Secondary blue tourmaline after garnet from elbaite-subtype
pegmatites; implications for source and behavior of Ca and Mg
in fluids

J 2018

Secondary blue tourmaline after garnet from elbaite-subtype pegmatites; implications for source and behavior of Ca and Mg in fluids

BUŘIVAL, Zbyněk a Milan NOVÁK

Základní údaje

Originální název

Secondary blue tourmaline after garnet from elbaite-subtype pegmatites; implications for source and behavior of Ca and Mg in fluids

Autoři

BUŘIVAL, Zbyněk a Milan NOVÁK

Vydání

Journal of Geosciences, Praha, Česká geologická společnost, 2018, 1802-6222

Další údaje

Jazyk

angličtina

Typ výsledku

Článek v odborném periodiku

Obor

10504 Mineralogy

Stát vydavatele

Česká republika

Utajení

není předmětem státního či obchodního tajemství

Odkazy

Plný text článku

Impakt faktor

Impact factor: 1.275

Označené pro přenos do RIV

Ano

Kód RIV

RIV/00216224:14310/18:00101182

Organizační jednotka

Přírodovědecká fakulta

Klíčová slova anglicky

tourmaline; garnet; subsolidus alterations; contamination; elbaite pegmatite

Změněno: 22. 3. 2019 13:33, Mgr. Zbyněk Buřival, Ph.D.

Anotace

V originále

Secondary blue tourmaline (schorl to Fe-rich fluor-elbaite to very rare Fe-rich fluor-liddicoatite) with quartz partially replace spessartine-almandine garnet and albite in elbaite-subtype pegmatites cutting pyroxene gneisses and calcite or dolomite marbles (at Tamponilapa and Tsarafara-Nord, Sahatany Valley, Madagascar) and paragneisses (at Ctidruzice, Moldanubian Zone, Czech Republic). Only garnet from the albite adjacent to an unit with Li-bearing minerals (Li-micas, Li-tourmalines) underwent this alteration, whereas associated primary tourmaline (schorl to Mg-bearing schorl) remained unaltered. Textural relations and chemical composition of the individual minerals suggest the following equation of replacement for averaged and simplified (Ca-free) compositions of garnet and secondary tourmaline from Tsarafara: 25 NaAlSi3O8 + 2 (Mn2Fe1)Al2Si3O12 + 12 H3BO3 + 4 LiF -> 4 (Na-0.75 square(0.25))(Al1.25Li1.00Fe0.50Mn0.25)Al-6(Si6O18)(BO3)(3)(OH)(3)F + 46 SiO2 + 11 Na2SiO3 + 3 MnO + 12 H2O Elevated contents of Al, Fe, Na and Mn in secondary tourmaline were likely sourced from the replaced garnet and albite, whereas the residual fluids supplied B, F, Li, and H2O. Garnet and associated primary tourmaline are rather Mg-rich but the secondary tourmaline is typically Mg-free. The contents of Ca are high in both tourmaline generations, but the secondary one is occasionally even more enriched compared to the associated primary tourmaline. Such a behavior of Mg and Ca suggests that no Mg was externally supplied during primary crystallization of primary tourmaline from the moment when pegmatite melt was sealed off the host rock. Negligible to none concentrations of Mg in secondary tourmaline show that the pegmatite system was closed to the host rocks during the hydrothermal alteration producing the secondary tourmaline generation. Evident absence of external Mg-contamination from host Ca, Mg-rich rock rules out also any contamination by Ca. High contents of Ca in primary tourmaline and garnet are related to originally Ca-enriched pegmatite melt contaminated before emplacement.

Návaznosti

GA17-17276S, projekt VaV

Název: Turmalín - indikátor geologických procesů

Investor: Grantová agentura ČR, Turmalín - indikátor geologických procesů

Citovat

BUŘIVAL, Zbyněk a Milan NOVÁK. Secondary blue tourmaline after garnet from elbaite-subtype pegmatites; implications for source and behavior of Ca and Mg in fluids. Journal of Geosciences. Praha: Česká geologická společnost, 2018, roč. 63, č. 2, s. 111-122. ISSN 1802-6222. Dostupné z: https://doi.org/10.3190/jgeosci.257.

@article{1438236,
   author = {Buřival, Zbyněk and Novák, Milan},
   article_location = {Praha},
   article_number = {2},
   doi = {https://doi.org/10.3190/jgeosci.257},
   keywords = {tourmaline; garnet; subsolidus alterations; contamination; elbaite pegmatite},
   language = {eng},
   issn = {1802-6222},
   journal = {Journal of Geosciences},
   title = {Secondary blue tourmaline after garnet from elbaite-subtype pegmatites; implications for source and behavior of Ca and Mg in fluids},
   url = {http://www.jgeosci.org/content/jgeosci.257_burival.pdf},
   volume = {63},
   year = {2018}
}

TY  - JOUR
ID  - 1438236
AU  - Buřival, Zbyněk - Novák, Milan
PY  - 2018
TI  - Secondary blue tourmaline after garnet from elbaite-subtype pegmatites; implications for source and behavior of Ca and Mg in fluids
JF  - Journal of Geosciences
VL  - 63
IS  - 2
SP  - 111-122
EP  - 111-122
PB  - Česká geologická společnost
SN  - 18026222
KW  - tourmaline
KW  - garnet
KW  - subsolidus alterations
KW  - contamination
KW  - elbaite pegmatite
UR  - http://www.jgeosci.org/content/jgeosci.257_burival.pdf
L2  - http://www.jgeosci.org/content/jgeosci.257_burival.pdf
N2  - Secondary blue tourmaline (schorl to Fe-rich fluor-elbaite to very rare Fe-rich fluor-liddicoatite) with quartz partially replace spessartine-almandine garnet and albite in elbaite-subtype pegmatites cutting pyroxene gneisses and calcite or dolomite marbles (at Tamponilapa and Tsarafara-Nord, Sahatany Valley, Madagascar) and paragneisses (at Ctidruzice, Moldanubian Zone, Czech Republic). Only garnet from the albite adjacent to an unit with Li-bearing minerals (Li-micas, Li-tourmalines) underwent this alteration, whereas associated primary tourmaline (schorl to Mg-bearing schorl) remained unaltered. Textural relations and chemical composition of the individual minerals suggest the following equation of replacement for averaged and simplified (Ca-free) compositions of garnet and secondary tourmaline from Tsarafara: 25 NaAlSi3O8 + 2 (Mn2Fe1)Al2Si3O12 + 12 H3BO3 + 4 LiF -> 4 (Na-0.75 square(0.25))(Al1.25Li1.00Fe0.50Mn0.25)Al-6(Si6O18)(BO3)(3)(OH)(3)F + 46 SiO2 + 11 Na2SiO3 + 3 MnO + 12 H2O Elevated contents of Al, Fe, Na and Mn in secondary tourmaline were likely sourced from the replaced garnet and albite, whereas the residual fluids supplied B, F, Li, and H2O. Garnet and associated primary tourmaline are rather Mg-rich but the secondary tourmaline is typically Mg-free. The contents of Ca are high in both tourmaline generations, but the secondary one is occasionally even more enriched compared to the associated primary tourmaline. Such a behavior of Mg and Ca suggests that no Mg was externally supplied during primary crystallization of primary tourmaline from the moment when pegmatite melt was sealed off the host rock. Negligible to none concentrations of Mg in secondary tourmaline show that the pegmatite system was closed to the host rocks during the hydrothermal alteration producing the secondary tourmaline generation. Evident absence of external Mg-contamination from host Ca, Mg-rich rock rules out also any contamination by Ca. High contents of Ca in primary tourmaline and garnet are related to originally Ca-enriched pegmatite melt contaminated before emplacement.
ER  -

BUŘIVAL, Zbyněk a Milan NOVÁK. Secondary blue tourmaline after garnet from elbaite-subtype pegmatites; implications for source and behavior of Ca and Mg in fluids. \textit{Journal of Geosciences}. Praha: Česká geologická společnost, 2018, roč.~63, č.~2, s.~111-122. ISSN~1802-6222. Dostupné z: https://doi.org/10.3190/jgeosci.257.

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