The South Kalgoorlie Operations are located in the Eastern Goldfields Superterrane of the Archean Yilgarn Craton. The SKO tenement package falls largely within the Kalgoorlie and Kurnalpi Terranes, which in turn are further subdivided into several structurally bound domains, which preserve distinct volcanism.

Stratigraphy for the Ora Banda and Kalgoorlie Domains is relatively well-known and comprises (from stratigraphically lowest) a lower basalt unit, komatiitic to high-magnesian basaltic rocks, an upper basalt unit and overlying felsic volcanic-sedimentary units. Conglomeratic and sandstone units unconformably overlie the upper felsic units adjacent to major shear zones. Layered mafic sills occur within various stratigraphic units and cross-cutting Proterozoic dykes also occur throughout the region. Metamorphic grade ranges from upper greenschist to upper amphibolite facies.

The deformation history of the area is generally divided into four main phases, comprising north directed thrusting with recumbent folding and stratigraphic repetition in D1. The second deformation (D2) resulted in north-northwest trending folds which are reflected in the dominant north-northwest trending fabric of the greenstone belts. Shortening continued during D3 with strike slip movement along northwest to north-northwest trending shear zones and D4 brittle faulting.

Mineralisation is common in shear zones along lithological contacts. Discordant veins may be grossly stratabound and restricted to specific lithologies. Deposits may run the complete spectrum from ductile to brittle fault and fracture zones though most goldhosting structures show features of brittle-ductile transition. While all Archean lithologies in Yilgarn greenstone belts may be mineralised, mafic volcanics and internal granitoids are the most productive hosts in areas of significant gold production.

The HBJ gold deposit is mined by a top down long hole open stoping (LHOS) method. This mining method was selected to minimise the impact of mining induced stress on the underground operations through the use of geotechnical driven mining sequences at the same time as increasing the extraction rates.

The orebody is accessed through the hanging wall by a central access from which north and south drives are developed.

An initial porphyry ore lode is encountered and developed. Further out in the footwall there is an ore unit sitting against an ultra-mafic contact. Development of the 2401 (ultra-mafic) lodes are delayed as late as possible but just in time for stoping extraction. The priority is placed on developing the western lode followed by a step over to the eastern lode for both the northern and southern extents. Once the stoping panels are mined back towards the main access, development from the access to the north and south can be completed thus completing development.

The stoping front retreats from both northern and southern extents towards the access following a top down LHOS method leaving rib pillars. Additional sill pillars are also planned on the eastern lodes where the ultra-mafic contact is present to ensure the safe extraction of the ore whilst minimizing the potential for footwall failure. The dimensions of the stopes vary depending on what lode they are extracting. On the western lodes, the stopes generally between 25 and 35m long and 17m high. On the eastern lodes, the stopes are smaller to minimize footwall exposure, generally between 15 and 20m long and 12m high.

The HBJ gold mine has been extracted down to a depth of 580m below surface. Possible extensions are being investigated both to the north (Mutooroo) and the south (South Jubilee) of the current workings. The ore body is still open at depth.

The Jubilee processing plant processes up to 1.2 Mtpa of free milling gold ore at an overall gold recovery of approximately ~90%.

The crushing circuit is three-stage consisting of a primary jaw crusher feeding a 6,000t live capacity coarse ore bin, operating at an average rate of 350 t/h, and a secondary and tertiary crusher circuit closed by a vibrating screen operating at an average rate of 200 t/h. The -8 mm crushing circuit product reports to the 3,500t live capacity fine ore bin.

Ore from the fine ore bin is fed to the grinding circuit via conveyor, quicklime is added to the belt for pH adjustment. The grinding circuit consists of a primary and secondary mill in closed circuit with hydrocyclones. The fine particles (80% less than 0.150 mm) report to the cyclone overflow, which is fed to the leaching circuit. The cyclone cluster is made up of Warman Cavex cyclones, with one cyclone diverted to the gravity circuit. The gravity circuit recovers coarse, free gold and consists of a screen, 30” Knelson Concentrator, and CS500 Acacia reactor. The gravity circuit recovers approximately 35% of the gold recovered by the Jubilee plant.

The leaching and adsorption circuit consists of three leach tanks and eight adsorption tanks. The product from the cyclone overflow is passed over a 0.8 mm aperture vibrating screen and the undersize reports to the first leach tank. Cyanide and oxygen are added to leach the gold into solution. The slurry flows through a splitter box, with each half reporting to a separate adsorption train (adsorption tanks are split into two parallel trains consisting of four tanks per train). Carbon is moved counter-current to the slurry flow and adsorbs the gold from solution. The slurry from the last two adsorption tanks flows over a tail screen prior to discharge to the tailing storage facility.

Loaded carbon is pumped from the circuit in daily batches. Gold is recovered from the carbon in the elution circuit. A split Anglo-American Research Laboratories process is utilised where the gold laden carbon is first acid washed, and then eluted in a column using hot caustic cyanide solution. At the completion of the elution step the barren carbon is sent to the kiln for regeneration prior to being returned to the adsorption circuit. The gold bearing solution is circulated through two electrowinning cells, where the gold in solution is electrowon onto stainless steel mesh cathodes. The gold bearing sludge is removed from the cathodes, smelted in a furnace and poured into gold bars for shipment to the mint.