【作者】 郭庆银；

【导师】 周美夫； 颜丹平；

【作者基本信息】 中国地质大学（北京） ， 构造地质学， 2010， 博士

【摘要】 鄂尔多斯盆地西缘褶冲带是我国北方东部构造和西部构造的转化带,研究其构造演化对了解我国北方构造体系转化,总结该区铀成矿规律,客观评价其铀成矿潜力具有重要意义。因此,本文以地球动力学和水成铀矿理论为指导,采用构造解析、同位素年代学和同位素地球化学的方法与技术,在全面分析前人工作的基础上系统研究了盆地西缘构造演化及其对铀成矿的控制作用。盆地西缘物源区碎屑锆石U-Pb测年和Lu-Hf同位素测试结果表明,3.5Ga时物源区就发生了壳幔分离形成了古陆核,后经2.6~2.7Ga和0.8~1.1Ga两次大规模的地壳增生以及吕梁、海西等多期岩浆活动的改造,地壳的成熟度较高,中酸性火山岩、碱性花岗岩等富铀岩石发育,向盆地内提供了充足的铀源。中-新生代,周边板块离散-汇聚作用以及构造应力场的转化控制了盆地西缘7阶段演化模式。燕山期南北向构造带与喜山期六盘山弧形构造带的斜交叠加造成了盆地西缘南、北两段的显著差异。晚三叠世(扇)三角洲砂体和中侏罗世低可容纳空间下的辫状河砂体空间展布稳定,岩石中富含有机质和黄铁矿,有利于砂岩型铀矿的形成,但强烈的构造变形降低了砂体的产铀潜力;早白垩世挤压背景下的辫状河砂体具有一定的规模,构造变形较弱,有利于地下水的渗入成矿。盆地西缘发育3种类型的铀矿化:层间氧化带型铀矿化品位高、规模大,主要产于直罗组下段(J2zh1)和马东山组(K1m)中,后生蚀变分带明显。铀矿化受构造、砂体、地下水渗入作用及后生蚀变控制,铀的沉淀、富集与氧化带前锋碱性-还原综合地球化学障有关;潜水氧化带型铀矿化品位低、规模小,受局部还原环境的控制;沉积成岩叠加后期改造型铀矿化品位低、厚度变化大,铀矿化主要受岩性岩相控制,后期淋滤改造使铀矿化进一步富集。构造是盆地西缘最主要的控矿因素,不但控制了蚀源区铀源岩的形成和出露,而且控制了盆地内找矿目标层的发育和变形。砂体、构造斜坡带和排泄构造的发育特征以及构造抬升作用控制了地下水的渗入与成矿作用。根据矿化特征和控矿因素分别建立了CYB、GJW和BTJ 3个不同类型的铀矿床(化)的成矿模式,并据其进行了铀矿资源评价与预测,圈定了4片成矿远景区。更多还原

【Abstract】 The thrust-fold belt at the western margin of Ordos Basin is the tectonic transformation belt between eastern and west structures of Northern China. It is of important significance for understanding the structural evolution of Ordos Basin and the tectonic transformation of the North of China, for summarizing uranium metallogenic regularity and evaluating the potentials of uranium metallogenesis. Thus, guided by geodynamics theory and the theory of hydrogenic uranium metallogenesis, this paper undertakes a comprehensive and systematic research on the tectonic evolution of the western margin of Ordos Basin and its control over uranium mineralization applying the approaches of tectonic analysis, isotope geochronology and geochemistry.According to the U-Pb dating and Lu-Hf isotope analytic results of detrital zircons from the provenance at the western margin of Ordos Basin, it is concluded that the paleo-continental nucleus was formed upon the crust-mantle differentiation in the provenance at 3.5Ga. After two-time considerable crustal accretion during 2.7~2.6Ga and 1.1~0.8Ga, as well as the reformation by the Lvliangian and Hercynian magmatic activities, the crust became higher in maturity and was abundant in uranium-rich intermediate-acidic volcanics and alkaline granites, which would supply the Basin with sufficient uranium sources.During Mesozoic and Cenozoic, divergence-convergence processes of the surrounding plates and the conversion of tectonic stress field resulted in 7-phase tectonic evolution of the western margin of the Basin. The oblique crossing superimposition of Yanshanian Meridional Tectonic Belt by Himalayan Liupanshan Arc-shaped Tectonic Belt led to the remarkable differences between the southern and northern sections of the western margin of Ordos Basin. Late Triassic fan delta sand bodies and Middle Jurassic braided stream sand bodies in lower accommodation space are stably distributed and enriched in organic substances and pyrites, which are favorable for the sandstone uranium mineralization. The intense structural deformation, however could reduce the uranium metallogenic potential of sand bodies. Early Cretaceous braided stream sand bodies formed under the compressive regime are of certain size and benificial to the infiltration of groundwater and uranium ore formation.There are three types of uranium mineralization at the western margin of the Basin: (1) Interlayer Oxidation Zone Uranium Mineralization: higher in grade and larger in size, occurring in the lower member of Zhiluo Formation (J2zh) and Madongshan Formation (K1m), of which the epigenetic alteration zoning is expressed obviously. Precipitation of uranium is associated with the alkalic-reducing geochemical barrier at the redox front. (2) Phreatic Oxidation Zone Uranium Mineralization: lower in grade and smaller in size, controlled by local reducing environment. (3) Sedimentary Diagenetic Superimposed Reformation Uranium Mineralization: also lower in grade with variable thickness, controlled by lithologies and lithofacies and may be further concentrated by epigenetic infiltration and reworking.Structures are the most predominant ore control factors. Not only the development and the outcroping of uranium source rocks in the provenance, but also the upgrowth and deformation of prospective target layers are controlled by tectogenetic movements. Infiltration of ground water and uranium metallogenesis are constrained by the characteristics of sand bodies, the structural slopes and the discharge structures. According to the mineralization features and ore-controlling factors, three type of uranium metallogenic models, i.e. CYB, GJW and BTJ, are established by the author. The uranium potentials are also evaluated and prognosis. Four prospective areas are have been outlined for further mineral exploration.更多还原