Bulk sampling adds lustre to Snap Lake

Over the course of the past two years, Winspear Resources (WSP-V) has encountered a complex kimberlite dyke and breccia system in and around Snap Lake at the Camsell Lake property within an area measuring roughly 4 by 4 km. While the source, or feeder system, has yet to be discovered, the NW Snap Lake dyke has become a potentially economic target in its own right following a surface bulk-sampling program that revealed a large population of gem-quality stones with the highest carat values ever reported in the Northwest Territories.

In the spring of 1998, Winspear collected a 199.7-tonne bulk sample of the NW kimberlite dyke from two surface pits set 235 metres apart. The dyke sub-crops on a peninsula that juts into the northwestern corner of Snap Lake. At both sample spots, the kimberlite dyke was covered by 2-2.5 metres of glacial debris.

The sample was processed at the Diavik plant in Yellowknife, using a cutoff equivalent to a square mesh screen size of 1.2 mm. It yielded a 228.9-carat parcel of diamonds, giving a preliminary grade of 1.14 carats per tonne. The parcel of stones included an impressive 21 diamonds weighing more than 1 carat, with the three largest stones weighing 10.87, 8.63 and 6.03 carats.

The stones were determined to be worth an average of US$301.43 per carat, based on three independent valuations carried out in Antwerp, Belgium, for an implied value of US$343.63 per tonne of kimberlite.

For comparison purposes, diamond values, along with implied tonnage values for the five pipes slated to be mined at the Ekati mine of BHP Diamonds and Dia Met Minerals (DMN-T), are as follows:

* US$130 per carat ($140.40 per tonne) for Panda;

* US$125 per carat ($50 per tonne) for Fox;

* US$122 per carat ($109.80 per tonne) for Koala;

* US$64 per carat ($59.52 per tonne) for Sable; and

* US$26 per carat ($110.76 per tonne) for Misery.

At the Diavik project of Rio Tinto and Aber Resources (ABZ-T), the A-154 South pipe is valued at US$63 per carat ($302.40 per tonne), the A-418, at US$56 per carat ($207 per tonne), the A-154 North at US$35 per carat ($84 per tonne), and the A-21 at US$38 per carat ($114 per carat).

Diamonds at the JD/OD 1 pipe at the Jericho project of Lytton Minerals (LTL-T) and New Indigo Resources (NDR-A) have an average value of US$60 per carat ($60.60 per tonne).

The diamond value of the 5034 pipe at the AK joint venture of Monopros, Mountain Province Mining (MPV-V) and Camphor Ventures (CFV-V) is valued at US$55 per carat ($82.50 per tonne).

The Camsell Lake property is 220 km northeast of Yellowknife and 110 km south of the original BHP/Dia Met Point Lake kimberlite discovery. The property is accessible by fixed-wing aircraft equipped with either floats or skis, depending on the season, or by helicopter. The Lupin winter road is only 10 km from the property’s northern boundary.

Winspear is the operator and owns a 68% interest in the 277,000-acre property. Aber holds the remaining 32%. A decision by Aber not to participate in the 1998 winter/spring field program caused its interest to shrink from 42.7%.

During a visit to Snap Lake, The Northern Miner, along with mining analysts and investment dealers, were briefed on the property’s history by Project Manager Walter Melnyk.

The NW dyke was discovered during a major drill program in the spring of 1997. The program was attempting to find the source of diamond-bearing kimberlite boulders uncovered by Winspear’s team of geologists on the northwestern arm of Snap Lake in the summer of 1996. The boulders were found in an area where a substantial amount of pyrope garnets and chromites (kimberlite indicator minerals) had been recovered from many of the till samples. Those boulders returned 33 macrodiamonds and 110 micros from 34 kg of material that had been collected from two sample sites. (A macro is defined here as measuring more than 0.5 mm in at least one direction.)

Near one of the boulder sites, a 60-kg sample of green clay material taken from a shallow pit yielded another eight macros. In addition, 20 macros were recovered from seven till samples down-ice of the boulders.

The 1997 drilling intersected hypabyssal-type kimberlite dyke material in 13 core holes along a strike length of 800 metres and a downdip extent of 600 metres. The kimberlite intervals ranged from 1.1 to 3.5 metres true thickness, for an average of 2.4 metres.

Melnyk said it was apparent from the drilling that the joint venture was outlining not a vertical system but a single, tabular, sheet-like body that strikes north and dips 13 to the east beneath Snap Lake.

Caustic fusion analysis of the 13 intersections yielded 149 macros and 252 micros from a 137.1-kg aggregate sample. Twenty-five of the macros exceeded 1 mm in at least one dimension, with the largest diamond measuring 1.79 mm.

The color and percentage of the recovered diamonds were described as white (43.7%), off-white (3.2%), grey (1%), yellow (39.2%), off-yellow (1.5%), amber (7.2%), brown (0.5%), green (2.7%) and pink (1%). About 87% of the diamonds were transparent. Winspear has since made no further comment on the color of the stones.

The NW dyke was further tested during the 1998 winter program by two holes that encountered similar kimberlite material along the dyke’s downdip projection, some 1,000 metres east of the most easterly hole drilled in 1997. “The first hole hit 2.8 metres of kimberlite, pretty well where it was supposed to,” said Melnyk. “The pierce point of the second hole (1.2 metres) lined up nicely with the rest of them.”

Melnyk added that the joint venture now has a good handle on the kimberlite, adding that there is one main dyke, with much thinner peripheral dykes lying close by, either above or below the main dyke.

This point is illustrated by a stepout hole off-section to the south, which intersected nine narrow dykes instead of the one main dyke. “There is something peculiar happening off to this area,” Melnyk opined.

Based on the results of the bulk-sampling program, Winspear commissioned mining consultant H.A. Simons to prepare a scoping study to evaluate the economic potential of the NW dyke. As part of that study, Winspear has begun a detailed, land-based delineation grid drilling program. Approximately 48 holes, representing 2,800 metres, will test an area of the peninsula measuring 800 metres along strike and 200-400 metres downdip. The holes are being spaced at 100-metre centres along each grid line and off-set 50 metres on adjacent lines. This phase of drilling will include several structural holes as well.

Melnyk said there are three main objectives of the drill program. The first is to determine the structural continuity of the dyke. “Is it a nice flat sheet, or are there ripples, warps or offsets. The kimberlite of course would have been injected along a pre-existing structure, and the nature of that kimberlite would be a reflection of that void or filling.”

The drilling will also determine the thickness variation of the dyke and at the same time, study the microdiamond population in the holes in an attempt to predict grade. Winspear will be collecting drill core data for geotechnical studies.

In addition to the grid drilling, a closely spaced, 16-hole program has been proposed for geostatistical purposes in preparation of taking a larger bulk sample this coming winter.

When The Northern Miner visited the property, the third hole of the delineation drilling program had been completed. Winspear has since completed a total of 12 holes. The program is expected to take about a month to complete.

Aber funds share

This time round, Aber has elected to fund its share of the current drill program, which is estimated to cost up to $1.3 million.

In a research report, David James, a mining analyst with Canaccord Capital, compares the NW dyke’s US$301 carat valuation at the 1.14-carat-per-tonne grade as being roughly equivalent to a gold grade of 1 oz. per ton. He suggests that a 10-to-12-million-tonne resource might be derived from a volume of rock measuring 800 by 1,800 by 2.4 metres.

If Winspear is successful at block
ing out tonnage, James suggests a small mine of 1,000-1,500 tonnes per day might be modelled.

The Camsell Lake property was privately staked in 1992 and later sold to Amarado Resources for $280,000. Amarado was short of funds at the time and unable to complete the purchase without the assistance of Commonwealth Gold and Winspear, which each received a 40% interest in the project for their financial input. In May 1993, Consolidated Newgate Resources reached an agreement with Winspear to exchange an interest in certain other diamond properties in the Northwest Territories for a 10% interest in the Camsell Lake property.

In early 1994, Aber became a partner after merging with Commonwealth Gold. Amarado, later renamed as AfriOre, sold its interest to Consolidated Newgate in January 1996. By year-end, Consolidated Newgate, had been renamed as Antler Resources and had merged with Winspear. Since 1994, Winspear has carried out an extensive amount of detailed till sampling and geophysical surveying.

Winspear found its first kimberlite, CL-25, back in 1994, with the assistance of Nickolai Pokhilenko, the chief research geologist for the Russian diamond company Almazy Rossii Sakha and head of the Laboratory for Diamond Deposits at the Institute of the Russian Academy of Sciences in Novosibirsk. Pokhilenko serves as a consultant to Winspear and has returned to Camsell Lake with several of his Russian colleagues every summer since the 1994 discovery.

Using an unique method of panning till samples for kimberlite indicator minerals while out in the field, Pokhilenko helped Winspear pinpoint the location of CL-25 on only his second day at Camsell lake. CL-25 was discovered within a small lake near the eastern claim boundary. Subsequent drilling of CL-25 yielded nine macros and 212 micros from 350.5 kg of core material.

A second small pipe, called CL-174, was discovered 150 metres northwest of CL-25 during the spring of 1995. CL-174 returned 10 macros and 274 micros from 622.2 kg of core sample.

Melnyk says that while both pipes are diamondiferous and interesting, they are nonetheless quite small and uneconomic.

The 1994 till sampling also defined an indicator train emanating from Snap Lake, 30 km west-northwest of the CL-25 and 174 kimberlites. In early 1996, Winspear attempted to identify the source of the indicators by drilling 115 short vertical drill holes into the southern part of Snap Lake to test the underlying bedrock. Four of those holes intersected narrow diamondiferous kimberlite breccia dykes. A composite 11.8-kg sample of core yielded 23 diamonds.

During the 1997 spring drilling program, a “blind” complex kimberlite breccia body was encountered at the site of Anomaly 186 on the northeastern side of Snap Lake. Two vertically drilled holes, collared 55 metres apart, each intersected 100 metres of kimberlite breccia beneath a 100-metre cap of granite.

One sample from the upper part of the first hole yielded two macros and nine micros from 39 kg of material. A second sample from the lower portion of the hole returned 20 macros and 36 micros from 43 kg of core.

In the second hole, no diamonds were recovered from an upper sample weighing 36.4 kg, but, lower down in the hole, a 35.2-kg sample yielded 20 macros and 38 micros. Selective sampling of both holes excluded large fragments of granititc rock.

Follow-up drilling was unable to find the source of the CL-186 kimberlite, although narrow intervals of both hypabyssal-type and kimberlite breccia were intersected.

“This still remains a mystery to us,” said Melnyk. “It is a scenario we have a tough time explaining.”

In the summer of 1997, Pokhilenko and his team discovered a train of kimberlite boulders on the southern peninsula of the lake extending approximately 1.2 km in length and 200 metres wide. Most of the boulders are massive kimberlite breccia containing xenoliths of both host and mantle-derived rocks. Petrographic studies suggest up to three types of kimberlite are present, including a small proportion of hypabyssal kimberlite similar in composition to the NW dyke.

A total of 214.1 kg of varying types of kimberlitic material was collected from four sites in the boulder train and returned 196 macros and 298 micros, with the largest stone measuring 3.475 mm.

This past winter, Melnyk and his team decided to pursue the source of these kimberlite boulders. A number of geophysical features were drill-tested as crews worked their way from the southern part of the peninsula out to the northeast. Kimberlite was hit in five of the holes, with three holes intersecting a hypabyssal type similar to the NW dyke. The other two holes encountered kimberlite breccia identical to the boulders and the four previous narrow kimberlite breccia holes.

Melnyk said the pierce points of the drill holes in the southern peninsula define a tabular sheet of kimberlite. “Both the breccia intersections and the hypabyssal appear to fall on the same plane, and that plane dips 13 to the north into Snap Lake.

In the northeastern peninsula, 1998 drilling encountered a 0.7-metre-thick interval of kimberlite breccia. Further drilling around this hole encountered hypabyssal-type kimberlite in four other holes. Melnyk says these pierce points fall on a plane that strikes in a northeasterly direction, with a shallow dip to the west towards the centre of the lake.

In total, 61 holes were drilled this past winter, 22 of which intersected kimberlite.

While the source, or sources, of this complex system of kimberlite and breccia dykes at Snap Lake has so far eluded Winspear, all evidence points to a focal point or root somewhere within Snap Lake.

“We’re not sure what we’re up against, but at the moment we are doing a lot of deep thinking to try to resolve the structural complexity out there,” said Melnyk.

Winspear hired consultant geologist Michael Stubley to map the Snap Lake area this summer. The area was last mapped in the 1940s by the Geological Survey of Canada. Encircling Snap Lake, Stubley found a highly metamorphosed, mafic, volcanic, layered amphibolite mixed with a distinctive litho gabbro unit and overlain by high-grade sediments and turbidites. This sequence is underlain by a highly magnetic granitic complex.

A big syncline structure runs through the middle of the lake. The area has been over-printed with a later stage of folding, forming a basin and dome interference pattern. Trending along the northern arm of Snap lake is a major crustal, braided fault system that can be traced for more than 50 km.

Stubley examined many of the associated linear features and found a relatively stable package with few breaks. The largest offset he measured was in the order of 25 metres.

The Snap Lake kimberlites are unusual in comparison. During our visit to the site, Pokhilenko shared his ideas on the genesis of the kimberlite system at Snap Lake. He suggested a deep-sourced kimberlite achieved an explosive state before reaching the surface, which would account for the radial kimberlite dyke pattern around Snap Lake. He believes the pipe may still lie several hundred metres below surface.