陕西旬阳地区小河金矿硫铅同位素组成及地质意义

Sulfur and Lead Isotope Compositions of the Xiaohe Gold Deposit at Xunyang, Shaanxi Province, and Its Geological Significance

小河金矿是近年来在南秦岭中带发现的中型金矿床,矿石类型为微细浸染型,矿床受地层和构造双重控制。在野外工作基础上,根据矿物组合及穿插关系划分了4个成矿阶段:Ⅰ,成矿早期少硫化物石英脉成矿阶段;Ⅱ,石英脉、黄铁矿、毒砂成矿主阶段;Ⅲ,石英脉-多金属硫化物成矿主阶段;Ⅳ,方解石、石英脉成矿晚阶段。其中Ⅱ、Ⅲ阶段是主要金矿化阶段。不同阶段样品的原位硫同位素结果显示:成矿早阶段石英脉期的黄铁矿δ^(34)S值为20.80‰~25.77‰,均值为23.59‰;主成矿期II阶段中黄铁矿、毒砂δ^(34)S值为15.46‰~19.12‰,均值为17.5‰;主成矿期Ⅲ阶段中方铅矿、闪锌矿δ^(34)S值为11.35‰~16.78‰,均值为13.88‰。硫同位素特征指示硫以沉积硫为主,成矿过程可能存在低δ^(34)S值热液的持续加入。金属硫化物Pb同位素测试结果显示^(206)Pb/^(204)Pb为17.8821~18.3674,^(207)Pb/^(204)Pb为15.6140~15.6741,^(208)Pb/^(204)Pb为38.0163~38.9342,指示小河金矿铅主要源于地壳,同时伴随幔源铅的混入。综合矿床地质特征及硫、铅同位素地球化学特征,认为小河金矿成矿过程可能存在流体混合作用。

The Xiaohe is a medium⁃sized gold deposit discovered in the central belt of the South Qinling Orogen in recent years.The ores are fine⁃disseminated,and the orebodies are controlled by both strata and structures.Based on field work,four metallogenic stages are divided according to mineral assemblages and crosscutting relationships:Ⅰ.Quartz veins with little sulfide in early⁃ore⁃stage;Ⅱ.Quartz veins with main⁃ore⁃stage pyrite and arsenopyrite in main mineralization stage;Ⅲ.Quartz veins with main⁃ore⁃stage polymetallic sulfides;Ⅳ.Late⁃ore⁃stage calcite and quartz veins.StageⅡandⅢare the main gold mineralization stages.In situ sulfur isotope analysis show that theδ^(34)S value of stageⅠpyrite=20.80‰-25.77‰(avg.23.59‰),stageⅡpyrite and arsenopyrite=15.46‰-19.12‰(avg.17.5‰),stageⅢgalena and sphalerite=11.35‰-16.78‰(avg.13.88‰).This indicates that the sulfur is mainly sedimentary⁃sourced,and there is continuous addition of low⁃δ^(34)S hydrothermal fluid during the ore⁃forming process.The sulfide Pb isotope analysis yielded^(206)Pb/^(204)Pb=17.882,1-18.367,4,^(207)Pb/^(204)Pb=15.614,0-15.674,1,and^(208)Pb/^(204)Pb=38.016,3-38.934,2,indicating that the lead was derived mainly from the crust with certain mantle input.Based on the deposit geological and S and Pb isotope characteristics,we suggest that fluid mixing occurred in the Xiaohe gold mineralization.