Discovery of Kimberlites in the Kirkland Lake Area Northern Ontario, Canada PART II: Kimberlite Discoveries, Sampling, Diamond Content, Ages and Emplacement

Exploration & Mining Geology, Vol. 1, No. 4, 1992

J.J. BRUMMER, Toronto, Ontario, Canada, D.A. MacFADYEN, Scarborough, Ontario, Canada, and C.C. PEGG, LAC Minerals, Toronto, Ontario, Canada

The early identification of a kimberlite dyke and the occurrence of pyrope garnet grains along a section of the Munro Esker north of Kirkland Lake encouraged the search for kim-berlites. Subsequent exploration using data from aeromagnetic surveys completed for the Kirkland Lake Initiatives Program (KLIP) resulted in the discovery of five kimberlite diatremes in the area north of Kirkland Lake and another one to the south. These are only a portion of the cluster of pipes found so far that probably occur in the area. Recovery of the diamonds present in four of the pipes yielded 16 stones, the largest being 0.17 carats. Unfortunately evaluation of the pipes is a problem due to the cover of glacial drift, up to 92 m in thickness, which makes it difficult to obtain an adequate bulk sample. A study of their ages, mostly from drill hole samples, suggest that the kimberlite diatremes and other alkaline ultramafic rocks were emplaced along a northwesterly zone of rift structures. These alkaline ultramafic rocks cut across all earlier rock types and have ages ranging from 121 Ma to 173 Ma. The zone of deformation, along which these rocks occur, has been named the Lake Timiskaming Structural Zone (LTSZ), a modification of Lake Timiskaming Rift Valley (LTRV). Ultramafic intrusions which were emplaced along the LTSZ can be traced from the James Bay Lowlands in the northwest to past Belleville on the north shore of Lake Ontario in the southeast, a distance of about 1070 km. As the emplacement of these rock types become known more are certain to be found by drilling selected aeromagnetic anomalies. The project has demonstrated that aeromagnetic surveys can be used successfully to identify covered kimberlite targets.