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The Panasqueira W-Sn deposit is the largest quartz-vein type deposit of the Iberian Peninsula and the most important wolframite deposit in Western Europe. The ore-veins are almost exclusively sub-horizontal. Besides ore-bearing sub-horizontal veins, the Panasqueira mine also contains barren quartz veins. There are essentially two generations of barren quartz: quartz, contemporaneous with the earliest regional metamorphism (QI), and recrystallized quartz, contemporaneous with the thermal metamorphism related to the granite intrusion (QII). Fluid inclusion studies (microthermometry and Raman) were undertaken in order to distinguish fluids contemporaneous with the barren quartz from those contemporaneous with the ore-bearing quartz (QIII). Fluid inclusion data indicate that the barren and ore-bearing quartz fluids are dominantly aqueous (93 to 98 mol% H20), with a nearly constant bulk salinity (8 to 12 wt% eq. NaC1), with the quantity of volatile component (determined by Raman spectrometry) higher in QIII, but never greater than 5 tool%. However, the CO2/CH4 + N2 ratio is different for each type of quartz. Volatiles are dominated by CH4 (10 to 96 tool% ZCH~) and/or N 2 (3 to 87 mol% ZN2) in the barren quartz and by CO2 (60 to 73 mol% ZCO2) in ore-bearing quartz. The bulk chemical composition of the fluids in QIII is comparable to that found commonly in hydrothermal fluids associated with wolframite mineralization, where Na > K > Ca and HCO3 > CI> SO,. A dispersion in TH (226 to 350 ~ found in QIII, together with a variation in the degree of filling (0.5 to 0.7) and with the consequent variation of fluid densities (0.70 to 0.79), may result from changes in the fluid pressure regime below lithostatic pressure, suggesting vein filling related to tectonic events.The well-known Panasqueira tungsten deposit, located in the Beira Baixa Province of Central Portugal, is the largest quartz-vein type deposit of the Iberian Peninsula and the most important wolframite deposit in Western Europe. Tin and copper are byproducts. The Panasqueira ore deposit consists of a dense swarm of sub-horizontal quartz-veins which host the wolframite mineralization. However, vertical and sub-horizontal barren quartzveins are also scattered throughout the district.A fluid inclusion study was undertaken in order to allow an easy and rapid distinction between barren and ore-bearing fluids, and consequently between barren and mineralized veins. Regional geologyThe Panasqueira tungsten-tin deposit is located in the Central Iberian Zone of the Iberian Massif (Fig. 1). Country rocks underlying the Panasqueira district consist of a belt of folded sedimentary rocks, regionally metamorphosed to lower greenschist-grade (chloritesericite) during the Hercynian orogeny. This belt is composed of two distinct sedimentary series (Thadeu 1951(Thadeu , 1977(Thadeu , 1979:1. A several thousand-metre-thick lower marine flyschoid series of schist and greywacke, referred to as Beira Schist Formation (Schist-greywacke complex), widely distributed in North and Central P...