A flurry of exploration in eastern Nunavut has resulted in several kimberlite discoveries.
Diamond exploration companies intensified their efforts in the region following the 2002 discovery, by
Although few details about the Qilalugaq discoveries are known, a mini-bulk drill sample of 9.1 tonnes collected from one of the kimberlites delivered a 2.36-carat parcel of diamonds for an implied diamond content of 0.26 carat per tonne, based on a 0.85-mm square mesh cutoff. Additional mini-bulk samples were collected from several of the pipes this spring. “Diamonds were recovered from four separate samples, though none of the samples contained values that would be expected to be economic,” states BHP Billiton in its most recent quarterly update on global exploration activities.
Elsewhere in the region, two kimberlites were discovered by Stornoway during the drilling of two magnetic geophysical targets on Wales Island, just off the western coast of Melville Peninsula. Wales Island is covered by 1,152 sq. km of prospecting permits jointly held by Stornoway,
The prospecting permits were issued in February 2004. This past August, Stornoway, acting as project operator, carried out a brief reconnaissance exploration program in nine days. During that time, ground magnetic surveys were completed on six discrete airborne targets.
Three of the geophysical targets were drilled using a lightweight, small-diameter, highly portable drill rig. Kimberlite was intersected in two of the three targets, about 7 km apart. A vertical hole into target W1 was collared in heavily altered kimberlite at 5.5 metres and remained in kimberlite until the end of the hole at 19 metres. The kimberlite is described as a “dark-grey-to-black, variably micaceous, sparsely macrocrystic hypabyssal, fine-grained intrusive.”
A second kimberlite body was found while testing target W3. A vertical hole encountered altered kimberlite at 21 metres of depth, continuing to the end of the hole at 37 metres. The W3 kimberlite appears distinctly different from W1 and is described as a “weathered ultramafic hypabyssal breccia, with abundant country rock xenoliths.” Less than 20 kg and 30 kg of sample were recovered from W1 and W3, respectively, owing to the small size of the core. Target W2 remains unexplained.
In addition, 35 till and sediment samples were collected for indicator mineral processing. Results from airborne magnetic surveys suggest the presence of multiple discrete targets. A more comprehensive exploration program is planned for 2005.
In early February of this year, the Nunavut mining recorder issued a record number of prospecting permits covering an unheard-of 64 million acres (259,000 sq. km) across the eastern region of Canada’s Far North. The Canadian exploration arm of
After initially striking a 50-50 joint venture arrangement with BHP Billiton on a surrounding 3.3-million-acre (13,400-sq.-km) package of ground, Diamonds North had the agreement amended to include its Amaruk project plus 3.5 million acres (14,150 sq. km) of additional ground held by BHP. As part of the arrangement, BHP Billiton will act as project operator over the merged area, which now exceeds 32,380 sq. km, and has agreed to incur all exploration costs up to the completion of a feasibility study within seven years in return for an extra 10% interest. BHP will have the right to earn an ultimate 65% stake in the project by arranging all financing to production.
This past summer, an 11,000-line-km airborne geophysical survey was flown over the central part of the project area, and about 3,000 till samples were collected as part of a $4-million program. During a brief reconnaissance visit to the project, kimberlite boulders and fragments were found in three separate areas. Boulders of kimberlite were found at five discrete sites forming a 2.3-km-long corridor on trend with the 2003 till sample that returned 1,350 indicator mineral grains. A 350-kg sample was collected for microdiamond analysis.
Kimberlite fragments were also traced over a distance of 600 metres to a lake at a second site, 10 km east of area 1. There was insufficient sample for diamond analysis. At a third location, about 30 km northeast of area 2 in the original BHP permits, small fragments of ultramafic kimberlite-like rock were recovered down-ice of a 2003 till sample that yielded 89 indicator mineral grains. Again, there proved to be insufficient sample for diamond analysis.
Diamonds North also joined forces with Kennecott, part of the
Kennecott completed 20,000 line km of airborne magnetic surveys over the project and collected 223 heavy mineral samples during the summer.
Led by Eira Thomas, Catherine McLeod-Seltzer and John Robins, Stornoway maintains varying interests in more than 12.5 million acres (or 50,600 sq. km) in the Melville Peninsula region. Stornoway’s field crew discovered the outcropping AV-1 kimberlite pipe at the end of the 2002 field season while conducting a brief reconnaissance program on the Aviat project. An initial 186-kg composite sample collected from the surface exposure of AV-1 returned 228 microdiamonds, including two stones (2.2 by 1.86 by 1.32 mm, and 2.08 by 1.34 by 1.06 mm) larger than a 1.18-mm square mesh screen size. The diamond distribution curve of this sample looked promising, suggesting the new discovery had high potential for larger, commercial-size stones.
Stornoway had initially acquired an interest in two property packages on the north end of Melville Peninsula in early 2002, based on positive kimberlite indicator mineral results from regional sampling by the Hunter Exploration Group in 2001. Soon afterwards, De Beers acquired a large property block of more than 28,000 sq. km on neighbouring Baffin Island, based on encouraging results from several seasons of regional till and stream-sediment sampling. De Beers’ property package is directly across the Foxe Basin from the Melville Peninsula.
At about the same time, BHP Billiton staked the 1.1-million acre (4,450 sq. km) Qilalugak project, near Repulse Bay at the southern end of Melville. Both De B
eers and BHP Billiton were rumoured to have discovered kimberlite float on each of their prospective property packages.
Melville Peninsula
Today, the Aviat project spans 5.5 million acres (22,300 sq. km ) across the Melville Peninsula. Stornoway is the operator and holds a 70% interest, while BHP Billiton owns 20% and the privately held Hunter group has a 10% carried stake. BHP purchased its interest in the Aviat project from the Hunter group in June 2003 for $7.1 million. BHP also paid $3 million for a minority stake in the Churchill project, just north of Rankin Inlet.
The outcropping AV-1 is exposed over an area measuring 76 by 13 metres at the edge of a small lake, 50 km west of the coastal community Igloolik. Drilling to date has defined a multi-phase kimberlite body measuring 225 metres long and up to 50 metres wide. The body is composed of macrocrystic hypabyssal kimberlite and a transitional tuffisitic breccia phase.
The exposed portion consists solely of hypabyssal kimberlite. Some 1,136 kg of kimberlite were originally retrieved from the AV-1 outcrop by surficial grab sampling in August 2002 and March 2003. In total, 1,613 microdiamonds were recovered by caustic fusion analysis, including 12 stones exceeding 1.18 mm square mesh and two diamonds caught on the 1.7-mm square mesh sieve.
Drilling last year on AV-1 intersected both kimberlite phases, delivering another 421 microdiamonds from 292 kg of hypabyssal material, and 316 stones from 239.7 kg of transitional kimberlite. The three largest diamonds measure 4 by 3.5 by 1.8 mm, 2.34 by 2 by 1.76 mm, and 2.4 by 1.48 by 1 mm. All were recovered from the transitional phase.
The hypabyssal and transitional phases of AV-1 have returned comparable microdiamond counts of 1.44 stones per kg and 1.32 stones per kg, respectively, though the transitional breccia appeared to have a better coarse diamond distribution potential.
The accompanying table (p. B7) provides a detailed look at the microdiamond distribution, including 2004 drilling results in which an additional 515 kg of AV-1 transitional phase material were found to hold 667 stones or 1.3 stones per kg.
White, transparent
A 7.4-tonne mini-bulk sample collected in 2003 from the surface exposure of AV-1 was analyzed strictly for macrodiamonds. It yielded 6.52 carats of diamonds exceeding 0.85 mm, for an implied grade of 0.88 carat per tonne. The largest stone recovered was a white transparent aggregate weighing 0.4 carat. Overall, the diamond population, consisting of predominantly dodecahedral and octahedral crystal forms as whole crystals and fragments, is dominated by white transparent stones, with lesser amounts of brown-coloured diamonds and little fibrous material.
One of the objectives of the 2004 spring drilling was to collect a mini-bulk sample from the transitional phase to test for larger diamonds. This drilling provided a 2.2-tonne sample of transition tuffisitic kimberlite for dense media separation analysis, which showed a diamond content of 0.65 carat per tonne at a 0.85-mm cutoff. The largest stone weighs 0.14 of a carat.
A further 832 kg of hypabyssal kimberlite collected during the spring drilling of AV-1 was analyzed for macrodiamonds; it yielded a sample grade of 0.78 carat per tonne, with the largest diamond weighing 0.17 carat.
It now appears that the diamond size distributions in both phases of AV-1 are similar, with the mini-bulk drill results consistent with the surface sampling. In total, 10.4 tonnes of kimberlite from AV-1 delivered an average sample grade of 0.83 carat per tonne.
“Both phases of kimberlite identified at AV-1 have returned potentially economic macrodiamond grades and appear to have similar diamond populations with comparable size distributions,” states Eira Thomas, Stornoway’s president.
This year, 4,175 till samples were collected from the Aviat project holdings, including 2,700 in the so-called Tremblay corridor, where more than 100 occurrences of kimberlite boulders have been mapped. The Aviat AV-1 and AV-2 discoveries lie in this east-west-trending corridor, which is defined by anomalous indicator mineral till samples taken in 2002 and 2003. The anomalous corridor extends over a distance of 75 km and ranges from 3 to 8 km in width. Stornoway notes that kimberlite indicator minerals have been found up-ice of AV-1 and AV-2.
Outside the Tremblay corridor, at least 10 discrete regions of anomalous kimberlite indicator minerals were identified for follow-up work.
AV-2 was discovered in the summer of 2003, about 4 km east-southeast of AV-1.
Surface exposure
The outcropping body was tested by a single inclined hole that intersected 2.6 metres of kimberlite beneath a surface exposure, followed by two other separate kimberlite sections of 9.3 and 3.1 metres. A second hole tested a magnetic anomaly, 75 metres southwest of the AV-2 showing, and hit 2.2-metre- and 6.5-metre-long sections of kimberlite.
A combined 39.4-kg drill sample of AV-2, including both hypabyssal and breccia phases, held 30 microdiamonds. The largest stone was a lone diamond caught on a +0.6-mm square mesh screen. In addition, a 48.6-kg sample collected from a surface exposure of AV-2 hypabyssal phase kimberlite contained 34 stones, including a diamond measuring 1.78 by 1.32 by 0.86 mm that was caught in the +1.18-mm-size sieve.
During the fall 2004 drill program, Stornoway tested four target areas near AV-1. The 8-hole program spanned 1,142 metres. A new surface showing of boulders at AV-2 was tested by a single hole, which cut 2.35- and 2.90-metre sections of heavily altered hypabyssal kimberlite, 35 metres east of the known body.
A hole angled at 45 into a geophysical response, 475 metres west of AV-1, intersected a narrow, 2.9-metre-thick kimberlite dyke, referred to as AV-1A.
A series of four holes was completed at the AV-4 occurrence of hypabyssal kimberlite boulders, which were discovered by prospecting earlier in the summer, 600 metres west of AV-1. Three of the holes encountered sections of both hypabyssal- and transitional-phase kimberlite over down-hole lengths ranging from 15 to 61 metres. A fourth hole, which intersected only 2.1 metres of kimberlite is thought to have missed the main body because of positioning. Microdiamond results from the AV-4 discovery are expected by the end of November.
A single hole into the AV-3 showing returned two narrow, altered kimberlite dyke sections. One was 0.37 metre wide; the other, 2.15 metres. A second hole, which targeted a boulder occurrence 250 metres to the south, encountered two small kimberlite intercepts of 0.1 and 0.23 metre but was stopped short of its target depth.
Another surface target, AV-5, which is represented by a train of kimberlite boulders up to 2.2 metres in diameter and spread over a distance of 500 metres, has yet to be drilled. Samples from each of the new discoveries, including surface grabs, have been submitted for indicator mineral and caustic fusion analysis, with results expected before year-end.
Geophysics
The results of 35,000 line km of helicopter-borne magnetic and electromagnetic surveys and 6,200 line km of airborne gravity surveys using BHP Billiton’s proprietary Falcon system will be interpreted over the course of the winter to identify targets for 2005. Next year’s program will begin with ground geophysics in March.
Stornoway also maintains a 50-50 joint venture relationship with BHP Billiton concerning a further 5.5 million acres (22,260 sq. km) of prospecting permits on the south-central portion of Melville Peninsula and a separate 1,531 sq. km package surrounding the Qilalugaq discoveries. This property package is held under the Alexis joint venture.
In addition, Stornoway holds a 30% interest in a further 1.5 million acres (6,070 sq. km) at Melville under two separate option agreements. The first agreement covers about 1 million acres in three properties: Gem, Fury and Sarcpa. These are being explored by Strongbow (formerly Navigator Exploration) and
Aviat discoveries.
The northernmost Fury property tacks on to the southern boundary of De Beers’ holdings on Baffin Island.
In 2003, a 14,500-line-km aeromagnetic survey was flown over the Fury permits and some 245 till samples were collected from the three property blocks. Five anomalous samples containing pyrope garnets were recovered from Fury, while a lone sample from Gem returned several mineral grains of probable kimberlite origin.
The two properties were targeted with a 2004 summer program of additional heavy mineral sampling and ground follow-up work over selected airborne targets.
The second option covers a further 1,880 sq. km in the west-central part of Melville, known as the Kingora property, which is being explored by Strongbow under a 60% earn-in agreement. Further till sampling was planned in 2004 as follow-up to an initial 42 samples collected during a reconnaissance program in 2003. BHP Billiton maintains a 10% carried interest covering the first $10 million spent under each option agreement.
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