Age of the Mengyejing potash deposit in the Simao Basin, southwest China: Constraints from detrital zircon U-Pb ages

The age of the Mengyejing potash deposit (MPD) in the Simao Basin, the only pre-Quaternary economically exploitable solid potash occurrence in China, has been the subject of debate for decades. It has been established that the ore-hosting Mengyejing Formation formed during the mid-Cretaceous based on radioactive and magnetic dating. The age discrepancy between the primary mid-Cretaceous and the squeezing of the Middle Jurassic is related to the lack of direct previous dating of the MPD itself. In this study, detrital zircon U-Pb dating of four clastic rock samples interbedded with the potash layers yielded the youngest zircon ages of 104.8, 106.5, 107.8, and 110 Ma. Taking into account the relatively large proportion of the youngest Cretaceous zircons and the Hf isotopic analysis, we propose that most of the Cretaceous zircons were derived from the contemporaneous volcanic activity that produced the tuff beds within the potash deposit and elsewhere in the Mengyejing For-mation, while only a small fraction of the Cretaceous zircons were found to be of detrital origin and have derived from the Bomi-Chayu and Dianxi-Burma batholiths. Consequently, the maximum age of the potash deposit of 110 to 105 Ma is the true depositional age of the strata and potash deposit.