Petrology and gold mineralization of the amphibolite belt, Ilesha area, Southwestern Nigeria

Abstract

The Ilesha amphibolite belt is composed of metasedimentary rocks and a mafic complex comprising mostly amphibolites and amphibole schists, with intercalations of talc bodies. These assemblages occur within a polycyclic basement of largely ancient gneisses and migmatites, and underlie alluvial gold deposits. In addition, the district is characterized by minor and major structural features including folds, fractures and lineaments which commonly have a northerly strike. Auriferous quartz veins are known to be emplaced along structural elements in the amphibolite complex. It is believed that the alluvial gold deposits were derived from weathered auriferous veins and veinlets. Sulfur contents of the amphibolites and amphibole schists are relatively high, supporting the occurence of sulfides, possibly in relation to primary gold. The mafic units are magmatic and are therefore considered the ultimate source of the vein-type gold deposits. On the basis of overall geological and geochemical characteristics, it is suggested that the mineralization was linked to metamorphic-hydrothermal processes.