Economic mineralisation of the Loch Maree Group and tectonic correlation of the Lewisianoid inliers of Scardroy and Orrin

McIntosh, Euan (2021) Economic mineralisation of the Loch Maree Group and tectonic correlation of the Lewisianoid inliers of Scardroy and Orrin. MSc(R) thesis, University of Glasgow.

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This project has twin aims: examining sulphide mineralisation within the Lewisian hosted Loch Maree Group (LMG) whilst testing correlation of the Gruinard Belt and Flowerdale inliers with the LMG, and dating along strike poorly studied Lewisianoid inliers within the Moine. This will provide a better understanding of the continuity – or not – of basement structures, and hence potential mineralisation, across the Moine Thrust. Whole rock multi-element assay, major and trace element analysis, and U-Pb dating of zircon were conducted across four main field areas of both economic and tectonic interest. These were: 1) the Gairloch Schist Belt of the LMG and Flowerdale inliers; 2) the Gruinard Belt; 3) the Scardroy inliers; 4) the Orrin inlier.

Exploration of the Gairloch Schist Belt reveals, in addition to the Kerry Road deposit, widespread but dominantly very low-grade sulphide mineralisation. An inlier of exhalative lithologies at Flowerdale is very likely correlatable with the main exposure of the Belt and records potentially economic grades of Au worthy of further investigation. A second inlier of highly altered ultra-mafic rocks remains enigmatic in both origin and position relative to the LMG or basement Lewisian. The Gruinard Belt records a late-Laxfordian age c. 1780 – 1670 Ma and hence cannot be correlated with the LMG as proposed by previous studies. It instead is considered to represent a separate association of supra-crustal material tectonically introduced into the basement gneisses c. 200 Ma after the accretion of the LMG. A well-defined Caledonian aged Pb-loss event and related zircon growth requires further study but may be related to fluid flow and heating during Caledonian nappe stacking.

Gneisses from the Scardory and Orrin inliers record dominantly Archean U-Pb protolith ages (c. 2.7 – 2.85 Ga) with Laxfordian and Renlandian metamorphic signatures while one sample presents a c. 1.7 Ga protolith age, suggesting Laxfordian magmatism within the inlier. This history, along with geochemical analysis of associated mafic and intermediate rocks, supports correlation with the Lewisian of the foreland and any Baltican heritage for the basement to the Northern Highlands is not expressed in this area. The shared basement between Hebridean and Northwest Highland terranes, as evidenced by correlation of Lewisianoid inliers with the foreland, allows for the LMG, associated mineralisation, and late-Laxfordian supracrustal rocks to exist east of the Moine Thrust. Although exactly along strike there is no evidence of LMG like rocks at Scardroy, likely due to lateral displacement across Moine thrust, however the belt may exist at depth below overlying Moinian cover.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Subjects: G Geography. Anthropology. Recreation > GB Physical geography
Q Science > QE Geology
Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences > Earth Sciences
Supervisor's Name: Neill, Dr. Iain
Date of Award: 2021
Depositing User: Theses Team
Unique ID: glathesis:2021-82545
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 29 Oct 2021 10:51
Last Modified: 29 Oct 2021 10:59
Thesis DOI: 10.5525/gla.thesis.82545

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