The Rosebery volcanogenic massive sulphide (VMS) deposit is hosted within the M t. Read Volcanics, a Cambrian assemblage of lavas, volcaniclastics and sediments deposited in the Dundas Trough between the Proterozoic Rocky Cape Group and the Tyennan Block.

Sulphide mineralisation occurs in stacked stratabound massive to semi-massive base metal sulphide lenses between the Rosebery Thrust Fault and the M t. Black Thrust Fault; the host lithology and the adjoining faults all dip approximately 45 degrees east.

Economic Zn-Pb-Ag-Au mineralisation occurs as massive, semi massive and disseminated base metal sulphide lenses located within the Rosebery host sequence.

Mining production is carried out by long-hole open stoping with a Decline Access. Stoping is conducted through both longitudinal retreat and transverse methods.

Mining lenses are divided into panels and are mined using a bottom-up sequence in a continuous 45 degree retreating either towards or away from level access drives. The nature of this mining sequence causes fluctuations in the grade profile of the short-term schedules. Each stoping panels contain between 3 and 5 sub-levels with crown pillars left in-situ between the backs of up-hole stopes and the lowest sill drive of the panel above.

Backfilling of stope voids is carried out using two methods; Cemented Rock Fill (CRF) and Rock Fill (RF). Up-hole (Crown) retreat stopes are left as an open void due to lack of access for fill placement.

Average stope strike lengths of 15m were used in W and X Lens while the other lenses used 20m. The height set to 20-25m (floor to floor) and the minimum mining width of 4.5m. The horizontal width has been adjusted to 4.65m to allow for the low dip of the ore body and to achieve the 4.5 m true widths.

Access to the orebody is through a decline 5.5 mH x 5.5 mW at a 1:7 gradient. The approximate standoff distance between orebody and stoping footwall and major infrastructure; stockpiles, vent rises, escape-ways, declines and ancillary development is 65-70m.

The current primary ventilation system supplies approximately 650m³/s (Measured at depth) of air to the underground mine, which is designed to allow extraction from the multiple ore lenses.

The Rosebery crushing circuit consists of a Primary Jaw Crusher and a Secondary Cone Crusher. During Crushing the ore size is reduced from around 650mm to P80 of 20mm. The Grinding Circuit consists of 2 x Primary Ball Mills and 3 x Secondary Ball Mills.

Metallurgical processing of ore at Rosebery involves crushing and grinding followed by flotation and filtration to produce saleable concentrates of copper, lead and zinc. Additionally, gold is partly recovered as doré following recovery from a gravity concentrator.

Gravity gold is recovered from the grinding circuits using 2x Knelson Concentrators. Gold Concentrates are leached in an Intensive Leach Reactor (ILR). Then recovered from the pregnant leach solution by electrowinning and thereafter the gold sludge is smelted.

The recovery sequence for sulphide minerals in the Flotation Circuit is Chalcopyrite (Cu), Galena (Pb), Sphalerite (Zn). Payable gold and silver is recovered with the copper and lead concentrates.