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A large concrete plug is now in place, sealing the last of four vertical openings to the former underground mine at Snap Lake.

The Return Air Raise (RAR), a hole to the bottom of the mine used to pump air out of the mine, was capped as of September 7. Three other shafts or raises were sealed off during active closure:

• Fresh Air Raise 1 & 2 used to pump fresh air into the underground
• Underground Services Building raise

The underground was flooded in 2017 after all hazardous materials were removed. The main portal used by people and equipment to access the mine and the conveyor portal that brought kimberlite to surface are to be permanently closed during 2024.

Capping the RAR was more complicated than the other openings due to the fact it was located across Snap Lake from the mine and could only be accessed by winter road in the winter or by helicopter. Materials needed to cap the RAR were brought to the location during the 2022 and 2023 winter road programs.

The two-layer concrete “plug” also had to be specially engineered due to the way the RAR was constructed during the early days of operation. Six contractors and consultants were involved with the work, including the MetNUNA closure contractor.

Michelle Peters, Snap Lake Mine Closure Manager, said: “This is an excellent example of how the various teams pulled together to safely complete this complicated task. This is an important milestone as we work toward achieving substantial completion of active closure in 2024.”

To install the two-layer plug, workers had to first install rock anchors into wall to support the formwork and rebar cage for concrete.

The concrete pour was slightly delayed due to the fact the helicopter required to lift the concrete to The helicopter lifted a total of 86 bucket loads of concrete over two days to compete the plug.

The first pour went successfully August 28 and the final pour was executed on September 7.