Phenakite and bertrandite: products of post-magmatic alteration of beryl in granitic pegmatites (Tatric Superunit, Western Carpathians, Slovakia). (18th October 2022)

• Record Type: Journal Article
• Authors: Uher, Pavel; Ozdín, Daniel; Bačík, Peter; Števko, Martin; Ondrejka, Martin; Rybnikova, Olena; Chládek, Štěpán; Fridrichová, Jana; Pršek, Jaroslav; Puškelová, Ľubica
• Is Part Of: Mineralogical magazine. Volume 86:Number 5(2022)
• Page Start: 715
• Page End: 729
• Publication Date: 2022-10-18
• Subjects: phenakite -- bertrandite -- beryl -- granitic pegmatite -- hydrothermal alteration -- Western Carpathians; Mineralogy -- Periodicals; Mineralogy -- Great Britain -- Periodicals; 549.05
• DOI: 10.1180/mgm.2022.99
• Languages: English
• ISSNs: 0026-461X

Abstract

Abstract: The beryllium silicate minerals phenakite and bertrandite have been identified in granitic pegmatite dykes of the beryl-columbite subtype of Variscan age (~340−355 Ma), associated with S- to I-type granitic rocks of the Tatric Superunit, Western Carpathians (Slovakia). The two beryllium silicates and associated minerals were characterised by electron microprobe analysis, back-scattered electron petrography and cathodoluminescence imagery, X-ray diffraction and micro-Raman techniques. Phenakite and bertrandite form euhedral-to-anhedral crystals and aggregates in irregular domains and veinlets replacing primary magmatic beryl. A detailed textural study revealed a close genetic association of phenakite and bertrandite with secondary fine-grained quartz, K-feldspar and muscovite. Locally, clay phyllosilicate minerals, (with compositions similar to those of Fe-dominant hydrobiotite, beidellite, nontronite and saponite) occur as the youngest minerals. During the post-magmatic (hydrothermal) stage of the pegmatites, infiltration of aqueous K-bearing fluids at T ≈ 200–400°C resulted in the breakdown of magmatic beryl to secondary assemblages containing phenakite and bertrandite.