Influencia del topacio en las condiciones de cristalización de las aplopegmatitas de Tres Arroyos (Badajoz, España)

Résumé

In the Tres Arroyos aplopegmatitic field (Central Iberian Zone; Iberian Massif) topaz is ubiquitous in all types of aplopeg- matites, appearing with a relatively high abundance (e.g., Garate-Olave et al., 2017). This Al-F-silicate occurs as individual crystals (<4 mm) or as interstitial aggregates comprising smaller crystals. Fluorine contents in analyzed topaz are in the range of 9.72–10.73 wt. %, with no considerable correlation with the associated type of aplopegmatite. In contrast, signifi- cant variations have been found in P contents, with P2O5 values from 0.00 to 1.00 wt. %. The lowest P2O5 values are mainly found in topaz from the barren and intermediate aplopegmatites, whereas those crystals from the Li-rich bodies show the highest contents. Although the mechanism for the incorporation of P in the topaz structure is not completely understood, the good correlation between Si and Al+P suggests that P may have been incorporated via the berlinite-type substitution mecha- nism in Tres Arroyos. According to experimental studies, the occurrence of topaz indicates that F contents in the melt should exceed 2.5–3.0 wt. % (e.g., Lukkari, 2007). Furthermore, the observed high P contents in some of the topaz crystals attests for the high availability of this element in the melts that gave rise to the Tres Arroyos aplopegmatites.