Postmagmatic magnetite–apatite assemblage in mafic intrusions: a case study of dolerite at Olympic Dam, South Australia

  • Olga B. ApukhtinaEmail author
  • Vadim S. Kamenetsky
  • Kathy Ehrig
  • Maya B. Kamenetsky
  • Jocelyn McPhie
  • Roland Maas
  • Sebastien Meffre
  • Karsten Goemann
  • Thomas Rodemann
  • Nigel J. Cook
  • Cristiana L. Ciobanu
Original Paper


An assemblage of magnetite and apatite is common worldwide in different ore deposit types, including disparate members of the iron-oxide copper–gold (IOCG) clan. The Kiruna-type iron oxide-apatite deposits, a subtype of the IOCG family, are recognized as economic targets as well. A wide range of competing genetic models exists for magnetite–apatite deposits, including magmatic, magmatic-hydrothermal, hydrothermal(-metasomatic), and sedimentary(-exhalative). The sources and mechanisms of transport and deposition of Fe and P remain highly debatable. This study reports petrographic and geochemical features of the magnetite–apatite-rich vein assemblages in the dolerite dykes of the Gairdner Dyke Swarm (~0.82 Ga) that intruded the Roxby Downs Granite (~0.59 Ga), the host of the supergiant Olympic Dam IOCG deposit. These symmetrical, only few mm narrow veins are prevalent in such dykes and comprise besides usually colloform magnetite and prismatic apatite also further minerals (e.g., calcite, quartz). The genetic relationships between the veins and host dolerite are implied based on alteration in the immediate vicinity (~4 mm) of the veins. In particular, Ti-magnetite–ilmenite is partially to completely transformed to titanite and magmatic apatite disappears. We conclude that the mafic dykes were a local source of Fe and P re-concentrated in the magnetite–apatite veins. Uranium-Pb ages for vein apatite and titanite associated with the vein in this case study suggest that alteration of the dolerite and healing of the fractures occurred shortly after dyke emplacement. We propose that in this particular case the origin of the magnetite–apatite assemblage is clearly related to hydrothermal alteration of the host mafic magmatic rocks.


IOCG deposits Olympic Dam Mafic magmatism Colloform magnetite Hydrothermal alteration Radiogenic isotopes 



We are grateful to Jay Thompson, Paul Olin, and Sandrin Feig (University of Tasmania) for assistance with analytical work. Qiuyue Huang, Alex Cherry, and Richelle Pascual are thanked for discussions and support. Thoughtful comments by Adam Simon and an anonymous reviewer helped to improve clarity and presentation. This study was funded by BHP Billiton and the Australian Research Council (Linkage Grant “The supergiant Olympic Dam U-Cu-Au-REE ore deposit: towards a new genetic model”).

Compliance with ethical standards

Conflict of interest

The authors declare that there is no conflict of interest, and no human or animal participants are involved or harmed in any way during the conduct of this research.

Supplementary material

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Supplementary material 1 (DOCX 153 kb)
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Supplementary material 2 (PDF 9546 kb)


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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Olga B. Apukhtina
    • 1
    Email author
  • Vadim S. Kamenetsky
    • 1
  • Kathy Ehrig
    • 2
  • Maya B. Kamenetsky
    • 1
  • Jocelyn McPhie
    • 1
  • Roland Maas
    • 3
  • Sebastien Meffre
    • 1
  • Karsten Goemann
    • 4
  • Thomas Rodemann
    • 4
  • Nigel J. Cook
    • 5
  • Cristiana L. Ciobanu
    • 5
  1. 1.School of Physical SciencesUniversity of TasmaniaHobartAustralia
  2. 2.BHP Billiton Olympic DamAdelaideAustralia
  3. 3.School of Earth SciencesUniversity of MelbourneParkvilleAustralia
  4. 4.Central Science LaboratoryUniversity of TasmaniaHobartAustralia
  5. 5.School of Chemical EngineeringUniversity of AdelaideAdelaideAustralia

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