U-Pb isochron age calculation and related issues in sandstone-hosted uranium deposits: A case study from the Hailijin uranium deposit, Songliao Basin, China

• Radiogenic lead loss in sandstone-hosted uranium deposits causes scattered and anomalously young in‑situ dating results. • Whole‑rock and mineral samples show consistent U‑Pb isotopic evolution trends. • The modified whole‑rock U‑Pb isochron method is currently the most robust approach for dating such deposits. • Mineralization age of the Hailijin uranium deposit aligns with magmatic‑rock and apatite fission‑track ages. Numerous techniques have been applied to determine the mineralization ages of sandstone-hosted uranium deposits, each with inherent advantages and limitations; however, no single method has yet achieved broad consensus. In this study, the Hailijin uranium deposit in the Songliao Basin, China, is taken as a case study, and an improved whole-rock U–Pb isochron dating method is applied. We present a systematic description of the theoretical basis, sampling strategy, analytical procedures, and data-processing workflow of this approach. In addition, the major factors influencing age determination in sandstone-hosted uranium deposits are discussed, and the reliability of the isochron method is critically evaluated. U–Pb isotopic data from 59 whole-rock samples collected from the Hailijin deposit over multiple years were compiled and analyzed, yielding ten distinct uranium mineralization episodes. Uranium minerals in sandstone-hosted deposits commonly exhibit poor isotopic closure, as processes such as the high mobility of radon (a daughter product of uranium decay) and alpha-recoil effects involving 234 U can result in substantial loss of radiogenic lead. As a consequence, mineralization ages obtained using many dating methods are prone to systematic underestimation. Importantly, the whole-rock isochron approach significantly reduces the impact of radiogenic lead loss. Theoretical derivation demonstrates that the U–Pb isotopic evolution of whole-rock samples follows the same principles as that of individual minerals, thereby validating the use of whole-rock samples for isochron age calculation. For the Hailijin deposit, the obtained mineralization ages show strong agreement with the regional thermal history, magmatic activity, and other geological events in the southern Songliao Basin. This consistency with the regional geological evolution provides indirect yet robust evidence that the whole-rock isochron method represents a reliable approach for determining mineralization ages in sandstone-hosted uranium deposits.