Tracing the Origin of Metasedimentary Rocks in the Tortiya Diamond Region (Northern Côte d’Ivoire)

Abstract

Metasedimentary rocks from the Tortiya diamondiferous region (northern C ô te 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 Al 2 O 3 -(CaO* + Na 2 O)-K 2 O 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. Al 2 O 3 /TiO 2 , 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.