Metallogenic Epoch And Ore Genesis Of Daxigou Gold Deposit According In Fengning Area, Northern Hebei Province

Located in the middle section of the northern margin of the North China Craton and the Inner Mongolia axis, Daxigou gold deposit is a newly descoveried deposit in the north section of the Hebei province. Based on collecting and restuding the results of previous studies and combined with field geological survey and detailed indoor research work, this research has analyzed the geological background and characteristics of the Daxigou gold deposit,discussed the geochemical and isotopic geochronology features of the main intrusions and the metallogenic chronology, finally summed up the genesis of the deposit. The main understanding made by this paper is as follows:1.The gold mineralization of Daxigou gold deposit occurs in Proterozoic porphyritic granodiorite as veins, stratoid layer and stratiform, and obviously controlled by tectonic fracture zone. The gold mineralization have a close spatial relationship with granitoid intrusions.2.The porphyritic granodiorite has similar geochemical characteristics with the S-type granites as well as the fine-medium grained granite and the granite porphyry are same as the A-type granite. The porphyritic granodiorite are the product of the collisional orogeny, whereas the the fine-medium grained granite and granite porphyry are formed in the crustal stretching and thinning environment in the anorogenic period. It’s worth noting that the granite porphyry and the porphyritic granodiorite has similar trace element characteristics, so that these intrusions may have some contact on the material sources and evolution course.3.The U-Pb isotopic dating analysis showes that, the porphyritic granite has the zircon crystallization age of(1858±12)Ma, the fine-medium grained granite is(1829±14)Ma, the alteration gabbro is(1807±18)Ma, all of these intrusions are the product of the Paleoproterozoic tectonic magmatic activities.The potassic granite and rhyolite belongs to the product of the Yanshanian tectonic magmatic activities, their zircon crystallization age are respectively(135~136)Ma and(133.8±1.0)Ma.4.The Re-Os isotopic dating analysis of the pyrite formed in main metallogenic period showes that, the Daxigou gold deposit gold mineralization occurred mainly at(283±20)Ma, belonging to the Hercynian tectono magmatism and related fluid activity.5.The crustal stretching and lithosphere thinning effect after impact during the late Paleozoic produced a large amount of alkaline magma. The magma may contaminated by old rocks during their ascending process, and finally crystalled and separated ore-rich fluid, the fluid transported along NE and implanted into the structure fracture zone. With the changes of the physical and chemical conditions, the gold and other mineral were finally unloading.6. The geological background and characteristics of the Daxigou, Xincheng and Jiaojia gold deposits are very similar, all of them are belonging to mesothermal vein-type gold deposit.7.The Early Permian in Hercynian epoch is an important period of tectono-magmatic activities and related gold deposits formation in the northern margin of the North China Craton, the granitoid intrusions of this period may be the favorable exploration target.