Brunswick’s success at depth could revive base metal camp

A single drill hole intersection near Brunswick Mining and Smelting’s (TSE) No. 12 mine has raised hopes in this picturesque province that large massive sulphide deposits are waiting to be found at depth in the Bathurst camp. First reported last year (T.N.M., Dec. 4/89), the 8.5-metre intersection assaying 14.25% combined lead-zinc was discovered at a depth of 1,100 metres in a previously unexplored area 750 metres north of the outer limits of Brunswick Mining’s main ore zone. Two surface drills are currently turning to follow-up on the initial discovery hole.

The intersection was a much- discussed topic at a base metals symposium attended by The Northern Miner because the 2,000-sq.- km camp has seen relatively little exploration below a depth of 1,000 metres. Of 5,169 holes filed with the government for assessment up to 1985, a little over 300 exceed 300 metres.

“As a regional geologist, I’m appalled at how little we know about what’s under our feet below 500 metres,” said Steven McCutcheon, a Bathurst regional geologist, who acted as chairman of the 4-day symposium. He and other mining officials, including Prospectors and Developers Association President Bob Stairs, are attempting to promote deep exploration in the camp in order to guarantee its long-term survival as a major metals producer.

A new massive sulphide deposit north of Brunswick No. 12 would go a long way to helping their cause.

Although three new mines have come into production near Bathurst in the past year, none compare with the Brunswick Mining and Smelting No. 12 orebody which hosts 74.9 million tonnes of proven reserves grading 8.87% zinc, 3.60% lead, 0.30% copper and 99.5 grams silver per tonne.

Brunswick’s Heath Steele and Stratmat divisions, brought back into production last year, host 3.9 million tonnes of grade 2.54% lead, 6.51% zinc, 0.67% copper and 68 grams silver in proven ore.

While the ore zone hosting East West Caribou Mining’s Caribou mine — soon to be acquired by manager Breakwater Resources (TSE) — is estimated to contain as much as 12.2 million tonnes of possible ore, proven reserves stand at only 1.9 million tonnes grading 7.93% lead and 3.58% zinc.

Bathurst’s other new mine, NovaGold Resources’ (TSE) Murray Brook, is a vat leach gold operation. The lead-zinc projects of Stratabound Minerals (ASE) and Marshall Minerals (ASE) may not go into production if the companies can’t negotiate a milling contract with either Brunswick or Breakwater.

However, as the limits of the Brunswick No. 12 have been defined, geologists are now having to look outside the orebody in an effort to locate new reserves. “If we don’t find more ore, we could be forced to reduce the tonnage produced to 8,500 from 10,500 tons per day,” said project geologist Jeff Hussey who is overseeing the drill program north of Brunswick’s No. 3 shaft.

“We could be forced to take a drop (in production rate) as early as 1996,” added chief geologist Bill Luff.

Like some of the other geologists who spoke at the base metals symposium, Hussey expects future drilling at depth to be guided by geological models like the one that has produced the discovery north of Brunswick No. 12.

Acting on a 1985 analysis of No. 12 and former Brunswick No. 6 mine which predicted that the Brunswick horizon should be repeated at depth, the company elected to drill from a drift on the mine’s 1,000-metre level. (The ore zone bottoms out at a depth of 1,025 metres where it hits a fold structure.)

After completing 3,100 metres of drilling, two bands of massive to sub-massive pyrite were intersected over a core width of 37 metres in hole 12-6603 at a depth of about 1,150 metres.

As a follow-up, the Brunswick team decided to drill a deep surface hole to test the potential of the Brunswick horizon 250 metres above hole 12-6603. However, as the target area could not be reached from level 1000, hole (A248) was drilled from surface about 350 metres further north. At a depth of 1,100 metres below surface it intersected 8.5 metres of massive sulphides averaging 4.61% lead, 9.91% zinc, 0.22% copper, 183 grams silver and 1.65 grams gold.

A pyrite section of the hole (T.N.M., Dec. 4/89) intersected 4.9 metres of 0.55% lead, 1.5% zinc, 0.18% copper, 17.5 grams silver and 0.34 grams gold.

“What we have here is one intersection not a deposit,” said Hussey who believes it represents a structural continuation of the Brunswick horizon. “There is still a lot of work to be done,” he said.

Having drilled two wedge holes from A248, which didn’t yield any economic intersections, Hussey says the Brunswick team will attempt to “close in” on A248 and drill below it probably to a depth of around 1,200 metres to 1,300 metres. “Our plan is to drill two pilot holes and then drill several wedge cuts using directional drilling methods,” he told The Northern Miner.

Representatives of a local mining community which is attempting to promote Bathurst as a favorable area for deep exploration are monitoring the Brunswick situation closely. As The Northern Miner noted during its visit, the predominant view is that politicians in Fredericton see mining as a declining force within the provincial economy.

The fact that Brunswick No. 12 will soon to be overtaken by Cominco’s (TSE) mammoth Red Dog mine as the world’s largest zinc producer has only reinforced that view.

However, a number of geologists who flew into Bathurst for the symposium, say that new investment in the camp is stifled by two main factors: The camp regarded as a “Noranda (TSE) lockup,” and companies seeking to have their ore custom-milled in the province must negotiate with Brunswick which in turn is owned 64.3% by Noranda.

Deep holes like the ones being contemplated at No. 12 are prohibitively expensive at $100,000 a crack for all but the biggest mining outfits.

But as Stairs put it at the symposium banquet, base metals exploration is “the name of the game” now and the history of Bathurst shows that it is an area where companies should be looking.