Hydrochemical characteristics of travertine-depositing hot springs in western of Yunnan, China

Abstract

The hydrochemical characteristics of 15 travertine-depositing hot springs and 7 hot springs that do not deposit travertine in western Yunnan of China are compared to obtain a better understanding of the hydrochemical factors affecting deposition of travertine from hot springs. The analyses of hydrochemical characteristics of the hot springs include the concentrations of Ca and HCO3, the percentage compositions of Ca among cations and HCO3 among anions, the milliequivalent ratio of Ca to HCO3 (γCa/γHCO3), the partial pressure of carbon dioxide (pCO2), saturation index (SI) and hydrochemical types of the water samples. All the travertine-depositing hot springs contain high concentrations of CO2, Ca and HCO3. Their partial pressures of CO2 (0.03–0.76 atm) are much higher than that of atmosphere (0.03% atm) and the values of pH range from 5.9 to 7.7. Hydrochemical investigations show that water samples in the travertine-depositing hot springs have relatively high TDS (higher than 590 mg/L) and they are mainly of HCO3–Ca type. The concentrations of Ca and HCO3 are higher than 55 mg/L and 300 mg/L, respectively, and the values of γCa/γHCO3 are in the range of 0.1–2. The saturation index values of calcite (SIc) are almost positive. By comparison, the concentrations of Ca and HCO3 in the hot springs that do not deposit travertine are relatively low, the range of value of γCa/γHCO3 is mostly lower than 1 and the hydrochemical types vary greatly. In addition, the concentrations of CO2, Ca and HCO3 decrease along the flow path of the travertine-depositing Nanni hot spring.