Eudialyte decomposition minerals with new hitherto undescribed phases from the Ilímaussaq complex, South Greenland

Eudialyte is a distinctive mineral in the agpaitic group of peralkaline nepheline syenites. The paper describes the alteration of eudialyte from the Ilímaussaq complex, South Greenland, which is the type locality for eudialyte, as well as for agpaitic rocks. Two types of alteration are distinguished: alteration of eudialyte to catapleiite is widespread in the complex, whereas alteration to zircon only occurs in strongly altered rocks. additionally, the fol-lowing minerals have been identified in the altered eudialyte: aegirine, K-feldspar, albite, analcime, fluorite, monazite, apatite, allanite, Y-fergusonite, Ce-fergusonite, fersmite, nacareniobsite-(Ce), uranothorianite, neptunite and grossularite.

Some unidentified Nb and/or REE minerals have been distinguished. The different styles of alteration can be explained by different late- and post magmatic conditions at different settings in the complex. Alteration to zircon is caused by fluids of external origin or by fluids expelled from intersecting lujavrite and pegmatite dykes.

Alteration to catapleiite is caused by late-magmatic interstitial fluids. The alteration has resulted in distinct fractionation of some elements; Zr is, for instance, located only in zircon and catapleiite, Nb and REE in separate minerals.