AUTHORS: Stuart Bull, David Selley, Murray Hitzman, Jaques Cailteux, David Broughton
ABSTRACT: Sequence and chemo-stratigraphic correlation of the Roan Group between the Zambian and Congolese parts of the central African Copperbelt indicates that the former represents the basin fringe and the latter a more basinward setting. In Zambia, where the condensed host succession is autocthonous around a series of basement inliers, the entire section is preserved and comprises four sequences beneath a major transgressive surface at the base the Mwashia Subgroup that marks the base of sequence 5. In this framework, the classical stratiform ores formed around the position of a major redox boundary at the base of sequence 1 (the Ore Shale). Sequence 1 was generated in response to rift climax, and is enveloped by underlying permeable syn-rift clastics, and an overlying succession of post rift carbonate and evaporites (sequences 2, 3 and 4) that formed longlived top seal that trapped circulating basinal brines. In the DRC, the Roan Group is ubiquitously dismembered and occurs as mega clasts within anticlinal cores and locally thrust sheets. In our model, this disruption represents mobilisation and dissolution of a major salt unit that formed between sequences 1 and 2 in this more basinward setting. The similarity of the mega clasts of Mines Series that form the Congolese ore bodies across the 300 km strike length of the belt, indicate that as in Zambia, the ores formed as stratiform sheets.
KEYWORDS: Stratiform sediment-hosted Cu, Copperbelt, Zambia, Congo
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