Geological Characteristics And Genesis Of Gemalong Silver Polymentallic Deposit In East Kunlun Orogenic Belt,Qinghai Province

Gemalong mining area is located in the eastern Kunlun orogenic belt in the northern part of the Qinghai-Tibet Plateau.The structural belt is connected with the Qinling orogenic belt in the east,separated from the Altun Mountain fault in the west,adjacent to the Qaidam Basin in the north,and separated from the Bayankala-Songpanganzi terrane in the south.There are four silver-gold orebodies,two silver-gold-lead orebodies,one gold orebody,one silver orebody,nine lead orebodies and one zinc orebody in the mining area.The ore-hosting wall rock of the mining area is the Late Triassic Erlashan volcanic rock.By comparing the regional silver polymetallic deposits and U-Pb zircon dating of rhyolitic tuff,it is inferred that the ore-forming age of the deposit should be later than that of the Late Triassic.According to the geotectonic location,ore-controlling structure,wall rock characteristics and ore-forming fluids of the deposit,it is inferred that the genetic types of Gemalong silver polymetallic deposits are low in silver-rich and base metals.Sulfide type?LS type?epithermal vein deposit.The main metallogenic period of the deposit is mainly controlled by the nearly north-south faults and ore bodies are mainly hosted in the nearly north-south faults.Metal minerals are sphalerite,galena,argentite,and a small amount of chalcopyrite and pyrite.Gangue minerals are mainly quartz,carbonate,kaolin and so on.Ore structure mainly includes medium-fine grained structure,residual metasomatic structure,emulsion droplet structure,etc.Ore structure mainly includes massive structure,vein structure,breccia structure and disseminated structure.The rhyolitic tuff of the Elashanzu formation is a set of peraluminous high potassium calc-alkaline rocks.The rocks were significantly enriched with large ionic lithophilic elements?LIFE?such as Rb,Ba,U,K,etc.,and the relative losses were high field intensity elements?HFSE?such as Nb,Ta,P,Ti,and the value of?Eu was between0.68 and 0.80,showing the geochemical characteristics of island arc volcanic rocks as a whole.The average value of Nb/Ta in the sample trace elements was 14.08,suggesting that the rhyolitic tuff in the mining area had mantle material involved in the diagenesis process,and it was speculated that it might be a mixture of magma formed by partial melting of basaltic rocks in the lower crust and mantle magma.The test of quartz vein inclusions in the main metallogenic period shows that the fluid in the main metallogenic period is low temperature medium high salinity medium low density fluid,the estimated metallogenic pressure is 13.39²2.84 Mpa and the metallogenic depth is 1.34².28 Km.The hydrogen-oxygen isotope test of rocks in the main metallogenic period shows that the hydrothermal fluid in the main metallogenic period is the mixture of magmatic water and atmospheric precipitation;the sulfur isotope study in the main metallogenic period shows that the variation range of the value of?³⁴S Narrow,0.6².2,the whole is close to zero.It is presumed that its material source is relatively single,mainly from deep magma.Through systematic geological study,the ore-forming age of the deposit should be later than the Late Triassic,mainly controlled by the North-South ore-controlling structure.The ore-forming elements are mainly Ag,Pb and Zn.The ore-controlling elements can be summarized as follows:Late Triassic continental volcanism-magmatism?thermodynamic+main source?+volcanic rocks of Orashan Formation?partial source+host rock?+near SN trending faults?ore-conducting+ore-hosting space?.)The genesis of the deposit should belong to the continental volcanic-subvolcanic type deposit of epithermal hydrothermal fluid.