ABSTRACT
Phosphorous, titanium deposits occurs in oxide-rich horizons within the layered gabbro and troctolitic zones of the upper part of the Sept-Iles Complex, Quebec. Recent estimates indicate 107.8 Mt of ore grading 15% apatite and 16 % ilmenite, or 6.19 % P2O5 and 8.41% TiO2 (McCann, 1998). The base of the deposit is formed by a series of nelsonite lenses composed of magnetite, ilmenite, apatite, olivine with minor plagioclase. The major part of the deposit is formed by oxide and apatite-rich gabbros (nelsonite-gabbro). The deposit is underlain by a magnetites and interlayered with a non-mineralized gabbro. Petrographic and geochemical investigations suggest that the mineralisation may be linked to a process of separation of an immiscible Fe-Ti oxide-apatite melt within the residual magma highly enriched in Fe, Ti, REE and incompatible elements including P by a fractional crystallization process.
