An analysis of U-Pb dating of detrital zircons and modes of occurrence of uranium minerals in the Zhiluo Formation of northeastern Ordos Basin and their indication to uranium sources

The Ordos Basin is an important large basin with multi-energy resources, around which a series of sandstone-type uranium deposits are developed. The Nalinggou uranium deposit located in the northeastern part was chosen as a study object. Five sandstone samples surrounding the ore-bearing segment in the Zhiluo Formation were selected to make detrital zircon U-Pb dating, while electron microprobe analysis was performed for some sandstone samples with uranium minerals. The ages are distributed as 5 major peaks:(2479±11) Ma-(2460±19) Ma, (2300-1950)Ma, (1896±21) Ma-(1820±32) Ma, (316-266) Ma and 165 Ma. The authors further arranged the age data of metamorphosed basement, khondalite belt and Late Paleozoic intrusions in the orogenic belt on the north margin of the Ordos Basin. These zones of detrital zircons ages are consistent with the ages of geological bodies in the orogenic belts on the northern margin of the Ordos Basin. Combined with the previous work about geochemistry and paleogeography, the authors hold that the provenance of sandstone of Zhiluo Formation in Nalinggou area was finally derived from the orogenic belt on the northern margin of the Ordos Basin. The uranium minerals are spread in and around the clastic grains, clay minerals, pyrites, and fractures in charcoal fragments. The radioactive anomaly measurement in the field work shows that the uranium source probably came from the pre-enrichment of clastic grains from the provenance at the diagenetic stage, and from the migration of the uranium-and oxygen-bearing water through later leaching of the highly radioactive bodies of the provenance.