秦岭凤太矿集区喷流沉积型铅锌矿床S、Pb同位素地球化学特征

Geochemistry of Sulfur and Lead Isotopic Compositions of Sedex Lead-zinc Deposits in Fengtai Mineral Cluster Region of Qinling Mountains

凤太矿集区位于秦岭泥盆系铅锌等多金属成矿带的中段，铅锌矿床主要产于中泥盆统古道岭组和上泥盆统星红铺组之间的硅质岩中。对区内三个典型铅锌矿床中S、Pb同位素组成研究表明，铅硐山、八方山、银母寺3个铅锌矿床金属硫化物的δ34S值变化范围较小，均不超过10‰。区内硫化物的δ34S值总体变化于4.3‰-13.2‰，指示S主要来自海水硫酸盐的还原作用。3个矿床矿石矿物的Pb同位素中206Pb/204Pb变化于17.775-18.180，207Pb/204Pb变化于15.457-15.805，208Pb/204Pb变化于37.977-38.670。各个矿床之间Pb同位素组成均有较大的重叠，暗示3个铅锌矿床具有相似的铅源。通过Pb同位素构造模式图解以及Δβ-Δγ分类图解分析表明，矿石铅来源于早古生代中期到末期扬子板块向华北板块之下俯冲以及晚古生代扬子板块、秦岭微板块向华北板块俯冲的历程中。

Fengtai mineral cluster region is located in the middle of Qinling Devonian lead and zinc polymetallic metallogenic belt. Lead-zinc deposits are mainly located in the siliceous rocks between Gudaoling group of the Upper Devonian and Xinghongpu group of the Middle Devonian. The analysis of S and Pb isotopic compositions of ore minerals in three typical ore deposits indicates that δ34S values of metal sulfide range no more than 10‰ in Qiandongshan, Bafangshan and Yinmusi lead-zinc deposits. The δ34S values of sulfides in the region range from 4.3‰ to 13.2‰, indicating that sulfur mainly came from seawater sulfate reduction. Among the lead isotope of three deposits, 206Pb/204Pb varies from 17.775 to 18.180, 207Pb/204Pb varies from 15.457 to 15.805, and 208Pb/204Pb varies from 37.977 to 38.670. Pb isotopic compositions have a large overlap, suggesting that the three lead-zinc deposits have similar sources of lead. The analysis of structure model diagram and Δβ-Δγ diagram of Pb isotope shows that lead came from the process that Yangtze plate subducted to North China plate in the middle of Early Paleozoic and Qinling microplate subducted to North China plate in the late Paleozoic.