The Kailis deposit is located within the eastern Goldfields province of the Archaean Yilgarn Block. It comprises a mafic and ultramafic sequence intruded to the west by a diapirically emplaced granitoid (Raeside Batholith). Weathering over the resource is intense and generally follows the shear zone down to a maximum depth of 80 to 100m.

Gold mineralisation is hosted in a quartz-sericite schist within a broad, shallow to moderately dipping shear zone with a strike length in excess of 1,800m. Mineralised intervals are often narrow (3 to 8m), but thicken to 15-20m in places. Higher grades tend to occur in the oxide and transitional zones with lower grade mineralisation in the fresh rock.

The Kailis deposit has successfully been mined by open pit in the past and in Stage 1 and Stage 2.

Open pit mining at the Thunderbox A Zone pit and Kailis Stage 1 pit were completed during FY2018.

The Kailis Stage 2 open pit commenced production in December 2018. Mining at Kailis Stage 2 continued during 2019 with the pit completed in March 2020 and significant post-mining stockpiles available.

The mining method employed at Kailis open pit was conventional open pit with hydraulic excavator and dump truck fleet, and drill and blast activity.

The Kailis reserve pit is designed as a successive cutback to the previously mined reserve. At present the mine is in “care and maintenance”. The cutback will be mined in appropriate manner such that it meets the operational efficiency, safety and production rates. Realistic mine schedules, operating costs and lead times have been applied to maintain an efficient mining operation.

Single stage crushing:
- SAG and ball mill grinding circuit.

Thunderbox mill to be expanded to 3.5Mtpa during FY22. The secondary crushing circuit will deliver a finer product size to the grinding circuit. Saracen has purchased two Sandvik crushers that will be utilised (currently in storage).

The Thunderbox mill employs a conventional crushing, grinding and CIL leaching process to extract the gold. The mill operated successfully between 2002 and 2007, processing in excess of 9Mt of ore. The conventional plant displayed excellent performance with gold recoveries between 93.4 to 96.6 % over the life of the mine. It has since been upgraded to include a gravity recovery circuit facilitating continued high recoveries with increased throughput rates. Ongoing supply of Thunderbox ore to the processing facility will continue to be sourced from a combination of open pit oxide and fresh rock from the underground operations.