Diamond studies confirm potential at Lac de Gras

Shareholders of Dia Met Minerals (TSE) have been told that the latest bulk-sampling programs, involving several kimberlites, are providing encouraging results which may lead to development of Canada’s first diamond mine.

The company’s partner, BHP Minerals Canada, has moved the project into the feasibility study stage, which could mean that a production decision will be made later this year or in early 1995. The Dia Met-BHP joint venture is in the Lac de Gras area of the Northwest Territories. BHP holds 51% and Dia Met 29%, with the remainder privately held.

“This has been an incredibly busy year with a lot of progress on the project,” said Rory Moore, manager of diamond exploration for BHP. Moore’s progress report was delivered to Dia Met shareholders at the company’s annual meeting in Kelowna, while a security guard kept a close eye on a number of diamonds on display from the Leslie pipe.

During the winter season (through April), drills tested the Koala, Panda, Falcon and Misery pipes, and did delineation drilling on the Fox and Leslie pipes as well.

The Koala pipe was the primary bulk-sampling target, and 6,600 stones yielding 893 carats were produced form holes ranging from 10.5/8 inches and greater diameters up to 30 inches. The Koala pipe consists of several stacked sub-horizontal phases, each of which was sampled separately. As a result, drilling was chosen for this pipe, as opposed to driving a decline, so as to ensure a more representative sample.

The total weight of the sample was 1,193 tonnes for an overall average of 0.75 carats per tonne. Although diamond evaluations varied depending on which zone the diamonds were from, the average value was US$110 per carat from the Koala pipe. The average value per tonne of kimberlite ore was US$82, although the middle zone has a much higher value of US$150 per tonne. “We had some trouble with the larger drill because of boulders in the overburden,” Moore said. “So we had to get creative to deal with that, such as using a downhole hammer.”

While the large-diameter drill was productive, — in that for every metre drilled, one tonne of sample was obtained — the technical problems and the short time frame for ice drilling did not allow for as much sample being collected as was hoped.

So far, the partners have extracted 1,572 tonnes of sample from the Fox pipe, which is being tested by way of underground decline. This sample was processed, yielding 360 carats from 36 tonnes of sample for an average grade of 0.23 carats per tonne. About 6,000 tonnes of bulk sample are planned for Fox, and the underground work will be completed in July.

Moore is particularly encouraged by the Panda pipe, situated 1.2 km from Koala and sampled last winter by 10.5/8-inch-diameter holes. A total of 270 carats were recovered from 230 tonnes of sample for an average grade of 1.18 carats per tonne. The diamond valuations were equally impressive, at US$127 per carat.

“This pipe is remarkably consistent and there is no horizontal layering whatsoever,” Moore said, adding that “most of the upper crater facies has been scraped away, which means the main body of the pipe is close to surface and ideal for open-pit mining.”

A large underground sample will be taken this summer from Panda. The decline is progressing well, down 200 metres, and should intersect kimberlite before the end of July.

The Misery pipe, often referred to as 93-J, proved to be something of a disappointment. While the grade was there — an average of 3.3 carats per tonne from the main Misery pipe and offshoot — the value (quality) was relatively low, from US$43 per carat from the main Misery and US$37 from Misery South.

As Moore points out, high diamond counts are not what make mines but, rather, a positive combination of grade (carats per tonne) and value per carat. Dia Met Chairman Charles Fipke said the company’s Territorial land package still has plenty of potential, with more exploration work planned for this summer. The company’s Alberta diamond exploration program will resume this fall, based on recent geochemical and geophysical work.