Abstract

Komatiite-hosted nickel sulphide deposits represent very valuable ore bodies, but very difficult exploration targets, mainly due to the limited extent of their primary magmatic footprint. However, hydrothermal alteration has the potential to remobilise base metals and Platinum Group Elements (PGE), extending the detectable footprint of this ore type. Four komatiite-hosted nickel-sulphide deposits, differing in geological setting, hydrothermal alteration style and metamorphic processes, were selected as case studies. In parallel, an empirical study of the mobility of base metals and PGE within an ore body during alteration was carried out, using the intrusion-hosted Kevitsa deposit (Finland) as a natural laboratory.

During this project, we identified the presence of a subtle geochemical halo characterised by anomalous Ni, As, Pd, Pt and Co concentrations within footwall lithologies, extending between 250 and 1780 meters away from the mineralisation. The size of this geochemical halo is larger than any observed magmatic footprint around komatiite-hosted nickel-sulphide deposits. These results shed the light on the important role of arsenic in their remobilisation and transport.

In parallel, results of the study of the mobility of Ni, Co, Cu, Au, and PGE in the Kevitsa natural laboratory provided more insights on the behaviour of base metals and PGEs in hydrothermal fluids, and highlighted the low mobility of Ni and PGE, in contrast to Cu and Au, during serpentinisation, hydration and greenschist metamorphism of mineralised ultramafic rocks.

Under specific conditions, such as the presence of arsenic, hydrothermal fluids have the potential to remobilise Ni, Co and PGE, and produce a detectable halo around massive nickel-sulphides. This Ni-Co-PGE-As halo extends farther than most of the exploration vectors known to date. A practical flowchart was developed to use this geochemical halo as an exploration tool, specifically using portable XRF, for which a protocol was established for core-yard use. Hydrothermal geochemical haloes are a complementary tool with great potential to improve nickel exploration targeting in environments which have undergone arsenic metasomatism.

Bio:

Originally from France, Margaux completed her undergrad in Paris (prepa BCPST at St Louis) and Nancy (National engineer school of Geology, ENSG). She then completed her Masters in collaboration with Lulea University of Technology in northern Sweden. In 2011, she moved to Perth to start her PhD at UWA, within the Centre for Exploration Targeting. During her time with CET, Margaux worked on hydrothermal footprints around magmatic nickel sulphide deposits, and will present the results of this study today. Over the last year, Margaux has been working at CSIRO as a post-doctoral fellow, looking at the physical processes related to the emplacement of magmatic nickel sulphide deposits.