N'Urganskii

This stock-like intrusion has a zonal structure and cuts Proterozoic gneisses, schists and limestones. In the peripheral areas the most abundant rock is granosyenite which is replaced inwards by peralkaline syenites; the central part consists of nepheline syenites. The peralkaline syenites consist of dominant microcline, but with orthoclase also present, aegirine-hedenbergite and minor biotite. The nepheline syenites contain microcline-perthite, nepheline, biotite, hastingside and minor aegirine-hedenbergite with accessory titanite, apatite and fluorite. Data on rock and mineral compositions are given by Kost'uk and Bazarova (1966).