Cassini is located on the southern section of the Widgiemooltha Dome. The geology of the Widgiemooltha Dome and the area to the south consists of a thrust repeated sequence of basic ultramafic extrusive and intrusives, with intercalated sediments and acid volcanics with nickel sulphide orebodies found at the base of the ultramafic sequence.

The Cassini orebody as interpreted in the Mineral Resource is split into eight lodes, labelled CS2-CS9. From a mining perspective, the Mineral Resource has been delineated into two main areas based on spatial characteristics. These mining areas have been named by the dominant lode (CS2 or CS4).

The CS2 Area (CS2, CS3, CS6, CS7 and portion of CS5 lodes) consists of east-west trending parallel lodes, mainly offset, dipping at ~45° to the south with thickness from ~1m to ~7m, averaging 3m. The CS2 Area extends from ~260mRL (approx. 50mbs) to ~-240mRL (480m vertical extent). Grades and orebody thickness are inconsistent above ~75mRL.

The CS4 Area (CS4, CS8, CS9 and portion of CS5 Lodes) consists of parallel lodes striking northwest/southeast at ~125° and dipping at ~75-80° to the southwest. Average widths for the CS4, upper CS5 and CS9 lodes are 2-3m, with the CS5 lode thickening to 5-7m and up to 11m in parts below ~-250mRL (grades in this area also increase). The area extends from ~100mRL to -380mRL. Grades and thickness are inconsistent above ~10mRL.

The Cassini mine will be accessed via a new box-cut and portal. The stope optimisation process showed that the economic portion of the Cassini orebody (commences from 250m below surface). Based on geotechnical analysis and the results of geotechnical drilling, the box-cut has been located ~700m to the south of the orebody where near-surface ground conditions are more favourable.

A twin decline system will be developed from the box-cut zone to the production zone, with access and return air declines excavated in parallel, allowing primary ventilation to be established early in the mine life. Ventilation and secondary egress will be via a raise system developed from the ventilation decline to the box-cut

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 development and provides void support for dilution mitigation. Vertical sub-level intervals are 15m floor-to-floor, allowing good drill and blast control. Areas with no 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 30m 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 stoping block 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.

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 a waste dump to be constructed close to the portal. Ore will be delivered to a run-of-mine (ROM) pad for subsequent haulage to KNC. 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. 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.

A minimum mining width (MMW) of 1.5m in the shallower-dipping CS2 area and 1m in the steeper-dipping CS4 area (true width) was designed.

Fill stopes had an additional 3% dilution at zero grade included to account for bogging of fill material. The total global average planned and unplanned stope dilution (including fill dilution) proportion within the mine plan stope shapes is 30%.

Mining recoveries of 95% were applied to stopes to allow for issues such as local ore body spatial variability and material left behind during remote loading.

Ore drives will be driven along strike and split-fired where possible to minimise development dilution. A shantyback profile has been applied in the shallower-dipping CS4 area. The drive profiles allow operation of a modern 5m3 loader fleet providing efficient productivity. A mining recovery of 100% and no unplanned dilution was assumed for ore development. Approximately 22% of the total 1.2Mt ore production will be from development, with the remaining 78% from stoping.

The ventilation circuit consists of fresh air flow into the portal and down the decline. Secondary fans located in the decline will route fresh air to working faces through flexible ducting. Return air will be drawn through a longhole rise system in the production area, through the ventilation decline and out of the mine via exhaust fans located on the ventilation rise surface collar in the box-cut.

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.