Geoscience BC Map 2010-2-1 / GSC Open File 6344

Distribution of the Chilcotin Group, Taseko Lakes and Bonaparte Lake map areas, British Columbia
by J. Dohaney, G.D.M. Andrews, J.K. Russell and R.G. Anderson

Report Components

Report Description
The Oligocene to Late Pleistocene Chilcotin Group comprises stratified olivine–phyric basaltic flows that underlie much of the Interior Plateau of British Columbia. The distribution of the Chilcotin Group portrayed on published maps is imprecise because of poor outcrop exposure on the plateau, multiple generations of mappers, and lack of consensus concerning definition of the Group. The thickest and most extensive sections are exposed in the valley–margins of major rivers (e.g. the Fraser River). This map contains part of the M.Sc. thesis work by Dohaney (2009) to collate and interpret multiparameter spatial datasets leading to a reassessment of the distribution of the Chilcotin Group within the Taseko Lakes (NTS 092O) and Bonaparte Lake (NTS 092P) map areas.

This new distribution map leads to several important conclusions:

  1. the Chilcotin Group is less extensive than shown in previous compilations for Taseko Lakes and Bonaparte Lake map areas by as much as 48%; by analogy, this implies that elsewhere the areal extent of the Chilcotin Group is also significantly over-estimated;
  2. the numerous areas indicated as not overlain by Chilcotin Group in the compilation constitute previously unidentified basement "windows" that are geologically and economically important;
  3. Chilcotin Group volcanism spanned the Oligocene to the Pleistocene (approximately 30 m.y. duration) and was centered in the central Fraser River area (south of Williams Lake) throughout the Pliocene—Pleistocene;
  4. episodic eruption of Chilcotin Group lavas was likely via a multitude of small–volume, short–lived, monogenetic vents, rather than a series of long–lived volcanic centres or fissures; and
  5. the Chilcotin Group is thickest where lavas ponded in paleo–valleys, a key indicator for mapping the distribution of Neogene channels in the Fraser Basin drainage.

Suggested References
Dohaney, J., Andrews, G.D.M., Russell, J.K., and Anderson, R.G. (2010): Distribution of the Chilcotin Group, Taseko Lakes and Bonaparte Lake map areas, British Columbia; Geological Survey of Canada Open File 6344 and Geoscience BC Map 2010-2-1; 1 sheet, scale 1:250 000.

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