A review of gold mineralisation in the Ashanti Belt of Ghana and its relation to the crustal evolution of the terrane

The Ashanti belt of Ghana is the key district of gold mineralisation in the Palaeoproterozoic terrane of West Africa. The area considered is covered by lithologies of the volcanic/sedimentary Birimian Supergroup (2.2-2.1 Ga) and the overlying Tarkwaian Group (<2132 Ma). Birimian and Tarkwaian rocks were jointly folded and metamorphosed under greenschist facies conditions during a single progressive deformation, the Eburnean tectono-thermal event or orogeny at about 2.1 Ga. Regional foliation and subparallel shear zones hosting mesothermal gold mineralisation developed during deformation coeval with metamorphism. Hydrothermal gold mineralisation is an integral constituent of the Palaeoproterozoic crustal evolution in Ghana. A metamorphic fluid model is preferred which involves fluid generation by devolatilisation reactions of Birimian strata at depth, during prograde metamorphisms in the course of the Eburnean orogeny.