Fe-Ti oxide ores in the Proterozoic Suwalki massif-type anorthosite, northeastern Poland, have been recognized through geophysical exploration and extensive drilling down to 2,600 m depth. The Fe-Ti oxide-rich rocks from Suwalki consist of vanadium-poor Ti-magnetite in lenses varying from the centimeter- to the kilometer-scale. Fe-Ti‐rich rocks are commonly layered and have gradational contacts with the host anorthosite; they do not represent well-defined intrusions such as the major Tellnes and Lac Tio deposits. Based on petrography, modal proportions, whole-rock analyses, and liquidus phase compositions of Fe-Ti oxide ores, the sequence of crystallization is as follows: plagioclase + Ti magnetite + ilmenite, followed by orthopyroxene, then clinopyroxene, and finally apatite. The comparatively low V content (0.20‐0.67 wt % V) in Ti magnetite results from relatively oxidized crystallization conditions. The diapiric emplacement of the anorthositic pluton influenced the crystallization of the Fe-Ti ores and is responsible for the crystal sorting controlled by the density contrast of liquidus phases. Polybaric crystallization of Fe-Ti oxide ores is evidenced by variable Al2O3 (ca. 1‐5 wt %) content of the associated orthopyroxene. Polybarism is responsible for the appearance of Fe-Ti oxides before orthopyroxene, due to the decreasing stability field of orthopyroxene with pressure.
The Sept Iles layered intrusion (Quebec, Canada; 564 Ma) is a large plutonic body with a diameter of 80 km and a thickness of 6 km made up from its base to top of a layered series with troctolite and gabbro, and an upper border series with anorthosite, capped by cupolas of A-type granite. Chilled margin compositions suggest a ferrobasaltic parental magma close to that of the Skaergaard intrusion, but much richer in iron and titanium. Samples from drill-cores and surface sampling of the 4·7 km thick layered series reveal a succession of massive troctolites and layered gabbros that contain 24 Fe–Ti oxide layers cm- to m-thick and many anorthositic autolithic blocks. The sequence of crystallization in the layered series is: plagioclase (An72–34) and olivine (Fo75–21) followed by magnetite and ilmenite, then Ca-rich pyroxene and finally apatite. An olivine gap is observed between Fo66 and Fo59. The saturation of Fe–Ti oxides before Ca-rich pyroxene is interpreted to be the result of the high FeOt and TiO2 contents and the low CaO content of the parental magma. Contamination by old continental crust has occurred during crystallization of the layered series, as indicated by Sr isotopic compositions (87Sr/86Sr564 = 0·70360–0·70497). The differentiation trend of the intrusion is interrupted by two large and many small reversals to more primitive compositions of cumulus phases, Cr content of magnetite and lower Sr isotope ratios. These reversals and the intermittent disappearance of some phases are interpreted as resulting from magma chamber replenishments by undifferentiated primitive basaltic magma and mixing with the resident magma.
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