• journal_title：The Canadian Mineralogist
• Contributor：Mercedes Fuertes-Fuente ; Agustin Martin-Izard ; Marie Christine Boiron ; Jose Mangas Viñuela
• Publisher：Mineralogical Association of Canada
• Date：2000-
• Format：text/html
• Language：en
• Identifier：10.2113/gscanmin.38.5.1163
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：38
• issue：5
• firstpage：1163
• section：Articles

In Galicia, in the northwestern part of the Iberian Peninsula, there are several occurrences of granitic pegmatites. One of them, known as Franqueira, is a metasomatic deposit of gem-quality chrysoberyl, emerald and phenakite. The pegmatite is associated with a two-mica peraluminous Hercynian granite, and intrude dunites of the Schistose domain in the Galician Tras-Os-Montes Zone. The composition of fluid inclusions in emerald and phenakite has been determined using a Raman microprobe to ascertain the paleofluid chemistry and the P–T conditions of fluid migration in the pegmatite. Three types of fluid inclusions have been identified in emerald and phenakite; three episodes of fluid circulation are distinguished. The first episode is represented by low-salinity aqueous-carbonic primary fluid inclusions in phenakite; these were trapped at 2.5 kbar and 400°C. An isothermal drop in pressure produced a second stage of fluid trapping under conditions of 400°C and 1 kbar. Fluid inclusions trapped in emerald indicate that during this second stage, it formed from phenakite and chrysoberyl in the presence of a CO₂- and CH₄-rich fluid. A third episode of fluid circulation suggests an independent stage of fluid circulation during late tectonic events, with temperatures ranging from 160° to 265°C and pressure below 0.5 kbar.