Metasedimentary
rocks from the Tortiya diamondiferous region (northern Côte d’Ivoire), located
in the Ivorian Paleoproterozoic domain, were analyzed with the aim of
identifying their different petrographic facies, constraining their provenance
and tectonic environment, and assessing the effects of sedimentary processes
and weathering on the signature of their source rocks. These analyses were
carried out with a view to helping trace the origin of Tortiya diamonds, which
are generally hosted in these metasediments. Major and trace element
geochemical data reveal that these samples are characterized by negative Eu
anomaly values, low to moderate weathering index values and a high
compositional variation index (ICV). These results led to the definition of
these metasediments as immature sediments potentially originating from rapid erosion and sediment deposition
from local sources. Chemical alteration index (CIA) values and Al2O3-(CaO*
+ Na2O)-K2O composition space suggest low to medium
degrees of meteoric alteration of the parent rock. These rocks therefore show
poorly differentiated compositions from the parent rock and poor sediment
sorting. Geochemical data and ratios of immobile elements, e.g. Al2O3/TiO2,
Cr/Th, Eu/Eu* and (La/Yb)n, indicate that the clastic materials derive mainly
from felsic to intermediate sources. Sedimentary tectonic discrimination
diagrams demonstrate that most of the samples from the Tortiya diamond-bearing
region were deposited on an active continental margin or in a continental
arc-island environment. Although this region has a long history of diamond
mining, its petrogenesis remains unresolved, and this petrogeochemical work is
a step towards initiating scientific research in the area.
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