Kaichinskii

Kaichinskii is situated on the northern slope of the Kok-Shaalsk Mountain ridge (Tyan-Shan) and a huge fracture zone. It cuts through upper Silurian schists, sandstones and limestones which form a large anticlinorium. Pyroxene and cordierite-biotite are developed in sandstones and schists adjacent to the steep contacts and limestones are altered to wollastonite skarns. The 20 km2 intrusion has an oval form with the longer axis trending northeastwards parallel to the strike of the folding of the country rocks. It comprises four intrusive phases: (1) melteigite and ijolite, (2) coarse-grained aegirine-augite syenites, which are the major phase, (3) trachytic and giant-grained peralkaline syenites and (4) tourmaline-bearing granites. There are dykes of alkaline and nepheline syenites, pegmatites and carbonatites. The melteigite and ijolite occur in the western part of the intrusion as xenoliths up to 60x20 m in aegirine-augite syenites. They are also found in the marginal parts of the intrusion as small veins and sills and among the contact altered sandstones and schists. The aegirine-augite syenites occupy 80% of the intrusion and are traversed by the trachytic and giant-grained alkaline syenites. Alkaline and nepheline syenite pegmatites are concentrated in the outer parts of the intrusion and form dykes up to 10 m thick and 2 km long. Carbonatites in the western section of the complex form veins and dykes with a width up to 0.8 km.