Mineralium Deposita

, Volume 23, Issue 2, pp 150–157 | Cite as

Complex unmixed spinels in layered intrusions within an obducted ophiolite in the Natal-Namaqua mobile belt

  • H. V. Eales
  • A. H. Wilson
  • I. M. Reynolds


Spinellids showing unmixed intergrowths of chromite or chromian spinel (sensu stricto) and magnetite or chromian magnetite are not known in mafic or ultramafic igneous rocks. They do occur within metamorphosed rocks that attained temperatures sufficiently high (upper amphibolite facies) for the formation of homogeneous Al-Cr-Fe3+-Ti spinel phases with compositions not matched in slowly cooled igneous rocks. In the Tugela Rand intrusion complex intergrowths of chromian spinel, chromian magnetite, ulvöspinel, ilmenite and a transparent aluminous spinel are observed and interpreted in terms of the thermal history of the rocks. Compositional differences between the separate areas of chromian spinel and chromian magnetite in complex intergrowths exhibited by the metamorphosed Tugela Rand and Mambulu Complexes confirm the extension of the magnetite-hercynite solvus (Turnock and Eugster 1962) towards magnesium- and chromium-rich compositions. The Tugela Rand spinellids are compared with those from the Carr Boyd Complex (Purvis et al. 1972) and the ultramafic rocks of the Giant Nickel Mine (Muir and Naldrett 1973) and the Red Lodge district (Loferski and Lipin 1983). Significant differences between the spinels from the Red Lodge district compared to the other three occurrences may reflect the different metamorphic histories of these areas.


Nickel Igneous Rock Thermal History Ultramafic Rock Sensu Stricto 
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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • H. V. Eales
    • 1
  • A. H. Wilson
    • 2
  • I. M. Reynolds
    • 1
  1. 1.Department of GeologyRhodes UniversityGrahamstownSouth Africa
  2. 2.Department of GeologyUniversity of NatalPietermaritzburgSouth Africa

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