Geochemical characteristics and sources of potassium and bromine in Salt-Lake Brines of the Junggar Basin, China

Salt lakes in the Junggar Basin, a typical inland arid basin in northwestern China, are characterized by localized abnormal enrichment of potassium (K) and bromine (Br), but the intrinsic mechanisms controlling this geochemical phenomenon remain poorly constrained. To address this question, we systematically analyzed 29 brine samples collected from seven representative salt lakes, and integrated hydrochemical composition, ion correlation, characteristic coefficients, and tectonic background to elucidate brine hydrochemical types, evolutionary processes, and the sources of K and Br. The results indicate that the brines are dominated by Na⁺-Cl⁻ and Na⁺- SO2- 4 systems, and can be classified into carbonate-type, sulfate-type (sodium sulfate and magnesium sulfate subtypes), and chloride-type, which correspond to distinct stages of hydrochemical evolution. Among the studied salt lakes, Dahong Salt Lake displays the most prominent K-Br anomalies, with maximum concentrations of 13.48 g/L for K⁺ and 485 mg/L for Br⁻, far exceeding both regional background values (K:~0.1–60 g/L; Br: 5 g/L; Br: ≥250–300 mg/L). Multiple lines of evidence, including hydrochemical diagrams (Piper and Gibbs plots), comparative hydrochemical analysis, regional tectonic evolution, and bromine-chlorine coefficient, collectively indicate that potassium and bromine in the K-Br-enriched salt lakes of the Junggar Basin are primarily derived from the evolution of paleoseawater. In addition, these K-Br-enriched brines incorporate secondary inputs from weathering of K-bearing silicate rocks in surrounding mountain ranges and from brines generated by localized dissolution of minor evaporite deposits within the basin.