Tourmaline at diagenetic to low-grade metamorphic conditions: Its petrologic applicability

This study characterizes natural black, blue, dark green, light green and pink tourmalines from granitic pegmatites of the Mata Azul Pegmatitic Field in central Brazil. The differences were assessed by applying electron-microprobe analysis as well as Mössbauer and optical spectroscopies. Mineral chemistry data show an increasing Mn/(Mn + Fe) atomic ratio as follows: black (0.01-0.02), blue (0.04-0.05), dark green (0.09-0.21), light green (0.33-0.42) and pink (0.68-1.00). The Mössbauer spectroscopy results show the presence of Fe 2+ (doublets with isomer shift (δ): 1.04-1.15 mm/s) for the black, blue, light green and dark green tourmalines. Fe 2+ is found in three different environments that are identified by quadrupole splitting (Δ) of 2.38-2.49 mm/s for the first, Δ = 2.13-2.34 mm/s for the second, and Δ = 1.54-1.71 mm/s for the third. The black sample spectrum has an additional fourth doublet (δ = 0.78 mm/s, Δ = 1.22 mm/s) that is assigned to an electron delocalization between Fe 2+ and Fe 3+. In the studied samples, the black color results most likely from high absorbance in all the visible spectra caused by Fe

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“…For this reason, tourmalines feature a wide range of colors and are frequently used as a gemstone. (Henry et al 2011;Henry and Dutrow 2012).…”

Section: Introductionmentioning

confidence: 99%

Chemical and spectroscopic characterization of tourmalines from the Mata Azul pegmatitic field, Central Brazil

Silva¹,

Moura²,

Queiroz³

et al. 2018

J. Geosci.

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“…Authigenic tourmaline is present as external halos partially around detrital tourmaline or as individual crystals. The halos are asymmetrical or monopolar, typical of a low temperature environment (≤300ºC; Henry and Dutrow, 2012), compatible with the caprock development and the temperature of the mineralizing event (150 to 200ºC) estimated by Perona et al (2018) based on fluid inclusion, organic matter maturity and sphalerite-galena isotope geothermometry.…”

Section: Discussionmentioning

confidence: 60%

“…They are also Na and O rich in the X and W positions, respectively, as expected for tourmalines formed under hypersaline and oxidizing conditions associated with evaporites. These chemical features are also shared by tourmalines in meta-evaporites at Liaoning (China) and Stolzenfeld (Namibia; Henry et al, 2008) and by tourmalines formed in oxidizing hypersaline environments associated with boiling processes such as in porphyry Cu deposits (Baksheev et al, 2011;Henry and Dutrow, 2012).…”

Section: Discussionmentioning

confidence: 90%

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Tourmaline records hydrothermal events related to Zn-Pb mineralization around the Murguía diapi.

Galdos

Canals

López

et al. 2019

GeActa

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The chemical composition of tourmaline has been used as a host environment register as well as a potential exploration tool for mineral deposits. In this study, the textural and chemical composition of tourmalines associated with Zn-Pb mineralizations around the Murguía diapir (Basque Cantabrian Basin, N Spain) are examined to verify if they record the mineralizing events in the area. Petrographically, tourmalines have been differentiated between inherited and authigenic. Colorless authigenic tourmalines are present as halos partially around green and pleochroic detrital grains or as individual crystals. Inherited and authigenic tourmalines are also chemically distinct. Authigenic tourmalines show different X-site occupancies, a Mg/(Mg+Fe) ratio above 0.77, and are aluminum rich and plot to the right of the povondraite-oxidravite join, above the schorl-dravite join. Inherited tourmalines plot within the alkaline (Na+K) group field, and have a Mg/(Mg+Fe) ratio below 0.77. These data suggest that authigenic tourmalines grew under reducing conditions, compatible with the hydrothermal event responsible for the ore deposition and caprock formation during the diapir ascent.Tourmaline. Salt diapir. Zn-Pb deposits. Basque Cantabrian Basin. KEYWORDS

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“…Because tourmaline accommodates Mg in a very wide range of P-T conditions from diagenetic (Henry and Dutrow 2012) to UHP terrains (van Hinsberg et al 2011;Lussier et al 2016), absence of Mg in tourmaline is very reliable evidence for lack of this element in the system and, consequently, lack of external contamination in this particular process.…”

Section: Contamination and Behavior Of Mg And Camentioning

confidence: 99%

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

Buřival¹,

Novák²

2018

J. Geosci.

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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 Ctidružice, 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. O 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 H 2 O. 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.

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Tourmaline at diagenetic to low-grade metamorphic conditions: Its petrologic applicability

Cited by 94 publications

References 57 publications

Chemical and spectroscopic characterization of tourmalines from the Mata Azul pegmatitic field, Central Brazil

Chemical and spectroscopic characterization of tourmalines from the Mata Azul pegmatitic field, Central Brazil

Tourmaline records hydrothermal events related to Zn-Pb mineralization around the Murguía diapi.

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

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