The Study Of The Geological Characteristics And Enrichment Regularities Of Mineralization Of Pengjiakuang Deposit In Rushan County, Shandong Province

Pengjiakuang Gold Deposit is located in Rushan County of Shandong Province, With its tectonic position, it’s between the Taocun-Jimo fracture and Wuji-Haiyang fracture in the eastern of Jiaodong, located in the northeastern margin of the Jiaolai basin. It is large gold deposit controlled by the detachment fault in the Muping-Rushan metallogenic belt. The late Mesozoic, Jiaodong region dynamics environment transformed from NW-SE to NW-SE to squeeze into the extension system, the surface of the earth formed depression by extension-detachment, the development to the queshan metamorphic core complex as the main body of the complex network structure, eastern jiaodong region came into the important metallogenic period.The main outdoor layers are the paleoproterozoic Jingshan group metamorphic rocks, Mesozoic Laiyang group conglomerate and Cenozoic quaternary strata. The magmatic rocks are well developed, and mainly be the Mesozoic Queshan monzonitic granite, diorite porphyrite and diorite. The analysis of zircon U-Pb dating of the coarse and fine grained diorite vein in the mining area which were formed before metallogenic period shows the age of 122.9±3.0 Ma and 123.9±3.8 Ma. And the mining structure developed, there are mainly the Queshan metamorphic core complex and Yazi fracture, detachment fault belt around the metamorphic core complex with the circular distribution. The rich ore surrounding rock is Jingshan group. The ore body are clearly controlled by the detachment fault of metamorphic core complex and its upper plate of tensile fracture, the largest fractures are the main basis of ore and ore controlling structures.Within the mining area 14 ore bodys are delineated, are mainly vein, overall course in nearly EW, lean to S, dip Angle is 5 ～ 55. Ore types are mainly pyritization marble qualitative tectonic breccia type, pyritization felsic and pyritization tectonic breccia type. The metal minerals of ore are mainly native gold silver, gold and pyrite followed by sphalerite, galena, chalcopyrite, bornite and so on. Ore structure are mainly cataclastic structure, porphyroclastic structure, idiomorphic-subhedral crystals structure; Ore tectonic with disseminated tectonic, breccia tectonic and dense disseminated tectonic. Wall rock alteration types have mainly potassium feldspathization, Sericitization, silicide and carbonatization, etc., The gold mineralization is closely related to silicification and sericitization.Fluid inclusion study of quartz indicates that the main mineralization fluid is the NaCl-H2O-CO2 system with the characteristics of low salinity (4.0～9.0wt%NaCl) and low density (0.60～0.95g/cm3). The metallogenic temperature is 280-340℃ and the forming pressure is 58.4～91.6MPa with the forming depth is 6.13～7.87km. The carbon hydrogen and oxygen isotope study indicates that the ore-forming fluid is given priority to water of mantle source, with a small amount of meteoric water. Lead, sulfur isotope research shows that the sulfur part from jingshan formation, there may be the mixture of mantle source material. The lead elements mainly comes from the upper mantle.Sulfur, lead, carbon,helium stable isotope studies show that the mineral is mainly derived from upper mantle or lower crust, and some may come from Jingshan Group. Finaily we determine the genetic type of Pengjiakuang gold deposit is mesothermal hydrotherm type gold deposit with mantle source liquid which is controlled by detachment fault system.The industrial orebody of Pengjiakuang gold deposit is strictly controlled by a series of detachment fault belts and the hanging wall brittle fractures. The ore bodies have the characteristics with zoning and piecewise enrichment in the trend. Vertically, the orebody mainly enriched in detachment fault zone and the upper plate of locally brittle fault zone by the abrupt change slowly, in the hanging wall brittle fault zone the ore body is smaller, while orebody has obvious thickening larger trend in detachment fault belt. The ore body has the disciplinarian of SW lateral extensive with a pitch angle of about 40～45 degree.Combining with the analysis of the space changing rule of ore-controlling tectonic belt, Segmented enrichment regularity, Plunging rule and the mechanisms of industrial orebody spatial orientation, on the basis of mineralization enrichment regularity, we forecast the three favorable target areas in the deep mining area and the periphery:(1) at the deep mining area south west of Pengjiakaung and the location of the detachment fault dip angle significantly slow as the favorable targets for hydrocarbon prospecting; (2) on the intersection part of east side detachment faults of Pengjiakuang mining area and Yazi fractures as the favorable targets for hydrocarbon prospecting; (3) on the west side of the Pengjiakuang mining area detachment fault belt is covered by quaternary, the contact zone of Jingshan group and Niushan rock mass, especially the development zones of tectonic breccia are favorable target area for prospecting.