Gold mineralisation at Cowal is most concentrated to a north-south orientated corridor hosted in second and third order structures marginal to and parallel to the Gilmore Suture. The gold deposits are hosted by a shallowing-upwards sequence of semi-conformable sedimentary, volcaniclastic, and volcanic rocks of trachydacitic and trachyandesitic composition that have been intruded by a diorite sill, andesite dome, and various dykes. The sequence strikes northeast–southwest and dips moderately 30° to 40° to the northwest.

The mineralisation at CGO comprises six deposits: E41E, E41W, E42, Galway/Regal, E46 and GRE46. GRE46.

The GRE46 zone trends north-south, dips vertical to -70° west, and extends approximately 2km along strike, 200m across strike and at least 1km down dip. Individual lenses in the GRE46 mineralised zone are 1-15m wide, 25-250m long, and extend 50-200m down dip. Lenses consist of narrow high-grade quartz carbonate, pyrite and base metal veins controlled within a structural north-south corridor, broad zones of alteration around lithology contacts and occasional zones of grade enrichment occur in dilatant structures within the deposit known as Quartz Sulphide Breccias. Host lithology varies from poorly mineralised massive intrusive diorite and fine volcaniclastic sediments through to the preferential mineralised trachydacitic lava in the north, lenses of coarse to conglomeritic volcaniclastic sediments and the andesitic Dalwhinnie lava unit to the east. Lithological contacts with strong competency contrasts also provide broad areas of mineralisation. The trachydacite is brittle with common hyaloclastite and peperitic textures, commonly brecciated to peppertic and is both a good geochemical and rheological host for Au mineralisation.

Vein orientation at the GRE46 deposit displays a distinct change in orientation on a nominal northing of 37,000mN. Vein in the south of the deposit are generally orientated at 50°/120°. Veins in the north of the deposit rotate clockwise and steep to a general dip direction of 70°/180°.

The Mineral Resource area which incorporates the E41, E42, E46 and the GRE46 has the following dimensions, 4,425 m (north), 2,500 m (east) and 1,300 m (elevation). GRE46 has dimensions of 1,600m (north), 800m (east) and 1,100m (elevation).

Mining method assessments indicated that sub-level open stoping (SLOS) with pastefill was the most appropriate mining method for the GRE46 underground deposit. This ensured maximum extraction of the economic portion of the deposit, while ensuring no surface subsidence due to the deposit being under Lake Cowal.

Mineable stope shapes were created using the Mineable Shape Optimiser (MSO) software from Datamine, according to stope design parameters established in the PFS. Stope shapes were created using Au grade as the MSO optimisation field at an incremental cut-off grade.

Stope shapes were informed by geotechnical assessment to determine stable stope spans. The typical sublevel interval is 30m, strike length of 20m and stope width of up to 20m.

All stopes above the 1080 mRL have been excluded from the design to ensure the oxide boundary is not intersected, reducing the likelihood of surface subsidence.

An Equivalent Linear Overbreak Sloughing (ELOS) stope dilution of 0.2m footwall and 0.2m hangingwall was applied in the MSO shape parameters. A further 5% stope dilution has been applied in the schedule to account for any further dilution that may occur.

Ore drive development had no dilution applied to prevent overestimation of metal. Other development has a dilution factor of 10% applied.

Mining recoveries were set at 100% for development activities, and 95% for stoping activities.

All material mined underground will be trucked to surface to the Run of Mine (ROM) pad or waste dump.

The following process plant modifications have been included in the study:
- a second primary jaw crusher dedicated to the treatment of underground ore. This crusher will remove tramp metal from the underground ore feed.

Processing of ores will be through the current plant which has been in operation since 2006. Laboratory test-work of underground ores indicates they will respond similarly to the current hard rock sulphide ores being processed from the existing open pit adjacent to the GRE46 underground.

The current processing facility utilises commonly used crushing and grinding circuitry followed by a combination of gravity, flotation and cyanide leaching methods for the recovery and extraction of gold.

The following process plant modifications have been included in the study:

- an additional FTL elution circuit and carbon regeneration kiln

- a deslimed tailings circuit located at the process plant's tailings area to supply tailings to the surface pastefill plant for operational backfill activities. The pastefill plant design parameters are based on a specification of 150m3/h.