Genese des depots de iron-titanium-phosphorus associes aux intrusions litees (exemples: l'intrusion mafique de Sept-Iles, au Quebec; Complexe de Duluth aux Etats-Unis) (French text)

Most iron (Fe), titanium (Ti), phosphorous (P), and vanadium (V) deposits are hosted in layered igneous complexes or anorthositic massifs. The oxide-rich rocks are either stratiform (layered) or discordant. The upper part of the Sept-Iles layered mafic intrusion contains a stratiform (layered) Ti-P deposit, whereas the Duluth Complex hosts discordant, oxide-rich bodies “OUI” intruded into troctolitic rocks at the base of the intrusion. This doctoral thesis will characterize these two types of oxide-rich rocks in order to investigate their origin, which at present is controversial. Three models are proposed for these types of rocks; crystal fractionation and accumulation of oxides, separation of a Fe-oxide liquid from the silicate magma, or metasomatism of the cumulate pile by migration of late magmatic fluids.; At both localities the oxide-rich rocks have been classified into three groups, rocks containing 10–30% oxides are referred to as disseminated ore; rocks containing 30–60 oxide are referred as matrix ore and rocks containing >60% oxide are referred to as massive ore. Both ilmenite and magnetite are present at most localities. The silicate minerals are olivine, plagioclase and clinopyroxene. In the more evolved rocks apatite is present. In particular at Sept Iles in the upper part of the oxide layer the rock consists of ∼60% Fe-oxides and 30% apatite, (nelsonite).; The oxide deposits in the Sept-Iles intrusion, which consist mainly of magnetitite and nelsonite (magnetite, ilmenite, apatite, and 0–5% silicate minerals) contain 33.53–69.01% Fe₂O₃, 7.94–26.95% TiO₂, 0.04–12.12% P₂O₅, and less than 2300 ppm V.; At Duluth, the OUI are concentrated along the west margin of the complex. The Boulder Lake North, Water Hen, Wyman Creek, and Longear deposits were chosen for study. The mineralizations contain 22.17–64.33% Fe₂ O₃, 4.28–32.69% TiO₂, 0.04–4.23% P ₂O₅, and 153–6805 ppm V.; The mineral compositions from both deposits are; olivines range from Fo₇₂ to Fo₄₁; plagioclase An₈₈ to An ₄₄, the magnetite Ti concentrations vary from 8–18%, V 0.1–0.2, the ilmenite contains <3% Al and Mg. (Abstract shortened by UMI.)...