鄂尔多斯盆地东北部中侏罗统直罗组下段沉积相及其对铀成矿的控制作用

Sedimentary facies of the lower part of Middle Jurassic Zhiluo Formation in northeastern Ordos Basin and its controls on uranium mineralization

综合前人的研究成果,结合野外地质考察,并通过1048个煤田和核工业部钻孔岩心的编录统计,将鄂尔多斯盆地东北部中侏罗统直罗组划分为上中下3段。作者将直罗组下段作为研究目标层,分析了其砂体特征、含砂率、地层厚度和底板埋深等分布情况,结合野外地质露头和测井解释资料的综合研究,将研究区直罗组下段划分出3种沉积相,分别为河流相、三角洲相和滨浅湖相。最后,通过东胜矿床沉积相与砂岩型铀矿的成矿关系研究,表明辫状河—辫状河三角洲相是鄂尔多斯盆地东北部最有利的沉积相,其次是曲流河—曲流河三角洲相,并简要阐述了东胜矿床外围今后找矿的重点区域为东胜地区西北部、榆林地区西部、横山地区西北部的辫状河道和三角洲平原分流河道发育的区域。

On the basis of summarizing the achievements of preresearchers, considering both the field geological survey and 1048 drilling core loggings from coal-mining companies and the Nuclear Industry, the Middle Jurassic Zhiluo Formation in the northeastern Ordos Basin was divided into three parts, the upper, the middle and the lower. This paper, aiming at the lower part of the Zhiluo Formation, analyzes the characteristics of sandbodies, the sand content, the thickness of each interval, and the depth of the floor. Combining with the integrated researches on the geologic outcrop and the interpretation of logging data, three types of sedimentary facies were divided in the lower part of the Zhiluo Formation, i.e. fluvial, delta, and shore and shallow lacustrine facies. Through the researches on the relationship between sedimentary facies and uranium metallogenesis in Dongsheng sandstone-type deposit, this paper reveals that the braided fluvial-braided fluvial delta facies is the most favorable in the northeastern Ordos Basin, and meandering fluvial-meandering fluvial delta facies the next. It also briefly described that in the future, the peripheral prospective areas of the Dongsheng deposit are the northwestern Dongsheng, the western Yulin and the northwestern Hengshan where braided channel and deltaic plain distributary channel are developed.