Abstract: The Baiyangping copper-silver polymetallic deposit in Lanping, Yunnan occurs dominantly in the quartz sandstones and siltstones from the Lower Cretaceous Jingxing Formation. The lead isotopic compositions of the ores from the deposit are similar to those of the sandstones from the Formation, implying that the crust-derived matter seems to have been involved in mineralization. The Zartman diagram and △γ-△β plot show that the ore lead has a mixed crust-mantle origin, with the μ values ranging between 9.43 and 9.65 and the Th/U ratios between 3.72 and 3.87. The sulfur in the ore deposit is derived from the deep-seated mantle sulfur mixed by the crustal sulfur. The mineralization of the copper-silver deposit took place in an open system, and the ore-forming material consists of the deep-seated mantle-derived material mixed by the crust-derived material.