塔里木盆地巴楚地区阿图什组砂岩型铀矿成矿流体特征研究OA

In recent years,profitable sandstone-type uranium mineralization has been discovered in the variegated red sandstone of Pliocene Atushi formation in the southern Bachu uplift,Tarim basin,indicating significant prospecting potential in this region.However,no research was reported on the source,nature,and evolution mechanism of the ore-forming fluids in this area.Therefore,the authors comprehensively applied petrographic thin section identification,scanning electron microscopy observation,major and trace element geochemistry,and stable isotope testing to systematically study the characteristics of sandstone uranium ore-forming fluids in the Bachu area.The findings are as follows:1)The sandstone of the Atushi formation is predominantly yellow in its primary depositional state,whereas the U-bearing sandstone and mineralized sandstone exhibit obvious recrystallization of micritic calcite,dolomitization,and higher organic matter contents,indicating the presence of late-stage alkaline organic hydrothermal fluid alteration.Coffinite occurs in organic matter and altered mica,while pitchblende occurs in quartz dissolution pores,reflecting that the ore-forming fluids are related to alkaline organic hydrothermal fluids.2)The geochemical characteristics of organic carbon,major elements,trace elements,and rare earth elements are significantly different from those of traditional infiltration-type(interlayer oxidation zone-type)sandstone uranium deposits,indicating that the ore-forming fluids are not uranium-bearing oxygenated groundwater but deep-derived organic reducing fluids.3)Comparison of carbon isotopes of extract group components shows that the organic fluids were originated from Cambrian source rocks,which are enriched in ore-forming elements such as U and can provide material sources for shallow uranium mineralization.In conclusion,it is considered that the ore-forming fluids in the Niaoshan area of the Bachu uplift are alkaline organic reducing hydrothermal fluids derived from deep Cambrian source rocks.This study not only enriches the theory of sandstone-type uranium mineralization but also provides certain geological basis for uranium exploration in this region.