The Kundana Operation hosts several deposits spatially associated with the Zuleika Shear Zone (‘ZSZ’), a NW/SE trending structure stretching more than 250km, separating the Ora Banda and Coolgardie Domains. Typically, deposits within the ‘ZSZ’ are comprised of narrow, high grade quartz veins, hosted within smaller shear structures formed at the contacts of the Archaean Greenstone stratigraphy’s belonging to the two domains.

Strike extents for each of the deposits are controlled by late-stage NNE trending sub vertical structures, exhibiting varying amounts of dextral offset. In total, the Kundana area is known to host more than 5Moz of gold, including the deposits Raleigh, Rubicon, Hornet and Pegasus.

The Raleigh deposit is hosted within the Strzelecki Shear, located at the stratigraphic contact between Andesite/Intermediate Volcanoclastic and Gabbro, with varying amounts of interflow sediment.

The main lode comprises a laminated quartz vein up to 2m true width and dipping 70º west, grading on average 55 gpt Au. Gold is typically associated with sphalerite and galena. The deposit is well defined with drilling showing economic mineralisation extending up to 750m below surface.

The Rubicon, Hornet and Pegasus deposits are all hosted within the K2 Shear, located at the stratigraphic contact between Intermediate Volcanoclastic and the Victorious Basalt, with varying amounts of Centenary Shale.

The main lode comprises several mineralising events which can be distinguished by the presence of laminated or brecciated quartz, and differing amounts of galena, sphalerite, arsenopyrite and pyrrhotite. Vein grades typically average 25gpt Au for the main lode with the structure varying in thickness from 0.5-4m and dipping 80º west. Several hangingwall lodes with varying orientation have also been identified and exhibit localised ore grades.

All three deposits remain open at depth, with drilling and underground development identifying distinct high grade zones plunging to both the north and south.

Kundana also employs the method of underhand long hole bench stoping with paste fill similar to that of the Kanowna Belle operation. This method is used to ensure that high extraction rates of the orebody are achieved as the orebody can grade from 5.0gpt to +31gpt plus. This mining method also assists with minimising any future stress impact on the Operation.

Ore drives are mined along the strike of the orebody following the high grade laminated quartz vein. Once the strike ore drive is completed a vertical rise is established and extraction of the ore between two levels is commenced. The ore body is significantly narrower that the Kanowna Belle ore body with stope widths typically in the order of 1.0m to 2.5m wide.

The Kundana Operations currently consist of four underground ore bodies. The Raleigh ore body is accessed form the Raleigh pit with underground stoping occurring at +650m below surface. The other three orebodies, Rubicon, Hornet and Pegasus, are accessed from the Rubicon pit and portal with stoping occurring between 200m and 400m below surface.

Ore from the Kundana operations is treated at the NST owned Kanowna Belle processing facility located adjacent to the Kanowna Belle mine.

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 incremental capacity increases since its initial construction and now has an annual throughput capacity of 1.88Mtpa. Processing at the current rate of ~1.82Mtpa of underground ore affords the processing plant the ability to substantially increase production should the need arise.

The crushing and grinding circuits are common for the free milling and refractory circuits.

The crushing circuit is a simple single stage circuit with a 240t capacity ROM bin feeding a Jaques double toggle 60x48 (185kw) crusher at a 420tph crushing capacity. The crushed ore, nominally minus 125mm reports to a 20,000t partially-covered coarse ore stockpile with a live capacity of about 1,000t.

This product is then reclaimed by an apron feeder and two vibrating feeders located under the stockpile and discharged onto a conveyor belt. The crushed ore is then conveyed to the grinding circuit.

The grinding circuit comprises an ANI Products 7.32m x 3.35m SAG mill operating in closed circuit with a Metso Nordberg HP200 recycle cone crusher and an ANI Products 4.72m x 7.01m Ball mill in closed circuit with cyclones. The SAG mill has a grate discharge and is steel lined, while the Ball mill has a trommel screen discharge and is rubber lined. The SAG mill has a variable speed drive with a range of 10 to 12 rpm, while the Ball mill has a fixed speed drive at 14.3 rev/min (75% of critical). The installed power for the SAG and Ball mills is 2,850kW. The grinding circuit throughput is currently around 160 – 190tph however it can be increased to 230tph if needed.

Pre-leach classification is achieved using a hydro-cyclone classifier circuit consisting of a cluster of 18 x 250mm cyclones that are fed from a central distributor. Only eight to nine of the cyclones are operated at any one time depending on volume of slurry in the milling circuit. Three of the cyclones in the cluster are dedicated to feed the Knelson gravity concentrator during the free milling ore campaigns. The cyclones are operated at a feed pressure of 110-130kpa.

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.

The slurry residence time in the CIP circuit is ~32 hours. Tank sizes vary across the circuit as a consequence of the 2007 circuit expansion project. The first two leach tanks (installed as part of the 2007 Expansion) have a working volume of ~1,400m3 each. The subsequent three tanks have working volumes of ~750m3 each and the final four tanks have working volumes of ~520m3 each.

The gold bearing steel wool is removed from the electrowinning cells, oxidized in a calcining oven and smelted directly with fluxes in a gas fired furnace. The smelt produces a vitreous slag containing all the base metals and impurities along with gold doré bars that contain ~70-85% gold and 15-30% silver.

The electrowinning, calcination and smelting processes are all performed inside a high security gold room.

For the free milling ores, the cyclone underflow stream from the three dedicated gravity circuit cyclones reports to a 1.8m wide by 4.2m long horizontal vibrating screen with 2.4mm by 15mm apertures to reject oversize material prior to feeding the Knelson Concentrator.

Gravity concentrate from the Knelson Concentrator is transferred in batches to a ConSep ACACIA Model CS2000 intensive leaching reactor to dissolve most of the gravity recovered gold. A concentrated caustic and cyanide solution (30% w/w NaCN) is heated to around 35°C and circulated through the concentrate bed for ~12 hours. The gold bearing solution is transferred to a storage tank for circulation through electrowinning cells for ~12 hours.

The roasting process makes the concentrate particles porous by burning off the sulphur and arsenic that surrounds the very fine gold particles. The porosity permits cyanide leaching and recovery of the otherwise occluded gold particles.