Abstract The Belmoral (Ferderber) gold mine, owned by Société Les Mines Belmoral Ltee, is situated 10 km NE of Val d’Or (Fig.1) in Bourlamaque Twsp., northwestern Quebec, near the centre of the Bourlamaque batholith. This contrasts with the location of other gold mines that are situated near the margin of the batholith, such as the Perron and Courvan mines at the eastern contact, the Sullivan mine at the western contact, and the Bras d’Or (Dumont) mine at the southern contact (Fig.1).

Abstract The Abitibi greenstone belt, which straddles the border between Ontario and Quebec in eastern Canada, represents one of the largest and best-preserved Neoarchean greenstone belts in the world. The belt consists of E-trending successions of folded volcanic and sedimentary rocks and intervening domes of intrusive rocks. Submarine volcanism occurred between 2795 and 2695 Ma. Six volcanic assemblages have been defined, recording submarine volcanism during specific periods of time. Komatiite successions within some of these volcanic assemblages are host to magmatic sulfide deposits. However, economically more important are volcanogenic massive sulfide (VMS) deposits, which contain a total of ~775 million tonnes (t) of polymetallic massive sulfides. Approximately half of the endowment is hosted by volcanic rocks of the 2704 to 2695 Ma Blake River assemblage. VMS deposits of this assemblage also account for most of the synvolcanic gold in the Abitibi greenstone belt, totaling over 1,100 t (~35 Moz). Submarine volcanism was followed by the deposition of large amounts of sedimentary material derived from a shallow marine or subaerial hinterland, created as a result of crustal thickening during an early phase of mountain building at ≤2690 to ≤2685 Ma. Submarine volcanic rocks and the overlying flysch-like sedimentary rocks of the Porcupine assemblage were affected by large-scale folding and thrusting during at least one deformational event prior to 2679 Ma. At this time, a terrestrial unconformity surface developed between the older and already deformed rocks of the Abitibi greenstone belt and molasse-like sedimentary rocks of the Timiskaming assemblage, which were deposited between ≤2679 and ≤2669 Ma. Deposition of the Timiskaming sedimentary rocks occurred in extensional basins and was locally accompanied by predominantly alkaline volcanism and related intrusive activity. Crustal shortening and thick-skinned deformation resulted in the structural burial of the molasse-like sedimentary rocks of the Timiskaming assemblage after 2669 Ma. Panels of Timiskaming deposits were preserved in the footwall of these thrusts, which are today represented by major fault zones cutting across the supracrustal rocks of the Abitibi greenstone belt. The structural history of these fault zones is complicated by late-stage strike-slip deformation. The Porcupine-Destor and Larder Lake-Cadillac fault zones of the southern Abitibi greenstone belt as well as second- and third-order splays off these fault zones are host to a number of major orogenic gold deposits. The gold endowment of these deposits exceeds 6,200 t (~200 Moz), making the Abitibi greenstone belt one of the economically most important metamorphic terranes in the world.

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 Epigenetic gold deposits in metamorphic terranes include those of the Precambrian shields (approx 23,000-25,000 t Au), particularly the Late Archean greenstone belts and Paleoproterozoic fold belts, and of the late Neoproterozoic and younger Cordilleran-style orogens (approx 22,000 t lode and 15,500 t placer Au), mainly along the margins of Gondwana, Laurentia, and the more recent circum-Pacific. Ore formation was concentrated during the time intervals of 2.8 to 2.55 Ga, 2.1 to 1.8 Ga, and 600 to 50 Ma. Prior to the last 25 years, ores were defined by grades of 5 to 10 g/t Au in underground mines; present-day economics, open-pit mining, and improved mineral processing procedures allow recovery of ores of < 1 g/t Au, which has commonly led to the recent reworking of lower gradEzones in many historic orebodies. Most of these deposits formed synchronously with late stages of orogeny and are best classified as orogenic gold deposits, which may be subdivided into epizonal, mesozonal, and hypozonal subtypes based on pressure-temperature conditions of ore formation. A second type of deposit, termed intrusion-related gold deposits, developed landward of Phanerozoic accreted terranes in the Paleozoic of eastern Australia and the Mesozoic of the northern North American Cordillera. These have an overall global distribution that is still equivocal and are characterized by an intimate genetic association with relatively reduced granitoids. The majority of gold deposits in metamorphic terranes are located adjacent to first-order, deep-crustal fault zones, which show complex structural histories and may extend along strike for hundreds of kilometers with widths of as much as a few thousand meters. Fluid migration along such zones was driven by episodes of major pressure fluctuations during seismic events. Ores formed as vein fill of second-and third-order shears and faults, particularly at jogs or changes in strike along the crustal fault zones. Mineralization styles vary from stockworks and breccias in shallow, brittle regimes, through laminated crack-seal veins and sigmoidal vein arrays in brittle-ductile crustal regions, to replacement- and disseminated-type orebodies in deeper, ductile environments (i.e., a continuum model). Most orogenic gold deposits occur in greenschist facies rocks, but significant orebodies can be present in lower and higher grade rocks. Deposits typically formed on retrograde portions of pressure-temperature-time paths and thus are discordant to metamorphic features within host rocks. Spatial association between gold ores and granitoids of all compositions reflects a locally favorable structural trap, except in the case of the intrusion-related gold deposits where there is a clearer genetic association. World-class orebodies are generally 2 to 10 km long, about 1 km wide, and are mined downdip to depths of 2 to 3 km. Most orogenic gold deposits contain 2 to 5 percent sulfide minerals and have gold/silver ratios from 5 to 10 and gold fineness >900. Arsenopyrite and pyrite are the dominant sulfide minerals, whereas pyrrhotite is more important in higher temperature ores and base metals are not highly anomalous. Tungsten-, Bi-, and Te-bearing mineral phases can be common and are dominant in the relatively sulfide poor intrusion-related gold deposits. Alteration intensity, width, and assemblage vary with the host rock, but carbonates, sulfides, muscovite, chlorite, K-feldspar, biotite, tourmaline, and albite are generally present, except in high-temperature systems where alteration halos are dominated by skarnlike assemblages. The vein-forming fluids for gold deposits in metamorphic environments are uniquely CO 2 and 18 O rich, with low to moderate salinities. Phanerozoic and Paleoproterozic ores show a mode of formation temperatures at 250° to 350°C, whereas Late Archean deposits cluster at about 325°to 400°C. However, there are also many important lower and higher temperature deposits deposited throughout the continuum of depths that range between 2 and 20 km. Ore fluids were, in most cases, near-neutral pH, slightly reduced, and dominated by sulfide complexes. Globally consistent ore-fluid δ 18 O values of 6 to 13 per mil and δD values of –80 to –20 per mil generally rule out a significant meteoric water component in the gold-bearing hydrothermal systems. Sulfur isotope measurements on ore-related sulfide minerals are concentrated between 0 and 10 per mil, but with many higher and much lower exceptions, indicating variable sulfur sources and an unlikely dominant role for mantle sulfur. Drastic pressure fluctuations with associated fluid unmixing and/or desulfidation during water/rock interaction are the two most commonly called-upon ore precipitation mechanisms. The specific model(s) for gold ore genesis remains controversial. Although the direct syngenetic models of the 1970s are no longer applicable, the gold itself may be initially added into the volcanic and sedimentary crustal rock sequences, probably within marine pyrite, during sea-floor hydrothermal events. Gold transport and concentration are most commonly suggested to be associated with metamorphic processes, as indicated by the volatile composition of the hydrothermal fluids, the progressive decrease in concentration of elements enriched in the gold deposits with increasing metamorphic grade of the country rocks, and the common association of ores with medium-grade metamorphic environments. Gold deposits of typically relatively low grade, which formed directly from fluid exsolution during granitoid emplacement within metamorphic rocks, are now also clearly recognized (i.e., intrusion-related gold deposits), but there are limited definitive data to implicate such an exsolved fluid source for most gold deposits within orogenic provinces. The fact that orogenic gold deposits are associated with all types of igneous rocks is a problem to a pure magmatic model. Hybrid models, where slab-derived fluids may generate rising melts that drive devolatilization reactions in the lower crust, are also feasible. Although involvement of a direct mantle fluid presents geochemical difficulties, the presence of lamprophyres and deep-crustal faults in many districts suggests potential mantle influence in the overall, large scale tectonic event controlling the hydrothermal flow system.

Abstract The Neoarchean Abitibi greenstone belt in the southern Superior Province has been one of the world’s major gold-producing regions for almost a century with >6,100 metric tons (t) Au produced and a total endowment, including production, reserves, and resources (measured and indicated), of >9,375 t Au. The Abitibi belt records continuous mafic to felsic submarine volcanism and plutonism from ca. 2740 to 2660 Ma. A significant part of that gold is synvolcanic and/or synmagmatic and was formed during the volcanic construction of the belt between ca. 2740 and 2695 Ma. However, >60% of the gold is hosted in late, orogenic quartz-carbonate vein-style deposits that formed between ca. 2660 and 2640 ± 10 Ma, predominantly along the Larder Lake-Cadillac and Destor-Porcupine fault zones. This ore-forming period coincides with the D 3 deformation, a broad north-south main phase of regional shortening that followed a period of extension and associated crustal thinning, alkaline to subalkaline magmatism, and development of orogenic fluvial-alluvial sedimentary basins (ca. <2679–<2669 Ma). These sedimentary rocks are referred to, in the southern Abitibi, as Timiskaming-type. The tectonic inversion from extension to compression is <2669 Ma, the maximum age of the D 3 -deformed youngest Timiskaming rocks. In addition to the quartz-carbonate vein-style, stockwork-disseminated-replacement-style mineralization is hosted in and/or is associated with ca. 2683 to 2670 Ma, early-to syn-Timiskaming alkaline to subalkaline intrusions along major deformation corridors, especially in southern Abitibi. The bulk of such deposits formed late-to post-alkaline to subalkaline magmatism and the largest deposits are early- to syn-D 3 (ca. 2670–2660 Ma), whereas the bulk of the quartz-carbonate vein systems formed syn- to late-D 3 and metamorphism. At belt scale, these illustrate a gradual transition, as shortening increases, in ore styles in orogenic deposits throughout the duration of the D 3 deformation event along the length of the Larder Lake-Cadillac and Destor-Porcupine faults. The sequence of events, although similar in all camps, was probably not perfectly synchronous at belt scale, but varied/migrated with time and crustal levels along the main deformation corridors and from north to south. The presence of high-level alkaline/shoshonitic intrusions, which are spatially associated with Timiskaming conglomerate and sandstone, large-scale hydrothermal alteration, and numerous gold deposits along the Larder Lake-Cadillac and Destor-Porcupine faults indicates that these structures were deeply rooted and tapped auriferous metamorphic-hydrothermal fluids and melts from the upper mantle and/or lower crust, late in the evolution of the belt. The metamorphic-hydrothermal fluids, rich in H 2 O, CO 2 , and H 2 S were capable of leaching and transporting gold to the upper crust along the major faults and their splays. Although most magmatic activity along the faults predates gold, magmas may have contributed fluids and/or metals to the hydrothermal systems in some cases. This great vertical reach explains why the Larder Lake-Cadillac and Destor-Porcupine fault zones are very fertile structures. The major endowment of the southern part of the Abitibi belt (>8,100 t Au) along the corridor defined by the Larder Lake-Cadillac and Destor-Porcupine faults may also suggest that these faults have tapped particularly fertile upper mantle-lower crust gold reservoirs. The concentration of large synvolcanic and synmagmatic gold deposits along that corridor supports the idea of gold-rich source(s) that may have contributed gold to the ore-forming systems at different times during the evolution of the belt.