西藏浦桑果铜铅锌多金属矿床S、Pb同位素组成及对成矿物质来源的示踪
Sulfur and Lead Isotopic Compositions of the Pusangguo CuPbZn Polymetallic Deposit in Tibet: Implications for the Source of Oreforming Material

摘要： 西藏浦桑果铜铅锌多金属矿床位于南冈底斯成矿带火山岩浆弧内，矿区矽卡岩型铜铅锌矿体主要呈透镜状和似层状近东西向赋存于白垩系塔克那组第四岩性段矽卡岩化大理岩中。基于野外地质调查和成矿地质条件，对矿床主要金属硫化物闪锌矿、方铅矿、黄铜矿等的S、Pb同位素特征进行研究，并结合前人数据，综合探讨矿床的成矿物质来源。结果表明，浦桑果矿床矿石金属硫化物的δ34S值介于-24‰~10‰之间，平均值为-040‰，硫同位素频率直方图具明显的塔式分布特征，指示硫可能与岩浆作用有关，硫同位素具岩浆硫特征，主要与闪长玢岩有关。矿石硫化物中206Pb/204Pb变化于18344~18625之间，平均值为18555； 207Pb/204Pb变化于15549~15794之间，平均值为15716； 208Pb/204Pb变化于3812~3934之间，平均值为39044；矿石铅同位素组成稳定，为正常普通铅。结合铅同位素μ值特征(937～982)及铅同位素构造环境演化图投图结果，综合表明浦桑果矿床的矿石铅主要来源于上地壳物质且伴有地幔物质的混染，铅同位素具壳幔混源的特征。
Abstract: The Pusangguo CuPbZn polymetallic deposit is located in the southern Gangdese volcanic magma arc, Tibet. The east to west trending skarn orebodies are bedded or lenticular, which mainly occurred in the skarnized marble of Cretaceous Takena Formation. On the basis of previous data and geological investigation, this study systematically analyses the characteristics of sulfur and lead isotopic compositions of sulfides including sphalerite, galena, chalcopyrite, and pyrite to discuss the source of oreforming materials.The results show that the δ34S values of sulfides range from -24‰ to 10‰, averaging -040‰,with the tower distribution features, indicating that the sources of sulfur have magmaderived sulfur features and is related to the dioritic porphyrite. 206Pb/204Pb ratios of sulfides vary from 18344 to 18625, averaging 18555; 207Pb/204Pb ratios range from 15549 to 15794, averaging 15716; 208Pb/204Pb ratios are between 3812 and 3934,averaging 39044. The lead isotopic compositions are stable and belong to the normal lead. Combining the μ values with the tectonic evolution diagram of lead isotope, it can be concluded that the lead is primarily sourced from the upper crust with minor involvement of mantlederived materials