This paper is the result of geothermal geological survey engineering.

Objective Geothermal exploration in Inner Mongolia started relatively late, and research on mid-deep geothermal resources needs to be further advanced. For regions with favorable geothermal conditions, it is essential to conduct an analysis of the geothermal geological conditions and their potential for development, understand the geothermal water circulation process from the perspective of geothermal water chemistry, and reveal the formation mechanism of the geothermal system.

Methods Based on the geochemical and isotope data of geothermal water from 14 geothermal wells in the Hohhot Plain area, this article analyzes and calculates the water chemical characteristics, thermal reservoir temperature, recharge elevation, geothermal water age, etc., and briefly analyzes the geothermal geological conditions and geothermal formation mechanism of the study area.

Results (1) The main chemical types of geothermal water in the Hohhot Plain area are Cl-Na type, Cl·SO₄-Na type water and Cl·HCO₃-Na type water, with Na⁺ being the dominant anion; geothermal water has a high degree of mineralization, ranging from 2.04 to 43.49 g/L, with an average value of 11.09 g/L, belonging to slightly saline water, saline water, or even salt water. (2) The analysis of the characteristic coefficients of geothermal water indicates that the dissolution of rock salt, evaporation and concentration, as well as the alternating adsorption of cations are the main water-rock interactions. (3) Geothermal water mainly originates from atmospheric precipitation. Evaporation effect is strong in the study area, leading to the enrichment of heavy isotopes. The δD and δ¹⁸O points are located to the right below the atmospheric precipitation line. (4) The apparent age of ¹⁴C in deep geothermal water is 10~20 ka BP years or more than 20 ka BP. Since it is weakly renewable or non renewable geothermal water, recharge must be considered during mining.

Conclusions The geothermal field types in the Hohhot area are medium-low temperature geothermal fields of geothermal heating conduction type and fault convection type. The estimated thermal reservoir temperature based on the SiO₂ geothermometer is < 100 ℃. The thermal reservoirs are mainly composed of Neogene sandstone thermal reservoirs, Cretaceous sandstone and conglomerate thermal reservoirs, Proterozoic marble and Archaeozoic bedrock fracture thermal reservoirs. The formation of the geothermal system is the result of deep circulation of groundwater under normal heat flow conditions. The atmospheric precipitation mainly recharged and infiltrated from the northern DaQing mountains, meanwhile, under the influence of the basement structure morphology that is deeper in the north and shallower in the south, and deeper in the west and shallower in the east, the geothermal water migrates to the southwest and northwest part of the Huhhot Depression. Overall, the geothermal geological conditions in the Hohhot Plain area are favorable. The water inflow of geothermal wells ranges from 49.02 to 5594.88 m³/d, and the exploitable thermal power of a single well is 2639 to 17785 kW, indicating great potential for geothermal development and utilization. However, for highly mineralized geothermal water, efforts should be made to popularize and optimize the recharge technology, and overcome problems such as equipment corrosion, pipeline scaling, local reservoir blockage.