|Type area:||NTS sheets 32D07, 32D08 and 32C05|
|Geological province:||Superior Province|
|Geological subdivision:||Abitibi Subprovince|
Table des matières
The Kewagama Group was first mentioned in the reports and 1:12,000 scale geological maps of Gunning (1936) and Gunning and Ambrose (1939, 1940). These authors were the first to present a consistent lithostratigraphic subdivision of the Cadillac-Malartic region. Their work led them to divide the stratigraphic pile known in the 1940s into two sedimentary sequences, the Kewagama and Cadillac groups, and two volcanic sequences, the Malartic and Blake River groups. At that time, the Kewagama Group included the current Kewagama and Pontiac groups. The Blake River Group included the current Blake River and Piché groups. Latulippe (1976), Dimroth et al. (1982), Imreh (1984, 1991) and Pilote et al. (2009) subsequently resumed the work of Gunning and Ambrose (1939, 1940) and advocated the use of the expression “Kewagama Formation”, which then referred only to sedimentary lithologies located between the Rivière-Héva and Dubuisson localities (sheets 32D01, 32D07 and 32D08).
The Mont-Brun Formation (nAmn) represents the central strip, which had historically been assigned to the Kewagama Group for several decades. The Caste Formation (nAlc), formerly known as the “Caste Group” (Dimroth et al., 1973; Dimroth and Rocheleau, 1979) or “Lac Caste Formation” (Dimroth et al., 1982), represents three lenses of tectonically segmented sedimentary rocks trapped between volcanics of the Kinojévis and Malartic groups. Based on similarities between three different sedimentary basins of similar ages in the Malartic, Cadillac and Rouyn-Noranda regions, named the Rivière Dufresnoy, Mont-Brun and Caste formations respectively, Goutier (1997) proposes to group them under the name Kewagama Group.
The various units of the Kewagama Group consist of turbiditic sedimentary rocks deposited in deep basins located on the periphery of volcanic centres. Specifically, the Kewagama Group consists of interfingering sandstone and mudrock forming centimetric beds, which show parallel lamination and normal sorting. These are generally separated from adjacent volcanic rocks by faults. The entire Kewagama Group was affected by regional metamorphism characteristic of the greenschist facies (Bouchard, 1979, 1981; Imreh, 1984; Tourigny, 1984).
The Rivière Dufresnoy Formation (nAdy) is the oldest unit; it outcrops on the eastern shore of Dufresnoy Lake and SE of Dufresnoy River (sheet 32D07). The Rivière Dufresnoy Formation sedimentary units consist of alternating grey lithic wacke (70%) and dark-grey to black mudrock (30%). The sequence also contains polygenetic conglomerate passages, observed, among others, in drilling in the Bouchard-Hébert Mine area (Goutier, 1997). Small sorted beds contain parallel lamination, suggesting turbiditic flows comparable to those of other units in the Kewagama Group. This formation locally lies on volcanics of the Blake River Group (Goutier, 1997).
Very characteristic outcrops of the Mont-Brun Formation are located on the shore of the Kinojévis River near the village of Mont-Brun (sheet 32D07). Typically, light grey sandstone and dark grey mudrock form millimetre to centimetre-thick beds created by turbidity currents. Contacts with adjacent volcanic units are commonly marked by faults. The Mont-Brun Formation extends from the Porcupine-Destor Fault in the Rouyn-Noranda region (sheet 32D11) to the south of the Camflo Mine, east of Malartic (sheet 32D01). In the Malartic region, this formation consists mainly of sandstone beds 15 cm thick on average, pelite beds approximately 5 cm thick, beds of conglomeratic sandstone no more than 20 cm thick and iron formations a few metres wide. Most sandstone beds are sorted. In addition, sandstone beds have beige alteration colour, while those in pelites are rather brownish.
The Caste Formation consists of turbiditic sandstone and mudrock located between the Aiguebelle and La Pause faults (sheets 32D07, 32D08 and 32C05). These rocks are similar to other turbidites observed in the Kewagama Group, with the exception of finer, more siliceous and black argillaceous beds. Some beds look like black chert.
Rocks of the Kewagama Group mainly outcrop in sheets 32D01, 32D06, 32D07, 32D08, 32C04 and 32C05. This group extends approximately 130 km from Duparquet Lake in the west to Senneville Lake in the east.
Feng and Kerrich (1991) dated the Caste Formation to <2691 Ma and Davis (1991, 1992) dated the Mont-Brun Formation between <2682 and 2687 Ma. These ages indicate that all turbiditic sedimentary rocks in the Malartic, Cadillac and Rouyn-Noranda regions are collectively of the same age and, moreover, younger than adjacent volcanics.
All the formations in the Kewagama Group are commonly bordered by faults along their contact with neighbouring volcanic units. In his studies of rocks of the Cadillac-Malartic region, Bouchard (1979, 1980) showed that sedimentary units of the Kewagama and Cadillac groups did not form a homoclinal sequence as originally proposed by Gunning and Ambrose (1940). On the contrary, they represent lithological assemblages bordered by major faults. Each of these sedimentary formations exhibits a distinctive deformation style and special interference patterns linked to polyphase tectonics, which are not found in adjacent volcanic units (Bouchard, 1981; Tourigny, 1984).
Does not apply.