Hydrogeochemical characteristics and genesis analysis of hot spring in Fuping County, Taihang Mountain Area

Fuping County of Hebei Province is located in the hinterland of Taihang Mountain, and hot spring are exposed to typical metamorphic rock strata and metamorphic core complex tectonic area. The hydrogeochemical and genesis analysis of hot spring is of certain guiding significance for the exploration and development of uplift mountain type geothermal resources in metamorphic rock area. Based on the natural geography and regional geothermal geological background of Fuping County, this paper adopts the means of field investigation, sampling and testing, comprehensively applies the methods of hydrogeochemistry and stable isotope to determine the hydrogeochemical characteristics and material sources of main ions of hot spring water, and preliminarily speculates the source of hot springs recharge and deep heat resource, etc. The results show that the water quality of hot springs in Fuping County is generally alkalescent, and the hydrogeochemical type of hot spring in metamorphic rock area is SO₄-Na type, in carbonate rock area is HCO₃-Ca·Mg type respectively. The hydrochemical evolution is dominated by weathering dissolution effect, and supplemented by the cation change effect. The SO₄ ²⁺ and Na⁺ in hot spring fluids mainly come from the dissolution of sulfides and silicates, while \mathrmHCO_3^- , Ca²⁺ and Mg²⁺ mainly come from the dissolution of carbonates. The recharge source of hot springs in the study area is precipitation from the atmosphere with a slight ¹⁸O drift phenomenon, and the recharge elevation is 1 500-2 600 m. It is presumed that the recharge area is located in the metamorphic rock area in the northwest of the study area and the carbonate rock area in the northeast. All the samples of hot springs in the study area have reached the theoretical equilibrium dissolution line of quartz, with the estimated geothermal reservoir temperature ranging from 56.46-133.71℃, and the circulation depth of 2 213.0-8 092.3 m. The heat source of the hot springs in the study area are mainly from the deep mantle branch structure, low-velocity high-conductivity layer and tectonic thermal, the ductile shear zone and deep fault as heat transfer channels, and the surface heat display is mainly controlled by the fault structure. The geothermal resources in the study area belong to deep cycle renewable energy, and the geothermal reservoir temperature reaches standard of medium and high temperature, which can further carry out the exploration and development of deep geothermal resources, promote the green and sustainable development of local economy, and help the rural area construction in Fuping County.