Hydrothermal replacement of garnet by tourmaline - an example
from LCT pegmatites in Sahatany Valley, Madagascar

k 2014

Hydrothermal replacement of garnet by tourmaline - an example from LCT pegmatites in Sahatany Valley, Madagascar

BUŘIVAL, Zbyněk a Milan NOVÁK

Základní údaje

Originální název

Hydrothermal replacement of garnet by tourmaline - an example from LCT pegmatites in Sahatany Valley, Madagascar

Autoři

BUŘIVAL, Zbyněk (203 Česká republika, garant, domácí) a Milan NOVÁK (203 Česká republika, domácí)

Vydání

Central European Mineralogical Conference, Skalský Dvůr, 22.-26. 4. 2014, 2014

Další údaje

Jazyk

angličtina

Typ výsledku

Prezentace na konferencích

Obor

10500 1.5. Earth and related environmental sciences

Stát vydavatele

Česká republika

Utajení

není předmětem státního či obchodního tajemství

Odkazy

book of abstracts

Kód RIV

RIV/00216224:14310/14:00075396

Organizační jednotka

Přírodovědecká fakulta

Klíčová slova anglicky

garnet; tourmaline; replacement; alteration; LCT; Madagascar

Změněno: 30. 4. 2014 14:36, Mgr. Zbyněk Buřival, Ph.D.

Anotace

V originále

In the pegmatites Tsarafara Nord and Tamponilapa, both tending to elbaite subtype, garnet and albite located close to Li-mineralized zone were partially replaced by a mixture of blue tourmaline and quartz. Spessartine-dominant garnets from the pegmatites Tsarafara Nord (Sps48-60Alm32-42Grs8-10) and Tamponilapa (Sps43-62Alm2244Grs3-21Prp0-3) are associated with primary tourmaline (schorl to Mg-rich schorl). Secondary tourmaline replacing garnet are of schorl to Fe-rich fluor-elbaite composition. Albite is close to the end member composition. The minerals from the Tsarafara Nord are slightly more fractionated with higher (Li, Mn, F) and less contaminated (elevated Ca, Mg, Ti) from host rock relative to the Tamponilapa. Textural relations showing replacement of garnet and albite by tourmaline and quartz suggest the simplified reaction: 24 NaAlSi3O8 + 3 (Mn1.6Fe1Ca0.4) Al2Si3O12 + 12 H3BO3 + 2 LiF => 4 (Na0.5Ca0.3v0.2) (Al1.5Fe0.75Li0.5Mn0.25) Al6 (Si6O18) (BO3)3 (OH3.5F0.5) + 46 SiO2 + 11 Na2SiO3 + 3.8 MnO2 + 0.4 O + 9 H2O + 4 H+ It is calculated based on stable = immobile Al, Fe and Ca and idealized compositions of primary garnet, albite and secondary tourmaline, which is generally enriched in Al, F, Li, and Mn and depleted in Ti, Mg and Fe compared to primary tourmalines. They are only sporadically associated with garnet and very likely do not participate in the replacement reaction. Because we assume a direct replacement of primary garnet and albite, the elevated contents of Al, Mn and Ca in secondary tourmalines reflects the compositions of primary garnet (Mn, Al, Fe, Ca) and of residual fluids (B, F, Li, H2O). Very low to negligible concentrations of Mg in secondary tourmaline suggest closed system to host rock during this alteration. The excess of Na and Mn may be dissolved in fluids and transported away as e.g., soluble sodium silicates. Apparently, no Mn-bearing minerals occur close to garnet as well.

Citovat

BUŘIVAL, Zbyněk a Milan NOVÁK. Hydrothermal replacement of garnet by tourmaline - an example from LCT pegmatites in Sahatany Valley, Madagascar. In Central European Mineralogical Conference, Skalský Dvůr, 22.-26. 4. 2014. 2014.

@proceedings{1181660,
   author = {Buřival, Zbyněk and Novák, Milan},
   booktitle = {Central European Mineralogical Conference, Skalský Dvůr, 22.-26. 4. 2014},
   keywords = {garnet; tourmaline; replacement; alteration; LCT; Madagascar},
   language = {eng},
   title = {Hydrothermal replacement of garnet by tourmaline - an example from LCT pegmatites in Sahatany Valley, Madagascar},
   url = {http://cemc2014.cz/abstracts-cemc2014.pdf},
   year = {2014}
}

TY  - CONF
ID  - 1181660
AU  - Buřival, Zbyněk - Novák, Milan
PY  - 2014
TI  - Hydrothermal replacement of garnet by tourmaline - an example from LCT pegmatites in Sahatany Valley, Madagascar
KW  - garnet
KW  - tourmaline
KW  - replacement
KW  - alteration
KW  - LCT
KW  - Madagascar
UR  - http://cemc2014.cz/abstracts-cemc2014.pdf
L2  - http://cemc2014.cz/abstracts-cemc2014.pdf
N2  - In the pegmatites Tsarafara Nord and Tamponilapa, both tending to elbaite subtype, garnet and albite located close to Li-mineralized zone were partially replaced by a mixture of blue tourmaline and quartz. Spessartine-dominant garnets from the pegmatites Tsarafara Nord (Sps48-60Alm32-42Grs8-10) and Tamponilapa (Sps43-62Alm2244Grs3-21Prp0-3) are associated with primary tourmaline (schorl to Mg-rich schorl). Secondary tourmaline replacing garnet are of schorl to Fe-rich fluor-elbaite composition. Albite is close to the end member composition. The minerals from the Tsarafara Nord are slightly more fractionated with higher (Li, Mn, F) and less contaminated (elevated Ca, Mg, Ti) from host rock relative to the Tamponilapa. Textural relations showing replacement of garnet and albite by tourmaline and quartz suggest the simplified reaction: 24 NaAlSi3O8 + 3 (Mn1.6Fe1Ca0.4) Al2Si3O12 + 12 H3BO3 + 2 LiF => 4 (Na0.5Ca0.3v0.2) (Al1.5Fe0.75Li0.5Mn0.25) Al6 (Si6O18) (BO3)3 (OH3.5F0.5) + 46 SiO2 + 11 Na2SiO3 + 3.8 MnO2 + 0.4 O + 9 H2O + 4 H+ It is calculated based on stable = immobile Al, Fe and Ca and idealized compositions of primary garnet, albite and secondary tourmaline, which is generally enriched in Al, F, Li, and Mn and depleted in Ti, Mg and Fe compared to primary tourmalines. They are only sporadically associated with garnet and very likely do not participate in the replacement reaction. Because we assume a direct replacement of primary garnet and albite, the elevated contents of Al, Mn and Ca in secondary tourmalines reflects the compositions of primary garnet (Mn, Al, Fe, Ca) and of residual fluids (B, F, Li, H2O). Very low to negligible concentrations of Mg in secondary tourmaline suggest closed system to host rock during this alteration. The excess of Na and Mn may be dissolved in fluids and transported away as e.g., soluble sodium silicates. Apparently, no Mn-bearing minerals occur close to garnet as well.
ER  -

BUŘIVAL, Zbyněk a Milan NOVÁK. Hydrothermal replacement of garnet by tourmaline - an example from LCT pegmatites in Sahatany Valley, Madagascar. In \textit{Central European Mineralogical Conference, Skalský Dvůr, 22.-26. 4. 2014}. 2014.

Podrobný výpis o publikaci