan Province: Constraints from fluid inclusion

The Gejiu polymetallic tin ore district, located in Yunnan Province, is the largest tin deposit over the world. The Kafang copper (tin) deposit is one component of it, characterized by enriched copper. There are two main kinds of ore-body in Kafang copper deposit.One is stratiform-like ore-body, and the other is contact ore-body. In this paper we carried out fluid inclusion study and isotope geochemistry analysis of the former kind ore-body, as well as the latter kind with isotope geochemistry analysis. The mineralization in the deposit can be divided into three stages, i.e. quartz-pyrrhotite-chalcopyrite stage ( I ) , quartz-calcite- chalcopyrite-pyrite stage (Ha) and quartz-calcite stage (Mb). The ore-forming fluids of the three stages physical-chemically changed from moderate-high temperature (363.9° C in average) , moderate salinity (20.18% NaCleqv in average) and low density (0.854g/ cm in average) via moderate temperature (283.2° C in average), moderate-low salinity (12.59% NaCleqv in average) and low density (0.863g/cm in average) to low temperature ( 185.Ot in average), low salinity (11.97% NaCleqv in average) and low density (1.001g/cm3 in average). The Laser Raman data of the ore-forming fluid inclusions shows that it is rich of H 2H2O, CH 4 in gas phase, and H 2H2O, CO 3 in liquid phase.Hydrogen isotope analysis and oxygen isotope analysis (δDH2O lies between-98%e ∼ -79%e: δ 18 OH2o lies between -0.82%e ∼ 7.09%e) show that the ore-forming fluid dominated by magmatic water in the early stage, but in late stage, it could be produced by mixing magmatic and meteoric water. The compositions of sulfur isotope show that sulfur of stratiform-like ore-body (δ 34 S lies between -0.86%e ∼ 3.8%e) was derived from Triassic basalt lava.Both Triassic basalt lava and Yanshanian granite provide sulfur for the ore-forming process (δ 34 S lies between -3.2%e ∼6.1%)