Mineral Potential of Portugal (1998)
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:
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 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 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.
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.
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
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.
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)
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
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Producing Areas of Industrial Minerals
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COMO CITAR ESTA PUBLICAÇÃO (HOW TO CITE THIS PUBLICATION):
Instituto Geológico e Mineiro (1998). Mineral Potential of
Portugal.
Versão Online no site do INETI:
http://e-Geo.ineti.pt/geociencias/edicoes_online/diversos/potential/indice.htm
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