| Titre | Origin of chromitites in the Esker Intrusive Complex, Ring of Fire Intrusive Suite, as revealed by chromite trace element chemistry and simple crystallization models |
| Télécharger | Téléchargement (publication entière) |
| |
| Licence | Veuillez noter que la Licence du gouvernement
ouvert - Canada remplace toutes les licences antérieures. |
| Auteur | Brenan, J M ;
Woods, K; Mungall, J E; Weston, R |
| Source | Targeted Geoscience Initiative 5: grant program final reports (2018-2020); par Targeted Geoscience Initiative Coordination Office; Commission géologique du Canada, Dossier public 8755, 2021 p. 25-43, https://doi.org/10.4095/328981  Accès ouvert |
| Année | 2021 |
| Éditeur | Ressources naturelles Canada |
| Document | dossier public |
| Lang. | anglais |
| DOI | https://doi.org/10.4095/328981 |
| Media | en ligne; numérique |
| Référence reliée | Cette publication est contenue dans Targeted
Geoscience Initiative 5: grant program final reports (2018-2020) |
| Référence reliée | Cette publication est reliée à Origin of
chromitites in the Ring of Fire Part II: trace element fingerprinting of contaminants |
| Formats | pdf; xlsx (Microsoft® Excel®) |
| Province | Ontario |
| SNRC | 43C/03; 43C/04; 43C/05; 43C/06; 43C/11; 43C/12; 43C/13; 43C/14; 43D/01; 43D/02; 43D/03; 43D/06; 43D/07; 43D/08; 43D/09; 43D/10; 43D/11; 43D/14; 43D/15; 43D/16; 43E/01; 43E/02; 43E/03; 43E/06; 43E/07;
43E/08; 43F/03; 43F/04; 43F/05; 43F/06 |
| Lat/Long OENS | -87.3167 -85.3833 53.3500 52.1500 |
| Sujets | gisements minéraux; chromite; prospection minière; genèse des minerais; minéralisation; cristallisation; cristallisation fractionnée; dynamique des fluides; établissement de modèles; géologie du
substratum rocheux; lithologie; roches ignées; roches intrusives; chromitites; granodiorites; roches volcaniques; komatiites; roches sédimentaires; formations ferrifères; roches métamorphiques; roches sédimentaires métamorphosées; géochimie des
éléments en trace; géochimie des éléments majeurs; formations de cumulus; silicates; olivine; géochimie du vanadium; géochimie du gallium; géochimie du chrome; géochimie de l'aluminium; géochimie du fer; géochimie du magnesium; roches hôtes; cadre
tectonique; magmatisme; mise en place; Archéen; Province de Superior ; géologie économique; géochimie; tectonique; Sciences et technologie; Nature et environnement; Précambrien |
| Illustrations | cartes de localisation; cartes géolscientiques généralisées; photographies; photomicrographies; graphiques; tableaux |
| Programme | Initiative géoscientifique ciblée (IGC-5) Gestion de la connaissance de IGC |
| Diffusé | 2021 10 27 |
| Résumé | (disponible en anglais seulement)
To better constrain the origin of the chromitites associated with the Esker Intrusive Complex (EIC) of the Ring of Fire Intrusive Suite (RoFIS), a total of 50
chromite-bearing samples from the Black Thor, Big Daddy, Blackbird, and Black Label chromite deposits have been analysed for major and trace elements. The samples represent three textural groups, as defined by the relative abundance of cumulate
silicate phases and chromite. To provide deposit-specific partition coefficients for modeling, we also report on the results of laboratory experiments to measure olivine- and chromite-melt partitioning of V and Ga, which are two elements readily
detectable in the chromites analysed.
Comparison of the Cr/Cr+Al and Fe/Fe+Mg of the EIC chromites and compositions from previous experimental studies indicates overlap in Cr/Cr+Al between the natural samples and experiments done at >1400oC, but
significant offset of the natural samples to higher Fe/Fe+Mg. This is interpreted to be the result of subsolidus Fe-Mg exchange between chromite and the silicate matrix. However, little change in Cr/Cr+Al from magmatic values, owing to the lack of an
exchangeable reservoir for these elements. A comparison of the composition of the EIC chromites and a subset of samples from other tectonic settings reveals a strong similarity to chromites from the similarly-aged Munro Township
komatiites.
Partition coefficients for V and Ga are consistent with past results in that both elements are compatible in chromite (DV = 2-4; DGa ~ 3), and incompatible in olivine (DV = 0.01-0.14; DGa ~ 0.02), with values for V increasing with
decreasing fO2. Simple fractional crystallization models that use these partition coefficients are developed that monitor the change in element behaviour based on the relative proportions of olivine to chromite in the crystallizing assemblage; from
'normal' cotectic proportions involving predominantly olivine, to chromite-only crystallization. Comparison of models to the natural chromite V-Ga array suggests that the overall positive correlation between these two elements is consistent with
chromite formed from a Munro Township-like komatiitic magma crystallizing olivine and chromite in 'normal' cotectic proportions, with no evidence of the strong depletion in these elements expected for chromite-only crystallization. The V-Ga array can
be explained if the initial magma responsible for chromite formation is slightly reduced with respect to the FMQ oxygen buffer (~FMQ- 0.5), and has assimilated up to ~20% of wall-rock banded iron formation or granodiorite.
Despite the evidence for
contamination, results indicate that the EIC chromitites crystallized from 'normal' cotectic proportions of olivine to chromite, and therefore no specific causative link is made between contamination and chromitite formation. Instead, the development
of near- monomineralic chromite layers likely involves the preferential removal of olivine relative to chromite by physical segregation during magma flow. As suggested for some other chromitite-forming systems, the specific fluid dynamic regime
during magma emplacement may therefore be responsible for crystal sorting and chromite accumulation. |
| Sommaire | (Résumé en langage clair et simple, non publié)
L'Initiative des géosciences ciblées (IGC) est un programme fédéral collaboratif. Ce programme fournit à l'industrie ce qui est requis pour la
prochaine génération des connaissances géoscientifiques et des techniques novatrices. Le résultat est l'identification des dépôts de minéraux en profondeur. Ce compendium est le résultat des récipiendaires des subventions d'IGC 2018-2020. |
| GEOSCAN ID | 328981 |
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