Geological-Geochemical Characteristics And Genesis Of The Jiamante Gold Deposit In The West Tianshan,Xinjiang Province

The Jiamante gold deposit is a hydrothermal gold deposit located in the Boluokenu polymetallic belt in the West Tianshan.It occurs in Neopaleozoic Dahalajunshan Formation of Yeliemodun basin mainly composed of crystal tuff and granitic porphyry.The ore bodies of the Jiamante gold deposit under control of NNW(F₅),NNE(F₆,F₇)fracture and volcanic breccia which include three ore types composed of quartz vein-type,altered rock type and breccias type.The metallic minerals predominantly consist of pyrite,galena,chalcopyrite and sphalerite,along with a very small amount of bismuthinite,tennantite,chalcocite and covellite;the nonmetallic minerals are dominated by quartz,calcite,sericite and chlorite.The ores are mostly characterized by disseminated structure,vein structure,mesh-vein structure,miarolitic structure,comb structure and breccia structure and distinguished by euhedral-subhedral structure,granular structure,xenomorphic granular structure,poiklitic structure,residual texture,reaction rim texture and metasomatic pseudomorph texture.Taking the ore body as center,the low temperature alteration are consist of silicification,beresitization(sericitization)and chloritization.Wall rock alterations such as silicification,pyritization and sericitization are closely related to gold mineralization.Two main paragenetic stages of the Jiamante gold deposit have been recognized based on petrographic observation,which are the quartz polymetallic sulfide stage chiefly contributing to gold mineralization and the carbonate stage.The LA-ICP-MS zircon U-Pb dating yielded a weighted average age of 365.9±3.0Ma for crystal tuff and 362.3±4.3Ma for granitic porphyry.The mineralization age of the Jiamante gold deposit could be constrained between 362Ma and 331Ma based on geochronological work in the study and considering the fossils of the Visean period in Lower Carboniferous Aqialehe Formation.Geochemical analysis results indicate that these magmatic rocks show high K calc-alkaline characteristics with enrichment in LREE,Rb,Th,K,and depletion in Sr,Ba,HREE,Nb,Ta,Ti and P.It suggests that crystal tuff and granitic porphyry have the characteristics of arc magmatic rocks.Crystal tuff and granitic porphyry were generated due to the southward subduction of the Junggar ocean beneath the Yili-Middle Tianshan plate.They were likely derived from partial melting of mafic lower crust,with involvement of mantle-derived magma interacted with subducted sediments.The study of fluid inclusion shows that the ore-forming fluids belonged to the system of low temperature,low salinity and low minilization depth.The fluid inclusion data indicates that the gold mineralization was a process of decrease in temperature,salinity and minilization depth.The research of isotope indicates that ore-forming fluids of the Jimante gold deposit were meteoric water-dominated and the ore components were derived from host rocks.After comprehensive analysis of all above,we proposal that the Jiamante gold deposit is an LS epithermal deposit.