Read Coal Geology: A brief overview of coal in Alberta with a focus onthe past coal mining in the Canmore area text version

Coal Geology: A brief overview of coal in Alberta with a focus on the past coal mining in the Canmore area

Gerry Stephenson, P. Eng.* Norwest Corporation, Calgary, Alberta and Steve Cameron Norwest Corporation, Calgary, Alberta [email protected] and Virginia Odegaard, P. Geol. Norwest Corporation, Calgary, Alberta [email protected]

INTRODUCTION The province of Alberta hosts the most extensive coalfields in Canada, accounting for approximately 70% of Canada's coal reserves. Most of the coal produced in Alberta is used as fuel for the generation of electricity as well as a source of energy for other purposes. Alberta coals are of Upper Jurassic, Cretaceous and Tertiary ages. They range in rank from lignite through subbituminous and bituminous to semi-anthracite, with the majority of the coal in the subbituminous category. In Alberta, these coals are found in three principal regions referred to as the Plains, Foothills and Mountain Regions. The Plains deposits, which contain the vast resources of subbituminous coals, show very little tectonic disturbance and dip very gently towards the mountains in the west. Moderate folding and faulting characterize the Foothills Region. The Mountain Region exhibits more intense structural deformation and hosts rare occurrences of semi-anthracite deposits such as those found in the Canmore area. The Town of Canmore owes its existence to the mining companies and the miners who began to exploit the coal deposits to produce fuel for the newly established railroad connecting the east and west coasts of Canada. Underground coal mining began in 1886 when the first portals of the No.1 Mine were opened in the outcrop of a coal seam in the valley of Canmore Creek. Mining operations continued until 1979 when the last mine was closed. During the intervening years, eight mines were operated which included both underground and surface mines. The geological complexity of these coal

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deposits, set against a backdrop of fluctuating coal markets during over ninety years of mining operations, necessitated the application of various and innovative approaches to coal mining in the Canmore area. CANMORE COAL GEOLOGY The Canmore coalfield lies within the northwesterly trending Cascade Coal Basin, which extends for approximately 80 km within the Front Ranges of the Canadian Rocky Mountains. The Canmore area is in the northern part of the basin along the Bow River Valley. Lower Cretaceous Age strata of the Kootenay Group subcrop in the Bow River Valley floor and crop out along northwesttrending ridges and depressions. The coal-bearing formation within the Kootenay Group is named the Mist Mountain Formation and consists of approximately 400m of fine-grained facies including siltstone, fine sandstone, shale and coal seams, representing continental, near-shore lagoonal and fluvial deltaic facies, with associated coalforming back swamps. The coal-bearing section is overlain by over 600m of finegrained facies of the Elk Formation. The actual contact between the Elk Formation and the Mist Mountain Formation is not well defined in the Cascade Coal Basin. It is generally defined as a gradational contact where the Elk Formation becomes increasingly coarse-grained upward in the stratigraphic sequence. Although thin coal seams do occur in the lower part of the Elk Formation, no coal seams of mineable thickness have been documented as occurring in the Elk Formation in the Cascade Coal Basin. In the Canmore area, the Cascade Coal Basin is bounded on the west by the Rundle Thrust Fault, which has positioned stratigraphically older beds over younger Kootenay Group strata. Repetitions within Paleozoic strata through folding and thrust faulting are evident in the Three Sisters Peaks southwest of Canmore. The mountains of the Fairholme Range, which comprises older and more resistant Paleozoic carbonate-rich rocks, form the boundaries of the basin to the northeast. The predominant feature of the Canmore coalfield is an asymmetrical syncline running parallel to, and abutting against, the range of mountains to the west, which includes Mount Rundle and the Three Sisters. The steep western limb of the syncline adjacent to the mountain range is vertical to overturned. The eastern limb exhibits dips or gradients varying up to 55 degrees and the presence of numerous small synclines in this limb results in a wide variation of gradient over short distances. CANMORE COAL MINING The geology of the Canmore coalfield is extremely complex in relation to the conditions with other coal areas in Western Canada. Such characteristics have the greatest impact on underground, and to a lesser extent, on surface mining.

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Methods of developing and operating the Canmore mines were affected by the intense folding and faulting associated with the complex geology: o The thickness of the coal seams within folded strata is extremely variable, often being increased several times within the fold axes or, at the other extreme, being pinched out completely. o Gradients from zero to 90 degrees were encountered during mining of the synclinal structure in this area. o The intensity of faulting is high in the Canmore area. Thrust faults of shallow angle, where movement of rocks has taken place along the weakest stratum in the sequence, specifically the coal seam, are common. Such movement often resulted in the shearing of the coal seams. o Tectonic forces have also greatly reduced the strength of the coal so that, throughout the field, the seams are very friable and contain an unduly high proportion of fines. o The coal contains very large quantities of methane that were released very abruptly during mining. These difficult conditions greatly increased the cost of underground mining. Individual operations covered only small areas due to discontinuities in each seam and economies of scale were, consequently, impossible. Surface exploration provided only a sketchy idea of the geology prior to commencing an operation. Beginning a new mine was always fraught with risk due to this uncertainty and the boundaries of each operation, whether due to faulting or thinning coal, were usually only determined when they were reached. Productivity per man shift in labour intensive operations could be quite high compared with other such operations. The gradients were used to transport coal by gravity while the friable coal made excavation from the face relatively easy. Thus the mines were relatively productive as long as wages were low. As wages began to rise mechanisation became necessary to improve productivity. However it was found that the heavy equipment such as continuous miners and shuttle cars, commonly used by other room and pillar operations, could not manoeuvre on the steep gradients while their capacity was reduced by the very high rates of emission of inflammable methane gas. In the last ten years of mining from 1970 to 1979 semi-mechanised systems were utilised with some success. In the mid 1960 `s surface mining was practiced on a small scale. Strangely enough it was the folding and thickening of the seams in the axes of the synclines and anticlines, which, when located close to the surface, created suitable conditions for the recovery of coal at low stripping ratios. In the end, the reserves located within a reasonable distance of the preparation plant were exhausted. It became clear that the more distant reserves still untouched to the south in the Wind Valley, required a high investment in extension and rebuilding of surface facilities. This could not be justified and, in

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1979, the last mine was closed after over ninety years of continuous coal extraction in the Canmore area.

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Coal Geology: A brief overview of coal in Alberta with a focus onthe past coal mining in the Canmore area

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