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.

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 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 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.