Hydrogeochemical and Isotopic Constraints on the Genesis of Strontium-Rich Mineral Springs in the Eastern Qaidam Basin, Tibetan Plateau.

Strontium-rich natural mineral water represents an important high-quality groundwater resource. However, the processes controlling Sr enrichment and the contribution of fault-controlled groundwater circulation to mineral water formation in cold-arid mountainous regions remain poorly constrained. In this study, the Yanglonggou Sr-enriched mineral spring system, located on the eastern margin of the Qaidam Basin on the Tibetan Plateau, was investigated. An integrated hydrogeochemical and isotopic approach was employed to elucidate the processes responsible for Sr enrichment. The results indicate that the groundwater exhibits a Ca-HCO3 hydrochemical facies, with hydrochemical evolution dominated by water-rock interaction. Groundwater is primarily recharged by precipitation and cryospheric meltwater, representing a modern groundwater circulation system with strong hydraulic connectivity. Geochemical modeling indicates that the continuous supply of dissolved Sr2+ is provided by the weathering of Sr-bearing silicate minerals and carbonate dissolution. Meanwhile, the persistent undersaturation of Sr-bearing minerals, including celestite and strontianite, limits Sr2+ removal and promotes progressive accumulation in groundwater. Collectively, these findings support a conceptual model involving recharge, groundwater circulation, fault-controlled flow, water-rock interaction, and Sr enrichment spring discharge. The fault system is indicated to function simultaneously as a preferential flow conduit and a local hydraulic barrier. This dual role is found to prolong groundwater residence time within Sr-bearing strata, thereby intensifying water-rock interactions and driving the formation of Sr-rich mineral water. A comprehensive evidence chain for the genesis of Sr-rich mineral water in cold-arid regions was established. New insights into fault-driven hydrogeochemical enrichment are provided, and a scientific framework for the exploration and sustainable management of similar mineral water resources is offered.