Isle Dieu boosts Matagami’s life

Noranda Inc.’s (TSE) Isle Dieu zinc-copper discovery in 1985 was a timely find. The 25-year-old Mattagami Lake mine, just across the road from Isle Dieu, will yield its last ton of ore late this year but Isle Dieu, just now starting production, will pick up where the original orebody left off. Without the new mine, the lack of Mattagami concentrates would have further pinched Noranda’s already-hungry copper and zinc smelters.

Isle Dieu has also staved off economic disaster for this village of about 2,000 situated roughly 220 km north of Val d’Or. Layoffs will occur, about 120 all told, but Isle Dieu will give the community another 7-year lease on life. And maybe, just maybe, another massive sulphide deposit will be found in the interim.

“This is a good example of just- in-time mining,” said John White, president of Noranda’s Zinc Group. “We’re replacing a 25-year-old mine that’s fading away.”

Both the Mattagami mine and another Noranda-owned mine nearby, known as Norita, are running out of ore, although Norita at least can boast serious exploration targets at depth. Were it not for Isle Dieu, the closings would have devastated the town. Instead, civic officials are celebrating the town’s quarter century of existence and, together with some of Noranda’s senior people, they rolled out the red carpet Sept 9 to welcome about 400 guests to the Isle Dieu opening.

Isle Dieu was discovered by surface diamond drills in 1985, but it required good geological sleuthing to find the massive sulphide target. The top of the orebody sits almost 1,000 ft below the surface, well beyond the range of geophysical detection techniques. Drills were moved onto the property because Noranda’s geologists had an inkling that the Key Tuffite horizon, a known host for the area’s zinc/copper mineralization, extended onto Isle Dieu ground. By 1986, they knew a mineable deposit existed.

With the closing of Mattagami fast approaching, the development of Isle Dieu was hastened. Shaft sinking and the sinking of a ventilation shaft proceeded simultaneously, so that the second level could be developed through the ventilation opening without disrupting the regular shaft sinking. Ordinarily, a ventilation raise is excavated after the shaft has been sunk, using a raise borer or some other method from underground to surface. Contractor J. S. Redpath opted for a small sinking hoist above the ventilation opening to allow for early development.

By the time The Northern Miner toured the operation during the week before the official presentations, Isle Dieu had been developed on four levels. The 3-compartment shaft had been sunk to its deepest point, at 2,125 ft, and was fully operational. A single ore/waste pass had been excavated down to a rock breaker (no crusher is needed here) below the fifth, or bottom, level.

Second-level development, at 1,400 vertical ft, resulted in a revised mining plan. Earlier, mechanized cut-and-fill had been proposed, but the top of the 1-A Zone was not smoothly dome-shaped as previously hypothesized from surface diamond drilling. Rather, it undulated in an irregular fashion, so the mine’s planners chose long-hole methods requiring overcut drill drifts driven from the main haulageway and drawpoint undercut drifts, or crosscuts, for mucking. Higher operating costs will result because of the extra development work.

This change has put commercial production behind schedule by a few months, said Claude Begin, superintendent of mining. Fortunately, it hasn’t altered the reserve, which stands at 2,064,200 tons grading 17.78% zinc, 1.03% copper, 2.34 oz. silver per ton and 0.013 oz gold. About 40% of that is proven ore.

“The configuration of the orebody has changed but the tonnage and grade is still there,” Begin said. “Our feeling is that two million tons is the minimum.”

Below the second level, the shape of Zone 1-B and Zone 2 has been established to the fourth level. There were no surprises here, and it appears that 4 1/2-inch, in-the- hole machines could drill off as much as 100 vertical ft, obviating the need for numerous expensive sub-levels during mining. The orebody does not extend below 2,000 ft, which would put the maximum depth of the mine at just below the fifth level. Mine planners also feel that the orebodies (Zones 1-A and 1-B, separated by a tonalite dyke, and the deeper Zone 2) have been fully delineated along strike. The maximum true thickness is 110 ft for the upper orebody and 80 ft for the Zone 2. The thickness of the zones decreases in all directions and together they are planar, running 1,200 ft east/west and 1,300 ft north/south. The dip is 45 degrees south.

On all levels below the second, miners are drifting and driving cross-cuts into the orebodies. Ore from a second-level stope, measuring 40 ft high, 75 ft long and 35 ft wide, has been mined and milled. The grades in the 8,500-ton sample were nearly identical to the reserve figures, although the copper grade was down somewhat, and zinc recovery rate from the Mattagami mill, which will process all the Isle Dieu ore, ran an average 97.3%. The planned mill recovery for Isle Dieu ore is 95%, producing an annual 115,000 tons of zinc concentrate grading 54% zinc. Another 15,000 tons of copper concentrate will be trucked to Noranda’s Horne smelter in Rouyn/Noranda. The zinc will be further processed at the company’s Canadian Electrolytic Zinc plant in Valleyfield, Que., near Montreal. To supply millfeed, the mine will operate at 1,500 tons per day.

The mine services, such as process water, compressed air, drinking water and backfill slurry (classified mill tailings) will be piped from Mattagami. With the old mine and its infrastructure nearby, development costs have been kept down. Only a headframe, hoistroom and ventilation building are on surface at Isle Dieu. The projected cost was $35 million, but the operators have come in under budget by about $2 million (this does not include prior exploration costs or interest on borrowed capital during construction).

At the same time, rather sophisticated micro-computer-based technology has been plugged into the system to monitor for noxious gases and problems in the electrical systems in pumps and at substations. A central computer base can control underground air flow through the ventilation fans and the flow of backfill. An underground seismic monitoring system is also being installed. All these measures should produce operating cost savings.