Geodynamic setting of Neoproterozoic nickel sulphide deposits in eastern Africa

Abstract

Four recently explored nickel sulphide deposits in East Africa are briefly described, and their geodynamic and palaeoenvironmental settings in the Neoproterozoic era are proposed. The area of East Africa considered lies at the southern margin of the Congo craton. This craton was assembled in the Palaeoproterozoic and microcontinental fragments were added at its southern margin in the Mesoproterozoic Irumi orogeny. In the early Neoproterozoic, the southern margin of the Congo craton was subject to rifting and widespread mafic magmatism, and island arcs may have developed off its eastern margin during this time. Final assembly of Gondwanaland in the late Neoproterozoic and Cambrian led to closure of the transient Mozambique and Zambezi oceans and widespread thermal and tectonic reactivation within the Congo craton and its adjacent marginal terranes. The Munali nickel deposit represents an early phase of basic magmatism in the early Neoproterozoic Katanga rift, hosted by a composite gabbro-ultramafic body emplaced at a high level in rift to passive margin sediments. The Mpemba, Rovuma and Nachingwea groups of deposits may also represent extensional basic magmatism at the southern margin of the greater Congo craton. However, an alternative setting for the Rovuma and Nachingwea deposits may be as small, subvolcanic intrusions in a more oceanic setting (island arc or back-arc basin) within the former Mozambique ocean.