European Current Research on Fluid Inclusions (ECROFI-XXI) Montanuniversität Leoben, Austria, 9–11 August, 2011. Abstracts, p. 134 134 Contrasting fluids on similar vein-type Pb-(Zn-Cu) deposits in Portugal Marques de Sá, Carlos and Noronha, Fernando CGUP - GIMEF, DGAOT-FCUP, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal Introduction Fluid inclusion (FI) studies of Pb-(Zn-Cu) deposits are being carried out in 8 deposits in NE and W Portugal: 4 in the Bragança district (NE Portugal): Ferronho (F), Vale da Madre (VM), Estevais (E) and Olgas (O); and 4 in the Aveiro District (W Portugal): Moinho da Pena (P), Carvalhal (C), Palhal (PA) and Telhadela (T). The study of these deposits encompasses mineralogical, geochemical and petrographical studies together with fluid inclusions studies. We now present preliminary results of the petrographic and microthermometric FI studies and the contrasting evolution of their T-x paths. Geology and Mineralogy The studied deposits are low temperature vein type deposits, formed in late to post-Variscan fractures. In the Bragança district the veins cross Ordovician phyllites and quartzites. The deposits form a lineament parallel to the main NNE-SSW Vilariça regional fault. The deposits of the Aveiro district occur in E-W fractures related to late stages of the Variscan and early Alpine orogenesis. They occur along a NE-SW fault which is a tributary of the main NW-SE Porto- Tomar regional fault. The veins cut across gneisses and mica-schists of lower Ordovician age. On both regions the veins are not spatially related to the synorogenic Variscan granites. All the veins are brecciated and composed of several generations of the main gangue, quartz with calcite (Cc) occurring in the Aveiro district deposits Palhal (PA) and Telhadela (T). In general there are three main quartz generations: earlier massive milky quartz (QI); translucent subhedral quartz (QII) contemporaneous with main ore stages; and late quartz in clear euhedral crystals with comb texture (QIII). Different quartz generations accompany different paragenetic stages. These paragenetic stages are: stage 0 (s0; QI, pre-ore); stage 1 (s1; QI-QIIa, Fe-As); stage 2 (s2; QIIa-QIIb, Cu-Zn); stage 3 (s3; QIIb- QIIc and Cc, Pb); stage 4 (s4; QIII, late). Main sulphides are s1: arsenopyrite and pyrite; s2: sphalerite and chalcopyrite; s3: galena. Several other rarer sulphides, sulphosalts, sulphates, carbonates and oxides occur earlier and later in the paragenesis. Fluid Inclusion Petrography Most of the studied FI are hosted by quartz except a few cases of FI in calcite from Palhal and Telhadela mines. All studied FI are two-phase aqueous inclusions (L w ) and present frequently an oval, rectangular or negative crystal shape, with sizes ranging from 5 to 100 µm (most common 10 µm). Petrographical studies enabled us to identify different assemblages of FI: isolated, defining crystal growth zones or in intragranular planes or swarms (primary or pseudosecondary in the last case); in transgranular planes or trails (secondary) (Roedder, 1984; Van den Kerkhof & Hein, 2001). The assemblages were correlated with the host quartz generation and by this way with the paragenetic stage. Flw is constant in most cases within one assemblage, although there are some cases of variable vapour bubble size within the same assemblage. Microthermometry Results About 100 FI were microthermometrically analyzed in each deposit, although in some cases results for the pair ice melting temperature - T m (ice) - and homogenization temperature - T h - were not possible to obtain, due to decrepitation, leakage or other undesirable irreversible phenomenons. Microthermometric results are summarized in Table 1. For each deposit T e , T m (ice) and T h means with standard deviation are presented according to paragenetic stage. Presence of Ca 2+ is probable as indicated by most of T e temperatures (Goldstein & Reynolds, 1994). Plotting a diagram (Fig. 1) of T m (ice) versus T h (L and V) of the inclusions allowed us to observe: 1) different fluid “paths” for each district; 2) a distinct ©Geol. Bundesanstalt, Wien; download unter www.geologie.ac.at