Geological And Geochemical Characteristics And Metallogenetic Mechanism Of The Shuangjianzishan Agpolymetallic Deposit,inner Mongolia

The super—large Shuangjianzishan Ag-polymetallic deposit is located in Banner of Bahrain,which is a super-large hydrothermal vein type deposit in the middle-southern part of Da Hinggan Mountains.The deposit includes 18,585 tons of Ag,1.91 Mt of Zn and 0.85 Mt of Pb,and there is still huge prospecting potential in deep and periphery of mining area.Based on previous studies,we conducted research on petrology,ore mineralogy,geochemistry,isotope chronology and fluid inclusions,discussed the geological and geochemical characteristics and genesis of the Shuangjianzishan Ag-polymetallic deposit.The main conclusions are as follows:?1?The LA-ICP-MS U-Pb age study was conducted on the zircon in the biotite granite,syengranite and granite porphyry beneath the cryptoexplosive breccia.The results are 134.2±2.2Ma,128.2±2.2Ma and 134.7±2.2Ma,respectively.The syengranite with molybdenite may be the metallogenic geological body.?2?The concealed granite bodies in the mining area are characterized by rich SiO₂,K₂O,poor Al₂O₃,quasi aluminous peraluminous,high-K calc-alkaline and A type granites.The trace elements have different characteristics.The total amount of trace elements in the black mica granite,the granitic granite and the granite porphyry is negatively correlated with the granitoid occurrence depth,and the large ion stone elements?Rb,Th,U,Zr,Hf?are enriched,and the high field and strong elements?Nb,Ta,Ba,Sr,P,Ti?are depleted.Rare earth elements are characterized by gently inclined"Seagull type",and the light and rare earth elements are moderately differentiated,and the REE distribution curves of granites are similar to the characteristics of tetrad effect.?3?The study of fluid inclusions shows that four types of fluid inclusions have been identified in ore-bearing quartz and calcite,which are mainly composed of liquid-rich inclusions,containing a small amount of gas-rich inclusions and pure liquid inclusions.The fluids are medium to low temperature?161⁴01°C?and low salinity(0.18⁵.7wt%NaCl_eqv),characterized by medium-high pressure?23.5⁸5.5MPa?.The results of laser raman probe show that the inclusions of quartz-calcite fluids are H₂O,CO₂ and SO₂.The?³⁴S values of sphalerite and galena shows that the minerals are derived from the source of deep magma,and Pb isotopes indicate that the minerals come from crust-mantle mixed source.?4?The Shuangjianzishan Ag-polymetallic deposit belongs to a magmatic medium-to-low temperature hydrothermal deposit.It is divided into several stages,including early sulfide stage,sulfide main mineralization stage and late stage quartz-carbonate stage.The main mineralization stage is about 135¹25Ma.