Macassa rescue effort continues

A rescue effort to find two miners trapped underground at the Macassa gold mine of Lac Minerals (TSE) west of Kirkland Lake, Ont., continued at presstime.

The pair, identified as Robert Sheldon, 34, and Leonce Verrier, in his 40s, were among 22 miners working underground Nov. 26 at about 8:20 a.m. when two rockbursts occurred within seconds of each other. Of the 20 who scrambled for safety, two were treated for minor injuries.

Lac has suspended mining operations at Macassa until both the recovery operation and its investigations into the incident are completed. During this time, recovery, support and vital maintenance teams will be the only people working on site.

An investigation of the cause of the rockburst is under way by Lac internally, as well as by a committee of external experts which was being assembled under the direction of Gordon Ley of Golder Associates. Macassa has a history of rockbursts. Stress naturally increases in rocks with depth and as a result of lateral tectonic processes. Mining disturbs the stress field, causing it to be concentrated in some areas and lessened in others. If the stress is concentrated beyond the strength of the rock, the result is a rockburst — a sudden, explosive failure.

The miners are believed to be trapped in a stope at the 6723 level, more than a mile below surface. The stope, a working area from which mineralization is extracted, is reported to be 340 ft. long, 20 ft. wide and 16-20 ft. high. To mine it, Lac is employing a method known as “under-cut-and-fill.” After a further review of the areas from 6623 to the 6723 stope where the two miners were last seen, and after taking into consideration the safety of the rescue teams, mine officials believe a rescue operation from the west end of the 6723 stope is not possible. The main concern is that a further worsening of the 6623 pillar, immediately above the west access manway, seems likely. Additional broken rock is also sliding into the area from the 6623 pillar. It is felt the west section of the 6623 pillar is unstable and will not be capable of ground support to protect rescue teams entering the stope. Efforts continued to concentrate on moving broken rock and material through an ore pass, which is continuously blocking, to the 6750 level. An alternative access was being considered. This work would entail development of level and sub-level drifts and a raise which will take in excess of 30 days. Once the area where the miners were last seen is accessible, removal of broken rock and material can commence. This work would continue 24 hours a day until the operation is complete.

Mine officials estimate about 5,000 tonnes of material caved in during the explosions.

The Macassa shaft, at 7,239 ft., is Canada’s deepest single-lift shaft. The 4-compartment shaft was placed into service in 1986.

In 1958, in Springhill, N.S., seven coal miners were rescued after spending eight and a half days trapped 2.5 miles underground. They drank their own urine to survive.

Macassa, on the outskirts of town, is Kirkland Lake’s last operating gold mine in a community that once had dozens. The mine has operated since 1933. The mine’s fortunes determine the fortunes of the 10,000 people who live in Kirkland Lake.

Production at Macassa in 1992 totaled 77,259 oz. gold. (In 1990, the mine yielded more than 100,000 oz.) Lac’s gold mines in Canada, the U.S. and Chile produced more than 1 million oz. in total in 1992.

Lac said its Lake Shore dredging operation and milling of the tailings at Kirkland Lake will continue to operate as normal.