Origin and evolution of Li-rich geothermal waters from the Kawu geothermal system, Himalayas: based on hydrochemistry and H-O, Li isotopes

There are 25 Li-rich geothermal fields (>15 mg/L) are displayed throughout nine geothermal zones in Tibet. The Kawu geothermal system is one of the representative high-enthalpy and Li-rich geothermal systems and is located in the Skaya dome, the Himalayas. Their boiling and hot and cold waters are Cl-HCO3-Na and HCO3-Ca types, respectively. The parent geothermal fluids are characterized by high Na, Cl, B, Si, As, Li, Rb+, Cs+ and F, and the Cl- concentration and enthalpy of the parent geothermal liquid are 515 mg/L and 1,485 J/g, respectively (corresponding to a temperature of 323.5 DEG;C). The stable oxygen and hydrogen isotopic compositions of geothermal fluids range from -19.7 to -23.4 PTSTHOUSND; and -155 to -181.2 PTSTHOUSND;, indicating that the ratio of magmatic water mixed into geothermal fluid is between 11.7% and 19.5%. The lithium content in the geothermal system is high (13.04 to 20.8 ppm), but the Li-7 is relatively low (1.06 to 1.72 PTSTHOUSND;). The high Cl, Li and B contents, constant Cl/Li and Cl/B ratios and low Li-7 indicate that they mainly originate from magmatic fluid, rather than from water rock reaction with the leucogranite and gneiss. While ascending from the reservoirs to the surface, the parent geothermal fluids gradually mixed with the meteoric waters infiltrated via brittle tensional small-scale faults, in turn forming four cooling processes upwelling patterns, i.e. conductive cooling, adiabatic cooling, mixing with cold water, and the combination of these processes.