Hydrogeochemical Characteristics and Formation Processes of Ordovician Limestone Groundwater in Zhuozishan Coalfield, Northwest China

Abstract Groundwater is essential for water supplies in arid and semi-arid region. Analyzing the characteristics and formation mechanisms of groundwater in mining area is crucial for coal mine water prevention and rational groundwater resources management. This study reached the hydrogeochemical characteristics and evolutions of Ordovician groundwater in the zhuozishan coal mine, northwest China.34 groundwater samples were collected for hydrogeochemical analyses and piper trilinear diagram, gibbs diagram, ion ratio diagram were used to research groundwater formation processes. The results indicate that the concentration of Na++ K+, HCO3−, Cl−, SO42−, TDS, and pH increase from the recharge area to the discharge area, however, that of Ca2+ and Mg2+ decreases.And each indicator varied greatly in the north and south of the coalfield. Hydrogeochemical types of the runoff from Zhuozishan Mountain to Gongdeer Mountain and then to the south-north directional change obviously. And the groundwater process is controlled by rock weathering action and cation exchange. Whereas the hydrochemical type of the runoff from Zhuozishan Mountain to the south is always SO4▪Cl-Ca▪Na type, and groundwater process is controlled from rock weathering action to evaporation concentration and reverse cation exchange. When it comes to ion source, Ca2+ and Mg2+ mainly origin from the silicate dissolution, while Na+ and K+ are mainly derived from cation exchange and barely from the halite dissolution. In summary,in the northern part of the coalfield, due to geological structure, a retention area is formed with groundwater, and the runoff process is disordered with a complicated formation process. The middle part is not blocked by the geological structure, the runoff direction do not change, so the formation of groundwater is simple. And in the southern part, due to the deepening stratum and fault blocking, a retention zone is formed, making groundwater formation process more complicated. This study will contribute to groundwater resources management and mine water inrush control in this coalfield and at other mines.