Enrichment mechanisms of lithium for the geothermal springs in the southern Tibet, China

As low-grade lithium (Li) extraction technology improves, Li-rich geothermal fluids may become an alternative Li source in the future. Most geothermal springs in southern Tibet, China, have notably high Li contents, but the fluids’ Li origins and enrichment processes remain unclear. Therefore, this study investigated the Li enrichment mechanisms in the study area based on 307 hydrogeochemical data of thermal spring waters selected from the literature. Our findings confirm that most Li-enriched geothermal springs in southern Tibet are chemically influenced by magma. Also, K-Mg and chalcedony geothermometers’ estimates indicated that most of the springs originate from shallow reservoirs with temperatures below 200 °C, although some higher temperature deep reservoirs may exist beneath Tibet. Moreover, we found that two hydrochemical processes mainly resulted in the relatively high Li concentrations in southern Tibet’s thermal fluids. First, magmatic Li enrichment resulted from the semi-molten state magma degassing rather than leaching from the surrounding rocks in the deeper reservoirs. Subsequent mixing of the Li-rich deep fluids with varying amounts of infiltrating groundwater formed the shallow reservoirs during ascent to the earth’s surface resulting in the observed differences in Li concentrations of the thermal springs from these reservoirs. Secondly, evaporation further concentrated the Li in the Li-rich geothermal springs in southern Tibet, resulting in higher Li levels than in other magmatic thermal springs. The present study could not establish the Li source for the Tibet thermal springs with low Cl concentrations because they may mix with large amounts of infiltrating groundwater; however, it is more likely that magmatic Li still accounts for a large portion of the total Li.