Based on favourable microdiamond results received from the Contwoyto-1 kimberlite at the Jericho project in Nunavut,
Contwoyto-1 was discovered in the fall of 1998, about 38 km southeast of the Jericho JD-1 and JD-3 pipes. Contwoyto-1’s discovery hole yielded 26 macrodiamonds and 143 micros from a 90.2-kg sample of kimberlite core. (A macro is defined here as exceeding 0.5 mm in at least one dimension.)
More results were recently reported from the first 85 metres of vertically drilled hole 11. A 121.9-kg sample returned 54 macros, including five stones measuring more than 1 mm, and 603 micros. The three largest stones recovered were an octahedron with an estimated weight of 0.092 carat and measuring 2.5 by 2.25 by 2 mm, a broken irregular stone weighing 0.033 carat and measuring 2.56 by 1.46 by 1 mm, and an octahedron weighing 0.023 carat and measuring 1.81 by 1.56 by 1.13 mm. Caustic fusion analysis of the remainder of hole 11 is continuing.
During the 1998 fall and 1999 winter programs, Tahera tested Contwoyto-1 with 18 core holes representing 2,000 metres of drilling. The pipe was probed to a maximum depth of 222 metres. Drilling has confirmed that the pipe is pear-shaped, with horizontal dimensions of about 60 by 80 metres. Contwoyto-1 remains open at depth. Preliminary estimates put the pipe in the 3-million-tonne range.
The Jericho project sits 420 km northeast of Yellowknife and 170 km northeast of the Ekati diamond mine. Tahera has initiated a feasibility study on the development of the JD-1 kimberlite pipe. If results warrant, the study will be expanded to include Contwoyto-1. Tahera has filed a project proposal with regulatory authorities, marking the beginning of environmental assessment and permitting.
The proposal is based on the seasonal open-pit mining of the land-based JD-1 pipe and construction of a diamond recovery plant at the nearby Lupin gold mine, subject to the implementation of the terms of a 1996 agreement between Tahera and mine owner
Tahera proposes trucking the kimberlite ore during the winter months along an ice road to the Lupin site, 27 km to the southeast. The processing plant will treat the kimberlite on a year-round basis, and tailings would be disposed of at existing facilities. A mine life exceeding 10 years is projected.
The JD-1 pipe is estimated to contain an indicated and inferred resource of 6.1 million tonnes grading 0.94 carat per tonne to a depth of 300 metres, equivalent to 5.7 million contained carats. The resource, calculated by Steffen, Robertson & Kirsten (SRK), is based on a 9,400-tonne underground bulk sample that was collected across three phases of the pipe in late 1996, as well as about 100 tonnes of earlier, large-diameter drill core.
SRK estimates a minable, open-pit resource of 3.8 million tonnes grading 1.01 carats per tonne to a depth of 180 metres, with a stripping ratio of 4.2-to-1.
A 10,539-carat parcel of diamonds recovered from the 9,400-tonne bulk sample was initially valued at US$59.61 per carat. The recovered stones were all larger than 1 mm and included a 40-carat stone. The largest gem-quality diamond was 23.89 carats. The stones were revalued in 1998 at US$69.65 per carat.
Another pipe, JD-3, lies under a small lake 7 km west of JD-1 and carries an inferred resource of about 10.5 million tonnes to a depth of 300 metres. A preliminary grade of 0.36 carat per tonne is based on the recovery of 16.6 carats of stones from 46.6 tonnes of large-diameter core and reverse-circulation drilling. The largest recovered stone weighed 3.6 carats.
A 1998 prefeasibility study of the JD pipes estimated that the capital cost of constructing a diamond mine at either Jericho or Lupin would be $125-150 million. The study concluded that the proposed project is marginal to sub-economic and that additional tonnage is required to enhance its economic potential.
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