Chrysoberyl and associated beryllium minerals resulting from metamorphic overprinting of the Maršíkov–Schinderhübel III pegmatite, Czech Republic

Abstract

The Maršíkov -Schinderhübel III (Hrubý Jeseník Mountains, Silesian Domain, Czech Republic) represents a classic example of chrysoberyl-bearing LCT granitic pegmatite of beryl-columbite subtype. A thin pegmatite dyke (up to 1 m thick) in biotite-amphibole gneiss is characterised by symmetrical internal zoning. Tabular and prismatic chrysoberyl crystals (3 cm) occur typically in the intermediate albite-rich unit and rarely in the quartz core. Chrysoberyl microtextures are quite complex; their crystals are irregularly patchy, concentric or fine oscillatory zoned and large variations of Fe content (1.1−5.3 wt.% Fe2O3; ≤0.09 apfu) are characteristic as well. Chrysoberyl compositions reveal dominant Fe 3+ = Al 3+ and minor Fe 2+ + Ti 4+ = 2(Al, Fe) 3+ substitution mechanisms in the octahedral sites. Tin, Ga, and V (determined by LA-ICP-MS) belong to the most characteristic trace elements incorporated in the chrysoberyl structure, whereas anomalously high Ta and Nb concentrations (thousands ppm) in chrysoberyl are probably caused by nano-to micro-inclusions of Nb-Ta oxide minerals (especially columbite-tantalite). Textural relationships between associated minerals, distinct schistosity of the pegmatite parallel to the host gneiss foliation and fragmentation of the pegmatite body into blocks as a result of superimposed stress are clear evidence for deformation and metamorphic overprint of the pegmatite. Primary magmatic beryl, albite and muscovite were transformed to chrysoberyl, fibrolitic sillimanite, secondary quartz and muscovite during high-temperature (~600 °C) and medium-pressure (~250−500 MPa) prograde metamorphic stage under amphibolite facies conditions. A subsequent retrograde, low-temperature (~200−500 °C) and pressure (250 MPa) metamorphic stage resulted in the

The Geology and Mineral Chemistry of Beryl Mineralization, South Eastern Desert, Egypt: A Deeper Insight into Genesis and Distribution

“…The investigated tremolite associated with beryl was formed at temperatures ranging from 415 to 451 • C, suggesting its secondary origin after primary amphibole (e.g., magnesiohornblende). This tremolite was formed after type I beryl, and can possibly be associated with the formation of type II beryl at a temperature range of 400-450 • C. This is consistent with the laboratory work that has estimated beryl temperature's of 400 • C in the presence of H 2 O and more hydrous conditions [62].…”