Kelvin yields significant diamond count

Originally discovered in the spring of 2000, about 9 km northeast of the Kennady Lake cluster in the Northwest Territories, the Kelvin kimberlite body was ignored until this year when De Beers Canada Exploration finally processed 184 kg of sample. The results indicate it is significantly diamondiferous, rivaling microdiamond counts from the promising 5034 and Hearne pipes at Gahcho Kue.

In total, 421 microdiamonds and 25 macros were recovered from 184 kg of sample collected from the two original discovery holes, including nine larger stones caught between a 1- and 2-mm square mesh size and five diamonds exceeding a 2-mm square mesh classification. (A macrodiamond is defined here as exceeding 0.5 by 0.5 mm in sieve size.)

The number of diamonds recovered and their size-frequency distribution are comparable to those of the 5034 and Hearne, two of the better pipes occurring in a cluster of five pipes in the Kennady Lake area of the Gahcho Kue joint-venture project. The grades of 5034 and Hearne were modeled by De Beers at 1.64 and 1.71 carats per tonne, respectively.

The project is owned 51% by De Beers, 44.1% by Mountain Province Diamonds (MPV-T) and 4.9% by Camphor Ventures (CFV-V). De Beers can boost its interest to 60% by advancing the project to commercial production, leaving Mountain Province with a 36% stake and Camphor with 4%.

In the spring of 2000, De Beers carried out exploration drilling at Gahcho Kue, testing 19 lake-covered geophysical targets, including Kelvin. Two holes returned kimberlite intervals of 40 and 23 metres (estimated true width) from Kelvin, while a third missed. Although actual dimensions remain unclear, a 3.3-metre-wide kimberlite dyke was discovered at a depth of 31 metres, about 200 metres south of the Kelvin body under the same narrow lake. Microdiamond results for the 3.3-metre intercept have never been reported. It has been suggested that the Kelvin body is possibly some sort of blowout occurring along an interpreted dyke system.

Kelvin is 3 km south-southwest of the Faraday kimberlite body, discovered in the spring of 1999. An angled hole intersected 34 metres of kimberlite from a down-hole depth of 38-72 metres, for a true width of 22 metres. A 40-kg sample from the Faraday discovery hole returned a previously reported 68 micros and six macros, including a single stone exceeding a 2-mm square mesh size.

Follow-up drilling in 1999 intersected 21 metres (or 15 metres true width) at a distance of 40 metres from the discovery hole. Another hole intercepted 2.54 metres of kimberlite about 160 metres northeast of the Faraday body, and a hole in 2001 cut three narrow intervals of kimberlite, the thickest being 1.74 metres, about 600 metres to the southwest. No microdiamond results were ever reported for these intercepts. Based on the limited drilling to date, the dyke system associated with the Faraday body appears to be at least 800 metres long.

The Kelvin kimberlite body was apparently put on the back burner after De Beers discovered the MZ Lake kimberlite sills, 20 km northwest of Kennady Lake.

“De Beers thought MZ Lake should take a higher priority,” Mountain Province President Jan Vandersande tells The Northern Miner, adding that the shallow-dipping MZ sills represented a potentially bigger target that was land-based. “In 1999 and 2000, there was more focus on finding big pipes or something big, so they lost interest in Kelvin . . . until they got the results back.”

MZ Lake

During the 1999 winter program, kimberlite dykes were discovered in MZ Lake. A large number of indicator minerals, mainly garnets, had been recovered on the western edge of the lake. The next year, a land-based target on the north shore of MZ Lake was drilled to a depth to 35 metres. The hole intercepted a flat-lying, 1.7-metre-thick section of kimberlite, plus five narrower intervals of kimberlite up to 0.7 metre width.

Following completion of a ground-penetrating radar survey that covered the entire length of the northern shore of the lake for a distance of 4 km, De Beers drilled seven short vertical holes on land in May 2001, intersecting narrow intervals of kimberlite in five of the holes. The intercepts ranged from 0.23 to 3.2 metres in thickness and were believed to represent a series of five distinct shallow-dipping sills. The distance between the two most easterly and westerly intercepts was nearly 4 km.

“It’s a big sill system, with lots of sills for kilometres and kilometres,” says Vandersande.

Sill 73

De Beers found four of the five sills to be diamondiferous, recovering a total 40 microdiamonds from 56 kg of treated kimberlite. The best results came from Sill 73, which returned 28 micros from a 5-kg sample. Sill 73 appears to extend at least 1 km in distance. During the spring of 2002, De Beers completed another 10 holes on Sill 73, cutting narrow intercepts of kimberlite ranging from 7 cm to 2.19 metres in thickness. This past year’s drilling on Sill 73 provided only 13.8 kg of sample material, from which just six micros were recovered.

In light of the promising microdiamond results from Kelvin, De Beers plans to return to Gahcho Kue in February and carry out ground magnetometer and gravity surveys over the Kelvin-Faraday area. Any promising targets will be drilled.

De Beers spent the winter of 2002 taking additional bulk drill samples from the 5034 and Hearne pipes to gain a better understanding of grade, diamond size, frequency distributions and values. The Gahcho Kue project falls just short of the critical economic threshold required to advance the project through to the final-feasibility stage.

Mountain Province and Camphor are currently awaiting updated diamond valuations for the 5034 and Hearne pipes, which are expected sometime around February, followed by an updated desktop study at the end of the first quarter.

In the accompanying table, the micro results for Kelvin and Faraday are compared against samples that are presumably representative of Hearne and 5034, using the more detailed square mesh sieve classification.

KelvinFaradayHearne5034