The Birimian rocks are major sources of gold and diamonds that extend through Ghana, Côte d'Ivoire, Guinea, Mali and Burkina Faso. They are named after the Birim River, one of the main tributaries of the Pra River in Ghana and the country's most important diamond-producing area. Ghana and Mali are the second and third largest producers of gold in Africa, respectively.The Birimian terranes in the south part of the West African craton are a mix of metamorphosed volcanic, sedimentary and plutonic rocks and low grade metavolcanics and metasediments. Almost half of the terranes consist of alkaline granites. The rocks formed over a period of about 50 million years between 2.200 Ga and 2.100 Ga years ago.