The prevention, control, and utilization of karst groundwater are prevalent issues in coal mining operations across North China. Karst water serves as both a potential hazard to safe coal production and an essential resource for domestic and agricultural use. However, decades of intensive, large-scale mining have significantly disrupted subsurface karst systems and intensified hydrogeochemical processes, particularly water-rock interactions. This study focuses on the Tengxian Coalfield in North China, where Ordovician and 14th limestone aquifers were sampled, and a multiwell drainage experiment was conducted in the Ordovician aquifer. Through a combination of multimethod approaches, the hydrochemical characteristics of karst groundwater under natural conditions and mining disturbances were analyzed. The evolutionary patterns and controlling factors of major ion concentrations in karst water were revealed. Results indicate that SO₄ ^2- and Na⁺ are the dominant anion and cation, respectively, with Cl-Ca identified as the primary water type, alongside a subset displaying SO₄-Na·Ca characteristics. Major ion sources include rock weathering and evaporative concentration, while mining-induced chemical evolution is primarily driven by cation exchange and anthropogenic activities. Under natural conditions, ion concentrations in the Ordovician limestone water remained relatively stable, indicating limited groundwater circulation and weak runoff. During water inrush events, enhanced water-rock interactions caused a transition in hydrochemical composition from low Na⁺(K⁺) and high Ca²⁺(Mg²⁺) to high Na⁺(K⁺) and low Ca²⁺(Mg²⁺). This research provides insights into the hydrochemical behavior and flow field evolution of karst groundwater in mining areas and offers a scientific basis for water hazard control and resource utilization under similar geological conditions.

Geothermal resources are one of the most valuable resources in renewable energy because of their advantages of green environmental protection, stability, and reliability. Carbonate rock type geothermal reservoirs have great research significance. Carbonate rock type geothermal resources are abundant in the Shandong area. In this paper, we take the carbonate-type geothermal reservoir in the Diaozhen area of Jinan City as the research object, analyze the regional geothermal geological conditions, and identify the geological structure. Through physical logging exploration, hydrochemical analysis, isotope testing, and drilling exploration, we reveal the geothermal genesis mechanism and construct the genetic model of the carbonate geothermal system. The results show that Diaozhen area belongs to a low-temperature geothermal field and weak open karst thermal reservoir and that the reservoir is mainly Ordovician Majiagou group limestone. The thermal insulation caprock is the overlying Quaternary and Neogene strata with a cumulative thickness of 1376 m. The results of geophysical exploration wells and drilling data verify that the Mingshui fracture is seen around 1630-1645m, and the diorite intrusion is seen at 1610m. The Mingshui fracture connects the deep and shallow aquifers and is a geothermal fluid migration channel. The geothermal water in the Diaozhen area is mainly from the recharge of atmospheric precipitation, with a rich ion content and easy enrichment of trace elements. The regional thermal reservoir is mainly recharged by the deep circulation lateral runoff of Ordovician karst water. After long-distance deep circulation migration, groundwater continuously absorbs heat from the surrounding rock and is heated to geothermal raw water in the deep part. Deep geothermal water rises along the water-conducting fracture and mixes with shallow cold water to form shallow, low-temperature geothermal water.