Pb-isotope constraints on base-metal mineralisation at Kipushi (Southeastern Zaïre)

Abstract The Kipushi ZnPbCu deposit, located in the northern extension of the Central African Copper Belt in southeastern Zaire, is a discordant ore body at the contact between a breccia body and adjoining host rocks of the Upper Proterozoic Lower Kundelungu Group. Model age data of galena indicate a probable mineralisation age of 454±14 Ma which is younger than the peak of the Lufilian tectonism and suggests that the mineralisation is epigenetic and post-dates the folding and brecciation at Kipushi. Pb-isotopic compositions of sulphide minerals and host rocks at Kipushi show little variation. Limited data from other deposits (Lombe, Kengere, and Kolwezi), also in the northern extension of the Copper Belt, suggest that the Pb-isotopic homogeneity extends over a large region which corresponds to the northern part of the Copper Belt and also to the outer, northern zone of the Lufilian fold belt. Pb from the Kinsenda ore deposit, located in the central zone of the Lufilian fold belt, differs from Kipushi and displays similarities to that of Musoshi, another deposit located in the central zone of the fold belt. The Kipushi data, in conjunction with other available data, form the basis of a model involving at least two distinct mineralisation events and which might apply to the Copper Belt as a whole: (1) an early event associated primarily with deposits of the stratabound type of Copper Belt deposit; this event occurred at or before c. 650 Ma and resulted in the CuCo mineralisation of the central part of the fold belt and was sourced from basinal fluids, and (2) a younger event responsible for vein type deposits, at 454±14 Ma, which produced the ZnPbCu mineralisation of the northern part of the fold belt and derived its metals from a magmatic or volcanic source.