Myra Falls drilling — Westmin targets new reserves

Exploration success is being achieved by Westmin Resources (TSE) on four separate areas of its Myra Falls mine property about 90 km by road from this scenic Vancouver Island community.

The company has been producing zinc and copper concentrates with significant gold and silver content at Myra Falls for more than 25 years, with current production from two underground mines, the Lynx and H-W. But because of low metal prices and various other factors, the mine complex has not been profitable in recent years.

During 1991, the operation was largely converted to more productive longhole stoping, and by year-end more than 70% of ore was being produced by this method. The work force was reduced to 456 employees (from a high of 721 in 1989), and operating costs fell to an average of $50 per tonne, or less, from over $66 per tonne in the previous year. Because of these and other initiatives, Westmin has achieved a modest positive cash flow at Myra Falls since last November.

While this improved operating performance bodes well for the future, so too do recent discoveries made by Westmin geologists as part of an ongoing multi-front exploration program that currently ranks among the most active in Western Canada.

When The Northern Miner visited Myra Falls in mid-March, 10 rigs were active on the property. Two of the rigs were completing a surface drill program in Thelwood Valley, but most were being used to further explore new discoveries or prospective areas from underground workings.

A highlight of the visit included an underground tour of the 18-level drift being driven to access the Gap and Battles zones, the most significant of several recent discoveries made at Myra Falls.

“It is cheaper for us to explore these zones by driving a drift and doing underground drilling than to explore from surface,” said geologist Rick Walker, a senior technical adviser at Myra Falls. “The front-end costs are higher but the drill information helps us with mine planning and the drifts represent mine development. The penalty is that it takes longer.” At the time of the visit, the drift was about 30% complete and was expected to reach the Battle zone area by the third quarter of this year. (The Battle zone will be reached before the Gap zone.) Full-scale production from the zones won’t begin until 1993, although mining of development ore will take place later this year.

The Gap zone was found on upper H-W rhyolite stratigraphy while the nearby Battle zone was found on the lower H-W horizon which hosts the main H-W orebody. Both zones were discovered in 1991 by underground drilling — the topography of the property is such that only a small percentage of the property can be explored economically from surface — although the geological and interpretive work leading to the discoveries began many years earlier. “It was an overnight success that took 15 years,” Walker said. At the time of our visit, the Gap zone was estimated to contain proven and probable geological reserves of 304,240 tonnes grading 2.9 grams gold and 178.4 grams silver per tonne, 2.4% copper, 1.1% lead and 15% zinc, plus an additional 330,000 tonnes of similar grade classed as possible reserves. The Gap zone now has a defined strike length of 201 metres, plus “reasonable extrapolations” to more than 250 metres. The reserves identified to date indicate a net smelter return of about $140 per tonne, compared with an average of roughly $57 per tonne for current production.

At this stage, the Battle zone appears to be less structurally complex than the Gap zone and is more than 190 metres wide, while Gap averages just 30 metres wide. Proven and probable reserves in the Battle zone are reported as 610,060 tonnes grading 1.4 grams gold, 56.3 grams silver, 2.6% copper, 0.6% lead, and 12.4% zinc, plus an additional 560,000 tonnes of similar grade in the possible category, which indicates a net smelter return of about $110. Westmin’s exploration team was encouraged by underground drilling on the Battle zone at the time of our visit because hole 14-910 had extended the zone by intersecting 11.5 metres grading 2.8 grams gold, 32.4 grams silver, 2.5% copper, 0.3% lead and 18.7% zinc. Three drill rigs continue to test the Battle lens.

The grades of mineralization being encountered in both the Battle and Gap zones are considerably higher than the average grade of ore mined and processed at Myra Falls in recent years.

As an example, a total of 1.08 million tonnes of ore was mined and processed in 1991, at an average grade of 2.1 grams gold, 26.2 grams silver, 1.7% copper and 3.3% zinc. But Westmin now estimates that last year’s exploration led to a net gain of 540,800 tonnes of “significantly higher grade ore,” as well as adding 1.7 million tonnes of possible ore.

Ongoing exploration is adding to these reserves. As of mid-March of this year, current reserves at Myra Falls stood at 11.15 million tonnes grading 2.2 grams gold, 43.5 grams silver, 2% copper, 0.4% lead and 5.2% zinc. The 18-level drift is also providing the initial drilling access to sketch out the H-W west extension. Twenty-four 24 holes had been drilled in this area at the time of the visit, but reserves were not calculated because the drilling was only on exploration-section intervals (more than 100 metres). The drilling was also from a bad angle, preventing good definition of the lens widths and thicknesses. Westmin indicated, however, that the grade of mineralization is similar to current ore reserves and thickness is averaging about six metres.

Exploration drilling in 1991 also boosted reserves at the Lynx mine by about 60%, and the high grade 43 block was also enlarged to more than 400,000 tonnes. These reserves are lower grade than the Battle and Gap zones, but still indicate a net smelter return well above that of current production. Westmin recently completed a surface drill program totalling 24,000 ft. in 21 holes on the Thelwood Valley aimed at discovering new ore on the H-W geologic horizon that could be mined from the H-W workings.

This work resulted in the discovery of the Trumpeter zone where zinc values of up to 29.2% and copper values of up to 11.6% were encountered over relatively narrow widths. But the drilling also encountered mineralization thought to correlate with the 43 block ore in the H-W mine, 600 metres to the west. Results from this drilling include 5.5 metres of 1.1 grams gold, 63.5 grams silver, 0.1% copper, 0.8% lead and 6.4% zinc.

Results from the surface drill program are being reviewed by Westmin’s geological team to improve their understanding of the geology and to allow for interpretive work before the next phase of drilling is proposed.