The Okanjande deposit fits the description of a crystalline flake graphite deposit in a paragneiss. The original rocks at the Okanjande deposit were arkoses, feldspathic quartzites and ortho-quartzites that have been subjected to high grade metamorphism to become feldspathic-quarzitic gneisses and graphitic quartzites.

The Okanjande deposit is a massive deposit with shallow dipping layering to the southeast. Its surface extent is approximately 900 m northeast to southwest and up to 820 m from northwest to southeast. The mineralization extends from surface and has been defined by drilling up to a depth of 90 m below surface. The mineralization is open at depth.

The Okanjande deposit reaches its highest grade and is thickest in the centre, with graphitic carbon grades and mineralization thickness decreasing towards the peripheries. The contacts of the graphite units are difficult to define as they tend to be transitional. The graphite mineralization is typically defined over zones of significant total graphitic carbon grade rather than discrete lithologies, since the mineralized and non-mineralized rocks can be petrographically and stratigraphically the same. Unmineralized / waste zones are typically graphitic poor gneisses/quartzite, interbedded within the graphitic gneiss/quartzite or irregular intrusive pegmatites and granites. Two other waste rocks identified at the Okanjande deposit include a pinkish coloured, phlogopite-rich quartzite, which is typically 2 cm to 3 cm thick; and a friable mica schist, which rarely exceeds 1 m in thickness. The mica schist may result in pit wall instability if exposed on bench faces (RUL, 1993; RUL, 1994).

The Okanjande deposit is a massive deposit with shallow dipping layering to the south-east. It extends on surface approximately 900 m northeast to southwest and up to 820 m from northwest to southeast. The mineralization extends from surface and has been defined by drilling up to a depth of 90 m below surface. The mineralization is open at depth. The deposit is extensively weathered to depths of generally between 10 m and 20 m. The thickness of the weathered zone increases in the southwest and northeast of the deposit. A transitional zone of partial weathering of 1 m to 5 m thickness overlies the fresh rocks. The thickness of the transitional zone increases to the northeast of the deposit. An altered zone was identified at depth in the western part of the deposit from core logging and petrographic studies. The altered zone is confined to shear zones in this area (RUL, 1993; RUL, 1994).

The structure of the Okanjande deposit is tenuous. The present interpretation of the deposit structure is an isoclinal to recumbent fold structure that was refolded on a NW-SE axis. This is suggested by the small-scale structures identified in the rocks. Steeply dipping E-W and NE-SW trending faults have been observed to cut across the deposit (RUL, 1993; RUL, 1994).

The mineralized gneisses/quartzites have banded, porphyroblastic or magmatic textures. These gneissic textures relate to varying degrees of mineralization (Imerys-Gecko, 2018):

• The “banded ore” has bands of high-grade graphitic quartzite interbedded with barren bands of quartzite;
• The “porphyroblast ore” consists of massive high-grade graphitic quartzite with medium to large sillimanite porphyroblasts. This mineralization style can be of relatively high grade. Graphite flakes in this mineralization style have preferential orientations which result in a schistose fabric; and
• “Migmatitic ore” is related to higher metamorphic grade and has magmatic folds that indicate early melts due to an increase in temperature during metamorphism. Generally, this mineralization style has the highest grades.

The major silicate minerals of the graphitic gneiss at Okanjande are quartz and K-feldspar. The most common mica is muscovite, comprising between 2% and 8% of the rock.

Sulphide mineral content in the samples varies between 2% and 7%. Pyrite and pyrrhotite are the most commonly occurring sulphide minerals, with approximately equal proportions. Other sulphide minerals were identified in trace amounts, including chalcopyrite, molybdenite and covellite (only observed in weathered rock). Sulphides occur in irregular patches or clusters of up to 20 mm across, or in veins associated with quartz, and a small proportion of the sulphide is associated with graphite flakes.

Five sulphate minerals (barite, gypsum, jarosite, sidorotil and melanterite) were identified. Barite occurs in small quantities and is the only primary sulphate mineral, while the other minerals are as a result of weathering and oxidation of sulphide minerals. Jarosite can make up more than 10% of the weathered rock and some of the jarosite particles are closely associated with graphite flakes. Sidorotil and melanterite are soluble iron sulphate minerals which occur in minor amounts in the weathered rock, commonly along joints and fractures. Sulphate minerals may occur at depth in fresh mineralisation due to oxidation along joints, faults and shears.

Rutile content in the Okanjande deposit samples is between 0.2% and 1.3% with an average of 0.8%. Rutile particle size is between 0.05 mm and 0.40 mm, with an average of 0.20 mm. Rutile grains are commonly enclosed in gangue minerals and most have no association with graphite. A small proportion of rutile has inclusions of graphite, zircon and sulphides. SEM analysis indicates that some rutile grains are high in vanadium occurring in solid solution within the rutile structure.

The graphite content of the analysed samples ranges between 3% and 18% TGC. The average flake size ranges between 500 µm and 800 µm. More than 85% of the graphite flakes occur as straight undeformed, well-crystallised, euhedral flakes, and free of interlaminated gangue minerals in unaltered ore. Only 3% to 12% of the graphite flakes are interlaminated with gangue minerals. Most of the flakes that are interlaminated with gangue minerals are very large flakes that occur in the form of books. A small proportion of the flakes (<5%) occur as tiny flakes or grains enclosed in the feldspar or muscovite grains.

In the western part of the deposit, approximately 15% of the graphite flakes in weathered rocks at depths below the observed levels of oxidation have altered textures. The altered graphite flakes are associated with localised shear stresses at depth along a zone trending northeast to southwest. Altered graphite flakes are curved, bent or broken, reducing flakes to smaller sizes. Graphite flakes with this texture are interlaminated with gangue minerals and are commonly rimmed with muscovite.

The Okanjande graphite deposit lends itself to being mined by opencast mining methods. The intention is to mine at an average rate of 631,450 tonnes of mineralised material per year which will be transported to the Okorusu plant for treatment.

The Okanjande Deposit was mined from August 2017 until October 2018, when mining ceased and the Okanjande Mine was placed on care and maintenance. The run of mine (“RoM”) graphite-bearing material was trucked to Okorusu for processing.

The intention is to mine the Okanjande deposit by making use of contractors who will supply their own mining equipment to deliver the graphite-bearing material to a product stockpile and the balance to a waste rock dump. Overburden will be stockpiled on a separate overburden stockpile. It is not envisaged that any waste material will be backfilled into the pit at this stage as there is further fresh graphite-bearing material at depth; this fresh graphite-bearing material will be the subject of a future economic assessment.

The mining contractors will also be responsible for crushing the ore (single-stage jaw crusher) and loading into side tippers to be transported to the plant at Okorusu.

The Minex geological model, which was reviewed by the MSA Mineral Resources team, was uploaded into Deswik mine design software. A pit shell was defined incorporating only the weathered graphite-bearing material and using geotechnical parameters as defined in the previous mine design contemplated by ImerysGecko. This pit shell did not yield the required tonnage for a 10-year mine plan at a planned production of 630,000 tonnes per annum (“tpa”). The pit shell was then reconfigured and expanded to include some of the transitional and fresh graphite-bearing material in order to achieve a 10-year life of mine at a production rate of approximately 630,000 tpa graphite-bearing material to achieve approximately 30,000 tonnes of product per annum (Figure 16-1). A recovery of 92% was used to determine the final saleable product.

The open pit design parameters considered are summarised below:
• Bench heights: 5m;
• Bench widths: 10 m to 70m;
• Slope angles: 45° to 55°;
• Cut-off Grade: 3% TGC;
• Dilution to RoM tonnes: 2%;
• Recovery: 92%.

Using the above design parameters, a mining schedule was developed to mine at a rate of approximately 630,000 tpa at an average Stripping Ratio (“S/R”) of 0.66 (tonnes of waste to one tonne of graphite-bearing material) over the 10-year period. The first four years consider only mining the weathered graphite bearing material. In the second quarter of Year 5 the mining of Fresh graphite-bearing material begins and continues until the end of the 10-year period. The ramp up to full production is rapid, with the first year’s mining opening up the pit utilizing the current established faces (in the historic Okanjande open pit) to create pit room to sustain the maximum tonnage required.

The total Graphite production at a 4% TGC cut-off over the 10-year LOM is 295 425 tonnes at an average rate of 29 543 tonnes per annum (tpa).

Mining is performed by two excavator teams operating at a rate of 3,000 tonnes per day (“tpd”) on both the waste and ore. 2 teams will be required for the first 5 years, reducing to 1 team for the last 5 years.

In Year 1, mining starts in the southwest portion of the pit and opens in all directions to create pit room. The volume of waste is high in the first year due to the expansion of the pit; this contributes to the high strip ratio in the first year of 2.46 tonnes of waste per one tonne of graphite-bearing material. The total tonnage to be mined decreases as the waste decreases, so equipment requirements will decrease after the first 5 years.

It is proposed that holes of 102 mm diameter are drilled into mineralised material and waste to get a final powder factor of 0.7 kg/m3

To achieve this powder factor with 102 mm holes and 5 m high benches, each bench is drilled on a 3 m by 3 m pattern and charged with an emulsion explosive agent. If one considers a charge length of 3 m and an emulsion density of 1.3, the mass of explosives per hole will be approximately 32 kg. The powder factor can be increased by reducing the burden and spacing if the fragmentation needs to be increased.

Drilling and blasting is planned to be done by the mining contractor or by their sub-contractor. Blocks corresponding to a week’s loading are to be drilled and blasted on a weekly basis. On blasting day, the explosive supplier does a bench delivery of emulsion and accessories for that blast and the mining contractor oversees the blast.

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The process design/development for the upcoming Northern Graphite processing plant may be separated into 4 distinct areas, each with its own level of engineering changes required:

1. Front-End Comminution: Due to the relative unsuitability of existing comminution equipment, restrictions in terms of accessibility and the cost of relocating this equipment, a completely new frontend comminution circuit is required. This allows for fit-for-purpose process equipment selection to optimize liberation and graphite flake preservation.

2. Flotation: The majority of the existing flotation processing equipment is suitable in terms of throughput capacity, type and condition; and suitable for repurposing in the new graphite process. The only new processing equipment to be included in the flotation circuit will be a polishing scrubber and 2 polishing stirred medial mills. The remainder of processing equipment will be refurbished and piping re-routed to match the updated flow she ........