Uralian-Alaskan-type mafic to ultramafic complexes form a narrow, 900 km long, N-Strending chain in the northern and central parts of the Ural orogenic belt. Characteristic features like their concentric lithologic zonation, the absence of orthopyroxene in the ultramafic rocks and platinum group element (PGE) mineralization, which is the source for economic PGE placer deposits, discriminate Uralian-Alaskan-type complexes from other mafic-ultramafic intrusions.

Alaskan-type ultramafic-mafic intrusions occur along a belt that extends from Duke Island to Klukwan in southeastern Alaska and fall into two age groups400 to 440 Ma; and 100 to 118 Ma. Most of the intrusions occur in the Alexander terrane or in the Gravina overlap assemblage, but they are not restricted to these terranes. The Alaskan-type ultramafic bodies range in size from sills only a few meters thick to intrusions about 10 km in maximum exposed dimension. Most of the bodies consist of magnetite-bearing hornblende clinopyroxenite or hornblendite, however many of the larger ones also include dunite, wehrlite, olivine clinopyroxenite, and, in some cases, gabbro.