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TitleGeologic and structural controls on ore style and distribution in the Archean Rainy River Gold deposit, Wabigoon Subprovince, Ontario: Preliminary results
AuthorPelletier, M; Mercier-Langevin, P; Tolman, J; McNicoll, V; Dubé, B; Richer-Laflèche, M; Beakhouse, G
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 37, 2014 p. 218-219
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130549
MeetingGAC-MAC 2014; Joint annual meeting of Geological Association of Canada and Mineralogical Association of Canada; Fredericton; CA; May 21-23, 2014
File formatpdf
NTS52D/09; 52D/10; 52D/15; 52D/16; 52E/01; 52E/02
AreaRainy River
Lat/Long WENS-95.0000 -94.0000 49.2500 48.5000
Subjectsstratigraphy; structural geology; economic geology; bedrock geology; structural features; Archean; mineralization; gold; mineral occurrences; igneous rocks; volcanic rocks; alteration; Rainy River Gold deposit; Wabigoon Subprovince; Rainy River greenstone belt; Precambrian
ProgramTargeted Geoscience Initiative (TGI-4), Volcanogenic Massive Sulfide Ore Systems
AbstractThe Rainy River gold project (measured and indicated resources of 177 Mt @ 1.09 g/t Au: 6.2 Moz) is located in the Archean Rainy River greenstone belt, part of the Wabigoon Subprovince in northwestern Ontario. Hosted mainly within felsic volcanic units, the deposit is set in a succession of variably altered basaltic to dacitic flows and associated volcaniclastic rocks. These volcanic products suggest a flow-dome-style volcanic center, with massive facies including aphanitic to strongly quartz±plagioclase-phyric flow-banded lobes, amygdular flows and flow-breccias, and volcaniclastic rocks consisting of fine-grained to lapilli-sized, largely monolithic fragmental units. Mineralization is correlated with well-developed sericite alteration best developed within felsic rocks. Local zones of chlorite-bearing alteration are preferentially developed within intermediate to mafic rocks. Additional alteration minerals noted locally include carbonates, epidote, garnet and biotite. The mineralized zones occur as a series of EW orientated elongate bodies, moderately south dipping, and subparallel to the main foliation (109°/46°S). High-grade ore shoots are elongated parallel to a SW-plunging stretching lineation (47°/233°). The ore (Au-Ag) is directly associated with disseminated sulphides (pyrite, sphalerite, chalcopyrite±galena, arsenopyrite and pyrrhotite) and sulphide-rich veinlets. Gold correlates with copper and zinc at the deposit scale. Rare visible gold and electrum occur with disseminated sulphides and are also present in folded, transposed and boudinaged sulphide±quartz-calcite-tourmaline veinlets. An envelope of intense sericite alteration is preferentially developed in the felsic volcaniclastic rocks coincident with gold-silver mineralization and a prominent zinc anomaly. Silver and lead form a slightly enriched halo around the Au-Zn-Cu zones. Pyrite analyses (LA-ICP-MS) indicate an early (pre-deformation) enrichment in Au with subsequent remobilization during metamorphism (pyrite recrystallization). The presence of deformed, foliated, and neither altered nor mineralized dykes crosscutting some ore zones and their associated alteration halos, coupled with deformed gold bearing veinlets suggest a pre- deformation mineralizing event. These cross-cutting relationships plus the nature of the ore support the working hypothesis of an early, synvolcanic gold system, overprinted by regional deformation. Detailed geological and structural mapping (drill core and surface), U-Pb zircon geochronology, lithogeochemistry, mineralogy, mineral chemistry, and isotopic mapping are the means taken to further define the deposit footprint, the effects of regional and local deformation on ore style and distribution. Although still hypothetical, the Rainy River deposit could represent a new type of economically viable Archean synvolcanic gold deposit.