Metallic Mineral Composition And Silver Enrichment Mechanism Of Huaaobaote Pb-Zn-Ag Deposit,Inner Mongolia

Huaaobaote Pb Zn Ag deposit,located in Inner Mongolia,is a large hydrothermal vein type deposit newly discovered in Daxinganling metallogenic belt in recent years.In this paper,microscopic observation,electron probe,X-ray scanning,inclusions temperature measurement,laser Raman composition testing and other techniques were used to study the types of metal minerals,the occurrence and enrichment of silver,the characteristics and evolution of ore-forming fluids,the ore-forming process and its genesis in the deposit.The results show that the metal minerals in the mining area are pyrite,galena,sphalerite,cassiterite,chalcopyrite,pyrrhotite,arsenopyrite,tetrahedrite with silver,freibergite,diaphorite,pyrargyrite,stephanite,argentite,bournonite,jamesonite,owyheeite,etc.In this mining area,silver mainly occurs in the form of independent silver minerals,and then in the form of isomorphism in galena,sphalerite and other minerals.New silver minerals have been found in the mining area:freibergite,diaphorite,stephanite,owyheeite.Silver mainly mineralizes during theⅡmetallogenic stage,and silver ions migrate in the form of sulfur-hydrogen complexes.At about230℃,the Ag⁺ore-forming fluid enters galena and other sulfide lattice spaces to replace Pb²⁺in the medium temperature and high sulfur fugacity environment,forming lattice silver.When the temperature drops to 170～200℃,Ag⁺will gradually saturate in the environment of low temperature,low sulfur fugacity and low salinity.reached saturation.Ag⁺combines with Sb³⁺,Cu²⁺and other ions to form a large amount of sulfide silver minerals.In the early stage of Hua’aobaote deposit,the ore-forming fluid’s uniform temperature variation range is 179.1～299℃,with an average value of 231.4℃;the uniform temperature variation range of fluid inclusions in the main mineralization stage is 146.1～281.8℃,with an average value of 206.1℃;In the late stage of mineralization,the uniform temperature of fluid inclusions ranged from 134.2～213℃,with an average value of 158.4℃.In the early stage of the fluid,there are CO₂-H₂O three-phase inclusions,mainly liquid-rich,gas-liquid two-phase inclusions and pure gas-phase inclusions.The composition includes CO₂,H₂O,CH₄,N₂,etc.;the main ore-forming stage includes three-phase containing daughter crystal,rich liquid phase,pure gas equivalent inclusions in the same area,and the composition includes CO₂,H₂O,CH₄;the late stage is mainly composed of rich liquid phase H₂O gas-liquid phase and pure liquid phase H₂O inclusions.Salinity 0.35-19.45ωT%,density 0.73-1.02 g·cm^-3,average 0.87 g·cm^-3.The mineralization depth is 0.69-2.57 km,with an average of 1.65km.The ore-forming fluid has the characteristics of mixing magmatic water and atmospheric precipitation,which is mainly the unsaturated solution with medium low temperature,medium low salinity and low density.The fluid has the evolution trend from high oxygen fugacity to low oxygen fugacity to high oxygen fugacity from early stage to late stage.The ore-forming materials mainly come from the upper mantle.The mixing and decompression of fluids during the process of mineralization（occurrence of cryptoexplosion and the development of fracture systems）may be an important mechanism of mineralization.The Huaaobaote deposit is a medium-low temperature medium-shallow hydrothermal vein type deposit controlled by faults and related to magmatism...