Hydrogeochemical characterisation of groundwater in fractured aquifers at Konkola mine in Chililabombwe, Zambia

Abstract

An extensive hydrogeological investigation was carried out at the Konkola Copper Mine (KCM), a major mining operation located in Chililabombwe, Zambia, to explore the hydrogeochemical properties of groundwater in fractured aquifers. The approach integrated multiple datasets, including a review of the regional and local geological settings, site-specific meteorological data, environmental isotopes, hydrochemical analyses and previous hydrogeological studies conducted at KCM. The primary aim was to enhance the understanding of both fractured and unfractured aquifers at KCM, which will contribute to the development of a more effective dewatering strategy for the mine. The study established a hydraulic link between fractured and unfractured aquifers as supported by similarities in δ²H and δ¹⁸O isotopic signatures that indicate shared recharge sources and groundwater mixing. In the investigated site, the prevailing hydrochemical facies is classified as Ca-HCO3, indicating that the chemistry of groundwater is dominantly influenced by rock-water interactions, particularly with the carbonaceous and siliceous rock formations affected by percolating water. The hydrochemical results revealed aquifer connectivity and inflow direction, supporting dewatering planning. The stable isotope ( δ²H and δ¹⁸O ) analysis suggests that groundwater recharge primarily occurs through rainfall originating from high latitudes and regional air circulations associated with cooler climate conditions, as evidenced by the depleted isotope signatures. Additionally, the similarities in isotopic (stable) signatures indicate a possible hydraulic linkage among the aquifers at KCM. Tritium analysis reveals ranges between 0.1 and 1.0 T.U., suggesting a mix of recently recharged and sub-modern water, further supporting the presence of hydraulic connections between the aquifers. Higher tritium levels indicate rapid infiltration within permeable aquifer systems, while lower values suggest deep- circulating or confined groundwater. Variations in tritium concentrations across and within aquifers, especially in the Hangingwall Aquifer (HWA) and fractured aquifer, highlight the mixing of distinct water sources. Based on the integrated hydrogeological investigation, the fractured aquifer at KCM has been identified as a zone of groundwater mixing. The overall groundwater flow is directed from the HWA and Lower Porous Conglomerate (LPC) towards the Footwall Aquifer (FWA) and the fractured aquifer. This report recommends that ongoing sampling of isotopes and water chemistry from rainfall, surface water bodies, and underground sources within the study area should continue. Such efforts are important for gaining a better understanding of the area’s hydrogeochemistry. Additionally, measures to exclude surface water should be improved iii to minimize seepage, as this study has observed a connection between surface water and groundwater.