Lying on the right bank of the central section of the Sokh River the Sokhskii intrusion is over 100 km2 in area. It forms an ethmolith (lopolith) with steep (70-80°) contacts which is located in the nucleus of an anticline of Silurian limestones which is overturned to the south. The form of the intrusion is well constrained by the geometry of lineations within it. The complex consists of (1) nepheline- and garnet-bearing trachytic textured syenites, (2) garnet-bearing trachytic syenites free of nepheline and (3) monzonites. The first two groups have many features in common and comprise the larger part of the massif whereas the monzonites either form bodies adjacent to the margins or form xenolith-like masses within the complex. There are gradations between all the rock types. The rock-forming minerals of the alkaline rocks are nepheline, microcline, plagioclase (andesine-labradorite), hornblende, biotite and garnet (grossular-andradite) with accessory zircon, apatite, fluorite, titanite and magnetite. The monzonites consist of diopside, hornblende, plagioclase and microcline with a mixture of analcime and muscovite. There are syenite and garnet-bearing nepheline syenite dykes. At the contacts the country rocks are phlogopitized and altered to marbles and skarns.