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dc.contributor.authorFinch, Adrian A.
dc.contributor.authorMcCreath, Jamie A
dc.contributor.authorReekie, Callum D.J.
dc.contributor.authorHutchison, William
dc.contributor.authorIsmaila, Abdulmalik
dc.contributor.authorArmour-Brown, Ashlyn
dc.contributor.authorAndersen, Tom
dc.contributor.authorSimonsen, Siri L.
dc.identifier.citationFinch , A A , McCreath , J A , Reekie , C D J , Hutchison , W , Ismaila , A , Armour-Brown , A , Andersen , T & Simonsen , S L 2019 , ' From Mantle to Motzfeldt : a genetic model for syenite-hosted Ta,Nb-mineralisation ' , Ore Geology Reviews , vol. 107 , pp. 402-416 .
dc.identifier.otherPURE: 258217284
dc.identifier.otherPURE UUID: 1c0c9c45-c0f6-4e77-bf5c-d61fd8794870
dc.identifier.otherRIS: urn:AD6D017CC88B05EE6AFB9FCF81D7BC3D
dc.identifier.otherScopus: 85062609822
dc.identifier.otherORCID: /0000-0002-3689-1517/work/55643768
dc.identifier.otherWOS: 000470194300026
dc.descriptionThis research summarises many years of field and lab studies on the area, but the most recent work (2016) has received funding from the European Union’s Horizon 2020 research and innovation programme (grant agreement No 689909).en
dc.description.abstractA genetic model for the Motzfeldt Tantalum-Niobium-rich syenite in south-west Greenland, considered to be one of the world’s largest Ta prospects, is presented. The Motzfeldt primary magma formed early in regional Gardar (1273 ± 6 Ma) rifting. Isotope signatures indicate that the Hf had multiple sources involving juvenile Gardar Hf mixed with older (Palaeoproterozoic or Archaean) Hf. We infer that other High Field Strength Elements (HFSE) similarly had multiple sources. The magma differentiated in the crust and ascended before emplacement at the regional unconformity between Ketilidian basement and Eriksfjord supracrustals. The HFSE-rich magmas crystallised Ta-rich pyrochlore which formed pyrochlore-rich crystal mushes, and it is these pyrochlore-rich horizons, rich in Ta and Nb, that are the focus of exploration. The roof zone chilled and repeated sheeting at the roof provided a complex suite of cross-cutting syenite variants, including pyrochlore microsyenite, in a ‘Hot Sheeted Roof’ model. The area was subject to hydrothermal alteration which recrystallized alkali feldspar to coarse perthite and modified the mafic minerals to hematite, creating the friable and striking pink-nature of the Motzfeldt Sø Centre. Carbon and oxygen isotope investigation of carbonate constrains fluid evolution and shows that carbonate is primarily mantle-derived but late-stage hydrothermal alteration moved the oxygen isotopes towards more positive values (up to 21‰). The hydrothermal fluid was exceptionally fluorine-rich and mobilised many elements including U and Pb but did not transport HFSE such as Ta, Hf and Nb. Although the U and Pb content of the pyrochlore was enhanced by the fluid, the HFSE contents remained unchanged and therefore Hf isotopes were unaffected by fluid interaction. While the effect on hydrothermal alteration on the visual appearance of the rock is striking, magmatic processes concentrated HFSE including Ta and the hydrothermal phase has not altered the grade. Exploration for HFSE mineralisation commonly relies on airborne radiometric surveying which is particularly sensitive to the presence of U, Th. A crucial lesson from Motzfeldt is that the best target is unaltered pyrochlore which was identified less easily by radiometric survey. Careful petrological/mineral studies are necessary before airborne survey data can be fully interpreted.
dc.relation.ispartofOre Geology Reviewsen
dc.rightsCopyright © 2019 The Author(s).en
dc.rightsCopyright © 2019 Elsevier B.V. All rights reserved. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and will be available following a 12-month embargo. The final published version of this work is available at
dc.subjectGardar Provinceen
dc.subjectHydrothermal alterationen
dc.subjectGE Environmental Sciencesen
dc.subjectQE Geologyen
dc.titleFrom Mantle to Motzfeldt : a genetic model for syenite-hosted Ta,Nb-mineralisationen
dc.typeJournal articleen
dc.contributor.institutionUniversity of St Andrews.School of Earth & Environmental Sciencesen
dc.contributor.institutionUniversity of St Andrews.Scottish Oceans Instituteen
dc.contributor.institutionUniversity of St Andrews.St Andrews Isotope Geochemistryen
dc.description.statusPeer revieweden

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