Differences in hydro-chemical characteristics and genesis of sandstone fissure water from the roof and floor: a case study in Haizi coal mine, Northern Anhui Province, China

The sandstone fissure aquifer of the Permian main mining coal seam is the direct water-filled aquifer of the coal mine in northern Anhui Province, China. Hydro-chemistry is important for solving the issue related to water disasters of coal mines, as it can be used for the determination of source of inrush water, and understanding the water-rock interaction process. In this paper, major ion concentrations of groundwater from the in the roof (RW) and floor (FW) in Haizi coal mine have been processed by statistical analysis and water-rock interaction analysis in order to study the differences of hydro-chemical characteristics and genesis. The results show that sandstone fissure water ion contents in RW and FW are obviously different; the chemistry type of FW is Ca-Mg-SO4, followed by HCO3-Cl and HCO3-Cl-SO4, and that of RW is HCO3-Cl, followed by SO4-HCO3-Cl. Compared with the fourth aquifer, Taiyuan group limestone water, goaf water, the proportion of Ca2+, Mg2+, SO42- in the FW and Cl-, HCO3- in the RW are significantly different. Factor analysis and water-rock interaction research show that the FW of 10th coal seam aquifer controlled by “removing sulfate,” silicate mineral dissolution and impact of groundwater runoff. However, the RW is mainly related with the dissolution of minerals, for example, salt minerals (e.g., mirabilite), bitter salt minerals (e.g., salt), silicate minerals, and the dissolution of gypsum.