Abstract: The ultramafic-hosted disseminated nickel sulphide deposit at Mount Keith, Western Australia, originally consisted of sulphide droplets and chrome spinels interstitial to olivine. During cooling, the sulphide droplets crystallized to pentlandite-pyrrhotine. Hydration and carbonation caused rimming and replacement of pentlandite-pyrrhotine by tochilinite, magnetite, and magnesite. These textures are interpreted in terms of diffusion between serpentinite matrix and the sulphide blebs.