Large ilmenite and titaniferous magnetite deposits are hosted in massive and layered intrusive complexes-dominantly ilmenite in Proterozoic anorthosite (subtype 26.1); and titaniferous magnetite in gabbro and leucogabbro (formerly termed gabbro-anorthosite; e.g. Wager and Brown, 1968) (subtype 26.2). Deposits of both subtypes include irregular discordant masses in layered or massive intrusions, and concordant oxide-rich layers produced during fractional crystallization. The principal ore minerals are oxides of iron and titanium: ilmenite (FeTiO₃), hemo-ilmenite (a solid solution of FeTiO₃-Fe₂O₃), magnetite (Fe304), and titaniferous magnetite. The term “titaniferous magnetite” refers to granular aggregates and exsolution intergrowths consisting of ilmenite, magnetite, hematite, and titanomagnetite (a solid solution of Fe₃O₄ Fe₂TiO₄).

The iron- and titanium-rich deposits are classified as two subtypes on the basis of the principal ore minerals and the petrology of the host intrusions. The proportions of the principal ore minerals vary from ilmenite-dominant in anorthosite host rocks to titaniferous magnetite-dominant in gabbro and leucogabbro host rocks. The dominant mineralogy determines whether deposits are of interest as resources of titanium and iron or mainly of iron (Gross, 1965, 1967a).

Subtype 26.1 deposits consist mainly of ilmenite and hemo-ilmenite with minor titaniferous magnetite, and form massive irregular discordant intrusions or layered bodies hosted in massif anorthosite. Important examples are Lac Tio (Lac Allard), Degrosbois, Lac des Pins Rouges, St. Urbain, and Ivry (Morin anorthosite) in Quebec, Canada; Tellnes and Egersund in Norway; and Ilmen Mountains in the former U.S.S.R.

Subtype 26.2 deposits consist mainly of titaniferous magnetite and minor ilmenite and complex Fe-Ti oxide mineral assemblages hosted in layered and/or massive intrusions of leucogabbro, gabbro, norite, and rocks of intermediate composition. Examples include Magpie Mountain, St. Charles, Lac Doré complex, Kiglapait, Newboro Lake, and Lodestone Mountain in Canada; Smaalands- Taberg in Sweden; Bushveld Igneous Complex in South Africa; Kachkanar and Kusinskoye in the former U.S.S.R.; Tahawus and Iron Mountain in the United States.