LITHIUM IN THE SUBSOIL OF UKRAINE Part 3. Mineralogy of lithium-bearing objects: feldspars

Abstract

Traditionally, feldspars are characterized in the following order: Volyn chamber pegmatites — Perzhansky ore node — kamyano-mohyla (stone grave) complex of Azov region — Kruta Balka rare-metal deposit — Shevchenkivske rare-metal deposit — rare-metal pegmatites of Inhulsky megablock. Feldspars in the chamber pegmatites of the Volyn are represented by maximum microcline-perthite, rarely by intermediate orthoclase and albite. Widely developed feldspars with close regularity, but different symmetry. The form of discharge is granular aggregates and polyhedral crystals. The outline of potassium feldspar crystals is varied. Crystals of only two morphological types have a clear arrangement: I — early high-temperature bar-like individuals, concentrated in the cavities of the graphic zone; II — columnar pseudohexagonal crystals in sinkholes. Among albite crystals, three morphological types are distinguished, depending on acidity-alkalinity and crystallization temperature. Feldspars of chamber pegmatites are well studied by radio spectroscopic, luminescent and genetic methods. Within the boundaries of the Perzhansky ore complex, multi-grained polygenic microcline-perthite dominates, the structural state of its potassium phase corresponds to a high degree of ordered distribution of Si and Al (maximum microcline). The evolution of the twin structure of potassium feldspars is briefly covered and illustrated. Pure microcline and amazonite (probably the purest on the Ukrainian Shield) were found in the perzhansky metasomatites. Feldspars are the leading minerals of the stone-burial complex of the Azov region, represented by microcline and microcline-perthite. A characteristic feature of the microcline rocks of the complex is the unique giant dendritic crystals of pink microcline. Feldspars in the Kruta Balka rare metal deposit are represented by albite, albite-oligoclase and microcline. Two feldspars — microcline and albite (in the form of perthites in microcline and independent aggregates) were diagnosed in the Shevchenkivske deposit. Microcline makes up 15-20% of the volume of pegmatites and represented by three generations. The mineralogy of feldspars in the pegmatites of the Inhulsky megablock is different. They are represented by monoclinic orthoclase, microcline and plagioclase (mostly albite, occasionally oligoclase). Their content in rocks is mostly >50%, but albite >potassium feldspar. In general, these feldspars have features uncharacteristic of rare-metal pegmatites: 1) high symmetry (monoclinic) and low order (t1 >0,7); 2) microperthite decay structure; 3) the initial and middle stages of monodomainization are manifested. These and other features of minerals are a consequence of the specific origin of pegmatites, which represent a new genetic type of deposits of rare elements — metapegmatites.