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 Cadillac mining camp is known for its numerous, but relatively small, orogenic gold deposits, which are spatially associated with the Larder Lake-Cadillac fault zone. The Lapa deposit, with a total endowment of 36 t Au (1.15 Moz), represents the largest gold deposit of the Cadillac mining camp. The Lapa deposit main ore zones are mostly hosted in the Piché Group ultramafic to intermediate volcanic units that are strongly transposed and separated by subvertical, anastomosed high-strain corridors that are part of the Larder Lake-Cadillac fault zone. There are 12 ore zones that are stacked from north to south, forming a series of subparallel, E-striking (main foliation-parallel), steeply dipping south to subvertical “lenses.” The ore consists mainly of very fine-grained (≤1 mm), disseminated sulfides (arsenopyrite and pyrrhotite with traces of chalcopyrite, pyrite, and sphalerite), sulfosalts, native Au, and native Sb. Three amphibolite-grade metamorphosed proximal alteration assemblages are present at Lapa, namely bio-tite-bearing, sericite-bearing, and actinolite-bearing assemblages. The distribution of the three assemblages, defined by the most abundant mineral, is at least in part controlled by the primary host-rock composition. The proximal alteration facies give way to chlorite- (upper half of the deposit at <1,000 m) and hornblende-bearing (lower half of the deposit at >1,000 m) assemblages a few meters to a few decimeters away from the ore zones. The isograd defined by the presence of actinolite in the proximal alteration assemblage and hornblende in the distal assemblage below 1,000 m correlates with a shift from an Au-As association in the lowermost levels of the mine to an Au-Sb association at depth. This variation is thought to be due to varying heat and fluid flow regimes at different times and crustal levels in the fault, with the upgrading of early, “low-grade” Au during prograde and retrograde metamorphism. The Cadillac camp, including the Lapa deposit, is an excellent example of the camp to deposit to stope controls exerted by the structural and lithologic setting on the nature, style, and geometry of greenstone-hosted orogenic gold deposits.

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 Larder Lake-Cadillac Break is a gold metallotect, which extends for more than 250 km from Matachewan in Ontario to Val-d’Or in Quebec. For much of its length it juxtaposes older komatiitic rocks against younger sedimentary units. Among the adjacent sedimentary rocks are distinctive intervals of polymict conglomerate and crossbedded sandstone, which make up part of the Timiskaming Group that unconformably overlies previously folded volcanic strata. Rocks in the vicinity of the break are commonly strongly carbonatized, with the type and abundance of carbonate minerals being controlled largely by protolith composition. Shoshonitic to alkalic igneous rocks occur along the break as volcanic units within the Timiskaming, as plutonic rocks in syn-Timiskaming stocks and plugs, and as local arrays of albitite dikes of intermediate composition. High-strain dislocative deformation is variably developed along the break but its intensity is in part a reflection of metasomatic phyllosilicates in the affected rocks. Gold deposits tend to form clusters along the break and their relationship to it is two-fold: a subset of geologically similar deposits are localized in direct proximity to the break but the majority of gold in the region is found in diverse settings away from it with no clear genetic connection.