At Collins River fresh roadcuts reveal serpentinite in contact with spilite and greywacke. Low birefringent fibrous diopside and hydrogrossular have grown at this contact due to alteration by the ultrabasic rock. The presence of this contact on both sides of the body and the body's general concordance with enclosing strata indicate sill intrusion above the minimum temperatures for serpentinisation. Steatite and serpentinite bodies to the east of the body probably originated by faulting of a larger ultramafic mass.