Diavik partners alter proposed plan

Ongoing feasibility and optimization studies at the Diavik diamond project in the Northwest Territories have led to a change in the proposed mining sequence of the kimberlite pipes.

Situated 300 km north of Yellowknife and 35 km southeast of the producing Ekati diamond mine, the project is a 60-40 joint venture between Diavik Diamond Mines, a subsidiary of Rio Tinto (RTP-N), and Aber Resources (ABZ-T). The partners are developing four kimberlite pipes — A-418, A-154 South, A-154 North and A-21 — that together contain a diluted minable reserve of 26 million tonnes grading 3.9 carats per tonne, with an average estimated value of US$56 per carat.

The four pipes lie just offshore of 20-sq.-km East Island in Lac de Gras. Diavik proposes to dam off the pipes with water retention dykes — one around the A-154 South and North kimberlite pipes, one around A-418, and one around A-21 — and open-pit mine all four pipes to depths of between 250 and 300 metres, followed by underground mining of the A-418 and A-154 South pipes to a depth of 400 metres.

The environmental assessment was filed in September 1998, and the partners hope to secure permits by the upcoming fall. Subject to a production decision, construction could start in early 2000, leading to commercial production in the second quarter of 2002.

A final feasibility study is to be completed early in the second quarter of this year. The study, which is considering production rates ranging from 1.5 to 1.9 million tonnes of kimberlite per year, is being prepared jointly be Nishi-Khon, the aboriginal Dogrib Nation Group of Companies, and the engineering firm SNC-Lavalin Group.

The capital cost of constructing the mine is estimated to be $875 million, with operating costs over the life of the operation pegged at $66 per tonne of kimberlite ore. The final feasibility study will provide updated cost estimates.

Engineering studies have determined that the water retention dykes required to mine the kimberlites by open-pit methods could be constructed more efficiently than previously envisioned, while still meeting Canadian safety regulations. Aber says the new construction plan will reduce construction material requirements, fuel and construction time, while allowing greater access to reserves in the A-154 South and North pipes.

The partners now say mining should begin with the A-154 pipes, instead of A-418, as previously planned. The A-154 dyke is to be constructed in 2000 and 2001, with open-pit mining slated to start in the second quarter of 2002 for a span of 10 years. Construction of the A-418 dyke would start in 2007.

In the revised plan, the A-21 pit would be mined over three years from approximately 2012 to 2014, compared with the previously planned period of 2012 to 2025. The 4 million tonnes of kimberlite ore from A-21 will be placed in the process plant area stockpile and will slowly be fed to the plant over the 3-year pit life and the following 5-year period.

Aber says this mining approach allows for a more efficient transition to underground mining. The project has a mine life of up to 22 years.

Exploration for additional resources outside of the mine plan is continuing in 1999 with an expected budget of $2.8 million. The program will include the drilling of two diamondiferous kimberlite pipes.