摘要
Abstract
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.关键词
北天山/花岗岩型铀矿/成矿岩体/岩石成因/早二叠世Key words
northern Tian Shan/granite-hosted uranium deposit/ore-forming intrusion/petrogenesis/Early Permian分类
天文与地球科学
