Hydrogeochemical Mechanisms and Hydraulic Connection of Groundwaters in the Dongming Opencast Coal Mine, Hailar, Inner Mongolia

The identification of water sources and hydraulic connectivity in different aquifers within coal mines is crucial for effective groundwater management and has important implications for mine safety, water resource conservation, and regional ecological protection. The Dongming opencast coal mine in Hailar City, Inner Mongolia, China, is threatened by groundwater leakage. However, the hydrochemical mechanisms, water sources, and hydraulic connectivity of the different aquifers in this area are still not well understood. In this study, we collected 24 samples from various water sources, including pore water in the Quaternary aquifer (QGW), pore-fissure water in the coal-bearing aquifer (CGW), drainage sump water from the mine pit (DSW), Morigele river water (MRW), and nearby snow water (SNW). These samples were analyzed for major and trace elements, as well as hydrogen (H), oxygen (O), and boron (B) isotope compositions. The results showed that the QGW and MRW hydrochemistry were similar, while the CGW and DSW had comparable characteristics. The H and O isotope analyses revealed that all of the groundwater samples originated from river water, while the B isotope analyses indicated the heterogeneous hydraulic connectivity between the different aquifers and the river. The research findings indicate that mining companies should continuously strengthen the monitoring of surface water and groundwater levels, further investigate the velocity and direction of groundwater flow, and gradually conduct quantitative research on hydraulic connections between surface water and different aquifers. This will provide more scientific basis for the prevention and control of groundwater leakage in mining areas. In this study, a combination of hydrochemical and non-traditional stable isotope geochemical methods was used to investigate the origin of groundwater in open-pit coal mines and its relationship with different water bodies. This represents a new exploration of research ideas and methods. This work has important implications for the study of the origin of groundwater and the measures for leakage prevention and control in open-pit coal mines and underground coal mines worldwide.