The Genesis Of Mogou Gold Deposit In Songxian,henan Province

Mogou gold deposit is located in Xiong'ershan-Waifangshan district,in the southern margin of North China Craton,which is the second largest ore-forming province for gold mineralization in China.Based on field work and analysis and previous literatures for the Mogou gold deposit,this paper focuses on the geological characteristics,C-H-O-S stable isotopes and fluid inclusions.We discuss the geological characteristics,source and evolution of the ore-forming fluid and ore-forming material,ore genesis and metallogenic mechanism.Some main results for my research are as follows:(1)All the ore bodies at the Mogou gold deposit occur in volcanics of the Xiong'er Group,which are controlled by the N-E trending faults.Wall rock alterations includ silicification,potassic feldspathization,carbonatation and kaolinization.Ore textures includ emulsion texture,idiomorphic or hypidiomorphic granular structure,erosion structure and net vein structure.Ore structures includthe disseminated structure and vein structure.The mineralization stages includ quartzpyrite stage,quartz-sulfide stage and quartz-carbonate stage.(2)The types of fluid inclusions are mainly NaCl?H2O type and CO2-NaCl?H2O type.They have different shapes including elliptical,quadrate and crescent,and compositions of inclusions have CO2,CH4,H2 O and H2 S.The peak value of homogenization temperature range from 220 ~ 280?(early stage)to 160 ~ 220?(middle stage)then to 160 ~ 180 ?(late stage),salinity range from 8 ~ 16 wt.%NaCl.eqv(early stage)to 6 ~ 12 wt.%NaCl.eqv(middle stage)then to 0 ~ 8wt.%NaCl.eqv(late stage);density range is 0.82 ~ 1.09 g/cm~3.The ore-forming fluid shows mesothermal,low density and low salinity.The peak value of ore forming pressure is around 20 ~ 30 MPa,the mean value of ore forming pressure for main stage is 27.48 MPa;the peak value of ore forming depth is around 2 ~ 3 km,the mean value of ore forming depth is 2.76 km.Generally,the ore-forming fluids show medium temperature,medium-low salinity and low density.(3)The C-H-O stable isotopes shows that the ore-forming fluid arederived from mixture of metamorphic and meteoric water,and S isotopes indicate that the ore-forming materials are derived from the remelting of the Taihua Group.Fluid boiling and water-rock reaction is considered as the main mechanism for gold mineralization.According to the comparison of geological and geochemical characteristics,the Mogou gold deposit belongs to orogenic gold deposit.The ore-forming fluid carried the ore-forming materials,migrated through the Machaoying fault,and ultimately deposited in N-E trending secondary faults.The ore-forming fluid mixed with meteoric water by fluid boiling and water-rock reaction,extracted materials from the Xiong'er Group,and deposited in a suitable place.