Hydrochemical Characterisation and Genesis Mechanism of Li-Rich Geothermal Waters in the High-Temperature Geothermal Areas of Western Sichuan, China

Lithium (Li) is a valuable resource with significant economic benefits and strategic importance. The extraction of Li from Li-rich geothermal fluids has low production costs and may be an essential source of Li in the future. The Li contents in the high-temperature geothermal systems of western Sichuan are high (most exceeding 1 mg/L) and reach the exploration standard. However, the Li source and enrichment processes of high-temperature geothermal fluids are not well known. Therefore, 30 groups of natural hot springs with Li ≥ 1 mg/L from Batang, Litang, and Kangding high-temperature geothermal systems were selected to analyse the Li enrichment mechanism in high-temperature geothermal water. The average exposed temperatures of Batang, Litang, and Kangding geothermal waters were 82.4°C, 53.7°C, and 61.9°C, respectively, and the hydrochemical types were HCO₃-Na. The average concentrations of Li in the geothermal waters of Batang, Litang, and Kangding were 2.32, 3.29, and 3.54 mg/L. Based on the δD and δ¹⁸O characteristics, the geothermal waters in the study area originated from meteoric water and snow-melt water. Magmatic water was also mixed during circulation, with Kangding geothermal water being the most mixed (25.0%). Strong water–rock interactions occurred during geothermal water runoff ascent, including silicate mineral dissolution, geothermal gas dissolution, and cation exchange. The deep reservoir temperatures in the geothermal systems of Batang, Litang, and Kangding were estimated to be 239°C, 200°C, and 242°C, and the shallow reservoir temperatures were 175°C, 86°C, and 116°C. Finally, two Li enrichment mechanisms were proposed: (1) Li in the geothermal waters of Batang and Litang geothermal systems mainly came from the leaching of lepidolite and spodumene during water–rock interactions. (2) Li in the Kangding geothermal system mainly originated from the input of magmatic water. This research deepens the understanding of Li enrichment mechanisms in high-temperature geothermal systems, which will be helpful for the exploration of geothermal Li resources.