Abstract

Mn-rich tourmaline (up to 8.89 wt% MnO) and fluorapatite (up to 9.15 wt% MnO) occur in an elbaite-subtype pegmatite from the Drosendorf Complex (near Eibenstein an der Thaya, Bohemian massif, Austria). Based on geological and radiometrical data (337 ± 5 Ma from Sm/Nd garnet-albite isochron) the pegmatite might be related to the Variscan Rastenberg type granodiorites or Weinsberg type granites. Coexisting minerals with Mn-rich, pink-brown to yellow-brown tourmaline and bluish, Mn-rich fluorapatite are quartz, feldspars, Mn-rich garnet (63 mol% spessartine), pink Mn-bearing muscovite (up to ∼0.3 wt% MnO), topaz, cassiterite and rarely, beryl and bertrandite. Tourmaline composition evolves from Mn-poor (0.09 apfu) schorl through Al-rich Mn-bearing (0.15–0.33 apfu) schorl, Mn-rich (0.58 apfu) Fe-bearing olenite-elbaite to Mn-rich (0.86–1.27 apfu) olenite-elbaite, which reflects the Mn-enrichment of the pegmatite system during the late stages of its evolution. Mn-rich Li-bearing olenite has the formulae x(Na0.71Ca0.010.28) Y(Al1.36Mn2+1.27Li0.34) ZAl6.00TSi6 B3 O27 [(OH)3 (F0.44,OH,O)] (8.89 wt% MnO) and X(Na0.84Ca0.03K0.010.12) Y(Al1.33Mn2+0.86Li0.51Fe2+0.06Ti0.020.22) ZAl6.00TAl(Si5.74Al0.26) B3 O27 [(OH)3) (F0.54 OH0.37 O0.09] (6.22 wt% MnO), with lattice parameters a = 15.9158(4) Å, c = 7.1201(2) Å (R = 0.021). This pegmatite has two different zones: a Mn-enriched zone and a Mg-enriched zone. The younger, fine-grained, Mn-enriched zone contains the Mn-bearing minerals described above which have low Mg contents. The coarse-grained, Mg-enriched zone contains Mg-bearing muscovite, tourmaline from the dravite-schorl series, and pale-green fluorapatite but essentially contains no Mn-bearing minerals. Interestingly, albite has a pale bluish-greenish color in the Mn-enriched zone while it has a white color in the Mg-enriched zone.

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