Deposit Geology
The Project area, comprising the Kudz Ze Kayah claim blocks within which the ABM deposit is located, encompasses units of the Grass Lakes group. The surface geology of the property was initially mapped by Cominco in 1996 at 1:20,000 scale (Schultz & Hall, 1997) and subsequently by BMC at 1:20,000 scale in 2017 (Baker et al., 2017).

The ABM deposit (comprising the ABM Zone and Krakatoa Zone) primarily comprises continuous, shallowdipping massive sulphide mineralization hosted within a thick felsic package of volcaniclastics and coherent sill/flow complex that locally make up the Kudz Ze Kayah formation.

Massive sulphide of the ABM Zone is hosted within a felsic rock package, whereas the Krakatoa Zone is predominantly hosted by a pre-mineralization mafic sill located within the felsic volcanic package. Mineralization at Krakatoa also occurs in the felsic hangingwall units stratigraphically overlying the mafic sill, in what is broadly interpreted to be the equivalent of the ABM mineralized position. Only scattered vein-style and disseminated mineralization occurs within the mafic sill lying stratigraphically below the ABM Zone.

The upper limits of the ABM and Krakatoa Zones are truncated near surface and overlain by glaciofluvial sediments. The massive sulphide mineralization at ABM occurs under approximately 2– 20 m of glaciofluvial overburden and is up to approximately 30 m in true thickness, whereas the Krakatoa Zone occurs under approximately 30 m of glaciofluvial overburden and is up to approximately 22 m in true thickness. The downdip margin of the ABM Zone appears to transition into a mixed and variably carbonaceous felsic volcanosedimentary package, whereas the Krakatoa Zone currently remains open at depth beyond the down-dip extent of the mafic sill.

A post-mineralization brittle fault zone (East Fault) offsets the ABM and Krakatoa zones, and angular clasts of sulphide are to be found within the fault zone breccias. The south-eastern margin of Krakatoa is cut by another late brittle fault zone of the same generation (Fault Creek Fault). There exists a marked difference in the stratigraphy east of the Fault Creek Fault, with recent drilling having identified a package to the east of the fault, dominated by felsic volcaniclastics and minor felsic intrusives, which transitions conformably up into the overlying Wind Lake formation. The marked change in volcanic stratigraphy across the Fault Creek Fault, despite little of no evidence of a significant offset of the Wind Lake formation basal contact, could potentially indicate the presence of a syngenetic fault structure along the south-eastern limit of the Krakatoa Zone. Recent attempts at a reconstruction of the ABM Zone and Krakatoa Zone into a single massive sulphide unit are also not consistent with the degree of movement along the East Fault that is observed at the Wind Lake formation basal contact. These features could indicate the presence of syngenetic fault structures either side of the Krakatoa Zone that was later the locus of late-stage brittle faulting. As such, the area east of the Krakatoa Zone remains a significant exploration target. A schematic geological cross-section through both the ABM and Krakatoa zones.

Mineralization

ABM Zone
Massive sulphide of the ABM Zone is up to 39 m true thickness, extending approximately 700 m along strike and approximately 500 m down dip. It dips to the north-northeast at approximately 35° near surface, transitioning to a dip of approximately 15° at around 200 m depth below the valley floor. The up-dip extent of the deposit is truncated by erosion and covered by approximately 2–20 m of glaciofluvial overburden.

Massive sulphide mineralization of the ABM Zone occurs as several stacked massive sulphide lenses to the west, transitioning to a single massive horizon at around 415,025 m E and extending to approximately 415,250 m E where it is then truncated by the post-mineralization East Fault. Stockwork and disseminated mineralization occurs equally both in the hanging wall and footwall to massive sulphide, and to a lesser degree between massive sulphide lenses.

Sulphide mineralization is dominated by pyrite, sphalerite, pyrrhotite (+ marcasite), galena and chalcopyrite, with minor arsenopyrite and a range of sulphosalts predominantly comprising tennantite-tetrahedrite and freibergite. Both the up-dip part of ABM Zone and most of Krakatoa Zone have elevated sulphosalt content relative to the remainder of the ABM deposit.

Krakatoa Zone
Krakatoa Zone mineralization, bound to the west by the East Fault and to the east by the Fault Creek Fault, is hosted within Kudz Ze Kayah formation that dips at 35° to the north-northeast. Although of lesser extent, the distribution of mineralization within the Krakatoa Zone is more spatially complex than the ABM Zone due to the stacked mineralized lens system. Massive sulphide mineralization occurs within three principal mineralized horizons:

1. The “Upper lens”, broadly interpreted as the stratigraphic equivalent to the ABM lens.
2. The “Main lens”, the major component of Krakatoa Zone in terms of sulphide mineralization with a true thickness up to 22 m.
3. A less pronounced and semi-continuous “Lower lens”.

Krakatoa Zone mineralization is broadly concordant with stratigraphic layering of the host rocks, extending over approximately 200 m of strike, at least 500 m down dip, and up dip to the base of glacial overburden of 20–30 m thickness.

Several pre- to syn-mineralization growth faults are thought to influence the massive sulphide bodies at Krakatoa in terms of offsets and changes in massive sulphide thickness. Both the large coherent mafic and aphanitic rhyolite bodies appear to have an influence on the spatial distribution of sulphide mineralization. As these bodies are themselves mineralized, it is likely that these coherent bodies acted as fluid aquacludes during mineral deposit formation.

Host rock types and alteration styles of Krakatoa Zone mineralization are for the most part similar to those encountered in the ABM Zone. The key difference is the degree of mineralization associated with the mafic sill, which below ABM Zone is only poorly mineralized. The Main lens comprises the bulk of mineralization at Krakatoa, with massive sulphide occurring both within the felsic volcanics immediately beneath the mafic sill, and within the mafic sill, after replacement of enclaves of felsic volcaniclastics and/or replacement of the mafic sill itself.

Pursuant to the mining plan contained in the Feasibility Study the majority of the ABM Deposit will be mined by open pit mining methods. It is expected that a single pit will be mined, with mining of the ABM Zone comprising four separate stages, and with the Krakatoa Zone mined in a single stage. A total of 14.0 Mt of ore and 138.4 Mt of waste will be mined by open pit mining methods, for an expected average LOM strip ratio of 9.9:1. The Stage One ABM Zone pit has an expected strip ratio of 6:1, in order to facilitate a rapid payback of pre-production capital.

Open pit mining is planned to be completed over a period of approximately 8.5 years, inclusive of pre-production mining requirements.

Underground mining has only been considered for the deeper portion of the Krakatoa Zone. The primary mining method that is planned to be utilized for the underground mine is underhand long hole stoping. All underground stope voids are planned to be filled with cemented paste fill.

The underground mine is planned to commence at the end of Year three (3), once Stage One of the ABM open pit has advanced sufficiently to allow access to in-pit portal locations.

Crushing
A reinforced concrete steel bridge, with retaining wall, extends from the ROM pad to the ROM bin dump point. This bridge provides access for the FEL. A Caterpillar 988 FEL or equivalent will be used to feed the crusher from the ROM pad. A 900 mm grizzly for scalping oversize material is installed on the ROM Bin which will have 20 minutes retention time (135 t).

ROM ore is withdrawn from the bin by an apron feeder and fed to a vibrating grizzly for removal of fines. The vibrating grizzly will operate ahead of the primary crusher to remove fines from the crusher feed. The Design Case throughput rate for the crusher was estimated to be 446 t/h, operating 13.5 hours per day.

Provision was made for tramp metal magnet on the Primary Crusher Discharge Conveyor, as well as a metal detector on the Coarse Ore Stockpile Feed Conveyor.

Insertable bag type dust collectors are provided to collect and filter out fugitive dust emissions from the materials handling circuit.

Normal crusher feeding practice will entail the crusher operator manning the FEL and loading the ROM bin. Video monitors in the FEL cab will allow the operator to monitor the status of the crusher during loading operations. An emergency stop switch located in the FEL cab will be capable of shutting down all crushing operations remotely from the cab.

Grinding – SAG and Ball Mills
The SAG Mill and Ball Mill grinding circuit are located at the southern end of the Process Building where the ore is fed from the Coarse Ore Stockpile via the SAG Mill Feed Conveyor. The grinding circuit will comprise an open circuit SAG Mill and a Ball Mill in closed circuit with cyclones.

The SAG Mill will be a 5.79 m diameter x 5.49 m effective grinding length (EGL), grate discharge, steel-lined mill, driven by a 2.7 MW single pinion drive. The SAG Mill will discharge over a 12 mm aperture trommel screen. Trommel oversize (pebbles and steel scats) will be returned to the SAG Mill Feed Conveyor by three recycle conveyors in series.

The Ball Mill be a 4.72 m diameter x 7.32 m EGL, overflow discharge, rubber-lined mill driven by a 2.7 MW single pinion drive. The mill will be driven by a fixed speed drive and will operate at nominally 75% of critical speed. The Ball Mill will discharge over a 10 mm aperture trommel screen. The oversize will discharge into a bunker for disposal as waste. The undersize will gravitate into the mill discharge hopper.

The SAG Mill trommel screen undersize will also gravitate to the mill discharge hopper, where the combined mill discharge will be diluted with process water and pumped via duty/stand-by pumps to a hydrocyclone cluster for classification. The overflow from the cluster will flow by gravity to the flotation feed trash screen, to remove any trash prior to flotation. A portion of the cyclone underflow can be directed to the SAG Mill to facilitate balancing of the grinding in the SAG Mill and Ball Mill as the SAG Mill will generally have spare capacity on most ore types.

A common liner handler will be used to facilitate removal and installation of the SAG Mill and Ball Mill liners during planned mill relines.

An overhead gantry crane will be used for recharging grinding media as well as maintenance of the mills and cyclones.

Provision has been made within the Grinding and Classification area to receive a gold recovery facility if required in the future.

Regrind – Vertical Mills
Regrinding the copper, lead and zinc rougher concentrates to P80 of 30 µm, 30 µm and 35 µm respectively has been included based on testwork. A single Metso SMD 355 kW unit was selected for each of the copper, lead, and zinc regrind duties. The plant layout has allowed space for an additional regrind mill should future expansion be required.

The flotation circuit is sequential, with copper, lead, and zinc recovered in that order. All flotation cells are mechanically agitated, forced air conventional cells. In addition to the flotation cells, the plant layout has allowed space for an additional flotation cells to be installed within the plant footprint should future ore sources warrant this.

Copper
Trash screen underflow slurry is pumped to the first of two 40 m³ agitated copper conditioning tanks, where flotation reagents are added. Conditioned slurry flows to the first of six 38 m³ rougher flotation cells in series. The first rougher cell will operate as a pre-float rougher which is then pumped to a single 8 m³ pre-float cleaner cell and the concentrate pumped to the copper final concentrate hopper. Pre-float cleaner tailings flows to the copper regrind mill. Tails from the pre-float rougher passes to the remaining rougher cells. Concentrate from the rougher cells is pumped to the copper regrind mill.