| Titre | Crystallographic controlled exsolution and metal partitioning in magmatic sulfide deposits |
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| Auteur | Smith, J; Graziani, R ; Petts, D; Regis, D |
| Source | Geochemistry vol. 83, issue 2, 125954, 2023 p. 1-14, https://doi.org/10.1016/j.chemer.2023.125954  Accès ouvert |
| Image |  |
| Année | 2023 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20220389 |
| Éditeur | Elsevier |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1016/j.chemer.2023.125954 |
| Media | papier; numérique; en ligne |
| Référence reliée | Photo(s) de RNCan dans cette publication |
| Formats | pdf |
| Sujets | gîtes magmatiques; cristallographie; pentlandite; pyrrhotite; analyses de sous-tissus; Intrusion de Crystal Lake ; minéraux métalliques; minéralogie; Sciences et technologie |
| Illustrations | images; diagrammes de distribution des éléments; diagrammes schématiques |
| Programme | Initiative géoscientifique ciblée (IGC-6) Systèmes minéralisés |
| Diffusé | 2023 05 01 |
| Résumé | (disponible en anglais seulement)
Magmatic sulfide liquids are effective at concentrating a range of metals. Within magmatic sulfide systems pentlandite, an exsolution product of monosulfide
solid solution (MSS), is the primary host of Ni, Co and significant concentrations of Pd. Over the last decade, LA-ICP-MS mapping has revealed non-uniform metal distributions and complexity to the metal patterns such as zonation and the linear
alignment of elements. Whereas the compatibility and partitioning behavior of chalcophile elements during sulfide fractionation are well constrained, there is little knowledge on the crystallographic control exerted on metal distributions. In this
study, LA-ICP-MS mapping of globular sulfides from the Crystal Lake Intrusion, Ontario (Canada), is complimented by EBSD analysis, revealing a strong crystallographic control on both the concentration of metals and pentlandite exsolutions. Elements
considered incompatible in the high temperature monosulfide solid solution (MSS) phase (e.g., Cr, V, As, Pb, Ag, Bi and Pd) are preserved as a microfabric, showing preferential concentration in association with the (0001) basal plane of pyrrhotite
and adjacent pentlandite. Where the [0001] axis is viewed perpendicular to the cut surface, the microfabric is considered to be an intersection lineation between the basal (0001) plane and the surface of the cut section. Pentlandite textures
described in magmatic sulfide deposits include granular, fan and laths/blades. Our observations indicate that marginal pentlandite exsolutions, are in optical continuity with granular exsolutions, providing insights into the growth of pentlandite at
MSS grain boundaries. We conclude that all pentlandite forms are crystallographically controlled by the hexagonal mineral system of MSS/pyrrhotite, with the [0001] c-axis of pyrrhotite corresponding to the ?111?axis of pentlandite. This axis also
acts as a twinning rotation axis for the two identified pentlandite orientations. Fan and lath textured exsolutions are considered geometrically equivalent structures, being reconstructed as flat disc-shapes developed parallel to the basal (0001)
plane of pyrrhotite, which acts as a preferred nucleation site. A network of low-angle grain boundaries are recognized as hexagonal or rectangular structures within pyrrhotite, with the morphology shown to be dependent on the orientation of the
crystals. As these features are again geometric equivalents, they can be reconstructed as intragrain hexagonal prisms. We speculate due to their localized development, that they could represent a plastic response of the pyrrhotite to accommodate the
increase in volume suggested to be associated with late pentlandite exsolutions and thus are the result of static lattice recovery. The microstructural and trace element observations presented here provide new context to some of the common textural
features of magmatic sulfide deposits, while importantly highlighting the strong crystallographic control on both metal distributions and sulfide textures. This study also importantly recognizes the dominance of hexagonal pyrrhotite within the ores
of the Crystal Lake Intrusion and likely other magmatic sulfide deposits. This has implications for mineral processing as its non-magnetic properties can result in dilution of Ni-Cu-PGE ores and thus requires special attention for the flotation
strategy. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Ce manuscrit étudie les contrôles de la mobilité des métaux lors de la formation de dépôts de Ni. Utilisant une nouvelle approche complétant la
cartographie in situ haute résolution avec l'analyse microstructurale, cette étude fournit des avancées significatives dans la compréhension du comportement des métaux lors de la formation du minerai en reconnaissant un contrôle cristallographique
fort sur les distributions métalliques et les textures de sulfure. De plus, ce manuscrit reconnaît l'utilisation potentielle de ces techniques combinées pour faire progresser la compréhension de la formation de pentlandite, qui est importante car
c'est le principal hôte de Ni dans les gisements de sulfures magmatiques canadiens, et sa formation est actuellement débattue dans la littérature. |
| GEOSCAN ID | 331116 |
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