MINERAL-DEPOSIT FORMATION IN PHANEROZOIC SEDIMENTARY BASINS OF NORTHEAST AFRICA - THE CONTRIBUTION OF WEATHERING

The intra- and epicontinental basins in northeast Africa (Egypt, Sudan ) bear ample evidence of weathering processes repeatedly having contri buted to the formation of mineral deposits throughout the Phanerozoic. The relict primary weathering mantle of Pan-African basement rocks co nsists of kaolinitic saprolite, laterite (in places bauxitic) and iron oxide crust. On the continent, the reaccumulation of eroded weatherin g-derived clay minerals (mainly kaolinite) occurred predominantly in f luvio-lacustrine environments, and floodplain and coastal plain deposi ts. Iron oxides, delivered from ferricretes, accumulated as oolitic ir onstones in continental and marine sediments. Elements leached from we athering profiles accumulated in continental basins forming silcrete a nd alunite or in the marine environment contributing to the formation of attapulgite/sepiolite and phosphorites. The Early Paleozoic Tawiga bauxitic laterite of northern Sudan gives a unique testimony of high l atitude lateritic weathering under global greenhouse conditions. It fo rmed in close spatial and temporal vicinity to the Late Ordovician gla ciation in north Africa. The record of weathering products is essentia lly complete for the Late Cretaceous/Early Tertiary. From the continen tal sources in the south to the marine sinks in the north, an almost c omplete line of lateritic and laterite-derived deposits of bauxitic ka olin, kaolin, iron oxides and phosphates is well documented.