Re-Os Ages for the Kourki Porphyry Cu-Mo Deposits, North West Niger (West Africa): Geodynamic Implications

Abstract

The study area is located at the southern end of the Gorouol greenstone belt, northwestern Niger. This region contains significant deposits of Copper and Molybdenum hosted in intrusive rocks metamorphosed in the green shale facies. This deposit was previously considered a porphyry system of Copper (Cu) and Molybdenum (Mo) without having been the subject of advanced research. The objective of this study is to confirm or refute this hypothesis and to date the mineralisation in an absolute manner in order to readjust the mineralising episode in the history of the West African Craton. The methodology used within the framework of this study is the isotopic dating by the Re-Os method carried out on the pyrites of the host rock. The results of this analysis give an age range between 2158 ± 50 Ma and 2110 ± 51 Ma for the Cu-Mo mineralisation. This age range represents the West African Craton scale to an episode of magmatic accretion. During this accretion, the subduction phenomena between the Crusts (Oceanic and Continental) would have been favourable for the formation of the Cu and Mo mineralisation of Kourki.

Mineralization and sustainable development in the West African Craton: from field observations to modelling

“…Finally, a genetic model was proposed for the Kourki granitoids, probably derived from partial melting of a metasomatized garnet-bearing amphibole rock with a crustal component, emplaced at ~2.137 Ga (Léger et al, 1992). Based on the isotopic analysis (Hallarou et al, 2020b), the host rock pyrites of the Cu-Mo mineralization have been dated between 2110±51 and 2158±51 Ma by the Re-Os isotopic system, consistent with the granitoids age. This occurred during the D 1 tectonic phase upstream of the Eburnean Orogeny, hence creating a juvenile Paleoproterozoic crust.…”