The Bingo carbonatite-ijolite-nepheline syenite complex, Zaire: geology, petrography, mineralogy and petrochemistry

Abstract

The Bingo complex, on which little information has been published heretofore, is located in northeastern Zaire, 30 km west of the western branch of the East African rift. Although outcrop is poor, fresh float has enabled construction of a geological map showing that the intrusion consists of ijolites cut and net-veined by nepheline and sodalite syenites. The ijolites include wollastonite-bearing varieties while some feldspathic; urtite also occurs. Calcite carbonatites underline some 8 km 2 and fenites are present. The rocks are described petrographically and microprobe analyses of most mineral phases, including the rare mineral götzenite, are given. The pyroxenes define a complete series in terms of diopside-hedenbergite-aegirine and range from sodic diopside/hedenbergite to aegirine-augite in ijolite pyroxene cores and rims with aegirine-augite and aegirine in the nepheline syenites. The presence of götzenite and eudialyte attests to the high peralkalinity of the nepheline syenites. The analyses, including many trace elements, of igneous silicate rocks and three carbonatites are given. As is typical for intrusions of this type, there is considerable incoherance in the chemical data of the igneous silicate rocks, but they do give some evidence of a continuous series from the ijolites to the nepheline syenites, which, together with the pyroxene data, are taken to indicate a fractionation series. There is no direct evidence of a genetic relationship between the carbonatite and the igneous silicate rocks.