The Eskay Creek deposit is known as an outstanding example of a high-grade, precious metal rich epithermal volcanogenic massive sulphide (VMS) deposit that formed in a shallow submarine setting. The deposit has features and characteristics typical of a classic VMS deposit: it formed on the seafloor in an active volcanic environment with a rhyolite footwall and basalt hanging wall, having chlorite-sericite alteration in the footwall and sulphide formation within a mudstone unit at the seafloor interface. What differentiates the Eskay Creek deposit from other VMS deposits are the high concentrations of gold and silver, and an associated suite of antimony, mercury, and arsenic. These mineralization features, along with the high incidence of clastic sulphides and sulphosalts, are more typical of an epithermal environment with low formation temperatures.

Several distinct styles of stratiform and discordant mineralization are present at the Eskay Creek Project, defined over an area approximately 1,400 m long and up to 500 m wide (The main body of mineralization, the 21B Zone, is a stratiform tabular body of gold-silver-rich mineralization roughly 900 m long, 60 to 200 m wide, and locally exceeding 20 m thick. Individual clastic sulphide beds range from 1-100 cm thick and become progressively thinner up sequence). Ore is composed of beds of clastic sulphides and sulphosalts containing variable amounts of barite, rhyolite, and mudstone clasts. Imbricated, laminated mudstone rip-up clasts were observed locally at the base of the clastic sulphide-sulphosalt beds, indicating turbiditic emplacement of some beds. In the thickest part of the orebody, pebble and cobble-sized clasts occur in a northward trending channel overlying the Eskay Rhyolite. The beds grade laterally over short distances into thinner, finer-grained, clastic beds and laminations.

Gold and silver occur as electrum and amalgam while silver mainly occurs within sulphosalts. Precious metal grades generally decrease proportionally with decrease in total sulphides and sulphosalts. Clastic sulphoside beds contain fragments of coarse-grained sphalerite, tetrahedrite, lead-sulphosalts with lesser freibergeite, galena, pyrite, electrum, amalgam, and minor arsenopyrite. Stibnite occurs locally in late veins, as a replacement of clastic sulphides, and appears to be confined to the central, thickest part of the deposit., suggesting a locus for late hydrothermal activity. Cinnabar is rare and is found associated with the most abundant accumulations of stibnite. Barite occurs as isolated clasts, in the matrix of bedded sulphides and sulphosalts, and also as rare clastic or massive accumulations of limited extent. Barite is more common towards the north end of the deposit.

Early exploration efforts focused on discordant-style, precious metal mineralization hosted in sulphide veins within the rhyolite, felsic intrusions, and the footwall volcanic units. Following recognition of more significant stratiform mineralization, exploration expanded further to the north, defining the 21 Zone deposits. Distinct zones were defined by variations in location, mineralogy, texture, and precious metal grades (Edmunds et al, 1994).

Stratiform style mineralization is hosted in black carbonaceous mudstone and sericitic tuffaceous mudstone of the Contact Mudstone located between the Rhyolite and the Hanging Wall Andesite. The stratiform-hosted zones include the 21B Zone, the NEX Zone, the 21A Zone (characterized by arsenic-antimony-mercury sulphides), the barite-rich 21C Mudstone Zone, and the 21Be Zone. Stratigraphically above the 21B Zone and usually above the first basaltic sill, the mudstones also host a localized body of base metal-rich, relatively precious metals-poor, massive sulphides referred to as the Hanging Wall or HW Zone.

The Project is located predominantly to the south of Tom Mackay Creek with a small portion extending to the north. Infrastructure will be located on the south side of Tom Mackay Creek, with the pit extending to the north beyond Tom Mackay Creek. Underground mining has previously been conducted in the northern portion of the Project at depth. The potential for underground development beneath the open pit was examined in preliminary evaluations during the 2021 PFS but was not included as part of the PFS. There is still potential for the inclusion of underground mining in future mining studies.

Each pit phase was designed to accommodate the proposed mining fleet. Mining will occur on 8 m benches with catch benches spaced either 8 or 16 m vertically depending on lithology type. The haul roads will be 30.2 m in width with a road grade of 10%.

The mine schedule plans to deliver 26.4 Mt of mill feed grading 3.37 g/t Au and 94.4 g/t Ag over a mine life of 10 years. Waste tonnage totalling 212 Mt will be placed into either non-acid generating (NAG) or potentially acid-generating (PAG) waste destinations. The overall strip ratio is estimated at 8.0:1. The mine schedule assumed a maximum of 2.9 Mt/a of feed will be sent to the process facility using a suitable ramp-up in year 1. A maximum descent rate of eight benches per year per phase was applied.

The proposed mine life includes 30 months of pre-stripping and 10 years of mining. Mill feed will be stockpiled during the pre-production years, with three grade stockpiles envisaged. A technical sample will be mined in Year -3 so that process performance of the mill can be evaluated on a bulk sample.

The mine equipment fleet is anticipated to be leased to lower capital requirements. Pre-production mining will be completed with 11.5 m3 loaders and 91 t rigid body trucks. This smaller fleet is better suited to the lower production tonnage requirements and narrower working conditions. With full production starting in Year 1, the primary loading units will be 22 m3 hydraulic shovels. Additional loading will be completed by a 23 m3 loader. The smaller loaders will shift to working at the primary crusher and site maintenance roles (snow removal, etc.). It is expected that one of the 11.5 m3 loaders will be at the primary crusher full time. The main production haulage trucks will be conventional 144 t rigid body trucks from Year 1 onwards. The support equipment fleet will be responsible for the usual road, pit, and waste rock storage facility (WRSF) maintenance requirements, but due to the climate conditions expected, will have a larger role in snow removal and water management.

Grade control will be completed with a separate fleet of RC drill rigs, with a 10 m x 5 m pattern in ore and 20 m x 10 m pattern in waste. Blasthole sampling will also be part of the initial grade control program to determine the best sampling method for operations.

There will be three WRSFs that will store the NAG waste. The largest will be located to the immediate west of the north and south pits, and two smaller WRSFs will be constructed to the west and northeast of the North pit respectively. A portion of the NAG waste will also be disposed of in the North pit as backfill. The WRSF design used a swell factor of 1.30. For the WDW facility, the lift height will be 20 m. Assuming a 37° face slope, the overall slope will be 26.5° with 13.6 m berm widths. A 37° face slope was also used for the in-pit backfill WRSFs. PAG waste will be sent to the TMSF to be submersed below water.

Pit designs were developed for the north and south pit areas. The north pit will consist of five main phases, while the south pit will only contain a single small phase. The pit optimization shells used to determine the ultimate pits were also used to outline areas of higher value for targeted early mining and phase development.

Equipment sizing for ramps and working benches is based on the use of 144 t rigid-frame haul trucks. The operating width used for the truck is 6.9 m. This means that single lane access is 23.3 m (twice the operating width plus berm and ditch) and double lane widths are 30.2 m (three times the operating width plus berm and ditch). Ramp gradients are 10% in the pit and WRSF for uphill gradients. Working benches were designed for 35–40 m minimum mining width on pushbacks. As the haul road grades exceed 5%, runaway lanes or retardation barriers will need to be incorporated into final execution designs as the project progresses to more detailed stages.

The crushing facility will be a single-stage crushing circuit that will process the run-of-mine (ROM) ore at a nominal processing rate of 473 t/h in Year 1 to Year 4 and 440 t/h from Year 5 onwards. The crushing facility will operate at 70% availability. The major equipment and facilities at the ROM receiving and crushing areas will include:
• Stationary ROM bin grizzly;
• ROM surge bin;
• Vibrating grizzly feeder;
• Primary jaw crusher;
• Coarse ore stockpile; and
• Stockpile reclaim apron feeders.

The ROM ore will be trucked from the open pit and dumped directly into the ROM surge bin or stockpiled on the ROM storage pad, which can be reclaimed by a front-end loader (FEL) for continuous feed. The ROM ore from the ROM bin will be withdrawn by the vibrating grizzly feeder where the coarse oversize will report directly into a single jaw crusher. The feed material will be crushed and will discharge from the crusher onto the primary crusher discharge conveyor delivering feed material to the coarse ore stockpile. The significant route length (725 m with 150 m lift) from the primary crusher to the coarse ore stockpile will require an overland conveyor.

The coarse ore stockpile feed overland conveyor will be fitted with a weightometer to monitor crushing plant throughput and assist with operational and metallurgical accounting. The coarse ore reporting to the coarse ore stockpile feed overland conveyor will be transferred to the coarse ore stockpile area. The coarse ore stockpile will provide 8 hours of live capacity.

Coarse ore from the stockpile will be reclaimed by two apron feeders at a combined nominal rate of 310 t/h discharging ore to the SAG mill feed conveyor to be fed into the SAG mill. The SAG mill feed conveyor will be equipped with a weightometer to provide data for feed-rate control to the grinding circuit.

Grinding and Classification
The primary grinding circuit for Year 1 to Year 4 will consist of only a SAG mill and ball mill in a closed circuit with classifying cyclones. A pebble crusher will be installed at the end of Year 4 and will start operating in Year 5. The primary grinding circuit for Year 5 onwards will consist of a SAG mill, pebble crusher and ball mill in a closed circuit with classifying cyclones.

The proposed ball mill circulating load is a nominal 250% of new feed.

The primary grinding circuit is designed for a product size 80% passing size (P80) of 100 µm. The SAG mill will be driven by a single 3.8 MW wound rotor drive motor (WRIM) with a liquid resistance starter (LRS) and slip energy recovery (SER) unit to allow for variable speed operation. The single pinion ball mill will be driven by a single 4.9 MW fixed speed WRIM with an LRS.

As required, steel balls will be added into the SAG mill and ball mill using a ball bucket and kibble system to maintain grinding efficiency.

Process water will be added with the coarse ore to the SAG mill to achieve a slurry density of approximately 70% solids (by weight). The SAG mill discharge will pass through a trommel screen. During Year 1 to Year 4, screen oversize will be returned to the SAG mill feed conveyor. Once the pebble crusher is installed and operated from Year 5 onwards, the trommel screen oversize will be transferred to the pebble crusher via a pebble crusher feed conveyor and the crusher product returned to the SAG mill feed conveyor. Undersize from the trommel screen will discharge directly into the cyclone feed pump box, where it will be diluted with process water and pumped to the cyclone distribution manifold via a cyclone feed pump. Cyclones will classify the feed slurry to achieve overflow stream of 30% solids (by weight) comprising product sized particles, whilst the cyclone underflow fraction of 72% solids (by weight) will report to the ball mill.

Cyclone underflow will be ground in the ball mill. Ball mill discharge will flow through the ball mill discharge trommel screen and remove any trash or broken mill balls, which will then be discharged to a concrete ball mill scats bunker. Trommel screen undersize will discharge into the cyclone feed pump box and combined with SAG mill trommel undersize.

The cyclone overflow will report to a trash screen via gravity, which will remove trash to a trash bin. Trash screen undersize will then flow by gravity to the rougher flotation circuit.

Maintenance activities in the grinding and classification area will be serviced by the mill area crane, which will be used for ball mill charging duties and maintenance activities. Spillages in the grinding and classification area will be pumped by the mill area sump pump into the cyclone feed pump box.

The plant will process material at a nominal rate of 2.9 Mt/y for Years 1 to 4 and 2.7 Mt/y for the remaining years with an average head grade of 3.2 g/t Au and 94 g/t Ag. The plant is designed to operate two shifts per day, 365 d/y with an overall plant availability of 92%. The process plant feed will be supplied from the Eskay Creek open pit mine and the process plant will produce gold concentrate to be sold to refineries.

The processing plant will consist of the following:
• Single stage crushing circuit (jaw), fed from the open pit mine;
• Coarse ore stockpile with reclaim system, fed from an overland conveyor;
• Primary grinding including a SAG mill, pebble crusher (installed at Year 4), and ball mill in closed circuit with hydrocyclones;
• Rougher flotation with conventional concentrate regrind and two stages of cleaning;
• Slimes classification via two stages of hydrocycloning, fed from the rougher flotation tails;
• Secondary grinding an ........