Helium and argon isotope trace in ore-forming fluid of Sawuer gold belt in Xinjiang,China

The helium and argon isotope compositions of fluid inclusions hosted in pyrite have been measured from Kuoerzhenkuola and Buerkesidai gold deposits in Sawuer gold belt, northern Xinjiang. The results show that fluid inclusion 3He/4He ratios are 0.64 Ra-4.25 Ra and 1.16 Ra-9.48 /Ra, 40Ar/36Ar ratios are 282-359 and 312-525 for Kuoerzhenkuola and Buerkesidai gold deposits respectively. The ore-forming fluids of two deposits possessed the same source and derived mainly from mantle beneath the island arc (including oceanic crust and oceanic sediments by sub duction of oceanic plate). They were diluted by incorporating meteoric water to form a mixture of mantle- and partial meteoric water-derived fluid. The ore-forming fluids of two deposits are of the same evolutionary histories. From the early to the late mineralization stages, the ratios of meteoric water/mantle- derived fluid in ore-forming fluid increased gradually. Based on these results and detailed geological and geochemical studies on the two deposits, it is proposed that the geneses of the two gold deposits are the same, being volcanogenic late-stage hydrothermal gold deposits occurring in the same volcanic apparatus.