Lithostratigraphy of the Neoproterozoic Shaba-type (Zaire) Roan Supergroup and metallogenesis of associated stratiform mineralization

Abstract

The Neoproterozoic Roan Supergroup of the Shaba (Zaire) metallogenic subprovince was largely affected by Pan-African Lufilian orogenic events, which generated important tectonic breccias. This paper reviews the sedimentological, lithostratigraphical and metallogenic information related to these terranes, with special reference to recent data, mainly from the Kambove district. The Shaba-type Roan sedimentary succession is subdivided from bottom to top into four Groups: R.A.T. (Roches Argilo Talqueuses), Mines, Dipeta and Mwashya. The succession is characterized by continental, tidal, lagoonal and reef lithofacies and contains several transgressive and regressive sequences. Two major cycles are recognized, each starting with continental or sub-continental deposition, followed by carbonated platform-type sediments (first cycle: R.A.T. + Mines; second cycle: Dipeta + Mwashya). These cycles translate as being a general transgression resulting from progressive widening and deepening of a rift-like basin. A major igneous event is clearly identified in the Lower Mwashya Formation (R-4.1), in the form of pyroclastic flows evolving to volcaniclastic strata in the central part of the Shaba arc (as at Shituru/Likasi and Kambove). The major metallic mineralizations of the Roan Supergroup occur as stratiform CuCo deposits, mainly located in the Mines Group (R-2). One occurrence is related to the R-2.1 and R-2.2.1 units (the classic lower and upper orebodies); one lenticular orebody is related to the R-2.3 Formation (Kambove Dolomite). Data from the Kambove district show characteristic vertical and lateral primary sulphide zonations similar to those reported in the Zambian-type deposits. The sulphide paragenesis confirms a ‘syn-diagenetic’ model of mineralization. Significant diagenetic enrichment has resulted from the variable and successive crystallizations of ore minerals, related to both the chemical-biological changes and the residual porosity of the host sediments. The origin of the metals remains speculative. Hypotheses of the leaching of the R.A.T. Group sediments and of the pre-Katangan basement are examined.