Panda, Chuata And Bunga

Teale and Smith (1923) briefly describe these three plugs of phonolite and nephelinite lying east of Gorongosa (No. 114-00-028). Chuata is a phonolite plug, the rock consisting of alkali feldspar phenocrysts up to 1 cm in length and nephelines up to 3 mm with rare microphenocrysts of aegirine-augite, aggregates of katophorite and patches of aegirine in a groundmass mostly of nepheline, microlites of aegirine and some orthoclase and zeolite. Two other samples from this occurrence are characterised by an isotropic base considered to be partly sodalite; phenocrysts are alkali feldspar, nepheline, hornblende and augite set in a matrix of laths of orthoclase and minute crystals of nepheline, aegirine and aenigmatite. The rocks of Panda and Bunga Hills are described as nephelinites, the former containing phenocrysts of nepheline, and sometimes aegirine-augite, magnetite and apatite, in a groundmass of euhedral nepheline and sodic pyroxene poikilitically enclosed in alkali feldspar. Other varieties from the same locality contain abundant augite phenocrysts, some biotite and have nepheline confined to the groundmass. In one specimen described from Bunga Hill the groundmass consists of minute nepheline crystals and clouds of microlites of augite and some magnetite, but is traversed by narrow channels of alkali feldspar, while other specimens contain approximately equal amounts of feldspar and nepheline and so are more correctly named phonolite.