鄂尔多斯盆地南部宁县新华地区直罗组沉积特征及铀成矿条件分析

Sedimentary Characteristics and Uranium Metallogenic Conditions of Zhiluo Formation in Xinhua Area,Ning County,Southern Ordos Basin

新华地区作为鄂尔多斯盆地南部中侏罗统直罗组找矿的重点地区之一,研究其沉积特征及铀成矿条件对指导该区砂岩型铀矿勘查工作至关重要。文章通过岩心观察及钻孔资料综合分析,编制了直罗组地层厚度、砂体厚度、含砂率、氧化率等值线图等系列图件,对直罗组沉积相及铀成矿条件进行了综合分析。结果表明:新华地区直罗组上段主要发育曲流河相沉积,可分为曲流河河道、边滩、天然堤以及河漫滩微相沉积,直罗组下段以辫状河相沉积为主,可分为辫状河河道、心滩、泛滥平原微相沉积,其中,直罗组下段辫状河河道砂体厚度适中,连通性好,富含还原物质,是有利的成矿相带。新华地区构造发育,存在构造天窗,层间氧化带发育,直罗组下段辫状河河道呈南北向展布,氧化带与砂体展布基本一致,具有有利的铀成矿条件。综合构造条件、沉积特征、后生蚀变特征和铀矿化信息,结合煤田自然伽马异常,认为研究区西北部店头赵村—白店—崔家岭一带是铀成矿最有利区域,可以作为直罗组砂岩型铀矿下一步勘查的重点目标区。

Xinhua area is one of the key areas for prospecting in the Middle Jurassic Zhiluo Formation in the southern Ordos Basin,the sedimentary characteristics and uranium metallogenic conditions play important role in guiding the exploration of sandstone type uranium deposits in this area.Based on core observation and comprehensive analysis of the drilling data,a series of maps such as thickness of Zhiluo Formation,sand body thickness and percentage,oxidation rate and uranium mineralization prospect prediction map,the sedimentary facies and uranium metallogenic conditions of Zhiluo Formation were analyzed comprehensively as well.The result showed that:the upper member of Zhiluo Formation in Xinhua area are mainly the sediments of meander river faces,which can be divided into meander river channel,side beach,natural bank and flood plain microfacies deposits,while the lower member of Zhiluo Formation are mainly the products of braided river deposition,which can be divided into braided river channel,channel bar and flood plain microfacies deposits.Among the developed faces,the braided river channel sand body of the lower member of Zhiluo Formation has moderate thickness,good connectivity and rich in reducing substances,which is favorable for uranoium mineralization.In Xinhua area,there are structural skylights and interlayer oxidation zones.The braided river channel in the lower part of Zhiluo Formation is distributed from south to north,and the oxidation zone and sand body distribution are basically the same,which is favorable to uranium mineralization.Based on the structural conditions,sedimentary characteristics,epigenesis alteration characteristics and uranium mineralization information,natural gamma anomalies,it was believed that the Zhaocun-Baidian-Cuijialing area is the most favorable area for uranium mineralization,and should be the key target area for the next exploration of sandstone type uranium deposits in Zhiluo Formation.