A bulk-sampling drilling program is under way at the Foxtrot property in north-central Quebec as
The inferred diamond content of these four small pipes — Renard 2, 3, 4 and 65 — exceeds half a carat per tonne, suggesting the the bulk sampling will deliver at least 300 carats of diamonds and provide a preliminary indication of value while defining the grade and tonnage.
“The challenges ahead of our joint venture are clear,” Ashton’s vice-president of exploration, Brooke Clements, told delegates at the Mineral Exploration Roundup, held recently in Vancouver. “We have demonstrated that kimberlites with potentially commercial diamond contents and commercial-size stones are present on the Foxtrot property. We now need to prove up enough tonnage of material with commercial grades to justify taking the project to the next level.”
Toward that end, the Ashton-Soquem joint venture has approved an ambitious $18-million campaign for 2004, with most of the work focused on Foxtrot. The program will entail collecting a 600-tonne bulk sample from the Renard cluster and continuing an aggressive program of exploration.
Since discovering Renard 1 and 2 by drilling classic kimberlite-type magnetic anomalies in the fall of 2001, the 50-50 joint venture has uncovered a new field of 10 diamondiferous kimberlitic intrusions. (A compilation of the microdiamond results is provided in Table 1.) Nine of the intrusive bodies are roughly aligned along a 2-km-long north-south axis.
The Foxtrot property covers 1,970 sq. km in the Otish Mountains region of Quebec. The project is currently accessible only by air, either from Chibougamau, 400 km to the south, or from the LG-4 hydroelectric facility, 140 km to the north. The nearest all-weather road services the LG-4 plant. Sixty kilometres to the south lies the idle Eastmain gold mine, which, when it was in operation, was serviced by a 200-km-long winter road.
In 2003, the Ashton-Soquem joint venture added two kimberlite discoveries (9 and 10) to the Renard cluster and collected mini-bulk samples from each of Renard 1, 2, 3, 4 and 65. Drilling during mini-bulk sample work determined that Renard 6 and 5 were actually one body, which was renamed Renard 65. A cumulative sample of 56 tonnes was collected in 2002 and 2003 by core drilling from Renard 2, 3, 4 and 65, which occur in a 0.5-sq.-km core area. (An 8.8-tonne sample of Renard 1, taken from just outside of the core area, returned just 0.78 carat of diamonds for an estimated diamond content of 0.09 carat per tonne.) With just 5 tonnes of sample from Renard 3 remaining to be processed, the dense-media-separation (DMS) analysis of 51.9 tonnes of kimberlitic material to date has delivered 33.3 carats of diamonds greater than 0.85 mm, including a 4-carat stone that remains embedded in drill core from Renard 65. (A breakdown of the DMS results by kimberlitic pipe is provided in Table 2.) In total, 24 diamonds larger than 0.2 carat were recovered.
The bulk-sampling portion of the 2004 program is budgeted at $12 million. A bulk-sample of at least 600 tonnes will be collected this winter and summer from a combination of core and large-diameter reverse-circulation (RC) drilling. Most of the core holes will be HQ-size (6.3 cm in diameter). That means a 200-metre vertical hole in kimberlite will yield a 1.5-tonne sample. The RC holes will be 30 cm in diameter, so a 150-metre hole should deliver about 15-20 tonnes of sample.
This winter, the joint-venture plans to drill a network of 30-40 vertical core holes in the Renard 2, 3, 4 and 65 kimberlitic bodies on a 20-metre grid, in addition to drilling 5-10 RC holes. One of the primary objectives of the winter program is to establish the grade of Renard 65 by collecting more than 100 tonnes. “Establishing the grade of Renard 65 is really important because, at 1.5 hectares, it’s our largest body, and three of our four largest stones come from that body,” says Clements. A 10-tonne mini-bulk sample will also be collected from last year’s Renard 9 discovery, which returned an impressive 178 microdiamonds from a 212-kg sample, including a 0.11-carat diamond described as a pale-brown composite crystal.
The results of the winter program will be used to guide the summer drilling of an additional 20-30 RC holes to collect the remaining 400 tonnes of samples.
The collection of more than 900 samples in the summer and fall of 2003 have helped define three “very strong” anomalous indicator mineral dispersion trains on the Foxtrot property, says Clements. The head of the North anomaly is 5 km north of the Renard cluster. One sample near the head of this discreet anomalous train yielded hundreds of indicator mineral grains and a 0.4-mm diamond. “We also found a number of pieces of kimberlite float nearby,” remarked Clements.
Within the confines of the Southeast anomaly indicator train, 3 km southeast of Renard, two pieces of kimberlitic float were found 500 metres apart. The Lynx anomaly is a strong, 2.5-km-wide indicator mineral train that contains a “healthy population of G10 or diamond-friendly garnets.” Kimberlitic float was found at three separate sites at the end of last year’s field season before being chased out of the bush by the weather.
Last fall, a new kimberlitic dyke system was uncovered by drilling; the system is 2 km west of the Renard cluster core, in an area up-ice of where three microdiamonds were recovered from two till samples spaced 350 and 750 metres apart. Two holes were drilled across a broad but weak geophysical anomaly at the head of the Lynx anomaly and intersected a 4-to-5-metre-wide zone of hypabyssal kimberlitic dykes, in which the largest dyke has an estimated true width of about 1 metre.
Abundant kimberlitic cobbles and boulders measuring up to 2 metres in diameter were found on surface 100 metres down-ice of the discovery holes. A 3.9-tonne sample of the boulders was treated by DMS and returned 4.63 carats of diamonds larger than a 0.85-mm square aperture screen, giving an estimated diamond content of 1.2 carats per tonne. The two largest diamonds are a colourless composite crystal weighing 0.96 carat and a 0.28-carat pale brown octahedron. Additional kimberlitic float was discovered 1.2 km north of the drill site. The Lynx area will be targeted with more exploration in 2004.
Follow-up geophysics and indicator mineral sampling are also planned for this summer, the objective being to define drill targets on the Tichegami mineral claims, 80 km south of the Renard cluster.
The Precambrian-age Superior Craton, underlying parts of Manitoba, Ontario and Quebec, is the largest stable platform of Archean crustal rocks in the world. Although there are notable exceptions, most diamond mines occur in the margins of Archean cratons. The advanced-stage Victor diamond project of
The Renard kimberlites have been age-dated at 631.6 million years, plus or minus 3.5 million years, based on the lead-uranium age analysis of perovskite cubes in the kimberlitic ground mass. Clements says there appear to be three main kimberlitic events on the Superior Craton: an early Cretaceous event about 150 million years ago, represented by the Kirkland Lake, Temiscamingue and Attawapiskat kimberlites; an event straddling the Proterozoic-Paleozoic boundary at 550-650 million years ago, which includes the Foxtrot, Lac Beaver and Wemindji kimberlitic intrusions; and the Kyle Lake and Desmaraisville events at about 1.1 billion years.
The Renard bodies are small kimberlitic intrusions, ranging from 0.3 to 1.5 hectares in size. Each consists of three basic rock types, including kimberlitic breccia, with variable country rock xenolith content, and macrocrystic hypabyssal kimberlitic material that generally exhibits a cross-cutting relationship to the breccia. Contacts with the country rock can be sharp or transitional, with the latter grading into highly fractured and brecciated zones of country rock, containing little or no kimberlitic material. This country rock breccia is often crosscut by macrocrystic kimberlitic dykes.
Ashton believes the Renard pipes have been eroded down 1.5 km in section to a level that encompasses the transition from root, or hypabyssal, to diatreme zone. The Renard bodies exhibit mineralogical and petrographic features common to both kimberlite and melnoite. Based on groundmass features, the Renards are transitional between melnoite and kimberlite, whereas whole rock-trace-element chemistry suggests a closer affinity to Group 1 kimberlite.
“In just over two short years, our joint venture has found a new Canadian diamond district,” said Clements. “2004 is going to be a real pivotal year for the project. We are going to learn a lot more about diamond content and the nature of the diamonds, and we are going to be exposed to a lot of [potential] kimberlitic discoveries through our exploration.”
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