Occurrence And Geochemical Characteristics Of Uranium Minerals In The Qianjiadian Uranium Deposit And Their Constraints On Mineralization

Research on mineralization of sandstone-type uranium deposits the carrier minerals are mostly gangue minerals such as calcite,pyrite,and clay minerals.However,these minerals have shortcomings as tracers of mineralization:there are widespread sedimentary diagenetic multistage genetic characteristics,making it difficult to determine whether they belong to the products of mineralization stages.In contrast,uranium minerals are the most direct carrier for studying uranium mineralization or tracing uranium ore-forming fluids.In view of this,this thesis takes the Qianjiadian uranium deposit in the southwest of Songliao Basin as the research object.Through field core observation,rock samples from the ore bearing strata of the Qianjiadian sandstone type uranium deposit were collected.Then,using polarizing microscope,scanning electron microscope,energy dispersive spectrometer,electron probe,and LA-ICP-MS in situ microanalysis methods,the types,morphology,and formation order of uranium minerals were systematically studied,and the geochemical characteristics of uranium minerals were analyzed.On this basis,combined with the ore-forming geological conditions of the deposit,the characteristics of uranium ore-forming fluid and mineralization are discussed.The main achievements and understandings are as follows:（1）The uranium minerals in the Qianjiadian uranium deposit are mainly coffinite and pitchblende,and a small amount of brannerite.Coffinite is colloidal and granular,and mainly exists in two forms:①coffinite is associated with clastic particles such as quartz,feldspar,cuttings,mica,zircon;②coffinite is associated with interstitial materials such as pyrite and clay minerals.Pitchblende is colloidal and granular,and mainly exists in two forms:①pitchblende is associated with quartz,cuttings,mica,organic matter,and rutile clastic particles;②pitchblende is associated with pyrite and clay minerals and other interstitials are associated,and a small amount is associated with siderite.Brannerite is granular and mainly exists between clastic particles.According to the interspersed relationship between minerals,coffinite can be divided into two phases:coffinite 1 and coffinite 2,and the comprehensive judgment of the formation sequence of the four uranium minerals from early to late is:coffinite 1→brannerite→pitchblende→coffinite2.（2）The average content of UO₂ in coffinite 1,brannerite,pitchblende,and coffinite2 is 69.10%,42.32%,79.1%,and 65.7%,respectively;The average content of Si O₂ is8.55%,3.89%,1.35%,and 7.12%,respectively.The total rare earth element ranges of coffinite 1,brannerite,pitchblende,and coffinite 2 are 11436～14441ppm,4415～4468ppm,5937～9818ppm,and 6855～10294ppm,respectively.In addition to coffinite 1 exhibiting heavy rare earth enrichment,brannerite,pitchblende,and coffinite 2 exhibit light rare earth enrichment,The average values ofΣLREE/ΣHREE were 0.89,2.95,1.91,and 1.33,respectively.Uranium content is closely related to trace element content.coffinite 1,pitchblende,and coffinite 2 exhibit a positive correlation between V,Nb,and U,while Sc,Y,Hf,and U exhibit a negative correlation.Ti,Re,Pb,Th and U in pitchblende also show a strong positive correlation,while U in brannerite shows a positive correlation with Pb,Th.The average U-Pb isotopic ratios of coffinite 1,pitchblende,and coffinite 2 have a decreasing trend.（3）Uranium minerals are generally formed in the oxidation-restoration transition environment.The formation of coffinite 1 is related to the interglash effects caused by surface fluids.The main evidence is:①coffinite 1 shows the enrichment of heavy rare earth,which accords with the enrichment law of heavy rare earth in interlayer oxidation zoning;②the REE distribution curve of coffinite 1 is similar to that of uranium ore in Dulaan Uul,an interlayer oxidized uranium deposit.The formation of brannerite,pitchblende,and coffinite 2 is related to basin thermal liquid activity.The main evidence is:①the formation of brannerite is generally higher than 120℃,which belongs to hydrothermal environment product.The Y/Ho ratio range of pitchblende and coffinite 2is 32.73～37.94,31.04～41.99,which is inferred that its formation is related to the thermal environment.The REE distribution curves of brannerite,pitchblende,and coffinite 2 are similar to those of uranium minerals in Mistamisk,a hydrothermal uranium deposit,and it is inferred that their formation is related to hydrothermal environment.