Abstract The Cadillac fault is generally thought to be coincident with a highly schistose zone, a few tens of meters thick, composed of chlorite-carbonate and talc-chlorite-carbonate schists (Gunning and Ambrose, 1940; Norman, 1946). However, outcrops on the Orenada zone noo2 property indicate that deformation related to the Cadillac fault has affected different rock types over a width of more than 200 m. It is therefore more appropriate to refer to the Cadi11ac tectonic zone (CTZ) than to the Cadi11ac fau1t. This outcrop zone exposes a lithological succession that can be extended using outcrops and drill hole data for more than 10 km. This succession differs from the one presented on the available compilation maps and has important implications for the regional “stratigraphy”.

Abstract The excursion begins with an examination of the stripped outcrop shown in figure 3 that exposes the various structural elements and mineralized veins described above in the text. This is followed by a N-S traverse on Oren ada Zone 2 to examine the boundaries of the Cadi11ac tectonic zone and its preserved lithologies.

Abstract The Astoria property is located 7 km south of the city of Rouyn in the Rouyn-Beauchastel area (Fig. 1). The Larder Lake-Cadillac Tectonic Zone (LCTZ) in this area extends along the contact between the Blake River volcanic domain to the north and the narrow Timiskaming sedimentary belt to the south. The LCTZ juxtaposes the Abitibi greenstone belt and the Pontiac metasedimentary sub-province (Card and Ciesielsky, 1986). The LCFZ was first defined as a 50 to 200 m wide zone of rusty weathered ankerite-talc-chlorite schist (Hawley, 1934; Wilson, 1962). A 7 km N-S section of continuous outcrop on the Astoria property (Fig. 1) shows that the Cadillac Fault Zone (CFZ) represents only one of numerous E-W linear zones characterized by moderately to intensely foliated rocks (hereafter E-W faults), generally located along lithological contacts. In the Rouyn-Beauchastel area, the LCTZ is defined as a band of E-W trending sub-parallel or anastomosing fault zones that juxtapose distinct lithological units (Gauthier, submitted). The objectives of this excursion on the Astoria property are to examine the structural features of E-W faults, the lithological succession and the distribution of gold mineralization within the LCTZ.

Abstract The Val d’Or mining district, located in the southern part of the Abitibi belt in the Superior Province, consists of a typical Archean supracrustal volcanosedimentary sequence, obliquely cut by narrow northeast-trending Proterozoi’c diabase dykes. The geology of the Val d’Or area is shown in figure 1. It was initially described by Gunning and Ambrose (1940) and Norman (1946, 1947), and was subsequently revised by Latulippe (1976), Imreh (1984) and more recently by Robert (1989). The northernmost volcanic unit in the Val d’Or area is an extensive ultramafic lava plain known as the Malartic Group. The Lower Malartic is mainly composed of komatiitic ultramafic lava and subordinate basaltic flows. The Upper Malartic, comprised of basaltic lava with horizons of ultramafic and felsic volcaniclastic rocks (lmreh, 1984), is dominated by two main schistosities, S 1 and S 2 S 1 , oriented northwest, is related to the principal flattening plane. S1 is reoriented by an east-west fabric (S2) which is related to asymmetrical Z-folds found over most of the Val d’Or area. The Kiena Mine, one of the mines we will visit during the second day of our tour, is hosted by the Upper Malartic Group. The Kewagama Group, located to the south of the Malartic Group, contains beds of metawacke and metapelite which have undergone two distinct folding events.axial planes related to the first folding event, oriented northwest, have been reoriented during a second phase of deformation that generated folds whose axial traces are oriented at 278 ° (Tourigny, 1984). The Blake River Group, dominating the Rouyn-Noranda district 100 km to the west of Val d’Or, pinches out between the metasedimentary Kewagama and Cadillac groups near the town of Malartic. Here, the Blake River Group is composed of brecciated basaltic lavas with a main schistosity oriented at 275 ° . The Cadillac Group, occurring to the south of the Blake River and Kewagama groups, is composed of metawacke and metapelite. Axial plane traces oriented at 284 ° terminate against the contact of the Blake River Group. The Piché Group is found only within the Cadillac tectonic zone in the Val d’Or area. It consists mainly of ultramafic lava. Where the deformation is intense, the lava is completely transformed to talc-carbonate schist. Where the deformation is less intense, spinifex textures are still visible. The Cadillac tectonic zone, generally oriented east-west, has been traced from Vauquelin township (east of Val d’Or) west to the border of Ontario and beyond.

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.