There are four chronological groups of carbonatite complexes in Ontario and Quebec. These are about 125 m.y., 565 m.y., 1075 m.y., and 1700 m.y., with a possible fifth at 1560 m.y. The recently proposed St. Lawrence Rift System is not considered to be a very likely control of carbonatite emplacement unless it includes a widespread system of branch faults. The coincidence of carbonatite complexes with the "Kapuskasing High" is striking and probably puts a minimum age of 1750 m.y, on the feature. Niobium is found in carbonatites of each age group.

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