Wafi–Golpu is a complex, multiphase mineralised system, comprising:
- Golpu porphyry copper–gold deposit;
- Wafi epithermal gold deposit;
- Nambonga porphyry gold–copper deposit.

The upper portions of the porphyry systems were overprinted by the high-sulphidation epithermal mineralisation at Wafi.

Golpu
The Golpu deposit extends over about 800 m north–south by 500 m west–east, and was drill tested to more than 2,000 m depth.

Porphyry-style veins are preserved within the clay alteration at the top of the Golpu deposit. These veins have had the copper–iron sulphides removed, leaving only a skeleton of quartz. Irregular molybdenite veins are preserved stable remnants of the porphyry mineralising event.

The dominant copper–gold-bearing sulphide species vary laterally and vertically within the deposit from an inner bornite (plus chalcopyrite) core, to chalcopyrite as the dominant copper sulphide, and grading out to a pyrite-only shell on the mineralisation margin.

The proportion, by volume, of disseminated copper–iron sulphides varies from trace to as much as 10%. Pyrite increases from near absent in the core to 10% on the margin in a reverse relationship to chalcopyrite. Disseminated sulphides are typically located at the site of relict iron-bearing phases including primary phenocrystic hornblende and hydrothermal alteration-derived biotite– magnetite.

The Hornblende Porphyry (Livana Porphyry) is the main mineralised porphyry. Other porphyries act either as weak mineralisers (e.g., Golpu Porphyry) or as benign hosts (wall rock) from adjacent mineralising porphyries. The mineralisation style in benign (wall rock) porphyries can change due to rheological contrast and chemical variations. Quartz vein stockworks occur on the intrusive margin in sedimentary rocks. Significant zones of quartz flooding may be present. The porphyry system is mineralised with gold, copper, silver and molybdenum:
- Gold, copper and silver trend from highest grade in the Hornblende Porphyry (Livana) core to background levels at the mineralised edge;
- Molybdenum content is low in the gold and copper maxima, but increases outwards to a maximum at the copper margin and declines to background beyond the copper mineralisation limits.

Wafi
The Wafi deposit has a surface area of approximately 1,100 m x 800 m and was drill tested to about 600 m below surface. A number of zones, including the A, B, NRG and Link Zones, were defined. The NRG Zone is the nonrefractory portion of the A Zone, and the Link Zone is a more discrete, higher-grade zone characterised by both high sulphidation and low sulphidation mineralisation. It is unclear if the high sulphidation and intermediate sulphidation events at Wafi are independent, or are a continuum of a single event.

The high sulphidation gold event alteration overprints the Golpu porphyry-style alteration and mineralisation, with the diatreme carrying fragments of the earlier porphyry alteration. The high sulphidation event was interpreted to have remobilised pre-existing porphyry-related copper from the phyllic–argillic-altered upper porphyry and deposited this as zoned enargite–tennantite– covellite–chalcopyrite mineralisation. Most of the gold in the high sulphidation overprint was introduced in association with pyrite.

The low sulphidation Link Zone, which occurs on the diatreme margin, between and below the Zones A and B high sulphidation gold mineralisation, is characterised by pyrite with lesser quartz (quartz–sulphide–gold style) veins, which are overprinted by more than one generation of pyrite– sphalerite–galena–carbonate veins (carbonate–base metal–gold style). Selective sampling shows the gold in this zone is related to the arsenian pyrite of the quartz–sulphide-style veins, while the multi-stage lowarsenic carbonate–base metal veins are not well gold-mineralised.

Advanced argillic alteration contains primary copper mineralisation as chalcocite, but gold occurs within pyrite or as electrum associated with pyrite–enargite–tetrahedrite. Mineralisation appears to broadly follow the metasedimentary and volcanic host rocks stratigraphy (i.e., 40–50° to the east, and northeast), and is often sub-parallel to bedding. The copper–gold-bearing lenses occur in kaolinite–chalcocite–pyrite and vuggy quartz ± covellite ± enargite bands that may reach 20 m in thickness.

Nambonga
The stock is a low-grade copper and gold mineralised system, and extends over an area of approximately 200 m x 200 m and to a vertical extent of at least 800 m.

Much of the mineralisation is associated with silicification, either pervasive or as veins. Quartz stockwork veins that may be as wide as 10 mm and stockworks overprint the porphyry, especially in the upper levels.

Mineralisation consists of disseminated and vein-style copper–gold mineralisation and structurally-controlled base metal mineralisation in steeply-dipping lodes. Chalcopyrite is the dominant copper sulphide mineral. Chalcopyrite and pyrite form anhedral grains ranging that can reach 0.2 mm in width, and tend to occur as centrelines to quartz veins. Magnetite forms anhedral grains that can be 0.4 mm wide, and is generally present in the margins of the quartz veins or in the wall rock adjacent to quartz veins. Minor magnetite, pyrite and chalcopyrite are disseminated through the host rock.

An evaluation of potential mining methods included consideration of block caving, sub-level caving (SLC), sub-level open stoping (SLOS), and open pit methods. Block caving was selected for the following reasons:
-Orebody geometry and geotechnical conditions;
-High productivity, low operating cost mining method;
-Higher-value material located at depth can be accessed earlier in the mine plan.

The proposed mine plan uses technology conventional to block cave operations, including mine design and equipment. Due to high surface ambient temperatures and humidity, and the depth of the mine, considerable ventilation and cooling capacity will be required to be installed to ensure the health and safety of mine workers.

The proposed mining method is block caving at three distinct elevations:

- The BC44 extraction level is planned at 4400 mRL, to extract a total of approximately 67 Mt of material over a seven-year period at a peak annualised 16.84 Mt/a production rate. During caving operations, ore from the block cave drawpoints will be delivered by diesel load–haul–dump vehicles (LHDs) to either of two underground gyratory crushers then conveyed to the Watut process plant on surface by an inclined conveyor system;
- The BC42 extraction level is planned at 4200 mRL, to extract a total of approximately 93 Mt of material over a nine-year period at a peak annualised 16.84 Mt/a production rate. Materials handling from drawpoint to the Watut process plant is identical to that proposed for BC44;
- The BC40 extraction level is planned at 4000 mRL, to extract a total of approximately 240 Mt of material over a 16-year period at a peak annualised 16.84 Mt/a production rate. Materials handling from drawpoint to the Watut process plant will be identical to that proposed for BC44.

Access to the mine workings will be via the Watut and Nambonga declines, with each generating waste rock that will either be used in construction activities, processed or deposited within the waste rock storage facilities (WRSFs). Block cave mining will not result in the production of waste rock because all material extracted from the block cave will be fed to the Watut process plant. Block cave mining will cause a subsidence zone of fractured rock to develop that will propagate to surface.

During the development of the block caving infrastructure, ore grade material will be temporarily stockpiled on the process plant terrace for later use during commissioning and initial production from the process plant. During caving operations, ore from the block cave drawpoints will be delivered by LHD vehicles to an underground crusher. The crushed ore will then be conveyed to the surface. The ore conveyor emerging at the Watut declines portal terrace will continue overland for approximately 600 m to deliver crushed ore to a coarse ore stockpile adjacent to the Watut process plant for processing.

The mine is planned to operate 24 hours per day, every day of the year, apart from scheduled and unscheduled shutdowns.

Coarse Ore Stockpile
Crushed ore will be conveyed to a single, conical, open stockpile which will have a live capacity of approximately 41.4 kt dry solids. The design basis average live residence time will be 20 hours, based on the Golpu flowsheet.

Coarse ore will be reclaimed from the stockpile by four belt feeders. Each feeder will be designed to provide 33% of the full feed rate to the SAG mill to enable three feeders to achieve nameplate capacity. Each belt feeder will discharge onto the mill feed conveyor that will transport crushed ore to the SAG mill feed chute.

Comminution Circuit
The comminution circuit will consist of a single SAG mill in open circuit, followed by two ball mills, configured in parallel, operating in closed circuit with dedicated classification cyclones. However, the comminution circuit is configured as a single SAB combination for the LEAN flowsheet for the first three years.

All three mills will share a common discharge sump. Scats/pebble return conveyors were incorporated into the circuit with a pebble crusher included, but deferred to the latter years of operation to accommodate harder ores at that time. Scats and pebbles will be recirculated via external conveyors to the SAG mill feed.

The Golpu flowsheet will be commissioned in two stages with the additional ball mill circuit brought on later to match the increased tonnage profile, resulting in a SAG/ball mill configuration with the two ball mills operated in parallel. The Golpu pyrite circuit will be commissioned the following year.

A pebble crusher is included in the scats/pebble circuit later in mine life when necessitated by the increased ore hardness of portions of BC40. The design caters for a possible future inclusion of a bifurcated chute and additional conveyors to return crushed pebbles to the ball mills in equal proportions should increase ore hardness towards the end of the LOM necessitate it.

The SAG mill will be operated in open circuit while each ball mill will be configured in closed circuit with a dedicated classification cyclone cluster. Each ball mill will have a circulating load of 240%. The SAG and ball mill are designed for operating at 75% of critical speed. The specific energy values used were obtained from testwork and are 6. kWh/t for the SAG mill and 9.2 kWh/t for the ball mills. The total charge volume ranges between 20–25% by volume in the SAG mill and 25–34% by volume in the ball mill. The ball charge volume is adjusted according to the demand and operation of the mill. The in-mill density designed for is 67% by mass for the SAG mill and 70% by mass in the ball mills. The discharge of both SAG and ball mills will be via a trommel screen.

Each ball mill will be operated in closed circuit with a classification cyclone cluster, the underflow will return to the mill while the cyclone overflow product will be routed across a 3 mm square aperture vibrating trash screen to protect downstream processes from ingress of oversize material in the event of the cyclones roping. Two standby cyclones are included in each classification cyclone cluster. The cyclone overflow product specification is a P80 of 106 µm and a density of 36% solids by mass to allow for a nominal dilution from the downstream trash screen spray water while maintaining a flotation feed density of 35% solids by mass.

Individual cyclone feed pumps will feed the separate cyclone clusters with cyclone underflow returning to the respective ball mill feed chutes. The mill feed conveyor will transfer ore (together with pebble/crushed pebble recycle) to the SAG mill feed chute. Steel grinding media will also be added to the mill feed hopper via an automated ball loading system.

The process plant will include the following:

-Crushed ore stockpile and reclaim;
-Single SAB milling circuit, with the ball mill operated in closed circuit with cyclones for operation at the lower design throughput of 8.42 Mt/a. This will be expanded to include a second ball mill, operating in parallel with the original ball mill circuit when the plant is expanded to a design capacity of 16.84 Mt/a. The target grind size is a P80 of 106 µm;
-A pebble crusher circuit is included. Pebbles are recirculated to the SAG mill during the 8.42 Mt/a LEAN and early years of the 16.84 Mt/a Golpu flowsheet with the pebble crusher included when necessitated by increased ore hardness in the later years of mine life;
-Copper flotation comprising rougher flotation, copper rougher cleaner (single Jameson cell) which processes the first rougher concentrate, copper concentrate regrind, followed by a three-stage copper cleaner, and cleaner–scavenger stage;
-Additional copper ........