大兴安岭中段闹牛山铜金矿床的硫铅同位素地球化学特征与成矿物质来源

摘要

通过对闹牛山铜金矿床硫、铅同位素的系统研究,探讨了其成矿物质的来源.同位素测试结果表明,δ(34S)=2.0×10-3～3.5×10-3,均为正值,呈塔式分布,峰值出现在2.0×10-3～2.5×10-3,具幔源硫和陨石硫的特征;矿石铅206 pb/204 Pb=18.169～18.510,207 pb/204 Pb=15.484～15.646,2088pb204 Pb=37.877～38.431,铅同位素组成较为均一,具正常铅的组成特点;且μ值和w值偏低,表明矿石铅源区富钍亏铀.在Zartman铅同位素构造模式图解中,投点主要落于地幔与造山带之间和造山带演化线附近;在ΔβΔγ成因分类图解上,12件测试样品落入上地壳与地幔混合的俯冲带岩浆作用成因铅同位素源区,4件样品落入地幔源铅的范围内,但与两源区界限临近.由此认为,闹牛山铜金矿床的成矿物质主要来源于地幔,并有上地壳物质的混染,这种认识对研究大兴安岭中南段铜多金属矿带的成矿规律具有指导意义.%S,Pb isotope of Naoniushan Cu-Au deposit is systematically studied to explore its ore material source.The ~4S values are positive,2.0× 10-3 ～3.5 × 10-3 distributed in tower shape with peak values of 2.0 × 10-3 ～2.5 × 10-3 that is characteristic of the mantle-derived sulfur and meteorite sulfur.Value of 206pb/204pb varies in the range of 18.169～18.510;207pb/204pb 15.484～15.646;208Pb/204pb 37.877～ 38.431 show more homogeneous Pb isotopic composition that is characteristic of normal Pb andμ,ω values are lower reflecting that the source area of the ore is rich in Th and depleted in U.In the Pb isotope tectonic discriminant diagram of Zartman main points of the values fall between the mantle and orogenic belt and near the evolution line of the orogenic bein Δβ-Δγ genetic classification diagram,values of 12 samples fall in the Pb isotope source area of subduction zone where upper crust and mantle material-mixed magma occur.;values of 4 samples in Pb source area of mantle but the fall points adjacent to the boundary of the subduction and the mantle source area.Therefore,it is believed that the main source of the deposit is the mantle and incorporated with the crustal material contamination.This is significance of guiding the study of metallogenic regularity of copper-polymetallic ore deposits in middle-south part of the Da Hinggan Mountains ore belt.