Gold is the only metal of economic significance present within the Luise Caldera. A number of mineralization styles have been recognized, ranging from early porphyry to late stage epithermal mineralization. Two of these represent economically significant phases of gold mineralization at Lihir.

• The most important is refractory potassium feldspar-sulphide mineralization. In this association, gold occurs primarily as sub micron size particles in sulphide minerals. Overall sulphide content is relatively high, with the average sulphur grade of the reserves being above 6%. The main sulphide mineral is pyrite, with the marcasite form present as an accessory mineral and rare arsenopyrite.

Gold also occurs as small (less than 100 micron) blebs within fine pyrite crystals. The sulphides are characterized by their fine grained nature, and have been deposited through wholesale flooding and deposition within all host rocks, imparting a sooty, dark grey coloring to the host rocks. Within the Lienetz and Kapit orebodies (and in some localized portions of Minifie) this style of mineralization has been associated with strong leaching of the original lithologies creating pinhole to open, vughy textures.

• The second significant style of gold mineralization occurs as a low sulphidation quartz-chlorite-bladed anhydrite association, more typical of epithermal style mineralization, deposited through the mixing of magmatic fluids with oxidizing near-surface water. Occasional free gold, up to several millimetres in size, has been observed in association with this mineralization style.

Mineralization occurs as discrete fracture filled veins through all levels of the deposits, and is inferred to be an overprinting style of epithermal mineralization associated with the cooling of the active geothermal system within the Luise Caldera. It is also characterized by relatively high, though erratic, gold grades when compared with the high sulphidation style of mineralization.

Production mining operations at Lihir are conducted by Newcrest using their own equipment fleet and workforce. A separate mining contractor operation using a smaller pioneering fleet is developing new areas on the steeply dipping caldera slopes. Production mining uses a fleet of 500t class hydraulic face shovels loading into 135t rear dump haul trucks. Ore and waste is drilled and blasted on 12m benches and mined in a single pass, except where excessive heave has required a second lift for safety reasons. The ground is frequently too hot for conventional explosives, requiring high temperature blasting products and specialized blasting procedures for mining in hot ground.

Ore is crushed in two primary crushing circuits. The first circuit consists of a 42 65” gyratory crusher and Abon toothed rolls crusher. Competent ore is crushed in the gyratory crusher and softer ore types in the Abon crusher. Both crushers discharge on to an overland conveyor up to a radial stacker for stockpiling ahead of the grinding circuits, providing mainly high grade ore to the third milling circuit (known as HGO2 circuit) installed as part of the major plant expansion.

The second primary crushing, installed for the plant expansion, consists of two jaw crushers operating in parallel. This circuit typically receives more competent lower grade ores and supplies the FGO and HGO mills via a separate overland conveyor and radial stacker.

Ground flotation grade ore from the FGO circuit Mill is subjected to simple bulk rougher flotation in a single roughing stage consisting of a bank of five 150m3 flotation tank cells. Ground flotation ore from the HGO circuit Mi ........