Coal rank changes in the Sydney and Pictou coalfields of Nova Scotia; cause and economic significance

CIM Bulletin, Vol. 77, No. 865, 1984

PETER A. HACQUEBARD, Geological Survey of Canada, Atlantic Geoscience Centre, Bedford Institute of Oceanography, Dartmouth, Nova Scotia

The coals of the Sydney and Pictou coalfields are generally classed as high volatile "A " and medium volatile bituminous coals but there are significant differences within and even beyond this rank. These are related to the observation that the coalification in eastern Canada is essentially post-defor-mational, resulting in a general increase of rank with depth in individual seams. Exploration drilling in the Sydney coalfield has shown that the rank increases offshore to M. V. bituminous at mineable depths and in the Pictou field to L. V. bituminous coal. There is also a marked easterly shift in rank within one seam at the same depth at Sydney, with the result that M. V. coal will be reached sooner in the Donkin Reserve area (at 700 m depth) than in the Lingan-No. 26 Reserve area (at 900 m depth). These rank changes are important for the manufacturing of metallurgical coke as shown with coke stability predictions based on petrographic analyses. The L. V. coal of the Pictou field can be used for blending purposes and is the only known L. V. deposit of mineable thickness in eastern Canada. In addition, the vertical rank changes between seams have been studied in ten boreholes. They are not constant within the confines of the Sydney coalfield. Four separate areas can be recognized, each with different coalification gradients, which can be related to changes in the paleogeothermal gradients. Variations of 2.5 degrees to 6.7 degrees C/100 m are indicated and geological causes for these changes are suggested.

Keywords: Coal mining, Coal rank, Sydney coalfield, Pictou coalfield, Coalification, Geology, Coking