lic, and relatively homogeneous dykes at Red Cross Lake, Manitoba. ... Lastovièky and Red Cross Lake dykes, (Fe, Mn)-bearing elbaite is the last at Roziiá and ...
Eur. J. Mineral. 1999,11,569-584 This paper was presented at the Tourmaline 97 meeting (Czech Republic)
Compositional evolution of tourmaline in lepidolite-subtype pegmatites JULIE B. SELWAY 1 , MILAN NOVAK 2 , PETR CERNY and FkANK C. HAWTHORNE Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2 1 e-mail: umselway @cc.umanitoba.ca 2 permanent address: Department of Mineralogy and Petrography, Moravian Museum, Zelny trh 6, CZ-659 37 Brno, Czech Republic
Abstract: Tourmaline from six pegmatites of the lepidolite-subtype was examined to determine compositional trends: symmetrically zoned La&oviàky, Dobrá Voda, Rozná, Dolni Bory and Radkovice dykes, Czech Repub lic, and relatively homogeneous dykes at Red Cross Lake, Manitoba. The five symmetrically zoned lepidolitesubtype pegmatites contain the following zones from the outermost zone inward: (1) granitic zone, (2) graphic zone, (3) blocky K-feldspar zone, (4) albite zone, (5) lepidolite zone, (6) quartz core and (7) rare-to-absent small pockets. The crystallization sequence of tourmaline was determined from the characteristic composition of tourmaline for each pegmatite zone and from the compositional zoning within individual crystals. In granitic and outer albite zones, black tourmaline ranges from foitite-schorl to schorl-foitite, and is associated with minor biotite close to the contact with the host rocks, and with abundant Fe-bearing muscovite. In the albite zones, dark blue and green elbaite-schorl is associated with pale greenish yellow Na-bearing muscovite. In the lepidolite zones, pink elbaite-rossmanite to rossmanite-elbaite occurs with purple lepidolite and minor pink and green lepidolite. Green (Fe, Mn)-bearing elbaite occurs in the quartz core at Rozná and is associated with cookeite in late pockets at Dobrá Voda and Dolni Bory. Late hydrothermal foitite occurs as terminations on zoned tourmaline crystals in pockets at Dobrá Voda. Based on paragenesis and textural relations, rossmaniteelbaite is the last tourmaline composition to crystallize in the Radkovice, elbaite-rossmanite is the last at Lastovièky and Red Cross Lake dykes, (Fe, Mn)-bearing elbaite is the last at Roziiá and Dolni Bory, and foitite is the last at Dobrá Voda. Lepidolite-subtype pegmatites contain foitite as the most primitive composition in the outermost pegmatite zones, and rossmanite or (Fe, Mn)-bearing elbaite as the most fractionated composi tions in the innermost pegmatite zones. In contrast, elbaite-subtype pegmatites in the literature contain Mg-rich schorl and either elbaite or rarely lidicoatite, respectively. Typically, tourmaline from lepidolite-subtype peg matites is Ca- and Mn-poor (
