espanolLa caracterizacion morfometrica de una cuenca hidrografica proporciona informacion esencia... more espanolLa caracterizacion morfometrica de una cuenca hidrografica proporciona informacion esencial para la planificacion y gestion de los recursos hidricos. El objetivo del trabajo fue la caracterizacion morfometrica de la microcuenca del Igarape Novo Mundo, municipio de Nova Brasilândia D’Oeste. Se analizaron las caracteristicas morfometricas, altitud, relieve y red de drenaje. La microcuenca tiene un area de 28,15 km², perimetro de 39,84 km, altitudes minima, media y maxima de 279, 342 y 459m, respectivamente, predominancia de relieve suave ondulado a fuerte ondulado (84,04 %), coeficiente de compacidad 2,10, factor de forma 0,35, indice de circularidad 0,22, patron de drenaje dendritico, 5a orden de drenaje, densidad de drenaje de 4,93 km km-2, indice de sinuosidad 23,09 % y tiempo de concentracion de 2,23 horas. Estas caracteristicas facilitan una mayor infiltracion de agua en el suelo, reduciendo los riesgos de erosion y baja susceptibilidad a las inundaciones. Por lo tanto, se recomienda la adopcion de practicas de manejo conservacionista para mantener la microcuenca con caracteristicas adecuadas. EnglishThe morphometric characterization of the river basin provides essential information for the planning and management of water resources. The objective was the morphometric characterization of the microbasin of the Igarape Novo Mundo, Nova Brasilândia D’Oeste, Rondonia. The characteristics of altitude, relief and drainage network were analyzed. The microbasin has an area of 28.15 km², with a perimeter of 39.84 km, with a minimum, average and maximum elevation of 279, 342 and 459 m, respectively, predominance of smooth to undulating waves (84.04 %), coefficient of compactness of 2.10, shape factor of 0.35, circularity index of 0.22, dendritic drainage pattern, 5th order of drainage, drainage density of 4.93 km km-2, sinuosity index 23.09 % and time of concentration of 2.23 hours. These characteristics provide greater infiltration of water in the soil, reducing the risks of erosion and low susceptibility to floods. Therefore, it is recommended to adopt conservation management practices to maintain the microbasin with adequate characteristics. portuguesA caracterizacao morfometrica da bacia hidrografica fornece informacoes essenciais para o planejamento e gestao dos recursos hidricos. O objetivo deste trabalho foi a caracterizacao morfometrica da microbacia do Igarape Novo Mundo, municipio de Nova Brasilândia D’Oeste. Analisou-se as caracteristicas morfometricas, altitude, relevo e rede de drenagem. A microbacia tem area de 28,15 km², perimetro de 39,84 km, altitudes minima, media e maxima de 279, 342 e 459 m, respectivamente, predominância de relevo suave ondulado a forte ondulado (84,04 %), coeficiente de compacidade de 2,10, fator de forma de 0,35, indice de circularidade de 0,22, padrao de drenagem dendritico, 5a ordem de drenagem, densidade de drenagem de 4,93 km km-2, indice de sinuosidade 23,09 % e tempo de concentracao de 2,23 horas. Estas caracteristicas proporcionam maior infiltracao de agua no solo, reduzindo os riscos de erosao e baixa suscetibilidade a enchentes. Portanto, recomenda-se adocao de praticas de manejo conservacionista para manter a microbacia com caracteristicas adequadas.
espanolCon este trabajo se caracterizo la morfometria de la subcuenca del rio Mutum-Parana, Amazo... more espanolCon este trabajo se caracterizo la morfometria de la subcuenca del rio Mutum-Parana, Amazonia Occidental. Se realizaron analisis geometricos (area, perimetro, indice de circularidad; coeficiente de compacidad y factor forma); relieve (pendiente, altitud minima, media y maxima; densidad de drenaje e indice de sinuosidad). Para el procesamiento de los datos su utilizo SRTM, software QGIS 2.10.0 (version Pisa) y el complemento TauDEM. La subcuenca tiene un area de 3.510,0284 km2 , perimetro de 315,5719 km, indice de circularidad de 0,4430, coeficiente de compacidad de 1,4914, factor forma de 0,3020, relieve plano a suave ondulado 82,65 % del area, altitud minima de 78 e maxima de 297 m, drenaje dendritico, con una densidad de 2,23 km km-2 e indice de sinuosidad de 1,1989. EnglishThe objective of this work was the morphometric characterization of the sub-basin of the Mutum-Parana River, Western Amazon. The geometric analyzes (area, perimeter, circularity index, compactness coefficient and shape factor), relief (slope, minimum altitude, average and maximum, and altimetric range) and drainage (classification, drainage density and sinuosity index). For SRTM data processing, QGIS 2.10.0 software (Pisa version) and TauDEM add- -in. The sub-basin has an area of 3,510,0284 km2 , a perimeter of 315.5719 km, a circularity index of 0.4430, a compactness coefficient of 1.4914, a shape factor of 0.3020, a flat relief to a smooth corrugation in 82,65 % of the area, minimum altitude of 78 and maximum of 297 m, dendritic drainage, with density of 2.23 km km-2 and sinuosity index of 1.1989. The sub-basin of the Mutum-Parana River has low susceptibility to flood occurrence, tendency of low runoff velocity and good drainage capacity portuguesObjetivou-se com o trabalho a caracterizacao morfometrica da sub-bacia hidrografica do rio Mutum-Parana, Amazonia Ocidental. Foram realizadas analises geometricas (area, perimetro, indice de circularidade, coeficiente de compacidade e fator forma), relevo (declividade, altitude minima, media e maxima, e amplitude altimetrica) e drenagem (classificacao, densidade de drenagem e indice de sinuosidade). Para o processamento de dados SRTM, software QGIS 2.10.0 (versao Pisa) e complemento TauDEM. A sub-bacia apresenta area de 3.510,0284 km2 , perimetro de 315,5719 km, indice de circularidade de 0,4430, coeficiente de compacidade de 1,4914, fator de forma de 0,3020, relevo plano a suave ondulado em 82,65 % da area, altitude minima de 78 e maxima de 297 m, drenagem dendritica, com densidade de 2,23 km km-2 e indice de sinuosidade de 1,1989. A sub-bacia do rio Mutum-Parana possui baixa susceptibilidade a ocorrencia de enchentes, tendencia de baixa velocidade de escoamento superficial e boa capacidade de drenagem
<p>A new tectonic model is presented to explain the tectonostratigraphic evolution ... more <p>A new tectonic model is presented to explain the tectonostratigraphic evolution of the Paleoproterozoic Karrat Group in central West Greenland and the polyphase deformation, magmatism and metamorphism in the Rinkian orogen recorded in Paleoproterozoic rocks and Archaean complexes. The Karrat Group (from c. 71°00’ to 73°00’ N) formed in an intra-cratonic sag basin after c. 2000 Ma with basal quartzites of the Qaarsukassak and Mârmorilik formations unconformably overlaying Archaean gneisses of the Rae Craton. From 1950 to 1900 Ma a carbonate platform represented by the Mârmorilik Formation developed toward the south, while rift related alkaline volcanic rocks represented by the alkaline member of the Kangilleq Formation and syn-rift siliciclastic and volcaniclastic sediments of the Nûkavsak Formation were deposited to the north. The rifting was succeeded by a back-arc system, represented by the transitional member of the Kangilleq Formation. Concomitantly with development of the back-arc system, arc-related granitoids of the Prøven Intrusive Complex (PIC) intruded into and along the basal contact of the Karrat Group around 1900 Ma with major pulses at c. 1870 and c. 1850 Ma. The Karrat Group and the magmatic arc rocks underwent HT-metamorphism at c. 1830–1800 Ma during the collisional phase of the Rinkian orogen. The metamorphic grade increases from greenschist facies in the south, to granulite facies in the north, where the metamorphism is associated with migmatization and emplacement of the S-type Qinngua leucogranites. Extensive thrust emplacement and folding characterize the Rinkian orogen south of the PIC and the eastern boundary of the magmatic arc is reworked along a top to ESE shear zone post-dating the HT-metamorphism. The ESE-ward emplacement of allochthonous thrust sheets during an early stage of thin-skinned tectonics is followed by NE-ward emplacement of basement nappes and finally by a NW-SE compression stage resulting in tectonic inversion of basin normal faults.  The back-arc extension and Cordilleran-type magmatism were driven by eastward subduction of oceanic crust during the Trans-Hudson Orogeny resulting from the convergence of the Superior, Meta Incognita and Rae Archean cratons between 1870–1800 Ma. The Karrat Group north of the PIC together with the time-correlative Piling Group of Baffin Island (Canada) probably represented the passive margin succession of the Rae craton that evolved into a forearc setting during the Trans-Hudson Orogeny. The Rinkian orogen is an example of Cordilleran-type tectonics resulting from the deformation of the Rae continental margin intruded by magmatic arc granites during subduction, followed by HT-metamorphism in the upper plate and the structuring of a back-arc fold and thrust system antithetic to the subducting plate.</p>
Igneous xenoliths have been identified within the Paleozoic Midtkap volcanic centers of North Gre... more Igneous xenoliths have been identified within the Paleozoic Midtkap volcanic centers of North Greenland that cut through Cambrian-Ordovician deep water trough sedimentary rocks that were subsequently deformed during the south-verging Ellesmerian Orogeny. The xenoliths were characterized geochemically and their zircons dated through the U-Pb technique. This provided ages ranging from 628 to 570 Ma, for xenoliths with granitic and monzonitic compositions, the former apparently older than the latter. These ages, coupled with the geochemical signature compatible with an arc setting, provide evidence for the presence of Timanian like basement in North Greenland. The structural setting suggests that the dated xenoliths belong to an allochthonous unit emplaced during the Caledonian Orogeny and deformed during the Ellesmerian Orogeny. Furthermore, this data provides new evidence for a northwestern extension (through continuation and/or through dispersal) of the late Neoproterozoic Timanide belt, from its type locality, in the Timan-Pechora region in Russia, through Svalbard, into North Greenland, to the Pearya Terrane on Ellesmere Island.
The Iberian Pyrite Belt (IPB) is one of the most outstanding ore provinces in Europe hosting some... more The Iberian Pyrite Belt (IPB) is one of the most outstanding ore provinces in Europe hosting some of the largest concentrations of massive sulphides and 22% of the world-class (>32 Mt) VMS orebodies. A significant number of (pyrite) mines are now inactive but some orebodies still remain unexploited; this is the case of Lagoa Salgada. It is the most NW orebody known and occurs beneath approximately 130 m of Cenozoic sediments which limits interpretation solely to borehole intersection data. The orebody is folded and interpreted to occur on the subvertical-overturned and intensely faulted limb of a SW verging anticline. It is hosted within a thick IPB volcanic sedimentary sequence and is made up of a central stockwork and a massive sulphide lens. An electron microprobe study revealed consistent trace amounts of indium in sphalerite, thus contrasting with the neighbouring Neves Corvo mine where indium is known to occur associated with stannite and stanoidite. The occurrence of elevated trace amounts of indium in sphalerite from Lagoa Salgada could make this orebody an attractive economic target beyond the traditional tinbase metal suite so far extracted in the Iberian Pyrite Belt.
The Jales gold district is located in Vila Pouca de Aguiar County, northern Portugal, approximate... more The Jales gold district is located in Vila Pouca de Aguiar County, northern Portugal, approximately 100 km ENE of the city of Porto. The district encompasses three areas with epigenetic mineralization of Variscan age. Mineralization is hosted in syn- to late-tectonic Variscan granites and in greenschist-facies metasedimentary rocks, ranging in age from Cambrian to Lower Devonian. Sulfide paragenesis proceeds from early Fe-As sulfides to late base-metal sulfides. The deposits proximal to the intrusion (Campo and Gralheira) are relatively sulfide rich and contain paragenetically late electrum associated with significant amounts of base-metal sulfides, whereas the deposit distal to the intrusion (Três Minas) is sulfide poor and contains high-fineness gold that is paragenetically early. Petrographic studies, coupled with arsenopyrite geothermometry and chlorite solid solution modeling indicate that fluid evolution was different at Três Minas than in the two other areas, explaining the distinct mineral assemblages and metal associations. At Três Minas, gold was precipitated early from sulfide complexes due to oxidation. During the early stage at high temperatures, silver and base metals were transported as chloride complexes and therefore were not affected by oxidation. At Campo and Gralheira, early oxidation was not as extensive as at Três Minas, and gold precipitated later due to decrease in H2S activity and cooling. During the lower-temperature late stage, silver was transported as a sulfide complex, so that decrease in H2S activity and cooling resulted in the precipitation of electrum, rather than high-fineness gold. Additionally, cooling destabilized chloride complexes carrying base metals, explaining deposition of significant amounts of base-metal sulfides at Campo and Gralheira.
Volcanic rocks from Serra Branca, Iberian Pyrite Belt, Portugal, consist of calc-alkaline felsic ... more Volcanic rocks from Serra Branca, Iberian Pyrite Belt, Portugal, consist of calc-alkaline felsic and intermediate rocks. The latter are massive andesites, whereas the former include four dacitic to rhyolitic lithologies, distinguishable on spiderdiagrams and binary plots of immobile elements. Zircon thermometry indicates that two felsic suites may have formed from different magmas produced at distinct temperatures, with only limited fractionation within each suite. Alternatively, all the felsic rocks can be related through fractionation of a single magma if the lower zircon saturation temperature obtained for one suite merely results from Zr dilution, mostly reflecting silicification. The relatively high magma temperatures at Serra Branca ease the classification of felsic rocks based on their HFSE contents and also indicate volcanogenic massive sulfide deposit favorability. This contrasts with other areas of the Belt that register lower magma temperatures and are subsequently barren. However, magma temperatures may have not been high enough to cause complete melting of refractory phases in which HFSE reside during crustal fusion of an amphibolite protolith, implying difficult discrimination of tectonic environments for the felsic rocks. The intermediate rocks were possibly formed by mixing between basaltic magmas and crustal material, compatible with volcanism in an attenuated continental lithosphere setting.
espanolLa caracterizacion morfometrica de una cuenca hidrografica proporciona informacion esencia... more espanolLa caracterizacion morfometrica de una cuenca hidrografica proporciona informacion esencial para la planificacion y gestion de los recursos hidricos. El objetivo del trabajo fue la caracterizacion morfometrica de la microcuenca del Igarape Novo Mundo, municipio de Nova Brasilândia D’Oeste. Se analizaron las caracteristicas morfometricas, altitud, relieve y red de drenaje. La microcuenca tiene un area de 28,15 km², perimetro de 39,84 km, altitudes minima, media y maxima de 279, 342 y 459m, respectivamente, predominancia de relieve suave ondulado a fuerte ondulado (84,04 %), coeficiente de compacidad 2,10, factor de forma 0,35, indice de circularidad 0,22, patron de drenaje dendritico, 5a orden de drenaje, densidad de drenaje de 4,93 km km-2, indice de sinuosidad 23,09 % y tiempo de concentracion de 2,23 horas. Estas caracteristicas facilitan una mayor infiltracion de agua en el suelo, reduciendo los riesgos de erosion y baja susceptibilidad a las inundaciones. Por lo tanto, se recomienda la adopcion de practicas de manejo conservacionista para mantener la microcuenca con caracteristicas adecuadas. EnglishThe morphometric characterization of the river basin provides essential information for the planning and management of water resources. The objective was the morphometric characterization of the microbasin of the Igarape Novo Mundo, Nova Brasilândia D’Oeste, Rondonia. The characteristics of altitude, relief and drainage network were analyzed. The microbasin has an area of 28.15 km², with a perimeter of 39.84 km, with a minimum, average and maximum elevation of 279, 342 and 459 m, respectively, predominance of smooth to undulating waves (84.04 %), coefficient of compactness of 2.10, shape factor of 0.35, circularity index of 0.22, dendritic drainage pattern, 5th order of drainage, drainage density of 4.93 km km-2, sinuosity index 23.09 % and time of concentration of 2.23 hours. These characteristics provide greater infiltration of water in the soil, reducing the risks of erosion and low susceptibility to floods. Therefore, it is recommended to adopt conservation management practices to maintain the microbasin with adequate characteristics. portuguesA caracterizacao morfometrica da bacia hidrografica fornece informacoes essenciais para o planejamento e gestao dos recursos hidricos. O objetivo deste trabalho foi a caracterizacao morfometrica da microbacia do Igarape Novo Mundo, municipio de Nova Brasilândia D’Oeste. Analisou-se as caracteristicas morfometricas, altitude, relevo e rede de drenagem. A microbacia tem area de 28,15 km², perimetro de 39,84 km, altitudes minima, media e maxima de 279, 342 e 459 m, respectivamente, predominância de relevo suave ondulado a forte ondulado (84,04 %), coeficiente de compacidade de 2,10, fator de forma de 0,35, indice de circularidade de 0,22, padrao de drenagem dendritico, 5a ordem de drenagem, densidade de drenagem de 4,93 km km-2, indice de sinuosidade 23,09 % e tempo de concentracao de 2,23 horas. Estas caracteristicas proporcionam maior infiltracao de agua no solo, reduzindo os riscos de erosao e baixa suscetibilidade a enchentes. Portanto, recomenda-se adocao de praticas de manejo conservacionista para manter a microbacia com caracteristicas adequadas.
espanolCon este trabajo se caracterizo la morfometria de la subcuenca del rio Mutum-Parana, Amazo... more espanolCon este trabajo se caracterizo la morfometria de la subcuenca del rio Mutum-Parana, Amazonia Occidental. Se realizaron analisis geometricos (area, perimetro, indice de circularidad; coeficiente de compacidad y factor forma); relieve (pendiente, altitud minima, media y maxima; densidad de drenaje e indice de sinuosidad). Para el procesamiento de los datos su utilizo SRTM, software QGIS 2.10.0 (version Pisa) y el complemento TauDEM. La subcuenca tiene un area de 3.510,0284 km2 , perimetro de 315,5719 km, indice de circularidad de 0,4430, coeficiente de compacidad de 1,4914, factor forma de 0,3020, relieve plano a suave ondulado 82,65 % del area, altitud minima de 78 e maxima de 297 m, drenaje dendritico, con una densidad de 2,23 km km-2 e indice de sinuosidad de 1,1989. EnglishThe objective of this work was the morphometric characterization of the sub-basin of the Mutum-Parana River, Western Amazon. The geometric analyzes (area, perimeter, circularity index, compactness coefficient and shape factor), relief (slope, minimum altitude, average and maximum, and altimetric range) and drainage (classification, drainage density and sinuosity index). For SRTM data processing, QGIS 2.10.0 software (Pisa version) and TauDEM add- -in. The sub-basin has an area of 3,510,0284 km2 , a perimeter of 315.5719 km, a circularity index of 0.4430, a compactness coefficient of 1.4914, a shape factor of 0.3020, a flat relief to a smooth corrugation in 82,65 % of the area, minimum altitude of 78 and maximum of 297 m, dendritic drainage, with density of 2.23 km km-2 and sinuosity index of 1.1989. The sub-basin of the Mutum-Parana River has low susceptibility to flood occurrence, tendency of low runoff velocity and good drainage capacity portuguesObjetivou-se com o trabalho a caracterizacao morfometrica da sub-bacia hidrografica do rio Mutum-Parana, Amazonia Ocidental. Foram realizadas analises geometricas (area, perimetro, indice de circularidade, coeficiente de compacidade e fator forma), relevo (declividade, altitude minima, media e maxima, e amplitude altimetrica) e drenagem (classificacao, densidade de drenagem e indice de sinuosidade). Para o processamento de dados SRTM, software QGIS 2.10.0 (versao Pisa) e complemento TauDEM. A sub-bacia apresenta area de 3.510,0284 km2 , perimetro de 315,5719 km, indice de circularidade de 0,4430, coeficiente de compacidade de 1,4914, fator de forma de 0,3020, relevo plano a suave ondulado em 82,65 % da area, altitude minima de 78 e maxima de 297 m, drenagem dendritica, com densidade de 2,23 km km-2 e indice de sinuosidade de 1,1989. A sub-bacia do rio Mutum-Parana possui baixa susceptibilidade a ocorrencia de enchentes, tendencia de baixa velocidade de escoamento superficial e boa capacidade de drenagem
<p>A new tectonic model is presented to explain the tectonostratigraphic evolution ... more <p>A new tectonic model is presented to explain the tectonostratigraphic evolution of the Paleoproterozoic Karrat Group in central West Greenland and the polyphase deformation, magmatism and metamorphism in the Rinkian orogen recorded in Paleoproterozoic rocks and Archaean complexes. The Karrat Group (from c. 71°00’ to 73°00’ N) formed in an intra-cratonic sag basin after c. 2000 Ma with basal quartzites of the Qaarsukassak and Mârmorilik formations unconformably overlaying Archaean gneisses of the Rae Craton. From 1950 to 1900 Ma a carbonate platform represented by the Mârmorilik Formation developed toward the south, while rift related alkaline volcanic rocks represented by the alkaline member of the Kangilleq Formation and syn-rift siliciclastic and volcaniclastic sediments of the Nûkavsak Formation were deposited to the north. The rifting was succeeded by a back-arc system, represented by the transitional member of the Kangilleq Formation. Concomitantly with development of the back-arc system, arc-related granitoids of the Prøven Intrusive Complex (PIC) intruded into and along the basal contact of the Karrat Group around 1900 Ma with major pulses at c. 1870 and c. 1850 Ma. The Karrat Group and the magmatic arc rocks underwent HT-metamorphism at c. 1830–1800 Ma during the collisional phase of the Rinkian orogen. The metamorphic grade increases from greenschist facies in the south, to granulite facies in the north, where the metamorphism is associated with migmatization and emplacement of the S-type Qinngua leucogranites. Extensive thrust emplacement and folding characterize the Rinkian orogen south of the PIC and the eastern boundary of the magmatic arc is reworked along a top to ESE shear zone post-dating the HT-metamorphism. The ESE-ward emplacement of allochthonous thrust sheets during an early stage of thin-skinned tectonics is followed by NE-ward emplacement of basement nappes and finally by a NW-SE compression stage resulting in tectonic inversion of basin normal faults.  The back-arc extension and Cordilleran-type magmatism were driven by eastward subduction of oceanic crust during the Trans-Hudson Orogeny resulting from the convergence of the Superior, Meta Incognita and Rae Archean cratons between 1870–1800 Ma. The Karrat Group north of the PIC together with the time-correlative Piling Group of Baffin Island (Canada) probably represented the passive margin succession of the Rae craton that evolved into a forearc setting during the Trans-Hudson Orogeny. The Rinkian orogen is an example of Cordilleran-type tectonics resulting from the deformation of the Rae continental margin intruded by magmatic arc granites during subduction, followed by HT-metamorphism in the upper plate and the structuring of a back-arc fold and thrust system antithetic to the subducting plate.</p>
Igneous xenoliths have been identified within the Paleozoic Midtkap volcanic centers of North Gre... more Igneous xenoliths have been identified within the Paleozoic Midtkap volcanic centers of North Greenland that cut through Cambrian-Ordovician deep water trough sedimentary rocks that were subsequently deformed during the south-verging Ellesmerian Orogeny. The xenoliths were characterized geochemically and their zircons dated through the U-Pb technique. This provided ages ranging from 628 to 570 Ma, for xenoliths with granitic and monzonitic compositions, the former apparently older than the latter. These ages, coupled with the geochemical signature compatible with an arc setting, provide evidence for the presence of Timanian like basement in North Greenland. The structural setting suggests that the dated xenoliths belong to an allochthonous unit emplaced during the Caledonian Orogeny and deformed during the Ellesmerian Orogeny. Furthermore, this data provides new evidence for a northwestern extension (through continuation and/or through dispersal) of the late Neoproterozoic Timanide belt, from its type locality, in the Timan-Pechora region in Russia, through Svalbard, into North Greenland, to the Pearya Terrane on Ellesmere Island.
The Iberian Pyrite Belt (IPB) is one of the most outstanding ore provinces in Europe hosting some... more The Iberian Pyrite Belt (IPB) is one of the most outstanding ore provinces in Europe hosting some of the largest concentrations of massive sulphides and 22% of the world-class (>32 Mt) VMS orebodies. A significant number of (pyrite) mines are now inactive but some orebodies still remain unexploited; this is the case of Lagoa Salgada. It is the most NW orebody known and occurs beneath approximately 130 m of Cenozoic sediments which limits interpretation solely to borehole intersection data. The orebody is folded and interpreted to occur on the subvertical-overturned and intensely faulted limb of a SW verging anticline. It is hosted within a thick IPB volcanic sedimentary sequence and is made up of a central stockwork and a massive sulphide lens. An electron microprobe study revealed consistent trace amounts of indium in sphalerite, thus contrasting with the neighbouring Neves Corvo mine where indium is known to occur associated with stannite and stanoidite. The occurrence of elevated trace amounts of indium in sphalerite from Lagoa Salgada could make this orebody an attractive economic target beyond the traditional tinbase metal suite so far extracted in the Iberian Pyrite Belt.
The Jales gold district is located in Vila Pouca de Aguiar County, northern Portugal, approximate... more The Jales gold district is located in Vila Pouca de Aguiar County, northern Portugal, approximately 100 km ENE of the city of Porto. The district encompasses three areas with epigenetic mineralization of Variscan age. Mineralization is hosted in syn- to late-tectonic Variscan granites and in greenschist-facies metasedimentary rocks, ranging in age from Cambrian to Lower Devonian. Sulfide paragenesis proceeds from early Fe-As sulfides to late base-metal sulfides. The deposits proximal to the intrusion (Campo and Gralheira) are relatively sulfide rich and contain paragenetically late electrum associated with significant amounts of base-metal sulfides, whereas the deposit distal to the intrusion (Três Minas) is sulfide poor and contains high-fineness gold that is paragenetically early. Petrographic studies, coupled with arsenopyrite geothermometry and chlorite solid solution modeling indicate that fluid evolution was different at Três Minas than in the two other areas, explaining the distinct mineral assemblages and metal associations. At Três Minas, gold was precipitated early from sulfide complexes due to oxidation. During the early stage at high temperatures, silver and base metals were transported as chloride complexes and therefore were not affected by oxidation. At Campo and Gralheira, early oxidation was not as extensive as at Três Minas, and gold precipitated later due to decrease in H2S activity and cooling. During the lower-temperature late stage, silver was transported as a sulfide complex, so that decrease in H2S activity and cooling resulted in the precipitation of electrum, rather than high-fineness gold. Additionally, cooling destabilized chloride complexes carrying base metals, explaining deposition of significant amounts of base-metal sulfides at Campo and Gralheira.
Volcanic rocks from Serra Branca, Iberian Pyrite Belt, Portugal, consist of calc-alkaline felsic ... more Volcanic rocks from Serra Branca, Iberian Pyrite Belt, Portugal, consist of calc-alkaline felsic and intermediate rocks. The latter are massive andesites, whereas the former include four dacitic to rhyolitic lithologies, distinguishable on spiderdiagrams and binary plots of immobile elements. Zircon thermometry indicates that two felsic suites may have formed from different magmas produced at distinct temperatures, with only limited fractionation within each suite. Alternatively, all the felsic rocks can be related through fractionation of a single magma if the lower zircon saturation temperature obtained for one suite merely results from Zr dilution, mostly reflecting silicification. The relatively high magma temperatures at Serra Branca ease the classification of felsic rocks based on their HFSE contents and also indicate volcanogenic massive sulfide deposit favorability. This contrasts with other areas of the Belt that register lower magma temperatures and are subsequently barren. However, magma temperatures may have not been high enough to cause complete melting of refractory phases in which HFSE reside during crustal fusion of an amphibolite protolith, implying difficult discrimination of tectonic environments for the felsic rocks. The intermediate rocks were possibly formed by mixing between basaltic magmas and crustal material, compatible with volcanism in an attenuated continental lithosphere setting.
Uploads
Papers by Diogo Rosa