Isotope Drift Characteristics in Ordovician Limestone Karst Water Caused by Coal Mining in Northern China

Samples from different areas near the Fengfeng Mine in northern China were analyzed for 2H and 18O isotopes. In the southern areas, the 2H and 18O isotopes exhibited no significant drift off the background. However, in the eastern area, the 2H isotope drifted remarkably, although 2H and 18O both drifted in some samples. In the northern area, the 2H and 18O both obviously drifted. The 2H drift is attributed to deuterium equilibrium due to water–rock interactions between the Ordovician limestone (OL) karst water and silicate minerals. The 18O drift probably came from water–rock reactions between OL water and carbonate minerals, along with the 18O equilibrium reaction. It was demonstrated that the dual drift were connected to water–rock reactions between the OL water, carbonate, and silicate minerals. Therefore, the drift was actually due to equilibrium exchange of OL water–rock interactions during the water level descent and ascent, which was closely related to the mining activities.