Chemical characteristics and evolutionary mechanism of hot spring water in Dabie Mountain area, Anhui Province

Objective The analysis and summary of the hydrochemical characteristics and evolution mechanism of the tectonically controlled hot springs in Dabie Mountain area, Anhui Province, is conducive to deepen the understanding of water−rock interaction under the unique geological background (orogenic silicic rocks), and can provide scientific basis for geothermal exploration and rational development and utilization in Dabie Mountain area.

Methods Based on the analysis of the basic characteristics of the chemical components of the hot spring in the study area, the water−rock interaction of the hot spring in the study area is studied by comprehensive use of Gibbs map, rock weathering map, ion ratio coefficient and mineral stability field map. In addition, the reverse hydrogeochemical simulation work was carried out with the help of PHREEQC software to quantitatively analyze the dissolution and precipitation of major minerals during the geothermal water cycle.

Results ① The hydrochemical types of the five hot springs in Dabie Mountain are mainly SO₄−Na and SO₄·HCO₃−Na, all of which are moderate−low temperature and weak alkaline hot springs; ② Eu values in hot springs in the study area show obvious positive anomalies, with light rare earth elements relatively abundant, medium rare earth elements second, and heavy rare earth elements relatively lacking; ③ The chemical composition of hot spring water in the study area is mainly affected by rock weathering. Na⁺ mainly comes from the leaching of silicate rocks (such as albite and sodium montmorillonite), and Ca²⁺ comes from the leaching of carbonate rocks and gypsum. The content of SO₄²⁻ is mainly affected by the dissolution of gypsum. The content of HCO₃⁻ is mainly affected by the dissolution of silicate rocks and carbonate rocks. ④ The water−rock interaction on the path of rainwater−deep circulation underground hot water is the dissolution of albite, anorthite, fluorite, gypsum, biotite , and CO₂, and the precipitation of sodium montmorillonite, calcite , and dolomite, and the cation alternating adsorption of Ca²⁺ replacing Na⁺ occurs.

Conclusions The path from rainwater to underground hot water belongs to the groundwater depth cycle. The complex lithology and structure of deep strata easily hinder groundwater runoff, slowing down groundwater velocity, and thus promote sufficient water−rock interaction in groundwater, completing the transformation of HCO₃−Ca rainwater into SO₄·HCO₃−Na and SO₄−Na weakly alkaline hot springs.