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.

Gold prospects on the permits occur exclusively in Birimian rocks and are generally associated with quartz veining on the margins of mafic and intermediate sills. Exceptions are the Essakane main zone (EMZ) deposit and the Sokadie prospects (the latter on the Alkoma 2 permit). The EMZ deposit is characterized by quartz veining in a folded turbidite succession of arenite and argillite. At the Sokadie prospect, the veins occur in a sheared volcaniclastic unit between undeformed andesite and metasediments. Gold has generally been found to occur with quartz veining on the contacts of rock units with contrasted competency and as filling of brittle fractures in folded sediments.

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. 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 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.

The vein arrays occur in the east limb, fold hinge (or fold axis), and west limb lithostructural 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 the 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 of the 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 near vertical 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 wall rock 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

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

Essakane consists of several operating sites. The EMZ main pit is mined in several mining phases and accounts for the majority of the production. The Falagountou, EMZ North, and South (Lao) satellite pits provide additional ore and operational flexibility.

Grade control is accomplished by RC drilling and sampling of the mineralized zone on a 10 m x 10 m pattern, or tighter, as required. For sterile sections of the pit, the grid may be widened out based on the nature of the contacts and/or other geological occurrences.

A fleet of four drill rigs are used for the 229 mm (9.0 inch) production blast holes. All blasting activities on site are executed by an explosives supplier. Holes are loaded with bulk explosive matrix and initiated with electronic detonators.

Grade movement during blasting is a critical issue at Essakane. For this reason, blast movement monitors (BMMs) are systematically used when blasting mineralized areas in order to measure vertical and horizontal displacement which allows for the adjustment of the post blast ore packets.

Waste material is being dumped in the WRDs located east of the main pit.

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

The expansion consisted of the addition of a secondary crushing circuit and a second process line (grinding, gravity concentration, and leach-CIL) in the CIL plant and included:
• One secondary crusher of 750 kW
• One SAG mill of 7 MW
• One ball mill of 7 MW
• Two pebble crushers, one on line A and one on line B
• Two gravity concentrators
• Eight CIL tanks.

The ore 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 preleach thickener. A portion of cyclone underflow goes to the gravity concentrators (two on each line).

IAMGOLD has conducted a number of investigations to upgrade the existing Essakane milling operation by identifying equipment throughput constraints at various plant capacities. The areas of focus were the crushing and grinding areas, with additional investigations into the CIL and tailings handling areas, the water balance, and the lime addition circuits.

A plant capacity of 15 Mtpa was initially targeted. This included 13.5 Mtpa of fresh rock evenly split between Line A and Line B, with 1.5 Mtpa of saprolite added to Line A after the crusher plant. During the bridging phase, the targeted plant capacity was revised to be based on 11.7 Mtpa of fresh rock. In other words, the grinding circuit will be designed to accommodate 11.7 Mtpa of fresh rock equivalent in terms of the total specific energy. This means that more than 11.7 Mtpa total ore can be processed, as long as the required total specific energy for the ore blend is less than or equal to 11.7 Mtpa of fresh rock. The expected ore split ratio according to the latest mine plan is 86.68% fresh rock, 10.34% transition, and 2.98% saprolite. Therefore, the annual tonnages for the different ore types, equivalent to 11.7 Mtpa of fresh rock specific energy, are 10.9 Mtpa of fresh rock, 1.3 Mtpa of transition, and 0.38 Mtpa of saprolite, totalling 12.6 Mtpa at these ore proportions.

Primary screening at the existing crushing circuit is currently achieved by using two grizzly screens in series. A number of studies have been conducted to improve the efficiency of this circuit and to allow for greater throughput. Although the plant capacity has been slightly reduced since the bridging phase, the same screen size is still being retained in the new proposed design.

A double deck vibrating screen will be used to replace the two existing grizzly screens. The crushing circuit will feed 1,912 t/h of ore. The primary crusher will produce a crushed product top size as large as 404 mm. The crushed product is screened by the primary screen with the oversize reporting to the secondary cone crusher. The screen undersize will report to the respective grinding line’s feed stockpile.

The pebble crusher on both Line A and Line B has a maximum capacity of 300 t/h at the current operating closed side setting (CSS) of 12 mm. In the case that the pebble crusher is bypassed, the by-passing flow rate is 300 t/h. Based on observations, the pebble discharge conveyor on each line does not have sufficient capacity to accommodate the crusher bypassing scenario. This is due to a delay in the amount of material remaining in the crusher for approximately 30 seconds. When this delayed amount is combined with the by-passed amount, the total conveyor throughput can be as high as 600 t/h. It was part of the study’s scope of work to upgrade the pebble discharge conveyors to allow proper operation during this by-pass scenario.

Crushing in heap leach recovery methods
Following the end of the existing CIL process plant operations, the heap leach operation will process 8.5 Mtpa of ore from a stockpile with a current estimated LOM for the heap leach operation of approximately five years.

Re-handled ore from a stockpile will be delivered to a local feed bin by a haul truck to feed a three-stage crushing plant consisting of an existing first and second stage crushing area, and a new HPGR tertiary crushing circuit. Cement will be added to the crushed ore via a rotary valve and screw conveyor suspended from a large overhead storage silo. The cement will also act as an alkalinity control reagent while agglomerating the crushed ore. The agglomerated crushed ore will be conveyed via a series of grasshopper conveyors and stacked onto the leach pad with a radial stacker (Lycopodium, 2019b).

A three-stage crushing circuit has been proposed for the Project to reduce the ROM with a F80 423 mm to a P80 7 mm. Feed to the crushing plant will be accomplished via a haul truck dumping re handled ore from a stockpile into a feed bin which directly feeds a gyratory crusher. Primary crushed ore will be drawn from the crushed ore bin at a controlled rate of 1,329 t/h via a variable speed apron feeder to send to a closed loop secondary crushing circuit. Primary crushed ore will first be fed to one horizontal vibrating screen where the oversize is further crushed by the secondary cone crusher in closed circuit with the horizontal vibrating screen. The undersize is considered as the final secondary crushed product, which will be transferred to a stockpile for storage. Secondary crushed ore will be reclaimed from the stockpile to feed the tertiary crushing circuit. The tertiary crushing circuit is comprised of an HPGR unit configured in a closed screening circuit. The undersize from the tertiary screens will be transferred by the tertiary crushing product conveyor to the fine ore bin. A metallurgical sampler will be installed at the tertiary crushing product conveyor for metallurgical accounting.

CARBON-IN-LEACH RECOVERY METHODS
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 pregnant solution obtained from the intensive leach reactor is processed by two dedicated electrowinning cells and the sludge recovered is filtered, dried, and smelted together with the sludge recovered from the elution circuit.

Plant tails are thickened and stored in the tailings pond. The water is reclaimed to the plant.

IAMGOLD has conducted a number of investigations to upgrade the existing Essakane milling operation by ........