Namibia

Okanjande/Okorusu Mine

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Overview

Mine TypeOpen Pit
StageRestarting
Commodities
  • Graphite
Mining Method
  • Truck & Shovel / Loader
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ShapshotOkanjande/Okorusu Project consist of the Okanjande graphite deposit and the Okorusu processing plant.

Production began in 2017, put on care and maintenance in 2018, acquired by Northern from Imerys Group in 2022.

Northern intends to move plant 80 km to Okanjande mine site and resume production in 2024.

Owners

SourceSource
CompanyInterestOwnership
Northern Graphite Corp. 100 % Indirect
Northern acquired 100% ownership of Northern Graphite Holdings (Namibia) (Pty) Ltd. which owns a 100% interest in Northern Graphite Processing (Namibia) (Pty) Ltd. (“NGP”) and a 100% interest in Northern Graphite Okanjande Mining (Pty) Ltd. (“NGOM”). NGOM holds Mining License (“ML”) 196 which covers the Okanjande graphite deposit.

Contractors

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Deposit type

  • Metamorphic

Summary:

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.

Reserves

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Mining Methods

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Comminution

Crushers and Mills

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Processing

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Production

CommodityUnitsAvg. AnnualLOM
Graphite kt 32308
All production numbers are expressed as concentrate.

Operational metrics

Metrics
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Annual mining capacity  ....  Subscribe
Annual ore mining rate  ....  Subscribe
Annual milling capacity  ....  Subscribe
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Ore tonnes mined, LOM  ....  Subscribe
Total tonnes mined, LOM  ....  Subscribe
Tonnes milled, LOM  ....  Subscribe
* According to 2022 study.

Production Costs

CommodityUnitsAverage
All-in costs Graphite USD  ....  Subscribe
C2 total cash costs Graphite USD  ....  Subscribe
Assumed price Graphite USD  ....  Subscribe
* According to 2022 study / presentation.

Operating Costs

Currency2022
OP mining costs ($/t mined) USD 4.66 *  
OP mining costs ($/t milled) USD  ....  Subscribe
Processing costs ($/t milled) USD  ....  Subscribe
G&A ($/t milled) USD  ....  Subscribe
Total operating costs ($/t milled) USD  ....  Subscribe
* According to 2022 study.

Project Costs

MetricsUnitsLOM Total
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OP OpEx $M USD  ......  Subscribe
Processing OpEx $M USD 90.1
Transportation (haulage) costs $M USD 37.8
G&A costs $M USD 63.4
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Pre-tax NPV @ 8% $M USD  ......  Subscribe
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Heavy Mobile Equipment

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Personnel

Mine Management

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