He-Ar, S, Pb and O isotope geochemistry of the Dabaiyang gold deposit: Implications for the relationship between gold metallogeny and destruction of the North China Craton

Abstract

The Dabaiyang gold deposit is located within the Zhang-Xuan gold mineralized zone, along the northern margin of the North China Craton (NCC). The ore mineralization is hosted within Precambrian metamorphic rocks, and is a typical quartz-vein type gold deposit with minor sulfide mineralization. Here we report He-Ar, S, Pb and O isotopes from this deposit with a view to trace the source of the ore-forming fluids and metals, and to evaluate the relationship among ore-formation, magmatism and craton destruction in the NCC. The ratios of 3He/4He and 40Ar/36Ar of the fluid inclusions in the pyrite of the Dabaiyang ores show a range of 1.4Ra–1.8Ra and 4974.4–15669.5, respectively, with the concentrations of 4He and 40Ar varying from 0.8 to 6.6 (10−7 cm3 STP/g) and 4.3 to 218.1 (10−7 cm3 STP/g), respectively. Our data suggest that mixed mantle and crust derived fluids were involved in the Dabaiyang gold mineralization, with ca. 17.1%–27.6% mantle-derived helium, as computed from crust-mantle mixing model. The δ34S values in the pyrite range from −10.40‰ to −11.90‰, with an average of −10.96‰, suggesting that the sulfur in the ore forming fluids was derived from a mixed-source of the Precambrian metamorphic basement and mantle. The Pb isotopic ratios in the pyrite from the ores show 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb in the range of 16.82 to 17.16, 15.33 to 15.43 and 36.77 to 37.22, respectively, indicating that the ore forming fluids, and by inference, the ore metals, were mainly derived from lower continental crust with minor contribution of mantle. The δ18OH2O values of the fluid inclusions in the gold-bearing quartz veins range from −1.04‰ to 4.36‰, suggesting the dominant role of magmatic water with minor contribution of meteoric water in the ore precipitation. Based on the analytical results of the isotopic compositions obtained in this study, combined with the previously published geochronological and He-Ar/S/Pb/O isotopic data, we suggest that the ore fluids and metals were derived from a mixed source involving contributions from mantle, crust and atmospheric water, and that the ore formation was associated with destruction of the North China Craton.