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The paragenesis and composition of bavenite-bohseite were investigated in fifteen granitic pegmatites from the Bohemian Massif, Czech Republic. Three types distinct in their relation to primary Be precursors, mineral assemblages, morphology and origin were recognised: (1) primary hydrothermal bavenite-bohseite crystallised in miarolitic pockets from residual pegmatite fluids; and secondary bavenite-bohseite in two distinct types: (2) a proximal type restricted spatially to pseudomorphs after a primary Be mineral (beryl > phenakite, helvine-danalite); and (3) a distal type on brittle fractures and fissures of host pegmatite. The mineral assemblages are highly variable: (1) axinite-(Mn), smectite, calcite and pyrite; (2) bertrandite, milarite, secondary beryl, bazzite, K-feldspar, muscovite-illite, scolecite, gismondine-Ca, analcime, chlorite; and (3) muscovite, albite, quartz, epidote, pumpellyite-(Mg), pumpellyite-(Fe3+), titanite and chlorite. Electron microprobe analyses showed, in addition to major constituents (Si, Ca and Al), minor concentrations (in apfu) of Na (≤0.24), Fe (≤0.10), Mn (≤0.10) and F (≤0.36). The type 1 hydrothermal miarolitic bavenite-bohseite is mostly Al-rich (2.00-0.67 apfu) relative to type 2 proximal bavenite-bohseite and bohseite after beryl, phenakite and helvine-danalite (1.56-0.46, 0.70-0.05, 1.02-0.35 apfu, respectively); and type 3 distal bavenite-bohseite typically after beryl (1.63-0.09 apfu). Raman spectroscopy revealed that the distance between the OH- vibrational modes decreases with increasing bohseite component. The Al content of secondary type 2 proximal bavenite-bohseite is controlled by the composition of the Be precursor whereas type 3 distal bavenite-bohseite with beryl as the Be precursor is more variable and the composition is governed mainly by the composition of fluids. Calcium, a crucial component for bavenite-bohseite origins, was derived from residual pegmatite fluids (Vlastějovice, Vepice IV or Trebíc Plutons) or external sources (e.g. Drahonín IV, Věžná I or Marsíkov). Primary type 1 hydrothermal bavenite-bohseite from miarolitic pockets might have crystallised at T ≈ 300-400°C and P ≈ 200 MPa, whereas the secondary type 2 and 3 bavenite-bohseite formed at T ≈ 300-100°C and P ≈ 200-20 MPa.

This work presents data for the mineral assemblages, composition and Raman spectroscopy of proximal secondary Be and associated minerals in pseudomorphs after beryl from granitic pegmatites located along the contacts of major regional geological units. The pegmatites differ in their position relative to the ductile to brittle shear zones within the Rozna-Olsi. ore field (U-deposit), Czech Republic. Extensive dissolution of beryl crystals in the beryl-columbite pegmatites Drahonin IV and Vezna I situated within or close to the shear zones is evident in contrast to minor alteration of beryl in the Dolni Rozinka and Kovarova pegmatites located outside of the shear zones. Near-total replacement of beryl crystals, up to 40 cm in length, from the Drahonin IV pegmatite, located in the Olsi shear zone formed the following secondary Be minerals in order of their abundance: bavenite-bohseite > bertrandite >> milarite > hydroxylgugiaite. This assemblage is also characterised by the presence of sulfides (pyrite, galena, sphalerite) and zeolites. Such an extensive replacement process required a substantial fluid flow and is very possibly related to the pre-uranium quartz-sulfide and carbonate-sulfide mineralisation events Rozna Olsi ore field. Alteration products resulting from breakdown of beryl Vezna I pegmatite follow the sequential substages (bertrandite + ± K-feldspar ± harmotone → epididymite + K-feldspar → hydroxylgugiaite + K-feldspar) and locally show cross-cutting textures. These assemblages were generated by post-magmatic residual fluids (early assemblage bertrandite + K-feldspar) as well as fluids related to a retrograde stage of metamorphism, compositionally contrasting with the host serpentinite, and perhaps also hydrothermal processes associated with the Olsi shear zone. The pegmatites Dolni Rozinka, located outside of the shear zones, exhibit only a low degree of alteration and have differing textural and paragenetic development. Highly variable assemblages of secondary minerals after beryl are excellent mineral indicators of hydrothermal overprinting in granitic pegmatites during a variety of subsolidus processes.

Mineral assemblages of primary and secondary Be-minerals were examined in intraplutonic euxenite-type NYF pegmatites of the Třebíč Pluton, Moldanubian Zone occurring between Třebíč and Vladislav south of the Třebíč fault. Primary magmatic Be-minerals crystallized mainly in massive pegmatite (paragenetic type I) including common beryl I, helvite-danalite I, and a rare phenakite I. Rare primary hydrothermal beryl II and phenakite II occur in miarolitic pockets (paragenetic type II). Secondary hydrothermal Be-minerals replaced primary precursors or filled fractures and secondary cavities, or they are associated with \"adularía\" and quartz (paragenetic type III). They include minerals of bohseite-bavenite series, less abundant beryl III, bazzite III, helvite-danalite III, milarite-agakhanovite-(Y) III, phenakite III, and datolite-hmggamte-(Y) III. Chemical composition of the individual minerals is characterized by elevated contents of Na, Cs, Mg, Fe, Sc in beryl I and II; Na, Ca, Mg, Fe, Al in bazzite III; REE in milarite-agakhanovite-(Y) III; variations in Fe/Mn in helvite-danalite and high variation of Al in bohseite-bavenite series. Replacement reactions of primary Be-minerals are commonly complex and the sequence of crystallization of secondary Be-minerals is not defined; minerals of bohseite-bavenite series are mostly the latest. Beryl usually occurs in pegmatites with rare tourmaline, whereas helvite-danalite bearing pegmatites are tourmaline-rich. Abundant tourmaline in pegmatites with helvite-danalite and its scarcity in beryl-bearing pegmatites indicate that early tourmaline crystallization affected activity of Al in the parental medium and thus may have controlled formation of primary Be-minerals (beryl - higher Al, helvite-danalite - lower Al) which crystallized later. Secondary Be-minerals with dominant minerals of bohseite-bavenite series and milarite suggest high activity of Ca in fluids. Variations in chemical composition (Al contents) of bohseite-bavenite series were controlled by the chemical composition of the precursor. High variability of primary magmatic Be-minerals within a single pegmatite district is exceptional and it is constrained by variable activities of Si and mainly Al, divalent cations - Ca, Mn, Fe, Zn and Mg, trivalent cations - REEs, Sc, and B, S, and fO2 in the individual pegmatites.