The LaRonde Penna World-Class Au-Rich Volcanogenic

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2007 Society of Economic Geologists, Inc.Economic Geology, v. 102, pp. 633–666The LaRonde Penna World-Class Au-Rich Volcanogenic Massive Sulfide Deposit,Abitibi, Québec: Mineralogy and Geochemistry of Alteration and Implicationsfor Genesis and Exploration*B. DUBÉ,† P. MERCIER-LANGEVIN,Geological Survey of Canada, 490 rue de la Couronne, Québec, Canada G1K 9A9M. HANNINGTON,**Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8B. LAFRANCE,***Ministère des Ressources naturelles, de la Faune, 82 boul. Québec, Rouyn-Noranda Québec, Canada J9X 6R1G. GOSSELIN,Agnico-Eagle Mines Ltd., Division Exploration, Val-d’Or, Québec, Canada J9P 4N9ANDP. GOSSELINGeological Survey of Canada, 490 rue de la Couronne, Québec, Canada G1K 9A9AbstractGold-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 LaRondePenna 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 fourstacked massive sulfide lenses within the upper member of the Bousquet Formation (2698–2697 Ma). The twomain ore zones, 20 North and 20 South, are sheetlike, massive to semimassive polymetallic sulfide lenses andstringer zones. Both lenses and sulfide stringers are deformed and transposed by the main foliation. The 20North lens (Zn-Au-Ag-Cu-Pb) is the main orebody. It is subdivided into two zones: the 20N Au and 20N Znzones. The 20N Au zone is a transposed and ribbon-textured gold- and copper-rich pyrite-chalcopyrite stringerzone overlain to the south by a 10- to 30-m-thick massive pyrite-sphalerite-galena lens (20N Zn zone). The 20South lens is an 8- to 10-m-thick gold- and zinc-rich massive sulfide and stringer zone located about 10 to 15m below the Cadillac Group sedimentary rocks ( 2687 Ma). At depth ( 1,900 m below surface), the 20 Northand 20 South lenses grade into aluminous zones composed mainly of ch staurolite assemblages that host transposed sulfide stringers and local semimassive to massiveAu-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 discordantto 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 the20N 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. Atdepth ( 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, andFe2O3(total) were strongly leached. The metamorphosed hydrothermal alteration associated with the 20 Southlens is characterized by a pink quartz-biotite-rutile-titanite assemblage very similar to that in the hanging wallof 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 advancedargillic alteration and has many similarities to that of metamorphosed high-sulfidation systems and particularly*Geological Survey of Canada contribution no. 20060353.† Corresponding author: e-mail, [email protected]**Present address: University of Ottawa, 140 Louis Pasteur, Ottawa, Canada ON K1N 6N5.***Present address: Cogitore Resources Inc., 1300 Saguenay, Suite 200, Rouyn-Noranda, Québec, Canada J9X 7C3.0361-0128/07/3672/633-34633

634DUBÉ ET ALa class of Au-rich VMS characterized by aluminous alteration. The LaRonde Penna and Bousquet 2-Dumagamideposits 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 andmineralization.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 hiatuseswithin the Bousquet Formation. These hiatuses represent major exploration targets especially when located inthe upper part of the Bousquet Formation. The aluminous alteration zones have accommodated most of thepostore 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 representexcellent targets for Au-rich VMS in metamorphosed terranes.IntroductionGOLD-RICH volcanogenic massive sulfide (VMS) deposits areimportant gold deposits in a strict economic sense (Poulsen etal., 2000). Like other VMS deposits they consist of synvolcanic banded and locally concordant massive sulfide lensesand adjacent discordant stockwork feeder zones. In these deposits, gold concentration (in g/t) exceeds the combined Cu,Pb, Zn grades in wt percent and thus constitutes the maincommodity (Poulsen and Hannington, 1995; Poulsen et al.,2000). Many gold-rich VMS deposits occur in deformed andmetamorphosed greenstone belts of various ages and maycontain local syntectonic quartz-sulfide or rarely quartz-tourmaline veins, which can complicate the interpretation of theirparagenesis. The timing of gold deposition (synvolcanic orsyntectonic) relative to the formation of the massive sulfideorebody is therefore the subject of much debate, particularlyin metamorphosed Precambrian terranes (Valliant andHutchinson, 1982; Stone et al., 1988; Arnold and Sillitoe,1989; Poulsen and Hannington, 1995; Bergman-Weihed etal., 1996; Sillitoe et al., 1996; Hannington et al. 1999; Huston,2000). It has been proposed that syngenetic volcanic-hosted,gold-poor base metal mineralization in some Archean examples was overprinted by syndeformation Au mineralization(Tourigny et al., 1989; Marquis et al, 1990a-c; Yeats andGroves, 1998).Although there are only a few world-class examples, theAu-rich polymetallic nature of these deposits makes them anattractive exploration target. The world production and reserves for Au-rich VMS deposits are 1,370 metric tonnes (t)Au, equivalent to 1.2 percent of the world lode gold production and reserves, including the Witwatersrand (120,689 t Au:Gosselin and Dubé, 2005a). Production and reserves of Canadian Au-rich VMS gold deposits are 870 t, which constitutesclose to 10 percent of the total production and reserves fromCanadian lode gold deposits (9,280 t Au: Gosselin and Dubé,2005b).Agnico-Eagle’s LaRonde Penna deposit (Fig. 1) is thelargest gold mine currently in operation in Canada. Production from the LaRonde Penna shaft began in April, 2000.More than 12 Mt of ore at 3.53 g/t Au (1.4 Moz of gold), 2.66percent Zn, 0.28 percent Cu, and 53.7 g/t Ag have alreadybeen extracted from the beginning of its production to 2005.Reserves and global resources as of December 31, 2005 were6.7 Moz Au from more than 46 Mt at an average grade of 4.51g/t Au, 2.04 percent Zn, 0.33 percent Cu, and 42.7 g/t Ag.LaRonde Penna is the second largest Au-rich VMS deposit,after the Horne deposit in Noranda, which produced 331 t Au0361-0128/98/000/000-00 6.00(Gosselin and Dubé, 2005b). Although Au-rich VMS depositsrepresent a key exploration target, detailed deposit-scalestudies of this style of mineralization are limited. TheLaRonde Penna deposit represents a key deposit in this context and an opportunity to contribute to the understanding ofthis deposit type.The LaRonde Penna deposit is located 1 km east of theBousquet 2-Dumagami deposit in the eastern part of theDoyon-Bousquet-LaRonde mining camp, which containsmore than 22.3 Moz Au (past production, reserves, and resources; Fig. 1). The Au-rich VMS deposits in the district arehosted by the upper portion of the Bousquet Formation ofthe Blake River Group (Lafrance et al., 2003; MercierLangevin et al., 2004; Mercier-Langevin, 2005). The BlakeRiver Group also hosts the VMS deposits located in thenearby world-class Noranda district, including two notablyAu-rich VMS deposits, Horne (331 t Au) and Quemont (66 tAu; Gosselin and Dubé, 2005b), and 17 other polymetallicCu-Zn Au VMS deposits.A synthesis of the Doyon-Bousquet-LaRonde mining district was undertaken in the summer of 2000 as a joint effortinvolving the Ministère des Ressources naturelles, de laFaune du Québec, the Geological Survey of Canada, Cambior Inc., Barrick Gold Corp., Agnico-Eagle Mines Ltd.,Ressources Yorbeau Ltd., Institut national de la recherchescientifique (INRS-ETE), and the Université du Québec àChicoutimi. The primary objective was to better understandthe regional and deposit-scale geologic characteristics of thedistrict. Part of the results were published in a series of Quebec government reports (Lafrance et al., 2003, Dubé et al.,2004; Mercier-Langevin et al., 2004).This paper accompanies two contributions by MercierLangevin et al. (2007a, b), which respectively describe the geology and geochronology and lithogeochemistry and paleotectonic setting of the LaRonde Penna deposit. Here, wesummarize the mineralogical and lithogeochemical signaturesof the hydrothermal system(s) of the LaRonde Penna deposit,discuss the timing of gold introduction, and investigate a genetic model for Au-rich VMS deposits, as well as explorationimplications in the district and elsewhere in greenstone belts.The study also demonstrates that distinctive Zn-Au and CuAu metal associations and diverse alteration types can coexistlaterally within a single VMS deposit.Regional Geologic SettingThe Doyon-Bousquet-LaRonde gold district is located 45km east of Rouyn-Noranda in the late Archean southern634

635LARONDE PENNA Au-RICH VMS DEPOSIT, ABITIBI, QUÉBEC: ALTERATION & EXPLORATION IMPLICATIONS625 000 mE650 000 mEKinojévis GroupQuebec700 000 mENorthernvolcaniczoneNPorcupine-DestorFaultFaille de aRondeHébécourt FormationOntario5 360 000 mNA675 000 mEDoyon-Bousquet-LaRondeMining campBlake River Group101Southernvolcaniczone5 335 000 mNRouyn-NorandaCadillac117ultarder Lake faCadillac GroupCadillac-LPontiac Group391B682 000 m E.t688 000 m E.arfouru692 000 m E.NsouthMouska71690 000 m E.Malartic GroupcPFaF686 000 m E.Laulriser684 000 m E.FaultMic MacLac Parfouru north 269982LaRonde PennaWestwoodWarrenmac269786XFaultder Lakeadillac-LarRivièrltautFueBousquet 1Bousquet 2Dumagami2698(2697)u Faultsqerder LakeCadillac-LaProterozoicdiabase dikeMooshla IntrusionLate stagetrondhjemite-tonaliteRhyolitic blue-quartzbearing sill-dikecomplexPiché GroupMafic volcanic andultramaficVolcanic rocksSedimentary rocksBlake River GroupBousquet FormationTimiskaming GroupUpper memberdacite-rhyodacite-rhyolitelocal basaltic andesitePolymictic conglomerateKewagama GroupWacke-siltstone andargilliteLower memberbasalt to rhyoliteEarly and intermediatestagesgabbro-quartz gabbro Hébécourt Formation-tonaliteBasalt-basaltic andesitelocal rhyoliteCadillac GroupWacke-siltstone, argillite,local conglomerate andiron-formation2697Fault2 km10Pontiac GroupPontiac GroupIntrusive rocks2698Lac ImauBoCLegend8726985 346 000 m N.27222697268767LaRonde 2Ellison65705 346 000 m N.2698ionOrionLacKewagama GroupAge of volcanic rocks (Ma)2697Age of intrusive rocks (Ma)2697Maximum age of sedimentaryrocks (Ma)High-strainedzoneMine in productionClosed minebeddingMineralized lensprojected up-dipDepositX prospect87Strike and dip ofmain (S2) foliationBedding withstratigraphic topFIG. 1. A. Location of the Doyon-Bousquet-LaRonde mining camp, Blake River Group, which includes the BousquetFormation. The inset shows the location of the Abitibi greenstone belt. B. Simplified geology of the Doyon-BousquetLaRonde mining camp (modified from Lafrance et al., 2005). U-Pb age from Lafrance et al. (2005) and Mercier-Langevinet al., 2007a)0361-0128/98/000/000-00 6.006355 348 000 m N.5 348 000 m N.tMont-Brun Formation5 350 000 m N.5 350 000 m N.680 000 m E.Malartic20 km100

636DUBÉ ET ALAbitibi greenstone belt of the Superior province of the Canadian Shield (Fig. 1A). The northern portion of the volcanicsuccession consists of the Hébécourt Formation which extends to the west to the Québec-Ontario border (Fig. 1A).The Hébécourt Formation consists of laterally extensivetholeiitic basalt and basaltic andesite flows, cogenetic gabbroic sills, and small isolated rhyolite flows. The BousquetFormation, which hosts most of the deposits, stratigraphicallyoverlies the Hébécourt Formation. The Bousquet Formationis part of the Blake River Group and constitutes a south-facing homoclinal sequence which is subdivided into lower(2699–2698 Ma) and upper members (2698–2697 Ma;Lafrance et al., 2003, 2005; Mercier-Langevin et al., 2004).Both of these members consist