Hydrogeochemical characteristics and temperature variations in fault-controlled, deep-circulation thermal springs elucidate water–rock interaction dynamics and hydrothermal circulation depths, providing critical insights into fault permeability and stress accumulation. To investigate the coexistence of high-temperature and medium-low-temperature thermal springs on small-scale faults and their distinct circulation mechanisms, hydrochemical and isotopic analyses were conducted on 13 water samples (9 proximal on the Xiangbaihe Fault) in western Yunnan. The hot springs along the Xiangbaihe Fault are predominantly classified as the Na-HCO₃ type, derived from carbonate and aluminosilicate hydrolysis. δ²H and δ¹⁸O confirmed a meteoric origin, with recharge elevations spanning 2465–3286 m (Gaoligong Mountain). Inverse hydrochemical modeling demonstrated progressive mineral transfer and water–rock interactions along the fault’s east–west axis. Conservative elements (Cl, Li) suggested a shared geothermal fluid source or reservoir affiliation. BLZ reservoir temperatures (194–221 °C) were classified as a high-temperature system, whereas others (58–150 °C) represented medium-low-temperature systems. Although each thermal spring represents a distinct geothermal system, reservoir interconnectivity is inferred. Notably, despite uniform lithology, variations in spring temperature and elemental composition are attributed to a subsurface magma chamber beneath BLZ, heterogeneous fault geometries, differential reservoir temperatures, and variable cold-water mixing ratios. This study establishes a framework for understanding groundwater circulation in small-scale fault-associated geothermal systems, with implications for tectonic activity monitoring and geothermal resource assessment.

The Shangri-La area lies within the Yunnan-Tibet geothermal belt, characterized by intense tectonic activity and abundant geothermal resource potential. However, existing studies have largely focused on individual hot springs, and a regional scale understanding of geothermal geology and fluid circulation mechanisms remains lacking. This study systematically elucidates the geological setting, hydrogeological characteristics, circulation mechanisms, and resource potential of the geothermal systems by integrating hydrogeological surveys with hydro chemical and isotopic analyses. The results indicate that the Zhongxiao Fault Zone and its associated secondary structures are the primary controllers of geothermal water distribution, serving as both thermal conduits and hydrogeological boundaries. The primary heat source is attributed to the natural geothermal gradient, supplemented by additional contributions from magmatic activity. The geothermal waters are classified as Na-HCO₃ or Ca-HCO₃ types and are notably rich in fluoride. The mean values of δD and δ¹⁸O for geothermal water were −127.86‰ and −15.53‰, respectively, exhibiting isotopic depletion compared with non-thermal water. The geothermal water samples plot near both the Global and Local Meteoric Water Lines while exhibiting a distinct mean ¹⁸O shift of +1.24‰, indicating that the systems are recharged by atmospheric precipitation and have subsequently undergone intense water–rock interaction. Analysis using the Na-K-Mg triangle diagram reveals that most geothermal water samples are immature waters. Thus, the quartz geothermometer provides more reliable estimates of reservoir temperatures. Calculations yield reservoir temperatures ranging from 70 °C to 123 °C, characterizing the system as a medium-to-low temperature resource. With an annual exploitable energy of 5.9 × 10¹⁴ J and high fluoride content, these resources can offer substantial potential for clean energy and balneotherapy.