Some are tabular while others are lensoidal or dike-like. Vary in size from a few million tons to well over 100 million tons. Setting Anorthosite complexes typically consist of an older massive gabbro overlain by younger anorthosite. The ores lie within the anorthosite, generally at the contact with the older gabbro. Layering within both the host and ore is absent.
Ores commonly contain inclusions of anorthosite indicating they are younger.
Cataclastic fabrics present in the anorthosites and gabbros, but lacking in the ores are thought to indicate the ore mineralization has migrated to its present location by some tectonic process. The host rock is generally a medium grained, anorthosite with the plagioclase andesine to labradorite in composition. With addition of pyroxene local gradations to gabbro are present. Ore minerals consist of magnetite, ilmenite, hematite, ulvospinel and rutile. Apatite is a common accessory as are nickel and copper sulfides.