Origin of ore-forming fluid in the Piaotang tungsten deposit in Jiangxi Province: Evidence from helium and argon isotopes

The Piaotang tungsten deposit in Jiangxi Province is one of the most important tungsten deposits in the South China Tungsten Metallogenic Province. In this study, we selected wolframite and chalcopyrite from the main mineralizing stage of the Piaotang tungsten deposit, and analyzed the helium and argon isotopic compositions in fluid inclusions of these minerals. The results show a 3He/4He ratios of 0.17 to 0.86 R/Ra, which fall within the range between continental crust (0.01–0.05 R/Ra) and air-saturated water (1 R/Ra), but are significantly lower than those of the normal mantle (6–9 R/Ra). Their 40Ar/36Ar ratios are between 354.5 and 590.7, which are slightly higher than the air-saturated water (295.5). Along with the other geochemical observation such as the lithium enrichments in the ore bodies and the ore-related granites, we suggest that the ore-forming fluid in the Piaotang tungsten deposit was mainly derived from crustal fluid. It may have mixed with some amounts of air-saturated water, but there was no considerable involvement of mantle-derived fluid.