Comparison of hydrogeological characteristics and genesis of the Xiaguan Hot Spring and the Butterfly Spring in Yunnan of China

摘要

The Xiaguan Hot Spring and the Butterfly Spring near Dali in Yunnan of China were sampled 5 and 3 times, respectively and their hydrogeological characteristics are discussed in this study. The TDS and hydrochemical type of these two springs are 1360 mg/L and HCO3-SO4-Na type, and 246 mg/L and HCO3-Ca-Mg type, respectively. The Butterfly Spring is enriched in Ca2+, Mg2+ and HCO3- due to dissolution of carbonate rocks. In contrast, the Xiaguan Hot Spring is enriched in Na+, K+, HCO3 and SO42 due to dissolution of albite, halite and ion exchange. The concentrations of the rare earth elements (REEs) in the Xiaguan Hot Spring and the Butterfly Spring range from 0.033 mu g/L to 0.071 mu g/L and 0.013 mu g/L to 0.018 mu g/L, respectively. The absolute concentrations of the medium rare earth elements (MREEs) and heavy rare earth elements (HREEs) are relatively higher than those of the light rare earth elements (LREEs) in the Xiaguan Hot Spring. The concentrations of the LREEs in the Butterfly Spring are relatively high. The delta H-2 and delta O-18 values of the Xiaguan Hot Spring and the Butterfly Spring vary from -102 parts per thousand to -107 parts per thousand and -11.6 parts per thousand to -13.8 parts per thousand, respectively, showing negative trends due to altitude effect. The data points of delta H-2 and delta O-18 of the two spring samples are close to the Global Meteoric Water Line and the Local Meteoric Water Line with a slight O-18 shift, indicating that the springs are meteoric in origin with a slight O-18 exchange with the surrounding rocks. The geothermal reservoir temperature of the Xiaguan Hot Spring estimated with SiO2 geothermometers ranges from 107.4 degrees C to 114.6 degrees C. The Xiaguan Hot Spring occurs in the metamorphic rocks of the Paleoproterozoic Cangshan Group, and is recharged from infiltration of precipitation and snow-melting water. After undergoing a deep circulation, the groundwater is heated by heat flow and rises along the Tangzipu fault to form a hot spring of deep groundwater circulation type. The Butterfly Spring emerges in the Silurian limestone. Groundwater receives recharge from precipitation and snow-melting water in the western mountainous area, flows eastward along the fissures, and emerges on the lower slopes as a spring of shallow groundwater circulation type with ambient temperature.