Provenance and depositional age of the Cryogenian ‘grand conglomérat’, host of the Kamoa Cu-deposit, Democratic Republic of Congo

Abstract

The Kamoa copper deposit (759 Mt, 2.67% Cu at 1% cut-off) is one of the largest copper deposits in the central African copperbelt. Mineralisation at Kamoa is hosted by the Cryogenian ‘grand conglomérat’, which was deposited in an intracratonic rift and its sub- basins associated with the break-up of Rodinia, and is equated to the ‘Sturtian’ glaciation, the oldest of the Neoproterozoic glacial events. Using detrital zircon geochronology, the provenance of synglacial and underlying pre-glacial units is compared, to evaluate the temporal dynamics of the sediment supply at Kamoa. The detrital zircon age distributions suggest that the ‘grand conglomérat’ was derived from locally exposed basement of the Mesoproterozoic Kibaran Supergroup and from significant recycling of underlying pre-glacial units, with minor contributions from distal, primary source areas. The stratigraphic differences in the distribution of zircon age populations of the strata at Kamoa may reflect changes in glacial dynamics or of rifting during deposition of the ‘grand conglomérat’. A Neoproterozoic zircon age population ~700 Ma is probably derived from rift-related volcanic rocks and is significant because it repositions the timing of mid-Neoproterozoic rifting in the Katangan basin and the maximum depositional age of the ‘grand conglomérat’. The new age constraints suggest that the midNeoproterozoic ‘Sturtian’ glaciation was globally diachronous.