LITHIUM IN THE SUBSOIL OF UKRAINE Part 4. Mineralogy of lithium-bearing objects: micas

Abstract

Part 4 of the publication "Lithium in the subsoil of Ukraine" provides a description, mostly typomorphic, of layered silicates of lithium-bearing objects — muscovite, micas of the isomorphic series of annite — trilithionite (formerly known as annite (lepidomelane) — protolithionite — zinnwaldite — cryophyllite — lepidolite), and micas from the biotite group. The mineralogy of mica are characterized in the following order: Volyn chamber pegmatites — Perzhansky ore node — Kamyanomohyla (stone grave) complex of Azov region — rare metal pegmatites of the Azov region and the Inhul megablock. Muscovite is a secondary low-temperature mineral of the chamber pegmatites of Volyn which grew after the crystallization of micas from the isomorphic series of annite-trilithionite. It is represented by the polytypes 2M1 and 3T. Muscovite is common mica in the Perga ore district; in greisens and some metasomatites, it is the main mineral. It contains an elevated amount of iron and belongs to the 1M polytype modification: muscovite (Fe)-1M. Muscovite is also found in the Kamyanomohylskyi complex of the Azov region, primarily in altered granites and greisens formed on them. Its characteristic feature is the elevated iron content and the 2M1 structure. Fuchsite, fibrous muscovite and sericite-1Md are also found here. Muscovite in rare-metal pegmatites is mostly a secondary mineral. Rare pink muscovite, fuchsite and lithium muscovite have been found in the Azov pegmatites. Muscovite is present in relatively small amounts in the Shevchenkivske deposit and is represented by two generations. Muscovite (Li, Fe)-1M is rarely found. The X-ray luminescent properties of muscovite from spodumene pegmatites are of great importance as they are the main typomorphic features of the development of the pegmatitic process. Muscovite is rarely found in petalite pegmatites of the Inhul megablock and is represented by two generations. Its constitution is not fully understood and is controversial. Li-Fe мicas in granites and pegmatites of Volyn are important type-minerals indicating the crystallization of granites and pegmatites from magma with high content of rare elements and volatile components, the degree of differentiation of chamber pegmatites, and the extent of post-magmatic processes. The distribution of octahedral cations in the crystal structure of micas also has typomorphic significance, reflecting the activity of volatile components, the rate of crystallization, and the degree of differentiation of chamber pegmatites. The processes of forming fully differentiated pegmatites are accompanied by a polytypic transformation: 1M → 3T → 1M. Lithium-iron micas in greisens and metasomatites have similar but somewhat different typomorphic significance of the Perzhansky ore district (in which the polytype 2O was discovered) as well as in the Kamyanomohylskyi complex of the Azov region. The article concludes with a discussion of the results of research on rare alkalies in iron-magnesium micas from various types of metasomatic rocks surrounding pegmatites in Polohivske and Stankuvatsko-Lypnyazhske ore fields.