Rank and Petrographic Composition of Selected Jurassic - Lower Cretaceous Coals of British Columbia, Canada

Abstract

ABSTRACT Rank and composition of Jurassic - Lower Cretaceous coals from four localities in the Crowsnest and Peace River Coalfields of British Columbia are described. The coals obtained from the Crowsnest Coalfield represent so called needle coals from the Elk Formation of the Kootenay Group, whereas coals of the Peace River Coalfield were obtained from the Gorman Creek and Bickford Formations of the Minnes Group and from the Gething Formation of the Bullhead Group. Rank, determined by vitrinite reflectance measurements, ranges from subbituminous C in the Crowsnest Coalfield to medium volatile bituminous in the Peace River Coalfield. Composition was determined by maceral analysis. Results indicate that, in general, coals from the Elk Formation in the south and from the Gorman Creek and Bickford Formations in the north are characterized by moderate to high concentrations of macerals of the liptinite group (alginite, sporinite and cutinite) and very small amounts of semifusinite and inerts. This maceral composition, together with occurrences of boghead (algal-rich) and cannel (spore-rich) layers associated with mainly unstructured vitrinite, is interpreted as an indication of a reed swamp to open-water swamp depositional environment. In certain parts of the Peace River Coalfield, increase of rank with depth (Hilt's Law) is masked by maceral composition. In some sections there is no rank change with increase in depth; instead, vitrinite reflectances are controlled by the total amount of liptinites in a given coal sample. The reflectance of vitrinite decreases gradually with increase in liptinite content. This effect is interpreted as being caused by diffusion of bituminous substances out of the liptinite macerals into the surrounding vitrinites. Coking and liquefaction properties of the coal are discussed. It can be demonstrated that low- to intermediate-rank coals from the Crowsnest and Peace River Coalfields, characterized by high amounts of so-called reactive macerals (vitrinite and liptinite), are excellent feed coals for liquefaction. They are, however, too low in rank and too rich in reactive macerals to produce a strong coke. Good coking properties are predicted for the higher-rank coals from the Peace River Coalfield, which are characterized by increasing amounts of inert macerals.