Geologically, Guinea is covered by a crust of a very large Archaean West African craton with its northern and western regions having formations of younger Proterozoic rocks and its eastern region consists green stone belts under the Birimian Supergroup which account for a major portion of West Africa’s gold and iron ore reserves. Weathering of tertiary sediments has resulted in laterisiation leading to the formation of very large bauxite deposits.
The geological formation of Guinean-Liberian belt is Precambrian and paleozolic rocks. Large Bauxite laterite deposits in the Silurian shale and Ordovician sandstone have been sourced in the tertiary of the dolerites; these are discovered in the Fouta Djalan mountain. In the northeastern part of the country the Birrimian gold has been located. In the crystalline area of the north and south east of the country the prime mineral is iron ore which has itabirites.