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Tourmalinite veins in vicinity of Třebíč, west-moravian part of the Moldanubian Zone


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Abstract

Two occurrences of tourmalinite veins were discovered in the vicinity of Třebíč (Moldanubian Zone). The tourmalinites crosscut biotite granites or migmatites as brownish‑black quartz-tourmaline (± K-feldspar, rutile) veins (tourmaline > 50 vol. %) from few mm to several dm thick. Tourmaline corresponds to dravite and oxy-dravite (XFe 0.35 - 0.56, Na 0.41 - 0.66 apfu) predominantly and usually shows sector or patchy zoning. The incorporation of Al, vacancy and minor Ca in tourmaline takes place via foitite (□Al Na-1(Fe,Mg)-1), Al2 (Mg, Fe)Si-1 and uvite (Ca(Fe,Mg) Al-1Na-1) substitutions. The tourmaline samples from the two studied tourmalinite localities differ in Al (5.97 to 6.39 vs. 6.55 to 6.81 apfu), Ca, Ti and F contents. The examined tourmalinites can be interpreted as crystallization products of boron rich fluids related to intrusion of peraluminous granites and/or aplites.

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