ABSTRACT The Neoarchean marked an important turning point in the evolution of Earth when cratonization processes resulted in progressive amalgamation of relatively small crustal blocks into larger and thicker continental masses, which now comprise the ancient core of our continents. Although evidence of cratonization is preserved in the ancient continental cores, the conditions under which this geodynamic process operated and the nature of the involved crustal blocks are far from resolved. In the Superior craton, deep-crustal fault systems developed during the terminal stage of Neoarchean cratonization, as indicated by the cratonwide growth of relatively small, narrow, syn-to-late tectonic (ca. 2680–2670 Ma) sedimentary basins. The terrigenous debris eroded from the uplifted tectono-magmatic source regions was deposited as polymictic conglomerate and sand successions in fluvial-dominated basins. The composition of the sedimentary rocks in these unique basins, therefore, offers a unique record of crustal sources and depositional settings, with implications for the geodynamic processes that formed the world’s largest preserved craton. Here, we compare the geochemical compositions of sandstone samples from six sedimentary basins across the Abitibi greenstone belt and relate them to their mode of deposition, prevailing provenance, and geodynamic setting during crustal growth and craton stabilization. The sandstones represent first-cycle sediment that is poorly sorted and compositionally very immature, with variable Al 2 O 3 /TiO 2 ratios and index of chemical variability values >1 (average of 1.36), reflecting a large proportion of framework silicate grains. The sandstones display chemical index of alteration values between 45 and 64 (average of 53), indicating that the detritus was eroded from source regions that experienced a very low degree of chemical weathering. This likely reflects a high-relief and active tectonic setting that could facilitate rapid erosion and uplift with a short transit time of the detritus from source to deposition. Multi-element variation diagrams and rare earth element patterns reveal that the lithological control on sandstone composition was dominated by older (>2695 Ma) pretectonic tonalite-trondhjemite-granodiorite and greenstone belt rocks. The sandstone units display large variations in the proportions of felsic, mafic, and ultramafic end-member contributions as a consequence of provenance variability. However, an average sandstone composition of ~65% felsic, ~30% mafic, and ~5% komatiite was observed across the basins. This observation is in agreement with recent models that predict the composition of the Neoarchean emerged continental crust for North America and supports the presence of a felsic-dominated Archean crust. The high proportion of felsic rocks in the upper crust requires continuous influx of H 2 O into the mantle and is best explained by subduction-related processes. In such a scenario, the detritus of the fluvial sandstones is best described as being controlled by uplifted and accreted continental arcs mainly composed of tonalite-trondhjemite-granodiorite and greenstone belt rocks.

Abstract 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 (D 3 ) 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 CO 2 -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 (D 3 ). 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 D 3 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 H 2 O-CO 2 -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.

Abstract The Timmins-Porcupine gold camp, with a total production of more than 2,125 tonnes (75 Moz) Au to date, represents the largest Archean orogenic greenstone-hosted gold camp worldwide in terms of total gold production. The gold deposits of the camp are distributed over 50 km of strike length along the Destor-Porcupine fault zone, including the giant Hollinger-McIntyre and Dome deposits. These two deposits are archetype examples of large Archean orogenic gold systems. The Dome mine, where the ore is centered on a folded unconformity between Tisdale volcanic rocks and Timiskaming sedimentary deposits, also illustrates the spatial relationship between large gold deposits and a regional unconformity. Gold-associated hydrothermal activity in the camp spanned a long period of time, as illustrated by early stage, barren to low-grade ankerite veins formed between ca. 2690 and 2674 Ma, i.e., prior to or very early in the development of the regional unconformity and sedimentation of the Timiskaming assemblage. Such early carbonatization may represent a key hydrothermal event in the formation of large orogenic gold deposits and illustrates the protracted nature of the large-scale CO 2 -rich metasomatism occurring before and during gold deposition. The bulk of the gold is, however, younger than the Three Nations Formation in the upper part of the Timiskaming assemblage (i.e., ≤2669 ± 1 Ma) and consists mainly of syn-main regional shortening deformation (D 3 ) networks of steeply to moderately dipping fault-fill quartz-carbonate ± tourmaline ± pyrite veins and associated extensional, shallow to moderately dipping arrays of sheeted and sigmoidal veins hosted in highly carbonatized and sericitized rocks. Formation of the gold deposits of the Timmins-Porcupine camp can be related to several key factors. The Destor-Porcupine fault zone represents a first-order control on the location of the camp as this major fault zone allowed large scale CO 2 -rich hydrothermal fluid upflow. The fault zone also controlled the location of the Timiskaming clastic basin, which is thought to have been developed as a result of early-stage synorogenic extensional faulting. Several of the orogenic gold deposits of the camp are spatially associated with the regional unconformity separating folded submarine volcanic rocks of the Tisdale assemblage form the syn-orogenic sedimentary deposits of the Timiskaming assemblage. The current level of erosion is deep enough to expose the unconformity and to maximize the chance of discovery of the orogenic deposits or their footprint, but allowed for preservation of at least part of the gold deposits that are mainly hosted in the highly reactive Fe-rich Tisdale basalt. Additional key factors include the presence of komatiitic and/or basaltic komatiite flows, of competent intrusions that predate the main phase of shortening of the belt and the occurrence of bends in the trace of the Destor-Porcupine fault zone that may have facilitated focus to ore-forming fluid upflow. Furthermore, the camp is characterized by complex structural and rheological discontinuities, competency contrasts, and early stage folds with associated fracture and fault networks that provided highly favorable ground preparation conditions. The exceptional gold enrichment of the camp requires that the hydrothermal fluids originated from favorable source rocks, lending support to the concept of provinciality, which may best explain the exceptional gold fertility of the southern Abitibi greenstone belt.