Bauxite or overburden? Evaluating the Minim-Martap plateau
The Minim-Martap plateau in Adamawa hosts a bauxite deposit with 12 Mt proven at 43.0% Al2O3, 3.8% SiO2, 14.0% Fe2O3 and 2.5% TiO2. Average ore thickness is 4.5 m and overburden is 2.5 m of clay and caprock. The plateau is 85 km from the railhead at Ngaoundal and about 300 km by rail from Douala port. Water is scarce in the dry season, and several villages farm the plateau surface. A company proposes an open pit producing 1 Mt/year of raw bauxite for export over 12 years, with no beneficiation and no alumina refinery. Total capital cost is estimated at US$120 million, and the current bauxite price assumption is US$45/t FOB. The ore is pisolitic and clay-rich in the upper metre.
1. Evaluate the ore quality against typical Bayer-process feedstock requirements. What testwork and possible beneficiation would you recommend?
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Typical Bayer feedstock prefers >50% Al2O3 and low reactive silica, often <2–3% SiO2, because silica consumes caustic soda and raises alumina losses. At 43% Al2O3, 3.8% SiO2, 14% Fe2O3 and 2.5% TiO2, the ore is moderate grade and high in iron and silica. Total SiO2 is not the same as reactive silica; the clay overburden and kaolinite in the ore may be more reactive than quartz.
Recommended testwork: available alumina and reactive silica by caustic digestion, mineralogy by XRD, and beneficiation by washing and screening to remove clay fines. If silica is mostly in clay, simple wet screening may upgrade the ore. If it is in the bauxite lattice, beneficiation will not help and the ore may need blending with a lower-silica source. Iron and titanium mainly affect red-mud volume, not alumina extraction.
2. Assess the infrastructure, social and environmental constraints. Would you recommend proceeding on the stated plan? Support your judgement with rough calculations.
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Rough economics: 1 Mt/year at US$45/t gives US$45 million/year revenue; over 12 years that is US$540 million undiscounted. Capital cost is US$120 million, before rail upgrades, port handling and environmental costs. The strip ratio is 2.5/4.5 ≈ 0.56:1, which is favourable, but the 12 Mt reserve is small for a dedicated export operation. Transport is the main constraint: 85 km by road to Ngaoundal plus about 300 km by rail to Douala; rail capacity and rolling stock may need investment. Water scarcity in the dry season conflicts with dust suppression and washing. Socially, several villages farm the plateau, so compensation, resettlement and land-access agreements are needed. Environmentally, bauxite dust and mine rehabilitation must be addressed.
Recommendation: do not proceed on the stated plan without a rail agreement, a resource upgrade and beneficiation testwork. A larger tonnage or a value-added alumina project would be needed to justify the infrastructure. The project is marginal at US$45/t.