Camp Lagopede, Foxtrot, Que. — It has long been speculated that those diamonds that have surfaced randomly and unexpectantly in the last couple of centuries across portions of the U.S., at the southern margins of glaciation, must have had their source in Canada. In Indiana alone, 35 diamonds have been recovered from stream beds through the years, including a 5-carat stone.
Long before the discovery of the Ekati and Diavik diamond finds in the Northwest Territories, John McPhee published a book titled In Suspect Terrain. In it he opined: “At least one pipe containing gem diamonds must exist somewhere near a line between Indianapolis and the Otish Mountains of Quebec.”
How prescient his remarks were, for in the fall of 2001,
The nine kimberlitic discoveries are grouped together in the Renard cluster in the south-central part of the Foxtrot property, 400 km northeast of the mining and forestry town of Chibougamau. These intrusive bodies are roughly aligned along a 2-km-long north-south axis. Six of the nine bodies — Renard 2, 3, 4, 65, 8 and 9 — are found in a “core area” measuring only half a square kilometre.
The Foxtrot property covers almost 2,000 sq. km in the Otish Mountains region and is accessible only by air. The nearest all-weather road, 140 km to the north, services a network of hydroelectric dams. About 55 km to the south lies the idle Eastmain gold mine, formerly serviced by a 200-km-long winter road from Temiscamie on Lac Albanel. The project is on the traditional land of the Cree Nation of Mistissini.
The Renard 1 through 8 kimberlitic intrusions were discovered in 2001 and 2002 as a result of drilling magnetic geophysical anomalies at the head of a prominent indicator mineral dispersion train. Renard 9 and 10 were found in 2003, as was the highly diamondiferous Lynx kimberlitic dyke system, 2 km farther to the west.
Ashton and Soquem joined forces in 1996 and spent the next five years quietly conducting heavy mineral sampling across an area measuring 425,000 sq. km. More than 1,700 samples were taken, representing a density of about 1 sample every 250 sq. km. Underlain by the Superior Craton, a stable platform of ancient Archean rocks, the northern Quebec area appeared to be under-explored for diamonds, and unlike Lac de Gras, there was no competition at the time, says Brooke Clements, Ashton’s vice-president of exploration. Of those 1,700 samples, only 30-40 contained kimberlite indicator minerals. In fact, the recovery of a single, 4-mm-long indicator mineral grain from one of the regional samples collected in 1997 was eventually traced back to the Foxtrot property, 40-50 km away.
“In 1999, we went back and did just a bit of follow-up and got more interesting results,” Clements tells The Northern Miner. “Then in 2000, we did more follow-up and got screaming results, which prompted us to stake the ground within 10 days of getting the results. Samples containing more than 1,000 indicator minerals were collected in some of these areas.”
“One sample was so hot (it contained 9,000-10,000 mineral grains) that Ashton did not wait for the indicator mineral chemistry before staking the ground. Indeed, the mineral chemistry turned out to be, in Clements’ words, “some of the best in North America, and as good as Lac de Gras.”
The chemical compositions of the recovered ilmenites and pyrope garnets were suggestive of a diamond-bearing host rock. Fresh angular features and kelyphitic rims on several of the pyrope garnets also suggested a nearby source. “We just knew we were right on a kimberlite,” says Clements.
All nine of the Renard bodies have proved to be diamond-bearing. Samples from the initial discovery holes returned a significant number of microdiamonds (see Table 1 for a detailed look at the microdiamond results for each of the discoveries). Moreover, some larger stones were recovered from these small drill core samples, including a 0.13-carat diamond measuring 4 by 2.7 by 1.9 mm from Renard 3. Says Clements: “In a small sample, when you start to get big diamonds it’s an indication you have the potential for good-size distribution or big diamonds.”
The Renard bodies are small kimberlitic intrusions ranging from 0.3 to 1.5 hectares in size. Each is composed of three basic rock types, including macrocrystic hypabyssal kimberlite, containing less than 15% country rock xenoliths, and kimberlitic breccia, with 15-95% xenolith content. Contacts along the country rock boundaries can be sharp or transitional, with the latter grading into highly fractured and brecciated zones of country rock, containing less than 5% kimberlitic material. This country rock breccia is often crosscut by macrocrystic kimberlitic dykes.
In each of the Renard bodies, there appears to be a main diatreme event. Prior to and after this event, there seems to have been hypabyssal activity in either dykes or small blows. Marginal country-rock breccia zones were created on the edges of the kimberlite as it intruded. Ashton has yet to develop a definite sense of grade distribution within the diatreme and hypabyssal zones in each of the bodies but says there are indications of a slight elevation in diamond grades in the hypabyssal in the Renard 2 and 3 bodies.
Since the intrusion of the Renard bodies, some 600 million years ago, Ashton believes the pipes have been eroded down as much as 1-1.5 km to a level somewhere in the transition between the diatreme and root 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 kimberlites.
57 tonnes
Over the course of 2002 and 2003, the joint venture collected mini-bulk drill core samples totalling 57 tonnes from Renard 2, 3, 4 and 65 — four of the bodies in the core area (Table 2 provides an analysis of the mini-bulk sampling results). In total, a 41.1-carat parcel of diamonds greater than 0.85 mm was recovered, giving an overall diamond content of 0.72 carat per tonne. The individual grades of the four bodies range from 0.53 to 1.44 carats per tonne. Nine of the biggest stones are over half-a-carat in size; the largest is a clear, 4-carat, octahedral-shaped diamond recovered from Renard 65, which remains embedded in a piece of drill core.
Clements is encouraged by the consistent appearance of these larger diamonds in the small samples. “These are significant kimberlite discoveries,” he asserts.
Renard 1, the first kimberlite discovery on the Foxtrot property, lies just outside the designated core area, 400 metres to the north. At 1.2 hectares, or 210 by 94 metres, it is the second-largest body in the Renard cluster. However, initial microdiamond results from Renard 1 were less encouraging than those from other bodies; as a result, the collection of a mini-bulk sample was deferred until the summer of 2003. Almost 9 tonnes of material extracted from seven holes yielded just 0.78 carat of diamonds greater than 0.85 mm, for an estimated diamond content of 0.09 carat per tonne (or 9 carats per 100 tonnes). The largest diamond recovered was a colourless octahedral weighing 0.12 carat.
The Renard 2, 3, 4 and 65 bodies in the core area cover a cumulative surface area of 3.4 hectares. Assuming these four pipes have vertical walls to a depth of 200 metres, there is the potential for more than 15 million tonnes of kimberlite based on a back-of-the-envelope estimate using a specific gravity of 2.6. It’s worth noting that kimberlite has been intersected in some of these bodies to a depth of 300 metres. Ashton has yet to report any k
imberlite resource estimates; instead it has focused on first establishing an underlying rock value.
“We have a cluster of kimberlites, with potentially commercial grade and some nice-looking diamonds,” says Clements. In order to establish a quantitative feel for the diamond value, the Ashton-Soquem joint venture approved an $18-million bulk-sampling and exploration program for 2004. The main objective was to collect a sample of at least 600 tonnes of kimberlite material from the Renard 2, 3, 4 and 65 bodies using both core and large-diameter reverse-circulation (RC) drilling. A bulk sample of this size is expected to yield a cumulative parcel of well over 300 carats of diamonds for preliminary valuation.
‘High margin error’
“It’s important to emphasize that the 300-carat diamond parcel will not give us an absolute value,” cautions Ashton President Robert Boyd. “Rather, it will give us an understanding of what the average value is, and it will have a high error margin.”
Typically, valuations are done on parcels of at least 3,000 carats for bankable feasibility studies.
During the winter phase of this program, completed in early April, 237 tonnes of kimberlitic material were extracted from the Renard 65 and 4 kimberlites using both large-diameter (27-cm) RC and core drilling. The winter drilling focused on sections of the bodies that are partially overlain by shallow lakes. Ashton recovered 140.3 tonnes from Renard 65, including 122.5 tonnes from five RC holes and 17.8 tonnes from 11 core holes. Approximately 97.1 tonnes of material were extracted from Renard 4. 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. This served to establish geology and grade control to aid the RC drilling.
Getting a handle on the grade of Renard 65 was an important component of the bulk-sampling program. At 1.5 hectares, Renard 65 is the biggest of the bodies in the core area. With the 4-carat diamond found there, it showed it could potentially have a good coarse diamond distribution, and the bigger stones are where the value lies. But if the 4-carat diamond is excluded from the grade estimate, Renard 65 has the lowest grade of the four core bodies, at 0.33 carat per tonne, based on a bottom stone size cutoff of 0.85 mm.
The winter bulk samples were processed during the third quarter (Table 3 provides a detailed look of the bulk sample results). The 139-tonne sample of Renard 65 returned 30.7 carats of diamonds greater than 1.18 mm, giving a grade of 0.22 carat per tonne. The four largest diamonds were a colourless, clear dodecahedron weighing 0.88 carat, a 0.83-carat brown-coloured dodecahedral, a 0.82-carat pale brown crystal, and a clear octahedron weighing 0.67 carat. Despite the absence of big-carat stones (such as the 4-carat diamond previously recovered), Ashton is not disappointed by the bulk-sample results of Renard 65. Says Clements: “These samples are still pretty small. We probably haven’t taken a large-enough sample to really test the big-stone possibilities there. We always knew the four-carat diamond was a bit of a nugget; that’s pretty clear.”
Octahedral crystal
A 39.8-carat parcel of diamonds was recovered from the 97.1 tonnes of bulk sample from Renard 4 for an implied diamond content of 0.41 carat per tonne. The grade came down a bit from the original mini-bulk sample estimate of 0.53 carat per tonne, which could be due to a higher, 1.18-mm screen size cutoff, versus 0.85 mm used in the mini-bulk sample. The five largest diamonds recovered from the winter bulk sample weigh 2.9, 0.69, 0.61, 0.59 and 0.56 carats apiece. The 2.9-carat diamond, a colourless octahedral crystal, is the second-largest stone thus far recovered from the Renard cluster.
To date, the 237 tonnes of processed bulk-sample material from Renard 65 and Renard 4 have delivered 70.6 carats of diamonds exceeding a 1.18-mm cutoff, for an implied grade of 0.3 carat per tonne.
During the winter 2004 program, mini-bulk sampling and delineation drilling were completed on Renard 9. About 5 tonnes of material were recovered from nine core holes. The Renard 9 results will not be available until after the completion of the bulk-sample processing. Renard 9 showed a strong microdiamond count in the initial discovery holes, returning an impressive 178 diamonds from a 212-kg sample. The largest stone was a pale brown composite crystal weighing 0.11 carat, caught in the 1.7-to-2.36-mm sieve size fraction.
This summer, Ashton completed the bulk-sampling program by gathering an additional 390 tonnes of kimberlitic material from the drilling of 15 RC holes and 23 core holes. This material includes about 157 tonnes from each of Renard 2 and 3, the two bodies that have so far shown the highest grades in the Renard cluster, as well as 55 tonnes from Renard 4 and 20 tonnes from Renard 65. Final bulk-sample results are expected in the first quarter of 2005.
Of the $18 million budgeted this year for Quebec, about $6 million is being used to conduct further exploration on the joint venture’s holdings. “We really want to try to find more tonnage outside the Renard cluster,” says Clements.
This past summer, field crews found new areas containing abundant kimberlitic cobbles and boulders while prospecting along the projected strike of the highly diamondiferous Lynx kimberlitic dyke occurrence. “We are finding kimberlite boulders just about everywhere,” says Clements.
Lynx
The Lynx anomaly is a strong, 4.5-km-wide indicator mineral train, with associated kimberlitic float, which contains a “healthy population of G10, or diamond-friendly, garnets.” One till sample, taken in 2000, contained 9,000-10,000 kimberlite mineral indicator grains and triggered the staking of Foxtrot, in the Lynx anomalous area. This sample returned a full suite of indicator minerals, including pyrope garnets, ilmenites, chrome diopsides, chromites, and, most importantly, diamonds. The strongest portion of this anomaly terminates near a linear topographic feature that strikes 345 and is believed to be the source of the Lynx kimberlite.
Last fall, while drilling a broad, weak geophysical anomaly in one area at the head of the Lynx indicator mineral train, the joint-venture partners intersected a 4-to-5-metre-wide zone of narrow hypabyssal kimberlite dykes, the largest being 1-metre thick. The discovery area was up-ice of where three microdiamonds had been recovered from two widely spaced till samples. The recovery of microdiamonds from till samples is quite a rare event and is deemed significant.
In addition, abundant kimberlitic float measuring up to 2 metres wide in diameter was found on surface 100 metres down-ice of the discovery holes. A 3.9-tonne sample of the boulders, treated by dense media separation (DMS), returned 4.63 carats of diamonds larger than 0.85 mm, 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 octahedral.
“Now we have to try to get that grade in a bedrock source that has some significant volume,” says Clements.
A 238.7-kg sample from this same site was treated by caustic fusion analysis, yielded a significant 594 microdiamonds, including three stones caught on the 1.18-mm screen size fraction. A second sample, comprising 77.2 kg of kimberlitic material, was collected from a surface site 1.2 km northwest of the Lynx discovery in an area now called Lynx North; it held 289 microdiamonds.
During the winter 2004 program, two additional holes were drilled in the vicinity of the Lynx discovery holes. The longest single intercept of kimberlite in each hole ranged from 1.1 to 2.7 metres thick. A second target at Lynx North was tested with two angle holes; the drilling encountered 3.9-to-6.8-metre-wide zones of narrow kimberlite dykes.
Dyke system
Further drilling along the Lynx anomaly was conducted in September. Kimberlitic dykes were intersected at 12 of the 13 sites, confirming the presence of a continuous or semi-continuous dyke system over a distance of at least 3.7 km.
“Just about everywhere we drilled at Lynx we got a dyke,” says Clements. “We have yet to get that thick intersection that we want, but there still is the potential to discover lots more within the Lynx anomaly.”
Ten of the kimberlite hits occur in a 1-km strike-length portion of the dyke system, referred to as Lynx South, at the southeastern end of the Lynx anomaly. The dyke system comprises zones ranging from 0.5 to 4.4 metres in width, and these contain greater than 50% kimberlite. The longest single intercept of kimberlite in each hole ranged from 0.5 to 3.7 metres thick. The average depth of overburden is less than 5 metres, and the dykes are interpreted to dip to the east at 15 to 50.
In conjunction with the drilling, two mini-bulk samples of kimberlitic boulders, each weighing about 5 tonnes, were collected from the northern and southern ends of the Lynx trend. These samples will be processed for diamonds in early 2005. The joint-venture partners will eventually sample each of the drill intercepts of the Lynx dyke system for microdiamond analysis.
“We want to focus on an area where we might be able to put together minable blocks of kimberlite,” says Clements. “That’s the objective of drilling known dykes.”
Elsewhere on the Foxtrot property, the joint venture drilled two target areas in the North anomaly, 6 km north of the Renard cluster. The North anomaly was first identified in 2003 by anomalous indicator mineral samples and is associated with kimberlitic float material. Microdiamonds greater than 0.4 mm in size have been recovered from five till samples collected within the anomaly. Two of the nine holes drilled this past summer intersected stringers of less than 10 cm of kimberlitic material. Ashton doesn’t believe this adequately explains the source of the North anomaly and plans to do more work. “We know it’s there somewhere,” says Clements. “We just weren’t fortunate enough to find it this time.”
Kimberlitic float
In the summer, Ashton collected 2,000 heavy-mineral samples at Foxtrot, mainly in order to define anomalous areas further. Pebble- and cobble-size kimberlitic float was discovered at three new sites as far away as 15 km from the Renard cluster. Outside of Lynx and Renard, Ashton has now defined five distinct indicator mineral anomalies, with associated kimberlite float. “We literally have hundreds of geophysical anomalies, any of which could be modeled as a kimberlite,” says Clements. “But at the moment, we don’t have any more Renard-type [bull’s-eye] geophysical anomalies.”
In addition to the work at Foxtrot, four targets were drilled on the Tichegami property, where, since 2000, Ashton and Soquem have held 546 sq. km of scattered mineral claims. Tichegami is 80 km south of Foxtrot. Kimberlitic dykes measuring 2.3 metres and 0.15 cm were intersected at two of the targets.
“The recovery of commercial-sized diamonds, the presence of a coarse stone population from Renard and Lynx, the identification of new targets beyond those areas, and the consistently encouraging chemical characteristics of the indicator minerals suggest that the full potential of the Foxtrot property has not yet been realized,” Ashton states in a quarterly report.
To continue going forward in 2005, the Foxtrot project needs some “threshold results.” That might mean good diamond values, good grades, or reasonable tonnage to justify resource delineation drilling and the taking of a larger bulk sample.
In 10 years of diamond exploration in North America, Ashton has discovered 67 kimberlite bodies is six jurisdictions, namely Nunavut, the Northwest Territories, Alberta, Ontario, Michigan and Quebec. “The most exciting thing we have done is our project here in Quebec,” says Clements. “We are working like crazy to put together grade, value and tonnage to see if we can come up with something that makes sense for an economic deposit.”
Be the first to comment on "Ashton, Soquem prove up Renard cluster at Foxtrot property"