Thejannelsepan Formation forms part of the 1.30 to 1.24 Ga Areachap Group. It is a pre-tectonic calc-alkaline volcano-sedimentary unit in the 1.2 to 1.0 Ga Namaqua Sector of the Namaqua-Natal Metamorphic Province. The main rock types are amphibolites with subordinate clinopyroxene or biotite. Although some primary volcanic textures have been identified, primary features are generally poorly preserved. Minor interlayered units include felsic metavolcanic rocks, pelitic schists and calc-silicate rocks which may represent primary marls. Field and geochemical evidence suggests that thejannelsepan Formation represents metamorphosed basaltic to intermediate lavas and associated sedimentary rocks which formed in a subduction-related arc setting.