吉尔吉斯斯坦北天山科克铀矿床石英正长岩地球化学特征及地质意义OA

In the Kyrgyz Northern Tian Shan(KNTS),two types of hydrothermal uranium deposits,namely volcanic-type and granite-type,have been identified.The volcanic-type uranium deposits are represented by the Almsinskoye deposits,whose orebodies are controlled by NE-trending faults and the contact zones between porphyry bodies and strata.The granite-type uranium deposit is typified by the Kok deposit,with orebodies hosted in Permian quartz syenite plutons and mainly controlled by intra-plutonic faults and fracture-altered alteration zones.This paper studied the the Kok uranium deposit by conducting petrological,lithogeochemical and isotopic geochronological analyses of the ore-hosting wall rocks.Combined with the regional tectonic evolution background,it briefly discussed the genetic type,source rock characteristics and formative tectonic setting of uranium-bearing granites,the characteristics of uranium mineralization,as well as the coupling relationship among plutons,structures,alterations and uranium mineralization.It was found that the ore-hosting wall rock was medium-coarse grained hornblende-bearing quartz syenite,belonging to metaluminous A-type granite which characterized by high silica and alkali contents,high potassium and low sodium abundances,high Fe/(Fe+Mg)ratios,relative enrichment of light rare earth elements(LREEs)and relative depletion of heavy rare earth elements(HREEs)with LREE/HREE ratios>5,weak negative Eu anomalies,and total Zr+Nb+Ce+Y concentrations>350×10-6.In the pluton,the uranium content ranges from 10.6×10-6 to 11.2×10-6,thorium content from 58.0×10-6 to 66.1×10-6,and Th/U ratios from 5.46 to 5.88,which can provide a material source for uranium mineralization.Zircon U-Pb dating yields a weighted mean age of 297.2±0.7 Ma,indicating that the pluton formed in the regional post-collisional extensional tectonic setting during the Early Permian.The solidification product of felsic magma might be generated by partial melting of the Mesoproterozoic metamorphic basement,mixed with crustal materials in the post-collisional extensional-transtensional tectonic regime.Zircon Ti thermometer calculations yield temperatures of 796.7-805.4℃,and oxygen fugacities(lgfO2)range from-14.6 to-7.17 with an average of-11.4,displaying high-temperature and high-oxygen-fugacity features,which suggests a strong potential for supplying uranium sources.From the Late Carboniferous to the Early Permian,the KNTS remained in a post-collisional extensional-transtensional setting with intense tectonic and magmatic activities.NW-trending and NE-trending faults developed along the nearly EW-trending regional structures,forming a series of meso-basic and meso-felsic intrusions,which laid a foundation for polymetallic and uranium mineralization.Uranium-rich granites provided the material basis,fault structures acted as fluid pathways and ore-hosting spaces,and fracture-altered zones created physicochemical conditions for the precipitation of uranium elements.