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Fully oxidized chromite in the Serra Alta (South Portugal) quartzites: chemical and structural characterization and geological implications

Published online by Cambridge University Press:  05 July 2018

Jorge Figueiras
Affiliation:
Dept. de Geologia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, Ediffcio C2, 5° Piso, P-1700 Lisboa, Portugal
Joāo C. Waerenborgh
Affiliation:
ITN, Dept. de Química, P-2686 Sacavém Codex, Portugal

Abstract

Several quartzite bodies outcrop along the Ferreira-Ficalho Thrust Fault (South Portugal), a major accident of the Iberian Variscan Orogen. The sediment is a very pure quartz sandstone, with trace amounts of ultra-resistant heavy minerals and chromite. Chemical characterization (microprobe analyses and Mössbauer spectroscopy) showed the chromite to be unique: besides being Zn-rich, complexly zoned and a cation deficient spinel, all the iron was found to be fully oxidized to Fe3+. Structure refinement of single-crystal X-ray diffraction intensities unambiguously identifies the mineral as a chromite and the Mössbauer data are consistent with tetrahedrally coordinated Fe3+ in the spinel structure. Current geodynamical models see the Ferreira-Ficalho Thrust Fault as a first-order suture resulting from a complex collision of two distinct continental blocks with partial obduction of the intervening oceanic crust. The chromite grains could be envisaged as remnants of an early erosion of this obducted oceanic crust, but its unique chemical character does not allow any definite conclusion. Yet, the complete quartzite heavy mineral contents and its petrographic features are not consistent with their deposition within a continental collision situation.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1997

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References

Basso, R., Carbonin, S. and Della Giusta, A. (1991) Cation and vacancy distribution in a synthetic defect spinel. Zeit. Kristallogr., 194, 111-9.CrossRefGoogle Scholar
Bernier, L.R. (1990) Vanadiferous zincian-chromian hercynite in a metamorphosed basalt-hosted altera-tion zone, Atik Lake, Manitoba. Canad. Mineral., 28, 3750.Google Scholar
Béziat, D. and Monchoux, P. (1991) Les spinelles chromozincifères du district aurifère de Salsigne (Montagne Noire, France). Eur. J. Mineral., 3, 957-69.CrossRefGoogle Scholar
Canil, D., Virgo, D. and Scarfe, C.M. (1990) Oxidation state of mantle xenoliths from British Columbia, Canada. Contrib. Mineral. Petrol., 104, 453-62.CrossRefGoogle Scholar
Chassagneux, F., Rousset, A. and Redoules, J.P. (1985) Élaboration et caractdrisation de chromites de fer(iii) a structure spinelle lacunaire. J. Sol. Stat. Chem., 56, 7483.CrossRefGoogle Scholar
Dallmeyer, R.D. and Martínez García, E. eds. (1990) Pre-Mesozoic Geology of lberia. Springer-Verlag. Berlin-Heidelberg-New York.CrossRefGoogle Scholar
Dyar, M.D., McGuire, A.V. and Ziegler, R.D. (1989) Redox equilibria and crystal chemistry of coexisting minerals from spinel lherzolite mantle xenoliths. Amer. Mineral., 74, 969-80.Google Scholar
Fair, C.K. (1990) MOLEN, Enraf-Nonius, Delft, The Netherlands.Google Scholar
Figueiras, J. and Barriga, F. (1990) Thin sections of heavy mineral concentrates: a new method of preparation. Gaia, 2, 1—3.Google Scholar
Figueiras, J. and Barriga, F. (1991) Zn-rich detrital chromites in Devonian quartzites of South Portugal. GAC-MAC-SEG Joint Annual Meeting. Pros. with Abstr.,16, A37.Google Scholar
Fonseca, P.E.T. (1995) Estudo da sutura varisca no SW ibérico has regiões de Serpa-Beja-Torräto e Alvito-Viana do Alentejo. PhD. thesis. Univ. Lisboa.Google Scholar
Gerardin, R., Ramdani, A., Gleitzer, C., Gillot, B. and Durand, B. (1985) Étude par spectrométrie Mössbauer de la localisation électronique dans des ferrites spinelles ayant un sous-réseau tetraédrique de valence mixte. J. Sol. Stat. Chem., 57, 215—26.CrossRefGoogle Scholar
Groves, D.I., Barrett, F.M., Binns, R.A. and McQueen, K.G. (1977) Spinel phases associated with metamorphosed volcanic-type iron-nickel sulfide ores from Western Australia. Econ. Geol., 72, 1224-44.CrossRefGoogle Scholar
Hovestreydt, E. (1983) On the atomic scattering factor for O2– . Acta Crystallogr., A39, 268.CrossRefGoogle Scholar
Ibers, J.A. and Hamilton, W.C. (eds) (1974) International Tables for X-ray Crystallography Vol 4: Revised and supplementary tables. Kynoch Press, Birmingham, England.Google Scholar
Liipo, J.P., Vuollo, J.I., Nykäinen, V.M. and Piirainen, T.A. (1995) Zoned Zn-rich chromite from the Näätäniemi serpentinite massif, Kuhmo greenstone belt, Finland. Canad. Mineral., 33, 537-45.Google Scholar
McGuire, A.V., Dyar, M.D. and Nielson, J.E. (1991) Metasomatic oxidation of upper mantle peridotite. Contrib. Mineral. Petrol., 109, 252-64.CrossRefGoogle Scholar
Munhá, J.M.U. (1976) Nota preliminar sobre o metamorfismo na faixa piritosa ibérica. Comun. Serv. Geol. Port., LX, 151-61.Google Scholar
North, A.C.T., Phillips, D.C. and Mathews, F.S. (1968) A semi-empirical method of absorption correction. Acta Crystallogr., A24, 351-9.CrossRefGoogle Scholar
Oliveira, J.T., Cunha, T.A., Streel, M. and Vanguestaine, M. (1986) Dating the Horta da Torre Formation, a new lithostratigraphic unit of the Ferreira-Ficalho Group, South Portuguese Zone: geological consequences. Com. Serv. Geol., 72, 129—35.Google Scholar
O'Neill, H.St.C. and Navrotsky, A. (1983) Simple spinels: crystallographic parameters, cation radii, lattice energies and cation distribution. Amer. Mineral., 68, 181-94.Google Scholar
O'Neill, H.St.C. and Navrotsky, A. (1984) Cation distribution and thermodynamic properties of binary spinel solid solutions. Amer. Miner. 69, 733—53.Google Scholar
Ribeiro, A., Antunes, M.T., Ferreira, M.P., Rocha, R.B., Soares, A.F., Zbyszewski, G., Almeida, F.M., Carvalho, D. and Monteiro, J.H. (1979) Introduction à la géologie générale du Portugal. Serviços Geológicos de Portugal. Lisboa, Portugal.Google Scholar
Roeder, P.L. (1994) Chromite: from the fiery rain of chondrules to the Kilauea Iki lava lake. Canad. Mineral., 32, 729-46.Google Scholar
Schermerhorn, L.J.G. (1971) An outline stratigraphy of the Iberian Pyrite Belt. Bol. Geol. Min., LXXXIII-IV, 239-68.Google Scholar
Schmidbauer, E. (1987) 57Fe Mössbauer spectroscopy and magnetization of cation-deficient Fe2TiO4 and FeCr2O4 Part I: 57Fe Mössbauer spectroscopy. Phys. Chem. Mineral., 14, 533-41.CrossRefGoogle Scholar
Sheldrick, G.M. (1993) SHELXL-93: Program for Crystal Structure Refinement. University of Göttingen, Germany.Google Scholar
Spry, P.G. and Scott, S.D. (1986) The stability of zincian spinels in sulfide systems and their potential as exploration guides for metamorphosed massive sulfide deposits. Econ. Geol., 81, 1446-63.CrossRefGoogle Scholar
Stone, A.J. (1967) Least squares fitting of Mossbauer spectra appendix to Bancroft, G.M., Maddock, A.G., Ong, W.K., Prince, R.H., Stone, A.J. J. Chem. Soc. (a), 1966.Google Scholar
Waerenborgh, J.C., Figueiredo, M.O., Cabral, J.M.P. and Pereira, L.C.J. (1994a) Powder XRD structure refinements and 57 Fe Mössbauer effect study of synthetic Zn1-xFexAl2O4 (0 < x ⩽ 1) spinels annealed at different temperatures. Phys. Chem. Mineral. 21, 460-8.CrossRefGoogle Scholar
Waerenborgh, J.C., Figueiredo, M.O., Cabral, J.M.P. and Pereira, L.C.J. (1994b) Temperature and composition dependence of the cation distribution in synthetic ZnFeyAl2-yO4 (0 ⩽ y ⩽ 2) spinels. J. Sol. Stat. Chem., 111, 300-9.CrossRefGoogle Scholar
Wood, B.J. and Virgo, D. (1989) Upper mantle oxidation state: Ferric iron contents of lherzolite spinels by 57Fe Mössbauer spectroscopy and resultant oxygen fugacities. Geochim. Cosmochim. Acta, 53, 1277-91.CrossRefGoogle Scholar
Wylie, A.G., Candela, P.A. and Burke, T.M. (1987) Compositional zoning in unusual Zn-rich chromite from the Sykesville district of Maryland and its bearing on the origin of ‘ferritchromite’. Amer. Mineral., 72, 413-22.Google Scholar