Sulfide gold mineralization at Stawell is typical of orogenic gold deposits.

Stawell is hosted by quartz-rich turbiditic sedimentary rocks (Albion Formation) that overlap a thick pile of tholeiitic basaltic lavas (Magdala Basalt). It is suggested that the host-rock (Stawell Facies) was originally a turbiditic sedimentary rock that was hydrothermally altered in response to seawater interaction with the hot basaltic pile. Subsequent regional greenschist metamorphism and ductile deformation culminated in the formation of the Magdala mineralized system and produced a complex pattern of hydrothermal alteration.

There are three mineralization styles at Stawell, being Magdala (separated into west and east flanks), Golden Gift and Wonga. The Magdala and Golden Gift ore types are hosted within the Magdala Volcanogenic. Within the Magdala Deposit there are three main ore types; Central Lode, Basalt Contact Lodes, and Magdala Stockwork Lodes. The East Flank mineralization introduces a new ore type: The Hampshire Lode.

Central Lode mineralization was a significant production source from Magdala early in the mine’s history. It is a quartz-rich shear lode ranging from 0.5m to 10m in width and generally dips 55° to 65° to the west with a total strike length of 4km and a down-dip extend of one kilometer. The overall structure is mineralized economic shoots that vary from 20m to 30m in strike up to 200m to 350m in strike. Free gold in the quartz is associated with pyrite, arsenopyrite and recrystallized pyrrhotite. Average mined grade for Central Lode is 4.0 g/t Au – 7.0 g/t Au.

Basalt Contact Lodes are located parallel to the Magdala Basalt and in ‘waterloo’ or reentrant positions. They are typically 2m wide and are represented by arrays of quartz sulphide tension veins immediately adjacent to the Volcanogenic Basalt contacts. Sulphides include pyrrhotite, arsenopyrite and pyrite and occur as alteration selvages on tension vein margins. The main alteration mineral is stilpnomelane, resulting in its dark color. The mineralization is isolated to the Magdala Volcanogenic package with none present in the adjacent Magdala Basalt. Ore shoot lengths range between 50m and 450m. The average mined grade for Basalt Contact Lodes is 4.0 g/t Au – 9.0 g/t Au.

The Magdala Stockwork Lodes are situated above major basalt noses and can be described as a hybrid between Central and Basalt Contact Lodes. They consist of large quartz tension vein arrays with arsenopyrite and pyrrhotite dominant sulphide mineralization. The strike extent is limited to 40m to 50m and limited vertically to between 30m and 50m. Average mined grade for Magdala Stockwork Lodes is 4.0 g/t Au – 7.0 g/t Au.

Unlike the Magdala Deposit there is only one identifiable ore type in the Golden Gift and this is termed the Golden Gift Stockworks. Though there is only one discernible ore type in the Golden Gift, the Golden Gift Stockworks contain a spectrum of all Magdala styles. Typical widths range from 8-12m up to 30m and the strike extents of shoots range between 150m and 400m. Areas of highest gold grades and largest widths are situated above major basalt noses which are present in most ore bodies. Quartz content is generally below 25%. Mineralization includes abundant recrystallized pyrrhotite and coarse grained arsenopyrite, pyrite and visible gold. Average mined grade is 4.0 g/t Au – 10.0 g/t Au.

No further underground mining is intended at the operation until an underground Mineral Reserve is reported. Currently an exploration program is underway with intent to define mineralization on the Eastern Flank.

Surface mining operations are planned around a conventional excavator and truck operation with light blasting activity only required in the very lower portion of the excavation. Additional controls are planned for air quality and amenity considerations around hours of operation, benching configuration, dust suppression and equipment specifications.

Surface mining activities are planned as an adaptation of conventional open cut mining where benching techniques of predominately rip and dig or free dig mining has been proposed. In order to provide best practice mitigation measures for air quality and amenity, the majority of operational activity will occur as low as practicable in the pit to enable upper benches to provide an element of shielding. In order to further preserve amenity operating hours are daylight hours only Monday to Friday. This is in order to appease community relations, as the proposed pit sits adjacent to the township of Stawell.

It is expected that much of the Big Hill Surface Mineral Reserve will be excavated without blasting as the majority of surface drill holes rank in the “Easy Digging” to “Easy Ripping” categories of the Pettifer and Fookes Excavatability Assessment. Some areas at depth reach the “Extremely Hard Ripping” category but these are the minority and light blasting is planned to be applied to these areas.

Surface mining plans commence with the excavation of the North Pit and a two stage cutback approach to mining of the South Pit with waste material from the South Pit being used to reconstruct the North Pit. Surface mining fleets at peak operation are to consist of five 90t trucks, a 120t excavator and a 190t excavator.

The gold processing facilities utilized at SGM comprise a standard Carbon-In-Leach (CIL) gold recovery circuit following crushing and grinding and sulphide flotation. The treatment plant consists of five unit processes:

- size reduction (crushing and milling);
- gravity gold recovery;
- flotation/ultra-fine grinding;
- leach-adsorption; and
- gold recovery.

Geographically the plant can be split up into five main areas. These are:
- the primary crushing circuit;
- the milling circuit;
- the flotation/ultra-fine grinding circuit;
- the leach-adsorption circuit; and
- the elution/electrowinning circuit.

Coarse gold (up to 30% of the gold in mill feed) was recovered from the milling circuit in self-cleaning centrifugal gravity concentrators. Approximately 75% of the ore requires further liberation of the gold from sulphides and this is achieved in a two stage flotation circuit where gold bearing sulphides (pyrite, arsenopyrite and some pyrrhotite) are concentrated. The sulphide was ground to approximately 0.01mm in an ultra-fine grinding mill to liberate enclosed gold (up to 20% of the gold in mill feed). The ground sulphides and flotation tail are recombined and sent to the CIL circuit.

Stawell ore exhibits various degrees of preg robbing of gold. Preg-robbing occurs when naturally occurring carbon species (graphite) in the ore rob gold from the pregnant liquor in the leach circuit, thus reducing the gold recovery. To combat this, kerosene was added to foul the naturally occurring carbon before it enters the leach circuit and a simple preg-rob index developed at SGM indicates the rate of addition needed for the kerosene to be most effective.