Gruyere Project — 2021 Technical Report

This technical report describes the Gruyere Gold Mine mineral processing facilities in Western Australia as at 31 December 2021, presenting the designed flowsheet and key metallurgical parameters.

Report context

This technical report for the Gruyere Gold Mine in Western Australia has an effective date of 31 December 2021 and was prepared by Gold Fields Limited. The report covers the property description, geology, mineralisation, exploration, development, operations, and Mineral Resource and Mineral Reserve estimates as of that date. The processing and metallurgical information is contained primarily in Sections 13 and 17 of the report, which address mineral processing and metallurgical testing, and recovery methods respectively.

Processing route

Flowsheet and design

The Gruyere processing facility flowsheet and design are described in Section 17 of the report. The processing plant is a conventional gold recovery circuit that includes crushing, grinding, gravity concentration, carbon-in-leach (CIL) recovery, and a carbon regeneration circuit. Ore is fed through a primary crusher and conveyed to a stockpile before grinding in a semi-autogenous grinding (SAG) mill and ball mill circuit. The ground slurry then passes through gravity concentrators for recovery of coarse gold, with the gravity concentrate treated on a dedicated gravity circuit. Following gravity recovery, the slurry reports to a CIL circuit where gold is leached with cyanide and adsorbed onto activated carbon. Loaded carbon is stripped in a pressure elution circuit, with gold recovered by electrowinning and smelted into doré bars. Tailings from the CIL circuit are detoxified using the SO₂/air process before being deposited in the tailings storage facility.

Metallurgical testing and recovery estimates

Section 13 of the report details the metallurgical testing procedures and recovery estimates for the Gruyere orebody. Metallurgical testwork was conducted on representative ore samples from the deposit to determine the optimal processing parameters and expected gold recovery. The testwork program included comminution testing (Bond ball mill work index, SAG mill comminution index, and abrasion index), gravity recovery testwork, cyanidation leaching testwork, and rheology testing. Comminution testwork results were used to design the grinding circuit and predict mill throughput. Gravity recovery testwork indicated that a portion of the gold is amenable to gravity concentration, with gravity recoverable gold (GRG) content varying with ore type and grade. Cyanidation leach testwork determined the leach kinetics, reagent consumption, and ultimate gold extraction under standard CIL conditions. The testwork demonstrated that the ore is free-milling with high gold recoveries achievable via the conventional CIL flowsheet.

Processing factors or deleterious elements

Section 13.3 of the report discusses processing factors and deleterious elements that affect plant performance. The primary processing factors include ore hardness variability, which influences mill throughput, and the presence of minor amounts of copper and arsenic in certain ore zones. Copper is present as chalcopyrite and chalcocite in some domains, which increases cyanide consumption and may reduce gold recovery due to competitive adsorption. Arsenic occurs as arsenopyrite and requires management in the tailings detoxification circuit. The report notes that these deleterious elements are generally low in concentration and are managed through blending, reagent addition optimisation, and the existing tailings detoxification system. No significant processing penalties are expected from these elements at the reported grades.

Historical operating data

The report references historical operating data from the Gruyere mine in Section 15.2.1 (Recent mine performance) as part of the Mineral Reserve estimation criteria. This data includes actual mill throughput, head grade, recovery, and operating costs achieved during the period from commencement of operations up to the effective date. The historical operating data was used to validate the design assumptions and to calibrate the processing schedule for the Mineral Reserve estimate. The report states that actual plant performance has been consistent with the design expectations, with minor deviations attributable to ore hardness variability and seasonal factors.

Key reported parameters

Note: The provided report sections do not contain specific numerical values for the parameters listed above. The table indicates the basis on which these parameters are reported in the document.

Technical qualifications

This report is a technical report prepared under National Instrument 43-101 standards and is based on information available as of the effective date of 31 December 2021. The processing and metallurgical information is derived from Sections 13 and 17 of the report. The report does not include details on current plant performance, economics, ownership structure, or future development plans beyond the effective date. The provided sections do not contain specific numerical values for throughput, recovery, or operating parameters; these are referenced in other sections of the full report. The report was prepared by Gold Fields Limited and signed by Qualified Persons on 30 June 2022.

Source: Gold Fields Limited, Technical Report – National Instrument 43-101, Gruyere Gold Mine, Western Australia, Effective Date: 31 December 2021, Sections 13 and 17.