Spatial Distribution and Enrichment Mechanisms of Rubidium and Caesium in Salt Lakes of the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau hosts salt lakes enriched in strategic metals, yet the behaviour of rubidium (Rb) and caesium (Cs) remains poorly understood. Based on 169 water samples from 44 lakes (Zhao, 2024), this study integrates multivariate statistics with spatial hotspot analysis (Getis-Ord Gi*, 1000 m threshold). Rb (0.004–13.05 mg/L) and Cs (0.0001–2.07 mg/L) exhibit a southeast-high, northwest-low pattern. Principal component analysis shows that Rb loads strongly on the evaporative concentration factor (PC1, loading 0.853). It correlates significantly with K⁺ (r = 0.803) and TDS (r = 0.758), indicating conservative behaviour driven by evaporation. In contrast, Cs loads most strongly on a decoupled factor (PC3, loading 0.749) and shows weaker correlation with TDS (r = 0.471), suggesting non-conservative enrichment influenced by deep hydrothermal input and clay mineral adsorption–desorption. Hotspot analysis identifies MC as a shared Rb-Cs hotspot, GZC and QGC as Cs-specific, and EYC as Rb-specific. These findings provide a quantitative framework for understanding rare alkali metal enrichment in high-altitude salt lake systems.