Overview

Project Highlights:

  • Fieldwork in southern Africa working directly with the minerals industry
  • First application of new dyke-sill emplacement models to mineralised mafic-ultramafic intrusions
  • Development of a new exploration model for craton-margin ore deposits

The recently recognised spatial correlation of major Ni-sulfide deposits with cratonic margins1 has revolutionised exploration in mafic-ultramafic intrusions, and focussed genetic models on integrating crustal-scale criteria. Host intrusions are dyke-sill and conduit/feeder systems2 that intrude metamorphosed basin sediments deposited during the onset of continental rifting and break-up. The origin of the magmas and metals is controversial3. Crustal fault systems at craton margins excellent pathways for the migration of fertile mantle melts from plumes impinging on the craton base and channelled to the margins, or from melting subcontinental lithosphere1.

However, few studies have considered the structural controls on the emplacement of such systems (4 is a notable exception). Dyke-sill complexes are commonly inferred to propagate via networks of faults, with the transition to sills being linked to neutral buoyancy or the interaction of the magma between perpendicular foliations. Recent studies of sill systems show their geometry is strongly dependent on the stress state5, and the response of existing structures is dependent on their mechanical properties, orientation, and magnitude of applied stress. This project is therefore timely, as it will be the first application of this new approach to models for Ni-sulphide systems.

The project will use the Neoproterozoic Zambezi and Mozambique belts at the Zimbabwe-Congo craton margins as an ideal natural laboratory to address Q1-5, where a number of mafic-ultramafic complexes and dyke-sill systems are present, emplaced during rifting6.

The project will address the following research questions:

  1. What are the sources of magma for mafic-ultramafic intrusions around the margin of a craton and are they related to rifting, plume activity, or melting of the SCLM?
  2. Which intrusions are mineralised, and are there key host rock/source controls on whether any particular body is mineralised?
  3. Using intrusion geometry, and the interaction with pre-existing structure, what was the dominant stress regime during emplacement?
  4. Is it possible to reconstruct a natural example of the model2 for magmatic sulfide metallogenesis in conduit systems?
  5. As an application to industry, what criteria must be used in a revised model for Ni sulfide prospectivity at craton margins?.
The Munali Ni deposit, Zambezi belt, Zambia.

Methodology

The research question Q1-5 will be addressed through the following objectives:

a) Fieldwork in southeast Africa to map and sample mineralised and barren mafic-ultramafic complexes to provide geological context and material for Q1-3.

b) Bulk geochemical and mineralogical analysis of intrusive rocks and their hosts for Q1 and Q2.

c) Geochronology (U-Pb on zircons) for individual intrusive bodes to construct a tectono-magmatic framework and provide evidence for Q1.

d) From a and c, reconstruct the structural regime of emplacement to address Q3.

e) From a-d, produce a model for the emplacement of mafic-ultramafic complexes in the region and provides a robust set of criteria for exploration models for craton-margin, conduit deposits.

There is flexibility within the project for the student to develop some of these aspects in more detail than others according to preference.

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 CENTA research themes.The project will involve industry collaboration from the start, and the student will gain training in exploration drill core logging, structural mapping and geochemical analysis in the field using portable XRF from the supervisors and Consolidated Nickel Mines. The laboratory work will include training in a range of geochemical and mineralogical techniques, including XRF, LA-ICP-MS, microprobe and SEM. Geochronology will be undertaken through a successful application to the NERC isotope facilities at NIGL. The student will present at international conferences and participate in relevant workshops.

Timeline

Year 1: Field training in southern Africa to sample outcrop and exploration drillcore from the intrusions in the Kafue region, Zambia. This will be timed for the dry season where access to well exposed intrusions is easiest. Follow up geochemical classification. Application to NERC isotope facilities for U-Pb dating.

Year 2: Geochronology and isotopic work at NIGL. Field season to focus on the structural geology of the intrusions classified geochemically and chronologically. Additional sampling of other intrusions in the broader region (Malawi, Mozambique) if required. Analysis of structural data.

Year 3: Tectono-magmatic and stress state reconstruction by way of synthesising data from years 1 and 2. Submission of papers to international journals.

You will be expected to present at UK (e.g. MDSG) and international confer

Partners and collaboration (including CASE)

The project team at Leicester have extensive experience in magmatic sulfide metallogenesis (Holwell), analytical igneous geochemistry (Barry) and the structural geology of dyke-sill complexes (Walker), coupled with very strong field experience. Simon Purkiss is CEO of Consolidated Nickel Mines, who own the Munali Nickel Mine in Zambia, and the exploration licence for a large part of the Kafue district. Dave Evans has a wealth of experience in the exploration for and study of Ni sulfide mineralisation in sub-Saharan Africa. Simon Tapster has applied high resolution U-Pb dating techniques to a range of ore deposit systems at the NERC isotope facility at NIGL.

Further Details

At Leicester you will interact with one of the most prominent economic geology research groups in the country, with links to industry and other research groups worldwide, including through the current NERC-funded, multi million pound TeaSe project.

Applicants should have some experience of economic geology, preferably in magmatic deposits, geochemical or mineralogical research and field geology. Industry experience is advantageous, but not essential.

For more details on this project, or copies of the references, please contact Dave Holwell (dah29@le.ac.uk) or 0116 252 3804