Summary:
The coal deposits for the Vista project are in the Western Canada Sedimentary Basin on the eastern edge of the Rocky Mountain Foothills. The area was formed during the Laramide orogeny and developed primarily from eroded and transported Canadian Cordillera sediments deposited in fluvial and floodplain environments during the Upper Cretaceous period and Paleocene epoch. Three major geological formations exist at the mine site: the Paskapoo, Coalspur, and Brazeau Formations. The Paskapoo overlies the Coalspur Formation, which overlies the Brazeau Formation. The Coalspur beds contain the major coal bearing sections. The Pedley Fault trends northwest/southeast along the southwestern boundary along the boundary of the coal deposits and separates the gently dipping coal beds from the steeper, faulted stratigraphy to the west. The surficial geology of the site consists of an upper layer of muskeg underlain by silty, sandy, and clayey glacial till.
Brazeau Formation
The Brazeau formation can be up to 2,000 m thick and consists of nonmarine mudstones, siltstones, and sandstones, with a chert-pebble conglomerate in the lower part of the formation. There are some thin coal beds interbedded with thin bentonites and coaly shales in the upper part of the formation that have been exploited by other mining operations but are not targeted by Coalspur.
Coalspur Formation
The Coalspur Formation consists of fluvially derived sediments that formed varying massive-to-thin interbedding of sandstone, siltstone, mudstone, and coal with some bentonite. The sandstone is largely grey and fine to coarse grained, with greenish-grey mudstone and siltstones. It was deposited in the end of Mesozoic and beginning of Cenozoic. The primary coal sources for the Phase II project are the Val d’Or, Arbour, McLeod, and McPherson zones. In many of these zones, the coal is interbedded with bentonite.
Paskapoo Formation
The Paskapoo Formation is the youngest strata in the area, and it is characterized as a Paleogene to earliest Eocene fluvial deposit dominated by siltstone and mudstone and interbedded with high-permeability, coarse-grained channel sands. The exposed area of Paskapoo Formation is over 65,000 km2, encompassing most of the southwestern Alberta and represents the uppermost bedrock unit over its area of occurrence.
The deposition of the Paskapoo Formation is unconformably over the Scollard Formation, which ages goes from the Upper Cretaceous to the lower Paleocene-aged. It’s characterized as a high-energy alluvial fan and floodplain deposits sourced from the eroding Rocky Mountains to the west. The Paskapoo’s deposition into the subsiding foreland basin formed an asymmetrical clastic wedge with a present-day maximum thickness of up to 850 m in the foothills, pinching out to a few tens of meters towards the plains. Demchuck and Hills (1991) divided the Paskapoo Formation into three members, named as Haynes, Lacombe, and Dalehurst.
Coal Seam Characteristics
Six coal zones have been identified within the lease boundary in descending order as the Val d'Or, Arbour, McLeod, McPherson, Silkstone, and Mynheer Zones. Each zone consists of multiple coal plies separated by clastic bentonitic parting material of variable thickness. The total coal thickness of the combined zones averages 28.3 m over the 200 m stratigraphic interval. Overall, the structure of the deposit consists of a monocline trending at 300° (N 60 W), dipping from between 6° at the northern boundary of the property to as steep as 15° at the southern boundary by the McLeod River. Several of the coal seams are correlatable to other properties in the region, including the Val d’Or, Arbour, Silkstone, and Mynheer seams at Coal Valley.
Val d’Or Seam
The Val d’Or seam is characterized by seven individual subseams over a 15 to 70 m interval. Subseams 1 through 5 consists of continuous coal units with thin bentonite or carbonaceous parting intervals. Subseam 6 consists of two coal layers separated by a thin carbonaceous mudstone at the north end of the mine lease boundary, that split and thin towards the south. Subseam 7 also consists of coal layers that split and thin towards the south. The interval thicknesses range from 0.8 to 5 m, and generally thin from north to south.
The Val d’Or seam lies on an upward-fining sandstone-siltstone-mudstone sequence, that is hard, nonbentonitic, and laterally consistent. Overlying the Val d’Or seam is a moderately thick continues sandstone-siltstone sequence.
Arbour Seam
The Arbour seam is characterized by multiple thin coal layers interbedded with carbonaceous mudstones and bentonites. The interval between the Arbour and the Val d’Or seam consists of a bentonitic mudstone to siltstone layer range from 0.5 to 3.7 m. Directly below the Arbour is a 2 m siltstone-sandstone layer followed by a bentonite zone ranging in thickness from 2 to 5 m.
McLeod Seam
The McLeod seam is characterized by three subseams that are generally thin, dirty, and split by bentonitic to carbonaceous mudstone and siltstones.
McPherson Seam
The McPherson seam is characterized by four correlatable subseams. Subseam 2 splits into three parts separated by sandstone units of variable thickness. Subseam 4 has been eroded by a thick sandstone unit. The McPherson seam lies on a siltstone-sandstone sequence and is overlain by mainly interbedded sandstone and siltstone layers.
Silkstone Seam
The Silkstone seam is characterized by a single coal interval and is approximately 60 to 80 m below the McPherson seam and was only penetrated along the western edge of the mine lease boundary. It does not contain any identifiable partings and can range from 1.5 to 1.7 m in thickness.
Mynheer Seam
The Mynheer Seam is characterized by two coaly zones separated by a sandstone unit and was only penetrated in one location within the mine lease boundary.