Cambior plans big things for Doyon

Roller coasters head up, as well as down, and for the Doyon mine, a short distance east of Rouyn-Noranda, the ride seems to be heading up again.

Doyon, which has suffered from high costs over the past two years, is seeing a program of underground development bear fruit, as its grades go up and costs go down. Added to that, a new operator, Cambior (CBJ-T), is making changes that promise better cost performance over the long haul.

When Cambior took over operation of the Doyon gold mine from Barrick Gold (ABX-T), it saw the mine as a “core strategic asset,” solidifying its presence in the Rouyn-Noranda camp. For Barrick, Doyon, though a solid performer, had never been central to its plans. It had inherited the mine when it took over Lac Minerals in 1994 and had other, larger projects to occupy its attention.

Cambior paid $95 million for Barrick’s half of Doyon, and took over operation at the beginning of 1998. The purchase made plenty of sense: Cambior owned the smaller Mouska gold mine next door, which already sent its ore to the Doyon mill, and the two operations could be integrated. The company’s Vzina mill, north of Rouyn-Noranda, was idle and some of its equipment could conceivably be put to better use expanding the Doyon mill. The purchase also included interests in nearby exploration properties that consolidated Cambior’s land package in the area.

Doyon, opened in 1980 by Lac and the Quebec Crown corporation Soquem, started as a relatively small open pit, but Lac rapidly developed a large underground reserve. When Royal Oak Mines (RYO-T) opened a bidding war for Lac in early 1994, operations deteriorated, since Lac’s attention was fixed on battling the takeover and not on running its mines.

In 1995 there was minimal development as Barrick began to turn the mine around. A 2-month strike in 1996 cost time and resources that would otherwise have gone into development of deeper levels. Lack of underground development forced the mill to process lower-grade, stockpiled ore, and with grades down, unit production costs went up, peaking in the first quarter of 1997 at US$357 per oz.

But by the end of 1997, the time and money that Barrick and Cambior had put into stope development had started to pay off; grade was up to 5.3 grams per tonne (from 3.5) and unit costs were down to US$228.

Development of higher-grade ore on the deeper levels is one facet of the Doyon story; another is the replacement of rock-fill with paste-fill, at what Cambior expects will be a considerable saving. The mine uses longhole open stoping, and Lac and Barrick had backfilled open stopes with cemented rock fill. Cambior saw the possibility of saving costs by putting in a paste-fill plant, which uses tailings from the mill, Portland cement and fly-ash to produce a fine-grained concrete product.

“Rock-fill is a lot of handling,” says Robert Marchand, superintendent of technical services — “double, sometimes triple handling.” In contrast, the paste-fill will be delivered by tremie pipelines to the stopes rather than skipped or hauled underground. The paste-fill plant was recently finished and should be providing fill, and saving on backfilling costs, this month.

Another Cambior priority has been increasing the capacity of the Doyon mill. At the beginning of the year, Cambior expected it would be bringing a ball mill from the Vzina plant, but a tweaking campaign in the Doyon mill may render that unnecessary. For example, the grinding circuit had been producing material with 80% passing 75m; allowing that to slide to 78% has decreased the grinding time without a loss of recovery, and the shorter grind has permitted the mill to process more ore per day.

Refractory copper- and tellurium-bearing ores from some of the underground zones used to slow the mill down, restricting mining in those areas. Now, work on the problem has allowed the mill to vary its reagents when processing the refractory material; the mine simply needs to let the mill know in advance when these ores are coming.

In all, the company expects to bump mill throughput to 1.4 million tonnes in 1998, up from 1.2 million tonnes the year before. With increased grade, the mine is on track to produce 230,000 oz., about double what it produced in 1997.

Underground services include upgrades to the compressed air system and the pump network. Now that development on the mine’s 8 and 10 levels (480 and 600 metres depth) is near completion, maintenance activities can be better co-ordinated to permit more organized maintenance work. “That’s where we think, in the next six months, we’re going to improve our costs — in mine services,” says Reynald Vzina, senior vice-president.

Mining will move below the 8 level in October, and exploration of deeper levels is in the works. Reserves stand at 10.3 million tonnes grading 6.7 grams gold per tonne, with a cutoff grade based on US$350 per oz. gold. A 4.6-million-tonne resource grading 4.6 grams is not believed to be economic at that price.

Exploration drilling, like mining, has been hampered by the lack of underground development, but as the deeper levels are pushed out, more drill stations will open up. “We need other access, for example on the 12 level, to drill off additional reserves,” says Daniel Doucet, chief geologist. “We don’t have access yet to have other reserves.”

The mine exploration budget is $2.9 million for 1998, but the great bulk of that has been devoted to drilling off stopes; only about $250,000 will go into “pure” exploration. Better access next year will allow more to be plowed into deep drilling, particularly in the western part of the mine.

The Doyon vein system makes a crude “J” pattern, with the curve to the west in an intrusive body mainly mapped as an alaskite granite. Ground in the intrusive rocks is reliable, and some smaller vein systems in the mine’s West zone have been mined from large open longhole stopes. Along the stem of the “J,” in an east-striking sequence of volcanic rocks and schists, ground conditions are not as favorable, but they still permit longhole stoping with backfilling. The vein structures are nearly vertical and plunge steeply to the west, so Cambior’s exploration strategy will centre on following the zones down-plunge.