Bogdo

The Bogdo complex has a diameter of about 2.5 km. The country rocks are Proterozoic to lower Cambrian dolomites and lower Jurassic sandstones and argillites. The complex consists principally of nepheline syenite and juvite. The latter forms several stock-like bodies which are composed of nepheline and K-feldspar with lesser amounts of aegirine, schorlomite, apatite, biotite, titanite and titanomagnetite. The northern part of the complex is composed principally of nepheline syenites the main rock-forming minerals of which are nepheline, K-feldspar and aegirine with subordinate titanite, apatite and sodalite. In the central part of the intrusion there is a ring zone 300 to 400 m wide of xenoliths consisting of fenites and marbles. To the south of the intrusion there is an isolated dyke up to 250 m wide of malignite and melteigite around which is a broad aureole of marbles.