Multi-stage pyrite genesis and epigenetic selenium enrichment of Greenburn coals (East Ayrshire)

Liam A. Bullock (Corresponding Author), John Parnell, Magali Perez, Adrian Boyce, Joerg Feldmann, Joseph G. T. Armstrong

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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.
Original languageEnglish
Pages (from-to)37-49
Number of pages13
JournalScottish Journal of Geology
Volume54
Issue number1
Early online date10 Jan 2018
DOIs
Publication statusPublished - May 2018

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selenium
pyrite
coal
mineralization
Dalradian
Visean
fluid
sulfur isotope
diabase
hydrothermal fluid
coal mine
metamorphic rock
fluid flow
porewater
Permian
sulfur
seawater

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Multi-stage pyrite genesis and epigenetic selenium enrichment of Greenburn coals (East Ayrshire). / Bullock, Liam A. (Corresponding Author); Parnell, John; Perez, Magali; Boyce, Adrian; Feldmann, Joerg; Armstrong, Joseph G. T.

In: Scottish Journal of Geology, Vol. 54, No. 1, 05.2018, p. 37-49.

Research output: Contribution to journalArticle

Bullock, Liam A. ; Parnell, John ; Perez, Magali ; Boyce, Adrian ; Feldmann, Joerg ; Armstrong, Joseph G. T. / Multi-stage pyrite genesis and epigenetic selenium enrichment of Greenburn coals (East Ayrshire). In: Scottish Journal of Geology. 2018 ; Vol. 54, No. 1. pp. 37-49.
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title = "Multi-stage pyrite genesis and epigenetic selenium enrichment of Greenburn coals (East Ayrshire)",
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.",
author = "Bullock, {Liam A.} and John Parnell and Magali Perez and Adrian Boyce and Joerg Feldmann and Armstrong, {Joseph G. T.}",
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",
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N1 - 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

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N2 - 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.

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