The recently discovered phosphate deposits in the northern part of the Volta basin and in the far western unit of the adjacent Dahomeyides chain are localized in the lower part of the Pendjari group of probable late Precambrian age. The deposits overlie the classic triad of West Africa including, from bottom to top, tillite, dolomitic limestone containing barite, and bedded chert, in part of volcanic origin, containing thin lenticular intercalations which are manganese rich. The most important of those deposits have reserves of about 100,000,000 metric tons.The phosphate deposits are located at the boundary between the West African craton to the northwest and the Pan-African (Cadomian) Dahomeyides orogenic belt to the southeast. The largest deposits are situated where the erosion surface beneath the Pendjari Group cuts down sharply through the underlying sequence of detrital rocks and eventually into the basement.The late Precambrian phosphate deposits of the northern Volta basin have many similarities with those of Upper Sinian and Lower Cambrian age of the Chinese platform and of the southern Siberia . All these deposits are similar in age and are associated with tillites, synvolcanic siliceous rocks, and manganiferous beds.