The Bukavu volcanic field lies to the south and southwest of Lake Kivu and extends for some 80 km from north to south. The somewhat smaller Kamituga volcanic field lies further to the south-southeast. The Bukavu field comprises three cycles the first of which is tholeiitic and the second alkaline while the rocks of the third cycle are generally silica undersaturated but less alkaline than the second (Kanika et al., 1981; Kampunzu et al., 1983). Lavas are predominant but there are pyroclastic rocks, forming cones, and the most evolved rocks form lava domes. The rock types of the alkaline series are olivine basalt, ankaratrite, basanite, hawaiite, mugearite, benmoreite, trachyte and phonolite. The hawaiites include biotite and the mugearites a brown amphibole. The benmoreites are alkali feldspar rocks with aegirine and opaque phases and may include any combination of fayalite, amphibole and biotite. Both trachytes and phonolites comprise alkali feldspar and aegirine; the former may contain fayalite, biotite and amphibole, while the latter include nepheline, fayalite, katophorite and aenigmatite. Brief petrographic descriptions and a range of rock analyses are given by Kanika et al. (1981) and Kampunzu et al. (1983). A fuller geochemical treatment, with trace element data, including REE, is that of Auchapt et al. (1987). Although the Kamituga field consists principally of tholeiitic basalts, according to Auchapt et al. (1987) the alkaline cycle is also represented here, but petrographic descriptions have not been found.