ABSTRACT

Sulfur isotopic compositions of sulfide minerals from mesothermal fissure-filling ore deposits of the Taishu mine have been investigated. The δ³⁴S values of 65 sulfide samples range from +2.7 to +6.4 permil, giving an average of +4.4 permil. Sulfide minerals exhibit a decreasing trend of δ³⁴S values: sphalerite > pyrrhotite > galena. Sulfur isotope temperatures estimated from sulfur isotopic fractionation between sphalerite and galena are 300° to 350°C, which agree with the maximum value of fluid inclusion temperature for quartz. From sulfur isotopic evidences and chemical equilibrium concept of ore deposition, it is suggested that the chemical condition of ore-forming fluid was restricted to low fO₂ and neutrality. The mean δ³⁴S value of sulfide minerals for each vein was found to increase from the early to the late vein. This progressive ³⁴S enrichment is presumably due to the pH change in ore-forming fluid during ore deposition.