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The Archean Côté Gold Au(-Cu) deposit is the first large gold deposit discovered in the Swayze greenstone belt of the Abitibi Subprovince. The deposit is a low-grade, large-tonnage type with a combined indicated and inferred resource of 8.65 M oz Au (245.2 t Au). The deposit is hosted by the Chester intrusive complex (CIC), a multiphase, subvolcanic intrusion composed of low-Al tonalite, diorite, and quartz diorite, plus magmatic and hydrothermal breccia bodies. The age of the tonalite and dioritic phases is constrained at 2741-2739 ± 1 Ma using high-precision isotope dilution - thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon geochronology. Although these phases are co-temporal and co-spatial, they appear to be petrogenetically unrelated. The CIC was emplaced into mafic metavolcanic rocks of the Arbutus Formation whose geochemistry reflects a back-arc environment. The tonalite of the CIC is coeval and co-genetic with the felsic to intermediate metavolcanic rocks of the Yeo Formation. Emplacement of the CIC into a shallow crustal level is inferred based on the incorporation of screens and inclusions of the Yeo Formation and is supported by the presence of textures in tonalite and dioritic rocks (e.g., granophyres, miarolitic cavities, and pegmatites), as well as Al-in-hornblende geobarometry results of ≤1.3 ± 0.6 kbars (1 kbar = 100 MPa). The CIC is petrologically similar to other subvolcanic, low-Al tonalite-trondhjemite-diorite intrusions that underlie volcanogenic massive sulphide (VMS)-type deposits and which themselves may contain syn-intrusion mineralization. Several geochemically unrelated dykes and deformation events crosscut and postdate the CIC. [ABSTRACT FROM AUTHOR]

Subvertically- to vertically-dipping Archean strata provide an excellent opportunity to study synvolcanic structures and internal organization of subaqueous volcanic complexes. The Abitibi greenstone belt in Quebec, Canada, hosts a number of these volcanic complexes and specifically the unique Blake River Megacaldera Complex. The Blake River Megacaldera Complex is composed of ( i) an initial shield phase known as the Misema Caldera and ( ii) two graben-type calderas known as the New Senator and Noranda calderas. The southern portion of the New Senator Caldera, the focus of this study, is of particular interest as the structure hosts the 54 Mt Horne Au-rich volcanogenic massive sulfide deposit. Detailed facies mapping, coupled with geochemical and geochronological analysis at multiple outcrop localities throughout the city of Rouyn-Noranda, Quebec, show that the stratigraphy of the New Senator Caldera is dominated by subaqueous effusive mafic volcanic facies with local felsic effusive and intrusive deposits. With the incorporation of structural data, we have used synvolcanic faults and dyke complexes to divide these facies into specific blocks within this region, here renamed the Rouyn-Pelletier sector. This study focuses on the facies and characteristics of the Pelletier, Senator, and Glenwood blocks and identifies the Évain, Stadacona, and Chadbourne blocks. Geochronological analysis reveals that facies of the Glenwood Block are approximately the same age as those of the felsic flows of the previously identified Horne Block. Together, all extrusive and intrusive volcanic facies from the Stadacona unit north to the Horne Creek fault compose a large caldera complex known as the Rouyn-Pelletier Caldera Complex. [ABSTRACT FROM AUTHOR]

Geological investigation of the rocks in the Elu Link has provided new information on the geodynamic origin of the Neoarchean (ca. 2716-2663 Ma) Hope Bay and Elu granite-greenstone belts. Stratigraphic and geochemical features of these rocks and those of the nearby Flake Lake area in the Hope Bay belt suggest that the two greenstone belts are contiguous, having similar mafic-dominated bimodal rocks comprising abundant basalts to andesites and less common dacites and rhyolites hosting gabbroic and trondhjemite-tonalite-granodiorite (TTG) intrusions. The corresponding parental magmas, whose evolution likely occurred via fractional crystallization and juvenile crustal contamination, formed from both deep and shallow mantle sources. The basalts, andesites, gabbros, and felsic volcanic rocks are variably tholeiitic to calc-alkaline. Chondrite- and primitive mantle-normalized profiles demonstrate (1) flat to slightly fractionated heavy rare-earth element (HREE) patterns with a weak negative Eu anomaly and (2) light rare-earth element (LREE) enriched and strongly fractionated HREE patterns with variable negative to positive Eu anomalies. In contrast, TTG rocks are calc-alkaline, with strong LREE enrichment, HREE depletion, and variable positive Eu anomalies. Altogether, the rocks exhibit Nb and Ti troughs, and variable Nb/Ta, La/Ta, and Zr/Hf ratios indicative of crustal contamination. Chalcophile elements and related ore deposits in the area are inferred to be formed from hydrothermal fluids mobilized during emplacement and after crystallization of their host rocks. An extensional, high-heat-flow back-arc tectonic environment is proposed to explain the stratigraphic and geochemical characteristics and the presence of large gold resources in these greenstone belts. [ABSTRACT FROM AUTHOR]

Recent advances in the use of Geographic Information Systems (GIS) software and analysis can be used in conjunction with traditional geoscience data sets to determine effective predictors for gold mineralization, from which mineral prospectivity maps can be generated that highlight potential exploration targets on a regional scale. In this paper, key components of the Archean lode gold deposit model for the Red Lake belt are selected and modeled using weights of evidence (WofE) analysis and logistic regression, leading to the creation of gold prospectivity maps. The best predictors for past and present gold producers in the Red Lake camp, according to WofE analysis include (1) elevated trace elements, Au, As, and Sb; (2) a number of alteration indices calculated from oxide geochemical data; (3) alteration characterized by pervasive and vein-style ferroan carbonate and elevated Au, As, Sb, and S anomalies; (4) proximity to the Mackenzie Island stock and diorite phases of the Dome stock; and, (5) tholeiitic basaltic flows and associated gabbroic rocks of the Balmer assemblage. Gold prospectivity maps produced by logistic regression using binary evidence maps highlight anomalous localities within known and highly prospective areas in the district (Madsen – Red Lake corridor, Balmertown – Cochenour – East Bay). In addition, a number of localities not known to contain significant deposits were also identified as prospective. [ABSTRACT FROM AUTHOR]

Seismic reflection line 2B was shot across the Archean Red Lake greenstone belt and Sydney Lake fault zone that marks the northern boundary of the English River metasedimentary belt, as part of the Western Superior Lithoprobe transect. Three-dimensional tomographic inversion of first arrival traveltimes recorded in this survey delineate the subsurface to depths as great as 1.5 km around this crooked two-dimensional seismic line. Within the Red Lake greenstone belt, P-wave velocities of 6.2–7.0 km s–1 occur at 500 m depth in the Mesoarchean Balmer assemblage, clearly distinguishable from the lower velocities of 5.1–6.1 km s–1 of the Neoarchean Confederation assemblage. Although the overall range of velocities in the metasedimentary rocks of the English River subprovince is similar to that found in the Confederation assemblage, lower velocities of 5.1–5.4 km s–1 are found in the upper 300 m of the metasedimentary rocks. In particular, two 2–3 km wide, east-northeast-striking zones of low velocity are associated with the Sydney Lake fault zone and the Pakwash Lake fault zone. Correlation of the velocities with the coincident reflection section suggests that these two faults delineate a fault-bounded block in the hanging wall of a more northerly fault zone that crops out within the Uchi subprovince. Anomalous regions of low velocity, which occur at the boundary between the Confederation and Balmer assemblages, and within the Balmer assemblage, may also be related to shear zones that have minimal near-surface expression, felsic lithologies, or hydrothermal alteration of the basalts. [ABSTRACT FROM AUTHOR]

The western Superior Province sustained rapid crustal growth in the interval 2.72–2.68 Ga through amalgamation of microcontinental crustal blocks and juvenile oceanic terranes. Recent field, isotopic, and geophysical surveys provide insight on the nature, timing, and scale of this accretionary growth. However, few places offer the rich tectono-stratigraphic and structural detail with which to establish accretion of oceanic and continental blocks as does the Savant–Sturgeon area. Here, 3.4–2.8 Ga continental crust of the Winnipeg River terrane is juxtaposed with 2.775–2.718 Ga juvenile oceanic rocks of the western Wabigoon terrane across a 2.85–2.75 Ga, southwest-facing, continental margin sequence. The continental margin was reactivated at ~2.715 Ga with the establishment of an arc, recorded by 2.715–2.70 Ga tonalite and associated intermediate volcanic rocks. This magmatic activity is interpreted to reflect north- and east-dipping subduction that led to consumption of a small tract of oceanic crust between the Winnipeg River and western Wabigoon terranes, ultimately leading to their amalgamation after 2.703 Ga. The telescoped fore arc also includes continental-derived turbiditic wacke, siltstone, and iron formation (Warclub assemblage) that are in tectonic contact with diverse oceanic rocks of the western Wabigoon terrane. Collision is bracketed between 2.703 Ga (the maximum age of marine fore arc deposits) and ~2.696 Ga (the minimum age of a late-tectonic pluton). Effects include thrust stacking and the development of shallow-plunging folds and bedding-parallel fabrics (D1), overprinted by steeply plunging inclined folds, steep foliations, and shear zones (D2). Collectively, these structures have penetratively reworked the suture between the ancient fore-arc and oceanic rocks in the Savant–Sturgeon area.Back to Table of Contents [ABSTRACT FROM AUTHOR]

The Grenville Province and other parts of the Canadian Shield contain major (>100 km long) high-strain zones, also called shear belts or ductile shear zones, that are hosted by heterogeneously deformed gneisses and schists. In well-exposed segments of three nontabular zones whose dip angle is known locally, at the erosion level and (or) in the shallow subsurface, we investigate the tangential shear strain (better called the tangential unit shear or TUS) without assuming that mineral-shape lineations, common varieties of stretching lineations, are effectively parallel to the local TUS direction. Employing a graphic technique that copes with the geometric conditions of general triaxial strain, we approximate the actual direction and find the sense of local TUS in parts of (i) the Parry Sound shear zone, Grenville Province; (ii) the South Range shear zone, Southern Province; and (iii) the Uchi – English River subprovince boundary zone, Superior Province. Information thus obtained for individual high-strain zones in Ontario confirms the validity of published hypotheses: (i) 1020–970 Ma, normal-sense distributed shearing in the Grenvillian thrust stack; (ii) northwest- directed thrusting of Huronian rocks over Archean basement; and (iii) north-directed thrusting of English River metasediments and associated migmatites onto the Uchi granite–greenstone terrain, under peak metamorphic conditions. [ABSTRACT FROM AUTHOR]