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Distribution, mineralogy and geochemistry of silica-iron exhalites and related rocks from the Tyrone Igneous Complex: Implications for VMS mineralization in Northern Ireland

Distribution, mineralogy and geochemistry of silica-iron exhalites and related rocks from the Tyrone Igneous Complex: Implications for VMS mineralization in Northern Ireland
Distribution, mineralogy and geochemistry of silica-iron exhalites and related rocks from the Tyrone Igneous Complex: Implications for VMS mineralization in Northern Ireland
Iron formations, hematitic cherts (jaspers), ‘tuffites’, silica-iron exhalites and other metalliferous chemical sedimentary rocks are important stratigraphic marker horizons in a number of volcanogenic massive sulfide (VMS) districts worldwide, forming during episodes of regional hydrothermal activity. The VMS prospective ca. 484–464 Ma Tyrone Igneous Complex of Northern Ireland represents a structurally dissected arc-ophiolite complex that was accreted to the composite margin of Laurentia during the Grampian orogeny (ca. 475–465 Ma), and a potential broad correlative to the VMS-rich Buchans–Robert's Arm arc system of the Newfoundland Appalachians. Silica-iron-rich rocks occur at several stratigraphic levels in the Tyrone Igneous Complex spatially and temporally associated with rift-related basalts (e.g., Fe–Ti-rich eMORB, IAT, OIB) and zones of locally intense hydrothermal alteration. In the ca. 475–474 Ma lower Tyrone Volcanic Group, these rocks are characterized by massive, 1–5 m thick blood-red jaspers, hematitic siltstones and mudstones, and intensely silica-hematite altered tuffs and flows. Their mineralogy is dominated by quartz–hematite ± magnetite–(chlorite-sericite ± tremolite/actinolite), with Fe concentrations rarely exceeding 10 wt.%. Relict textures (including the presence of coalesced spherules of silica-iron oxides) in rocks exposed at Tanderagee NW, Creggan Lough and Tory's Hole are indicative of seafloor exhalation, whereas replacement of the original volcanic stratigraphy is evident to varying degrees at Tanderagee, Beaghbeg and Bonnety Bush. In the structurally overlying ca. 473–469 Ma upper Tyrone Volcanic Group, chemical sedimentary rocks include recrystallized: (i) thin and laterally-restricted jaspers in thick sequences of graphitic pelite at Boheragh; and (ii) laterally-persistent sulfidic cherts and ironstones dominated by quartz–hematite–magnetite–(chlorite) or quartz–pyrite–(chlorite) in sequences of tuff at Broughderg. Compared to chemical sedimentary rocks associated with VMS deposits worldwide, their geochemical characteristics are most similar to silica-iron exhalites of the Mount Windsor Subprovince (SE Australia) and jaspers of Central Arizona, Bald Mountain (Northern Maine), the Urals, Iberian Pyrite Belt and Løkken ophiolite (Norway). Positive Eu anomalies (at Slieve Gallion and Tanderagee NW), elevated Cu + Pb + Zn, Au, Fe/Ti, Fe/Mn, Sb, Ba/Zr and Fe + Mn/Al, together with low REE, Sc, Zr and Th, are indicative of a greater hydrothermal component and potentially more VMS-proximal signatures. Based on bulk ironstone geochemistry, Bonnety Bush, Tanderagee NW-Creggan Lough, Broughderg and Drummuck (Slieve Gallion) are considered the most VMS prospective areas in the Tyrone Igneous Complex and warrant further exploration.
Iron formation, Ironstone, Jasper, Exhalite, Tuffite, VMS, Grampian, Taconic
0375-6742
148-168
Hollis, Steven P.
3dd0519f-bc6c-49c0-9cc2-9a8c5cac9aa1
Cooper, Mark R.
68d782fa-c882-41e0-a21e-b1a88bf34f99
Herrington, Richard J.
118a02cb-b04d-4110-a96a-a227ae6ccb8f
Roberts, Stephen
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Earls, Garth
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Verbeeten, Alicia
af7e61f9-cba7-4aab-abcb-123c39b7cbd6
Piercey, Stephen J.
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Archibald, Sandy M.
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Hollis, Steven P.
3dd0519f-bc6c-49c0-9cc2-9a8c5cac9aa1
Cooper, Mark R.
68d782fa-c882-41e0-a21e-b1a88bf34f99
Herrington, Richard J.
118a02cb-b04d-4110-a96a-a227ae6ccb8f
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
Earls, Garth
2cbfc172-8668-4180-8950-e2fbd27df51e
Verbeeten, Alicia
af7e61f9-cba7-4aab-abcb-123c39b7cbd6
Piercey, Stephen J.
f7f07830-ee80-4158-8438-799e38795f78
Archibald, Sandy M.
f8079c8d-15a4-44ad-b951-48300d4c24e1

Hollis, Steven P., Cooper, Mark R., Herrington, Richard J., Roberts, Stephen, Earls, Garth, Verbeeten, Alicia, Piercey, Stephen J. and Archibald, Sandy M. (2015) Distribution, mineralogy and geochemistry of silica-iron exhalites and related rocks from the Tyrone Igneous Complex: Implications for VMS mineralization in Northern Ireland. Journal of Geochemical Exploration, 159, 148-168. (doi:10.1016/j.gexplo.2015.09.001).

Record type: Article

Abstract

Iron formations, hematitic cherts (jaspers), ‘tuffites’, silica-iron exhalites and other metalliferous chemical sedimentary rocks are important stratigraphic marker horizons in a number of volcanogenic massive sulfide (VMS) districts worldwide, forming during episodes of regional hydrothermal activity. The VMS prospective ca. 484–464 Ma Tyrone Igneous Complex of Northern Ireland represents a structurally dissected arc-ophiolite complex that was accreted to the composite margin of Laurentia during the Grampian orogeny (ca. 475–465 Ma), and a potential broad correlative to the VMS-rich Buchans–Robert's Arm arc system of the Newfoundland Appalachians. Silica-iron-rich rocks occur at several stratigraphic levels in the Tyrone Igneous Complex spatially and temporally associated with rift-related basalts (e.g., Fe–Ti-rich eMORB, IAT, OIB) and zones of locally intense hydrothermal alteration. In the ca. 475–474 Ma lower Tyrone Volcanic Group, these rocks are characterized by massive, 1–5 m thick blood-red jaspers, hematitic siltstones and mudstones, and intensely silica-hematite altered tuffs and flows. Their mineralogy is dominated by quartz–hematite ± magnetite–(chlorite-sericite ± tremolite/actinolite), with Fe concentrations rarely exceeding 10 wt.%. Relict textures (including the presence of coalesced spherules of silica-iron oxides) in rocks exposed at Tanderagee NW, Creggan Lough and Tory's Hole are indicative of seafloor exhalation, whereas replacement of the original volcanic stratigraphy is evident to varying degrees at Tanderagee, Beaghbeg and Bonnety Bush. In the structurally overlying ca. 473–469 Ma upper Tyrone Volcanic Group, chemical sedimentary rocks include recrystallized: (i) thin and laterally-restricted jaspers in thick sequences of graphitic pelite at Boheragh; and (ii) laterally-persistent sulfidic cherts and ironstones dominated by quartz–hematite–magnetite–(chlorite) or quartz–pyrite–(chlorite) in sequences of tuff at Broughderg. Compared to chemical sedimentary rocks associated with VMS deposits worldwide, their geochemical characteristics are most similar to silica-iron exhalites of the Mount Windsor Subprovince (SE Australia) and jaspers of Central Arizona, Bald Mountain (Northern Maine), the Urals, Iberian Pyrite Belt and Løkken ophiolite (Norway). Positive Eu anomalies (at Slieve Gallion and Tanderagee NW), elevated Cu + Pb + Zn, Au, Fe/Ti, Fe/Mn, Sb, Ba/Zr and Fe + Mn/Al, together with low REE, Sc, Zr and Th, are indicative of a greater hydrothermal component and potentially more VMS-proximal signatures. Based on bulk ironstone geochemistry, Bonnety Bush, Tanderagee NW-Creggan Lough, Broughderg and Drummuck (Slieve Gallion) are considered the most VMS prospective areas in the Tyrone Igneous Complex and warrant further exploration.

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More information

Published date: December 2015
Keywords: Iron formation, Ironstone, Jasper, Exhalite, Tuffite, VMS, Grampian, Taconic
Organisations: Geochemistry

Identifiers

Local EPrints ID: 384083
URI: http://eprints.soton.ac.uk/id/eprint/384083
ISSN: 0375-6742
PURE UUID: c548f4ca-398d-4074-8bbc-ca93bf8769d6
ORCID for Stephen Roberts: ORCID iD orcid.org/0000-0003-4755-6703

Catalogue record

Date deposited: 16 Nov 2015 16:48
Last modified: 22 Oct 2019 00:57

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