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During the last semester I had an opportunity to study thin-section samples of Li-F granites, Etyka massif located in the Eastern Transbaikalia (Fig. 1). Granites form a small intrusive body of Jurassic age which is a part of Hangilayskiy ore cluster. There are several W, Sn, Be, Ta deposits related to plutons of peraluminous (Al/(2Ca+Na+K)>1), subalkali ((Na2O+K2O)>8 wt. %) granites (Syritso et al., 2011, Zaraisky et al., 1997). Due to relatively low melt viscosity, saturation with the volatile elements (F, H2O) and enrichment in some rare elements (Li, Be, Rb, Ta, W, Nb) (Fedkin, 2000) the mineral composition and textural features of Li-F granites are particularly interesting for study.
Figure 1. The location of the Etyka granite massif, Eastern Transbaikalia.
The most part of the pluton is composed of coarse-grained microcline-albite granites (Fedkin, 2000), where microcline often has light green color (amazonite) due to the impurities of lead, divalent iron and some other elements (Seltmann et al., 1999). These granites are characterized by the presence of mica siderophyllite-polythionite and polylithionite-trilithionite series - zinnwaldite, lepidolite (vol. 10% ). Topaz is relatively common here and occurs in the amount of 5-10 vol. % , the fluorite is less abundant (vol. 1% ).
A well-known feature of the Etyka granites is a poikilitic texture formed by rounded quartz grains (2-3 mm in size) containing numerous inclusions of predominantly albite. Frequently albite is oriented concentrically inside the quartz grains. Such forms is often referred to the "snowball" textures (Fig. 2a, b).
Figure 2. a - Poikilitic quartz grains with elongated albite crystals inside. "Snowball" texture. b - the position of extinction ; XPL, 45x zoom magnification.