Metamorphism, Metasomatism and Conditions of Formation of Industrial Minerals of the Sillimanite Group of the Fennoscandian Shield

Abstract

The group of sillimanite minerals includes kyanite, sillimanite and andalusite, modifications. It is shown that high-alumina complexes are widespread throughout the Fennoscandian Shield, but the sources (protoliths) are sedimentary-volcanogenic formations of the preceding stages. Three metamorphogenic types of high-alumina formations have been identified: the Keivian (Archean), the Svekofennian (Paleoproterozoic) and the Southwestern Gneissian (Mesoproterozoic). The connection with tectono-metamorphic cycles has been established. The Keivian metamorphogenic type is characterised by the formation of high-alumina complexes under conditions of high pressures and average temperatures of amphibolite and less frequently granulite facies of metamorphism. The main industrial mineral is kyanite. The second metamorphogenic type (Svecofennian) is associated with the Svecofennian Province. The manifested metamorphism corresponds to a metamorphic series of low and medium pressures and medium and high temperatures. The main industrial mineral is andalusite. Two areas are distinguished: southeastern and northwestern. The third metamorphogenic type (Southwestern Gneissian) characterised by a wider range of PT conditions of metamorphism, which is reflected in the formation of industrial minerals of the sillimanite group (sillimanite and kyanite). Polycyclic metasomatosis of the acid-leaching stage plays the main role in the formation of deposits of the sillimanite group of minerals.