The Athabasca oil sand deposit covers 4.4 × 10⁶ ha., of which 0.2 × 10⁶ ha. are amenable to surface mining. In-place reserves of crude bitumen are estimated to be 114.5 × 10⁹ cu m (720 × 10⁹ bbl), of which 11.8 × 10⁹ cu m (74 × 10⁹ bbl) are within the surface minable interval of less than 46 m. The Syncrude mine site covers 2,850 ha., has in-place reserves of 0.24 × 10⁹ cu m (1.5 × 10⁹ bbl), and commenced production in 1978 with a plant design capacity of 20,500 cu m (129,000 bbl) of synthetic crude per day. The geologic complexities of the oil-bearing McMurray Formation and the overburden zone have had a major impact on engineering consideration at the Syncrude mine.

The Cretaceous McMurray Formation was deposited along a transgressive shoreline between two regional highlands and is interpreted to be mainly estuarine. Paleotopographic lows in the underlying Devonian limestone are filled with salt marsh clays and fluvial water sands. The overlying oil-bearing part of the McMurray Formation is subdivided into a basal fluvial sand, a middle thick estuarine unit with interbedded tidal flat clays, and an upper low-marine unit. Dipping beds contributing to possible highwall instability are associated with estuarine and marine channels.

The overburden zone ranges up to 30 m thick and is composed of marine mudstones and indurated siltstones of the Cretaceous Clearwater Formation and overlying Pleistocene tills, lacustrine clays, and glaciofluvial granular materials, all of which impact on the mine plan.

Detailed documentation of the depositional facies is a prerequisite in geotechnical consideration and mine planning of an oil sand mining operation.

End_of_Article - Last_Page 742------------