EXPLORATION ’94 — Kirkland camp has long history of

While gold mining near Kirkland Lake, Ont., began in 1918, the first rockburst was not reported until 1929.

Seven mines were developed along narrow, quartz-bearing veins which are associated with several fault systems known as the Main Break, or the Kirkland Lake Fault.

The three rockbursts that occurred Nov. 26, 1993, in the vicinity of the 6,600-ft. level of the Macassa mine of Lac Minerals (TSE), trapping two miners, has led to further study of the phenomenon.

David Hedley, who has a doctorate in rock mechanics and works as an independent consultant, is one of the experts Lac Minerals brought in to investigate the recent rockbursts.

The first reported rockburst in the camp occurred in 1929 at the Kirkland Lake gold mine, Hedley explained. In the early 1930s, both the Lake Shore and Teck- Hughes Gold mines reported the occasional rockburst, “but in 1934 everything really picked up, especially at Lake Shore, Teck-Hughes and Wright-Hargreaves Mines.”

He defined a rockburst as “as a violent and sudden failure of rock.” About 1934, the number of rockbursts shot up. They peaked about six years later, when roughly 350 were reported in Ontario. At least two-thirds of these were in the Kirkland Lake camp. As mining activity increased, so did the number of rockbursts, Hedley explained.

During the mid-1960s, rockbursts in Ontario peaked at about 150, mainly because of activity at Wright-Hargreaves Mines and Lake Shore Mines. In March, 1961, Lake Shore recorded a 4.3-Mn (Nuttli magnitude scale) rockburst, the second-largest recorded in Canada. This occurred in the same area as the one in January, 1957.

This rockburst affected stopes on five levels, blocking them at the face, and the drifts were blocked over six levels near the stope face. Hedley reports that after the 1957 Lake Shore burst, one year was required to complete rehabilitation work; after the 1961 occurrence, this area of the mine was apparently abandoned, as there are no further records to indicate activity.

In 1964, a 4.2-Mn burst hit the Wright-Hargreaves mine, which destroyed the No. 4 shaft and effectively closed the operation, Hedley said. While the most rockbursts were reported at Lake Shore, the Teck-Hughes mine also had its problems. In 1958, two 3.1-Mn magnitude rockbursts hit the mine, which caused the company to abandon the lower part of the south shaft. After rockburst activity peaked in the mid-1960s and until recently, activity had decreased significantly. But in the 1980s, the number of rockbursts increased, not just in the Kirkland Lake camp but also in Elliot Lake, Sudbury and Red Lake.

Macassa became fairly active again in 1982. In 1984, it reported a 3.1-Mn burst, the largest ever recorded at the mine. This burst happened between shifts, after blasting. (About half of all rockbursts happen between shifts and are usually created by blasts.)

While Macassa’s recent rockburst was a multiple burst, Hedley said multiple rockbursts happen about one in 10 times and tend to be isolated occurrences. From 1931 until 1992, 1,050 rockbursts were reported at six different mines in the Kirkland Lake camp.

In a report prepared for Lac, Hedley said: “There were many more rockbursts than were reported, either occurring in abandoned areas of mines, or out in the wall rocks with no associated damage. In addition, so-called `strain bursts’ of fewer than five tons were too numerous to keep account of at most mines.”

Included in these bursts were 200 that were rated heavy, 290 medium and 560 light. “In general,” Hedley said, “heavy bursts are those with a rock displacement of more than 50 tons, medium is 15-50 tons and light is 5-15 tons.”

Lake Shore reported 479 rockbursts between 1931 and 1964, while Wright-Hargreaves reported 227 between 1932 and 1964. Macassa had 222 between 1936 and 1992.

A total of 51.4 million tons of material was displaced by the rockbursts. Hedley’s research indicates that most bursts occurred at Wright-Hargreaves, Lake Shore, Teck-Hughes and Macassa and that these tended to be the deepest mines with the highest tonnage mined and thus the most extensively mined-out. Noting that rockbursts are unpredictable, Hedley said “the best hope is trying to reduce the severity and develop methods of protecting the labor force.”

Tragically, since the first rockburst was reported, about 40 people have been killed by such occurrences in the Kirkland Lake camp, he said. — The writer is a journalist based in Kirkland Lake.