The Granitic Pegmatites of the Fregeneda Area (Salamanca, Spain): Characteristics and Petrogenesis

E. Roda Robles1, A. Pesquera Perez1, F. Velasco Roldan1 and F. Fontan2
1 Departamento de Mineralogia y Petrologia, Universidad del País Vasco 644, E-48080, Bilbao, Spain
2 Laboratoire de Minéralogie, Université Paul Sabatier, F-31000 Toulouse, France

Abstract: Pegmatites of the Fregeneda area, Salamanca, Spain, show a zonal distribution, from barren to enrichment in Li, Sn, Rb, Nb>Ta, B and P. They intrude pre-Ordovician metasediments which were metamorphosed to sillimanite-zone conditions near the Lumbrales granite. Field, mineralogical and petrographic data show the following zonal sequence from the granite outward: (1) barren pegmatites (pegmatites T1, T2, T3 and T4) with quartz, K-feldspar > albite, muscovite, tourmaline ± andalusite ± garnet; (2) intermediate pegmatites (types T5 and T6), characterized by the occurrence of beryl and Fe-Mn-Li phosphates; and (3) fertile pegmatites (dykes T7 and T8), with lepidolite, cassiterite, columbite, albite > K-feldspar, montebrasite and spodumene.

Tourmaline from different pegmatites shows significant compositional variations. Trace element variations in mica and K-feldspar suggest that the origin of the different pegmatitic bodies may be explained by three different paths of fractional crystallization of melts generated by partial melting of quartzo-feldspathic rocks.

Keywords: granitic pegmatites • mineralogy • trace element modelling • petrogenesis

Mineralogical Magazine; August 1999 v. 63; no. 4; p. 535-558; DOI: 10.1180/002646199548709
© 1999, The Mineralogical Society
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