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See detailPetrogenesis of the Kabanga-Musongati layered mafic-ultramafic intrusions in Burundi (Kibaran Belt): geochemical, Sr-Nd isotopic constraints and Cr-Ni behaviour
Duchesne, Jean-Clair ULg; Liégeois, Jean-Paul ULg; Deblond, André et al

in Journal of African Earth Sciences (2004), 39

A succession of mafic-ultramafic layered intrusions forms an alignment in the boundary zone between the Kibaran belt and the Tanzania craton. The intrusions represent a continuous series of cumulate rocks ... [more ▼]

A succession of mafic-ultramafic layered intrusions forms an alignment in the boundary zone between the Kibaran belt and the Tanzania craton. The intrusions represent a continuous series of cumulate rocks. For instance, in the Mukanda-Buhoro and Musongati (MBM) contiguous bodies, the series starts with dunite and passes to lherzolite, pyroxenite, norite, gabbronorite and anorthosite on top. Cumulate textures are conspicuous in all rock types and cryptic layering characterises cumulus mineral compositions, thus evidencing fractional crystallization as a major differentiation mechanism. The increase of Cr in the ultramafic members of the series indicates that chromite was not a liquidus mineral in dunite and lherzolite rocks, thus unable to form chromitite layers. The high Ni-content of dunite seems to preclude the existence of conjugate Ni-rich sulphide deposits. The 87Sr/86Sr initial ratio is relatively constant and averages 0.7087, with some values up to 0.712 due to local assimilation. Fine-grained rocks from the MBM area are isotopically (Nd and Sr) similar to the MBM cumulates. Modelling their crystallization produces cumulus mineral compositions similar to those in the Musongati ultramafic rocks, which suggests a broadly picritic parental magma. On the other hand, fine-grained rocks from the Nyabikere area are not related to the Nyabikere cumulates. Nd and Sr isotope ratios show that the MBM magmatism is related to an enriched source, possibly an old subcontinental lithospheric mantle. The Nyabikere dykes, as well as the Waga dykes, come from a depleted mantle source, as do the A-type granitoids occurring in the same boundary zone. Several lines of evidence point to two types of parental magmas, a picritic magma, and a more evolved magma, broadly similar to the Bushveld Main Zone magma. [less ▲]

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See detailPetrographic evidence for primary hagendorfite in an unusual assemblage of phosphate minerals, Kibingo granitic pegmatite, Rwanda
Fransolet, André-Mathieu ULg; Hatert, Frédéric ULg; Fontan, François

in Canadian Mineralogist (2004), 42(Part 3), 697-704

A sample from the Kibingo granitic pegmatite, Rwanda, shows a striking assemblage of an alluaudite-group mineral with heterosite. The core of alluaudite s.l. is strongly pleochroic in blue green to ... [more ▼]

A sample from the Kibingo granitic pegmatite, Rwanda, shows a striking assemblage of an alluaudite-group mineral with heterosite. The core of alluaudite s.l. is strongly pleochroic in blue green to pinkish grey hues, and is rimmed by an irregular border, weakly pleochroic in yellow brown to greenish yellow tints. The pleochroic core is very rich in Na (up to 9.35% Na2O), whereas the yellowish green border is depleted in Na (3.75% Na2O) and more oxidized. The decrease of the Na contents is not accompanied by significant variations of the ratio Fe-tot/(Fe-tot + Mn). This mechanism represents the progressive transition of hagendorfite to alluaudite sensu stricto, and results from an oxidation, Na+ + Fe2+ --> rectangle + Fe3+. Heterosite exhibits cracks that are parallel to one of the cleavage directions, and that are favorable to the development of a product of alteration, identified as cyrilovite. Heterosite shows a chemical composition close to the idealized formula (Fe0.853+Mn0.153+)PO4, with a Mg content constant and quite low, i.e., 0.023 Mg apfu. The Kibingo heterosite seems to be the Fe-richest member known so far. The heterosite corresponds to an oxidized Fe-rich member of the triphylite - lithiophilite series, a member that was initially in equilibrium with the primary hagendorfite. The ratio Fe-tot/(Fe-tot + Mn) of the two minerals of this assemblage is different: the value is about 0.70 ire hagendorfite, and 0.85 in the former triphylite. The temperature of formation of hagendorfite is estimated at about 600degreesC. Contrary to the information in the literature, the Kibingo pegmatitic body differs from the amblygonite pegmatite of Mwaka and could be a poorly evolved neighboring pegmatitic lens. [less ▲]

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See detailPetrographical and sedimentological contributions to the Lower Devonian in eastern Belgium
Catot, E.; Goemare, E.; Dejonghe, L. et al

Conference (1994)

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See detailPetrographical differentiation between Palaeozoic oolitic ironstones from France, Belgium and Germany and application to the provenance study of archaeological artefacts – preliminary results
Dreesen, Roland; Savary, Xavier; Goemaere, Eric et al

Conference (2013, February 07)

Samples of Palaeozoic oolitic ironstone beds susceptible of having being used as raw materials for Neolithic red ochres, have been petrographically investigated. The preliminary results of this first ... [more ▼]

Samples of Palaeozoic oolitic ironstone beds susceptible of having being used as raw materials for Neolithic red ochres, have been petrographically investigated. The preliminary results of this first comparative analysis are quite encouraging: microfacies differences have been observed between Ordovician oolitic ironstones from Normandy (France), late Upper Devonian oolitic ironstones from Belgium and uppermost Lower Devonian to lowermost Middle-Devonian (Emsian-Eifelian) oolitic ironstones from the Eifel area (Germany). Petrographical differentiation is based upon contrasting grain size, mineralogy (hematite/chlorite ratio) and typology of the ferruginous ooids, besides differences in mineralogy, diagenetic history and lithologic nature of the host sediments. Most conspicuous are differences in ferruginous ooid typology, including “true” concentric ooids, superficial ooids, algal oncoids and pseudo-ooids (ferruginized cortoids and rounded bioclasts). “Flax seed” or Clinton-type iron ores (rich in flattened ooids) and “fossil iron ores” (essentially composed of ferruginized bioclasts) can be identified as well as transitional or mixed types. Homogenous and well-sorted, often flattened and fine-grained ferruginous “true” ooids (flax seed ore) with alternating hematite and chlorite cortices in a sideritic- chloritic or fine siliciclastic matrix, are characteristic for the Ordovician (Llanvirn) oolitic ironstones of Normandy (basal part of the Urville Shales). Locally, weathered levels exist, enclosing limonitic (goethitic) crusts. Medium-sorted, fine-to coarse- grained ferruginous hematitic pseudo-ooids (ferruginized bioclasts) in a bioclastic limestone matrix (fossil ore) characterize the Lower-Middle Devonian boundary oolitic ironstone beds (Heisdorf and Lauch Formations, Eifel Synclines). Finally, well- to medium-sorted heterogenous, fine- to medium-grained, pure or mixed flax seed- and fossil ore-type hematitic oolitic ironstones in siliclastic and/ore carbonate matrices, characterize the Belgian Latest Upper Devonian (Famennian) ironstone deposits (Hodimont Formation, Famenne Shales Group). Several stratigraphic levels do exist within the Lower Famennian and basal part of the Upper Famennian in the Namur, Dinant and Vesdre Synclinoria, but the lowermost Famennian one is the only level that has been mined. Within some of the younger Famennian oolitic ironstone levels, proximal and distal facies can be distinguished on the basis of microfacies differences and mineralogy of the ferruginous pseudo-ooids. Only the proximal hematitic facies of the lowest stratigraphical oolitic ironstone level (level I) is supposed to have been used in prehistoric times for the manufacturing of ochre. Diagenetic sideritization and dolomitization, particle deformation as well as sulphide mineralizations, affect most of the studied oolitic ironstones. However, the intensity of these mineralizations varies strongly (even within the same deposit) and depends on local tectonics. A distinction can be made between the Emsian-Eifelian and Famennian fossil iron ores, based on the nature of the bioclasts and other ferruginzed components). Eifelian oolitic ironstones contain ferruginized crinoids, bryozoans, trilobites, brachiopods, goniatites besides ferruginized siliciclastic intraclasts, whereas the Famennian ones are dominated by ferruginous ooids and algal oncoids, mixed with ferruginized bioclasts including crinoids, bryozoans, brachiopods, ostracods, algae and incertae sedis, and locally intraclasts (ferruginized stromatolitic crusts). Distal facies contain slightly Fe-impregnated bioclasts only such as crinoid ossicles and display a higher chlorite/hematite ratio. Thin sections have been made in archeological objects (red ochre), allowing a first comparative petrographical analysis indicating their probable geological and geographical provenance. References Ph. Joseph, 1982. Le minerai de fer oolithique Ordovicien du Massif Armoricain: sédimentologie et paléogéographie. Thèse présentée à l’Ecole Nationale Supérieure des Mines de Paris. 325 p. R. Dreesen, 1989. Oolitic ironstones as event-stratigraphical marker beds within the Upper Devonian of the Ardenno-Rhenish Massif, in: Young, T.P. & Taylor, W.E.G. (eds), Phanerozoic Ironstones. Geological Society Special Publications, n°46, pp. 65-78 Rath, S., 2003. Die Erforschungsgeschichtede Eifel-Geologie. Ph.D. Dissertation, Rheinisch- Westfälische Technische Hochschule Aachen, 239 p. [less ▲]

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See detailPétrographie des roches du Westphalien B dans le bassin du centre de Liège
Darimont, Anne ULg

in Annales de la Société Géologique de Belgique (1976), 99

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See detailPétrologie sédimentaire: des roches aux processus
Boulvain, Frédéric ULg

Book published by Ellipses (2010)

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See detailPetrology and geochemistry of rapakivi-type granites from the crystalline basement of NE Poland
Baginski, Boguslaw; Duchesne, Jean-Clair ULg; Vander Auwera, Jacqueline ULg et al

in Geological Quarterly (2001), 45(1), 33-52

The collection of 80 rock samples coming from drillcores of 8 localities from the Mazury Complex (Polish part of the crystalline East European Craton) and representing different rock types from ... [more ▼]

The collection of 80 rock samples coming from drillcores of 8 localities from the Mazury Complex (Polish part of the crystalline East European Craton) and representing different rock types from monzodiorites to leucogranites, were studied for major, trace and REE elements by XRF and ICP-MS methods. The range in composition of investigating rocks varies from 46% to 76% SiO2 contents. All of them show similar REE distributions, what suggests that they are genetically linked. They also plot along a major trend with many similarities to the jotunitic liquid line of descent (LLD) defined in AMCG rocks from Rogaland (Norway). Each group of rocks has however its own characteristics considering specific elements, such as REE, Sr or Zr. [less ▲]

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See detailPetrology and geochemistry of the noritic Hogstad layered body (Rogaland, southwestern Norway) : evidence of a jotunitic parent magma
Vander Auwera, Jacqueline ULg; Duchesne, Jean-Clair ULg

in Demaiffe, Daniel (Ed.) Petrology and geochemistry of magmatic suites of rocks in the continental and oceanic crusts (1996)

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See detailPetrology of the Lyngdal granodiorite (southern Norway) and the role of fractional crystallization in the genesis of Proterozoic rapakivi-like granites
Bogaerts, Michel; Scaillet, Bruno; Liégeois, Jean-Paul ULg et al

in Precambrian Research (2003), 124(2-4), 149-184

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See detailUn peu de vocabulaire
Baiwir, Esther ULg

in Lempereur, Françoise; Bertha, A. (Eds.) 100 ans de menuiserie dans l'arrondissement de Verviers (2005)

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See detailPeuple absent, peuple introuvable. Le fantôme du XIXe siècle
Durand, Pascal ULg

in Hermès (2005), 42

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See detailUn peuple et ses pères. Lubumbashi entre démodernisation et postmodernité. Approche des associations locales de type ONG
Poncelet, Marc ULg; Pirotte, Gautier ULg

in Charlier, Jean-Emile; Moens, Frédéric (Eds.) Modernité et recomposition locale du sens (1999)

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See detailPeuple, populaire, populisme
Durand, Pascal ULg; Lits, M.

in Hermès (2005), 42

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See detailPeuple, populaire, populisme
Durand, Pascal ULg; Lits, Marc

in Hermès (2005), 42

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