TOURMALINE IN GRANITIC PEGMATITES AND THEIR COUNTRY ROCKS, FREGENEDA AREA, SALAMANCA, SPAIN

ENCARNACIÓN RODA, ALFONSO PESQUERA and FRANCISCO VELASCO
Departamento de Mineralogía y Petrología, Universidad del País Vasco/EHU, Aptdo, 644, E-48080, Bilbao, Spain

Abstract

In the northwestern part of the province of Salamanca (Spain), many Li-, Sn-bearing and barren granitic pegmatites occur. These bodies display a zonal distribution northward from the Lumbrales granite, with a degree of evolution increasing with distance from the granite contact. Tourmaline appears as an accessory mineral in the barren pegmatites, as well as in their country rock. In both cases, the tourmaline belongs to the schorl-dravite solid-solution series. Tourmaline shows textural and compositional variations in relation with the pegmatite type. Subhedral to euhedral prismatic, very fine- to medium-grained (<6 mm - 10 cm), zoned grains are most common. In the country rock, tourmaline appears as prismatic- euhedral, very fine-grained (<6 mm) crystals. Their Fe/Mg value changes considerably among the different pegmatite types, providing insight to the degree of evolution of the associated pegmatites: those richest in Fe and poorest in Mg are associated with the most evolved bodies. Tourmaline from the country rocks shows compositional characteristics inherited from the host schists: similarity of the shape of the REE patterns for tourmaline and the schists, and a high content in Cr, Hf, Th and U.

Keywords: tourmaline, granitic pegmatite, schorl-dravite, Fregeneda, Spain.