Mineralisation occurs within Lower Ordovician sandstones, siltstones and mudstones that have been weakly metamorphosed and tightly folded about north-trending axes. The western limbs of the known anticlines dip approximately 70°W, eastern limbs 85°W to 85°E and fold axial planes dip approximately 80°W. The regional strike of the bedding is northerly. The quartz veins are located predominantly within fold limbs in structurally controlled bodies known as lodes and stockworks. Lodes and stockworks are hosted in west-dipping fault zones (e.g. the Llanberris Mako fault zone). Mineralisation is characterised by notable quantities of coarse gold (>80% +100-micron gold) and very coarse gold (locally >50% +1,000-micron gold) hosted in the quartz veins. A high nugget effect is observed, where grades over a few metres may reach 50 g/t Au or higher, but reduce to a few g/t Au out of the high grade.

The gold-quartz veins at Ballarat are characterised by a high-nugget effect and the presence of coarse, often visible gold particles (>100 pm in size). This is typical of most Central Victorian gold deposits. They rank amongst the most difficult of ore deposits types, in terms of producing an accurate and precise resource estimate.

The current mine production plan is based on a combination of ore generated from the development along the strike of the ore zone, mechanised drift and fill and longhole bench stoping. Geotechnical conditions and geometry of the ore bodies are highly variable and the mining method is selected to suit. Long hole stoping s a combination of “up-hole retreat" stopes with no backfill, and stopes where a top and bottom access is present allowing the stope void to be backfilled. The bulk of future production is scheduled from three main areas Llanberris. Sovereign and Britannia compartments.

Waste rock produced directly from waste development headings is used to support the hanging wall in stopes where crown access is available. Loose rock fill is used in preference to cemented rock fill when the length of the entire stoping panel is less than or equal to the maximum unsupported span.

The cement slurry pre-mix is mixed with the waste rock underground at sumps located in close tramming distance to the stope requiring backfilling. The cement slurry, with a water cement ratio of 0.8, is pre-mixed by a batch plant on the surface and transferred to the CRF mixing sump by an underground agitator. Based on the backfilling requirements, a maximum of four agitator loads per shift are required.

Crushing plant
The coarse grained nature of the Ballarat ore allows liberation of minerals at 1 mm to 5mm in size; hence no grinding mills are required for ore comminution. Instead the plant utilises three stages of crushing.
- Front end loader from ROM (run of mine) stockpiles to grizzly
- 14 inch [35 cm] static grizzly to ROM bin
- Hawk vibrating feeder discharging from ROM bin into primary crusher. Two thirds pan one third 75 mm grizzly. Variable speed to control feed rate to circuit
- Primary crusher – Jaques 42 by 30 single toggle jaw crusher
- Electromagnetic separator for tramp metal removal – M&O Equipment RCDF8
- Back up tramp metal detector interlocked with conveyor if tramp is detected
- Vibrating incline screen – Hawk, single deck with 30 mm screen mats
- Secondary crusher taking screen oversize. Allis Chalmers 60 inch [1.5 m] Hydrocone crusher, with gap set at ~20 mm
- Secondary crusher product and screen undersize combine and conveyed to fine ore storage bins. Secondary crusher in open circuit (no size control on product)
- Fine ore storage consists of two bins each of approximately 450 t working capacity
- Typical crushing rates 200 to 250 t per hour. Batch crushing as required with sufficient crushed ore storage to satisfy night time gravity circuit operation without having to crush (noise minimisation).

Tertiary crushing and screening
- Two fine ore bins each have two Hawk vibrating pan feeders to control feed of ore from fine ore bin – only one bin discharges at a time. Speed is variable and driven off belt weightometer output to control feed rate to circuit
- Milltronics Accumass BW500 belt weigher
- Feed material sampled here to provide head grade and moisture
- Static belt magnet to remove ferrous tramp metal
- Tertiary screening – two Joest wet horizontal vibrating screens, one with 5 mm aperture polyurethane screen panels and one with 1 mm aperture polyurethane screen panels. The 5 mm screen sets the entry size into the jig recovery circuit and is 2,450 mm by 6,100 mm in size and the 1.6 mm screen sets the exit size from the jig recovery circuit and is 2,450 mm by 7,320 mm in size. Both screens operate in parallel and in closed circuit with the VSI crushers
- Combined screen oversize (> 5 mm and >1.6 mm) conveyed to Vertical Shaft Impact crushers
- Static belt magnet protecting VSI from tramp metal
- Tertiary crushers – Duty Crusher is Auspactor VS300RR DD Vertical Shaft Impact crusher with 600KW of installed power. Standby Crusher is Auspactor VS200RR DD Vertical Shaft Impact crusher with 300 KW of installed power. Feed rate is 55 to 70 t per hour of new feed with 250% to 300% circulating load. Final product size P80 approximately 800 microns
- VSI discharge conveyed back to 5 mm vibrating screen – closed circuit
- Jig tailings also returns to Tertiary/screening circuit via the 1.6 mm screen
- Gravity jigs are in closed circuit with the VSI – jig tailings are re-crushed and re-jigged until particle size is <1.6 mm before they leave the circuit. This is to maximise gravity gold recovery and minimise over-grinding.

The gold processing plant was constructed in 2005 and was purposely designed to suit the coarse grained nuggetty Ballarat ore with the aim of capturing gold and sulphides at the point of liberation without over-grinding. The gold and sulphide minerals are separated away from the waste using the difference in density.

The processing plant consists of a three stage crushing and screening plant, a gravity separation circuit with pressure jig separators, falcon concentrator and tables to recover both direct smeltable gold as well as sulphide concentrate, the latter requiring further processing via the Intensive Leach Plant (ILR).

The gold processing facility has a capacity of around 500,000 t per annum however the current capability is 250,0001 of ore per annum (50% rostered availability).

The gold associated with the sulphides is not refractory and can be leached directly with cyanide. The sulphide concentrates are first ground in a small ball mill to a si ........