justificação do valor científico
The W/Sn province is one of the most important of Europe. It contains many deposits of several types. Many spectacular exposures can be found either in outcrop and underground.
The Panasqueira mine specifically is a world famous field trip destination and a major source of spectacular mineral samples with perfect crystalline forms. Field relationships are easily seen and interpretable.
The Panasqueira tungsten-tin deposit is located in the CIZ of Iberian Massif. Country rock that underlay the Panasqueira district consist of folded metasedimentary sequences, regionally metamorphosed to low grade (chlorite-sericite) during the Hercynian orogeny. This sequence is mainly composed by a several thousand-metre thick lower marine flyschoid series of schist and greywacke, referred to as “Beira-Schist Formation (BSF)” (Complexo-Xisto-Grauváquico-CXG) (Thadeu 1951, 1973, 1977, 1979). Bussink (1984) refers to the existence of about 0, 17% of organic matter in certain lithologies ofthe CXG.
During the main episode of regional deformation (D1), the BSF was folded into a series of tight and upright isoclinal folds striking NW-SE, accompanied by a penetrative, sub-vertical slaty cleavage (S1).
The Panasqueira district is flanked to the Northeast by the Serra da Estrela batholith (late to post-tectonic granites) and to the east by Fundão batholith (syn to late-tectonic) both Hercynian in age (Ferreira et al.1987).
In the Beira-Schists at Panasqueira, the thermal metamorphism related to the emplacement of Hercynian batholith, produced an extensive recrystallization characterised by elliptical spots (usually composed of biotite and chlorite and more rarely of cordierite and chiastolite) (Thadeu 1951).
The large extension of spotted schists to the east suggests that a batholith is present at a shallow depth beneath the surface. The results of an intensive drilling campaign confirm the shallow southward-dipping surface of an underlying batholith (Snee et al. 1988).
A greisened granitic cupola topped by a silica cap is found in the deeper levels of the underground mine workings (Kelly and Rye 1979).
Aplite dikes, regarded as the equivalent of the granite, are abundant throughout the district and predate the hydrothermal ore vein swarm.
Sub-vertical dolerite dykes are also common, they are interpreted to be late Hercynian in age because they are not affected by the regional metamorphism, although they are altered at the contact with the hydrothermal ore veins.
Sub-vertical faults are also abundant and can host a distinctive carbonate-sulphide mineralization (Lourenço, 2002).
Isotopic determination of a two-mica granite (muscovite dominantly secondary), cute by drilling, give a whole-rock, Rb-Sr ages of 289+4 m.y. with a high initial 87 Sr /86 Sr ratio of 0.713 (Priem and den Tex 1984).
Snee and al. (1988) using high-precision 40Ar/39Ar age-spectrum technique on 13 muscovites dating the major ore-forming stages and concluded that these stages occurred as short lived pulses over the relatively long time period between 296.3 + 0.8 and 291.6 + 0.8 m.y..
Quartz veins
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 quartz-veins are also scattered throughout the district (Noronha et al. 1992).
The ore-bearing veins usually occupy flat sets of open joints. These flat joints are not restricted to the vicinity of the mine and have a regional extension. Individual veins are from 5 to 100 cm thick (averaging 30 cm).
Vein Mineralogy
The mineral assemblage reveals a series of mineralizing stages separated in time by brecciation episodes. The dominant component of the veins is quartz, which can be separated into different types on the basis of the morphology and texture (in most of the veins).
Cassiterite is one of first minerals and is, generally, contemporaneous with quartz muscovite and topaz (+ arsenopyrite) that represent the earliest mineral association (Orey 1972), wolframite come after cassiterite and is the main oxide of the “oxide silicate stage” (OSS). Economically this first stage is by far the most important. This is followed by the second main stage the main sulphide stage (MSS) (arsenopyrite, pyrite, pyrrhotite, sphalerite, chalcopyrite, stannite) and the “pyrrhotite alteration stage” (pyrite, marcassite chalcopyrite, galena, Pb-Bi-Ag sulphosalts and siderite) (PAS). A latter stage characterised by a widespread carbonate deposition, dolomite and calcite, can be also considered (LCS). (Kelly and Rye 1979, Polya 1989).
Bussink, R.W. (1984) - Geochemistry of the Panasqueira tungsten-tin deposit,Portugal. Geologica Ultraiectina, 33, 170 pp. (Thesis).
Ferreira, N., Iglesias, M., Noronha, F., Pereira, E., Ribeiro, A. & Ribeiro, M.L., 1987. Granitóides da Zona Centro IBERICA e seu enquadramento geodinamica. In: Geologia de los Granitóides y Rocas asociadas del Macizo Hespérico Bea, et al. (eds) Editorial Rueda, Madrid (Libro Homenaje a L.C. Garcia de Figuerola), pp 37-51.
Kelly, W.C., Rye, R.O. (1979) - Geologic, fluid inclusions and stable isotope studies of the tin-tungsten deposits of Panasqueira, Portugal. Econ.Geol., 74 : 1721-1822.
Lourenço, Alexandre (2002). Paleofluidos e mineralizações associadas às fases tardias da Orogenia.Departamento de Geologia. Faculdade de Ciências da Universidade do Porto. 326 pp. (Tese).
Noronha, F., Doria, A., Dubessy, J., Charoy, B.(1992): Characterisation and timing of the different types of fluids present in the barren and ore-veins of the W-Sn deposit of Panasqueira, Central Portugal. Mineral. Deposita, 27, 72-79.
Outros valores e sua justificação
Traditional mining village well preserved with beautiful mountain panorama. Many operating equipments and also an old treatment plant near river Zêzere (Lavaria do Rio).
Minerals shop in the office of the Mining company.