The Ballarat goldfield is positioned in the hanging-wall of the crustal-scale north-south striking, west-dipping Williamson Creek reverse fault. Three north-trending mineralised zones are identified in the Ballarat goldfields: Ballarat East, Ballarat West (including Ballarat South) and Little Bendigo. Gold mineralisation is hosted by Ordovician turbidites of the Castlemaine Supergroup.

The Ballarat Goldmine is located in the Ballarat East goldfield and lies on the eastern limb of the Ballarat Anticline. The turbidites were folded into a series of north-south trending, tight, upright chevron-style anticlines with wavelengths ranging from 50 m to 300 m. Numerous parasitic folds occur around the hinge zones of the larger folds. The three major fold lines of the Ballarat East goldfield are the Sulieman, Scandinavian and First Chance Anticlines.

The Ballarat goldfields are divided into multiple ‘compartments’ by a series of major faults referred to as cross courses. Cross-course faults are sub-vertical, brittle faults that are un mineralised yet play an important role in the distribution of mineralisation, and gold tenors are relatively consistent within individual compartments. Cross courses typically trend northeast or northwest and have displacements ranging from centimetres to several hundreds of metres.

The Ballarat goldfield is an orogenic gold deposit. Vein mineral assemblages include several generations of quartz with chlorite, sericite, albite and carbonate minerals. Arsenopyrite and pyrite are the dominant sulphide minerals with galena, sphalerite, chalcopyrite and pyrrhotite also commonly observed. The estimated percentage of sulphide minerals in the veins is 2%. The host rocks show bleaching, carbonate aggregates, disseminated pyrite, arsenopyrite and pervasive halos of sericitic alteration around quartz veining.

Mineralogical observations that gold may occur in fractures within sulphide minerals or attached to the margins of sulphide grains indicate that gold was deposited after the sulphides. Gold occurs as native gold particles that range in size from several microns up to 30 mm.

The Ballarat Goldmine has three major productive lines of reef, located on anticlines of the same name: the Sulieman minor Line, the Scandinavian Line and the First Chance Line. A minor gold bearing line is the Oregon line to the east of current development. The major folds are continuous along the length of the goldfield. Each line of reef is divided into several compartments ranging in length from 150m to 500m along strike.

Gold mineralisation occurs as en-échelon vein arrays linked to vertically stacked shallow to steep west-dipping reverse faults that cross cut the eastern limb of the anticlines. West-dipping faults are generally narrow (< 1 m wide) and mineralisation is constrained within the fault plane. The Mako Fault Zone (MFZ) in the Llanberris Compartment is an example of a west-dipping reverse fault zone. The fault zones dip between 20o and 70o, extend up to 250m along strike (north-south), 90m down dip and ranges in thickness from 0.5m to 6m. Veining comprises a combination of massive quartz, weakly laminated quartz, brecciated quartz and stockwork veins. Later faults, offsetting early stage veining, have been observed amongst a complex zone of shearing and fault gouge development.

The current mine covers a relatively narrow area approximately 400 metres in width and five kilometres in length, extending to a depth of approximately 760 m below the surface.

Primary access underground is via the Woolshed Gully decline, nominal dimensions of 4.6 metres high and 4.6 metres wide at a gradient of 1:6.5 down to a depth of approximately 130 metres below the surface. The mine entrance (portal) is located at the southern end of the mine.

The decline system below the Woolshed Gully decline has been developed at nominal dimensions of 5.3 metres high by 5.0 metres wide at a gradient of 15%. At approximately 1,200 m from the portal, twin declines split into the Suleiman decline (approximately 1,900 m long) and the Woah Hawp decline (approximately 3,700 m long).

Underground mining includes development drilling, ground support, blasting, loading and hauling. All works are carried out by GPG as an “owner-operator”. Production drilling and mechanised cable bolting are carried out by a separate contractor (MacMahon).

Underground development is carried out using conventional drill and blast techniques with twin boom 1000V electric hydraulic jumbos. Jumbos drill blast holes in development faces, blast holes are then charged with explosives and fired breaking the rock. Jumbos are also utilised for the installation of ground support in the walls and backs of the excavation.

The ground support design for mine development considers the expected prevailing ground conditions and service life of the excavation. For example, the minimum support requirements for:
• Capital infrastructure/permanent access with a life span greater than two years includes galvanized primary support (split sets) and secondary support (full encapsulated rock bolts or cable bolts) and floor to floor surface support (typically 50 mm fibrecrete)
• Waste access or ore development with a life span less than 12 months includes black or galvanized primary and secondary support and surface support less than 0.5 m from the floor (typically mesh).

Rubber-tyred diesel-powered loaders and trucks are used to move broken rock (ore and waste) from development drives or stopes.

Development waste is preferentially placed in underground voids (development or stope) as backfill or trucked via the decline to the surface waste rock facility. Ore from development or stopes is trucked via the decline to the surface ROM pad.

The current mine production plan is based on a combination of ore generated from Jumbo development along the strike of the ore zone and longhole open stoping. The mining method is selected based on geotechnical conditions and geometry of the ore body.

A minimum stope width of 2.5 m is used in the current mine plan based on levels approximately 20 m vertically apart. Production drilling involves the drilling of either 64 mm or 76 mm diameter production holes. Long hole stoping is a combination of “blind uphole” stopes with no backfill and stopes where top access is present allowing the stope void to be backfilled.

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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 overgrinding. The gold and sulphide minerals are separated away from the waste using the difference in density. Approximately 70% of the recovered gold is ‘free’ and is directly smelted into bars, with the other 30% present as sulphide-bound gold which must be leached first. Silver is a minor component in the gold produced at Ballarat with only 0.2% to 0.5% Ag present in the gold bullion produced.

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).

A flotation circuit is also used to recover fine gold an ........