Utren

The 40 km2 Utren intrusion is located in the core of a syncline (Perchuk, 1964) in lower Silurian schists and sandstones. The intrusion is divided into northern and southern sectors by xenoliths of schist up to 300 m across. The margins of the intrusion consist of quartz syenite, which also veins the country rocks, and this merges into trachytic nepheline syenites in the central parts. Biotite-, amphibole- and pyroxene-bearing varieties of nepheline syenite can be distinguished as can sodalite and cancrinite types. The intrusion is cut by biotite granite dykes which often contain tourmaline.