Depositional age and metallogenic model of K-bearing sand-gravel brine in pediment alluvial fans of the northern Qaidam Basin, Tibetan Plateau

• Multiple dating methods (OSL, ESR, TCN) were integrated to address the challenges in dating loose Quaternary alluvial fan sediments. • Sand-gravel brine reservoirs in north QB were formed during the Middle Pleistocene (1.1–0.3 Ma). • Kunhuang Tectonic Movement and mid-Pleistocene Climatic Transition drove the evolution of huge alluvial fan as SGB reservoir in north QB. • The northward migration of the depocenter creates the solute recharge for K-bearing Sand-gravel brine deposits. • The evolution of ‘fan-lake’ system in closed catchments indicate potential for SGBs formation in other sub-basins of QB. The K-bearing sand-gravel brine (SGB) deposits have been discovered in the large pediment alluvial fans in the northern and western Qaidam Basin (QB) on the northern Tibetan Plateau (TP). The metallogenic model of the brine deposits remains controversial. In particular, the formation age of the reservoir and its formation mechanism are still unclear. In this study, by utilizing lithological logging, K-content profiling, and multi-dating (OSL, ESR, TCN) of three deep cores, we refined the reservoir chronology and metallogenic model of the new SGB deposits in the Mahai Basin, northern QB. Some key conclusions include: 1) The SGB reservoir was deposited during the Middle Pleistocene (1.1–0.3 Ma), which was driven by the combination of Kunhuang tectonic movement and mid-Pleistocene transition climatic events (1.2–0.6 Ma). 2) A hypothesis was proposed that the sedimentation of salt layers in the terminal salt lakes is later than the formation of alluvial fan in a closed sub-playa. This assumption is verified by the forming ages of fan-lake (salts) in the Dalangtan and Mahai playas. Combining with the spatial-temporary evolution of the anti-S shape on the playas in the QB, we proposed that the age and scales of salt-forming in the respective sub-playa can indicate the depositional age and extent of corresponding SGB. 3) The northward migration of the depocenter in the Mahai Basin, driven by tectonic tilting, led to the lateral migration of brines and the subsequent formation of K-bearing SGB deposits within the pediment alluvial fan reservoirs. 4) The metallogenic model of the fan-lake system in the QB can serve as a theoretical foundation for prospecting deep brine resources in the pediment alluvial fans of various playas, both now and in the future