The Bissa and Bouly gold deposits all occur within an approximate 90 km NW-SE zone, comprising Birimian volcano-sedimentary rocks of the Boromo greenstone belt. The belt consists of mafic volcanic rock, minor felsic volcanic rock and extensive sedimentary units, intruded by Eburnean granitoids, all of which have undergone incipient to low greenschist facies metamorphism (Huot and Sattran, 1987).

The Bissa Hill, SW, IOSE, Z51, Z52 and Boken Zandkom deposits all fall within an approximate 9km NE-SW oriented corridor (“the Bissa-Zandkom corridor”) in the northeastern portion of the Boromo greenstone belt. This corridor comprises a series of interbedded argillaceousarenaceous sediments, alongside sequences of mafic volcanic rock. The thick metasedimentary sequence represents the principal host to mineralisation. Structurally, the lithological assemblage at Bissa-Zandkom appears to be tightly folded, with a broad NE to ENE trend, and is offset by several large-scale faults that trend NW-SE. At least two phases of deformation can be identified at the mine-scale, including an earlier D1 and later D2, resulting in a re-folded fold sequence.

Mineralisation at the Bissa and Bouly deposits is primarily orogenic and structurally controlled, with a secondary lithological control. The most significant mineralised zones are associated with anastomosing networks of quartz and quartz-carbonate veins (or stacked, parallel “arrays” of veins) developed within major brittle-ductile shear zones. Two main types of mineralised veins are recognised within the deposits of the Bissa-Zandkom corridor; namely a) the main gold-bearing quartz veins in the central part of steep shear zones, which are often axial planar shears; and b) complex vein systems of gently inclined and steep extensional fractures, developed both within the shear zones barren wall rocks, and along folded bedding planes and lithological contacts. Similar mineralisation styles are observed across the Bissa-Bouly deposits.

Gold mineralisation is most commonly developed in either quartz-sulphide veining ± carbonates and tourmaline, or disseminated and fracture filling sulphides and magnetite. Across most deposits, the primary sulphide species is pyrite, with minor chalcopyrite and arsenopyrite and very rare native gold.

Boken Zandkom, IOSE, SW, Bissa Hill and Yimiougou all strike NE-SW, dipping moderatelysteeply to the NW. Bouly, Z51 and Z52 are also NE-SW striking, but dip steeply to the SE. All of the deposits of the Bissa-Zandkom corridor have a moderate north-easterly mineralisation plunge. Trends associated with the satellite deposits of Zinigma, Samtenga, Ronguen and Gougre are varied.

As is typical in the region, the Bissa and Bouly deposits are variably oxidised. The oxidation sequence typically comprises a thin (0 to 20 m) lateritic layer at surface, which overlies a welldeveloped oxidised saprolitic zone. This normally progresses into a transitional zone, comprising a mixture of saprolite and fresh bedrock, with un-altered fresh rock typically around 50 m to 125 m below surface. Secondary enrichment of gold within the laterite layer is common.

Current mining operations at Bissa are focused on a number of different open pits.

Bissa gold mine operates a typical modern open pit operation with drilling and blasting followed by load and haul allowing for selective mining of the ore. The material lithologies are divided into four main categories: Saprolite, Laterite, Transition, and Fresh.

The mine has several significant opportunities to extend the LoM but this will depend on the exploration program and the gold price.

Crushing
RoM ore is screened at 800 mm on a stationary grizzly, with oversized broken using a rockbreaker. The primary crusher is a Metso C140 jaw crusher operating with a nominal CSS of 170 mm. The crusher is preceded by a 150 mm aperture vibrating grizzly. Crushed ore reports to an open stockpile.

Grinding
The first grinding stage consists of a 8.5 x 4.35 m SAG mill (6000 kW) that is closed with a 10 mm slotted aperture screen. A Pebble Crusher was installed in 2014 crushing a recycle rate of approximately 12%. Screen undersize reports to the 6.1 x 9.05 m (6000 kW) ball mill, which operates in closed circuit with a bank of 380 mm cyclones. After screening for trash removal, cyclone overflow reports to the CIL circuit.

The Bissa process plant treats non-refractory oxidised saprolite and transitional and fresh saprock hosted gold ore through a conventional carbon-in-leach (“CIL”) circuit, producing doré on site.

The plant commenced production in 2013 at a design production rate of 3 Mtpa; however, the plant was expected to be capable of processing 4 Mtpa or even higher with ore blends containing high levels of Oxide and Transitional ore. The current throughput is nominally 4.8 Mtpa with a maximum of 33% Fresh ore in the feed blend.

Cyanidation
The cyanidation circuit consists of six 2900 m3 mechanically agitated tanks, giving a circuit residence time of 26 hours at the original design feedrate of 3 Mtpa and a slurry density of 42% solids. Cyanide is added to the first tank, and compressed air is sparged into each tank. The tanks are fitted with mechanically swept vertical wedge wire interstage screens, and carbon is transferred using recessed impeller pumps. The carbon resid ........