Silver mineralization at the Vale das Gatas tungsten mine, Portugal

Abstract

The Vale das Gatas tungsten mine is situated at the contact between Hercynian granite and CambrianPrecambrian crystalline schists a few kilometers north of the village of Sabrosa, near Vila Real, in northern Portugal. Wolframite has been the principal product of the mine although several other metals of economic interest are known to occur there. The silver content of the ores was attributed by earlier workers to the presence of tetrahedrite and schapbachite, whilst this work shows matildite, pavonite, acanthite, and argyrodite to be present, together with Ag-bearing galena. The textures and compositions of these phases are described with preliminary results of fluid inclusion studies. K E V w O R D S : silver, tungsten, Portugal, Vale das Gatas, matildite, pavonite, galena.

Geochemistry of cassiterite and wolframite from tin and tungsten quartz veins in Portugal

“…Different wolframite compositions are found in the same quartz vein crosscutting the same host rock and sharing the same parent granite, a fact which may be attributed to local changes in fluid composition (Nakashima et al, 1986). Fluid inclusion studies of quartz associated with wolframite from Vale das Gatas deposit give a mean homogenisation temperature of 225 ± 6°C, which is not corrected for lithostatic pressure and therefore is regarded as minima and a salinity of 6 wt.% NaCl equivalents (Gaspar et al, 1987), i.e., roughly similar to those from Panasqueira. Therefore, the distinct compositions of wolframite from Vale das Gatas and Panasqueira are not controlled by the temperature and depend on the fluid compositions.…”