Australia

Agnew Complex

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Categories

Overview

Mine TypeOpen Pit & Underground
Commodities
  • Gold
Mining Method
  • Sub-level stoping
  • Longhole open stoping
  • Room-and-pillar
  • Truck & Shovel / Loader
  • Cemented paste backfill
Production Start1980
Mine Life2028
ShapshotAgnew comprises the amalgamated Agnew and (former) Lawlers mines. Agnew currently operates two underground mines, namely Waroonga and New Holland.

Mining in the Barren Lands open pit was completed in 2023 and portal development for the underground operations commenced.

Agnew is one of the first gold mines in the world to generate over half of its electricity requirements from renewable sources.

LOM extension remained a key focus area for Agnew in 2023. Further early-stage exploration continues across the broader tenement package on prioritised prospects.
Related Asset

Owners

SourceSource
CompanyInterestOwnership
Gold Fields Ltd. 100 % Indirect
The Agnew Gold Mining Company Proprietary Limited (AGMC), was incorporated as the legal entity holding and conducting mining activity on the Agnew mineral leases. Gold Fields holds 100% of the issued shares of AGMC through its 100% holding in the issued shares of Orogen Holding (BVI) Limited.

Contractors

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Deposit type

  • Vein / narrow vein
  • Breccia pipe / Stockwork
  • Hydrothermal

Summary:

Agnew is located in the northern portion of the north-northwest trending Archean Norseman-Wiluna Greenstone Belt, which forms part of the Yilgarn Craton, a 2.7 Ga granite-greenstone terrain in southern Western Australia.

Gold deposits along the Norseman-Wiluna Greenstone Belt are hosted within a diverse range of rocks, including basalts and dolerites, fine to coarse-grained sedimentary rocks, and felsic to intermediate intrusives. Host rocks are commonly metamorphosed to greenschist or lower amphibolite facies. Gold mineralisation is typically structurally controlled, occurring within a network of shear zones proximal to major regional faults. The most important gold mineralisation styles are shear hosted quartz-carbonate bearing breccia lodes and associated quartz vein arrays, together with finely disseminated gold associated with zones of strong hydrothermal alteration. Alteration comprises silica or albite-rich zones, associated with ankerite, sericite, biotite or amphibole, together with pyrite, pyrrhotite or arsenopyrite as sulphide-bearing phases.

The most substantial gold deposits and the focus of most previous exploration and mining activity at Agnew are located along the western limb of the Lawlers anticline (Waroonga, Redeemer and New Holland complexes) spatially related to the north-northwest trending Waroonga and EMU shears.

Although all Agnew deposits broadly occur at the intersections between structures and stratigraphy, there are subtle differences in alteration and mineralisation that are controlled in part by the local host rock chemistry. Mineralisation zones are discontinuous with short range predictability.

Significant deposits are also found on the eastern limb (e.g. McCaffery, Fairyland) and associated with late-stage geological cross-structures (Lawlers). These deposits were explored and mined by previous owners of the Property.

While most of the western limb deposits are broadly related to intersections between structures and mafic-ultramafic stratigraphy, there are subtle differences in alteration and mineralisation controlled in part by the local host rock chemistry. Songvang is unusual in its relatively high lead, silver and fluorine content, possibly reflecting input from tonalite and porphyry intrusions. There also appears to be a slight decline in mineralisation temperatures from south to north, associated with the north plunge of the Lawlers anticline and resultant erosion of the overlying, lower temperature rocks to the south. This temperature change is reflected in the changing mineralisation styles from south to north, with biotite-garnet alteration assemblages dominating to the south and quartz veining to the north.

The New Holland complex is located between the Waroonga and EMU shears within a locally mineralized zone known as the Glasgow Lass trend, hosted by sedimentary rocks of the Scotty Creek Formation. The sedimentary rocks at this locality strike north-south and dip steeply to the west. Gold mineralisation is largely confined to quartz veins wil n sandstone and siltstone. Ore zones occur in discrete veins at low angles, dipping predominantly to the east. Higher grade westerly dipping quartz veins are also present in sandstone. The eastern contact of the sandstone is erosional and sharp, resting on siltstone. The western contact is gradational, fining to very fine-grained sand and siltstone.

Reserves

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Mining Methods

  • Sub-level stoping
  • Longhole open stoping
  • Room-and-pillar
  • Truck & Shovel / Loader
  • Cemented paste backfill

Summary:

The mining process and methods comprises two principal activities: (i) developing access to the orebody: and (ii) extracting the orebody once accessed. These two processes apply to both surface and underground mines.

Open pit
In open pit mining, access to the orebody is achieved by stripping the overburden in benches of fixed height to expose the ore below. This is most typically achieved by drilling and blasting an area, loading the broken rock with excavators into dump trucks and hauling the rock and/or soil to dumps. The overburden material is placed on designated waste rock dumps.

Extraction of the orebody involves a similar activity as in stripping the overburden. Lines are established on the pit floor demarcating ore from waste material and the rock is then drilled and blasted. Post blasting, the ore is loaded into dump trucks, based on a defined ‘dig plan® demarcating the position of the ore and waste boundaries post the heave and throw movement caused by the blasting, and hauled to interim stockpiles or directly to the crusher at the process plant, while the waste is hauled to waste rock dumps.

There has been no open pit mining at Agnew since 2012, but this will change in H2 2022 with Barren Lands Open pit planned to start.

Open pit mining will be by conventional drill and blast, with truck and shovel operations. Overall, the pits represent 4 % of the total reserve ounces for Agnew.

The open pits are seen as a consolidated approximate 12-month duration opportunity to ensure critical mass in mobilizing a contractor to complete all the open pits then de-mobilize. The drill, blast, truck and shovel equipment supplied will be supportive of mining the narrow orebodies with minimum dilution.

The open pits will be sequenced together to optimize the waste strip and expedite the ore to the processing facility. Agnew is not expecting to build significant stockpiles for future processing.

Mining in the Barren Lands open pit was completed in 2023 and portal development for the underground operations commenced.

Underground
For Agnew’s underground mines, access is through single or multiple decline haulages extending from surface portals. Horizontal and decline development at various intervals from the main decline, known as levels, extend laterally and provide access to the ore horizons for mining.

Once an orebody is accessed for mining (or stoping), production activities consisting of drilling, blasting, cleaning, ground support and transporting rock, which are carried out on a daily basis.

Broken ore is loaded straight from the stope face into trucks, using mechanical loaders, and hauled to the surface by underground dump trucks via the declines. Application of backfill or paste fill to the mined-out areas to support the ground is based on local conditions and is not always required in shallow underground mining areas.

Both Waroonga and New Holland are established mines with existing infrastructure. The Redeemer Complex is proximal to the historic underground, and includes establishment of a new portal, surface infrastructure, declines, and underground infrastructure.

Mining operations at Agnew are carried out by a mixture of owner-operators and contractors, with equipment replacement schedules and leasing requirements considered in the mine plans. The reserves life of mine plan and associated financial models include sufficient infrastructure and sustaining capital investment for all mines to execute the life of mine plan.

Waroonga
The primary mining method at Waroonga is long-hole sublevel stoping with paste fill.

Waroonga is predominantly mined using open stoping with cemented paste fill where required. The underground mining is carried out under contract to Barminco including the supply of all equipment.

The mining method at Waroonga involves development of a hangingwall access drives parallel to the orebody, from which crosscuts are mined into the mineralized lode. Ore drives are mined north and south, with long-hole open stopes of 15 m to 25 m strike lengths. The level spacing is 20 m to 25 m floor to floor. Stopes, once complete, are backfilled with cemented paste fill where required, produced from screened dry tailings with the addition of sand and cement as a binder. Backfill is used for regional stability, minimize mining spans and to increase ore extraction ratios.

The general sequence for most of the mine is top-down, maintaining a 45° advancing front, retreat mining along strike under exposed paste fill from the mined-out levels. In some areas, including the upper parts of the FBH orebody and Waroonga North, a bottom-up mining sequence was introduced to provide additional mining areas.

The Edmunds orebody sits in the footwall of the Kim South lode and is generally accessed from the Kim South crosscuts after paste filling on the level that has been completed. The Edmunds mining method is similar to the Kim South orebody, with a retreat stoping sequence. Edmunds strike lengths are between 15 m to 20 m, and all stopes are paste filled allowing improved extraction of the ore.

The mining method employed for the Main orebody evolved considerably over previous years. Modifications and redesigns to both on-level development and stoping extraction are made as the geological and geotechnical understanding improves.

The FBH mining area is located approximately 350 m along strike to the south of the Kim South orebody, and consists of multiple north-south narrow lodes dipping 65° to the west. The mining method for FBH is long-hole open stoping with paste fill. Stoping is top-down or bottom-up. FBH uses parallel developed tunnels with stoping retreating to the central accesses. Stope sizes are adjusted depending on competent or poor ground conditions.

New Holland
The mining methods used for the Mineral reserves at New Holland are inclined room and pillar and long-hole open stoping. All underground mining is completed by an owner-operator team.

Long-hole open stoping is the principal ore extraction method, accounting for the majority of ore tonnes. Where necessary, rib and crown pillars are employed to maintain the stability of the stopes. Arch designed stope crowns assist stability.

Island pillars optimize extraction and are incorporated into the mine design when the dominant westerly-dipping structures are encountered. Pillar spans and spacing are based on the results of numerical stability modelling.

Redeemer
The undeveloped Redeemer Zone 2 and Barren Lands underground is offset to the north of the former Redeemer mine which is backfilled with tailings. Redeemer Zone 2 is 1 m to 10 m wide, with the majority of the targeted ore ranging from 1.5 m to 3.0 m wide at an inclination of 70 ° to 90 °. The mine is 200 m to 500 m below surface with an orebody horizontal extent of circa 400 m.

Redeemer Zone 2 and Barren Lands underground will be mined by long-hole open stoping with rib pillars and selective paste fill, top-down and a circa 45 ° geotechnical production front. A central access design allows for northern and southern ore drives along the orebody. Stoping retreats to the central access.

Comminution

Crushers and Mills

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Processing

  • Gravity separation
  • Carbon re-activation kiln
  • Centrifugal concentrator
  • Crush & Screen plant
  • Concentrate leach
  • Agitated tank (VAT) leaching
  • Inline Leach Reactor (ILR)
  • Carbon in pulp (CIP)
  • Elution
  • Carbon adsorption-desorption-recovery (ADR)
  • Solvent Extraction & Electrowinning
  • Cyanide (reagent)

Summary:

The Agnew processing plant consists of a tertiary crushing circuit, followed by a two-stage ball milling circuit with gravity and a conventional leach/CIP gold recovery circuit (1.35Mtpa capacity).

The plant capacity was increased to 1.35Mtpa at the end of 2022.

The gravity circuit comprises two 40" QS40 Knelson concentrators with dedicated InLine Leach Reactor for intensive cyanidation of the gravity concentrate.

The leach circuit is comprised of three air agitated Pachuca leach tanks each providing an effective volume of 4,100 m3. The adsorption circuit consists of six air agitated Pachuca adsorption tanks with an effective volume of 3,000 m3. Each adsorption tank is fitted with “V" style inter-stage screens and an airlift carbon advance system. Loaded carbon is recovered from the first adsorption tank via a vibrating loaded carbon screen. Loaded carbon from the adsorption circuit reports to the acid wash hopper where it undergoes a hot hydrochloric acid wash.

Acid washed carbon is loaded into a pressure Zadra elution column followed by electrowinning at approximately 130°C and 350 kPa. The elution column has a 3.0 t capacity and one elution is conducted each day. Barren carbon from the elution circuit is regenerated in a carbon regeneration kiln.

Gold sludge from both the gravity and electrowinning circuits is washed and filtered. The sludge is further refined through smelting and crude doré is poured. Gravity doré bars are approximately 90 % to 95 % gold whereas doré bars from the CIP circuit are dependent on ore feed characteristics and can vary between 65 % and 80 % gold. Doré is dispatched to the Perth Mint refinery for further processing into gold bullion.

Recoveries & Grades:

CommodityParameter2023202220212020201920182017
Gold Recovery Rate, % 95959594.694.294.294.4
Gold Head Grade, g/t 66.65.85.85.76.496.5

Production

CommodityUnits2024202320222021202020192018
Gold koz 000000000000000000238
All production numbers are expressed as metal in doré. ^ Guidance / Forecast.

Operational metrics

Metrics202320222021202020192018
Plant annual capacity 1.35 Mt1.35 Mt1.35 Mt1.3 Mt1.3 Mt1.3 Mt
Waste 4,037 kt1,450 kt
Ore tonnes mined 1,326 kt1,108 kt1,048 kt1,294 kt1,284 kt1,216 kt
Total tonnes mined 5,363 kt2,559 kt1,941 kt2,044 kt1,961 kt1,955 kt
Tonnes processed 1,342 kt1,198 kt1,254 kt1,357 kt1,231 kt1,178 kt
Waste UG 893 kt750 kt678 kt739 kt

Production Costs

CommodityUnits2024202320222021202020192018
All-in sustaining costs (sold) Gold USD 00000000 00000000 00000000 00000000 00000000 1,152 / oz   1,026 / oz  
All-in costs Gold USD 00000000 00000000 00000000 00000000 00000000 1,152 / oz   1,026 / oz  
^ Guidance / Forecast.
Net of By-Product.

Financials

Units2024202320222021202020192018
Capital expenditures (planned) M USD 78  
Growth Capital M USD 16  31  32  9   41  
Sustaining costs M USD 54.5  54.4  56.3  43   35.5  
Capital expenditures M USD 70.4  85.1  88.2  52   76.1   73  
Revenue M USD 473.6  427.9  402  411.5   304.6   301.1  
Operating Income M USD
Gross profit M USD

Heavy Mobile Equipment

HME TypeModelQuantity
Drill Atlas Copco 2
Drill 2
Jumbo Sandvik 2
Jumbo Sandvik 2
Loader Caterpillar 4
Loader Caterpillar 4
Truck (underground) Atlas Copco 8
Truck (underground) 4

Personnel

Mine Management

Source Source
Job TitleNamePhoneProfileRef. Date
General Manager Operations Craig Bradshaw LinkedIn Apr 18, 2024
Maintenance Superintendent Jim Innes LinkedIn Apr 18, 2024
Process Manager Matt McKee-Duff LinkedIn Apr 18, 2024
Underground Mine Manager Nick Tait LinkedIn Apr 18, 2024
Vice President of Mining Jason Sander +61 (0) 8 9088-3801 LinkedIn Apr 18, 2024

EmployeesContractorsTotal WorkforceYear
314 473 787 2023
308 503 811 2022
605 2021
605 2020
605 2019
605 2018
605 2017
620 2016

Aerial view:

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