Audrey on schedule with Mobrun mill

Minnova executives suspected that Audrey would not be able to deliver enough ore from the former 1,000 tonne-per-day open pit operation to keep their Norbec mill running at full capacity. Minnova holds a 30% non-contributing interest in the project.

Audrey met its production targets for all but one month. Now, thanks to a concerted exploration effort, the picture has changed dramatically at what can only be described as one of the most promising operations in the Noranda mining camp.

With the discovery of a large massive sulphide lens about 240 m southeast of the mine workings, Audrey says it has outlined between 7.1 and 7.6 million tonnes (depending on metal prices) grading 0.67% copper, 5.14% zinc, 1.2 oz silver and 0.053 oz gold per ton in proven and probable reserves. Massive sulphides

Audrey says it has also located 14.8 million tonnes of massive sulphides in the recently discovered 1100 lens which, when combined with a proven inventory of 1.1 million tonnes in four other lenses, should support mining for at least 14 years.

Tabled in March, the reserve increase was considered large enough to justify expenditures of $19 million on a 1,500-tonnes-per- day on-site milling facility. The mill was needed because of Minnova’s decision to process ore from its new Ansil copper mine at Norbec.

When The Northern Miner visited the Mobrun mine site recently, some of the most experienced contract companies in Quebec were putting the finishing touches to the mill just eight weeks before it is expected to be up and running.

“We will have a 2-month break-in period in July and August and we hope that everything is ready by September,” said Vice-president Michel Bouchard. He has been overseeing mill construction and underground development since Audrey called a halt to production last August.

If everything goes according to plan, Audrey will churn out more than 2.6 million lb copper and 5 million lb zinc in addition to 36,000 oz silver and 7,000 oz gold by the end of December. Before shutdown, more than 2 million lb copper, 6.1 million lb zinc, 6,606 oz gold and 31,570 oz silver were produced in the first five months of 1988. Main lens

Most of this year’s output will come from the Main lens which has sustained the operation since it went into production in June 1987. But Audrey will also “sweeten” ore extracted from the Main lens by mixing it with ore from the newly discovered 850, 870 and 930 lenses.

With an average grade of 0.79% copper, 2.46% zinc, 0.89 oz silver and 0.07 oz gold, the new lenses contain much higher copper and gold values than the original Main zone.

Situated in stratabound volcanics within the same geological unit, the four lenses are being accessed via a 4-compartment, 379-m (1,245- ft) production shaft on six levels.

When The Northern Miner toured the underground workings, drift crews were within one drilling round of making contact with an extension of the Main lens on the fourth level. “We should reach the 850 and 870 lenses in July,” said Bouchard who believes there is “enough room” between the zones to support the theory that more sulphides could be found beneath the 800 hectares which Audrey controls. Similar deposits

Formulated by Bouchard and geologists Pierre Jean Lafleur and Carl Caumartin, the theory is supported by the experience of companies mining similar deposits.

When production resumes, Audrey will use long hole open stope techniques to mine the Main lens at a rate of 800 tonnes per day and shrinkage stoping in the new lenses at a rate of 300 tonnes per day. That should leave about 400 tonnes of vacant capacity in the mill.

“We had lengthy discussions about using long hole methods on the 850, 870 and 930 but we thought there would be more dilution (using that method) ,” said Bouchard. Historically, Audrey has experienced a dilution factor of about 10%.

About 75,000 tonnes of material has already been drilled and is waiting to be blasted in two stopes on the second level. The shutdown has also given Audrey a chance to rehabilitate the crusher and other underground equipment. “When we start again, everything will be in tip top shape,” said Bouchard.

On the exploration front, Audrey is still testing for close-to-surface extensions of the new 1100 lens. “Up to now we know it starts at a depth of 1,200 ft but we want to know how high it goes,” said Bouchard. Different horizon

With a strike length of 400 m, a depth of 400 m and a true thickness of 60 m, the 1100 is on a different horizon than the other lenses, much lower in the stratigraphy. The fact that it remains open in all directions, “opens up a lot of exploration possibilities,” Bouchard told The Northern Miner.

But for now, Audrey is putting all its energy into completing the $19-million milling facility and getting back into production.

Although the facility was designed by Kilborn Engineering, Audrey is acting as general contractor and all of the work has been subcontracted out to local companies. “We are using proven equipment as well as some of the better things we could think of to make it more efficient,” said Bouchard.

The semi-autogenous grinding mill, ball mill, flotation circuit and concentrator will all be housed in the same building and flotation circuits have been enlarged to reflect the high copper and zinc grades of the 1100 lens. As the mill is designed specifically to treat ore from the 1100 lens, (design grades used for mill construction have now been changed to 1.5% copper and 6.0% zinc) it will be under-utilized by about 400 tonnes per day until 1992 when the 1100 is scheduled to come on stream. Milling costs

While changes to previous capacity of the mill have upped the cost of mill construction to $19 million from $17.8 million, total mining and milling costs will drop to $32.28 per tonne from $39.31 when the mill is complete, according to Bouchard.

An exceptionally cold winter has been the only hurdle in an otherwise straight forward construction process, according to project manager Denis Gagnon who sees no reason why the facility can’t be up to full speed by September.

That will come as good news to some of the potential investors that Audrey President Guy Hebert is attempting to attract during a 2- week tour of Europe. With a 28% stake in the Rouyn-Noranda company, Northgate Exploration (TSE) of Toronto is also monitoring Audrey’s progress.

“We are nearly back into production and we are looking forward to some good times,” said Bouchard.

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