Phosphate Deposits of the Senegal-mauritania-guinea Basin (West Africa): A review

Among the four areas of calcium phosphate mineralization in the Senegal-Mauritania-Guinea Basin, only the Taïba deposit in Senegal has been in production since 1960 by the Compagnie Sénégalaise des Phosphates de Taïba (CSPT). The N’Diendouri-Ouali Diala (Matam) deposit has been producing some phosphate as well since 2008. The other two areas, Bofal-Loubboïra in Mauritania and Saliquinhé-Farim in Guinea-Bissau, were discovered and explored three decades ago, but never put into production because of their distant location or unfavourable geological conditions. Recently, however, mining companies have become interested in their potential.The two eastern (Bofal-Loubboïra and N’Diendouri-Ouali Diala) and western (Taïba-Tobène and Saliquinhé-Farim) deposit areas are identified by specific characteristics concerning their lithostratigraphy, initial marine environment, paleogeography, types of phosphate grains in the ore, structure of the mineralization traps of phosphate grains, processes of syn-sedimentary reworking and winnowing of the grains, chemical composition of the ores, etc. The western deposits stand out because of a complex evolution of the mineralization in an environment that changed from marine to continental, and by their pedogenetic paleo-weathering in the site of their final concentration. This weathering caused a complete leaching of all calcite and enrichment in phosphate (natural pre-enrichment of the ore), and occurred during the Late Eocene to earliest Oligocene.We discuss the characteristics of these four West African phosphate deposit areas, stressing the similarities between the Taïba and Saliquinhé deposits, as well as the succession of complex geological processes, first marine and then continental, that led to their formation.