The Qaidam basin serves as the primary reservoir of potash salt resources and the key production base for potash fertilizer in China. Recent geological explorations have identified a novel type of potassium-bearing sand and sandstone pore brine deposit in the western foreland alluvial fan of the basin. This newly discovered deposit is believed to contain significant potassium chloride resources, with the brine displaying prominent attributes of high sodium and chlorine levels, and a mineralization model resembling that of "inherited halite rock". Located as a secondary basin and distinct from the Kunteyi basin on the northern margin of Qaidam, the Mahai basin is a small lake basin characterized by various types of brines (intercrystalline brines, confined brines, sand-gravel brines, anticlinal structure brines, etc.). In this study, by conducting a comparative analysis of the major and trace ion content, salinity, and hydrogen and oxygen isotope composition of river water and various brines in the Mahai basin, the following main conclusions have been drawn:① The average K+ content and TDS value of the sand-gravel brines in the Mahai basin are 2.16 g/L and 254.2 g/L, respectively, indicating a notably high ratio of Na++ Cl-/TDS (0.94). These brines belong to the Na-Cl type hydrochemical classification; ② While the potassium K+ content and TDS value of the sand-gravel brines in the Mahai basin are lower than those in the surface brines, intercrystalline brines, and confined brines of Mahai Salt Lake, they are close to the minimum threshold required for industrial potassium salt exploitation, suggesting a certain potential for resource development. The spatial distribution of K+ in sand-gravel brines, intercrystalline brines, and confined brines closely aligns with potassium-containing evaporites. Considering the salinity gradient and gravitational effects influenced by differences in brine TDS and burial depth, it is suggested that the salt solute and potassium in sand-gravel brines originate from the recharge of intercrystalline brines and confined brines; ③ Through the utilization of the K-B-Li equivalent map and analysis of varying B content in different water sources, it is demonstrated that the sand-gravel brines consist of a mixture of Yuqia River water, intercrystalline brines, and confined brines; ④ The δD-δ18O values of the sand-gravel brines in the Mahai basin range from -56.9‰ to -17.6‰ and -5.70‰ to +6.00‰ for hydrogen and oxygen isotopes, respectively. These values exhibit similar characteristics to the confined brines and intercrystalline brines, evenly distributed on both sides of the local evaporation line. Additionally, as the 2H-18O increases, the concentrations of B and Li also increase. These findings indicate that the sand-gravel brines have undergone evaporation and concentration. Consequently, the sand-gravel brines have been inheriting solutes from intercrystalline brines and confined brines over a long period, including ions such as K+, Na+, and Cl-, leading to their similar H-O isotopic signatures.