Louvicourt mine up and running

With the first shipment of copper concentrates having been delivered in August, the Louvicourt mine near Val d’Or, Que., is well on its way to becoming Canada’s next major base metals producer.

The mine, owned 30% by Aur Resources (TSE), 25% by Teck (TSE) and 45% by Novicourt (TSE), began processing ore in July from the first stope on the 655 level and from the stockpile of development ore. Mill throughput is scheduled to rise to about 2,400 tonnes per day by the end of 1994, a short five and a half years after the discovery. Full-scale production of 4,000 tonnes per day is expected by mid-1995.

Developed at a cost of about $280 million, some $40 million below the original estimate, the mine is expected to operate for at least 12 years based on current reserves. At a copper price of US$1 per lb., payback of the invested capital will be achieved in about 3.5 years.

Copper production is expected to rise to more than 100 million lb. in 1997 from 22 million lb. in 1994. Zinc production will reach the 40-50-million-lb. level during the same period, and appreciable gold and silver will also be produced.

In April, undiluted geological reserves were recalculated at 16 million tonnes averaging 3.4% copper, 2.2% zinc, 31 grams silver and 0.9 grams gold per tonne. This figure is composed mainly of material between the 475 and 880 levels, where the bulk of the underground definition drilling is completed. It also includes 2.6 million tonnes above the 475 level, which were calculated from previous surface drilling. The deposit remains unexplored below a depth of 960 metres.

These reserves are about 40% less than what had been calculated from surface drilling. Aur President James Gill says there are two main reasons for the reduction in reserves. One is that two deep surface holes in the high-grade portion of the deposit were incorrectly located, despite the use of up to four independent survey techniques. This resulted in the loss of about 3 million tonnes of high-grade copper ore.

The other main reason for the decrease was the incorrect assumption that the orebody consisted of multiple tabular sulphide lenses which were continuous between drill holes, as opposed to the highly folded sulphide lenses now known to be the case.

Copper concentrate, containing both gold and silver, will be shipped to the Horne smelter in Rouyn-Noranda, Que., under the terms of an 8-year contract with Noranda (TSE).

Zinc concentrates will be shipped to the Noranda facility at Valleyfield, Que., until June, 1995, while negotiation of a longer-term contract is undertaken for the Aur and Teck share of the concentrates.

Aur reports that production to the end of September totaled 9.5 million lb. copper, 5.2 million lb. zinc, 136,445 oz. silver and 4,387 oz. gold. Operating costs are estimated at $40 per tonne of ore milled. Construction and development work began in the winter of 1991-1992, following a 60-hole surface drilling program. A feasibility study determined that two shafts would be sunk simultaneously. The exploration shaft, at the eastern end of the deposit, was sunk to a depth of 750 metres to allow early development and definition drilling of the upper portion of the deposit. The production shaft, situated closer to the centre of the deposit, was targeted to a depth of 965 metres. Once full production commences, the exploration shaft will be used as a ventilation raise.

Lateral development began on the three upper levels in April, 1993, following completion of the exploration shaft. Additional lateral development was carried out on the lower levels in March, 1994, following the sinking of the production shaft.

The mine design is based on an alternate primary and secondary transverse blasthole stoping method. The ore is accessible via six main levels connected to the production shaft at 90-metre intervals, and also via a series of sublevels spaced at 30-metre intervals and connected by an internal ramp. It is expected that the principal access drives on all the main levels will be completed in early 1995.

The main underground services — including handling and crushing of ore, and ventilation and pumping systems — were installed in early 1994, following the sinking of the production shaft. These systems are expected to be fully operational by the first quarter of 1995.

Underground definition drilling began in April, 1993, and is still ongoing. Systematic drilling is being carried out on north-south sections at 30-metre intervals, followed by infill drilling at 15-metre intervals. To date, more than 100 km of underground drilling have been completed, and four drills continue to operate (two on the 30-metre preliminary program and two on stope definition). Preliminary definition of the entire deposit, at 30-metre centres, is expected by year-end.

Underground exploration and development continue to provide insight into the complexity of the Louvicourt deposit. Gill shared some of this knowledge in a recent presentation to the Toronto branch of the Canadian Institute of Mining, Metallurgy and Petroleum.

The Louvicourt area is underlain by an east-west-striking, steeply dipping and south-facing sequence of Archean-aged metavolcanic rocks. The volcanic package consists of thick mafic and ultramafic flows of the Lower Malartic Group, overlain by calc-alkaline, intermediate-to-felsic rocks of the Upper Malartic Group.

The deposit itself occurs within a 1-to-2-km-thick felsic sequence at the base of the Upper Malartic Group. This felsic group, referred to as the Val d’Or Formation, has a strike length exceeding 30 km and hosts four base metal deposits which, collectively, have produced more than 30 million tonnes of ore.

Amongst the most important findings of the underground program was that the Louvicourt rocks have undergone at least two phases of folding. The first phase appears to be responsible for the initial thickening of the massive sulphide lenses on the east side of the deposit. The second phase is thought to have generated the steep plunge of the orebody.

Late faults represent an added level of geometric complexity, as they overprint the entire refolded structure and displace the ore. The most important set of faults is a steeply dipping one which trends west-northwest. The mineralization consists of massive sulphide lenses and associated stringer or stockwork zones. It was initially thought, based on surface drilling, that the deposit consisted of several individually stacked ore lenses. However, Aur technical staff now believes there is one, or at most two, principal sulphide horizons which have been repeated by folding and faulting in the eastern portion of the deposit.

The ore envelope has an overall east-northeast strike, dips at 70 degrees to the north and exhibits a steep easterly plunge. Drilling to date indicates that the ore zone has maximum dimensions of 300 metres along strike, 500 metres downdip and is 100 metres thick.

The bulk of the ore consists of massive and semi-massive sulphides, principally pyrite

and chalcopyrite, with lesser amounts of sphalerite and rare pyrrhotite. Gold occurs mostly in native form, or as electrum, enclosed within chalcopyrite or along chalcopyrite-pyrite grain boundaries.

Texturally, the massive sulphides are banded. Originally thought to be primary, the banding is now recognized as being structurally controlled. Stringer or stockwork mineralization accounts for about 20% of the ore. It typically consists of irregular wisps and veins of massive chalcopyrite up to 50 cm thick, hosted in dark chloritic material. The stringer zone is generally confined to the western and northwestern portions of the deposit, where, in plan, it takes a form that is generally perpendicular to the overall trend of the massive sulphides.

Copper is the metal of greatest economic interest in the deposit. The highest grades occur within the massive sulphides, in the lower portion of the deposit. Here, grades of 10-15% copper over widths of 25 metres are common. Copper and zinc tend to be mutually exclusive, with the highest zinc grades generally occur
ring in the eastern and upper portions of the deposit. An exception to this is the high-grade lens in the central part of the deposit. Gold shows a similar distribution to that of zinc, with grades in excess of 4 grams per tonne occurring in the upper eastern and central portions of the deposit. The high-grade copper-zinc lens in the central portion of the deposit is also enriched in gold, with net smelter returns of up to $200 per tonne.

According to Gill, the hydrothermal alteration at Louvicourt is characteristic of that which is found in most volcanogenic massive sulphide deposits. Although alteration studies are at an early stage, the following progression has been noted:

* an outer, halo-like, sericitic facies;

* an extensive black chlorite pipe facies, which extends for more than 200 metres below the massive sulphides;

* a relatively small, semi-conformable, carbonate facies, stratigraphically above the massive sulphide lenses; and

* a semi-conformable green chlorite facies, which locally contains coarse garnet and/or magnetite.

The alteration zone, which is restricted to the sulphide horizon and footwall rocks, is about five times larger than the area covered by the massive sulphides.