Escádia Grande

Gold - Tin - Tungsten
Escádia Grande

EDM holds exploration rights in an area called Escádia Grande, for mineral gold, silver, copper, lead, zinc, tin, antimony and tungsten.

Contract nº MN/PP/009/14, concluded with the DGEG on 23 September 2014 has a duration of 3 years (2014-2017), with the possibility of two extensions for 1 year each. The area covers the municipalities of Góis, Pampilhosa da Serra, Castanheira de Pêra, Arganil and Pedrogão Grande, with an area of 252.75 Km2.

Throughout the exploration area, minerals of two types are known: stannous-tungstiferous (Sn-W), auro-argentiferous (Au-Ag) and auro-antimonic (Au-Sb).

The mining activity occurred over a long period of time, from the Roman era up to the 1970s. In 1957, Couto Mineiro de Góis was founded with around seventeen concessions, including the Vale de Pião and Sandinha (Senhora da Guia Mine) concessions, which correspond to the most important tin and tungsten mines, respectively. The Escádia Grande (Au) mine operated until the late 1950s and represented the most important gold mine in the region.

REGIONAL GEOLOGY

The exploration area is in the southwest sector of the Central Iberian Zone near the contact point with the Ossa Morena Zone and belongs to the Góis-Segura stannous-tungstiferous metallogenic belt. This strip has an area of approximately 8,000 km2 and is known to possess large deposits which gave rise to the mines of Panasqueira (W-Sn-Cu), Argemela (Sn), Segura (W-Sn-Pb) and Góis (W-Sn).

The Góis region is located in the Serra da Lousã and is marked by steep reliefs, among which the Penedos de Góis are particularly notable. These reliefs consist of quartzite ridges dating back to the Ordovician period which belong to the Armorican Quartzite Formation, and reach an altitude of around 1,043 metres. The Penedos de Góis are hard land forms, rather elongated in a N30ºW direction. These reliefs are embedded in older schist and greywackes belonging to the Schist Greywacke complex of the Beiras Group, which dates back to the Neoproterozoic era, where the two previous lithologies predominate but conglomeratic levels also occur. The Schist Greywacke Complex is divided in this region into three formations, which bottom-up are: The Caneiro Formation, the Boque Serpins Formation and the Colmeal Formation.

To the northwest, the Schist Greywacke Complex is separated from sedimentary deposits of the Cretaceous to the Quaternary by the Góis fault. This fault, which runs in a NE-SW direction, is the main structure of the region and now has an inverse movement that causes the thrust of the older Schist Greywacke Complex over the more recent Meso-Cenozoic units.

The folding in the region is fairly well demonstrated across the whole area, anticlines and synclines being visible in a NW-SE direction corresponding to the 3rd stage of variscan deformation and associated cleavage. Several faults in dominant directions NNE-SSW, N-S and NE-SW occur in the area and may present locally significant fills of quartz.

HISTORICAL BACKGROUND

Throughout the exploration area there are various known mineral deposits of Sn-W and Au-Ag(Sb), many of which are being mined on different scales.

The deposits and former Sn-W mines are located mainly in the NW sector of the exploration area and belonged to the Góis mining field. Mining in this metallogenic province reached its peak during World War II, the tungstiferous zone being the most productive area of Portugal at that time.

In 1957, the Góis Mining Field was founded with around seventeen concessions, including the Vale de Pião and Sandinha (Senhora da Guia Mine) concessions, which correspond to the most important tin and tungsten mines, respectively. The Senhora da Guia Mine operated between 1949 and 1972. During this period 8 levels of galleries were opened over a distance of 350 m and reaching a depth of 126 m. The operations focused on sub-vertical quartz veins with tungstiferous mineralization. The Vale Pião mine operated between 1946 and 1969 and mined sub-horizontal quartz veins, predominantly stanniferous mineralization. After the closure of the mine in the 1980s, the SFM carried out a prospecting campaign in which 25 surveys were conducted covering the area of the mining works and its surroundings, drilling a total of 3,200 metres.

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Geological background of the Escádia Grande area
Mineralização estano-tungstífera

The stannous-tungstiferous mineralizations mainly occur at the N-NW zone of the exploration area and are associated with non-outcrop granitic intrusions.

The mineralizations of Sn-W occur in two types of structures: veins and breccias/stockworks.

The vein structures, generally of a NW-SE direction, are characterized by quartzose filling with cassiterite, wolframite and, more rarely, scheelite. These may be sub-vertical and sub-horizontal, both lying in a general NW-SE direction. They have thicknesses not exceed 0.60 m and as well as the useful mineralization, they also contain sulphides (arsenopyrite, pyrite, sphalerite, pyrrhotite, chalcopyrite), mica, tourmaline and apatite. The Senhora da Guia Mine (W) essentially mined sub-vertical veins with wolframite. The Vale Pião Mine (Sn) mined sub-horizontal quartz veins, predominantly cassiterite and some wolframite.

The structures of the type breccia/stockwork are identified in two places: in the former Vale Pião Mine and the Vale Moreiro – Casal Loureiro sector. Installed in late Variscan to alpine shear zones (NNE-SSW), these structures have essentially tungstiferous, and to a lesser extent, stanniferous mineralization.

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Geology and location of former mines of Senhora da Guia (W) and Vale Pião (Sn-W) and Vale Moreiro – Casal Loureiro sector
Auriferous mineralization

The auriferous mineralizations are associated with quartz vein structures and sulphides that occur in NW-SE shear zones.

At the Escádia Grande mine, auriferous mineralization occurs in vein structures of tabular and lenticular morphology in the general direction of N30º-55ºW, variable pitch of between 50º-60ºSW and thickness of between 0.50 to 0.70 m. The vein structures exhibit essentially quartzose filling with arsenopyrite strongly associated with the auriferous mineralization, but also other sulphides (galena, sphalerite, pyrite) and chlorite. This deposit is affected by faults in NNE-SSE and ENE-WSW directions, making significant tailings, in particular horizontal, which displace the mineralized structure.

The area of Vale Pião was also mined by the Romans for gold. In this sector, breccia were identified in a NNE-SSW direction with quartz and sulphides that may be the carrier structures of the auriferous mineralization.

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Geology and former mining operations of Escádia Grande mine