Sigfusson Northern Ltd. completed the second phase of Tailings Management Area (TMA) dams in September 2020. It entailed the raise and extension of clay core dams with rock shells in areas with deep saturated organic layers and irregular bedrock. Prior to raising, existing material was reworked and retested to ensure competent material was constructed on. Dam extensions were required in areas of original ground below future dam crest, organic material was stripped to find competent ground. Once achieved, a key trench was excavated and clay core placement began. Where bedrock was encountered, slush grout and dental concrete were required to ensure effective bonding at the dam abutments. Horizontal and vertical filters were constructed simultaneously with the core. Placement of rock for the upstream and downstream shells followed lifts of core and filter placement as required. Geotextile, geomembrane liners, and concrete cloth were also laid as part of the design. Compliance with criteria such as maximum lift differentials between materials and a stringent Quality Control Program for soils and compaction testing were critical during construction.

Overall length of the Tailings Management Dams raised/extended was approximately 8,500 metres with a volume of over 1.5 million cubic meters of material moved in 2019 and 2020 seasons.

Water management was a significant and ongoing concern during construction. Continuous pumping was necessary to ensure the dams were constructed under optimal conditions.

Schedule was crucial for this work. Sigfusson crews worked 24/7 to ensure milestone dates were met for the mine’s production requirements.