Abstract The Noranda camp in the southern Abitibi greenstone belt comprises over 20 volcanogenic massive sulfide deposits hosted by volcanic rocks of the 2704–2695 Ma Blake River Group. Decades of research and exploration have provided a firm understanding of the characteristics of these deposits as well as the geological controls on deposit location. Observations made on the deposits of the Noranda camp significantly contributed to the syngenetic model of massive sulfide formation and shaped the current understanding of ancient and modern sea-floor hydrothermal systems. The Horne and Quemont deposits, which are the largest deposits in the Noranda camp, are hosted by 2702 Ma felsic volcanic successions dominated by volcaniclastic rocks. The massive sulfide ores of these deposits largely formed through processes of subseafloor infiltration and replacement of the highly permeable wall rocks. Laterally extensive hydrothermal alteration halos dominated by chlorite and sericite surround the replacement ores. The Horne deposit formed in an extensional setting in a graben bounded by synvolcanic faults. Rapid extension accompanying deposit formation resulted in the upwelling of mantle-derived mafic melts and the emplacement of a thick package of mafic rocks in the stratigraphic hanging wall of the deposit. Most of the massive sulfide deposits in the Noranda camp are hosted by a 2700–2698 Ma bimodal volcanic succession that formed in a large volcanic subsidence structure to the north. The ~2,000-m-thick lava flow-dominated volcanic package is floored by the large, multiphase, synvolcanic Flavrian pluton. The deposits in this part of the Noranda camp are small (<5 million tonnes) and primarily formed as sulfide mounds on the ancient sea floor. Synvolcanic structures provided cross-stratal permeability for the hydrothermal fluids and controlled the location of volcanic vents. Thin tuffaceous units mark the sea-floor positions hosting the massive sulfide mounds within the flow-dominated volcanic succession. The concordant massive sulfide lenses overlie discordant alteration pipes composed of chlorite- and sericite-altered rocks. Contact metamorphism associated with the emplacement of the ~2690 Ma Lac Dufault pluton converted the hydrothermal alteration pipes into cordierite-anthophyllite assemblages. Recent brownfields exploration successes have demonstrated that massive sulfide discoveries are still possible in one of Canada’s most mature mining camp through three-dimensional geological modeling performed at the camp scale. Geologic target generation through computer modeling has reversed the general trend of progressively deeper exploration with time in the Noranda camp. Deep exploration currently focuses on the reevaluation of a previously uneconomic low-grade ore zone at the Horne deposit.

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.