Sedete

The Sedete intrusion is situated 25 km south of the Guli complex of which Egorov (1969) considers it to be a satellite. The alkaline rocks outcrop over an area of about 12 km2 and the intrusion is sill-like in form. It was discovered in 1959 and first described by K.M. Shichorina (Egorov, 1991) with further investigations carried out by Egorov (1969). The country rocks are Devonian limestones and early Permian sandstones. The intrusion is layered with the lowest horizon composed of olivine melanephelinite (olivine 5-20%, clinopyroxene 30-65%, titanomagnetite 5-15% and K-feldspar 5-10%) and nepheline picrites, which have a higher content of olivine (up to 30-45%). These rocks grade gradually upwards into melteigites that are composed mainly of clinopyroxene (diopside-augite) with nepheline, biotite, titanomagnetite, titanite, perovskite and olivine, minor apatite, K-feldspar, phlogopite and rare aegirine-augite. The melteigites pass upwards through medium-grained malignites enriched in K-feldspar into nepheline syenites. The nepheline-bearing alkaline syenites, which include malignite and shonkinite, have pyroxene contents up to 60-70% by volume and titanomagnetite, biotite, apatite, olivine and albite are present in minor amounts. The layering is considered to have developed in situ after the intrusion of the melteigite magma and is illustrated by Egorov (1991, Fig. 8) in a cross section.