Iron-titanium rich grains occurring along the coastline of Senegal - Characterization and a study of their origins

Iron-titanium rich grains ('ilmenites' to a various degree of weathering) o ccuring along the coast line of Senegal and deriving from various parent un its are characterized from their size, texture, magnetic and geochemical pr operties. Both the corresponding data and their multivariate analysis lead to the conclusion that the 'ilmenite' grains derive from various sources, m ainly local ones, except in the area of Saint-Louis where occur more distal grains from Mauritania. In the North of Cap Vert and in the South of Gambi a, the 'Continental Terminal' formation represents the main source of the ' ilmenite' grains. Along the 'Petite Cote', 'ilmenites' derive mainly from t he Maastrichtian formations of the 'Massif de Ndiass'. Volcanic formation o f the Cap Vert area does not represent a major source, except in the area o f the extremity of the peninsula. The old ferricretes do not significantly contribute to the recent accumulation. The 'ilmenites' concentration along the beach line is controlled by the different sedimentary cycles; the nouak chottian transgression beeing probably the most important event. In the Sen egalese basin, a significant amount of the 'ilmenites' originated from the 'Continental Terminal' formation appears to derive from basic metamorphic r ocks of the Mauritanide orogen. In the northern part of the basin,'ilmenite ' assemblage contains grains suggesting intermediate to acidic magmatic par ental rocks. The calc-alkaline igneous complex from the structural units em placed in the late Paleozoic on the NW margin of the Mauritanide orogen, an d the Reguibat uplift, are two possible sources. The 'ilmenite' association found in the Maastrichtian formation probably derives from various paleozo ic formations but its primary origin can not be deciphered. (C) 1999 Elsevi er Science Limited. All rights reserved.