Coppper orebodies in the basal lower Roan meta-sediments of the Chingola open pit area Zambian Copperbelt

Abstract

Lenticular copper concentrations in basal atenaceous and rudaceous members of the Katanga System occur in basins in Basement gneiss and schist in an area of rugged palaeotopography at the Chingola Open Pit sector of Nchanga Mine on the Zambían Copperbelt. The gneisses and schists, as well as the unconformably overlying Katanga meta-sediments with their stratiform orebodies, have been folded into-overturned to recumbent structures .in which the westerly to northwesterly trend of anticlinal and synclinal axes is closely controlled by the old ridges and valleys, respectively. The overfolding is in turn the result of the incompetent behavior of the gneisses and schists which rode over the rigid buttress formed by the massive Nchanga Granite during orogenesis. Secondary redistribution of copper is believed to have taken place during the folding at one of the orebodies, which is located in the most intensely deformed area. Otherwise the present copper concentrations are still in their original stratigraphic positions. The close spatial relationship between the palaeoridges, the meta-sediments and the associated copper concentrations, suggests a common origin of both sediment and copper from the old ridges. Pre-existing copper lodes in the Basement gneiss and schist are invoked as the source of the copper, which was reconcentrated, either by detrital or chemical means or a combination of these processes, into the sediments at no great distance from the original lodes some of which are still preserved directly under the cupriferous sediments.