Hydro-geochemistry evolution in Ordovician limestone water induced by mountainous coal mining: A case study from North China

This research aimed to investigate the changing mechanism of hydro-geochemistry in Ordovician limestone karst (OL) water induced by mountainous coal mining activities. Thus, the hydro-geochemistry evolution of OL water over 40 years within a typical northern mountainous coal mine named Fengfeng Mine was studied by using Piper diagram, Gibbs scheme, ions correlation and Principal component analysis (PCA) methods. Results showed that, except for HCO₃^-, the ions of Ca²⁺, Mg²⁺, SO₄^2-, Na⁺+K⁺, Cl^- and total dissolution solids (TDS) values all increased by years as mining continues. Different hydro-geochemical characteristics in different periods can reflect different water-rock interactions. Accordingly, sulfates dissolution gradually took place of carbonates in water-rock interaction. Especially, OL water-rock interactions in different periods were all affected by rock weathering and evaporation-concentration together. At last, evaporation-concentration co-effect dominated the hydro-geochemistry evolution slowly, along with significant cations exchange over years.