Margaux Le Vaillant
Thesis: Characterisation of the nature, geometry and size of hydrothermal remobilisation of base metals and platinum group elements in magmatic nickel sulphide deposit systems. Implications for exploration targeting.
Magmatic nickel-sulfide deposits are highly valuable but extremely challenging exploration targets, characteristically lacking the distinctive geochemical haloes that allow small targets to be identified from sparse drilling. Consequently, undiscovered deposits are highly likely to exist at depth, even in well-explored terranes. The genesis of magmatic nickel-sulfide deposits has been extensively studied over the years. Consequently, the extensive knowledge acquired about primary magmatic processes and geophysical detection methods has been comprehensively applied to exploration targeting. However, the study of secondary processes affecting nickel-sulfide deposits, especially post-magmatic circulation of hydrothermal and metamorphic fluids, has received little attention within the research community. The remobilization of metals during post-deposition hydrothermal alteration has the potential to result in large haloes, whose recognition could potentially increase exploration success rates for magmatic nickel-sulfide deposits. This study aims at defining the nature and the 3D geometry of the footprint created by the remobilization of base metals, gold and platinum group elements within the rocks surrounding nickel-sulfide ore bodies. Three representative komatiite- and mafic-hosted nickel-sulfide systems with varying mineralization styles, host rock, styles of hydrothermal overprint (e.g. serpentinite versus talc-carbonate alteration) and metamorphic grades are used as case studies.
Preliminary geochemical results are promising as they show anomalous base metal enrichment in host rocks away from the ore body. The challenge is now to pin point the processes that lead to the formation of the hydrothermal stain surrounding the deposits, and to assess whether this hydrothermal stain is larger in some cases than the detectable geophysical footprint. An experimental study has been designed in order to understand to which degree base and precious metals may be remobilized by hydrothermal fluids. In fact, the key elements missing from our understanding of the size and nature of hydrothermal footprints surrounding magmatic nickel-sulfide deposits revolve around the poorly constrained behaviour of critical elements such as nickel, cobalt and the PGE in hydrothermal solution. Through the combination of new field observations and critical experiments aimed at answering fundamental questions about the geochemistry of nickel, cobalt and PGE in hydrothermal systems, the ultimate goal of this study is to enlarge the detectable mineralogical and lithogeochemical footprints of magmatic nickel-sulfide deposits.
Why my research is important
Magmatic nickel sulphide deposits are challenging but highly attractive exploration targets, with in-situ value in some cases in excess of a billion dollars worth of contained metal. Deposits also tend to occur in clusters, such that a single discovery can open up an entire cam. Hence, defining geochemical haloes represents a significant advance in improving exploration success rates and has huge potential economic benefits for Australia, both in the direct value of new mineral discoveries and in the multipliers in job and infrastructure creation.