Petrography and perovskite U-Pb age of the Katuba kimberlite, Kundelungu Plateau (D.R. Congo): Implications for regional tectonism and mineralisation

Abstract

The Kundelungu Plateau in the southeast of the Democratic Republic of the Congo (DRC) hosts numerous kimberlites, but up to now, only 34 bodies have been mapped. Locating these occurrences is hampered by the presence of sand cover on the plateau, a few tens of meters thick. Thus, most of the known pipes occur at the edge of the plateau where erosion has removed most of the sand cover. We report here on the Katuba kimberlite, a volcaniclastic kimberlite typical of a diatreme environment, with xenoliths of peridotite, carbonate, sandstone and shale, and lapilli-like microstructures. U-Pb analysis of perovskites from the Katuba kimberlite provides an age of 23 ± 1.8 Ma for the intrusion. Considering the age of 33 ± 4 Ma for perovskites from the Msipashi kimberlite pipe (also located on the same plateau), this new age suggests that the kimberlite magmatism in the Kundelungu Plateau lasted at least for 10 myr. The emplacement of these kimberlites is coeval with the opening of the Mweru graben, which is part of the East African Rift System (EARS), with structures oriented generally NW-SE and NE-SW. Some copper mineralisations inside the Katanga copperbelt, including those at Dikulushi and Kipushi, are located in similar structures, suggesting that the fluids responsible for the remobilisation of the mineralisation may be related to the kimberlite magmatism. Alternatively, the trigger for both the remobilisation of the mineralisation and the kimberlite magmatism is the tectonism that lead to the opening of the EARS. The upwelling of the asthenosphere or the mantle plume associated with the kimberlite magmatism may have supplied sufficient heat for fluid generation or contributed to the remobilisation of fluids. The location of the Katuba kimberlite along the NW-SE structures that were reactivated during the rifting inducing the opening of the Mweru graben, and which themselves are crosscut by the Luizi impact structure, provides another constraint on the relative age of the Luizi structure, which must be younger than the NW-SE structures and older than the emplacement of the Katuba kimberlite.