Contrasting mechanisms for crustal sulphur contamination of mafic magma: evidence from dyke and sill complexes from the British Palaeogene Igneous Province

Hughes, H. S. R., Boyce, A. J. , McDonald, I., Davidheiser-Kroll, B., Holwell, D. A., McDonald, A. and Oldroyd, A. (2015) Contrasting mechanisms for crustal sulphur contamination of mafic magma: evidence from dyke and sill complexes from the British Palaeogene Igneous Province. Journal of the Geological Society, 172(4), pp. 443-458. (doi:10.1144/jgs2014-112)

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Abstract

The addition of crustal sulphur to magma can trigger sulphide saturation, a process fundamental to the development of some Ni–Cu–PGE deposits. In the British Palaeogene Igneous Province, mafic and ultramafic magmas intrude a thick sedimentary sequence offering opportunities to elucidate mechanisms of magma–crust interaction in a setting with heterogeneous S isotope signatures. We present S-isotopic data from sills and dykes on the Isle of Skye. Sharp contrasts exist between variably light δ4S in Jurassic sedimentary sulphide (−35‰ to −10‰) and a local pristine magmatic δ34S signature of −2.3 ± 1.5‰. Flat-lying sills have restricted δ34S (−5‰ to 0‰) whereas steeply dipping dykes are more variable (−0‰ to −2‰). We suggest that the mechanism by which magma is intruded exerts a fundamental control on the degree of crustal contamination by volatile elements. Turbulent flow within narrow, steep magma conduits, discordant to sediments, and developed by brittle extension or dilation have maximum contamination potential. In contrast, sill-like conduits emplaced concordantly to sediments show little contamination by crustal S. The province is prospective for Ni–Cu–PGE mineralization analogous to the sill-hosted Noril’sk deposit, and Cu/Pd ratios of sills and dykes on Skye indicate that magmas had already reached S-saturation before reaching the present exposure level.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Boyce, Professor Adrian and McDonald, Mrs Alison
Authors: Hughes, H. S. R., Boyce, A. J., McDonald, I., Davidheiser-Kroll, B., Holwell, D. A., McDonald, A., and Oldroyd, A.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Journal of the Geological Society
Publisher:Geological Society of London
ISSN:0016-7649
ISSN (Online):2041-479X
Copyright Holders:Copyright © 2015 The Authors
First Published:First published in Journal of the Geological Society 172(4):443-458
Publisher Policy:Reproduced under a Creative Commons License
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