The Sydney coalfield of Nova Scotia, Canada

Abstract

In size, production and remaining resources, the Sydney coalfield is the largest field in eastern Canada. It is nearly entirely submarine and extends from northeastern Cape Breton Island to almost as far as Newfoundland, occupying an area estimated at 36,300 km 2. During 205 years of mining, some 410 million t have been produced and the total remaining “demonstrated” resources, present in ten seams, have been calculated at 1,800 million short tons, T (1 short ton=0.907 t). Of this in situ tonnage about 300 million may be suitable for metallurgical purposes and 1,500 million T can be classed as thermal coal. Some 82% of the total estimate is contributed by four seams, of which the Harbour seam is the main producer. The present annual production is between 3 and 4 million T and all mining is done in the submarine area. The main problems with submarine mining are ventilation and haulage time. The latter increases with the distance from the shore and results in reduced production. A west to east cross-section through five seams illustrates the development of coal and shows the phenomenon of depositional splitting and rejoining, caused by the interaction of fluvial sedimentation and peat accumulation. Fossil rivers forming “wants” or “wash-outs” in the coal seams are the principle geological obstructions to mining. Structural difficulties are minor as the field is only gently folded and no main faults are present. All coal of the Sydney field is classed as high volatile A bituminous, but there are significant changes within and beyond this category. These are related to the observation that the coalification is essentially post-deformational. This has resulted in an increase in rank with depth, as well as regionally from west to east within the same seam. Coke stability data indicate that these rank changes are economically favourable, because the coking characteristics of the coal improve with depth and towards the east. Petrographically, a normal, banded bright coal is represented, consisting of alternating bands of vitrite, clarite, clarodurite, durite and fusite. Durite bands occur sporadically, rarely exceeding 3 cm, and are present as “inertinite-rich” durite and “exinite-rich” durite. The latter consists of a groundmass of matted exinite and some of these bands could be traced over a lateral distance of some 50 km within the Harbour seam section. Microlithotype analyses show that, within each seam section, four coal facies types can be recognized, namely: the forest-terrestrial-moor (Ftm), the forest-moor (FM), the reed-moor (RM) and the open-moor (OM) facies. All coal seams of the Sydney field have low ash yields, which range from 5% to 9%. However, the sulphur content is generally high and varies between seams from 2.5% to 6.2%. The average volatile matter content is 36% and calorific value averages 7,524 kcal/kg (13,545 Btu/lb).