At Agbaou, the target deposit type being explored for is the mesothermal auriferous sulphide (pyrite + pyrrhotite) and quartz vein style mineralization. The gold mineralization within Agbaou deposit is hosted within a specific quartz vein type that occurs along a broad area and can be characterized by a wide range of quartz-vein types, brecciation, boudinage, sericitic and carbonate alteration.

The lateritic cover is generally between five and ten metres thick with a very well developed weathering profile is over much of the area.

Mineralization at Agbaou can be broadly separated into two categories: laterite cap (generally >0.5g/t Au) and primary (free gold and sulphide hosted). The laterite cap, which covers the entire deposit area, is of variable thickness (1 to 5m) and represents secondary (re-mobilized) mineralization. The primary mineralization is associated with a system of gold bearing quartz-veins hosted by tightly folded Birimian-age sedimentary and volcanic rocks. The quartz veins can occur within either meta-volcanic or meta-sedimentary rocks, but the host rock is typically strongly sheared. The primary mineralized envelope is broad (60 to 100m), consisting of a number (up to seven zones in Agbaou Main) of mineralized zones that generally follow the limb of the regional fold. Particulate gold mineralization is located within quartz veins and along wall rock-quartz vein boundaries.

The mineralized quartz veins at Agbaou have a visually distinctive texture that has been described as “mottled”. Gold mineralization is also associated with variable amounts of sulphides, mainly pyrrhotite and pyrite. These veins are easily identifiable in the diamond drilling core intersections from the fresh rock below the saprolite/fresh rock boundary. The deposits are aligned along a northeast trending, steeply southeast dipping structure that marks the axial plane of the large-scale, regional fold.

Contractor-based mining was the preferred option for Agbaou and BCM was the selected mining contractor. BCM is responsible for the site preparation (including removal of vegetation) haul road construction, excavation and haulage of ore to the Run of Mine (“ROM”) pad and waste to the waste dumps, oversize breakage and equipment maintenance.

The mining operations are based on the use of hydraulic excavators and haul truck fleet engaged in conventional open pit mining techniques. The excavators load the free-dug or blasted material into the haul trucks, with the ore being transported to the processing area and the waste to the designated local waste dumps. Access roads will be developed as required for access into new areas. Where necessary, the main arterial roads outside of the pits, will be constructed to a minimum 30m width, including berms and drainage areas.

Topsoil in mining areas will be recovered during the pit preparation phase and stockpiled for future use with progressive waste dumps and possible pit rehabilitation.

The majority of the gold mineralized material will be transported to the ROM area, and discharged directly into the feed hopper.

The in-situ materials in hard and semi-hard rock will require drilling and blasting to assist fragmentation and subsequent loading. The oxide portion of the ore body is free digging or may be in need of light blasting in certain areas.

CRUSHING AND ORE STOCKPILING
The crushing plant will treat both saprolite and bedrock ore at a rate of approximately 300 wet tonnes per hour to deliver a product size of 100% passing 150mm through a primary jaw crushing circuit. Design availability is for 80% utilization for the crushing circuit.

ROM ore is trucked and either placed on the ROM pad or tipped directly into a 200 tonne ROM bin fitted with a 1000mm x 800mm inclined static grizzly to scalp off any oversize material. Ore is transferred from the bin by a mechanical apron feeder that discharges crusher feed onto a vibrating grizzly feeder with 120mm spacing. The vibrating grizzly feed undersize material is pre-scalped to provide cushioning and conveyor belt protection from the oversize material which is discharged into and through a single toggle Jaw Crusher that reduces the ore size to 100% passing 150mm. The crushed product and the scalped undersize product is then conveyed to a 45t live capacity surge bin, with a rill overflow stockpile feed system incorporated into the design. The crushing rate is nominally adjusted to run inline via process control with the SAG mill feed rate set-point. An emergency feed stockpile of approximately 12,500t is maintained for emergency feed to supply the grinding circuit for planned and crushing circuit breakdown maintenance requirements. Emergency crushed ore feed is reclaimed from the stockpile using a suitably sized Front End Loader to maintain SAG mill feed rate set-points.

MILLING AND CLASSIFICATION
The milling circuit is comprised of a primary SAG mill with a grate discharge operating in open circuit with a re-grind overflow ball mill that is capable of treating approximately 250 dry tonnes per hour (“dtph”) of saprolite ore and approximately 182dtph of bedrock ore. The SAG mill operates in open circuit while the ball mill runs in closed circuit receiving 100% of the cyclone underflow product from the classifying cyclone cluster.

Crushed ore reclaimed from the surge bin and is conveyed to the SAG mill. Dilution water is added to the SAG mill to achieve the required 50% w/w solids density for saprolite material and 70% for bedrock in the SAG mill discharge for optimum grinding efficiency. The mill feed dilution water is added and controlled as a ratio of the SAG mill solids feed rate. The ratio control constant can be adjusted from the relevant SCADA® screen to account for varying mill feed rate and ore moistures.

The 5.1m diameter x 5.5m long SAG mill installed with a rubber composite lining is driven by with a 2500kW motor and has a grate discharge. The mill is designed to operate at 75% critical speed but the operational speed can be varied to optimize grinding efficiency and maximize the life of the installed lining system for the differing ore types. The ball load is approximately 9% by volume, while the total SAG mill load is 25%.

Hydrated Lime is added to the SAG mill feed conveyor via a screw feeder to maintain pH set points in the CIL circuit. The SAG mill slurry passes through a polyurethane panel fitted trommel where undersize material discharges into a common hopper. The slurry is delivered to the cyclone cluster, where fine material (cyclone over-flow) 80% passing 75 micron is transferred to the CIL circuit and coarse material (cyclone underflow) is gravitated to a 4.5m x 6.9m long overflow EGL 2.5kw ball mill for re-grind.

Discharge from the ball mill also passes through a polyurethane lined trommel where underflow (ball mill discharge) also passes into the common discharge hopper. Combined slurry is diluted with process water to a solids density of 54% for saprolite and 61% for bedrock, and pumped to a cyclone cluster for re-classification. The cyclone cluster classifies the slurry to produce an overflow of 80% passing 75µm at 40% for saprolite and 43% for bedrock that gravitates onto a vibrating trash screen for removal of any trash material prior to the slurry entering the CIL circuit.

A portion of the cyclone underflow, at a solids density of 70% for both saprolite and bedrock, is routed to the gravity circuit for recovery of coarse gold by a Knelson Concentrator, before being treated by a batch system intensive cyanidation circuit.

The process plant is designed to treat either 1.6Mt per annum of saprolite ore or 1.34Mt of bedrock ore, or a combination of the two ore types if required.

The proposed process design criteria consist of crushing, ore stockpiling, milling and classification, gravity and in-line leach reactor (“ILR”), CIL, cyanide detoxification, tailings disposal, acid wash, elution, electrowinning and gold room, carbon regeneration, consumables, oxygen and air services; and water services.

GRAVITY CONCENTRATION
A portion of the cyclone underflow feed stream reports onto a gravity scalping screen to remove the +2.5mm coarse material. Dilution water will be added to the scalping screen feed box to decrease the concentrator feed solids density to 55% for saprolite ore and 50% for bedrock ore. The screen oversize returns to the ball mill feed stream to be re-ground and re-classified while the screen
undersize is fed to a gravity concentrator to recover the free gold. Concentrator tails gravitate back to the common mill discharge sump.

The leaching of gravity concentrates is a batch recovery and treat process using an ILR. The leach solution is prepared by first adding caustic to water for pH adjustment and then sodium cyanide to a 2% concentration. The leaching of gold is effected by circulating the 2% cyanide solution through a rotating reactor drum. At the end of the leach cycle, which ranges between 14–16hrs, the drum is stopped and the solution gravitates to the ILR sump.

The pregnant eluate in the gravity pregnant tank is re-circulated through a dedicated electrowinning cell for the recovery of gold.

CARBON IN LEACH
The CIL circuit consists of six tanks, each with a live volume of 2000m³, resulting in a total retention time of 25.6 hours for saprolite ore and 36.8 hours for bedrock ore. Each of the six CIL tanks are equipped with dual impeller agitators to keep the slurry and carbon particles in suspension during the leach process.

Regenerated, eluted or virgin carbon is added to the last CIL tank. Recessed impeller vertical spindle pumps are installed in the CIL tanks to periodically transfer carbon upstream from CIL tank 6 to CIL tank 1. Loaded carbon in CIL tank 1 is periodically pumped onto a vibrating loaded carbon screen for downstream acid washing and elution purposes. The slurry is returned to CIL tank 1. High pressure water is sprayed on the screen to ensure that clean carbon reports as screen oversize to the acid wash column. The tails slurry leaving the last CIL tank gravitates to a carbon safety screen where carbon is recovered as oversize and slurry reports to the cyanide detoxification circuit.

ACID WASH AND ELUTION
Loaded carbon recovered from CIL tank 1 is discharged from the loaded carbon screen into a dedicated acid wash column. The acid wash column is sized to accommodate 6 tonnes of loaded carbon. During the acid wash cycle dilute hydrochloric acid solution (3% HCl) is circulated from the acid wash tank through the acid wash column. The solution exiting the column returns to the acid wash tank via the external strainers that prevent any carryover of carbon from the column to the acid wash tank.

The elution of gold from loaded carbon is done using the Split Anglo American Research Laboratories method (“AARL”). Firstly the carbon in the elution column is pre-heated, then split eluate from the previous strip is pumped from the split eluate tank via the recovery and primary heat exchangers into the elution column with cyanide and caustic solution to give a 3% caustic, 2% cyanide by volume solution. The loaded carbon is treated at temperature with the caustic and cyanide solution to release the gold adsorbed onto the carbon, further recovery of gold is achieved by rinsing the heated carbon bed with a number of bed volumes of quality filtered raw water, resulting in the stripping (desorption) of gold from the carbon into a pregnant solution.

The pregnant solution discharges from the elution column into a dedicated pregnant eluate tank for recirculation and recovery of gold onto stainless steel cathodes in the electro-winning circuit. Each elution cycle runs for a period of 6.5 hours, and the heating cycle is in operation for approximately 4.5 hours of that cycle. At the end of each elution cycle, stripped (barren) carbon is hydraulically transferred to the feed hopper for reactivation of the carbon in the regeneration circuit.

CARBON REGENERATION
Upon completion of the elution cycle, the carbon batch is hydraulically transferred to the feed hopper of the regeneration kiln or, on occasion to the CIL circuit. Barren carbon is thermally regenerated in an electric kiln to remove organic contaminants and to maintain the activity of the carbon. Regenerated carbon is subsequently transferred to the last CIL tank.

ELECTROWINNING AND GOLD RECOVERY
The pregnant eluate from the elution column is directed to fill the pregnant tank. When the electrowinning circuit is available, the pregnant solution is re-circulated through the CIL electro-winning cell. Sludging type stainless steel mesh cathodes are utilized to electro-win gold from the pregnant eluate solution. Gold is deposited as a loosely adhering fine sludge onto the surface of stainless steel knitted mesh cathodes.

The loaded cathodes are periodically raised, pressure washed with a guerny, to remove the gold sludge from the cathodes and sludge is decanted to a vacuum filter to de-water and advance to the calcine step before once again being fluxed and smelted to produce bullion.

At the end of smelting, the furnace crucible contents are poured into cascading moulds mounted on a trolley. The bullion collects in the bullion bar moulds while slag flows and collects in slag moulds. When both phases cool and solidify the glassy slag phase is easily broken away from the metallic phase, leaving a relatively pure gold bar.

When the gold bars have cooled down, they are quenched for further cooling, cleaned with a needle gun to remove any traces of adhering slag. Then they are sampled, labeled, weighed and stored in a safe prior to dispatch to the refinery.