Paper presented by Roberto Jesus Flores at Perumin 2019 - Arequipa, Peru.
A company operating a copper mine in central British Columbia, Canada is seeking a permit for expansion. Since mine operations pose a potential risk to fish-bearing habitat located adjacent to the Site, provincial regulations require modelling of metal loadings from groundwater as part of a site-wide water quality assessment prior to the mine obtaining the expansion permit. This study was carried out to assess the extent that mineral precipitation and adsorption attenuate metal loadings from groundwater and their potential to inform mine closure planning, including when and where to best direct remediation efforts.
Previous modelling studies used a mass balance approach to predict groundwater metal loadings to surface water; however, this approach over-predicted metal loadings when compared to analytical results from samples collected from monitoring wells. In this study, metal attenuation was modelled using United States Geological Survey (USGS)software PHREEQCI in an alluvial aquifer down-gradient of a pit lake and inactive heap leach pile. Sensitivity analyses were completed by varying iron-hydroxide and calcium carbonate concentrations, and groundwater velocity. Model results were calibrated to groundwater analytical results from wells located on the flow path.
The results predict continued metal attenuation, primarily through metal adsorption and co-precipitation, provided groundwater remains buffered against acidic input. Continued acidic input 30 to 40 years post-closure will result in desorption of weakly adsorbed metals (Cd and Co) and potentially result in adverse impacts to the aquatic environment.