Overview

Porphyry copper deposits (PCDs) represent relatively small stocks that are commonly intruded at the base of arc volcanoes and above large magma bodies that are the main source of fluids, sulphur and metals. Fertile systems reflect the successful passage of magmas up through the crust where key ore forming processes have occurred. Identifying whether the necessary steps for ore formation have occurred is key to determining prospectivity. However, identifying these processes is often difficult because the host rocks for PCDs are often not representative of the conditions at which ore fluids were generated. The source of such fluids is located deeper and is seldom exposed at the erosion level of the deposit. However, certain robust accessory minerals within PCDs are commonly inherited from deeper, ore-forming regions and retain a time-sequential record of these critical processes. These minerals are also known to host inclusions of less robust minerals such as Cu-rich sulphides. Accessory minerals thus act as powerful proxies for mineralising processes.

This project aims to identify key magmatic-hydrothermal processes in the formation of arc-related PCDs. These processes will be investigated using integrated, high precision, in situ measurements of trace element and isotope suites in multiple accessory minerals (zircon, apatite and titanite) and in mineral inclusions. Quantitative characterisation of accessory mineral assemblages and their inclusions will be carried out using Zeiss’ automated Mineralogic Mining software to determine textural/timing relations.

Taal and Pinatubo represent two active arc volcanoes in the Phillippines and there is strong evidence that the latter is underlain by an active porphyry system. These sites will allow a detailed comparison of magmas associated with active mineralised and barren volcanic systems. By contrast, the Criffell pluton in Southern Scotland is a Devonian granite that has been tectonically juxtaposed with volcanic/shallow intrusive units that are associated with copper deposits. The unusual preservation of both deep and shallow parts of this Cu-bearing magma system makes it an ideal area to investigate mineralisation processes in different parts of a magmatic system.   

Pinatubo, Philippines is an ideal location to investigate the compositional signal left in accessory minerals by processes that influence mineralisation such as mafic magma injection.

Methodology

Volcanic and plutonic samples will be collected during field seasons in the Philippines and Southern Scotland. Mineral separation and sample preparation will be carried out at the University of Leicester.

Quantitative petrographic mineral assessments will be conducted using Zeiss’ automated Mineralogic Mining software in conjunction with Mr Shaun Graham at Zeiss in Cambridge.

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 University of Leicester (UoL) and instruments at two NERC facilities – the Isotope Geoscience Laboratories (NIGL)  and at the UK’s only Secondary Ion Mass Spectrometer (SIMS) facility at the University of Edinburgh.

These data will be integrated to establish a rigorous and mineral-informed model for porphyry development in two subduction-related settings.

 

Training and Skills

CENTA students benefit from 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to the student's projects and themes. 

You will become proficient in the use of analytical equipment including quantitative evaluation of minerals (Zeiss), SEM (UoL), high-resolution mass spectrometry (UoL and NIGL) and Secondary Ion Mass Spectrometry (University of Edinburgh). This combination of state-of-the-art analytical methods to investigate novel and fundamental scientific questions will provide you with a unique set of skills that will be attractive to industrial and academic employers. You will join a thriving community of igneous and applied researchers, and work closely with members of two major NERC-funded projects (FAMOS - From Arc Magmas to Ore Systems, and TeaSe – Te and Se Cycling and Supply).

 

Timeline

Year 1: A thorough review of the latest literature will be conducted. Fieldwork and sample collection will be conducted in the Philippines and Scotland. Training in mineral separation and SEM imaging will be provided at the University of Leicester. Industrial training in automated mineralogy will be carried out during a placement at Zeiss. An application to the EMMAC NERC facility in Edinburgh will be made for isotope analysis.

Year 2: Ongoing analysis of samples at the University of Leicester and Edinburgh. Further industrial training will be provided by Zeiss. Application for analytical time at NIGL.

Year 3: Integration of data will provide a model for magma evolution and mineralisation in two distinct tectonic settings. Publication of papers and conference presentations, including the opportunity to present at international meetings, will be part of the schedule from year 2 onwards.

 

Partners and collaboration (including CASE)

Dr Andrew Miles investigates magmatic processes in relation to crustal evolution using the chemistry of robust accessory minerals. Drs Dave Holwell and Dan Smith are lead researchers in magmatic processes related to mineralisation. All supervisors are partners on two NERC funded consortium projects (FAMOS and TeaSe) that focus on magmatic-hydrothermal processes.

Mr Shaun Graham is an Applied Development Engineer at Carl Zeiss Microscopy with experience in automated mineralogy to improve and optimise mineral processing and performance.  

 

Further Details

Contact Andrew Miles, University of Leicester, ajm131@le.ac.uk