Metallogenesis of Cobalt-bearing Mineralisation in the English Lake District

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Metallogenesis of Cobalt-bearing Mineralisation in the English Lake District
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Adam Edward Eskdale

A thesis submitted for the degree of
Doctor of Philosophy
of
Royal Holloway, University of London


Department of Earth Sciences
Royal Holloway, University of London
29th September 2023
Thesis Information
Project Title: Metallogenesis of Cobalt-bearing Mineralisation in the English Lake District
Student Name: Adam Edward Eskdale
Student Number: 100931540
Supervisory Team:
1. Dr Dave Lowry (primary supervisor), Department of Earth Sciences, RHUL.
2. Dr Amy Gough (secondary supervisor), Heriot-Watt University, Edinburgh.
3. Dr Sean Johnson (secondary supervisor), University College, Dublin.
4. Dr Queenie Chan (internal advisor), Department of Earth Sciences, RHUL.
External Examiner: Dr Kathryn Goodenough, Principal Geologist, British Geological Survey Edinburgh.
Internal Examiner: Dr Alexander Dickson, Professor in Geochemistry, Department of Earth Sciences, RHUL.
Submitted for Examination: 29/09/ 2023
Viva Examination: 18/12/ 2023
Re-submitted with corrections: 18/03/ 2024

Author Declaration
I, Adam Edward Eskdale, hereby declare that this thesis and the work presented in it is entirely my own. Where I have consulted the work of others, this is always clearly stated.
The word counts stated here are exclusive of reference lists and any additional article information provided by the publisher which is not part of the main body of text.
Word count: 55,870
Word count (inclusive of appendices, references, figure captions): 98,812 
Abstract
Cobalt (Co) is essential in the development of carbon-neutral technologies with high criticality due to a significant lack of currently known primary Co-bearing deposits. This situation has facilitated a surge of research interest within the European and UK space. This study investigates and compiles data on the occurrence and distribution of polymetallic, vein-hosted, Co-bearing mineralisation across metallogenetic terranes in Canada, Scandinavia, and the UK. This demonstrates the polymetallic vein-type mineralisation is prevalent across Wales, SW England, the Canadian Shield, and Caledonian Norway with strong associations to NE-SW trending structures, felsic intrusives, and Paleoproterozoic - Paleozoic volcano-sediments. These metallogenetic characteristics are comparable to Ulpha, Scar Crag, and Dale Head mine localities in the UK Lake District, a case study area to understand the genesis behind this style.
Co-bearing mineralisation is identified at Ulpha historic mining sites as cobaltite (CoAsS) growths and trace element concentrations within associated As-Bi-Cu-Fe sulphides. These sulphides and sulpharsenides represent a novel paragenetic sequence for the locality. Local host rock geochemical concentrations indicate the Skiddaw Group is the likely source of Co, which alongside base metals were leached and re-concentrated by circulating hydrothermal fluids as a result of Ordovician – Devonian magmatism emanating heat. Sulphur isotopic studies of sulphide minerals at Ulpha and at two other Co-bearing sites in the region (Scar Crag, Dale Head North), further indicate the likely source of ore-sulphur is the underlying Skiddaw Group shale lithology, with possible influence from the Borrowdale Volcanic Group (BVG) at Ulpha.
The UK ‘Geochemical Baseline Survey of the Environment’ (G-BASE) stream sediment geochemical dataset was utilised, the dimensionality of the multivariate G-BASE data reduced resulting in geochemical maps that correlate strongly with regional, 625k scale geological boundaries for the Skiddaw Group, Borrowdale Volcanic Group, and Ordovician-Devonian felsic intrusives. These combined with the geological factors highlighted to associate with Co-bearing vein mineralisation identified ten prospective areas for Co-bearing mineralisation, six of which were visited in-field: Black Combe, Devoke Water, Coniston, Tilberthwaite, Seathwaite, and Keld. Base metal sulphides were identified as disseminations in the local volcano-sedimentary host rocks or in quartz-chlorite veins, reflecting similar mineral textures and assemblages to the Co-bearing veins.