Student: David Mole

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

Supervisors: Dr Marco Fiorentini, Dr Nicolas Thebaud, Prof Cam McCuaig and Dr Kevin Cassidy

Sponsors: Australian Research Council, Norilsk, St Barbara, BHP Billiton Nickel West

Research topic:

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 has evolved from 3.0 Ga to 2.6 Ga.

The study area for this project is the south Youanmi terrane, from the Marda Complex in the north to Ravensthorpe greenstone belt in the south. The northern areas (Marda, Southern Cross) are unmineralised in terms if komatiite-hosted Ni, and the southern belts (Forrestania, Lake Johnston, Ravensthorpe) are mineralized. The project will also sample across the Ida fault in the western Eastern Goldfields in order to constrain the paleo-craton margin, as identified by Champion and Cassidy (2007; see map below).

The primary aims for the project are (1) to establish a terrane-belt scale exploration tool, whereby prospective/unprospective regions can be identified based on isotopic terrane analysis; (2) investigate the evolution of the Yilgarn craton and subsequent implications for Early Earth evolution; (3) quantify the affect of lithospheric architecture on magmas emplaced through it, and (4) constrain the affects of lithospheric architecture on the tectonostratigraphic evolution of greenstone belts.  

(a) Sm-Nd isotope map from Champion and Cassidy (2007), which clearly shows the striking architectural difference between the Youanmi terrane and the Eastern Goldfields; the south Youanmi is poorly constrained and this project is aimed at defining this area isotopically. (b) Lake Hope (Lake Johnston region) at sunset, taken during the March 2009 fieldtrip with GSWA.