The Jundee-Nimary gold is hosted within a 4km (long) and 2.5km (wide) sequence of Achaean basalts and weakly differentiated dolerite sills separated by sedimentary rocks (carbonaceous shales, cherts, and siltstone) and dacitic porphyries. Younger felsic and intermediate porphyries and dolerite dykes intrude the sequence. The mine sequence is bounded to the west by a thick succession of felsic volcanics and volcaniclastics, and mineralisation diminishes eastwards as the mafic package becomes more magnesium–rich to ultramafic in composition.

The age of the gold mineralisation is approximately 2,700 million years (Archaean), and is controlled by a series of complex brittle fractures. Over 70% of the gold is hosted within the more brittle dolerite units with the remaining 30% associated with the basalts. The field has undergone multiphase deformation – folds, thrusts, strike and oblique slip faults. The gold is hosted within narrow, discontinuous quartz +/- carbonate veins (typically <0.5m wide) which contain abundant visible gold.

Low grade mineralisation occurred with the first phase of faulting. This was followed by the emplacement of large dacitic intrusions which locked up the initial fault lines causing some abutment pressure – during the second faulting phase this abutment pressure prevented the faults from slipping as easily as before causing a “ripping” between the two fault lines fracturing the rock and causing a relatively large low pressure zone. Gold-rich fluids then flowed into these low pressure zones (main mineralization event). There is minor post mineralisation faulting which causes some minor offsets of the loads.

Currently all ore is sourced from Jundee underground operations which yield ~1.0M tonnes ore each year. There are three underground portals which provide access to the various underground lode structures – Barton, Gateway and Invicta portals. The Barton portal contains three actively working ore bodies (Nim3, Lyons and Westside) with Invicta consisting of the Invicta (remnants), Cardassian and Deakin ore bodies, while the Gateway and Gringotts ore bodies are mined from the Gateway portal.

Currently all ore is sourced from Jundee underground operations which yield ~1.0M tonnes ore each year. There are three underground portals which provide access to the various underground lode structures – Barton, Gateway and Invicta portals. The Barton portal contains three actively working ore bodies (Nim3, Lyons and Westside) with Invicta consisting of the Invicta (remnants), Cardassian and Deakin ore bodies, while the Gateway and Gringotts ore bodies are mined from the Gateway portal. The underground mining is being carried out by an up-hole long-hole open stoping sequence as its primary method. No backfill or paste is used.

The Jundee Processing circuit is a conventional CIL plant with a hard rock processing capacity in excess of 1.8M tonnes per annum. The current blend ratio is 100% underground ore.

The crushing circuit is two-stage consisting of a C125 jaw crusher and HP6 secondary crusher closed by a double deck banana screen with a nominal 400 tonne per hour crushing capacity. The crushing circuit can operate in either full secondary crush or partial secondary crush modes to suit milling requirements. The crushing circuit feeds a reclaim stockpile with a 25,000 tonne capacity. Three variable speed belt feeders below the reclaim feeders ensure steady and controlled grinding circuit feed.

The grinding circuit comprises of two mills. The 5.5m diameter x 8.2m EGL ANI SAG mill is low aspect with a 3,850 kilowatt motor. The SAG mill normally operates in open circuit, but has the capability to be operated in closed circuit SAG only configuration. The 4.3m diameter x 6.7m EGL Nordberg ball mill fitted with a 2,20 0kw motor operates in closed circuit with hydrocyclones. The grinding circuit throughput is greater than 220 dry tonnes per operating hour on 100% blend of underground ore. Oversize material from the SAG mill trommel screen reports to a pebble crusher for size reduction. The HP100 pebble crusher is driven by a 90kW motor. The crusher typically operates with a closed side setting of 14mm. The crushed product from the pebble crusher is fed back into the SAG mill feed.

Classification is achieved using a cyclone cluster consisting of 22 cyclones. Eight to 15 of the cyclones are operated at any one time depending volume of slurry in the milling circuit. The cyclones are operated at a feed pressure of 110- 130kpa to achieve a leach feed sizing target of 80% passing 106 microns.

The Jundee mill feed contains sufficient coarse gold to support the inclusion of a gravity concentration process in the milling circuit. The cyclone underflow product of up to four cyclones is diverted to a gravity circuit that comprises 2 x 30” Knelson concentrators. Approximately 40% of gold in the mill feed is recovered via the gravity circuit. The concentrate produced by the Knelson’s is fed to an in-line leach reactor (ILR) that uses a high concentration cyanide-caustic solution to rapidly leach the gold. Gold is recovered from this solution by means of an electro-winning process in the gold room.

The cyclone overflow slurry reports to the carbon- in-leach circuit for the processing of non-gravity recoverable gold. The circuit comprises two leach tanks and six adsorption tanks where the gold is leached into a solution and adsorbed onto carbon. Carbon containing adsorbed gold is referred to as loaded carbon. Each tank has a volumetric capacity of 1,700m3 allowing a minimum slurry residence time in the leach and adsorption circuit of approximately 30 hours. A balance of approximately 70 tonnes of carbon is maintained in the adsorption to ensure optimal gold recovery.

Six tonne batches of loaded carbon are recovered from adsorption tank 1 daily. Gold is then recovered from the loaded carbon in a desorption process in the elution circuit. The Jundee elution circuit is based on the Anglo-American Research Laboratories elution process in which the loaded carbon is first acid washed to remove impurities that may hinder the refining process. The gold is then eluted using hot (120ºC) caustic cyanide solution. This process removes gold adsorbed onto carbon into a pregnant solution.

The pregnant solution produced from the desorption and gravity ILR process is then circulated through separate electrowinning cells for approximately 20 hours. During this stage gold is electroplated onto cathodes that have been wrapped with steel wool. The barren solution remaining at the end of the electrowinning cycle is returned to the first leach tank to fully utilise the cyanide in solution and allow for the recovery of any residual gold.

The gold laden steel wool cathodes are removed from the electrowinning cells, oxidized in a calcining oven and combined with a flux in the smelting process. The flux is used to ensure the gold bars produced in this process are as pure as possible. Impurities report to a vitreous slag and gold doré bars produced contain approximately 86.5% gold and 12% silver.

The electrowinning, calcination and smelting processes are performed inside a secure gold room.