Gracefield
Gracefield consists of an earlier 7.5 km2, crescent-shaped intrusion of syenite with minor melasyenite and nepheline syenite and a later 4 km2 biotite 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).
Gracefield consists of an earlier 7.5 km2, crescent-shaped intrusion of syenite with minor melasyenite and nepheline syenite and a later 4 km2 biotite syenite.
North of Cawood a body of nepheline-bearing gneiss, about 1.5 km across, is surrounded by marble, but contacts are not exposed. Most of the occurrence consists of homogeneous gneiss with 5-20% biotite and amphibole and some 10% nepheline.
Numerous arcuate carbonatite dykes are emplaced in a large body of aplite, while many breccia bodies are found both in the aplite and the surrounding syenites and gneisses. Fenitization is associated with both types of body.
Carbonatite occurs at Dam Lake 15 km north-northeast of Quinnville (031-00-114).
In the Haycock Mine the iron mineralization is related to veins adjacent to which is a zone of fenitization. This involves development of phlogopite, eckermannite, apatite, aegirine, hematite, calcite, baryte and quartz. Thought to be contemporaneous with the Meach Lake carbonatites.
A small body of carbonatite lies 1.9 km north-northeast of Quinnville. Unfortunately the outcrop was built over before it could be studied in detail.
This large quarry in massive Ottawa limestone contains carbonatite dykes that occupy regionally developed shatter zones at intervals of 50-100 m. They parallel a set of normal faults trending approximately east-west. The largest dyke, the most northerly, ranges in thickness from 1.2 to 0.3 m.
Intruded into igneous and metamorphic rocks of the Grenville Province close to the fault defining the northern margin of the Ottawa Graben, the Chatham-Grenville stock consists of two early syenites and two later granite intrusions.
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.
A poorly exposed dyke of alnoite-type similar to others occurring to the north and west of Montreal is found near St Lin.