钱家店凹陷HLJ铀矿带姚家组下段铀的赋存状态及成矿时代

Occurrence and Mineralization Age of Uranium Ores of the Lower Member of Yaojia Formation From HLJ Ore Belt in Qianjiadian Sag

钱家店凹陷HLJ铀矿带是近年来松辽盆地西南部砂岩型铀矿找矿取得的重大新突破。文章通过对含矿层姚家组下段富铀砂岩矿石开展详细的宏微观岩矿鉴定、扫描电镜、能谱分析和全岩U-Pb同位素测年等工作,查明了矿石的基本岩石学、矿物学、铀赋存状态和年代学特征,初步探讨了砂岩铀成矿机制及过程。结果表明,砂岩矿石本身的炭屑和黄铁矿等还原介质偏低,属于一套成分和结构成熟度中等的原生弱还原性的河流相碎屑沉积建造,并发育了高岭石化、蒙脱石化、铁白云石化、黄铁矿化等酸性和碱性伴生的蚀变矿物组合;矿石中铀主要为热液改造成因的胶状含铀、钛、锆、硅的复合物,且不均匀地赋存在矿石局部强吸附还原域内的黏土杂基、各类碎屑、含钛矿物及铁白云石的边部或孔隙中,并不与某种组分呈明显的正相关性。矿石全岩U-Pb同位素测年结果表明,区内姚家组下段砂岩存在(79±14)Ma和(44.4±5.6)Ma的两期成矿作用,分别对应于嫩江期末的坳陷构造初始反转-挤压抬升持续成矿事件和始新世早期的碱性热液瞬时渗出-叠加改造成矿事件。钱家店控凹F1断裂反转活动和深部热液渗出联合控制了该区姚家组下段砂岩渗入-渗出耦合叠加铀成矿作用和过程,导致了铀矿带偏窄、矿体埋深较大、品位富、后期无氧化叠加的典型特征。

The HLJ sandstone type uranium ore belt was recently discovered in the Qianjiadian sag,southwestern of Songliao Basin.Litho-mineralogy,uranium occurrence and chronology for the sandstone ores of the Lower Member of Yaojia Formation were studied through conducting detailed macro-micro petrographical identification,scanning electron microscope,energy spectrum analysis and bulk rock U-Pb isotopic dating.Meanwhile,the uranium metallogenic mechanism and process of sandstone ores were preliminarily discussed in the paper.The results showed that the sandstone ores,with primary weak reductive nature of little native carbonaceous debris and pyrites,belong to a set of fluvial facies clastic sedimentary formation bearing medium composition and structural maturity.Acid and alkaline associated altered mineral assemblages are generally occurred in the ores,including kaolinization,montmorillonization,ferrodolomitization and pyritization respectively.Uranium occurrences are mostly composed of thermal-reformed genetic U-Zr-Ti-Si mixtures which are unevenly distributed in the edges or pores of clay matrix,various detritus,titanium bearing minerals and ankerite in the local strong adsorption-reduction domain of the ores.These uranium components show no obvious positive correlation with a certain kind substance.Results from UPb isotopic dating showed that there were two uranium mineralization events of(79±14)Ma and(44.4±5.6)Ma in the Lower Member of Yaojia Formation in the study area.The first lower-temperature mineralisation came into being due to the initial tectonic inversion and compression uplift of depression at the end of Nenjiang era,and the second relatively high-temperature hydrothermal transformation mineralization developed owing to the instantaneous invasion of alkaline hydrothermal solution in the Eearly Eocene.The inversion activity of F1 fault and deep hydrothermal fluid penetration in the Qianjiadian sag jointly controlled the various fluids infiltration coupling uranium mineralization process of the Lower Member of Yaojia Formation,resulting in the typical characteristics of narrow uranium ore belt,large burial and rich grade of ore body,and no oxidized superposition in the later stage.