Ngara Hill

An east-west-trending arcuate area of aegirine gneisses and aegirine-bearing quartzo-feldspathic granulites and gneisses extends for about 6 km and is up to 1.5 km wide. It forms a series of parallel ridges on which stands the sharp peak of Ngara Hill (Bloomfield, 1965b). At Ngara Hill the gneisses are banded on scales from 2-3 cm to several 10s of metres. Various scales of banding are illustrated by Bellingham and Bromley (1973) and involve combinations of aegirine, aegirine-biotite and mafic aegirine gneiss with all the contacts sharp. Typical aegirine gneisses contain 10-20% aegirine, which in some rocks is partly replaced by a riebeckitic amphibole, about 30% microcline, a little andesine, up to 35% quartz and accesory magnetite, titanite, zircon, apatite, allanite and biotite, with the last a major phase in gneisses found near the summit of the hill; pyrochlore has also been noted. A rock analysis is given by Bloomfield (1965b).