Genesis and evolution of deep K-rich confined brine in Mahai Basin, Qinghai-Tibet Plateau

Abstract

Abstract Mahai Basin (MH), situated in the northern Qaidam Basin (QB), occurred abundant K-rich brine resources. The study on origin of deep K-rich confined brine and variation in K-Mg elements correspond to evolution in MH light on the significance of the sustainable development and utilization of brine deposits. This study presents multiple isotopes (δ18O and δD, 87Sr/86Sr) and hydrochemical characteristics for river waters, surface brines, intercrystalline brines, confined brines, gravel-type brines and anticlinal brines in the MH. The results indicate that: (1) Compared with anticlinal brine, confined brine is characterized by high K, low Ca and Sr contents, and close to the supply path of water chemistry in Yuqia River (from Na-HCO3-SO4 field to Cl-SO4 field in Ca-SO4-HCO3 equivalent diagram), deciphering river water is the main water source for confined brine. (2) The δ18O-δD values of confine brine are spatially various in MH and fall on the right side of the local evaporation line in this study, which implies that confined brine underwent evaporation and concentration successively. (3) The 87Sr/86Sr ratios (0.7114298–0.7114522) of confined brine is between river water and Lenghu anticlinal water, and both river water and confine brine dominate in low Sr field, further verified that more recharge budget of river water. (4) Combining with the evolution of sedimentary facies (Dezongmahai lake area as an example), K and Mg concentrations in MH increased progressively from west to east and from south to north, demonstrating the enrichment of K and Mg aligns to the evolution of MH and northeastern part of this basin serving as the final depositional center.