Análise de balanços
Nabais, Carlos Alberto da Fonseca
1997
Search results
54 records were found.
At Segura two-mica granite, muscovite granite and granodiorite veins intruded the schist-metagraywacke complex. Aplite and stanniferous pegmatite veins cut granites and country rock. Subhorizontal Sn-W quarz veins and Ba-Pb-Zn quarz veins intruded the country rock and granites. The abandoned mining area was exploited for Sn, W, Ba and Pb until 1953. In soils and stream sediments, the are anomalies of Sn,W, Ba, As and Cu related to Sn-W quarz veins, whereas Ba, Pb and Zn anomalies are associated with the Ba-Pb-Zn quarz veins. Soils are contaminated in As, Sn, B and Ba, and should not be used for agriculture and residences. The highest As contamination is associated with Sn-W quarz veins. The soils contaminated in As mus not be used for commerce and industry. The spring and stream waters are contaminated in As, Fe and Mn. The waters are not drinkable and they may not be used for agriculture.
A região de Segura é uma área mineira actualmente abandonada, tendo sido explorada para Sn, W, Ba, PB e Zn entre 1942 e 1953. Os jazigos minerais são filões de pegmatito granítico estanífero-litinífero, filões de quartzo com cassiterite e volframite e filões de quartzo com barite, galena e blenda. Os pegmatitos graníticos e os filões de quartzo mineralizados intruíram dominantemente o Complexo Xisto-Metagrauváquico, de idade Câmbrica, embora alguns atravessem também os granitos hercínicos. A cassiterite dos pegmatitos estanífero-litiníferos é zonada e possui exsoluções de mangano-columbite e de magano-ferrocolumbite, particularmente nas zonas escuras. A cassiterite dos filões de quartzo com cassiterite e volframite não é zonada e não apresenta exsoluções. A cassiterite destes filões de quartzo é mais rica em Ti e mais pobre em Nb e Nb+Ta do que a cassiterite dos pegmatitos. A volframite ocorre apenas nos filões de quartzo com cassietrite e volframite e é enriquecida na componente ferberite. Nestes filões de quartzo, foram, ainda, encontrados moscovite, pirrotite, arsenopirite, pirite, blenda, calcopirite, estanite, matildite e schapbachite. Nos filões de quartzo com barite, galena e blenda, ocorrem conjuntamente cristais de apatite, moscovite, clorite, cobaltite, pirite e calcopirite. A barite tem composição homogénea.
Na região de Segura, a geoquímica da biotite mostrou que os filões de pórfiro granodiorítico e o granito de duas micas não estão relacionados. A geoquímica da moscovite sugere que o granito de duas micas, o dominante na região, e o granito moscovítico correspondem a dois magmas distintos, mas os filões aplíticos estarão relacionados com o granito moscovítico, enquanto o pegmatito granítico estanífero-litinífero derivará do granito de duas micas por diferenciação. A lepidolite do pegmatito terá substituído a moscovite magmática. A moscovite hidrotermal tem composição distinta da moscovite magmática. A moscovite hidrotermal dos filões de quartzo com barite, galena e blenda distingue-se quimicamente da moscovite hidrotermal dos filões de quartzo com cassiterite e volframite.
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At Segura, tin-bearing Hercynian two-mica granite, muscovite granite and aplite and granitic pegmatite veins and also granodiorite porphyry veins intruded the Cambrian schist-metagraywacke complex but aplite and pegmatite also intruded the granites. Variation diagramas of most major and trace elements of the rocks and muscovites show fractionation trends from muscovite granite to aplite and that the two granites are not related. They probably have origin in two distinct granite magmas derived from the muscovite granite by fractional crystallization of K-feldspar, quartz and ilmenite. Feldspars from this granite and aplite are the richest in P2O5 but K-feldpars retains the highest value. Variation diagramas of rocks and biotites and compositions of plagioclases show that granodiorite porphyry veins are not related. Variation diagrams of muscovites show fractionation trends from two-mica granite to pegmatite containing lepidolite, which replaces muscovite.
No plutão de Castelo Branco, distinguem-se cinco granitóides, G1 a G5, dispostos concentricamente do núcleo para o bordo do plutão. Os diagramas de variação, seus perfis de terras raras, dados isotópicos Rb/Sr e as composições das plagioclases indicam que: a) o granito de grão médio a fino moscovítico-biotítico (G1), o granodiorito de grão médio a fino, levemente porfiróide, biotítico-moscovítico (G2) e o granito de grão grosseiro moscovítico-biotítico (G5) correspondem a três pulsações magmáticas distintas resultantes da fusão parcial de materiais metassedimentares; b) aquele granodiorito G2, o granodiorito de grão médio a grosseiro, porfiróide, biotítico-moscovítico (G3) e o granito de grão médio a grosseiro, porfiróide, de duas micas (G4) definem uma sequência de diferenciação magmática. Além disso, G2, G3 e G4 permitem estabelecer uma isócrona Rb-Sr de rocha total de idade 300±16Ma e 87Sr/86Sr inicial de 0.7113±0.0033. G3 e G4 derivam do magma granodiorítico G2 por cristalização fraccionada do quartzo, plagioclase e biotite. G1,G2 e G5 têm a idade de 310±Ma obtida por U-Pb em cristais isolados de zircão e monazite. 87Sr/86Sr inicial é de 0.07090±0.0011, 0.7108±0.0024 e 0.7120±0.0003 para G1,G2 e G5, respectivamente, para esta idade. Foram obtidas idades de 297±Ma a 303±3Ma em monazites dos cinco granitóides por U-Pb-Th, utilizando uma microssonda electrónica.
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U-bearing quatrz veins and related waters from Mondego Sul mine (Central Portugal)
Five granitic rocks, concentrically disposed from core to rim, were distinguished in the Castelo Branco
pluton. U-Pb-Th electron microprobe monazite ages from granitic rocks are similar and ranging between
297-303 Ma. The granitic rocks from Castelo Branco pluton are 310 ± 1 Ma old, obtained by U-Pb
(ID-TIMS) in separated zircon and monazite crystals, indicating a similar emplacement age for all granitic
rocks of the pluton. Initial 87Sr/86Sr isotopic ratios and εNd310 and δ18O values suggest three distinct pulses
of granitic magma and that they are derived from partial melting of heterogeneous metasedimentary
materials. The other granitic rocks are related by magmatic differentiation and show small variations in
(87Sr/86Sr)310, εNd310 and δ18O. The granitic pluton of Castelo Branco shows a rare reverse zoning.
Geochemistry of microgranular enclaves and host granodiorite from Oledo, Central Portugal
Uranium minerals from the Picoto uranium mine area (Central Portugal)
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No plutão de Oledo-Idanha-a-Nova, as relações estruturais, dados geoquímicos de três granitóides e seus minerais e os dados isotópicos obtido para o granodiorito biotípico, granodiorito de duas micas e granito moscovítico-biotítico sugerem que provêm de fontes magmáticas distintas. Os resultados obtidos por U-Pb em zircões e monazites e por U-Th-Pb em monazites revelam concordância e indicam uma idade de instalação entre 479-480 Ma, sugerindo que se trata de maciços graníticos com sincronismo de instalação.
Li-bearing granitic aplite-pegmatite veins containing muscovite, montebrasite, natromontebrasite, lepidolite, topaz,cassiterite and manganocolumbite crop out in Segura area. Primary lepidolite contains more F, Rb and less Al than primary muscovite. Primary natromontebrasite has more Na, F and less Li and OH than montebrasite. Cassiterite is zoned showing sequences of alternating parallel darker and lighter zones. The darker zones are strongly pleochroic, oscillatory zoned, show exsolved Manganocolumbite and have more Nb and Ta than the lighter zones. Manganocolumbite is oscillatory zoned.
At Segura there are different minerals containing phosphorus in their compositions. K-feldspar of granitic rocks has higher P2O5 than coexisting plagioclase. K-feldspar and ablite of Li-bearing granitic pegmatite veins have higher P2O5 content than those of respective feldspar fro two-mica granite, probably due to fractional crystallization of the granite magma. Feldspars from muscovite granite and aplite veins have the highest P2O5 content and these rocks are related. Hydroxiapatite occurs in granitic rocks and quartz veins. Fluorapatite also occurs in two-mica granite and muscovite granite. Coexisting montebrasite and natromontebrasite were found in Li-bearing pegamtite veins. Gormanite occurs in the muscovite granite. Mimetite with unusual As/P ratio of 1.04 and kintoreite are alteration products of galena in quartz veins.
The Castelo Branco pluton is exposed over an area of 390 Km2 and consists of five late- to post-tectonic Hercynian granitic rocks, which intruded the Cambrian schist-metagraywacke complex. They are concentrically arranged. A medium- to fine-grained muscovite>biotite granite (G1) crops out in the pluton’s core and is surrounded by a medium- to fine-grained, slightly porphyritic biotite>muscovite granodiorite (G2), encircled by a medium- to coarse-grained porphyritic biotite>muscovite granodiorite (G3), grading into a medium- to coarse-grained porphyritic biotite = muscovite granite (G4). A coarse-grained muscovite>biotite granite (G5) forms only external parts of the pluton in the N and NE.
At Segura, aplite-pegmatite veins with casserite and lepidolite, Sn-W, and Ba-Pb-Zn quartz veins were exploited; mine tailings were left exposed. Sn, W, B, As, and Cu anomalies in stream sediments and soils are related to the Sn-W quartz veins, while Ba, Pb and Zn anomalies are associated with the Ba-Pb-Zn veins. Soils are contaminated in Sn, B, As, and Ba and must not be used for agriculture and human residences or industry. The waters are contaminated in As, Fe and Mn and should not be used for human and agricultural activities. Sn, B, Cu, and Pb were not detected in waters.
At Segura, granitic pegmatite veins with cassiterite and lepidolite, hydrothermal Sn–W quartz veins and Ba–Pb–Zn quartz
veins intruded the Cambrian schist–metagraywacke complex and Hercynian granites. Cassiterite from Sn–W quartz veins is
richer in Ti and poorer in Nb and Nb + Ta than cassiterite from granitic pegmatite. Wolframite from Sn–W quartz veins is
enriched in ferberite component. The Sn–W quartz veins contain pyrrhotite, arsenopyrite, sphalerite, chalcopyrite, stannite,
matildite and schapbachite and the Ba–Pb–Zn quartz veins have cobaltite, pyrite, sphalerite, chalcopyrite, galena and barite,
which were analyzed by electron microprobe. The presently abandoned mining area was exploited for Sn, W, Ba and Pb until
1953. Stream sediments and soils have higher concentrations of metals than parent granites and schists. Sn, W, B, As and Cu
anomalies found in stream sediments and soils are associated with Sn–W quartz veins, while Ba, Pb and Zn anomalies in
stream sediments and soils are related to Ba–Pb–Zn quartz veins. Sn, W, B, As, Cu, Ba, Pb and Zn anomalies in stream
sediments and soils are also related to the respective old mining activities, which increased the mobility of trace metals from
mineralized veins to soils, stream sediments and waters. Stream sediments and soils are sinks of trace elements, which depend
on their contents in mineralized veins and weathering processes, but Sn, Wand B depend mainly on a mechanic process. Soils
must not be used for agriculture and human residence due to their Sn, B, As and Ba contents. Waters associated with
mineralized veins were analyzed by flame atomic absorption spectroscopy (FAAS) and ICP-AES have high As, Fe and Mn and
should not be used for human consumption and agriculture activities. The highest As values in waters were all related to Sn–W
quartz veins and the highest Fe and Mn values were associated with the Ba–Pb–Zn quartz veins. No significant acid drainage
was found associated with the old mine workings.
O plutão de Castelo Branco é constituído por cinco granitóides peraluminosos (GI a GV), que se dispõem concentricamente do núcleo para o bordo, com uma idade de implantação de 310±1 Ma, obtida por U-Pb em cristais isolados de zircão e monazite. As suas características estruturais, mineralógicas, geoquímica das rochas e dos minerais, perfis de terras raras e composição isotópica sugerem que o granito de grão médio a fino moscovíticobiotítico (GI, no centro do plutão), o granodiorito de grão médio a fino, levemente porfiróide, biotítico-moscovítico (GII) e o granito de grão grosseiro moscovítico-biotítico (GV, no bordo do plutão) correspondem a três pulsações magmáticas distintas. Estas rochas granitóides resultaram da fusão parcial dos materiais metassedimentares da rocha encaixante. O magma do granodiorito de grão médio a fino, levemente porfiróide, biotítico-moscovítico (GII), originou o granodiorito de grão médio a grosseiro, porfiróide, biotítico-moscovítico (GIII) e o granito de grão médio a grosseiro, porfiróide, de duas micas com quantidades idênticas de biotite e moscovite (GIV) por cristalização fraccionada de plagioclase, quarzto, biotite e ilmenite, dispostos desde o núcleo para o bordo do plutão. Este plutão apresenta um raro zonamento inverso.
Na região da mina de Fonte Santa ocorrem filões de quartzo mineralizados em W, com scheelite, que cortam quartzitos do Ordovícico Inferior aflorantes nas imediações de granitos Variscos, e que se relacionam com a zona de cisalhamento de Moncorvo-Bemposta. Alguns filões com scheelite têm quartzo recristalizado e brechificado e sulfuretos associados, tendo sido explorados para volfrâmio (W) entre 1942 e 1982. As águas relacionadas com a mina da Fonte Santa são pouco mineralizadas, com condutividade eléctrica < 965 μ S/cm, e classificadas como de tipo misto. A maioria dos valores de pH (pH = 5.0 - 8.5) indicam que não há drenagem ácida significativa associada às actividades mineiras e os valores mais ácidos (pH = 3.4) foram obtidos numa lagoa da mina. Nas águas associadas com os filões mineralizados e antigas explorações foram encontradas concentrações elevadas de Fe e Mn que proíbem o seu consumo humano e utilização na agricultura.
U-bearing minerals from the Picoto uranium mine area, central Portugal
Algumas rochas graníticas do norte e centro de Portugal possuem fosfatos. A triflite altera-se para vivianite maganífera, ludlamite azul, fosfoferrite e mitriadite nos filões aplíticos de Vidago, que também possuem brushite, ludlamite e perlofite verde. A triflite do granito moscovítico de Paredes da Beira altera-se para estrengite. Childrenite e eosforite ocorrem nos granitos de Paredes da Beira e Penamacor-Monsanto e aplito de Vidago. Gormanite foi encontrada no granito moscovítico de Segura. os filões aplito-pegamtíticos litiníferos de Gonçalo e Segura possuem montebrasite e natromontebrasite. Nos filões de quartzo de Segura, há mimetite e quintoreíte que resultaram da alteração da galena.
Geochemistry of granitic rocks from Gouveia area, Central Portugal
Contamination of waters related to abandoned W-Sn mines (Murçós, NE Portugal)
Weathering and hydrochemistry associated with the old mine workings at Fonte Santa (NE Portugal)
The impacts of Sn-W, Ba-Pb-Zn and W-Au-Sb old mine workings on the environment at Central Portugal
The genesis of I- and S-type granitoid rocks of the early Ordovician Oledo pluton, Central Iberian Zone (Central Portugal)
Os filões de quartzo com scheelite da mina da Fonte Santa atravessam a formação do Quartzito
Armoricano, do Ordovícico Inferior. A mineralização é de tipo “stockwork”, ocorre associada ao
leucogranito sin-F3, da Fonte Santa, que aflora a 250 m a Sul do jazigo e relaciona-se com a zona de
cisalhamento Moncorvo-Bemposta (Silva e Pereira, 2001). O leucogranito é de grão médio a fino,
moscovítico, com foliação N80ºW, subvertical. Possui quartzo, microclina, albite, moscovite, turmalina,
silimanite, zircão, apatite, e ilmenite. As amostras alteradas com microclinização e moscovitização
intensa contêm clorite, columbite-tantalite, volframite, ixiolite rica em W e óxidos de ferro. É um granito
peraluminoso, do tipo S, muito evoluído e estanífero com Sn > 44ppm (Silva, 2000). Alguns filões têm
quartzo parcialmente recristalizado, por vezes brechóide, impregnado de sulfuretos preenchendo
microfissuras e fracturas. A paragénese dos filões é constituída por quartzo, moscovite, clorite, turmalina,
scheelite, pirrotite, pirite, esfalerite, calcopirite, galena, óxidos de ferro, sulfatos de Fe e fosfatos de Pb,
Fe e Al. A mina da Fonte Santa foi explorada para W entre 1942 e 1982 (Triede, 2002). As águas
associadas à mina da Fonte Santa, são pouco mineralizadas, com condutividade específica < 150 μS/cm,
de tipo misto, bicarbonatadas ou sulfatadas. A maioria dos valores de pH (5.0 e 9.2) indicam que não há
uma drenagem ácida significativa na região, tal como encontrado noutros locais (e.g., Antunes et al.,
2002). Os valores mais ácidos (pH: 3.4-3.5) foram encontrados na lagoa da mina.
A deformação Varisca está na origem da maioria das rochas granitóides da zona Centro Ibérica (ZCI). O magmatismo Ordovícico é raro na ZCI, tendo sido encontrados novos dados geocronológicospara rochas granitóides atribuindo-lhes uma implantação no Ordovício Inferior. Na área de Oledo-Castelo Branco ocorrem dois plutões, contactando lateralmente de idades e características geoquímicas distintas.
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Na região da mina de Fonte Santa ocorrem filões de quartzo mineralizados em W, com scheelite, que cortam os quartzitos do Ordovícico Inferior e estão relacionados com a zona de cisalhamento de Moncorvo-Bemposta. Alguns filões com scheelite têm quartzo recristalizado e brechificado e sulfuretos, tendo sido explorados para W entre 1942 e 1982. As águas relacionadas com a mina da Fonte Santa são pouco mineralizadas, com condutividade eléctrica < 965 μ S/cm, e classificadas como de tipo misto. A maioria dos valores de pH (pH = 5.0 - 8.5) indicam que não há drenagem ácida significativa associada às actividades mineiras e os valores mais ácidos (pH = 3.4) foram obtidos numa lagoa da mina. Nas águas associadas com os filões mineralizados e antigas explorações foram encontradas concentrações elevadas de Fe e Mn que proíbem o seu consumo humano e utilização na agricultura.
At Segura area, two-mica granite, muscovite granite, granitic aplite veins and Libearing granitic aplite-pegmatite veins from Cabeco Queimado intruded the Cambrian schist-metagraywacke complex. Aplite veins also intruded both granites. Variation diagrams of major and trace elements of the granitic rocks show fractionation trends for: a) two-mica granite and Li-bearing aplite-pegmatite veins; b) muscovite granite and aplite veins. Least square analysis for major elements and modelling of trace elements indicate that: a) the Li-bearing aplite-pegmatite veins were derived from the two-mica granite
by factional crystallization of quartz, plagioclase, potash feldspar and biotite; b) the aplite veins were derived from muscovite granite by fractional crystallization of quartz, plagioclase, potash feldspar and ilmenite, which is supported by the similar δ18O values. The increase of δ18O values from two-mica granite to aplite-pegmatite veins suggests that fractional crystallization was accompanied by assimilation of metasedimentary material (AFC process). The pegmatite veins are REL-Li pegmatites and belong to the LCT family.
The occurrence of amblygonite-montebrasite, lepidolite, cassiterite, ferrocolumbite, manganocolumbite and microlite suggest that Li-bearing granitic aplite-pegmatite veins are highly differentiated.
Several types of peraluminous Hercynian granites containing generally more primary muscovite than Fe2+-biotite + chlorite, have mainly A/CNK values greater than 1.15, but ranging between 1.01 and 1.41 and δ18O values of 10.34-13.52% and are interpreted of S-type. A Mg-biotite granidorite of I-type having A/CNK of 0.99-1.10 and δ18O of 8.84% also occurs in the Gouveia area. Variation diagrams of major and trace elements for the oldest four granites and granodiorite show five independent fractionation trends, suggesting that they correspond to five distinct granitic magmas. The granites are probably originated by partial fusion of heterogeneous metasedimentary materials, while granodiorite may result from partial of igneous material or has a mantelic origin.
Phosphate minerals are common in northern and central Portuguese granitic rocks. Childrenite, eosphorite and intermediate compositions in this solid-solution séries occur in muscovite granites at Paredes da Beira and Penamacor-Monsanto, muscovite-biotite granites at Penamacor-Monsanto and in aplite veins at Vidago. The composition of childrenite and eosphorite are similar in each of these localities. Germanite occurs in a muscovite granite at Segura.
The Early Ordovician Oledo pluton consists of four distinct granodioritic to granitic phase (G1–G4), which
intruded a Cambrian schist-metagraywacke complex, but were themselves intruded by a Late Carboniferous
pluton. ID-TIMS U–Pb ages for zircon and monazite from these granitic rocks indicate emplacements within
a short period of time at 479–480 Ma. Granodiorite G1 is the most deformed rock with shear zones and
deformation at the border. G1 and G3 contain fine-grained biotite tonalite and biotite granodiorite
microgranular enclaves, which are darker and richer in mafic minerals than the host granodiorites. The
geological, mineralogical, geochemical and Sr, Nd and O isotopic data show that tonalitic and granodioritic
enclaves and host G1 are of I-type and were related predominantly by a fractional crystallization process.
Least-square analysis of major elements and modelling of trace elements indicate that granodioritic enclaves
and host G1 could be derived from the tonalitic enclave magma by fractional crystallization of plagioclase,
grunerite, biotite and ilmenite. Granodiorite G2 is of hybrid origin. Most variation diagrams for granodioritic
enclaves and host G3 granodiorite and their biotites show linear trends. Modelling of major and trace
elements of granodioritic enclaves indicate that they result from mixing of relatively primitive granodiorite
magma with magma derived from crustal melting. Tonalitic enclaves correspond to globules of a more mafic
relatively primitive magma. Granite G4 has the most pronounced crustal signature and is of S-type.
The zoned pluton from Castelo Branco consists of Variscan peraluminous S-type granitic rocks. A muscoviteNbiotite granite in
the pluton's core is surrounded successively by biotiteNmuscovite granodiorite, porphyritic biotiteNmuscovite granodiorite grading
to biotite=muscovite granite, and finally by muscoviteNbiotite granite. ID-TIMS U–Pb ages for zircon and monazite indicate that
all phases of the pluton formed at 310±1 Ma. Whole-rock analyses show slight variation in 87Sr/86Sr310 Ma between 0.708 and
0.712, ɛNd310 Ma values between −1 and −4 and δ18O values between 12.2 and 13.6. These geological, mineralogical,
geochemical and isotopic data indicate a crustal origin of the suite, probably from partial melting of heterogeneous Early Paleozoic
pelitic country rock. In detail there is evidence for derivation from different sources, but also fractional crystallization linking some
of internal plutonic phases. Least-squares analysis of major elements and modelling of trace elements indicate that the porphyritic
granodiorite and biotite=muscovite granite were derived from the granodiorite magma by fractional crystallization of plagioclase,
quartz, biotite and ilmenite. By contrast variation diagrams of major and trace elements in biotite and muscovite, the behaviours of
Ba in microcline and whole-rock δ18O, the REE patterns of rocks and isotopic data indicate that both muscovite-dominant granites
were probably originated by two distinct pulses of granite magma.
The quartz veins containing scheelite from Fonte Santa mine cut the Lower Ordovician quartzites. A
muscovite–biotite granite (G1) and a muscovite granite (G2), both S-type, crop out close to the Fonte Santa
mine and are related to the Moncorvo–Bemposta shear zone. The most altered samples of G2 show intense
muscovitization and microclinization and contain chlorite, columbite–tantalite, wolframite, W-ixiolite and
Fe-oxides. The tin-bearing granites contain 18 ppm (G1) and 73 ppm (G2) Sn. The most altered samples of
G2 correspond to a tungsten granite. The quartz veins contain muscovite, chlorite, tourmaline, scheelite,
pyrrhotite, pyrite, sphalerite, chalcopyrite, galena, arsenopyrite, iron oxides, Fe sulfates, phosphates of Pb, Fe
and Al. The Fonte Santa mine area was exploited for W between 1942 and 1982. At the end of November
2006, a flood event damaged the tailings dam of Fonte Santa mine, releasing contaminated material and
increasing contaminant levels in water within the area of influence of the mine. The waters related to the
Fonte Santa mine are poorly mineralized, with electrical conductivity of b965 μS/cm, and of a mixed type or
HCO3
− and SO4 2− types. Most pH values (5.0−8.5) indicate that there is no significant acidic drainage in the
region, as found in other areas. More acidic values (pH=3.4) were found in the mine's lagoon. Waters
associated with mineralized veins and old mine activities have Fe and Mn concentrations that forbid their
use for human consumption and agriculture. Natural Na, Mg and K water contents are associated with the
alteration of albite, chlorite and muscovite of country rock, while Ca with the W-bearing quartz veins.
Weathering agents are carbonic and sulphuric acids and the latter has a strong influence in areas draining
fine-grained mine tailings.
Na região mineira de Murçós, a exploração de scheelite e cassiterite em filões hidrotermais de quartzo com W>Sn ocorreu em quatro cortas a céu aberto e em galerais subterrâneas, entre 1948 e 1976. Como resultado da exploração mineira formaram-se três lagoas confinadas e permanentes, nas quais foram aplicadas técnicas de fitoremediação com macrófitas, entre 2005 e 2007. Os filões W>Sn de Murçós contêm essencialmente quartzo, moscovite, turmalina, scheelite, cassiterite, volframite, pirrotite, arsenopirite, pirite, esfalerite, calcopirite, galena, bismuto nativo, rara pirrotite e estanite, para além de minerais tardios como bismutinite, joseite, matildite, anglesite, zavaritskite, escorodite e roosveltite. A área mineira abandonada localiza-se próximo de zonas rurais, sendo as águas utilizadas na agricultura e algumas para consumo humano. As águas das lagoas de mina são ácidas, com elevados valores de condutividade eléctrica e de SO42-, Ca, Mg, Mn, Al, Zn, Sr, Ni e Co. Contudo, a maioria das águas da área apresentam baixos teores de metais, sendo classificadas como cálcio-sulfatadas e de tipo misto. Estas águas não devem ser usadas para consumo humano nem para a agricultura devido aos teores elevados de As, Fe, Mn, Al, Cd, Ni e SO42-.
DOI:10.1016/j.gexplo.2010.05.001
The quartz veins containing scheelite from Fonte Santa mine area were exploited for W between 1942 and
1982. At the end of November 2006, a flood event damaged the dam land of Fonte Santa mine and metal
content of water increased. Fonte Santa mine area cuts the quartzites close to the Fonte Santa muscovite
granite. The granite contains quartz, microcline, albite, muscovite, chlorite, columbite-tantalite, volframite,
W-ixiolite and ilmenite. The quartz veins contain muscovite, chlorite, tourmaline, scheelite, pyrrhotite,
pyrite, sphalerite, chalcopyrite, galena, arsenopyrite, magnetite, jarosite, phosphates of Pb, Fe and Al. The
waters related to the Fonte Santa mine are poorly mineralized, with electrical conductivity < 965 μS / cm, of
mixed type or HCO3
- and SO4
2- types. These waters have Fe and Mn contents that forbid to use that for
human consumption and agriculture. Sodium, Mg and K water contents are associated with the alteration of
albite, chlorite and muscovite of country rock, while Ca is related to the W-bearing quartz veins.
Tailings deposited over the Castanheira, a stream which flows through the old Ag–Pb–Zn Terramonte mine area, showed a great potential environmental risk due to sulphide weathering, facilitated by the tailings–water interaction. The high concentrations of Al, Fe, Pb and Zn in the tailings are associated with the exchangeable, reducible and sulphide fractions and suggest sphalerite and pyrite occurrences. Oxidation of pyrite is responsible for the low pH values (3.38–4.89) of the tailings. The water from the Castanheira stream is not suitable for human consumption due to high concentrations of SO4 2−, Mn, Al, Cd, Ni, and Pb. The lowest concentrations of metals and metalloids were detected in downstream stretches of the Castanheira. However, As, Fe and Zn in deeper sediments tend to increase downstream. Significant concentrations of trivalent forms of arsenic were detected in water samples. In downstream stretches of the Castanheira, some free ions (Fe2+, Mn2+ and Zn2+) also predominate and the water is saturated with ferrihydrite, goethite, hematite, lepidocrosite and magnetite.
The abandoned Alto da Várzea radium mine exploited quartz veins containing ore minerals and U-bearing minerals, such as autunite and torbernite. The area is located on a Variscan two-mica granite that intruded the schist–greywacke complex. The mine was exploited underground from 1911-22 and was closed down in 1946. This mine was not restored and actually a commercial area is deployed.A total of ten surface water and groundwater samples were collected in the study area between 2008/09. Most water samples have pH values ranging from 4.3 to 6.8 and are poorly mineralized (EC=41-186 μ S/cm; TDS=33-172 mg/L). However, the waters are contaminated with NO2-, Mn, Cu, As and U and must not be used for human consumption and some of them in agricultural activities. The water contamination is mainly associated with the old radium mine and human activities developed in the area.
A biotite granodiorite and seven Sn-bearing two-mica granites crop out in the Gouveia area, central Portugal.
A SHRIMP U–Th–Pb zircon age from the granodiorite, and monazite ages from four of the two-mica granites,
show that they are of Early Ordovician (~480 Ma) and Permo-Carboniferous, i.e. Variscan (~305 and 290 Ma)
age respectively. The Variscan two-mica granites are late- and post-D3. Major and trace element variation in
the granitic rocks and their biotite and muscovite indicate mainly individual fractionation trends. The granitic
rocks are mostly depleted in HREE relative to LREE. The biotite granodiorite is probably derived from igneous
lower crust, as evidenced by low initial 87Sr/86Sr (0.7036), high εNdT (+2.5) and moderate δ18O (8.8‰). The
two-mica granites are probably derived by partial melting of heterogeneous mid-crustal metasediments,
mainly metapelite and some metagraywacke, as evidenced by their high initial 87Sr/86Sr (0.7076–0.7174),
δ18O (10.7–13.4‰) and major element compositions. However, variation diagrams for major and trace
elements from two of the muscoviteNbiotite granites and their micas define fractionation trends. Rb–Sr
whole-rock analyses from the two granites are perfectly fitted to a single isochron and the rocks have subparallel
REE patterns; the younger granite is derived from the older by fractional crystallization of quartz,
plagioclase, biotite and ilmenite (tested by modelling major and trace elements). Most of the Sn-bearing
granites are derived from distinct magma batches. They result from partial melting of a heterogeneous midcrustal
metasediment. They do not represent a crustal anomaly in tin. Fractional crystallization is responsible
for the increase in the Sn contents of the granites and their micas. Muscovite has a higher Sn content than
coexisting biotite and is the principal host mineral for Sn in these rocks.
The old Senhora das Fontes uranium mine, in central Portugal, consists of quartz veins which penetrated along fracture shear zones at the contact between graphite schist and orthogneiss. The mine was exploited underground until a depth of 90 m and was closed down in 1971. The ores from this mine and two others were treated in the mine area by the heap-leach process which ended in 1982. Seven dumps containing a total of about 33,800 m3 of material and partially covered by natural vegetation were left in the mine area. A remediation process took place from May 2010 to January 2011. The material deposited in dumps was relocated and covered with erosion resisting covers. Surface water and groundwater were collected in the wet season just before the remediation, in the following season at the beginning of the remediation and also after the remediation in the following dry season. Before, at the beginning and after the remediation, surface water and groundwater have an acid-to-alkaline pH, which decreased with the remediation, whereas Eh increased. In general, before the remediation, uranium concentration was up to 83 μg/L in surface water and up to 116 μg/L in groundwater, whereas at the beginning of the remediation it increases up to 183 μg/L and 272 μg/L in the former and the latter, respectively, due to the remobilization of mine dumps and pyrite and chalcopyrite exposures, responsible for the pH decrease. In general, after the remediation, the U concentration decreased significantly in surface water and groundwater at the north part of the mine area, but increased in both, particularly in the latter up to 774 μg/L in the south and southwest parts of this area, attributed to the remobilization of sulphides that caused mobilization of metals and arsenic which migrated to the groundwater flow. Uranium is adsorbed in clay minerals, but also in goethite as indicated by the geochemical modelling. After the remediation, the saturation indices of oxyhydroxides decrease as pH decreases. The remediation also caused decrease in Cd, Co, Cr, Ni, Pb, Zn, Cu, As, Sr and Mn concentrations of surface water and groundwater, particularly in the north part of the mine area, which is supported by the speciation modelling that shows the decrease of most dissolved bivalent species. However, in general, after the remediation, Th, Cd, Al, Li, Pb, Sr and As concentrations increased in groundwater and surface water at south and southwest of the mine area. Before and after the remediation, surface water and groundwater are contaminated in U, Cd, Cr, Al, Mn, Ni, Pb, Cu and As. Remediation caused only some improvement at north of the mine area, because at south and southwest part, after the remediation, the groundwater is more contaminated than before the remediation.
The Pinhal do Souto mine exploited a quartz vein containing uranium minerals, mainly autunite and
torbernite. This vein intersects a two-mica granite containing 10 ppm U and uraninite. The mine was
exploited underground and produced 93091 kg U3O8 between 1978 and 1989 and was then closed down.
Two dumps were left in the mine area and these are partially covered by natural vegetation. Groundwater
and surface water have a similar slightly acid-to-alkaline pH. The 2
2
UO is abundant and complexed
with 2
3 CO , under neutral to alkaline pH. Metals and arsenic concentrations in the water increase during the
dry season due to the evaporation. Uranium concentration in the water increases (up to 104.42 g/l) in the
wet season, because secondary uranium minerals are dissolved and uranium is released into the water. Soils
tend to retain a higher concentration of several metals, including U (up to 336.79 mg/kg) than stream
sediments (up to 35.68 mg/kg), because vermiculite from the former could adsorb it more easily than could
kaolinite from the latter. The Fe-oxides precipitate retains the highest concentrations of several metals,
including U and Th (up to 485.20 and 1053.12 mg/kg, respectively) and the metalloid As, because it is richer in oxyhydroxides and organic matter than stream sediments and soils. The median concentrations of Fe, As,
Cd, Pb, Sb, Th, U, W and Zn in soils from this area are higher than in European soils of the FOREGS data.
Waters from dry and wet seasons, stream sediments and soils are contaminated and must not be used. This
area was compared with another Portuguese abandoned uranium mine area. The former mine caused a lower
environmental impact attributable to it having lower sulfide concentration and mineral alteration than in the
latter.
In the Segura area, Variscan S-type granites, aplite veins and lepidolite-subtype granitic aplite-pegmatite veins intruded the Cambrian schist-metagraywacke complex. The granites are syn D3. Aplite veins also intruded the granites. Two-mica granite and muscovite granite have similar ages of 311.0 ± 0.5 Ma and 312.9 ± 2.0 Ma but are not genetically related, as indicated by their geochemical characteristics and (87Sr/86Sr)311 values. They correspond to distinct pulses of magma derived by partial melting of heterogeneous metapelitic rocks. Major and trace elements suggest fractionation trends for: (a) muscovite granite and aplite veins; (b) two-mica granite and lepidolite-subtype aplite-pegmatite veins, but with a gap in most of these trends. Least square analysis for major elements, and modeling of trace elements, indicate that the aplite veins were derived from the muscovite granite magma by fractional crystallization of quartz, plagioclase, K-feldspar and ilmenite. This is supported by the similar (87Sr/86Sr)311 and δ18O values and the behavior of P2O5 in K-feldspar and albite. The decrease in (87Sr/86Sr)311 and strong increase (1.6‰) in δ18O from two-mica granite to lepidolite-subtype aplite-pegmatite veins, and the behaviors of Ca, Mn and F of hydroxylapatite indicate that these veins are not related to the two-mica granite.
The occurrence of amblygonite–montebrasite, lepidolite, cassiterite, columbite-(Fe), columbite-(Mn) and microlite suggests that lepidolite-subtype granitic aplite-pegmatite veins are highly differentiated. Montebrasite shows a heterogeneous Na distribution and secondary lacroixite was identified in some montebrasite areas enriched in Na. Unusual Mn > Fe cassiterite is zoned, with the alternating darker zones being strongly pleochroic, oscillatory zoned, and containing more Nb and Ta than the lighter zones. Inclusions of muscovite, apatite, tapiolite-(Fe), ixiolite and microlite are present both in lighter and darker zones of cassiterite. It shows exsolutions of columbite-(Fe), columbite-(Mn,Fe) and columbite-(Mn), particularly in darker zones.
In the abandoned Mortórios uranium mine area there are quartz veins containing wolframite and sulphides and basic rock dykes with torbernite and autunite cutting a porphyritic granite. The basic rock dykes were exploited and produced about 27 t of U3O8, from 1982 to 1988. There are an open pit lake and nine dumps. Surface water and groundwater are contaminated in U, As, Cd, Cr, Cu, Fe, Mn, Ni and Pb. Stream sediments are contaminated in U, As, Th and W, which are adsorbed by smectite, kaolinite and iron- and aluminium- oxy-hydroxides. The maximum U concentrations are of 1268 μg/L in the open pit lake, 100 μg/L in surface water, 103 μg/L in groundwater and 81.5 mg/kg in stream sediments all downstream of the open pit lake and dumps. Further downstream the U concentration in water decreases, due to the high mobility of U (VI), but the U concentration in stream sediments increases. Calcium uranyl carbonate dominates in the open pit lake, but uranyl carbonate complexes dominate in surface water and groundwater. The maximum As concentrations are 56.0 μg/L in the open pit lake, 63.4 μg/L in the surface water and 66.7 μg/L in the groundwater, both downstream of the open pit lake and dumps. The arsenic occurs as As (V). The Mortórios area is compared with two other areas exploited from open pits, all located in the uranium-bearing Beira area of central Portugal. Vale de Abrutiga produced 90 t of U3O8 between 1982 and 1989 and Mondego Sul produced 75 t of U3O8 from 1987 to 1991. The two mines consist of quartz veins containing sulphides, saleeite and meta-saleeite at Vale de Abrutiga and with sulphides, autunite, torbernite, meta-uranocircite and meta-saleeite at Mondego Sul cutting the Schist-graywacke Complex. The mine area of Vale de Abrutiga with the highest exploitation of U3O8 has strongly acidic to slight alkaline water, which is the most contaminated. Mortórios with the lowest exploitation presents a higher contamination of slightly acidic to alkaline water than that of acidic to alkaline water from Mondego Sul, but the former has As (V), whereas the latter has As (III), which is toxic. The stream sediments from Mortórios present the lowest contamination, except for Th that has a higher median value than that from Vale de Abrutiga. Stream sediments from Mondego Sul have higher U, Th, Pb and lower Co, Cr, Cu and Zn median values than those of Vale de Abrutiga.
