巴音戈壁盆地塔木素铀矿床地质特征及铀成矿模式研究

巴音戈壁盆地为中国北方重要的能源盆地。笔者通过对盆地内塔木素铀矿床地质特征研究,发现矿床产于因格井凹陷巴音戈壁期微斜坡,晚白垩世和古近纪剥蚀窗口的发育,为成矿流体向盆地内运移提供了有利条件;矿床的主要目的层为下白垩统巴音戈壁组上段二岩段,为扇三角洲-湖泊沉积,扇三角洲砂体发育。巴音戈壁组上段二岩段与巴音戈壁组上段一岩段、三岩段构成有利的"泥-砂-泥"地层结构,有利于含铀含氧水向盆地内运移和层间氧化作用的发生。矿床内氧化带可划分为完全氧化带、氧化还原过渡带和还原带,矿体主要位于氧化还原过渡带中,受氧化带前锋线和氧化还原过渡带控制。矿床内参与铀成矿作用的还原介质主要为内部还原介质和外部还原介质。内部还原介质为目的层本身的有机质、黄铁矿等;外部还原介质为巴音戈壁组上段一岩段、三岩段暗色泥岩中发育的有机质、深部油(气)等。盆地内铀矿化与盆地的构造热事件密切相关,铀成矿作用表现为3期,第一期早白垩世中-晚期((109.7±1.5)Ma～(115.5±1.5)Ma),第二期为晚白垩世晚期—古近纪((45.4±0.6)Ma～(70.9±1.0)Ma)、第三期为新近纪((12.3±0.2)Ma～(2.5±0)Ma)。塔木素铀矿床矿体主要为砂岩型、砂泥混合型、后生泥岩型和同沉积泥岩型,矿体受层间氧化带和沉积相变控制明显。通过矿床构造、目的层沉积体系、氧化带、有机质和铀矿化等特征的研究,建立了矿床铀成矿模式和矿体成因模型,为后期铀成矿作用标志的研究奠定了基础。

Geological characteristics and uranium metallogenic model of Tamusu uranium deposit in Bayin Gobi Basin

Bayin Gobi Basin is an important energy basin in northern China. Based on a study of the geological characteristics of the Tamusu uranium deposit, the authors found that the deposit was developed on the Bayin Gobi micro-slope of Ingejin sag, and the denudation windows of Late Cretaceous and Paleogene period provided favorable conditions for the migration of ore-forming fluids into the basin. The main target bed of the deposit is the 2nd member of the Lower Cretaceous Upper Bayin Gobi Formation, composed mainly of fan delta-lacustrine deposits and fan delta sandbodies. The 2nd member of the Upper Bayin Gobi Formation, the 1st member and the 3rd member of the Upper Bayin Gobi Formation formed a favorable "mud-sand-mud" stratigraphic structure, which is conducive to the migration of uranium-bearing oxygen-bearing water into the basin and the occurrence of interlayer oxidation. The oxidation zones in the deposit can be divided into complete oxidation zones, oxidation-reduction transition zones and reduction zones. The orebodies are mainly located in the oxidation-reduction transition zones, which are controlled by the front of the oxidation zone and the oxidation-reduction transition zones. The reductive media involved in uranium mineralization were mainly internal reductive media and external reducing media. The internal reductiuon media were composed of the organic matter and pyrite of the target layer itself, the external reduction media were the organic matter developed in the dark mudstone of the 1st and 3rd member of the Upper Bayin Gobi Formation, and the deep oil (gas) and some other materials. Uranium mineralization in the basin was closely related to the tectonic-thermal events in the basin. Uranium mineralization occurred at three stages:the first stage occurred in the Middle and Late Early Cretaceous, from(109.7±1.5) Ma to (115.5±1.5) Ma; the second stage occurred in the Late Cretaceous, from(45.4±0.6) Ma to(70.9±1.0) Ma; the third stage occurred in the Neogene, from(12.3±0.2) Ma to(2.5±0) Ma. The orebodies of the Tamusu uranium deposit are mainly of sandstone type, sand mud mixed type, later mudstone type and syngenetic type. The mudstone type is controlled obviously by interlayer oxidation zone and sedimentary facies transformation. The uranium metallogenic model and orebody genetic model of the deposit were established by studying the characteristics of the deposit structure, target bed sedimentary system, oxidation zone, organic matter and uranium mineralization, which lays a foundation for the study of the indicators of late uranium mineralization.