Carbonatite is reported at St-Andre in the SOQUEM Annual Report for 1968 (Gold and Marchand, 1969, p. 10) but no further details are available.
You are here
Apart from the major complex of Mount Royal, Montreal Island is also cut by numerous alkaline dykes and many, though fewer, sills. The dykes encompass many varieties and are most abundant in the vicinity of Mount Royal. Although the majority of the sills are only some 0.5 m or less in thickness, and will not be dealt with individually, others are considerably thicker, more extensive and have often been named and described individually so that they are afforded separate entries and brief descriptions in the catalogue. They are not confined to Montreal Island but also occur to the west and east (see Fig. 61). For general accounts see Clark (1952, p. 84) and Gold and Marchand (1969); Eby (1985c) gives ages and detailed chemistry for mafic dykes. There are several dykes, pipes and diatremes of monticellite- and melilite- bearing alnoitic rocks in the vicinity which are included in the catalogue, but bodies of (?)kimberlitic rock such as the pipes on Ile Bizard, which do not contain melilite, are excluded, as are breccia diatremes lacking alkaline rock fragments or matrix such as those on Ile Ronde and Ile Ste-Helene.
A line of ten intrusions extending eastwards from Oka via Mount Royal to Mount Megantic is known as the Monteregian Hills and has been the subject of numerous papers. Eby (1984a, 1984b, 1985a and 1985b) has made the most recent comprehensive study and much of the earlier work is cited by him.
A poorly exposed dyke of alnoite-type similar to others occurring to the north and west of Montreal is found near St Lin.
The Ste-Monique sill caps a number of small hills over an area of approximately 3x1 km. It is probably 6-7 m thick, although contacts are not exposed.
The Brilund pipe, which underlies a low, wooded hill, is about 150x100 m and cuts Potsdam sandstone. It has been extensively drilled (Gold and Marchand, 1969, Fig. 1_5.).
The Oka Hills rise to 215 m above the St Lawrence Lowlands and represent an inlier of some 115 km2 of Precambrian gneisses surrounded by Palaeozoic sedimentary rocks.
The Como pipe outcrops as a low mound of appoximately 200x500 m. The rock is a monticellite alnoite with phenocrysts of poikilitic phlogopite, monticellite and augite in a matrix of melilite, phlogopite, monticellite and calcite with accessory opaques, perovskite and apatite.
The Ile Cadieux pipe is exposed on a low hill 180 m in diameter, but contacts cannot be seen. The rock is alnoitic consisting of phlogopite, forsterite, monticellite, titansalite and melilite with accessory apatite, magnetite, perovskite, calcite, scapolite and zeolite.
An alnoitic dyke in the river south of Ste-Anne de Bellvue, at the extreme southwest end of the Island of Montreal, is no longer exposed.
Outcrops of what may be a single sill (Clark, 1952, p. 96) are found at many localities on Ile Jesus the most extensive being just north of Sainte-Dorothee. The sill is 5.7 m thick at Ste- Dorothee with upper and lower chilled contacts, and intrudes Lower Ordovician Beekmantown dolomite.
The Francon Quarry, St-Michel district, Montreal is in the lower and middle parts of the Trenton limestone (Ordovician), and contains a silico-carbonatite sill associated with which is a very extensive suite of rare minerals.