The LaRonde Penna World-Class Au-Rich Volcanogenic Massive Sulfide Deposit, Abitibi, Quebec: Mineralogy and Geochemistry of Alteration and Implications for Genesis and Exploration

Abstract

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-musc...

A new period of volcanogenic massive sulfide formation in the Yilgarn: a volcanological study of theca2.76 Ga Hollandaire VMS deposit, Yilgarn Craton, Western Australia

“…The sphalerite-rich zone, between 120 and 135 m, is notable for enrichment in Zr and Mn and complete loss of K. Similar gains (Mn, Fe and Mg) and losses (Na, K) have been described for a number of VMS deposits (e.g. Franklin et al 1981;Large et al 2001b;Dube et al 2007).…”

“…The positive correlation between gold and copper contents is strong evidence for coprecipitation from the same mineralising fluid (Franklin et al 2005;Dube et al 2007Dube et al , 2014, and the gold in Hollandaire Main is not related to overprinting of gold mineralisation on a VMS deposit (e.g. Mt.…”

“…Dube et al 2007Dube et al , 2014. By normalising each oxide and element to Zr, an established immobile element in the Hollandaire succession (as demonstrated by the positive correlation in Figure 8b), and plotting against the average least altered metasediment composition (as described in the previous paragraph), also Zr-normalised, we can determine element gains (plot above the 1:1 isocon line) from element losses (plot below the 1:1 line) and determine which elements are immobile (plot on the isocon line), for the hangingwall, footwall and ore zone (Figure 9bÀd).…”

Lithogeochemical and Stable Isotopic Insights into Submarine Genesis of Pyrophyllite-Altered Facies at the Boco Prospect, Western Tasmania

“…Although argillic and advanced argillic alteration assemblages are key features of subaerial high-sulfidation epithermal systems, similar styles of subaqueous synvolcanic aluminous alteration are inferred from some ancient Au-rich VHMS deposits-for example, LaRonde Penna, Abitibi belt, Canada (Dubé et al, 2007). This style of alteration is also increasingly recognized in some modern arcs and back arcs (e.g., de Ronde et al, 2005;Paulick and Bach, 2006).…”

Basaltic to andesitic volcaniclastic rocks in the Blake River Group, Abitibi Greenstone Belt: 1. Mode of emplacement in three areas1This article is a companion paper to Ross et al. 2011. Basaltic to andesitic volcaniclastic rocks in the Blake River Group, Abitibi Greenstone Belt: 2. Origin, geochemistry, and geochronology. Canadian Journal of Earth Sciences, 48: this issue.2MRNF Contribution BEGQ 8439-2010/2011-1. Natural Resources Canada, Earth Science Sector Contribution 20100253.

“…1) hosts numerous volcanogenic massive sulphide (VMS) deposits, several of which -most notably the Horne and the LaRonde Penna -are world-class (Gibson and Watkinson 1990;Kerr and Gibson 1993;Dubé et al 2007;Gibson and Galley 2007;Mercier-Langevin et al 2007a, 2007b. The BRG consists dominantly of submarine volcanic rocks, traditionally interpreted to have formed lava plains, volcanic edifices and subsiding basins (e.g., Spence and de Rosen-Spence 1975;Goodwin 1977Goodwin , 1982Dimroth et al 1982Dimroth et al , 1985Gibson and Watkinson 1990;Péloquin et al 1990Péloquin et al , 2008.…”