Chiperone and Derre are the highest peaks in a group of mountains and hills of nepheline syenite and syenite. Smaller hills include Pandibue, Muembili, Conguene (Congene), Missouge, Missecue, Langoma and Mongoe. The complex consists of several curving intrusions, which extend over about 30 km in a northwest-southeasterly direction, intruded into Precambrian migmatites, gneisses and granulites. The central parts of the more substantial parts of the complex tend to be of nepheline syenite around which is syenite grading into quartz syenite. Some rocks have a gneiss-like fabric. The nepheline syenites consist of perthite, microcline, albite, nepheline, which may be partly replaced by cancrinite, biotite and accessory zircon, titanite, magnetite, pyrochlore and calcite (Coelho, 1959a; Cilek, 1989). Little information is available on the syenites but Cilek (1989), quoting Russian work on the Conguene part of the complex, refers to biotite-hornblende and biotite-pyroxene-hornblende syenites with up to 5% quartz.