The Macraes deposit is an example of an orogenic style gold deposit. This style of deposit is recognized to be broadly synchronous with deformation, metamorphism, and magmatism during lithospheric-scale continental-margin orogeny (Groves et al., 1998). Most orogenic gold deposits like Macraes occur in greenschist facies rocks. Orogenic deposits typically formed on retrograde portions of pressure- temperature time paths during the last increments of crustal shortening and thus postdate regional metamorphism of the host rocks (Powell et al., 1991 and references therein). Orogenic deposits can be subdivided into epizonal, mesozonal, and hypozonal based on pressure-temperature conditions of ore formation. The Macraes deposit falls into the mesozonal category with mineralisation having occurred near to the brittle-ductile transition at about 300°C.

In orogenic deposits the association between gold and greenschist grade rocks is commonly thought to be related to: 1) the large fluid volume created during the amphibolite and/or greenschist transition and released into the greenschist zone; 2) the structurally favourable brittle-ductile zone that lies just above this transition; 3) fluid focusing and phase separation that are most likely to occur as fluids ascend into the greenschist pressure-temperature regime and/or gold solubility shows a sharp drop under greenschist facies temperatures (Phillips, 1991). Fluid migration along fault-fracture networks was likely to be driven by episodes of major
pressure fluctuations during seismic events.

Mineralisation distribution is broadly consistent along the HMSZ but shows considerable variability in grade, width, continuity and geometry at mine-scale. This variability is attributed to the local development of the HMSZ structure during mineralisation and the influence of host rock lithology, particularly with respect to competency contrasts.

There is a strong empirical correlation between gold, arsenic, scheelite, silicification and strain intensity within the HMSZ. Gold-scheelite-pyrite-arsenopyrite mineralisation is associated with replacement and fissure quartz veins within D4 post-metamorphic shear zones. Shear parallel quartz veins and cataclastic shears contain the highest gold and scheelite grades (Lee et al. 1989).

The following four types of mineralization occur within the HMSZ at Macraes (Mitchell et al., 2006):

- Mineralised schist. This style of mineralisation involved hydrothermal replacement of schist minerals with sulphides and microcrystalline quartz. Mineralisation was accompanied by only minor deformation;

- Black sheared schist. This type of schist is pervaded by cm to mm scale anastomosing fine graphite and sulphide bearing micro shears. This type of mineralisation is typically proximal to the Hangingwall Shear. Scheelite mineralisation occurs in the silicified cataclastic shears;

- Shear-parallel quartz veins. These veins lie within and/or adjacent to the black sheared schist and have generally been deformed with the associated shears. The veins locally crosscut the foliation in the host schist at low to moderate angles. Veins are mainly massive quartz, with some internal lamination and localized brecciation. Sulphide minerals are scattered through the quartz, aligned along laminae and stylolitic seams. These veins range from 1cm to > 2m. Scheelite mineralisation is associated with quartz veining in some areas; and

- Sheeted veins (laminated veins) locally known as ‘stockwork veins’. These veins occur in the Intrashear Schist and can consist of numerous steeply dipping veins. Stockwork veins are typically traceable for 1-5m vertically with most filling fractures that are 5 – 10cm thick but can be up to 1m thick. These veins generally display evidence of incremental opening.

Gold is closely associated with pyrite and arsenopyrite in all the above styles of mineralisation. Rarely free gold up to 300µm occurs in quartz veins, but most gold occurs as 1-10µm scale blebs hosted in and near sulphide grains (Angus, 1993).

OPEN PIT:
Conventional open cut bench mining methods are used at the Macraes Goldfield. Pits are excavated on level benches 2.5m high within the ore zone (approx. 2.8m high after blasting) and 4m high within the waste zone.

Hydraulic backhoe excavators in the 250t and 360t class are used for mining ore and waste

Ore is mined with different techniques depending on the style of mineralisation.

- Hanging wall lode ore is mined by first removing the hanging-wall waste with an excavator under visual control of a geological technician, then mining the exposed ore. Footwall ore is selectively removed from the underlying footwall waste if it can be visually controlled, otherwise the footwall ore is diluted with the wedge of underlying waste; and
- Stockwork ore is generally mined within the defined ore blocks. Ore blocks are defined with the guidance from a conditionally simulated grade control model.

With this mining method and equipment, the smallest selective mining unit (SMU) used when defining ore blocks is 4m by 4m by 2.5m high (approximately 100t), but blocks are generally a minimum of 500t to minimise dilution.

Key open pit schedule assumptions:
Cut-off grade 0.4g/t
Operating time Max 5,700hrs/yr for loading units and 5,500hrs/yr for trucks
Truck payloads 178 dry tonnes
Excavator productivity EX3600: 2,800 dry tph; EX2500: 1,850 dry tph
Vertical advance 10m per month in ore zone, 15m per month in waste zone
Excavator proximity 50m.

Drilling and blasting requirements differ depending on the material zone. Ore zone material includes all material within the main hanging wall shear zone including all ore grade material and the waste zone is the overlying overburden waste rock.

The primary mine loading fleet consists of three Hitachi EX3600 hydraulic excavators (22m3 capacity) and one Hitachi EX2500 hydraulic excavator (15m3 capacity).

A single haulage fleet consisting of Caterpillar 789C and 789D mechanical drive rear-dump trucks are used for all mine haulage duties. These trucks match up with the 22m3 and 15m3 hydraulic excavators with a nominal four and six passes per truck respectively. Truck rated payload is 178 dry tonnes (182 wet tonnes).

Cat 992- and 988-wheel loaders are used to re-handle ore from the ROM blending stockpiles into the crushers.

Generic pit design parameters:
- Minimum mining width of lowest 5m cut - 30m;
- Minimum mining width of cutbacks - 60m;
- Ramp width (including 1 x windrow) - 30m;
- Inside turning radius on switchbacks - 15.0m;
- Maximum ramp gradient - 10%;
- Maximum bench height - 22.5m;
- Minimum berm width - 7.5m (15m berm interval), 10m (22.5m berm interval).

UNDERGROUND:
The Frasers underground orebody encompasses the down dip continuation of the Hangingwall shear mined in the Frasers open pit. The orebody is relatively shallow dipping (15 – 20 degrees) to the east. The orebody is tabular with undulations and has a thickness varying between 5 to 30 metres.

The Frasers underground mine targets the high-grade ore zone at the top of the Hangingwall shear.

The mining method used underground involves 15-metre-wide open stopes with 6 metre yielding pillars between stopes. Mining areas are separated by 20 metres to 60 metres wide regional pillars. The mining areas are generally restricted to about 120 metres width and 160 metres length. Mine production targets the highgrade ore at the top of the 30 metres thick mineralisation. Stope heights vary between drive height (5 metres) and up to 25 metres.

Mining constraints require pillars between the stopes, transverse pillars, regional pillars, ore loss factors, dilution, and recovery assumptions. The mined tonnes and ounces are consequently less than the mining resource target. For a typical panel layout recovery is 62% of the tonnes and 50% of the ounces.

The most utilised mining method at FRUG is retreat long hole open stoping. In addition, sub-level caving is used to recover some of the regional pillars after they are no longer required. Declines and access drives are mined to a 5.0mW x 5.5mH arched profile. Ore drives are mined to a 5.0mW x 5.0mH profile. This allows enough space for services, secondary fans, vent ducts and mobile equipment.

The plant's crushing and grinding comprises the following components and stages:

- Two single stage jaw crushing circuits, which reduce the ore to a top size of approximately 200mm; the products from these two circuits are directly fed to the two SAG mills and an emergency feeder on the conveyor system feeding the higher capacity circuit provides continuity of feed to the grinding
circuit if the jaw crusher feed is interrupted;

- A complex grinding circuit to reduce the particle size of the ore to 80% passing at 130 µm; the original, higher capacity crushing circuit feeds a 2,300kW SAG mill and the new crushing circuit feeds a 1,500kW SAG mill; discharge from the two SAG mills is combined with the discharge from one of the two ball mills (2,300kW) and directed to the primary cyclone cluster. Discharge from the higher capacity ball mill (2,500kW) is fed to the secondary cyclone cluster. The underflows from both cyclone clusters are combined and fed in parallel to the flash flotation circuit and two ball mills (2,300kW and 2,500kW);

- Regrind of the flotation concentrate is performed in a 900kW ball mill to 80% passing of 15 µm to improve pressure oxidation kinetics;

The Macraes Process Plant recovers gold by concentrating the metal into a relatively small fraction of flotation concentrate, oxidising the reground concentrate in a pressure oxidation autoclave, washing the oxidised residue and then utilising a carbon-in-leach process to recover gold from the residue.

In detail the plant comprises:
- A flash flotation circuit made up of roughing and cleaning stages. The circuit is fed from the circulating load of the grinding circuit via cyclone underflows to recover the bulk of fast floating sulphide minerals containing high gold content in the coarser size fraction;

- The main flotation circuit made up of roughers, scavengers, cleaners, recleaners and cleaner scavenger flotation cell trains to produce a gold bearing sulphide concentrate at optimum sulphur grade for the downstream pressure oxidation circuit;

- Limestone is added to the regrind circuit discharge to control net acid generation in the pressure o ........