Mesoproterozoic Sm–Nd and U–Pb ages for the Kunene Anorthosite Complex of SW Angola

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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“…U-Pb dating of zircon in a mangerite from this complex gives an age of 1371 ± 2.5 Ma (Mayer et al, 2004).…”

Section: Spatial and Temporal Distributionmentioning

confidence: 92%

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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“…Dikes and sills of the dark anorthosite intruded pale anorthosite, and contain xenoliths of the latter. Plagioclase from the northern KIC anorthosites has an average composition of 70 ± 5% normative An [9], whereas the southern one is An43-53 (white anorthosite) and An43-75 (dark anorthosite) [12]. [9]), indicating the location of the four Fe-Ti(-V) oxide occurrences studied in the present paper: Dongue Sul (1), Tchimbueio (2), Tchingunguanganda (3) and Chiange Velho (4).…”

Section: Introductionmentioning

confidence: 57%

“…Andesine (An ) anorthosites are described to contain the most important magmatic Fe-Ti oxide ores, even if significant resources are described also for labradorite metamorphism on the KIC [20]. Finally, at the eastern side, between 10% and 15% of the KIC is covered by the Pliocene-Quaternary alluvial sediments of the Kalahari Unit [8,9] (Figure 1). …”

Section: Introductionmentioning

confidence: 99%

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Fe–Ti(–V) Oxide Deposits of the Kunene Anorthosite Complex (SW Angola): Mineralogy and Thermo-Oxybarometry

Villanova-de-Benavent

Torró

Castillo-Oliver

et al. 2017

Minerals

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Abstract:The Kunene Intrusive Complex (KIC), in NW Namibia and SW Angola, is one of the largest Proterozoic anorthosite massif-type exposures in the world. A geochemical, mineralogical and petrological study of four Fe-Ti(-V) oxide bodies located in the understudied Angolan part of the KIC has been performed. The massive Fe-Ti(-V) oxide bodies, locally apatite-rich (nelsonites), are lenticular or dike-like. They consist mostly of titaniferous magnetite, ilmenite and minor aluminous spinel, apatite, olivine and graphite. Titaniferous magnetite displays a wide variety of subsolvus features, including aluminous spinel-magnetite-ulvöspinel exsolutions and ilmenite (Trellis) exsolutions. This work estimated the composition of the titaniferous magnetite prior to the exsolution, in order to calculate the temperature and oxygen fugacity of the different lithologies of each ore body. The thermo-oxybarometry results obtained range from 600 • C to 820 • C and f O 2 from 10 −24.7 to 10 −14.7 . These values do not correspond to magmatic crystallization in equilibrium, but to a later re-equilibration. In addition, the mineralogical and geochemical results indicate that the studied ore bodies contain economic reserves of Ti, V, and possibly of P and REE.

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“…O fracionamento de magmas mantélicos de composição básica é indicado na formação de anortositos do tipo maciço como o Kunene Intrusive Com-INTRODUÇÃO Os anortositos são rochas singulares (unique) e apesar do pouco volume crustal são identificados principalmente em terrenos Arqueanos e Proterozóicos de todos os continentes, com expressivas ocorrências na América do Norte, África, Europa e Antártica. Estão presentes desde o inicio do desenvolvimento do sistema solar como podemos constatar a partir de sua abundância na crosta da Lua (Heather & plex, Angola-Namíbia (Mayer et al 2004;Drüppel et al 2007), Labrador Anorthosite, Canadá (Morse 2006), Bjerkrein-Sokndal Intrusion, Noruega (Wilson & Overgaard 2005), Bengal Anorthosite, India (Mukherjee et al 2005), Tin Zebane Layered Intrusion, Argélia (Aït-Djafer et al 2003) e Oranjekom Anorthosite, África do Sul (Geringer et al 1998), entre outros. A fusão de rochas máficas crustais em porções profundas de antigos cinturões colisionais continentais é postulada para a geração de anortositos em associação com gabros e com granitos tipo rapakivi como descritos na Koperberg Suí-te, África do Sul (Geringer et al 1998;Duschesne et al 2007), no Korosten Complex, Ucrânia (Bogdanova et al 2004;Shumlyanskyy et al 2006), Laramie Anorthosite, USA (Scoates et al 2003) e no magmatismo tardia pós-colisional do Cinturão Araçuai-Ribeira, Espirito Santo (Wiedeman et al 2002).…”

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Estruturas primárias e tectônicas do Anortosito Capivarita, Pântano Grande (RS): significado e implicações na sua evolução petrológica

Philipp¹,

Formoso²,

Dossin³

et al. 2010

RBG

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Revista Brasileira de GeociênciasRuy Paulo Philipp et al. 40(1): 99-110, março de 2010 Arquivo digital disponível on-line no site www.sbgeo.org.br 99Estruturas primárias e tectônicas do Anortosito Capivarita, Pântano Grande (RS): significado e implicações na sua evolução petrológica Resumo O Anortosito Capivarita é uma unidade de idade Mesoproterozóica, constituída por anortositos, com presença subordinada de anortositos com granada, metagabros e anfibolitos. Apresenta relações intrusivas com os paragnaisses de alto grau do Complexo Várzea do Capivarita e encontra-se como pendentes de teto nos Granitos Encruzilhada do Sul e Pitangueiras, de idade Neoproterozóica. Estudos estruturais, petrográficos e mineralógicos caracterizaram os anortositos e os gabros como representantes de um magmatismo metaluminoso relacionado a série toleítica. Os protólitos são dominados por anortositos, com ocorrência de corpos tabulares de composição gabróica e níveis de granada anortositos e rochas ricas em óxidos de Fe-Ti, constituindo uma associação de anortosito do tipo maciço. A estrutura bandada é definida por variação composicional e de tamanho de grão, indicando que os anortositos apresentam uma evolução relacionada a processos de fracionamento mineral. As feições estruturais, petrográficas e os padrões composicionais são muito similares aos descritos em anortositos de idade Paleoproterozóica. A presença dominante de anortositos, com anfibolitos associados sugere que a porção principal desta associação pode representar acumulações de plagioclásio formadas pelo fluxo magmático e/ou por flotação, associada ao assentamento gravitacional. As feições estruturais primárias e composicionais dos anortositos sugerem que este magmatismo ocorreu sob condições anorogênicas, em um ambiente estável, provavelmente cratônico. Após a sua cristalização o anortosito foi afetado por um evento de metamorfismo regional orogênico sob condições da fácies anfibolito superior a Granulito. Palavras-chave:Anortosito Capivarita, gabros, tipo maciço, septos do embasamento, Cinturão Dom Feliciano. Abstract Primary and tectonics structures of Capivarita Anortosite, Pântano Grande, RS: meaning and implication from petrologic evolution. The Capivarita Anorthosite is a unit of Mesoproterozoicage constituted by anorthosite with subordinate presence of garnet anorthosite, metagabros and amphibolites. The anorthosite shows intrusive relationship with high degree paragneisses of Várzea do Capivarita Complex and occurs as a roof pendant in the Neoproterozoic Encruzilhada do Sul and Pitangueiras granites. Structural, petrographic and mineralogical studies characterized the anorthosite and amphibolites as magmatism probably related to tholeitic series. The protoliths are dominated by anorthosites with occurrence of garnet anorthosites and rocks rich in Fe-Ti oxides, constituting an association of massif-type anorthosite. The banded structure is defined by regular variations in composition and size of grains, probably related to mineral fractionation process. The str...

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Mesoproterozoic Sm–Nd and U–Pb ages for the Kunene Anorthosite Complex of SW Angola

Cited by 100 publications

References 26 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

Fe–Ti(–V) Oxide Deposits of the Kunene Anorthosite Complex (SW Angola): Mineralogy and Thermo-Oxybarometry

Estruturas primárias e tectônicas do Anortosito Capivarita, Pântano Grande (RS): significado e implicações na sua evolução petrológica

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