Hydrogeochemistry of Lithium-Bearing Brines of the Shu-Sarysu Sedimentary Basin

Natural lithium-bearing brines are gaining strategic importance as an alternative to traditional hard-rock deposits. Approximately 78% of the identified global lithium resources are hosted in hydromineral environments, including continental brines, oilfield formation waters, and geothermal fluids. The Shu–Sarysu sedimentary basin in southern Kazakhstan is one of the most extensive, yet poorly studied, brine provinces in Central Asia. This study provides a comprehensive hydrogeochemical characterization of lithium-bearing brines in the Moiynkum structural zone of the Shu–Sarysu basin, based on regional field sampling, multielement analysis, and GIS data integration. Water samples were collected from four deep gas production wells (perforation depths of 2029–2290 m) at the Ayrakty and Amangeldy fields. Analytical data demonstrate highly concentrated chloride–calcium–sodium brines with total dissolved constituent concentrations (TDS, calculated as the sum of analyzed ions) ranging from 140.1 to 272.1 g/L, with lithium content of 24.46–55.11 mg/L, strontium 680.5–1648.2 mg/L, rubidium 4.31–8.42 mg/L and cesium 0.317–0.420 mg/L. Piper and Durov diagrams classify the samples as highly evolved Na–Ca–Cl to Ca–Na–Cl formation brines typical of deep, long-residence sedimentary formation waters. Lithium enrichment is interpreted to reflect the combined influence of several processes: water–rock leaching of Li-bearing lithologies, evaporative concentration of ancestral brines, clay-mineral ion exchange, and possible deep fluid contributions, whose relative roles remain to be constrained by isotopic data. The compiled GIS-integrated database, combining new analytical data with archival hydrogeochemical records, delineates two promising lithium-bearing provinces and identifies priority areas for further exploration. The results indicate that the Shu–Sarysu Basin is a prospective region for further exploration of lithium-bearing formation waters in Kazakhstan. The recorded Li concentrations fall within the lower range of sedimentary-basin brines currently being evaluated for lithium extraction, although their economic and technological feasibility remains to be established.