Geochemistry of gold quartz vein walls from Jales (northern Portugal)

Neiva, A.M.R.; Neiva, J. M. Cotelo; Silva, M.M.V.G.

doi:10.1016/0009-2541(90)90083-j

Cited by 13 publications

(10 citation statements)

References 14 publications

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“…The intersections of the curve for granitic melts (Johannes and Holtz, 1996) and the Si-isopleths for muscovite containing 3.1 apfu Si (Massone and Schreyer, 1987;Massone and Szpurka, 1997) are about 633 and 625°C (estimated from Klein et al, 2008). Application of the Si-in phengite barometer (Massone and Schreyer, 1987;Massone and Szpurka, 1997) gives an estimated emplacement pressure of 4.5-4.8 kb which, assuming a density of 2.8 g/cm 3 for the mainly phyllitic hanging-wall rocks (Neiva et al, 1990), corresponds to a minimum intrusion depth of 17-18 km. This pressure estimate depends on the assumed crystallization temperature for muscovite.…”

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confidence: 99%

Geochemical and isotopic constraints on the petrogenesis of Early Ordovician granodiorite and Variscan two-mica granites from the Gouveia area, central Portugal

Neiva

Williams

Ramos

et al. 2009

Lithos

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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 87 Sr/ 86 Sr (0.7036), high εNd T (+ 2.5) and moderate δ 18 O (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 87 Sr/ 86 Sr (0.7076-0.7174), δ 18 O (10.7-13.4‰) and major element compositions. However, variation diagrams for major and trace elements from two of the muscovite N biotite 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.

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confidence: 99%

Geochemical and isotopic constraints on the petrogenesis of Early Ordovician granodiorite and Variscan two-mica granites from the Gouveia area, central Portugal

Neiva

Williams

Ramos

et al. 2009

Lithos

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“…Gold and silver were not detected in the country mica-schists, but Au was detected in the mica-schist at 2 m from the Campo gold quartz vein and in direct contact with the vein, showing the highest Au value adjacent to the vein, while Ag was only detected adjacent to this vein (Neiva et al, 1990). So the mica-schist does not seem to be the direct source of gold and silver.…”

Section: The Granitic Rocks and Origin Of Gold Quartz Veinsmentioning

confidence: 86%

“…At the Campo gold quartz vein walls, the Jales granite and mica-schist are hydrothermally altered and enriched in S, As, Zn, Sb, Cu, Sn, Pb and Au, mainly in direct contact with the vein (Neiva et al, 1990). The mica-schist contains more sulphides then the granite, particularly adjacent to the vain.…”

Section: The M a I N Gold Quartz Veins A N D The Veins I N Exploltatlmentioning

confidence: 99%

“…The fact that hydrothermally altered granites and mica-schists at the gold quartz vein walls are enriched in white mica support this hypothesis, because neutral to slightly alkaline solutions originating in the field of maximum gold solubility as a bisulphide complex, produce sericite as the most common potassium aluminosilicate in alteration assemblages (Romberger, 1986). Besides, Au cannot have been transported as a chloride complex, because granite and mica-schist lose C1 at the Campo gold quartz vein walls (Neiva et al, 1990).…”

Section: Calcite Chalcedonymentioning

confidence: 99%

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The gold area of Jales (northern Portugal)

Neiva

1990

Terra Nova

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The hydrothermal gold quartz veins of Jales cut Hercynian granitic rocks, Pre‐Ordovician, Ordovician and Silurian schists. They occur along Hercynian NNE‐SSW, NE‐SW and WNW‐ESE faults and are probably related to the Jales granite. Some are over 2 km long and have a thickness of 0.02–2 m. The only exploited quartz veins are from Campo and Desvio which contain several ore‐shoots (25t Au exploited since 1933). The veins from Jales area also have good Au reserves. Quartz and arsenopyrite dominate in the gold quartz veins with a banded structure. Electrum and gold are included in sulphides, sulphosalts and quartz and also in veinlets cutting these minerals. Silver occurs in electrum, argentite, galena, freibergite and polyargyrite. Several minerals were analysed by electron microprobe. The primary minerals, some showing recurrences, belong to six paragenetic stages formed between 550 and 30°C and separated by faulting.

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“…Total concentrations of Ce, La, Sc and Y reach higher values in the Ria de Aveiro than in several kinds of continental materials, such as in the Bulk Continental Crust and Upper Continental Crust (Rudnick and Gao, 2003), World Shale Average (Piper, 1974), the European Shale (Haskin and Haskin, 1966), and Portuguese granites (Neiva et al, 1990;Gomes and Neiva, 2002;Martins et al, 2009) (Table 3). However, the highest and mean REE values in the study area are slightly lower than in the NW Iberia Continental Shelf sediments (Araujo et al, 2007), namely in the Holocene Galician Muddy Deposits (Table 3).…”

Section: Discussionmentioning

confidence: 99%

Rare Earth Elements Used as Fingerprints of Differentiated Sediment Sources in the Ria De Aveiro (Portugal)

Martins¹,

Dardon²,

Frontalini³

et al. 2016

J. Sed. Env.

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This work focuses on the distribution and the controlling factors of rare earth element (REE) total concentrations and fractionation patterns in fine sediment fractions of 53 samples collected along the main channels of the Ria de Aveiro, a northern Portuguese coastal lagoon. Total and available concentrations and residual phases of REE and total concentrations in three chemically partitioned fractions (S1 -adsorbed by clay and co-precipitated with carbonates; S2 -adsorbed by organic matter; S3 -adsorbed by amorphous Mn hydroxides) are analysed. These data are joinly analysed with physicochemical, textural and mineralogical and other geochemical data. Sediment samples mainly consisted of phyllosilicates, quartz, plagioclase and K-feldspars. Cerium (Ce) is the most abundant REE in the residual phase and displays the lowest total available percentage, whereas Yttrium (Y) is the most available. The highest total concentration and residual concentration (R) of Ce, Lanthanum (La), Scandium (Sc) and Y are mostly related to fine grained sediments, suggesting that their distributions are conditioned by lagoon hydrodynamics. The dissimilar distribution of REE-S1, REE-S2 and REE-S3 indicates differentiated sedimentary processes. The enrichment of REE-S2 and REE-S3 is related essentially to biogeochemical processes inside the lagoon. The REE-S1, as well as Ce-S1/Sc-R, trace sediments supplied from the northern areas suplyed mostly by the Douro River outflow and from the Antuã River. In the past, the sediments suplyed by the Douro River through the litoral drift contributed to the formation of the lagoon islands. Thus the relatatively high Ce-S1/Sc-R values inside the lagoon allowed the identification of: sediments supplied from the litoral drift and deposited near the lagoon mouth, erosional processes of the lagoonal islands and sediments supplied by the Antuã River. This work demonstrates that the available concentrations of rare earth elements can be considered as important tools for investigating sediment sources and dispersion in a coastal system.

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Geochemistry of gold quartz vein walls from Jales (northern Portugal)

Cited by 13 publications

References 14 publications

Geochemical and isotopic constraints on the petrogenesis of Early Ordovician granodiorite and Variscan two-mica granites from the Gouveia area, central Portugal

Geochemical and isotopic constraints on the petrogenesis of Early Ordovician granodiorite and Variscan two-mica granites from the Gouveia area, central Portugal

The gold area of Jales (northern Portugal)

Rare Earth Elements Used as Fingerprints of Differentiated Sediment Sources in the Ria De Aveiro (Portugal)

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