This report describes the process plant design, current operating performance, and process description for the Chirano gold mine in Ghana.
Report context
The Chirano gold mine, originally developed by Red Back Mining, commenced commercial production in October 2005 and was acquired by Kinross in September 2010. The mine comprises the Akwaaba, Suraw, Akoti South, Akoti North, Akoti Extended, Paboase, Tano, Obra South, Obra, Sariehu and Mamnao open pits and the Akwaaba and Paboase underground mines. In 2008 the plant was expanded to a design throughput capacity of 3.5 Mtpa by Lycopodium Engineering. This technical report is dated 30 September 2022.
Processing route
Background
The Chirano plant has been treating ore at approximately 3.4 Mtpa from the various pits and underground as a blend comprised of both fresh and oxide ore.
Plant Design
The Chirano process plant is comprised of the following circuits:
- Primary crushing of run-of-mine (ROM) material in open circuit
- Secondary and Tertiary crushing in closed circuit with screening
- Mill feed surge bin with an overflow feed to a dead stockpile for mechanical reclaim
- Open circuit primary ball mill operating with two parallel secondary ball mills in closed circuit with cyclones
- In-circuit crushing of the primary mill scats
- Trash screening and thickening of cyclone overflow before leaching
- Gold leaching in a single pre-leach tank followed by nine CIL tanks
- Two Zadra elution circuits with dedicated acid wash columns and regeneration kilns
- Gold room housing three electrowinning cells
- Carbon screening of the CIL tails followed by disposal of tailings to an unlined TSF.
Process Description
Crushing
The crushing circuit includes a primary jaw crusher, a secondary cone crusher, and three tertiary cone crushers. Crusher screens are provided as part of the closed-circuit arrangement.
Milling
The milling circuit consists of one grate-discharge primary ball mill (converted from a SAG mill) and two secondary ball mills (one overflow design and one converted from a SAG mill to overflow design). The primary mill scats are processed through an in-circuit crusher.
Gravity Circuit
The gravity circuit is noted as de-commissioned.
Pre-Leach Thickening
Cyclone overflow is directed to a pre-leach trash screen followed by an 18 m diameter high-rate pre-leach thickener.
Carbon in Leach
Gold leaching is conducted in a single pre-leach tank of 3,200 m³ live volume, followed by nine CIL tanks each of 1,300 m³ live volume. All tanks are flat-bottomed with dual hydrofoil impeller agitators.
Tailings Disposal
Carbon screening of the CIL tails occurs prior to disposal of tailings to an unlined tailings storage facility.
Carbon Treatment
Two Zadra elution circuits are provided, each with a dedicated acid wash column (5 t carbon capacity, mild steel butyl rubber lined) and elution column (5 t carbon capacity, 304 stainless steel). Two regeneration kilns are installed, each horizontal tube type (321 SS) rated at 250 kg/h, diesel-fired.
Electrowinning
Electrowinning cells are installed as part of the elution circuits. The gold room houses three electrowinning cells.
Gold Room
The gold room contains the electrowinning cells for gold recovery from the elution circuits.
Reagents
Cyanide and lime are consumed in the process, with consumption rates reported in the plant performance data.
Plant Process Services
Plant process services are provided to support the above circuits.
Key reported parameters
| Parameter | Unit | Design Value | Operating Data (Nov 2021 – Apr 2022) | Testwork Basis |
|---|---|---|---|---|
| Plant throughput capacity (design) | Mtpa | 3.5 | , | As designed by Lycopodium Engineering (2008) |
| Actual milling rate | Mtpa | , | ~3.4 | Historical operating data |
| Head grade (monthly range) | g/t | , | 1.14 – 1.51 | Six-month operating data |
| Gold recovery (monthly range) | % | , | 84.77 – 88.63 | Six-month operating data |
| Cyanide consumption (monthly range) | kg/t | , | 0.16 – 0.24 | Six-month operating data |
| Lime consumption (monthly range) | kg/t | , | 1.21 – 1.92 | Six-month operating data |
| Crushing circuit availability (monthly range) | % | , | 72.8 – 91.2 | Six-month operating data |
| Crushing circuit effective utilisation (monthly range) | % | , | 74.0 – 78.0 | Six-month operating data |
| Milling circuit availability (monthly range) | % | , | 89.7 – 96.1 | Six-month operating data |
| Milling circuit effective utilisation (monthly range) | % | , | 86.9 – 92.1 | Six-month operating data |
Project website: https://www.kinross.com/news-and-investors/news-releases/press-release-details/2022/Kinross-completes-sale-of-Chirano-mine-in-Ghana/default.aspx
Technical qualifications
This technical report presents the Chirano process plant as described by the original designer Lycopodium Engineering for the 2008 expansion. The operating data represents historical performance from November 2021 to April 2022 and does not constitute a feasibility study or production forecast. The gravity circuit is reported as de-commissioned with no replacement or modification described. No testwork programs are described in the recovery methods section. The report does not include detailed metallurgical testwork data, life-of-mine planning, or economic analysis within the processing sections reviewed.
Source: NI 43-101 Technical Report on Chirano Gold Mine, Ghana, 30 September 2022, Section 17.
