New understanding on lead isotopic compositions and lead source of the Bainiuchang polymetallic deposit,southeast Yunnan,China

The Bainiuchang deposit,located at the central tin-polymetallic ore belt of southeast Yunnan,is associated with large scale Ag,Pb,Zn reserves.However,the genesis of the deposit is controversial.With early Pb isotopic data of ore minerals from the Bainiuchang deposit,former researchers concluded that lead was mainly derived from the leaching of basement rocks,and the deposit was formed through two mineralization stages,i.e.,hydrothermal sedimentation stage and magmatic hydrothermal metallogenetics stage.Lead isotopic composition of the Bainiuchang deposit was systematically studied with the latest lead isotopic data in this study.The Pb isotope ratios of ore minerals from the Bainiuchang deposit are 206 Pb/ 204 Pb = 17.264–18.537,207 Pb/ 204 Pb = 14.843–15.862,208 Pb/ 204 Pb = 38.481–39.424.As for the Pb isotopic composition of feldspar of monzogranite from the Bozhushangranite rocks,the ratios are 206 Pb/ 204 Pb = 18.301–18.387,207 Pb/ 204 Pb = 15.611–15.67,208 Pb/ 204 Pb = 38.677–38.904,while those of ore minerals from contact zone type deposits(ore spots) of the Bozhushan granite rocks are 206 Pb/ 204 Pb = 18.302–18.417,207 Pb/ 204 Pb = 15.603–15.692,208 Pb/ 204 Pb = 38.596–38.868.The Pb isotope ratios of the samples from regional strata and drilling of mining strata are 206 Pb/ 204 Pb = 18.307–19.206,207 Pb/ 204 Pb = 15.622–15.809,208 Pb/ 204 Pb = 38.436–39.932.The orebodies have lead isotopic compositions similar to those of feldspar in granites,but are different from those of strata samples.Therefore,lead in the Bainiuchang deposit was mainly derived from magmatism,but may be contaminated slightly by strata in the process of magma intrusion.Based on geological characteristics and recently geochemistry and chronology data,sedimentary mineralization is not the main process in the Bainiuchang deposit,and magmatism is the key factor for mineralization.