Mafic- ultramafic rocks are key windows to probe mantle composition and mantle- crust interaction process, and also important hosts of Ni, Cu, PGE and Cr metal resources. Their various occurrences are related to different genetic types of mineralization. Ophiolites mainly host chromite deposits, while Alaskan- type complexes could contain PGE deposits. Chromite, PGE as well as Ni- Cu sulfide deposits may occur together in an individual large layered complex. Such mineralization difference is basically interpreted as dependence of tectonic setting, and composition and evolution of parental magmas, but critical controls have not been well constrained. Previous studies are focused on partial melting of mantle sources, wall- rock assimilation, and fractional crystallization during magma upward ascent. Role of fluids in mineralization receives little attention. Recent experimental and petrogeochemical results have revealed that fluid activity during magma evolution may have played a significant role in metal transportation and enrichment, particularly with growing knowledge of metal occurrence and partitioning behavior. A hot topic in magmatic deposits is to constrain geochemical behavior, transportation and deposition of Cr and PGE during fluid exsolution from magmas. This paper presents a summary of mineralization differences in various mafic- ultramafic complexes and records of fluid activities during chromite and/or PGE mineralization, and addresses dependence of fluid property and composition for deposit formation. We thus suggest that systematic comparisons between ophiolite, layered complex and Alaskan- type complex will well document the topic.