Gold and copper mineralization at Telfer consists of stratiform reefs and stockworks hosted by sedimentary rocks of the Malu Formation of the Lamil Group. The Lamil Group comprises relatively weakly deformed and metamorphosed Proterozoic sediment units northeast of the Camel-Tabletop Fault. The important attributes of the Lamil Group are the presence of abundant carbonate units, and weakly developed penetrative deformation.

The topography at the Telfer mine site is dominated by two large scale asymmetric dome structures with steep west dipping axial planes. Main Dome is located in the southeast portion of the mine and is exposed over a strike distance of 3km north-south and 2km east-west before plunging under transported cover. West Dome forms the topographical high in the northwest quadrant of the mine and has similar dimensions to Main Dome. Both fold structures have shallow to moderately dipping western limbs and moderate to steep dipping eastern limbs.

Mineral Resources reported for the Telfer mining centre consist of:
• open pit stockwork and reef mineralization in Telfer Main Dome and West Dome;
• stockwork and reef mineralization mined underground in the Telfer Underground SLC mining operation;
• stockwork mineralization in the VSC below the SLC.

Mineralization within the Telfer deposit is controlled by structure and lithology. Several styles of mineralization were recognized, namely narrow high-grade reefs, pod-like mineralized bodies, sheeted vein-sets and large areas of low grade stockwork mineralization, with the latter forming the majority of the sulphide resource. The primary mineralization was overprinted by surface weathering processes.

The sulphide mineralization is characterized by fresh sulphides, predominantly pyrite and chalcopyrite. The main copper minerals listed in order of occurrence are chalcopyrite, chalcocite and bornite with minor cobaltite and nickel-sulphide. Primary gold generally occurs as free grains, on sulphide boundaries and to a minor degree with silica grains.

Primary gold mineralization is typically associated with pyrite/chalcopyrite sulphides and quartz/dolomite gangue. There is a correlation between vein frequency and gold grade.

Weathering locally modified the mineralization, to depths typically up to 200m, with the boundary between oxide and primary mineralization being irregular. The weathering profile produced local areas of supergene enrichment where the copper to sulphur ratio is characteristically higher. Supergene minerals include gold with limonite/goethite, malachite and chrysocolla in the depleted oxide zone, giving way to chalcocite, pyrite, digenite, covellite, tenorite and cuprite at depth in primary mineralization. The copper to sulphur ratio decreases with depth below the supergene zones. Copper is, in general, more mobile in these supergene area zones than gold. The depth of oxidation is closely related to the structural framework and typically exists to approximately 200m below surface, although local areas show oxidation down faults in excess of 500m below surface.

The highest concentration of gold and copper grades occurs within bedding sub-parallel reef systems. In Main Dome a total of 21 reef structures were identified from drill hole data or mapping of surface and underground exposures within the Open Pit Mineral Resource, and include 10 E-Reefs within the Outer Siltstones, the MVR within the Middle Vale Siltstone and the M10 to M50 series of reefs within the Malu Formation. The primary characteristics of the reef systems are:
• broadly concordant to lithological boundaries;
• laterally extensive (greater than 1km) both along strike and dip;
• true thickness of 0.1m to 1.2m, averaging between 0.3m and 0.7m;
• high relative nugget effect;
• variable dip varying from flat at the crest of Main Dome to about 40º on the eastern flank of Main Dome;
• gold grade is typically high but variable: 5 g/t Au to 50 g/t Au;
• copper grade ranges between 0.2% Cu and 1.5% Cu.

Stockwork mineralization is characterized by narrow, often discontinuous veins that crosscut stratigraphy. Large domains of stockwork mineralization were defined in the open pits and also within the Telfer Deeps and Vertical Stockwork Corridor Mineral Resources. Stockwork mineralization is best developed in the axial zones of Main Dome and West Dome and is discordant to lithological boundaries, although some stratigraphic units have more abundant stockworks than others and vein intensity within stockwork can be greater adjacent to reefs. Stockworks are laterally extensive, between 0.1km to 1.5km scale and the geometry of the stockwork zones is related to structure and stratigraphy.

Stockwork mineralization can also include areas of breccia dominated by quartz, carbonate and sulphides.

Mining methods at Main Dome and West Dome are the same. Current mining activities at the Telfer open pits are conducted via conventional truck and shovel operations, standard waste rock dumps and stockpiling and reclaim of lower grade ore. An excavator configured load fleet is utilised to selectively extract ore material from a total twelve metre design bench height via three 4m high ‘flitches’. The 4m ‘flitches’ are used in order to reduce ore dilution and loss. Bulk waste is stripped via two 6m ‘flitches’. Productivities, availabilities and utilisations used within the production schedule have been based on current performance.

Open pit operations within the Main and West Dome pits have traditionally focused on the selective extraction of the ore material within the Mineral Reserve through the use of the site excavator fleet. This configuration of this equipment, and selective ore mining approach adopted for ore mining, has led to the use of 12m benches comprising of three 4m ‘flitches’.

The Telfer underground consists of the Telfer Sub level Cave (SLC) and selective M Reef operations. The Western Flanks is yet to be mined. The deposits are beneath the Main Dome open pit and previously known as Telfer Deeps.

The Telfer SLC is being mined using the sub-level cave method. SLC involves the development of a series of parallel cross-cuts through the orebody in a regular geometrical pattern. Ore is progressively recovered from drawpoints developed in the crosscuts. As material is loaded from a drawpoint, broken ore above the extraction level progressively mixes with material from higher levels in the cave.

Loaded ore is tipped down an ore pass system to the haulage level where it is trucked to the underground crushing station. A hoisting shaft facilitates transport of ore to surface, from a hoist depth of approximately 1,100m.

A new treatment plant was constructed on-site and commissioned in late 2004. Two products are generated, namely gold doré and a gold bearing copper concentrate.

Minor amounts of oxide ore are scheduled for processing in a dump leach operation as an adjunct to the main treatment route, with the dump leach output being incorporated within the overall gold doré production total.

The feed ore for the Telfer treatment plant is sourced from both open pit and underground mining operations. Owing to the range of ore types with differing mineralization of both gold and copper, together with variation in ore hardness, the treatment flowsheet is relatively complex. Two parallel process trains have been incorporated through the grinding and flotation circuits in the treatment plant which has a nominal throughput capacity of 20Mtpa of ore. In practice however, the throughput rate generally varies between 17Mtpa and 23Mtpa depending upon the ore characteristics. There is a general operating strategy to blend ore on the coarse ore stockpile in order to control the feed to the treatment plant in terms of the ore grade and hardness.

The circuit was designed to maximize the recovery of the value minerals, starting with a flash flotation and gravity recovery section within the grinding circuit intended to capture the coarse free copper and gold mineralization that is liberated early in the process route. The milled product from the grinding stage passes to the copper flotation circuit where the residual copper is recovered, together with a proportion of the gold that is associated with the copper minerals as well as a proportion of liberated gold. Approximately 5% of the gold in the ore is within the pyrite mineralization which reports to the copper circuit tailings. Tailings from the copper circuit are therefore processed through the pyrite flotation circuit from which the recovered pyrite concentrate is processed through a cyanidation leach circuit for final gold extraction. The gold is extracted from the leach liquor by means of adsorption onto activated carbon followed by stripping and electrowinning.