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.

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 size of 130 microns and sent to the cyanide leaching circuit. Only the sulphide concentrate which equates to approximately 5% of the total ore mass is leached. Hence the leaching plant differs from many gold processing facilities that employ CIP/CIL to leach the entire volume of ore.

Leaching occurs in two rotating drum leach reactors (Gekko ILR’s) to ensure maximum contact between cyanide and the gold. The gold is dissolved into solution and then separated from the barren solids by thickening. The solution is pumped across a resin column where the gold is transferred onto an ion exchange. The resin performs a similar role to carbon in a conventional CIP/CIL circuit. The resin is periodically stripped of its gold into a concentrated gold solution which forms the electrolyte feed to the electrowinning circuit. The gold is plated out of the electrolyte using an electrical current and deposited onto stainless steel cathode wool. The wool is periodically stripped of its gold and the gold is smelted in a gas fired furnace to form gold doré.

The residual cyanide remaining in the leach tailings is destroyed prior to disposal in the tailings storage facility. The cyanide destruction process is known as the INCO method and uses sodium metabisulphite and copper sulphate for the destruction of the cyanide complexes.