山东沂沭断裂带中段南小尧金矿元素地球化学特征及其地质意义

Elemental Geochemistry Characteristics and Their Geological Significance of Nanxiaoyao Gold Deposit in the Middle of Yishu Fault Zone,Shandong,China

南小尧金矿位于山东沂沭断裂带中段,发育蚀变岩型和石英脉型金矿体。通过对南小尧金矿3种矿石(黄铁绢英岩化绿片岩、黄铁矿化绿泥石化糜棱岩和石英-硫化物脉)及黄铁矿主、微量元素特征分析,探讨其成矿物质与成矿流体特征、构造条件和成矿机制。结果表明:3种矿石整体富集Co、Ni,稀土元素总含量较低,成矿流体来源于深部,Eu异常为弱的负异常向正异常过渡,流体的性质可能发生变化;黄铁矿Au与Ag质量分数之比低于0.5且贫As,成矿流体的温度较高;3种矿石的形成可能与火山活动有关,其中黄铁绢英岩化绿片岩和石英-硫化物脉的形成与火山、次火山热液有关,火山热液可能来自于燕山期的火山活动;矿石原岩可能为沉积岩和偏碱性的中—基性岩浆岩,矿石的成矿物质可能来源于深部地幔。综上所述,南小尧金矿的成矿物质与成矿流体均来自于深部,由于火山-岩浆活动而向上涌入,随着大气降水的注入,成矿环境由弱还原向弱氧化转变,这种转变加速了Au的沉淀,使Au在不同的构造位置富集成矿,形成不同类型的金矿。

Nanxiaoyao gold deposit,is located in the middle of Yishu fault zone,Shandon,develops the altered type and quartz vein type ores.According to the characteristics of major and trace elements of three types of ores（including greenschist with beresitization,mylonite with pyritization and chloritization,and quartz-sulfide vein）and pyrites in Nanxiaoyao gold deposit,the characteristics of metallogenic materials and fluids,tectonic settings and metallogenic mechanism were discussed.The results show that the three types of ores are enriched in Co and Ni,and depleted in REE,indicating that their metallogenic fluids may be all from the deep,and the Eu varies from slightly negative anomaly to positive anomaly,showing that the characteristics of metallogenic fluids may be changed;the ratio of mass fraction of Au to Ag of pyrite is less than0.5,and As is poor,indicating that the temperature of fluid is high;the formation of all ores may be related to volcanism,and the metallogenic fluid of greenschist with beresitization,and quartz-sulfide vein could be from volcanic and subvolcanic activities in Yanshanian;the protoliths of ores may be sedimentary rocks and alkaline intermediate-basic magmatic rocks,and the metallogenic materials of ores may be derived from deep mantle.In conclusion,the metallogenic materials and fluids in Nanxiaoyao gold deposit are all derived from deep;because of the upward with the volcanic-magma activity,the metallogenic environment changes from weak reduction to weak oxidation by blend of meteoric water,enhancing the Au precipitation and forming the distinct gold deposits in different tectonic settings.