铀储层结构与成矿流场研究:揭示东胜砂岩型铀矿床成矿机理的一把钥匙

以鄂尔多斯盆地北部的砂岩型铀矿为目标,在铀储层形成发育的沉积学背景研究基础上,重点通过砂分散体系、沉积物粒度、隔挡层厚度和孔隙度的定量分析,精细地刻画了直罗组铀储层的外部几何形态和内部复杂结构,充分展示了铀储层的定量非均质性。依据盆地构造充填演化阶段、铀成矿年代学和地学空间信息三维可视化平台,分别对5个演化阶段的古地貌进行了恢复,并对不同演化时期的铀储层空间位置给予了准确定位,从而揭示了直罗组铀储层从沉积到接受铀成矿再到铀矿被改造期间的空间形态演化历史。在盆地构造充填演化研究、古地貌恢复和铀储层定量非均质性分析的基础上,重建了5个不同时期古地下水系统结构和参数的空间变化面貌,并运用地下水数值模拟方法再现了研究区5个演化阶段成矿古流场的特征及其演化规律。综合分析认为,铀储层的空间演变和内部非均质性制约了成矿流场的基本格局,成矿流场又无疑控制着层间氧化带的发育和铀成矿。当铀储层形成期的古水流方向与主成矿期地下水流场方向总体一致时有利于铀成矿,而当两者流向垂直时则成矿效率降低。

Uranium Reservoir Architecture and Ore-forming Flow Field Study:A Key of Revealing Dongsheng Sandstonetype Uranium Deposit Mineralization Mechanism

In Dongsheng uranium deposit of northeast Ordos Basin,on the base of sendimetology setting study of uranium reservoir,the reservoir of sandstone-type uranium,external configuration and internal structure of uranium reservoir in Zhiluo Formation were portrayed in detail,by means of sandstone distributary system,barrier bed thickness and quantitative analysis of porosity,which showed quantitative heterogeneity of uranium reservoir.According to basin evolutionary stage,uranium metalizing chronology and 3D visualized platform of geological spatial information,palaeogeomorphology of five important evolutionary phases in study area was recovered and the spatial position of uranium reservoir of each evolutionary phase was located precisely.This revealed spatial configuration evolutionary process of uranium reservoir in Zhiluo Formation from depositional stage to uranium metallizing stage,then to uranium reform stage.On the base of basin evolutionary study,palaeogeomorphology study and quantitative heterogeneity analysis of uranium reservoir,plaeo-groundwater system structure and parametric spatial variation of five different stages were reconstructed.Metallogenic paleo-flow field characteristics and its evolutionary rule of five evolutionary stages in study area were reproduced by using groundwater numerical simulation.Generally,metallogenic flow field characteristics were controlled by the external configuration and internal heterogeneity of uranium reservoir,which affected the development of interlayer oxidation zone and mineralization process.When the paleo-groundwater of uranium reservior formation stage was in agreement with groundwater flow field of main metallizing phase,uranium deposited easily.When they were vertical,mineralization ability decreased.