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Volume 61 Supplement 1

Special Issue: Magnetism of Volcanic Materials-Tribute to Works of Michel Prévot

Rock magnetism and microscopy of the Jacupiranga alkaline-carbonatitic complex, southern Brazil

Earth, Planets and Space volume 61, pages 161–171 (2009)Cite this article

Abstract

This study of the Cajati deposit provides evidence that the ore was neither purely hydrothermal, nor volcanic in origin, as previous workers have proposed. The ores were formed from magnetite-rich magmas, hydrothermally altered and intruded at an indicated crustal depth in excess of 500 m. The mineralogical and textural association between magnetite and magnesioferrite in the carbonatite, and between the titanomagnetite and magnesioferrite-Ti mineralization in the pyroxenite of hedenbergite, seems to be analog mineralizations strongly related to the ionic substitution of Fe2+ by Mg. Relatively high Q ratios (≥5) for Jacupirangite-pyroxenite may indicate a thermo remanent magnetization (TRM) by the ore during post-metamorphic cooling, however it can also be developed from chemical remanent magnetization (CRM). Vector plots for the pyroxenite samples show reasonably linear and stable magnetic components. The intensity decay curves show that only two components of magnetizations are likely present. Continuous susceptibility measurements with increasing temperature show that the main magnetic phase seems to be magnetite. Maghemite is probably produced during the cooling process. Susceptibility recorded from low temperature (liquid nitrogen (-196°C)) to room temperature produces typical curves, indicating Verwey transition of magnetite. Hysteresis parameters point out that nearly all values fall in a novel region of the Day plot, parallel to but below magnetite SD + MD mixing curves.

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Authors and Affiliations

  1. Laboratorio de Paleomagnetismo y Geofisica Nuclear, Instituto de Geofisica, UNAM, Ciudad Universitaria, 04510, México DF, Mexico

    Luis M. Alva-Valdivia, María L. Rivas-Sánchez & Avto Goguitchaichvili

  2. Géosciences Montpellier, Université Montpellier II, 34095, Montpellier Cedex 05, France

    Luis M. Alva-Valdivia & M. Perrin

  3. Depto. Geología Económica, Instituto Potosino de Investigación Científica y Tecnológica A. C, San Luis Potosí, S. L. P., Mexico

    Héctor López-Loera

  4. Departamento de Geologia, Universidade Federal do Paraná, Jardim das Américas, Curitiba, Paraná, Brazil

    Omar Ferreira Lopes

  5. Planejamento de Lavra/Geologia, BUNGE Fertilizantes S/A Unidade Cajati, Sao Paulo, Brazil

    Thiago Bastos Bonás

Authors
  1. Luis M. Alva-Valdivia
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  2. M. Perrin
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  3. María L. Rivas-Sánchez
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  4. Avto Goguitchaichvili
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  5. Héctor López-Loera
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  6. Omar Ferreira Lopes
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  7. Thiago Bastos Bonás
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Correspondence to Luis M. Alva-Valdivia.

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Alva-Valdivia, L.M., Perrin, M., Rivas-Sánchez, M.L. et al. Rock magnetism and microscopy of the Jacupiranga alkaline-carbonatitic complex, southern Brazil. Earth Planet Sp 61, 161–171 (2009). https://doi.org/10.1186/BF03352896

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Key words

  • Rock-magnetism
  • microscopy
  • Jacupiranga complex
  • Brazil