Manganese deposits of the Oudalan province in the northeast of Burkina Faso, and Ansongo Inlier in eastern Mali

• We present exploration data for several manganese deposits in West Africa.
• We report on the geological and metallogenic context of the deposits.
• We report on the deposit styles and mineral composition.
• We present information about manganese in the Ansongo Inlier.

At least 15 manganese deposits crop out in the West African craton in Mali, Burkina Faso, Ghana and Cote d'Ivoire. There average grade estimates range from 17 to 52% total Mn oxide and average volume of 5–19 Mt of ore; they consequently provide an attractive target for exploration and eventual exploitation. The Tambão and Béliata Mn oxide deposits in the Oudalan province (northeast of Burkina Faso), and Takavasita, Agualla and Tondibi Mn oxide deposits in the Ansongo Inlier (eastern Mali) generally crop out as a saprolitic residuum that formed during the Miocene to Eocene and are enriched in manganese to 52% total Mn oxide. The saprolitic residuum is overlain by blocky to botryoidal manganese-rich duricrusts that form part of the resource portfolio. The residuum overlies deeply weathered manganese-bearing carbonates, shales and volcaniclastic siltstones of the Birimian Supergroup (2.3–2.1 Ga) that form a low-grade resource and likely formed in a heat-driven seawater convection system that provided hydrothermal solutions from submarine volcanic centers. They are typically intercalated with mafic-intermediate volcanic rocks.