SIMS U–Pb dating of uranium mineralization in the Katanga Copperbelt: Constraints for the geodynamic context

Abstract

The Katanga Copperbelt, in the southeastern part of the Democratic Republic of the Congo (DRC), occurs within the Pan-African Lufilian fold-and-thrust belt and hosts numerous uraniferous mineral occurrences in addition to the world-class sediment-hosted copper and cobalt ore deposits. In the 1950s and 1960s, Cahen et al. gave a relatively wide range of U mineralization ages, using U–Pb dating on whole-rock samples. Although these ages nowadays appear as inaccurate because of large error ranges, they were frequently used to discuss the regional geodynamic events. This paper offers a reappraisal of the age range previously published, using in-situ SIMS U–Pb analyses. Based on these analyses, two ages are regarded as analytically reliable and significant (652.3 ± 7.3 Ma and 530.1 ± 5.9 Ma), and hence as having implications for the understanding of geological and geodynamic context in the study area. In the Katanga Copperbelt, the siliciclastic rocks of the Lower Roan Group are slightly enriched in uranium. A major U mineralization/(re-)mobilization episode took place at ~ 652 Ma, during proto-oceanic rift basin development. This phase took place in an extensional tectonic regime and led to the (re-)mobilization of U within fractures and voids. Such deposits are observed along the ~ 250 km-long Kalongwe–Luishia tectonic lineament. This metal concentration was reworked at ~ 530 Ma, at the occasion of the climax of Lufilian deformation and metamorphism. This event gave rise to the U deposits in the southern border of the Katanga Copperbelt (and in Northern Zambia). The Kolwezi deposit is a deposit located further to the North. Notwithstanding its initial position further to the south, the deposit is heavily faulted and the thrusts and faults could have focused the fluids associated with the deformation, at ~ 530 Ma.