The diamond hunt is exploding with new kimberlite discoveries beyond the Slave Craton in Canada’s Far North. Recent discoveries are reported near Rankin Inlet and on the Melville Peninsula in eastern Nunavut — frontier regions that have seen little in the way of diamond exploration.
The initial holes were drilled vertically, but as the program went on, Cumberland changed the orientation and angled the 100-metre-long holes to pass through the kimberlite into the host rock sediments. “We thought that would better represent the kimberlite facies,” says Kerry Curtis, Cumberland’s president and CEO.
Glen Dickson, a director of Cumberland, adds: “We felt we were testing these bodies better with angle holes. We were concerned we were running down one particular phase within the hypabyssal zone. It made more sense to cut across it.”
The bulk of the kimberlite core is tentatively interpreted to be macrocrystic hypabyssal facies, with local sections of heterolithic breccia composed of sediment host-rock fragments in a kimberlite matrix. These brecciated sections are interpreted as wallrock breccias. Indicator minerals are present in the core.
Based on the magnetic geophysics, the kimberlite discoveries look like pipes, says Dickson. “No question about it, but in fairness, we only have one hole in most of the targets; some have two. The shape of these things definitely has not been resolved. The size and dimensions remain to be flushed out.” Some of the holes ended in kimberlite and some didn’t, Dickson added.
Once the core has been logged, selected samples from each hole will be sent to the Saskatchewan Research Council for caustic fusion analysis. Curtis expects microdiamond results will be available in anywhere from 45 to 90 days.
Covering 371 sq. km and centred 20 km north of Rankin Inlet, the Meliadine East project is a 50-50 joint venture between Cumberland and Comaplex. Meliadine has been the focus of gold exploration since the fall of 1989, when Comaplex and Asamera Minerals jointly discovered promising gold values while prospecting over an area that was later named the Discovery zone. The pair had been drawn to the region by the results of a single hole drilled in the early 1970s by the Rankin Nickel Syndicate, which tested a coinciding magnetic and electromagnetic anomaly. That hole had intersected 3.43 grams gold per tonne across 2 metres in what was described as a sulphide-rich zone in a chloritic, magnetite-rich quartzite. The host rock turned out to be iron formation.
A large package of ground was staked in February 1990, covering an east-west structural trend extending from the western shores of Hudson Bay inland for 70 km.
Cumberland bought out Asamera’s interest in each of the Meliadine, Meadowbank and Parker Lake projects in mid-1993. The western half of the Meliadine property was subsequently optioned to Australia’s
In early 2001, WMC announced its intention to divest itself of its stake in Meliadine West following a corporate decision to get out of the gold business. WMC has since shopped the project around at a reported price tag of US$22 million.
Cumberland and Comaplex, each of which has a 22% interest, are carried all the way through to production on the project and hold a right of first refusal pertaining to the sale of WMC’s stake in Meliadine West.
The slowdown at Meliadine West gave Cumberland and Comaplex the opportunity to evaluate the potential of their adjoining, wholly-owned Meliadine East project, which covers the eastern, 35-km-long extension of the Meliadine gold trend. “It gave us a little more time to look at the big picture,” says Curtis. “Things were pretty fast and furious out there for quite a few years.”
Meliadine East hosts several gold showings, including the Discovery zone, which contains an indicated resource of 1.8 million tonnes grading 6.72 grams, or 398,000 oz.
WMC handed over magnetic data from a regional airborne survey flown over the Meliadine properties, including the eastern extension, in 2001. “When I reviewed those data, there were just too many of these discrete targets not to follow up,” says Dickson. “It wasn’t as if there was just one or two; there appeared to be a whole cluster.”
Earlier exploration drilling (for gold targets) on Meliadine East had intersected several narrow kimberlite dykes and one ultrapotassic dyke. The dykes were encountered at depths ranging from 19 to 121 metres and up to 1.9 metres in width.
The 192-million-year-old kimberlite dykes were the focus of an academic thesis by Michael Seller, but according to Dickson, the dykes were never tested for microdiamonds. “They certainly weren’t our focus, by any means.”
Parker Lake
Cumberland and Comaplex originally held an interest in the Parker Lake property, centred 120 km northwest of Rankin Inlet, about halfway to Baker Lake. In the summer of 1993, regional mapping by the Geological Survey of Canada (GSC) uncovered at least two highly diamondiferous alkaline lamprophyre dykes at Parker Lake. An initial, 22-kg surface sample from the Akluilak (or Thirsty Lake) prospect yielded 1,513 microdiamonds, including two stones exceeding 0.5 mm in one dimension. A 32.8-kg check sample confirmed the find, returning a total of 1,163 stones, including six larger stones greater than 0.5 mm in one direction.
The Akluilak dyke is quite narrow, ranging from 0.3 to 1.50 metres wide, and is described as an ultrapotassic lamprophyre, or minette. The dyke is Proterozoic in age, and, at 1.84 billion years old, is kin to the Christopher Island volcanics, a huge suite of ultrapotassic rocks.
With Cumberland’s permission, De Beers processed a 7.8-kg sample from the dyke in 1995 and retrieved 6,680 microdiamonds, including 3,972 microcrystals under 0.074 mm in size. Three stones measured more than 0.5 mm in one dimension. The results prompted De Beers to take a much larger, 1-tonne sample to check for commercial-size stones.
The dyke is unusual, considering the large amount of diamond microcrystals. As well, is it said to be the only known occurrence of minette containing the diamond indicator minerals Cr-pyrope, Cr-diopside, picroilmenite and magnesium olivine.
The Akluilak dyke was considered uneconomic because of its limited size potential and the poor quality of its diamonds. Dickson says a lot of the diamonds had a poor shape; they had been re-absorbed and burnt. In addition, the diamond size distribution curve falls off sharply, casting doubt on the potential for recovering larger stones.
In 1996, Cumberland identified several other similar diamond-bearing dykes and conducted extensive heavy-mineral sampling across the Parker Lake property, recovering more than 460 samples. “We just didn’t find enough to continue to pursue it,” says Dickson.
In 2002, the exploration focus at Meliadine East shifted to diamonds from gold. Limited till sampling was conducted in the early summer down-ice of the circular geophysical features. Cu
mberland and Comaplex were highly encouraged by the results, with 64 of the 82 till samples collected returning kimberlite indicator minerals, and 19 samples having multiple grains. The latter samples contained 155 of the 234 indicator mineral grains recovered, including various combinations of olivine, ilmenite, garnet and chromite.
In total, eight pyrope garnets were found in seven samples, two of which had significant diamond-associated G10 subcalcic compositions. Eleven of the 18 recovered chromite grains were classified as kimberlitic, with one grain bearing diamond-inclusion-type chemistry.
Cumberland re-flew the area in the fall of 2002 with a 4,000-line-km airborne survey, confirming the mag signatures of more than 25 obvious circular features. “I am convinced we are in a kimberlite field out in that area,” says Dickson, understandably optimistic after hitting kimberlite on 11 of the 12 targets drill-tested.
Churchill
Shear operates, and has a 51% interest in, the 4,164-sq.-km project, which extends more than 100 km inland from the western shores of Hudson Bay. The Churchill project covers some promising kimberlite indicator mineral chemistry and hundreds of geophysical anomalies. Under a deal struck with the privately held Hunter Exploration Group in mid-2002, Northern Empire is earning a 35% interest in the project by spending $750,000 on exploration.
Prior to the start of drilling, Hunter Exploration sold its remaining 14% stake in Churchill to
The Churchill drilling is so far enjoying an envious success ratio. Kimberlite has been intersected in each of the first three targets drilled. The first hole tested the centre of a circular magnetic low anomaly and intercepted kimberlite at a depth of 11 metres. The vertically drilled hole intersected more than 90 metres of kimberlite before shutting down while still in kimberlite at a depth of around 100 metres.
Drill core from the new discovery, called Qaumallak, is described as macrocrystic kimberlite and breccia, with visible olivine macrocrysts and picroilmenite. The second kimberlite body, known as Kalluk-1, was discovered 6 km north of the first, while drilling a circular magnetic low measuring 150 by 150 metres. The third kimberlite, Kalluk-2, was drilled 4 km east of Qaumallak. The target was a circular magnetic high measuring 225 by 300 metres. Drilling continues.
Shear and Hunter Exploration Group established the Churchill joint venture in June 2001 as a conceptual play. The pair felt the area justified further investigation for diamonds, given its cratonic setting, favourable regional structure, and the known presence of kimberlite dykes.
Results from sampling in the summer of 2001, performed under the supervision of Edmonton-based APEX Geoscience, showed that kimberlite indicator minerals were widely dispersed over the region. This led the partners to acquire more than 2,185 sq. km of contiguous mineral claims and exploration permits. Of the 48 regional till samples collected, 26 confirmed kimberlite indicator mineral grains were recovered by the Saskatchewan Research Council from 19 samples.
G10 garnets
Microprobe work by R.L. Barnett Geological Consulting confirmed the recovery of six sub-calcic G10 garnets bearing promising diamond inclusion chemistry, as well as eight G9 garnets, one eclogitic garnet, six chrome diopside grains (five believed to be mantle-derived and/or sourced from kimberlite) and five olivine grains.
During the summer of 2002, a high-resolution airborne magnetic survey totalling 16,307 line km was flown over the area, revealing 226 anomalies of interest. An additional 135 regional till samples collected returned 120 microprobe-confirmed indicator mineral grains (in 30 samples). One sample contained 45 pyrope garnets and two eclogitic garnets. In addition, two separate occurrences of kimberlite float were discovered.
Of the 107 total pyrope garnets identified in 29 samples, 46% are G10 sub-calcic pyropes with favourable diamond inclusion chemistry. “The sampling has yielded a regional composite plot with excellent G10 chemistry, and that tells us there’s a field of kimberlites present that includes kimberlites with high diamond potential,” says John Kaiser, publisher of the Bottom-Fishing Report newsletter.
Based on results of the 2002 field program, the joint venture more than doubled its land position at Churchill. This spring, ground magnetics and horizontal-loop electromagnetics were conducted over 31 airborne anomalies, further defining 23 drill targets. Crews have been re-mobilized to resume ground geophysical surveys, the objective being to upgrade additional aeromagnetic targets.
An adjoining, 1,550-sq.-km package of ground was recently optioned to
Melville Peninsula
The Rankin Inlet play is stealing some of the limelight from the Aviat play on Melville Peninsula, where Northern Empire and
The Aviat holdings cover much of the northern part of the Melville Peninsula, some 750 km northeast of Rankin Inlet, and include newly acquired ground across the Foxe Basin on Baffin Island. The Baffin Island claims adjoin the southern boundary of a large, 28,000-sq.-km property package acquired by
The northern boundary of De Beers’ holdings is about 400 km southeast of
The Cargo 1 pipe was further tested with three delineation holes. Caustic fusion analysis on 1,018 kg of kimberlite material returned 241 microdiamonds, including one diamond (2.14 by 1.68 by 1.14 mm) captured on a 1.18-mm square mesh screen and one stone (2.34 by 2.25 by 1.65 mm) exceeding 1.7-mm square mesh.
Hunter Exploration established the Aviat joint venture in early 2002 by optioning a 35% interest each to Northern Empire and Stornoway. The area had been a work in progress for the Hunter Group for several years. Regional till sampling had shown favourable kimberlite indicator mineral chemistry, including the recovery of G10s.
While conducting regional sampling on behalf of the joint venture last summer, personnel for APEX Geoscience discovered the outcropping AV-1 kimberlite at the edge of a small lake. AV-1 is exposed over an area measuring 76 by 13 metres. An initial, 186-kg composite surface sample of AV-1 returned 228 microdiamonds, including five stones larger than a 0.85-mm square mesh screen size and two stones exce
eding 1.18 mm. Based on a petrographic analysis of the indicator minerals, the AV-1 kimberlite holds moderate-to-high diamond potential and is dominated by an impressive eclogitic garnet population. “The microdiamond size distribution curve suggests a grade in the range of 0.5 to 1 carat per tonne,” predicts Kaiser.
Double-edged
Ground geophysics completed over the discovery area in early March 2003 show a prominent, double-lobed magnetic anomaly at least 135 metres long and about 35 metres wide. A further 760.2 kg of composite sample material taken in March returned 1,145 microdiamonds, including eight stones exceeding a 1.18-mm square mesh screen size and one stone larger than 1.7 mm square mesh. The four largest stones measure 2.42 by 2.22 by 2.1 mm, 2.12 by 1.78 by 1.5 mm, 2.06 by 1.9 by 1.3 mm, and 2.08 by 1.42 by 0.7 mm. Caustic fusion results have yet to be received from 200 kg of material.
In addition to the AV-1 discovery, a field of diamond-bearing, angular kimberlite boulders, up to half a metre in size, was found 2 km southwest of the AV-1 outcrop. A 46-kg sample yielded 92 micros, none of which exceed a 0.6-mm square mesh screen classification. The kimberlite boulders are believed to be from a source other than AV-1, based on the direction of ice movement.
BHP Billiton, which has a large property block at the southern end of the Melville Peninsula, has purchased a 20% participating stake in the Aviat project from Hunter Exploration for $7.1 million cash. The Hunter Group retains a 10% carried interest.
Under terms of the sale, Northern Empire and Stornoway will have earned their collective 70% interest in the Aviat project, and BHP Billiton will pay all of the costs associated with taking the first 200 tonnes of bulk sample from the project area.
In the meantime, Northern Empire and Stornoway have agreed to merge and thereby consolidate their respective 35% interests in the Aviat joint venture. Stornoway shareholders will receive 0.8734 of a Northern Empire share for each share held.
Twin also carried out regional till sampling, collecting 489 samples from the main claim block and doubling its land position to 2,135 sq. km.
Since the formation of the Aviat joint venture, the project has received only a preliminary geological assessment, and has been covered with less than 300 regional till samples. Anomalous indicator mineral samples have been returned throughout the project area, including two samples that contained kimberlite fragments.
The 2003 program, budgeted at $4.5-5 million, is already under way. An airborne magnetic survey over the Aviat North property will be followed by a follow-up program of prospecting, mapping, ground geophysics, till sampling and drilling.
The Aviat joint venture has farmed-out some of its non-core holdings on Melville Peninsula and Baffin Island.
In February, Art Ettlinger’s
Dunsmuir applied for the prospecting permits based on the results of a 2002 program of till sampling conducted as follow-up work to previous sampling by BHP Billiton in 2000 and 2001. BHP Billiton identified widely distributed kimberlite indicator minerals from about 50 or 60 samples taken. “When they showed us the data, there were three anomalous areas,” says Ettlinger, Dunsmuir’s president. “We focused on an area containing a handful of pyropes, which we viewed as significant.” Ettlinger notes that this area is ideal for sampling because the till cover is relatively thin and the glacial ice history is simple.
Dunsmuir collected 180 additional till samples and outlined a well-defined anomalous corridor of pyrope indicator minerals extending over a distance of 34 km and up to 6 km in width. The distribution and number of indicator mineral grains suggest that more than one kimberlite source may be present in the area. The corridor consists of predominantly G9 pyrope garnets and a good collection of eclogitic garnets that are in the diamond stability field, as well as diamond inclusion chromites and some chrome diopsides.
Near the head of the train, kimberlite is attached to one of the pyrope grains, and several garnet grains exhibit kelyphitic rims, indicating a nearby source.
Dunsmuir is preparing to return to the field in early July and double the amount of sampling, targeting both the head of the train and, internally, where indicator mineral counts pick up. In addition, the company will follow-up on two other anomalous areas. Approximately 15 km to the southwest of the Nanuq corridor, a second indicator mineral train may be emerging. A third anomalous area lies 40 km to the south. These newly identified areas also contain suites of indicator minerals, including chromites and eclogitic garnets, as well as G9 and G10 pyropes. Airborne geophysical work is planned for later in the summer.
Under the terms of the agreement, Dunsmuir is required to spend $1 million each year exploring the specific areas it chooses from BHP Billiton’s database. Should Dunsmuir make a kimberlite discovery and advance it to the point of a 25-tonne bulk sample, BHP will have the right to back-in for a 60% interest by reimbursing Dunsmuir for 300% of its project expenditures to that point. If BHP elects to fund the project through to production, it can earn a further 10%.
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