Metallogenic model of potassium-bearing brine deposits in nonsalt reservoirs of China and analogues in sedimentary basins worldwide

Potash salts and potassium (K)-rich brines are essential raw materials for potash fertilizer production and play a vital role in safeguarding global resources and food security. Two types of K-bearing brines are widely distributed in evaporite basins: shallow salt-lake intercrystalline brines hosted in salt reservoirs and deep Meso-Cenozoic clastic pore brines within nonsalt reservoirs. The recently identified deep sand-gravel brine (SGB) in the piedmont alluvial fans of the Altyn Tagh–Saishiteng Mountains on the northern Tibetan Plateau constitutes a newly discovered brine-type potash resource hosted in nonsalt reservoirs. Based on hydrogeochemical investigations, isotopic tracing, and mass-balance calculations, this study clarifies the provenance and metallogenic mechanism of SGB and compares the metallogenic models of salt lake brines (salt reservoirs) and clastic pore brines (nonsalt reservoirs) in worldwide sedimentary basins. Our results reveal that the SGB on the northern Tibetan Plateau is of meteoric origin and shares similar geochemical signatures with adjacent intercrystalline brines in the corresponding playas. Constrained by salinity and gravity gradients as well as tectonic compression, intercrystalline brines in the terminal salt lakes supply abundant K to the sand-gravel reservoirs in the pediment alluvial fans, forming an integrated fan–lake recharge mineralization system. Systematic variations in Sr concentrations and 87Sr/86Sr ratios document solute inheritance associated with paleolake depocenter migration. These analyses clarify a dual inheritance recharge model for the genetic relationship between paleolake-derived intercrystalline brines and the resulting SGB. This model clarifies the genetic linkage of K-bearing brines in both salt reservoirs and nonsalt reservoirs in the sedimentary basins of China (the Kuqa, Lop Nur, Sichuan, and Jianghan basins) and around the world (Altiplano–Puna Plateau, North America, and Saudi Arabia) and provides a new theoretical basis for deep potash brine exploration in analogous sedimentary basins.