Source:
p. 29
Ownership - 90% IAMGOLD / 10% Gov’t of Senegal.
AGEM Senegal SUARL Exploration (AGEM), a wholly owned subsidiary of IAMGOLD, controls the Property.
Deposit Type
- Vein / narrow vein
- Laterite
- Orogenic
- Saprolite
Summary:
The Project consists of four (4) deposits, Malikoundi/Boto 2, Boto 5, Boto 4 and Boto 6, all of the late orogenic type.
At Boto, the material near the surface consists of a layer of regolith which is varying in thickness and includes lateritic plateaus. Few rocky outcroppings are visible in the property; the banks of streams and rivers serve as the main source for geological observations. Only drilling can provide a detailed knowledge of the geology below surface. Drilling data and geological interpretation were used to create a regional representation of Boto geology.
Boto can be divided into three north trending litho-structural domains (020° N) that are well delineated in both induced polarization (IP) and magnetic surveys. From west to east, the three domains are:
• Western Flyschoid Domain.
• Central Deformation Corridor.
• Eastern Siliciclastic Domain.
Malikoundi/Boto2, Boto 4, and Boto 6.
At Malikoundi/Boto 2, Boto 4 and Boto 6, the regolith is composed of pedolith (soil, ferricrete, and laterite), saprolite, and transition weathering profiles (saprock) that average 8 m, 20 m, and 10 m in thickness, respectively. The detailed study of regolith has made it possible to distinguish between transported and in-situ regolith. The assay results from up-dip expressions of mineralized zones, confirm in-situ mineralized regolith. Mineralization in fresh rock is mainly associated with pervasive albite alteration and pyrite.
Interpretation of structural data collected from oriented drill core has shown differences between Malikoundi/Boto 2, Boto 4, and Boto 6. Boto 6 is characterized by a bedding strike of 025° N, whereas Malikoundi/Boto 2 appears to have two bedding strike directions of 015° N and 030° N. The two bedding strike directions observed at Malikoundi/Boto 2 may result from ductile deformation within the impure marbles and laminated detrital sediments. Contrary to other parts of the structural corridor, a significant rotation of bedding strike to 147° N is noted in the drill core at Boto 4.
At Malikoundi/Boto 2, a 30° to 60° westward- dipping thrust fault has been observed in drill core at the contact between the Guémédji sandstone and the sequence of marble/laminated sediments. Of particular interest is a large lens of Guémédji sandstone that lies above the fault. This over-riding block of sandstone from the north end, cut out and moved from the Guémédji sandstone unit, is the main host of mineralization in this prospect. As a result of these movements, this lenticular block was severely fractured against adjacent rocks, and this fracturing was the conduit through which the gold-carrying fluids circulated and the mineralization was deposited. Thus, the fracturing associated with the sandstone lens is the principal carrier of mineralization in facies as diverse as sandstone, pelites, agglomerates, cipolin (unclean marble), or sometimes even syntectonic diorite. This overlap/shear fault was also identified further south in Boto 4 and Boto 6, further north of the Falémé River to the Fekola Gold Mine in Mali (called Medinandi permit), owned and operated by B2Gold; as well as further south to the Tammy permit (Mali). Several different units of cipolin were observed and these units played the role of deformation trends as well as permeability barriers to mineralizing fluids. At Malikoundi North, one of the units of cipolin corresponds to the mineralization zone having accommodated the deformation related to the circulation of mineralizing fluids.
Cipolin units can be subdivided into:
• Stratigraphic Cipolin In-situ: these marbles are distorted but remain in their stratigraphic place and are generally thick.
• Cipolin of Re-crystallized Deformation: these marbles are very distorted and re-crystallized and have been spread along shear structures by deformation. They no longer correspond to the stratigraphic orientation, but to a structural orientation usually making the junction between two different stratigraphic cipolins that were thus accommodated; their thickness is generally low, with an average thickness between 2-3 m and only rarely surpassing 10-15 m.
Boto 5.
The weathering profile of Boto 5 is considerably deeper than that of Malikoundi/Boto 2, Boto 4 and Boto 6. Boto 5 is covered with a layer of pedolith 10 m to 40 m thick under which the saprolite layer can reach up to 80 m thick. The transitional layer under the saprolite is between 10 m to 40 m thick.
The lithological units at Boto 5 strike 015°-020° and include shale, carbonaceous sediment, and basalt. An albitealtered diorite dike that hosts the mineralization at Boto 5 cross-cuts the stratigraphy, striking 045° N dipping between 45° W and 60° W towards the west, approximately 30 m wide, and containing fragments of host rock in places.Four deformation phases occurred at Boto 5. An early phase of brittle-ductile deformation led to the emplacement of barren tourmaline veins. This was followed by reverse brittle-ductile faulting overprinted and reactivated on the northeast trending structures. Gold-bearing quartz-tourmaline veins were formed during this phase. The D2 structures were subsequently covered by a third ductile deformation phase. The latest deformation event is characterized by north-northwest and northeast trending brittle faults that offset the mineralization into blocks.
Similar to the majority of the deposits found in the Kédougou-Kéniéba inlier, gold mineralization at Boto is considered to be of the orogenic type. The orogenic gold deposits in the Birimian Province have been classified into three groups (Pre-, Syn-, and Post-orogenic). The characteristics of Boto mineralization are more similar to those of the post orogenic class.
The Malikoundi/Boto 2, Boto 4 and Boto 6 deposits are hosted by a turbiditic sedimentary sequence, with mineralization concentrating along the contacts of the litho-structural domains. The association of orogenic deposits with turbiditic sequences is well documented by Poulsen et al. (2000). Turbidite-hosted gold deposits within the eastern Kédougou-Kéniéba inlier are controlled by north-northeast trending structures linked to the SMSZ and, occur within the vicinity of intersecting north-northeast and north-north-west structures. At the Malikoundi/Boto 2, Boto 4 and Boto 6 deposits, gold is typically associated with pyrite, which is either disseminated along fractures (crackle-breccia hosted type) or along brittle-ductile veins.
Alteration assemblages observed at Boto 5 differ from those observed at Malikoundi/Boto 2, Boto 4, and Boto 6. The Boto 5 deposit is hosted in a diorite dike that contains abundant endogenic albite or has been pervasively altered to albite. The host rock at Boto 5 is highly deformed and contains a stockwork of quartztourmaline-pyrite veins. Although differing in appearance, this style of brittle- ductile deformation and veining is consistent with an orogenic gold mineralization model.
Summary:
Open pit mining was selected as the method to examine the development of the Project located in Senegal. This is based on the size of the resource, tenor of the grade, grade distribution and proximity to topography for the Malikoundi and Boto 5 deposits.
While resource models were developed for Malikoundi, Boto 4, Boto 5 and Boto 6 only the Malikoundi and Boto 5 models were used for the Feasibility Study mine plan.
Pit designs were developed for the Boto pit areas – Malikoundi, Malikoundi North and Boto 5 pits. The pit optimization shells used to determine the ultimate pits were also used to outline areas of higher value for targeted early mining and phase development.
Geotechnical berms of 12 m to 20 m in width were designed in the Malikoundi and Malikoundi North pits at the base of the weathering (transition) zone. For Boto 5, flatter slopes on the hangingwall material were recommended and ramps were incorporated in this material to act as geotechnical berms. In addition, a geotechnical berm was recommended at the 150 level in Boto 5 with a width of 30 m.
Equipment sizing for ramps and working benches is based on the use of 95 tonne rigid frame haul trucks. The operating width used for the truck is 6.9 m. This means that single lane access is 21.4 m (2x operating width plus berm and ditch) and double lane widths are 28.3 m (3x operating width plus berm and ditch). Ramp gradients are 10% in the pit for uphill gradients and 8% uphill on the dump access roads. Working benches were designed for 35 m to 40 m minimum on pushbacks, although some pushbacks in the Malikoundi pit did work in a retreat manner to facilitate access.
Boto 5 was envisaged as a contract mining operation using 40 tonne trucks, but the same road and ramp requirements were applied as for Malikoundi.
The Malikoundi pit is designed as 4 phases within the main pit. Phase 0 as the initial pit is called is a subset of Phase 1 to drive quickly to fresh rock for tailings dam construction purposes. Malikoundi North is a single-phase pit as is Boto 5.
Malikoundi.
Phase 0 is a subset of Phase 1 with the purpose of driving quickly to fresh rock for construction purposes in addition to material for road and other infrastructure items. It is the first phase mined in the Project. The Phase elevations range from 165 masl to the pit bottom of 105 masl.
Phase 1 expands on Phase 0 and is also developed from the north and advanced south. It has elevations ranging from 165 masl to a pit bottom of 60 masl. This is primary ore source early in the mine life.The ramp starts further to the north to avoid disrupting material flow from Phase 0.
Phase 2 is also accessed from the north but slightly further than Phase 1. Phase 2 is unique in that it has multiple exits to allow mining from both the hangingwall and footwall at the same time as mining in Phase 1 is advancing. This provides the mine planning team the flexibility to advance one side over the other quickly to accommodate rainy seasons and also the future development of Phase 2. Phase 2 has elevation limits of 165 masl to a depth of -40 masl.
Phase 3 is a deepening of the southern area of Phase 2. This will be a single access phase to save on waste and exits to topography on the south side. The geotechnical berm is evident in the design at the base of the transition zone. The multiple access points of Phase 2 assist Phase 3 by not disrupting material movement from Phase 2 and offer the ability to shorten haul profiles at different times in the mine life. Phase 3 extends from the same 165 masl level to a final depth of -160 masl or 325 m at the deepest point.
Malikoundi North.
The Malikoundi North pit is designed as a separate satellite pit to the north of the main Malikoundi pit. It consists of a single small, narrow mining phase that is accessed with a slot from the north end of the pit. The haul road will be to full operating width, except for the single lane for the bottom benches. This phase is located immediately to the east of the proposed water storage facility. Malikoundi North has an elevation variation from 160 masl to 50 masl.
Boto 5.
The Boto 5 phase was designed as a separate satellite pit to the south of the main Malikoundi pit. It consists of a single mining phase that is accessed with a wrap-around ramp access from the northwest corner of the pit. The haul road will be to full operating width, except for the single lane for the bottom benches. The pit ranges in elevation from 205 masl to 85 masl.
Processing
- Agitated tank (VAT) leaching
- Carbon in pulp (CIP)
- Carbon adsorption-desorption-recovery (ADR)
- Elution
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
Flow Sheet:
Summary:
The proposed process facility will consist of the following process areas:
• Primary crushing and coarse ore storage.
• Grinding, utilizing a SSAG circuit.
• Leach-CIP Carousel circuit.
• Gold recovery and carbon handling circuit (consisting of a cold acid wash followed by a pressure Zadra elution circuit and horizontal carbon regeneration kiln).
• Tailings disposal in a lined TMF with natural degradation of residual cyanide.
Ore Receiving and Crushing.
A static grizzly (600 x 600 mm), mounted above the ROM bin, will prevent the ingress of oversize material. A mobile rock breaker will be used to break oversize material retained on the static grizzly. Ore will be withdrawn from the ROM bin, by a variable speed apron feeder, directly into a jaw crusher, which will operate in open circuit. Crushed ore from the crusher will discharge directly onto the primary crusher discharge conveyor, which will convey the crusher product to the mill feed bin.
Recoveries & Grades:
Commodity | Parameter | Avg. LOM |
Gold
|
Recovery Rate, %
| ......  |
Gold
|
Head Grade, g/t
| 1.71 |
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Reserves at December 31, 2019:
Category | Tonnage | Commodity | Grade | Contained Metal |
Probable
|
29,040 kt
|
Gold
|
1.7 g/t
|
1,593 koz
|
Indicated
|
40,567 kt
|
Gold
|
1.6 g/t
|
2,033 koz
|
Inferred
|
8,196 kt
|
Gold
|
1.8 g/t
|
469 koz
|
Aerial view:
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