METAMORPHIC ZIRCON IN FE-TI ORES, MORIN ANORTHOSITE COMPLEX (GRENVILLE PROVINCE, QUEBEC)

The ca. 1.15 Ga Morin Anorthosite Complex and its associated Fe-Ti oxide ore deposits are located in the Allochthonous Monocyclic Belt of the Grenville Province, Quebec. Samples from the Ivry deposit are dominated by ilmenite (85-90%) and contain (in decreasing abundance) plagioclase, orthpyroxene, green spinel, clinopyroxene, K-feldspar, amphibole, biotite, apatite, quartz, pyrite, pyrrhotite, and chalcopyrite. The ilmenite contains multiple generations of well-developed hematite exsolution. Unlike other Fe-Ti deposits in the Morin Complex, Ivry ores have high zirconium contents and do not contain primary magnetite.

The order of igneous crystallization in Ivry ores (determined by SEM) is ilmenite, clinopyroxene, orthopyroxene, plagioclase + sulfide minerals, and spinel. Igneous silicate and sulfide minerals occur between euhedral ilmenite crystals (sometimes as thin films), suggesting crystallization from an intercumulus liquid. Spheres of sulfide minerals, suggesting sulfide liquid immiscibility, occur within and surrounding plagioclase grains. Baddeleyite and srilankite were not observed in the Ivry ore samples. Thin zircon coronas form between ilmenite (the probable source of zirconium), and plagioclase (the source of silica). Hercynite spinel also seems to supply zirconium in some cases. The occurrence of zircon does not correlate with exsolution in ilmenite. Zircon is also rarely present as discrete euhedral crystals. The zircon, currently undated, might have formed during cooling after Morin Complex emplacement, or during the 1.08 Ga Ottawan orogeny.