Giga Metals Corp has announced the results of a prefeasibility study (PFS) on its majority-owned Turnagain nickel-cobalt project in British Columbia, Canada, that could use both trolley assist technology, as well as an autonomous haulage system.

Turnagain is owned by Hard Creek Nickel Corp, a joint venture owned by Giga Metals (85%) and Mitsubishi Corporation (15%).

The PFS outlined annual production averaging 37,288 t/y of nickel and cobalt in concentrate over the nominal full operating rate period (years 3 to 28) based on a 30-year project life with a strip ratio of 0.4 tonnes waste per tonne of ore

It also highlighted Scope 1+2 carbon intensity of less than 1.8 tonnes of CO2 per tonne of Ni in concentrate.

The PFS builds on significant metallurgical and engineering studies and confirms the ability of Turnagain to produce high-quality nickel concentrate, Giga Metals said. It has been led and prepared by Tetra Tech Canada Inc along with input from industry expert consultants.

Giga Metals said: “The PFS demonstrates a long-life, large-scale project that will deliver high-grade nickel sulphide concentrate with no significant deleterious impurities, into commercially proven processes such as pyrometallurgical smelters or hydrometallurgical refining using pressure oxidation facilities.”

The project, Giga Metals says, has notable responsible mining characteristics beyond the low-carbon production including the following:

• Sequestration of CO2 through naturally occurring mineral carbonation, transforming the tailings management facility into a permanent carbon mineralisation facility;
• Safe and efficient tailings storage using centreline and downstream tailings dams in sub-aerial valley impoundment;
• A near-neutral water balance; and
• Being located in a well-regulated and experienced mining jurisdiction that has adopted First Nations’ rights to achieve informed consent during the permitting process.

The capital cost associated with the project has been slated as $1.89 billion with a post-tax IRR and NPV of 11.4% and $574 million at a long-term nickel price of $9.75/lb, with 78% payability for nickel in concentrate.

The Turnagain open-pit deposit will be developed using large haul trucks (227 t capacity), loaders, and electric shovels to minimise unit costs, the company says.

“Proven trolley-assist technology and autonomous haulage technology have been selected for reduced total costs and environmental footprint,” it added.

The mining operations are scheduled for a 28-year mine production period to support a 30-year processing plant operating period, and include the Horsetrail, Northwest and Duffy mineralized areas (collectively, the Horsetrail zone). The orebody is mined as a single main pit with five pushback phases through the life of mine and a small satellite pit for the Duffy zone. Overall main pit dimensions are approximately 2 km x 1.5 km.

The mine plan will deliver an annual processing plant feed rate of 32.85 Mt/y (90,000 t/d) after the installation of the second processing train in Year 1. The resource will be selectively mined with low-grade materials placed on a low-grade ore stockpile for later recovery. The maximum low-grade ore stockpile size has been reduced by 82% from the 2020 preliminary economic assessment to 34 Mt, which represents an approach that accounts for regulatory expectations to minimise stockpiling as well as practical mining operations.

Processing of Turnagain ore is conventional, Giga Metals says, with the processing plant consisting of the following:

• A primary crusher followed by two trains of closed-circuit secondary crushing and HPGRs;
• Two grinding trains, each comprising two closed-circuit ball mills in series;
• Two rougher flotation trains, each comprising two banks of rougher cells;
• Two trains of three-stage cleaning circuits plus cleaner-scavenger flotation;
• Concentrate thickening and two trains of pressure filtration; and
• Associated utility and reagent systems.

The processing plant will be installed in slightly offset stages to maximise the efficiency of construction and commissioning. The second processing train will be installed and commissioned parallel to the first train in the first full year of operations. The primary crusher is located adjacent to the mine to reduce haul distances and the crushed ore is conveyed to the processing facility located across the Turnagain River and above the tailings management facility. This allows for energy-efficient conveying of crushed ore and eliminates high-pressure pumping of slurries. All equipment selected is commercial-scale industry-standard, including mechanical flotation cells, the company added.

Turnagain concentrate is expected to be high grade, averaging 18% Ni and 1.1% Co, with low levels of deleterious impurities. Iron, sulphur and magnesium are expected to be within typical ranges for smelter operation, with nominally 30-35% Fe, 20-25% S and 4-6% Mg.