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Ghana
Ahafo Mine

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 Location:
92 km W from Kumasi, Ghana

  Regional Office:
Plot 40/41 Senchi Street
Airport Residential Area PMB Airport Post Office
Accra
Ghana
Phone030-701-1852
WebsiteWeb
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  • Overview
  • Owners
  • Geology
  • Mining
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  • Reserves
  • Costs & Financials
  • Fleet
  • Personnel
  • Filings & News

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Overview

StageProduction
Mine TypeOpen Pit / Underground
Commodities
  • Gold
Mining Method
  • Truck & Shovel / Loader
  • Sub-level open stoping (SLOS)
  • Longhole open stoping
  • Longhole stoping
  • Backfill
Processing
  • Counter current decantation (CCD)
  • Agitated tank (VAT) leaching
  • Carbon in leach (CIL)
  • Elution
  • Solvent Extraction & Electrowinning
  • Cyanide (reagent)
Mine Life11 years (as of Jan 1, 2019)
The Ahafo mine commenced commercial production in 2006 and currently operates a mill, two pits and an underground operation.
Ahafo has two primary ore zones: Ahafo South and Ahafo North. Mining is currently underway at Ahafo South.
Latest NewsNewmont Reports 2020 Mineral Reserves of 94 Million Gold Ounces Replacing 80 Percent of Depletion     February 10, 2021


Owners & OPERATOR

 
CompanyInterestOwnership
African Underground Mining Services (operator)
Newmont Corp. 100 % Indirect

Deposit Type

  • Vein / narrow vein
  • Orogenic

Source: Source p.47

Summary:

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.


Mining Methods

  • Truck & Shovel / Loader
  • Sub-level open stoping (SLOS)
  • Longhole open stoping
  • Longhole stoping
  • Backfill

Source: p.27,172,175,180,184-1

Summary:

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.


Crushing and Grinding
Source: Source p.191-197
Crusher / Mill TypeModelSizePowerQuantity
Gyratory crusher 1
Cone crusher Metso Nordberg MP800 600 kW 2
SAG mill 1
Ball mill 7.31m x 11.9m 1300 kW 1


Processing

  • Counter current decantation (CCD)
  • Agitated tank (VAT) leaching
  • Carbon in leach (CIL)
  • Elution
  • Solvent Extraction & Electrowinning
  • Cyanide (reagent)

Flow Sheet: Source

Summary:

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.

Recoveries & Grades:

CommodityParameter202020192018201720162015
Gold Recovery Rate, % 89.694.19492.390.389.6
Gold Head Grade, oz/ton 0.050.090.060.050.050.05

Production:

CommodityUnits202020192018201720162015
Gold koz 480643436349349332
All production numbers are expressed as metal in doré.

Operational Metrics:

Metrics202020192018201720162015
Total tonnes mined 44,221 k tons41,075 k tons37,634 k tons39,632 k tons38,510 k tons40,087 k tons
Ore tonnes mined 87,225 k tons8,559 k tons8,068 k tons7,310 k tons6,434 k tons7,216 k tons
Waste 35,496 k tons32,516 k tons29,566 k tons32,322 k tons32,076 k tons32,871 k tons
Tonnes milled 10,548 k tons7,298 k tons7,019 k tons7,611 k tons8,013 k tons7,316 k tons
Daily mining rate 95 kt95 kt95 kt95 kt95 kt
Annual milling capacity 11 Mt10 Mt6.5 Mt6.5 Mt6.5 Mt6.5 Mt

Reserves at December 31, 2020:
Ahafo South Open Pits: Cut-off grade utilized in 2020 reserves not less than 0.67 gram per tonne.
Ahafo South Underground: Cut-off grade utilized in 2020 reserves not less than 3.10 gram per tonne.
Ahafo North: Cut-off grade utilized in 2020 reserves not less than 0.50 gram per
tonne.

CategoryOreTypeTonnage CommodityGradeContained Metal
Proven & Probable Total 148,400 kt Gold 2 g/t 9,540 koz
Measured & Indicated Total 51,500 kt Gold 2.15 g/t 3,560 koz
Inferred Total 25,800 kt Gold 1.96 g/t 1,630 koz

Commodity Production Costs:

CommodityUnits20202019201820172016
Total cash costs (sold) Gold USD 78 / oz† 624 / oz† 741 / oz† 766 / oz† 895 / oz†
All-in sustaining costs (sold) Gold USD 980 / oz† 820 / oz† 864 / oz† 961 / oz† 1,152 / oz†
† Net of By-Product.

Financials:

Units20202019201820172016201520142013
Sustaining costs M USD 78  98  40  43  54   57   92  
Capital expenditures M USD 120  213  264  181  87   92   104   170  
Revenue M USD 853  880  
Pre-tax Income M USD 278  295  99  70  -8   74   221   344  


Heavy Mobile Equipment as of December 31, 2020:
Source: Source p.42
HME TypeSizeQuantity
Loader 6
Shovel 3
Truck (haul) 141 t 38
Truck (haul) 60 t 8

Mine Management:

Job TitleNameProfileRef. Date
Health & Safety Manager Chuck Burns LinkedIn Feb 25, 2021
Mine Maintenance Superintendent Colin Evans LinkedIn Feb 25, 2021
Mine Manager Alex Kofi Annin LinkedIn Feb 25, 2021

Staff:

Total WorkforceYear
2,500 2018
2,500 2017
2,500 2016
3,500 2015

Corporate Filings & Presentations:

DocumentYear
Form 10-K 2020
Other 2020
Year-end Mineral Reserves 2020
Form 10-K 2019
Year-end Mineral Reserves 2019
Form 10-K 2018
Other 2018
Technical Report 2018
Year-end Mineral Reserves 2018
Form 10-K 2017
Year-end Mineral Reserves 2017
Form 10-K 2016
Other 2016
Year-end Mineral Reserves 2016
Form 10-K 2015
Press Release 2015
Other 2005

News:

NewsDate
Newmont Reports 2020 Mineral Reserves of 94 Million Gold Ounces Replacing 80 Percent of Depletion February 10, 2021
Newmont Goldcorp’s Ahafo Mill Expansion in Ghana Processes First Ore September 3, 2019
Newmont Mining Declares Commercial Production at Subika Underground in Ghana November 26, 2018

Aerial view:

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