Mineralogy and geochemistry of Fe-Ti oxide and apatite (nelsonite) deposits and evaluation of the liquid immiscibility hypothesis

Kolker, Allan

doi:10.2113/gsecongeo.77.5.1146

Cited by 120 publications

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“…Philpotts (1967) proposed that immiscibility is responsible for the origin of certain Fe-Ti oxide and apatite rocks. Kolker (1982) also favored this model for the origin of nelsonites, mainly to explain field evidence such as discordant veins and dykes intruding the host anorthosite (Fig. 17a).…”

Section: Immiscibilitymentioning

confidence: 85%

“…Unlike oxide-apatite gabbronorites (Owens and Dymek, 1992) these rocks are devoid of silicates. Some nelsonites display modal proportions close to one third apatite, two thirds Fe-Ti oxide (Philpotts, 1967;Kolker, 1982) but this is not a general rule. Apatite is commonly fluorine-rich (Dymek and Owens, 2001) and REE-rich (Duchesne, 1999).…”

Section: Nelsonitementioning

confidence: 90%

“…Moreover, the relative proportion of oxides and apatite, ca. 2/3 oxides and 1/3 apatite (Kolker, 1982), does not necessarily indicate an origin related to immiscibility. This could instead simply reflect cotectic proportions of Fe-Ti oxides and apatite crystallizing from a silicate melt, which are not then sorted during the concentration process.…”

Section: Immiscibilitymentioning

confidence: 93%

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Fe–Ti–V–P ore deposits associated with Proterozoic massif-type anorthosites and related rocks

Charlier

Namur

Bolle

et al. 2015

Earth-Science Reviews

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a b s t r a c t a r t i c l e i n f oMagmatic 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 anorthositemangerite-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 fO 2 variations. Postcumulus 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, solidstate 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...

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Section: Immiscibilitymentioning

confidence: 85%

Section: Nelsonitementioning

confidence: 90%

Section: Immiscibilitymentioning

confidence: 93%

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Fe–Ti–V–P ore deposits associated with Proterozoic massif-type anorthosites and related rocks

Charlier

Namur

Bolle

et al. 2015

Earth-Science Reviews

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“…D'un point de vu économique ces roches peuvent représenter une source importante de phosphore et de Fe-Ti (Kolker, 1982).…”

Section: Ou Aux Stades Tardifs D'intrusions Litées (Voir Paragraphesunclassified

“…La roche la plus insolite de cette famille de roche est la nelsonite. et Kolker (1982), les nelsonites ont le plus souvent une texture homogène, i. e-équigranulaire à grains fins ( Fig. 1.1).…”

Section: Introductionunclassified

Saturation des minéraux phosphatés dans les magmas silicatés :

Tollari¹

2007

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Evidence of silicate immiscibility within flood basalts from the Central Atlantic Magmatic Province

Shellnutt

Dostál

Iizuka

2013

Geochem Geophys Geosyst

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[1] The role silicate-liquid immiscibility plays in the formation of macro-scale, bimodal volcanic/plutonic igneous complexes, and Fe-Ti oxide deposits is debated as the rock compositions produced by immiscibility are similar to those produced by other petrological processes. Within the flows of the North Mountain basalt of the Central Atlantic Magmatic Province are centimeter-thick granophyre layers. The granophyre layers are a mixture of mafic (i.e., ilmenite, magnetite, ferroaugite, plagioclase, stilpnomelane, ferrorichterite) and felsic (i.e., sanidine, quartz) minerals and highly siliceous (>75 wt% SiO 2 ) mesostases. Petrological modeling indicates that the siliceous mesostasis 1 sanidine 1 quartz 6 ferrorichterite represents a Si-rich silicate immiscible melt whereas the ferroaugite 1 plagioclase 1 stilpnomelane represent the Fe-rich silicate immiscible liquid. The identification of naturally occurring silicate-liquid immiscibility at scales greater than micron level is an important observation which may be useful in identifying volcanic and plutonic rocks which formed by macro-scale silicate-liquid immiscibility.

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Mineralogy and geochemistry of Fe-Ti oxide and apatite (nelsonite) deposits and evaluation of the liquid immiscibility hypothesis

Cited by 120 publications

References 0 publications

Fe–Ti–V–P ore deposits associated with Proterozoic massif-type anorthosites and related rocks

Fe–Ti–V–P ore deposits associated with Proterozoic massif-type anorthosites and related rocks

Saturation des minéraux phosphatés dans les magmas silicatés :

Evidence of silicate immiscibility within flood basalts from the Central Atlantic Magmatic Province

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