| Summary: | The exploration of the origin of hot spring is the basis of its development and utilization. There are many low-medium temperature hot springs in Nanjing and its surrounding karst landform areas, such as the Tangshan, Tangquan, Lunshan, and Xiangquan hot springs. This article discusses the origin characters of the Lunshan hot spring with geological condition analysis, hydrogeochemical data, and isotope data. The results show that the hot water is SO4–Ca type in Lunshan area, and the cation content of SO4 is high, which are related to the deep hydrogeological conditions of the circulation in the limestone. Carbonate and anhydrite dissolutions occur in the groundwater circulation process, and they also dominate the water–rock interaction processes in the geothermal reservoir of Lunshan. The hot water rising channels are deeply affected by the NW and SN faults. Schematic diagrams of the conceptual model of the geothermal water circulation in Lunshan are plotted. The origin of Tangshan, Tangquan, and Xiangquan hot springs are similar to the Lunshan hot spring. In general, the geothermal water in karst landforms around Nanjing mainly runs through the carbonate rock area and is exposed near the core of the anticlinal structure of karst strata, forming SO4–Ca/SO4–Ca–Mg type hot spring with the water temperature less than 60°C. The characters of the hot springs around Nanjing are similar, which are helpful for the further research, development, and management of the geothermal water resources in this region.
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