The Geological Characteristics And Genesis Research Of Songjiagou Gold Deposit, Muping, Shandong Province

Songjiagou Gold Deposit is located in Muping District, Yantai, Shandong Province. With its tectonic position, it’s located in North China Plate and Yangtze Plate collision zone. More specifically, it lies in the northeastern margin of the Jiaolai basin, which is on the east side of Yi-Mu Fault. It is a large-size gold deposit controlled by fissure zone. The Jiaodong region dynamics environment transformed from NW-SE extruded system to NW-SE extension system in late Mesozoic. Eastern Jiaodong region came into the important metallogenic period.The outcropped strata are of precambrian system, Mesozoic strata and the Quaternary strata. Magmatic rock is common developed in the region, mainly includes the the Mesozoic Queshan medium-fine grained weak gneissic monzonitic granite, dioritic porphyrite and lamprophyre. The analysis of zircon U-Pb dating of the lamprophyre vein in the mining area shows the age of 164.2±4.9Ma. Structure is well developed in the mining area, what is more the ore body is clearly controlled by the steeply tensile fractures and fissure zone, which are the main ore-depositing structure and ore-controlling structure.There are 35 ore bodys in the mining area, the morphology of which mainly are mainly irregular vein, with the overall direction of north east, dips southeastly, and dip angle is 75°～87° with 35°～50° in part. The metal minerals of ore are mainly electrum, native gold and pyrite, followed by rare chalcopyrite, sphalerite, galena, magnetite and so on. Ore textures are mainly idiomorphic-subhedral crystals texture, cataclastic texture and interstitical texture; Structures of ores are mainly dense massive structure, nodular structure, vein structure, disseminated structure, and breccia structure. Type of wall rock alteration is mainly pyritized-phyllite, silicification, carbonatization, etc. The hydrothermal stage can be divided into 4 stages:I. Quartz-pyrite stage, Ⅱ. Quartz-sericite-pyrite stage, Ⅲ. gold-quartz-polymetallic sulfide stage, Ⅳ. Coarse-grained pyrite-carbonatite stage, the Ⅱ and Ⅲ stage are the main mineralization stages.The analysis of fluid inclusions of ore indicates that the main ore-forming fluids are H2O-CO2-NaCl system; which is characteristic of low salinity(5.0-12.0wt%NaCl) and low density(0.64-0.96g/cm3). The metallogenic temperature is concentrated in 200～240℃. The ore-forming pressure is 40-62MPa, fluid inclusions and geological data suggest that the ore-forming process occurred in depths of is 5.01-6.34km. Isotope results about hydrogen and oxygen showed that the ore-forming fluids is mainly the mantle-derived fluid-based and accompanied by a small amount of atmospheric precipitation joined. Isotope studies of sulfur showed that the forming material comes mainly from Jingshan Group and lead isotope is characteristic of deep source.In summary, determine the genetic type of Songjiagou gold deposit belong to mesothermal hydrotherm type gold deposit with mantle fluid involved in.The industrial orebody of Songjiagou gold deposit controled by the extensional dipping fault and dense fissure zone lies in Laiyang Group of Early Cretaceous. Orebody shows obvious segmented enrichment phenomenon that mainly enrich in partial NE fracture position, and the mineralization decreased significantly in partial NEE fracture. In tendency, orebody enrich in the position where the angle turn steeply. The ore-controlling faults of metallogenic period show left-lateral normal fault. Orebody lateral plunging regularity is not obvious, and the ore bodies pitch NE with a pitch angle of 30°～50°. Denudation extent in the northeast edge of Jiaolai Basin decreased gradually from west to east, and Songjiagou gold deposit located in the minimum area. Base of comprehensive analysis of mineralization enrichment regularity and the regional denudation extent, we get that areas of the Songjiagou gold deposit have some potential for prospecting in deep and peripheral areas. Orebody...