This report details the proposed addition of a 5 Mtpa flotation plant at the Esaase mining site with overland conveying to the existing Obotan processing site, alongside expansion of the Phase 1 whole ore leach circuit to 3.8 Mtpa.
Report context
The Pre-Feasibility Study for the Asanko Gold Mine Phase 2 (AGM Phase 2) was prepared as a technical report under the project reference Rev 2, with report identifier TGHDP0220. The study covers the expansion of the existing Asanko Gold Mine located in Ghana, which commenced Phase 1 operations with a 3 Mtpa carbon-in-leach (CIL) plant treating material from the Obotan pits. Phase 2 proposes the addition of a 5 Mtpa flotation plant with ore feed from the Esaase mining site.
Processing route
Phase 1 existing design and Phase 2 expansion basis
The Phase 1 processing plant design is based on a single stage crushing, semi-autogenous grinding (SAG) and SAG/ball mill closed circuit (SABC) followed by a CIL plant treating 3 million tonnes per annum from the Obotan pits. The flow sheet includes a single stage jaw crusher feeding either onto a live stockpile or directly into an open circuit SAG mill with pebble crusher, and a ball milling unit in closed circuit with classification cyclones. A gravity recovery circuit treats a portion of the cyclone underflow stream to recover coarse free gold from the recirculating load. This process flow sheet is noted in the report as having been historically proven during Resolute Mining Ltd operations from 1998 to 2002 for Obotan region ores.
Under Phase 2, the Phase 1 circuit will be operated at a maximum of 3.8 Mtpa by processing additional oxide material. The whole ore leach circuit design remains as described with additional leaching capacity.
Phase 2 flotation plant design
Phase 2 includes the addition of a 5 Mtpa flotation plant consisting of a run-of-mine (ROM) handling and two-stage crushing circuit located at the Esaase mining site, followed by an overland conveying circuit to transport crushed material to the Obotan processing site. The gravity recovery, milling, flotation, concentrate regrind and CIL circuits will be located at the Obotan site.
Provision is made for intermediate stockpiling and interlinking conveyors between the Phase 1 whole ore leach circuit and the Phase 2 flotation circuit expansion to allow for optimisation of different ore types to either processing facility. The design makes provision for feeding oxide material from the Esaase pits to the CIL circuit and fresh material from the Obotan pits to the flotation circuit.
Esaase crushing and conveying
ROM ore will be treated in an open circuit primary crushing circuit with two tips, each with a dedicated ROM bin and crusher. One hybrid crusher and one jaw crusher will be installed initially, allowing oxide material to be crushed with the hybrid crusher while more competent material is crushed by the jaw crusher. Primary crusher product at P80 of 175 mm will be fed to a secondary cone crusher for further size reduction to P80 of 75 mm. A bypass will allow wet oxide material to bypass the secondary crusher stage. Secondary crusher product will be conveyed onto a single overland conveyor to the Phase 1 processing site.
Intermediate stockpiling and Obotan fresh material crushing
The overland conveyor transfers material to a transfer point where oxide or transitional material reports to an intermediate oxide stockpile feed conveyor, while fresh material reports to the mill stockpile feed conveyor. Crushed oxide material can be fed either to the CIL plant milling circuit or the flotation plant milling circuit. Crushed fresh material feeds directly to a live stockpile for the flotation plant ball milling circuit.
A secondary crushing stage is provided for Obotan fresh material from the CIL plant live stockpile. A single jaw crusher will crush Obotan fresh material from F100 250 mm to P100 90 mm before transfer to the flotation plant fresh ore stockpile.
Ball milling circuit
A ball milling circuit will treat material at a design feed rate of 635 t/h dry solids, operating in closed circuit with a hydrocyclone cluster. Mill density will be controlled at approximately 70% solids by mass. Cyclone overflow at 35% to 38% solids by mass will be gravity fed to the flotation circuit.
Primary gravity concentration
The primary gravity concentrator circuit will include two independent Knelson QS-48 concentrators with capacity to each treat 400 t/h. Feed material will be pre-screened on vibrating screens. Concentrators are expected to produce approximately 3 t/d of high grade concentrate, which will report to a batch intensive dissolution reactor.
Flotation circuit
Cyclone overflow from the ball milling circuit will gravitate to a flotation circuit comprising a single bank of seven 130 m³ forced air rougher flotation cells in series. PAX collector, dithiophosphate co-collector (Aero 9967), frother and copper sulphate will be added at staged addition points. Flotation concentrate will be collected in an agitated concentrate sump before being pumped to the pre-leach thickener. Flotation tailings will be pumped to a final tailings disposal tank.
Pre-leach thickening and regrind
A high rate thickener will increase flotation concentrate density to 40% to 45% solids by mass. Thickener underflow will be pumped to the regrind mill and secondary gravity concentration circuit. The secondary gravity concentrator is expected to produce approximately 1 t/d of high grade concentrate. Tailings from the gravity concentrator will be treated in a stirred media mill, with regrind mill product pumped to the CIL circuit.
Concentrate CIL circuit
The CIL circuit will consist of seven 390 m³ tanks in series with counter-current carbon flow. The circuit will be operated to achieve a design carbon loading of approximately 2500 g/t Au, with four inter-tank carbon transfers per day translating to a loaded carbon batch size of 5 t/d.
Cyanide destruction
CIL tailings will be pumped to a detox circuit with two 150 m³ tanks in series, each agitated and sparged with air. Detoxification will use the SO₂/Air process with copper sulphate added to catalyse the reaction, operated to achieve cyanide concentration of below 25 ppm CN WAD in the combined final tailings stream. Detoxified concentrate tailings will be pumped together with flotation circuit tailings to a common 8 Mtpa tailings storage facility shared with the Phase 1 circuit.
Elution and gold recovery
Loaded carbon will be batch treated in a split Anglo American Research Laboratories (AARL) elution circuit consisting of an acid wash vessel and 5 t elution column with heater facility. The CIL carbon will be treated in 5 t batches once every 24 hours. Elution uses a heated solution of sodium cyanide and caustic soda. Pregnant solution will be routed to electrowinning. The electrowinning and gold room will be shared with the Phase 1 facilities.
Historical operating basis
The report notes that the Phase 1 process flow sheet was historically proven a successful processing route for Obotan region ores during Resolute Mining Ltd operations from 1998 to 2002.
Key reported parameters
| Parameter | Units | Phase 1 Gravity-CIL Circuit (Design) | Phase 2 Gravity-Flotation-Conc CIL Circuit (Design) |
|---|---|---|---|
| Plant capacity | t/a | 3,800,000 | 5,000,000 |
| LOM average head grade | Au g/t | 1.76 | 1.66 |
| Fresh sulphides grade | Au g/t | 2.116 | 1.63 |
| Transitional grade | Au g/t | 1.35 | 1.99 |
| Oxides grade | Au g/t | 1.36 | 1.64 |
| LOM average overall recovery | % | 91.11 | 90.65 |
| Gravity recovery (LOM average) | % | 39.9 | Not stated separately |
| Crushing plant feed rate | tph | 741 | 819 |
| Milling plant feed rate | tph | 475 | 633 |
| ROM feed size (F100) | mm | 800 | 800 |
| Flotation feed size (F80) | µm | n/a | 75 |
| Flotation residence time | min | n/a | 45 |
| Flotation slurry feed density | % w/w | n/a | 38.8 |
| Flotation mass pull to concentrate | % | n/a | 9 – 12 |
| Leach feed size (F80) | µm | 106 | 15–20 |
| Leach residence time | h | 24.0 | 24.0 |
| Leach slurry feed density | % w/w | 45.0 | 37.6 |
| Number of CIL tanks | # | 7 | 7 |
| LOM average CIL cyanide consumption | kg/t | 0.91 | 6.48 |
| LOM average lime consumption | kg/t | 0.92 | 4.0 |
| Elution circuit type | , | Split AARL | Split AARL |
| Elution circuit size | t | 5.0 | 5.0 |
| Frequency of elution | batches/day | 2 | 1 |
| Cyanide destruction process | , | SO₂/Air Process | SO₂/Air Process |
Project website: https://www.asanko.com/
Notes on recovery values:
- Phase 1 recovery (91.11%) is based on test work and includes calculated discount factors for CIL solution gold losses (0.01 g/l Au in solution at 42% solids), fine carbon gold losses (40 g carbon per ton milled at 50 g/t Au), and a scale-up/ramp-up discount of 0.3% over life of mine.
- Phase 2 recovery (90.65%) is based on test work and includes calculated discount factors for concentrate CIL solution gold losses (0.04 g/l Au in solution at 35% solids), fine carbon gold losses (10 g carbon per ton milled at 50 g/t Au), and a scale-up/ramp-up discount of 0.54% over life of mine.
Technical qualifications
The Phase 2 capital cost estimate was developed to a nominal accuracy of -/+15%, inclusive of allowances for contingencies and estimating inaccuracies of 8.5% in aggregate (amounting to US$27 million). The Phase 1 capital cost estimate was developed to a nominal accuracy of -/+10%, with 8.3% aggregate contingency allowances (US$22.75 million). The engineering has been developed to support these capital cost estimate accuracies.
The process description is based on a pre-feasibility study level of engineering and testwork. Performance parameters are design criteria derived from testwork and include calculated discount factors for losses and scale-up effects. The report states that economics are preliminary in nature and there is no certainty that financial outcomes as presented will be realised.
Source: Asanko Gold Inc, Asanko Gold Mine Phase 2 Pre-Feasibility Study, Reference: Rev 2, Our Ref: TGHDP0220. Relevant sections: 1.14 Recovery Methods, 1.15 Operating Costs, 1.16 Capital Costs, 1.17 Economic Analysis, 17 Recovery Methods, 17.1 AGM Phase 1, 17.2 AGM Phase 2.
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.
Obotan Gold Project — NI 43-101 Technical Report
This report describes a proposed processing plant design for the Obotan Gold Project based on a conventional single-stage crushing, SAG and ball milling, and carbon-in-leach flowsheet.
Report context
This National Instrument 43-101 Technical Report for the Obotan Gold Project, prepared for Adansi Gold Company (GH) Ltd, presents the process design and recovery methods for the proposed treatment plant. The report references historical processing data from Resolute Mining Ltd operations at the Obotan region from 1998 to 2002 and incorporates results from recent metallurgical testwork.
Processing route
Summary of Proposed Flowsheet
The Project Plant design is based on a typical single stage crushing, SAG and ball milling circuit (SABC), carbon in leach (CIL) flowsheet. It includes single stage jaw crushing to a surge bin with reclaim from a dead stockpile and open circuit SAG mill, feeding cyclones that in turn operate in a closed circuit with a ball mill. A pebble crusher will receive scats from the SAG mill, crush them and return them to the SAG for further grinding. The hydrocyclones will achieve the final product size of P80 106 μm. A gravity circuit will be utilised to treat a portion of the cyclone feed stream to recover coarse free gold from the recirculating load. The milled product will gravitate to a trash screen before entering a pre-leach conditioning tank. A seven stage carbon-in-leach (CIL) circuit will be used to leach and adsorb gold from the milled ore onto activated carbon. An AARL elution circuit will be used to recover gold from loaded carbon. Cyanide in the CIL tailings will be detoxified using the SO2/Air process subsequent to thickening. The detoxified tailings are then pumped to the tailings storage facility.
The report notes that this process flow sheet is well known in industry, and is relatively low risk as it has historically been proven a successful processing route for Obotan region ores during Resolute Mining Ltd operations of 1998 to 2002.
Design Basis
The milling capacity is designed for 3,000,000 tpa of primary ore, with a maximum crushing and wet plant capacity of 3,840,000 tpa to allow for higher throughput when treating soft oxides. Mechanical availability of 85% for the crushing plant and 91.3% for the wet plant is assumed, supported by crushed ore storage and standby equipment in critical areas. Sufficient automated plant control is specified to minimise the need for continuous operator interface while allowing manual override and control when required.
Crushing Circuit
The crushing circuit has been designed as a single stage jaw crusher with intermediate surge capacity. A run of mine (ROM) grizzly aperture was selected based on the vendor recommended maximum ore feed size to the crusher. The primary jaw crusher has been sized on the basis of operating at 85% utilisation at a feed rate in excess of the mill feed requirement, assuming 60% of the vibrating grizzly split goes to oversize, and at a P80 of 150 mm. This product size was selected as it is suitable for SAG milling and minimises material handling issues, which may have become significant in a multistage crushing plant when treating tropical ores with high clay content.
The crushing circuit has been designed to operate at a treatment rate in excess of the mill feed rate. Crushed ore will report to a surge bin designed to smooth out fluctuations in the mill feed rate caused by crusher feed surges. The excess crushed ore will be stockpiled so that reclaimed ore can be fed to the process plant using a front end loader via an emergency ore feed bin during periods of crusher maintenance. All conveyor and equipment chutes have been designed to accommodate tropical clays and minimise circuit downtime, duct blockages and hang-ups.
A crushed ore surge bin with a nominal capacity of 250 tonne is specified. The surge bin overflow will be conveyed to a dead stockpile. Ore from the dead stockpile will be reclaimed by front end loader to feed the mill during periods when the primary crusher is offline.
Grinding and Classification
The milling circuit incorporates a primary SAG mill and secondary Ball mill in closed circuit with a cyclone bank and a pebble crusher. The SAG Mill, Ball Mill and pebble crushing circuit was selected in place of a single stage SAG mill and pebble crusher as it offered greater operating flexibility while also producing a cyclone overflow product with less variability in product size and production rate. The mills were designed with similar size drives to minimize the requirements for spares.
The process design criteria specify a grated primary SAG mill with a recycle pebble crusher and a secondary overflow Ball mill with a cyclone bank and associated infrastructure to produce a cyclone overflow product with P80 size of 106 µm.
Large diameter cyclones have been selected for the classification duty to reduce the potential for spigot blockages occurring from coarse SAG mill discharge material. While this might limit operational flexibility, the report states it provides the most robust operating circuit.
Gravity Concentration
The gravity recovery circuit has been designed based on a 40% gold recovery to gravity concentrate. Gravity concentration for removal of coarse gold will be from dedicated ports on the cyclone feed distributor. The recovered gravity gold concentrate will be leached in an intensive leach reactor. A separate electrowinning circuit has been provided for the intensive cyanidation solution to assist with metallurgical accounting and eliminate any potential impact on the operation of the carbon elution and electrowinning circuit.
Leach and Carbon Adsorption Circuit
A CIL circuit incorporating seven stages with a preconditioning tank is specified. The main drivers for the design of the CIL circuit are leach recovery and tailings solution grade. The overall tank volumes have been sized based on the greater volume required to give a minimum leach residence time.
Elution and Goldroom Operations
An AARL desorption circuit with electrowinning and gold smelting to produce doré bars is specified.
Tailings Treatment and Disposal
Cyanide destruction will be achieved using the SO2/Air process. Tailings thickening and pumping to a tailings storage facility (TSF) is specified.
Reagents and Process Services
Associated reagents and O2 generation by PSA (pressure swing adsorption) are specified. Process water supply is included in the design.
Key reported parameters
| Parameter | Unit | Design Value | Basis |
|---|---|---|---|
| Milling capacity (primary ore) | tpa | 3,000,000 | Design |
| Maximum crushing and wet plant capacity | tpa | 3,840,000 | Design (for soft oxides) |
| Crushing plant mechanical availability | % | 85 | Design assumption |
| Wet plant mechanical availability | % | 91.3 | Design assumption |
| Primary crusher product size (P80) | mm | 150 | Design |
| Final grind size (cyclone overflow P80) | μm | 106 | Design |
| Gravity gold recovery to concentrate | % | 40 | Design basis |
| CIL stages | number | 7 | Design |
| Surge bin nominal capacity | tonne | 250 | Design |
| ROM grizzly oversize split | % | 60 | Design assumption |
| Crusher utilisation | % | 85 | Design basis |
| Historical operations period | years | 1998 to 2002 | Historical (Resolute Mining Ltd) |
Project website: https://www.mining.com/pmi-gold-corporation-agreement-to-purchase-contiguous-mining-lease-with-the-obotan-gold-project/
Technical qualifications
The report states that the combined SAG and Ball milling capacity has been based on a nominal treatment rate of 3.0 Mtpa of primary ore with characteristics as per those seen in previous metallurgical test work and confirmed by recent variability testing. The crushing circuit and wet plant has been designed to treat up to approximately 3.8 Mtpa of ore, under the assumption that oxide ores will have properties resembling oxide ores treated by Resolute Amansie Ltd. Historically, these ores have had lower milling work indices than the Nkran primary ore, which would allow an increased mill throughput for a given mill size.
The report does not provide actual plant performance data, testwork results, or operating parameters from the proposed plant as it has not been constructed or commissioned at the time of the report. All processing parameters are design criteria unless otherwise noted as historical operating data. No economic analysis, mineral resource or reserve estimates, or project ownership information is included in this processing section. The report does not specify the current status or development stage of the project beyond the process design presented.
Source: Adansi Gold Company (GH) Ltd, Obotan Gold Project, National Instrument 43-101 Technical Report, Reference: 11906 0367:P:ck Revision A, Section 17 Recovery Methods.
Esaase Gold Project — 2011 Technical Report
This report documents the 2011 prefeasibility study for the Esaase Gold Project in Ghana, detailing the proposed mineral processing flowsheet and supporting metallurgical testwork.
Report context
The Esaase Gold Project technical report, dated 4 November 2011, was prepared by Coffey Mining Pty Ltd as a National Instrument 43-101 compliant technical report. The report presents the results of a September 2011 prefeasibility study, including metallurgical testwork and a proposed process plant design. The project was at an advanced stage of evaluation, with both open pit mining and processing considered in the study.
Processing route
Testwork History
Metallurgical testing for the Esaase Gold Project was conducted over multiple phases leading up to the September 2011 prefeasibility study. The testing programme included mineralogical characterisation and metallurgical testwork, with the results forming the basis for the process flowsheet design presented in this report.
Mineralogy
The gold mineralisation at Esaase is described in the report through dedicated mineralogical studies that supported the metallurgical testwork. These studies provided essential information on the deportment of gold and associated sulphide minerals that guided the selection of the processing route, although the specific mineralogical compositions of the ore types are not described in the sections of the report provided.
Metallurgical Testwork
Metallurgical testwork was undertaken as part of the project evaluation and is documented in the report under Section 13.1.3. The testwork programme was designed to assess the process response of the Esaase ore to the proposed flowsheet. The specific results of this testwork are not detailed in the extracted report sections provided, but they contributed to the metallurgical design criteria used for the prefeasibility study.
Process Flowsheet
The proposed process flowsheet for the Esaase Gold Project, as presented in the September 2011 prefeasibility study, incorporates the following unit operations:
- Primary ore crushing followed by stockpiling
- Grinding and classification
- Gravity concentration
- Rougher spiral circuit
- Concentrate regrind
- Pre-leach thickening
- Carbon in leach (CIL) for gold recovery
- Carbon elution and gold recovery
- Cyanide detoxification
The complete process plant design is described in Section 17 of the report, from which the above unit operations were identified.
Key reported parameters
| Parameter | Unit | Reported Value | Basis |
|---|---|---|---|
| Project name | , | Esaase Gold Project | , |
| Study date | , | September 2011 | Prefeasibility study |
| Report date | , | 4 November 2011 | , |
| Process throughput | , | Not reported | , |
| Gold recovery | , | Not reported | , |
| Ore feed grade | , | Not reported | , |
| Mine life | , | Not reported | , |
| Grinding | , | SAG/Ball mill circuit (assumed from text) | Proposed design |
| Gravity circuit | , | Included | Proposed design |
| Flotation | , | Not explicitly stated; spiral circuit proposed | Proposed design |
| Leaching | , | Carbon in leach | Proposed design |
| Crushing | , | Primary crushing to stockpile | Proposed design |
Technical qualifications
The following limitations apply to the processing information provided in the report:
- The report does not provide detailed throughput, recovery, or production rate figures in the report, meaning such data is not available for presentation.
- The full metallurgical testwork results are not described in the sections of the report provided for this summary, and therefore the readers are referred to the full technical report for these details.
- The process flowsheet design is presented as proposed for the September 2011 prefeasibility study and does not show historical plant operating data, as no such data exists for this project.
- The report does not provide specific equipment sizing, power consumption, or reagent consumption data in the sections examined.
- Information on the historical operating performance of processing circuits at this site is not applicable, as the project had not been constructed at the date of the report.
Source: Esaase Gold Project, Ghana, 43-101 Technical Report, 4 November 2011.
