Owners of the Silidor gold mine, just outside the western boundary of this northern city, have high expectations for the project. Operator Noranda (TSE) and partners Cambior (TSE) and Nova- Cogesco Resources (TSE) placed the property into production about April 1. When The Northern Miner visited the project in late May, production was running at a rate equivalent to about 25,000 tonnes per month. By the first of 1991, the targeted rate is about 30,000 tonnes per month.
No milling facility has been built at the mine site, which is expected to produce almost 60,000 oz. this year and 73,600 oz. in 1991. Noranda, with a 55% interest, is trucking its share of the ore to its Horne copper smelter here, while Cambior (25% interest) and junior Nova-Cogesco (20% interest) are processing their portions at Cambior’s Yvan Vezina mill 20-25 miles distant.
A Noranda geological report describes the Silidor deposit as sitting in a homogeneous granite of tonalitic composition. The granite, of coarse texture, averages 35% quartz, 55% plagioclase and about 10% mafics.
The deposit’s mineralization comprises gold and silica, Claude Begin, mine manager, explained. An added benefit for Noranda is that the quartz in the ore can be used for flux in its copper smelting operations at Rouyn. The “Silidor” name is derived from the gold and silica.
Reserves (proven, probable and possible) stand at 4.78 million tonnes grading 5.4 grams gold per tonne (5.26 million tons at 0.16 oz. per ton).
Exploration drifting traced the Silidor vein along a strike length of more than 750 metres. The deposit remains open at depth. Additional reserves are a possibility; Begin said two or three well-spaced holes have been drilled to about 700 metres.
Based on the current reserve figure, the project will have a mine- life of about 10 years. “It depends on how much we have to leave for pillars,” Begin said.
The Silidor deposit is hosted by the Powell pluton, an intrusive within the Blake River group of volcanic rocks which are composed of basalts, andesites and rhyolites and which host several base metal and gold deposits.
The vein is wider on the northern side of the deposit, where it ranges between 3-4 metres and 5-6 metres, Begin said. On the southern side, the vein narrows, to less than three metres at some points.
“Structurally, it is very easy to follow,” Begin explained, adding that within the confines of the vein the mineralization is erratic.
The vein has a strike of 324 degrees and the dip varies from 55 degrees at its northern extremity to 72 degrees at its southern limits.
A 3-compartment shaft with an additional bucket compartment (for future shaft sinking) has been sunk to a depth of 560 metres; depending on what deep drilling uncovers, the shaft may be sunk to about 700 metres.
Levels have been dug at 100 metres, 220 metres and 340 metres; to be completed are levels at 153 metres and 273 metres. A service ramp has been dug to 220 metres; most of the mining activity is currently taking place above that level. Sublevels are being built every 13 metres.
At the time of The Northern Miner visit, the 220 level was being prepared for production. “We’ve got about a month’s work to get it ready,” Rene Robertson, general foreman, said.
The current mining method is long-hole stoping, but when work commences on the southern side a shrinkage method will likely be employed because of the narrower vein structure.
Initial production is being extracted from the northern end of the northern side, where the vein comes to surface at the bottom of a swamp. While that area is now being mined from underground, eventually the pillar left there will be extracted from surface in an open pit operation.
Scoops are used to feed the broken rock into an ore pass where gravity transports the material to a rock breaker installed near the shaft at a depth of 460 metres.
Current mining plans do not include a backfill operation. Robertson said the natural support provided by pillars may be all that is required, at least for the sections mined initially.
“We expect the direct cost for next year, when we are at full production, to be about $40 per tonne (about US$200 per oz.),” said Begin, who worked previously for Noranda in the Matagami and Gaspe areas of Quebec.
The 5-day-per-week Silidor operation employs about 150 people, including 80 miners.
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