Elemental and Multiple Isotopic (H, O, Sr, B, and Li) Constraints on the Origin and Sources of Brine in the Bieletan Section of Qarhan Salt Lake, Northwestern China

Brines in playas and salt lakes provide crucial raw materials for potassium and lithium products in fertilizers and the energy sector. In this contribution, elemental and multiple H, O, Sr, B, and Li isotopic constraints were employed to determine the sources and origin of brines in the Bieletan Section (BLT) of Qarhan Salt Lake, northwestern China. The δD-δ18O results demonstrate that the brines of BLT mainly originated from river waters. The correlations of [Li] vs. [B], δ7Li vs. [Li] and δ11B vs. [B]/[Cl] suggest that the original provenance and silicate weathering played important roles in the elemental and isotopic signatures of B and Li in these river waters, which had been obscured by evaporation and concentration of brines and the related precipitation and redissolution of salt minerals during the evolution of brines in the salt lake. Strontium isotopes rule out the recharge of CaCl2 fluids from the northern fault zones for brines in BLT. Finally, the combination of elemental composition and Li, Sr, and B isotopes suggests that the current brine in BLT is mainly sourced from the Wutumeiren River and has experienced constant and intense evaporation to form the highly concentrated brine. By contrast, the contribution of the Golmud River/Tuolahai River and the CaCl2 spring water from the north fault zone to the brines in BLT is negligible. Our results highlight that integrated elemental and multiple isotope analyses are more effective for achieving a precise and comprehensive understanding of the source-to-sink process in the river–salt lake system.