Karst hydrogeological characteristics of Jindong large coal basin, northern China

Jindong coal basin is one of the 14 large coal basins planned and constructed by the state, and groundwater resources play an important role in supporting the sustainable development of the coal basin. To improve the understanding of deep karst hydrogeological characteristics of the coal basin, the combination of techniques (i.e., 1:50,000 and 1:100,000 surveys, geophysical prospecting, drilling, dynamic monitoring, hydrochemistry and isotopes, etc.) was used to characterize the hydrogeological structures of deep-buried aquifers and analyze the evolution characteristics of groundwater systems under the conditions of long-term and large-scale coal mining. Deep Cambrian Zhangxia formation oolitic limestone water-rich aquifer was newly discovered in this survey, which characterized by the development of karstic fissures and strong water-richness in the effective structural zone. The dissolubility of the Cambrian Zhangxia formation oolitic limestone is weaker than that of the Ordovician Majiagou formation and Carboniferous Taiyuan formation limestone, but stronger than that of the Ordovician and Cambrian dolomite. Controlled by Jinhuo fault zone, there are many large karst groundwater-bearing basins distributed on both sides, such as Jincheng basin, Yangcheng basin, Changzhi basin, etc., and water yield in the center of the basins can reach more than 10,000 m(3)/days. Main types of karst groundwater storage structures in study area are syncline basin type, fault fracture zone type and permeable-impermeable contact zone type. Affected by coal mining, the dynamic conditions of karst groundwater have changed significantly, mainly manifested in the movement of the boundary of the karst groundwater system, the decline of the groundwater level, the attenuation of karst springs flow, and the complex conversion of multi-source water. The variation characteristics of the spring flow can be subdivided into three stages, namely relatively stable stage, rapid decline stage and slow decline stage. The main controlling factors of these three stages are atmospheric precipitation, coal mining and karst water exploitation, respectively. The regional groundwater circulation pattern under coal mining can be divided into shallow groundwater flow system, deep groundwater flow system and local groundwater flow system. The local groundwater flow system was mainly affected by coal mining, which was manifested as the concentrated discharge of groundwater to goaf. The results of this study will provide scientific basis for groundwater exploration and exploitation and sustainable development of coal basins.