Preliminary Map 63 covers the geological setting of the south half of the Elk Valley coalfield in southeastern British Columbia. It is a 1:50 000-scale compilation that depicts the geology of the Lewis thrust sheet within NTS 82G/15 and 82J/2. The boundaries of the map are the traces of the Lewis thrust fault on the east, the Bourgeau thrust fault on the west, and latitudes 50 degrees, 15 minutes north and 49 degrees, 45 minutes north on the north and south. The Greenhills and Alexander Creek synclines underlie the south half of the Elk Valley Coalfield. The map area includes three operating coal mines in the Elk Valley Coalfield (Line Creek, Fording and Greenhills) and part of the Balmer mine in the Crowsnest Coalfield.
Geology has been derived from: published mapping by the British Columbia Geological Survey Branch; published and unpublished regional mapping by the Geological Survey of Canada; and unpublished mapping by coal mine and oil exploration company geologists.
The map area lies within the Front Ranges of the Rocky Mountains and is underlain by carbonate and clastic sedimentary rocks of Devonian to Cretaceous age. In addition to world-scale coal resources, the area contains phosphorite units and is currently being explored for its petroleum potential.
All southeastern British Columbia coal occurrences are within the Lewis thrust sheet. West-to-east horizontal displacement of the thrust sheet was at least 19 kilometres at the latitude of Fording Mountain. Folds in the surface of the Lewis thrust were mapped in outcrop in the Tornado Pass area and inferred in the subsurface from evidence acquired during drilling of the California Standard Fording Mountain well. Outcrop expressions of subsurface folds in the Lewis thrust include the Alexander Creek syncline in the east, and the combination of the Fording Mountain anticline and the anticline that passes through Wisukitsak Range and Erickson Ridge (82G/1 5) in the west. The west-dipping Erickson normal fault, part of the Flathead fault system, can be traced over nearly the entire length of the map area. It separates coal occurrences on Harmer Ridge at the north end of the Crowsnest Coalfield and in the Greenhills syncline from occurrences throughout the length of the Alexander Creek syncline.
The oldest rocks exposed in the map-area are Devonian carbonates of the Palliser formation. These are overlain by carbonates and siltstones of the Mississippian Rundle group. Pennsylvanian and Permian calcareous sandstones of the Rocky Mountain Supergroup follow, then siltstones and shales of the Triassic Spray River Group. The Jurassic Fernie Formation comprises shales, sandstones, siltstones, limestones and phosphorites. The Jurassic to Cretaceous Kootenay Group rocks contain coal measures and are the prime economic target in the area. Lower Cretaceous Blairmore Group chert pebble conglomerates sandstones and mudstones are overlain by Upper Cretaceous Belly River Formation shales and sandstones. All the older rocks are locally covered by Quaternary deposits that vary from till to gravel to silt and alluvium.
Coal deposits in southeastern British Columbia occur in the Jurassic-Cretaceous Kootenay Group. Kootenay Group overlies the marine Fernie Formation of Jurassic age. The basal Kootenay sandstone, the Morrissey Formation, is a coastal deposit, which forms a consistent, easily mapped unit. The overlying Mist Mountain Formation has average total thickness of 500 metres; 8 to 12 percent consists of humic coal seams, which range in thickness to 12 metres or more. The overlying Elk Formation contains lenticular humic and sapropelic coal seams up to approximately 1 metre in thickness. No marine strata are known in either the Mist Mountain or Elk Formations. Overlying the Kootenay Group is the Cadomin Formation, the basal conglomerate of the Lower Cretaceous Blairmore Group.