Rumphi And Mphompha (North Vipya)

Rumphi is a large igneous complex of approximately 60x15 km which includes granite, syenite, diorite and nepheline syenite (Hopkins, 1973; Kemp, 1975), of which the nepheline syenites form a discrete body known as Mphompha, which is the North Vipya intrusion of Bloomfield (1965b). Hopkins (1973), who described the southern half of the Rumphi complex, indicates that a riebeckitic amphibole is present in the quartz syenites and granites, whereas for the northern half Kemp (1975) describes the syenites as comprising microcline perthite, a little oligoclase/albite, aegirine and aegirine-augite and a number of amphiboles including arfvedsonite and riebeckite. These alkaline minerals are apparently not present in the quartz syenites and granites. The outer contacts of the Mphompha intrusion appear not to be exposed but it seems probable that Mphompha was intruded into the surrounding granites and syenites. Mphompha is oval in outline with two smaller, circular bodies lying within syenites some 1.5 km north of the main intrusion. The nepheline syenite is a coarse rock of microcline perthite, a little oligoclase/albite, up to 40% nepheline, a calcic amphibole, and minor aegirine-augite, which may be present as cores to the amphibole, and biotite; sodalite occurs in some rocks. There are small areas of more mafic rocks which are described by Kemp (1975) as malignite and ijolite. The latter rock consists of pyroxene and amphibole prisms and smaller irregular grains of the same minerals set in masses of optically continuous nepheline. Seven analyses of nepheline-bearing rocks are in Kemp (1975).