Postgraduate Profiles

David Mole

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Thesis: Quantifying melt-lithosphere interactions in space and time: nickel mineral systems in the Archaean Youanmi terrane of the Yilgarn craton

Since the nickel boom of the 1960s, research into komatiite-hosted nickel sulphide systems has focused on the deposit and mine-scale environment. This has led to a greater understanding of the geochemical, physical and stratigraphic interactions favourable to the formation of nickel sulphide systems, subsequently allowing the development of more advanced and efficient exploration targeting initiatives and models. However, very few projects have looked at komatiite systems on a regional-craton scale. In this project, we look to investigate how geotectonic setting, nature of the lithosphere and lithospheric architecture affect the characteristics and prospectivity of komatiites in the Archaean greenstone belts of the Yilgarn craton, and also how these interactions may localise and concentrate komatiite systems to form large, world-class Ni deposits or ‘camps’. To do this we are using U-Pb SHRIMP dating, LA-ICP-MS Lu-Hf isotope work and whole-rock Sm-Nd analyses of granites and felsic volcanics, which are derived from crustal material and hence represent an isotopic ‘snap-shot’ at the time given by U-Pb dating. This allows us to have isotope data which is temporally and spatially constrained and as a result we can investigate how the lithospheric architecture evolved from 3.0 Ga to 2.6 Ga, and how this evolution affects magmas erupted through it.

Why my research is important

This project is important for a number of reasons:

1. Scale – This research goes beyond the mine/deposit scale processes and looks at the large-scale tectonic, and stratigraphic processes which shape how the lithosphere behaved and evolved at the time of komatiite emplacement at 2.9 Ga.

2. New concept – The use of Lu-Hf and Sm-Nd isotopes to produce spatially and temporally constrained maps is a new technique, and has implications for early earth evolution and mineral exploration techniques.

3. It has been shown by other workers, especially Graham Begg and the GEMOC group, that early, lithospheric architecture and lithospheric terrane evolution plays a major, first-order control on the location, size, and type of nickel deposits, both high-Mg komatiitic and low-Mg LIP/basaltic. Constraining the geochemical architecture of the south Youanmi through the mid-early Archaean will subsequently have fundamental implications for further nickel exploration in the area, as well as other mineral systems (Gold, Iron) which are also linked to geodynamics and tectonics.

Funding

Jan 2009

Jan 2012

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