BRENDA

Bill Scribner was there at the beginning. Today he is mine superintendent. As the closing deadline approaches, he told The Northern Miner Magazine, “there are a lot of mixed emotions from the old-time employees. A lot of people still don’t think it will shut down. It’s one of those things. There’s that hope in the back of their minds that Brenda will find more ore.”

That is not likely, however. “In an attempt to add to the existing ore reserves, exploration drilling was carried out, first in the bottom and later on in the north-west corner of the existing pit. However, no economic mineralization was identified.” So states the 1988 annual report.

Mine crews are currently stripping the final pit pushback, which provides access to about 11 million tonnes grading 0.19% copper and 0.036% molybdenum. (Molybdenum accounts for nearly half of Brenda’s annual revenue.) This new material actually postponed the closing by nearly one year. Current mining rate (ore and waste) is about 50,000 tonnes per day. Ore is being drawn from the pit bottom. Two 60R Bucyrus Erie 12 1/4-inch rotary drills drill off 50-ft benches on a 28×28-ft pattern. Ici Explosives (c-i-l) delivers explosives (ammonium nitrate for dry holes and an ammonium nitrate slurry called Nitrex for wet holes) to the pit from a plant nearby. Two Marion 182 11-cu-yd, a Marion 191 13-cu-yd and a P & H 2100 13 cu-yd shovels load the 100-ton Lectrahaul trucks.

Last year, the only serious mining problem was wall stability in the south corner of the pit. Pit wall monitors, made by Aga Geodimeter of Canada, have been installed. As well, holes are drilled horizontally at 100-ft vertical intervals into the walls in a fan-shaped pattern to relieve hydrostatic pressures. Pre-shearing has also become standard practice to buffer the final wall against production blasts. The pit is kept dry by Flygt pumps and Peerless booster pumps which must handle up to 1.5 million gallons per day at peak periods.

Over the years, snowstorms have been a continual problem. The average snowfall at Brenda runs about 8 to 10 ft a year. But in difficult years operators grappled with as much as 27 ft of snow. “As long as we could keep the trucks rolling and continue sanding the roadways, we were okay,” said Scribner.

Milling at Brenda begins with a conventional crushing circuit that involves a 60×89-inch gyratory Allis- Chalmers primary crusher, two 7-ft Nordberg standard cone crushers as secondary units and a tertiary system of another four 7-ft Nordbergs. The crushing plant is a closed circuit to prevent oversize from going into fine ore bins. Four identical but independent circuits, each consisting of Dominion rod (13.5×18-ft) mills and ball (13.5×22-ft) mills, make up the grinding circuit. The product then reports to a rougher flotation circuit, a cleaning flotation circuit, and a separator that divides the molybdenum and copper concentrates. The copper is shipped by B.C. Rail to Vancouver and then on to Japan. Molybdenum concentrates are delivered to a roaster in Belgium.

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