This study investigated the natural attenuation of zinc in mine drainage at the Galkeno 300 mine site, located at the northern limit of the discontinuous permafrost zine in central Yukon Territory. The mine drainage contains ~150 mg/L Zn where it exits the mine; where these same waters enter the receiving environment of Christal Creek, the Zn concentrations have been reduced to ~2 mg/L. The research program examining this natural attenuation consisted of two phases. Phase 1 was comprised of a site investigation along with the collection of samples for chemical analyses and laboratory testing. Phase 2 consisted of laboratory characterisation and testing of samples collected during Phase 1.
The Phase 1 site investigation was carried out during summer 2000. A climate station was established to monitor precipitation and temperature during the study period. Site water balance was monitored through the erection of two weirs; input exceeded outputs by and averages of 16%, indicating a minor degree of dilution. Water samples collected at sites along the longitudinal mine drainage flowpath showed no temporal trends, but clearly outlined a dramatic decrease in Zn concentrations with distance from the adit. Soil samples of upper organic and lower mineral horizons were collected from within and immediately adjacent to the flowpath. Chemical analysis of aliquots of these samples clearly showed elevation of Zn concentrations in samples in contact with mine drainage; upper organic horizons samples in particular were found to contain highly anamalous Zn levels.
The Phase 2 laboratory investigation subjected the collected samples to physical and chemical characterisation, as well as batch adsorption testing and column leaching with synthetic and natural mine drainage. Batch adsorption tests showed the organic soils to have the highest Zn attenuation capacity; in particular, organic soils from the midpoint of the site (site C) were found to have the highest adsorptivity. Similar results were obtained in the column leaching and desorption test; organic samples from site C had both the highest Zn attenuation capacity and and the greatest degree of Zn retention under increasingly aggressive desorbing conditions.
Selective extractions of the collected soils showed that the oxide fraction was the repository for much of the soil zinc. In the organic sils in particular, the oxide fraction dominates the geochemical fractionation of Zn in Galkeno 300 soils. High concentrations of Mn are removed form the mine drainage simultaneously with Zn; the coprecipitation of Mn-Zn oxides appears to be the dominant process of natural attenuation of Zn at the Galkeno 300 site.
