In the vicinity of Arvida, about 30 km west-northwest of Chicoutimi, are found dykes ranging from a few cm to 1 m thick and ranging from carbonatite to calcareous kimberlite. Three types are distinguished by Gittins et al. (1975): (a) primarily kimberlitic types of olivine, replaced variously by talc or antigorite, zoned phlogopite, apatite and Ti-magnetite set in a matrix of phlogopite, calcite, apatite and Ti-magnetite; (b) carbonatitic types composed essentially of calcite, often as phenocrysts, with lesser amounts of phlogopite, apatite and magnetite; and (c) intermediate types referred to as 'kimberlitic- carbonatitic'. Calcite dykes with a comb-structue and xenoliths of the adjacent anorthosite are rare. All the dykes have chilled margins with dendritic calcite and acicular apatite. Rock and mineral analyses are given by Gittins et al. (1975). Currie (1976a, p. 135) describes the dykes as striking north to northeast, and in this direction at about 20-25 km lies the St-Honore carbonatite (031-00-147), although a connection does not seem to have been suggested. The dykes also strike towards a prominent, circular aeromagnetic anomaly that underlies the aluminium smelter at Arvida, and which does not seem to have been investigated (J. Gittins, personal communication, 1984). Gittins is now of the opinion that the Arvida dykes are probably types of lamprophyre.
CURRIE, K.L. 1976a. The alkaline rocks of Canada. Bulletin, Geological Survey of Canada, 239: 1-228.
DOIG, R. and BARTON, J.M. 1968. Ages of carbonatites and other alkaline rocks in Quebec. Canadian Journal of Earth Sciences, 5: 1401-7.
Gittins, J. personal communication, 1984.
GITTINS, J., HEWINS, R.H. and LAURIN, A.F. 1975. Kimberlitic-carbonatitic dikes of the Saguenay River valley, Quebec, Canada. Physics and Chemistry of the Earth, 9: 137-48.