High grade keeps Campbell at the head of the class

It has been like that at Balmertown, Ont., since the high-grade G zone was discovered at the 1,000-ft level back in 1953. Until then, Campbell’s original operators didn’t know whether they had a mine on their hands. “It was nip and tuck before they got down to the seventh level,” says chief geologist Ray Church, who is still exploring an orebody that remains open at depth.

With production expected to hit 242,000 oz in 1988, there seems little doubt that Campbell will continue to be the crown jewel in Placer Dome’s portfolio of gold producers. A minimum 7.4 million tons of known reserves is enough to keep the operation going for at least 18 years, and Mine Manager Stewart Reid sees no geological reason why the ore should be disrupted below current mine workings, which extend down to the 27th level at 4,000 ft.

So with its long-term future almost guaranteed, Reid has been busy overseeing a modernization program that will maintain the mine’s position in an industry that is turning increasingly to automation. Still to be completed, the program has so far touched on just about every aspect of the operation, which is running full tilt at about 1,075 tons per day.

When The Northern Miner visited the Campbell operation recently, the company had just spent $12.6 million on new grinding facilities. It was also attempting to incorporate the entire milling operation into a computerized central control system. So far, only the grinding, flotation and leaching circuits are included on the Foxborough sms Control Unit. The next step is to bring the crushing circuit, roaster and grinding circuit into the system, which is controlled by a single operator. He sits in a control unit on the flotation floor between the new grinding circuit and the old mill. When it is finished, mill superintendent John Frostiak will be able to monitor the entire system through a large computer terminal that sits conveniently in the corner of his office.

Other improvements to the mill include a carbon-in-pulp circuit, which has been added to the end of the flotation circuit, and a new backfill plant. Considered vital to an operation that places ever-increasing demands on its ground support systems, the backfill plant allows the operator to monitor the ratios of cement and tailings being piped down to underground stopes. “Before the system was commissioned, we couldn’t control the strength of the material we were sending underground,” Reid says.

Although the Campbell roasting system is considered “pretty hard to beat”, Placer Dome is testing bioleaching technology in a new pilot facility. The bacteria- enhanced gold recovery system is reputed to be much cleaner than roasting, which emits sulphur dioxide. Although scientists say bioleaching can improve recovery rates achieved in conventional milling methods by as much as 70%, Frostiak hasn’t noticed any dramatic improvements.

He is simply preparing the company for the inevitable day when Campbell is required to make dramatic reductions in its sulphur dioxide emissions. As part of a voluntary emission reduction program, Campbell shuts down its plant when the wind is blowing towards Balmertown. The new systems have reduced manpower levels by 15% in the Campbell mill. Placer Dome is also replacing outdated equipment in other parts of the operation. It has made its hoist safer and more efficient by spending about $1 million to install computer-controlled acceleration and de-celeration. “We still need an operator when the hoist is approaching its destination, but he won’t be thrown around in the cage when a power outage occurs,” Reid says.

As a result of the recent changes at Campbell, any additional increases in tonnage must be accompanied by an expensive shaft-sinking program. Before he retires, Reid will recommend that the shaft be extended below 4,317 ft. But Henry Brehaut, Placer Dome’s senior vice- president of Canadian operations, says those recommendations (if they are forthcoming) will not be carried out in the near future.

A more immediate worry is the ground support problems. These are becoming a greater concern as the mine gets deeper. In a bid to limit seismic activity at a mine which has a history of rockbursts and to provide the necessary ground support, Campbell uses cut-and-fill in at least 98% of its mining. A limited amount of long- hole mining is also being used to recover the top portion of crown pillars where the ground is thought to be suspect.

Since 1983, the company has spent about $250,000 on a microseismic monitoring system. It allows Campbell to detect ground activity from an office in the dry area. Using 64-channel geophones, which are installed at strategic areas throughout the underground workings, the system monitors mine-wide events as they occur. “It has allowed us to prepare underground work spaces and gain a better understanding of what the ground is really doing,” Reid says.

While the equipment is considered an improvement, it couldn’t prevent the death of an underground supervisor from a rockburst last October. He and two co- workers had been inspecting drill holes on the 14th level when a rock face burst. He was killed by the force of the blast. The co-workers managed to escape to a safety station and make their way to the surface.

“We have not yet found the key to predicting rock bursts,” says Reid, who adds that the microseismic equipment has not yet provided the answers. Nevertheless, he believes that if it wasn’t for the microseismic system, there may have been more accidents from bursts at Campbell. “Without it, we wouldn’t know exactly where the rock burst occurred and we could send people into dangerous areas,” says Tony Makuch, assistant chief engineer.

He and other members of the Campbell engineering staff are participating in a university study in which all the information collected on the system over a number of years will be analysed. Meanwhile, they can use the system’s video display screen to look for high stress points in an area which extends into the neighboring Dickenson mine, where workings now extend down to level 38.

Most of the ore mined from Campbell last year was mined from the G and L zones, which lie between the 14th and 19th levels. While miners are starting to drift on the 23rd level, it isn’t yet known where the bottom of the orebody is located. “We probably won’t find the bottom until we deepen the shaft below 4,317 ft,” says Church.

One of only five chief geologists to have worked at Campbell since operations began in 1949, Church follows set procedures laid down by his predecessors. “We don’t get told to go out and replace the 400,000 tons that were mined last year,” says Church. But he is reasonably sure that more ore will be found on the lower levels. In fact, Church has stayed at Campbell for 17 years because he probably couldn’t find more gold anywhere else than he is finding now. Reid, meanwhile, plans to retire this year after 12 years in the manager’s seat. “My mandate has been to maintain the facility in the best shape I can,” he says. His successor may attempt to pry more gold from the Campbell orebody by increasing recoveries above 95% or improve on the $100.7 million in operating earnings achieved in 1987. But whoever takes over, the new manager will be expected to maintain the mine’s lofty position as one of the world’s most secluded but profitable gold producers.

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