Dolerite sills in the western portion of the Huab River Valley have an outcrop area in excess of 600 km² and individual sills are up to 130 m thick. They intrude both the Damara basement and overlying Karoo Sequence sediments and are frequently transgressive. The sills and associated dykes are separated into four distinct dolerite magma types which are distinguished from each other by different ratios of incompatible element abundances. All the dolerite types are tholeiitic, containing both normative hypersthene and olivine. They are relatively primitive in character with rather high concentrations of Mg, Ni and Cr and low concentrations of incompatible trace elements (e.g. Ba, Zr, and Nb). The Huab sills are compositionally different from the basaltic lavas of the overlying Etendeka Formation and from most of the dolerite types which intrude the lavas. They are closest in composition to the Horingbaai dolerites, a suite of late-stage intrusives into the Etendeka Formation with MORB affinities. The compositional variations within individual sills are consistent with crystal fractionation processes which appear to have operated both by gravitational separation and accumulation of early-formed phenocrysts, and by flow differentiation.