Abstract
Carboniferous coals of the Ayrshire Coalfield are enriched in selenium (Se) relative to average UK and world compositions, substituting for sulphur in pyrite. Greenburn surface mine coals are characterized by syngenetic concretionary pyrite (c. 15% total area), occurring as bedding-parallel banding, and later-formed (epigenetic) cross-cutting pyrite in cleats (c. 9% total area). In these, sulphur isotope compositions for both syngenetic and epigenetic pyrite include isotopically light and heavy variants, suggesting diagenetic and hydrothermal fluid formation. Late/post-Visean cleat-filling pyrite is enriched in Se (up to 266 ppm) compared to the earlier-formed material (Se up to 181 ppm).
Anomalous Se may have been sourced from near-by sulphidic Dalradian metamorphic rocks. Initial Se sequestration is associated with syngenetic pyrite mineralization, absorbed from seawater and pore waters, with additional Se introduced from fluids mobilized during epigenetic pyrite formation. Cleats from local brittle fracturing provided channels for fluid flow and a locus for precipitation of comparatively high-Se pyrite. Permian dolerite intrusions may have provided an enrichment source and/or fluid distribution mechanism. The Se concentrations of the Greenburn coals relate to multi-stage mineralization, with cleat-filling pyrite showing the highest Se content, and highlight the potential for high Se in similarly altered and fractured coal deposits worldwide.
Anomalous Se may have been sourced from near-by sulphidic Dalradian metamorphic rocks. Initial Se sequestration is associated with syngenetic pyrite mineralization, absorbed from seawater and pore waters, with additional Se introduced from fluids mobilized during epigenetic pyrite formation. Cleats from local brittle fracturing provided channels for fluid flow and a locus for precipitation of comparatively high-Se pyrite. Permian dolerite intrusions may have provided an enrichment source and/or fluid distribution mechanism. The Se concentrations of the Greenburn coals relate to multi-stage mineralization, with cleat-filling pyrite showing the highest Se content, and highlight the potential for high Se in similarly altered and fractured coal deposits worldwide.
| Original language | English |
|---|---|
| Pages (from-to) | 37-49 |
| Number of pages | 13 |
| Journal | Scottish Journal of Geology |
| Volume | 54 |
| Issue number | 1 |
| Early online date | 10 Jan 2018 |
| DOIs | |
| Publication status | Published - May 2018 |
Bibliographical note
The authors wish to thank Kier Group for site access and providing seam-constrained Greenburn Surface Mine Complex coal samples. We thank David Richardson (Kier Group) for sharing his knowledge of the Greenburn site and local geology, as well as additional average sulphur content seam data. Critical comments from David A. Spears, Yakov E. Yudovich and Colin J R Braithwaite are gratefully acknowledged. Funding provided by NERC Security of Supply programme (grant NE/L001764/1).Supplementary material: LA-ICP-MS maps for Fe, Se, Ag, As, Cu, Hg, Pb and Te for Greenburn coal samples from seams
9300 Lime and 6900 Burnfoot Bridge are available at https://doi.org/10.6084/m9.figshare.c.3967860