Epigenetic pyrite in a low-sulphur, sub-bituminous coal from the central Alberta Plains

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Pyrite of epigenetic origin occurs locally within the Highvale No. 2 coal seam of the central Alberta Plains. Discrete pyrite crystals appear as euhedral octahedrons (10-20 μm in size) which may coalesce and from sheets which are present on the cleat face of the coal. Iron-rich groundwaters have reacted with reduced sulphur, on and near the surface of the coal cleat and precipitated this sulphide. The source of the reduced sulphur is probably the coal itself. Distribution of pyrite within this seam is governed by cleat frequency, which, in turn, is governed by coal petrography and geochemistry. In the lower part of this seam the coal is bright, ash content is low (< 10%), the cleat is well developed and pyrite is present. In contrast, in the upper part of this seam the coal is predominantly dull, due to high intertinite maceral content and high ash (15-20%), the cleat is poorly developed and pyrite is not observed. Timing of formation of this pyrite is undetermined, but is post-cleat development. © 1992.

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International Journal of Coal Geology

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