Natural carbon mineralization and its control on the geochemical evolution of coal-based aquifers in the Salt Range, Punjab, Pakistan.

Hydrochemical analysis of the Salt Range was conducted to understand carbon weathering and its impact on groundwater evolution within the complex geological framework of Punjab. Our results showed that groundwater samples were alkaline with a pH range of 7.0-8.6 and 7.8-8.8 for the eastern Salt Range (ESR) and Trans-Indus Salt Range (TSR), respectively, while that of the Central Salt Range (CSR) was acidic to moderately alkaline ranging between 5.7 and 7.5. The water types of Ca-Mg-HCO, Ca-Mg-Cl, and Ca-Cl were the dominant hydro-chemical facies in ESR and CSR sites. However, groundwater of the TSR site falls under Ca-Mg-Cl, Ca-Cl and mixed types of Ca-Mg-SO. Our new findings suggest that groundwater chemistry is primarily controlled by rock dominance and reverse ion exchange reaction, followed by evapotranspiration processes. The wells of ESR, CSR, and TSR were reported with higher levels of Fe and Zn. Regarding the suitability for irrigation, sodium adsorption ratio (SAR), magnesium adsorption ratio (MAR), sodium percentage (Na%), Kelley's ratio (KR), and potential salinity (PS) at all three sites (ESR, TSR, and CSR) had the potential to become a salinity hazard. The conceptual model of geochemical evolution shows that both local and regional salinization is driven by local geology and intensive coal mining activities. The neutralization capacity of the parent geological formation buffers the acidity and lowers the overall trace element enrichment. The potential of natural weathering could be further explored as a solution to coal mining's impact on the environment.