The Ahafo mine is composed of three orogenic gold deposits that have oxide and primary mineralization. The gold is hosted in brittle shear zones cutting granitic intrusives that have kilometer-scale vertical and lateral extent. Gold occurs primarily in pyrite and secondarily as native gold in quartz veins.

Ahafo has two active open pits, Subika and Awonsu. Subika added an underground operation, which reached commercial production in November 2018, and Awonsu completed a layback in November 2019.

Open pit mining is conducted at Ahafo South using conventional techniques and an Owneroperated conventional truck and shovel fleet.

Underground mining is currently conducted using conventional stoping methods, and conventional mechanized equipment. Underground mining is conducted by contractor African Underground Mining Services (AUMS).

Open Pit Operations use a standard drill-and-blast, truck-and-shovel configuration. The prime mining fleet consists of three Liebherr 9400™ front shovels, one Liebherr 994 backhoe, thirty-eight CAT785™ haul trucks and Sandvik D45KS™ drills. Support equipment includes CAT dozers, graders, water trucks and backhoes.

Newmont currently employs nine Sandvik Drilltech D45KS™ drill rigs for blasthole production drilling and three Sandvik DR560™ rigs for pre-split drilling. Blastholes are drilled on average at 9.5 m vertical (i.e. 1.5 m as a sub drill) for grade control sampling in fresh rock. The pattern size used is 4.0m × 4.5m pattern spacing for both ore and waste in all pits.

The Subika underground mining operations are split into two areas:
• The Upper mining zone, above the 840 relative level (RL); also known as the upper Yoda area;
• The Central mining zone (corridor) below the 840 RL; also referred to as the Central area.

The mine plan assumes the use of a number of different mining methods, including:
• Sub-level open stope (SLOS): to be used above 840 RL;
• Long-hole open stope retreat (LHOSR): to be used above the 750 RL in the Central zone;
• Long-hole retreat with rockfill (LHSRF): to be used in the transition zone between the 750 and 665 RLs in the Central zone;
• Single lens retreat (SLR): to be used below the 665 RL in the Central zone, and in the North and South mining zones; stopes will be paste-filled.

Mining operations in the Sub level open stope (SLOS) zone will use existing infrastructure and spirals created on a 40 m level spacing to access the stopes. These stopes are mined from the lowest stope level upward in stope groups to create large open stopes. The ore on these levels is loaded directly from the mining extraction level to trucks and hauled up the existing main decline to the surface, and placed on stockpiles. Surface haulage equipment transports stockpiled material to the process plant.

To access the lower ore, below the 840 RL, a set of twin declines will be developed off the existing main haulage decline. The twin declines will be developed as a figure eight or elongated spiral configuration with one full rotation at 50 m intervals. The declines will be connected via a link drive that will act as a ventilation, escapeway and haulage connection between the two declines.

Both declines will act as a primary ventilation circuit with fresh air. Additional ventilation will be sourced through fresh air ventilation raises connected at the link drives and the foot wall drives below the 750 RL. The fresh air raise will deliver refrigerated air from the surface refrigeration system. The return air will be taken from the access drives above the 750 RL and from the ends of the foot wall drives below the 750 RL, using return air raises connected to the main fans at the surface and Portal 2.

Level accesses will be created off the decline at 25 m intervals to cross the ore zone from levels 800 to 700 RL. Below the 700 RL, the level interval will be increased to 35m.

Above the 750 RL, infrastructure such as substations, pump cuddies and sumps will be developed on these access drives. On these levels the ore drives will be developed from the access drives along the ore lenses identified as containing the mineralization for eventual stoping. The ore drives will be driven to the extents of the defined mining corridor and stoping will retreat from the end of the orebody towards the accesses. These stopes will be mined top-down. Stopes will be mined from the end of the ore drives back to the level access. Pillars will be left between stopes along the mine level for regional stability. Stopes will be mucked using remote mucking equipment back to an ore pass created between levels. Trucks will be loaded from the level below the mining extraction level via the material placed in the ore pass. The trucks will travel up the spiral declines to the main haulage decline and exit and enter via the North portal.

Below the 725 RL, the access drive from the decline will connect to a footwall drive that will be offset from the ore zone by 30 m. Stope access drives will be driven off the footwall drives to develop the stopes in the mineralized zone. The footwall drive will be used for infrastructure to connect ventilation returns, ore passes, substations, sumps and other infrastructure to support the mining on the levels. The mining direction for stopes in the areas below the 750 RL is centerout. Thus, stopes will be mined from a specified centralized location out to the extents of the orebody. These stopes will be mined bottom-up.

For stopes between the 750 and 665 RL, pillars will be left between stopes along the mine level for regional stability. Stopes will be mucked using conventional and remote mucking equipment back to the foot wall drive. Trucks will be loaded from the level below the mining extraction level via the material placed in the ore pass. When stope mining is completed, the stopes will be backfilled with rockfill using truck tips and remote loading. Stopes must be backfilled before adjacent stopes can be mined in the sequence.

For stopes below the 665 RL, no pillars will be left between stopes along the mine level for regional stability. Stability will be provided by backfilling the stopes with paste fill after the stopes have been mined. Stopes must be mined in sequence from a center-out, bottom-up approach with the mine sequencing a critical factor in controlling the high stress potential of these stopes. Stopes will be mucked using conventional and remote mucking equipment back to the footwall drive.

Trucks will be loaded from the level below the mining extraction level via the material placed in the ore pass. When stope mining is completed, the stopes will be backfilled with paste fill from a surface plant facility. Paste fill will be directed to the stopes through fill pipes from the surface to underground. Once a stope is filled and the backfill cured for the time required, the adjacent stope can be mined.

The available mining fleet for underground mining consists of five underground loaders and eight haul trucks, each with a 60-tonne payload.

The daily production rate is approximately 95,000. tonnes.

The primary source of ore for 2019 will be from stockpiles and Subika, which will produce significant tonnes of high-grade ore. Three 9400 diggers will be located in Subika from May 2019 to the last quarter of 2019, when mining is planned to start in Awonsu Phase 3. Subika mining will constitute stripping of large quantities of waste from pit Phase 4. Mining will be completed in Subika by 2024, while Awonsu Phase 4 will be the last pit to be completed in 2029.

The processing plant was commissioned in 2006 to process 7.5 million tonnes of primary and oxide ore per year. With the depletion of oxide ore, the current plant throughput has decreased to 6.5 million tonnes per year. The processing plant consists of a crushing plant, a grinding circuit, carbon in leach tanks, elution circuit, counter current decantation circuit and a tailings disposal facility.

The Ahafo Mill Expansion was completed in October 2019 that expanded the existing plant by approximately 3.5 million tonnes per year through the installation of a new crusher, a single stage SAG mill and two leach tanks.

Wet Circuit
The undersize of the trash screens reports to the 42 m Ø pre-leach thickener with the thickener overflow recycled to the milling circuit as process water. The pre-leach thickener underflow is pumped to CIL leach and adsorption tanks in series. Carbon is added to the CIL tanks and flow countercurrent to the process slurry. The CIL tailings is discharge onto the carbon safety screens before being pumped to the countercurrent decantation (CCD) circuit.

The CCD circuit consist of two 42 m Ø thickeners. The overflow from the thickeners is recycled back to the process as process water while the underflow is pumped to the tailings disposal tank. Tailings are discharged via a spigot system into the TSF.

Stripping and Dore Production
The loaded carbon is recovered via a carbon recovery screen and treated in the elution and electrowinning circuit. Loaded carbon is acid washed with dilute hydrochloric acid in an 18 t acid wash column prior to transfer into an elution column where it is presoaked in a cyanide/caustic solution for 30 minutes to elute gold. The pregnant eluate is then rinsed from the carbon by as many as 10 bed volumes of water heated to 130º C. The resultant pregnant solution is pumped to electrowinning cells in which the gold is deposited on cathodes. The gold sludge on the cathodes is washed, dried and smelted in a furnace to produce doré. Doré is shipped to Switzerland to be refined to bullion at Valcambi.

A CCD circuit was commissioned in 2008 to recover cyanide from CIL tailings prior to discharge to the TSF. Recovered cyanide is effectively re-used in the CIL circuit and weakly acid-dissociable cyanide (CNWAD) levels in the plant tailings are effectively controlled to ensure the discharge limit of 50 ppm CNWAD is not exceeded.

A gravity circuit that was initially included in the plant was decommissioned in 2010.