Goose Site Geology
The Goose Site includes the Llama, Llama Extension, Umwelt, Echo, Nuvuyak, and Goose Main deposits; it has a consistent stratigraphic model that can be applied to all deposits. The folded Beechey Lake turbiditic metasediments, including oxide and silicate banded iron formation (BIF) horizons have been broken down into a modelled stratigraphy consisting of, from oldest to youngest: the lower sediments that contain a subordinate interbedded deep iron formation (DIF); the lower iron formation (LIF); the middle mudstone, the upper iron formation (UIF); and the upper sediments. This sequence is cut by quartz-feldspar porphyry dykes (QFP) and later gabbroic dykes.

Property Mineralization
Gold mineralization on the Property is spatially correlated to iron formation stratigraphy, and as a result, the mineralization geometry is relatively continuous along the plunging antiform/synform structures; however, within the modelled mineralized zones, gold grades can be variable. Further details on the mineralization at the Property are provided in the subsections below.

Llama and Llama Extension Deposits
Gold mineralization is hosted in both iron formation and clastic sedimentary lithologies, as well as rarely within quartz veins in the QFP dykes. Late gabbro dykes are known to post-date the timing of gold mineralization and do not host economic concentrations of gold. Banded oxide-facies iron formation, consisting of chert + grunerite + magnetite, hosts most of the known gold mineralization. Silicate-facies iron formation consisting of actinolite + chert + grunerite, and locally interbedded clastic sediments hosts relatively lesser gold concentrations. Clastic sediments consisting of greywacke, siltstone, and mudstone are noted to be mineralized, but typically return low levels of gold, with locally elevated gold assays related to veining. In some cases, felsic dykes have been proven to host gold; however, to date the amount is considered relatively insignificant and associated with mineralized veining.

Umwelt Deposit
Similar to the Llama deposit, gold mineralization at the Umwelt deposit is focused within a structural corridor that is axial plane parallel. Gold mineralization is strongly associated with quartz veining and sulphidized iron formation lithologies, most commonly associated with arsenopyrite ± pyrrhotite ± pyrite. Pyrite and pyrrhotite are the most common sulphides in the Umwelt deposit, with pyrrhotite becoming significantly more prominent as the goldmineralized zone plunges to the southeast. Arsenopyrite is the most common sulphide associated with visible gold, occurring as fine- to coarse-grained, euhedral, individual masses of crystals, occasionally located preferentially along banding planes, trailing along fractures, as vein halos, or as clusters along vein margins. Pyrrhotite appears as two textures within the deeper portions of this deposit; in the first, pyrrhotite is fine-grained and appears to be locally replacing magnetite in zones of intense sulphidization; the second texture is coarsegrained, and more blebby in nature. This second texture is later than the magnetite-replacement pyrrhotite and clusters along fine fractures, within veins, and along vein margins. Gold-mineralized zones are characterized by sulphide and silica alteration including quartz flooding, accompanied by shearing and veining. Visible gold is locally present, especially when sulphides are greater than 10% and when coarse-grained arsenopyrite and pyrrhotite are present.

Echo Deposit
Gold mineralization at the Echo deposit is concentrated in, but is not limited to, the lower contact of the iron formation with interbedded sediments. Brittle deformation is prominent at the contact; there is also a moderate amount of shearing present locally. A poorly mineralized QFP intrudes proximal to the structurally influenced contact and is interpreted to be closely related to the timing of gold mineralization. Alteration consists of varying amounts of grunerite + chlorite + quartz + calcite ± biotite. Mineralization associated with higher gold values (up to 120 g/t Au) consists of pyrrhotite + pyrite + arsenopyrite occurring with quartz veining, as well as replacement of the host rocks. The overall sulphide content ranges from trace to 10% over 0.5 m.

Nuvuyak Deposit
Discovered in 2018, the Nuvuyak deposit is located approximately 850 m along strike and 1,000 m down plunge of the Goose Main deposit. The central antiform extends from the Goose Main deposit and continues through an area of intense D2 cross folding that had previously been drill tested, recovering encouraging mineralization. At the Nuvuyak deposit, the central QFP dyke continues to follow the axial-planar structural zone, and gold mineralization is predominantly hosted in polyphase-folded LIF stratigraphy. The tight- to isoclinal-antiform geometry is very similar to that of the Goose Main deposit. Gold mineralization consists of pyrrhotite mineralization within fractures, replacement zones in brecciated host rock, and veins with locally rich arsenopyrite zones and abundant visible gold. Sulphide mineralization is associated with quartz veining, shearing, and moderate to strong amphibole and chlorite alteration.

Goose Main Deposit
Most of the observed gold mineralization at the Goose Main deposit is associated with quartz veins, silicification, and shearing. Gold mineralization occurs within silicified and variably sulphidized iron formation and, to a lesser extent, mixed iron formation and meta-sedimentary units located in the underlying central greywacke, modelled as DIF. Observed sulphide minerals include pyrite, arsenopyrite, and pyrrhotite. Gold mineralization is associated with accessory chlorite, carbonate, hornblende, and grunerite. Visible gold is locally present, especially when sulphides are greater than 10% and when coarse-grained arsenopyrite is present.

DEPOSIT TYPES
The gold deposits at the Property are hosted by sulphidized oxide and silicate iron formation rocks, and clastic sediments that are cut by barren and sulphide-bearing quartz veins. Analogous deposits occurring in this region of the Arctic include the Lupin Mine approximately 225 km west of the Property (Bullis et al, 1994), the Meliadine district at Rankin Inlet (Carpenter et al., 2005), and the Meadowbank deposit north of Baker Lake (Sherlock et al., 2004).

Within Canada, BIF-hosted gold deposits commonly occur within Archean-aged greenstone belts, typical of the shield areas of northern Ontario, Quebec, NWT, and Nunavut. Generally, BIF host rocks are thinly banded sedimentary rocks with alternating iron-rich and cherty (siliceous) layers.

In BIF-hosted gold deposits, gold mineralization is commonly associated with quartz veining, shearing, and zones of hydrothermal alteration suphidizing the host silicate and oxide iron formations (mainly pyrite, pyrrhotite, and/or arsenopyrite). Gold mineralization is mainly located along shear zones associated with tightly folded and structurally complex BIF horizons that provide favourable chemical and structural traps. This understanding is being applied in the current exploration strategy for the Property.

Sabina’s Project includes the Goose and George Project sites, the only sites on the Property with resource estimates. Multiple deposits have been explored at both sites. This Updated Feasibility Study focuses on the Goose Site and on the deposits that have Mineral Resources estimated in the Measured and Indicated categories. Mine planning has been completed for the Umwelt, Llama, Goose Main, and Echo deposits, and excludes Llama Extension, and Nuvuyak.

Open Pit Planning
MP reviewed the open pit design and dilution estimates for Umwelt, Llama, and Goose Main.

The following main steps were part of the planning process for Echo:
• Defining optimization parameters, such as gold price, preliminary operating-cost estimates, pit wall angles, preliminary dilution, and metallurgical recovery estimates for the design of Echo pit
• Developing the Echo operational design for the ultimate pit using MineSight
• Determining incremental (or mill) COG based on economic parameters for each deposit
• Determining external mining dilution based on mineral inventory block model using MineSight
• Creating LOM production schedule to maximize economic return while satisfying the plant feed and mine production constraints and considering the underground mine production
• Calculating hauling distances, per bench and phase, according to the LOM plan for the Echo pit and the defined haulage network
• Estimating equipment fleet and personnel requirements from the LOM production schedule.

General Design Parameters The general open pit design parameters used in the Echo detailed design are as follows:
• Pit walls
- Bench height, single bench mining, 5 m
- Height between catch benches, 20 m
- Bench face angle, 55° to 75° (variable as per Knight Piésold geomechanical guidance)
- Berm width, 8.6 to 10 m (variable).
• Haul roads (in and out of pit)
- Total road width allowance, 20 m
- Running surface on final two-way roads, 15 m
- Berms, 3.8 m wide (40° slope)
- Ditch, 1.0 m wide
- Ramp grades, 10% standard and 12% for pit bottom access
- Single-lane road allowance, 15 m
- Specific areas for caribou crossing may be established.
• Operations road (general light vehicle traffic and occasional heavy equipment)
- Width, 8 m to 10 m
• Mining
- Minimum pushback operating width, 50 to 60 m
- Minimum pit bottom width, 25 to 30 m
- Pit bottom sub-out depth, 5 m.

Open Pit Mine Production Schedule The Project open pit mines were designed to produce a total of 9.9 Mt of ore and 99.0 Mt of waste rock over a 14-year period (including two years of pre-production), yielding an overall open pit strip ratio of 10.1:1 (t:t).

The open pit and underground mine production schedule includes only the deposits at the Goose Site (Echo, Umwelt, Llama, and Goose Main). Due to the limited production capacity of the underground mines, specifically their inability to produce the full 3,000 t/d to 4,000 t/d mill feed, the open pit mines will supplement ore feed.

Underground Mining
The Goose Site has four deposits with the necessary grade, continuity, and tonnage to be considered for underground mining—namely Umwelt, Llama, Goose Main, and Echo. All four deposits have sufficient economic underground resources to support an underground mining operation. Each of the underground mines would be located below open pits.

Underground Mining Method Selection
The underground mining method was selected based on orebody characteristics, such as grade, dilution, dip, continuity, and thickness. Estimated productivity and selectivity of the mining methods were also considered. Four mining methods were considered:
• CF
• DF
• Post-pillar cut-and-gill (PPCF)
• Longhole stoping with URF as backfill.

Post-pillar-cut-and-fill (PPCF) was also considered but not selected.

Most mining methods that require cemented backfill were disregarded, due to the high cement freight costs to site. The exceptions were CF and DF, which were selected for the extraction of the crown pillar in Umwelt, Llama, and Goose Main. CF with CRF, with a primary–secondary sequence, was selected for Umwelt due to the added flexibility and higher recovery of the mining method when compared to PPCF.

The CF method was selected for the Umwelt deposit due to its variability, shallow dip, and thickness. While the orebody dip of the Goose Main deposit is sufficient for longhole stoping, the resulting increase in internal and external dilution reduced the number of stopes that were produced by MSO, enabling DF to have better economic results.

Cut-and-Fill Mining Method
CF is a flexible and selective mining method, well suited to thick, shallow-dipping orebodies. Primary and secondary headings alternate in a grid pattern that spans the width of the orebody. Headings follow the drill, blast, muck, ground support cycle typical of advancing a normal heading. Primary and secondary headings would then be predominately backfilled with CRF and URF, respectively. In the crown pillar at Umwelt, both primary and secondary headings would be backfilled with CRF to create a plug prior to placing tailings in the open pit above the crown pillar. Primary headings must be completed before adjacent secondary headings begin to advance. The heading design for Umwelt is 5 m wide by 5 m high.

Drift-and-Fill Mining Method
DF mining is similar to CF, as it follows the typical mining cycle of drill, blast, muck, and ground support with the same type of equipment. DF differs from CF in that it has only a single heading per level; alternatively, if multiple headings do occur, there is a permanent pillar between the headings. DF does not have a primary to secondary sequence or grid. CF headings sizes also remain the same to allow for a grid pattern, whereas DF consists of headings that vary in width. DF is a flexible and selective mining method, well suited to thin and relatively highgrade ore bodies.

Longhole Stoping Mining Method
Longitudinal longhole stoping is a cost-effective mining method that is well suited to steep tabular deposits with a hanging wall to footwall thickness greater than a few metres. Overcuts and undercuts are typically advanced along strike to the end of the orebody on each sub-level. On retreat, the stope is drilled and blasted from the overcut, and ore is removed from the undercut. Once the ore is removed, the stope is backfilled with, in this case, URF. URF use requires that permanent rib pillars be left between adjacent stopes.

As with the previous methods, multiple mining blocks have been proposed, with permanent sill pillars between them. Longitudinal longhole stoping can be reasonably productive and is typically more cost effective than highly selective mining methods such as DF or PPCF.

Primary Crushing
Mineralization from open pit and underground mining operations will feed a vibrating grizzly–primary jaw crusher system, which produces a product size P80 of approximately 100 mm.

Feed material to the crusher system will be hauled by 64-tonne haul trucks from the ROM stockpile or from the mines. Material will be stockpiled near the jaw crusher or direct-dumped through a static grizzly into a dump pocket. Stockpiled material will be re-handled using a loader. Extreme oversize material from the static grizzly will be removed for later size reduction using mobile machinery.

A vibrating grizzly feeder will draw material from the dump pocket. The spacing between the rails on the grizzly feeder will be 100 mm. The vibrating grizzly oversized material will discharge directly into the primary jaw crusher. A rock breaker is also provided for any long-aspect-ratio oversize not removed by the static grizzly. The undersized material will bypass the crusher and feed directly onto the primary crusher discharge conveyor.

Screening
The screen-feed conveyor will collect product from all three crushers and feed onto a double-deck vibrating banana screen. An electromagnet and metal detector are provided to protect downstream equipment from tramp metal ingress.

The top deck aperture will be 30 mm and a bottom deck aperture will be 10 mm, generating an undersize product stream P80 of approximately 9.5 mm. The oversize from the top screen deck will convey to the secondary crusher, while middlings from the second screen deck will convey to the tertiary crusher.

Screen undersize is transferred using two conveyors to the fine mineralized material stockpile dome.

Secondary and Tertiary Crushing
The secondary crusher will reduce the screen oversize (+30 mm) to a nominal product size P80 of approximately 22 mm using a standard mantle configuration with a closed side setting (CSS) of 22 mm.

The tertiary crusher will reduce the middling screen fraction (+10 mm to 30 mm) to a nominal product size P80 of approximately 13 mm using a short-head mantle configuration with a CSS of 13 mm. After the expansion to 4,000 t/d, a splitter box will be added above the existing tertiary crusher to divert half of the middling screen fraction to a newly installed tertiary crusher of identical configuration.

Both crushers discharge to a common conveyor system for recirculation back to the double-deck banana screen. A common bypass chute from the crusher feed bins is also designed to allow for each crusher to be shut down individually to allow for maintenance at a reduced overall throughput rate.

Fine Ore Stockpile and Reclaim
The fine-mineralized material storage facility will consist of a dome-covered stockpile with two in-line belt feeders located within a corrugated pipe reclaim tunnel. The belt feeders will transfer material to the conveyor feeding the ball mill.

The mineralized material storage facility will have a 2,000-tonne live capacity that can support process plant operations for 16 h when the crushing plant is not operating. The total capacity of the stockpile is 10,000 tonnes, which corresponds to approximately three days storage. Each belt feeder can provide the total throughput to the plant when required. The stockpile will be managed using a dozer to ensure the total capacity can be used effectively when needed. The live capacity of the stockpile will be reduced to 12 hours after the expansion of the plant to 4,000 t/d.

For pH management of downstream processes, quicklime will be added to the reclaim conveyor from a lime silo via a screw feeder.

Grinding
The grinding circuit will consist of a ball mill operating in closed circuit with a hydrocyclone cluster and a fine-grind mill operating in closed circuit with a hydrocyclone cluster. Material from the fine ore stockpile will be fed to the ball mill via the ball mill feed conveyor. The grinding circuit will operate at a nominal throughput of 136 t/h (fresh feed) and produce a target final particle size P80 of approximately 50 µm. The ball mill will be 4.6 m in diameter by 8.8 m effective grinding length, driven by a 3.3 MW motor.

Water will be added to the ball mill to maintain the charge in the mill at a constant slurry density. Slurry will overflow from the ball mill to a trommel screen, attached to the ball mill discharge end. The ball mill trommel screen oversize will overflow into a trash bin for removal from the system. The trommel is also removable to allow for simple access to the mill interior for maintenance.

The ball mill hydrocyclone cluster will classify the feed slurry into coarse and fine fractions. The coarse underflow will feed the ball mill for additional grinding. The fine overflow with a nominal P80 of approximately 106 µm will flow by gravity to the fine-grind mill cyclone feed pump box for classification prior to additional grinding. The ball mil hydrocyclones have been designed to facilitate a 400% recirculating load, although under normal operations this will perform at 300%. Additional grinding will be performed by a 1.5 MW fine-grinding stirred mill to achieve the final grind P80 of approximately 50 µm. On expansion of the plant to 4,000 t/d, a secondary stirred mill will be installed in parallel to provide extra-fine grinding capacity. The ball mill product size will be coarsened to a P80 of approximately 212 µm to facilitate the higher throughput rate without changing the ball mill.

A portion of the primary hydrocyclone underflow will be pumped to a trash screen, which in turn feeds a gravity concentrator circuit. A portion of the secondary hydrocylone underflow will also be handled similarly with a dedicated gravity concentrator.

Summary
The process selected for the Back River Project is based on testwork described in Section 13 and consists of a leach and carbon adsorption process comprising: crushing; grinding; gravity concentration; leaching; carbon adsorption; detoxification; carbon elution and regeneration; gold refining; and tailings thickening and disposal.

The mill is designed with a nominal capacity of 3,000 t/d at a planned average feed grade of 6 g/t Au. The crushing circuit will operate at an availability of 70%. Milling and leaching circuits will operate 24 h/d, 365 d/a, at an availability of 92%.

An expansion of plant nominal capacity to 4,000 t/d is planned for Year 2 of operation under the same operating schedule of 24 h/d, 365 d/a, at an availability of 92%.

The 3,000 t/d plant will consist of the following unit operations:
• Primary crushing—a vibrating grizzly and jaw crusher in open circuit producing a final product P80 of approximat ........