Kalgoorlie Operations consisted of three separate mining areas, Kanowna Belle, South Kalgoorlie Operations (SKO) and the greater Kundana area. The sale of Northern Star's EKJV, Kundana and Carbine assets completed on 18 August 2021.

Kanowna
The Kanowna Belle deposit is hosted within a series of volcaniclastic sediments ranging in grain size from shale to conglomerates. These rocks are respectively separated into hangingwall and footwall sequences by a major 60° S-SE dipping zone of structural disruption and mineralisation.

The footwall sequence is dominated by the Golden Valley conglomerate, a mafic-dominated unit interbedded with the felsic-dominated Cemetery conglomerate. The hangingwall sequence comprises three main volcaniclastic units, these are the QED rudite, the Lowes sandstone and the Grave Dam grit, which is the dominant unit.

The sequence has been intruded by the Kanowna Belle porphyry, which is granodioritic in composition. At least 70% of the known gold mineralization is hosted by the Kanowna Belle porphyry, with the remaining mineralisation hosted by sedimentary units.

Mineralisation at Kanowna Belle occurs in both supergene enriched horizons in the near surface environment (oxidised to transitional material) and at depth in primary fresh rock sulphide hosted gold. The primary mineralisation at Kanowna occurs in discrete ‘lodes’ or ‘shoots’.

Weathering over the Kanowna deposit is typically to a depth of 70m across the deposit, and is characterised by saprolitic clays.

A zone of supergene gold enrichment is located above the Kanowna Belle deposit in a thin variably developed blanket over a 600m by 250m area. The supergene enrichment zone typically occurs 35m above the primary deposit at the transition between completely oxidised and transitional material.

The Lowes Shoot is the main zone of mineralisation in the mine. It hosts 80% of the total resource and is characterised by a consistent ore grade of 4gpt across its width, with areas of higher grade being sub-parallel to the FSZ or the orientation of the regional cleavage. Mineralisation in the Lowes shoot is characterised by micro-fracturing, abundant quartz carbonate-pyrite veins and minor secondary breccias. Quartz-sericitecarbonate-pyrite breccias also occur parallel to major structural zones.

Two overprinting temporally and mineralogically distinct mineralisation events are recognized in the Kanowna Belle Deposit:
- An early high level (epizonal) Gold-Telluride mineralisation event;
- Later Pyrite associated mineralization.

In the Gold-Telluride phase of mineralisation, gold occurs as blebs of free gold in association with Telluride minerals. The most common telluride minerals observed are Altaite (Lead Telluride), Coloradoite (Mercury Telluride) and Melonite (Nickel Telluride). Texturally the gold-telluride mineralisation occurs as microfracture and microvug infill. Volumetrically, this phase of mineralisation accounts for less than 10% of the gold endowment at Kanowna Belle.

Gold in this mineralisation phase occurs mostly as fine grained (less than 10 microns (µm)) inclusions in pyrite or as very fine-grained gold located in arsenic rich growth zones in pyrite. Free gold occurs in minor proportions, and typically occupies D2 extensional sites adjacent to pyrite crystals.

Mineralisation also sits in the Velvet deposit, 500m west of the main Lowes deposit and 600m below surface. Gold mineralisation at Velvet is hosted within an intrusion of intermediate composition that broadly follows a sub vertical hanging wall splay of the Fitzroy Shear Zone. The splay structure, locally termed ‘Velvet Mylonite’, is characterized by a well-developed porphyroclastic fabric and is separated from the Fitzroy shear Zone by a zone of massive carbonate (mainly dolomite) breccia. Gold is also typically fine grained, with two different mineralisation styles at Velvet also existing.

Typical ore assemblages contain 0.5 to 1.5% sulphur and 40ppm arsenic. Kanowna Belle ore is generally refractory, meaning that oxidation (i.e. roasting) is required to maximise gold extraction. The Pyrite associated mineralisation provides the majority of gold produced from the Kanowna Belle Orebody.

South Kalgoorlie
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 a rheological contrast.

Kalgoorlie Operations consisted of three separate mining areas, Kanowna Belle, South Kalgoorlie Operations (SKO) and the greater Kundana area. The sale of Northern Star's EKJV, Kundana and Carbine assets completed on 18 August 2021.

Kanowna Belle
The Kanowna Belle gold deposit is mined by longhole stoping and underhand longhole bench stoping with paste fill methods. This mining method was selected to minimise the impact of mining induced stress on the underground operations by geotechnical driven mining sequences and a fill system integral in the mining cycle.

The mining method used at Kanowna Belle underground is called longhole open stoping (LHOS). Mining of the LHOS commences with the development of drives (tunnels) on each level and the sides of these are supported by cement grouted roof bolts, mesh and shotcrete. These drives delineate the boundary of the stope. Each LHOS is 15-30m wide, up to 50m long and 120m high. Depending on size each stope may contain between 20,000 to 50,000 tonnes of ore.

The Kanowna Belle gold mine has been extracted down to a depth of 1,301m below surface with a possible extension into lower E block, further development of the Troy and Sims loads located in the hangingwall, higher in the mine. The Velvet deposit sitting 500m west of the main Lowes ore body is also a substantial part of the production and open a depth.

All mining operations are operated by NSMS, excluding diamond drilling which is contracted.

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).

Kanowna Belle
The Kanowna Belle processing plant is a complex and versatile plant that includes separate circuits for processing free-milling and refractory gold ores. The plant has undergone progressive upgrades since its initial construction and now has an annual throughput capacity of approximately~ 2Mtpa of hard rock underground ore.

The thickened slurry is pumped to the leaching and adsorption circuit where the recoverable gold is extracted by cyanidation. The cyanidation circuit is a traditional CIP circuit that consists of three leach tanks and six subsequent adsorption tanks. Oxygen is injected into the first two leach tanks by injection down the agitator shaft and also by injection into a Multimix Injector system installed within a pumped, recirculating slurry stream. Oxygen is injected into the third leaching tank via a single oxygen lance located beneath the lower impeller on the agitator. Oxygen is supplied from a BOC managed liquid oxygen cryogenic storage ........