Agnew is situated in the northern portion of the Norseman-Wiluna Greenstone Belt of the Yilgarn Craton, Western Australia. Locally, the belt comprises a sequence of mafic to ultramafic volcanics and associated interflow sediments, which were folded to form the Lawlers anticline. The mafic and ultramafic volcanics of the Lawlers anticline are unconformably overlain by a sequence of clastic sediments comprising the Scotty Creek formation. The sedimentary rocks were metamorphosed to lower greenschist facies, comprising conglomerates and very fine to very coarse-grained pebbly sandstones and siltstones. The Agnew deposits are broadly hosted by the intersections between various structures and the relative stratigraphy. Gold mineralisation largely occurs in quartz veins in the sedimentary units of the Scotty Creek formation. Orogenic greenstone gold deposits (hydrothermal) are hosted in several different styles of lodes. 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.

Agnew operates two underground mines, namely Waroonga and New Holland, now amalgamated into the Agnew One Mine Complex. At Waroonga, ore is sourced from the Waroonga North, Kath, Fitzroy Bengal Hastings (FBH), Main and Kim lodes, accessed via declines. New Holland mining occurs in four primary areas: Sheba South, Sheba, Cinderella and Himitsu. These areas are accessed via declines.

The primary mining method at Waroonga is long-hole sublevel stoping with paste fill. The New Holland mining method depends on the geometry of the ore structure with the primary method being long-hole open stoping.

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The Agnew processing plant consists of a three-stage crushing circuit, two stage in-series ball milling circuit with two Knelson gravity concentrators, an in-line leach reactor and gravity electrowinning circuit. The carbon in pulp (CIP) circuit consists of air agitated Pachuca tanks, followed by a pressure Zadra elution circuit with carbon generation. The CIP process involves mixing milled ore with lime and water to form a 45% solids slurry with a pH of approximately 10. A cyanide solution is used to extract gold (Au) from the slurry. Carbon is added to the solution to capture gold via adsorption. The gold is then recovered from the carbon under high temperature and pressure using sodium hydroxide and sodium cyanide. Gold is plated onto stainless steel mesh via a process of electrowinning. The primary waste product from the process is a slurry (tailings) containing reject fines, process chemicals and cyanide residues with an elevated pH. This tailings slurry is deposited into TSF3 (Redeemer In-pit Tailings Facility) which has been active since May 2004.