Geochemical and isotopic characteristics of geothermal springs hosted by deep-seated faults in Dongguan Basin, Southern China

• Geochemical and isotopic compositions of geothermal and natural springs were studied.
• Geothermometric calculation indicated the reservoir temperatures of 131.0 to 138.9 °C.
• Geothermal springs were recharged by meteoric rain water.
• Groundwater migrating and being heated were very quick during subsurface circulation.

Chemical and isotopic compositions of thermal springs and non-thermal springs and well from Dongguan Basian of Southern China were measured and used to assess the mechanism of hydrothermal system hosted by deep-seated faults. Thermal springs had relatively higher temperatures and dissolved ion contents than non-thermal springs and wells, and were classified as water chemistry type of HCO3-Na + K. The reservoir temperatures were determined with their chemical compositions, and 131.0 to 138.9 °C estimated by a quartz geothermometer after steam loss were regarded as the most suitable assessment. Inadequate equilibrium between water and rock interaction is mostly speculated and the mixing with shallow non-thermal groundwater probably has minor contribution to the thermal springs. Stable isotope compositions of thermal springs ranged from − 45.1‰ to − 40.8‰ for δD and from − 7.2‰ to − 6.9‰ for δ18O, respectively. These isotopic results were almost identical to those of non-thermal springs. All the thermal and non-thermal groundwater samples scattered around the meteoric water lines, thus indicating meteoric water origin without further influences of evaporation and groundwater–rock interaction. The similarity of thermal and non-thermal groundwater in chemical and isotopic compositions suggested that groundwater migrating and being heated very quickly in a relatively fast conductive fracture system hosted by deep-seated faults mostly represented the mechanism of thermal springs.