Lolekek

This plug comprises a central intrusion of carbonatite 400 m in diameter surrounded by an 800 m wide collar of ijolitic rocks. The carbonatite forms Lolekek Hill but the surrounding ijolites are only discontinuously exposed away from the hill. The carbonatite is a banded rock, the bands being parallel to cliffs that are developed around the hill. It is composed principally of calcite, with some dolomitic patches, apatite and a little biotite, but zircon, pyrite, pyrochlore, baddeleyite, magnetite and tremolite have been identified in acid isoluble fractions. The silicate rocks (Trendall, 1962) include ijolite, olivine melteigite and nepheline syenite. The ijolites are heterogeneous nepheline-pyroxene rocks in which the latter mineral is generally pale green but may be zoned to deep green aegirine rims; titanite is abundant and biotite and an opaque phase sometimes occur. On the western side of the hill is found a small exposure of a pyroxene-rich rock containing olivine which is much corroded and replaced by biotite; the only felsic mineral is natrolite. The nepheline syenites may contain euhedral nepheline and aegirine crystals in a mosaic of orthoclase, or large orthoclase plates that include numerous pyroxene and nepheline inclusions. Late veins of orthoclase rock cut the ijolites. There are a number of hills on the plains around Lolekek consisting of phonolite, nephelinite, olivine melanephelinite and agglomerate that may be remnants of a cone that was fed through the Lolekek vent (Trendall, 1965b). However, the rocks of some of these hills could be intrusive, the field relationships generally being obscure. An extensive area of phonolitic lavas and agglomerates three kilometres south and southeast of Lolekek may be part of an original cone, or could derive from the Kadam volcano (No. 22) to the east. Trendall (1962), however, considers that they probably originated at Lolekek.