| Titre | Hydrothermal alteration mineralogy and geochemistry of the Archean world-class Canadian Malartic disseminated-stockwork gold deposit, southern Abitibi Greenstone Belt, Quebec, Canada |
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| Auteur | De Souza, S; Dubé, B; Mercier-Langevin, P; McNicoll, V; Dupuis, C; Kjarsgaard, I |
| Source | Economic geology and the bulletin of the Society of Economic Geologists vol. 114, no. 6, 2019 p. 1057-1094, https://doi.org/10.5382/econgeo.4674 |
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| Année | 2019 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20180016 |
| Éditeur | Society of Economic Geologists |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.5382/econgeo.4674 |
| Media | papier; en ligne; numérique |
| Formats | pdf (Adobe® Reader®); html |
| Province | Québec |
| SNRC | 32C/04; 32D/01 |
| Région | Malarctic; Val d'Or |
| Lat/Long OENS | -78.2333 -77.9833 48.1833 48.0833 |
| Sujets | Archéen; prospection minière; gisements minéraux; gîtes de substitution; or; minéralisation; cadre tectonique; orogenèse; antécédents tectoniques; altération hydrothermale; magmatisme; intrusions; mise en
place; sédimentation; métasomatose; métamorphisme; cristallisation; roches hôtes; géologie du substratum rocheux; lithologie; roches métamorphiques; faciès à schiste vert; roches sédimentaires; grauwackes; mudstones; roches ignées; roches intrusives;
monzodiorites; granodiorites; brèches; caractéristiques structurales; zones de failles; fractures; clivage; eprentes; filons de quartz; qualités des minerais; datation radiométrique; déformation; Ceinture d'Abitibi Greenstone ; Zone de faille de
Larder Lake-Cadillac ; Groupe de Pontiac ; Assemblage de Timiskaming ; géologie économique; minéralogie; géochimie; géochronologie; Sciences et technologie; Nature et environnement; Précambrien |
| Illustrations | cartes de localisation; cartes géolscientiques généralisées; photographies; coupes transversales; enregistrements de carottage; tableaux; photomicrographies; graphiques |
| Programme | Initiative géoscientifique ciblée (IGC-5) Systèmes aurifères |
| Diffusé | 2019 09 01 |
| Résumé | (disponible en anglais seulement)
The Canadian Malartic stockwork-disseminated gold deposit is an Archean world-class deposit located in the southern Abitibi greenstone belt. It contains over
332.8 tonnes (t; 10.7 Moz) of Au at a grade of 0.97 ppm, in addition to 160 t (5.14 Moz) of past production (1935-1981). Although the deposit is partly situated within the Larder Lake-Cadillac fault zone, most of the ore occurs up to ~1.5 km to the
south of the fault zone. The main hosts of the mineralized zones are greenschist facies turbiditic greywacke and mudstone of the Pontiac Group (~2685-2682 Ma) and predominantly subalkaline ~2678 Ma porphyritic quartz monzodiorite and granodiorite.
These intrusions were emplaced during an episode of clastic sedimentation and alkaline to subalkaline magmatism known as the Timiskaming assemblage (<2680-2670 Ma in the southern Abitibi). The orebodies define two main mineralized trends, which are
oriented subparallel to the NW-striking S2 cleavage and the E-striking, S-dipping Sladen fault zone. This syn- to post-D2 ductile-brittle to brittle Sladen fault zone is mineralized for more than 3 km along strike.
The ore mainly consists of
disseminated pyrite in stockworks and replacement zones, with subordinate auriferous quartz veins and breccia. Gold is associated with pyrite and traces of tellurides defining an Au-Te-W ± Ag-Bi-Mo-Pb signature. The orebodies are zoned outward, and
most of the higher-grade (>1 ppm Au) ore was deposited as a result of iron sulfidation from silicates and oxides and Na-K metasomatism in carbonatized rocks. The alteration footprint comprises a proximal alteration envelope (K- or
Na-feldspar-dolomite-calcite-pyrite ± phlogopite). This proximal alteration zone transitions to an outer shell of altered rocks (biotite-calcite-phengitic white mica), which hosts sub-ppm gold grades and reflects decreasing carbonatization,
sulfidation, and aNa+/aH+ or aK+/aH+ of the ore fluid.
Gold mineralization, with an inferred age of ~2664 Ma (Re-Os molybdenite), was contemporaneous with syn- to late-D2 peak metamorphism in the Pontiac Group; it postdates sedimentation of the
Timiskaming assemblage along the Larder Lake-Cadillac fault zone (~2680-2669 Ma) and crystallization of the quartz monzodiorite. These chronological relationships agree with a model of CO2-rich auriferous fluid generation in amphibolite facies rocks
of the Pontiac Group and gold deposition in syn- to late-D2 structures in the upper greenschist to amphibolite facies. The variable geometry, rheology, and composition of the various intrusive and sedimentary rocks have provided strain
heterogeneities and chemical gradients for the formation of structural and chemical traps that host the gold. The Canadian Malartic deposit corresponds to a mesozonal stockwork-disseminated replacement-type deposit formed within an orogenic setting.
The predominance of disseminated replacement ore over fault-fill and extensional quartz-carbonate vein systems suggests that the mineralized fracture networks remained relatively permeable and that fluids circulated at a near-constant hydraulic
gradient during the main phase of auriferous hydrothermal alteration. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Le gisement aurifère Canadian Malartic, situé dans la portion sud de l'Abitibi, contient 10.7 Moz d'or à une teneur de 0.97 ppm (réserves et
production). Ce contenu en or s'ajoute aux 5.5 Moz produites entre 1935 and 1981 à partir de trois mines souterraines. Quoique le gisement soit partiellement localisé dans la zone de faille Larder Lake - Cadillac (FLLC), la majeure partie du minerai
est située à une distance pouvant atteindre 1.5km au sud de celle-ci. Le minerai consiste en pyrite disséminée dans des stockwerk et des zones de remplacement, et localement en veines et brèches. L'or est associé à la pyrite et des traces de
tellures, molydène et galène, de même qu'à une altération hydrothermale complexe. Le contexte géologique et les caractéristiques du gisement permettent de mettre en valeur le potentiel aurifère des sédiments le long de la faille FLLC et d'autres
failles similaires et contribue à améliorer les modèles d'exploration dans des contextes similaires. |
| GEOSCAN ID | 308145 |
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