中国北方砂岩型铀矿深部探测新发现及其意义

在充分利用油气勘探钻井和地震资料的基础上,结合中国北方砂岩型铀矿调查工程,北方砂岩型铀能源矿产基地深部探测技术示范项目在中国北方系列盆地获得了砂岩型铀矿深部探测新发现,实现了新区、新层位找矿突破。在鄂尔多斯盆地西南缘,700~2000 m深白垩系洛河组风成沉积体系内新发现了铀矿(化)体。在准噶尔、塔里木、柴达木、酒泉、松辽等盆地新发现多处深部铀异常区。这些深部铀矿(化)体和铀异常区的发现,有效拓展了砂岩型铀矿的研究领域和找矿空间,将对砂岩型铀矿的理论研究和勘查产生深远的影响。系列研究表明,中亚铀成矿带和中国北方具有相似的铀成矿地质背景,赋矿地层普遍具有红层控矿的特点。相对于早期重视在还原性地层中研究氧化砂体及其成矿机理,本次工作中新发现的铀矿(化)体或铀异常多位于红色氧化环境中,而后期还原性含烃流体的灌入对于铀成矿具有重要控制作用。因此,氧化地层(红层)中还原性砂体(褪色蚀变)的研究应引起更大的关注。中国北方具有优越的成矿地质背景和古气候条件,包括丰富的铀源、大规模的砂体、后期的构造挤压(反转)形成的断裂和构造圈闭等,为流体提供了迁移通道和聚集场所。构造活动触发了地表含氧含铀流体和深层含烃流体的运移,构筑起了补?径?排流体成矿系统,尤其在古油气藏(断裂)边缘(顶部)形成的斜坡带,两种流体相互作用、耦合,巨量铀富集成矿。

New Deep Exploration Discoveries of Sandstone-type Uranium Deposits in North China

A few new discoveries of sandstone-type uranium deposits have been achieved in the basins in North China based on combined analyses of results of deep exploration in the new areas,new ore-bearing layers,and the drilling and seismic data of oil and gas exploration as well.Uranium mineralization was discovered at the southwestern Ordos Basin in the eolian sediments of the Cretaceous Luohe Formation at depth of 700 m to 2000 m.Several uranium anomalies have also been recognized in the Junggar,Tarim,Qaidam,Jiuquan and Songliao basins.The above discoveries show promising potential for exploration of the sandstone-type uranium deposits,and will shed lights on theoretical research and future exploration.The geological backgrounds of uranium mineralization in North China are similar to those of Central Asia.The ore-bearing formations are commonly characterized by ore-controlling red-layers,therefore,more attention should be paid to the oxidized sand bodies.Even though the role of the reductive strata was emphasized by many researchers,these newly discovered uranium orebodies or anomalies are mostly located in oxidation environment,whereas injection of reducing hydrocarbon-bearing fluid may play an important role in uranium mineralization.Thus,we argue that more attention should be paid to the reducing sand bodies(fading alteration)in oxidized formation(red layer).North China has abundant uranium source rocks,large-scale sand bodies,compressional faults and tectonic traps,which may provide the migration channels and concentration spaces for the fluids,and therefore,are advantageous for uranium ore mineralization.Tectonic activities may trigger the migration of supergene oxygen-bearing uranium-bearing fluid and hydrocarbon-bearing fluid,the coupling and interaction of the two kinds of fluids can lead to the enrichment and mineralization of a huge amount of uranium in the slope belt at the edge(top)of ancient oil and gas reservoirs(faults).