Shallow groundwater chemical evolution, isotopic hyperfiltration, and salt pan formation in a hypersaline endorheic basin: Pilot Valley, Great Basin, USA

Endorheic basin brines are of economic significance as sources of boron, iodine, magnesium, potassium, sodium sulfate, sodium carbonate, and tungsten, and they are a major source of the critical metal lithium. Although evaporation is the primary hypersalinization driver for evaporative water bodies, recent investigations have proposed more novel mechanisms for some subsurface brine. This investigation explores shallow groundwater hypersalinization. The chemical evolution and isotopic fractionation of shallow hypersaline groundwater in the clay-rich arid endorheic basin sediments of Pilot Valley, Great Basin (USA), were investigated. Groundwater evolves from fresh in the mountain bedrock and alluvial fans, to brackish and saline at the alluvial fan–playa interface, and to hypersaline in the upper 12 m of basin sediments. Alluvial fan systems are isolated from each other and have varying groundwater 3 H and 14 C travel times. Nonevaporative in-situ isotopic fractionation of up to −8‰ in δ 18 O is attributed to clay sequence hyperfiltration. Groundwater flow-path sulfate and chloride mineral dissolution is the primary driving mechanism for both interface and basin groundwater evolution. Evaporation only impacts the groundwater quality in a small portion of the basin where the groundwater is within ~1 m of the ground surface. Here capillary action carries dissolved soluble salts to the land surface. Episodic flooding redissolves and carries the precipitated salt to the annually flooded salt pan where it accumulates as a salt crust during the dry season. The Pilot Valley model may help explain the buildup accumulative layers of soluble salt that when remobilized becomes subsurface brine. Les saumures de bassins endoréiques ont une importance économique en tant que sources de bore, d’iode, de magnésium, de potassium, de sulfate de sodium, de carbonate de sodium, et de tungstène, et elles constituent une source majeure de lithium, un métal critique. Bien que l’évaporation soit le principal moteur de l’hypersalinisation pour les masses d’eau exposées à l’évaporation, des recherches récentes ont proposé de nouveaux mécanismes pour certaines saumures de subsurface. Ces recherches explorent l’hypersalinisation d’eaux souterraines peu profondes. L’évolution chimique et le fractionnement isotopique des eaux souterraines hypersalines peu profondes dans les sédiments du bassin endoréique aride riche en argiles de Pilot Valley, du Grand Bassin (Etats-Unis d’Amérique) ont