SEMAFO's technical report on the Siou underground prefeasibility study, effective December 31, 2017, keeps the Mana plant in Burkina Faso unchanged as mining moves from open pit to underground.
The NI 43-101 technical report on the Mana Property, Burkina Faso, disclosing the results of the Siou Underground Prefeasibility Study, was prepared for SEMAFO Inc. and SEMAFO Burkina Faso S.A. Both the report and its mineral reserve estimate have an effective date of December 31, 2017. The report's summary of recovery methods describes a plant that has been running since 2008 and states that the planned change from open pit to underground mining will not change the processing.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report effective date | December 31, 2017 | Not applicable | Siou Underground Prefeasibility Study |
| Operator | SEMAFO Inc. | Not applicable | Through SEMAFO Burkina Faso S.A. |
| Plant constructed | 2008 | Not applicable | Not applicable |
| Ore processed, 2008 to 2017 | 22,790,647 | t | From the Wona, Kona, Nyafé, Siou and Fofina pits |
| Average head grade, 2008 to 2017 | 2.8 | g/t Au | Not applicable |
| Overall recovery, 2008 to 2017 | 90.8 | % | Not applicable |
| Gold produced, 2008 to 2017 | 1,863,186 | oz | Not applicable |
| Projected ore processed, 2018 to 2025 | 17,912,948 | t | At 2.94 g/t Au |
| Projected average recovery, 2018 to 2025 | 86.1 | % | Not applicable |
| Projected gold production, 2018 to 2025 | 1,455,945 | oz | 2018 excludes processing of ROM pad material |
| Power supply | Diesel generation | Not applicable | Station next to the process plant |
Overview
The Mana flowsheet is a standard SABC comminution circuit followed by carbon-in-leach (CIL), Zadra elution, gold electrowinning and tailings disposal. Slurry tails from the CIL circuit are pumped to the tailings storage facility, and supernatant water is recycled to the mill. According to the report, the plant's operating results correlate very well with laboratory tests carried out over the years on the different ore types, including oxide and sulphide mineralization.
From 2008 to 2017 the plant treated 22,790,647 tonnes from five open pits at an average of 2.8 g/t Au, with an overall recovery of 90.8%, for 1,863,186 ounces of gold.
Key Process Stages
Comminution. A standard SABC circuit, semi-autogenous and ball milling with pebble crushing, grinds the ore.
Carbon-in-leach. Gold is leached and adsorbed onto activated carbon in the CIL circuit.
Elution and electrowinning. Loaded carbon is stripped in a Zadra elution circuit, and gold is recovered from solution by electrowinning.
Tailings. CIL tails are pumped to the tailings storage facility, and supernatant water is returned to the mill.
Additional Interesting Data and Summary
The production schedule for 2018 to 2025 projects 17,912,948 tonnes at 2.94 g/t Au and an average recovery of 86.1%, for 1,455,945 ounces. Annual recovery in the schedule ranges from 75.1% in 2024 to 88.8% in 2019, and annual gold output peaks at 213,868 ounces in 2023. The mining contractor for the Siou underground mine was to mobilize in the third quarter of 2018.
The site's power comes from a diesel-fuelled generation station next to the process plant, supplied from an on-site bulk fuel storage facility. Other facilities include the tailings storage facility, a water storage and supply dam, five runoff basins, sediment ponds, accommodation camps and a wastewater treatment plant.
In summary, the 2017 study keeps Mana's SABC-CIL plant as it is, on the strength of nine years of operation at a 90.8% overall recovery, and plans the underground Siou ore to be treated through the same circuit.
Key Processes
- SABC comminution
- Carbon-in-leach
- Zadra elution
- Gold electrowinning
- Tailings storage with water recycling
Source: SEMAFO Inc., Mana Property, Burkina Faso, NI 43-101 Technical Report Disclosing the Results of the Siou Underground Prefeasibility Study, effective date December 31, 2017.
Consolidated report summaries
The following former standalone pages about this operation were consolidated here in October 2026. They are retained for source traceability; dates and figures reflect each report’s own effective date and may be superseded by the current information above.
Mana Property — 2012 Technical Report
The Mana processing plant is designed with a nominal capacity of 4,000 mtpd, with reported expansions achieving up to 7,200 tpd in bedrock feed and 8,000 tpd in a saprolite/bedrock blend, underpinned by crushing, SAG and pebble crushing, and secondary ball milling stages.
Report context
The Mana Property technical report, dated 2012, presents a reserve and resource update for the project in Burkina Faso. The following processing description shows the plant configuration as of the report date, based on information provided by Sylvain Duchesne, P.Eng., General Manager of Construction and Engineering. All stated capacities and equipment details are drawn solely from this 2012 document.
Processing route
Introduction and overall flowsheet
Gold at Mana is recovered through a metallurgical plant with a nominal capacity of 4,000 mtpd. The report states the plant underwent various expansion stages, reaching throughput up to 7,200 tpd in bedrock and 8,000 tpd in a blend of saprolite and bedrock. The document notes that, to date, current plant capacity always exceeded expectations. The processing route comprises primary crushing, SAG milling with pebble crushing and screening, and secondary ball milling, followed by a CIL circuit.
Crushing and stockpiling
Run-of-mine (ROM) ore is loaded by a WA600 front-end loader onto a static grizzly screen to handle slabby material. A rock breaker reduces oversize material remaining on the static screen, which measures 625 mm by 665 mm. Fine material drops into a 150-tonne capacity ROM bin. Ore is extracted from the bin by a primary apron feeder (1,524 mm by 7,000 mm) and fed to a vibrating scalper (1,500 mm by 4,000 mm) to further separate fines. Coarse material from the scalper feeds directly into a 36-inch by 48-inch (950 mm by 1,250 mm) single-toggle jaw crusher.
The jaw crusher produces a product with a P80 of 100 mm at a rate of 400–500 wtph, allowing for a 17-hour-per-day crushing operation. This schedule permits regular daily maintenance of the crushing plant. The jaw crusher handles ROM ore with a maximum lump size of F100 of 665 mm. Fines from the scalper discharge directly onto a conveyor belt. Primary crushed material is transferred onto a 48-inch conveyor belt, where a scale maintains constant throughput. A magnet at the head pulley removes trash steel.
Ore is then transferred onto a mobile stacker conveyor, which stockpiles around 25,000 to 30,000 tonnes of crushed ore. Stockpiled ore is withdrawn by two apron feeders in parallel (4,500 mm by 900 mm each), each handling about 200 tph of crushed ore, and drops onto the mill feed conveyor. Ore is weighed again to maintain steady throughput into the grinding circuit. Hydrated lime is added from a dry lime system onto the mill feed conveyor belt for CIL circuit pH control, maintained at pH 10.5.
Grinding and classification
The grinding circuit comprises a semi-autogenous grinding (SAG) mill in closed circuit with a vibrating screen and a pebble crusher. The SAG mill is a 7.92-meter-diameter by 2.74-meter Allis Chalmers unit equipped with a 2,387 kW variable-speed motor and operates with 10–15% ball charges depending on ore hardness. Variable-speed control provides flexibility for processing various ore types.
Discharge from the SAG is split between fine and coarse material. Coarse material (greater than 15 mm) is crushed in closed circuit by a pebble crusher (HP200) and returned to the SAG for further grinding. Fine material (less than 15 mm) is pumped to a vibrating screen (2.1 meters by 5.2 meters). The screen uses 9.5/3.2 mm slotted aperture panels. Oversize material returns to the SAG mill, while undersize material reports to the secondary ball mills discharge pump box. The report cites a circulating load for the SAG of around 50–60% (fine plus coarse) and a product size P80 of around 1,200–3,500 μm, depending on throughput.
Secondary grinding is performed by two open-discharge ball mills. One is a 5.3-meter-diameter by 7.0-meter Outotec mill equipped with a 3,500 kW variable-speed motor, controlled through a liquid resistance starter and heat exchanger system. The original report text is cut off mid-sentence, and no further details on the second ball mill are provided in the available evidence.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Nominal plant capacity | 4,000 mtpd | Design |
| Throughput, bedrock | Up to 7,200 tpd | Historical operating data |
| Throughput, saprolite/bedrock blend | Up to 8,000 tpd | Historical operating data |
| Jaw crusher product size (P80) | 100 mm | Design |
| Jaw crusher feed rate | 400–500 wtph | Design |
| Crushing operation schedule | 17 hours per day | Design |
| ROM bin capacity | 150 tonnes | Design |
| Static grizzly openings | 625 mm x 665 mm | Design |
| Scalper size | 1,500 mm x 4,000 mm | Design |
| Jaw crusher type | 36" x 48" (950 x 1,250 mm) single toggle | Design |
| ROM maximum lump size (F100) | 665 mm | Design |
| Stockpile capacity | 25,000–30,000 tonnes | Design |
| Apron feeders under stockpile | 2 units, 4,500 mm x 900 mm, each ~200 tph | Design |
| SAG mill diameter | 7.92 m | Design |
| SAG mill length | 2.74 m | Design |
| SAG motor power | 2,387 kW | Design |
| SAG ball charge | 10–15% | Design/operating |
| Pebble crusher | HP200 | Design |
| Vibrating screen size | 2.1 m x 5.2 m | Design |
| Screen apertures | 9.5/3.2 mm slotted | Design |
| SAG circulating load | 50–60% | Operating data |
| SAG product size (P80) | 1,200–3,500 μm | Operating data |
| Secondary ball mill (Outotec) dimensions | 5.3 m diameter x 7.0 m | Design |
| Secondary ball mill motor power | 3,500 kW | Design |
| CIL pH setpoint | 10.5 | Design/operating |
Project website: https://manaproperty.in/
Technical qualifications
The 2012 report provides a description of the plant as of its date, but several limitations must be noted. The report does not include any recovery or metallurgical performance data, such as gold recovery rates or plant availability figures. It does not present a mass balance, water balance, or detailed process design criteria beyond the equipment sizes and throughputs listed. The description is provided by a company general manager, but the report does not specify any testwork that generated the stated capacities; the figures for 7,200 tpd and 8,000 tpd are presented as achieved operating rates rather than results of a formal testwork program. The original report text ends mid-sentence in the secondary grinding section, so any details on the second ball mill, leach circuit, tailings, or ancillary systems are not available from the supplied evidence.
Source: “Mana Property , 2012 Technical Report,” Advanced Technical Report, Mana Property, Burkina Faso, Reserve and Resource Update, page 132, Section 17- Recovery Methods.
Advanced Technical Report — Mana Property, Burkina Faso
This report presents an independent technical review of resources and reserves for the Mana gold deposits in Burkina Faso, based on drilling completed to the end of 2011.
Report context
This technical report was prepared by SGS Geostat for Semafo to support the annual disclosure of mineral resources and reserves for the Mana property following the 2011 exploration campaign. The report describes the basis and methodology used for modeling and estimation of the gold deposits on the Mana property, with an effective date of July 11, 2012. The report covers mineral processing and metallurgical testing, mineral resource estimates, mineral reserve estimates, mining methods, and recovery methods for the Mana property.
Processing route
Current mine processing
The Mana mine began operation in March of 2008 with a 2,000 tpd mill which was progressively upgraded up to a current capacity of 8,000 tpd in blended ores. Installations include a carbon in leach mill with crusher, SAG mill, two ball mills, reactive cells, gold room and ancillary services. Since the opening of the Mana mine, Semafo has progressively upgraded the capacity from 2,000 tpd to the current output of 8,000 tpd for blended ores.
A total of 2,448,170 tonnes was processed to the mill in 2011, with an average head grade of 2.76 g/t Au, and an overall gold recovery of 88%. The ore processed was a blend of Wona, Nyafe (North, Center and Filon 67) and low grade ore stockpiled on the run of mine (ROM) pad. The process plant always treats a blend of various ore types to maximize its throughput and gold production. Most of the ore treated during 2011 was in saprock and bedrock.
Crushing
The crushing circuit forms part of the carbon in leach mill with crusher, SAG mill, two ball mills, reactive cells, gold room and ancillary services.
Grinding and classification
The grinding circuit includes a semi-autogenous grinding (SAG) mill that was added in 2010 to increase the mill throughput to 6,000 tpd. In February 2011 a fourth phase of plant expansion to attain up to 7,200 tonnes per day in bedrock and up to 8,000 tpd in blended ore was launched. The primary changes to the processing plant included: addition of a pebble crusher, utilization of the third ball mill previously used as back-up, addition of two CIL tanks, addition of a thickener, additional generators, critical spares and some equipment capacity upgrades.
Leach and adsorption circuit
The leach and adsorption circuit uses carbon in leach technology. Two additional carbon in leach tanks were added in 2010 to optimize gold recovery. The plant includes reactive cells as part of the CIL circuit.
Elution and gold room operation
The gold room operation includes carbon acid wash, carbon stripping via a Zadra elution circuit, carbon regeneration, electrowinning and gold room facilities. These components form part of the processing plant infrastructure.
Tailings disposal and water management
Water for processing is collected from a network of wells, collected from the tailings and accumulated behind an earthen dam constructed to collect seasonal runoff. A 58 km pipeline between the Mana water dam and the Mohoun River was under construction and should be operational before year end. It is designed to pump up to 450 m³/hour, or a maximum of 3.5 Mm³ of water per year. This, in addition to the water captured from the rainy season, should be sufficient to feed a 14,000 tpd operation.
South sector metallurgical testwork
The metallurgical testing for the South sector (Yaho, Fofina, and Fobiri) was based on 111 representative core and RC composite samples. SGS South Africa executed a variety of tests using current mill process conditions. Testwork included: comminution including JK Drop weight (9 samples), Bond Abrasion (9 samples), Bond Crushability (9 samples) and Bond Ball Mill Work Index (9 samples), Gravity Recoverable Gold (3 samples) test and Carbon-in-leach (CIL) (72 samples). The core/RC composite samples were carefully chosen to represent roughly 90% of ore body tonnage. Individual samples were diluted when necessary with core waste to respect averaged ore body head grades. Variability of the ore was also evaluated with specific samples. Variability in the South sector indicating higher localized zones of sulphide such as pyrite, pyrrhotite, arsenopyrite and graphitic zones were individually sampled (12 special samples) and tested by SGS to verify their response to the current Mana CIL process.
Based on these results, a standard CIL process showed good response when the ore is fully oxidized (saprolite) but mitigated response in partially oxidized (saprock) and sulphide ore (bedrock). Consequently, Semafo decided to investigate other process routes such as sulphide flotation, sulphide concentrate regrinding and ultimately, oxidation to seek better gold recoveries. Representative samples were sent to HRLTesting Laboratories in Queensland-Australia to investigate these process options. Preliminary testwork indicated good potential to improve recovery rates but final results were still pending.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Current mill capacity | tpd | 8,000 | Design (blended ores) |
| Plant expansion target (bedrock) | tpd | 7,200 | Design |
| Plant expansion target (blended ore) | tpd | 8,000 | Design |
| 2011 mill throughput | tonnes | 2,448,170 | Historical operating data |
| 2011 average head grade | g/t Au | 2.76 | Historical operating data |
| 2011 overall gold recovery | % | 88 | Historical operating data |
| Wona-Kona CIL recovery (saprolite) | % | Not separately reported | Historical operating data |
| Wona-Kona CIL recovery (saprock) | % | Not separately reported | Historical operating data |
| Wona-Kona CIL recovery (bedrock) | % | Not separately reported | Historical operating data |
| Nyafe sulphide zone CIL recovery | % | <20 | Testwork (3 samples) |
| Fobiri CIL recovery (saprolite) | % | 84 | Testwork |
| Fobiri CIL recovery (saprock) | % | 71 | Testwork |
| Fobiri CIL recovery (bedrock) | % | 19 | Testwork |
| Fofina CIL recovery (saprolite) | % | 92 | Testwork |
| Fofina CIL recovery (saprock) | % | 74 | Testwork |
| Fofina CIL recovery (bedrock) | % | 26 | Testwork |
| Yaho CIL recovery (saprolite) | % | 87 | Testwork |
| Yaho CIL recovery (saprock) | % | 84 | Testwork |
| Yaho CIL recovery (bedrock) | % | 48 | Testwork |
| Fobiri resource proportion (saprolite) | % | 42 | Resource estimate |
| Fobiri resource proportion (saprock) | % | 9 | Resource estimate |
| Fobiri resource proportion (bedrock) | % | 49 | Resource estimate |
| Fofina resource proportion (saprolite) | % | 28 | Resource estimate |
| Fofina resource proportion (saprock) | % | 11 | Resource estimate |
| Fofina resource proportion (bedrock) | % | 61 | Resource estimate |
| Yaho resource proportion (saprolite) | % | 33 | Resource estimate |
| Yaho resource proportion (saprock) | % | 30 | Resource estimate |
| Yaho resource proportion (bedrock) | % | 37 | Resource estimate |
| Resource cut-off grade (within optimized pit shells) | g/t Au | 0.5 | Design parameter |
| Resource cut-off grade (below optimized pit shells) | g/t Au | 1.2 | Design parameter |
| Reserve cut-off grades | g/t Au | Determined case by case | Design parameter |
Technical qualifications
The Nyafe deposit appeared to have low recoveries within the parts of the sulphide zone (3 samples with less than 20% recovery). A more comprehensive study was ongoing to better define the limits of the sulphide mineralization. Reserves reported herein have been adjusted downward to account for the losses resulting from the refractory ore.
New metallurgical tests had shown that the sulphide portions for the Fofina, Fobiri and Yaho deposits had low recoveries with traditional CIL treatment (19%-48% recovery). Consequently, Semafo undertook a new series of metallurgical tests to define a treatment method that would enable higher recoveries for this material, with results pending at the time of reporting.
No reserves were reported for the Fobiri, Maoula and Yaho deposits. The Yaho deposit had a significant impact on the resource base, although at a lower average grade than other deposits on the Mana Property.
The resource estimate was completed using a database containing 4,394 holes and trenches totaling 546,305 metres which were completed almost entirely since 1997. Most of the drilling in 2011 was focused on expanding and refining the resources in the Fofina, Fobiri, Yaho and extensions to Wona-Kona.
Source: Advanced Technical Report, Mana Property, Burkina Faso, Reserve and Resource Update as of December 31, 2011, effective date July 11, 2012, Sections 13 and 17.
