Taparko-Bouroum Group Property is underlain by geology considered to be similar to that of other Birimian-age volcano-sedimentary sequences. Hence, this region is considered prospective for orogenic gold deposits, which typically exhibit a strong relationship with regional arrays of major shear zones.

The gold mineralization found at Taparko and Bouroum may be characterized as formed in a classic mesothermal setting during the later stages of orogenic events, with a strong structural control. As such, these deposits are not expected to show a strong grade or mineralogical zoning that is typical of epithermal gold deposits. At Taparko, segments of an extended shear zone host quartz veins that carry gold mineralization, as well as the surrounding rocks within the shear zone, over significant widths. At Bouroum, a structurally complex setting has produced several smaller deposits that are characterised by strong gold enrichment in structurally-controlled shoots.

Gold at Taparko occurs predominantly associated with the Taparko shear zone, a northwesterly trending splay off the regional Markoye Fault, located along a thin band of metavolcanic and metasedimentary rocks enclosed by granodiorite. This structure, traced over a strike length >10km, dips at 40° to 50° to the northeast.

Gold-bearing, sulphide poor quartz veins and veinlets occur throughout most of the known length of the Taparko shear zone, but economically important mineralisation is restricted to a number of discrete zones which include the GT Zone in the south, the contiguous 2N/2K Zone and the 3/5 Zone further north.

The GT Zone, the most southerly and highest grade auriferous zone was the source of the initial production from the mine, and has a strike extent of 400m The gold mineralisation is concentrated in the upper of two quartz vein systems over true widths between 5 and 15m. The lower quartz vein system is virtually barren.

Zone 2 extends over a distance of 500m, subdivided into 2N, (southern) and 2K (northern), and separated by a short very low grade interval. Zone 2 is characterised by relatively local and restricted accumulations of white quartz with good gold grades in a generally low-grade environment.

Zone 3/5 is the largest of the individual ore zones with an overall quartz content of 60% and extends over a distance of 1,100m. The gold grade distribution has excellent grade continuity above cut-off and is not substantially different between the quartz veins and the shear zone material itself. The width of the zone above cut-off varies from 10 to 20m, dipping to the east.

Mining operations currently consist of three separate open pits located at Taparko (the 3/5 Pit, the 2N/2K Pit and the GT Pit), and one satellite open pit located at Bouroum.

The open pits are operated by hydraulic excavators loading pre-blasted ore/waste for onward processing/disposal via rigid body dumptrucks. Mining is currently based on 10m high benches for ore and waste and both are excavated on 2.5m high lifts.

Recently, the blast planning has been rearranged to ensure that about 50kt (approximately 10 days production) have been blasted ahead of production to compensate for the lead time to obtain blast hole assays from the site laboratory.

Taparko uses two diesel hydraulic rigs to drill 114mm diameter holes to a depth of 10m in ore and in waste with 0.5m of subdrill. The blasting patterns are 3.5m x 3.5m in hard rock and transitional strata and 4.0m x 4.0m in the weathered upper strata. These drill patterns are set out in advance of drilling by the site survey teams.

In addition to the drill rigs, a modern emulsion explosive truck is used. The supporting infrastructure includes a dedicated explosives plant including high explosives and initiating explosives magazines surrounded by bunkers and emulsion storage tanker, all contained within a secure compound.

At each drill point a representative sample of the ore from the drill chippings around the collar of the blasthole and the dust collector from the drill rig are taken. Continuous samples are taken per 2.5m run of the drill and the samples are sent to the site laboratory for assaying and in general there is a five day turnaround time for the results. Samples are analysed per 2.5m run as this is the maximum height of the layers that are excavated hence the 10m bench is blasted in a single blast but excavated in four layers. The mine plans to always have 10 days i.e. c50kt of rock blasted in advances to allow for any delays in the site laboratory assay turnaround.

The average reported grade of the ore is 3.0g/t Au from the 3/5Pit, 1.8g/t Au from Pit 2N/2K and 3.4g/t Au from the GT Pit. The average overall grade for Taparko is reported at being 2.85g/t Au.

All the final faces are now drilled and pre split to aid the definition of the final face and the overall stability of the final high walls.

The low grade ore is loaded and hauled to a new established dedicated stockpile adjacent to each working pit. This saves vehicle turnaround time and results in increased ore production. The intention is to treat this material at the end of the mine life.

The waste material that comes from the hangingwall side of the orebody is hauled to the waste dumps. The majority of the waste going to the dumps is hard rock from Pit 3/5 and GT Pit and a mixture of laterites, saprolites and saprock from Pit 2N/2K. Two waste dumps have been positioned to reduce haul travel times.

The Taparko processing plant consists of conventional crushing, grinding and carbon in leach (CIL) circuits which recover gold for the production of doré.

Run-of-mine material is initially crushed using one of two crushing circuits depending on whether it is classified as being “hard” or “soft”, after which it is ground using a rubber lined ball mill, operating in closed circuit with a cluster of hydrocyclones, to a target p70 of 75µm.

The ground pulp is mixed with sodium cyanide at a concentration of 0.4g/l and the gold allowed to leach into the solution from which it is recovered using activated carbon. This carbon is separated from the pulp using a series of screens after which it is washed and the gold extracted using an atmospheric Zadra elution process.

Leaching of the cyclone overflow product takes place in a conventional carbon in leach circuit consisting of six 830m3 tanks.

The leach circuit has a designed residence time of 24 hours between fresh pulp entering the first tank and the leached residue exiting the sixth tank; however, because of the increase in plant throughput, the residence time has reduced to approximately 16 hours.

Taparko metallurgical staff report that this has resulted in a circa 1-2% reduction in overall gold recoveries and as such, plan to install a further two leach tanks in order to increase the leach residence time to 20 hours whilst maintaining current throughput levels.

Leaching of the ore takes place at a pulp density of 44% solids with sodium cyanide added at a maintained concentration of 0.4g/l in the first tank falling to 0.3g/l in the sixth.

The leach tanks are not air sparged and the pulp viscosity is not reported to be high.

Gold is recovered from the leach solution using activated carbon which is added to the sixth tank at a rate of 10g/l. This is then transferred in a counter-current direction against the flow of pulp using a series of inter-tank screens and transfer pumps through the circuit to the second tank where it is removed and sent for elution.

On completion of the leaching, the leach tailings pass to an 18m diameter thickener where they are first thickened and then sent to the tailings dam. All process water is recovered and returned to the grinding circuit.

Extraction of the gold from the loaded carbon takes place in a desorption circuit consisting of an elution column with acid pre-wash.

Loaded carbon, assaying between 3-3.5kg/t Au is first washed using cold acid after which it is placed into an elution column and stripped, again using acid but at an increased temperature of 120°C and pressure of 2.8-3.0 bar.

Each elution cycle takes between 15 and 17 hours to complete with approximately 4t of loaded carbon treated per day.

Once the cycle is complete, the eluate passes to a single, eight cathode, electrowinning cell where the gold is recovered onto steel wool cathodes. These cathodes are washed to produce a gold rich sludge which is then filtered, calcined and smelted using standard techniques to produce doré bars containing approximately 70% Au.

The original design capacity of the plant was 1.0Mtpa; however, since 2010, attempts have been made to increase the total capacity to 1.5Mtpa. This has resulted in a number of changes to the plant operating parameters, most significantly an increase in the grind size of the mill product, which has resulted in an overall reduction in the amount of gold recovered.