Sedimentology of the Shangoluwe breccias and timing of the Cu mineralisation (Katanga Supergroup, D. R. of Congo)

Abstract The origin of breccias in the Neoproterozoic Katanga Supergroup in D.R of Congo is still a matter of debate. At the Shangoluwe Cu deposit located in the Kambove mining district (central part of the Lufilian arc), the sedimentary breccias bearing Cu mineralisation have been investigated for lithological and sedimentological study, quantitative analysis of the breccias fragments and fault kinematic analysis in order to understand the origin of the breccias, their lithostratigraphic position and the timing of mineralisation. At Shangoluwe, three sedimentary breccias sequentially deposited within the Kundelungu rocks can be identified on the basis of the nature of the matrix and fragments; from bottom to the top, the Ferruginous Breccias, the Dolomitic Breccias and the Siliceous Breccias. These breccias were deposited as lenses. The presence of debris and grain flows, a finely laminated matrix, pseudo-stratification, normal and reverse graded-bedding, and the presence of interbedded siltstone, sandy shale, dolomitic shale, shale and dolomite, are considered as evidence of a sedimentary origin of the breccias. The log normal distribution of the fragments indicates that gravity flow was the main deposition mechanism. The Ferruginous and Dolomitic Breccias are regarded as contemporaneous with the Kundelungu Group. They were deposited as lenses interbedded in the Kanianga and Mongwe formations, both affected by the Lufilian orogeny (D1 - Kolwezian and D2 – Monwezian phases). The Siliceous Breccias are post-orogenic as shown by the presence of an erosional and angular unconformity respectively on the Dolomitic Breccias and the Kundelungu formations. Therefore, the Siliceous Breccias are attributed to the Lower Palaeozoic Biano Subgroup and the lithostratigraphy of the Biano Subgroup is proposed for revision accordingly. Copper mineralisation post-dates the deposition of the breccias, the dissolution of dolomite fragments and in-situ fragmentation. This mineralisation occurred during late- to post-orogenic extension of the Lufilian orogeny, and was remobilised during the Cenozoic.