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

Abstract

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 μg/L to 0.071 μg/L and 0.013 μg/L to 0.018 μg/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 δ2H and δ18O values of the Xiaguan Hot Spring and the Butterfly Spring vary from −102‰ to −107‰ and −11.6‰ to −13.8‰, respectively, showing negative trends due to altitude effect. The data points of δ2H and δ18O of the two spring samples are close to the Global Meteoric Water Line and the Local Meteoric Water Line with a slight 18O shift, indicating that the springs are meteoric in origin with a slight 18O exchange with the surrounding rocks. The geothermal reservoir temperature of the Xiaguan Hot Spring estimated with SiO2 geothermometers ranges from 107.4 °C to 114.6 °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.