SILIDOR

Thus began a 4-year, $24.4-million exploration program which has since blocked out 4.1 million tonnes of mineralization (undiluted) over a strike length of about 900 m to a depth of about 700 m. The ore occurs as three types, according to chief geologist Dr Chris Kloeren: in quartz veins, in a mineralized, bleached tonalite and as a carbonatized breccia with 1% to 5% pyrite. At a cutoff grade of 3 g gold per tonne, that block averages 3 m in width at an average grade of 6.1 g gold per tonne (0.18 oz gold per ton). That’s wide enough for low-cost mining methods such as longhole open- stoping. And the zone is still open at depth.

A shaft was sunk by J. S. Redpath, starting in the hangingwall, cutting through the ore zone at the 340-m level and continuing on to a total depth of 551 m in the footwall rocks. The shaft location was designed in such a way that it would be situated central to the mineable tonnage. The shaft was completed as part of an underground exploration program that included track drifts driven on five levels, all within the ore zone. That work produced about 85,000 tonnes of mineralization grading about 5.6 g gold per tonne for metallurgical testing.

To joint-venture partners Noranda (55%), Cambior Inc. (25%) and Nova- Cogesco Resources (20%), that all adds up to an orebody, even at today’s $367-(us)-per-oz gold prices. A $31.5- million development program was announced in August, 1989, to bring the mine into production at a rate of 3,300 tonnes per month beginning in January, 1990. The stockpile was split between the three partners for separate treatment. Cambior has treated 45% of the 80,000-tonne stockpile in its Vezina mill in Destor Twp. (Nova- Cogesco receives 44% of the gold produced), and Noranda was in the process of treating its 55% share at its Horne smelter in Rouyn-Noranda.

At the time of our visit, mine contractors Ross Finlay of Val d’Or had driven a ramp to the 93-m level and excavated three stations on sub-levels spaced 13 m apart (on the 60-, 73- and 86-m levels) in preparation for longhole mining above the 220-m level. The ramp will be driven from the 220-m level upwards to meet the downward spiralling ramp. Where the orebody dips at about 70 degrees (in the south end of the zone), the shrinkage mining method will be used. And where the zone flattens out to 55 degrees and widens out to between 8 and 9 m (in the north end), longhole open stoping is the method of choice. About 60% of the mine’s total production will come from longhole stopes and 40% from shrinkage. Total ore extraction will be about 85%. The ore contains some joints but has a very high rock quality designation of 85 to 90. Rock mechanics work performed by the Noranda Research Centre has concluded that the rock is competent, so no backfill will be required in the open stopes. The company is looking to mine at a cost of $40 per tonne. About 150 people are needed to run the operation.

Development crews were also working on the 460-m level installing a hydraulic hammer and grizzly arrangement through which the ore will pass before being hoisted to surface. Ore and waste passes have been driven conventionally by Alimac raising. These raises are oriented at the same angle as the ore zone so that access on each haulage level is a constant distance from the orebody. All haulage from the drawpoints (which will be spaced every 10 m) to the orepasses will be done with load-haul-dump machines.

There will be 80 contract miners on the site this fall, working three shifts per day, seven days a week. By the end of 1989, the company hopes to cut back to a 5-day work week.

Noranda, as operator of the project, is bidding on 1-boom hydraulic jumbos, 2-cu-yd and 3.5-cu-yd load-haul- dump machines for development work and longhole machines for drilling 2-inch-diameter production holes. “We ha ve preferences but will wait for the bids before we decide,” mine director Claude Begin said.

Once the ore is hoisted to surface in two 7.5-tonne skips by a 3-m-diameter, 1,550-hp Nordberg hoist, it will be dumped into a 300-tonne ore bin to be constructed next to the headframe. (Hoisting from a loading pocket on the 500-m level, this hoist is more than enough to satisfy production requirements.) Trucks then will haul the ore either to the Horne smelter or the Vezina mill. One will go to the Horne, another will go to the Vezina, and so on. In other words, the ore will be split between the partners by tonnage, not grade. There is some uncertainty about what mill head grades and dilution will be, but no problem is expected with the metallurgy.

“We don’t know if we’ll recover our costs if gold goes down to $325 (us) per oz,” Begin said. “But it all will be a question of people and equipment.” If, when the company begins to mine it, Noranda sticks to the same basic fundamentals it used to find the deposit, who knows? Maybe luck will be with the mine.

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