Although results are still pending for more than half of a 635-tonne bulk sample collected from a core area of the Renard kimberlite cluster in north-central Quebec, it would appear that the lack of big-carat stones, combined with a growing percentage of lower-quality, brown-coloured ones, could hurt valuations.
As part of a major program to recover at least 300 carats of diamonds for preliminary valuation purposes, partners
So far, the bulk sampling campaign has delivered lower-than-expected diamond grades for both Renard 65 and 4 and failed to match the 4-carat diamond (a clear octahedral) discovered last year embedded in a piece of core from Renard 65. During the winter phase of the 2004 drilling program, which focused on sections of the kimberlitic intrusions partially overlain by shallow lakes, Ashton recovered samples representing 140.3 tonnes from Renard 65, including 122.5 tonnes from five large-diameter reverse-circulation (RC) holes and 17.8 tonnes from 11 core holes. Ashton used vertical core holes to drill off each of the four bodies on a 20-metre grid pattern to an average depth of 210 metres. The core drilling provided geological control for the positioning of the RC holes.
Covering a surface area of 1.5 hectares and measuring 280 metres long at an average width of 60 metres, Renard 65 is the largest of the Renard bodies.
The 122.5-tonne RC sample yielded just 26.69 carats of diamonds greater than a 1.18-mm recovery screen size, for an estimated grade of 0.22 carat per tonne (or 22 carats per 100 tonnes). More disappointing was that the two biggest stones in the 122.5-tonne sample weighed only 0.83 and 0.82 of a carat and were described as brown and pale-brown dodecahedral shapes. According to John Kaiser, publisher of the Bottom-Fishing Report, the magic words signalling high-quality diamonds are “clear and colourless.”
The smaller core sample of 17.8 tonnes showed a similar grade of 0.23 carat per tonne based on the recovery of 4.05 carats of diamonds, including a colourless, clear dodecahedral-shaped stone weighing 0.88 of a carat and a colourless, clear octahedral weighing 0.67 of carat.
The original mini-bulk samples from the Renard cluster were processed using a lower-recovery screen size of 0.85 mm, which may account for the drop in grade. Renard 65 had originally shown a grade of 0.54 carat per tonne based on the recovery of 10.06 carats of diamonds exceeding a 0.85-mm cutoff in a sample of 18.4 tonnes. But if the 4-carat diamond is excluded, the grade estimate falls to 0.33 carat per tonne. In total, 40.8 carats of diamonds have been recovered from 159 tonnes of Renard 65, giving an overall grade of 0.26 carat per tonne.
In a bid to learn more about the distribution and placement of the 4-carat diamond, Ashton drilled one more RC hole, at the northern end of Renard 65, this summer. The results of the 20-tonne sample are pending.
Renard 4
The second-largest pipe in the cluster is Renard 4, which measures 160 metres long by 70 metres wide, or one hectare in surface area. The second-biggest diamond recovered to date is a colourless, octahedral-shaped, 2.9-carat stone obtained during winter drilling on Renard 4; that program recovered 74.1 tonnes from three large-diameter RC holes in the southeastern portion of the body and 23 tonnes from 15 core holes drilled across the southern half.
The 23-tonne sample of kimberlitic core material held 8.99 carats of diamonds for a grade of 0.39 carat per tonne, using a recovery screen size of 1.18 mm. The two largest diamonds weighed 0.61 and 0.49 of a carat. A 30.83-carat parcel of diamonds was recovered from the 74.1 tonnes of RC sample from Renard 4 for an implied diamond content of 0.42 carat per tonne. The larger RC bulk-sample held the 2.9-carat stone, as well as a 0.69-carat diamond described as a grey dodecahedral crystal. The grade of the winter bulk-sample is down somewhat from the original mini-bulk sample estimate of 0.53 carat per tonne.
This summer, Ashton collected an additional 55 tonnes from Renard 4 by drilling two RC holes in the southwestern corner of the kimberlite and eight core holes across the northern half. Although the results of the RC sample are not yet available, some 9.3 tonnes of kimberlitic core samples delivered 4.62 carats of diamonds, for a grade of 0.5 carat per tonne. An additional 1.8 tonnes of sample, collected from a surface excavation on an exposure in the northeastern corner of Renard 4, contained 3.09 carats. The largest diamonds recovered from the cumulative 11.1 tonnes are a pale brown fragment weighing 0.49 carat and a grey composite crystal weighing 0.37 carat.
So far, 123.3 tonnes of processed material from Renard 4 have yielded 55.57 carats, giving an implied grade of 0.45 carat per tonne.
Highest grades
Ashton completed the 2004 bulk-sampling campaign by gathering 157 tonnes of kimberlitic material from each of Renard 2 and 3, the two bodes that have so far shown the highest grades in the Renard cluster. In the latest batch of results, an 11.5-tonne drill core sample from the Renard 2 kimberlitic pipe was found to hold 13.3 carats of diamonds greater than a 1.18-mm recovery screen size, giving an estimated grade of 1.15 carats per tonne. The three biggest diamonds recovered from the sample batch were a brown 1.18-carat tetrahexahedroid-type crystal, a brown 0.94-carat octahedral, and a grey 0.76-carat octahedral composite.
The 11.5-tonne sample was collected by drilling eight core holes into Renard 2, which measures roughly 120 by 65 metres, or 0.6 hectare. The latest results are substantially higher in grade than those returned by earlier mini-bulk samples. A previous, 13.5-tonne sample collected from Renard 2 by drilling in 2002 and 2003 yielded 8.72 carats above a 0.85-mm cutoff, for an estimated diamond content of 0.64 carat per tonne. The three largest stones were a colourless, clear octahedron weighing 0.91 carat, a colourless composite crystal of 0.39 carat, and a colourless 0.38-carat composite.
At 0.3 hectare in surface area, Renard 3 measures 145 by 25 metres. An 8.63-tonne sample was taken during the summer of 2004 by drilling eight core holes into the body. The sample returned 5.89 carats of diamonds, including a clear partial crystal weighing 0.88 carat, for an implied grade of 0.68 carat per tonne. This is well off the previous mini-bulk drill samples, which showed a diamond content averaging 1.44 carats per tonne. The two largest diamonds in the earlier sampling included a colourless, 1.82-carat octahedral and a pale brown octahedron weighing 1.01 carats. The results from about 150 tonnes of material collected from each of the Renard 2 and 3 pipes by RC drilling are expected sometime in the first quarter.
Soquem, Ashton’s partner at Renard, is a Crown corporation of the Quebec government.
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