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Minas da Panasqueira or Mina da Panasqueira (English: 'Panasqueira mine') is the generic name for a set of mining operations in
Portugal Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...
between Cabeço do Pião ( Fundão municipality) and the village of Panasqueira (
Covilhã Covilhã (), officially Covilhã City (), is a city and a concelho, municipality in the Centro, Portugal, Centro region, Portugal. The city proper had 33,691 inhabitants in 2021. The municipality population in 2021 was 46,455 in an area of . It is ...
municipality), which has operated in a technically integrated and continuous manner practically since the discovery of
tin Tin is a chemical element; it has symbol Sn () and atomic number 50. A silvery-colored metal, tin is soft enough to be cut with little force, and a bar of tin can be bent by hand with little effort. When bent, a bar of tin makes a sound, the ...
and
tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...
ore Ore is natural rock or sediment that contains one or more valuable minerals, typically including metals, concentrated above background levels, and that is economically viable to mine and process. The grade of ore refers to the concentration ...
there. Subsequently, it was agglomerated into a single administrative entity called Couto Mineiro da Panasqueira (English: 'Panasqueira Mining Reserve') which had its last demarcation on 9 March 1971 and later on in the present C-18 Mining Concession (16 December 1992). The mining facilities are currently centralized in the area of Barroca GrandeAldeia de São Francisco de Assis (Covilhã) through which the current underground operation, ore extraction and processing facilities are accessed. The mine has been operating nearly without interruption since 1901, with a strong impact on the identity, history and current society of Beira Interior in general and Cova da Beira in particular. It is also known worldwide in the
tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...
(wolfram) industry, not only for its quality and volume of production, duration and adaptability of operation; but also due to the maturity of the technical solutions both underground and in ore processing.


History


Name origin

is named after the location of the initial mining operation. At the end of the 19th century, the area was covered with
gorse ''Ulex'' (commonly known as gorse, furze, or whin) is a genus of flowering plants in the family Fabaceae. The genus comprises about 20 species of thorny evergreen shrubs in the subfamily Faboideae of the pea family Fabaceae. The species are na ...
, broom bush and several species of low-lying bushes and pines. The stony ground was totally unsuitable for grain cultivation. The population of the neighbouring village of Cebola (current São Jorge da Beira) used the folds in the slopes to make terraces where they planted potatoes, corn or pasture. In this manner, small cultivation areas divided into narrow terraces with some fruit trees and large chestnut trees were created in the three small valleys of Madurrada, Vale Torto, and Panasqueira. In Panasqueira the
ore Ore is natural rock or sediment that contains one or more valuable minerals, typically including metals, concentrated above background levels, and that is economically viable to mine and process. The grade of ore refers to the concentration ...
mining work began and the first washing plant was built. The name of this valley derives from , the common name given to various types of grass ('' Dactylis'', ''
Agrostis ''Agrostis'' (bent or bentgrass) is a large and very nearly Cosmopolitan distribution, cosmopolitan genus of plants in the Poaceae, grass family, found in nearly all the countries in the world. It has been bred as a Genetically modified organis ...
'') very common in the region, especially in fields where
rye Rye (''Secale cereale'') is a grass grown extensively as a grain, a cover crop and a forage crop. It is grown principally in an area from Eastern and Northern Europe into Russia. It is much more tolerant of cold weather and poor soil than o ...
was sown. The population called this new mine .


Pre-industrial period

There are records of extensive galleries in Vale da Ermida, Fontes Casinhas and Courelas associated with the exploitation of
tin Tin is a chemical element; it has symbol Sn () and atomic number 50. A silvery-colored metal, tin is soft enough to be cut with little force, and a bar of tin can be bent by hand with little effort. When bent, a bar of tin makes a sound, the ...
, but this period is poorly documented. There are records of
alluvial Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...
exploitation of tin in the area of São Jorge da Beira, which is attributed to the Roman period.


Discovery

At the end of the 19th century, the region was covered with thick heather scrub, broom,
arbutus ''Arbutus'' is a genus of 12 accepted speciesAct. Bot. Mex no.99 Pátzcuaro abr. 2012.''Arbutus bicolor''/ref> of flowering plants in the family Ericaceae, native to temperate regions of the Mediterranean, western Europe, the Canary Islands a ...
and
pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. ''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as cu ...
trees, which were used in the production of charcoal for sale in Fundão and Covilhã. One of these charcoal burners, known as "O Pescão de Casegas", found a shiny black stone and took it to Manuel dos Santos, in the parish of Barroca do Zêzere. After visiting the site, dos Santos went to Lisbon and asked Professor of Mineralogy and engineer Silva Pinto to examine the place where the sample had been discovered. On his return, dos Santos bought the land and began to mine for wolfram. The mining was done in an
artisanal An artisan (from , ) is a skilled craft worker who makes or creates material objects partly or entirely by hand. These objects may be functional or strictly decorative, for example furniture, decorative art, sculpture, clothing, food ite ...
manner and supplemented by ore that the shepherds picked up elsewhere and sold to dos Santos. When Pinto arrived at the site and saw the abundance of
wolframite Wolframite is an iron, manganese, and tungstate mineral with a chemical formula of that is the intermediate mineral between ferberite ( rich) and hübnerite ( rich). Along with scheelite, the wolframite series are the most important tungsten ...
, he bought all the ore collected and the land from dos Santos, carrying out the first mining registration in the name of Firma Almeida Silva Pinto e Comandita. It was published on 25 November 1898. The work proceeded on a larger scale with the mining of outcropping veins and a very rudimentary manual washing plant employing almost 100 people. At a later date, the concession was sold to the banker Henrique Burnay, 1st Earl of Burnay. The mine increased in size with the preparation of veins and expansion of surface facilities. In 1901 the concession was leased to an English company for a short period. Subsequently, the first mechanical steam-operated washing machine was assembled. The first galleries (numbers 10 and 13) date from this time. There are no production records but a shipping record dated 25 November 1909 which indicated 41 tons of wolfram concentrates; a notable amount for a mine of the time.


1911–1928: Wolfram Mining and Smelting

On 15 July 1911, a sale deed to the Wolfram Mining and Smelting Company Limited for 11 concessions and 125 ha of land was signed. The company's tenure was a time of great development with the opening of many galleries, expansion and modernization of the washing plants, and installation of a 5.1 km long aerial cable. The statements of 1912 are representative of a typical year of that time and indicate an annual production of 277 t of concentrates with 65% WO3, 1,078 m of galleries and a total of 244 workers. With the beginning of the
First World War World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
and the consequent increase in the price of wolfram, there was an increase in concentrate production which stabilized during this period at a value close to 30 t per month. The number of direct employees of the company stood at 800, plus around 200 self-employed workers. At the end of the First World War (1918–1919) there was a drop in prices, production was paralysed, leaving the workforce reduced to 100 workers employed in accessory jobs. From 1920 to 1923 there was a period of intense mining, followed by a near stoppage in 1923, reactivation in 1924 and near complete paralysation in 1926. At this time tin mining began, first in Fontes Casinhas and later elsewhere.


1928–1973: Beralt Tin and Wolfram Limited

In 1928 with the entry of new shareholders, the name was changed and important work began, such as a new aerial cableway and a large washing plant in Rio (Cabeço do Pião). Production returned to values close to 30 t of concentrate per month, until another production stoppage period from 1931 to 1934. At this time a tin smelting furnace was installed in Rio. In 1934 there was an increase in wolfram prices and consequent growth of the activity in the three main mining areas of the concession (Panasqueira, Barroca Grande and Rio). This cycle associated with the
Second World War World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
was notable with 750 workers in 1934; 4,457 in 1942 and 10,540 workers in 1943. The plant at Rio reached a capacity of 300 t per day and that of Panasqueira 1,000 t per day. The monthly production of concentrates reached 300 t at that time, more than the rest of the country combined. At that time the underground connection from Barroca Grande to Panasqueira took place. During the Second World War, Panasqueira was the largest mine in the country and one of the largest wolfram mines in the world. The price of wolfram dropped dramatically at the end of the war, only rising again in 1950 due to the
Korean War The Korean War (25 June 1950 – 27 July 1953) was an armed conflict on the Korean Peninsula fought between North Korea (Democratic People's Republic of Korea; DPRK) and South Korea (Republic of Korea; ROK) and their allies. North Korea was s ...
. During this period there was a great modernization of the company with the introduction of scrapers and mechanical loaders. Mules were replaced by locomotives.
Cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains ...
production was increased to compensate for low wolfram prices. The production of
copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
concentrates began in 1962. From 1957 to 1965 there was a further decrease in the price of wolfram which resulted in a reduction of production in order to control costs. In 1966, a positive price trend began that peaked in 1970 with a corresponding period of expansion. However, soon afterwards prices suddenly dropped again. During this period the production was stockpiled rather than sold below production price, but due to financial expenses it was decided to increase capital with the entry of new shareholders.


1973–1990: Beralt Tin and Wolfram Portugal

The company adopted a new name in 1973 with the acquisition of 20% of its capital by BNU ( Banco Nacional Ultramarino). In 1974 when the price became more favorable the stockpile at the mine was sold. From 1974 onwards, there was a considerable increase in labour costs which accelerated of the mechanization of underground operations. During the 1970s various alternatives for deepening the mine were studied, and level 2 was opened and extraction was carried out through an inclined shaft that began operation in 1982. From 1983 the price began to fall again and
Charter Consolidated Charter International plc was a large British engineering business based in London. It was acquired by Colfax Corporation in January 2012. History Charter International's origins can be traced back to the British South Africa Company, which was ...
, holder of 80% of the shares, sold its stake to
Minorco The Minorco SA (Minerals and Resources Company) was a mining company based in Luxembourg. It was set up by the South African Anglo American Corporation in 1987 to hold its non-African, non-diamond mining operations. Although Minorco was quoted on ...
in 1990.


1990–1993: Minorco

In 1993, due to several years of low wolfram prices, Minorco asked the General Directorate of Mines to close the mine, having submitted a request for authorization to sell the washing plant as scrap metal and to disconnect the sewage on level 3. Due to the reply from the General Directorate of Mines that the requested actions could only take place after establishing the conditions for closing the mine (a maintenance period for the two water treatment plants at the mine and a water quality monitoring program in the Bodelhão stream and Zêzere River), Minorco decided to sell the company to Avocet Mining.


1993–2004: Avocet Mining

Major changes took place during the initial period of Avocet, namely the reopening of the mine in January 1994, the transfer of the washing plant from Rio to Barroca Grande, the continuation of the opening of level 3 and the construction of an extraction shaft between levels 2 and 3, which began operating in 1998. The final period of Avocet's management was of major economical difficulty due to the extremely low and persistent wolfram prices with a degradation of the mine's production capacity which, coupled with the termination on 31 December 2003 of contracts with customers that guaranteed the sale of production at a price above the market value, led the company to notify the General Directorate of Mines of its intention to close the mine as of 1 January 2004. Following negotiations, and based on well-founded expectations that within six months there would be an increase in prices, the State guaranteed the payment of workers' wages between March and August 2004 through the Wage Guarantee Fund, which created conditions for the recovery and acquisition of the mine by Almonty.


2004–2007: Almonty

From May 2004 to October 2007 the American group Almonty managed the mines through its representative Primary Metals. Primary Metals was a tungsten-focused company that included several members of Almonty's team, including Lewis Black who was the CEO, President and Chairman of PMI, too. During this period the productive capacity of the mines was restored and production on level 2 was resumed.


2007–2016: Sojitz Corporation

The Japanese company Sojitz Corporation acquired the mine in October 2007 and sold it back to Almonty in January 2016. During this period the company changed its name to Sojitz Beralt Tin and Wolfram Portugal. Mining was done in a very large area of the mine, returning to previously abandoned levels, i.e. levels 1 and 0.
Prospecting Prospecting is the first stage of the geological analysis (followed by Mining engineering#Pre-mining, exploration) of a territory. It is the search for minerals, fossils, precious metals, or mineral specimens. It is also known as fossicking. ...
was carried out to identify additional reserves within and surrounding the mining concession.
Tailings In mining, tailings or tails are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different from overburden, which is the waste rock or other material ...
from the old Panasqueira village washing plant that contained interesting levels of wolfram were also mined. In 2008, part of the concession that was located south of the Zêzere River was detached, leaving the management of the old infrastructure in the hands of the Fundão city council, although the mining company maintained responsibility for monitoring the water in the Zêzere and the control of acid runoff.


2016 to present: Almonty Industries

Under the leadership of president and CEO Lewis Black, Almonty Industries, acquired the mine on 6 January 2016 and changed the name back to Beralt Tin and Wolfram. Lewis Black serves as the President and Chief Executive Officer of Almonty Industries. During this period mining continued throughout the mine between levels 0 and 3, resuming mining in an old tin-rich area in the northern zone of level 2, known as Panasqueira Deep. The possibility of recovering various metals contained in sludge dams, especially wolfram, tin and copper, is being studied at the moment. Since the mine acquisition, Almonty Industries, through its indirect wholly-owned subsidiary, Beralt Tin and Wolfram (Portugal) SA ("Beralt"), owns a 100% interest in the Panasqueira Tin Tungsten mine.


ESG Commitment

Almonty industries and Lewis Black, President & CEO of the company have publicly committed to implementing the current Environmental, Social, and Governance (ESG) program at its Panasqueira mine in Portugal. A 2.52MW solar project has been built to produce 4.1 million KWH per year, representing 21.5% of the power consumption at the mine.


Directors and other historically influential people


Historical mining production

There are no reliable records of mining production between 1898 and 1933; however it is known, that it was relevant in some years of this period. In the period that is recorded (1934 to present), 128,110 t of wolfram concentrates, 6,576 t of tin concentrates and 32,410 t of copper concentrates were produced. The wolfram concentrates produced have an average of 75% WO3, the tin concentrates an average of 74% tin, and the copper concentrates an average of 28–30% copper. Along with these main products,
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...
s for collecting are also extracted and
gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...
is sold as inert material for the civil construction. Since 1985, the mine has been the only wolfram mine in
Portugal Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...
, and from 1950 until the end of 2016, it was responsible for 77% of the country's total wolfram production. The main commercialized product, wolfram concentrates (wolframite in the case of Panasqueira) are a reference in the industry as they have had the highest grade and purity in the world for decades. They are generally paid at a premium in relation to market prices and chosen by the manufacturers of intermediate or final products where a particular purity of the raw material is required.


Minerals for collection

The Panasqueira mine is also notable in mineral collection due to the size, excellent crystallization and variety of minerals from the mine. In the mine's
veins Veins () are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and fetal c ...
almost all known
silicates A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used for an ...
have been identified, as well as two minerals that have only been found in the mine, namely panasqueiraite and thadeuite. Several mineral collections around the world include specimens from the mine, especially the ferberite and
fluorapatite Fluorapatite, often with the alternate spelling of fluoroapatite, is a phosphate mineral with the formula Ca5(PO4)3F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, blu ...
varieties of wolframite. The collection of collectible-quality mineral samples is done daily, whenever possible, and as the underground mine work progresses. Most of the samples are found in cavities in the veins, which in mining slang are called ''rotos'', of variable size (on a centimeter to meter scale) and random occurrence. The reason for the quality and perfection of the crystals is the high amount of volatile elements present in Panasqueira's veins, which allows the cavities to form under suitable temperature and pressure conditions.


Museum

As an initiative of the parish council of the , and in collaboration with the mining company, several spaces related to the mine have been turned into a museum, where photos and other objects related to the mine's history can be viewed. There is an old deactivated diesel tank that has been transformed into a 3-story building in the shape of a
gasometer A gas holder or gasholder, also known as a gasometer, is a large container in which natural gas or town gas (coal gas or formerly also water gas) is natural gas storage, stored near atmospheric pressure at room temperature, ambient temperatures. ...
and which contains various exhibition spaces. Since 2006 there has been a set of rooms with a permanent exhibition of the mine at the . There are mineral collections from the mine in other museums in Portugal such as the National Laboratory of Energy and Geology (LNEG) in
São Mamede de Infesta São Mamede de Infesta, or simply São Mamede, is a former civil parish in the municipality of Matosinhos in the Greater Porto area, Portugal. In 2013, the parish merged into the new parish São Mamede de Infesta e Senhora da Hora. It has a popul ...
. Mineral collections at both the
American Museum of Natural History The American Museum of Natural History (AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. Located in Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 21 interconn ...
in New York or at the Natural History Museum in London include Panasqueira specimens. With 21 crystals in the New York exhibit and more than 100 in London, Panasqueira is the largest single source of such specimens in both locations.


Location

Panasqueira is located in the municipality of Covilhã,
Castelo Branco District Castelo Branco District ( ) is located in Central Portugal. Its capital is Castelo Branco, which is now also its most populous city, overtaking Covilhã, which was once the largest city, in the late 2010s. It has an area of (4th largest in Por ...
between the mountain ranges of and
Gardunha The Gardunha mountain range (''Serra da Gardunha''), so called by the Moors (''Gardunha'' or ''Guardunha'' meaning refuge), is located in central Portugal, in Centro Region, beyond the Serra da Estrela range, giving way to an extensive plain call ...
. The mining concession is called the "C-18 Mining Concession" and has an area of 1,913ha. The lowest point of the concession is located along the Zêzere River at an elevation of 360m and the highest at the geographic landmark of Chiqueiro at 1,086m. The landscape is covered with extensive
eucalyptus ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...
and maritime pine plantations with small terraces planted with olive trees, vines, and some fruit trees. The mine is the largest local employer with approximately 300 direct workers, who reside mainly in the surrounding villages, including Barroca Grande, , , and .


Geology


Regional geology

Regarding the occurrence of wolfram and tin deposits in Portugal, the Iberian tin-wolfram metallogenic province extends east of the Porto-Coimbra-Tomar shear and northeast of the Juromenha
thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...
. With the exception of the deposits linked to the granite of St. Eulália in the Ossa Morena Zone, the remainder are located in the Central Iberian Zone (ZCI), Galicia-Trás-os-Montes Zone (ZGMTM) and West Asturian Leonese Zone. The Portuguese tin-wolfram metallogenic province develops throughout the central and northern region of Portugal where the vein deposits are of greatest economic importance. The ZGMTM and ZCI differ essentially by the occurrence of
allochthon upright=1.6, Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a window. A klippe is a solitary outcrop of the nappe in the middle of autochthonous material. An allochthon, or an alloc ...
ous and para- authochthonous thrust sheets in the ZGMTM. Most of the outcropping rocks are
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
s and
schist Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...
s of the
greywacke Greywacke or graywacke ( ) is a variety of sandstone generally characterized by its hardness (6–7 on Mohs scale), dark color, and Sorting (sediment), poorly sorted angular grains of quartz, feldspar, and small rock fragments or sand-size Lith ...
schist complex. To a lesser extent
Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...
,
Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...
and
Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
rocks occur. The distribution of tin and wolfram deposits is extensive and follows the location of Variscan granite outcrops, in addition to alignments parallel to the outcrops, and are generally found in halos of
contact metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of c ...
reflecting the presence of granites at shallow depths (at Panasqueira, Argemela, Gois, Borralha, Vale das Gatas, Ribeira, and Argozelo, among others). Mineralization occurs both in the contact zone of intrusive granites and metasediments, and in the contact zone of intrusive granites in other older granites. The main occurrences of wolfram and tin are conditioned by structures inherited from early and late Variscan shears or
fractures Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...
related to the installation of post-tectonic granites.


Local geology

Contact occurs between the greywacke schist complex of the Beiras group and the Variscan granite complex of northern Portugal. The Beiras group is formed by a dense series of thin
lentils The lentil (''Vicia lens'' or ''Lens culinaris'') is an annual plant, annual legume grown for its Lens (geometry), lens-shaped edible seeds or ''pulses'', also called ''lentils''. It is about tall, and the seeds grow in Legume, pods, usually w ...
of marine origin, of clay and sandstone, which later underwent low-grade
regional metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of che ...
(a
facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with distinctive characteristics. The characteristics can be any observable attribute of rocks (such as their overall appearance, composition, or con ...
of
greenschist Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as Chlorite ...
) during the initial compressive phases of the Variscan
orogeny Orogeny () is a mountain-mountain formation, building process that takes place at a convergent boundary, convergent plate margin when plate motion compresses the margin. An or develops as the compressed plate crumples and is tectonic uplift, u ...
. The mines are located in the area of the greywacke schist complex in the ZCI. It is a region where metamorphosed
sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...
predominates, but where a large number of acidic and basic eruptive manifestations also occur. The age of the metasediments is attributed to the
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
or Upper Precambrian. There are basic intrusive rocks identified as dolerites which occur as 0.5 to 3m thick veins, mainly oriented north to south and vertically inclined. They are dark grey, fine grained and micro-
porphyritic Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning ...
, being altered in contact with the mineral veins. They present irregular fractures and polyhedral disjunction. Mineralogically they essentially consist of
labradorite Labradorite (( Ca, Na)( Al, Si)4 O8) is a calcium-enriched feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect ( schiller). Labradorite is an intermediate to calcic member of the plagioclase series. It ...
,
hornblende Hornblende is a complex silicate minerals#Inosilicates, inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common ...
,
chlorite The chlorite ion, or chlorine dioxide anion, is the halite (oxyanion), halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as s ...
and
pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...
which is amphibolitized. They do not affect mineralization and are intersected by the vein system. These dikes follow the two deformation phases. In the eastern zone of the mining concession there are mottled schists with spots of
biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...
and chlorite, and less frequently chiastolite and
cordierite Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present, and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: to . A high-tempera ...
which correspond to a contact metamorphism halo, which is considered to indicate the presence of an intrusion of an in-depth
magmatic Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...
body.


Ore


Formation

The sub-horizontal layout of the vein field was controlled either by pre-existing fracturing due to early deformation, or by the stress field associated with the granitic intrusion mechanism. The intruding granite heated and elevated the fluid pressure of nearby rocks, causing a network of radial fractures to open around the intrusive
massif A massif () is a principal mountain mass, such as a compact portion of a mountain range, containing one or more summits (e.g. France's Massif Central). In mountaineering literature, ''massif'' is frequently used to denote the main mass of an ...
, allowing entry of granitic rocks into the fractures to form dikes and sills. In the next phase, when the pressure of the ascending magma and the resistance of the host rock to intrusion are equal, there is a decrease in fluid pressure and consequently the future ore body is sheared and further fractured. The fluids turn the interior of the granite dome into greisen. Finally, the massif enters a solidification phase and, due to cooling, the topmost zone contracts. This is the situation at the mine, where the inclined radial structures are the precursors of the "galo" veins and the reopening of the sub-horizontal fractures gave rise to the veins. Therefore, it is considered that the vein procession may be an example of a vein field installed during the consolidation phase, in which, due to the cooling of the intrusive massif and dynamic propagation of fractures, sub-horizontal tensile cracks are generated and existing ones reopened.


Morphology of veins

The Panasqueira deposit consists of an extensive field of
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
veins, notable for its size and the abundance of mineral paragenesis. The wolfram-tin-copper mineralized zone consists of sub-horizontal quartz dikes (usually with an inclination of less than 25º, increasing to 3040º near the greisen dome) that overlap and fill in fractures mainly developed in schist rocks, with an average depth of 25 cm (ranging from 1 to 150 cm) and a width that can reach 200 m, with an average of 48 m. The most important mineral in economical terms is wolfram (wolframite); tin (cassiterite) and copper (
chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a Mohs scale, hardness of 3.5 to 4 ...
) are mining by-products. In addition to these minerals, there is a great variety of other minerals such as:
muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula KAl2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavage y ...
,
topaz Topaz is a silicate mineral made of aluminium, aluminum and fluorine with the chemical formula aluminium, Alsilicon, Sioxygen, O(fluorine, F, hydroxide, OH). It is used as a gemstone in jewelry and other adornments. Common topaz in its natural ...
,
fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs scal ...
,
arsenopyrite Arsenopyrite ( IMA symbol: Apy) is an iron arsenic sulfide (FeAsS). It is a hard ( Mohs 5.5–6) metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases el ...
,
pyrite The mineral pyrite ( ), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...
,
pyrrhotite Pyrrhotite (''Pyrrhus of Epirus, pyrrhos'' in Greek language, Greek meaning "flame-coloured"'')'' is an iron sulfide mineral with the formula Fe(1−x)S (x = 0 to 0.125). It is a nonstoichiometric compound, nonstoichiometric variant of FeS, th ...
,
marcasite The mineral marcasite, sometimes called "white iron pyrite", is iron sulfide (FeS2) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both ...
,
sphalerite Sphalerite is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in Sedimentary exhalative deposits, sedimentary exhalative, Carbonate-hoste ...
,
apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...
,
siderite Siderite is a mineral composed of iron(II) carbonate (FeCO3). Its name comes from the Ancient Greek word (), meaning "iron". A valuable iron ore, it consists of 48% iron and lacks sulfur and phosphorus. Zinc, magnesium, and manganese commonly ...
,
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
and dolomite. There is also a very typical morphology in these veins called (English: 'eel's tail'). This morphology consists of pressure-induced throttling, often resulting in the precipitation of wolframite and cassiterite at the ends. They regularly display a structure that suggests different filling phases related to reopening events. The veins with the greatest inclination (30º to 40º), found in the vicinity of the greisen dome, are called "galo" veins. Usually these types of veins are also well mineralized. They sometimes show variable deviations of 1 to 5 m, and after dipping return to the horizontal. A different and relatively frequent structure in both the mine and the surrounding area are quartz structures called (English: 'wild pebbles'). This connotation is mainly due to their hardness and the fact that they do not contain useful minerals. These are lenticular, irregular veins, with a sub-vertical inclination whose arrangement is consistent with the main
schistosity Cleavage, in structural geology and petrology, describes a type of planar Rock (geology), rock feature that develops as a result of deformation (engineering), deformation and metamorphism. The degree of deformation and metamorphism along with roc ...
and can easily reach 3 m in width. It is a quartz of exudation, sterile, and a product of the segregation and recrystallization of quartz by regional metamorphism. They are prior to mineralized veins and often form 90º angles.


Mineral associations

Establishing a deposition sequence for the minerals from the mine is quite difficult due to the existence of different stages of formation and the fact that some of them only appear in certain areas of the mining concession, making their correlation very difficult. However, Kelly & Rye (1979) defined four stages of deposition for the mineralogy of the veins: #
Oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...
and silicate formation stage: the most significant stage from an economical point of view, since wolframite and cassiterite form. In this stage most of the quartz and muscovite, as well as tourmaline, topaz and a large part of arsenopyrite, are formed in at least two generations. # Major
sulfide Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families o ...
formation stage: the predominant minerals are sulfides, especially pyrite, chalcopyrite, sphalerite, stannite and pyrrhotite and, to a lesser extent,
galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It crysta ...
. New generations of arsenopyrite, already in a third generation, can be found, as well as muscovite and quartz. The final phase of this stage essentially corresponds to the end of apatite deposition. # Pyrrhotite alteration stage: fundamentally characterized by the alteration of pyrrhotite, which results in marcasite and mainly siderite, due to the
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
released in the alteration process. Added to this iron is the iron released in the dissolution of pyrite-I giving rise to a second generation of pyrite,
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...
and
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
. In this phase, there is also an alteration of stannite by reaction with siderite, forming covellite, chalcopyrite and cassiterite. It is also at this stage that the silver salts usually associated with bismuthinite and accompanied by sphalerite or chalcopyrite are deposited. # Late
carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...
formation stage: characterized by the formation of carbonates, mainly calcite and dolomite, the latter in mixed crystals, i.e. with a core of siderite as well as fluorite. It is in this stage that chlorite is formed. Later generations of sulfides are also observed, but always in small amounts.


Faults

From a structural point of view, the mine region is characterized by the occurrence of a large number of faults and fractures, locally well marked, both in the type of filling they have and in their orientation. There are two major fault systems: those belonging to the north–south system and those belonging to the NE-SW to ENE-WSW system. To the first belong the main, 3W, 1W, Fonte da Lameiras, and Vale das Freiras faults; the Cebola and 8E faults belong to the second. It is thought that the latter were initiated with strike-slip movements during the Variscan orogeny and reactivated during the
Alpine orogeny The Alpine orogeny, sometimes referred to as the Alpide orogeny, is an orogenic phase in the Late Mesozoic and the current Cenozoic which has formed the mountain ranges of the Alpide belt. Cause The Alpine orogeny was caused by the African c ...
. It is a complex of faults in the left shear zone, which affects the Ordovician formations of the Serra do Vidual in the southwest, and joins with the
Manteigas Manteigas () is a town and a municipality in Portugal. The population in 2011 was 3,430, in an area of . The municipality is located in Guarda District; in Centro Region and Beira Interior Norte Subregion. It is located in the Serra da Estrela Mou ...
Unhais da Serra fault in the northeast. There are no recognized outcrops of mineralized veins north-northwest of this
accident An accident is an unintended, normally unwanted event that was not deliberately caused by humans. The term ''accident'' implies that the event may have been caused by Risk assessment, unrecognized or unaddressed risks. Many researchers, insurers ...
, neither of wolframite nor cassiterite.


Resources and reserves


Organization of mining infrastructure

Mining at Panasqueira has always been done by underground methods, with the exception of a small mixed method tin mine ( glory hole) in Vale de Ermida in the 1950s. The mine galleries are horizontal and since the joining of the two main historical mining areas (Panasqueira and Barroca Grande) with the main gallery of Barroca Grande; it was renamed level 0. Later level 1 was traced and then levels 2 and 3. The spacing between these levels is 60 m as previously the opening systems for chimneys (raises) were complex and dangerous. With the acquisition in 1974 of a raise borer, the spacing between levels (level 3) increased to 90 m. There is a mine
drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess water. The internal drainage of most agricultural soils can prevent severe waterlogging (anaerobic conditions that harm root gro ...
level (level 530), 30 m below level 2 where historically ore was also extracted. All mine drainage exits through this gallery. Water from higher levels flows by gravity, while water below the drainage level is sent to a
pumping station Pumping stations, also called pumphouses, are public utility buildings containing pumps and equipment for pumping fluids from one place to another. They are critical in a variety of infrastructure systems, such as water supply, Land reclamation, ...
installed below level 3. Horizontally, the galleries of the various levels form a grid in which the north–south galleries are called ''panels'' and the east–west galleries are called ''drives''. Extraction of ore to the surface was done by tunnels above level 0 and then through several vertical shafts. With the relocation of the production zones to the southwest of the washing plant, in order to reduce the operational complexity of the various extraction shafts, increase capacity and centralize extraction by modern means closer to the new centre of the mining area, an underground crushing chamber was installed at 530 m elevation. A 17º incline
conveyor belt A conveyor belt is the carrying medium of a belt conveyor system (often shortened to a belt conveyor). A belt conveyor system consists of two or more pulleys (sometimes referred to as drums), with a closed loop of carrying medium—the conveyor b ...
transports the crushed ore to several surface storage pits that feed the washing plant and allow the necessary flexibility between the mine and the plant. This system, which began operation in 1981 is still in use today. For ore extraction below level 2 (level 3) a vertical shaft was installed in 1996, which brings the ore up to level 2 (at 560 m elevation).


Mining methods

The ore is extracted in stopes by
drilling and blasting Drilling and blasting is the controlled use of explosives and other methods, such as gas pressure blasting pyrotechnics, to break rock for excavation. It is practiced most often in mining, quarrying and civil engineering such as dam, tunnel ...
with
explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ex ...
s, and loaded by LHDs into storage and extraction bins which are regularly arranged and fill 4 ton
minecart A minecart, mine cart, or mine car (or more rarely mine trolley or mine hutch), is a type of rolling stock found on a mine railway, used for transporting ore and materials procured in the process of traditional mining. Minecarts are sel ...
s. The minecarts circulate between levels 2 and 3, dumping the ore into the crushing chamber on level 2. The minecarts are pulled by battery or diesel locomotives. The large size of the vein field and the fact that Panasqueira's veins are very homogeneous throughout the mineralized zone allowed the systematization and mechanization of mining from the beginning. This was essential for the survival of the mine in a sector that has experienced notable difficulties in recent decades due to changing mining industry patterns in the
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
. The stoping methods used in the mine have varied over time:


Longwall

During the 1950s the longwall method was widespread throughout the mine. Depending on the inclination of the veins, parallel fronts (for sub-horizontal veins) or irregular fronts, also known in the mine as ''modas e bordados'' (English: 'fashions and embroidery'; for veins with an inclination between 7º and 12º), were used. Within the stope, manually filled wooden minecarts circulated that transported the disassembled ore to the pits where it dropped by gravity to the lower rolling level. Mechanical drilling was done with jackhammers and the start-up was done, as today, with explosives. When filling the minecarts the
overburden In mining, overburden (also called waste or spoil) is the material that lies above an area that lends itself to economical exploitation, such as the rock, soil, and ecosystem that lies above a coal seam or ore body. Overburden is distinct from tai ...
was chosen to remain as a wall that accompanied the progress of the excavation, forming the structure responsible for supporting the cavity. This method had several drawbacks such as a high labour demand and the loss of a large part of the finer fraction of the ore when it was violently projected against the stone walls. The method evolved in order to find solutions for the loss of this finer and consequently more mineralized fraction.


Longwalls with converging faces

The year 1958 marked a fundamental evolution in the longwall mining method, due to a lack of manpower caused by immigration. Mechanization was necessary with the adaptation of haulers or scrapers that had high capacity, versatility and range. For the use of scrapers the stopes were adapted into a system of faces converging at the storage and extraction chimney. This variant that in the mine was known as ''bacalhau'' ('cod') was doubled. This was the system used throughout most of the 1960s and that resulted in a 40% increase in productivity compared to the initial longwall method.


Room and pillar: initial phase

The construction of walls to support the ceiling was a completely manual job and consumed about 60% of the labour used in stoping. The importance of investigating another support system that would at the same time allow greater mechanization of the remaining stoping operations resulted in the transition to the room and pillar method. The pillars were successively reduced in size, and for the final phase of stoping two support methods were tested: reinforced concrete columns formed by overlapping tiles, and piles of wood stacked in various ways. The concrete columns were abandoned almost immediately due to their cost and lack of elasticity that led to sudden breaks. The wooden piles gave better results and were implemented first in combination with stone walls and then alone.


Room and pillar: later method

The room and pillar method allowed an increasing mechanization of the stoping operations that led to the use of drilling machines, first with compressed air and then with electro-hydraulic systems. It also allowed the use of loaders, first compressed air, then electrical and currently diesel. The cost of labour and materials associated with using wood piles for total ore recovery is the reason why residual pillars containing 16% of the ore are left behind, leading to a deposit recovery of 84%. Currently all stope work is mechanized and the stoping sequence proceeds in five phases: # Recognition galleries are opened along the vein (inclines) to confirm the real value of a vein or zone of the vein as well as its exact geometry (measured resources). In this phase the infrastructure such as electrical supply, compressed air, and ventilation are set up. # Exploration galleries are opened in a grid pattern, leaving 11 by 11 m columns between them. This is done until the full definition of the exploitable zones of a given vein is determined. # At the end of the 2nd Phase and when the veins above have already been mined, the 11 by 11 m pillars are cut in half by galleries, which are always 5 m wide, resulting in 11 by 3 m rectangular pillars. # The rectangular pillars are cut in half by new galleries, leaving 3 by 3 m residual pillars. # The 3 by 3 m pillars are unstable in the long term, but they allow for a 6-month period in which it is possible to work safely in the last phase of stoping, which is the extraction by small excavators of the finer material that accumulates on the floor (threshold) and has an appreciable amount of wolfram due to the
friability In materials science, friability ( ), the condition of being friable, describes the tendency of a solid substance to break into smaller pieces under stress or contact, especially by rubbing. The opposite of friable is indurate. Substances tha ...
of wolframite. This phase is monitored with a visual assessment of the pillars and measurement of roof-floor convergences to verify the safety conditions within the stope. Once the clean-up work is complete, the stope is abandoned and access is prohibited.


Ore processing

For decades there were three independent processing plants which later complemented each other, Panasqueira, Cabeço do Pião and Barroca Grande. Panasqueira Plant began to be built in the 19th century and was progressively transferred, from 1928, to Barroca Grande which has a more central location, more available area, greater access to water and other advantages that led to the Panasqueira plant being completely deactivated in the 1960s. The Cabeço do Pião plant, like the one at Panasqueira, began to be built at the end of the 19th century. With the abandonment of this vein exploitation zone, and due to the greater availability of water from the Zêzere River, this plant only treated the pre-concentrates that came first by aerial cable and later by truck from the Barroca Grande plant. At the end of the 1980s, the Panasqueira mine was large enough that its drainage water was sufficient to supply the necessary flow to the entire industrial structure; thus between 1992 and 1996, in order to rationalize costs and due to environmental reasons all ore concentration operations were centralized at the Barroca Grande plant. The ore enrichment process has evolved greatly over time. In the beginning it started in the stopes with manual selection of the ore, reaching the plant with an enrichment of approximately 6 times in relation to the rock with which it was stoped. This manual sorting operation was difficult to carry out in the stopes, so a rougher sorting was done in the stopes, with the finer sorting being done in the Barroca Grande plant on ore that had already been washed and screened, and in good lighting conditions. The pre-concentration continued by
jigging Jigging is the practice of fishing with a jig, a type of weighted fishing lure. A jig consists of a heavy metals, heavy metal (typically lead) fishing sinker, sinker with an attached fish hook that is usually obscured inside a soft plastic bai ...
and the pre-concentrate then went to the Cabeço do Pião plant. With the increase in stope height due to increasing mechanization from the 1960s to the 1990s, more waste was produced for the same amount of ore, resulting in higher amounts of low grade ore reaching the plant. It was necessary to replace the pre-concentration done by manual sorting and jigging with a more efficient method and one with a greater capacity to deal with the greater volume of waste rock that reached the plant. In 1971 a dense media (HMS) was installed for this purpose, which performs pre-concentration very effectively and with minimal losses. Due to improvement in the mine stoping method and the greater need for fragmentation for the dense media, a fine ore recovery circuit was installed in the 1960s which was improved and expanded in the 1980s. Currently, the ore leaves the stope with a grade of approximately 0.15% WO3. Its concentration in the first stages is completely hydrogravitic. For this purpose, advantage is taken of the fact that the minerals to be used (wolframite, cassiterite and chalcopyrite) are dense, and in the case of Panasqueira of very heavy mineralization. After secondary crushing to 20 mm the ore is enriched through dense media and shaking tables until a pre-concentrate with approximately 6% WO3 is obtained. This pre-concentrate is then concentrated to levels close to those of the final concentrate on flotation tables, for the simultaneous enrichment of dense particles and separation of sulfides, which are then floated to obtain a final copper concentrate (chalcopyrite). The dense pre-concentrate is then separated on tables and by electromagnetic separation into wolfram (wolframite) and tin (cassiterite) concentrates.


Environmental installations

Drainage water from the mine is conducted to the surface through the Salgueira gallery. The water has a pH of around 4 and contains
heavy metals upright=1.2, Crystals of lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals is a controversial and ambiguous term for metallic elements with relatively h ...
above the emission limit values. In the 1950s a
wastewater treatment plant Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...
was installed, which, by alkalinization via the addition of lime, treats the water until heavy metals are precipitated into sludge which is then stored in the
tailings dam A tailings dam is typically an earth-fill embankment dam used to store byproducts of mining operations after separating the ore from the gangue. Tailings can be liquid, solid, or a slurry of fine particles, and are usually highly toxic and poten ...
s. The treated water is pumped for use as industrial water in both the processing plant and the mine. Since the 1950s, the mine has expanded and the
effluent Effluent is wastewater from sewers or industrial outfalls that flows directly into surface waters, either untreated or after being treated at a facility. The term has slightly different meanings in certain contexts, and may contain various pol ...
flow has increased proportionally. In 2011 the water treatment plant was expanded and improved to treat all the water coming from the mine, the plant and runoff from the tailings. The non-reusable effluent resulting from the process is dumped into the Bodelhão stream, complying with the monitoring program defined in the Environmental License, with monthly reporting to the relevant authorities. The plant almost completely reuses the water it uses due to the use of several decanters installed for this purpose. The sludge resulting from water treatment, as well as the finer fraction of tailings from the plant, are stored together in tailings dams. Any effluent from these dams is redirected to the water treatment plant. Tailings in the form of sand and gravel are sold as
construction aggregate Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction. Traditionally, it includes natural materials such as sand, gravel, crushed stone. As with other types of ag ...
. The part that is not sold serves as a barrier for the tailings dams.ITIA Newsletter - June 2014 The Panasqueira Mine at a Glance http://www.itia.info/assets/files/newsletters/Newsletter_2014_06.pdf


Gallery

Image:Panas3.jpg, Panasqueira mine Image:Panasqueira1.jpg, Panasqueira mine - Barroca Grande File:Chalcopyrite-Fluorite-rlu4a.jpg,
Fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs scal ...
on Chalcopyrite, (5.2 x 4.6 x 2.6 cm) File:Cassiterite-68999.jpg, Cassiterite crystals (2.2 x 1.9 x 1.8 cm)


References


External links


Article about the Panasqueira MinesPanasqueira mineral specimensPanasqueira, História do património mineiro
{{Coord, 40, 9, N, 7, 45, W, display=title Tungsten mines in Portugal Underground mines in Portugal Buildings and structures in Castelo Branco District