Origin of the giant Allard Lake ilmenite ore deposit (Canada) by fractional crystallization, multiple magma pulses and mixing

摘要: Abstract The late-Proterozoic Allard Lake ilmenite deposit is located in the Havre-Saint-Pierre anorthosite complex, part of allochtonous polycyclic belt Grenville Province. Presently world's largest Fe–Ti oxide deposit, it had a pre-mining amount excess 200 Mt at grades over 60 wt.% hemo-ilmenite. main ore body funnel-shaped intrusion, measuring 1.03 × 1.10 km and 100–300 m-thick. Two smaller bodies are separated by faults anorthosite. an ilmenite-rich norite (or ilmenitite) made up hemo-ilmenite (Hem22.6–29.4, 66.2 wt.% on average), andesine plagioclase (An45–50), aluminous spinel locally orthopyroxene. Whole-rock chemical compositions controlled proportions plagioclase ± orthopyroxene which supports cumulate origin deposit. Ore-forming processes further constrained normal reverse fractionation trends Cr concentration cumulus that reveal multiple magma emplacements alternating periods fractional crystallization mixing. Mixing magmas produced hybrids stability field resulted periodic alone. unsystematic differentiation arising from succession pulses, hybridisation, alone or together with suggest formed within conduit. This dynamic emplacement mechanism associated continuous gravity driven accumulation oxides possibly buoyancy fractionating ferrobasalt explains huge occurrence sapphirine high-alumina orthopyroxene (7.6–9.1 wt.% Al2O3) lacking exsolved involvement metamorphic overprint during synchronous Ottawan orogeny, also responsible for strong textural equilibration external granule due to slow cooling.