Magmas, fluids, faults and metals
Re-assessing the controls on magmatic-hydrothermal W-Sn-Cu-As-Zn-Pb mineralisation and zonation associated with the Cornubian Batholith, SW England.
The W-Sn-Cu-As-Zn-Pb ore field, centred upon the Early Permian Cornubian Batholith, is a global exemplar of magmatic-hydrothermal mineralisation associated with peraluminous granites and mineral zonation, where there is often a progressive change in dominant mineral assemblage with distance from the granite (W-Sn ± As proximal and Cu, Zn and Pb distal).
The heterogeneous distribution of metals and mineralisation styles around “emanative centres”, including the anomalous occurrence of substantial Cu with peraluminous granite, indicates a complex relationship between magmatism, separation of magmatic volatile phases, faulting and fluid mixing.
Changes in source melting and differentiation control the broad distribution of granite types and metal prospectivity (Simons et al., 2017).
The focus of this project is to characterise the fluid types involved in mineralisation and how their structurally controlled migration and mixing has controlled variations in the distribution of mineral assemblages and metals.
The project is focussed upon the systematic analysis of melt and fluid inclusions in different granite types and mineralisation styles from across the SW England orefield. These will be used to determine:
- The compositional variability of primary exsolved magmatic-hydrothermal fluids and their control by evolving melt compositions.
- The parameters controlling precipitation of ore metals from these solutions (e.g. cooling, phase separation, wall-rock reaction).
Careful sample mineralogy and petrography, including SEM, QEMSCAN and cathodoluminescence techniques, will underpin the fluid inclusion microanalysis using microthermometry and laser ablation ICP-MS.
Isotopic analysis of minerals will be used to evaluate alternative models for the source and evolution of fluids. These data will be combined with the distribution of syn-magmatic fault systems and historical metal production, to provide a re-evaluation of the controls on mineralisation, mineral zonation and the origin of 'emanative centres'.
The project will utilise material from collections at the Natural History Museum, Imperial College London and Camborne School of Mines but will require fieldwork to collect samples from areas where cross-cutting relationships between intrusions and vein sets can be documented in detail.
Current and recent exploration by the CASE partners has provides an unparalleled opportunity to sample from diamond drill core samples.
Supervision and training
The student will spend 90% of their time at the University of Exeter (UoE) where they will be based for their fieldwork and receive training in GIS/sample collection/preparation, transmitted/reflected microscopy, SEM/QEMSCAN (automated SEM), cathodluminescence, electron probe microanalysis and preliminary microthermometric evaluation of inclusion fluids.
The student will spend 10% of their time at the Natural History Museum (CASE partner institution) where they will receive training in laser ablation ICP-MS analysis of granite melt inclusions and inclusion fluids in granite-hosted magmatic quartz and inclusion fluids in representative hydrothermal vein parageneses.
We are looking for a well-qualified and highly motivated Earth Sciences/Geology graduate who wishes to carry out a PhD in mineralogy/petrology and economic geology. Excellence in geochemistry and mineralogy are essential; experience of microanalytical techniques and statistical data evaluation are desirable.
How to apply
Apply for this PhD through the Exeter University website.
The closing date for applications is Friday 8 January 2021 23:59 GMT. Interviews will be held between 8 and 19 February 2021. For more information about the NERC GW4+ Doctoral Training Partnership please visit nercgw4plus.ac.uk
Simons, B.J., Shail, R.K. & Andersen, J. 2016. The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England. Lithos, 260, 76-94.
Simons, B.J., Andersen, J.C.Ø., Shail, R.K. & Jenner, F.E. 2017. Fractionation of Li, Be, Ga, Nb, Ta, In, Sn, Sb, W and Bi in the peraluminous Early Permian Variscan granites of the Cornubian Batholith: precursor processes to magmatic-hydrothermal mineralisation. Lithos, 278-281, 491-512.
Wilkinson, J.J., Stoffell, B., Wilkinson, C.C., Jeffries, T.E. & Appold, M.S. 2009. Anomalously metal-rich fluids form hydrothermal ore deposits. Science, 323, 764-767.