A test sample of 9.1 tonnes of kimberlite collected from follow-up core drilling on one of the kimberlite discoveries delivered a 2.36-carat parcel of stones consisting of 70 diamonds with a cutoff exceeding 0.85 mm square mesh. The implied grade is 0.26 carat per tonne.
In the spring, BHP will carry out additional bulk sampling on this pipe and on several nearby pipes, as well as test and evaluate other targets on the property.
The Qilalugaq property is at the southern end of Melville Peninsula and covers about 1.1 million acres (4,450 sq. km). BHP Billiton has carried out till sampling and airborne geophysical surveys, including its proprietary FALCON system, since it began exploring the area in 2000.
Diamond exploration in eastern Nunavut has heated up, fuelled by the highly prospective discoveries of
Stornoway is exploring close to 12 million acres (48,600 sq. km) on the Melville Peninsula through several separate joint ventures. At 5.5 million acres (22,260 sq. km), the Aviat joint venture covers the bulk of the landholdings and includes the AV-1 kimberlite pipe and the newly discovered AV-2, a dyke-like kimberlite body. Stornoway holds a 70% interest in Aviat, whereas BHP Billiton owns 20%, and the privately led Hunter Group, 10% (carried).
In early February, Stornoway was granted 5.5 million acres of permits immediately south of Aviat plus another 378,336 acres of claims comprising the Alexis property beside BHP Billiton’s Qilalugaq property.
Stornoway and BHP Billiton have entered into a 50:50 agreement to jointly explore these latest permits and claims.
As well, Stornoway acquired permits totaling 284,547 acres on Prince of Wales Island, immediately west of the Melville Peninsula. The ground will be explored under an equal joint-venture agreement between Stornoway, BHP Billiton and
The Melville Peninsula is in the High Arctic region of eastern Nunavut, about 2,800 km due north of Toronto. In spite of its remote location, tide water access allows for fuel and exploration supplies to be shipped to the project.
Stornoway initially acquired an interest in two property packages totalling 1.3 million acres (5,260 sq. km) on the Melville Peninsula in early 2002, based on positive kimberlite indicator mineral results from regional sampling by the Hunter Group in 2001. (BHP Billiton purchased a 20% working interest in the Aviat project from the Hunter Group in June 2003 for $7.1 million.) Soon afterwards,
Both De Beers and BHP Billiton were rumoured to have discovered kimberlite float on each of their prospective property packages, says Dean Besserer of Edmonton-based APEX Geoscience in a technical report. APEX managed the 2002 and 2003 Aviat exploration programs on behalf of Stornoway.
“Suddenly an area we knew little about was being investigated by two of the world’s largest diamond explorers, and by ourselves,” Stornoway President Eira Thomas told delegates at the Mineral Exploration Roundup conference, held recently in Vancouver.
Stornoway went in with a modest program in 2002, expanding on previous sampling work with additional regional till sampling and prospecting. Of the 491 samples collected in and around the Aviat properties during the summer of 2002, 65 were anomalous in diamond indicator minerals. Regional samples were taken every 1-5 km along 7.5-to-15-km spaced lines. Infill sampling using 1.5-km spaced lines was done in several areas of specific interest. The overall sample density was about 1 sample for every 50 sq. km.
“Based on the results of that work, we were finding there was evidence of two kimberlite clusters emerging — one in the north and one in the south,” says Thomas. Kimberlite fragments were found in two of the samples. Literally on the last day of the 2002 summer field program, geologists discovered the outcropping AV-1 kimberlite.
“It’s an incredibly fortunate discovery,” added Thomas.
Northern block
The field crew had originally been on their way to Baffin Island to collect the last of the regional samples, but bad weather turned them away. Instead, they decided to focus on the centre of the northern block and take a few more samples. While flying over the property, the geologists touched down to investigate an “unusual greenish weathered outcrop,” which turned out to be nothing more than chloritized granite. It was on their way back to the helicopter that they stumbled across boulders of kimberlite in a creek. The boulders were traced more than 2 km away to the AV-1 source, an exposed kimberlite showing at the edge of a small shallow lake. The AV-1 discovery outcrops over an area measuring 76 by 13 metres.
Stornoway sat on the news of the discovery until February 2003 in order to tie up an additional 6 million acres (24,280 sq. km) of mineral claims and prospecting permits. Some 1,136 kg of kimberlite were 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, giving a microdiamond count of 1.42 stones per kg. Based on the microdiamond results, the diamond distribution curve suggests good potential for large, commercial-size stones.
The AV-1 showing was tested last summer with seven angle holes drilled from four setups. Based on the drilling, the kimberlite body is believed to be at least 160 metres long and 40-60 metres wide. It remains open to the east and to depth.
AV-1 is a macrocrystic, type-1 hypabyssal kimberlite about 530 million years old. Hypabyssal kimberlite was intercepted in all holes except one and shows good correlation with the double-lobed magnetic high anomaly identified from ground geophysics. In addition to the hypabyssal kimberlite, a second, non-magnetic, brecciated macrocrystic kimberlite phase was encountered in five of the holes. The breccia is a true tufficitic kimberlite breccia, which is typical of the kimberlites found in South Africa . . . but not so typical of the kimberlite in the Lac de Gras region or the Slave Province.
“We believe that this body is a kimberlite pipe . . . and that we are looking at lower diatreme hypabyssal transition,” said Thomas.
Caustic fusion analysis on 531.7 kg of core samples recovered 737 microdiamonds. The three largest stones 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 breccia phase. The hypabyssal and breccia phases of AV-1 have returned comparable diamond counts: 1.44 diamonds per kg and 1.32 diamonds per kg, respectively. However, judging from these initial results, the breccia has a coarser diamond distribution.
“We are recovering large stones from relatively small samples,” stressed Thomas.
Nickel thermometry work on the pyrope garnet chemistry has identified three basic populations. “Groups A and B are not particularly interesting in terms of the diamond potential, but the third group did identify a high-temperature phase, suggesting deep lithosphere sampling,” said Thomas. “The more exciting story is told by the eclogitic garnets. A high proportion of the eclogitic garnets have a strong diamond signature.”
This past summer, a representative mini-bulk sample of 7-8 tonnes was collected from the grided surface exposure of AV-1. This sample will be processed for larger-size diamonds over the next 8-10 weeks.
A second outcropping kimberlite body, AV-2, was discovered during the summer of 2003, about 4 km east-southeast of AV-1. The dyke-like body was tested by a single inclined hole that intersected 2.6 metres of kimberlite beneath the surface exposure, followed by two other separate kimberlite sections of 9.3 metres and 3.1 metres. A second hole tested a magnetic anomaly 75 metres southwest of the AV-2 showing and encountered 2.2-metre-long and 6.5-metre-long sections of kimberlite.
A combined 39.4-kg sample of AV-2, including both breccia and hypabyssal phase kimberlite, delivered 30 microdiamonds. The largest stone was a lone diamond caught on a +0.6-mm square mesh screen.
“We didn’t have a lot of data going into the 2003 program to generate drill targets,” said Thomas, who added that “the main thrust of our drilling campaign at Aviat will actually happen in 2004.”
In 2003, the joint venture spent $5 million exploring Aviat in an aggressive program that included the collection of 2,300 till samples, 56,900 line km of airborne geophysical surveys, and 1,102 metres of core drilling. The joint venture covered about one-third of the project area with magnetic surveys. The line spacing varies between 50 and 200 metre throughout the landholdings. Several airborne magnetic anomalies have been identified for follow-up in 2004, though Thomas notes the area is complex and that AV-1 itself does not show up well on the airborne survey.
Results from the first of the priority till samples, now being processed, are expected by March. The till sampling at the end of 2002 identified a dense anomalous cluster in and around AV-1, including several unsourced up-ice anomalies, as well as “numerous” other anomalies scattered throughout the north holdings. Thomas is highly encouraged by the pyrope plot of target 446-447, which exhibits different chemistry from that of AV-1, suggesting evidence of multiple kimberlite intrusions in this new field.
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