Côte d’Ivoire’s popularity as a mining destination is increasing. Nicolaas Steenkamp tells us more about its minerals and geology.
The rock types found are dominated by granulite and migmatitegneiss, with some granitoids and banded iron formations in remnant supracrustal belts. These rocks were affected by at least two orogenic mountain building events.Almost the entire Ivory Coast is underlain by extremely ancient metamorphic and igneous crystalline basement rock between 2.1 and more than 3.5 billion years old, comprising part of the stable continental crust of the West African Craton.
The coast is marked by a strip of prominent recent sediments, extending offshore. Coastal sedimentary basins formed as a result of the rifting apart of the supercontinent Pangaea, during the opening of the Atlantic Ocean.
The oldest mining is related to gold and alluvial diamonds. Native gold is hosted in steeply dipping quartz veins near the boundaries of volcanic belts and sedimentary basins, in disseminated and massive sulphide deposits or as alluvial gold in river gravels. Gold is also found as paleoplacer alluvial gold and is included in conglomerates and sericite-quartz schist with grades up to 3g/t.
Diamonds have been found in alluvial deposits, south of Korhoga at Tortiya and at Seguela. Kanangone, Seguela, and Tortiya have kimberlite intrusions, but none have been found to contain diamonds to date.
Iron is another important mineral for Côte d’Ivoire. The Monogaga deposit near Sassandra is a Minette Oolitic type iron deposit formed in the Miocene and Pliocene ages, and has a 40% iron concentration. Mount Gao, Segaye, Tia, Tortro, and Klahoyo all have Lake Superior type magnetite deposits.
In recent years, there has been an increase in interest in the high-grade manganese deposits. The manganese occurs as carbonates, silicates and oxides, and reaches concentrations of up to 47% in lenticular bodies, in the north-western regions of the country. The underlying phyllite and gondite became enriched in manganese near the Blafa-Gueto hills and Mokta, forming the residual caps.
The tropical weathering products and resulting clays are also of importance as they contain laterite deposits. Biankoumo has nickel-rich laterite soils on top amphibolite gneisses, close to the border with Guinea. These nickel deposits contain an appreciable amount of cobalt. West Africa is also known for its bauxite deposits and Côte d’Ivoire hosts significant deposits, although not as large as neighbouring Guinea.
The country is endowed with a large number of other mineral deposits that have not been developed in most cases. These range from nickel-copper deposits associated with platinum group minerals to beach heavy mineral sand deposits of titanium, tantalite, and glass sand. There are also modest offshore oil and gas reserves.
Nicolaas Steenkamp is an independent geological consultant.