| Titre | The LaRonde Penna world-class Au-rich volcanogenic massive sulfide deposit, Abitibi, Québec: mineralogy and geochemistry of alteration and implications for genesis and exploration |
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| Auteur | Dubé, B; Mercier-Langevin, P; Hannington, M; Lafrance, B; Gosselin, G; Gosselin, P |
| Source | Economic geology and the bulletin of the Society of Economic Geologists vol. 102, 2007 p. 633-666, https://doi.org/10.2113/gsecongeo.102.4.633 |
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| Année | 2007 |
| Séries alt. | Secteur des sciences de la Terre, Contribution externe 20060353 |
| Éditeur | Society of Economic Geologists |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.2113/gsecongeo.102.4.633 |
| Media | papier; en ligne; numérique |
| Formats | pdf |
| Province | Ontario; Québec |
| SNRC | 32D/11; 32D/12; 32D/13; 32D/14 |
| Région | Abitibi-Temiscamingue |
| Lat/Long OENS | -80.0000 -79.0000 49.0000 48.5000 |
| Sujets | gîtes volcanogènes; or; géochimie de l'or; ceintures de roche verte; pyrite; chalcopyrite; genèse des minerais; gisements minéraux; altération hydrothermale; assemblages de minéraux; oxydes;
minéralisation; activités d'exploration; prospection minière; Groupe de Blake River ; Formation de Bousquet ; Groupe de Cadillac ; géologie générale; minéraux métalliques; minéralogie |
| Illustrations | cartes géologiques généralisées; cartes de localisation; coupes transversales; photographies; tableaux; graphiques; histogrammes |
| Programme | Initiative géoscientifique ciblée (IGC-3), 2005-2010 |
| Diffusé | 2007 06 01 |
| Résumé | (disponible en anglais seulement)
Gold-rich volcanogenic massive sulfide (VMS) deposits consist of synvolcanic banded and concordant massive sulfide lenses and adjacent stockwork feeder zones in
which gold concentration in g/t Au exceeds the combined Cu, Pb, Zn grades in wt percent and thus constitutes the main commodity. The Agnico-Eagle LaRonde Penna deposit is a world-class Au-rich VMS (production, reserves and resources of 58.8 Mt at
4.31 g/t Au) located in the eastern part of the Blake River Group of the Abitibi greenstone belt. The deposit comprises four stacked massive sulfide lenses within the upper member of the Bousquet Formation (2698-2697 Ma). The two main ore zones, 20
North and 20 South, are sheetlike, massive to semimassive polymetallic sulfide lenses and stringer zones. Both lenses and sulfide stringers are deformed and transposed by the main foliation. The 20 North lens (Zn-Au-Ag-Cu-Pb) is the main orebody. It
is subdivided into two zones: the 20N Au and 20N Zn zones. The 20N Au zone is a transposed and ribbon-textured gold- and copper-rich pyrite-chalcopyrite stringer zone overlain to the south by a 10- to 30-m-thick massive pyrite-sphalerite-galena lens
(20N Zn zone). The 20
South lens is an 8- to 10-m-thick gold- and zinc-rich massive sulfide and stringer zone located about 10 to 15 m below the Cadillac Group sedimentary rocks (<2687 Ma). At depth (>1,900 m below surface), the 20 North and 20
South lenses grade into aluminous zones composed mainly of quartz-pyrite-kyanite-andalusite-muscovite- Zn-rich staurolite assemblages that host transposed sulfide stringers and local semimassive to massive Au-rich pyrite and chalcopyrite layers. The
synvolcanic hydrothermal alteration now corresponds to mappable upper greenschist-lower amphibolite- grade metamorphic assemblages. The footwall of the 20 North lens is characterized by a large discordant to semiconformable distal quartz-biotite ±
garnet assemblage, which transitions laterally into a proximal quartzgarnet-
biotite-muscovite zone. The abundance of pink Mn-rich garnet porphyroblasts increases toward the 20N Au zone. The hanging wall of the 20 North lens is characterized by a
meter-thick zone of fracture-controlled pink alteration composed of quartz, biotite, rutile and/or anatase, and titanite associated with barren sulfide stringers. The garnet-rich assemblage in the footwall records gains in MnO, Fe2O3(total), and MgO
and losses of Na2O. In the hanging wall, Fe2O3(total), S, and CO2 were added to the rocks with a slight increase in K2O, and CaO. At
depth (>1,900 m), the Au-rich aluminous replacement zone is a (up to 30 m) thick, highly strained zone composed of
a quartz-pyrite-kyanite-andalusite-chalcopyrite-gold assemblage. All oxides except Al2O3, SiO2, and Fe2O3(total) were strongly leached. The metamorphosed hydrothermal alteration associated with the 20 South lens is characterized by a pink
quartz-biotite-rutile-titanite assemblage very similar to that in the hanging wall of the 20 North lens. Toward the ore zone, the pink assemblage is gradually replaced by a proximal quartz-muscovite-green mica-pyrite assemblage, which hosts the
sulfide mineralization.The aluminous alteration at LaRonde Penna is interpreted to be the metamorphic equivalent of an advanced argillic alteration and has many similarities to that of metamorphosed high-sulfidation systems and particularly a class
of Au-rich VMS characterized by aluminous alteration. The LaRonde Penna and Bousquet 2-Dumagami deposits are interpreted to represent one large hydrothermal system in which variable contributions of hydrothermally modified seawater and magmatic
volatiles contributed to the different styles of alteration and mineralization. The study illustrates that diverse styles of Au-rich VMS can coexist within the same deposit. In terms of exploration, almost all sulfide lenses or hydrothermal
alterations minerals are located at or near volcanic hiatuses within the Bousquet Formation. These hiatuses represent major exploration targets especially when located in the upper part of the Bousquet Formation. The aluminous alteration zones have
accommodated most of the postore strain due to their ductility and are transformed into schists. Consequently, the alteration product coincides spatially with the deformation zones despite the lack of a genetic relationship. Quartz-and Mn-rich
garnet-biotite assemblages and/or aluminous schists with anomalous gold and/or zinc in intermediate to felsic transitional to calc-alkaline volcanic or volcaniclastic rocks located underneath a sedimentary cover represent excellent targets for
Au-rich VMS in metamorphosed terranes. |
| GEOSCAN ID | 222896 |
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