Hydrogeochemical characteristics and forming reason of Ordovician limestone groundwater in Zhuoshan Coalfield

The ordovician limestone groundwater in Zhuozishan Coalfield is the main water source of regional coal mining and also an important water source of Wuhai City. Thus,the research on hydrogeochemical characteristics and cause analysis of Ordovician limestone water in Zhuozishan Coalfield is of great significance for prevention and control of mine water as well as development and utilization of water resources. In this study,34 groups of Ordovician limestone water samples were collected in Zhuozishan Coalfield,and the chemical characteristics and control factors of groundwater were analyzed through comprehensive use of Piper trilinear diagram,Gibbs diagram,and the ratio relationship of ions. The research results show that ionic concentration of Na++K+,HCO-3,Cl- and SO2-4 in Ordovician limestone water increases from the recharge area to the discharge area,while that of Ca2+ and Mg2+ decrease. Each indicator varied greatly in the north and south of the coalfield. The hydrochemical type of runoff from Zhuozishan Mountain to Gander Mountain and then to the north and south varied significantly,which was mainly controlled by rock weathering type and experienced positive ion exchange. While the hydrochemical type of the runoff from Zhuozishan Mountain to the south was always SO4·Cl-Ca·Na type,and the control effect changed from rock weathering to evaporation concentration. It mainly experienced reverse ion exchange. The Ca2+ and Mg2+ in Ordovician limestone water in coal mine were mainly from silicate dissolution,while the Na+ and K+ were mainly from ion exchange and less from rock-salt dissolution. The whole Zhuozishan Coalfield can be divided into three hydrochemical characteristic regions in the north,middle and south. In the north of the coalfield,due to geological structure,a retention area was formed with groundwater,and the runoff process was disordered with a complicated formation process. The middle was not blocked by the geological structure,the runoff direction did not change,and the formation of groundwater was a simple process. In the south,due to the deepening stratum and fault blocking,a retention zone was formed,making the formation of groundwater a more complicated process.