The source and differential enrichment mechanisms of lithium in Gudui geothermal field: Constraints from enrichment and dilution processes of geothermal-type lithium

As a typical high-temperature geothermal system in the Qinghai-Xizang Plateau, the Gudui geothermal field (GDGF) shows notably high lithium content. Compared with other Li-rich geothermal fields, GDGF exhibits differential enrichment of lithium. Furthermore, few studies have focussed on investigation of the depletion of lithium during the ascent of geothermal fluids. Therefore, this study investigated the source, mechanism of differential enrichment of lithium and depletion mechanism of lithium. The δ_D and δ18O plot and the two-endmember modeling of Sr isotope indicate that geothermal fluids in GDGF were affected by magmatic water and mixing ratios are range from 0.8 to 12 %. Furthermore, the Li isotope mass balance model shows that the leucogranite distributed near GDGF is the primary source of lithium in geothermal fluids. The correlations between Na, K, Li and Cl concentrations indicate that the geothermal waters in eastern and western region originate from different parent geothermal fluids. The δ_D-Cl plot and enthalpy-chloride diagram reveals that the geothermal water in WGDGF was mainly formed by mixing with shallow surface water, and multiple boiling processes took place in EGDGF. In addition, Lithium in the geothermal fluids might be absorbed by the clay minerals widely distributed in the EGDGF, which causes the depletion in the rise process. In conclusion, the differential enrichment model of lithium in GDGF was constructed.