Genesis of volcanic-hosted gold deposits in the Sawur gold belt, northern Xinjiang, China: Evidence from REE, stable isotopes, and noble gas isotopes

The Sawur gold belt, the Sawur Mountains, northern Xinjiang, China, is the eastwards extension of the Zarma-Sawur gold-copper belt in Kazakhstan. The Kuoerzhenkuola and Buerkesidai gold deposits are the two largest volcanic-hosted gold deposits in this belt, and are spatially associated with Early Carboniferous calc-alkaline volcanic rocks of the Heishantou Formation. They are hosted in a caldera structure consisting of volcanic rocks and subvolcanic rocks, and controlled by a caldera fracture system superimposed by regional faults. The host rocks are main andesite in the Kuoerzhenkuola deposit, and carbonaceous silty tuff in the Buerkesidai deposit, respectively.Rare earth element (REE) chemistry, stable isotopes (H, O, C, S), radiogenic isotope (Pb), and noble gas isotopes (He and Ar) have been used to discriminate the sources and evolutionary histories of the ore-forming fluid, and to evaluate the genesis in the Kuoerzhenkuola and Buerkesidai volcanic-hosted gold deposits. The ore-forming fluids of the two deposits share the same origin, with δ18O and δD data indicating that the water of ore fluids was derived from magmatic water, diluted by meteoric waters. 3He/4He and 40Ar/39Ar values suggest that the He in the ore fluids consists of a mixture of mantle He with minor components of meteoric water He. δ34S values (0.33 to 2.85‰) show that the sulfur isotope composition of the ore fluids is characterized by mantle sulfur. Lead isotope compositions indicate that the majority of the lead in the ore fluids is mantle-derived, with minor lower crust-derived lead. Whole rock and pyrite REE data show that the volcanic rocks could have been a fertile source for the metals. The mantle-derived component in the ore-forming fluids from the two deposits decreased, and the meteoric water gradually increased from early to late mineralization stages. Carbon and oxygen isotopes suggest that late stage mineralization may have been influenced by limestone. Ar–Ar geochronological data show that mineralization is synchronous or contemporary with volcanic activity. Based on geological and geochemical studies of the two deposits, we suggest that the two volcanic-hosted gold deposits in the Sawur gold belt can be classified as volcanogenic hydrothermal gold deposits.