Abandoned Gold Mine Closure
Client: SLR Consulting Public Works Canada
Location: Gordon Lake, NWT
Type: Geohazard Assessment Acid Mine Drainage
In September of 2012, ParklandGEO partnered with SLR Consulting (Canada) Ltd. (SLR) to conduct a Phase III Environmental Site Assessment at five former gold mine sites on the shores of Gordon Lake, NWT., about 85 km northeast of Yellowknife. The sites included the Camlaren, Kidney Pond, Burnt Island, Goodrock and Treacy mine sites. ParklandGEO scope of work included completing a geotechnical investigation and Acid Mine Drainage (AMD) assessment ParklandGEO worked closely with SLR during the field investigation to complete the field work portion of the project.
ParklandGEO field work scope involved the following:
- Complete a visual assessment of all physical hazards on the sites (i.e. mine shafts, waste rock piles, portals, etc.);
- Complete a stability analysis of the existing tailings dyke at Camlaren;
- Survey the sites for potential landfill and landfarm areas and borrow material sources;
- Collecting representative samples of bedrock and soil using a small excavator and hand augering;
- Survey waste rock and borrow material sources for volume estimates; and
- Assess AMD potential and collect samples of waste rock, trench rock, ore and tailings to be submitted for acid rock drainage testing.
Representative samples of bedrock and soil was shipped back to ParklandGEO Sherwood Park laboratory. Index testing consisting of moisture contents, grain size distribution and Atterberg Limits was completed on select samples to help classify the different soils encountered at the sites.
The AMD samples were submitted for acid base accounting (ABA) testing and kinetic testing (Humidity Cell testing using the MEND method). The results of the ABA testing was interpreted by ParklandGEO to determine acid generation potential of the sites (ABA testing). Kinetic testing results were analyzed to determine the rate of acid generation of the material identified as potentially acid generating. The testing was used to determine the rate of acid generation of the material, thus the impact of AMD at each site.
With the assessment of the physical hazards, ParklandGEO determined the physical hazard risks to the public and provided recommendations to minimize the risks. Some hazards like shallow trenches at Goodrock and a stope breakthrough at Camlaren were considered a low risk, as such no risk mitigation plans were required. Others were considered a significant risk, like the open mine shaft(s) on Burnt Island and Goodrock and portals at Burnt Island and Kidney Pond.
Recommendations to close off the mine shafts included backfilling with nearby waste rock or plugging them with expanding polyurethane foam.