Geological, geophysical and geochemical considerations for exploration in clay-covered areas: a review

CIM Bulletin, Vol. 72, No. 804, 1979

B. W. SMEE and A. K. SINHA, Resource Geophysics and Geochemistry Division, Geological Survey of Canada, Ottawa

Glacial lake sediments or glaciolacustrine deposits form a significant portion of the Canadian, Scandinavian and Russian landscapes. Furthermore, 50per cent of the Archean volcanic belts within the Canadian Shield area are covered wholly or in part by these deposits. Because of the high electrical conductivity and low hydraulic conductivity of these compact sediments, the application of geophysical (electrical) and geochemical techniques in such areas becomes a difficult task. The presence of these sediments has therefore hampered exploration for metallic sulphide deposits in some of the most important metallogenic environments of Canada. Similar problems exist in some tropical countries, such as Australia, where the overburden may be very conductive.In this paper, the extent and provenance of the glaciolacustrine deposits within the Canadian Shield are described. The geochemical and geophysical factors that hinder exploration in the clay belts are reviewed, with case histories of successful and unsuccessful applications of some of these techniques. The most successful geochemical technique used within glacial clay belts is the sampling of lodgement till beneath the clay cover, and the analysis of the heavy mineral fraction of that till. Surficial sampling has not been successfully applied.Some geophysical techniques, more specifically electromagnetic and magnetic induced-polarization techniques, have detected mineralization beneath substantially deep clay or saline overburden layers. Some suggestions have been made, such as the use of onions in hydrogeochemical surveys and the use of wide-band multi-frequency EM systems. When implemented, they will hopefully make the current geochemical and geophysical methods more effective in exploration for base metal sulphides within clay-covered terrains.
Keywords: Exploration techniques, Mineral exploration, Geophysical exploration, Geochemical exploration, Overburden, Clay, Lake sediments, Glaciolacustrine deposits, Till sampling, Hydromorphic dispersion, Biogeochemistry, Soils, Precambrian Shield.