Characterization and timing of the different types of fluids present in the barren and ore-veins of the W-Sn deposit of Panasqueira, Central Portugal

Abstract

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...

A numerical approach for the formation of chlorite and sulphide-bearing greisen: a study based on the Navalcubilla system (Spanish Central System)

“…This occurred where Ca, Mg and Fe were approximately 10% of their analysed concentration (Table 1, fluid [2]). These amounts are close to the cation/Na ranges found by Polya (1989), Heinrich et al (1992) and Noronha et al (1992) in similar systems.…”

“…A similar situation was found by Charoy (1981) and Rankin and Alderton (1985) in Cornwall. However, comparison with similar systems of the Iberian Peninsula indicates that this early alteration was related to the circulation of COz and NaCl-rich fluids at temperatures between 600 and 250~ (Mangas, 1987;Noronha et al, 1992;Tornos et al, 1993a). Superimposed on hydrothermal rocks related with the early stage or unaltered granitoids there is a second hydrothermal event dated at 267-1-7 Ma (K-Ar dating of sericites in the chlorite-rich greisen).…”

Importance of mantle derived fluids during granite associated hydrothermal circulation: He and Ar isotopes of ore minerals from Panasqueira 1 1Associate editor: R. Wieler

“…Described by Sawkins (1990) as one of the most studied collision related hydrothermal ore deposits in the world, further major studies have been carried out by Marignac (1982), Bussink (1984), Snee et al (1988), Polya (1988Polya ( , 1989, Noronha et al (1992), Polya et al (2000), and the reader is referred to these for a more detailed description of the geology and paragenesis than the outline, based on these studies and the seminal work of Kelly and Rye (1979), provided below.…”

Geochemistry and Mineralogy of Mill Tailings Impoundments from the Panasqueira Mine (Portugal): Implications for the Surrounding Environment

“…The paragenesis is complex. Four stages of mineral formation are generally accepted by most of the authors who have studied this deposit: (1) the oxide-silicate phase (quartz, wolframite; cassiterite); (2) the main sulphide phase (pyrite, arsenopyrite, pyrrothite, sphalerite, chalcopyrite); (3) the pyrrothite alteration phase (marcasite, siderite, galena, Pb-Bi-Ag sulphosalts); and (4) the late carbonate phase (dolomite, calcite) (Breiter 2001;Corrêa de Sá et al 1999;Correa and Naique 1998;Noronha et al 1992). At Panasqueira, more than 65 minerals, including sulphides, sulphosalts, oxides, carbonates, silicates, phosphates, and tungstate minerals, have been identified (Kelly and Rye 1979).…”