Economic Geology and Mineral Resources
What this domain tests
Economic Geology tests ore-forming processes, deposit classification, resource evaluation and the mineral wealth of Cameroon. Expect questions on grade and tonnage, exploration methods, and the difference between a resource and a reserve.
Core rules and concepts
- Ore deposit classes: magmatic segregation (chromite, Ni-Cu sulphides), hydrothermal (veins, porphyry Cu-Au, epithermal Au), sedimentary (banded iron formation, phosphorite, limestone), placer (gold, diamond, rutile, cassiterite), residual/lateritic (bauxite, nickel laterite), evaporite (halite, gypsum) and supergene enrichment.
- Grade is the concentration of the valuable element: % for base metals, g/t for gold, ppm for rare metals. Cut-off grade is the lowest grade that can be mined economically.
- Resource = tonnage/grade known or inferred; reserve = economically mineable part of a resource, after dilution and recovery.
- Exploration sequence: regional mapping, stream-sediment and soil geochemistry, geophysics (magnetics, EM, IP, gravity), trenching, drilling, assaying, feasibility.
- Cameroon: bauxite at Minim-Martap and Ngaoundal; iron at Mbalam and Kribi; gold at Bétaré-Oya and Batouri; diamond at Mobilong; limestone at Figuil; rutile at Akonolinga; nickel-cobalt at Lomié; oil and gas in the Douala Basin and at Kribi.
Worked example
A deposit contains 200 Mt at 1.5% Cu. Metal content = 200 × 0.015 = 3 Mt Cu. With 90% metallurgical recovery, recoverable Cu = 2.7 Mt. At $8,000/t the gross metal value is 2.7 × 8,000 = $21.6 billion, before capital, operating and refining costs. If the cut-off is 0.8% Cu, the whole 200 Mt qualifies, but a 0.5% halo around it would not be reserve without a higher price or lower costs.
Traps that cost marks
Using resource and reserve interchangeably; mixing % and g/t (1% = 10,000 g/t); assuming all bauxite is aluminium metal; confusing placer and lode gold; ignoring recovery and cut-off; forgetting that grade must be reported with a cut-off and a tonnage.