Abstract The Val d’Or mining district, located in the southern part of the Abitibi belt in the Superior Province, consists of a typical Archean supracrustal volcanosedimentary sequence, obliquely cut by narrow northeast-trending Proterozoi’c diabase dykes. The geology of the Val d’Or area is shown in figure 1. It was initially described by Gunning and Ambrose (1940) and Norman (1946, 1947), and was subsequently revised by Latulippe (1976), Imreh (1984) and more recently by Robert (1989). The northernmost volcanic unit in the Val d’Or area is an extensive ultramafic lava plain known as the Malartic Group. The Lower Malartic is mainly composed of komatiitic ultramafic lava and subordinate basaltic flows. The Upper Malartic, comprised of basaltic lava with horizons of ultramafic and felsic volcaniclastic rocks (lmreh, 1984), is dominated by two main schistosities, S 1 and S 2 S 1 , oriented northwest, is related to the principal flattening plane. S1 is reoriented by an east-west fabric (S2) which is related to asymmetrical Z-folds found over most of the Val d’Or area. The Kiena Mine, one of the mines we will visit during the second day of our tour, is hosted by the Upper Malartic Group. The Kewagama Group, located to the south of the Malartic Group, contains beds of metawacke and metapelite which have undergone two distinct folding events.axial planes related to the first folding event, oriented northwest, have been reoriented during a second phase of deformation that generated folds whose axial traces are oriented at 278 ° (Tourigny, 1984). The Blake River Group, dominating the Rouyn-Noranda district 100 km to the west of Val d’Or, pinches out between the metasedimentary Kewagama and Cadillac groups near the town of Malartic. Here, the Blake River Group is composed of brecciated basaltic lavas with a main schistosity oriented at 275 ° . The Cadillac Group, occurring to the south of the Blake River and Kewagama groups, is composed of metawacke and metapelite. Axial plane traces oriented at 284 ° terminate against the contact of the Blake River Group. The Piché Group is found only within the Cadillac tectonic zone in the Val d’Or area. It consists mainly of ultramafic lava. Where the deformation is intense, the lava is completely transformed to talc-carbonate schist. Where the deformation is less intense, spinifex textures are still visible. The Cadillac tectonic zone, generally oriented east-west, has been traced from Vauquelin township (east of Val d’Or) west to the border of Ontario and beyond.

Abstract The Val d’Or mining district, located in the southern part of the Abitibi belt in the Superior Province, consists of a typical Archean supracrustal volcanosedimentary sequence, obliquely cut by narrow northeast-trending Proterozoi’c diabase dykes. The geology of the Val d’Or area is shown in figure 1. It was initially described by Gunning and Ambrose (1940) and Norman (1946, 1947), and was subsequently revised by Latulippe (1976), Imreh (1984) and more recently by Robert (1989). The northernmost volcanic unit in the Val d’Or area is an extensive ultramafic lava plain known as the Malartic Group. The Lower Malartic is mainly composed of komatiitic ultramafic lava and subordinate basaltic flows. The Upper Malartic, comprised of basaltic lava with horizons of ultramafic and felsic volcaniclastic rocks (lmreh, 1984), is dominated by two main schistosities, S 1 and S 2 S 1 , oriented northwest, is related to the principal flattening plane. S1 is reoriented by an east-west fabric (S2) which is related to asymmetrical Z-folds found over most of the Val d’Or area. The Kiena Mine, one of the mines we will visit during the second day of our tour, is hosted by the Upper Malartic Group. The Kewagama Group, located to the south of the Malartic Group, contains beds of metawacke and metapelite which have undergone two distinct folding events.axial planes related to the first folding event, oriented northwest, have been reoriented during a second phase of deformation that generated folds whose axial traces are oriented at 278 ° (Tourigny, 1984).

Abstract The Malartic gold camp is located in the southern part of the Archean Superior Province and straddles the Larder Lake-Cadillac fault zone that is between the Abitibi and Pontiac subprovinces. It comprises the world-class Canadian Malartic deposit (25.91 Moz, including past production, reserves, and resources), and smaller gold deposits located along faults and shear zones in volcanic and metasedimentary rocks of the Abitibi subprovince. North of the Larder Lake-Cadillac fault zone, the Malartic camp includes 2714 to 2697 Ma volcanic rocks and ≤2687 Ma turbiditic sedimentary rocks overlain by ≤2679 to 2669 Ma polymictic conglomerate and sandstone of the Timiskaming Group. South of the fault, the Pontiac subprovince comprises ≤2685 Ma turbiditic graywacke and mudstone, and minor ultramafic to mafic volcanic rocks and iron formations of the Pontiac Group. These supracrustal rocks were metamorphosed at peak greenschist to lower amphibolite facies conditions at ~2660 to 2658 Ma, during D 2 compressive deformation, and are cut by a variety of postvolcanic intrusions ranging from ~2695 to 2640 Ma. The Canadian Malartic deposit encompasses several past underground operations and is currently mined as a low-grade, open-pit operation that accounts for about 80% of the past production and reserves in the camp. It dominantly consists of disseminated-stockwork replacement-style mineralization in greenschist facies sedimentary rocks of the Pontiac Group. The mineralized zones are spatially associated with the Sladen fault and ~2678 Ma subalkaline to alkaline porphyritic quartz monzodiorite and granodiorite. Field relationships and isotopic age data for ore-related vein minerals indicate that gold mineralization in the Canadian Malartic deposit occurred at ~2665 to 2660 Ma and was contemporaneous with syn- to late-D 2 peak metamorphism. The smaller deposits in the camp include auriferous disseminated-stockwork zones of the Camflo deposit (1.9 Moz) and quartz ± carbonate-pyrite veins and breccias (0.6 Moz) along faults in chemically and mechanically favorable rocks. The age of these deposits is poorly constrained, but ~2692 Ma postmineral dikes, and ~2625 Ma hydrothermal titanite and rutile from the Camflo deposit highlight a long and complex hydrothermal history. Crosscutting relationships and regional geochronological constraints suggest that an early episode of pre-Timiskaming mineralization occurred at >2692 Ma, shortly after the end of volcanism in the Malartic camp, and postmetamorphic fluid circulation may have contributed to concentration or remobilization of gold until ~2625 Ma. However, the bulk of the gold was concentrated in the Canadian Malartic deposit during the main phase of compressive deformation and peak regional metamorphism.

Abstract The Canadian Malartic low-grade bulk tonnage gold mine (total production and reserves of 303.3 t or 10.7 Moz at 0.97 g/t) is located in the Archean Abitibi greenstone belt, immediately south of the crustal-scale Larder Lake-Cadillac fault zone. The deposit is predominantly hosted in clastic metasedimentary rocks of the Pontiac Group and, to a lesser extent, in subalkaline porphyritic quartz monzodiorite and granodiorite. The quartz monzodiorite and granodiorite yielded syn-Timiskaming U-Pb ID-TIMS zircon ages of 2677.8 ± 1.5 and 2678.4 ± 1.7 Ma, respectively. The ore, which is characterized by a Au-Te-W-S-Bi-Ag ± Pb ± Mo metallic signature, mainly consists of quartz-carbonate vein stockworks and replacement zones with disseminated pyrite. The ore zones are dominantly oriented subparallel to a NW-striking S 2 foliation and to the E-striking and S-dipping Sladen fault, thus forming NW-SE and E-W mineralized trends. In both the sedimentary rocks and the quartz monzodiorite, the proximal and distal alteration zones are characterized by the presence of calcite and ferroan dolomite, respectively. In the sedimentary rocks, the ore zones show a wide distal biotite alteration halo with proximal assemblages made up of albite and/or microcline with pyrite. The quartz monzodiorite comprises a distal hematite-bearing alteration zone that is overprinted by proximal microcline + albite + quartz + pyrite replacement zones. The metallic signature of the ore, the presence of mineralized stockworks, the potassic alteration (biotite/microcline), and an association with ca. 2678 Ma porphyritic intrusions suggest the possibility of an early, syn-Timiskaming magmatic-hydrothermal auriferous event in the area. However, this study indicates that gold mineralization and its distribution at Canadian Malartic are largely controlled by D 2 deformation and related features such as faults, shears, and high-strain zones. Of particular importance are the S 2 cleavage developed in the hinge zone of F 2 folds, and the Sladen fault. Molybdenite from high-grade ore yielded a Re-Os age of 2664 ± 11 Ma that is compatible with a syn-D 2 timing for the bulk of the mineralization. The main characteristics of the Canadian Malartic deposit are thus best explained by a syndeformational event (D 2 ; ca. 2670–2660 Ma) potentially superimposed onto a gold-bearing magmatic/hydrothermal intrusion-related system associated with Timiskaming-age porphyritic intrusions emplaced along the crustal-scale Larder Lake-Cadillac fault zone.