Lac Rouge is an approximately circular body of 25 km2 forming a depression corresponding to a positive aeromagnetic anomaly. It is poorly exposed. Nepheline-bearing rocks occur in a north- south trending ridge about 1.6 km in length by 250-300 m wide. The rocks are coarse, mesocratic syenites of orthoclase microperthite and towards the centre of the occurrence nepheline forms large porphyroblasts essentially replaced by cancrinite, thomsonite, natrolite and sodalite. Biotite and lesser hastingsitic amphibole are present with large euhedral zircons. Nepheline-rich pegmatites occur (Currie, 1976a, p. 199). Corriveau (1984, p. 305) reports the fenitization of country rock amphibolite and quartzite, and gives an exposure map (Corriveau, 1985, Fig. 22.5).