尼日尔阿泽里克地区阿萨乌阿组沉积相特征及其控矿作用

Sedimentary facies of the Assaousas formation and the control of uranium mineralization in the Azelik area,Niger

通过研究阿泽里克地区阿萨乌阿组野外露头剖面、钻孔岩芯、测井曲线等,结合室内镜下薄片鉴定,认为其沉积相为辫状河流沉积,由此划分出河道与洪泛平原两个亚相,并识别出了两条主河道。阿萨乌阿组沉积厚度较薄,沉积时间短暂,在阿萨乌阿末期,由于快速的水进,阿泽里克地区由河流迅速转换为湖泊,结束了阿萨乌阿组沉积,随后沉积了约300 m厚的伊腊泽尔组湖相泥岩。辫状河道砂岩以中—粗粒砂岩、砾岩为主,长石、岩屑含量高,泥质含量极少,分选、磨圆度较差,成分、结构成熟度低,原生孔隙度高。辫状河道砂体在纵向上、横向上交错切割、叠置,分布稳定,连通性好,利于成矿流体在砂体中流通,并为铀成矿提供了良好的容矿空间。阿泽里克砂岩型铀矿明显受阿萨乌阿组河道砂体控制,辫状河道沉积相为该区重要的控矿因素之一。

Abstract：Through studies on the field outcrop, drillhole core and core logging in combination with the microscope analysis on thin and thick sections, the authors believe that sedimentary facies of the Assaousas formation was deposited in the braided stream envi ronment in the Azelik area. Thus the river channel and flood plain were subdivided and two main fluvial channels are identified. The stratum thickness of Assaousas formation is thin which was deposited in the short period. At the end of the Assaousas period, the fluvial facies were transformed rapidly into lacustrine facies, then the sedimentation of Assaousas formation ended because of fast water intru sion,subsequently approximately 300 m thick of lacustrine facies mudstone was deposited. The braided channel facies sandstone layer dominated with the sandstone and conglomerates, which is characterized with poorly sorted, poorly rounded and middle coarse, rich feldspar and clasts, poor shale content, poor textural maturity and compositional maturity and high primary origin porosity. The braided channel bodies cut and superpose vertically and laterally each other, distribute stable and connect well which are favorable for circulat ing of the mineralization fluids and provide suitable structural space for the uranium mineralization. The uranium mineralization in the Azelik uranium deposit area is apparently controlled by the braided channel facies sandstone body which is one of important mineraliza tion controlling elements.