Geochemical Characteristics And Genesis Of Nanxiaoyao Gold Deposit In Shandong Province,China

The Nanxiaoyao gold deposit locates at the Gongdanshan uplift area in central region of Yishu fault zone,at the eastern edge of the Yishui-Tangtou fault.In this paper,taking Nanxiaoyao gold deposit as the research object,and the geochemical characteristics are used to explore the genesis of gold deposit with gold-bearing sulfides during the ore-forming period etc.Study on the characteristics of trace elements in sulfides,the sulfur is richer than the iron,which means that pyrites are characterized by iron depletions.So it is possible that Fe occurred isomorphism replacement in these pyrites.The S/Fe,Au/Ag and Fe/(S+As)ratio of pyrite indicates that the gold deposit was formed in medium depth and medium-low temperature environment,and the ns/nFe,Au/Ag and Fe/(S+As)values are 1.81?2.27,0.0012?0.2416,0.81-0.89,respectively.As the diagrams of Co-Ni and As-Co-Ni shows,the formation of gold deposit could be closely linked with magmatic activity,and the gold deposit may undergo post-depositional hydrothermal reformation;and the main ore-forming hydrothermal fluids are mainly volcanic and subvolcanic hydrothermal.The proportion of the mantle helium of fluid inclusion in pyrite is 2.01%?2.55%in Nanxiaoyao gold deposit,the He-Ar isotope system of fluid inclusion in pyrite shows that the characteristic of ore-forming fluid is the crust-mantle mixing.The ore-forming fluids may mainly come from the crust,mixed with some mantle fluid and a small amount of meteoric water at the same time.The sulfur isotope values of the sulfide range from-3.2%?to 2.9%?,showing the characteristics of deep source sulfur.The U-Pb age of zircon from ores is 2527±12Ma,which may represent the formation age of Paleoproterozoic basement.In summary,under the tectonic setting of forming a ductile deformation zone in the Jinning period,the Mesozoic melted magma and the volcanic and subvolcanic hydrothermal fluids along the Yishu fault zone,bringing a large volumes of ore-forming materials and ore-forming fluids to the formation of gold deposit,and as the metallogenic conditions changed,the gold was enriched and precipitated in the appropriate structural locations in medium-deep metallogenic environment.