Copper And Gold Mineralization Associated With Ductile Brittle Deformation Zone

The newly found Lingyun Copper Deposit is located in the East Tianshan,South Tianshan Orogenic Belt.This deposit is controlled by a large brittle-ductile deformation zone and is thought to be a difficult to identify,and new type of copper deposit.Lingyun gold deposit which is being explored was found in the similar geological setting.A series of copper and gold deposits are controlled by the large brittle-ductile deformation zone.So what are the key factors that control the Deposit?What are the ore-forming mechanism and genesis types?The study of ore-forming process is of considerable significance for metallogeny and prospecting orientation.Based on the field geological observation,petrography,mineragraphy,geochemistry of mineral deposit are used to constraint the tectonic setting and Cu-Au mineralization progress in this paper.The understanding and progress are as fllowed:?1?The ore-hosted rocks of copper bodies are gray green mylonites.Based on the microscopic identification and geochemical analysis,the protolith is andesite crystal tuff not celadon mylonitization keratophyre which proposed by predeccessors,in which yields an age of 407.8±1.3Ma by zircon LA-ICP-MS U-Pb analysis.The age and the geochemical analysis indicate that the andesite crystal tuff was formed in oceanic island arc setting during northward subduction of South Tianshan Ocean,and this formation should be belonged to aerbisimaibulake Formation Lower Devonian.?2?Mineralization can be divided into two stages.the first stage?the main metallogenic stage?is quartz-polymetallic sulfide phase.The mineral compositions are chalcopyrite+bornite+quartz,which fill along the metamorphic andesite crystal tuff foliation fissure;The second stage is ankerite-polymetallic sulfide phase.The mineral assemblage are chalcopyrite+bornite+ankerite,which fill in minor Angle oblique foliation.?3?The initial(¹⁸⁷Os/¹⁸⁸Os)_t of Copper ore chalcopyrite is 18.54±0.67,Chondrite-normalized patterns REE of ore minerals and ore-hosted rock are similar,showing the characterize of left steep and right flat trend,LREE enrichment and HREE depleted.Ore-forming materials are mainly deprived from crustal source,also the metamorphic andesite crystal tuff may provide parts of the ore-forming metals.?4?The ore rocks don't have significant alterated zonation,and the mineralization is mainly related to epidotization and sericitization.Sericites,growing along mylonite's foliation and lineation,have obvious symbiosis contaction with chalcopyrite and bornite in the main metallogenic stage.The altered mineral sericites'plateau age is 292.3±2.4Ma,while Re-Os dating of three main metallogenic stage chalcopyrite samples yields an isochrones age of the 297.9±3.4Ma.The two ages,within the error range,showed the metamorphism,deformation and the ore-deforming age at the Late Carboniferous to Early Permian period.The strata and copper body are cutted by the diorite,and the LA-ICP-MS U-Pb ²⁰⁶Pb/²³⁸U weighted average age of zircons is 221.0±1.4Ma,which can be restrict the superior limit of ore-forming age.?5?The occurrence of Au in gold deposit are mainly three main patterns.Au mainly presents as invisible nanometer-sized particles of native Au?Au⁰?or sosoloid Au?Au⁺?in pyrites and pyrrhotites crystal lattice;Au mainly presents as visible micrometer-sized particles of native Au?Au⁰?in pyrites crystal;Au mainly presents as visible micrometer-sized particles of native Au?Au⁰?in the boundarie and fractures of pyrites.Silver was associated mineral with Au in pyrites and pyrrhotites.It mainly uneven distributes in pyrites and presents as invisible nanometer-sized particles of native Ag?Ag⁰?;Re-Os dating of four gold-bearing pyrite samples yields an isochrones age of the 306.0±2.4Ma,which is consistent with the inferior limit of age of regional strike-slip shear zone.?6?As discussed above,combined with the regional tectonic setting,The Lingyun Cu-Au deposit was formed latter than closing of northward subduction of South Tianshan Ocean.The thrust nappe structure and strike-slip shear developed during continental colution,which may result in deep metamorphic fluid that extract the preliminary enrichment of ore-forming elmemts in deep Earthcrust or in the metamorphic crystal tuff.Then these elements unload in the suitable place.In summary,we argue that Lingyun Cu-Au Deposit is belong to the collision-orogeny type of Cu-Au deposit.It is certainly positive significance for regional prospecting that the genesis type of Lingyun Copper-gold Deposit is determianed.