Ambler Metals – a joint venture between Trilogy Metals and South32 – on Thursday announced the outcome of a feasibility study for the Arctic base and precious metals project, in north-western Alaska.

With an estimated initial capital requirement of $906-million and sustaining capital of $114-million, the project has a payback period of 2.6 years, Toronto-listed Trilogy said in a statement.

The study calculated that Arctic has an aftertax net present value (NPV) of $1.1-billion and an internal rate of return (IRR) of 27%, using long-term metal prices of $3/lb for copper, $1.10/lb for zinc, $1/lb for lead, $1 300/oz for gold and $18/oz for silver.

At current spot prices, the NPV is $1.3-billion and the IRR is 29.6%.

Prepared by Ausenco Engineering Canada, the study outlines plans for establishing an openpit mine and mill complex for a 10 000 t/d operation, producing an average of 155-million pounds of copper, 192-million pounds of zinc, 32-million pounds of lead, 32 165 oz of gold and 3.4-million ounces of silver each year over 12 years.

Cash costs have been estimated at $0.32/lb of payable copper and the total all-in cash cost at $0.98/lb.

Based on the feasibility level metallurgical work on the sulphide mineralisation, the average recoveries are projected to be 89.9% for copper, 90.6% for zinc and 79.0% for lead, in their respective concentrates. Over 60% of the recovered payable silver and gold report to the lead concentrate at 95% payable.

"Arctic is a special project due to its unique high-grade polymetallic nature. The only other time that I've seen a project of this quality where the grades were similar was in an underground mining scenario.  However, Arctic is mineable in an openpit scenario,” said Trilogy president and CEO Tony Giardini.

The Arctic deposit is located in the Ambler mining district in a geographically isolated area, with no current road access or nearby power infrastructure.

Last month, the US Bureau of Land Management signed a record of decision for the Ambler Mining District Industrial Access Project, approving the development of the northern route to provide access to the Ambler district.