ABSTRACT

Sulfur isotope ratios of sulfide minerals from the Akatani, Iide and Waga-Sennin skarn deposits formed in the “Green Tuff” region, fall in a rather broad range from +2.8 to +8.9‰. Estimated formation conditions of ores, that is, high oxygen fugacities and relatively low temperatures and pH, certify the predominance of sulfate sulfur over sulfide sulfur in the ore-forming solutions. Irreversible, fast precipitation of sulfide minerals from such sulfate-dominant solutions is thought to have resulted in insignificant isotopic fractionation between aqueous sulfate and sulfide minerals. The obtained range of isotopic values is almost identical with those for sulfide minerals from other type, vein and kuroko, deposits in the “Green Tuff” region. This regularity of sulfur isotope values for many different type deposits in the region suggests the possibility that ore sulfur was supplied from a common provenance, such as Miocene felsic igneous rocks, without any significant isotopic fractionations in the transportation and precipitation processes.