Based on preliminary geological modelling of four pipes, the Diavik project in the Lac de Gras area of the Northwest Territories is estimated to contain resources of 36 million tonnes of kimberlite, defined to a depth of 400 metres.
The four pipes — A-154 South, A-154 North, A-418 and A-21 — are the subject of an $80-Million bulk-sampling and prefeasibility study by Aber Resources (ABZ-T) and partner Diavik Diamond Mines, a subsidiary of London-based RTZ-CRA. The study is expected to be completed later this year.
The pipes lie in the western claim area of the project, which hosts 45 known pipes. The A-154 South pipe, which is estimated to contain 12 million tonnes to a depth of 400 metres, averages 4.2 carats per tonne to a depth of 250 metres. The recent drilling of five additional large-diameter holes will be used to calculate a grade to a depth of 400 metres.
That pipe yielded nearly 12,800 carats in a 2,900-Tonne underground bulk sample. Independent valuations on a representative sample of 5,658 carats were carried out in Antwerp, Belgium. Under market conditions in early 1997, the diamonds were worth an average of US$67 per carat, suggesting a value of US$63 per carat for the entire bulk-sample parcel.
The A-154 North pipe is 250 metres northeast of pipe A-154 South. A 156.81-Carat parcel, recovered from 71.7 tonnes of large-diameter drill core, returned a grade of 2.19 carats per tonne to a depth of 250 metres. Those diamonds were valued at US$35.10 per carat.
Recent drilling at A-154 North boosted the resource estimate there to 10 million tonnes to a depth of 400 metres, compared with the previous estimate of 5.3 million tonnes to a depth of 250 metres. In a release, the company stated that no further testing of A-154 North will be conducted, as the upper portion is minable from the open pit of A-154 South.
Meanwhile, a 3,000-Tonne underground bulk sample from the A-418 pipe, situated 750 metres southwest of A-154 South, is being processed in Yellowknife, N.W.T. Valuation of the sample, however, is not expected until June.
The A-418 pipe is estimated to contain 9 million tonnes to a depth of 400 metres, compared with a previous calculation of 5.8 million tonnes to a depth of 250 metres. Previous drilling there recovered 247.5 carats from 62.3 tonnes of kimberlite for a grade of 3.97 carats per tonne. Initial valuations averaged US$64.10 per carat.
The A-21 pipe, situated 5 km southwest of A-154 South, is estimated to contain a resource of 5 million tonnes to a depth of 400 metres.
A single, large-diameter hole drilled in 1996 recovered 21.49 carats from 6.9 tonnes of kimberlite for a preliminary grade of 3.11 carats per tonne. The pipe was recently tested with five additional large-diameter drill holes.
Diavik Diamond Mines owns 60% of the Diavik project, with the remainder held by Aber.
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