Elet'Ozerskii (Elet'Ozero)

A layered intrusion, with an area of about 100 km2, Elet'ozerskii cuts through Archaean granite gneisses which have been altered to skarns and melted. The complex has a concentric, zoned structure, the peripheral part being composed of a layered gabbro series; the central area is occupied by nepheline syenites. Between these two rock groups is an arcuate body of clinopyroxenites. The gabbros are intersected by dykes of dolerite, spessartite, alkaline syenite pegmatite, syenite porphyry, bostonite and carbonatite. The gabbro series is represented by plagioclase-bearing wherlites which grade upwards into orthoclase gabbros and orthoclase plagioclasites. Rhythmic layering involves alternation of leucocratic layers composed essentially of plagioclase and melanocratic layers of pyroxene, olivine and titanomagnetite. The nepheline syenites, the central area of which covers about 10 km2, also form dykes and veins which intersect the layered gabbroid series and also the accompanying dyke rocks (dolerite and spessartite). The nepheline syenites comprise nepheline, microcline and aegirine with lesser arfvedsonite, biotite, apatite, zircon, titanite, ilmenite, titanomagnetite and spessartine. The pegmatites comprise microcline, sodic plagioclase and nepheline with accessory pyrochlore, zircon, titanite, columbite, fersmite, thorite and orthite. Carbonatite constitutes the matrix of an "explosion" breccia in the northern part of the complex. It is a calcite carbonatite with biotite, titanite and rare-earth minerals.