The Early Jurassic (190 ±1 million years ago (Scheel, 2007)) Turnagain complex comprises a central core of dunite with bounding units of wehrlite, olivine clinopyroxenite, clinopyroxenite, representing crystal cumulate sequences, hornblende clinopyroxenite and hornblendite.The complex is elongate and broadly conformable to the northwesterly trending regional structural grain.

The ultramafic rocks are generally fresh to mildly serpentinised; however, more intense serpentinisation and talc-carbonate alteration occur along faults and restricted zones within the complex. The central part of the ultramafic body is intruded by granodiorite to diorite, and hornblende–plagioclase porphyry dikes and sills.

Showings of semi-massive and massive sulphides have been identified by work to date. These semi-massive and massive zones, plus broad zones of disseminated sulphides, are generally hosted by dunite and wehrlite near the southern and eastern margins of the ultramafic body. The central and northern dunite is largely devoid of sulphide minerals although their highly magnesian olivine is more enriched in nickel (up to 0.20 to 0.30 weight percentage) than the olivine in the peridotites and pyroxenites of the Horsetrail and Northwest zones, which may be nickel-depleted in areas of sulphide mineralisation. Nixon (1998) suggests that these features are further evidence of fractional crystallisation of the ultramafic magma.

Primary sulphide minerals consist of pyrrhotite with lesser pentlandite (iron-nickel sulphide) and minor chalcopyrite. Some bornite has been reported. Interstitial and blebby sulphides, with grain sizes ranging from 1 to 4 mm, are evident in widespread disseminated zones seen in drill cores. With increasing concentrations, these intercumulus sulphide grains coalesce to form net-textured sulphides. Semi-massive and massive sulphides, and rare sulphide matrix breccias, were also noted in drill cores over intervals not exceeding a few tens of centimetres.

The principal mineral zones identified to date on the Turnagain property include the following:

• The Horsetrail Zone and surrounding area have been the focus of most of the historic and recent diamond drilling. Results to date suggest a northwest to west-northwest trend for these zones, which consist of broadly dispersed, disseminated to intercumulus sulphide mineralisation in both dunite and wehrlite and serpentinised equivalents. Sulphide grains range in size from 0.5 to 5 mm and commonly occupy interstices between olivine grains. Drill core samples from the Horsetrail Zone have a median of 0.23% total nickel with grades ranging from 0.01% to 4.89% total nickel. Total cobalt grades range from 0.001% to 0.480% with a median of 0.013% Co. There appears to be a spatial relationship between graphitic xenoliths, increasing clinopyroxene content in the ultramafic host rocks and the incidence of sulphide mineralisation. Where present, chalcopyrite occurs along the margins of pyrrhotite and in narrow veinlets. Relatively unaltered dunite adjacent to the Horsetrail Zone may contain total nickel values of 0.20% to 0.30%, virtually all of which is in the crystal lattices of the silicate mineral olivine and consequently is not of economic importance.

• The Northwest Zone is contiguous with, and lies northwest of, the Horsetrail Zone. This zone has mineralisation styles and grades similar to the Horsetrail Zone, but is intruded by several mafic and felsic dikes which dilute the overall grade. Drill core samples from the Northwest Zone have a median grade of 0.20% total nickel with grades ranging from 0.01% to 2.86%. Total cobalt grades range from 0.001% to 0.166%. The Horsetrail and the Northwest Zones form a zone approximately 2,000 m long in the east-west direction, and 550 m wide from north to south and have been tested by 251 drill holes.

• The Hatzl Zone mineralisation consists of disseminated and net textured pyrrhotite and pentlandite hosted by dunite and wehrlite. This mineralisation is similar to, and may be continuous with, the Horsetrail Zone. The Turnagain River flows between the two zones and the region below the river has not been sufficiently drill tested to exclude the potential of additional mineralisation. The Hatzl Zone is 1,150 m long in a northeast direction and 300 m wide in a northwest direction and has been tested by 17 drill holes.

• The Duffy Zone mineralisation lies 500 m northeast of the Horsetrail Zone and consists of disseminated sulphides similar to those within the Horsetrail Zone. Grades range from 0.014% to 0.525% total nickel. The Duffy Zone is 300 m in diameter and does not crop out. It was discovered by exploration drilling in 2006. The zone has been tested by six drill holes.

The geological setting of the sulphide mineralization at the Turnagain deposit is unusual, in that it is hosted by an Alaskan-type complex, which is a magmatic environment that is not generally noted for its sulphide potential. Nixon (1998) concluded that the iron-nickel-copper Fe-Ni-Cu) sulphides in the Turnagain complex are of magmatic origin, and that wall rock inclusions observed in drill core may have provided a mechanism for sulphur saturation and precipitation of Fe-Ni-Cu sulphides. This has been confirmed by sulphur and lead isotope results reported by Scheel (2007).

Disseminated and rare net-textured mineralization at Turnagain is hosted in dunite, wehrlite, olivine clinopyroxenite and clinopyroxenite and serpentinized equivalents. Sulphides comprise pyrrhotite, pentlandite, chalcopyrite and trace bornite. Valleriite occurs where serpentinization is intense.

The Turnagain deposit will be mined using an open pit mining method, employing high volume trucks and shovels. The use of large mining equipment will achieve high mining rates and ensure the lowest possible mine operations unit costs. The waste and mineralized rockwill require blasting and typical grade control methods using blast-hole sampling.

The mine will feed the crusher at an average rate of 45,000 t/d during the first five years and increase to an average of 90,000 t/d thereafter. The resource will be mined for 37 years at these rates based on a 365-day production year.

To access the most economic mineralisation in the early years and provide a smooth strip ratio throughout the life of mine, mineralisation production from the Horsetrail pit is scheduled from five mining phases. Stage 1 will commence at the centre of the pit, where the highest grade and lowest strip ratio will be encountered.

An elevated cut-off grade will be employed in the initial production years to enhance the economics of the project. Mineralisation that is below the mine high-grade (HG) direct feed cutoff, but of sufficient grade to cover the cost of milling and rehandling once it is hauled out of the pit, will be classified and stockpiled by categorised value for subsequent rehandling. Stockpile reclaim will occur at the end of the mine life or it will be blended with the ROM feed as the appropriate opportunity arises. Low-grade (LG) stockpiles will be placed in the same facility as the waste dump to avoid additional costs.

Pit waste and LG material will be hauled to a waste dump and stockpile complex southwest of the pit, past the crusher and coarse ore stockpile facilities. The design is capable of containing all scheduled waste and LG material in the LOM plan. Current geochemistry data suggest there is insignificant acid generating potential in the waste rock. There is also the potential that if deemed cost effective and geochemically acceptable, waste rock can be utilised as buttress material for the TMF in Flat Creek valley, thus it is conceivable that the waste and LG storage facilities will have minimal impact at the end of mine life. Further studies will be undertaken to confirm this possibility.

The mineral processing plant is designed for two grinding trains, four rougher flotation trains, and two cleaner and cleaner scavenger trains at full capacity. This configuration allows for phased construction of the mill. The first phase at 50% of the full capacity will simply comprise one crushing train, one grinding train, two rougher flotation trains, and one cleaner and cleaner scavenger train. For the first five years, the plant throughput will average 16.4 Mt/a. Thereafter, for Years 6 to 35, the average throughput will be 32.9 Mt/a.

In summary, the process plant will consist of:
• ROM crusher feed hopper
- conveyors
- ore reclaiming systems
• one primary crusher and two crushed ore stockpiles
• two parallel secondary crushing circuits, with each circuit consisting of:
- two 3.0 x 7.3 m double-deck coarse screens in parallel
- two cone crushers in parallel, each with 933 kW motors
• two parallel tertiary crushing HPGR circuits, with each circuit consisting of:
- 2.6 m diameter x 2.4 m wide HPGR with 9,000 kW of installed power
- one HPGR edge recycle conveying system
• two parallel primary ball mill grinding circuits, with each circuit consisting of:
- 7.9 m diameter x 13.7 m long (26 x 45 ft) ball mill with 18,000 kW of installed power
- one 14-place cluster of 0.84 m diameter cyclones
• two parallel secondary ball mill grinding circuits, with each circuit consisting of:
- 7.9 m diameter x 13.7 m long (26 x 45 ft) ball mill with 18,000 kW of installed power
- one 10-place cluster of 0.66 m diameter cyclones
• four parallel trains of rougher flotation, each with 6 x 630 m3tank cells
• two parallel trains of cleaner flotation in three stages
• concentrate thickening and filtration
• tailings facility reclaim water system (part of the TMF) for process water
• fresh water will be used for pump gland seals, reagent mixing and other special requirements
(e.g., hydraulic unit cooling).

All buildings and conveyors are enclosed with proper dust suppression and collection systems to address exposure to any silicates or fibrous materials.

ROM plant feed will be delivered to a dump pocket by haul trucks on top of the gyratory crusher. Crushed material from the gyratory crusher will be reclaimed by an apron feeder and conveyed to the primary stockpile.

Ore from the primary stockpile will be reclaimed using apron feeders and transported to the secondary crushing splitter chute via conveyor belt. A self-cleaning permanent magnet will be installed along the conveyor belt to remove unwanted tramp metals from the bulk materials ahead of the secondary crushing circuit. The two secondary cone crushers are operated in an open circuit with fines scalping and parallel configuration. There is a double-deck, multi-slope, vibrating screen installed ahead of each of the secondary cone crushers with the crusher fed directly from the screen oversize. Conveyors will have variable speed drives to facilitate the crusher choke feed requirement. Subsequently, the crushed product will join the screen undersize onto a conveyor belt before being transported to the HPGR feed bin. The edge material from the HPGR discharge will be recycled back to the HPGR feed, while the HPGR product (centre) will proceed to the secondary stockpile at the concentrator plant via a 4 km overland conveyor.

Each grinding circuit consists of two closed-circuit (with hydrocyclones) ball mills operated in series for primary and secondary grinding. The primary ball mill will be operated in a “direct” closed-circuit configuration with a cyclone cluster; the primary ball mill will receive feed from the secondary stockpile reclaim. The primary ball mill discharge will pass through a trommel for ball scats removal and into the pump box prior to entering the primary cyclone cluster for size classification. Primary cyclone underflow will feed back to the primary ball mill. Primary cyclone overflow will flow by gravity to a pump box and be pumped to the secondary cyclone cluster. Secondary cyclone underflow will flow to the feed of the secondary ball mill. The secondary ball mill will be operated in an “indirect” configuration, as the secondary ball mill feed must first pass through the secondary cyclone cluster to scalp final-grind material to the overflow stream. The secondary ball mill product will pass through a trommel before entering back to the pump box ahead of the secondary cyclone cluster. Secondary cyclone cluster overflow will report to the rougher feed conditioning tank prior to being pumped to the rougher flotation circuit.

Building from the previous 2011 AMC PEA and Hatch’s previous 2018 conceptual study, the mineral processing plant was designed to treat 90,000 t/d of ROM ore and consists of a crush-grind-flotation flowsheet.

One key consideration in the design of the processing plant is the phased concentrator construction approach, whereby the concentrator starts up at 50% capacity before expanding to full capacity (i.e., 45,000 t/d for the first five years, and 90,000 t/d thereafter).

The concentrator, when running at full capacity (90,000 t/d), will consist of the following major unit operations:

• four parallel trains of rougher flotation, each with 6 x 630 m3 tank cells
• two parallel trains of cleaner flotation in three stages
• concentrate thickening and filtration
• tailings facility reclaim water system (part of the TMF) for process water
• fresh water will be used for pump gland seals, reagent mixing and other special requirements (e.g., hy ........