Magmatic and Postmagmatic Processes in Tin-mineralized Granites: Topaz-bearing Leucogranite in the Eurajoki Rapakivi Granite Stock, Finland

The Early Permian Cornubian Batholith was generated during an extensional regime following Variscan convergence within the Rhenohercynian Zone of SW England. Its component granites can be classified, using mineralogical, textural and geochemical criteria, into five main types, all of which are peraluminous (A/CNK >1.1): G1 (two-mica), G2 (muscovite), G3 (biotite), G4 (tourmaline) and G5 (topaz). G1 granites formed through up to 20% muscovite and minor biotite dehydration melting of a metagreywacke source at moderate temperatures and pressures (731-806°C, >5 kbar). Younger G3 granites formed through higher temperature, lower pressure (768-847°C, <4 kbar) biotite-dominated melting of a similar source. Partial melting was strongly influenced by the progressive lower-mid crustal emplacement of mafic igneous rocks during post-Variscan extension and a minor (<5-10%) mantle-derived component in the granites is possible. Two distinct fractionation series, G1-G2 and G3-G4, are defined using whole rock geochemical and mineral chemical data.Variations in the major elements, Ba, Sr and Rb indicate that G1 and G3 granites underwent 15-30% fractionation of an assemblage dominated by plagioclase, alkali feldspar and biotite to form, more evolved G2 and G4 granites respectively. Decreasing whole rock abundances of Zr, Th and REE support fractionation of zircon, monazite, apatite and allanite. Subsolidus alteration in G2 and G4 granites is indicated by non-primary muscovite and tourmaline and modification of major and trace element trends for G3-G4 granites, particularly for P 2 O 5 and Rb. Topaz (G5) granites show low Zr, REE and extreme enrichment in Rb (up to 1530 ppm) and Nb (79 ppm) that cannot be related in a straightforward manner to continued differentiation of the G1-G2 or G3-G4 series. Instead, they are considered to represent partial melting, mediated by granulite facies fluids, of a biotite-rich restite following extraction of

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“…DePaolo, 1981), fluid overprint (e.g. Haapala, 1997) and fractional crystallisation (e.g. Teixeira et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

Simons

Shail

Andersen

2016

Lithos

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“…This relationship is common to cassiterite from highly fractionated granites and pegmatites worldwide and diferent to those from hydrothermal cassiterite-quarz-vein deposits and greisen deposits [44]. Although cassiterite is main ore mineral in greisens, data about Nb, Ta, and W concentrations are rare [46][47][48][49][50]. Cassiterites from greisens are usually distinctly depleted in Fe, Nb, and Ta in comparison to cassiterites from granites, pegmatites, and hightemperature quarz veins.…”

Section: Mn)mentioning

confidence: 99%

“…This depletion is also signiicant for cassiterites from examined greisens. The depletion in Nb, Ta, and Fe could be explained by lower crystallisation temperature of greisen cassiterites [48].…”

Section: Mn)mentioning

confidence: 99%

Petrology, Geochemistry and Mineralogy of Greisens Associated with Tin-Tungsten Mineralisation: Hub Stock Deposit at Krásno–Horní Slavkov Ore District, Czech Republic

René¹

2018

Contributions to Mineralization

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The greisens evolved in the apical part of the Hub stock, formed by weakly greisenised topaz granites, are predominantly represented by Li-mica-topaz and topaz-Li-mica greisens. These greisens, relative to weakly greisenised topaz granites, are enriched in Ca, F, Fe, Li, Si, Sn and W and depleted in Al, K, Mg, Na, Ti, Y, Zr and ΣREE. Weakly greisenised topaz granites show convex tetrads in the normalised REE paterns. Compared to topaz granites, the greisens display lower ΣREE concentrations, partly higher negative Eu anomaly, high Y/Ho and low Zr/Hf ratios. Li-micas occurring in greisens are represented by zinnwaldite. Chemical composition of cassiterite is near to ideal SnO 2 (>99 wt.% SnO 2 ). The wolframite is represented by manganoan ferberite.

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“…2. The highly fractionated topaz granites in the northern part of the batholith have, in general, anomalously high Rb and low Sr and Zr concentrations (Table 1; see also Haapala, 1997 andLukkari, 2007). At a given SiO 2 value, the A/CNK value of the granites varies considerably, probably because of the effect of feldspar accumulation, with high relative Al (high A/CNK) characterizing the samples with excess feldspar (Fig.…”

Section: The Silicic Rocks Of the Suomenniemi Complexmentioning

confidence: 99%

Geochronology of the Suomenniemi rapakivi granite complex revisited: Implications of point-specific errors on zircon U-Pb and refined λ<sub>87</sub> on whole-rock Rb-Sr

Rämö¹,

Mänttäri²

2015

Bull. Geol. Soc. Finland

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Multi-grain isotope dilution and secondary ion microprobe zircon U-Pb as well as wholerock Rb-Sr isotope dilution data on the late Paleoproterozoic Suomenniemi rapakivi granite complex (exposed on the northern flank of the Wiborg batholith in southeastern Finland) are discussed in the light of point-specific errors on Pb/U and proposed new values of the decay constant of 87 Rb, λ 87 . U-Pb zircon data on hornblende granite and biotite granite of the main metaluminous-marginally peraluminous granite fractionation series of the Suomenniemi batholith indicate crystallization in the 1644-1640 Ma range, with a preferred age at 1644±4 Ma. A cross-cutting hornblende-clinopyroxene-fayalite granite is probably slightly younger, as are quartz-feldspar porphyry dikes (1634±4 Ma) that cut both the main granite series and the metamorphic Svecofennian country rocks of the Suomenniemi batholith. Recalculation of whole-rock Rb-Sr data published on the main granite series of the batholith by Rämö (1999) Sr i of 0.7062±0.0024. This relatively high initial ratio is indicative of a major Proterozoic crustal source component in the granites of the batholith. The main granite series of the batholith probably cooled relatively rapidly to and below the closure temperature of the Rb-Sr isotope system, with little subsequent subsolidus adjustment. The three discrete silicic magmatic phases of the batholith (the main granite series, the hornblende-clinopyroxene-fayalite granite, and the quartz-feldspar porphyry dikes) were all probably emplaced before the main volume of rapakivi granite (the Wiborg batholith proper) in southeastern Finland. The Suomenniemi batholith thus represents an early magmatic precursor to the classic Wiborg batholith and was emplaced clearly before the massive rise of isotherms associated with the ascent and crystallization of the magmas that formed the bulk of the Wiborg batholith system. Keywords (GeoRef Thesaurus, AGI): granites, rapakivi, batholiths, absolute age, U/Pb, zircon, geochemistry, isotopes, Rb/Sr, thermal ionization mass spectroscopy, secondary ion mass spectroscopy, Proterozoic, Suomenniemi, Finland *Corresponding author e-mail: tapani.ramo@helsinki.fi Editorial handling: Jussi S. Heinonen (jussi.s.heinonen@helsinki.fi)Geochronology of the Suomenniemi rapakivi granite complex revisited: Implications of point-specific errors on zircon U-Pb and refined λ 87 on whole-rock Rb-Sr 26 IntroductionThe classic Wiborg rapakivi granite batholith of southeastern Finland and its satellite intrusions were emplaced into the Paleoproterozoic Svecofennian metamorphic crust as a sequence of discordant, epizonal complexes that are overwhelmingly silicic but also include members of basic and rare intermediate rocks (Haapala & Rämö, 1990;Rämö & Haapala, 2005). The main igneous body -the Wiborg batholith proper -is ~ 150 km in its current exposed diameter, with one-third concealed under the Gulf of Finland and underneath Neoproterozoic-Paleozoic sedimentary rocks in the south. The Wiborg batholith probably co...

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Magmatic and Postmagmatic Processes in Tin-mineralized Granites: Topaz-bearing Leucogranite in the Eurajoki Rapakivi Granite Stock, Finland

Cited by 124 publications

References 29 publications

The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

Petrology, Geochemistry and Mineralogy of Greisens Associated with Tin-Tungsten Mineralisation: Hub Stock Deposit at Krásno–Horní Slavkov Ore District, Czech Republic

Geochronology of the Suomenniemi rapakivi granite complex revisited: Implications of point-specific errors on zircon U-Pb and refined λ<sub>87</sub> on whole-rock Rb-Sr

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