A geophysical and geotechnical study to determine the hydrological regime of the Central Manitoba gold mine tailings deposit

Extraction of gold from quartz-carbonate shear zones has left a barren deposit of tailings at Central Manitoba mine, which remains unchanged after 70 years. In this study, the shape of the basin, the groundwater and surface water flow regime, and the electrical conductivity of the tailings have been delineated using a combination of geotechnical, geophysical, and geochemical techniques. Groundwater and surface water flow from the north-south-fractured bedrock outwards to the east and west. A component of upward groundwater movement in the deposit is due to evaporation in hot, dry summers, limited recharge from precipitation, and the tailings basin being a local groundwater discharge zone. Electromagnetic surveys indicate that the thickness of the tailings and underlying peat bog material increases from similar to 1 m at the south of the tailings to similar to 5 m at the north. The surveys provided an effective way of mapping the spatial distribution of acidic pore fluids and associated increased salinity. Zones of acidification, occurring mainly on the south side of the tailings, support the hypothesis that acidification is due to differential settling during the initial discharge of carbonate and sulfide minerals.