Wang Junxian, Li Ziying, He Feng, Bai Fengtian, Qiu Linfei, Guo Jian, Zhang Chuang
Beijing Research Institute of Uranium Geology, CNNC, No. 10 Xiaoguandongli, Chaoyang District, Beijing, 100029, China.
National Key Laboratory of Uranium Resource Exploration-Mining and Nuclear Remote Sensing, Beijing, 100029, China.
Sci Rep. 2024 Nov 6;14(1):27004. doi: 10.1038/s41598-024-75930-z.
The source of uranium is an important research topic related to the exploration of sandstone-type uranium deposits, and potential uranium sources in deep basins are often overlooked. Black organic-rich shale is a common uranium-bearing rock in deep sedimentary basins. However, relatively few studies have investigated the migration of uranium during hydrocarbon generation in and release from uranium-rich shale. In this study, the uranium-rich shale in the Chang 7 member of the Yanchang Formation of the Upper Triassic in the Ordos Basin was selected to investigate the migration of uranium and other trace elements during the thermal maturation of uranium-rich shale via a semiopen pyrolysis simulation system. The gas and liquid products as well as the solid residue were thoroughly analysed by means of multiple instruments. The results showed that uranium significantly migrated before hydrocarbon generation (Ro < 0.61%), with a leaching rate between 12.1% and 18.8%. The leaching rate of uranium during the hydrocarbon generation stage (0.63% < Ro < 1.35%) was relatively low, ranging from 0 to 7.2%. Cu, Pb, Zn, Mo, and other trace elements also migrated considerably during the early stage of thermal evolution, with leaching rates ranging from 2.9 ~ 11.6%. The yield of low-molecular-weight organic acids (LOAs) was the highest in the early stage of thermal maturity, and the LOA yield exhibited a good correlation with the leaching rates of Cu, Pb, Zn, Co, Mo, etc. The generation of LOAs from source rocks was conducive to the leaching and migration of trace elements. Moreover, according to a statistical analysis of published geochemical data, the total organic carbon (TOC) content, uranium content, and U/TOC ratio in shale decreased significantly with increasing burial depth, indicating that uranium migrated significantly upon kerogen hydrocarbon generation during thermal evolution. Therefore, uranium-rich shale is an important deep uranium source in sedimentary basins.
铀源是与砂岩型铀矿勘查相关的重要研究课题，而深部盆地中的潜在铀源常常被忽视。富含有机质的黑色页岩是深部沉积盆地中常见的含铀岩石。然而，针对富铀页岩在生烃过程中铀的迁移及释放的研究相对较少。本研究选取鄂尔多斯盆地上三叠统延长组长7段的富铀页岩，通过半开放热解模拟系统，研究富铀页岩热成熟过程中铀及其他微量元素的迁移情况。利用多种仪器对气体、液体产物以及固体残渣进行了全面分析。结果表明，铀在生烃前（Ro＜0.61%）显著迁移，淋滤率在12.1%至18.8%之间。生烃阶段（0.63%＜Ro＜1.35%）铀的淋滤率相对较低，为0至7.2%。Cu、Pb、Zn、Mo等微量元素在热演化早期也有较大迁移，淋滤率在2.9%至11.6%之间。低分子量有机酸（LOAs）的产率在热成熟早期最高，且LOAs产率与Cu、Pb、Zn、Co、Mo等元素的淋滤率具有良好的相关性。源岩中LOAs的生成有利于微量元素的淋滤和迁移。此外，根据已发表地球化学数据的统计分析，页岩中的总有机碳（TOC）含量、铀含量以及U/TOC比值随埋藏深度增加而显著降低，表明热演化过程中干酪根生烃时铀发生了显著迁移。因此，富铀页岩是沉积盆地中重要的深部铀源。
