Metallogenic Geological Characteristics And Genesis Of The Nagengkangqieergou Ag-polymetallic Deposit,East Kunlun Orogen,NW China

The Nagengkangqieergou Ag-polymetallic deposit is located in the eastern part of the East Kunlun orogenic belt,north of the Kunzhong deep fault.In recent years,breakthrough progress has been made in the exploration and prospecting of Ag-polymetallic deposits in the East Kunlun area,and many hydrothermal Pb-Zn and Ag-polymetallic deposits have been successively discovered,such as Nagengkangqieergou Ag-polymetallic deposit,Harizha Ag-polymetallic deposit,Keyonglongwa Ag-polymetallic deposit,Yongbageng Ag-polymetallic deposit,Gemalong Pb-Zn deposit,and Halongxiuma polymetallic deposit.The Nagengkangqieergou deposit is a large hydrothermal vein type Ag-polymetallic deposit discovered for the first time in East Kunlun.Previous studies mainly focused on the shallow vein Ag-mineralization.In this study,we found that there is disseminated Cu mineralization in the deep part of the mining area,and there are zoning characteristics of disseminated mineralization,breccia type mineralization and vein mineralization from deep to shallow,and the corresponding fluid inclusions of gangue minerals change from gas phase inclusions,though gas-liquid two-phase inclusions to liquid inclusions.Combined with the latest exploration progress,the mineralization is further divided into disseminated Cu mineralization period,vein Ag mineralization period and epigenetic period.The Cu mineralization period is mainly marked by quartz-pyrite-sphalerite-chalcopyrite-arsenopyrite vein.The Ag mineralization period can be divided into quartz-pyrrhotite-chalcopyrite-sphalerite stage(the main metallogenic stage of deep copper-lead-zinc mineralization),quartz-arsenopyrite-lead-zinc-silver sulfide stage(the main metallogenic stage of shallow silver-rich mineralization)and carbonate-pyrite stage.In this paper,the age of the rhyolite porphyry is 253.2±1.7 Ma,which was formed in the Late Permian.The content of Si O₂ in vein disseminated mineralized rhyolite porphyry is75.56%?76.01%,Na₂O+K₂O is 4.09%?7.68%,K₂O/Na₂O is 0.92?11.78,A/CNK is 1.05?2.41,which belongs to high silicon,high potassium and calc-alkaline peraluminosite rock.The veinlet disseminated mineralized rhyolite porphyry is obviously enriched in large ion lithophile elements(LILE)such as Rb,and K,and depleted in high field strength elements(HFSE)such as Nb,Ti and P;the total amount of rare earth(?REE)is 245?265ppm,and the light and heavy rare earth elements are significantly fractionated((LA/Yb)_N=7.76?9.96),and show a negative Eu anomaly(?Eu=0.03?0.38).Combined with the previous data,it is considered that the shallow vein Ag mineralization period(silver main mineralization period)may be related to the rhyolite and plutonic rock mass of 217Ma.According to the comprehensive analysis,the Nagengkangqieergou deposit may have experienced the superimposed mineralization process of the Cu mineralization period of 253Ma and the Ag mineralization period of 215-225Ma,which belongs to the spatial superposition of metallogenic systems in different times.Based on the study of the metallogenic characteristics and genesis of the deposit,this study carried out the prospecting prediction of the deep and edge parts of the mining area,and pointed out that the deep part of the XI ore belt and the extension along the structural belt to both ends have a good prospecting potential,and the southwestern vein rock development area of the II mineralization belt has the prospecting potential similar to that of the XI ore belt.