Kyidinskii

This intrusion is emplaced in sedimentary rocks of Permian age. There were two periods of intrusion the first involving syenites, which were affected by a folding episode, and the second essexites which cut the syenites and folded structures. The main minerals of the syenites are K-feldspar (50-70%), plagioclase (10-30%), quartz (0-15%), alkali pyroxene and amphibole (2-10%) with accessory nepheline, magnetite, apatite, titanite, zircon, orthite, fluorite, eudialyte and riebeckite. The riebeckite occurs in leucocratic facies of the quartz syenites. In the syenites in which eudialyte occurs it is an interstitional phase. The main minerals of the essexites are plagioclase (50-60%), pyroxene (20-30%), K-feldspar (10-25%) and olivine (0-7%); among the accessories are nepheline, apatite, magnetite, pyrite, titanite and zircon. As well as Kyidinskii, there are two other intrusions along the upper reaches of the River Dikara-Bigay (right tributary of the Upper Taimyra River) which have the same composition and structure.