V. N. Ogorodnikov

Rare and rare-earth elements in kyanite ores of Kola peninsula and the Urals

Authors distinguish two groups of productive metamorphogenic-metasomatic rocks enriched with high-alumina minerals: stratified horizons in the stratum of plagiogneisses of early Archean and Proterozoic ages widely spread in Karelia and the Kola peninsula (Keyv formation) – aluminous (kyanite) formation of shields of the ancient platforms (metamorphic, Keyv type); unstratified metasomatic rocks that form the internal and external suture zones of the gneiss blocks, polyfacial metamorphic complexes of the andalusite-sillimanite and kyanite-sillimanite thermodynamic types, formed along the uneven-aged, typically pelitic rocks, widely manifested in the Urals – aluminous formation of folded belts (hydrothermal-metasomatic, Ural type). Comparison of the distribution of rare-earth elements in the rocks enclosing kyanite deposits of Keyv suite and Ural deposits revealed that they have the same type of directivity, but in the rocks of the Kola peninsula, the amount of rare-earth elements is higher. The reason is, apparently, a larger process of metamorphism and alkaline magmatism in the Kola peninsula in the Precambrian. A detailed study of kyanite deposits allowed to determine polygenic and polychronic properties of kyanite ores, as well as to identify three natural morphogenetic ore types: metamorphic, metamorphogenic-metasomatic and metasomatic. Comparison of the rare-earth elements shows that the metamorphogenic kyanites contain the greatest amount of rare-earth elements, and the lowest contents are characteristic for the metasomatic kyanites from quartz veins selvages and kyanite porphyroblasts of recrystallization zones. Deposit reserves of the metamorphogenic-metasomatic kyanites are low. In order to increase their economic importance the authors advise to implement the industrial development of kyanite deposits containing rare and rare-earth elements at levels that allow under certain dressing technologies to carry out their complementary profitable extraction.

The kyanite group deposits: Conditions of formation

689 Natural high alumina minerals of the kyanite group (kyanite, sillimanite, and andalusite) may be formed in different ways. Among the complex depos its, we may distinguish the formation of regional meta morphic andalusite, kyanite, and sillimanite gneiss and schist and the associated formation of aluminosil iceous metasomatic rocks controlled by acid leaching during the processes of postmigmatite metasomatism [1–5].

Polychronity and polygeneity of pegmamtites of gneissic-amphibolitic complexes as a result of continuous-discontinuous development of suture zones: Example of the Ufalei metamorphic block in the Middle Urals

In suture zones of the Urals, geological and physical-chemical conditions for formation of large ore and nonmetalliferous deposits existed during each geodynamical environment of development of the Urals. The development was predetermined by the duration and discontinuous-continuous existence of these structures, and the latter promoted the development of polygenetic and polychronic pegmatites of various types (by depth and productivity) and other postmagmatites. It has been shown in the example of the Ufalei metamorphic block that pegmatites of different ages (from R2 to P) are often spatially combined. In this paper, two age diagrams are presented: the first one is for geological events that took place in the Ufalei metamorphic block; the second one is for Vendian pegmatites in it. The value of this paper is determined by the fact that the data obtained in Ufalei block could be used for study of postmagmatites within its analogs, which are gneissic-amphibolitic complexes of the Northern Urals, and especially by the fact that the project “Polar Urals, Industrial Urals” is implemented there.