Abstract

Stratigraphic, volcanological, petrological, and fluid dynamic studies suggest that Archean komatiite-associated nickel sulfide deposits in Western Australia formed by thermal erosion of unconsolidated sulfidic sediments beneath channelized lava flows. Geochemical and Nd isotope data for the type area at Kambalda suggest that mineralized lava channels are less contaminated than barren flanking segments of the flow, owing to high discharge rates and continuous replenishment within the channel. This interpretation has several implications for the mode of emplacement of sulfides, their degree of equilibration with the host komatiite, and the compositions of sulfide ores: (1) the solubility of sulfur in komatiite is relatively low, so most of the sulfide in eroded sediments will be melted and remain as a dense layer at the base of the flow or be incorporated into the turbulently flowing komatiite as immiscible sulfide droplets; (2) sulfide ores will not necessarily be in equilibrium with overlying koma-tiites but will record equilibration with variably contaminated lavas during initial stages of emplacement and crystallization; and (3) ore compositions will vary from channel to channel (shoot o shoot) depending on (i) the composition of the hybridized komatiite, (ii) the fluid