The western arm of the Lufilian Arc in NW Zambia and its potential for copper mineralization

Abstract

Parts of the Kasai Shield, a western foreland to the Lufilian Arc and the western arm of this orogen are traced into NW Zambia. The Kasai Shield comprises a suite of metamorphic and igneous rocks (dated at ∼2540–2560 Ma) and extensive porphyritic granites (dated at ∼2050 Ma). Imbricate thrusts and NE-trending shears and mafic dykes in the Kasai Shield may be Kibaran structures. Weakly deformed Katanga Supergroup strata overlie the Kasai Shield in the western foreland and include Mwashia Group lavas dated at ∼765 Ma. This new date provides a minimum age for the siliciclastic strata of the underlying Roan Group that host world-class copper–cobalt deposits elsewhere in Zambia and the Democratic Republic of Congo. It also provides a maximum age for overlying glacial strata at the base of the Kundelungu Group. Altered volcanic pods locally in contact with Kundelungu glacial strata are dated at ∼735 Ma. This new date confirms that the basal Kundelungu glacial deposits (Grand Conglomerat) are attributable to the global Sturtian glacial event, here dated at between ∼765 and ∼735 Ma. Katangan strata and their igneous/metamorphic basement are severely deformed in the Lufilian Arc. The basement is exposed in the core of the Kabompo Dome and includes a porphyritic granite dated at ∼1940 Ma. Roan Group sedimentation took place on a passive continental margin or in a rift basin during the initial stages in the fragmentation of Rodinia. An eastern carbonate platform passes laterally into western siliciclastic sediments. Eruption of mafic (andesitic) volcanics in the Mwashia Group marks the rift-drift stage of Rodinia fragmentation. Re-activated NE-trending basement structures controlled the orientation of the volcanic rift although feeder dykes indicate E–W extensional forces. The Lufilian Arc was generated by closure of the rift/oceanic basin caused by the collision between a southerly `Kalahari Plate' and a northeasterly `Congo–Tanzania Plate'. NW-directed thrusting in the western arm and NE-directed thrusting in the eastern arm suggest that the arcuate shape of the orogen was caused by an indenter of the southern plate impinging on the northern plate. Anomalous concentrations of copper and cobalt occur in Kundelungu Group sedimentary strata juxtaposed next to copper-bearing extrusive volcanic rocks.