Rank variation, coalification pattern and coal quality in the Crowsnest coalfield, British Columbia

CIM Bulletin, Vol. 78, No. 881, 1985

DAVID E. PEARSON, David E. Pearson & Associates Ltd., Victoria, British Columbia, and DAVID A. GRIEVE, British Columbia Ministry of Energy, Mines & Petroleum Resources, Fernie, British Columbia

A rank-map of Crowsnest coalfield, showing the distribution of the bituminous coal measures and the locations of major structures, has been produced from vitrinite reflectance measurements on over 600 coal samples. The timing of coalification in relation to these major structures has also been determined. In the west-central portion of the coalfield a complete stratigraphic succession of coal measures which rides on major thrust surfaces is all of high-volatile bituminous rank, but despite the structural discordance no break in rank is discernible across these structures. The thrust faults therefore predate much of the coalification. Three major valleys expose cross sections of the folded coal measures and in each an increase in vitrinite reflectance is demonstrable as individual seams are traced from ridge crest to valley floor. Thus, in these sections, a significant amount of coalification post-dates folding. The proportion of this post-folding coalification is found to increase toward the south of the coalfield. A late gravity-fault, exposed along the east crop of the coalfield, places high-volatile coal-bearing successions in contact with low-volatile coal and demonstrably is a reactivated thrust fault. Coalification at this locality occurred between these two different ages of faulting. The variations in rank and the subtleties of the coalification pattern have, together with systematic changes in the maceral composition of coal seams, had a profound effect on coal quality in the coalfield. Coking coals with a variety of properties occur together with some coals that have no caking capacity.

Mots Clés: Coal preparation, Coalification, Rank gradients, Stratigraphy, Coal quality, Structural setting, Crowsnest coalfield.