Geodynamic Model Of Metallogeny Of Haigou Large Gold Deposit, Jilin Province

The Haigou gold deposit is located in a transitional tectonic area between the eastern sector of the Xing'anling-Mongolian Orogentic Belt(XMOB) and the northern margin of the North China Plate, where a famous NE trending Liangjiang Fault crosscuts with the NW trending Qingchaguang-Jinyinbie Fault.In the study area, a large NE trending fault, called Dunhua-Mishan Fault ,is located to the east, about NE Jinan-Songjiang Fault is located in the south,and there are Fu'erhe Fault and Jiapigou Fault which are nearly paralleled with Qingchaguan-Jinyinbie Fault. Exposed formations are mainly Longgang Rock Group and Jiapigou Rock Group of Archean,Jinan group,Seluohe complex and Qingbaikou system of Proterozoic, and Jurassic and Cretaceous of Mesozoic,and Quaternary of Cenozoic; regional magmatic activity is strong, so intrusive rocks of different ages which is developed a wide range include two parts of the late Archean and Mesozoic granitic rocks; volcanic rocks include Mafic-Intermediate Volcanic--sub-volcanic rocks of Mesozoic series and Basalt of Cenozoic; Fracturing structure which is relatively developed can be divided into two systems: the EW fault system of the paleo-asiatic tectonic domain and the NE-NNE fault system of Mesozoic, and each fault system is composed of a number of fault with the same distribution.In the mining area, exposed strata is mainly low-grade metamorphic of Mesoproterozoic (Seluohe Group), and Qingbaikou system of Late Mesoproterozoic , Jurassic and Cretaceous of Mesozoic and Cenozoic partially; exposed intrusive rocks are Late Archean tonalite rocks, Hercynian biotite granite, Yanshanian monzonite-adamellite and pyroxene diorite and diorite porphyry, etc.; the fracture is made up of four groups with NE-NEE, NW,nearly SN and EW, in which NE-NEE trending fault is the main ore-hosting structure. Deposit is composed of a few dozen gold-bearing quartz vein which mainly distributed the NE-NNE-trending fault in Yanshanian monzonite-adamellite. gold-bearing quartz vein are parallel with the distribution at equal interval.In accordance with auriferous quartz veins spatial distribution characteristics, gold-bearing quartz vein of the mining area is divided into three groups, namely No. 28,38,43 group.The mineralization type is sulfid quartz vein,and the main ore minerals are native gold, pyrite, galena, chalcopyrite, sphalerite, etc., and gangue minerals are mainly quartz and calcite. In accordance with formation orders, combination features and relationships of these minerals, mineralization can be divided into four phases: milky white quartz vein stage, gold-smoke gray quartz-pyrite vein stage, gold-polymetallic sulfide stage and calcite stage.The wall-rock alteration are mainly K-feldspar, albitization, pyrite, and sericite, and chlorite, and so on, in the deposit. Gold comprises mainly visible gold and micro gold.In the deposit,the fluid inclusions consists of gas-liquid two-phase mainly and a few the pure gas inclusions,and the size is 5~10μm. According to gas-liquid ratio, inclusions can be divided into 15%～30% and 30%～50% of the two groups, and the shape is rounded,oval-shaped and irregular-shaped. One-component gas-liquid two-phase CO2 inclusions in the early melting temperature mainly concentrated in the-57～-56℃, homogenous temperature is mainly 28～30℃; homogenization temperature of NaCl-H2O fluid inclusions of two-phase is 150℃~350℃, and different temperatures correspond to different stages of mineralization; salinity is 5.41%～11.93% and density is 0.54-0.96g/cm3, so ore-forming fluids is the low-salinity, low-density fluid; calculated mineralized pressure is 54-87MPa, and forming depth is 1-4km; components by laser Raman studies have shown that gas compositions of inclusion is mainly CO2,H2O and CH4.The main ore-forming fluid which is CO2-rich and CO2-CH4-H2O system shows the characteristics of metamorphic fluids.Including to the CL image analysis and LA-ICP-MS U-Pb age of testing of zircon in porphyrite diorite, results showed that zircon in diorite porphyrite include three groups:Ⅰ. Archean (2515±34Ma),Ⅱ.Paleoproterozoic(1815±130Ma),Ⅲ.Mesozoic(131~122Ma).The third group zircon is formation of zircon in crystallization processes of porphyrite diorite, and diorite porphyrite is dike rock which isformed in the end of mineralization, which limited that gold deposits of the ore-forming age is 170~140Ma; through analysis of the first zircon with shear fracture group, combined with regional geological features, I can speculate that mineralized thermal power source of Haigou gold deposits come from tectonic suture zone between Paleo-Asian Ocean tectonic system with the North China platform occurring Jiapigou - Haigou ductile shearing which dued to connecting between New ancient terrane with Xing'anling-Mongolian Orogentic belt after Xing Meng orogenesis. Mineralized fluids resulted in transformation in extrusion and extension. By studying the previous stable isotope data, combined with the characteristics of fluid inclusions, I came to the conclusion that forming fluid of Haigou gold deposits which shows propertiy of reductive fluid is mixed hydrothermal solutions consisted of magma melting of water by the lower crust metamorphic rocks and meteoric water. Mineralized material sources of gold deposit is mainly derived from the lower crust,and a little come from Seluohe Group.Approval of the ore-forming fluids, ore-forming age, mineralized thermal power source and mineralized material sources shows that: the southern Archean terrane collaged to the north of XMOB after the formation of XMOB, which make tectonic suture zone between he Paleo-Asian Ocean tectonic system and the North China platform occur strong ductile shearing along Jiapigou-Haigou, which made the lower crust occur in mobilization and formed ore-bearing fluid. In the rising progress along the fracture, Fluid is mixed by meteoric water and leachied Seluohe Group resulting in obtaining part of ore-forming materials, and ultimately is precipitated in the form of sulfur-hydrogen complex in the NE fault,which formed Haigou gold deposits.Haigou gold deposit which developed in shear zones is continental orogentic gold deposits.