Mineral assemblages and compositional variations in bavenite–bohseite from granitic pegmatites of the Bohemian Massif, Czech Republic

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