Stable isotope geochemistry of three typical gold deposits in the West Qinling

Stable isotope study indicates that theδ 34 S values of the Baguamiao gold deposit,Liba gold deposit and Xiaogouli gold deposit have a narrower range than those of sediment-hosted deposits and a wider range than those of magmatic or volcanic-hosted deposits.The sulfur was derived from mixing of the sulfur source of seawater sulfate reduction and the deep magmatic sulfur source.Theδ 18 O andδD values of fluid inclusions fall in the overlapped,transitional field of magmatic water and meteoric water but are closer to the magmatic water field and show more pronounced isotopic features of magmatic water.The 3 He/ 4 He ratio of Au-bearing quartz veins is higher than that(n×10 -8 )of the crust and lower than that(n×10 -5 )of the mantle,implying a crust-mantle mixing source for He.The aforesaid isotope geochemical evidence indicates that there is a certain genetic relation between gold mineralization and magmatism.Magmatic rocks are spatially closely related to gold deposits.Dikes are well developed in the area.They act as the hanging walls and footwalls.The spots or stains in host rocks are thermometamorphic minerals and hydrothermal alteration minerals such as pyrite,pyrrhotite,arsenopyrite,chlorite,quartz,sericite,biotite,cordierite,andalusite,tourmaline and carbonates,indicating that granites provided thermodynamic forcing for mineralization.Based on the stable isotope geochemistry of the Baguamiao,Liba and Xiaogouli gold deposits,combined with the metallogenic environment and regional metallogenic characteristics,the authors suggest that gold deposits in the Fengtai-Xicheng-Limin area are notably different from finely disseminated(Carlin type)gold deposits in that the former are genetically similar to magmatic hydrothermal deposits.