巴丹吉林盆地居延海坳陷乌兰苏海组砂岩特征及铀成矿地球化学环境分析OA

Badain Jaran Basin,as one of the medium-sized basins in China,is relatively low in the level of uranium exploration.In recent years,good uranium mineralization clues have been discovered in Wulan Suhai Formation of Upper Cretaceous,Badain Jaran Basin.However,the genesis of the geochemical environment for uranium mineralization in this formation are not clearly understood.To explore the features of geochemical environmental indicators and analyze the characteristics of elemental changes,summarize the indicator elements related to uranium enrichment,the article studied the petrological and mineralogical characteristics,major,trace and rare earth elements of the sandstones of different colors(brownish red,yellow/brownish yellow,light gray/gray,dark gray/blackish gray)from Wulansuhai Formation of Upper Cretaceous of Juyanhai depression in Badain Jaran Basin.Based on the geochemical environmental indicators,the geochemical environmental characteristics of each subzone were determined,and the elemental variation characteristics of each subzone were compared.Research shows that:① The mineral compositions of sandstones of different colors are similar,with quartz,potassium feldspar and plagioclase being the main minerals.Based on the analysis and judgment of clay mineral content and mineral types,light gray/gray sandstone has a relatively high maturity of composition,followed by dark gray/grayish black sandstone,while brownish red sandstone and yellow/brownish-yellow sandstone have the lowest maturity of composition.② From brownish red to yellow/brownish-yellow sandstone → light gray/gray sandstone → dark gray/grayish-black sandstone,the w(U)value keeps increasing,the Th/U ratio keeps decreasing,and the U element gradually accumulates.The total C,S,and △Eh gradually increase,indicating that the rock's reducing capacity gradually enhances.The concentration Clark values of U and Mo continue to rise,especially in the dark gray/grayish black sandstone,the concentration Clark value of U is significantly higher.Mo enrichment represents that the enrichment of U in this layer/formation is a typical interlayer oxidation origin.③ The rare earth distribution patterns of sandstones of different colors are generally consistent,showing a right-leaning type with enriched light rare earths and deficient heavy rare earths.The rare earth element distribution curves of brownish red sandstone and dark gray/grayish black sandstone are relatively concentrated,while those of yellow/brownish yellow sandstone and light gray/gray sandstone are relatively dispersed.indicating that the epigenetic transformation of yellow/brownish-yellow sandstone and light gray/gray sandstone is relatively stronger.Through Macroscopic,microscopic and laboratory analysis of different colored sandstones of Wulansuhai Formation,redox zones were believed have developed from the edge of the basin to the center and vertically from the strata,the brownish red sandstone referred as the primary red zone,the yellow/brownish yellow sandstone referred as to the retroactive oxidation zone,and the light gray/gray sandstone referred as to the transition zone,while the dark grey/grayish black sandstone as the reduction zone.Based on previous exploration results and proportion of uranium mineralization clues distributed in each zone,in the later exploration process should be focus the delineated oxidation-reduction transition zone,followed by the reduction zone.