The Lefa gold mine lies within the Siguiri Basin, part of the Paleoproterozoic Birimian terrain of the West African Craton. Host lithologies are typically Paleoproterozoic (2.2-2.1 Ga) volcanosedimentary greenstone belts, metamorphosed to greenschist facies (or higher) and intruded by felsic plutons. Deformation is associated with a system of NE-SW trending crustal-scale ductile shear zones, related to the Eburnean orogeny, a protracted series of orogenic events spanning 2.2-2.0 Ga. These deformation zones are considered fundamental to the development of gold mineralisation.
Localised finely-laminated white and pale yellow limestones occur towards the north of the licence. Three post-Birimian sedimentary packages occur within the Lefa area, namely:
- Neoproterozoic fluvial and shallow marine sandstones;
- Eocene paleo-valley fill loosely consolidated sandstones; and
- post Post-Eocene transported colluvium.
Intrusive lithologies within the basin consist of basic to intermediate sheet intrusives and the Maléa intrusion. Two sets of dykes are identified, corresponding to a swarm which exhibits trends of circa 105-285° and 055-235°. In addition to the dykes, the basin is also intruded by numerous dolerite sills ranging from a few metres to tens of metres in thickness.
Mineralisation at Lefa is hosted within the “Lefa Corridor”, which lies within the Siguiri Basin. This is a zone which is some 10 km wide, underlain by an upper clay ........