Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dubé, B. Articles by Gosselin, P. Search for Related Content GeoRef GeoRef Citation

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

B. Dubé and P. Mercier-Langevin

Geological Survey of Canada, 490 rue de la Couronne, Québec, Canada G1K 9A9

M. Hannington^**

Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8

B. Lafrance^***

Ministère des Ressources naturelles, de la Faune, 82 boul. Québec, Rouyn-Noranda Québec, Canada J9X 6R1

G. Gosselin

Agnico-Eagle Mines Ltd., Division Exploration, Val-d’Or, Québec, Canada J9P 4N9

P. Gosselin

Geological Survey of Canada, 490 rue de la Couronne, Québec, Canada G1K 9A9

Corresponding author: e-mail, bdube{at}nrcan.gc.ca

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 amphibo-lite–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 quartz-garnet-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, Fe₂O_3(total), and MgO and losses of Na₂O. In the hanging wall, Fe₂O_3(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 Fe₂O_3(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.

This article has been cited by other articles:

				D. Gaboury and V. Pearson Rhyolite Geochemical Signatures and Association with Volcanogenic Massive Sulfide Deposits: Examples from the Abitibi Belt, Canada Economic Geology, November 1, 2008; 103(7): 1531 - 1562. [Abstract] [Full Text] [PDF]

				P. C. Thurston, J. A. Ayer, J. Goutier, and M. A. Hamilton Depositional Gaps in Abitibi Greenstone Belt Stratigraphy: A Key to Exploration for Syngenetic Mineralization Economic Geology, September 1, 2008; 103(6): 1097 - 1134. [Abstract] [Full Text] [PDF]

				S. J. Piercey, E. C. Chaloux, A. S. Peloquin, M. A. Hamilton, and R. A. Creaser Synvolcanic and Younger Plutonic Rocks from the Blake River Group: Implications for Regional Metallogenesis Economic Geology, September 1, 2008; 103(6): 1243 - 1268. [Abstract] [Full Text] [PDF]

				P. Mercier-Langevin, B. Dube, B. Lafrance, M. D. Hannington, A. Galley, R. Marquis, J. Moorhead, and D. W. Davis A Group of Papers Devoted to the Laronde Penna Au-Rich Volcanogenic Massive Sulfide Deposit, Eastern Blake River Group, Abitibi Greenstone Belt, Quebec: Preface Economic Geology, June 1, 2007; 102(4): 577 - 583. [Full Text] [PDF]

				P. Mercier-Langevin, B. Dube, M. D. Hannington, D. W. Davis, B. Lafrance, and G. Gosselin The LaRonde Penna Au-Rich Volcanogenic Massive Sulfide Deposit, Abitibi Greenstone Belt, Quebec: Part I. Geology and Geochronology Economic Geology, June 1, 2007; 102(4): 585 - 609. [Abstract] [Full Text] [PDF]

				P. Mercier-Langevin, B. Dube, M. D. Hannington, M. Richer-Lafleche, and G. Gosselin The LaRonde Penna Au-Rich Volcanogenic Massive Sulfide Deposit, Abitibi Greenstone Belt, Quebec: Part II. Lithogeochemistry and Paleotectonic Setting Economic Geology, June 1, 2007; 102(4): 611 - 631. [Abstract] [Full Text] [PDF]