The operation consists of two open pits in the Saddleback Greenstone Belt, a fault bounded sliver of Archaen volcanic and shallow level intrusive rocks surrounded by granite and gneissic rocks. The main zone of gold mineralisation occurs over a strike length of more than five kilometres and a width of approximately one kilometre.

For descriptive purposes the Boddington deposit is subdivided into Wandoo South and Wandoo North at approximately 12200 N, subdividing the two main centers of bedrock mineralization.

Wandoo South is centered on a composite diorite stock, the Central Diorite, which has a known strike length of approximately 1,200 m and thicknesses varying from 300 m to 600 m. Five intrusive phases are known within the stock.

The southern portion of the Central Diorite strikes north, and dips subvertical and steeply to the west, with an apparent southerly plunge. To the north, the strike of the diorite changes from north to northwest, following the orientation of a transecting dolerite dyke. The dip changes from westerly, to subvertical, to steeply to the southwest.

The Central Diorite mineralization becomes patchy towards the southern end of Wandoo South, although the high-grade Southern Diorite Deeps zone is hosted within the southern portion of the same diorite. Down-dip extensions of the Central Diorite remain open, but the diorite body appears to pinch out towards the northwest.

Wandoo North is dominated by diorites, with lesser fragmental volcanic rocks. The diorites at Wandoo North are mainly porphyritic, compared to the predominantly aphyric diorites of Wandoo South. Wandoo North and Wandoo South are broadly similar, and formed as part of the same mineralized system.

Mineralization
Alteration types associated with gold and copper mineralization are clinozoisite–biotite– actinolite-sulfide ± silica veins/veinlets/fractures/clots and late actinolite–sulfide veins with clinozoisite–biotite and/or albite alteration haloes. These vein types form the basis of the stockwork mineralization of the Wandoo deposit. The majority of these mineralized late actinolite veins are not large enough to be correlated between drill holes; the exception is the Main Actinolite Vein in Central Diorite. However, broad zones of actinolite and clinozoisite alteration can be traced for a few hundred meters.

The interpreted sequence of alteration assemblage is roughly analogous to that which occurs within porphyry-style deposits. However, the alteration is not well zoned as for typical ‘porphyry style’ copper–gold deposits, but rather focused into lithological, structural, or alteration zones. Garnet, commonly found in porphyry deposits, has not been identified in the alteration mineral assemblage in the Boddington mine area.

The structural setting for the gold–copper–molybdenum mineralization is a major regional sinistral-strike-slip regime controlled by east–southeast to west–northwest compression.

The major mineralized structures in the Wandoo resource area are:
• D1 north–south-trending, near vertical, silica–biotite shear zone ± quartz veins; The Jarrah East quartz vein is hosted by a D1 shear zone and mineralized by later crosscutting D4 deformation;
• D2 north–south-trending, near vertical, quartz–sericite ± arsenopyrite shear zone ± quartz veins;
• D3 northeast-trending, near vertical and 50º northwest-dipping, quartz–albite ± pyrite shear zone ± quartz veins. The Herring Fault is a D3 type quartz–albite strongly-foliated shear zone (possibly a sheared felsic porphyry) overprinted by a late-D3 quartz ± albite ± epidote ± pyrite shear zone. A D3 shear zone hosts the Jarrah West quartz vein that was later mineralized as a result of cross-cutting D4 structures.
• D4 northwest-, north–northwest- and east–west-trending biotite ± actinolite ± clinozoisite ± sulfides (pyrrhotite–chalcopyrite) shear zones. The main northwest- and north– northwest-trending anastomosing D4 corridor is centered on the Wells Formation. The main east–west-trending, high-grade gold–copper, A2-type actinolite veins are mainly concentrated in the Wandoo South deposit area, which is interpreted as the regional dilation site. The Wandoo deposit contains D1 and D2 shear zones that are commonly overprinted and reactivated during D4 by biotite-sericite weakly to moderately foliated. All D1, D2, and D4 structures are observed to rotate to some degree into parallelism.

Two mineralization stages have been recognized at the Project. The earliest phase consists of widespread silica–biotite alteration and complex quartz + albite + molybdenite ± muscovite ± clinozoisite ± chalcopyrite veins, all of which are variably deformed by ductile shear zones.

The second, major, alteration stage cross-cuts the first, and comprises:
• Quartz + albite + molybdenite ± muscovite ± biotite ± fluorite ± clinozoisite ± chalcopyrite veining;
• Clinozoisite + chalcopyrite + pyrrhotite + quartz + biotite veins that host low-grade Au-Cu mineralization;
• Actinolite + chalcopyrite + pyrrhotite ± quartz, carbonate + chlorite veins that host highgrade mineralization;
• The bulk of the gold mineralization is associated with the late-stage fracture-centered clinozoisite–actinolite-biotite–sulfide alteration event with gold grades in this alteration being typically less than 3 g/t Au and averaging approximately 0.5 g/t Au to 1 g/t Au. The second mineralizing alteration style of late actinolite sulfide veining (with biotite – clinozoisite salvage) contains generally higher levels of gold, averaging 5 g/t Au to 8 g/t Au, but ranging from 30 g/t Au to 70 g/t Au in the larger veins.

Gold distribution typically displays the following characteristics:
• Visible gold generally occurs as inclusions and at grain boundaries with grain size generally less than 15 µm;
• Visible gold occurs within both silicate and sulfide species. Within the sulfides, visible Au is most common in chalcopyrite, pyrrhotite and pyrite, mainly because these are the most dominant sulfide species in the deposit. Molybdenite, arsenopyrite, and sphalerite also contain visible Au;
• There is no preferred association of visible gold with arsenopyrite;
• Within the non-sulfide minerals, actinolite and quartz have the most common association with visible Au;
• It is very common for visible Au to be associated with bismuth. In decreasing order of abundance, the bismuth species are: (i) native Bi; (ii) maldonite (Au2Bi); (iii) hedleyite (Bi4Te); and (iv) hessite (Ag2Te);
• The highest concentration of visible gold is at Jarrah (location of the underground quartz vein). Elsewhere, the visible gold is evenly distributed through the deposit, although still relatively rare.
• The Wandoo resource sulfide distribution is dominated by chalcopyrite (CuFeS2), pyrite (FeS2) and pyrrhotite (FeS), listed in decreasing order of abundance. The distribution of sulfide species has been examined and the following additional observations noted:
• The distribution of the three major sulfide species is reasonably consistent across the deposit, with: (i) increased concentrations of chalcopyrite at Southern Diorite Deeps, Blob and Pipeline; (ii) pyrrhotite is best-developed at Pipeline and Southern Diorite Deeps along with other higher concentrations at Central Diorite; and (iii) pyrite is best-developed at Pipeline and Southern Diorite Deeps;
• Arsenopyrite (FeAsS) is most common within the South Zone, Far North and Blob domains of Wandoo North. This is consistent with the review of the arsenic distribution from the exploration database;
• Molybdenite (MoS2) is mainly within Southern Diorite Deeps, Central Diorite, North Diorite and A Breccia domains, which is consistent with the review of molybdenum distribution from the exploration database;
• Cubanite (CuFe2S3) almost always occurs as exsolution lamellae within chalcopyrite and is distributed throughout the deposit based on petrographic review.

Boddington is mined by a conventional truck-and-shovel operation. Equipment is owneroperated and includes a large mining truck fleet (240-tonne class), electric rope shovels, support equipment, and drills. Mining is done predominantly on 12 m benches.

All drilling operations are performed by Newmont with Newmont owned rigs.

Vertical production holes are drilled vertical (229 mm diameter) with a nominal bench height of 12 m, with 1.5 m subdrill for a 13.5 m overall hole length. Wall control holes are 127 mm diameter for batters and buffers and 115 mm diameter for pre-split. A variety of angles and lengths are used to suit various geotechnical based ground control domains. All rigs are GPS controlled for hole positioning and on-board telemetry systems for recording depth, angle, drill time etc.

Production blasting utilises augered and pumped Heavy ANFO blends, with a nominal approximately 500 kg per hole. Crushed aggregate, produced on site, is used as stemming for the top 3.7 m of each hole. Electronic detonators are used for ore blasts whereas nonel detonators are used on waste blasts. Nominal Powder Factors on production blasts vary from 1.18 to 1.40 kg/m3.

The wall control configuration features a triple bench design; a 70° or 75° angled batter on the top bench is followed by a single pass 24 m vertical pre-split for the second and third benches. All first bench blasts are fully free faced.

In 2020, the Board of Directors approved investment in an Autonomous Haulage System at Boddington in Australia to enhance safety and productivity, while also extending mine life. Once fully operational in 2021, Boddington will be the world’s first open pit gold mine with an autonomous haul truck fleet. Boddington has a current capacity to mine approximately 235,000 tonnes of material per day.

The processing plant has a nominal capacity to process approximately 40 million tonnes of ore per year with optimization projects underway to further increase this capacity.

The process consists of primary crushing, closed circuit secondary and High Pressure Grinding Rolls (HPGR) tertiary crushing, ball milling, and hydrocyclone classification to generate a milled product with a P80 of 150 micrometers (µm) at a slurry density of around 35% solids.

Coarse Crushing (in mining area)
The mine haul trucks dump ore to two primary crushers (60/113 MK-II gyratory crusher). Crushed ore is transferred via an overland conveyor to a 230,000 t capacity (40,000 t live capacity) stockpile adjacent to the processing plant. Dozers operating on the coarse ore stockpile can increase the total storage capacity up to 400,000 t.

Fine Crushing and Screening (process plant)
Three apron feeders reclaim ore from beneath the coarse ore stockpile and delivers the ore to the secondary crusher feed conveyor and the six secondary crushers (MP1000 cone crusher, five original with a sixth crusher installed in late 2010), which are operated in closed circuit with four coarse screens (three original with a fourth coarse screen installed in 2010).

Oversize material returns to secondary crushing and the fine material reports to the tertiary crushing plant that consists of four HPGRs. The tertiary product is stored in a 20,000 t fine ore bin ahead of the ball milling circuit. Fine ore is reclaimed from the bin via eight reclaim belt feeders (two per four parallel milling trains) and delivered to the fine screens ahead of ball milling. Each line consists of two screening units.

Undersize material from the screens reports to one of four cyclone feed hoppers and the oversize returns to the HPGRs for additional crushing. Cyclone clusters classify the finely-crushed particles, with the finer cyclone overflow material (80% passing 150 µm) reporting to the flotation distribution box and the coarse cyclone underflow material to a split between the ball mills or flash flotation cell (for free gold recovery).

Tails from the flash flotation cells are recycled back to the ball mills for further grinding. The target final product grind size from the milling circuit is 80% passing 150 µm, although increased throughput rates in 2011 and 2012 resulted in grind size P80 coarsening to 170 to 190 µm at times. Improved process control and increased ball mill operating power draws have reduced the grind size back to around 150 to 160 µm at the elevated throughput rates.

The regrind plant consists of two Verti-mills (one duty and one standby) with product reporting, via cyclone clusters, to the cleaner flotation plant. The cleaner flotation facility has three sequential stages with final product being transferred to the concentrate thickener, then storage in two, 1,000 m3 tanks before being sent to the filtration plant. Concentrate is trucked to the port of Bunbury to be exported by sea.

The milling plant includes a three stage crushing facility (two Primary crushers, six Secondary crushers and four high pressure grinding rolls), four ball mills, a flotation circuit and carbon in-leach circuit. The flotation circuit process recovers gold-copper concentrate before the material is then processed by a traditional carbon-in-leach circuit where the remaining gold is recovered to produce doré.

The processing plant has a nominal capacity to process approximately 40 million tonnes of ore per year with optimization projects underway to further increase this capacity.

The cyclone overflow from the mill circuit is treated in a flotation circuit that produces a copper–gold concentrate for export. Rougher and scavenger flotation concentrates are reground and cleaned to achieve an acceptable final concentrate grade. The concentrate is thickened and filtered before being trucked to port.

Cyclone overflow from the mill circuit is treated in a flotation circuit that produces a copper– gold concentrate for export. Rougher and scavenger flotation concentrates are reground and cleaned to achieve an acceptable final concentrate grade. Concentrate is thickened and filtered before being trucked to the port of Bunbury.

The cleaner scavenger tailings stream is thickened and leached under elevated cyanide levels. Scavenger tailings are thickened and leached in a conventional leach/adsorption circuit. Leached slurry from the cleaner scavenger tailings leach circuit is delivered to the scavenger tailings circuit for combined recovery of gold.

Leach residue is pumped to the residue disposal area, and residual CNwad is maintained below a targeted level by a Caro’s acid cyanide destruction plant. This facility can treat the following streams:
• Decant water returning to the plant so that cyanide levels do not inhibit flotation;
• Decant water recycling to the decant pond to maintain CNwad levels in the pond at an average of 30 ppm and a not-to-exceed level of 50 ppm;
• Residue slurry from the plant to protect the decant pond from excursions caused by shortterm variability in the copper head grade.

The carbon from the scavenger tailings adsorption circuit is treated by conventional split Anglo American Research Laboratory (AARL) method elution and reactivated in horizontal reactivation kilns. Gold recovery from the eluate is by electrowinning, cathode sludge filtration and drying, and smelting.

There is a flash flotation and gravity circuit installed in the process plant. These circuits have not been operated and remain decommissioned.

Gold and Copper Recovery to Concentrate
The flotation distribution box transfers cyclone overflow product from each of the four parallel grinding lines in to three parallel trains comprising, eight-unit flotation cells. Concentrates produced by cells #1 and #2 report to the coarse cleaner cells for final cleaning, and product from the other cells reports to regrind thickening.

The regrind plant consists of two Verti-mills (one duty and one standby) with product reporting, via cyclone clusters, to the cleaner flotation plant. The cleaner flotation facility has three sequential stages with final product being transferred to the concentrate thickener, then storage in two, 1,000 m3 tanks before being sent to the filtration plant. Concentrate is trucked to the port of Bunbury to be exported by sea.

The cleaner circuit has a scavenger circuit consisting of six cells. Cleaner scavenger tailings are leached in a dedicated circuit of nine leach tanks with the product combining, for further leaching, with the tails from the eight-unit flotation cells.

Gold Smelting and Bullion Production
Scavenger flotation tails report via a flotation tailings thickener to two five-unit leach tank trains. From the leach tanks, it transfers to two trains of seven carbon-in-leach (CIL) tanks and finally transferring to the residue disposal area (RDA). Activated carbon used in the leaching process to adsorb gold leached into solution reports to a two-train elution plant. Each elution plant has two elution columns, two heat exchangers and two elution heaters. The barren carbon product from the elution columns is transferred to the carbon reactivation plant before transfer back to the CIL train, and the gold solution transfers to the electrowinning circuit. The final product from the eight-unit electrowinning circuit reports to the gold furnace for smelting.