Halogen (F, Cl and Br), S and δ37Cl variations within grains of Cl-rich minerals sodalite and eudialyte from peralkaline rocks of the Ilímaussaq intrusion were determined using Secondary Ion Mass Spectrometry (SIMS). Samples show either sodalite and eudialyte in direct contact, or sodalite/eudialyte embedded in Cl-free minerals (nepheline, feldspar). Comparing samples allows deciphering potential halogen and S exchange between these minerals during rock cooling.
Results suggest that sodalite (7 wt%) and eudialyte (1.2 wt%) have remarkably constant Cl concentrations. In samples with adjacent sodalite and eudialyte F increases at sodalite boundaries and decreases at eudialyte boundaries. In sodalite not in contact with eudialyte F concentrates at the edges, something obscured by F-rich inclusions. In eudialyte not in contact with sodalite F is constant with no variations at the edges. Br is also constant in eudialyte, but in sodalite its concentration decreases towards the edges. S also is constant in eudialyte, and concentrates significantly at the edges of sodalite, especially strongly if sodalite contacts eudialyte. In hydrothermal eudialyte Cl is low at the edge with higher concentrations away from the edge. Br and S correlate with Cl while little F variation is observed.
δ37Cl in eudialyte is higher than in adjacent sodalite. Within individual grains δ37Cl is higher at the edges than in the centre. Between sodalite grains δ37Cl can vary a few tenths of a permille, while between eudialyte grains, variations can even be higher. In hydrothermal eudialyte δ37Cl increases significantly at the grain boundary with values up to +3.5‰.