Macassa mine expects to produce 100,000 oz. in 1990

The year 1990 is shaping into a memorable one for LAC Minerals’ (TSE) Macassa mine. Located in Teck Twp., Ont., the heart of the Kirkland Lake mining camp, Macassa is the most westerly of seven former gold producers that made Kirkland Lake a boom town until the late 1960s. Production in 1990 from the newly modernized and expanded No. 3 shaft is expected to increase by 20% over 1989. The mine will probably produce about 100,000 oz. this year, compared with 82,540 oz. in 1989, well over the previous forecast of 85,000 oz. Gerry Gauthier, LAC’s senior vice-president of operations, says, “The year has been full of surprises.” According to Gauthier, stopes 25 to 30 ft. wide, averaging 0.50 oz. per ton or more, have not been uncommon.

As well, precision mining techniques have resulted in nearly 100% ore recovery and zero dilution. Most of this year’s production windfall has come from the 04 Break and the associated Hanging Wall Splay between the 4700 and 7050 levels, although stockpiled ore was also used.

As of Dec. 31, 1989, Macassa’s proven and probable reserves were 1,513,000 tons grading 0.51 oz. at a cutoff grade of 0.30 oz. Reserve estimates will be upgraded at the end of the year and will take into consideration any high-grade mineralization found along the 05 Break.

The biggest surprise of the year was perhaps the record levels of gold output and production tonnage in March. For the first time in the mine’s 57-year history, gold output reached 12,353 oz. smashing the previous single month record of 9,000 oz. The mine also produced a record 18,311 tons, compared with last year’s monthly average of 13,790 tons. The average monthly gold yield in 1989 was 6,878 oz. The recovered grade for the month averaged 0.68 oz. and mill recovery averaged 96.8%.

Overall mine performance for the year has been exceptional. In the first quarter to March 31, Macassa produced 27,495 oz., compared with 20,396 oz. in the same period last year, for an increase of 35%. Cash production costs averaged US$245 per oz., compared with US$313 last year. The average recovered grade came to 0.54 oz. per ton and mill recovery averaged 96%.

In the second quarter to June 30, production declined somewhat to 25,525 oz., compared with 20,803 oz. last year, for an increase of 23%. Cash production costs for the 6-month period averaged US$251 versus US$301 last year. For the 6-month period, recovered grade averaged 0.52 oz. and mill recovery averaged 95.6%.

Macassa boasts the deepest mine shaft in the Northern Hemisphere — the 4-compartment No. 3 shaft to 7239 ft. — completed in May, 1986, for $37 million. Annual output has been increasing ever since new areas were opened up for exploration and development, and improved mining equipment and methods increased tonnages. Not surprising, a milestone was reached on May 23, as Macassa celebrated three million ounces of gold production.

A fully automated system to monitor rock bursts and seismic activity in the mine was completed in 1989. The network of 20 geophones will detect areas of increased seismic activity. Rockbursts are being controlled through careful mine planning and sophisticated ground control methods such as cemented rockfill, cable bolting, cable slings and sequenced mining.

A southern Ontario consulting firm visits the mine annually conduct stress surveys that will predict troublesome areas and thereby assist in the design of openings and stopes.

Gerhard Meyer, Kirkland Lake resident geologist, says the area is known for its brittle rock formations. As well, being close to the Kirkland Lake Main Break, potential for rock bursts and seismic activity is even greater, especially at the increased depth of the Macassa.

Mining operations have also benefited from improved ground control. Cemented backfill and sequenced mining techniques have helped raise the recovered grade by decreasing dilution of the ore, and the use of cable bolts and slings instead of timber for underground support has reduced costs.

In July, 1988, the fully automated, 1250-ton-per-day mill was completed. A $20-million carbon- in-pulp (CIP) facility replaced the inefficient Merrill Crowe, cyanidation zinc precipitation circuit of the former mill. The mill treats up to 600 tons per day of ore from Macassa and 750 tons per day of tailings from LAC’s Lake Shore project. For the first half of the year, gold recoveries were averaging about 70% for the tailings project and 95.7% for Macassa. In the second half, recoveries for Macassa have been averaging over 96%.

Underground exploration this year concentrated on the promising 05 Break, east of the No. 3 shaft, and to the north and east along the zone. Narrow high-grade mineralization has also been found by drifting on the 6100 and 6600 levels of the 05. On one section of the 6100 level, for example, the 05 ran 0.36 oz. per ton across 5.9 ft., for a length of 160 ft. Another 166-ft. length ran 0.48 oz. over 6.8 ft.

At the same time, Gauthier points out that, when diamond drilling, the typical “hit ratio” for the Macassa is about 20-25% and gaps of 200-500 ft. are common in uneconomic mineralization.

The 05 was discovered in 1988, 1,300 ft. north of the 04, at a depth of about 4,000 ft. Still open downdip and to the east, the 05 Break, as of April this year, had been drifted for roughly 400 ft. on the 6100 and 6600 levels. So far proven reserves are estimated at 70,000 tons grading 0.44 oz. gold. Estimates are that it may take up to four years to define the 05 structure within the mine.

Gauthier is also excited about exploration potential on the extreme eastern boundary of the property. In 1987, within 50 ft. of the eastern boundary, a diamond drill hole was collared on the 3,000-ft. level and intersected 0.30 oz. across 6 ft., north of the 04 Break. Although the intersection actually occurred on the old Lakeshore mine property being worked by Newfields Minerals (TSE), it was a hint that the zone might extend on to LAC’s Macassa property.

LAC recently reported encouraging values from its drifting program along the 4750 level of the 04 Break extension on to the adjacent 18-claim property of Queenston Mining (TSE). Last year LAC agreed to conduct 5,000 ft. of drifting and 15,000 ft. of diamond drilling from its own underground workings, west of the shaft. Assays are not yet available to confirm the occurrence of economic mineralization.

To date, of the three drifts that continue across the North-South fault gap, none have found ore. Under the terms of the joint venture agreement with Queenston, LAC is the operator of the project and can earn a 65% interest on the first 400,000 oz. produced from the Kirkland Lake West property.

This year, underground exploration and development will cost about $3.5 million, of which $1.3 million will be spent on underground development and $2.2 million on exploration.

Meyer says the Macassa mine has been the backbone of the community since the late ’60s, when long-lived gold mines like the Wright Hargreaves, Lakeshore, and Teck-Hughes ran out of ore, after 45 to 50 years of production. Many generations of dedicated miners have made their mark on the mine since operations began in 1933. As of June, 1990, the mine had 317 employees on its payroll.