MOBRUN

“We had our own plans on how to develop the 1100 lens, but now those plans are upside down,” said mine director Jean-Bailly. “The deal is too fresh for us to say exactly how that development will proceed. That will have to be worked out between Audrey and Minnova over the next several months.”

The deal cuts the financial risks and also increases the pool of technical expertise required to produce at a rate of 3,000 tonnes per day. This factor alone is expected to reduce mining costs to below the $30-per-tonne mark. This, in turn, could increase mineable reserves, said Chief Geologist Pierre-Jean Lafleur. In the 1100 lens, probable reserves are about 6.6 million tonnes grading 0.66% copper, 5.84% zinc, 1.71 g gold and 43.5 g silver per tonne (0.05 oz gold and 1.27 oz silver per ton). “The mineralization here is more coarse-grained, which means we should get higher recoveries by expending the same amount of energy as we do in the main lens,” Lafleur said. Audrey and Minnova are no strangers to each other, so production of the new zone is expected to proceed smoothly. Audrey will remain as operator of the mine.

One option for developing the 1100 lens includes extending the existing shaft and drifting to the lens on three levels, linked by an internal ramp to provide additional access to sublevels. But a more probable option involves cutting underground haulage distances by sinking a production shaft.

Either way, both companies will be virtually guaranteed millfeed for the foreseeable future. The 1100 lens is still open at depth. Audrey was preparing to turn over its new $21-million mill in mid-August. The mill will employ 18 operators per shift, five staff and six mechanics, explained concentrator superintendent Pierre Pelletier. The number of employees was kept to a minimum by including a semi-autogenous grinding (sag) mill in the grinding circuit (thus eliminating a crushing circuit) and by installing everything under one roof.

Project Manager Denis Gagnon figures Audrey saved at least $7 million by procuring about 90% of all equipment and managing construction of the mill on its own. Since underground work is well ahead of mill construction, getting the mill completed on time is crucial to the rapid payback of capital invested in the operation. By procuring mostly used milling equipment from all over North America, Audrey has cleverly prevented the possibility of the mill-completion falling behind schedule. Some of the new equipment for the mill, new flotation cells, were three months late in delivery, Pelletier said. “There’s no way we would have met our deadline if we had ordered all new equipment.” Mill construction began in May, 1988.

Our tour began in the conveyor walkway, from the 800-tonne ore bin in the headframe to the 2,000-tonne mill ore bin. The walkway is well- lighted by windows on both sides and is completely enclosed and insulated, which is also true of the main mill building. “If the mill operators feel good in their workplace, they will perform better,” Jean-Bailly says. The structural steel and cladding of the main mill building is second-hand too. It came from the Selbie mine, north of Rouyn-Noranda. Inside, no space is wasted. Even so, space has been reserved for a crusher in the event that operations eventually expand. Kilborn Ltd. engineered the mill.

The milling circuit includes two stages of grinding, separate copper and zinc flotation circuits and a dewatering circuit that includes thickening and pressure filtering. The used, 16×18-ft (4.8×5.4-m), 1,100-hp sag mill came from the Mount Pleasant mine in New Brunswick. A 10.5×15-ft (3.15×4.5-m), 1,000-hp ball mill and two smaller (400-hp and 75-hp) mills round out the grinding/regrinding section. Audrey has replaced the liners in all the mills with Skega rubber liners. All the 200-cu-ft Denver flotation cells came from usmx in the U.S. The Larox pressure filter, which will dewater the concentrate, is also a used unit. It came all the way from Noranda’s Goldstream mine in British Columbia. Noranda plans to re-open that mine next year. “Perhaps they should check the mill before making a production decision,” Pelletier said jokingly.

On the electrical side, a motor control centre was constructed to reduce voltages when starting motors. Audrey has spent $300,000 to improve the local electrical distribution system and some 15 Km of electrical wiring was used in the mill.

An Outokompu on-stream x-ray analyser will sample flow streams throughout the mill. All process control instrumentation is being installed by Promec, a local contractor. Compressed air will be supplied by two 600-cu-ft-per-minute Sullair compressors.

Two concentrates, one grading 18% to 20% copper with gold and silver values and one grading 52% zinc, will be stored in an 80-ton (73-tonne) and a 110-ton (100-tonne) bin respectively. These bins are constructed over a truck loadout facility. Audrey will truck the copper concentrate to Noranda Inc.’s nearby Horne smelter while the zinc concentrate has been sold to Eldor Raw Materials of the U.S., which will sell it to various smelters.

Underground, mine plans are well advanced, with operators waiting for the mill to start up. About 200,000 tonnes of ore have already been drilled off in the 22 stope ready for blasting. There were about 50 people working underground during our August visit, working two shifts per day, five days a week. That number was expected to rise to about 130 by the end of September. “We’re having no problem attracting miners to come to Rouyn- Noranda.” Jean-Bailly said. “Many of them are working in remote locations and welcome the opportunity to live in a larger community.”

This year and next, Audrey plans to mine the remainder of the ore in the 22 stope, then mine the crown pillar up to the open pit, Mine Captain Roger Flamand said. Dilution in the 22 longhole open stope is about 5% to 10%. Drilling was to have started in September from the open pit. Holes measuring 16.5 cm (6.5 inches) in diameter will be used to blast the 180,000-tonne pillar which is about 150 m long, 14 m wide and 200 m high. This muck will be hauled from drawpoints on the second level and dumped into a short orepass which feeds a 440-tonne-per-hr, 48-inch (122-cm) jaw crusher about 20 m below the second level. An Allied hydraulic hammer breaks oversize material on the grizzly above the crusher.

Once it is completely mucked out, the 22 stope will be backfilled with some 200,000 tonnes of low-grade material stockpiled on surface. That material is beginning to generate acid mine drainage and returning it to the underground stope will eliminate a long-term treatment problem, Jean- Bailly said.

The 23 stope will provide mill feed for the next two years. It will be mined by the vertical crater retreat method using 16.5-cm (6.5-inch) diameter drill holes, ranging from 45 to 51 m deep. This drilling will be contracted out by year-end, Jean-Bailly explained. Crews were preparing to slash out to the full width of the orebody in the 23 stope during our visit. Three other lenses (the 850, 870 and 930) are small but rich. The 870 lens, for example, contains ore worth about $150 per ton at today’s metal prices.

One high-grade copper zone, averaging 2% to 3% copper, is very importa
nt to the project. By blending it with the ore, most of the precious metals values can be recovered in the mill. Without the copper, those values could not be recovered and the mill would not be justified. About 50% of Audrey’s revenues comes from precious metals content of the ore.

The 850 stope was being developed for shrinkage stoping, using a pneumatic Alimak raise climber. We saw crews installing timber manways as the raise was being stripped. Dilution is expected to be 10% to 15% in the shrinkage stope. The 870 and 930 stopes also are being developed.

The shallow mine is serviced by a 2-compartment shaft down to the second level and a 4-compartment shaft to the bottom level. Two 4.1-tonne (4.5-ton) skips take about one minute to come up from the loading pocket on the 650-ft (195-m) level. Some ore will be hoisted from the 1,200-ft level, but the hoist should have no problem meeting mill demand, Jean-Bailly said.

Underground equipment includes two 5-cu-yd and three 2-cu-yd Eimco- Jarvis-Clark load-haul-dump machines, one hydraulic boom jumbo, three 3-inch-diameter Gardner Denver longhole machines (rubber- tired), three locos and four mucking machines.

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