EXPLORING FOR DIAMONDS AND THE NORTH — Great Lakes glacial

On four occasions during the last 1.5 million years, most bedrock surfaces in Canada were scoured by glacial erosion. Diamonds originally present in kimberlite bodies were plucked, transported and scattered along paths travelled by the glaciers. Since 1863, 83 stones have been found in glacial sediments surrounding the Great Lakes.

Only two of the diamonds were located in Canada. The others were located in glacial drift scattered south of the Great Lakes; 34 of the stones were found in Indiana (site of the first discovery). The drift diamonds ranged in size up to 80 carats, but most were under one carat.

Most researchers feel that the source of most of these diamonds is located in the James Bay Lowlands. Surveys by Selco (1960), Canadian Rock Company (1963) and the Ontario Division of Mines (1975) recognized 53 pyrope grains (kimberlite-indicator minerals) in 32 locations in the James Bay Lowlands, near the Kapuskasing High (a positive gravity anomaly that extends across the James Bay Lowland area from Chapleau to Moosonee).

The first recorded diamond discovery in Canada was made near Peterborough, Ont. Details of the discovery are vague, but it was apparently found while digging a railway bed. The stone is described as a rough broken diamond weighing 33 carats.

Another diamond located in drift is the Jarvi diamond, named after its finder, Reno Jarvi of South Porcupine, Ont. This 0.255-carat stone was discovered late in 1971, during the course of a geochemical survey, on an asker in the southwest corner of Sheraton Twp., Ont., 42 km west of the Munro esker. Its source is thought to be to the north, somewhere along the direction of ice transport, probably near the area underlain by the Kapuskasing High.

— From “Diamonds in Canada,” by J.J. Brummer, in the CIM special volume “The Geology of Industrial Minerals in Canada.”