The Agnew gold mine is an underground mining operation located near Leinster in Western Australia. The project is fully owned and operated by South Africa-based miner Gold Fields.
The Agnew gold property was discovered by Paddy Lawlers’ prospecting party in 1894, while the Western Mining Corporation (WMC) purchased the Waroonga leases in 1976 and commenced open-pit mining in 1980. The New Holland deposit was discovered in 1991 and underground mining started in 1998.
Gold Fields acquired the Agnew mine from WMC in 2001 and subsequent explorations led to the discovery of the Kim South lode at Waroonga in 2002.
The Agnew mine produced 219 thousand ounces (Koz) of gold in 2019 compared to 239Koz in the previous year.
Agnew became the first mine of Gold Fields to be powered by solar energy with the commissioning of a 4MW on-site solar farm in August 2019, while a 56MW comprehensive renewable energy facility integrating wind, solar, and a battery energy storage system (BESS) was completed in May 2020.
It enables the mine to meet up to 70% of its total power requirements from renewable energy sources.
Project location and geology
The Agnew gold mine is located within the Norseman-Wiluna Greenstone Belt, approximately 23km west of the town of Leinster in Western Australia. The project site covers a total area of approximately 600km2.
The Agnew gold property lies in the northern portion of the Norseman-Wiluna Greenstone Belt of the Yilgarn Craton which is dominated by a sequence of folded mafic to ultramafic volcanics and associated interflow sediments.
Mineralisation and reserves
The gold mineralisation at Agnew occurs in the Scotty Creek Formation hosted largely in quartz veins within the sedimentary units.
The total mineral reserves at the Agnew property were reported as 4.6 million tonnes (Mt) 2637kt grading 5.17g/t Au and containing 772 thousand ounces of gold as of December 2019.
The total mineral resources were estimated to be 14Mt grading 5.6g/t Au and containing approximately 2.5 million ounces (Moz) of gold.
Agnew hybrid renewable power station make-up
The Agnew hybrid renewable station comprises an 18MW wind farm equipped with five GW140 3.57MW wind turbines from Goldwind, a 4MW solar farm fitted with 10,710 solar panels, a 13MW/4MWh battery energy storage system (BESS), as well as a 21MW gas/diesel engine power plant. The entire components are controlled via an advanced microgrid system.
The lithium-ion BESS at the Agnew mine comprises six of Saft’s Intensium® Max+ 20M, 20ft containers along with a power conversion system, transformer, and MV switchgear installed in three 40ft containers.
The Agnew hybrid renewable energy facility was developed by EDL, an Australian company focussed on renewable energy development, which will also operate the facility for a period of 10 years.
The Australian Renewable Energy Agency (ARENA) provided funding of £10.5m ($13.5m) for the Agnew hybrid renewable project under its Advancing Renewables Program.
Mining operations at Agnew
The underground mining operations at Agnew are currently being carried out at the Waroonga and the New Holland underground complexes.
The current mining operations at Waroonga are based on the Kim South, FBH, and the Main North ore bodies, while the New Holland mining operations comprise the Genesis, New Holland, Cinderella, and the Sheba ore bodies.
The bulk run of mine (ROM) ore supply is received from the high-grade FBH, Cinderella, and Sheba lodes.
The Wahroonga underground mine uses Long-hole sub-level stoping with paste fill as the primary mining method. The underground decline access portal is located at the previously mined Waroonga open-pit.
The mining operations at New Holland have based on the retreat up-hole long-hole mining as the primary method. The underground mine is accessed via twin declines with the surface portals located at the Genesis and the New Holland open-pits.
The processing facility for the Agnew mine has a design capacity to process 1.3 million tonnes of ore per annum (Mtpa).
It houses a three-stage crushing and a single-stage grinding plant, a six-stage conventional carbon-in-pulp (CIP) circuit, and a gravity circuit comprising a Knelson concentrator and an in-line leach reactor.
The CIP circuit comprises leach and absorption tanks followed by a pressure Zadra carbon elution circuit.
The overall gold recovery rate at the Agnew processing plant is estimated to be approximately 93.5%.
Barminco is the current mining contractor for the Agnew underground mining operations.
EDL was contracted to build and operate the Agnew hybrid renewable energy facility, while French battery manufacturer Saft was contracted by EDL for delivering the lithium-ion BESS for the project.
Goldwind Australia, in joint venture partnership Nacap, a subsidiary of US-based Quanta Services, was contracted by EDL for the engineering, procurement, and construction (EPC) of the wind farm for the Agnew mine.