The Essakane Gold Mine occurs in the Paleoproterozoic Oudalan Gorouol greenstone belt in northeast Burkina Faso. The stratigraphy can be subdivided into a succession of lowergreenschist facies meta sediments (argillites, arenites, and volcaniclastics), conglomerate, and subordinate felsic volcanics, and an overlying Tarkwaian-like succession comprising siliciclastic meta-sediments and conglomerate. Each succession contains intercalated mafic intrusive units that collectively comprise up to 40% of the total stratigraphic section.

The Essakane Gold Mine consists of one mining permit (the Essakane Mining Permit), which contains the Essakane main zone deposit (EMZ deposit) and the Falagountou deposit, and seven exploration permits (the Essakane Exploration Permits), all located on contiguous ground.

The addition of the heap leach process in 2018 has increased the EMZ Mineral Reserve inventory. The Falagountou deposits have no Mineral Reserves attributed to the heap leach process due to the distance they are located from the EMZ pit and the short mine life, which ends in 2020 for the West pit and 2021 for the East pit.

The EMZ deposit is a greenstone hosted orogenic gold deposit. Specifically, it is a quartzcarbonate stockwork vein deposit hosted by a folded turbidite succession of arenite and argillite (Figure 7-6). The laminated sedimentary units are part of turbidite sequences. The regular laminated unit is composed of very regular alternating sandstone, siltstone, and grey-black argillite. The lateral extension of this unit is limited. The irregular laminated unit is thicker than the regular bed and is mainly composed of an argillite unit (more than 65% of the whole rock). This irregular laminated unit is also made of an alternating sequence of sandstone, siltstone, and poorly sorted argillite.

Gold occurs as free particles within the veins and is also intergrown with arsenopyrite +/- tourmaline on vein margins or in the host rocks. Disseminated arsenopyrite in the host rock rapidly decreases away from the veins and is strongly associated with the gold mineralization. The same relationship is seen away from lithological contacts, which generally show higher densities of bedding-parallel veining. Oriented diamond core drilling shows that significant concentrations of gold with arsenopyrite can be found in the arenite-argillite lithological contacts in association with quartz veining or in veinlets of massive arsenopyrite. Deeper below the main arenite unit, significant concentrations of gold are found in association with coarse arsenopyrite in the argillitic unit. The gold particles occur without sulphides in the weathered saprolite. The gold is free-milling in all associations.

The EMZ deposit is an anticlinal fold with flexural slips between layers and is westward thrusting along weakness planes parallel to bedding, with minor displacement.

The quartz veins fill brittle extension and shear deformation structures caused by the folding with at least three distinct sets of veins (Figure 7-8) and two phases of quartz veining and gold mineralization.

The vein arrays in the EMZ deposit are complex and consist of the following:
• Early bedding parallel laminated quartz veins caused by flexural slip and showing ptygmatic folding;
• Late, steep extensional quartz veins as vein filling in extension and shear joints formed by the folding;
• Axial-planar pressure solution cleavage (with pressure solution seams normal and parallel to bedding). All veins may be displaced by two sets of late opposing thrusts as shown in Figure 7-9.

The vein arrays occur in the east limb, fold hinge (or fold axis), and west limb litho-structural domains. The geology and economic potential of the EMZ deposit is dominated by the persistent east limb main arenite. The top contact of the east limb domain is a sharp, sheared contact with no significant gold mineralization above it. The shearing appears to be parallel to bedding, however, some loss of vertical succession has occurred. The main arenite below this contact is the lower coarse grained part of a Bouma cycle. The locus of bedding parallel deformation and alteration is within the east limb main arenite. Graphitic argillite occurs immediately above the contact. The deformation shifts into the hanging wall argillite unit to the north of the EMZ deposit.

Mineralization has been confirmed to over 550 m vertically below surface, however, the full depth extent in the fold hinge and east limb is still unknown. The geometry of the fold hinge zone is an anticlinal flexure that is easily recognized in the pit and oriented drill cores. The fold closure is sharp and sometimes truncated by thrusts and the transition from east limb to west limb takes place over a few metres. The position of the fold axis is often marked by a breccia in the arenite unit. The fold hinge zone in the argillite unit is marked by tight kink structures and sheath folds with rapid transitions from east dipping footwall rocks to nearvertical west limb beds below the fold axial plane.

Arsenopyrite and pyrite occur within and adjacent to quartz veins as well as disseminated throughout areas of wallrock alteration. Traces of chalcopyrite, pyrrhotite, galena, and hematite occur with arsenopyrite. Minor amounts of tourmaline with rutile are found in the main arenite and in interbedded arenite stringers in the footwall argillite. Remobilized graphite can be found associated with tourmaline.

The fine-grained argillites can be strongly enriched in tourmaline and have also been subjected to quartz, carbonate, sericite, and quartz alteration. Fine needles of rutile are generally associated with the tourmaline. Sulphide mineralization preferentially occurs in the coarser arenaceous layers.

The EMZ deposit is characterized by multiple quartz and quartz carbonate vein sets and stringers. Arsenopyrite and pyrite tend to be late and concentrated near the margins of the veins or in late cross cutting stringers. The paragenetic sequence of veining is thought to be as follows:
• Early quartz-carbonate-albite-(sericite) veins.
• Quartz veins with tourmaline and pyrite containing gold.
• Diffuse quartz-albite-carbonate veins with arsenopyrite.
• Later tourmaline-rutile-arsenopyrite stringers with gold.
• Late skeletal pyrite and carbonate-quartz-pyrite stringers.

Falagountou deposit mineralization.
Due to the intense artisanal mining (“orpaillage”) activity, no detailed geological mapping has been carried out over the Falagountou deposit. Observations, from visits within orpailleur workings, indicate that gold is located in smoky quartz veins injected in a sequence of fine to medium detrital sediments, similar to those found at the EMZ deposit that have been intruded and metamorphosed by shallow dioritic dykes.

Drill cutting and core observations have confirmed that the gold mineralization is structurally controlled, hosted in sheared and brecciated zones in the hanging wall contacts between sedimentary and intrusive rocks along a north-northwest to north trend. Gold is associated with quartz veins and is found disseminated into the wallrock, as well. There is a strong spatial relationship between the gold mineralization structures and the swarm of intrusive dykes that intrude the sedimentary sequence, suggesting that part of the fluid responsible for the gold deposition may have been exsolved from the dioritic magma during its emplacement. The alteration assemblage encountered is silica-calcite-chlorite. Pyrite and arsenopyrite are the main sulphide minerals observed to date, both in sedimentary rocks and the dioritic dykes.

Mining is carried out using a conventional drill, blast, load, and haul surface mining method with an owner fleet. Current mining production is approximately 50 Mtpa.

The Essakane Gold Mine consists of several operating sites. The Essakane main pit is mined in several mining phases and accounts for over 80% of the production. The Falagountou and Essakane North satellite pits provide additional ore and operational flexibility.

The Essakane main pit comprises a total of seven mining phases. Mining by phases provides a sufficient quantity of ore by postponing and scheduling the mining of waste evenly over time. The average width of push-backs is 120 m and is limited to 30 m in certain areas. Mining by phases also provides effective operational flexibility through the simultaneous opening of several fronts, and the optimization of truck cycle times through good ramp system management.

All blasting activities on site are executed by an explosives supplier. Holes are loaded with bulk explosive matrix and initiated with electric detonators.

Ore is processed using two stages of crushing, semi-autogenous grinding, ball mill grinding, pebble crusher grinding (SABC), gravity concentration, and a CIL gold plant. The UFS proposed a process plant throughput rate of 7.5 Mtpa. During construction, some debottlenecking improvements were made to the design, resulting in a revised nameplate capacity of 9.0 Mtpa based on processing 100% saprolite ore. Due to further operational improvements, plant throughput has increased beyond the constructed design capacity.

Fresh rock mill feed has gradually increased from 2012 onwards. To maintain gold production levels, with increasing proportions of hard rock in the mill feed, an expansion was completed in 2014. The objective was to double the hard rock processing capacity from 5.4 Mtpa on a 100% hard rock basis to 10.8 Mtpa.

The ore coming from the mine is crushed in a gyratory crusher and in a cone crusher. The crushed ore is stockpiled either in a pile for Line A or Line B. The ore is reclaimed with apron feeders and feeds SAG mills on each line. The pebbles from the SAG mills are diverted to their respective pebble crusher in closed circuit. The ore passing through the SAG mill discharge screen feeds a pack of cyclones. Cyclone underflow returns to the ball mill. Cyclone overflow is sent to the pre-leach thickener. A portion of cyclone underflow goes to the gravity concentrators (two on each line).

The thickened ore feeds two parallel lines consisting of one leach tank followed by CIL tanks. Once loaded with gold, the carbon is screened, acid washed, and eluted. The pregnant solution is sent to the gold room for electrowinning, drying, and finally, smelting into doré bars.

Eluted carbon is regenerated in a kiln and reused in the CIL circuit. Carbon fines generated from the circuit are recovered in bags for further gold recovery.

The gravity concentrate feeds an intensive leach reactor. The cathode obtained from the intensive leach reactor is then dried and smelted together with the cathodes from the elution circuit.

Plant tails are thickened and tails are stored in a tailings pond and water is recovered to the plant.