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The structure and petrology of the Cnoc nan Cuilean Intrusion, Loch Loyal Syenite Complex, NW Scotland

Hughes, Hannah S. R., Goodenough, Kathryn M., Walters, Abigail S., McCormac, Michael, Gunn, A. Gus and Lacinska, Alicja 2013. The structure and petrology of the Cnoc nan Cuilean Intrusion, Loch Loyal Syenite Complex, NW Scotland. Geological Magazine -London- 150 (5) , pp. 783-800. 10.1017/S0016756812000957

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In NW Scotland, several alkaline intrusive complexes of Silurian age intrude the Caledonian orogenic front. The most northerly is the Loch Loyal Syenite Complex, which is divided into three separate intrusions (Ben Loyal, Beinn Stumanadh and Cnoc nan Cuilean). Mapping of the Cnoc nan Cuilean intrusion shows twomain zones: a Mixed Syenite Zone (MZ) and a Massive Leucosyenite Zone(LZ), with a gradational contact. The MZ forms a lopolith, with multiple syenitic lithologies, including early basic melasyenites and later felsic leucosyenites. Leucosyenite melts mixed and mingled with melasyenites, resulting in extreme heterogeneity within the MZ. Continued felsic magmatism resulted in formation of the relatively homogeneous LZ, invading western parts of the MZ and now forming the topographically highest terrane. The identification of pegmatites, microgranitic veins and unusual biotite-magnetite veins demonstrates the intrusion’s complex petrogenesis. Cross-sections have been used to create a novel 3D GoCadTM model contributing to our understanding of the intrusion. The Loch Loyal Syenite Complex is known to have relatively high concentrations of rare earth elements(REEs), and thus the area has potential economic and strategic value. At Cnoc nan Cuilean, abundant REE-bearing allanite is present within melasyenites of the MZ. Extensive hydrothermal alteration of melasyenites here formed steeply dipping biotite-magnetite veins, most enriched in allanite and other REE-bearing accessories. This study has thus identified the area of greatest importance for further study of REE enrichment processes in the Cnoc nan Cuilean intrusion.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Uncontrolled Keywords: Sutherland; Caledonian; rare earth elements; allanite; indigenous resources.
Publisher: Cambridge University Press
ISSN: 0016-7568
Funders: Natural Environment Research Council
Date of First Compliant Deposit: 30 March 2016
Last Modified: 15 May 2023 14:17

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