Dalbykha

Dalbykha is a complex intrusive body having a zonal ring structure. It occupies an area of about 3 km2 (Butakova and Egorov, 1962; Bagdasarov and Danilin, 1982). The central stock of the complex (0.3x0.5 km) is composed of melteigite having clinopyroxene as the principal mineral (augite and titanaugite) and with nepheline, biotite, titanomagnetite, titanite and perovskite as well as minor olivine, aegirine-augite, apatite, phlogopite and K-feldspar. Ijolite forms a broad ring around the central stock and consists of nepheline (55-65%), clinopyroxene (25-40%) and titanomagnetite, biotite, phlogopite, melanite, perovskite, titanite and apatite as minor constituents. Later nelsonite and phoscorite containing apatite, magnetite, tetraferriphlogopite and pyrochlore were formed and occur as veins in the older rocks and xenoliths in the younger ones. Younger still are coarse-grained biotite and biotite-pyroxene-calcite carbonatites which form an incomplete outer ring to the complex. These carbonatites are cut by finer grained calcite carbonatites containing tetraferriphlogopite and richterite. A francolite-rich weathered crust extends over Dalbykha and there are numerous radial dykes around it. The dykes comprise phonolite, nephelinite, alnoite, monchiquite and melilite nephelinite.