COMMENTARY — CANMET assists Selbaie, Dickenson

To ensure the stability of their copper-zinc mining project, operators of Les Mines Selbaie in northwestern Quebec are monitoring excavations with time domain reflectometry (TDR).

The cable-testing technique has been provided by the Canada Centre for Mineral and Energy Technology (CANMET) to measure any movement of the rock mass between Selbaie’s open-pit and underground mines. In so doing, it provides an accurate representation of the rock displacements at any given time and location.

CANMET and Selbaie installed eight coaxial cables at the mine, and the former continues to support the analysis of the readings for the mine. Selbaie is planning to install 10 more cables itself.

In TDR, metallic coaxial cables are cemented into holes drilled into the ground. Any movement affects the hole and breaks the cement, thereby deforming the cable. All changes in cable geometry are monitored, and the intensity and location of any disturbance are recorded.

Denis Caron, Selbaie chief engineer, says TDR provides more accurate information at less cost than other instrumentation.

Selbaie entered production in 1981 and by its 10th anniversary had milled more than 14 million tonnes of copper-zinc mineralization.

At Red Lake, Ont., CANMET and Dickenson Mines have collaborated on an air-quality assessment study involving the use of tracer gas to establish re-entry time after a blast, when certain contaminants can exceed their legislated limits.

Not only did the tracer gas provide a quick and accurate analysis (and at less cost than the conventional technique); it also removed the necessity of sending a 3-person rescue team down the mine to determine post-blast air quality.

The study also identified an air loss of 22% within the gold mine, representing $80,000 per year in power costs. All ventilation controls are being repaired to minimize air leaks.

David Mchaina, Dickenson’s director of environmental services, says tracer gas allows for “extremely good ventilation planning,” adding that “it’s economical and quick and it really helped us.”

Tracer gas (inert and non-toxic) can be injected into a body of air and then sampled downstream. The presence of the gas can be accurately determined, even at low concentrations, by gas chromatography.

Dickenson has instituted a monitoring program, with CANMET analyzing the air samples, to ensure a reliable supply of fresh air.

— From a recent publication of the Ottawa-based Canada Centre for Mineral and Energy Technology.