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Petrological and geochemical characteristics of REE mineralization in the A-type French Creek Granite, New Zealand

  • Regine Morgenstern
  • Rose E. Turnbull
  • Paul A. Ashwell
  • Travis W. Horton
  • Christopher Oze
Article
  • 98 Downloads

Abstract

The French Creek Granite, New Zealand, is an alkaline intrusion with enrichment in rare earth elements (REE). Petrography and whole-rock geochemical signatures demonstrate that the c. 82–84-Ma French Creek Granite is a composite granitoid, dominated by a ferroan, weakly peraluminous biotite alkali feldspar granite to syenogranite, with subordinate quartz-alkali feldspar (QAF) syenite. Maximum total REE + Y contents are higher in the granite and felsic dikes relative to the marginal QAF syenite, cogenetic mafic Hohonu Dike Swarm, and pegmatites. Our findings suggest that REE and high-field-strength element enrichment in the unaltered French Creek Granite is a function of partial melting from an enriched HIMU-like lithospheric mantle source, minor crustal assimilation, and extensive magmatic differentiation. Primary (magmatic) REE enrichment is defined by the occurrence of allanite, zircon, apatite, fergusonite, monazite, perrierite, and loparite, which are commonly associated with interstitial biotite. French Creek Granite samples from a phyllic-sericitic alteration zone in the Eastern Hohonu River are strongly elevated in REE relative to unaltered French Creek Granite, indicating remobilization and secondary REE enrichment by hydrothermal fluids. The REE are hosted in bastnäsite group minerals, monazite, xenotime, and zircon. Quartz protuberances, dilatational microfractures, and dike emplacement indicate that this alteration is structurally controlled. The δ13C and δ18O values of secondary carbonate veinlets are consistent with mixed low-temperature (~ 250–260 °C) magmatic hydrothermal fluids containing mantle-derived carbon. These fluids were likely part of a late-stage porphyry-type system operating during the same mantle degassing and extensional episode that was associated with the emplacement of the French Creek Granite and lamprophyric dikes of the Hohonu Dike Swarm, and initial Tasman Sea spreading. Results from this study provide an important insight into the complex processes responsible for REE enrichment in alkaline igneous systems.

Keywords

REE mineralization Carbonatite metasomatism Petrogenesis French Creek Granite Bastnäsite 

Notes

Acknowledgments

We would like to thank F. Fend and S. Salvi for reviewing this work, under the supervision of Associate Editor R. Linnen. We also thank the lab technicians at the University of Canterbury, and Stefan Cook, Anders Lenskjold, and Marie Eugène for their help in the field. We are especially grateful to Geoff Price, David Shelley, and Roger Townend for their expert advice and would like to acknowledge Todd Waight, Quinten van der Meer, Henry Dillon, Matthew Sagar, James Scott, Jarg Pettinga, and Jacqueline Dohaney for their helpful discussions and feedback. Thanks also to Quinten van der Meer for providing three samples of Hohonu Dike Swarm for the analytical work. Mike Palin is thanked for the assistance with LA-ICP-MS analysis and data reduction.

Funding information

This research was supported by grants awarded to RM from the Todd Foundation, New Zealand Federation of Graduate Women Canterbury Branch, Freemasons New Zealand, Brian Mason Scientific and Technical Trust [#201428], and the Geoscience Society of New Zealand. Funding for RM and RET was also provided by the New Zealand Government through direct core funding to GNS Science.

Supplementary material

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© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.University of CanterburyChristchurchNew Zealand
  2. 2.GNS ScienceLower HuttNew Zealand
  3. 3.GNS ScienceDunedinNew Zealand
  4. 4.Geology DepartmentOccidental CollegeLos AngelesUSA

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