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Nb-Ta oxide minerals from miarolitic pegmatites of the Baveno pink granite, NW Italy (Articolo in rivista)

Type

Articolo in rivista (Classe)
Prodotto della ricerca (Classe)

Label

Nb-Ta oxide minerals from miarolitic pegmatites of the Baveno pink granite, NW Italy (Articolo in rivista) (literal)

Anno

2001-01-01T00:00:00+01:00 (literal)

Alternative label

Aurisicchio C., De Vito C., Ferrini V., Orlandi P. (2001)
Nb-Ta oxide minerals from miarolitic pegmatites of the Baveno pink granite, NW Italy
in Mineralogical magazine (Print)
(literal)

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Aurisicchio C., De Vito C., Ferrini V., Orlandi P. (literal)

Pagina inizio

509 (literal)

Pagina fine

522 (literal)

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The crystal-chemistry of Nb and Ta minerals represents the key to reconstruct the genetic process responsible for the evolution of rare-element enriched batches of felsic magmas. The main aim of these kind of studies is that to collect geochemical data from well known LCT and NYF pegmatites to characterize complex ones which seems to have mixed nature. The chemistry of Nb and Ta minerals associated with others petrogenetic indicators, present in the pegmatite assemblage, helps in the identification of contaminating factors which allow change between geochemical families. (literal)

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65 (literal)

Rivista

Mineralogical magazine (Rivista)

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Impact Factor 0,988 (literal)

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This paper stresses the petrogenetic significance of the minerals of Nb and Ta, two strategic elements whose technological application are well known. Study of Nb and Ta oxides and complex oxides has recently developed considerably in the attempt to reconstruct the evolution of rare element-enriched pegmatites. The western side of the south Alpine basement was intruded by many granitic bodies of calc-alkaline affinity. Each body shows distinct petrochemical features related to magma evolution. The pink granite facies displays a distinct alumino-alkaline petrochemical character and crystallized from a volatile-rich (H2O, F, Cl and etc.) magma which produced miarolitic cavities and their characteristic NYF paragenesis: fluorite, zinnwaldite, Y REE- silicates and phosphates, gadolinite, zeolite, Sc- and Be-silicates, and Nb- Ta-oxides. Nb and Ta minerals found mainly belong to aeschynite-group and polycrase series and have very small dimension, wide compositional range and complex chemical zoning. Two new varieties the niobo-aeschynite-(Y) and The titano-vigezzite have been identified. The samples analysed are all metamict. Their structure are disordered but there is no clear link with their U and Th content. Baveno granite is of Permian age (277 +/- 8 Ma), a period during which alfa decays could have induced structural disorder. (literal)

Note

ISI Web of Science (WOS) (literal)

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Aurisicchio C.: Istituto di Geoscienze e Georisorse (CNR) - Sezione di Roma; De Vito C.: Dipartimento Scienze della Terra, Università degli Studi di Roma \"La Sapienza\"; Ferrini V.: Dipartimento Scienze della Terra, Università degli Studi di Roma \"La Sapienza\"; Orlandi P.: Dipartimento Scienze della Terra, Università degli Studi di Pisa (literal)

Titolo

Nb-Ta oxide minerals from miarolitic pegmatites of the Baveno pink granite, NW Italy (literal)

Abstract

Chemical composition and cell parameters were ascertained on new data from Ti-Nb-Ta complex oxides from the miarolitic pegmatites of the Baveno pink granite (Southern Alps, NW Italy). The crystals are tiny, single or aggregated in smal sprays, prismatic or tabular, from yellow-orange to brownish in colour. Typical associates minerals include fluorite, zinnwaldite, gadolinite-group minerals and Sc-minerals. Cavity paragenesis in typical of NYF pegmatites, and shows two stages of crystallization developing in magmatic-pneumatolitic and hydrothermal conditions. X-ray data show that som oxides belong to the aeschynite mineral group; others are polycrase and fersmite. Aeschnyte and polycrase are chemically heterogeneous and structurally disordered because of their metamict state. This disorder does not always seem to be related to radionuclide contents. Two main trends are indicates, considering the behaviour of Y. The high Y contents fit with very low Ca an LREE contents in the A site; the HREE contents follow the t TREND. In the B site, Ti is the dominant cation, followed by some Nb and very little Ta. Small quantities of Y fit with increasing Ca, U, Th and REE contents. In the B site, Nb cations often exceed those of Ti. Th contents are often greater than those of T. Besides the already known aeschnyte-(Y) and vigezzite, new varieties, 'titano-vigizzite' and 'niobo-aeschnyte-(Y)', are identified here in he Baveno miarolitic cavities. Samples 14 (analysis a) and 2502 (analysis b) have Ca as the main occupant of the A site, followed by Y, Th and REE; in the B site, Ti prevails over Nb. These compositions cannot be considered as pure vigezzite, but as a new variery called 'titano-vigezzite'. In the same way, analysis a of sample 3 may be considered a new variety of aeschnyte-(Y), with Nb prevailing over Ti in the B site, and here called 'niobo-aeschynite on polycrase (sample 3194) allows some inferences on the crystallization sequence. (literal)

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