This technical report provides updated Mineral Resource and Mineral Reserve estimates as at 31 December 2020 for the operating Wassa Gold Mine in Ghana, and summarises a Preliminary Economic Assessment of potential underground expansion into the Southern Extension zone.
Report context
The Wassa Gold Mine is an operating gold mine located near the village of Akyempim in the Wassa East District, Ghana's Western Region, approximately 80 km north of Cape Coast and 150 km west of Accra. The mine is owned and managed by Golden Star Wassa Limited (GSWL), in which Golden Star Resources (GSR) holds a 90% interest and the Government of Ghana holds the remaining 10%. This NI 43-101 Technical Report, dated March 2021, provides updated information as at 31 December 2020, including Mineral Resource and Mineral Reserve estimates prepared in accordance with the 2014 CIM Definition Standards and 2019 Best Practice Guideline. The report also contains a summary of a 2020 Preliminary Economic Assessment (PEA) for potential expansion of the underground mine to extract the Inferred Mineral Resource in the Southern Extension zone. The PEA is a scoping-level study that is conceptual in nature, has no impact on the Mineral Reserves, and does not rely on any assumptions supporting the Mineral Reserves. Units are metric and monetary units are United States dollars unless otherwise stated.
Processing route
Current processing plant design and operation
The Wassa processing plant is a conventional carbon-in-leach (CIL) plant with a four-stage crushing circuit producing a product size of p80 less than 8 mm. The crushing circuit feeds two independent ball mills, each of 3 MW, producing a grind size of p80 less than 75 μm. The grinding circuit includes gravity recovery by Knelson concentrators and intensive leaching in an Acacia reactor. Cyclone underflow has cyanide and oxygen added prior to pumping to the leach circuit via the in-line reactor pipeline. The CIL circuit consists of six stages of agitated leaching with an residence time of 18 to 20 hours at full capacity. Loaded carbon is acid washed and stripped, and gold is electrowon onto steel mesh prior to smelting to produce doré bars. The processing plant has capacity to process up to 2.7 Mtpa.
Paste backfill plant
A 4,000 tpd paste plant was recently completed and is part of the site infrastructure supporting the underground mining operations.
Processing schedule for the Mineral Reserve plan
The processing schedule for the Mineral Reserve plan covers the period from 2021 to 2026. Total feed over the life of mine is 10,852,000 tonnes at an average gold grade of 2.84 g/t, containing 990,000 oz of gold. Feed is sourced from underground mining operations and from low-grade stockpiles. The average gold recovery over the life of mine is 93.9%, producing 930,000 oz of gold. In the first year (2021), the plant is scheduled to process 2,072,000 tonnes at 2.70 g/t with 94.4% recovery, producing 170,000 oz. Annual production peaks in 2024 at 199,000 oz from 2,228,000 tonnes at 2.95 g/t and 93.9% recovery. The processing plant capacity exceeds mine production in all years for the Mineral Reserve plan.
Metallurgical test work
Test work programs have been completed which are reflective of processing plant performance and used samples that reasonably represent the plant feed scheduled in the Mineral Reserve plan. No significant metallurgical issues were identified, and this has been validated by actual plant performance. For the PEA, limited metallurgical test work has been completed for the Southern Extension mining area. Results generally suggest processing will be consistent with current operations, but there is minor variability and further test work may identify that planned recoveries and throughput rates may not be achieved.
Processing in the PEA
The PEA production schedules are constrained within current processing capacity of 2.7 Mtpa. The PEA assumes that methodologies and design quantities are based on proven, currently available technologies. The PEA processing schedule for the Southern Extension zone shows a production phase life of 11 years (years 7 to 17 of the project) at a production phase rate of 294 koz/yr.
Key reported parameters
| Parameter | Unit | Design / Actual | Basis / Source |
|---|---|---|---|
| Plant capacity | Mtpa | 2.7 | Design capacity |
| Crushing product size (p80) | mm | < 8 | Design specification |
| Grind size (p80) | μm | < 75 | Design specification |
| Ball mill power (each of 2) | MW | 3 | Design specification |
| CIL residence time | hours | 18 – 20 | Design specification |
| Gold recovery (Mineral Reserve plan, average) | % | 93.9 | Plan based on test work and plant history |
| Gold recovery (historical, reported as forward assumption) | % | 94.1 | Supported by test work and plant history |
| Plant feed (Mineral Reserve plan, total) | '000 t | 10,852 | Production schedule |
| Feed gold grade (Mineral Reserve plan, average) | g/t | 2.84 | Production schedule |
| Contained gold in feed (Mineral Reserve plan, total) | '000 oz | 990 | Production schedule |
| Gold produced (Mineral Reserve plan, total) | '000 oz | 930 | Production schedule |
| Paste plant capacity | tpd | 4,000 | Design specification (recently completed) |
| Gold recovery (PEA, Panels 4-6 modifying factor) | % | 95.0 | Testwork and scoping study assumption |
| Gold recovery (PEA, Panels 7-8 modifying factor) | % | 75.0 | Testwork and scoping study assumption |
| PEA production phase rate | koz/yr | 294 | Scoping study schedule |
| PEA production phase life | years | 11 | Scoping study schedule |
Project website: https://www.gsr.com/
Technical qualifications
This Technical Report was prepared by GSR based on published material, data, professional opinions, and unpublished material from work completed by GSR, including information provided by and discussions with third-party contractors and consultants. Major contributions by contractors and consultants have been reviewed and approved by Qualified Persons (QPs) as follows: environmental impact assessment studies by Golder Associates (Ghana and South Africa); long-range model resource estimate by SRK (Toronto); short-range model wireframe and resource estimate by SRK (Moscow); geotechnical assessment by OreTeck Mining Solutions (Australia); metallurgy and processing assessment by MineScope Services (Australia); mine ventilation assessment by SRK (US); tailings storage facility design and geotechnical assessments by Knight Piésold Ghana; and paste backfill studies by Outotec (Canada) Ltd. The QPs responsible for this report conducted site visits as detailed in the report. The report relies on environmental impact assessment studies and a legal title opinion prepared by experts who are not qualified persons. The PEA is a scoping-level study that is conceptual in nature and there is no certainty that further geological drilling will result in the determination of higher Mineral Resource classification, nor that production and financial outcomes will be realized. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. The PEA has been prepared within a framework that includes production schedules to appropriately consider conversion risk of the Inferred Mineral Resource, methodologies and design quantities based on proven currently available technologies, mine production constrained within current processing capacity (2.7 Mtpa), costs to show current operational experience, and minimisation of capital demand needed to establish full production.
Source: NI 43-101 Technical Report (March 2021), Wassa Gold Mine, Sections 1, 2, 3, 4, 5, 6.
