Audrey cuts ribbon at Bouchard-Hebert mine

More than 300 people gathered underneath a large tent here in the heart of the Abitibi greenstone belt to raise a glass of cheer to Quebec’s newest polymetallic producer.

The Bouchard-Hebert mine, formerly known as the Mobrun mine and the 1100 lens exploration project, was officially unveiled by Audrey Resources (ME), which, in turn, is 75%-owned by gold-producer Cambior (TSE).

The deposit was renamed to honor Michel Bouchard and Guy Hebert who, in addition to being on staff at Audrey since its inception, were key to developing the project.

The list of guests at the inauguration included mining executives, government representatives and local contractors. Also on hand were The Northern Miner and other news media, who were guided through a first-hand tour of the underground operation.

Once we had descended to the eighth level, Chief Engineer Pierre-Dennis Gagnon explained some of the project’s fine points. “One of the key advantages of this mine is the geometry of the orebody. Because the lens is vertical, we can bulk-mine it using large-scale, long-hole stopes. This greatly enhances the economics of the project, making our development and operating costs much lower.”

At the end of 1994, reserves were estimated at 9.8 million tonnes averaging 4.3% zinc and 0.8% copper, as well as 1.2 grams gold and 34.4 grams silver per tonne. This represents an increase of more than 1.3 million tonnes over the estimate provided upon completion of the March, 1994, feasibility study. Currently, there is enough ore to support a mine for 14 years, and both Audrey and Cambior agree there is potential to find other reserves at depth and along strike.

Commercial production began on New Year’s day, 1995, since which time the first stope has been mined out, yielding 156,000 tonnes of ore.

Although stope sizes are expected to vary, primary stopes will be about 15 metres wide and 60 meters high, and secondary stopes are expected to measure 20 by 60 metres. The stopes should contain between 30,000 and 150,000 tonnes of ore. A ramp from the eighth level will be used to gain access to the deposit, and production will come from seven levels spaced at 60-metre intervals.

At present, ore is being mined from the second stope at a rate of 2,000 tonnes per day, with production drilling of the third stope already in progress.

Total mine production is expected to be 700,000 tonnes annually at an average cost of $31 per tonne.

Once the rock is blasted, ore is moved to the surface using both a 560-metre underground conveyor and a fully automated 3.7-metre-diameter production hoist. Many of the mine’s other functions, including backfilling of the excavated stopes and ventilation, are also fully automated.

The ore, upon reaching the surface, enters a conventional milling circuit, with semi-autogenous grinding and two flotation circuits used to recover the zinc, copper, gold and silver.

Two concentrates — one rich in zinc, the other in copper — are produced, which are stored in bins and shipped to refineries for final treatment. About 85% of the mine’s tailings are converted into paste backfill which is gravity-fed underground to the exhausted stopes — a practice which poses less threat to the local environment than conventional tailings disposal. The remaining 15% of the tailings are sent to an exterior pond.

At the opening ceremony, Cambior President Louis Gignac commented on the impact that the new mine is having on the region.

“The hardest thing [about this business] is to get a mine going. We were lucky here because we already had a lot of the infrastructure in place.” He added that exploration and development costs amounted to about $50 million, 80% of which went into the local economy.

The upper zone of the Mobrun deposit was discovered in 1955 after Rio Algom completed a roadside electromagnetic survey. The name Mobrun was derived from an acronym for “Mobile Road Unit.”

In the fall of 1985, Audrey gained a 50% stake in the project from Corporation Falconbridge Copper. After increasing its interest to 70% in 1987, Audrey put the Main zone into production, using both underground and open-pit mining methods. The Mobrun operated until early 1992, producing more than 1.5 million tonnes averaging 2.4% zinc and 0.9% copper, plus 2.4 grams gold and 27 grams silver per tonne.

When the Main zone was still in production, Audrey, by means of a pulse-electromagnetic survey, discovered the 1100 lens. In 1992, Cambior considered the property’s potential and decided to buy a 65% interest in Audrey.

The 1100 massive sulphide lens lies within a sequence of pyroclastic tuffs and rhyolites. The top of the mineralized zone lies 320 metres below the surface and is about 400 metres high, 300 metre wide and varies in thickness from 3.2 to 0.55 metres.

The mine employs 125 people and is expected to produce 30,000 tonnes of zinc, 5,400 tonnes of copper, 19,000 oz. gold and 37,000 oz. silver on an annual basis.