The geology, petrology, and geochronology of the Archean Côté Gold large-tonnage, low-grade intrusion-related Au(–Cu) deposit, Swayze greenstone belt, Ontario, Canada

Abstract

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. The deposit is hosted by the Chester intrusive complex (CIC), a multi-phase, subvolcanic intrusion comprised 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 to 2739 ± 1 Ma using high-precision 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. The CIC is petrologically similar to other subvolcanic, low-Al tonalite-trondhjemite-diorite intrusions that underlie VMStype deposits and which themselves may contain syn-intrusion mineralization. Several geochemically unrelated dykes and deformation events crosscut and postdate the CIC. Most of these Archean plutonic rocks belong to the high-Al tonalite-trondhjemite-granodiorite (TTG) suite, whereas the low-Al tonalite-trondhjemite-diorite (TTD) suites are subordinate (Martin et al. 2005). Low-Al TTD suites have been documented to form small, composite synvolcanic intrusions in rift environments that underlie and are considered the heat and/or metal source for spatially related VMS mineralization (Campbell et al. 1981; Cathles 1981; Franklin 1996; Barrie et al. 1999; Galley et al. 2000; Galley 2003; Yergeau et al. 2015). The low-Al composite intrusions are compositionally equivalent to FII and FIII-type rhyolites, and as such, are prospective for base metal mineralization (Lesher et al. 1986). Some of these intrusions have been documented to host Cu-Mo(-Au) mineralization with a porphyry-type affinity (Friske 1974 The Côté Gold deposit represents a significant new discovery (2009/2010 Rogers et al. 2013) for several reasons: (1) it is the first large gold deposit (i.e., >1 M oz Au) of any type discovered in the SGB, compared to the gold-rich Abitibi greenstone belt (AGB); (2) the deposit defines a new gold environment in that the mineralization (disseminations, veins and breccias) is hosted by a ca. 2741 to 2939 Ma, high-level, subvolcanic tonalite-diorite-quartz diorite intrusive complex which is atypical in the AGB (Robert et al. 2005); and (3) based on Re-Os dating of molybdenite that is co-genetic with gold mineralization, the deposit ...

Petrogenetic Study of the Multiphase Chibougamau Pluton: Archaean Magmas Associated with Cu–Au Magmato-Hydrothermal Systems

“…It is thus unclear whether diorite, tonalite, or both magmas were essential to the development of Central Camp mineralization, as the mineralizing processes that formed these deposits remain to be elucidated. It should, however, be noted that other Neoarchean magmato-hydrothermal systems, such as the Côté-Gold Au-(Cu) deposit (Ontario), are associated with multiphase plutons composed of diorite and low-Al tonalite [106].…”

Tonalite-Dominated Magmatism in the Abitibi Subprovince, Canada, and Significance for Cu-Au Magmatic-Hydrothermal Systems

“…the depth of partial melting, geodynamic models referring to progressively steeper subduction to explain the HREE content of TTG suites become unreasonable [47,48]. The main synvolcanic magmatic-hydrothermal systems documented in the Abitibi Subprovince are genetically related to TTD suites, i.e., to plutons that may contain hybrid magmas (Chester intrusive complex) or both TTG and hybrid magmas (Chibougamau pluton), according to published REE-profiles [5,6]. These plutons may contain a significant amount of mantle-derived magma, and in both cases, the mineralizing systems have been discussed and compared to porphyry deposits [49].…”

“…In greenstone belts, the main magmatic phase produced magmas with tholeiitic affinities (mafic lava flows and layered intrusions), as well as tonalite-and granodiorite-dominated large-volume batholiths [2][3][4]. In the Abitibi Subprovince, an additional rock type (diorite) is observed as part of tonalite plutons associated with Cu-Au magmatic-hydrothermal systems [5,6]. The petrogenetic evolution, as well as the geodynamic and economic significance of the tonalite, granodiorite, and diorite suite, is not fully resolved [4].…”

“…Less recognized mineralization corresponds to magmatic-hydrothermal systems related to intermediate-felsic intrusions of the synvolcanic period. These systems are considered as porphyry-style mineralization, and examples include the Central Camp Cu-Au and the Côté-Gold Au-(Cu) deposits associated, respectively, with the Chibougamau pluton and the Chester intrusive complex [5,6] (Figure 1). In greenstone belts, granitoid intrusions of the synvolcanic period are mostly tonalite-trondhjemite-granodiorite (TTG) suites [9,10], which are felsic (>64 wt% SiO 2 ), aluminous (>14-16 wt% Al 2 O 3 for 70 wt% SiO 2 ), and Fe-Mg-poor ([Fe 2 O 3T + MgO + MnO + TiO 2 ] < 5 wt%) intrusive rocks characterized by a low K 2 O/Na 2 O ratio (<0.6) [10].…”

“…Most TTG suites are also HREE-depleted which reflects their derivation from high-pressure partial melting of mafic crust-i.e., garnet amphibolite [10]. However, the Chibougamau and Chester intrusive complexes are too mafic to be classified as TTG suites, as they contain significant amounts of diorite, and thus, are referred to as tonalite-trondhjemite-diorite (TTD) suites [5,6].…”