Efforts to trace the sources of glacially transported diamonds of the Great Lakes region by study of large scale glacial ice movements have not been successful. Lack of adequate diamond records, the complexity of the glacial transport process, the small size of kimberlite pipes, an inadequate appreciation of their possible distribution and the questionable value of glacial indicator boulders, all are suggested reasons for failure to find the diamond sources.

Relatively complete records of the drift diamonds have been assembled. Two areas rich in stream diamond finds, Plum Creek, Wisconsin, and southern Indiana, were studied by heavy mineral, pebble lithology, till fabric and bedrock examination methods. No diamonds or kimberlite indicator minerals were found. These studies show that the stream diamonds are more likely to have been carried in by glacial ice than to have been derived from nearby ancient placers or local kimberlites. A difference in purple/red garnet ratios between the two areas for both bedrock and till indicates that there may be more than one provenance area for the diamonds. Till heavy mineral suites to the north of Lake Superior were richer in amphibole and pyroxene than those from Plum Creek and southern Indiana, indicating that much more detailed work would be necessary to establish trains of glacial transport across the Great Lakes.

Two methods of using glacial erratics to give mean ice movement directions within stages, and to outline sectors of provenance are proposed. Caution is urged when drawing conclusions from finds of jasper conglomerate, tillite and other glacial erratics because these boulders may have been eroded from more than one source area or moved more than once by glaciers.

Attention is drawn to the continent-wide distribution of diamonds and the implication of this in the search for the source of the drift diamonds. It is recommended that future investigators consider the value of two proposed tectonic models of basement flexure and rifting to assist in outlining the most favourable areas for kimberlite prospecting.

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