Framboids by David Rickard;

Author:David Rickard;
Language: eng
Format: epub
Publisher: OUP Premium
Published: 2021-02-15T00:00:00+00:00

9.2.2. Trace Elements in Pyrite in Coal

The trace element contents of pyrite in coal have been the subject of extensive investigations because of their health impacts, and environmental and economic importance. Elements such as Hg can lead to hazardous air pollutants during combustion of coal feed, and As is an important potential hazard in acid mine drainage; both elements are potentially hazardous to health. From the scientific point of view, coal is derived mainly from freshwater peat deposited in a dominantly terrestrial environment and thus these data could complement the data from dominantly marine sediments. However, sulfur-rich coals, which contain more abundant pyrite, are characteristically affected by marine incursions (Chou, 2012) and therefore their pyrite trace element contents should be similar to those of other marine sediments. A further problem is that pyrite in coal is formed during its whole geologic history and not just during the early peat stage. For example, coal basins are widely subject to regional fluid migration (Gayer and Rickard, 1994) leading especially to the deposition of vein- and cleat-filling pyrite, often enriched in trace elements such as As, Se, Mo, Sb, Tl, Cu, and Hg (e.g., Diehl et al., 2004; Diehl et al., 2012). Even the pyrite in the original peat may also show several generations, although the earliest generation is often framboid-rich. Of course, not all framboids are from this early generation, and framboids also act as centers for further deposition of later pyrites, as in marine sediments.

The reports of the trace and minor elements in pyrite in coals show extreme variations in the concentrations of these elements (e.g., Kolker, 2012), even exceeding those of pyrite in marine sediments. There is a general thesis that the earliest generations of pyrite in coals have lower trace element loads than later generations. However, a contemporary study of the trace element concentrations of pyrite in peat, which would help determine the contribution of early generations of pyrite, has not been reported.

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