大坪超大型金矿床铅和硫同位素组成特征及其地质意义

Lead and Sulfur Isotope Characteristics and Geological Implication of Daping Gold Deposit

云南大坪超大型金矿床是哀牢山金矿带内最具代表性的金矿床之一,矿体赋存于海西期桃家寨闪长岩体内,矿石类型以石英脉型为主,与金伴生的是以黄铁矿、方铅矿为主的各种硫化物。本文对该矿床主成矿阶段石英脉型矿石中方铅矿的铅、硫同位素地球化学特征开展了系统研究,结果表明：大坪金矿床主成矿阶段铅同位素具有较窄的206Pb/204Pb值和相对较高的207Pb/204Pb值及208Pb/204Pb值,但变化范围不大,分布于正常铅范围。通过计算获得相关特征参数,利用铅构造模式图及相关图解综合分析,表明矿石铅为壳幔混合铅;硫同位素组成变化范围为-4.9‰-9.2‰,平均值为3.12‰,偏离陨石硫的范围,而与基性岩类的硫同位素组成非常接近,表明硫主要来源于深部,反映了地幔硫遭受地壳物质混入后的硫同位素组成。该矿床的成矿物质为深部幔源物质混合了壳源物质。

Daping gold deposit,located in the southern Yunnan,is representative gold deposit in Ailao Mountain gold belt.The ore bodies are hosted in Hercynian Taojiazhai diorite body.The ore is mainly quartz vein-type,with a variety of sulfide like,pyrite and galena.The geochemical characters of Pb and S isotope of galena are studied.The quartz-vein-type ores formed in main mineralization stage show that the Pb isotope has a relatively narrow ratio of 206Pb/204Pb and a relatively high ratio of 207Pb/204Pb and ratio of 208Pb/204Pb with a small-group change and normal distributing range of Pb.Interrelated character parameter with calculation is found to analyze the conformation mode of Pb.Pb in the ore is from crust-mantle mixed lead.The composition of sulfur isotope within variation ranges is-4.9‰ to 9.2‰,and average value is 3.12‰,which deviates the scope of aerolitic sulfur but highly approaches the value of basic rocks.Sulfur is mainly from the deep part,while the composition of sulfur isotopes is after S in mantle mixed with substance of the crust.Studies suggest that metallogenic mass of the deposit is from mixture of deep mantle-derived and crust-derived mineral.