湘南江永铅锌矿床成因:来自S、Pb同位素约束

Genesis of the Jiangyong Pb-Zn deposit in southern Hunan:constraints from S-Pb isotopes

江永铅锌矿是湘南的一处大型铅锌矿床,其主矿体矿石硫化物δ^(34)S值变化范围为1.1‰~3.5‰,平均值2.2‰,硫主要来源于壳—幔源混熔岩浆。矿石^(206)Pb/^(204)Pb、^(207)Pb/^(204)Pb、^(208)Pb/^(204)Pb比值分别为18.895~19.01、15.805~15.811、39.297~39.324;花岗闪长岩体岩石^(206)Pb/^(204)Pb、^(207)Pb/^(204)Pb、^(208)Pb/^(204)Pb比值分别为18.67~18.76、15.68~15.75、38.83~39.05;铅同位素构造模式图和△β-△γ成因分类图解揭示,两者铅同位素组成相同,都主要为上地壳铅,是由同一岩浆体系分异形成,可能来源于古老基底岩石。S、Pb同位素示踪江永矿床成矿物质主要来源于壳—幔混熔岩浆,少量来自赋矿地层。湘南江永大型铅锌矿的矿床类型为燕山期岩浆热液充填—交代型。

The Jiangyong lead-zinc mine is a large-scale lead-zinc deposit in southern Hunan Province. Based on the field geological survey,this study carried on S-Pb isotopic anlaysis on ores and the wall rocks of the main orebody and comprehensive comparative with regional similar deposits. The δ^34 S values of the mainorebody range from 1.1 ‰ to 3.5 ‰,with an average value of 2.2 ‰,implying that sulfur is mainly from the crust-mantle mixed magma. The ^206 Pb/^204 Pb,^207 Pb/^204 Pb and^207 Pb/^204 Pb ratio of ore rocks are 18.895 ～ 19.01,15.805 ～ 15.811 and 39.297 ～ 39.324 respectively. The^206 Pb/^204 Pb,^207 Pb/^204 Pb and^207 Pb/^204 Pb ratio of wall rocks are 18.67 ～ 18.76,15.68 ～ 15.75,38.83 ～ 39.05 respectively. Both the tectonic model diagram and △β-△γ genetic classification diagram of lead isotope show that the two types of rocks have the same Pb composition,mainly upper crust Pb,which indicated that the two types of rock originated from the same magma fractionation system and possibly belong to ancient basement rock. Therefore,the ore-forming materials of the Jiangyong deposit mainly derived from crust-mantle mixed magma,while a small amount of material is from the mineralized strata,in terms of both its geological characteristics and its isotope geochemical features.