Lessons from the past
The geology and minerals of
Côte d’Ivoire
Côte d’Ivoire’s popularity as a mining destination is increasing. Nicolaas
Steenkamp tells us more about its minerals and geology.
A
[34] MINING MIRROR JUNE 2019
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.
West Africa is also known for its bauxite deposits
and Côte d’Ivoire hosts significant deposits,
although not as large as neighbouring Guinea.
lmost 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 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.
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
Geological surveys by Ironridge, one of the companies active in Côte d’Ivoire
www.miningmirror.co.za