Geology And Geochemistry Of Kengdenongshe Gold And Polymetallic Deposit In Maduo,Qinghai

The Kengdenongshe deposit which is located in the eastern part of the East Kunlun orogenic belt is a newly discovered large gold and polymetallic deposit in recent years which is mainly made of gold,silver,lead and zinc,it belongs to the sub-metallogenic belt of accretionary wedge in Eastern Kunlun.There are three main problems in the study of the deposit which are: whether there is exhalative sedimentary mineralization or not;the source of ore-forming material and the age of ore bearing strata.Therefore,based on the characteristics of metallogenic geological background and ore deposit geology,this paper mainly studies the host rocks and the source of material and fluid which eventually led to the formation of this ore deposit by means of studying the petrology?mineralogy?fluid inclusions?geochronology and petrochemistry,then this paper makes clear of the age of ore bearing strata and discusses the source of ore-forming materials and the types of this deposit.The orebodies,mainly in the form of vein and stratoid,are located in the fracture zone and the rhyolitic-volcaniclastic rock that intercalated with silicolite in the hanging wall of fault and the porphyry in deep.The baritization and silicification have closely related to metal mineralization.The ore minerals are mainly electrum?sphalerite?galena?chalcopyrite and tennantite;the gangue minerals are mainly barite?quartz and calcite.The weighted average U-Pb age of zircon in rhyolitic ignimbrite which in the main ore-bearing strata of the ore deposit is 259.5±1.7Ma?MSWD=2.3?,this age represents the ore-bearing strata is formed in the middle-late Permian.The rock assemblages and petrochemical characteristics show that the formation was formed in the littoral-neritic environmentaround of the continental margin arc in the middle-late Permian when the paleo-Tethys Ocean?Buqingshan-Animaqing ocean?was subducted northward.The main and trace elements,REE and Si-O isotope studies of silicolite show that it is volcanic genesis of silicolite which contaminated the continental margin materials rather than hydrothermal sedimentary silicolite.The "lamellar" barite is not primary sedimentary structure,but formed by the meteoric water heated by the magma,and the "lamellar" structure is the result of ductile shearing in the later stage.The S element required for diagenesis mainly comes from sea water,and Ba element mainly comes from magmatic rocks.The formation of ore deposits may be related to orogenic motion,and the metallogenic age should be later than the surrounding rock(P_2-3).The metal material that needed for the mineralization mainly comes from the volcanic clastic rock formation and granitic intrusive rocks.The sulfur mainly comes from seawater and the formation of marine sulfates.The ore-forming fluid is mainly seawater driven by magmatic heat,and meteoric water is added at the later stage of mineralization.Kengdenongshe gold and polymetallic deposit controlled by the fault structure should be a hydrothermal metamorphic gold-silver-lead-zinc deposit which is closely related to silicification and barite alteration.