There are two mining areas in the Durkin North mine plan, being the D1/D2 area and the D3/D5 area. The D1/D2 area strikes predominantly east-west with a strike length of ~550m, extending from ~-85mRL (~420 mbs) to -260mRL (175m extent). This area gently plunges to the north resulting in a long strike over a relatively small vertical extent. The orebody in D1/D2 is generally narrow (1-3m), with one main lode and a small hangingwall splay in the southern area. The orebody dips to the north, with dips ranging from relatively shallow dipping (down to 45° in parts) up to 75°. The D3/D5 area strikes southeast/northwest with a strike length of ~380 m, extending from -270mRL to -450mRL (180 m extent). The plunge in this area tends to vertical. Dips are generally steeper than D1/D2, ranging from 65-80° to the north-east. The D3/D5 area contains several closely spaced economically extractable lodes in parallel, with widths 1-3m.

The Long Mineral Resource generally strikes northwest-southeast. The Mineral Resource is spread out over an extensive area. Ore pod strike lengths are variable, ranging from 20-30m to ~500m. Some areas dip steeply and continuously to the north-east at approximately 70-80°, while other ore pods are flat dipping at 15-25°. The orebody is generally less than 2m thick.

The Durkin North mine is planned to be accessed both through the existing Long mine and the existing Otter mine. Both mines are accessible and require minimal rehabilitation. The Durkin North access decline will be developed from both sides and will connect Long and Otter when broken through. The Long designs are all located within the existing Long capital development. Long orebodies will initially be accessed through the Long-Victor portal. Once the Durkin decline has broken through, all access will be via the Otter portal, as this provides a shorter haul distance than the Long-Victor portal with additional ventilation benefits.

Based on the orebody spatial and geotechnical characteristics, the primary mining method proposed is bottom-up longitudinal longhole stoping (LHS) with modified Avoca assuming cemented rockfill (CRF). This mining method requires minimal capital and development and provides void support for dilution mitigation.

Vertical sub-level intervals are 14-16m floor-to-floor, allowing good drill and blast control. Areas without top access (i.e. crown stopes or levels directly beneath sill pillars) will be mined using conventional longhole open stoping, retaining in-situ pillars for support. Maximum open stope strike lengths of 20m have been applied based on geotechnical studies. Slots to open stoping spans have been designed assuming handheld development methods. Subsequently mined stopes in filled levels will be fired against fresh CRF without the requirement for additional slotting.

Stopes will be mined from the ends of the orebody retreating towards central level accesses from the decline, with each stoping level to be completed before stoping in the level above commences. The Durkin North stoping blocks will be split into independent panels of several levels to allow concurrent mining, with each panel separated by a 1.5m thick high strength (8% cement) CRF sill pillar. The Long stoping blocks are sufficiently spatially separated to allow independent mining without sill pillars.

Drilling and blasting will be carried out using conventional electric over hydraulic drill rigs and diesel charge wagons. A modern diesel mechanised fleet will load and haul broken material to surface. Mullock will be delivered to the existing waste dumps at Otter and Long. Ore will be delivered to the existing ROM pad for subsequent haulage to the toll-treatment processing plant by road trains. Waste for fill will be backhauled from surface and mixed with cement delivered by agitator trucks to the fill location. Loaders will deliver the CRF (3% cement) to the stoping voids.

A MMW of 1m was applied for both areas. Additional unplanned stope dilution assumptions were applied assuming ‘skins’ of a certain thickness on each hangingwall and footwall contact. Durkin had a 0.5m skin applied (final mining void 1.5m) and Long had a 0.5m skin included for filled stopes and 1.0m for open stopes. The Durkin ore had a subsequent additional allowance for unplanned dilution at zero grade (inclusive of fill dilution).

The Long stopes had an additional 2% dilution at zero grade included to account for bogging of fill material.

At Durkin North, mining recoveries of 95% were applied to filled stopes to allow for issues such as local orebody spatial variability and material left behind during remote loading. For open stopes, a mining recovery of 68% was applied to allow for retention of rib pillars in these areas. Mass firing stopes through access intersections had a mining recovery of 80% applied.

At Long, a mining recovery of 95% was applied to filled stopes, and 90% to open stopes. 5m thick rib pillars were placed every 20m along strike in the open stoping areas based on geotechnical studies.

Ore drives will be driven along strike under geological control. A shanty-back profile has been applied in the shallower-dipping areas of Durkin. The drive profiles allow operation of a modern 3m3 loader fleet providing efficient productivity. A mining recovery of 100% and no unplanned dilution was assumed for ore development. Approximately 32% of the total 1.2Mt ore production will be from development, with the remaining 68% from stoping.

Prior to breakthrough of the Durkin access, the ventilation circuits will be separate. Fresh air will be drawn through the Long and Otter portals by primary fans located on the existing return air rises to surface. Secondary fans located in the decline will route fresh air to the Durkin access working faces through flexible ducting. Once breakthrough of the Durkin access occurs, fresh air will be drawn through the Otter decline and Durkin access, past the Durkin and Long workings and out of the ventilation rises at Long.

Specialist underground contractors will provide equipment, personnel and consumables required for the works. Mincor will supply technical support, environment health and safety (EHS) support, site management and diesel.

Ore mined from operation will be trucked to the surface and stockpiled at the KNC (Kambalda Nickel Concentrator). A front-end loader will then be used to transport ore from the surface stockpile at the KNC into the ROM bin to feed the mill at a predetermined blending mix. The KNC design was based on a conventional sulphide processing route using traditional grinding and flotation technology to produce saleable nickel-copper-cobalt concentrate.