The groundwater mixing mechanism and hydrogeochemical processes driven by coal mining in the typical area, Northern...

The interconnected disturbances induced by coal mining activities significantly alter the groundwater flow system, triggering multi-scale hydrodynamic-hydrochemical co-evolution processes. Based on hydrochemistry, deuterium and oxygen-18 isotopes, Pearson correlation analysis, and Bayesian mixture model methods, this study systematically evaluated the evolution of the groundwater flow system and the hydrochemical processes driven by coal mining in the Nalinhe mining area in the northern Ordos Basin, China. The results showed that the main ions in the groundwater of Quaternary and Cretaceous aquifers are Ca²⁺, Na⁺, HCO₃⁻, and SO₄²⁻, while the main ions in the Jurassic aquifer are SO₄²⁻ and Na⁺. The hydrochemical types vary with depth, transitioning from HCO₃⁻-Ca²⁺ in the Quaternary to HCO₃⁻-Na⁺·Ca²⁺ in the Cretaceous, and finally changing to SO₄²⁻-Na⁺ in the Jurassic. The variance explained by ion composition (52.07%) strongly correlates with rock weathering processes. The Cretaceous aquifer is the primary source of water inflow into mining areas, accounting for 64.25%, while the Quaternary and Jurassic aquifers contribute 18.32% and 17.43%, respectively. In this study, the hydrogeochemical evolution method and Bayesian mixing model were combined to reveal the impact of coal mining activities on groundwater circulation patterns. These findings provide valuable insights for constructing groundwater flow models and effectively managing groundwater inflow in mining regions.