| Titre | Distribution of siderophile elements during sulphide fractionation within magmatic Ni-Cu-PGE systems: a LA-ICP-MS investigation of the Crystal Lake Intrusion, 1.1 Ga Midcontinent rift |
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| Auteur | Smith-Holder, J ;
Bleeker, W; Petts, D C |
| Source | Ore Geology Reviews vol. 148, 105002, 2022 p. 1-23, https://doi.org/10.1016/j.oregeorev.2022.105002  Accès ouvert |
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| Année | 2022 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20220088 |
| Éditeur | Elsevier |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1016/j.oregeorev.2022.105002 |
| Media | papier; numérique; en ligne |
| Formats | pdf; html |
| Région | Lac Supérieur |
| Lat/Long OENS | -89.6833 -89.2333 48.1667 47.9997 |
| Sujets | Intrusion de Crystal Lake ; Sciences et technologie; Nature et environnement; géologie générale |
| Illustrations | cartes de localisation; diagrammes; photographies; tableaux |
| Programme | Initiative géoscientifique ciblée (IGC-5) Systèmes minéralisés de sulfure massif volcanogénique - métaux de base - sources et processus |
| Diffusé | 2022 09 01 |
| Résumé | (disponible en anglais seulement)
Within the magmatic pyrrhotite-pentlandite-chalcopyrite assemblage, which is ubiquitous of many Ni-Cu-PGE deposits, the spatial distribution of PGEs and
semi-metals during both sulphide fractionation and low temperature alteration is not well documented. In-situ characterisation of sulphides provides a mechanism to trace the behaviour of elements during ore formation, with trace element distribution
patterns providing valuable insights at the microscale into the genesis of magmatic sulphide deposits. Here we report trace element data determined by quantitative LA-ICP-MS mapping for a suite of variably altered samples from the taxitic rocks of
the undeformed Crystal Lake Intrusion, within the 1.1 Ga Midcontinent Rift. Combining LA-ICP-MS data with detailed petrography and multivariate statistics helps identity the processes responsible for elevated metal concentrations and observed trace
element distribution patterns within Ni-Cu-PGE systems. Such data can also improves our understanding of the effects fluid interaction and assimilation of volatile rich rocks has on the metal contents of sulphides. Element maps reveal complex
distribution patterns throughout the disseminated sulphides of the Crystal Lake Intrusion, which are notably enriched in Pd relative to the massive sulphides developed locally along the basal contact. Replacement of the primary sulphides by low
temperature phases is restricted to the northern limb of the intrusion and results in heterogeneous distributions and elevated concentrations of As, Pd, Ag and Bi along fractures. Zonation of As, Mo, Ru, Rh, Re and Bi is observed in both pentlandite
and chalcopyrite. Within the globular ores, petrographic observations suggest the pyrrhotite-chalcopyrite contact with which 'contact' pentlandite resides along, may not be indicative of the initial boundary between monosulphide solid solution (MSS)
and the residual sulphide liquid. This has implications for the interpretation of trace element zonation patterns, which in the case of this study are not considered to be indicative of formation by peritectic reaction. We suggest much of the trace
element zonation observed in the Crystal Lake Intrusion relates to inheritance from previous grain boundaries and as such, the possible presence of high temperature pentlandite can only be identified through statistical clustering of the LA-ICP-MS
data. With multivariate statistical analyses revealing subtle geochemical features within each phase, discrete mineralising events and sulphide generations are recognised. Within the locally vapour saturated taxites of the southern limb, a new
microfabric is documented within the globular ores, revealing a close spatial relationship between enhanced trace element concentrations and microstructures within undeformed magmatic sulphides. The microfabric, which is defined by V, Cr, As, Pb and
Bi and less frequently by Mo, Rh, Pd and Re, is prevalent in unaltered coarse pyrrhotite and in contact, granular and fan textured pentlandite, and is developed in association with both silicate-capped and uncapped sulphide globules. Regardless of
the exact mechanism by which the microfabric formed (e.g., fluid interaction, exsolution, gravitational compaction), this study highlights that regional deformation is not required to drive the preferential enrichment of select elements along
discrete planes. Only as more high resolution element map data become available will it become apparent if the microfabric is a common feature of magmatic Ni-Cu-PGE deposits or a unique characteristic of the Crystal Lake Intrusion. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Le manuscrit présente de nouveaux modèles de distribution spatiale à haute résolution pour les éléments traces dans les sulfures magmatiques et
discute des observations clés et de leurs implications pour les systèmes Ni-Cu-PGE. L'étude fournit des informations sur le comportement des éléments lors de la formation du minerai. Le manuscrit documente également un nouveau schéma de distribution
des éléments traces en combinant la pétrographie détaillée avec la cartographie LA-ICP-MS. Ce nouveau microfabric a des implications pour notre compréhension de la façon dont certains métaux résident dans les sulfures magmatiques et pourrait suggérer
que certains éléments sont plus susceptibles d'être remobilisés ultérieurement par les fluides. |
| GEOSCAN ID | 330124 |
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