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TitleFracture-controlled hydrothermal alteration at the Canadian Malartic deposit: Toward a multiphase model for Archean intrusion-related low-grade bulk tonnage gold deposits
AuthorDe Souza, S; Dubé, B; McNicoll, V; Dupuis, C; Mercier-Langevin, P; Creaser, R
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 37, 2014 p. 70 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130595
PublisherGAC MAC
MeetingGAC-MAC 2014; Joint annual meeting of Geological Association of Canada and Mineralogical Association of Canada; Fredericton; CA; May 21-23, 2013
Mediaon-line; digital
File formatpdf
NTS32D/03NE; 32D/06; 32D/07
AreaRouyn Noranda; Lac Chassignolle; Malartic
Lat/Long WENS -79.5000 -78.5000 48.5000 48.1667
Subjectseconomic geology; hydrothermal deposits; hydrothermal alteration; mineral occurrences; mineral deposits; mineral potential; mineralization; gold; volcanogenic deposits; sulphides; sulphide deposits; Archean; Abitibi Greenstone Belt; Malartic Deposit; Precambrian; Proterozoic
ProgramTargeted Geoscience Initiative (TGI-4) Gold Ore Systems
Released2014 01 01
AbstractThe Canadian Malartic gold deposit (P&P reserves 10.1Moz, 311Mt@1.01 g/t) is hosted by subvertical clastic metasedimentary rocks of the Pontiac Goup and <=2678 Ma sub-alkaline to transitional, fine- to medium-grained porphyritic monzodiorite located immediately south of the Larder-Lake-Cadillac Fault Zone. The main cleavage (S2) in the Pontiac Group is NW-striking and axial-planar to F2 folds. Ore zones are dominantly oriented sub-parallel to S2 and to the EW- striking Sladen Fault. Ore minerals comprise pyrite+native gold+tellurides with traces of sphalerite+chalcopyrite+galena and molybdenite that yielded a Re-Os age of ca. 2664 Ma. The assemblage Bi-Te-W-S-Ag±Pb±Mo defines the bulk metallic signature of the ore. Monzodiorite in the footwall of the Sladen Fault shows an early distal alteration consisting of a reddishcoloured calcite+hematite+biotite±pyrite assemblage associated with quartz+pyrite+galena+biotite veins. This assemblage is overprinted by proximal pink- to greyish-coloured replacement zones comprising microcline+carbonate+albite+rutile±biotite. These alterations show K2O, CO2, and S progressive mass gains in the distal to proximal assemblages. Mineralized coarse-grained ?pegmatitic? quartz-carbonate-feldspar-biotitemuscovite- tourmaline-scheelite veins, also present in the greywacke, are locally superimposed on these alteration assemblages. In the hanging-wall of the Sladen fault and along NW-SE ore zones, the greywacke shows distal, dark pervasive calcite-biotite alteration and proximal, lightcolored albite-microcline-quartz-pyrite±biotite±calcite alteration assemblages. These occur as bedding- and shear zone-controlled replacement zones, and as thin selvages of quartz-calcitebiotite veinlets. NW-SE-oriented mineralized shear zones and veinlets are preferentially developed in the hinge zone and faulted short limbs of F2 folds. The distribution and composition of alteration assemblages in the sedimentary rocks is strongly influenced by protolith composition and competence contrasts (greywacke/mudrock). Nevertheless, these alterations show Na2O, CO2 and S show consistent gain, whereas K2O is characterized by variable gain/loss behaviour. Laminated quartz-pyrite-galena veins and breccia with visible gold are locally overprint these earlier alterations. Biotite in the mineralized alteration zones in the greywacke and monzodiorite is F- and Mg-rich, contrasting with the background biotite, defining hydrothermal and exploration vectors. This study reveals that the deposit resulted of the superposition of hydrothermal and structural events including a ?2678 Ma syn-Timiskaming magmatic-hydrothermal phase of mineralization inferred by the Bi-Te-W-S-Ag±Pb±Mo metallic signature, the presence of mineralized stockworks, and potassic alteration (biotite/microcline). This magmatic-hydrothermal phase shares analogies with Archean oxidized syenite porphyryassociated disseminated gold deposits. However, at least part of the mineralization (or remobilization) and its actual distribution and geometry are controlled by a syn-D2 event, as indicated by the nature and chronology of alteration/deformation and the ca. 2664 Re-Os molybdenite age.

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