THE BINGO CARBONATITE-IJOLITE-NEPHELINE SYENITE COMPLEX, ZAIRE - GEOLOGY, PETROGRAPHY, MINERALOGY AND PETROCHEMISTRY

The Binge complex, on which little information has been published here tofore, is located in northeastern Zaire, 30 km west of the western br anch of the East African rift. Although outcrop is poor, fresh float h as enabled construction of a geological map showing that the intrusion consists of ijolites cut and net-veined by nepheline and sodalite sye nites. The ijolites include wollastonite-bearing varieties while some are feldspathic; urtile also occurs. Calcite carbonatites underlie som e 8 km(2) and fenites are present The rocks are described petrographic ally and microprobe analyses of most mineral phases, including the rar e mineral gotzenite, are given. The pyroxenes define a complete series in terms of diopside-hedenbergite-aegirine and range from sodic diops ide/hedenbergite to aegirine-augite in ijolite pyroxene cores and rims with aegirine-augite and aegirine in the nepheline syenites. The pres ence of gotzenite and eudialyte attests to the high peralkalinity of t he nepheline syenites. The analyses, including many trace elements, of igneous silicate rocks and three carbonatites are given. As is typica l for intrusions of this type, there is considerable incoherance in th e chemical data of the igneous silicate rocks, but they do give some e vidence of a continuous series from the ijolites to the nepheline syen ites, which, together with the pyroxene data, are taken to indicate a fractionation series. There is no direct evidence of a genetic relatio nship between the carbonatite and the igneous silicate rocks.