N.W.T. diamonds show high quality: gem expert

One of many highlights of The Northern Miner’s recent tour of Lac de Gras, N.W.T., was a videotaped commentary by John Gurney. The diamond expert was discussing the quality of diamonds being recovered by joint-venture partners BHP Minerals Canada and Dia Met Minerals (TSE).

A picture can be worth a thousand words, and such was the case when the camera zoomed in on a sample of diamonds (totaling 50 carats in weight) from a borehole that tested a kimberlite pipe on ground held by BHP and Dia Met. One did not need to be a gemmologist to be impressed by the outstanding color and clarity, as well as the excellent crystal formation which suggests good conditions for preservation.

The gems and near-gems from this sample averaged US$250 per carat, with the larger stones valued at US$1,000 per carat. The overall value (including industrials) averaged US$112 per carat, with 85% of the value attributed to the larger stones.

The most spectacular specimens were two octahedra, or eight-side stones. One specimen was just over two carats, the other just under two — and both appeared to be flawless. According to Gurney, the Gemmological Institute of America color rating of these “whitest-of-white” gems was in the E-F range. “It is exceptional to find this color, particularly in the larger stones,” Gurney said of the borehole sample.

These stones rank just below the highest-rated D-color diamonds, which are so rare that fewer than 5,000 cut stones (0.5 carats or larger), in all clarity grades, are produced annually. Color grading is based on a whiteness or colorless scale, with value diminishing with increasingly yellow-brown or grey stones. The blue, green and pink “fancies” are statistically so rare that they are off the scale in terms of value per carat. Consequently, they almost never show up in exploration sampling.

But as Gurney told a group of explorationists in Vancouver in late 1993, “mines are made on white diamonds, not colors.” Gurney also cautions that the size distribution of diamonds is an important factor in determining the economics of a kimberlite pipe. “It is better to compare weights (carats) than to compare micro-macro diamond counts. There are pipes with lots of micros, but not macros.”

Indeed, it is now evident that the size of the stones (up to the 3-to-4-carat range) being recovered from exploration-stage programs exceeds the original expectations of the BHP-Dia Met joint venture. This bodes well for the potential of the valuable, larger stones, some of which are so rare they typically do not show up until production.

The size of each stone affects its value per carat, and experts say it would take about three carats of total weight of the smaller stones to equal one 1-carat stone in value. Thus, one diamond weighing five carats would equal about 15 carats of 1-carat diamonds in value.

Results to date suggest that some N.W.T. kimberlites may indeed resemble producing kimberlites in Eastern Russia. Diamonds from this region are noted for their exceptional color and clarity and for a high proportion of sharp-edged, flat-faced octahedra — an excellent shape for cutting. In contrast, production from South Africa is predominantly dodecahedra (12-sided), which means some resorption took place as the diamonds were brought to surface by the kimberlites. The proportion of dodecahedra is also reported to be high (about 90%) in the kimberlites of Western Russia (near Arkhangelsk, northeast of St. Petersburg).

The diamonds in Siberia are predominantly peridotitic in origin, according to Gurney, who commented that “nice gem stones can grow in a peridotitic environment.” He noted, however, that most diamond mines have both peridotitic (P-type) and eclogitic (E-type) diamonds. African mines can vary widely. Orapa, for example, has mostly E-type, while Finch has mostly P-type diamonds.

Elsewhere in the

Northwest Territories

Exploration programs in the region are gearing up again now that cold weather is making the ice thick enough to support drill rigs.

* Drilling has begun on Barexor Minerals’ (ME) Aylmer Lake property, near Lac de Gras. The program will test targets outlined by geophysical and geochemical surveys. The proceeds from two private placements totaling $750,000 will be used to fund the work.

* Leeward Capital (VSE) is mobilizing a crew to its Angikuni Lake property, near Dubawnt Lake. Initially, Leeward will drill four or five magnetic targets with coincident indicator minerals. To date, 21 targets have been identified. The work will be financed from a $650,000 private placement. * RJK Explorations (CDN) and Garden Lake Resources (VSE) report that half of the 394 overburden samples collected to test 64 airborne geophysical targets on their Point Lake-Humpy Lake property have been analyzed. Four G-10 garnets and 31 G-9 garnets have been identified in samples taken down-ice from 14 targets. In addition, uvarovite (chrome) garnets and picro-ilmenites have been recovered from the samples. Based on these results, eight targets have been designated for diamond drilling.

RJK and operator Garden Lake are earning a 55% interest from Aaron Oil (ASE). * Meanwhile, Garden Lake and RJK have found pyrope garnets in several samples collected down-ice from four geophysical targets on their Warburton Bay property. Further processing is under way and additional samples will be collected from the remaining 149 targets this summer.

Saskatchewan

* Consolidated Pine Channel Gold (VSE) and partner Golden Peaks Resources (VSE) have mobilized a winter drill camp on their 50-50 Tobin Lake joint venture near Squaw Rapids. Previous drilling intersected breccia, believed to represent “a distant reworked epiclastic component of a crater facies kimberlite pipe complex.” A geophysical program is under way to identify targets for drilling.

* After completing an in-house review of 1993 results, Better Resources (VSE) is recommending a $1-million follow-up program, to include drilling of targets in the Val Marie area. Heavy mineral sampling has been done and geophysical work will be carried out to outline targets. More ground geophysics is planned in order to confirm drill targets.

The company has 20% of a syndicate formed to stake additional claims in the Val Marie area of southern Saskatchewan. To date, about 60,000 acres have been applied for. R. Chaplin and VSE-listed Faith Mines also have a 20% interest in the syndicate; other subscribers with 10% interests are VSE-listed Island-Arc Resources, Perimeter Ventures, Ebony Gold and Hawk Mountain Resources.

Ontario and Quebec

* Partners Wiscan Resources (ASE), Murgor Resources (VSE) and Consolidated Goldhawk Resources (ASE) have discovered a kimberlite on their holdings in Duplessis Twp., Que.

A 45 hole, drilled to test a magnetic anomaly, intersected 160 ft. of kimberlite and associated diatreme breccia. Further drilling will attempt to define the size and extent of the pipe. Wiscan has a half interest, with Murgor and Consolidated Goldhawk holding the balance.

Under a financing agreement with Wiscan, KWG Resources (ME) has the option to earn a 65% stake by financing further exploration through feasibility. * Explorations Diabior (ME) has three drills testing some 60 geophysical targets on its holdings in the Le Tac and Senneterre areas of Quebec. * An exploration program is planned for Soocana Explorations’ (ASE) Esquega Twp. property, near Wawa, Ont. At least 16 potential kimberlite targets have been identified in the southeastern portion of the township. Overseas

Next month, the Russians plan to open a diamond exchange in the Yakutia region of east-central Siberia. The exchange would sell rough and polished gem diamonds, as well as industrial diamonds and other stones and precious metals. It is expected to sell US$50 million in gems by year-end.