Burovskii

The Burovskii occurrence is located in a contact zone of Cambrian rocks, including limestone, with Lower Devonian volcanics. In plan the intrusion is oval in shape and occupies an area of about 70 km2. It is composed of coarse-grained, often trachytic peralkaline syenites, which contain 85-90% perthitic alkali feldspar as well as aegirine-augite, and rarely aegirine. Quartz-bearing peralkaline syenites are also present. Nepheline syenite forms a number of small bodies among the peralkaline syenites. They are porphyritic with alkali feldspar phenocrysts up to 5-6 cm in diameter. The nepheline syenites also contain 10-25% nepheline, in some varieties 4-8% sodalite and 6-8% mafic minerals including aegirine-augite, amphibole and biotite. The nepheline syenites are albitized, with the formation in some places of albitite. The last intrusions are aphyric and porphyritic basalt dykes and syenite porphyry veins.