The geological context of gems in the Velasco Pegmatitic District, Argentina

Abstract

The Velasco Pegmatitic District is located in the Velasco range, La Rioja province, northwestern Argentina. The Velasco range is made up of several granitic units of different petrography, magmatic evolution and age among which are the Huaco and Sanagasta granites. The pegmatites in the Velasco district have a spatial and genetic relationship with these granites and belong to the rare-element class, beryl type, beryl-columbitephosphate subtype. The pegmatites are usually zoned and the K-feldspar zone is generally the most important for gem-quality beryl. Heliodor and aquamarine varieties are present and these crystals can be cut to yield products of attractive beauty. Other beryl crystals with poor transparency can be utilized for cabochons or tumble polished. Rock-crystal and rosequartz are also present in some pegmatites from the Velasco district.