Multistage Growth of a Rare-Element, Volatile-Rich Microgranite at Argemela (Portugal)

Charoy, B.; Noronha, Fernando

doi:10.1093/petrology/37.1.73

Cited by 77 publications

(57 citation statements)

References 18 publications

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“…Trace-element content of quartz populations is consistent with the Lowenstern & Sinclair (1996) model whereby quartz accommodates certain trace elements (e.g. Similarly, generation of evolved melts has been proposed by Charoy & Noronha (1996), the Argemela model, in which a crystal mush is lubricated by a melt which is enriched in volatiles and rare elements during successive steps of crystallisation. A somewhat similar model for melt generation has been applied to larger systems by Candela (1991Candela ( , 1994 and Candela & Blevin (1995), which they term the percolation cluster model.…”

Section: Pegmatite Formation At East Kemptvilleðinterplay Of Magmaticsupporting

confidence: 82%

The nature and origin of pegmatites in a fluorine-rich leucogranite, East Kemptville Tin Deposit, Nova Scotia, Canada

Kontak¹,

Ansdell

Dostál

et al. 2001

Transactions of the Royal Society of Edinburgh: Earth Sciences

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Pegmatites at the East Kemptville Sn±Zn±Cu±Ag deposit occur within a F-and Prich, 370 Ma topaz±muscovite leucogranite, the most evolved phase of the chemically zoned Davis Lake Pluton. Structural observations and geochronology indicate that the leucogranite intruded into an active shear/fault zone environment. Pegmatites are preferentially located near the roof zone of the intrusion and include: (1) quartz±feldspar pods ( 1±2 m) aligned parallel to a foliation in the leucogranite. Such pegmatites have marginal aplites or may be cored by aplites;(2) aplite±pegmatite zones with well-developed crenulate and unidirectional solidi®cation textures; and (3) muscovite-bordered miarolitic cavities lined with quartz±feldspar § cassiterite. Associated with areas of pegmatites are irregular-to cuspate-shaped zones enriched in muscovite. Mineralogically the pegmatites are simple, consisting of clear to black quartz, albite, microcline perthite and muscovite; topaz may be enriched in aplites coring pegmatites and coarse euhedral cassiterite is rare.Chemically the leucogranites marginal to pegmatites are similar to the host leucogranite, but some aphanitic felsic dykes indicate extreme diVerentiation, as re¯ected by REE depletion and Penrichment. Enrichment of pegmatitic feldspar in P 2 O 5 (to 1 wt. %) indicates that melts contained 2±3 wt. % P 2 O 5 , whereas muscovite chemistry (to 5 wt. % F) re¯ects the F-rich nature of the melt. Trace and REE contents of pegmatitic feldspars are consistent with local segregation of volatilerich melts to form pegmatites rather than extreme crystal-chemical fractionation.Fluid inclusion studies of pegmatitic quartz and cassiterite indicate the presence of a highly saline brine (40 wt. % eq. NaCl; Na > K > Fe > Mn > Ca > Sr) of magmatic origin. Isochores modelled for a 40 wt. % eq. NaCl¯uid constrain pegmatite formation at 550±600 C, thus the depressed solidus is consistent with the volatile-rich (F, P, H 2 O) nature of the melt. Stable isotopes demonstrate that a magmatic¯uid (¯1 8 O H 2 Oˆ ‡ 5 : 5 to ‡10 ,¯D H 2 Oˆ¡ 33 to ¡41 for 450±500 C) equilibrated with the pegmatites and the system cooled abruptly at c. 425 C.The low volume of pegmatite at East Kemptville suggests that the melt was not near volatile saturation, instead pegmatite generation is interpreted to have resulted from rapid decompression related to the active shear zone setting of the granite. Although feldspar chemistry re¯ects a local segregation model, the chemistry of aphanitic dyke rocks indicates that the leucogranite did evolve into a more fractionated melt. The local presence of cassiterite in pegmatites and miarolitic cavities indicates that locally, saturation of Sn occurred, but not throughout the EKL where elevated Sn contents are attributed to in®ltration of mineralising¯uids (i.e. deuteric alteration).

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Section: Pegmatite Formation At East Kemptvilleðinterplay Of Magmaticsupporting

confidence: 82%

The nature and origin of pegmatites in a fluorine-rich leucogranite, East Kemptville Tin Deposit, Nova Scotia, Canada

Kontak¹,

Ansdell

Dostál

et al. 2001

Transactions of the Royal Society of Edinburgh: Earth Sciences

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“…This appears contradictory by comparison with the composition of the B1 facies from the Beauvoir granite, which has higher Ta than Nb contents, with Nb/Ta ratio in the range of 0.4-0.9 and ∼0.6 on average [12,13]. Similarly Ta > Nb contents were also found in other PHP-RMG worldwide, for instance, in Portugal (Argemela granite [62]), France (Montebras granite [13]), Germany (Ehrenfriedersdorf pegmatite [63]), and China (Yichun granite [13]; Laohutou granite [64]). Due to the higher solubility of tantalite relative to that of columbite in peraluminous granitic magmas [3,65], one can expect a late Ta enrichment relative to Nb in the residual melt and thus a high Ta/Nb ratio in the exsolved magmatic fluid, despite low partition coefficients for Nb and Ta between an aqueous fluid and silicate melt in granitic systems ( fluid-melt [Ta] < fluid-melt [Nb] < 0.1) [3,[66][67][68].…”

Section: Magmatic Signature Of the Early Primary Fluids From Thementioning

confidence: 97%

Geochemical Signature of Magmatic-Hydrothermal Fluids Exsolved from the Beauvoir Rare-Metal Granite (Massif Central, France): Insights from LA-ICPMS Analysis of Primary Fluid Inclusions

et al. 2017

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The Beauvoir granite (Massif Central, France) represents an exceptional case in the European Variscan belt of a peraluminous raremetal granite crosscutting an early W stockwork. The latter was strongly overprinted by rare-metal magmatic-hydrothermal fluids derived from the Beauvoir granite, resulting in a massive topazification of the quartz-ferberite vein system. This work presents a complete study of primary fluid inclusions hosted in quartz and topaz from the Beauvoir granite and the metasomatized stockwork, in order to characterize the geochemical composition of the magmatic fluids exsolved during the crystallization of this evolved rare-metal peraluminous granite. Microthermometric and Raman spectrometry data show that the earliest fluid (L1) is of high temperature (500 to >600 ∘ C), high salinity (17-28 wt.% NaCl eq), and Li-rich ( e < −70 ∘ C) with Na/Li ratios ∼5. LA-ICPMS analyses of L1-type fluid inclusions reveal that the chemical composition of this magmatic-hydrothermal fluid is dominated by Na, K, Cs, and Rb, with significant concentrations (10 1 -10 4 ppm) in rare-metals (W, Nb, Ta, Sn, and Li). This study demonstrates that primary fluid inclusions preserved the pristine signature of the magmatic-hydrothermal fluids in the Beauvoir granite but also in the metasomatized W stockwork, despite the distance from the granitic cupola (>100 m) and interaction with external fluids.

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“…However, cassiterite may also occur in some aplites and locally in granites (Charoy and Noronha, 1996;Gomes and Neiva, 2002). These specialized granite suites are predominantly derived by partial melting of heterogeneous metasedimentary rocks (S-type granites), as indicated by Sr and Nd isotope data from several areas of Portugal and Spain (Neiva, 2002;Neiva et al, 2009Neiva et al, , 2011Ruiz et al, 2008), including the Carrazeda de Ansiães area, as well as from other zones of the European Variscides, like the Land's End pluton, Cornwall, England (Müller et al, 2006) and Erzgebirge, Germany (Romer et al, 2011).…”

Section: Tin-bearing Granites Of Central Iberian Zone and Their Originmentioning

confidence: 99%

The role of fractional crystallization in the genesis of early syn-D3, tin-mineralized Variscan two-mica granites from the Carrazeda de Ansiães area, northern Portugal

Teixeira

Neiva

Gomes

et al. 2012

Lithos

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Multistage Growth of a Rare-Element, Volatile-Rich Microgranite at Argemela (Portugal)

Cited by 77 publications

References 18 publications

The nature and origin of pegmatites in a fluorine-rich leucogranite, East Kemptville Tin Deposit, Nova Scotia, Canada

The nature and origin of pegmatites in a fluorine-rich leucogranite, East Kemptville Tin Deposit, Nova Scotia, Canada

Geochemical Signature of Magmatic-Hydrothermal Fluids Exsolved from the Beauvoir Rare-Metal Granite (Massif Central, France): Insights from LA-ICPMS Analysis of Primary Fluid Inclusions

The role of fractional crystallization in the genesis of early syn-D3, tin-mineralized Variscan two-mica granites from the Carrazeda de Ansiães area, northern Portugal

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