The Geological And Geochemical Characteristics And Mineralization Genesis Of The Huanaote Pb-Zn-Ag Deposit In Inner Mongolia,China

The Huanaote Ag-Pb-Zn polymetallic deposit is located in the Dongwuzhumuqinqi,Inner Mongolia Autonomous,and is a typical epithermal vein-type deposit in the southern Greater Hinggan metallogenic belt.This study focuses on geological settings,geochemical characteristics and the sources of ore-forming fluids and materials,obtaining the following conclusions:1.The fine-and coarse-grained biotite monzonitic granites yield zircon U-Pb ages of 324±2.2Ma?early Carboniferous?and 316±2.2Ma?late Carboniferous?,respectively.The two types of monzonitic granites have similar geochemical characteristics;they belong to high potassic calc-alkaline series and are of peraluminous rock.The zircon Hf isotopic values indicate a source which came from the younger crust accreted from the depleted mantle during the Mesoproterozoic and Neoproterozoic,related to the closure of Paleo-Asian Ocean.2.The metallic minerals in ores are mainly galena,sphalerite,arsenopyrite,pyrite,stannite,bournonite,native bismuth,bismuthinite,wittichite,lillianite,cosalite,silver-bearing tetrahedrite and freibergite,of which the main silver-bearing minerals are lillianite,cosalite,silver-bearing tetrahedrite and freibergite in the form of native silver and isomorphism.3.The fluid inclusions can be divided into liquid-rich,gas-rich,pure vapor and halite-bearing inclusions.The ore-forming fluids had the characteristics of low-medium temperature,low-medium salinity,and low density.And the low pressure indicates a shallow metallogenic depth.The gas phase compositions of fluid inclusions in fluorite are mainly H₂ and CO₂.The gas phase compositions of fluid inclusions in quartz are mainly CH₄,CO₂ and H₂O,and the liquid component is mainly H₂O.The component of pure gas inclusions is mainly CO₂.Argon and helium isotopic values suggest that the ore-forming fluids came mainly from mantle fluid.Hydrogen and oxygen isotopic values indicate a mixture source of both magmatic and meteoric water for the ore-forming fluids.4.The composition of the isotopes of sulfur demonstrated that the source of sulfur in ores is estimated from a mix of igneous rock sulfur and sedimentary rock sulfur.Lead isotope compositions of sulfides in the Hanaote deposit indicate that the metallogenic materials are mainly derived from the mantle and partly from the upper crust.5.The earlier deep mantle-derived magma transported uptowards along the tectonic fractures and extracted ore-forming materials from the wall rocks,forming ore-forming fluids which carried the ore-forming elements in the form of complexes.The magma broke the overlying rocks,which resulted in the decreasing of pressure.Fluid boiling and the interfusion of atmospheric water led to the change of fluid phy-chemical properties.Ore-forming elements precipitated in advantaged tectonic positions.