Abstract: Miocene Miles Canyon basalts play a critical role in the historical development and modern economics of the City of Whitehorse. Where cut by the Yukon River, the unnavigable waters at Miles Canyon and the Whitehorse Rapids formed a natural terminus that became a transportation hub that in turn encouraged settlement. Today, this basalt is responsible not only for efficient and economical hydroelectric power, but also for hosting the groundwater resources for many of Whitehorse's rural residents. Much of the city is underlain by Cretaceous granodiorite of the Whitehorse Batholith, which is a relatively poor aquifer due to its lack of porosity. Miles Canyon basalt however, has significantly higher innate hydraulic permeability and thus provides better opportunities for additional groundwater resources and aquifer development. Miles Canyon basalts have reported hydraulic conductivity values around 2 x 10^-6 m/s, which are 20 to 50 times higher than reported hydraulic conductivity values for unfractured granodiorite aquifers. As such, the loci of basalt limits have important implications for the siting of productive private water wells.

This paper summarizes details of Miles Canyon basalt occurrences within the limits of the City of Whitehorse and provides updated mapping of the extent and distribution of the basalt within the City. The discussion includes a summary of six outcrop observations, twelve water-well record data, a shallow reflected seismic survey and interpretation of regional aeromagnetic data related to basalt distribution. Thickness of Miles Canyon basalt intersected in drill holes ranges from as little as 1.8 m up to 110 m, although most drill holes did not penetrate the total basalt thickness.

Authors: Pearson, F.K., Hart, C.J.R., and Power, M.

Keywords: bedrock mapping, water-well data

NTS Mapsheet(s): 105D

Citation: Pearson, F.K., Hart, C.J.R., and Power, M., 2001. Distribution of Miles Canyon basalt in the Whitehorse area and implications for groundwater resources. In: Yukon Exploration and Geology 2000, Emond, D.S. and Weston, L.W. (eds.), Exploration and Geological Sciences Division, Yukon Region, Indian and Northern Affairs Canada, p. 235-245.

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