Bedrock geology

The study area lies within a recently released 1:100 000 scale compilation geology map of the Timmins area (Ayer and Trowell, 1998). A generalized version of the compilation map is presented in Figure 2. The area is underlain by rocks of the Abitibi Subprovince intruded by Proterozoic diabase dykes with a number of different trends and ages. The Abitibi Subprovince is a 800 km by 300 km Archean "granite-greenstone" domain accreted along the southern margin of the Superior Province. It is dominated by supracrustal and granitoid rocks with a range of ages from 2.75 to 2.67 Ga (Jackson and Fyon, 1991). The area contains part of the Porcupine mining camp, one of the pre-eminent lode gold mining districts in the world. Significant copper, zinc and silver production has also come from a number of volcanic-associated massive sulphide deposits. Komatiite-associated nickel deposits have been intermittently mined south and east of the study area. Operating mines within the study area include the giant Kidd Creek Cu-Zn-Ag mine in Kidd Township, the Pamour gold mine in Whitney Township, and the Bell Creek and Hoyle Pond gold mines in Hoyle Township. Past-producers include the Davidson-Tisdale, Hugh Pam, Reef, Owl Creek, and Hallnor gold mines in the southeast part of the area and the Kam-kotia, Jameland and Canadian Jamieson Cu-Zn-Au-Ag mines near Kamiskotia Lake.

Quaternary geology

Regional ice flow patterns

Ice-flow indicators, including striations, and grooves, crag and tail features, and flutings indicate a complex sequence of ice flow in the Abitibi region (Figure 3). Initially, ice flowed to the northwest across the area. Northwest oriented bedrock sculpting and striations at the Lower Sturgeon hydroelectric dam on the Mattagami River are spectacular examples of this oldest ice flow event (Paulen and McClenaghan, 1997). Veillette (1995) suggested that the northwestward ice flow is associated with the early growth of the Laurentide Ice Sheet. Ice flow subsequently shifted counterclockwise, to the west-southwest (220°-240°), then south (170°-200°) and finally southeast (180°-160°) and southwest (180-200°). GSC Open File 3033 (Veillette and McClenaghan, 1996) shows striations locations and provides a more detailed explanation of ice flow patterns across the entire Abitibi region. Surface tills sampled in this study were deposited by later stages of ice flow to the southwest, south and southeast.

Surficial geology

Surficial geology of the study area is summarized in Figure 4 from 1:50,0000 scale maps of Richard (1983a,b) and Paulen and McClenaghan (in press) and can be used as a general guide to glacial sediment thickness. Glacial sediments are thin (<1 m) in areas dominated by bedrock. The southeast half of the area is covered mainly by thick (> 10 m) glaciolacustrine clay and silt deposited in glacial Lake Ojibway. The north half of the area is dominated by thick (>10 m) deposits of clay-rich Cochrane Till, glaciolacustrine clay and silt and 1 to 3 m of organic material in poorly drained areas.

Cochrane Till, named originally for its occurrence near the town of Cochrane (Hughes, 1956; 1965), forms a thick (2 to 8 m) continuous blanket over large parts of the north half of the area. It is a grey-brown to brown, carbonate-rich clayey silt till with 1 to 5% clasts by volume and 25 to 35% carbonate in the matrix (Paulen and McClenaghan, in press). Paleozoic carbonate rocks originating in the Hudson Bay Lowlands comprise more than 70% of the clasts in Cochrane Till. The southern limit of this till sheet, informally referred to as the "Cochrane limit", extends almost the south edge of the study area along the Mattagami River valley.

Matheson Till, first recognized near the town of Matheson 60 km to the east (Hughes, 1965; McClenaghan, 1992a), occurs as thick deposits in isolated patches (Figure 4) or in thin pockets around the edges of bedrock outcrops (see Richard, 1983a,b). It is an olive-grey carbonate-rich, silty sand till with 10 to 35 % clasts by volume and 15 to 25% carbonate in the matrix. Carbonate clasts and matrix material have been transported south from Paleozoic rocks in the Hudson Bay Lowlands. Matheson Till in southwest corner of the study area is very sandy, contains abundant granitic clasts and contains very little matrix carbonate (<5%). Till there is very locally derived. Matheson Till that is overlain by thick deposits of glaciolacustrine clay and silt is not accessible by surface sampling techniques, except for drilling.

Ice-contact and glaciofluvial deposits are tens of metres thick and are contained in five north-trending esker ridges. Aeolian sand overlies sediments on the flanks of the eskers south of the Cochrane Limit. Extensive peat deposits, 1 to 3 m thick, overlie poorly drained, flat lying glaciolacustrine sediments and Cochrane Till.

Since deglaciation, soil has developed on glacial sediments. Areas underlain by glaciolacustrine clay and Cochrane Till are covered by gleysols and luvisols. Podzolic soils have developed on sandy sediments and Matheson Till and mesisols and humisols have developed over peatlands (Department of Agriculture, 1978). The humus layer of the soil profiles varies from 2 to 30 cm thick and is 6 cm thick on average.