Advancing micro-analytical isotopic and trace-element ICP-MS techniques for future applications to ore genesis and exploration

This project is hosted at the British Geological Survey and is jointly supervised by Dr Simon Tapster and Dr Matthew Horstwood.

Magmatic systems and their associated ore deposits are the end-products of protracted events that lead to complex and diverse signatures of geochemical processes and source inputs. Although whole-rock (bulk) analyses provide first-order assessments that can be used to great effect, there is an ever increasing need to assess system heterogeneity by delving into the wealth of information contained in the mineral-scale records of magmatic and ore forming systems. In order to interrogate these mineral-scale records, tracer isotopic systems (e.g. Lu-Hf, Sm-Nd, Rb-Sr, Pb-Pb) and trace element data need to be measured at a level of precision greater than system variations, whilst simultaneously achieving a spatial resolution that can be linked to detailed petrographic and geochronological records. For many isotopic and trace element analyses throughout the Earth Sciences, inductively coupled plasma mass spectrometry (ICP-MS) is the versatile tool of choice. However, there are significant limitations to conventional methods of sample introduction that arise from low volumes of material, low elemental abundance, or the absence of well characterised reference materials. Until recently, these limitations have left considerable amounts of high resolution (spatial resolution or analytical precision) geological information ‘off-limits’.

The new MVX-7100ul workstation developed by Teledyne-CETAC Technologies provides novel sample introduction technology for ICP-MS analysis that utilises a material quantity that can be reduced by at least an order of magnitude compared to standard solution analysis methods, whilst maintaining comparable levels of precision and accuracy in isotopic ratio determination. This technological leap realises the possibility to analyse isotopic systems and

trace elements within samples previously thought to be present at too low an abundance and has the potential to have major impact in geochemical analysis. The challenge now faced is to turn a proof of concept into routine methods for both scientific research and industry application.

The aim of this project is to provide the transition between the state-of-the-art MVX-7100ul workstation technology and end-user applications. This will be achieved by:

1. Defining measurement capabilities in low volumes or low concentrations of accessory phases commonly used for geochemical analyses within the Earth Sciences;
2. Exploring new avenues of research utilising isotopic tracers (e.g. Lu-Hf, Sm-Nd, Rb-Sr, Pb-Pb) in non-conventional mineral phases where the elements of interest occur in low abundance;
3. Improving characterisation of widely-used reference materials required throughout Earth sciences for micro-analytical work;
4. Developing effective ways of linking your novel data sets to petrographic and U-Pb geochronological data to explore current paradigms and issues surrounding magmatic and ore forming systems in unprecedented detail.

The project outcomes will be fed back to the product developer and CASE partner Teledyne-CETAC Technologies to improve capability and efficiency of the MVX-7100ul workstation.

This research project will be focussed on the application of the MVX-7100ul workstation to (Multi-collector and Single collector) ICP-MS analysis. Using a range of synthetic solutions and geological reference materials you will map out the achievable measurement precision and accuracy at low sample amounts, for a suite of widely-used tracer isotope systems and less commonly measured trace-elements. You will design and carry out experiments to evaluate potential matrix effects that mimic natural systems/minerals, and develop suitable ion exchange chemistry procedures to deal with the issues encountered for different elements, minerals and mineral volumes. These results will then be used to: 1) Identify efficiencies and trade-offs for analytical routines; 2) Provide new or better assessments of trace element and isotopic reference values for commonly used material; 3) target a number of key geological case studies that showcase the advantages of the techniques you have developed and how these can be coupled with detailed petrography and high-precision U-Pb geochronology to gain new insights into magmatic and ore forming processes.