The gold area of Jales (northern Portugal)

Neiva, J. M. Cotelo; Neiva, A.M.R.

doi:10.1111/j.1365-3121.1990.tb00072.x

Cited by 12 publications

(3 citation statements)

References 9 publications

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“…The occurrences of very small amounts of cassiterite, wolframite and scheelite in a few of these veins suggest that they may be genetically linked to the W-Sn deposits, which are closest to granite (Couto et al, 1990). Fractionation of felsic magma may concentrate gold (Neiva and Neiva, 1990;Neiva, 1992).…”

Section: Mineralizing Environmentmentioning

confidence: 99%

Antimony quartz and antimony-gold quartz veins from northern Portugal

Neiva

Andráš

Ramos

2006

Geochimica et Cosmochimica Acta

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In northern Portugal, there are two main areas containing antimony, lead-antimony and antimony-gold deposits. The antimony and lead-antimony quartz breccia veins from the Bragança district are mainly hosted by Silurian phyllites. The antimonygold quartz breccia veins from the Dú rico-Beirã region are mainly hosted by the Cambrian schist-metagraywacke complex and also Ordovician phyllites and quartzites. These veins are up to 200 m long, but their thickness ranges from a few centimeters to 3.6 m.In each deposit, some minerals show multiple paragenetic settings, suggesting that mineral precipitation is a polyphase process. Arsenopyrite, pyrite and pyrrhotite are the earliest sulfides to form. The earliest generation of euhedral gold is earlier than or contemporaneous with arsenopyrite and earlier than pyrrhotite and pyrite. Berthierite and stibnite are the most important antimony-bearing minerals. Stibnite is most abundant. Later anhedral gold grains are present within fractures between arsenopyrite and stibnite and in stibnite, which is partially replaced by the gold. Gold inclusions rarely occur in quartz. Carbonates precipitated in the last hypogene stage.The drastic fluid cooling during the mineralizing event was an important cause of mineralization. However, acidification of fluids might have been the main mechanism for stibnite precipitation, as it would have destabilized Sb(OH) 3 . Gold associated with arsenopyrite, pyrite and quartz was probably carried as a bisulfide complex by the early aqueous carbonic fluid with 2 wt% equiv. NaCl at 290-340°C, while the late generation of gold associated with berthierite and stibnite was transported as a bisulfide complex by the H 2 O-NaCl (2 wt% equiv.) fluid at 128-225°C.Variscan folding, long deep faults, shear zones, and deformation in the Bragança district and Dú rico-Beirã region would have provided anomalous crustal heat flow to sustain the extensive and long-lived hydrothermal activity. The metamorphic fluids derived from the country metasediments and heated meteoric water, which also leached metals from these metasediments, were responsible for the origin of the mineralized veins. The lead isotopic data for stibnite indicate a homogeneous source of lead of crustal origin, from a dominant metasedimentary source, for the studied antimony, lead-antimony and antimony-gold quartz veins. This is consistent with related European mineralizations.Previously, hydrothermal alteration halos around Archaean orogenic gold deposits have been documented at the metre to 100 m scale centred around the gold lode. The preferred model for this spatial relationship and the available fluid inclusion and stable isotope data was a one fluid model with gold deposition largely caused by fluid-wallrock reactions and phase separation. Camp-scale studies in the St. Ives gold camp and at the Kanowna Belle and Wallaby deposits in Western Australia have documented camp-scale hydrothermal alteration cells which are asymetric to gold.Several hundred metres to kilometre scale magnetite-pyrite or ...

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Section: Mineralizing Environmentmentioning

confidence: 99%

Antimony quartz and antimony-gold quartz veins from northern Portugal

Neiva

Andráš

Ramos

2006

Geochimica et Cosmochimica Acta

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“…A importância de Canudos é exaltada pelas incontáveis teses, dissertações, livros, abordagens na música, na fotografia, nos filmes. Essa importância é refletida por Neiva (2017), em sua obra "Canudos, uma nova batalha":…”

Section: Luiz Paulo Neivaunclassified

Canudos, essa história não pode morrer!

Neiva

2023

PdI

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Trata-se de um relato sobre o processo de criação e instalação de uma série de equipamentos de memória sobre o massacre dos conselheiristas, entre 1896 e 1897, no evento histórico chamado Guerra de Canudos, bem como, uma forma de convite aberto à população brasileira e mundial para conhecer esses equipamentos e seus acervos: uma condição para se conhecer o Brasil e seu devir revolucionário, através das pegadas do Belo Monte. [Recebido em: 20 nov. 2022 – Aceito em: 15 dez. 2022]

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“…Some authors (e.g. Neiva and Neiva, 1990), suggested a genetic relation between hydrothermal-fluid activity and late-stage fractional crystallization of granites for the Portuguese gold deposits. In contrast, Noronha et al (2000) concluded that the gold ores in quartz veins appear to be the result of three successive periods of fluid circulation in response to high heat flow and the intrusions of the granites: Stage 1 corresponds to the deposition of a milky quartz after the emplacement of synorogenic peraluminous granites; Stage 2 is characterized by a clear quartz and some sulfides and minor gold overprinting the early milky quartz associated with a fluid flow related with orogenic uplift and tectonic reactivation; and Stage 3 is characterized by intense microfissuring of the earlier minerals, deposition of more sulfides (galena, chalcopyrite and bismuthinite) in addition to native bismuth and sulfosalts (Pb-Bi-Ag dominant).…”

Section: Introductionmentioning

confidence: 99%

Supergene gold enrichment in the Castromil-Serra da Quinta gold deposit, NW Portugal

Cruz

Noronha²,

Santos³

et al. 2018

Mineral. mag.

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Several gold deposits hosted mainly by Variscan granites and Precambrian to Palaeozoic metasediments occur in the northwestern part of Portugal. Most of these deposits were mined by the Romans (in the period I BC to II AD) as open pits and surface galleries. The Castromil-Serra da Quinta gold deposit is an important example of such a mined site; it occurs in the Dúrico-Beirã Au province located in the Central Iberian Zone (CIZ) in the western branch of European Variscan belt, mainly on the eastern flank of the Valongo anticline. Open pits and underground galleries at Castromil-Serra da Quinta exploited the gossan formed from the weathering of primary mineralization. The gossan is composed essentially of goethite, scorodite and clay minerals. A recent drilling campaign at Castromil-Serra da Quinta has provided samples of the primary mineralization below the oxidation level. Different modes of gold occurrence are defined based on metallographic studies of both the gossan and drill cores. Gold I occurs encapsulated in primary sulfide minerals, mainly arsenopyrite and pyrite; Gold II is also associated with the main primary sulfides, but occurs along grain boundaries and in microfractures of the sulfides or in associated quartz veins; and Gold III occurs as free gold particles in iron oxides within the gossan. In the gossan samples, it is difficult to distinguish whether the gold particles hosted in oxides correspond to Gold I, Gold II, or both, so these particles are described as Gold I–II and they are commonly surrounded by very much smaller particles of Gold III. Scanning electron microscope (SEM) and electron probe microanalysis (EPMA) data for the different gold particles reveal that Gold I is poorer in Ag (~15.5–39.76%) than Gold II (37.46–51.45%), whereas Gold III corresponds to native gold (<16.11% Ag). Gold III is thought to reflect gold enrichment in the upper level of the deposit, resulting from weathering processes that affected the primary Au (Bi) mineralization.

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The gold area of Jales (northern Portugal)

Cited by 12 publications

References 9 publications

Antimony quartz and antimony-gold quartz veins from northern Portugal

Antimony quartz and antimony-gold quartz veins from northern Portugal

Canudos, essa história não pode morrer!

Supergene gold enrichment in the Castromil-Serra da Quinta gold deposit, NW Portugal

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