Li-bearing tourmalines in Variscan granitic pegmatites from the Moldanubian nappes, Lower Austria

Abstract

Crystal structures, chemical (including light elements) and spectral data (optical and Mössbauer spectroscopies) were used to characterize coloured (brown, pink, green) tourmalines from three granitic pegmatites from the Moldanubian nappes (Königsalm, Maigen and Blocherleitengraben; Lower Austria). The tourmalines can be classified as fluor-schorl, schorl, foitite, magnesiofoitite, olenite and ''fluor-elbaite'' with varying Li contents, up to $1.2 wt% Li 2 O. Coexisting minerals are quartz, plagioclase (up to An 7), microcline, garnet (spessartine-almandine), muscovite, biotite (annite), very rare lepidolite, apatite, monazite-(Ce), xenotime-(Y), allanite-(Ce) and zircon. The chemical composition of the Fe 2þ-rich tourmaline samples (up to $1.0 wt% TiO 2) varies from fluorschorl, with a ¼ 15.987(2), c ¼ 7.163(2) Å to X (& 0.63 Na 0.37) Y (Fe 2þ 1.12 Al 1.09 Mg 0.56 Mn 2þ 0.08 Fe 3þ 0.07 Li 0.02 Ti 4þ 0.01 Zn 0.01 & 0.04) Z (Al 5.74 Mg 0.26) (BO 3) 3 [Si 5.96 Al 0.04 O 18 ] V (OH) 3 W [(OH) 0.95 F 0.05 ], strongly dichroic (pink and blue) foitite, with a ¼ 15.9537(2), c ¼ 7.1448(4) Å , to X (& 0.51 Na 0.49) Y (Fe 2þ 0.97 Al 0.93 Mg 0.75 Fe 3þ 0.23 Mn 2þ 0.04 Li 0.01 Ti 4þ 0.01 & 0.06) Z (Al 5.72 Mg 0.28) (BO 3) 3 [Si 5.95 Al 0.05 O 18 ] V (OH) 3 W [(OH) 0.91 O 0.06 F 0.03 ], magnesiofoitite, with a ¼ 15.9476(4), c ¼ 7.1578(4) Å. The chemical composition of the Al-and Lirich and Mn 2þ-bearing (up to $5.7 wt% MnO) samples varies from X (Na 0.84 Ca 0.02 & 0.14) Y (Al 1.35 Li 0.78 Mn 2þ 0.65 Ti 4þ 0.01 & 0.21) Z Al 6 (BO 3) 3 [Si 5.92 Al 0.04 B 0.04 O 18 ] V (OH) 3 W [F 0.81 (OH) 0.19 ], ''fluor-elbaite'' with a ¼ 15.8887(3), c ¼ 7.1202(3) Å , to X (Na 0.76 Ca 0.12 & 0.12) Y (Al 1.52 Li 0.69 Mn 2þ 0.43 Fe 2þ 0.09 & 0.27) Z Al 6 (BO 3) 3 [Si 5.71 B 0.29 O 18 ] V (OH) 3 W [F 0.69 (OH) 0.31 ], B-rich ''fluorelbaite'', with a ¼ 15.8430(3), c ¼ 7.1051(3) Å. A positive correlation between the ,T-O. and ,Z-O. bond lengths in tourmalines where the Z site is only occupied by Al (R 2 ¼ 0.617) is useful to correct the ,Z-O. bond length for the inductive effect of the varying ,T-O. bond length. This is important for producing accurate assignments for the different 6-coordinated sites in tourmaline. On the basis of Sm-Nd (garnet, monazite), U-Th-Pb, and U-Pb ages (monazite), the pegmatites crystallised during the Variscan tectonometamorphic event in the Visean (339 AE 4 Ma Maigen, 332 AE 3 Ma Königsalm). These ages are in the range of the earliest intrusions of the South Bohemian pluton (Rastenberg type durbachites). However, on the basis of the spatial relationship of the pegmatites and the Rastenberg type intrusions, a linkage of the intrusive body and the pegmatites is unlikely. Alternatively, the pegmatites may have evolved as granitic pegmatitic melts during decompression from the surrounding country rocks in the frame of exhumation of the Moldanubian nappes after the peak of the Variscan metamorphism.

Thermal stability of extended clusters in dravite: a combined EMP, SREF and FTIR study

“…= mean atomic number; Superscript letters: A = (y − x, y, z); B = (y − x, −x, z); C = (x, x − y, z); D = (y − x + 1/3, −x + 2/3, z + 2/3); E = (-y + 2/3, x −y + 1/3, z + 1/3); F = (-y, x − y, z). Transformations relate coordinates to those of (9) 11.32 (9) Y-O1 1.9710(11) 1.9872 (10) Y-O6 C (×2) 1.9849 (9) 1.9908 (9) Y-O2 B (×2) 1.9982 (9) by Ertl et al (2012). The calculated values are very similar for both samples: δ Al-Mg = 0.31 and 0.27 for drv and drv800, respectively, which correspond to a slightly more ordered distribution for the heat-treated sample.…”

Tetrahedral substitutions in tourmaline: a review

“…Significant amounts of [4] Al are also found in pegmatitic Al-rich and Li-bearing tourmaline species (elbaite, liddicoatite, olenite, "oxyrossmanite"). Quite commonly these [4] Al-and Li-bearing tourmalines also contain significant amounts of [4] B (Ertl et al, 2005(Ertl et al, , 2009(Ertl et al, , 2010(Ertl et al, , 2012a(Ertl et al, , 2012bHughes et al, 2000;Lussier et al, 2009;Schreyer et al, 2002).…”

“…Over the last 20 years many examples of substitution of Si by B have been found in natural and synthetic tourmalines (Ertl et al, 1997(Ertl et al, , 2005(Ertl et al, , 2006(Ertl et al, , 2007(Ertl et al, , 2008(Ertl et al, , 2012a(Ertl et al, , 2012b(Ertl et al, , 2015Hughes et al, 2004;Kutzschbach et al, 2016Kutzschbach et al, , 2017Lussier et al, 2008Lussier et al, , 2009Schreyer et al, 2000Schreyer et al, , 2002. Using the crystallographic and analytical techniques that are most commonly employed today it is difficult to verify the presence of B at the T site.…”

“…An elbaite from Nuristan, Afghanistan, contains 20 ppm Be (Ertl et al, 2006). Fluorelbaites from pegmatites, which may have evolved from granitic pegmatitic melts during decompression from the surrounding country rocks during exhumation of the Moldanubian nappes (Lower Austria) after the peak of the Variscan metamorphism, exhibit lower Be contents of 5-13 ppm (Ertl et al, 2012b). The [4] B-rich olenite samples (with varying Fe 2+ -contents) from Koralpe contain up to 37 ppm Be and, similar to the zoned tourmaline from the Himalaya Mine, California, the Be content increases simultaneously with the Al content (Ertl et al, 2006;Hughes et al, 2004).…”

Vanadium-rich Muscovite from Austria: Crystal Structure, Chemical Analysis, and Spectroscopic Investigations

“…Pressure-temperature estimates of the metamorphic conditions, derived from typical GrtþSilþKfsþBt-gneisses and some GrtþOpx-amphibolites, are 700-1100 MPa/700-800 8C and aH 2 O ,, 1 (Petrakakis & Jawecki 1995, Petrakakis 1997, Petrakakis et al 1999. This Variscan MP/HT event (around 340 Ma) was accompanied by strong decompression-induced anatexis of fertile lithologies (Petrakakis et al 1999, Ertl et al 2012. Although the graphite deposit is also assumed to be of Proterozoic origin, quartz-feldspar dikes (containing mica and tourmaline) within the graphite schist could be related to decompressioninduced anatexis during the uplift of this unit.…”