Environmental geochemistry of near-neutral waters and mineralogy of zinc and lead at the Angouran non-sulphide zinc mine, NW Iran

Abstract

This study aims to investigate the geochemistry of major ions, trace and rare earth elements (REE) near the Angouran Zn-Pb mine. Thermodynamic modelling and saturation indices were computed using PHREEQC. Process and tailings water samples of the Calcimin processing plant were near neutral (pH=5.8–7.9) and had high concentrations of SO4 (1179–15,000mg/L), Zn up to 18,529mg/L, Pb up to 1780μg/L, As up to 465μg/L and Cd up to 230μg/L. Water of the Angouran pit was neutral-alkaline (pH=7.6–8.25) with low concentrations of SO4 (21–87mg/L), elevated concentration of Zn up to 27mg/L, Pb up to 586.3μg/L and Cd up to 33μg/L. Water flowing out of the Angouran Mine adit was neutral-alkaline (pH=7.5–8.05) with variable SO4 content (30–2294mg/L), Zn content up to 8mg/L, Pb up to 123μg/L and As up to 35.4μg/L. Elements As, Pb, Cd, Ni and Zn concentrations in the plant waters were higher than USEPA effluents limits. Generally, the types of water in the plant and the mine ranged from Zn-SO4, Na+K-SO4 to Ca-HCO3, respectively. North-American Shale Composite (NASC) normalised patterns of the mine and the spring water samples showed middle REE (MREE) and high REE (HREE) enrichment. The most toxic elements including Pb, Cd, Ni, and Zn were predicted as cationic form in the plant water. The prediction further showed that smithsonite (ZnCO3), hydrozincite Zn5(OH)6(CO3)2, hemimorphite Zn4Si2O7(OH)2, and beudantite (PbFe3(AsO4)(SO4)(OH)6) were oversaturated in some water samples.