Sources and Enrichment Mechanisms of Li-Rich Geothermal Springs in the Mediterranean-Himalayan Belt: Modelling From Li Isotope and Hydrochemistry

Abstract

The eastern extension of the Mediterranean-Himalayan geothermal belt contains numerous geothermal springs with anomalously high lithium (Li) content. These springs have long discharged substantial Li resources to the surface, underscoring their potential as a Li-rich geological feature of significant interest. This study utilises field investigations of typical high-temperature, Li-rich geothermal springs in this region, along with Li isotope tracing, hydrogeochemical analysis, and simulation, to elucidate the mechanisms behind the anomalous Li enrichment in these springs and to establish a model for Li enrichment in geothermal systems. Our findings reveal that high-temperature geothermal springs along the Yarlung Tsangpo Suture Zone in Tibet exhibit the highest recorded Li concentrations, generally exceeding those in other geothermal springs in the eastern extension by 1–2 orders of magnitude, with some even reaching concentrations suitable for industrial extraction. The discrepancy between the δ⁷Li values calculated for the geothermal springs and those measured, as well as the water–rock interactions simulated by PHREEQC, suggests that the Li leached solely from surrounding rocks is insufficient to account for the observed concentrations, indicating the presence of additional Li sources. In conclusion, the anomalous Li enrichment observed in these springs results from a combination of deep magmatic fluids, regionally Li-enriched rocks, and intense water–rock interactions. The upwelling of residual magmatic fluids from partial crustal melting along the Yarlung Tsangpo Suture Zone plays a major role in forming geothermal springs with unusually high Li content. In contrast, springs formed by mantle-derived magma, volcanism, or solely by water–rock interactions generally show only slight Li enrichment.