Record details

Title
    Niobium-tantalum oxide minerals from complex granitic pegmatites inteh Moldanubicum, Czech Republic: primary versus secondary compositional trends
Statement of responsibility
    Milan Novák, Petr Černý
Other titles
    Granitic pegmatites: The Černý - Foord volume (Variant.)
Author
    Černý, Petr
    Novák, Milan, 1952-
Language
    anglicky
Source title - serial
    Canadian mineralogist
Vol./nr.
    Vol. 36, no. 2
Pages
    p. 659-672
Year
    1998
Notes
    5 obr., 1 fot., 6 tab., 3 s. bibl.
    Francouzské resumé
    il.
    Zkr. název ser.: Canad. Mineralogist
Subject group
    chemismus minerálů
    frakcionace chemická
    hydrotermální podmínky
    mineralogie topografická
    moldanubikum
    niob
    oxidy
    pegmatit
    podmínky P-T
    skupina columbitu
    tantal
Geographical name
    Chvalovice (Prachatice)
    Česká republika
    Dobrá Voda (Třebíč)
    Laštovičky (Žďár nad Sázavou)
    Nová Ves (Český Krumlov)
Keyword
    Complex
    Compositional
    Czech
    Granitic
    Inteh
    Minerals
    Moldanubicum
    Niobium-tantalum
    Oxide
    Pegmatites
    Primary
    Republic
    Secondary
    Trends
Abstract (in english)
   Compositional trends of Nb,Ta-oxide minerals in four complex granitic pegmatites (lepidolite and petalite subtypes) in the Moldanubicum, Czech Republic, covering primary (magmatic) and secondary (hydrothermal replacement) stages of crystallization, were investigated. The primary stage is characterized by ferrocolumbite to manganocolumbite, followed after Fe- and Mn-depletion by Ca- or Sb-rich minerals: microlite (Nova Ves), rynersonite (Chvalovice) and stibiotantalite (Dobrá Voda, Laštovičky). Compositional paths in columbite are similar to those of lepidolite pegmatites; the other primary Nb, Ta-oxide minerals exhibit Ta/(Ta+Nb) values significantly higher relative to columbite. Decreasing Nb/Ta and the cation sequence Fe - Mn - (Sb,Ca) are typical of the primary stage. The secondary stage displays a broad spectrum of mainly fracture-filling secondary phases, such as diverse microlite-group minerals, cesstibtantite, manganotantalite, ferrotantalite and ferrotapiolite.
   which replace stibiotantalite, microlite and rynersonite; columbite in outer pegmatite units remains unaffected. The Ta/(Ta + Nb) values of the secondary phases are comparable to those of their precursors. The general sequence of major A-site cations in hydrothermal Nb,Ta-oxide minerals, (Sb) - Ca - Mn - Fe, is reversed relative to that of the primary stage, and it may represent a universal pattern of hydrothermal replacement of primary Nb,Ta-oxide minerals in comparable granitic pegmatites. The composition of microlite-type minerals and textural relations indicate that the secondary hydrothermal stage includes a broad range of P-T-X conditions from early subsolidus replacement at &500-350°C, -2.5 -2.0 kbar (Nová Ves, Dobrá Voda) to near-surface weathering at <100°C (Chvalovice). The likely source of the Sb, Ca, Mn and part of the Fe seems to be the fluid phase exsolved from the residual melt or the replaced primary mineral; the host rock may be a source of Fe (Chvalovice)
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    16. 4. 2008
Import date
    8. 8. 2012