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Mineral Potential of Portugal (1998)

1. Preamble

A complex and diversified geology endows Portugal with a considerable mineral potential, leading to the occurrence of considerable number of ore, industrial and ornamental stone deposits.

Mineral exploitation has a present considerable high level originated from world class deposits, as Neves-Corvo (Cu, Sn) and Panasqueira (W), but also from a lot of some other deposits producing salt, feldspar, uranium, kaolin, ball clay and fire clay, ornamental stones and some other mineral substances. Portugal is presently the main UE producer of copper, tin and tungsten concentrates and 6th world producer of ornamental stones.

Exploration activity is also at a high level considering the relative small extent of the territory (roughly 90 000 Km2). Large international companies and junior international companies conduct exploration mainly focused on base and precious metals.

Portuguese territory covers half of the Iberian Pyrite Belt (IPB) which is considered the main metallogenic province of the European Union, where occurrences of polymetallic massive sulphide deposits like Neves-Corvo and Aljustrel, in Portugal, Rio Tinto, Sotiel, Los Frailes, Las Cruces, etc., in Spain. The IPB is the main primary source of base metals in the EU.

Hesperian granites and associated metamorphics in the north and central part of the country are associated with tungsten and tin mineralisations, Panasqueira being the biggest wolframite mine out R P. China.

The potential in precious metals is well known since ancient times and is spread out geographically all over the country, occurring in diverse forms and different geological settings (veins, skarns, shear zones, placers, etc.).

The general framework of the activity has favourable characteristics, which is considered one of the reasons, linked with the recognised mineral potential, of the present level of activity. Institutional stability, mineral rights granting mineral property, good infrastructure, incentives to investment, affordable qualified work for European standards, a light fiscal burden are several others reasons why activity is so interesting.

This publication lies in the framework of the public mission of the Instituto Geo1ógico e Mineiro (national geological survey) of promoting corporate investment, both national and foreign, which may be complemented to all those interested with the provision of all the basic information about geology, hydrogeology, geophysics, geochemistry and drilling data in archive or assistance in defining exploration targets and strategies.

You are welcome!

President of the Board

Luís Rodrigues da Costa

 

2. Geological and Mining Background

The Hesperian MassifFrom a geological viewpoint, Portugal is a considerably diverse and complex country, these characteristics providing it with important potential in various mineral resources.

The territory can be subdivided, in geological terms, into 2 large groups: the Hesperian Massif and the Epi-Hercynian Covering, the latter including the western and southern Meso-Cenozoic borders, and also the basins of the Tagus and Sado rivers.

The Hesperian Massif, in which predominantly metallic mineral resources occur, can in turn be divided into various geotectonic units (Fig. 1), as described below (Ribeiro et al., 1979; Quesada, 1992):

  • Galicia - Trás-os-Montes Zone - This is characterised mainly by the existence of two mafic and ultramafic polymetamorphic massifs known as Bragança and Morais. The surrounding formations date chiefly from the Silurian period and are characterised by the existence of acid and basic volcanic rock, which make contact with the massifs via larger thrust systems. Binary granite, "alkali" and porphyritic granite, biotite and "calcalkali" granite also occur. The chrome, platinum and, possibly, copper, nickel and cobalt potential of the Morais and Bragança massifs is worth stressing, as is the potential for tungsten, tin, precious metals, uranium and, probably, polymetallic sulphides in the surrounding formations (Goínhas et al., 1992).
  • Central Iberian Zone - This is mainly characterised by the predominance of the formations of the so-called Schist-Greywacke Complex, consisting of a flysch-type series dating from the Cambrian and Late Precambrian period. There are also large areas of "alkali" and "calcalkali" granitoids, in which various types of granite can be distinguished. Worth highlighting is the occurrence, in the Douro-Beiras sector, of continental formations from the Carboniferous period, where various coal mines have been exploited (Douro Carboniferous Belt).

    Also worth mentioning in this geotectonic unit are important mineralisations of tungsten and tin, normally associated with the contact between the granite and the metasediments, and the existence of precious metals, frequently associated with arsenic and antimony, as in the Valongo/Gondomar Gold-Antimony Belt, for example. There are also important mineralisations of uranium, many of which have been exploited, related with late tectonic and metallogenetic phenomena that have affected the post-tectonic "calcalkali" granite.

  • Ossa - Morena Zone - This is an extremely complex and diverse unit which begins with a polymetamorphic Precambrian, followed by Cambrian and Silurian formations, and ends with a flysch sequence from the Late Devonian period.

Contact with the Central Iberian Zone is carried out via an important shear zone which stretches from Oporto to Cordoba in Spain (Blastomylonitic Belt).

With regard to magmatism, the NE sector has a predominance of granitic rocks, chiefly "calcalkali", porphyritic, biotitic, similar to those in the north and centre.

To the south, the basic character of the intrusions gradually increases, with "calcalkali" becoming predominant: gabbros, diorites, serpentinites and anorthosites (which form the recently named Beja ophiolite complex), various different porphyries, and later intrusions comprising gabbrodiorites, granodiorites, tonalites and granites (which constitute what is known as the Evora Massif).

The most important mineral occurrences are base metals, which are associated with the Cambrian-Ordovician volcanic sedimentary complex, precious metals, chiefly related with the Precambrian formations, and tungsten and tin in the Sta. Eulália granitic complex, not to mention the potential for chrome, nickel, cobalt and platinum in the basic and ultrabasic rocks on the north and south margins of this zone.

With regard to non-metallic minerals, this geotectonic unit is rich in ornamental rocks, particularly marble.

  • South Portuguese Zone - The Ossa - Morena Zone and this unit are joined by the Ferreira - Ficalho thrust (partially over the Beja-Acebuches complex), which runs approximately E-W to the east and NW-SE to the west.

The South - Portuguese Zone is characterised by the existence of a volcanic sedimentary complex (VS) from the Late Devonian - Early Carboniferous period, overlain by a Culm flysch sequence; underlying this complex is the so-called "Phyllite-Quartzite Group". The oldest formations in this zone date from the Early Devonian period and belong to the "Pulo de Lobo" Formation, which includes phyllites, quartzites and rare acid and basic volcanic rocks. The acid volcanic rocks in the volcanic sedimentary complex constitutes the metallotect of the massive polymetallic sulphides that are characteristic of the Iberian Pyrite Belt, the most important metallogenetic province in Portugal in which the Lousal, Aljustrel, Neves Corvo and S. Domingos mines are located.

We shall not go into the geological aspects of the Epi-Hercynian Covering, but shall touch on its non-metallic resources, namely sands, gypsum, clay, kaolin, limestone, diatomite and salt, further on.

 

3. Historical Overview of Mining in Portugal

The mining of mineral resources in Portugal was initially carried out by the Phoenicians, but was intensely and mainly developed by the Romans.

The first mining operations would have taken place in "gossan" type oxidation zones (for copper, zinc, lead, gold and silver) and gold-bearing placers (Carvalho, 1994). The Romans would later intensely exploit gold and polymetallic sulphide vein deposits. To better comprehend the size of the work involved, one need look no further than Três Minas, to the north of Vila Real, from which approximately 10 million tons of material was extracted; and in Aljustrel (southwest of Beja), mine shafts reached a depth of 120 metres.

Then followed a lengthy break in the mining of mineral resources in Portugal which was only occasionally interrupted, the exploitation of alluvial gold in Adiça near Lisbon during the XII century is one example of this.

From the middle of the last century, coinciding with the start of the industrial revolution, mining once more became an important industry in Portugal, with the first mining concessions being granted in 1836.

By the end of the X1X century, approximately 300 concessions had been awarded, the main substances exploited being polymetallic sulphides (Aljustrel, S. Domingos), tungsten and tin (Panasqueira), and antimony and gold (Valongo/Gondomar).

Exploration Permits for Metallic Substances (1980 to 1997)
Exploration Permits for Metallic Substances (1980 to 1997)

At the start of the XX century, there was a marked increase in coal annual production.

The two world wars, particularly the Second World War, led to a great demand for tungsten, which in turn led to increased exploration and exploitation of not only this element but tin as well, as these two elements are generally related spatially and/or structurally. Production of the concentrates of these substances peaked during 1942 at 5700 tons for tungsten, the main producing mines being Panasqueira, Borralha, Argozelo, Montesinho, Vale das Gatas and Ribeira.

The country also possesses important uranium deposits, with approximately 4200 tons of U3O8 produced between 1950 and 1990.

From the start of the fifties but mainly in the eighties, exploration underwent somewhat of a boom in Portugal (Fig. 2 and 3), at first including tungsten and tin in the centre and north of the country and later concentrating to precious metals and base metals, the latter sought principally in the Pyrite Belt in the south, where a remarkable number of mineral masses have been discovered: Moinho (1955), Feitais (1963), Estação (1968), Gavião (1970), Salgadinho (1974), Neves Corvo (1977) and Lagoa Salgada (1992).

The most important of these discoveries, in which the IGM (Geological and Mining Institute) has always played an important role, was the Neves Corvo deposit: since the mine came into operation, Portugal has become the largest producer of copper (1988) and tin (1990) in Europe as well as tungsten from the last operational mine (Panasqueira).

Portugal is also an important producer of ornamental rocks, particularly marble, even at the international level.

Exploration of Mineral Deposits (Situation as of 1/98)
Exploration of Mineral Deposits (Situation as of 1/98)

Main Gold Occurrences and Deposits
Main Gold Occurrences and Deposits

 

4. Precious Metals

As mentioned earlier, it has always been known that the Iberian Peninsula is rich in precious metals, and these are to be found the length and breadth of Portugal. We shall begin with a description of the various occurrences and deposits, citing the most recent exploration results obtained either by the IGM itself or private companies. We shall also briefly describe the areas that show potential for these metals so as to provide a short to medium term forecast for this mining sector in Portugal.

A description of the most important deposits follows, then, grouped by location within the geotectonic units referred to above (Fig. 4):


Galicia - Trás-os-Montes Zone

  • JARIÇA/EDROSA - Auriferous mineralisation occurs associated with sulphides (arsenopyrite, pyrite, sphalerite, galena and chalcopyrite) and embedded in a Silurian volcanic sedimentary complex, clearly controlled by the Hercynian orogeny (Knopf et al., 1990), which causes an alignment of the mineralised structures (quartz and porphyry veins) in a NNW-SSE direction. The company Prominas has been exploring this area since 1986.
  • POÇO DAS FREITAS - The mines in this area date back to Roman times and have left behind a series of small open pits, the largest of which is roughly 100 metres long and 80 metres in width. Mineralisation, which is associated with stockworks of quartz veins, occurs embedded in granitic rocks, running parallel to the large Régua/Verin fault and corresponding to a possible shear zone.

Cogema prospected this zone between 1986 and 1990, and carried out an economic viability study on the north structure of the old Limarinho works. This points to the existence of possible reserves of 2.07 tons of gold with an average grade of 2.8 g/t.

An exploration license for this area was recently awarded to the Australian company Northern Territory Gold Mining N.L..

  • TRÊS MINAS - This was the largest Roman mine in Portugal, and consists of three open pits running WNW-ESE, two of which are of an impressive size (Ribeirinha and Covas), the largest approximately 500m long, 100m wide and 80m to 100m deep. There are also numerous shafts and galleries (the largest of which is 250 metres in length with a 5 x 1.5m cross-section). It is estimated that 10 millions tons of material have been mined here.

As in the NW of Spain, the Romans employed the "ruina montium" mining technique, which was usual practice for low grade, high tonnage deposits. Gold occurs associated with arsenopyrite and pyrite, in quartzite lenses interstratified with Silurian shales, and appears to be of syngenetic (paleoplacers) and epigenetic (tectonic control) origin. This area was studied by the Portuguese company SPE between 1984 and 1988, and an exploration license is currently awarded to a consortium formed by the Societé Minière du Bourneix, a French company belonging to the Cogema group and the EDM, a state-owned Portuguese company. The area also includes the Jales zone, which we describe below.

  • JALES - The first mining operations carried out in this zone also date back to Roman times, and has become this century the largest gold mine in Portugal. Hydrothermal gold-bearing quartz veins occur here in two main directions (NE-SW and WSW-ENE), coincident with sub-vertical fractures embedded in Hercynian granites and schists, greywackes and quartzites from the Schist-Greywacke Complex, and mainly from the Silurian age. These lodes are sometimes as long as 2.5 kms and although their thickness varies, they never exceed 1 metre width. The two main lodes, which run in a NE-SW direction, are known as Campo and Desvio. Gold and electrum occur associated with quartz and sulphides (arsenopyrite, most common, pyrite, pyrrhotite, chalcopyrite, sphalerite, tetrahedrite, galena). Grade is fairly irregular, although figures of 30-40 g/t Au were frequently found. Since 1933, the mine has produced approximately 25 tons of gold and 100 tons of silver; at the time of its closure in 1992, it had reached a depth of 620 m. A consortium formed by Minas de Jales and BP Minerals, which later transferred its position to RTZ, prospected the area between 1984 and 1991; as mentioned earlier, it is currently awarded to Soc. Min. Bourneix/EDM. The latter recently determined that the Campo lode continues approximately 600 m south of the old mining works, in a structure known as the Horta vein, although mineral grade is highly variable. In the Gralheira structure - a shear zone with several veins, running in a WSW-ENE direction, embedded exclusively within metasedimentary Silurian rocks and located NE of the Campo and Desvio lodes - the consortium has also been able to determine the existence of a mineralised zone that extends for at least 1850 metres and is roughly 15 metres thick. A pre-viability study is currently being carried out on this structure; possible future exploitation might also allow complementary exploitation of the Campo zone.
  • LATADAS/FREIXEDA - Mineralisation occurs in quartz veins embedded in the Trás-os-Montes volcanic-siliceous and quartz-phyllite Silurian complexes, which are occasionally intruded by alkali granites. The veins that run predominantly in a NE-SW and E-W direction, in a shear zone, were also worked by the Romans. The gold is mostly associated with W, As, Cu, Pb, Zn and Sb polymetallic sulphides. The firms Cogema and Rena prospected this zone between 1986 and 1992; the IGM is currently carrying out a mining evaluation project here.
  • VILA VERDE/PONTE DA BARCA - Prospecting carried out by the IGM at the end of the eighties uncovered a NE-SW alignment that had gold-bearing potential, the following areas being the most important:

Marrancos - mineralisation is related with a shear zone which affects the Silurian metasediments, these transformed into hornfels by contact metamorphism. In the zone affected by this shearing, breccias and silicifications are to be found accompanied by sulphide mineralisations (arsenopyrite and pyrite) with gold.

Godinhaços - mineralised structures (gold + arsenopyrite) are located exclusively in the granite of Vila Verde. There appears to be lithological control of the mineralisation, the veins running predominantly in an NE-SW direction.

Grovelas - characterised by the occurrence of a dense network of joints filled with arsenopyrite and running predominantly N 25º - 40º E and N 50º - 70º E. There appear to be two mineralised axes, the intersection of which could prove to be an enrichment zone. Also worthy of mention is the existence of old Roman mining works.

A concession for exploration in this area was recently applied for by the company RTZ.


Central - Iberian Zone

  • VALONG0/GONDOMAR - This gold-antimony belt is situated in Baixo Douro region, northeast of Oporto and stretches from Esposende to Castro Daire in a distance of 90km. Besides Sb-Au occurences exist also Au-As, Pb-Zn (Ag) and Sn-W mineralisations, which are located in the large Valongo anticline and in the Carboniferous syncline, embedded in metasedimentary formations dated from Precambrian and/or Cambrian to Carboniferous and more rarelly in hercynian granites.

In remote times, initially the Pheonicians, later and chiefly the Romans, exploited gold in this mining district. At the end of the XIX century, this belt was extensively mined for antimony; and, as a sub-product, gold contained in quartz veins. We can remark the production from the ancient mines of Ribeiro da lgreja (Sb-Au), Montalto (Sb-Au) and Banjas (Au-As) not forgetting the silver Terramonte mine that during the sixties was one of the most important in Europe. Lead and zinc were also mined here.

Studies undertaken by EDM and BRGM, from 1988 to 1993, indicated the occurrence of gold-antimony mineralisations of stockwork type in Alto do Sobrido and of saddle reefs type in Banjas. From recent works carried out by IGM resulted the important discovery that gold is not restricted to the quartz veins but pervades, within shear zones, the pores and fractures of their host rock; in consequence of this discovery quartz stockworks and silicified mineralised bodies with gold and antimony were found in Alto do Sobrido and these orebodies illustrate the excellent mineral potencial of the area.

A consortium between EDM and Connary Minerals, applied recently for an exploration licence, including Alto do Sobrido and Banjas areas.

  • CASTROMIL - This area, which was first mined in Roman times, is located within a Hercynian granite near its contact with Silurian metasediments, part of the Eastern flank of the Valongo anticline. The latter is characterised by the occurrence of various gold/antimony deposits, as mentioned earlier. Two important orthogonal fault systems occur in this zone: NW-SE and NE-SW. The latter, which is more recent, is of great metallogenetic importance and appears to represent the hydrothermal conduits. Gold is essentially disseminated along veins in the silicified granite, running NW-SE, related with a shear zone and frequently associated with sulphides (arsenopyrite and principally pyrite). Besides the silicification, other alteration phenomena, such as sericitisation and kaolinisation, also play an important role. In paragenetic terms, three stages of mineralisation are considered: ferro-arseniferous (quartz + arsenopyrite I + pyrite I + pyrrhotite + bismuth ?), zinciferous (sphalerite + chalcopyrite), and remobilisation (arsenopyrite II + galena + gold).

Mining operations will begin in 1998 by the Irish firm Connary Minerals, PLC in two fields: Covas de Castromil and Serra da Quinta, separated by the Sousa river and the Oporto-Pocinho railway. For the first of these fields, proved reserves of 2,147,000 tons have been determined with an average grade of 1.9 g/t Au (cut-off of 0.5 g/t) and probable reserves of 270,000 tons with 1.8 g/t Au. For Serra da Quinta, probable reserves are put at 743,000 tons with 2.8 g/t Au.

This area was previously prospected by Billiton between 1988 and 1992. In 1994, the IGM carried out a re-evaluation study of the deposit, which proved decisive for the future exploitation.

  • PENEDONO - In this area, also worked by the Romans, various gold-bearing quartz veins occur. These are sub-vertical and run predominantly in a NE-SW direction. Gold is chiefly to be found in the arsenopyrite and does not appear to be restricted to lode-beaning structures: it also occurs in the wall rock, normally heavily sericitised Hercynian granite near the contact with the Cambrian metasediments of the Schist-Greywacke Complex. Around 50 years ago, this area produced gold (Stº. António mines) with an average grade of 14 g/t. Prospecting studies are currently being carried out on it by the firm Sociedade Mineira de Moimenta, which has concentrated mainly on the Docotim (Paredes da Beira) and Stº. Ant6nio (Penedono) structures.
  • CARAMULO - Another area worked by the Romans, this was recently studied by the IGM. Gold occurs associated with pyrite and arsenopyrite in quartz lenses. There is b tectonic control, suggesting the existence of a NNW-SSE shear zone, parallel and related to the Oporto-Tomar thrust system with a maximum width of 500 metres and a length of several kilometres. Taking both this and the geochemical mapping of gold obtained from soil samples into account, it is likely that mineralisation also occurs in the shist -greywacke wall rocks. Exploration rights for this area were recently applied for by RTZ.
  • ESCÁDIA GRANDE - At this old mine, that was also worked by the Romans, there was gold production during the forties. Mineralisation occurs associated with quartz vein structures running NW-SE, dipping SW, probably related with the Oporto-Tomar thrust system, and consists of polymetallic sulphides (pyrite, arsenopyrite, sphalerite, galena and chalcopyrite) in which the gold is finely disseminated. The wall rock belongs to the Schist-Greywacke Complex and is frequently altered by silicification and carbonisation phenomena, with which the mineralisation is associaled.
  • PORTALEGRE - This area is located within the Tomar-Badajoz Blastornylonitic Belt. Gold occurs predominantly associated with silicified, chloritised and carbonated metavolcanic sedimentary levels of the Precambrian Série Negra in the Mosteiros and S. Martinho (Alter do Chão) sectors. In the latter, the existence of Plio-Pleistocene covering deposits (gravel) bearing secondary gold mineralisation is also worthy of mention. These facts were uncovered by exploration studies undertaken by the IGM between 1992 and 1994. Exploration rights for the area were awarded to the firm Portuglobal in 1995, which has been studying it since this time. Drilling recently executed by the company in the S. Martinho sector have provided extremely positive results (2m with 49 g/t Au, 4m with 12.7 g/t Au and 33.43m with 1.2 g/t Au).

The gold is usually accompanied by pyrite, pyrrhotite and arsenopyrite.

  • MONTEMOR-O-NOVO - Gold-mineralisations are concentrated in tabular zones, normally characterised by heavy silicification and embedded in a Precambrian volcanic sedimentary sequence along a belt over 30 kilometres in length. This area, initially studied by the IGM, has been investigated by several private companies (RTZ, BP, Portuglobal) since 1984. Research undertaken has determined the existence of various deposits with marked lithological and tectonic control, the most important of which are located in the SE sector of the area: Banhos, Casas Novas, Chaminé, Ligeiro, Caras, Covas and Braços. Some free gold occurs, but normaly it is associated with grains of arsenopyrite and loellingite.

In 1991, RTZ presented - with a cut-off of 1 g/t Au - measured and indicated reserves in respect of Chaminé, Braços 2 and Casas Novas and inferred in respect of Ligeiro, Caras, Covas, Braços 1 and Banhos, a total of 2.17 million tons with 2.7 g/t Au.

In 1996, based on new works and economic re-evaluation, undertaken by the London subsidiary of the firm A.C.A. Howe International, Portuglobal recorded an increase in gold reserves using a cut-off of 0.5 g/t Au. The company has then presented a global reserves value (measured + indicated + inferred) of 4.9 million tons with an average grade of 1.8 g/t An, and continues to explore the area.


South - Portuguese Zone

  • CAVEIRA, ALJUSTREL and S. DOMINGOS - Gold has been mined here since Roman times in gossan zones of polymetallic sulphide deposits, embedded in a volcanic sedimentary complex dating from the Late Devonian - Early Carboniferous period.

Prospecting is currently underway in Aljustrel (EDM/Portuglobal) and S. Domingos (RTZ), mainly concentrating on base metals (and as such shall be dealt with in greater detail in the respective chapter) but without overlooking the potential that may still exist in these areas for precious metals. With similar aims in mind, the Canadian firm Crockite Mining recently applied for exploration rights for the zone of Caveira/Lousal.


Secondary Deposits

Despite the fact that they have been intensely exploited in Roman times, they are not properly studied.

The most important are the deposits of Alva (Arganil), Arouce (Ceira River), Monfortinho (Erges River), Penamacor (Basdgueda River.), Milreu and Martinchel (Zézere River), Rosmaninhal and Constãncia-Abrantes (Tagus River). The volume of sand and gravel extracted from these sites has been calculated at several million cubic metres. Some of them also contain channels that have been hewn in the bedrock to help concentrate the gold.

Based on the above considerations and the metallogenetic characteristics of the country, we can define the following areas as being potentially rich in precious metals (Fig. 5): Vila Verde/Germil(2), Valongo/Gondomar(6), the Blastornylonitic Belt (1), the Alentejo GoldArsenic -Antimony Belt(13) (Au,Ag), Caminha/Braga(l), Gerês/Mogadouro(3), ErvedosalArgozelo (4), the Douro Scheelitic Belt (5), the Paiva Tungstiniferous Belt(7) , Arouca/S. Pedro do Sul(8), Trancoso/Figueira de Castelo Rodrigo(9), Goís-Segura(10) (W, Sn, An), Sousel/Barrancos(12), Magnetitic-Zinciferous Belt(14) and Porphyries of Beja(15) (Zn, Cu, Pb, Ag, An).

We feel that in the future special attention should be given to three metallogenetic scenarios, none of which have been thoroughly investigated in Portugal(Veigas et al., 1992):

a) The mineral deposits occurring in the Blastornylonitic Belt(11) or its dependent areas, characterised by b tectonic control, frequently in shear zones as equally happens in the Galicia-Trás-os-Montes and Central-Iberian Zones, related with the Régua Verin and Vilariça faults.

b) Gold-bearing mineral deposits associated with granitic intrusions and occurring within it or in the contact with the wall rock (especially skarns) and as a result potentially existing in belts also favourable to W and Sn mineralisations, probably in geochemical spatial relationship with these elements (1, 3, 4, 5, 7,8,9, 10).

Potential Areas for Precious Metals
Potential Areas for Precious Metals

c) Mineralisations occurring in the surrounding formations (Silurian volcanic sedimentary complex) of the Morais and Bragança massifs, characterised by their association with polymetallic sulfides and/or shear zones.

 

5. Base Metals

Portugal's main base metal resources are located in the south of the country in the OssaMorena and South Portuguese zones, the Pyrite Belt in the latter being the most important. Given the different metallogenetic characteristics of these two geotectonic units, we shall sub-divide our presentation in the same manner.


Ossa Morena Zone

Main Old Mines, Deposits and Occurrences of Base Metals in Ossa Morena ZoneBelow is a summary of the primordial geological and mineral characteristics of the different "Belts" that occur in the Ossa-Morena Zone, together with a description of the most important mineral occurrences which may in some way reflect the metallogenetic models that are representative of each Belt (Fig. 6). The IGM has carried out exploration work in all of them, having presently an important know-how, obtained during that activity.

I - NORTH ALENTEJO AREA

Given the nature, typology and regional geological setting of the mineral occurrences, this area is split into three belts:

  • Arronches - Campo Maior Belt
  • Alter do Chão - Elvas Belt
  • Sousel - Barrancos Belt

IA - ARRONCHES - CAMPO MAIOR BELT

This belt basically consists of Late Precambrian formations belonging to the Tomar -Badajoz Blastornylonitic Belt.

Occurrences of copper and, more rarely, lead are represented by the old Tinoca, Azeiteiros and Balôco mines. Stratiform mineral occurrences, with disseminated sulphides, are located near the contact between different types of gneiss and associated with a felsic volcaniclastic formation.

The existence of high metamorphic gradients, related with important tectonic accidents and consequent hydrothermal activity, resulting in silicification, chloritization and muscovitization phenomena, appears to have significantly contributed to the concentration of mineralisations of pyrite, chalcopyrite, pyrrhotite, magnetite and, more rarely, argentiferous galena.

IB - ALTER DO CHÃO - ELVAS BELT

This belt essentially corresponds to Cambrian formations. Occurrences of Cu, Pb and Zn are mainly related with intermediate-acid Cambrian metavolcanics, sometimes with associated agglomerated tuffs. Small ocurrences of Pb-Zn are also known to exist in the Early Cambrian carbonated formation, particularly where this is more fractured and silicified.

IC - SOUSEL - BARRANCOS BELT

This basically corresponds to Cambrian, Ordovician, Silurian and Devonian formations.

There are essentially three types of mineralised structure here: vein, stratiform and disseminated types.

In the first, which basically consists of copper mineralisations, there exist subconcordant veins and veins that are completely discordant from the formations in which they are embedded. The most important of the sub-concordant veins are perhaps Miguel Vacas and Mociços ore-bodies, situated at the base of the Silurian, and Urmos, located in basic metavolcanics (spilites) from the Mid Cambrian.

The most important of the discordant veins are Minancos, from the base of the Silurian, Bugalho Mine, in Silurian formations not far from its base and near the Messejana fault, and Zarnbujeira, in Ordovician formations. The Mostardeira, Aparis and Botefa veins are also discordant, and all are situated on the SW flank of the Terena syncline, which is essentially made up of flysch formations from the Devonian period.

With regard to stratiform mineralised structures, these are closely related to a CambrianOrdovician discordance. Mineralisations basically include pyrite, sometimes massive and rare chalcopyrite, sphalerite and galena. Mineralisations of pyrite, sphalerite and galena also occur in dolomitic limestones from the Early Cambrian, in microfractures and particularly in brecciated facies.

The disseminated mineralisations formed essentially of pyrite and chalcopyrite are associated with post-Silurian, intermediate-acid, sub-volcanic structures and constitute the cement of eruptive breccias. Mineralisation is more intense when the elements of these breccias are predominantly of a carbonated nature.

II - ÉVORA - BEJA MASSIFS

In view of the nature, typology and regional geological setting of the mineral occurrences, 3 belts have been defined in these massifs:

  • Arraiolos - St. Aleixo Belt
  • Magnetitic - Zinciferous Belt
  • Porphyry Belt

IIA - ARRAIOLOS – STº. ALEIX0 BELT

Various ocurrences of copper, mainly of vein type, are known to exist here, some of which have been exploited on a small scale (Azaruja, Monte do Trigo, Reguengos and SC. Aleixo). These mineralisations are related with both granodiorite intrusions and basic volcanics commonly spilitized.

IIB - MAGNETITIC - ZINCIFEROUS BELT

This basically comprises Cambrian, Ordovician and Silurian formations, intruded by several Hercynian granitic massifs such as Pias and Pedrogão.

The most important deposits in this belt are Algares (Cu, Pb, Zn) and Balsa (Pb, Zn) in the Portel region, Enfermarias (Zn, Cu, Pb) and Preguiça (Zn, Pb), in Moura and Sobral da Adiça regions respectively, and other occurrences of Pb, Sb, Ag, Zn in the Ficalho-Moura-Vale de Vargo triangle.

The Balsa and Preguiça deposits are associated with dolomitic limestone; those at Algares and Enfermarias are related with an intermediate-acid volcanic episode which occurred at the base of the Early Cambrian, contemporaneous with a carbonated sedimentation, with which an important hydrothermal system is associated.

The Enfermarias "hidden deposit", located essentially by gravimetry and confirmed by drilling, illustrates nicely base metal prospecting in the Magnetitic - Zinciferous Belt. Deposits of Zn and Pb are also represented in paleokarsts, which contain very high levels of these elements, an example of which is the old Vila Ruiva mine.

The european firm Exminco recently applied for exploration rights for an area that includes these deposits.

IIC - PORPHYRY BELT

This covers a wide area in which sub-volcanic and volcanic rocks - namely rhyodacites, felsites, spilites and basalts - predominate and which are surrounded to the NE and SW by diorites, gabbros and ultrabasic rocks. The most significant mineral occurrences are Corte Pereiro, Caeirinha, Alcáçovas, Peroguarda and Asseiceiras.


South-Portuguese Zone

This zone is characterised by the Iberian Pyrite Belt (IPB), which is known around the world for its large deposits of massive polymetallic sulphides and plays an important role in supplying Europe with base metals.

Up until the eighties, the prospecting of massive polymetallic sulphide deposits was mainly carried out in areas where formations of the Volcanic Sedimentary Complex (VS), potential bearers of sulphide masses, outcropped or were expected to lay at depths not significantly exceeding 300 metres(Oliveira et al., 1998).

These areas were thoroughly prospected during the sixties, during which there was a marked turnaround in the methodology that had hitherto been used as a result of the evolution in the geological models related with the formation of these deposits and the introduction of new prospecting techniques and systematic gravimetric coverages, which in turn brought about great improvements in discovering mineral deposits. The changes in both corporate sector and in official departments led to important discoveries being made, most of them situated near mining centres or known occurrences, as referred above.

The Pyrite Belt has been of great interest to private companies in the mining sector for many years, this clearly reflected in the number of prospecting contracts that have been signed with the Portuguese State.

The discovery of Neves-Corvo in 1977 allowed a new deposit type to be defined for the IPB, in which the levels of base metals, Cu and Sn in particular, are extraordinarily high. As this type of mineral deposit can be economically exploited at depths of more than 500 metres, there was a change of strategy on the part of several mining companies in respect of the geological- structural characteristics of the areas they wished to explore. From that moment on, prospecting at great depths thus became viable, as the discovery of a deposit with similar characteristics would support the necessary investment.

These facts, coupled with the scientific and technological breakthroughs that took place during the eighties (in respect of both the geology and metallogeny of the IPB, and the geophysical techniques applied - advances in high sensitivity airborne magnetometry and time domain electromagnetics, as well as data processing), meant that prospecting in this metallogenetic province moved into areas where the VS ocurred at great depths bellow the flysch sediments and/or the Tertiary. ln recent years this trend continued, the number of companies prospecting in such areas has risen as technological advances and computer data processing have boosted their ability to detect mineral masses at hitherto unreachable depths and/or in particular adverse geological contexts such as conductive overburden.

Targets that might prove of interest in those areas are mostly located at great depth, where potential mineral-bearing horizons occur under a thick covering of flysch or beneath nappes, the thickness of which is often uncertain. The depth of drilling here reach levels that were unthinkable several years ago, these usually around the 600 m and 1000 m mark, occasionally going even further.

Despite those developments, the basic tools used since the sixties - gravimetry combined with specialized geological mapping, and magnetometry (with ground vertical component surveys replaced by high-resolution total field airborne surveys and ground follow-up work) - still play a major role.

Other complementary geophysical techniques are also routinely used, mostly in previously detected gravimetric anomalies. Those include vertical electrical soundings, time-domain electromagnetic soundings and borehole logging, and other electrical techniques such as induced polarization and magnetotelurics. In a limited fashion, reflection seismics has also been used. Another geochemical technique that has been used is the enzyme leaching of soil samples.

Although a few localized helicopter surveys, namely aeromagnetic and EM (INPUT and frequency domain) had been done in the eighties, a recent regional airborne high resolution magnetic and 256 channel spectrometric geophysical survey, has been contracted by one of the main operators in Portugal, RTZ. Those coverages have greatly contributed towards better geological mapping, defining regional geological structures, tectonic acidents, buried volcanic axes, and conductors, providing information that might indicate the presence of mineral masses deep bellow the surface.

Parallel to the activity carried out by private companies, the IGM also plays an important role, either through its own projects or through the services provided to these companies. Its work as led to the direct or indirect discovery of several masses of massive polymetallic sulfides and the promotion of certain areas later awarded to private companies.

During the nineties, prospecting on part of mining companies has showed no signs of letting up.

The IGM has continued to foster exploration work in this important province, by moving into less attractive areas, like the Tertiary Basin of the Lower Sado river, to the north of the Grândola fault. This led to the discovery of a new deposit of massive polymetallic sulphides, known as Lagoa Salgada, located far from any mining centre or known occurrence, which increased the mining potential of the IPB. Situated in an area where the VS is covered by sediments, and the interpretation of the gravity anomalies is hampered by the paleorellef and horst and grabens structures, controlled by the Paleozoic basement, this event captured the imagination of a great many firms, and was largely responsible for a wave of new prospecting requests.

Geological Setting of the Portuguese Pyrite BeltAll the different actions being carried out on the Pyrite Belt by both private companies and the IGM itself has led to a wealth of new geological information, which is being collected and stored in a general database.

We now move on to the most important mineral deposits and mines in this metallogenetic province (Fig. 7), from NW to SE although other deposits do exist (Caveira, Montinho, Chança, Salgadinho and Cercal, the last currently being mined for Fe and Mn):

LAGOA SALGADA - In this area, located in the Tertiary Basin of the Sado River but included in the NW segment of the IPB, the IGM has carried out varied exploration work which, thanks mainly to gravimetry, has uncovered several targets. In one of them, situated roughly 12 km NE of Grândola, a mass of polymetallic sulphides was discovered in August 1992 at a depth of 128 metres under tertiary covering (Fig. 8).

Boreholes executed in the central and NW nuclei oft he gravimetric anomaly of Lagoa Salgada have revealed a pyrite-bearing acid volcanic sequence accompanied by polymetallic sulphides, the NW nucleus the richer of the two (Oliveira et al., 1998). Here, the mineral mass is embedded in a volcanic sequence highly altered by an important hydrothermal system. The main volcanic facies are composed of intermediate - acid lavas and autoclastic breccias with abundant feldspar megacrystals, and fine, sometimes porphyrous, chloritic-sericitic volcanics; intercalated layers of possible lapilli are frequent. Note that the enormous tectonic complexity that affects the mineralisation and wall rock makes investigation of the zone extremely difficult.

As mentioned, this area was studied by the IGM until 1993, at which time it was awarded to a consortium of two companies, EDM and RTZ.

To date, three types of ore have been distinguished:

a) Complex, massive, banded sulphides, very finely grained, containing interesting grades of lead and zinc and not rare Cu/Au enrichment zones.

b) Stockwork mineralisation with concentrations of base metals.

c) Gold mineralisation associated with silicified shear zones, with arsenopyrite.

The following are some of the figures obtained from boreholes executed in the NW nucleus: during the drilling of LS 22 78.55 m with 0.35% Cu, 4.79% Pb, 7.52% Zn, 94.65 g/t Ag and 1.34 g/t Au were intersected and in LS 04 63.13 m with 0.48% Cu: 2.66% Pb, 2.96% Zn, 0.26% Sn, 69.91 g/t Ag and 0.98 g/t Au were obtained. In the central nucleus, LS 18 intersected 12.05 m with 0.08% Cu, 0.08% Pb, 0.20% Zn, 12.83 g/t Ag and 4.37 g/t Au.

The mineralised mass begins with an iron hat of variable thickness - never greater than 20m -where there is marked enrichment of precious metals, Sn and some times Pb. This enrichment in Au and Ag is also visible in the first section of the mass, immediately underlying, due to supergenic phenomena, or next to important thrusts and consequent remobilizations. The gossan has the following paragenesis: goethite, hematite, amalgams of Ag - Hg, chalcocite, neodigenite, covellite, bornite and mimetite. The primary mineralisation is composed mainly of pyrite with the following minerals: sphalerite, arsenopyrite, tetrahedrite, tennantite, galena, lollingite, chalcopyrite, cassiterite, stannite, meneghinite and pyrrhotite.

LOUSAL - Old mine situated on the SW flank (inverse) of the Lousal anticline. Mineralisation is found in a deep, narrow syncline, characteristic of the VS occurring here, which is deeply folded within isoclinal structures. Several masses have been recognised with tonnages of 100,000 tons to over 3MT, essentially pyrite, generally lenticular, aligned along the axis of the folds, dipping roughly 80º to the SW and extending several hundred metres with variable thickness.

The ore is relatively poor in Cu (<0.7%) and in Pb + Zn (1.1 - 3.5%), with annual production at the start of the seventies totalling between 230,000 and 250,000 tons. The mine was closed down in 1987.

ALJUSTREL - Mining at this important mineral deposit dates back to Roman times, the target being the outcroping masses of S. João and Algares. An important archaeological find was made here: two bronze tables inscribed with the mining law of those times.

In this area, the VS occupies the axis of an anticlinorium running in a NW-SE direction and is characterised by the existence of an important sequence of acid pyroclastic rocks, subdivided into lower and upper series(Silva et al., 1997). These rocks are in turn subdivided into two laterally equivalent series. In the central part of the structure there is a sequence which includes the lower unit with tuffs with megacrystals, and the upper with green tuffs; laterally, the lower series is characterised by the existence of volcanics with felsic facies; and the upper, known as the tuffs of the mine formation, is the bearer of masses of massive polymetallic sulphides.

The Messeiana fault has a sinistral displacement of roughly 2.5 km, causing locally a change in the direction of the structures from NW-SE to E-W Later it caused the NW block to lower and be covered by tertiary sediments. Thus, the sector of the Gavião deposit, which constitutes the extension of the Aljustrel structure, presents a tertiary cover of 60 - 90m.

The following masses have been recognised: Algares, S. João, Moinho, Feitais, Estação and Gavião, all occurring in well defined structural positions in the Aljustrel Anticlinorium, running parallel and symmetrical to the alignments of the felsic facies, mine tuffs which are: the S. João Syncline, containing the deposits of S. João, Moinho, Algares and the NE Gavião mass; a second alignment symmetrical to the latter includes the SW Gavião mass; finally, the Feitais and Estação deposits are located on the NE flank of the referred anticlinorium.

S. João and Algares were exploited up until the mid-sixties, the latter now exhausted, Moinho and Feitais were mined in more recent decades, while mining operations have never taken place at Estação and Gavião.

Various types of ore can be distinguished in the Moinho and Feitais deposits: coarse "banded", rich in chalcopyrite; massive, essentially pyritic and fine "banded", rich in sphalerite and galena.

To date, the following resources are known, excluding stockwork mineralisations:

Deposit Tonnage (Mt) Cu% Zn% Pb%
Moinho 44.1 0.85 2.98 1.10
Feitais 54.0 0.43 3.43 1.12
Gavião 25.7 1.51 2.98 1.01
Estação ~20 ~0.31 ~4.84 ~1.51
S. João ~45 ~0.87 ~3.37 ~1.20
(in SEG Guidebook Series, vol. 27)

The Algares deposit, which is currently exhausted, should have contained mineral resources greater than 50 Mt. An evaluation of the remaining deposits is still to be carried out, particularly for S. João and Estação. An exploration licence contract for Estação deposit was recently started by a consortium formed by the firms EDM and Portuglobal; boreholes are currently being drilled and intersecting the mineralised mass.

NEVES CORVO - This important mine is geologically situated at the end of the Neves Corvo - Rosário Anticline, a structure that runs NW-SE, the axis of which dips to SE, with deposits on both flanks (T.Oliveira et al., 1997). Various groups of sub-vertical faults occur which affect the mineral deposits and also low-angled overthrusts, related with repetitions of volcanic sedimentary and flysch units. These deposits are situated in the upper part of a volcanic sedimentary sequence (VS), mainly acid, and composed of three sequences of acid tuffs, separated by shales formations, with a discontinuous level of black shales immediately beneath the mineralised masses. Due to the abovementioned overthrusts, the flysch and volcanic sedimentary units repeat above the top of the mineral mass.

Geological, geophysical and geochemical prospecting work begun by the IGM and carried on by a Portuguese-French consortium (Sociedade Mineira de Santiago, S.M.M. Peflarroya and SEREM - BRGM) led to the drilling and intersecting in 1977 of the first deposit (Neves). Next, three more important deposits were discovered, Corvo, Graça and Zambujal, with a fifth deposit discovered in 1988 (Lombador). In 1980, the consortium gave way to Somincor (Sociedade Mineira de Neves Corvo, SA).

In 1985, RTZ Metals, Ltd (the Rio Tinto - Zinc Group) acquired the French interest in Somincor (49%), the remaining 51% held by the state-owned Portuguese firm EDM. Production of copper was begun at the end of 1988, with tin production in 1990. From 1988 to the end of 1995 the mine produced 8.7 Mt of copper ore, containing 790,000 tons of copper metal, and 2.2 Mt of tin ore, containing 41,140 tons of tin metal. Annual production currently stands at 1.9 Mt of copper and tin ore; plans to extend production to include zinc are being studied.

These deposits are composed of lenticular masses of massive polymetallic sulphides, also containing stockwork mineralisation in the footwall host rock, and are distinguished from other Pyrite Belt deposits by their high copper and tin contents and a highly metal zonation. This latter fact, related with the segregation of base metals, favours the division into copper, tin and zinc ores, as well as massive "barren" pyrite.

Three main types of ore occur:

a) "Rubané" - occurs at the top of massive sulfide masses, particularly at the Corvo orebody, and is composed of chloritic shales, siliceous shales and chert-carbonate breccia, with sulphide veinlets sub-parallel to perpendicular to the stratification and sometimes with tight lenses and bands of massive sulphides. The sulphides contained here are mostly cupriferous.

b) Massive sulphides - composed of approximately 95% of fine grained sulphides, in which pyrite predominates, followed by chalcopyrite, tennantite and bornite. In the polymetallic lenses the main zinc mineral is sphalerite ; galena occurs disseminated or in millimetric bands in the massive sphalerite. The main tin minerals are cassiterite and minor stannite, normally associated with high grade copper ore, at the base of the deposits in particular but also at its top. This ore can be split into 5 sub-types: cupriferous (MC), characterised by disserninations and bands of variable thickness of chalcopyrite in the massive pyrite and with a Cu content greater than 2%; cupriferous with broad bands of tetrahedrite/tennantite or sphalerite (MH), which introduce high levels of penalty elements, such as As, Sb, Hg and Zn; rich cupriferous ore (MS), with more than 1 % tin and composed of massive or banded chalcopyrite containing elements of massive cassiterite; stanniferous (MT), in which there is abundant cassiterite and a tin content of more than 8%; zinciferous (MZ), rich in sphalerite, which occurs as centimetric bands in the massive pyrite, bands which may contain disseminations of galena.

c) Fissural - stockwork - type mineralisation, including the "breecia" of the base of the Corvo mass, which occurs in the footwall shales and in acid volcanic rocks, usually in discordant veins and veinlets of sulphide minerals. Pyrite and chalcopyrite predominate, although cassiterite and sphalerite also occur, always accompanied by intense hydrothermal alteration of the host rocks.

This mineralisation can be subdivided into three sub-types: cupriferous (FC), with more than 2% Cu, present in veins and veinlets rich in chalcopyrite; stanniferous (FT), with more than 1 % Sn, present in veins rich in cassiterite, together with pyrite and, to a lesser extent, chalcopyrite; zinciferous (FZ), with more than 3.3% zinc, present in veins and vemlets rich in sphalerite.

In June 1996, mineral resources were calculated as follows:

Metal Mineralisation
and ore type
One
103 tons
% Cu Cu metal
103 tons
% Sn Sn metal
103 tons
% Zn Zn metal
103 tons
Copper Massive sulphides – MC 16,229 7,25 1,176,75 0,33 - 1,50 -
Fissural - FC 8,326 3,90 324,87 0,19 - 0,92 -
Rubané – RC 5,842 6,32 369,37 0,17 - 0,43 -
Total 30,397 6,16 1,870,99 0,26 - 1,13 -
Tin Massive sulphides – MS 1,406 14,22 199,96 1,65 23,19 2,08 -
Massive sulphides – MT 43 8,31 3,57 13,37 5,75 0,72 -
Fissural – FT 80 3,71 2,97 4,16 3,33 1,29 -
Rubané – RT 377 1,40 5,27 4,93 18,59 0.08 -
Total 1,906 11,11 211,78 2,67 50,86 1,62 -
Zinc Massive sulphides – MZ 43,874 0,47 206,29 0,09 - 6,11 2,680
Fissural – FZ 1,105 0,39 31 - - 3,39 38
Rubané – RZ 1,270 0,41 5,21 0,04 - 4,88 62
Total 46,249 0,47 215,80 0.09 - 6,01 2,780

S. DOMINGOS - The sequence and characteristics of the mineral-bearing volcanic sedimentary complex (VS) in this area are poorly exposed and understood, their structural aspects being particularly complicated. The upper levels of the VS are covered by a fairly thin turbiditic sequence overlain by Phyllite-Quartzite Group formations.

Nevertheless, a volcanic sequence composed of rhyolites, jaspers and diabases can still be observed in old works. This mine was extremely important in the past, and in fact dates back to Roman times. Between, 1858 and 1966, the "Mason and Barry Company" mined around 25 million tons of ore, by open-cast operations going down to a depth of 120m with additional underground work to a depth of 400m (Carvalho et al., 197 1).

The ore was composed chiefly of massive pyrite with a maximum grade of 10% copper and 14% zinc-lead, and average grades of 1.25% Cu, 2-3% Zn and 45-48% S.

Given the occurrence of massive polymetallic sulphides in the formations (Silurian volcanic sedimentary complex) surrounding the Morais and Bragança massifs, as well as several geological and metallogenetic similarities with the Pyrite Belt, it is our opinion that the Trás-os-Montes zone is worth investigating.

Nevertheless, the main target will still be the Pyrite Belt, in which exploration will continue to be carried out in zones characterised by (Oliveira et al., 1998):

  • Areas of high tectonic complexity, where barren allochthonous terranes thrust over more recent geological formations with high mineral potential.
  • Structural alignments, in which the VS can be found at great depth beneath more recent Paleozoic Flysch formations in Baixo Alentejo.
  • Areas within the Sado River Tertiary Basin, where the VS can occur at depths ranging from a few dozen to several hundred metres beneath Ceno-Anthrepozoic formations.

In the latter, the IGM is currently carrying out a research project in an area between Sta Catarina de Sítimos and Figueira de Cavaleiros, where gravimetry has been used as the basic prospecting technique, although complemented by others. Various gravimetric targets have been recognised (Fresta, Rio de Moinhos, Lameira, Chaparral, Mte. Branco da Loira, Vale Sabroso) and drilled (except the latter two). Two boreholes in Rio de Moinhos (Fig. 9) have intersected formations belonging to the VS, with characteristics that point to the potential existence of sulphide mineral occurrences (chloritization of acid tuffs, small stockworks, brecciated textures, occurrence of a layer of jasper roughly 30m thick) and have revealed the existence of a new volcanic axis in the Pyrite Belt situated NE of the structural alignment which includes the Lagoa Salgada deposit.

 

6. Other Metals

Tungsten and tin

The existence of a tungsten and tin metallogenetic province on the Peninsula, which in Portugal overlays the Galicia - Trás-os-Montes and Central - Iberian Zones, has long been known. In this province, gold and silver occur with a certain zonality at regional scale in relation to tungsten, hence the fact that the potential areas in these two groups of substances sometimes coincide.

We shall not cover the tin contained in the polymetallic sulphide deposits of the Pyrite Belt in this chapter as these occur in a completely different metallogenetic context.

Geotectonic Units and Main W,Sn Deposits and Mines in PortugalThe primary deposits or occurrences of W-Sn (Fig. 10) are for the most part either directly or indirectly linked with granites, with differing typology: aplite-pegmatites (Lagares de Estanho - Queiriga), intra and extra-batholithic stockworks (Bejanca-Vouzela and Fonte Santa - F. Espada à Cinta) and vein type. The latter are more common and account for most production of wolframite in the country( Goínhas, 1987).

They are generally found in contact metamorphic aureoles, sometimes a great distance from the granite outcrops, in which case it is assumed their relationship with fairly deep, non-outcropping granitic domes (Panasqueira, Argemela, Góis, Borralha, Vale das Gatas, Ribeira, Argozelo, etc.).

Besides these examples, there is also the special case of the skams with scheelite, formed by contact metasomatism, which - in accordance with the wall rock structure -some geologists divide into two types: stratoid (Cravezes-Mogadouro, Stª Leocádia-Armamar, S. Pedro da guias-Tabuaço, etc.) and vein type (most of the skams in the Castelo Melhor-Escalhão region, near to the River Águeda and the Spanish border, however the most important ones in the Escalhão - Barca d'Alva sector are from the stratoid type).

The most promising areas for the occurrence of large deposits correspond to various types of geostructural settings (Fig. 11):

a) Areas covered by monotonous schist series where the existence of non-outeropping granitic dome is presumed. An example of this is the Schist-Greywacke Complex situated to the south of the Estrela Mountain, and in particular the belt running E-W between Góis and the Spanish border, which covers the Góis, Panasqueira and Argemela mines. In this area, the main model is probably the Panasqueira deposit: mineralised sub-horizontal veins related with a non-outcropping, partially greisenized, leucogranitic dome.

b) Structural alignments of regional dimension containing various types of Sn-W deposits and small outcropping or sub-outcropping dome of differentiated granitoids. An example of this is the extensive WNW-ESE alignment that runs from near Ervedosa, through the Tuela, Agrochão and Murçós mines, and then, after being rejected by the Vilariga fault, continues eastwards towards the Ribeira and Argozelo mines in Trás-os-Montes area. The standard deposit type has not yet been fully defined but could be similar to that of Tuela, with vast stockwork zones with a high density of mineralised veins and remobilisation along strike-slip faults running subparallel to the regional structural alignment.

Potential Areas in W, Sn Mineralizations
Potential Areas in W, Sn Mineralizations

c) Granitic areas containing multiple intrusions differing in terms of mineralogy, metallogeny and chronology. In some cases, specific parageneses for a certain type of intrusion can be defined, distributed according to specific schemes of zonation, generally accompanied by hydrothermal alteration phenomena.

d) Circumscribed granitic massifs, with differentiated composition from regional granites and its metamorphic aureoles. Outcrops are small in size, circular in shape or slightly elongated along one of the axes and may resemble outcropping domes, the possible metallogenetic models fitting any of the types described in a) and b). The circumscribed massifs in the Arouca region, running in a NW-SE direction, are - in this context - one of the areas with greatest potential for the occurrence of intra- or extra-batholithic stockwork deposits.

A brief mention to the secondary alluvial-type tin and tungsten deposits, of reduced economic interest given their small size. The most important of these, however, are Nave de Haver (Sabugal), Gaia (Belmonte) and, to a lesser degree, Bejanca (Vouzela), Massueime (Pinhel) and Stª Eulália (Elvas), and Vale do Tâmega (Ribeira da Pena) alluvium, amongst others.

In relation to the skarns with scheelite, special mention should be made of the potential of the so-called Douro Scheelite Belt, which includes the whole of the area where the formations of the Schist-Greywacke Complex and the sintectonic granites make contact. This is situated to the north and south of the Douro river between the meridians of Freixo de Espada à Cinta and Régua. Besides numerous occurrences, several interesting deposits have also been recognised: Cravezes (Mogadouro), Stª Leocádia (Armamar) and S. Pedro da Águias (Tabuaço).

Another zone or belt of interest from an exploration point of view located in a similar geological context is the so-called Trancoso-Figueira de Castelo Rodrigo Belt.

In the Serra de Arga zone (Minho district) - besides the existence of tin-niobium-tantalum mineralisation- small deposits of scheelite stratoid type occur in skarns, interstratified in Silurian formations and in relation with the post-tectonic granites of Vila Nova de Cerveira and Covas: Cerdeirinha, Covas, Lapa Grande, Argela and Cabração.

We have already referred to the production of tungsten and tin concentrates, which reached maximum levels during the Second World War and the main producing centres. Of these, only the Panasqueira mine remains in operation (we continue to exclude the special case of Sn at Neves Corvo), which in 1996 produced 1342 tons of wolframite concentrates with a W03 grade of 72.96%, 15 tons of cassiterite concentrates with an Sn grade of 70.77% and 550 tons of chalchopyrite concentrates with a Cu grade of 28.50%.

Future production should stabilise around traditional figures: 2100 tons of wolframite, 45 tons of cassiterite and 600 tons of chalcopyrite concentrates.

The mineralised zone consists of series of sub-horizontal quartz veins, which overlap and fill the joints of fractures occurring in schist rock. These veins vary in thickness from 1 to 150 centimetres, the average thickness of the veins currently being mined around the 30-40 cm mark.

Besides the main minerals being mined - wolframite, cassiterite and chalcopyrite - various other minerals occur, such as sphalerite, topaz, apatite, fluorite, triplite, marcasite, siderite, arsenopyrite and muscovite, not to mention many others. The mine is in fact, famous for the occurrence of valuable collection samples.


Uranium

The known uranium deposits in Portugal are situated in the Central Iberian Zone (Fig. 12). They are located within Hercynian granitic batholiths or in the metasediments of exocontacts and occupy a structurally high position, which can be deduced from the presence of numerous pegmatites and metasedimentary enclaves (Dias et al., 1970).

Location of the Main Uranium Deposits in PortugalThe granites, occurring in the form of circumscribed massifs, belong to a calcalkaline series, are generally post-tectonic and are heavily fractured, particularly the NNE-SSW to ENE-WSW and NNW-SSE to NW-SE systems, pointing to a N-S maximum compression direction (Goínhas, 1987).

In the Beiras region, the largest and most productive area for uranium, the granite is intersected by numerous dykes of basic rock.

In this region, the intragranitic uranium bearing veins can be any of the following types:

  • jasperized veins;
  • quartz veins;
  • basic rock veins;
  • granitic breccia,
  • sometimes with limonite;

In the equally productive Alto Alentejo region, intragranitic uranium deposits are of the quartz veins and granitic breccia types.

Jasper type deposits have a characteristic paragenetic association: quartz, hematite, sphalerite, pitchblende, pyrite, galena, ankerite, chalcopyrite and coffinite. The pitchblende dates from the late Hercynian.

Mineral occurrences of all the other types essentially consist of hexavalent uranium minerals (secondary uranium minerals).

Support for uranium mineralisation in peribatholithic deposits, which also occur in the Beiras and Alto Alentejo regions, is provided by the formations of the Schist-Greywacke Complex.

These deposits are also almost totally composed of secondary uranium minerals, with pitchblende fairly rare.

Although this type of uranium dissemination deposit in metamorphic schists that contact with granite represents a very important percentage of total known uranium reserves, its genesis is controversial. Deposits such as Nisa (Alto Alentejo), Azere (Beira Alta) and Horta da Vilariga (Trás-os-Montes) are important examples of this type of mineralisation.

Occurrences related with concentrations of soil-leached uranium have also been detected in the Western Meso-Cenozoic Margin.

Potential Areas for Uranium MineralizationGeologically favourable zones for prospecting uranium in Portugal are described below. These are organised by their geological settings and in decreasing order of their potential (Fig. 13):

  • Hercynian granites in known productive zones (Beiras and Alto Alentejo - CentralIberian Zone) and other interesting vein occurrences (granites from the NE of Trás-osMontes, Galicia-Trás-os-Montes Zone and Évora Massif, OssaMorena Zone): - vein type deposits;
  • Metasediments from the Schist-Greywacke Complex and possibly from the Silurian, in particular in the contact metamorphism aureole (exo and endocontact) with productive granites in the Galicia -Trás-os-Montes Zone and the Central-Iberian Zone: - Iberian disseminated type deposits;
  • Ampelitic and/or pyritic schists from the Paleozoic, in particular in the Ossa-Morena Zone: - disseminated type deposits in Silurian black schists;
  • Nepheline syenite from the Serra de Monchique: - deposits associated with alkaline intrusions from the tertiary age;
  • Continental sediments from the Meso-Cenozoic age from the Western Margin and, possibly, from the Southern Margin: - sandstone type deposits;
  • Sediments from inland Paleogene basins or from hydrographic basins of large rivers, particularly in the cover zones of productive granites:- sandstone type disseminated deposits.

In the portuguese uranium metallogenetic province demonstrated reserves in the known deposits in the Beira and Alto Alentejo regions are around 8200 tons of uranium metal.

No mines are currently operational, although environmental processing of water originating from the Quinta do Bispo and Bica deposits produces around 20 tons Of U308 concentrates per year.


Lithium

Portugal occupies an important position in terms of lithium production. This is mainly due to the exploitation of aplite-pegmatite veins, rich in lepidolite, embedded in a late Hercynian granite, porphyritic, monzonitic, in the region of Gongalo (Guarda).

In this zone, mining at Alvarrões produced a total of 3155 tons of ore in 1996. After processing, this provided 892 tons of milled ore with a content of 1.05% of Li20 and 1527 tons of crushed ore with a content of 0.65% of Li20.

Lithium-bearing lodes are characterised by a geochemical association of A1-Na-Ca-PRb-Li-B-Sr and occupy a system of sub-horizontal fractures running predominantly NS, with cassiterite, tantalite and beryl also occurring.

Other potential lithium-bearing areas exist: the region between the Barroso and Alvão mountain ranges, for example, in which the IGM recently carried out exploration. Mineralisation deposits are associated with aplite-pegmatite veins, rich in spodumene, embedded in Silurian metasediments composed of micaschists and quartziferous schists with intercalations of black schists (Fig. 14). Regional exploration, both geological and geochemical, led to the selection of three structures, Afijó, Veral and Adagoi, which were recognised by drilling (Fig. 15). The following table shows their main characteristics and the most significant values of Li found within them.

Characteristics of studied structures
Structure Direction Dipping Maximum thickness Outcrop extension
Alijó N 15º W 75º W 37m 380m
Veral N 10º E 18º to 35º W 8.5m 280m
Adagoi N 25º E 50º TO 65º NW 35m 300m

Geological Cross Section of the Alijó Structure

Most significant Li values for the 3 drilled structures
Mineralised structure Borehole Length Li Grade
Alijó ALJ – 1 12.50 0.21
Alijó ALJ – 2 12.00 0.51
Alijó ALJ – 3 37.00 0.58
Veral VR - 1 3.88 0.40
Veral VR – 2 1.50 0.33
Veral VR – 3 2.95 0.37
Veral VR –4 5.50 0.16
Adagoi ADG -1 3.40
2.72
0.06
0.03
Adagoi ADG – 2 11.45
4.07
0.54
0.51
Adagoi ADG –3 3.16
3.60
4.72
0.48
0.23
0.34

As we have mentioned, the lithium occurs chiefly in the form of spodumene, but also in amblygonite and, more rarely, petalite, eucryptite and montebrasite, the pegmatite facies clearly the. richest in lithium.

The results of this phase of the project have led to the reconnaissance of a large extension of the aplite-pegmatite field with spodumene, a NW-SE alignment of more than 20 km identified parallel to the 3rd stage of Hereynian deformation. This type of lithium mineralisation is independent in space and in time from others of Sn-Nb-Ta and W, occurring in the zone.


Rare earths

Portugal's geostructural characteristics lend it great potential for the occurrence of rare earths. This has been confirmed by mineralometric studies and radiometric surveys.

With the exception of the Alter Pedroso zone, where hyperalkaline rocks have been investigated by the firm ERCROS, this group of elements had never been prospected in Portugal.

Regional exploration is currently carried out in the Beira Baixa and North Alentejo regions by IGM, involving geological mapping, alluvial and stream sediment sampling and radiometric surveys, the aim being the selection of targets to investigate at a later stage.

Prospecting is aimed at detecting Rare Earth bearing minerals, such as monazite -nodular monazite in particular - in sedimentary rock areas (more or less metamorphised) and xenotime, without overlooking other minerals such as apatite and allanite.

Study and Inventory of the Potential in Rare Earth ResourcesMineralometric data on the North Alentejo (Fig. 16) suggests that, to date, nodular monazite rich in light rare earths has originated chiefly from the disintegration of the ridges of the Ordovician quartzites on the southwest flank of the Portalegre Syncline, even in the case of Reveladas (Marvão), where the alluvial samples were collected in the midst of the Silurian formations, but close to these ridges.

Normal monazite appears to be chiefly associated with granite, as is the case of the Fronteira granite and tertiary gravel, originated from it.

As far as the lithogeochemistry of the Ordovician is concerned, it is the radioactive quartzites interstratified in the schists immediately above the thick base quartzites that are rich in rare earths, and not the schists itself (Fig. 17). This finding for the radioactive quartzites, previously known in Alegrete (Portalegre), mapped in detail in the Vale de Cavalos area as part of an IGM project and now also detected in Penha Garcia, goes against existing data on the levels of schists with nodular monazite, rich in rare earths, particularly europium, in other places of Europe and America.

Comparison of Analytical Results for Rare Earth Elements in the Vale de Cavalos Area


Nickel, cobalt and chrome

The occurrence of these metals in Portugal has not been sufficiently investigated, although various metallogenetic scenarios point to their potential existence. These are briefly described below:

a) Morais and Bragança mafic and ultramafic massifs. The IGM is carrying out geological, geochemical and geophysical exploration around Alimonde, where chromite-bearing peridotite formations (dunites) occur. The first phase of this research is nearing its conclusion.

b) Évora Massif of the Ossa-Morena Zone. Parts of this area have geological and metallogenetic characteristics that are similar to those of the Água Blanca zone (Monasterio - Spain), in which an important deposit of Ni was recently discovered with geological reserves of 23 Mt with 0.75% Ni and 0.55% Cu at a cut-off of 0.3% Ni.

c) Basic and ultrabasic complexes occurring on the north and south edges of the Ossa-Morena Zone. In the north sector, the Finnish firm Outokumpu holds an exploration license for an area which has shown potential for Ni, particularly in the Alter do Chão, Elvas and Campo Maior massifs.

Several firms are interested in prospecting the Beja ophiolite complex to the south, although the area remains free.

 

7. Non Metallic Mineral Resorces in Portugal

Non metallic mineral resources - rocks and industrial minerals constitute a sector of large economic relevance in Portugal due to the important volumes produced and processed and the number of workers involved.

This is a very dynamic industrial activity which has progressively been modernised in order to meet the more advanced extractive and processing technologies thus contributing for higher levels of production and quality and for increased competitiveness in the markets.

The activity in this sector includes two main branches:

  • Rocks
  • Industrial Minerals


1 - Rocks

1.1 - Dimension stones

Marbles, limestones and granites are the dominant materials and are responsible for about 96% of the total production; the remaining includes slate, nepheline syenite, acid porphyry, gabbro, diorite, shale, serpentine and gneiss.

The present production of dimension stones is approximately 1,200,000 tpa from which about 40% is exported. Exportation has changed considerably in the last decade due to the increase in the value of the exported products: from the total exportation in 1995, 71 % were processed products, 17 % slabs and only 12% blocks.

Considering the production of dimension stones all over the world, Portugal ranks parallel with Brazil in 6th place.

Portugal also imports unprocessed dimension stones from other countries for upgrading its value.

  • Marbles

Marbles are mainly produced in the anticline of Estremoz and represent approximately 55% of the total production of dimension stones. The pink type, named Rosa Puro, is the most valued.

Other areas, such as Viana do Alentejo, Trigaches and Ficalho, although small, produce very beautiful ornamental types with a variety of colours ranging from greenish and greyish to black and white.

In the anticline, at Borba, there is a centre (CEVALOR) for studying, evaluating and promoting dimension stones.

  • Limestones

Limestones including breccia limestones are mostly produced in Maciço Calcário Estremenho (MCE) where several ornamental types occur and also in the Algarve.

Limestones can be differentiated by its texture and colour being the "Moca creme" and "Alpinina" the most valued types.

Microcrystalline limestones are produced at Sintra and exibhit several patterns of colour like white, pink, yellow, red, blue and black. The reserves of these limestones are small.

The production of limestones is about 300,000 tpa which represents 25% of the global production of dimension stones.

  • Granites

Ornamental granites can he found dispersed all over the country although with a higher density in northern areas such as Viana do Castelo, Braga, Viseu, Porto, Braga and Vila Real. In the South this type of granite occurs in Portalegre district.

They show a large diversity of textures and colours with predominance of greyish and pinkish.

Ornamental granites represent the subsector with the highest growth rate in recent years. Nevertheless the present production is still in third place after marbles and limestones (20%).

The production of similar rocks, such as slate, acid porphyry, serpentine, nepheline syenite and others is small. The reserves are small as well.

The global reserves of granites are very large and further detailed studies in some areas are needed.

  • IGM INTERVENTION

Geological and Mining Institute intervention in the domain of dimension stones involves geological, geophysical, analytical and technological studies and drilling, with the aim of selecting areas where the rocky massives show adequate features for the production of ornamental types. In the selected areas the unexpected geological risks are reduced and it is possible to obtain higher rates of exploitation with adequate block sizes.

These factors improve competitiveness.

As said before the reserves of dimension stones in Portugal are very large.

However if exploitation of marbles was economically possible by underground mining the reserves of this type of dimension stone could be considerably Increased. IGM is presently engaged in performing studies on this subject.

1.2 - Industrial stones

All the above mentioned stones can have alternative uses when they are not adequate for ornamental purposes, the most common use being crashed stones for road building and construction. There are however other important industries which depend on this type of resources using wastes or quarries opened for that goal. The use of quarrying wastes is generalized in Portugal; granite wastes have the highest rate of utilisation.

1.2.1 - Use of quarrying wastes
  • From granites and similars

The most common use is the production of cobblestones for paving. This use is an important subsidiary industry with a large incidence in foreign markets. These wastes are also used for masonry and other purposes.

  • From marbles and limestones

Besides the most common uses, marbles and limestones wastes are also used in several industries, such as production of lime, agricultural correctives, ceramics, animal food, chemical industry, filler and others.

1.2.2 - Quarries for industrial uses
  • Dolomitic limestones

They are mined in several places in the country being the most important producers those localised in Sesimbra and in Maciço Calcário Estremenho. Dolomitic limestones are mainly used for siderurgical, glass and ceramic (refractory) industries.

  • Limestones for crashed stones

The production of crashed stones from limestones is a very important activity being the main producing areas located in Cantanhede, Serra de Sicó, Maciço Calcário Estremenho, Alenquer, Arrábida e Loulé. The annual production is about 20 Mt.

  • Limestones for "Calçada portuguesa"

This use is responsible for an important traditional industry located in Maciço Calcário Estremenho. The "Calçada portuguesa", a kind of paving made of small black and white cubes, is used in many portuguese towns and cities and is becoming largely appreciated abroad.

  • Limestones for paper industry

This is a sector that has evolved very quickly-and is now using a large space formerly occupied by kaolin. Due to their whiteness, low abrasivity, low cost and abundant reserves, oolitic limestones are replacing kaolin as filler in the paper industry.

The main producing centre are located in Serra de Sicó and Maciço Calcário Estremenho. Some wastes from very white marbles of Estremoz are also used in the paper industry.

  • Limestones for cement and lime industry

Limestones for these industries are supplied by large quarries located in Cabo Mondego, Souselas, Pataias, Maceira, Pé da Pedreira (MCE), Alhandra, Arrábida and Loulé. The production is approximately 10 Mtpa.

  • Granites for crashed stones, paying and construction

There is a great number of quarries dispersed in the granitic massives mainly in northern Portugal at Viana do Castelo, Vila Real, Braga, Porto, Viseu, Guarda. Other producing regions are Aveiro, Castelo Branco and Évora.

The present production is around 20,000,000 tpa.


2- Industrial Minerals

2.1 - Ceramic raw materials

From all Portuguese industrial minerals the ceramic raw materials play an important role as they supply an industry of great economical relevance.

  • Kaolin

Portugal is rich in kaolin for ceramic uses. However the country is also a small importer of this raw material for special uses, namely for certain types of porcelain. The origin of kaolin in Portugal is geologicaly diverse including sedimentary deposits of different ages and primary deposits formed by hydrothermal process and weathering of granites, gneisses and acid porphyries. Arkoses have recently became a very relevant resource due to their content in kaolin - besides k-feldspar and silica sands. The kaolin subsector has shown a great dynamism with the aims of increasing quality levels, diversifying uses and penetrating in foreign markets. Although Portuguese kaolin is essentially appropriate for ceramics it also plays a small role as filler and coating in the paper industry and as a filler in other industries.

Most of the total kaolin Production (200,000 tpa) is used by the important Portuguese ceramic industry: sanitaryware, tableware, refractories and wall and floor tiles.

The producing areas are mainly distributed in the regions of Viana do Castelo, Braga, Porto, Aveiro, Coimbra and Santarém. The known reserves are higher than 50,000,000 t. There are still potential geological formations that need to be better studied.

2.2 - Feldspar

Traditional sources of this raw material used as a ceramic fondente were associated to granitic pegmatites from which quartz and feldspar were separated by hand.

The progressive depletion of this kind of resource made it necessary to search for alternative sources. Presently feldspar is mainly obtained from aplitic and aplitic pegmatites formations and weathered moscovitic granits. After milling and purification these raw materials are used in the form of feldspathic sands.

Another important source are the arkoses in which high quality feldspar rich in potassium oxide occur in association with kaolin and silica sands, some with high purity levels. The importance of these arkoses is growing due to the high quality of the raw materials and the huge reserves. There are also very large aplitic pegmatites formations presently under study. Their technological properties indicate that these formations can be considered a good ceramic fondente. Some pegmatites at Guarda contain lepidolite and are being mined. Others, rich in spodumene, located in Vila Real, are being studied aiming its use in ceramics.

Feldspathic sands, byproducts of old tin mines, are also used as ceramic fondente after purification involving magnetic separation.

The total production of feldspar and feldspathic sands is about 150,000 tpa. Portugal is also a small importer and exporter of high quality feldspar.

The potential of Portugal for ceramic products is very large and there is the opportunity for the country to become a great exporter.

The occurrences are mostly associated to granitic massives that are located mainly in the area of Chaves, Braga, Viseu, Guarda and Évora. The arkoses occur in deposits situated in the region of Comibra.

2.3 - Common clays

Common clays are very abundant and they are predominantly distributed in the western and southern mesocenozoic coastal zone. There are about 200 processing plants dispersed by those zones producing bricks, roof tiles, wall and floor tiles and other products for construction. Some of these plants belong to important industrial groups but in general they are family companies. This is a sector which has progressively been modernized with advanced technologies. This modernization brought along an important evolution in what concerns the knowledge of the deposits, the control of the quality and the uses of the raw material.

Common clays occur mainly in the areas of Chaves, Bragança, Aveiro, Coimbra, Leiria, Lisboa, Santarém and Faro.

Due to their mineralogical and chemical properties some clays are appropriated for manufacturing thermo swelling products used as insulators and for producing light bricks. These clays occur in the area of Ansião in Central Portugal where there is a modern plant in operation.

The reserves of common clays are very important and they can supply the processing sector for a very long time. Besides the reserves already known there are extensive potential areas needing further studies. IGM develops research activities regarding the study of large sedimentary basins with the aim of increasing reserves and finding out new sources of this raw material.

IGM also provides geological and analytical assistance to the extractive sector.

2.4 - Ball clays

Ball clays are illite kaolinitic clays with mineralogical, chemical and technological properties that allow their use in porcelain, sanitaryware, glaze, floor and wall tiles. Ball clays supply a very important processing sector with high economical relevance mainly in terms of exportation.

The deposits are located in a restrict area on the central coastal zone of Portugal: Águeda, Anadia, Redinha, Pombal and Barracão where reserves are scarce (5,000,000 t). An effort to find new deposits has been developed by IGM and there are field data pointing out that it might be possible to increase the reserves for more confortable levels.

Within the field of the ceramic raw materials the ball clays subsector is the more advanced in what concerns the knowledge about deposits, extraction technologies, homogenization, quality control and rational utilisation of resources. In order to meet these requirements a careful and very selective extraction and a continuous chemical, mineralogical and technological control are needed in the quarrying process. With this aim the companies are being equipped with their own laboratories. A plant of atomisation is being established representing an important advance within this subsector.

Some of the ball clays with low quality are used as aglutinants in the production of animal feed, supplying the whole domestic market and also being exported.

It is worthy mentioning the fact that this is a pioneer subsector in the environmental recovery of exploited areas.

2.5 - Special sands

Special sands are very pure silica sands, in general very well calibrated.

They have usually a small content of kaolin (up to 6%) and heavy metals. After a process of purification that can include washing, classification, magnetic separation and flotation they are used in ceramics, glass, including crystal glass, and foundry. They are also used in other industries in the form of powders.

The reserves are very large distributed in eolian, fluvial and marine pliocene deposits from which the more important are situated in the areas of Figueira da Foz, Marinha Grande, Pombal, Leiria, Alenquer, Santarem, Rio Maior and Setubal.

Other source of silica sands is associated to the exploitation of kaolin as a byproduct.

2.6 - Talc

Tale is a raw material presently in great demand in ceramics besides its use as filler in many industries, such as paper, paints and rubber.

Tale deposits occur at the ultrabasic and basic massives of Bragança and Morais in Trás os-Montes where the reserves are not large.

Due to the contamination mostly by iron oxides and chromite portuguese talc presents grayish and yellowish colour and shows a medium level of quality, needing a process of purificating by magnetic separation. Portugal imports talc for more exigent uses.

The annual production is about 10,000 t.

2.7 - Other industrial minerals

2.7.1 - Gypsum

Portugal is self sufficient in black gypsum to supply the cement industry and agricultural uses. The output of white gypsum, some with high grade of brightness is small and there is the need to import large amounts, uncalcined and calcined, for wallboard, plaster, pharmaceutical, ceramics (mould), hydraulic lime and other uses.

The main producing areas are Soure, Souto da Carpalhosa (Leiria), Óbidos and Loulé.

Annual production is about 500,000 tpa mostly black gypsum.

The reserves are large but there are potential areas needing further detailed studies.

2.7.2 - Salt rock

There are several diapir zones in Portugal from which three areas are in production: Matos do Carriço (Figueira da Foz) and Matacães (Torres Vedras), where salt is extracted by solution, and Lou1é, operating by underground mining. These extracting unities supply mainly the chemical industry. Only a small amount is used in food industries.

The potential for salt rock production is large in association with extensive diapir zones in the west and south coastal zones.

The production is about 500,000 tpa, including brines.

Exploration of Non-Metallic Mineral Deposits (Situation as of 6/97)
Exploration of Non-Metallic Mineral Deposits (Situation as of 6/97)
2.7.3 - Diatomite

Diatomite is mostly used as a filter aid (beer, wine, oils, fruit juices, water treatment, and others) bult also as a mild abrasive (tooth paste), polish and filler.

In Portugal there are large deposits of diatomite, mainly at Rio Maior, but their characteristics concerning the frustules and their content in clay make them a low quality filter (slow filter). Its competitiveness as filter aid is low in the foreign markets.

Diatornite utilisation in structural ceramic industry (light bricks) may become more interesting besides present current uses in Portugal which include abrasives, fillers and insulating materials.

Only a small deposit located at Óbidos is being mined and its production is about 2000 tpa. Others, located at Rio Maior, Tomar and Sesimbra are not in operation.

Producer Areas of Ornamental and Industrial Stones
Producing Areas of Industrial Minerals
Producer Areas of Ornamental and Industrial Stones Producing Areas of Industrial Minerals