Ingili

The Ingili complex has an area of about 30 km2 and is located within a dome-like structure in Archaean basement. It has a concentric form with the 3 kilometre diameter nucleus of the complex formed of schorlomite ijolite and melteigite with bands of urtite; these rocks have a taxitic structure. In the central part the ijolites and melteigites have a coarse-grained and giant-grained texture in which crystals of pyroxene and melanite may reach 10-20 cm, and sometimes 50 cm, across. Amongst the ijolites and melteigites are small xenoliths of pyroxenite which are greatly corroded by nepheline and have gradual transitions to nepheline-pyroxene rocks. The nucleus of the complex is surrounded by a ring 2-3 km wide of rocks of widely diverse compositions. They include leucocratic nepheline gabbro, theralite, nepheline syenites including albite, cancrinite, aegirine, biotite and amphibole varieties, nepheline pyroxenites, nepheline-amphibole rocks and carbonatites. Very intensive alkaline and carbonate metasomatism has affected the rocks of this zone and has given them a homogeneous character. The sequence of development of the rocks of the ring zone is as follows: (1) emplacement of the stock of ijolite-melteigites which resulted in the formation of metasomatic "theralites" (fenites) which were generated at the expense of basement gneisses. (2) Intrusion of carbonatites of the first generation, which are mainly located in the theralites. (3) Intrusion of numerous veins and small bodies of nepheline-cancrinite and albite-cancrinite syenites, tinguaite and ijolite porphyry. (4) Emplacement of carbonatites of the second generation, which are calcitic and dolomitic in composition.