Geothermal hydrogeochemical conditions and genesis of the Mianhuakeng uranium deposit, South China

Abstract

The Mianhuakeng geothermal system, hosted in a uranium-bearing granitoid environment, exhibits a high surface heat flow (62.7–90.4 mW/m²), indicating significant geothermal potential. This study integrated geochemical and isotopic analyses to elucidate the origin, evolution, and controlling mechanisms of the system. Isotopic evidence indicates that meteoric water is the primary recharge source, infiltrating to depths of 1617–4030 m, resulting in estimated geothermal reservoir temperatures ranging from 56 °C to 111 °C. Geochemical studies suggest that the mixing of deep geothermal water and water-rock interactions, such as silicate weathering (e.g., albite, biotite), sulfate dissolution (gypsum), and cation exchange, lead to the enrichment of Na⁺, Ca²⁺, SO₄²⁻, and HCO₃⁻. Moreover, the co-dissolution of fluorite and biotite as well as the mixing of deep fluid may be the cause of the high F⁻ level in geothermal water. The radioactive heat production of uranium-bearing granite is a major heat source in the study area that provides to the thermal regime of geothermal systems, with an average heat production rate of 5.14 μW/m³. A conceptual model based on hydrogeochemistry was proposed, providing a few new insights into the characteristics of geothermal systems in granitoid environments.