Overview

Project Highlights:

  • Carry out research that bridges the fields of igneous petrology and economic geology
  • Conduct fieldwork and add to our understanding of active volcanic centres in the Philippines.
  • Integrate with two existing multi-institutional, Leicester-led NERC consortia projects (TeaSe and FAMOS).

 

Overview:

Porphyry copper deposits (PCDs) are low grade, high tonnage magmatic-hydrothermal ore deposits. Typically, extensive veining and alteration are centred around relatively small stocks intruded into the upper crust in arc volcanic environments, and above large magma bodies that are the main source of fluids, sulphur and metals. Fertile systems reflect the successful passage of magmas from the mantle through the crust, where key ore-forming processes occur. These include volatile saturation, fluid extraction, and injection of volatile-rich mafic magmas into existing evolved crystal mushes. Identifying whether all the necessary steps for ore formation have occurred is key to determining prospectivity in any arc terrain.

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 actual source of such fluids is usually located deeper in the magma plumbing system and is often not exposed at the erosion level of the deposit. Certain robust accessory minerals found within PCDs are commonly inherited from deeper, ore-forming regions of the magmatic system and retain a time-sequential record of these critical processes. These minerals are also known to host inclusions of less robust minerals – including magmatic sulphides important for Cu enrichment and transport. These minerals thus act as powerful proxies for mineralising processes.

The overarching scientific aim of this study is 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. A further aim of this project will be to assess the extent to which different accessory minerals retain information from different parts of the magmatic system. Chemically fingerprinting key ore-forming processes in accessory minerals formed during different stages of magma evolution will provide a useful and more cost-effective tool for further PCD exploration.

Taal and Pinatubo represent two active arc volcanoes in the Philippines and there is strong evidence that the latter is underlain by an active porphyry-like system. These sites will allow a detailed comparison of magmas that have generated mineralised and barren systems within the same volcanic arc.

Figure 1: 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

Samples will be collected during field seasons in the Philippines. Mineral separation and sample preparation will be carried out at the University of Leicester.

High resolution imaging of accessory minerals will be conducted using a new suite of Scanning Electron Microscopes (SEM) at the University of Leicester. This imaging will help identify distinct compositional regions within different accessory minerals. Furthermore, textural relations within and between accessory minerals will be fully assessed using this technique.

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 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.

Training and Skills

 

  • Fieldwork: two weeks fieldwork in the Philippines. Training will be provided
  • Analytical skills: Mineral separation and sample preparation will be carried out at the University of Leicester (UoL). A full textural analysis will be conducted using a new suite of in-house Scanning Electron Microscopes (SEM). A suite of trace elements and isotopes will be analysed in a range of accessory minerals using a combination of high precision instruments: in-house Laser-Ablation Inductively Coupled Mass Spectrometer (LA-ICP-MS), and 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.
  • 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.  

Timeline

Year 1: A thorough review of the latest literature will be conducted. Fieldwork and sample collection will be conducted in the Philippines. Training in mineral separation and SEM imaging will be provided at the University of Leicester. An application to the EMMAC NERC facility will be made for isotope analysis. Attendnace at national conference.

Year 2: Ongoing analysis of samples at the University of Leicester and Edinburgh. Application for analytical time at NIGL. Presentation of results at large national and international conference.

Year 3: Integration of data will provide a model for magma evolution and mineralisation. Publication of papers. Presentation at large national and international conference.

Partners and collaboration (including CASE)

Dr Andrew Miles, Dr David Holwell and Dr Dan Smith investigate igneous processes related to mineralisation and are partners on two NERC funded consortium projects (FAMOS and TeaSe) that focus on magmatic-hydrothermal processes.

Further Details

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