Elliot Lake, Ontario

• Maps A, B, C & D [PDF, 8.5 Mb, viewer]

At Elliot Lake, uranium deposits in Precambrian sedimentary bedrock were mined from the 1950's to the 1990's. Ironically, the bedrock hosting the deposits is not regionally "anomalous" for uranium on the Radioactivity Map of Canada. This reflects regional differences in rock-forming minerals and bedrock types. Granites of the Superior Province underlie the northern part of inset map A and have higher uranium concentrations (indicated on inset map B as >3 ppm uranium) than the uranium ore-bearing sedimentary bedrock exposed in the southern part of inset map A. From ground studies, uranium concentrations in the granites of the Superior Province are 15 ppm compared to crustal average levels of 2 ppm. The radiometric expression of Superior Province granitic bedrock [of this area] is partially masked by glacially transported surficial deposits impoverished in uranium. The broad uranium patterns on inset map B are a result of a wide (5km) flight line spacing which requires considerable averaging in the contouring of the data.

Inset map C displays a detailed radiometric survey (flight lines spaced at 500m) of the blue highlighted area on inset maps A and B. This map reveals uranium anomalies relating to specific sedimentary horizons which host the uranium deposits and are not visible on inset map A or the regional Radioactivity Map of Canada. The two small anomalies in the center of inset map B (Quirke and Nordic Zone) relate to radioactive mine waste in areas near Elliot Lake. Inset map D displays a detailed radiometric survey (flight lines spaced at 100m) of the open box on inset maps A and B. This map provides information on the distribution of uranium-bearing mine waste (which contains a range of elements) and can be an environmental and health concern if the waste escapes into the drainage system. Slightly increased uranium levels over the Elliot Lake townsite (lower left of inset map D) are related to increased exposure of the surface due to vegetation removal, ground filling, leveling and, in places, to uraniferous radioactive waste rock from the mines which has been used as road and land fill. This potential environmental and health hazard has been subsequently cleaned up.

This material was extracted from Figure 1H: "Environmental applications of gamma ray spectrometry surveys", by B.W. Charbonneau, R.J. Hetu and J.M. Carson (Radiation Geophysics), in "Environmental geochemistry and geochemical hazards", compiled by R.D. Knight and R.A. Klassen, included in "A synthesis of geological hazards in Canada", Geological Survey of Canada Bulletin 548, edited by G.R. Brooks, 2001.