Chemistry and genetic implications of tourmaline and Li-F-Cs micas from the Valdeflores area (Cáceres, Spain)

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Chemistry and genetic implications of tourmaline and Li-F-Cs micas from the Valdeflores area (Cáceres, Spain)

机译：Chemistry and genetic implications of tourmaline and Li-F-Cs micas from the Valdeflores area (Cáceres, Spain)

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Pervasive metasomatism that involved the formation of tourmaline-rich rocks and influx of Li. F. and Cs into Ordovician psammo-pelitic metasediments occurred in the Valdeflores area (Cáceres. Spain). Numerous Li- and Sn-bearing. mineralized, greisen-type veins also can be observed here, in the vicinity of geochemically specialized granites. Tourmaline- rich rocks appear as: (1) massive, fine-grained, dark green to black rocks: and (2) fine- scale tourmaline-rich laminae, which alternate with quartz-rich layers parallel to the bedding. Electron microprobe analyses indicate that the tourmaline lies mostly within the space defined by the exchange vectors from dravite: FeMg -1 (schorl), ⃞AlNa -1 Mg -1 (foitite), AlOMg -1 (OH) -1 (olenite), and CaMgNa -1 Al -1 (uvite). The Fe/(Fe+Mg) ratio ranges mainly from 0.87 to 0.54 and increases with Al in the Y-site. Analytical results and substitutional relations show an insignificant elbaite component. Mica in the tounnalinized rocks is very fine-grained (mostly 50 μm). White mica ranges from lithian muscovite-phengite to lepidolite/zinnwaldite, containing up to 8.40 wt F. 6.0 wt Li 2 O, and 10.73 wt FeO. Dark mica shows a variable color and has compositions characterized by relatively high contents of Cs 2 O (1.14-2.78 wt) and F (1.94-8.08 wt), with a deficit in K 2 O (5.75- 9.04 wt). Log (f H₂O /f HF ) of fluids in equilibrium with biotite in the tourmaline-rich rocks was 4.02-4.17 at T ≈ 400 °C. Log (f H₂O /f HF ) values of fluids in equilibrium with topaz (X F ≈ 0.8) in country rock adjacent to contacts with veins, and in equilibrium with am- blygonite-montebrasite (X amb = 0.2) in the veins were about 4.30-4.60 and 6.4-6.7, respectively. Tliese variations denote the existence of gradients in relative a HF more than differences of temperature during metasomatism. The lack of tourmaline in the veins is interpreted to reflect the alkalinity and low Fe-Mg contents in the fluids, which precluded the formation of tourmaline. Consequently, most of the boron was expelled into metasediments where tourmaline was produced as a result.

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《The American mineralogist》 |1999年第2期|55-69|共15页
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Departamento de Mineralogía y Petrología, Universidad del país Vasco 644, 48080 Bilbao, Spain;

Departamento de Mineralogía y Petrología, Universidad de Granada, E-18002 Granada, Spain;

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Chemistry and genetic implications of tourmaline and Li-F-Cs micas from the Valdeflores area (Cáceres, Spain)

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