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See detailThe origin of nelsonite and high-Zr ferrodiorite associated with Proterozoic anorthosite
Duchesne, Jean-Clair ULg; Liégeois, Jean-Paul

in Ore Geology Reviews (2015), 71

A petrological and geochemical (major and trace elements, Sr-Nd isotopes) study of two nelsonite occurrences (the Kydlandsvatn and Hestnes deposits) in the Rogaland anorthosite province (Southern Norway ... [more ▼]

A petrological and geochemical (major and trace elements, Sr-Nd isotopes) study of two nelsonite occurrences (the Kydlandsvatn and Hestnes deposits) in the Rogaland anorthosite province (Southern Norway) reveals that both deposits are cumulates but were generated from strikingly different magmas and processes. The Kydlandsvatn deposit was formed from a primitive jotunite similar to the Bjerkreim-Sokndal parental magma by crystal accumulation. By contrast, the Hestnes cumulate, with high REE and Zr contents, negative Eu anomaly, Cr-rich magnetite, Nb-rich ilmenite and high Nb/Ta and Zr/Hf whole-rock ratios appears to result from the crystallization of an immiscible Fe-rich and Si-poor melt under highly oxidized conditions. Other jotunites/ferrodiorites with high Zr-contents are typically associated with anorthosites in the Rogaland, Laramie and Adirondacks anorthosite complexes. In Rogaland, they also have an identical Sr-Nd isotope signature as the Hestnes nelsonite. These high-Zr jotunites cannot have been produced through extreme differentiation of ordinary jotunite magmas. Their formation from direct melting of a crustal source or assimilation of a nelsonite cumulate is highly unlikely. Occurrence of a high-Zr jotunite at the margin of a quartz mangerite dyke is evidence that immiscibility takes place, though furtively, along the jotunite liquid line of descent. It is suggested here that high-Zr jotunites in dyke rocks or parental to high Zr-nelsonites resulted from fractional crystallization of a Fe-rich immiscible melt formed at higher pressures in the polybaric evolution of anorthosites, conditions that are not yet explored experimentally. [less ▲]

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See detailShort note: Synthetic ilmenite as a blank to XRF trace element determination
Duchesne, Jean-Clair ULg; Bologne, Guy

in Geologica Belgica (2011), 14(1-2), 103-106

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See detailXRF major and trace element determination in Fe-Ti oxide minerals
Duchesne, Jean-Clair ULg; Bologne, Guy

in Geologica Belgica (2009), 12(3-4), 205-212

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See detailA-type magmatic suites as tracers of the lower crust
Vander Auwera, Jacqueline ULg; Bogaerts, Michel; Liégeois, Jean-Paul et al

in AGC/GAC – AMC/MAC – SEG – SGA Abstract Volume (2008), 33

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See detailThe Grader layered intrusion (Havre-Saint-Pierre anorthosite, Québec) and genesis of nelsonite and other Fe-Ti-P ores
Charlier, Bernard ULg; Sakoma, Emmanuel; Sauvé, Martin et al

in Lithos (2008), 101(3-4), 359-378

The Grader layered intrusion is part of the Havre-Saint-Pierre anorthosite in the Grenville Province (Quebec, Canada). This intrusion has a basin-like morphology and contains significant resources of ... [more ▼]

The Grader layered intrusion is part of the Havre-Saint-Pierre anorthosite in the Grenville Province (Quebec, Canada). This intrusion has a basin-like morphology and contains significant resources of Fe–Ti–P in ilmenite and apatite. Outcropping lithologies are massive oxide alternating with anorthosite layers, banded ilmenite–apatite–plagioclase rocks and layered oxide apatite (gabbro-)norites. Drill cores provide evidence for stratigraphic variations of mineral and whole rock compositions controlled by fractional crystallization with the successive appearance of liquidus phases: plagioclase and ilmenite followed by apatite, then orthopyroxene together with magnetite, and finally clinopyroxene. This atypical sequence of crystallization resulted in the formation of plagioclase–ilmenite–apatite cumulates or “nelsonites” in plagioclase-free layers. Fine-grained ferrodiorites that cross-cut the cumulates are shown to be in equilibrium with the noritic rocks. The high TiO2 and P2O5 contents of these assumed liquids explains the early saturation of ilmenite and apatite before Fe–Mg silicates, thus the nelsonites represent cumulates rather than crystallized Fe–Ti–P-rich immiscible melts. The location of the most evolved mineral and whole rock compositions several tens of meters below the top of the intrusion, forming a sandwich horizon, is consistent with crystallization both from the base and top of the intrusion. The concentrations of V and Cr in ilmenite display a single fractionation path for the different cumulus assemblages and define the cotectic proportion of ilmenite to 21 wt.%. This corresponds to bulk cotectic cumulates with ca. 8 wt.% TiO2, which is significantly lower than what is commonly observed in the explored portion of the Grader intrusion. The proposed mechanism of ilmenite-enrichment is the lateral removal of plagioclase due to its relative buoyancy in the dense ferrodiorite melt. This plagioclase has probably accumulated in other portions of the intrusion or has not been distinguished from the host anorthosite. [less ▲]

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See detailEmpirical calibration of the V partitioning between magnetite and ilmenite as an oxybarometer
Duchesne, Jean-Clair ULg; Vander Auwera, Jacqueline ULg; Charlier, Bernard

in EOS : Transactions, American Geophysical Union (2007), 88(52), 54-08

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See detailIlmenite composition in the Tellnes Fe–Ti deposit, SW Norway: fractional crystallization, postcumulus evolution and ilmenite–zircon relation
Charlier, Bernard ULg; Skar, Oyvind; Korneliussen, Are et al

in Contributions to Mineralogy & Petrology (2007), 154(2), 119-134

Major and trace element XRF and in situ LA-ICP-MS analyses of ilmenite in the Tellnes ilmenite deposit, Rogaland Anorthosite Province, SW Norway, constrains a two stage fractional crystallization model of ... [more ▼]

Major and trace element XRF and in situ LA-ICP-MS analyses of ilmenite in the Tellnes ilmenite deposit, Rogaland Anorthosite Province, SW Norway, constrains a two stage fractional crystallization model of a ferrodioritic Fe-Ti-P rich melt. Stage 1 is characterized by ilmenite-plagioclase cumulates, partly stored in the lower part of the ore body (Lower Central Zone, LCZ), and stage 2 by ilmenite-plagioclase-orthopyroxene-olivine cumulates (Upper Central Zone, UCZ). The concentration of V and Cr in ilmenite, corrected for the trapped liquid effect, (1) defines the cotectic proportion of ilmenite to be 17.5 wt% during stage 1, and (2) implies an increase of D VIlm during stage 2, most likely related to a shift in fO2. The proportion of 17.5 wt% is lower than the modal proportion of ilmenite (ca. 50 wt%) in the ore body, implying accumulation of ilmenite and flotation of plagioclase. The fraction of residual liquid left after crystallization of Tellnes cumulates is estimated at 0.6 and the flotation of plagioclase at 26 wt% of the initial melt mass. The increasing content of intercumulus magnetite with stratigraphic height, from 0 to ca. 3 wt%, results from differentiation of the trapped liquid towards magnetite saturation. The MgO content of ilmenite (1.4–4.4 wt%) is much lower than the expected cumulus composition. It shows extensive postcumulus re-equilibration with trapped liquid and ferromagnesian silicates, correlated with distance to the host anorthosite. The Zr content of ilmenite, provided by in situ analyses, is low (<114 ppm) and uncorrelated with stratigraphy or Cr content. The data demonstrate that zircon coronas observed around ilmenite formed by subsolidus exsolution of ZrO2 from ilmenite. The U-Pb zircon age of 920 ± 3 Ma probably records this exsolution process. [less ▲]

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