Diagenetic origin of the stratiform Cu–Co deposit at Kamoto in the Central African Copperbelt

Abstract

Sediment-hosted stratiform ore deposits that underwent metamorphism and orogenesis are interpreted either to have a multiphase origin that might in part predate these events or to be exclusively related to fluid migration during the orogeny. This controversy concerns the formation of many world-class sediment-hosted ore deposits such as in the Central African Copperbelt. Here we present Re–Os dating results for disseminated and stratiform Cu–Co sulfide pseudomorphs after anhydrite in nodules and layers from the Copperbelt. Results demonstrate that at least some of the ores formed at around 800 Ma during rifting and basin development, and thus predate the Pan-African Lufilian orogeny. Younger Re–Os ages, i.e., between 682 ± 28 and 230 ± 36 Ma, may be due to the replacement of the early Cu–Co sulfides by younger sulfide phases. Alternatively, these younger ages may result from the disturbance or resetting of the Re–Os system during recrystallization/metamorphism or the transition of chalcocite from its high- to its low-temperature polymorph.