Sulfide gold mineralization at Fosterville is relatively homogenous with only one deposit type present. There are minor variations in the host rock type and structural setting. Fosterville-type deposits form a sub-group of orogenic gold deposits that are typified by gold occurring in fine grained arsenopyrite and/or pyrite disseminated in country rocks as a selvage to faults or veins. Fosterville-type deposits and classic vein-hosted deposits are effectively end members with many orogenic gold deposits displaying features of both.

The mineralization is structurally controlled with high-grade zones localized by the geometric relationship between bedding and faulting. Mineralized shoots are typically 4m to 15m thick, 50m to 150m up/downdip and 300m to 1,500m+ downplunge. These sulfide bodies are the primary targets for exploration activities, especially where there is potential for grades in excess of 3 g/t Au (i.e. above underground resource cut-off gold grades).

Gold is presently mined in two forms at FGM: Sulfide-Hosted Gold and Visible Gold.

Sulfide-Hosted Gold:

Sulfide Gold Mineralization at FGM occurs mainly as gold atoms trapped within the crystal lattice of disseminated arsenopyrite and pyrite (sulfides). These sulfide minerals precipitate in the wall rock as selvage alteration proximal to veins that penetrate the host rock. Associated alteration mineralogy within veins is predominantly euhedral to amorphous quartz-carbonate, with minor amorphous albite-chlorite-epidote.

Arsenopyrite crystals occur as 0.05-6mm long acicular needles in random orientations. The disseminated pyrite associated with gold mineralization occurs as crystalline pyritohedrons 0.1mm to 2mm in size. Electron microprobe analyses and metallurgical test work indicates that the arsenopyrite contains 100 g/t Au to 1,000 g/t Au and the auriferous pyrite 10 g/t Au to 100 g/t Au (Roberts et al., 2003). Approximately 80% of sulfide-hosted gold occurs in arsenopyrite, with the remaining 20% hosted by pyrite.

The quartz–carbonate veining forms in several styles that range from isolated veins through to stockwork veining. The quartz–carbonate veining is barren of sulfide gold. Broad zones of sulfide selvedge altered zones are located where stockwork veining occurs. This can allow a pervasive body of sulfide mineralization in the wall rock around that stockwork veining to form, with widths up to several meters.

Visible Gold:

Visible gold is observed within quartz carbonate veins, with a noticeable increase in recent years as underground mining and diamond drilling has advanced deeper. Visible gold particles are predominantly specks (up to 3mm), however, they can be up to 5mm in size, and are observed in drill core, underground development face/wall mapping, and stope sampling. The width of quartz-carbonate veining that contain visible gold is variable, with widths ranging from a few millimeters to several meters (true thickness). The veins usually have incomplete infill with druse quartz within those voids. Visible gold can be found as specks in narrow linear trends as well as isolated specks without a clear trend. Alteration mineralogy associated with veins that host visible gold includes quartz - carbonate (ankerite), with minor occurrences of fibrous boulangerite (Pb5Sb4S11) as inclusions in euhedral quartz or as fibrous growths within void spaces. Selvedge sulfide alteration can be present, proximal to veins hosting visible gold.

The visible gold has a spatial association with stibnite (Sb2S3). However, the stibnite mineralization can occur without visible gold (Henderson, 2014). The rationale for the one way correlation is likely due to the stibnite mineralization occurring in different events, but utilizing the same structurally favorable locations. Stibnite mineralization has also been observed in all areas of the underground workings at FGM and has been observed in some open cut pits within MIN5404.

Since the completion of the Harrier Open Cut Mine in early December 2007, the sole source of ore had been the underground operations until Q2 2011 when ore feed became available from a series of open pit cut backs on the Harrier Pit, John’s Pit and O'Dwyer's South Pit. Since the completion of O'Dwyer's South cut back in Q4 2012, the sole source of ore has been from the underground operations. The current Life of Mine (LOM) plan contains ore sourced from underground operations only.

The underground mine commenced declining in March 2006 with production first recorded in September 2006. Development and stoping have been conducted in the Phoenix, Falcon, Ellesmere, Kink, Vulture, Raven, Robin and Harrier ore bodies since that time. As at January 1, 2017 works are planned to continue in the Phoenix, Central, Harrier and Robin ore bodies. All areas are planned to be extracted using open stoping techniques with the application of Cemented Rock Fill (CRF) where applicable and practical. Selection of the specific mining method within the open stoping regime is based upon previous experience at the Fosterville Mine and expectations of ore zone geometry and geotechnical conditions. A standard level interval of 20 vertical meters can be applied across all mining areas. However, this can be varied as is required to maximize the extraction of the economic material. The Phoenix to 4240rl, Harrier below 4500rl, Central and Robin ore bodies are accessed from a footwall decline position while the Phoenix below 4240mRL and Harrier ore body above 4500mRL are accessed from the hangingwall.

Underground mining is conducted using a conventional fleet including jumbos, production drills, loaders, trucks and ancillary equipment. Current mining is undertaken as owner miner.

Since the commissioning of the processing plant in 2004, all processing models for the mill have been based on actual plant performances. The processing budget takes into consideration the mining schedule (ore source location, tonnes to be mined and gold grade), and predicted sulfur grades to be processed.

The process plant incorporates the following unit operations:

- Single stage crushing with a primary jaw crusher;

- Open stockpile with reclaim tunnel;

- 20ft diameter by 20ft length Semi-autogenous grinding (SAG) mill;

- A gravity circuit to recover coarse gold from the grinding circuit recirculating load;

- Flotation circuit to produce a gold bearing sulfide mineral concentrate and a barren residue;

- 8ft diameter by 13ft length flotation concentrate regrind mill;

- A gravity circuit to recover coarse gold from the flotation concentrate with gravity circuit concentrate being direct smelted;

- A Bio-oxidation circuit consisting of BIOX® reactors to oxidize the flotation concentrate, releasing gold from the sulfide mineral matrix;

- A three-stage CCD circuit to separate the gold bearing oxidized solid residue from the solubilized acid oxidation products;

- A liquor neutralization circuit to neutralize acid and precipitate arsenic as stable basic ferric arsenate and sulfate as calcium sulfate (gypsum) using both ground limestone and lime slurries;

- A limestone grinding facility comprising a single wet ball mill operated in closed circuit with a hydrocyclone to produce ground limestone slurry for pH control in the BIOX® tanks and neutralization of sulfuric and arsenic acids produced from oxidation of gold bearing sulfide
minerals;

- Carbon-in-leach (CIL) circuit, with a pH adjustment tank at the head of the circuit, to leach gold from oxidized material and load the cyanide soluble gold onto activated carbon;

- Heated Leach (HL) circuit to combat preg-robbing capabilities of the non-carbonaceous carbon always present in the Fosterville orebody. Specialized in-house technology unique to Fosterville; and

- Pressure Zadra elution circuit to remove gold from carbon, followed by electro-winning recovery and smelting to doré.