Evolution and uranium mineralization of the northern Ordos Basin revealed by detrital zircons of the Jurassic strata

Abstract

Stable sedimentary basins with complex evolutionary histories generally develop various epigenetic resources, such as sandstone-type uranium deposits. However, the genetic linkage between basin evolution and subsequent uranium mineralization remains unclear. Detrital zircon is a robust mineral, and its U-Pb ages and Lu-Hf isotopes are essential for tracing the evolution of sedimentary basins. The Ordos Basin is the largest intracontinental basin and uranium deposit region in the North China Craton. It consists of Cambrian to Ordovician marine deposits and Carboniferous to Jurassic terrestrial successions, and the origins of the terrigenous clastic sequences are dominantly influenced by the neighboring orogenic belts. This study presents new whole-rock elemental data, detrital zircon U-Pb ages, and Lu-Hf isotopes for the sandstones from the Jurassic Zhiluo Formation of the northern Ordos Basin. With data from the Paleozoic sedimentary rocks of the basin and the southern Central Asian Orogenic Belt, this study aimed to determine sediment provenances, the evolution of the northern Ordos Basin, and the potential implications for uranium mineralization. Detrital zircons from the Zhiluo Formation are generally rounded and preserve magmatic zoning structures. Their ages display four populations, 330−245 Ma, 470−350 Ma, 2100−1650 Ma, and 2750−2200 Ma, which are consistent with the tectono-thermal events of the Central Asian Orogenic Belt and the Yinshan Belt to the north, and the Alxa Block to the northwest. Both their detrital zircon ages and εHf(t) values are similar to those of the underlying sedimentary rocks. In addition, the formation has recycled carbonaceous debris, diverse clastic fragments, and Triassic fossils, and its sandstones show low index of compositional variability values (0.79−0.97) and high SiO2/Al2O3 (5.33−7.25) and Th/Sc (0.71−1.97) ratios. These lines of evidence suggest that the detritus of the Zhiluo Formation was partially derived from the underlying sedimentary strata. It should be noted that the Paleozoic to Mesozoic strata of the northern Ordos Basin also have detrital zircon age patterns and εHf(t) values similar to those of the southern Central Asian Orogenic Belt, and the secular evolution of the Ordos Basin is therefore considered to have been controlled by subduction of the Paleo-Asian Ocean and collision between the Central Asian Orogenic Belt and the North China Craton, as well as the post-collisional crustal extension that ensued. The carbonaceous debris in the Zhiluo Formation provided a reductive environment for the subsequent crystallization of reducing minerals and uranium mineralization.