Nedostupnyi

This is a small (8 km2) intrusion lying in a fracture zone located in the nucleus of an east-west-trending anticline composed of Silurian schists. There are two principal phases the first of which is diorite the second nepheline syenite. The latter has assimilated country rock schists. Sharp contacts between the diorite and syenite have not been observed. There is a gradual transition between nepheline syenites and alkaline syenites, the latter having been produced by assimilation of schist by the former, and between the alkaline syenites and a marginal facies, which gives the intrusion a distinct zonality. The diorites are developed in a narrow zone in the northwestern part of the intrusion and contain biotite and hornblende and large amounts of apatite and titanite. There are many veins of alkaline syenite.