This technical report describes a proposed three-phase processing plant design combining whole-ore leach, gravity/CIL, and refractory treatment using flotation and BIOX technology for the Massawa Gold Project.
Report context
The Massawa Gold Project NI 43-101 Technical Report is dated 23 July 2019. The report presents a proposed processing plant design for treating oxide, transition, whole-ore leach (WOL) sulphide, and refractory sulphide ores from the project. The design is based on well-known and established gravity/CIL technology, with a refractory process incorporating sulphide flotation, regrind, and BIOX technology to be supplied by Outotec at a later stage.
Processing route
Phase 1 – Oxide ore processing
Oxide ore will be processed through primary crushing using a mineral sizer, followed by milling, gravity recovery, and carbon-in-leach (CIL). Gold recovery stages include acid wash, elution, electrowinning, and regeneration. Tailings will undergo detoxification prior to disposal. During Phase 1, the SAG mill will be operated in open circuit.
Phase 2 – Fresh (sulphide) ore processing
Fresh sulphide ore will be processed through primary crushing using a jaw crusher and secondary crushing using a cone crusher, with mill feed bin storage, milling, and gravity recovery. The gravity tailings will feed the CIL circuit for gold recovery from carbon, followed by detoxification of solids prior to disposal. During Phase 2, the ball mill will be in closed circuit with a hydrocyclone cluster.
Phase 3 – Refractory ore processing
Refractory ore will be processed through primary and secondary crushing, mill feed bin storage, milling, and gravity recovery. The gravity tailings report to a flotation circuit consisting of a single bank of five roughing stages. Flotation concentrate is sent for regrinding, then to concentrate thickening, and finally to the BIOX stock tank. The BIOX reactors comprise five equidimensional reactors configured in parallel followed by four secondary reactors operating in series. Feed concentrate from the stock tank is diluted before being fed to the primary BIOX reactors. After BIOX treatment, the material reports to CIL for gold recovery from carbon, followed by detoxification of tails prior to disposal.
Common process features
Milling will consist of a primary semi-autogenous grinding (SAG) mill, secondary ball mill, and a pebble crusher. Pebbles generated from the SAG mill will be conveyed to a pebble crusher for further size reduction and re-circulated to the SAG mill, especially when treating competent ore. The discharge from both mills will be combined in a cyclone feed sump and pumped to the cyclone cluster for classification.
A proportion of the cyclone feed will be fed to the gravity circuit for recovery of gravity gold, with the cyclone underflow gravitating to the ball mill for further size reduction. Gold will be recovered from the gravity concentrates through a combination of intensive cyanidation and electrowinning facilities. Gravity recovery tailings will be transferred back to the mill feed for further liberation. Gold that is not gravity recoverable is recovered through the CIL process.
Depending on the phase, the overflow from the cyclone cluster will either be pumped to a pre-leach thickener (Phases 1 and 2) or to the flotation circuit (Phase 3). The thickener underflow for Phase 1 and 2 material will feed the seven-stage CIL circuit. The resultant CIL tailings slurry will be subjected to a partial cyanide destruction process prior to being pumped to the tailings disposal and storage facilities.
During Phases 1 and 2, oxide, transition, and WOL sulphide ore will be campaigned through the plant separately or in combination. Oxide rock will be crushed through a mineral sizer during Phase 1, whereas during Phases 2 and 3, transition and sulphide rock will be crushed through a primary jaw crusher and stockpiled with bypass allowances directly to the milling circuit for the softer and stickier ores.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant throughput, Phases 1 and 2 | 2.4 Mtpa | Proposed design |
| Plant throughput, Phase 3 (refractory) | 1.2 Mtpa | Proposed design |
| Crushing, Phase 1 | Mineral sizer | Proposed design |
| Crushing, Phases 2 and 3 | Primary jaw crusher, secondary cone crusher | Proposed design |
| Milling | Primary SAG mill, secondary ball mill, pebble crusher | Proposed design |
| SAG mill configuration, initial phase | Open circuit | Proposed design |
| Ball mill configuration, transition and sulphide ores | Closed circuit with hydrocyclone cluster | Proposed design |
| CIL circuit | Seven-stage | Proposed design |
| Flotation circuit, Phase 3 | Single bank of five roughing stages | Proposed design |
| BIOX reactors | Five primary reactors in parallel, four secondary reactors in series | Proposed design |
| Gold recovery from gravity concentrates | Intensive cyanidation and electrowinning | Proposed design |
| Tailings treatment | Partial cyanide destruction prior to disposal | Proposed design |
Technical qualifications
This technical report is based on a proposed plant design. No historical operating data or testwork results for the Massawa Gold Project processing plant are presented in the cited sections of the report. The refractory process design, including BIOX technology, is noted to be supplied by Outotec at a later stage, indicating that detailed engineering for this portion of the plant had not been completed at the time of reporting.
Source: Massawa Gold Project NI 43-101 Technical Report, 23 July 2019, Section 17 Recovery Methods.
