Lead Isotopic Composition and Lead Source in the Bainiuchang Ag-polymetallic Deposit, Yunnan Province, China

TheBainiuchang deposit in Yunnan Province, China, is located geographically between theGejiu ore field and the Dulong ore field. In addition to the >7000 t Ag reserves, the deposit also boasts oflarge-scale Pb, Zn and Sn reserves with a lot of dispersed elements (In, Cd, Ge, Ga, etc.). We havedetermined systematically the Pb isotope composition of the deposit. The Pb isotope ratios of the oresthat are of sea-floor exhalative sedimentary origin in the northwest of the mining district, are206Pb/204Pb = 17.758-18.537, 207Pb/204Pb = 15.175-15.862 and 204Pb/204Pb = 37.289-39.424, while those ofores that are of magmatic hydrothermal superimposition origin in the southeast of the mining district,are 206Pb/204Pb=17.264-18.359, 207Pb/204Pb = 14.843-15.683 and 208Ph/204Pb = 36.481-38.838,respectively. In terms of the Pb isotope composition of feldspar in magmatic rocks or magmatic whole-rock samples from the mining district, we have determined the Pb isotope composition and acquiredthe Pb isotope ratios as: 206Pb/204Pb = 18.224-18.700, 207Pb/204Pb = 15.595-15.797 and 208Pb/204Pb =38.193-39.608. Then, in the fight of the Pb isotope composition of metamorphic rock samples from theProterozoic basement exposed in the Dulong ore field, we have determined the Pb isotope compositionand obtained the isotope ratios as: 206Pb/204Pb=18.434-19.119, 207Pb/204Pb = 15.644-15.693, and208Pb/204Pb - 38.514-38.832. nd the Pb isotope ratios of Cambrian sedimentary rocks, which areexposed in the Bainiuchang mining district, are 206Pb/204Pb = 18.307-19.206, 207Pb/204Pb =15.622-15.809, and 208Pb/204Pb = 38.436-39.932. By comparing the two types of ores with respect totheir Pb isotope compositions, it is indicated that lead in the Bainiuchang deposit was derived largelyfrom the lower-crust granulite which is earlier than Neoproterozoic in age, but the Yanshanianmagmatic hydrothermal fluids probably provided a part of ore-forming elements such as Sn for the oreblocks in the south of the mining district.