Kiiskii

The Kiiskii occurrence has a circular form and occupies 12 km2. The country rocks are granite gneisses and crystalline schists of Lower Proterozoic age. Four stages can be distinguished in the formation of the complex the first of which involved emplacement of urtite, ijolite, melteigite and jacupirangite in the central and northern parts of the occurrence. These rocks are characterized by highly variable compositions and textures.Ijolites are the most abundant and comprise nepheline and aegirine-diopside. During the second stage nepheline syenites were developed over most of the western part of the occurrence. They consist of nepheline, orthoclase-perthite, aegirine-diopside and hastingsite. Rocks of the third stage are leucocratic syenite porphyries which occupy the central and eastern parts of the complex. They contain orthoclase-cryptoperthite as phenocrysts up to 1 cm in diameter in a groundmass composed of orthoclase, albite, biotite and calcite. The fourth stage consists of veins of tinguaite and camptonite-monchiquite which are found throughout the intrusion, as are small bodies of trachytic porphyry. All the rocks were intensively altered and replaced by K- and Na-feldspar and carbonate. This resulted in the production of amphibole-apatite, biotite-apatite and feldspar-carbonate rocks. The central part of the massif is occupied by calcite carbonatite with dolomite, ankerite, siderite and calcite veinlets with rare earth mineralization. What stage is represented by the carbonatites has not been determined.