Origin and evolution of groundwater in the Goharzamin mine area using hydro-geochemical and isotopic analyses

Determining the source of groundwater infiltrating mine pits is one of the most interesting challenge for mining engineers and designers. The uncontrolled groundwater flow will delay the planned schedule and have a negative impact on extraction costs and mining operations. Determining the groundwater source by hydrochemical and isotopical interpretations in the Goharzamin iron mine, located in south-central Iran, plays a significant role in comprehending hydrochemical and hydrogeological processes and designing an effective dewatering system in this mining area. Through three phases of groundwater sample collection from seepages and boreholes, a total of 75 samples were gathered for analysis, including 12 samples containing heavy metals and stable isotopic data (D and ¹⁸ O), 5 samples containing ¹⁴ C and ¹³ C, and another 5 samples containing ³ H data. Results indicated that all samples belonged to saline and brackish water categories (EC > 4 mS cm ^− 1 ), with a predominant sequence of Cl ⁻ -SO ₄ ²⁻ -HCO ₃ ⁻ -NO ₃ ⁻ , and Na ⁺ -Ca ²⁺ -Mg ²⁺ -K ⁺ for anions and cations, respectively. Conservative tracers (Cl, Br, and B) and stable isotopes demonstrated that Kheirabad Salt Lake (located approximately 13 km north of the mine) is unlikely to be the source of groundwater. Radiocarbon and tritium age dating suggested that the majority of groundwater in the mining area was infiltrated during the Holocene and late Pleistocene epochs (paleowater) rather than being replenished by recent rainfall. Hydrochemical variations observed in samples collected during the wet season are generally attributed to the mixing of surface water and groundwater at fractures around the mine pit.