Research On Geological Features And Genesis Of The Guocheng Gold Field, Jiaodong

Guocheng gold field is situated in the central south of Mu-Ru gold metallogenic belt, controlled by the NE trending Guocheng fault in the south of Muping-Jimo fault zone. Its tectonic position is very unique in that it lies in the intersection of different tectonic units, with Sulu UHP metamorphic belt in the southeast, Jiaolai basin in the southwest and Jiaobei terrane in the northwest. There are four mineralization zones in the ore field, including Tudui mineralization zone, east of Tudui mineralization zone, Shawang mineralization zone and east of Shawang mineralization zone from west to east. It is a gold deposit of sulfide mineralization, apparently different, in mineralization types, from other gold deposits in Jiaodong area.Based on the full understanding and analysis of previous data, geological characteristics of the deposit are further summarized through field geological investigation and indoor research. By analyzing geochemical characteristics of wall rocks, ores and gold-bearing minerals, complemented by data of sulfur isotope, lead isotope and oxygen isotope, ore-forming geological conditions and ore-forming physicochemical conditions are concluded. The source of ore-forming materials and ore-forming fluid is further analyzed, as well as the genesis of the deposit.Study on regional metallogenic background shows, Guocheng gold field, the formation of which is related to the tectonic regime transition in Mesozoic, has a unified geodynamic background with other gold deposits in the Jiaodong area. According to host rocks, deposits can be divided into Tudui-type gold deposits and Shawang-type gold deposits. The former are mainly hosted in marble, Jinshan group, followed by granulite, amphibolite, and so on; the latter are mainly hosted in adamellite, belonging to Muniushan rock body. Orebodies are strictly controlled by faults. The boundary of gold field is controlled by NE trending Guocheng fault in the first level, the distribution of ore mineralization belts controlled by NNE trending fault belts in the second level, and the distribution of ore bodies (veins), which shows echelon type and conjugation type in the profile, controlled by faults in the third level.Pyrite and pyrrhotite that bear gold minerals are mainly magmatic hydrothermal origin, and characteristics of rare earth elements in them reflect differences in the nature of ore-forming fluid. The sulfur of ore comes mainly from surrounding rocks belonging to Jingshan group, with some deep source sulfur added. Lead, a mixture of different end-member components, have deep source characteristics, mainly from mantle. Isotopic characteristics of hydrogen and oxygen reveal that the ore-forming fluid is the mixture of magmatic hydrothermal fluid and meteoric water. Fluid inclusion studies indicate that the ore-forming fluid in the main metallogenic period belongs to H2O-CO2-NaCl-CaCl2 system, in middle-high salinity. The fluid is rich in CO2, which reflects, to a certain extent, that the mineralization is a response to mantle activity.Through comprehensive research, it can be concluded that Guocheng gold field belongs to magmatic hydrothermal gold deposits at middle-high temperature with adding of mantle fluid. The ore field is strictly controlled by fault structures. Mineralization is mainly vein sulfide mineralization and formed by filling of ore-forming fluid. Above all, deposits in the ore field can be protocoled as vein sulfide type gold deposits.