French River (Bigwood-Rutter)
The French River occurrence, referred to by Currie (1976a, p. 196) as 'Bigwood-Rutter' and by Duke and Edgar (1977) as 'Bigwood', consists of two lenses of nepheline syenite within a sheath of alkaline syenite.
Canadian occurrences of alkaline rocks have previously been listed and described in some detail in the monograph by Currie (1976a), although a significant number that have come to light since that publication will be found here. These new localities notably include extensive areas of peralkaline granites in Newfoundland, and of alkaline volcanics and intrusives in British Columbia, and it seems likely that many future discoveries will be concentrated in the latter area.
Many of the more northerly carbonatite occurrences are only poorly known and have not been dated. Although generally badly exposed, many have been drilled but rarely have findings been published. Many Canadian occurrences have been investigated for their economic potential (see, for instance, Ferguson, 1971) and important mining operations for nepheline syenite at Blue Mountain and Nb at St-Honore are taking place, with active exploration and appraisal for phosphate and vermiculite elsewhere. A number of occurrences in Ontario is described by Parsons (1961) and nearly 30 Ontario carbonatites have recently been re-investigated by R.P. Sage, although his internal reports were not available when the present accounts were compiled. K-Ar ages on numerous carbonatites in eastern Canada are given by Gittins et al.(1967) and of a broader range of alkaline rocks by Doig and Barton (1968). Rb-Sr ages and Sr isotopic ratios for many Ontario occurrences have been published by Bell et al. (1982).
The French River occurrence, referred to by Currie (1976a, p. 196) as 'Bigwood-Rutter' and by Duke and Edgar (1977) as 'Bigwood', consists of two lenses of nepheline syenite within a sheath of alkaline syenite.
Near Brule Creek in Springer Township (Fig. 43) small outcrops of granitic rocks are locally shattered and fenitized. A drill hole to over 200 m encountered fenitized rocks cut by carbonate veins.
A carbonatite-pyroxenite complex outcrops on Iron Island and other small islands in Lake Nipissing but is mostly hidden beneath the lake. However, many drill holes into the bottom of the lake as well as on the islands have enabled mapping of a large part of the complex.
Most of Burritt Island is underlain by fenitized granitic rocks which grade southwards through quartz fenites into syenitic fenites of K-feldspar and aegirine. The fenites on the eastern side of the island are cut by aegirine-rich dykes with some carbonate and altered nepheline.
This is an elliptical complex of 3.2x2.7 km much of which lies beneath Lake Nipissing, the outer fenite ring of which crops out on five islands. Extensive drilling and tunnelling have allowed some definition of the extent of the complex.
Callander Bay is an almost circular complex some 3 km in diameter centred on Callander Bay at the eastern end of Lake Nipissing.
An area of fenitization at Powassan (Fig. 43) similar to that in Springer Township 031-00-082) is reported by Currie (1976a, p. 84).
An area of fenitization associated with lamprophyric dykes, east of Lake Nosbonsing, is similar to that in Springer Township 031-00-082).
A small area (1.3 km2) of nepheline syenite gneiss occurs 19 km southwest of the town of Mattawa. The gneiss contains 5-25% nepheline, sodic hastingsite, 40-60% oligoclase and sometimes garnet. A pyroxene, which is present in some rocks, is described as omphacite.
The Brent crater forms an almost circular depression 3-4 km in diameter. The central part of the crater is occupied by Ordovician limestones, around which are Precambrian gneisses. Around the periphery of the crater the rocks are variably fractured or brecciated and metasomatized.