Lithium possesses exceptionally high economic and strategic significance. China’s lithium resources rank second globally, predominantly found in salt lake brine. Recently, clay-type lithium deposits have been discovered in the Mahai Salt Lake within the Qaidam Basin, featuring a broad distribution area, stable production layers, and thick strata. This paper investigates the mineral sources and mining circumstances of the clay deposits in the study area through the principal trace elements and Sr and Li isotopes of the clay rocks. The study reveals that the sedimentation of the clay deposits in the study area is mainly semi-brine–brackish water phase sedimentation, formed in a shallow water environment of weak oxidation. A terrigenous source characterizes the clay sediment. The tectonic setting of the study area shares common traits with a continental island arc-active continental margin, and the abundant lithium clay rocks mainly receive contributions of feldspar, amphibole, pyroxene, etc. The primary sediment source of the clay deposits mainly stems from igneous and quartz sediment source areas. The ⁸⁷Sr/⁸⁶Sr value indicates that the Sr source of the clay rocks in the study area is the shallow over-pressured brine and Yuka River water, mainly derived from the weathering dissolution of silicate rocks. The δ⁷Li value indicates that the lithium in the lithium-rich clay rocks mainly originates from the release of lithium from silicate minerals in the surrounding mountain ranges, carried by Yuka River water, and from the supply of lithium from the deep Ca-Cl type water body. The research findings establish a foundation for the future exploration and development of clay-type lithium deposits in salt lake regions.

The Reshui area, located to the northeast of the Qinghai–Tibet Plateau, exhibits complex geological conditions, well-developed structures, and strong hydrothermal activities. The distribution of hot springs within this area is mainly controlled by faults. In this paper, five hot springs from the area were taken as the research object. We comprehensively studied the geochemical characteristics and genetic mechanism of the geothermal water by conducting a field investigation, hydrogeochemistry and environmental isotopic analysis (⁸⁷Sr/⁸⁶Sr, δ²H, δ¹⁸O, ³H). The surface temperature of the geothermal water ranges from 84 to 91 °C. The geothermal water in the area exhibits a pH value ranging between 8.26 and 8.45, with a total dissolved solids’ (TDS) concentration falling between 2924 and 3140 mg/L, indicating a weakly alkaline saline nature. It falls into the hydrochemical type CI-Na and contains a relatively high content of trace components such as Li, Sr, B, Br, etc., which are of certain developmental value. Ion ratio analysis and strontium isotope characteristics show that the dissolution of evaporite minerals and carbonate minerals serves as a hot spring for the main source of solutes. Hydrogen and oxygen stable isotope characteristics findings indicate that the geothermal water is primarily recharged via atmospheric precipitation. Moreover, the tritium isotopic data suggest that the geothermal water is a mixture of both recent water and ancient water. Moreover, the recharge elevation is estimated to be between 6151 and 6255 m. and the recharge area is located in the Kunlun Mountains around the study area. The mixing ratio of cold water, calculated using the silicon enthalpy equation, is approximately 65% to 70%. Based on the heat storage temperature calculated using the silicon enthalpy equation and the corrected quartz geothermal temperature scale, we infer that the heat storage temperature of geothermal water in the area ranges from 234.4 to 247.8 °C, with a circulation depth between 7385 and 7816 m. The research results are highly valuable in improving the research level concerning the genesis of high-temperature geothermal water in Reshui areas and provide essential theoretical support for the rational development and protection of geothermal resources in the area.

The Balun Mahai Basin (BLMH), located in the northern Qaidam Basin (QB), is endowed with substantial brine resources; however, the genetic mechanisms and potential of these brine resources remain inadequately understood. This study investigated the intercrystalline brine (inter-brine) in BLMH, performing a comprehensive geochemical analysis of elemental compositions and H-O-Sr isotopes. It evaluated the water source, solute origin, evolutionary process, and genetic model associated with this brine. Moreover, a mass balance equation based on the ⁸⁷Sr/⁸⁶Sr isotopic ratio was developed to quantitatively evaluate the contributions of Ca-Cl water and river water to the inter-brine in the study area. The results suggest that the hydrochemical type of inter-brine in the north part of BLMH is Cl-SO₄-type and in the south part is Ca-Cl-type. The solutes in brine are mainly derived from the dissolution of minerals such as halite, sylvite, and gypsum. The hydrochemical process of brine is controlled by evaporation concentration, water–rock interaction, and ion exchange interaction. Hydrogen and oxygen isotopes suggest that the inter-brine originates from atmospheric precipitation or ice melt water and has experienced intense evaporation concentration and water–rock interaction. The strontium isotopes suggest that the inter-brine was affected by the recharge and mixing of Ca-Cl water and river water, which controlled the spatial distribution and formation of brine hydrochemical types. The analysis of ionic ratios suggest that the inter-brine is derived from salt dissolution and filtration, characterized by poor sealing and short sealing time in the salt-bearing formation. The differences in hydrochemical types and spatial distribution between the north and the south are fundamentally related to the replenishment and mixing of these two sources, which can be summarized as mixed origin model of “dissolution and filtration replenishment + deep replenishment” in BLMH.