- The magnetic susceptibility of granite is affected by the action hydrothermal fluids that serves to leach out or deposit new magnetic minerals.
- Hydrothermal alteration can occur during emplacement and crystallisation, associated with the alteration of granitic mineral (greissenisation), deposition of key resources (Li, U) and be an indicator of geothermal potential.
- Clear sustainability and resource potential applications and links.
Granite intrusions are key targets for deep geothermal energy and for key strategic resources needed for mobile and renewable technologies (e.g., Lithium, Tin, Tungsten, Tantalum, Ceasium and Rubidium). The way these resources are concentrated geologically is related to both emplacement and crystallisation of the granite body and subsequent exposure to hydrothermal systems. Hydrothermal fluids can originate from within the granite magma from volatiles concentrated as it crystallises and from meteoric fluids that circulate through fault zones that intersect the intrusion. The key exploration targets are hydrothermally altered zones within and around the granite intrusion where economically important minerals are found in exploitable concentrations.
Understanding of the structures and focussing mechanisms of economic domains from exposed rocks is needed enhance the geological models and predictive targets for new deposits within granites.
Marginal pegmatite rich, aplitic and leucocratic zones in granite plutons often exhibit markedly lower magnetic susceptibility (e.g., Stevenson et al., 2007; Stevenson 2009). Unpublished pilot data from the Tregonning Granite, Cornwall, show negative magnetic susceptibilities in those areas. In these cases the accumulation of volatiles has altered the granite and reduced the amount of iron bearing minerals such as magnetite, leading to a lower magnetic susceptibility. In this project we will study the magnetic properties of the regions within an immediately around granite intrusions affected by hydrothermal alterations, which typically carry economically relevant minerals. The overarching aim of this project is to assess the viability of magnetic susceptibility as an exploration tool. To this aim, our objectives are to carry out detailed rock magnetic and structural geological analyses that will establish the connection between magnetic mineralogy, faults (which controls hydrothermal alteration paths) and mineralisation in granite bodies The events will be linked to radio-isotopic geochronological data to interpret how and when these features evolved from magma to late alteration (a 4-dimensional view).
Figure 1: Screen shot from a 3D photogrammetric model of Rinsey Cove, Cornwall, part of the Tregonning Granite. https://skfb.ly/o7KJI
Work will include field work involving structural and mineralogical mapping of key granite sections. This mapping will use digital mapping and drone survey techniques (e.g., Fig. 1). Field work will primarily aim to collect a suite of oriented block samples form a range of hydrothermal granite outcrops. Potential field areas include Cornwall, Scotland, Ireland and can make use of existing samples in house and in collaboration with other ongoing projects.
HostUniversity of Birmingham
- Dynamic Earth
Carl Stevenson (Birmingham)
Marco Maffione (Birmingham)
Simon Tapster (BGS)
Chris Yeomans (Cornish Lithium)
Anya Lawrence (Birmingham)
Rock magnetic analyses: detailed magnetic characterisation of various lithologies will be performed in the PUMA paleomagnetic laboratory at the University of Birmingham. Magnetic characterisation involves measuring different magnetic properties including the remanence, bulk magnetic susceptibility and its variation at high and low temperature, anisotropy of magnetic susceptibility (AMS), isothermal remanent magnetization (IRM,) and anhysteretic remanent magnetization (ARM).
Structural and mineralogical mapping of granite sections: Digital capture techniques including digital mapping using FieldMOVE app, Gigapan and drone based photogrammetry 3D modelling. Structural models based on detailed field mapping will be carried out using MOVE suite.
Employ high-precision and novel isotopic tools at the Geochronology and Tracers Facility, BGS, to capture the timing of emplacement and alteration histories linked to the petrography of sample suite. Magmatic evolution will be constrained by ID-TIMS U-Pb of high temperature mineral phases. Whereas cooling and alteration histories will be constrained by in-situ Rb-Sr techniques utilising the Thermo NEOMA collision cell technology.
Training and skills
Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.
Technical training opportunities include field work on Cornish Granites and related hydrothermal deposits. This includes oriented sampling methods as well a structural geological analyses and mapping. Digital data capture will also form part of the field work including drone flying for photogrammetry capture and follow up structure from motion (SfM) processing. This data will be merged with geological 3D modelling software using industry leading MOVE suite.
The main laboratory training will be in rock magnetic analysis, using a variety of techniques used to characterise all the possible magnetic properties of a rock sample. The training and the analyses will be done in the PUMA paleomagnetic laboratory of the University of Birmingham.
The student will have training in state-of-the-art isotopic techniques and geochronology, as well as sample characterisation through the Rock Volume characterisation cluster at the BGS.
Partners and collaboration
As a pioneering mineral exploration and development company, Cornish Lithium are focused on environmentally responsible extraction of lithium from geothermal waters and hard-rock in the historic mining district of Cornwall. The region is largely under-studied given its world-class potential for critical raw materials such as lithium, copper, tin and tungsten that are all essential to the green transition. Furthermore, geopolitical agendas have pushed the need for domestic sources of these metals to be identified and extracted to reduce dependence on international imports and mitigate the impact on UK manufacturers from rising raw materials costs.
Further details on how to contact the supervisor for this project and how to apply for this project can be found here:
For any enquiries related to this project please contact Carl Stevenson, [email protected].
To apply to this project:
- You must include a CENTA studentship application form, downloadable from: CENTA Studentship Application Form 2024.
- You must include a CV with the names of at least two referees (preferably three) who can comment on your academic abilities.
- Please submit your application and complete the host institution application process via: https://sits.bham.ac.uk/lpages/LES068.htm. Please select the PhD Geography and Environmental Science (CENTA) 2024/25 Apply Now button. The CENTA application form 2024 and CV can be uploaded to the Application Information section of the online form. Please quote CENTA 2024-B42 when completing the application form.
Applications must be submitted by 23:59 GMT on Wednesday 10th January 2024.
Background theory, granite structural geology, magnetic theory, fieldwork planning and location selection, field sampling training, drone survey training, initial field campaign, initial magnetic analyses.
Magnetic analyses and characterisation experiment design, further fieldwork, structural modelling and analyses. Isotopic analyses.
Completion of magnetic and isotopic analyses and consolidation of granite hydrothermal and magnetic properties (publication on this), assessment of exploration methodology based on magnetic properties and development of calibration or key learnings and outputs (publication).
This project may also work with industry partners. Part of the work plan will involve initiating partnerships and there is therefore the opportunity to set up and carryout placements with relevant partners.
Stevenson, C.T., Owens, W.H. and Hutton, D.H., 2007. Flow lobes in granite: The determination of magma flow direction in the Trawenagh Bay Granite, northwestern Ireland, using anisotropy of magnetic susceptibility. Geological Society of America Bulletin, 119(11-12), pp.1368-1386.
Stevenson, C., 2009. The relationship between forceful and passive emplacement: The interplay between tectonic strain and magma supply in the Rosses Granitic Complex, NW Ireland. Journal of Structural Geology, 31(3), pp.270-287.