鄂尔多斯盆地塔然高勒地区砂岩型铀矿含矿层砂岩特征及成矿作用

Characteristics and metallogenesis of ore-bearing sandstone in the Tarangaole sandstone type uranium deposit, Ordos Basin

【研究目的】近几年,砂岩型铀矿在北方发展较为迅速,塔然高勒地区砂岩型铀矿地质勘探取得了重大找矿发现。通过对塔然高勒地区砂岩型铀矿进行研究,有利于更好探寻深部砂岩型铀矿的分布规律及岩石学、矿物学赋存形态。塔然高勒地层结构与纳岭沟、大营铀矿床具有相似的地质特征,但研究区含矿层岩石特征、铀矿物的赋存状态尚不明确。【研究方法】本文通过钻孔岩心观察、系统取样及详细的显微镜下鉴定,并对塔然高勒地区铀矿石进行了电子探针分析。【研究结果】研究结果表明:研究区中侏罗统直罗组下段砂岩以长石岩屑砂岩和岩屑长石砂岩为主,成分成熟度和结构成熟度较低,具有近物源沉积的特点。电子探针分析结果表明,铀矿物主要以沥青铀矿、铀石及少量的钛铀矿、含钛铀矿为主。【结论】背散射图像显示铀矿多与黄铁矿及有机质矿物共同分布,表明黄铁矿及有机质矿物为铀矿物的形成提供了还原剂。成岩过程中溶蚀作用及后生蚀变现象的发育,为铀的富集沉淀提供了有利条件。观察含矿目的层砂岩中的蚀变现象及蚀变矿物特征,表明各黏土矿物在一定的物理化学条件下发生相互转变,地球化学环境的改变造成了黏土矿物间的相互转化,进一步改变赋矿砂体的地球化学环境。

[Objective] In recent years, sandstone type uranium deposits have developed rapidly in North China. The geological exploration of sandstone type uranium deposits in the Tarangaole area has made significant discoveries. Through the study of sandstone type uranium deposits in the Tarangaole area, it is helpful to better explore the distribution rules of deep sandstone type uranium deposits and the occurrence patterns of petrology and mineralogy. The stratigraphic structure of Tarangaole is similar to that of Na Linggou and Da Ying uranium deposits, but the rock characteristics of ore bearing strata and the occurrence of uranium minerals in the study area are not clear. [Methods]In this paper, through core observation, systematic sampling and detailed identification under microscope, the uranium ore in Tarangaole area was analyzed by EPMA. [Results] The results show that the sandstones in the lower member of Zhiluo Formation of Middle Jurassic are mainly feldspathic lithic sandstone and lithic arkose,With low compositional maturity and structural maturity, and have the characteristics of near provenance deposition. [Conclusions] The results of electron microprobe analysis show that the main uranium minerals are pitchblende, uranite and a small amount of ilmenite. The backscatter images show that uranium deposits are mostly distributed together with pyrite and organic matter minerals, indicating that pyrite and organic matter minerals provide reducing agents for the formation of uranium minerals.The development of dissolution and epigenetic alteration during diagenesis provides favorable conditions for uranium enrichment and precipitation. By observing thealteration phenomena and the characteristics of altered minerals in sandstone of ore bearing Tarangaole bed, it is shown that the clay minerals transform each other under certain physical and chemical conditions. The change of geochemical environment causes the mutual transformation of clay minerals and further changes the geochemical environment of ore-bearing sand bodies.