Geological Survey of Canada's contributions to understanding the composition of glacial sediments

Drift compositional studies were initiated at the Geological Survey of Canada (GSC) in the mid-1960's in projects that drew heavily on the technology and approaches developed in Fennoscandia over the previous century. As this research progressed and expanded in the 1970's, its Fennoscandian character diminished and, like the geochemical exploration research program that it closely paralleled, drift prospecting began to acquire a distinctly Canadian character, imposed by the geographical and logistical constraints of climate and asymmetric population distribution. GSC research has increasingly focused on understanding and explaining the geochemical expression of the mineralogical composition of glacial sediments that are unaltered or only slightly altered by postdepositional weathering. Because glacial sediments are generated largely by crushing and abrasion, their various mineral and lithological components attain characteristic size modes based on physical properties such as cleavage and hardness. This size sorting by physical properties is expressed geochemically by chemical partitioning in various size ranges. Also, the crushing process disaggregates fresh bedrock and incorporates all of its mineral components, labile as well as stable, into glacial sediment. GSC research has concentrated on the best ways to sample and analyze drift to avoid the compositional size bias and potential weathering alterations of labile minerals, so that geochemical analyses truly representative ofprovenance may be attained. As it has become possible to filter provenance signals from noise generated by weathering, partitioning, sediment facies misidentification, and stratigraphic variations, the principles of glacial dispersal of components of economic and environmental significance have been clarified and dispersal patterns mapped.