Abstract

Algal structures such as stromatolites have long been recognized as closely associated with the cupriferous dolomitic shales of the Katanga Supergroup of Zaire and Zambia. Discovery of bioherms and biostromes in the predominantly arenaceous deposits of the Mufulira copper mine indicates a similar origin, with the more common copper deposits in dolomitic shale and their barren gaps due to bioherms.Renfro (1974) recognized the worldwide association of sabkhas, algal mats, and stratiform copper deposits. His interpretation of sabkha environments in cyclic depositional sequences at Mufulira is corroborated by detailed features in the mine.Recognition of abundant carbonized debris of algal mat, from 0.5 m down to microscopic size, in the marine sediments of Mufulira indicates an accumulation of decomposing vegetable debris that is more than sufficient to promote anoxic conditions in the bottom waters of the lagoons, with resulting precipitation of copper and iron sulfides contemporaneously with sedimentation.Compaction of algal material explains the 80 percent contraction of sun-cracked mud flakes. Also compaction by roughly two-thirds of the algal-rich graywacke and the C orebody accounts for the rapid sagging of overlying sabkha and terrestrial sediments, which was followed by a second marine invasion allowing deposition of the B orebody and central graywacke. Similar rapid compaction of the latter under its cover of sabkha and red-bed sediment caused further sagging, marine invasion, and deposition of the A orebody and graywacke vertically above the C and B graywackes.Although Renfro's hypothesis of mineralization by ascending groundwaters may account for some initial precipitation of sulfides beneath algal mats, the bulk of the preserved mineralization at Mufulira exhibits features more compatible with syngenetic deposition of sulfides associated with decaying transported algal material in marine lagoons.

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