Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Petr Černý, Fryer, Ron Chapman

Apatite from granitic pegmatite exocontacts in Moldanubian serpentinites

Journal of the Czech Geological Society, volume 46 (2001), issue 1-2, 15 - 20

Geochemical features of apatite from three contact assemblages of granitic pegmatites intersecting serpentinized peridotites were examined to test their dependence on the character of the pegmatites, which are considerably modified by reaction with the ultrabasic host rocks. The cation content of all three apatit? samples does not deviate from the usual Ca-rich composition with only negligible Fe, Mn, Mg, Na and traces of Si, U, Th and Pb. However, the REE and Y contents are quite variable among the three occurrences. In the oligoclase+phlogopite assemblage of the footwall contact of the Věžná I pegmatite, the Fap₈₁OHap¹⁸Clap₁ apatite contains minor Y, REE, Fe and Mn, conforming to the presence of Y- and REE-bearing minerals in the parent beryl-columbite-subtype pegmatite body. In the phlogopite rimming simple plagioclasite veinlets at Věchnov, the REE-poor, HREE- and Y-depleted OHap₅₉Clap₂₈Fap₁₃ with Fe>Mn and slightly elevated Sr reflects the geochemically primitive signature of the pegmatites, mobilized from adjacent gneissic lithologies. At Heřmanov, the HREE-depleted Fap₈₁OHap₁₇Clap₂ associated with phlogopite and minor actinolite is slightly Sr- and Ba-enriched but otherwise rather close to the composition of the Věžná I apatite. This and other evidence suggests that the adjacent quartzo-feldspathic rock may represent a primitive rare-element pegmatite rather than a migmatitic mobilizate.