Earth Sciences Report 1989-02

Author(s) Date 1988-12-31

This report is the conclusion of a three-part series that describes and attempts to explain regional coal quality variations within the foothills/mountains region of Alberta. Proximate and ultimate analysis variables, plus some vitrinite reflectance and maceral analyses, are examined for the Jurassic-Lower Cretaceous Kootenay Group, Lower Cretaceous Luscar Group, the Lower Paleocene Coalspur Formation, and the Upper Paleocene Obed-Marsh coal bearing units.

The study has two major components: 1) a statistical analysis and mapping of coal quality data provided by the Energy Resources Conservation Board, and 2) a geologic models section, in which regional and local in-seam coal quality variations are examined from a geological perspective. The first component is designed to describe, characterize, and set limits for the coal quality variables while the second component should provide from a geological perspective, insight as to why and how these quality parameters vary as they do.

The statistical analyses and maps of coal-rank related variables (e.g. volatile matter, fixed carbon, calorific value, and vitrinite reflectance) show that coals in this region range from semianthracite to subbituminous A and that the present suite of data is sufficient to describe the regional rank variations within the four coal-bearing units. Coal quality variables related to the original depositional environment (e.g. ash and sulfur) show highly variable regional and statistical distributions. These variables must be examined on a local, individual seam and in-seam basis. On a regional scale, there is insufficient data set to accurately describe these variables.

The geologic models section shows that coal rank for the base of the Gates Formation parallels, the disturbed belt, and in general, decreases toward the disturbed belt. This distribution is explained by a combination of original depth of burial in the foreland basin and a minor syndeformational coalification component. Coals at the base of the Kootenay Group increase in rank from south to north. Coalification of the Kootenay coals is thought to be related to a combination of depth of burial, geothermal gradient, and deformational history. The coalification pattern of the Coalspur Formation and Obed-Marsh coals is largely predeformational.

Ash content of these coals is generally separable into three components: inherent ash derived from original plant mineral matter, water derived clastic partings, and air deposited volcanic ash horizons. Water derived clastic partings are usually thick enough, from a mining perspective, to be easily removed from the coal. Inherent ash contents tend to vary vertically and laterally within a seam, often being lowest near the middle of the seam. Thin, airborne volcanic ash partings are usually impossible to separate during mining; they also tend to be high in montmorillonitic minerals and sometimes double the overall mined ash content from that expected with inherent ash only.

Sulfur values for all coals examined are very low (0.2-0.5%, db) by international coal standards. However, elevated values commonly occur at the base, top and immediately below major waterborne clastic partings or overlying fluvial or tidal deposits. These elevated values are typically only in the 0.5-0.7% (db) range, though values as high as 3.0% (db) have been recorded for some seams.

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Macdonald, D.E., Langenberg, C.W. and Gentzis, T. (1989): A regional evaluation of coal quality in the foothills/mountains region of Alberta; Alberta Research Council, ARC/AGS Earth Sciences Report 1989-02, 76 p.