Structural significance of the lead isotopic composition of the Shibaqinghao gold deposit, Central Inner Mongolia

Abstract：There are two types of gold orebody in the Shibaqinghao gold deposit：mylonite ore and quartz vein ore.The Pb isotopic composition for mylonite ore is characterized by lower Pb isotope ratios, with 206Pb/204Pb=16.63 to 17.45, 206Pb/204Pb=15.31 to15.48 and 206Pb/204Pb=36.52 to 38.85, and its lead dynamic evolution curve is very close to the model curve of the mantle lead evolution and consistent with the lead isotopic composition of the typical ductile shear zone gold deposit——the Houshihua gold deposit in the area. These suggest that gold in the mylonite ore might be derived from country rocks, and that the ore is the product of late Paleoproterozoic (2040 Ma) ductile shear metamorphism-deformation. The Pb isotopic composition of quartz vein ore is characterized by higher Pb isotope ratios, with 206Pb/204Pb=18.23 to 19.74, 206Pb/204Pb=15.69 to 15.89 and 206Pb/204Pb=38.64 to 40.13, and its lead dynamic evolution curve is very close to the model curve of the upper crust lead evolution and consistent with the lead isotopic composition of the typical Yangshanian magmatic-hydrothermal gold deposit——the Donghuofang gold deposit in the area, suggesting that it is magmatic-hydrothermal gold mineralization. The Donghuofang gold deposit resulted from overlapping of two mineralizations of different natures. This supports the view proposed by the author that the deposit was controlled by overlapping structure.