Hydrochemical differences and origins of karst waters around the Jinan Pluton, North China

The periphery of the Jinan Pluton, North China, contains abundant cold-water and geothermal karst resources, constituting a natural observatory for investigating karst water origins and hydrogeochemical evolution. To advance the understanding of the occurrence pattern and origins of karst waters around the Jinan Pluton, a total of 36 samples of karst groundwater were collected and analyzed for hydrochemical constituents via ion chromatography (IC) and inductively coupled plasma optical emission spectrometry (ICP-OES), and isotopic composition. The results are as follows: (1) Along the south-to-north regional groundwater flow path, cold-water and geothermal karst groundwaters around the Jinan Pluton exhibit significantly distinct hydrochemical types. From shallow cold-water karst (spring water) to deep geothermal karst systems, the hydrochemical types become progressively more complex, accompanied by a continuous increase in the extent of water–rock interaction. (2) Within the geothermal field north of the Yellow River, the observed gradual increase in total dissolved solids (TDS) of geothermal karst water from west to east can be attributed to two main factors. First, the geothermal karst water in the western segment of the geothermal field receives significant recharge from the Yellow River. Second, the karst water level in the eastern segment of Jinan is the lowest across the study area, making it the convergence center of regional karst groundwater flow, which results in a relatively isolated hydrogeological environment with respect to the surface. This study reveals karst water hydrochemical evolution near the Jinan Pluton to guide water resource utilization and protection.