Thermal erosion by komatiites at Kambalda, Western Australia and the genesis of nickel ores

Abstract

Huppert et al.1 calculated that komatiites flow turbulently, transfer heat efficiently to their substrate, and thus potentially produce thermal-erosion channels in sequences onto which they were erupted. Their suggestion that komatiite-hosted (Kambalda-type2) nickel ores reside in such channels has led to resurgence of interest in volcanic models for ore emplacement3–5 and caused controversy6,7. Such models have important implications, not only to ore-genetic studies but also to interpretation of the geochemistry of komatiites8 and their Sm–Nd systematics9,10. Here we demonstrate that interspinifex Fe–Ni–Cu sulphide ores, which underlie some hanging wall massive sulphide ores at Kambalda the site of one of the world's major nickel deposits, formed through thermal erosion of underlying komatiite flows and possibly also sediments, providing proof of thermal erosion. However, we caution against the general application of thermal-erosion models to the eruption of komatiites. It seems that significant thermal erosion occurred rarely, and only where basal concentrations of highly thermally conductive sulphide liquid were present at the base of localized lava channels. Isotope data11,12 and theoretical considerations13 suggest that the komatiites were contaminated by crustal rocks before eruption, although there is limited evidence that localized contamination, including sulphide assimilation4, may also have occurred below lava channels localized in pre-existing embayments or troughs.