Abstract

Stratiform copper and lead mineralization occurs in detrital sediments at the base of the Cretaceous at several locations in Africa: Merija (Cu-Pb) and Bou-Sellam (Pb-Zn) in Morocco, Cachoeiras (Cu) in Angola, Kroussou (Pb) in Gabon, and Ain-Sefra (Cu) in Algeria.From the author's observations in Morocco, Angola, and Gabon, it appears that:(1) On a regional scale, the mineral concentrations are distributed at the edge of a continent which was being eroded during Lower Cretaceous time. They are hosted by conglomerates, sandstones, and siltstones deposited in laguno-deltaic conditions at the boundary between the continent and sedimentary basins.(2) On a local scale, the discontinuous, stratiform mineral occurrences are mainly controlled by paleochannels of highly variable size and by the nature of the sediments.(3) In detail, the mineralization is associated with carbonate cement and surrounds the detrital grains. It commonly follows the normal bedding or cross-bedding. It may also be found as "clouds" or, less commonly (Bou Sellam in Morocco), in special forms resembling arrowheads.The author believes that the copper and lead were derived from the continent and transported from it along with the detrital material of the host rocks. These metals would have been deposited as sulfides during the formation of the cement in the host rocks. The role of imbibition waters during the diagenesis and compaction of the sediments is mentioned. The mineralization would be diagenetic. After the consolidation of the host rocks the metals underwent weak epigenetic remobilization, associated with tectonic movements.

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