Anthropogenic and Geogenic Mercury in Surface Waters in the Mature Bathurst Mining Camp, New Brunswick, Canada

Interactions between a cyanide leach used for Au extraction and cinnabar-bearing gossan tailings at the Murray Brook mine have led to the development of an Hg-enriched contaminated groundwater plume that discharges to the nearby Gossan Creek. Naturally occurring cinnabar in the area poses a challenge in distinguishing mining-related contamination from background Hg concentrations. Surface water data from throughout the Bathurst Mining Camp was used to establish interelement relationships compared to pH and the spatial distributions of Hg, SO42-, Cl, Cu, NO3-, Zn, Pb, and Ca/HCO3- values. Statistical significance of anomalous measurements was evaluated to assess geogenic versus anthropogenic contributions of min-ing associated elements. Watershed analysis indicated that the Murray Brook tailings facility may sit on a basinal divide with potential for tailings leachate-impacted groundwater and surface water migration toward the northeast as well as northwest toward Gossan Creek. Elevated NO3- was detected in two streams south-west of Gossan Creek alongside greater than normal Hg concentrations. Other locations in the study area away from the Murray Brook area show little geochemical evidence for impact of mining on surface waters despite Hg concentrations as high as 0.019 mu g L-1. Points with geogenic Hg concentration on the order of 0.01 mu g L-1 were observed throughout the study area, particularly in the Upsalquitch River tributaries south-west of Gossan Creek and in the surface waterbodies west of the Restigouche deposit, indicating weathering of cinnabar-bearing gossan.

Automated summary

Interactions between cyanide leach and cinnabar-bearing gossan tailings have resulted in Hg-contaminated groundwater that discharges to Gossan Creek. The presence of naturally occurring cinnabar complicates the identification of mining-related contamination. The study analyzed surface water data to assess the impact of mining-associated elements and found evidence of migration towards Gossan Creek.