Hydrogeochemical characteristics and formation of the Ivory Spring in Jiacha County of Tibet

Located in the alpine region of the Qinghai-Tibet Plateau, the Ivory spring is famous for its travertine deposition resembling an “ivory”. Research on the formation mechanism of the Ivory spring is helpful for the geological environment protection of travertine landscapes, and is of great significance to the studies of paleoenvironmental evolution and neotectonic activities in the Yarlungzangbo tectonic belt. Taking the Ivory spring and its travertine as the research object, this paper discusses the formation mechanism of the Ivory spring and its travertine landscape, estimates the age of travertine formation, and describes the evolution trend of the travertine landscape through the compositions of the travertine, the chemical compositions of the spring water and hydrogen and oxygen isotopes through correlation analyses. The results show that the elevation of the ivory spring is 3 208 m, the temperature, 16.1 ℃, the pH value, 6.06-6.64, and the total dissolved solid, 1 521.1-1 524.2 mg/L. The spring water is weakly acidic and brackish water. The cations are dominated by sodium and calcium, and the anions by bicarbonate and chloride, and the water is of HCO3-Ca type. The Ivory spring has relatively high concentration of Cl and Na, and slightly higher total dissolved solids. Data points of hydrogen and oxygen isotopes fall near the global meteoric water line, indicating that the Ivory spring is mainly of meteoric origin, with long runoff route and slow circulation speed, and undergoes strong water-rock interactions. The Ivory spring is of dissolved and precipitated type, and its chemical compositions are derived from the dissolution of carbonate minerals and silicate minerals in the process of water-rock interactions. The chemical compositions of the Ivory spring’s travertine is mainly calcium carbonate, accounting for 63.07% and the secondary component is silicon dioxide, accounting for 10.19% . The Ivory springs is a normal-temperature spring type with the calcification and silicidation as the supplement. Estimation of calcium balance indicates that the Ivory spring’s travertine was formed at 13,800 years ago and its deposition rate is about 0.27 mm/a.