Abstract Most deposits of platinum group elements (PGE), chromite, and vanadiferous magnetite occur in mafic intrusions. Several represent some of the most laterally continuous and uniform, in terms of grade and thickness, of all orebodies. Such continuity presents one of the major challenges to orebody modeling, in that any proposed process must be able to operate uniformly across enormous areas within a magma chamber. Their size also creates a mass-balance problem, especially for Cr, in that the required source reservoir for some deposits exceeds the size of the currently preserved intrusive body. Whether chromitite layers result from magma addition (with three options for the compositions of the added magma—ultrabasic, plagioclase rich, or siliceous melt), changes in oxygen, water, or total pressure, or some other process has yet to be demonstrated definitely. Podiform chromitite deposits in ophiolites possibly owe their genesis to concentration from basic magma by an aqueous phase. Some models for PGE mineralization mimic those listed for chromitite layers. The mineralization may be primary magmatic, accumulating with the silicate phases, either in some association with sulfide liquid, chromite, or independently, or it may postdate silicate accumulation, having been extracted from very low grade PGE source in vertical sections of footwall cumulates. Identifying definitive criteria to support or negate these processes proves elusive. The abundance of orthopyroxene over clinopyroxene in ultramafic cumulates, and a transition from ultramafic (with Cr-rich pyroxene) to mafic rocks (Cr-poor pyroxene), are two common, but not universal, features of stratiform PGE deposits. Vanadium strongly partitions into magnetite, which forms the major source of this metal. Models for the genesis of magnetitite layers often have a strong analogy with hypotheses about chromitite layers, but fundamental differences do exist, most prominent being the lack of any evidence for magma addition relating to magnetite formation. Density sorting of cumulus minerals is more plausible for magnetite than from chromite deposits. Hypotheses for the origin of PGE, Cr, and Vmineralization have been strongly influenced by observations on the Bushveld Complex that hosts well over half the world’s resources in all these commodities. Such dominance possibly impedes the development of models that might have applicability in other intrusions but where current economic nonviability reduces their apparent significance.