柴北缘青龙沟金矿床闪长玢岩锆石年代学、黄铁矿原位硫同位素和微量元素特征及找矿启示

Zircon geochronology,in-situ sulfur isotopes,and trace elements of pyrite in diorite porphyrite of Qinglonggou Gold Deposit,Northern Margin of Qaidam,and its implications for prospecting

青龙沟金矿床是柴北缘滩间山金矿田内重要的金矿床之一,矿体主要分布在中元古代万洞沟群含碳白云质大理岩中,其次为侵入地层的闪长玢岩中。但是,一直以来闪长玢岩年代学、源区及金成矿物质来源、金含量变化特征等问题没有得到很好的解决,在一定程度上制约了矿床成矿作用及外围找矿勘查研究。选取青龙沟金矿床含金闪长玢岩,利用LA-ICP-MS对锆石U-Pb年代学和黄铁矿原位硫同位素、微量元素展开研究。研究成果表明:闪长玢岩形成时代为早二叠世(293.0 Ma±1.8 Ma),锆石εHf(t)值为-3.5~4.8,两阶段模式年龄T DM2为912~1375 Ma,源区物质来自中元古代中下地壳,并有幔源物质参与。闪长玢岩中黄铁矿具有低δ^(34) S值、低Au含量、高As含量和高w(Co)/w(Ni)值(δ^(34) S=4.01‰~4.58‰;w(Au)=0.10×10^(-6)~0.49×10^(-6),平均值0.26×10^(-6);w(As)=404.61×10^(-6)~9546.27×10^(-6),平均值5779.62×10^(-6);w(Co)/w(Ni)=3.86~97.37),明显区别于赋矿含碳白云质大理岩中黄铁矿δ^(34) S值、Au含量、As含量和w(Co)/w(Ni)值(δ^(34) S=8.4‰~15.8‰,w(Au)=1.92×10^(-6)~30.28×10^(-6),w(As)=9029.20×10^(-6)~130727.48×10^(-6),w(Co)/w(Ni)=0.11~0.38),表明金成矿物质可能源自早二叠世深部岩浆挥发分或地幔脱气作用,黄铁矿金含量低,对矿床成矿贡献较小,矿床深边部及外围找矿方向仍应以万洞沟群含碳白云质大理岩为主,其次为岩浆岩。

Qinglonggou Gold Deposit is a significant gold deposit in Tanjianshan Goldfield,northern margin of Qaidam.The ore bodies are mainly hosted in Mesoproterozoic carbon-bearing dolomitic marble of the Wandonggou Group,with some found in intrusive diorite porphyrite.However,the diorite porphyrite s chronology,source,origin of gold-bearing materials,and gold content variation have not been adequately addressed,limiting the understanding of mineralization and the potential for further exploration.Zircon U-Pb geochronology and in-situ sulfur isotopes and trace elements in pyrite from gold-bearing diorite porphyrite were analyzed using LA-ICP-MS.The findings reveal that the diorite porphyrite formed in the Early Permian(293.0 Ma±1.8 Ma),with zirconεHf(t)values ranging from-3.5 to 4.8 and a two-stage model age(T DM2)between 912 and 1375 Ma,indicating material from the Mesoproterozoic middle-lower crust with mantle contributions.Pyrite in the diorite porphyrite exhibits lowδ^(34) S values,low Au content,high As content,and elevated w(Co)/w(Ni)ratios(δ^(34) S=4.01‰-4.58‰;w(Au)=0.10×10^(-6)-0.49×10^(-6),averaging 0.26×10^(-6);w(As)=404.61×10^(-6)-9546.27×10^(-6),averaging 5779.62×10^(-6);w(Co)/w(Ni)=3.86-97.37),differing significantly from theδ^(34) S,Au content,As content,and w(Co)/w(Ni)values of pyrite in the carbon-bearing dolomitic marble host rock(δ^(34) S=8.4‰-15.8‰,w(Au)=1.92×10^(-6)-30.28×10^(-6),w(As)=9029.20×10^(-6)-130727.48×10^(-6),w(Co)/w(Ni)=0.11-0.38).This suggests that gold mineralization likely originated from deep-seated Early Permian magma or mantle degassing.The low gold content in pyrite suggests a limited contribution to mineralization,with exploration efforts focusing primarily on gold bodies within carbon-bearing dolomitic marble,followed by magmatic rocks.