Bambuiskii

The Bambuiskii massif consists of two bodies divided by the Bambu’ river valley. They cut Lower Cambrian dolomites and dolomite-bearing limestones, which occur as numerous roof xenoliths. Their size varies from several metres to 700 x 250 m. The eastern massif covers 6 x 1.8 km and is predominantly composed of diorites and gabbro-diorites. In the upper part of the intrusion shonkinites and essexites are developed as an elongate body over 1 km in length. Hybrid rocks with garnet (sviatonossites), comprising aegirine-diopside, garnet, microcline and basic plagioclase, occur at the contact between shonkinites, essexites and carbonate sediments. The western massif, covering 4 x 1.5 km, is composed of alkaline biotite syenites, nepheline syenites and garnet syenites. Basic rocks are not extensively in the western massif and occur only in contacts with carbonate sediments. In the contact zone the following sequence of rocks is found, from the central part of the massif towards the contact, biotite syenite – biotite diorite – biotite-pyroxene gabbro – pyroxenite. Nepheline syenite comprises microcline-perthite (23-52%). Albite (15-35%), nepheline (21-50%) and biotite (3-10%). Hastingsite, aegirine-augite and calcite may be present and accessories include apatite, titanite, magnetite, zircon and fluorite.