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The hydrothermal footprint of nickel sulphide mineral systems

Western Australia and Kevitsa, Finland

The ultimate goal of this project is to enlarge the detectable footprint of magmatic nickel sulphide deposits. In this study, the research team will focus on the mineralogical and lithogeochemical footprints around syngenetic magmatic nickel sulphide deposits, which arise from the interaction of these deposits with later hydrothermal fluids. 

Magmatic nickel sulphide deposits are highly valuable but extremely challenging exploration targets, characteristically lacking in the kind of distinctive geochemical haloes, which can enable small targets to be identified from sparse drilling. While some of these deposits are geophysical EM targets, many are not, and those that are commonly camouflaged by the presence of neighbouring barren conductors. In many cases, near misses (e.g. beyond the range of down-hole EM) are effectively complete misses. Primary magmatic chemical haloes in host rocks are effective in some environments but not others, and are absent from many deposits. In consequence, the rate of discovery of new deposits of this style has slowed dramatically since the initial surge of exploration success between 1966 and 1973.

As a result, this new project will provide a new approach in order to aid exploration in brownfields terranes. Undiscovered deposits are highly likely to exist at depth, even in mature well-explored terranes, but are likely to be deformed, altered and offset from readily detectable magnetic host rock units. Such targets may be highly attractive, high-grade deposits worth billions of dollars. The ultimate goal is to enlarge the detectable footprint of these targets. In this study, the research team will focus on the mineralogical and lithogeochemical footprints around syngenetic magmatic nickel sulphide deposits, which arise from the interaction of these deposits with later hydrothermal fluids. Hydrothermal footprints are in common use in gold and Cu-Zn exploration, but have so far received little attention from nickel explorers, mainly because the nature and the scale of the alteration halo are largely unconstrained. This is a window of opportunity: the new knowledge acquired from this study will aid exploration for nickel sulphide systems at multiple scales, and will be applied in the interpretation of isolated “orphan” drill holes under cover in greenfields terranes, as well as in more data-rich mine-scale environments. An essential component of this work will be in developing an understanding of the nature and timing of deformation and alteration of the orebodies used as case studies. In fact, fluids are likely to be focussed along major fractures and shear systems active during deformation of the orebody. The effects of these fluids will be superimposed on the effects of early burial-related, pre-deformation alteration such as sea-floor serpentinisation. Therefore, an essential component of the deposit-scale studies that will comprise this project will be to relate the alteration history of the deposits and their host rocks to their structure in 3D. This understanding will provide context for researching the hydrothermal footprints of the deposits.