松辽盆地钱家店铀矿床层间氧化带分带性的岩石磁学判识及其机理

Magnetic parameters have advantages of high speed, low cost and high sensitivity for characterizing zonation of interlayer oxidation zone of sandstone-hosted uranium deposits. However, studies on characterizing zonation of interlayer oxidation zone systematically using magnetic susceptibility remain rarely reported. In addition, little attention has been paid to studies about mechanism for variation of magnetic parameters within interstratified oxidation zone. It has been found by applicants that the magnetic susceptibility is highly related with the interlayer oxidation zone from Qianjiadian uranium deposit in the southern Songliao Basin. So, this project aims to illustrate rock magnetic identification for characterizing zonation of interlayer oxidation zone and its mechanism from the Qianjiadian uranium deposit. Using a series of tests including magnetic susceptibility, isothermal remanent magnetization, anhysteretic remanence, hysteresis parameter, thermal demagnetization curve, scanning tunneling microscopy, transmission electron microscopy and X ray diffraction, the characteristics of the magnetic parameters and magnetic minerals from the interlayer oxidation zone will be described. The response of the magnetic parameters to the changes of species, size, content and morphology of the magnetic minerals will be illustrated. The magnetic parameters will be used to establish a quantitative model for characterizing zonation of the interlayer oxidation zone. Based on these data, the characteristics of magnetic minerals from the subzones within the interlayer oxidation zone will be correlated to discuss variations of magnetic minerals during the interlayer oxidation, and then the mechanism of characterizing zonation of interlayer oxidation zone using magnetic parameters will be revealed. Expected results of this project will optimize studies about characterizing zonation of interlayer oxidation zone of sandstone-hosted uranium deposits and prepare the ground for studying metallogenic regulation and mineralization of sandstone-hosted uranium deposits using magnetic parameters as proxies, which can enrich the research contents of sandstone-hosted uranium deposits and expand the applications of rock magnetism.

岩石磁性参数在砂岩型铀矿床层间氧化带分带性研究中具有快速、经济、灵敏度高等优点，然而国内外这方面的研究却很少，同时，对引起层间氧化带中磁化率出现差异的机理解释缺乏定量数据约束。申请者在进行松辽盆地钱家店铀矿床研究中发现了磁化率与层间氧化带关系密切，因此，本项目拟以该矿床为对象，利用各种磁学测量、偏光显微镜、电子探针、扫描电镜、XRD等方法研究层间氧化带的磁性参数和磁性矿物特征，建立磁性参数对磁性矿物种类、大小、含量及形貌等特征变化的量化响应关系，优选合适的磁性参数构建层间氧化带的岩石磁学分带模型，探讨层间氧化过程中磁性矿物特征的变化及磁性参数相应的响应，揭示层间氧化带分带性的磁学判识机理。预期成果将从岩石磁学角度进一步优化砂岩型铀矿床层间氧化带分带性研究，为磁性参数作为替代指标研究层间氧化带砂岩型铀矿成矿规律、成矿作用等奠定理论基础，丰富砂岩型铀矿的研究内容，并拓宽岩石磁学方法的应用领域。

钱家店铀矿是近年来松辽盆地发现的第一个超大型砂岩型铀矿床。该矿床沿层间氧化作用的方向上依次出现红色砂岩→黄色砂岩→灰色不含矿砂岩→灰色含矿砂岩→原生灰色砂岩。该矿床不同类型砂岩中识别出的矿物蚀变作用类型有：赤铁矿化、褐铁矿化、黄铁矿化、粘土化、碳酸盐化和铀矿化。矿床经历了成岩期中性-弱碱性环境→成矿早期酸性环境→成矿晚期弱碱-碱性环境→成矿期后碱-强碱性环境的转变。. 钱家店铀矿床中钛铀矿-铁白云石-闪锌矿-方铅矿-黄铜矿-黄铁矿等典型热液矿物组合的发现预示其受热液作用明显，区别于以往典型层间氧化带砂岩型铀矿。磁性参数测量显示受热液作用影响的铀储层磁化率和天然剩磁强度明显降低。磁性矿物分离和鉴定发现，该铀矿床中的磁性矿物主要为钛磁铁矿，且其在辉绿岩接触带附近的铀储层中明显减少，说明辉绿岩侵入所引起的热流体活动造成了强磁性矿物——钛磁铁矿的减少，进而导致铀储层磁化率和天然剩磁强度明显降低。. 定量表征了钱家店铀矿床层间氧化带中黄铁矿的类型、粒径、含量及元素组成等特征，厘定了其生成序列，指出两种黄铁矿组合（截面不光滑胶状黄铁矿+草莓状黄铁矿微晶加大莓球体+草莓状微晶集合体和表面形态完整的自形立方体黄铁矿+表面形态完整的半自形晶黄铁矿+自形八面体黄铁矿）与铀成矿关系密切。阐明了松辽盆地钱家店铀矿床中碳酸盐胶结物的类型、生成序列及微区地球化学特征，厘定了铁白云石胶结物属于铀成矿阶段的产物，指出成矿期流体具有低盐度、强还原性等特点。