About the Project
Project highlights
• Research that bridges the fields of igneous petrology and economic geology
• Placement with Carl Zeiss Microscopy to develop new automated approaches to mineral characterisation
• Fieldwork in the central/western US Rocky Mountains to understand magmatic processes in post-subduction settings and associated mineralisation
• Develop analytical experience with a range of high precision analytical instruments at a number of UK-based facilities
Gold, together with increasingly desirable ‘e-tech elements’ (tellurium, Te and selenium, Se) are commonly associated with alkali magmas formed in post-subduction settings. This link remains poorly understood. One suggestion is that these deposits form from hydrous magmas generated by partial melting of subduction-modified lithosphere and hydrous, sulphide-bearing cumulates in the roots of former volcanic arcs. When these fertile, hydrous residues experience a second stage of post-subduction melting, the redissolution of sulphides is thought to liberate elements such as Au, Te and Se. However, the role of cumulates and other subduction-modified sources in the formation of post-subduction magmas and their consignment of economically important elements remains largely untested.
This project will use a suite of robust accessory minerals found in such magmatic systems, including zircon, apatite, titanite, and magnetite to develop a petrogenetic model for post-subduction magmatism and mineralisation. The robust nature of accessory minerals means that they may often be inherited from deeper and unexposed parts of the magmatic system. They may also carry with them a cargo of less resilient minerals (such as magmatic sulphides) in the form of inclusions. Compositional zoning combined with high precision analytical techniques also offer an exciting opportunity to develop a time-sequential record of key magmatic processes.
Cenozoic magmatism in the central and western United States was initially subduction-related but became progressively more alkali as subduction waned and a post-subduction, extensional tectonic regime developed. The most economically significant Au, Te and Se deposits are associated with the more alkali, post-subduction magmas. The textural and compositional characteristics of accessory minerals will be analysed from a range of igneous rocks that span this transition to reveal important changes in source, process and endowment of economically important elements.
Methodology: Volcanic and plutonic samples will be collected during a field season in the Rocky Mountains, central and western USA. Mineral separation and sample preparation will be carried out at the University of Leicester (UoL).
Quantitative petrographic mineral assessments will be conducted using Zeiss’ automated Mineralogic Mining software in conjunction with Mr Shaun Graham at Zeiss in Cambridge, and using a brand new Zeiss SEM at Leicester. Information will be gathered about the abundance of accessory minerals and their inclusion phases.
A suite of trace elements and isotopes will be analysed in a range of accessory minerals using a combination of high precision instruments. These will include an in-house Laser-Ablation Inductively Coupled Mass Spectrometer (LA-ICP-MS) at the UoL to analyse trace element compositions and asses the ability of accesory minerals to distinguish different crystallising environments. Further analytical time will be sought at two NERC facilities – the National Isotope Geoscience Laboratories (NIGL) and at the UK’s only Secondary Ion Mass Spectrometry (SIMS) facility at the University of Edinburgh. This work will seek to utilise Hf and O isotopes in order to assess the relative importance of mantle and crustal inputs during magma generation.
These data will be integrated to establish a rigorous and mineral-informed model for post-subduction magmatism and associated mineralisation.
Enquiries
For Project enquiries contact Dr Andrew Miles, University of Leicester, [Email Address Removed]
Funding Notes
NERC is part of Research Councils UK (RCUK) and therefore this funding is only available to Home/EU applicants.
The studentship is available for full-time registration and will cover all tuition fees for up to four academic years together with an annual tax-free stipend; the RCUK rate for 2018/19 is £14,999. The successful applicant will receive an RTSG (Researcher Training Support Grant) of £2,750 per annum towards e.g. travel, conferences and running costs. An additional £1,000 pa will be contributed by the CASE partner towards the RTSG. Additional costs incurred by the student visiting and working in the CASE establishment (e.g. travel and subsistence) will be covered by the CASE partner.
References
Bruand, E., Storey, C., Fowler, M. 2014: Accessory phases (titanite, apatite, zircon) in late Caledonian high Ba-Sr plutons, Scotland: petrogenetic and source implications. Journal of Petrology, 55 (8), 1619-1651.
Buret, Y., von Quadt, A., Heinrich, C., Selby, D., Walle, M., Peytcheva, I. 2016. From long-lived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemcistry of zircon crystals at Bajo de la Alumbrera (NW Argentina). Earth and Planetary Science Letters, 450, 120-131.
Halter, W.E., Heinrich, C.A., Pettke, T., 2005. Magma evolution and the formation of porphyry Cu-Au ore fluids: evidence from silicate and sulphide melt inclusions. Mineralium Deposita, 39, 845-863.
Kelley, K.D. and Ludington, S., 2002. Cripple Creek and other alkaline-related gold deposits in the southern Rocky Mountains, USA: influence of regional tectonics: Minerlalium Deposita: 37, 38-60.
Muller, D., Groves, D.I., 2015. Halogen contents of mineralised versus unmineralised potassic igneous rocks. Mineral Resource Reviews. Pp 227-245.
Richards, J., 2009. Postsubduction porphyry Cu-Au and epithermal Au deposits: Products of remelting of subduction-modified lithosphere. Geology, 37, 247-250.
Continue with Facebook
