Charactering alteration and its geochemical signature provides critical information relevant to ore-deposit genesis and its related footprint; for porphyry-type deposits, zoned potassic-phyllic-propylitic alteration and metal enrichment are critical features. Here we integrate earlier lithological and mineralogical studies of the (10+ Moz Au) Archean Côté Gold porphyry-type Au(-Cu) deposit (Ontario, Canada) with identified alteration types to provide exploration vectors. The ca. 2740 tonalite-quartz diorite-diorite intrusive complex and co-temporal Au(-Cu) mineralization as disseminations, breccias and veins are co-spatial with ore-related alteration types (amphibole, biotite, muscovite). An early, locally developed amphibole event coring the deposit is followed by emplacement of a Au(-Cu) mineralized biotite-rich magmatic-hydrothermal breccia body and broad halo of disseminated biotite and quartz veining. These rocks record gains via mass balance calculations of K, Fe, Mg, LILE, and LREE with Au, Cu, Mo, Ag, Se and Bi. Later muscovite alteration is enriched in K, Rb, Cs, Ba, CO2, and LOI with varied Au, Cu, Mo, Te, As, and Bi values. A strong albite overprint records extreme Na gains with the loss of most other elements, including ore metals (i.e., Au, Cu). Together these data define an Au-Cu-Mo-Ag-Te-Bi-Se core co-spatial with biotite breccia versus a peripheral stockwork and sheeted vein zone with a Te-Se-Zn-Pb-As association. These features further support the posited porphyry-type model for the Côté Gold Au(-Cu) deposit.

The Greenstone orogenic gold deposit is located in the Beardmore-Geraldton belt (BGB) along the boundary between the granite-greenstone Wabigoon subprovince and the metasedimentary Quetico subprovince of the Archean Superior craton, Canada. The deposit is hosted by ca. 2700-2694 Ma turbiditic sandstone, banded iron formation, and ca. 2694 Ma feldspar-quartz porphyry, which underwent strong deformation within the 1 km- wide Bankfield-Tombill deformation zone along the southern margin of the BGB. The deformation zone includes folds and cleavage that formed during early D1 thrust imbrication of the BGB, S-shaped folds and fabrics that formed during D2 sinistral transpression, and Z-shaped folds, fabrics, and localized shear zones that formed during D3 dextral reactivation of the deformation zone. Gold mineralization is associated with folded, early-D1, quartz-carbonate veins (V1) and with NE- to E-striking, syn-D 2 , tourmaline-quartz veins (V2) as well as quartz- carbonate veins (V3). The V1 and V3 veins are surrounded by sericite-carbonate-pyrite +/- albite-rutile alteration halos, and the V2 veins are surrounded by carbonate-tourmaline-pyrite +/- pyrrhotite-chalcopyrite alteration halos. Gold was deposited during fluid-rock sulfidation reactions that resulted in the formation of inclusion-poor pyrite with Ni-Co-As primary crystallographic zoning and inclusion-rich pyrite enriched in Au and other metals (Ag-As-Bi-Co-Ni-Pb-Sb-Te). Hydrothermal alteration associated with the deposition of the veins produced a broad, up to 250 m wide, sericite-carbonate alteration envelope, with S, Te, As, W, and Bi as the best pathfinder indicators to gold mineralization. Contrary to previous studies, which attributed the formation of gold deposits in the BGB to late-D3, our results suggest that gold was emplaced during early-D1 and D2 and involved multiple hydrothermal fluid pulses during several deformation events, as suggested for other major Archean orogenic gold camps associated with major fault zones such as the Timmins and Kirkland Lake camps in the Abitibi subprovince of the Superior craton.

The Abitibi greenstone belt, extending from northeastern Ontario to northwestern Quebec in Eastern Canada, is the largest belt of Neoarchean supracrustal rocks on the planet, and also one of the richest in terms of base and precious metals, including several critical and strategic metals. This chapter presents an overview of the geology and metallogeny of the Abitibi greenstone belt. It highlights the exceptional mineral wealth of this belt and illustrates the typology of mineral systems and their distribution in space and time. The Abitibi greenstone belt comprises several sequences of volcanic and sedimentary rocks generally oriented east-west, folded and intersected by several faults and intrusive bodies. The Abitibi greenstone belt is a region with an exceptional wealth of mineral resources. It contains a variety of metals, which are concentrated in various types and styles of deposits. Gold is the main metal of the belt.

Free Access Appendix 2: Metallogeny of the Abitibi Greenstone Belt, Canada Patrick MERCIER-LANGEVIN, Patrick MERCIER-LANGEVIN Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorBenoît DUBÉ, Benoît DUBÉ Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorMichel G. HOULÉ, Michel G. HOULÉ Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorValérie BÉCU, Valérie BÉCU Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorAnne-Aurélie SAPPIN, Anne-Aurélie SAPPIN Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorJean-Luc PILOTE, Jean-Luc PILOTE Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorSébastien CASTONGUAY, Sébastien CASTONGUAY Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this author Patrick MERCIER-LANGEVIN, Patrick MERCIER-LANGEVIN Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorBenoît DUBÉ, Benoît DUBÉ Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorMichel G. HOULÉ, Michel G. HOULÉ Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorValérie BÉCU, Valérie BÉCU Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorAnne-Aurélie SAPPIN, Anne-Aurélie SAPPIN Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorJean-Luc PILOTE, Jean-Luc PILOTE Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this authorSébastien CASTONGUAY, Sébastien CASTONGUAY Geological Survey of Canada, Natural Resources Canada, Quebec, CanadaSearch for more papers by this author Sophie Decrée, Sophie DecréeSearch for more papers by this author Book Author(s):Sophie Decrée, Sophie DecréeSearch for more papers by this author First published: 26 December 2023 https://doi.org/10.1002/9781394264841.app2 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onEmailFacebookTwitterLinkedInRedditWechat References Bécu , V. , Dubé , B. , Mercier-Langevin , P. 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The Beardmore-Geraldton belt (BGB) is a boundary zone between the Wabigoon and Quetico subprovinces of the Archean Superior Province, Canada. It consists of interleaved metavolcanic and metasedimentary panels that were imbricated during an early D1 thrusting event and regionally folded during a D2 event. D1 and D2 steepened stratigraphy and produced contact-parallel shear zones and a regional bedding-parallel cleavage, which controlled the development of a D3 dextral transpression zone. During D3, the panels deformed by pure shear and were overprinted by a second regional cleavage. Bedding and the early cleavage acted as subvertical planes of anisotropy that were reactivated during D3 dextral shearing. Z-shaped drag folds and pre-existing D1 and D2 folds are parallel to a shallowly-plunging (20 degrees -30 degrees) stretching lineation, which together with the fold axes rotated towards the extensional flow apophysis during D3 shearing. As the lineation and fold axes are oblique to the sub-horizontal shear direction expressed by the intersection between synthetic shear bands and the early cleavage, the reactivated shear zones are transpression zones with shallowly-plunging lateral extrusion and triclinic symmetry. Thus, the shear zones are transpressive within a regional tectonic transpression zone that extends across the BGB and over 500 km along the Quetico-Wabigoon boundary.

Zircon provides essential information on the age and oxidation state of magmatic systems and can be used to characterize magmatic-hydrothermal Au mineralizing systems. Using the Douay intrusion-related gold system (IRGS) as a type example of Neoarchean syenite-associated mineralization (Abitibi greenstone belt), we demonstrate that zircon from altered quartz-monzonite rocks can also be used to infer the age of a magmatic-hydrothermal event. Here, zircon chemistry is used to identify the following sequence of events at the Douay exploration project: (1) the crystallization of zircon at ~2690 Ma in evolved residual melts with distinct U-contents (quartz-monzonite magma); (2) the extensive radiation damage for the U-rich grains over a period of ~10–15 My; and (3) the alteration of zircon grains at ~2676 Ma by interaction with magmatic-hydrothermal mineralizing fluids derived from syenite and carbonatite intrusive phases. This study also distinguishes extensively altered zircon grains from pristine to least-altered zircon formed in distinct magmatic environments using a Th/U vs. U discrimination diagram.

The Beardmore-Geraldton Belt (BGB) is a major gold camp along the boundary between the granite-greenstone eastern Wabigoon subprovince and the metasedimentary Quetico subprovince of the Archean Superior Province, Canada. New detrital zircon geochronology suggests that the metasedimentary rocks of the BGB and northern Quetico subprovince were derived from the erosion of the eastern Wabigoon subprovince that is dominated by ca. 2900-2680 Ma rocks but also comprises crust as old as > 3200 Ma. Uplift of the eastern Wabigoon subprovince as a result of convergence and compression along its southern margin exposed those rocks to erosion and shed sediments in the Quetico basin to the south. Sedimentation in the Quetico basin is bracketed between ca. 2700 Ma, the age of the youngest detrital zircon population, and 2694.0 +/- 1.0 Ma, the crystallization age of cross-cutting feldspar-quartz porphyries (FQP). Continued convergence facilitated the thrust-imbrication of the metavolcanic rocks of the eastern Wabigoon subprovince with the metasedimentary rocks of the Quetico basin resulting in the assembly of the BGB. This resulted in crustal thickening, the introduction of hydrated mafic rocks at the base of the crust, and partial melting of these rocks to form TTG suite melts at depths >50 km, as suggested by the geochemical characteristics of the FQP intrusions. Imbrication and thrusting ended with the emplacement of the stitching, 2690 +/- 1 Ma Croll Lake Stock, which has a high transition elements and ferromagnesian oxides signature of sanukitoid suite rocks. It formed during delamination of the lower crust or slab break-off from magmas generated by mixing of hot, mantle material with TTG suite melts at depths > 50 km. The early geological evolution of the Geraldton gold camp is broadly similar to that of other major Archean gold camps associated with major faults and/or terrane boundaries, where deposition of fluvial conglomerate and turbiditic sandstones in fault-bounded basins overlying older volcanic rocks is accompanied by magmatic activity and the upward migration of gold-bearing hydrothermal fluids, while differences between the Geraldton and other camps may be explained by craton-scale variations in geodynamic processes.

The Westwood deposit (4.5 Moz Au) is hosted in the 2699–2695 Ma Bousquet Formation volcanic and intrusive rocks, in the eastern part of the Blake River Group, southern Abitibi greenstone belt. The Bousquet Formation is divided in two geochemically distinct members: a mafic to intermediate, tholeiitic to transitional lower member and an intermediate to felsic, transitional to calc-alkaline upper member. The Bousquet Formation is cut by the synvolcanic (2699–2696 Ma) polyphase Mooshla Intrusive Complex, which is cogenetic with the Bousquet Formation. The deposit contains three strongly deformed (D2 flattening and stretching), steeply S-dipping mineralized corridors that are stacked from north to south: Zone 2 Extension, North Corridor, and Westwood Corridor. The North and Westwood corridors are composed of Au-rich polymetallic sulfide veins and stratabound to stratiform disseminated to massive sulfide ore zones that are spatially and genetically associated with the calcalkaline, intermediate to felsic volcanic rocks of the upper Bousquet Formation. The formation of the disseminated to semimassive ore zones is interpreted as strongly controlled by the replacement of porous volcaniclastic rocks at the contact with more impermeable massive cap rocks that helped confine the upflow of mineralizing fluids. The massive sulfide lenses are spatially associated with dacitic to rhyolitic domes and are interpreted as being formed, at least in part, on the paleoseafloor. The epizonal, sulfide-quartz vein-type ore zones of the Zone 2 Extension are associated with the injection of subvolcanic, calc-alkaline felsic sills and dikes within the lower Bousquet Formation. These subvolcanic intrusive rocks, previously interpreted as lava flows, are cogenetic and coeval with the intermediate to felsic lava flows and domes of the upper Bousquet Formation. The change from fractional crystallization to assimilation- and fractional crystallization-dominated processes and transitional to calc-alkaline magmatism is interpreted to be responsible for the development of the auriferous ore-forming system. The Westwood deposit is similar to some Phanerozoic Au ± base metal-rich magmatic-hydrothermal systems, both in terms of local volcano-plutonic architecture and inferred petrogenetic context. The complex volcanic evolution of the host sequence at Westwood, combined with its proximity to a polyphase synvolcanic intrusive complex, led to the development of one of the few known large Archean subaqueous Au-rich magmatic-hydrothermal systems.

La ceinture de roches vertes de l’Abitibi (Canada) est exceptionnelle par la richesse de ses gisements métalliques, gisements d’or orogénique, gisements de métaux de première nécessité (Cu, Zn) de type sulfures massifs volcanogènes ou encore de nickel-chrome dans des roches magmatiques. Mercier-Langevin et al. synthétisent les différents gîtes et gisements de cette province exceptionnelle.

In central Yukon, the Neoproterozoic to Carboniferous complexly deformed Rackla belt is along the northern boundary of the Selwyn basin. Toward the eastern end of the Rackla belt, a series of gold deposits in the Nadaleen trend exhibit similarities with Carlin-type deposits of the southwestern United States and may represent some of the best examples of this type of mineralization outside Nevada. These replacement-style gold deposits are hosted in two Neoproterozoic carbonate-dominated intervals and in a Paleozoic siltstone/mudstone unit at the contact with less permeable strata. In Neoproterozoic-hosted deposits, mineralized zones are grossly concordant with bedding. Favorable host rocks (including sedimentary units formed through debris flows) form complexly shaped faulted anticlines that constituted mixed stratigraphic/structural traps for mineralizing fluids. This and the association of gold with arsenic-rich pyrite, the common occurrence of realgar/orpiment, alteration styles dominated by decarbonatization of impure carbonate rocks, late Au-stage calcite characterized by a depleted δ18O signature, the very low base metal content and Ag/Au ratio, and enrichment in a series of diagnostic pathfinder elements (Hg, Tl ± Sb, As) are among the key features that are consistent with classification of the eastern Rackla belt as a Carlin-type district. Mineralization style varies significantly at the centimeter to 10-m scale, indicating that mineralizing fluids exploited permeable pathways, regardless of their sedimentary and/or tectonic origin. Alternating finely laminated limestone, siltstone, and floatstone intervals are the dominant host rocks to mineralization in the Conrad, Sunrise, and Osiris deposits. Premineralization fractures acted as feeders for selective bed replacement, and premineralization calcite vein networks, preferentially dissolved by early acidic fluids, acted as conduits to later gold-bearing fluids. Limited evidence suggests that synmineralization deformation was relatively minor and possibly dominated by oblique strike-slip faulting.

The Westwood deposit, located in the Archean Doyon-Bousquet-LaRonde mining camp in the southern Archean Abitibi greenstone belt, contains 4.5 Moz (140 metric t) of gold. The deposit is hosted in the 2699–2695 Ma submarine, tholeiitic to calc-alkaline volcanic, volcaniclastic, and intrusive rocks of the Bousquet Formation. The deposit is located near the synvolcanic (ca. 2699–2696 Ma) Mooshla Intrusive Complex that hosts the Doyon epizonal intrusion-related Au ± Cu deposit, whereas several Au-rich volcanogenic massive sulfide (VMS) deposits are present east of the Westwood deposit. The Westwood deposit consists of stratigraphically stacked, contrasting, and overprinting mineralization styles that share analogies with both the intrusion-related and VMS deposits of the camp. The ore zones form three distinct, slightly discordant to stratabound corridors that are, from north (base) to south (top), the Zone 2 Extension, the North Corridor, and the Westwood Corridor. Syn- to late-main regional deformation and upper greenschist to lower amphibolite facies regional metamorphism affect the ore zones, alteration assemblages, and host rocks. The Zone 2 Extension consists of Au ± Cu sulfide (pyrite-chalcopyrite)-quartz veins and zones of disseminated to semimassive sulfides. The ore zones are spatially associated with a series of calc-alkaline felsic sills and dikes that crosscut the mafic to intermediate, tholeiitic to transitional, lower Bousquet Formation volcanic rocks. The metamorphosed proximal alteration consists of muscovite-quartz-pyrite ± gypsum-andalusite-kyanite-pyrophyllite argillic to advanced argillic-style tabular envelope that is up to a few tens of meters thick. The North Corridor consists of auriferous semimassive to massive sulfide veins, zones of sulfide stringers, and disseminated sulfides that are hosted in intermediate volcaniclastic rocks at the base of the upper Bousquet Formation. The Westwood Corridor consists of semimassive to massive sulfide lenses, veins, zones of sulfide stringers, and disseminated sulfides that are located higher in the stratigraphic sequence, at or near the contact between calc-alkaline dacite domes and overlying calc-alkaline rhyodacite of the upper Bousquet Formation. A large, semiconformable distal alteration zone that encompasses the North Corridor is present in the footwall and vicinity of the Westwood Corridor. This metamorphosed alteration zone consists of an assemblage of biotite-Mn garnet-chlorite-carbonate ± muscovite-albite. A proximal muscovite-quartz-chlorite-pyrite argillic-style alteration assemblage is associated with both corridors. The Zone 2 Extension ore zones and associated alteration are considered synvolcanic based on crosscutting relationships and U-Pb geochronology and are interpreted as being the distal expression of an epizonal magmatic-hydrothermal system that is centered on the upper part of the synvolcanic Mooshla Intrusive Complex. The North and Westwood corridors consist of bimodal-felsic Au-rich VMS-type mineralization and alteration produced by the convective circulation of modified seawater that included a magmatic contribution from the coeval epizonal Zone 2 Extension magmatic-hydrothermal system. The Westwood Au deposit represents one of the very few documented examples of an Archean magmatic-hydrothermal system—or at least of such systems formed in a subaqueous environment. The study of the Westwood deposit resulted in a better understanding of the critical role of magmatic fluid input toward the formation of Archean epizonal intrusion-related Au ± Cu and seafloor/subseafloor Au-rich VMS-type mineralization.

In central Yukon, the Neoproterozoic to Carboniferous complexly deformed Rackla belt is along the northern boundary of the Selwyn basin. Toward the eastern end of the Rackla belt, a series of gold deposits in the Nadaleen trend exhibit similarities with Carlin-type deposits of the southwestern United States and may represent some of the best examples of this type of mineralization outside Nevada. These replacement-style gold deposits are hosted in two Neoproterozoic carbonate-dominated intervals and in a Paleozoic siltstone/mudstone unit at the contact with less permeable strata. In Neoproterozoic-hosted deposits, mineralized zones are grossly concordant with bedding. Favorable host rocks (including sedimentary units formed through debris flows) form complexly shaped faulted anticlines that constituted mixed stratigraphic/structural traps for mineralizing fluids. This and the association of gold with arsenic-rich pyrite, the common occurrence of realgar/orpiment, alteration styles dominated by decarbonatization of impure carbonate rocks, late Au-stage calcite characterized by a depleted delta O-18 signature, the very low base metal content and Ag/Au ratio, and enrichment in a series of diagnostic pathfinder elements (Hg, Tl +/- Sb, As) are among the key features that are consistent with classification of the eastern Rackla belt as a Carlin-type district. Mineralization style varies significantly at the centimeter to 10-m scale, indicating that mineralizing fluids exploited permeable pathways, regardless of their sedimentary and/or tectonic origin. Alternating finely laminated limestone, siltstone, and floatstone intervals are the dominant host rocks to mineralization in the Conrad, Sunrise, and Osiris deposits. Premineralization fractures acted as feeders for selective bed replacement, and premineralization calcite vein networks, preferentially dissolved by early acidic fluids, acted as conduits to later gold-bearing fluids. Limited evidence suggests that synmineralization deformation was relatively minor and possibly dominated by oblique strike-slip faulting.

The sources of metals enriched in Archean orogenic gold deposits have long been debated. Metasedimentary rocks, which are generally accepted as the main metal source in Phanerozoic deposits, are less abundant in Archean greenstone belts and commonly discounted as a viable metal source for Archean deposits. We report ultralow-detection-limit gold and trace element concentrations from a suite of metamorphosed sedimentary rocks from the Abitibi belt and Pontiac subprovince, Superior Province, Canada. Systematic decreases in the Au content with increasing metamorphic grade indicate that Au was mobilized during prograde metamorphism. Mass balance calculations show that over 10 t of Au, 30,000 t of As, and 600 t of Sb were mobilized from 1 km(3) of Pontiac subprovince sedimentary rock metamorphosed to the sillimanite metamorphic zone. The total gold resource in orogenic gold deposits in the southern Abitibi belt (7500 t Au) is only 3% of the Au mobilized from the estimated total volume of high-metamorphic-grade Pontiac sedimentary rock in the region (25,000 km(3)), indicating that sedimentary rocks are a major contributor of metals to the orogenic gold deposits in the southern Abitibi belt.

The Archean low-grade, large-tonnage Côté Gold Au(-Cu) deposit is the first large gold deposit discovered in the Swayze greenstone belt, Ontario, Canada. The deposit is hosted by the Chester Intrusive Complex, a low-Al composite, subvolcanic intrusion composed of tonalite, quartz diorite, and diorite that was previously constrained to ca. 2741 to 2739 Ma (U-Pb zircon). Presented here is the first detailed study of the mineralization and related alteration, along with the relative and absolute age (U-Pb, Re-Os) constraints on gold mineralization. The earliest hydrothermal stage is represented by rare Au-bearing amphibole-rich veins and breccias. The main ore stage consists of biotite-rich alteration centered on an Au(-Cu)–bearing magmatic-hydrothermal biotite breccia body with spatially related disseminated biotite and veins of both sheeted and stockwork type. Extensive fracture-controlled and replacement-style Au ± Cu-bearing muscovite alteration overprints biotite-altered rocks in the core of the deposit. Barren fracture-controlled and disseminated epidote alteration is localized to the north of the deposit and above the magmatic-hydrothermal biotite breccia. Late, texturally destructive albite alteration overprints the mineralized hydrothermal alteration in the deposit core. U-Pb isotope dilution-thermal ionization mass spectrometry and laser ablation-inductively coupled plasmamass spectrometry ages for hydrothermal titanite from amphibole (2745 ± 3 Ma) and albite (2737.5 +2.2/–1.8, 2745 ± 9, and 2736 ± 7 Ma) alteration assemblages constrain hydrothermal activity to ca. 2740 Ma. The timing of gold and sulfide mineralization is also constrained by two Re-Os molybdenite ages of 2736.1 ± 11.4 (biotite alteration) and 2746.8 ± 11.4 Ma (muscovite alteration). These new ages overlap with the ca. 2741 to 2739 Ma magmatism for the Chester Intrusive Complex, thereby suggesting a synintrusion, magmatic-hydrothermal origin for the gold mineralization and related alteration. This is significant, as it represents a new gold metallogenic event in the Abitibi subprovince, for which regional importance remains to be defined. Considering the spatial association of the deposit with a dioritic intrusion and the temporal overlap of igneous activity with alteration (i.e., amphibole, biotite, sericite) and mineralization (i.e., breccias, veins, disseminations), the deposit is interpreted as an Archean magmatic-hydrothermal ore system sharing analogies with Phanerozoic Au-Cu porphyry deposits. It suggests that Archean porphyry-type deposits can form in low-Al composite intrusions, which are known to host Cu-Mo-Au breccia, vein, and disseminated mineralization and underlie temporally and genetically related felsic to intermediate volcanic rocks that host volcanogenic massive sulfide deposits.

The Timmins-Porcupine camp, with >2,190 metric tons Au (70.5 Moz) produced between 1906 and 2019, is the world’s largest Archean orogenic gold camp. The gold deposits of the camp are distributed over ~50 km of strike length along the Destor-Porcupine fault zone. This includes the world-class Hollinger-McIntyre and Dome deposits, which represent archetypal examples of large orogenic quartz-carbonate gold systems. The Dome deposit, where the ore is centered on a folded unconformity between Tisdale volcanic rocks and Timiskaming sedimentary units, also illustrates the spatial relationship between large gold deposits and a regional unconformity. Ore-forming hydrothermal activity in the camp spanned a prolonged period of time, as illustrated by early-stage, low-grade ankerite veins formed between ca. 2690 and 2674 Ma. This was prior to or very early relative to the development of the regional unconformity and sedimentation of the Timiskaming assemblage, and subsequent main-stage gold deposition. The bulk of the gold in the district is younger than the Three Nations Formation of the upper part of the Timiskaming assemblage (i.e., ≤2669 ± 1 Ma) and was deposited syn- to late-main phase of shortening (D3) in the Timmins-Porcupine camp from about 2660 to 2640 ± 10 Ma. The early carbonatization represents a significant early-stage hydrothermal event in the formation of large structurally controlled gold deposits such as Dome and illustrates the protracted nature of the large-scale CO2-rich metasomatism occurring before and during gold deposition. Ores in the Timmins-Porcupine camp mainly consist of networks of steeply to moderately dipping fault-fill quartz-carbonate ± tourmaline ± pyrite veins and associated extensional, variably deformed, shallowly to moderately dipping arrays of sigmoidal veins hosted in highly carbonatized and sericitized rocks and formed during main regional shortening (D3). In contrast, at the Timmins West mine, the Thunder Creek and 144 GAP deposits are early- to syn-Timiskaming intrusion-associated deposits that slightly predate to overlap the main phase of D3 horizontal shortening in which the associated intrusions mainly played a passive role as an older mechanical and chemical trap rock. The formation of the gold deposits of the Timmins-Porcupine camp is due to several key factors. The Destor-Porcupine fault zone represents a deeply rooted first-order structure and tapped auriferous metamorphic fluids and melts from the upper mantle-lower crust. The fault zone has channeled large volumes of auriferous H2O-CO2-rich fluids to the upper crust late in the evolution of the belt. Several of the gold deposits of the camp are spatially associated with the regional Timiskaming unconformity. The current level of erosion is deep enough to expose the unconformity and to maximize the chance of discovering the quartz-carbonate style of orogenic deposits or the associated hydrothermal footprint, but also allowed for preservation of at least part of the gold deposits that are mainly hosted in the highly reactive Fe-rich basalt of the Tisdale assemblage. Additional key factors include the presence of komatiitic and/or basaltic komatiite flows, competent pre- and syn-Timiskaming subalkaline and alkaline intrusions that predate the main phase of shortening, and the occurrence of a flexure in the trace of the Destor-Porcupine fault zone that may have further facilitated and focused the ore-forming fluid upflow in the most endowed part of the camp. The complex structural and rheological discontinuities, competency contrasts, and early-stage folds with associated fracture and fault netorks in the camp provided highly favorable ground-preparation conditions.

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 D2 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-D2 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.