| Titre | Origin of chromitites in the Ring of Fire Part II: trace element fingerprinting of contaminants |
| Télécharger | Téléchargement (publication entière) |
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| 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 interim reports 2018-2019; par Benn, D; Brenan, J M; Fuller, K; Grondahl, C; Layton-Matthews, D; Leybourne, M I; Linnen, R; Martins, T; Milidragovic, D ; Moynihan, D P; Mungall, J E; Nixon, G T; Padget, C D W;
Pattison, D R M; Rempel, K U; Scanlan, E J; Scoates, J S; Tsay, A; Voinot, A; Van Wagoner, N A; Weston, R; Williams-Jones, A E; Woods, K; Zajacz, Z; Commission géologique du Canada, Dossier public 8620, 2019 p. 5-18, https://doi.org/10.4095/314998  Accès ouvert |
| Année | 2019 |
| Éditeur | Ressources naturelles Canada |
| Document | dossier public |
| Lang. | anglais |
| DOI | https://doi.org/10.4095/314998 |
| Media | en ligne; numérique |
| Référence reliée | Cette publication est contenue dans Targeted
Geoscience Initiative 5, Grant Program interim reports 2018-2019 |
| Référence reliée | Cette publication est reliée à Origin of
chromitites in the Esker Intrusive Complex, Ring of Fire Intrusive Suite, as revealed by chromite trace element chemistry and simple crystallization models |
| Formats | pdf (Adobe® Reader®) |
| 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; 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; magmas; mise en place; dynamique
des fluides; formations de cumulus; silicates; olivine; géochimie du gallium; géochimie du zinc; géochimie du vanadium; cristallisation fractionnée; roches hôtes; altération; microscopie des lames minces; Archéen; Province de Superior ; géologie
économique; géochimie; Sciences et technologie; Précambrien |
| Illustrations | cartes de localisation; cartes géolscientiques généralisées; photographies; graphiques |
| Programme | Initiative géoscientifique ciblée (IGC-5) Gestion de la connaissance de IGC |
| Diffusé | 2019 08 29 |
| Résumé | (disponible en anglais seulement)
To expand on the existing database documenting the trace element composition of ROFIS chromites, and to constrain models of their origin, a total of 45
chromite-bearing samples from the Black Thor, Big Daddy, Blackbird, 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. A search of the element partitioning literature has shown that of the elements that are readily detectable in the chromites, Ga, Zn and V show contrasting behaviour in their olivine- and chromite-melt partitioning. Specifically,
these elements are ambivalent (D ~ 1, Zn) to moderately incompatible in olivine (V, Ga), but moderately compatible in chromite (D~3-6), and hence their behaviour in magmas will depend on the relative proportions of the two phases that are
crystallizing. Simple fractional crystallization models 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 komatiite magma
crystallizing olivine and chromite in normal cotectic proportion, and no evidence of the strong depletion in these elements expected for chromite-only crystallization. The spread in the Ga-V data can be explained if the magma responsible for chromite
formation has assimilated up to ~10% of wall-rock banded iron formation, or granodiorite, or up to 50% of metasediment. The Zn-Ga variation amongst the RoFIS chromitites shows large variation, well outside that expected for the extent of
crystallization or assimilation that can reproduce the V-Ga array. This is interpreted to be the consequence of both the availability and mobility of zinc at subsolidus conditions. A filter applied to the data to exclude the most silicate-rich, and
hence 'zinc exchangeable' samples, as well as those with visible alteration, results in a small subset of samples whose zinc contents are consistent with BIF assimilation, excluding granodiorite or metasediment as important contaminants, at least for
the samples considered. Despite the evidence for contamination, results suggest that the RoFIS chromitites crystallized from normal cotectic proportions of olivine to chromite, and therefore no specific causative link between contamination and
chromitite formation. The specific fluid dynamic regime during magma emplacement may therefore be responsible for crystal sorting and chromite accumulation. Ongoing work will be to conduct laboratory experiments to better constrain the partitioning
of Ga, V and Zn between olivine, chromite and komatiite at conditions relevant to genesis of the RoFIS to further refine the crystallization models developed thus far. |
| 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 2018-2019. |
| GEOSCAN ID | 314998 |
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