Sources and enrichment mechanisms of lithium, rubidium, and cesium in waters of magmatic-hydrothermal systems

Geothermal waters of magmatic-hydrothermal systems are typically characterized by high concentrations of lithium (Li), rubidium (Rb), and cesium (Cs), offering significant potential for resource utilization. However, their sources and enrichment mechanisms remain poorly understood. This study systematically compiles 1299 water samples from magmatic-hydrothermal systems worldwide, along with 194 representative samples from non-magmatic hydrothermal systems for comparative analysis. By examining these magmatic-hydrothermal systems under various tectonic settings, the study aims to elucidate the genesis and enrichment mechanisms of Li, Rb, and Cs. The concentrations of Li, Rb, and Cs in geothermal waters discharged from magmatic-hydrothermal systems range from below detection limits to as high as 480 mg/L, 170 mg/L, and 49.7 mg/L, respectively. In most cases, water-rock interaction is the primary source of these elements. Nevertheless, geothermal waters with exceptionally high Li, Rb, and Cs concentrations, particularly those with Cs significantly enriched relative to Rb, are influenced by magmatic fluids exsolved during advanced magmatic differentiation. At divergent plate boundaries, thin crust and limited mantle magma evolution result in low Li, Rb, and Cs concentrations and low Cs/Rb ratios. In intraplate hotspots, advanced magmatic evolution produces moderate concentrations and Cs/Rb ratios. In contrast, at convergent plate boundaries, complex subduction and magmatic processes drive significant enrichment, yielding exceptionally high Cs/Rb ratios. The enrichment of Li, Rb, and Cs involves multiple geological processes, including pre-enrichment during subduction-related dehydration, partial melting, magmatic differentiation, and geothermal water cycling. This study provides the first comprehensive summary of the sources and enrichment mechanisms of Li, Rb, and Cs in magmatic-hydrothermal systems, offering theoretical insights for geothermal resource development, rare metal exploration, and the coupling of deep Earth dynamics with surface geological systems.