Hostname: page-component-cd9895bd7-8ctnn Total loading time: 0 Render date: 2024-12-23T20:26:57.508Z Has data issue: false hasContentIssue false
  • English
  • Français

The magnetite ore districts of the southern Aosta Valley (Western Alps, Italy): a mineralogical study of metasomatized chromite ore

Published online by Cambridge University Press:  05 July 2018

P. Rossetti ,
G. D. Gatta ,
V. Diella ,
S. Carbonin ,
A. Della Giusta  and
A. Ferrario
P. Rossetti
Affiliation:
Dipartimento di Scienze Mineralogiche e Petrologiche, Università degli Studi di Torino, Italy
G. D. Gatta*
Affiliation:
Dipartimento di Scienze della Terra, Università degli Studi di Milano, Italy CNR-Istituto per la Dinamica dei Processi Ambientali, Milano, Italya
V. Diella
Affiliation:
CNR-Istituto per la Dinamica dei Processi Ambientali, Milano, Italya
S. Carbonin
Affiliation:
Dipartimento di Geoscienze, Università degli Studi di Padova, Italy
A. Della Giusta
Affiliation:
Dipartimento di Geoscienze, Università degli Studi di Padova, Italy
A. Ferrario
Affiliation:
Dipartimento di Geoscienze, Università degli Studi di Padova, Italy
*
* E-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

In the southern Aosta Valley (Italian Western Alps), several massive magnetite bodies occur within serpentinized ultramafic rocks belonging to the Mesozoic meta-ophiolite nappe. The ultramafic rocks consist of lherzolite with minor dunite bodies and show a high pressure metamorphic overprint. The results of a multi-methodological study, based on optical microscopy, electron microprobe analysis and single-crystal X-ray diffraction, are reported here in order to give new insights into (1) the mineralogy and crystal chemistry of spinels and silicates and (2) the genesis of the massive magnetite bodies. Chromium-rich relict cores inside the magnetite grains suggest a derivation from primary chromite concentrations. The major-element behaviour shows the presence of two chromite types: a Cr2O3-rich (Al2O3-poor) type and a Cr2O3-poor (Al2O3-rich) type. Magnetite ore deposits probably represent the product of transformation from a chromite proto-ore which formed in ultramafic rocks pertaining to an ophiolite suite. The transformation of chromite to magnetite occurred during multiple stages: the pre- metamorphic setting of the ultramafics and the petrographic evidence suggest that metasomatism started before the onset of the alpine metamorphism and was active during the early alpine, eclogite- facies metamorphic overprint related to a subduction process under high fluid activity.

Keywords

chromitemagnetiteserpentinizationhigh pressureocean floormetasomatismPiemonte Zone.
Type
Research Article
Information
Mineralogical Magazine , Volume 73 , Issue 5 , October 2009 , pp. 737 - 751
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2009

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Andreozzi, G.B., Princivalle, F., Skogby, H. and Della Giusta, A. (2000) Cation ordering and structural variations with temperature in MgAl2O4 spinel, An X-ray single-crystal study. American Mineralogist,, 85, 1164—1171.CrossRefGoogle Scholar
Baldelli, C., Dal Piaz, G.V. and Lombardo, B. (1985) Ophiolite eclogites from Verres, Western Alps, Italy. Chemical Geology, 50, 87—98.CrossRefGoogle Scholar
Ballevre, M. and Merle, O. (1993) The Combin Fault, compressional reactivation of a Late Cretaceous- Early Tertiary detachment fault in the Western Alps. Schweizerische Mineralogische und Petrographische Mitteilungen, 73 , 205 —227.Google Scholar
Beltrando, M., Hermann, J., Lister, G. and Compagnoni, R. (2007). On the evolution of orogens, Pressure cycles and deformation mode switches. Earth and Planetary Science Letters, 256, 372—388.CrossRefGoogle Scholar
Beltrando, M., Lister, G., Hermann, J., Forster, M. and Compagnoni, R. (2008) Deformation mode switches in the Penninic units of the Urtier Valley (Western Alps): Evidence for a dynamic orogen. Journal of Structural Geology, 30, 194—219.CrossRefGoogle Scholar
Benciolini, L., Lombardo, B. and Martin, S. (1988) Mineral chemistry and Fe/Mg exchange geothermometry of ferrogabbro-derived eclogites from the Northwestern Alps. Neues Jahrbuch für Mineralogie Abhandlungen, 159, 199—222.Google Scholar
Bistacchi, A., Dal Piaz, G.V., Massironi, M., Zattin, M. and Balestrieri, M.L. (2001) The Aosta-Ranzola extensional fault system and Oligocene-Present evolution of the Austroalpine-Penninic wedge in the north-western Alps. International Journal of Earth Sciences, 90, 654—667.CrossRefGoogle Scholar
Cimmino, F., Messiga, B., Piccardo, G.B. and Zeda, O. (1979) Titanian clinohumite-bearing assemblages within antigorite serpentinites of the Gruppo di Voltri (Western Liguria), inferences on the geodynamic evolution of the Piedmontese ultramafic section. Ofioliti, 4, 97—120.Google Scholar
Cimmino, F., Messiga, B. and Piccardo, G.B. (1981) Le caratteristiche paragenetiche dell’evento eo-alpino di Alta Pressione nei diversi sistemi (pelitici, femici, ultrafemici) delle ofioliti metamorfiche del Gruppo di Voltri (Liguria occidentale). Rendiconti della Societal Italiana di Mineralogia e Petrografia, 37, 419—446.Google Scholar
Compagnoni, R., Elter, G., Fiora, L., Natale, P. and Zucchetti, S. (1979) Nuove osservazioni sul giacimento di magnetite di Cogne in Valle d’Aosta. Rendiconti della Societa Italiana di Mineralogia e Petrografia, 35, 755—766.Google Scholar
Compagnoni, R., Elter, G., Fiora, L., Natale, P. and Zucchetti, S. (1980) Magnetite deposits in serpenti- nized lherzolites from the ophiolitic belt of the Western Alps, with special reference to the Cogne deposit (Aosta Valley). Proceedings of the International Symposium on ‘Mafic Ultramafic Complexes’ (Athens 9-11 October), 3, 376—394.Google Scholar
Dal Piaz, G.V. (1971) Alcune osservazioni sulla genesi delle ofioliti piemontesi e dei giacimenti ad esse associati. Bollettino dell’Associazione Mineraria Subalpina, 8, 365—388.Google Scholar
Dal Piaz, G.V., Pennacchioni, G., Tartarotti, P. and Carraro, F. (2009) Carta Geologica d’ltalia 1:50.000: Foglio 091 (Chatillon). Servizio Geologico d’ltalia, Regione Autonoma Valle d’Aosta, http://www.apat.gov.it/MEDIA/carg/ Allestimento/091_Chatillon/Foglio.htm, (in press).Google Scholar
Della Giusta, A., Princivalle, F. and Carbonin, S. (1986) Crystal chemistry of a suite of natural Cr-bearing spinels with 0.15 4Cr 41.07. Neues Jahrbuch für Mineralogie Abhandlungen, 155, 319—330.Google Scholar
Della Giusta, A., Princivalle, F. and Carbonin, S. (1987) Crystal structure and cation distribution in some natural magnetites. Mineralogy and Petrology, 37, 315—321.CrossRefGoogle Scholar
Di Colbertaldo, D., füria (di), E. and Rossi, F. (1967) Il giacimento a magnetite di Cogne in Val d’Aosta. Rendiconti dell’lstituto lombardo-Accademia di Scienze e Lettere, 101, 361—394.Google Scholar
Diella, V., Ferrario, A. and Rossetti, P. (1994) The magnetite ore deposits of the Southern Aosta Valley, chromitite transformed during an alpine meta- morphic event. Ofioliti, 19, 247—256.Google Scholar
Elter, G. (1971) Schistes lustres et ophiolites de la zone piemontaise entre Orco et Doire Baltie (Alpes Graies). Hypothese sur l’origine des ophiolites. Geologie Alpine, 47, 147—169.Google Scholar
Elter, G. (1987) Carte Geologique de la Vallee d’Aoste. S.E.L.C.A., Firenze, Italy.Google Scholar
Fontana, E., Panseri, M. and Tartarotti, P. (2008) Oceanic relict textures in the Mount Avic serpenti- nites, Western Alps. Ofioliti, 33, 105–118.Google Scholar
Gatta, G.D., Kantor, I., Boffa Ballaran, T., Dubrovinsky, L. and McCammon, C. (2007) Effect of nonhydrostatic conditions on the elastic behaviour of magnetite, An in-situ single-crystal X-ray diffraction study. Physics and Chemistry of Minerals, 34, 627—635.CrossRefGoogle Scholar
Gil Ibarguchi, J.I., Mendia, M. and Girardeau, J. (1991) Mg- and Cr-rich staurolite and Cr-rich kyanite in high-pressure ultrabasic rocks (Cabo Ortegal, northwestern Spain). American Mineralogist, 76, 501—511.Google Scholar
Huttenlocher, H.F. (1934) Die Erzlagerstattenzonen der Westalpen. Schweizerische Mineralogische und Petrographische Mitteilungen, 14, 21–149.Google Scholar
Jan, M.Q. and Windley, B.F. (1990) Chromian spinel- silicate chemistry in ultramafic rocks of the Jijal Complex, Northwest Pakistan. Journal of Petrology, 31, 667—715.CrossRefGoogle Scholar
Kornprobst, J., Ohnenstetter, D. and Ohnenstetter, M. (1981) Na and Cr contents in clinopyroxenes from peridotites, a possible discriminant between ‘subcontinental’ and ‘sub-oceanic’ mantle. Earth and Planetary Science Letters, 53, 241—254.CrossRefGoogle Scholar
North, A.C., Phillips, D.C. and Mathews, F.S. (1968) A semi-empirical method of absorption correction. Acta Crystallographica A, 24, 351—359.Google Scholar
Ottaway, T.L., Wicks, F.J., Bryndzia, L.T., Kyser, T.K. and Spooner, E.T. (1994) Formation of the Muzo hydrothermal emerald deposit in Colombia. Nature, 369, 552—554.CrossRefGoogle Scholar
Paraskevopoulos, G.M. and Economou, M.I. (1980) Genesis of magnetite ore occurrences by metasomatism of chronite ores in Greece. Neues Jahrbuch für Mineralogie Abhandlungen, 140, 29—53.Google Scholar
Piccardo, G.B. (1984) Le ofioliti metamorfiche del Gruppo di Voltri, Alpi Liguri, caratteri primari ed interpretazione geodinamica. Memorie della Societal Geologica Italiana, 28, 95–114.Google Scholar
Rolfo, F., Compagnoni, R. and Tosoni, D. (2004) Geology and petrology of the Austroalpine Chatillon Slice, Aosta Valley, Western Alps. Geodinamica Acta, 17, 91–105.CrossRefGoogle Scholar
Rossetti, P. and Zucchetti, S. (1988) Early-alpine ore parageneses in the serpentinites from the Balangero asbestos mine and Lanzo Massif (Internal Western Alps). Rendiconti della Societal Italiana di Mineralogia e Petrografia, 43, 139—149.Google Scholar
Routhier, P. (1963) Les gisements metalliferes. Masson, Paris, 1282 pp.Google Scholar
S.A.N.C. (1931) Brevi cenni sulla miniera di Cogne e sui varii impianti per la frantumazione, l’arricchi- mento ed il trasporto del minerale. Bollettino della Societal Anonima Nazionale Cogne - Miniere Altiforni Acciaierie, 1, 1—41.Google Scholar
Scambelluri, M., Hoogerduijng Strating, E.H., Piccardo, G.B., Vissers, R.L. and Rampone, E. (1991) Alpine olivine- and titanian clinohumite-bearing assemblages in the Erro-Tobbio peridotite (Voltri Massif, NW Italy). Journal of Metamorphic Geology, 9, 79—91.CrossRefGoogle Scholar
Sheldrick, G.M. (1997) SHELX-97. Programs for crystal structure determination and refinement. University of Gottingen, Germany.Google Scholar
Stella, A. (1921) Le miniere di ferro d’ltalia. Lattes, Torino, Italy, 426 pp.Google Scholar
Tartarotti, P. and Martin, S. (1991) Ultramafic rocks in the Mount Avic eclogitic ophiolites, Italian Western Alps. Terra Abstracts, 3, 96.Google Scholar
Tartarotti, P., Benciolini, L. and Monopoli, B. (1998) Brecce serpentinitiche nel Massiccio ultrabasico del Monte Avic (Falda ofiolitica Piemontese): possibili evidenze di erosione sottomarina. Atti Ticinesi di Scienze della Terra, 7, 73—86.Google Scholar
Tracy, R.J. (1991) Ba-rich micas from the Franklin Marble, Lime Crest and Sterling Hill, New Jersey. American Mineralogist, 76, 1683—1693.Google Scholar
Treloar, P.J. (1987) The Cr-minerals of Outokumpu. Their chemistry and significance. Journal of Petrology, 28, 867—886.CrossRefGoogle Scholar
Wilson, A.J.C. and Prince, E. (editors) (1999) International Tables for X-ray Crystallography, Volume C, Mathematical, physical and chemical tables (2nd Edition), Kluwer Academic, Dordrecht, The Netherlands.Google Scholar