METASOMATISM IN THE NORTH QOROQ CENTER, SOUTH GREENLAND - APATITE CHEMISTRY AND RARE-EARTH ELEMENT TRANSPORT

The North Qoroq syenite centre forms part of the Gardar Province of So uth Greenland. Extensive metasomatism, associated with the evolution o f syenitic magmas, has resulted in redistribution of the rare-earth el ements (REE), originally concentrated by magmatic processes, in both t he syenites and surrounding granite-gneiss and quartzite country rocks . An important host for REE is apatite which can occur id significant quantities. Metasomatic apatites show complex, concentric, but irregul ar patterns of zonation, clearly seen using CL and BSE imaging. This z onation is related to successive pulses of metasomatising fluids. Elec tron microprobe analysis confirms the presence of significant quantiti es of REE in the apatites. The dominant cation exchange mechanism prop osed is Ca2+ + P5+ reversible arrow REE(3+) + Si4+. In contrast to apa tites from the nearby Ilimaussaq intrusion, there is no significant Na present in the structure and exchange reactions involving Na+ and REE (3+) 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 origina l and modified by metasomatism, whereas, those in the quartzite are me tasomatic in origin. REE were probably transported as carbonate, fluor ide or fluor-carbonate complexes, and reflect the activity of a F--ric h, CO32--rich fluid phase.