Arctic Copper-Zinc-Lead Project

The Arctic copper-zinc-lead project is an open-pit mine located in Alaska, US. Trilogy Metals is the owner and developer of the deposit.

The pre-feasibility study (PFS) of the Arctic project was completed in February 2018, while a NI43-101 technical report on the PFS report was completed in April 2018. The deposit is being developed with an estimated investment of £555m ($780m) and is expected to have a life of 12 years.

It is expected to produce approximately 159 million pounds (Mlbs) of copper, 199Mlbs of zinc, and 33Mlbs of lead, on an average. In addition, it is expected to produce 30,600 ounces (oz) of gold and 3.3Moz of silver.

Arctic copper-zinc-lead project reserves

The probable ore reserves at the Arctic copper-zinc-lead deposit are estimated to be 43Mt, grading 2.32% copper (Cu), 3.24% zinc (Zn), 0.57% lead (Pb), 0.49% gold (Au), and 36% silver (Au).

Mining and ore processing at the Arctic copper-zinc-lead project

Conventional open-pit mining method, involving truck shovel operation, will be used at the Arctic copper-zinc-lead deposit.

The processing plant at Arctic will have a capacity to treat 10,000 tonnes per day (t/d) of massive and semi-massive sulphide mineralisation. The plant will consist of three operational units for crushing, grinding, and flotation. The run-of-mine (ROM) material will be crushed at a jaw crusher located at the primary crushing facility.

The crushed material will undergo grinding in two stages, which includes a semi-autogenous grind (SAG) mill and a ball mill, which operates in closed circuit with classifying cyclones. The grind size of the cyclone overflow will be roughly 80% passing 70μm.

The hydrocyclone overflow will pass through talc pre-flotation, followed by conventional bulk flotation, and zinc flotation. Copper, lead, and associated gold and silver are proposed to be recovered at the bulk flotation circuit.

The rougher bulk concentrate will be cleaned and followed by copper and lead separation to produce a lead concentrate and a copper concentrate. The average annual dry concentrate production is estimated to be 246,723tpa of copper, 29,493tpa of lead, and 180,219tpa of zinc.

The resultant copper, zinc, and lead concentrates will be thickened and filtered before being shipped to the customers.

Infrastructure

The mine can be reached through the State of Alaska highways and through a private road owned by AIDEA and access roads owned by Trilogy Minerals. The project will also be accessible through the Ambler Mining District Industrial Access Project (AMDIAP) road.

Power supply will be provided by six 4.4MW LNG generators, which produce a total of 17.6MW.

The project is located within the valley of Sub-Arctic Creek, a tributary to the Shungnak River. The Sub-Arctic Creek has a catchment area of 26.5km².

Process water will be sourced from the reclaim in the tailings management facility (TMF).

Workers will be accommodated at three different accommodation camps, equipped with separate power generation and heating capabilities, water treatment, and sewage treatment plants.

Contractors involved

SRK Consulting prepared the preliminary economic assessment (PEA) of the Arctic copper-zinc-lead project.

The PFS report for the project was prepared by Ausenco Engineering Canada. Trilogy Metals also engaged Amec Foster Wheeler Americas and SRK Consulting to support Ausenco.

Arctic copper-zinc-lead project location, geology, and mineralisation

The Arctic copper-zinc-lead project is situated in the Ambler mining district, which lies in the Northwest Arctic Borough (NWAB) in Alaska. The deposit is located roughly 270km to the east of the town of Kotzebue and 37km north-east of the Kobuk village.

The Main Sulphide Horizon, the Upper South Horizon, and the Warm Springs Horizon are the three mineralised horizons at the deposit. The Main Sulphide Horizon is subdivided into the south-east zone, the central zone, and the north-west zone.

The Arctic deposit is defined as two or more discrete horizons of sulphide mineralisation, which hosts main resources and is contained in a deformed isoclinal fold.