A small surface sample of kimberlite float and outcrop collected by
The 1,157-kg Artemisia sample returned only 0.2 carat of diamonds greater than a bottom-size 0.8-mm square mesh screen cutoff, for an implied grade of just 0.17 carat per tonne. By comparison, the commercial grades of the six Ekati mine pipes range from 0.3 to 3.5 carats per tonne and average 1 carat, while the four Diavik pipes range from a low of 3 carats to a high of 5.2 carats per tonne.
The largest diamond recovered was a colourless octahedral aggregate measuring 2.25 by 1.75 by 1.35 mm. The next two largest stones were whole colourless crystals that measured 2.05 by 1.93 by 1 mm and 2.05 by 1.38 by 1.2 mm.
The 1,157-kg surface sample of Artemisia was collected from three separate sites within the 150-by-140-metre interpreted body. The sample was taken from surface exposures of kimberlite talus and outcrop, and may not be representative of the entire pipe. The limited size of the sample renders it too small to be considered significant at this early stage.
Ashton plans to take a larger, more representative, 5-to-10-tonne sample by core drilling. The Artemisia kimberlite was discovered during last fall’s drilling on the Kim property, 50 km south of Coronation Gulf. Kim is one of four properties held under the Slave regional joint venture between Ashton and
The north Slave Craton region of Nunavut lies 450 km north of Yellowknife and is centred 75 km south of Coronation Gulf and 100-120 km southeast of Kugluktuk (formerly known as Coppermine). The area was originally staked for diamonds sometime between 1992 and 1993, but as new kimberlite camps emerged farther south at Lac de Gras, Kennady Lake, Snap Lake and Jericho, diamond exploration shifted to the south.
“We thought the area still had quite a bit of potential for some economic discoveries,” Ashton’s project manager, Jeff Ward, told delegates attending the recent Cordilleran Exploration Roundup in Vancouver.
In 1997, as land began to lapse, Ashton staked the 970-sq.-km Ric property; it then staked the Kim property, farther to the north; and last year, the joint venture added the Vic and Eokuk properties. Separately, Ashton acquired an option to earn up to a 59.5% interest in the Kikerk Lake project held by
Prior to November 2001, there were only three or four operators of diamond projects in the north Slave Craton. However, the new diamond-bearing Artemisia and Potentilla kimberlite discoveries by Ashton, along with Kennecott Canada Exploration’s promising Anuri diamondiferous kimberlite find, have sparked a staking rush in the north Slave Craton that result in the acquisition of as much as 40,000 sq. km. Upwards of 30 juniors now hold interests in claim blocks blanketing the newly dubbed, ever-expanding Coronation Gulf district. The buzz at the Cordilleran Roundup and preceding Cambridge Investment show was that brokered financing is available for any company holding diamond properties.
Prior to 2000, only four kimberlite bodies had been found in the north Slave Craton, including: two discovered by
In 2000 and 2001, nine more kimberlite bodies were found in the region, including three by Ashton. All nine are diamond-bearing, and some contain significant early-stage microdiamond counts.
Ashton’s three most recent kimberlite finds — Artemisia, Potentilla and the Perseus sill-like body — are all land-based and were found either in outcrop or kimberlite float. At each of these discoveries, diamonds were recovered from overlying till samples.
The Perseus kimberlite was discovered in 2000 following several years of reconnaissance exploration that identified a broad indicator train in the northwestern corner of the Ric property. Detailed follow-up sampling at the head of this train recovered diamonds in till at two sites. Kimberlite float was mapped over a strike length of 1.4 km. Boulders of kimberlite, mostly cobble-size but ranging as large as 1 metre in diameter, were found 500 metres down-ice of Perseus. Ground geophysics generated a linear magnetic feature that corresponded to the cutoff of the both the indicator mineral train and the kimberlite float.
Subsequent drilling in 2000 and 2001 intercepted a 10-metre-thick, shallow-dipping kimberlite body at four separate sites along a 470-metre strike length. In total, 87 microdiamonds were recovered from 318 kg of tested core samples. No macros exceeding 0.5 mm in at least one dimension were recovered. “Although these results aren’t stellar, they gave us an early indication of the potential of kimberlites in the area to host diamonds,” says Ward.
In late 2000, Ashton entered into a joint-venture arrangement with Caledonia on the Kikerk Lake property, 35 km north of Ric. Ashton is earning an initial 52.5% interest by spending $750,000 on exploration. By funding Caledonia’s share of expenditures on the 154-sq.-km property through completion of a bankable feasibility study, Ashton can boost its interest to 59.5%, thereby diluting Caledonia to a 10.5% stake. Northern Empire can maintain its 30% interest by contributing its share of exploration costs.
Ashton immediately carried out heavy mineral sampling to delineate further a previously defined anomalous area of kimberlite indicator minerals. The work confirmed the target areas at the head of the mineral trains, with the recovery of kimberlite float at the head of the westernmost train. A diamond shard, measuring 1.37 by 0.99 by 0.87 mm, was found in a till sample taken near the head of the dispersion train associated with the Potentilla discovery.
Ground geophysics at the head of the indicator trains identified four isolated magnetic high targets and one linear magnetic feature. In the fall of 2001, Ashton drill-tested two of the anomalies, intersecting the Potentilla kimberlite with the first hole into an isolated, strong magnetic high on the westernmost train. A vertical hole drilled in the centre of the anomaly intersected kimberlite breccia diatreme beneath 10 metres of overburden to a depth of 142.3 metres, before passing into a hypabyssal phase. The hole was shut down while still in hypabyssal kimberlite at a depth of 184.7 metres.
A second hole collared from the same site at an angle of 53 to the south intersected kimberlite breccia from 9.7 to 98.4 metres down-hole, followed by 8.6 metres of hypabyssal kimberlite before passing into sedimentary rock. Potentilla has yielded 230 micros and 22 macros from a 207.8-kg aggregate drill sample of the two distinct facies. Samples of the diatreme phase weighing 129.1 kg returned 160 micros and 15 macros. Seven of the macros exceeded 0.5 mm in two dimensions, with the largest stone measuring 2.13 by 1.94 by 0.87 mm. The deeper hypabyssal phase returned 70 micros and seven macros from 78.7 kg of core. Three of the macros were greater than 0.5 mm in two dimensions, with the biggest stone measuring 0.8 by 0.52 by 0.39 mm.
Magnetic signature
The magnetic signature of Potentilla measures about 140 by 60 metres; however, a subtle magnetic halo extends north of the magnetic high. Wards says the subtle magnetic feature corresponds well with a topographic depression that is surrounded by sedimentary outcrop, and may well represent the less magnetic diatreme phase encountered in the upper levels of the dr
ill holes. “It’s possible that Potentilla is much larger than we initially thought,” says Ward.
Two additional holes tested the linear feature and intersected narrow kimberlite stringers and breccia zones.
As Ashton was evaluating the Kikerk Lake property, it was also focused on an area central to the Kim property, 10 km west of the Potentilla discovery. “Heavy mineral sampling got us into an area that clearly warranted further follow-up,” Ward says. Sampling and prospecting within an indicator mineral train identified two separate locations where diamonds in till corresponded with kimberlite float. The outcropping Artemisia kimberlite was subsequently discovered at the head of the southernmost train.
Artemisia occurs in outcrop or as talus and in situ boulders, and the kimberlite has been mapped over an area of 150 by 140 metres. The body appears to be open to the north and to the west, where it plunges into a valley.
Last fall, Ashton drilled one vertical hole into the centre of this occurrence and intersected homogeneous diatreme facies kimberlite down to a depth of 169 metres, before shutting down in kimberlite. In total, 812 micros and 86 macros were recovered from 246 kg of drill core. Sixteen of the macros are greater than 0.5 mm in two dimensions. The largest recovered stone measured 1.23 by 1.15 by 1.1 mm.
In addition, 85.5 kg of surface samples, which were collected from the same sites as the larger 1.2-tonne sample, returned 309 micros and 34 macros. Twelve of the macros exceeded 0.5 mm in two dimensions.
Ashton is gearing up to fly airborne geophysical surveys over almost all of its north Slave Craton properties, which will be quickly followed by ground geophysics in preparation for possible drilling in the spring. There are 10 unexplained kimberlite indicator mineral trains on all of Ashton’s north Slave Craton properties. By mid-March, Ashton hopes to be taking 5-to-10-tonne mini-bulk samples of both the Artemisia and Potentilla kimberlites.
“The recent success by Ashton and its competitors in the north Slave, combined with the aggressive exploration programs planned by numerous companies in 2002, certainly makes the Coronation diamond district one of the most exciting exploration plays in Canada today,” says Ward.
A further 80 km to the south,
Anuri
The Anuri kimberlite was discovered in July 2001 at the head of a prominent, 15-km-long indicator mineral dispersion train dominated by abundant chrome diopside and pyrope garnets. Anuri was found under the northern bay of Napaktulik Lake, 50 metres from shore. The mineral train emanating from Anuri was defined by heavy mineral sampling conducted between 1995 and 2000.
The geophysical anomaly over Anuri is subtle. Kennecott used a combination of magnetic, electromagnetic (EM) and gravity surveys to define targets in the area. A 0.3-mgal gravity low and a weak airborne EM anomaly coincide with a break in a diabase dyke. Based on geophysics, Anuri is estimated to measure 140 by 125 metres.
Angled at 45, the discovery hole into Anuri intersected kimberlite over an estimated true width of 134 metres. A second core hole drilled at an approximate right angle to the first intersected an estimated true width of 90 metres at 150 metres of depth.
In total, 600 micros and 337 macros were recovered from 656 kg of processed kimberlite core. Sixty-one of the macros are larger than 0.5 mm in two dimensions, and nine of the stones exceed 1 mm in two dimensions. The largest diamond recovered weighed three-quarters of a carat.
The Anuri kimberlite consists of a green-grey, matrix-supported micro-breccia containing abundant country rock xenoliths, diamond indicator minerals and mantle nodules. The matrix is predominantly fine-grained serpentine country rock, with xenocrysts. Indicator minerals observed in the core include pyrope garnet, eclogitic garnet, chrome diopside, ilmenite and olivine, with clinopyroxene and olivine dominating.
The kimberlite has intruded Archean granitic basement that, at present, is overlain by a thin, 20-metre thrust sheet of Proterozoic shale. Xenolith fragments in the kimberlite are dominated by the shale but also include chert and granite.
The Anuri discovery prompted Kennecott to stake more ground in the area and conduct follow-up exploration within a 20-sq.-km radius around Anuri. Kennecott followed with the discovery of a second kimberlite body, immediately east of Anuri. Drilled from the shore at 45, the discovery hole intercepted 36 metres of kimberlite at a down-hole depth of 294-330 metres. Microdiamond analysis on 129.4 kg of core from Anuri East yielded 75 micros and 34 macros, including five diamonds greater than 0.5 mm in two dimensions and a single stone exceeding 1 mm square mesh.
The width of the mineral train coming off the Anuri kimberlite is quite extensive, approaching 2 km. Tahera director Hugo Dummett told delegates at the Cordilleran Roundup that he suspects they will find at least another two or three kimberlites at the head of the large dispersion fan.
A third kimberlite, known as Qamutiik, was found 9 km northwest of the Anuri kimberlites. The land-based kimberlite was tested by two holes. Microdiamond counts have not been reported for this find.
Exploration drilling at Rockinghorse is expected to resume this month. The program, budgeted at $1.5 million, will further evaluate the potential of the Anuri kimberlites, along with 25 other targets.
Jericho
Kennecott is concurrently evaluating Tahera’s Jericho project, 120 km southeast of Rockinghorse. The major has until September to decide whether to incorporate the project into the existing joint venture between Tahera and itself. Kennecott would then have 24 months to commit to a mine plan. During the initial 12-month option term, Kennecott must spend at least $1 million to drill a minimum of 20 kimberlite targets on the Jericho claims.
Comprising 2,500 sq. km, the Jericho project lies 26 km north of the Lupin gold mine and 430 km northeast of Yellowknife. Five kimberlites have been found on the Jericho properties, including the Jericho (JD/OD-1), JD/OD-3, Contwoyto-1 and JD/OD-2 pipes, along with a new kimberlite discovered in April 2001.
The focus of the Jericho project has been the land-based Jericho pipe, lying 400 metres south of Carat Lake. Discovered in 1995, it contains a total resource of 7.1 million tonnes grading 0.84 carat per tonne, equivalent to 5.9 million carats. A June 2000 feasibility study by SRK Consulting concluded that a combined open-pit and underground mining operation on the Jericho pipe could produce an estimated 3 million carats over a mine life of eight years based on a probable minable reserve of 2.5 million tonnes grading 1.19 carats per tonne.
Jericho is a multi-phase pipe that is dominated by the eclogitic assemblage. A re-evaluation of the diamonds by WWW International Diamond Consultants in early 2000 indicated a value range of US$75-88 per carat.
During a reconnaissance field program carried out in the fall of last year, Kennecott uncovered diamond-bearing kimberlite float at the end of a mineral train terminating 900 metres west of the Jericho pipe. A 7-kg sample yielded one micro and six macros.
A further 8 km south of the Jericho, Kennecott has identified several gravity lows at the heads of several unresolved mineral trains.
“If another pipe like Jericho can be discovered, then we’ve got something very exciting,” says Tahera President Joseph Gutnick.
Farther to the south, BHP Diamonds, a wholly owned division
BHP can earn a 55% interest in any of the four known kimberlites, including the Ranch Lake pipe, by taking a 200-tonne bulk sample before July 2003 and completing a feasibility study.
Separately, BHP will have the right to earn an initial 51% interest in any new discoveries on the surrounding 2,000-sq.-km ICE claims by completing a 200-tonne bulk sample. BHP can boost its interest to 65% by funding a feasibility study, and should BHP elect to arrange project financing for Tahera, BHP will acquire a further 5%.
The Ranch Lake kimberlite was discovered in 1993. With an estimated resource of 40 million tonnes, the pipe has never been systematically tested. Initial drilling returned 38 micros and six macros from 208.1 kg of sample. A 28.45-tonne mini-bulk drill sample in 1994 yielded 112 diamonds weighing 5.38 carats, for an implied grade of just 0.189 carat per tonne. The pipe exhibits three main geological units, with apparent distinct diamond grades and stone frequency distribution.
BHP is processing 525 till samples collected last fall from the ICE claims, and results are expected sometime in April.
Elsewhere in the Coronation Gulf district,
Knife Lake
The Canadian exploration division of De Beers discovered the multi-phase pipe in 2000. Delineation drilling has confirmed the pipe’s dimensions as being 390 by 230 metres. De Beers is earning a 70% interest in the 10-sq.-km Knife Lake property, 80 km south of Coronation Gulf.
Rhonda also holds a 100% interest in 325 sq. km of adjoining ground, which it has held for many years and which it previously explored for base metals. Results are awaited from more than 500 till samples taken this past summer.
Joining the staking frenzy that engulfed the Coronation district toward the end of last year were several hardened diamond explorers, including Randy Turner’s
The Northair Group’s Northern Empire Minerals and
Stornoway is a sister company to Northern Empire and led by Bruce McLeod. The company has transformed itself into a diamond exploration vehicle, with exposure to 1,922 sq. km in the Coronation district. Stornoway has added Eira Thomas to its board and appointed Robin Hopkins as chief technical officer. Exploration plans include airborne geophysics, followed by till sampling and prospecting. Stornoway has announced a $2-million financing through the sale of flow-through and non-flow-through units priced at 70 apiece.
Other juniors with various levels of participation in the North Slave include:
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