Metasomatism in the North Qôroq Centre, South Greenland: Apatite Chemistry and Rare-Earth Element Transport

David A. Rae, Ian M. Coulson and Andrew D. Chambers
School of Earth Sciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Abstract: The North Qôroq syenite centre forms part of the Gardar Province of South Greenland. Extensive metasomatism, associated with the evolution of syenitic magmas, has resulted in redistribution of the rare-earth elements (REE), originally concentrated by magmatic processes, in both the syenites and surrounding granite-gneiss and quartzite country rocks. An important host for REE is apatite which can occur in significant quantities. Metasomatic apatites show complex, concentric, but irregular patterns of zonation, clearly seen using CL and BSE imaging. This zonation is related to successive pulses of metasomatising fluids. Electron microprobe analysis confirms the presence of significant quantities of REE in the apatites. The dominant cation exchange mechanism proposed is Ca2+ + P5+REE3+ + Si4+. In contrast to apatites from the nearby Ilímaussaq intrusion, there is no significant Na present in the structure and exchange reactions involving Na+ and REE3+ for Ca2+ have not occurred.

Apatites from the quartzite are fluor-apatites, while those from the granite-gneiss are more Cl-rich. These differences reflect the fact that granite-gneiss apatites are original and modified by metasomatism, whereas, those in the quartzite are metasomatic in origin. REE were probably transported as carbonate, fluoride or fluor-carbonate complexes, and reflect the activity of a F-rich, CO2−3-rich fluid phase.

Keywords: apatite • metasomatism • rare-earth elements • cathodoluminescence • Igaliko • Gardar • South Greenland

Mineralogical Magazine; February 1996 v. 60; no. 398; p. 207-220; DOI: 10.1180/minmag.1996.060.398.14
© 1996, The Mineralogical Society
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