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See detailFe–Ti–V–P ore deposits associated with Proterozoic massif-type anorthosites and related rocks
Charlier, Bernard ULg; Namur, Olivier; Bolle, Olivier ULg et al

in Earth-Science Reviews (2015), 141(0), 56-81

Magmatic rocks containing economic concentrations of iron, titanium, vanadium and phosphorous are commonly associated with massif-type anorthosites and related rocks. This rock association is part of the ... [more ▼]

Magmatic rocks containing economic concentrations of iron, titanium, vanadium and phosphorous are commonly associated with massif-type anorthosites and related rocks. This rock association is part of the anorthosite–mangerite–charnockite–(rapakivi-)granite suites that are restricted to the Proterozoic. Understanding the geochemistry and emplacement mechanisms of ilmenite, magnetite and apatite ore deposits is crucial for exploration, efficient mining operations and ore processing. This review discusses the controlling factors on the grade of an ore, its mineralogy, and its major and trace element distribution. We present petrogenetic models of currently mined deposits (Lac Tio, Tellnes, Damiao) and discuss the characteristics of minor ore bodies from anorthosite provinces worldwide (Grenville, North China Craton, East European Craton, Rogaland, Laramie). Models of formation of anorthosite and related rocks are presented, as well as the nature of the possible parental magmas of the suite. A mineralogical classification of Fe–Ti ores is proposed: (1) Gabbro-noritic ilmenite ore ± apatite ± magnetite; (2) Ti-magnetite-dominated ore; (3) Nelsonite (Fe–Ti oxides + apatite); and (4) Rutile-ilmenite ore. The stability of ilmenite and magnetite is then critically reviewed and the influence of various factors, particularly oxygen fugacity and crystallization pressure, is examined. We discuss liquidus compositions of Fe–Ti oxides and the behavior of important trace elements such as Cr and V, both of which are sensitive to fO2 variations. Post-cumulus evolution of both oxides can occur due to re-equilibration with trapped liquid, re-equilibration with ferromagnesian silicates, exsolution, oxidation, reaction between ilmenite and magnetite, and metamorphic overprinting. These various processes are described and their effects on the oxide geochemistry are emphasized. Several potential ore-forming processes have been invoked and can explain the formation of huge concentration of ilmenite, ± magnetite, ± apatite. Fractional crystallization can be combined with crystal sorting and plagioclase buoyancy to produce relative enrichment of dense ore minerals. Silicate liquid immiscibility can segregate conjugate Si-rich and Fe-rich melts, the latter being enriched in Fe–Ti–P. Magma mixing can produce hybrid magmas located in a single-phase field of the phase diagram and precipitate a pure ilmenite cumulate. Alternative processes are also described, such as ejection of Fe–Ti-enriched residual melts by filter-pressing and compaction, solid-state remobilization of ilmenite in veins, and hydrothermal transport of Fe and Ti from the host anorthosite followed by concentration in veins and lenticular ore bodies. The magnetic properties of Fe–Ti ore deposits present contrasting signatures, depending on whether the natural remanent magnetization is dominated by hemo-ilmenite or multi-domain magnetite. Micro- and macro-scale deformation features of ore rocks are intimately correlated with magma emplacement, and with ballooning of the anorthosite diapir associated with gravitational sagging of dense ore bodies. Exploration perspectives show that oxide-apatite gabbronorites are interesting targets because ilmenite in these rocks is poorer in Cr and Mg, and because the Ti-resource may be combined with apatite and vanadiferous magnetite. [less ▲]

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See detailMagma flow and feeder chamber location inferred from magnetic fabrics in jotunitic dykes (Rogaland anorthosite province, SW Norway)
Bolle, Olivier ULg; Besse, Michal; Diot, Hervé

in Tectonophysics (2010), 493(1-2), 42-57

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See detailSveconorwegian (Grenvillian) Massif type anorthosites and related granitoids result from postcollisional remelting of a continental arc root
Vander Auwera, Jacqueline ULg; Bolle, Olivier ULg; Bingen, Bernard et al

in EOS : Transactions, American Geophysical Union (2009), 90(52), 11-02

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