The SKO is located within the Eastern Goldfields Superterrane and the 842sqkm tenement package traverses across the Coolgardie, Ora Banda, Kambalda and Boorara Domains. Mineralisation is associated with the greenstone sequence that consists of a mafic to ultramafic volcanic succession that is overlain by an intermediate to felsic volcano-sedimentary sequence.

The structural architecture is dominated by NNW-trending crustal scale shear zones including the Boulder-Lefroy, Zuleika, Abattoir, Boorara, Kunanulling, Binduli and Spargoville structural corridors. These structural corridors are the key influencers of mineralisation in the greater Kalgoorlie district and to date have yielded a mineral endowment of over 100Moz.

Mineralisation styles within the district is a combination of Orogenic and Paleoplacer style deposits. Mineralisation is controlled by Brittle-Ductile shear zones, 1st and 2nd order structures that act as Lithostratigraphic contacts (as fluid conduits) through late stage brittle structures. Mineralisation is also associated with fertile sulphidised intrusive porphyries and layered mafic intrusions with chemically reactive lithologies that provide arheological contrast.

South Kalgoorlie HBJ Underground
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.

All underground mining operations are operated by Northern Star Mining Services (NSMS).

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 gol ........