Hydrochemical Constraints on the Flowing Paths of Groundwater in Limestone Reservoirs beneath the Pingdingshan Coalfield in North China

Abstract The karst groundwater of Cambrian limestone may become an important water source for industry and agriculture in the Pingdingshan area, and is also a potential threat to mining safety. Therefore, to find out the origin, flow paths, and hydrogeochemical processes of karst groundwater beneath the Pingdingshan coalfield, a total of 16 water samples were collected. Our findings confirmed that the karst groundwater is mainly recharged by precipitation. The precipitation can directly supply the deep aquifer of the karst water system through the southwest limestone outcrops, and this area mostly includes the southern part of mines No. 11, No. 9, and the hidden outcrops in the southern part of mine No. 2. What is more, the areas adjacent to the synclinal axis, including mines No. 10, No. 12, and No. 8, may be the main discharge areas. A mixing model of 87 Sr/ 86 Sr and Sr showed that in the southwest Pingdingshan coalfield, the proportion of precipitation decreased gradually from the recharge area to the discharge area, ranging from 89.1% to 17.1%. Besides, the northeast Pingdingshan coalfield is another recharge area for the whole karst system, thus, the infiltrating groundwater will indirectly supply the deep aquifer through Quaternary deposition near the mine No. 13. Our research results can provide theoretical support for the prevention and control of groundwater disasters and the development and utilization of regional groundwater resources in the coalfield in Northern China.