砂体非均质性是铀成矿的关键因素之一——鄂尔多斯盆地东北部铀成矿规律探讨  

Sand body heterogeneity:one of the key factors ofuranium metallogenesis in Ordos basin

作　　者：焦养泉[1] 陈安平[2] 杨琴[1] 彭云彪[2] 吴立群[1] 苗爱生[2] 王敏芳[1] 徐志诚[1] 

机构地区：[1]中国地质大学资源学院,湖北武汉430074 [2]核工业208大队,内蒙古包头014010

出　　处：《铀矿地质》2005年第1期8-15,共8页Uranium Geology

基　　金：中国核工业地质局"十.五"重点生产科研项目 (HDKY2 0 0 2 0 5 0 1 ) ;中国地质大学 (武汉 )博士后流动站研究专题项目 ;中国地质大学岩石圈演化与矿产资源重点实验室开放基金项目 (MGMR2 0 0 2 1 4)

摘　　要：在鄂尔多斯盆地东北部 ,铀成矿与直罗组底部砂体的非均质性关系密切。砂体非均质性主要表现在平面和垂向上 ,其中 ,砂体平面非均质性可以通过砂分散体系来表征 ,而垂向非均质性则可以通过隔挡层和沉积物粒度来表征。在平面上 ,铀成矿主要分布于辫状河沉积体系向辫状河三角洲沉积体系过渡的辫状分流河道一侧 ,最佳成矿区则位于辫状分流河道砂体的频繁分岔处和从无隔挡层到隔挡层突发区的河道砂体边缘 ,且随着隔挡层数量和厚度的增加 ,铀成矿几率和品位逐渐降低 ;在垂向上 ,隔挡层的存在可以导致多个垂向序列单元、层间氧化带和铀矿卷头的发育。统计发现 ,中砂岩和细砂岩是铀成矿的最佳载体 ,所以在每个垂向序列单元中 ,铀矿通常位于辫状分流河道砂体的中下部。铀的成矿机理一方面可能是砂体非均质性通过对成矿流体运移状态的影响进而实现对铀成矿的控制 ,另一方面可能与沉积环境相变导致还原性物质的增加有关。通过砂体非均质性研究而总结的铀成矿规律是进行铀成矿空间定位和预测的基础。The uranium metallogenesis in northeastern Ordos basin is closely related to sand body hetero-geneity of the bottom sand body of Zhiluo Formation,Middle Jurassic.The sand body heterogeneity is expressed both in horizontal and vertical directions.Of them,the horizontal sand body heterogeneity may be characterized by sand disperse system,while the vertical heterogeneity is chartacterized by isolated barrier bed and sediment gramularity.On plane,the uranium mineralization is mainly distributed in braided distributary channel where the braided stream depositional system is transferring to delta depositional system.The optimal metallogenic area is always located in places where braided distributary stream channels are frequently branching,and at the periphery of channel sand body of the abrupt zone from the area without isolated barrier bed to the area with isolated barrier bed.In addition,with the increase of the number and the thickness of the barrier beds,the probability of uranium metallogenesis and the grade of uranium are decrease.In vertical direction,the existence of isolated barrier bed may result in the formation of multiple vertical sequence units,and the development of interlayer oxidation zone and uranium roll.Statistics show that medium-grained and fine-grained sandstone are the best lithologic hosts for uranium mineralization.So,uranium deposits generally exist in the lower-middle part of braided distributary channel sand bodies in each vertical sequence unit.On one hand,the mechanism of uranium metallogenesis might be originated form the effect of sand body heterogeneity on the migration state of ore-forming fluids to control uranium metallogenesis,and on the other hand,the sedimentary facies change leads to the increase of reducing substances.The uranium metallogenic regularity summarized on the basis of heterogeneity study of sand body is the base for the spatial localization and prognosis of uranium mineralization.

关 键 词：砂体非均质性 隔挡层 砂岩型铀矿 直罗组 鄂尔多斯盆地 

分 类 号：P612[天文地球—矿床学]