Abstract

The Dollyberry Lake volcanics occur at the base of the Huronian Supergroup and outcrop ~15 km north of Elliot Lake, Ontario. Ten specimens were collected from each of 36 sites in the volcanics and from a further five sites in stratigraphically equivalent volcanics ~9 km east of Elliot Lake. Alternating field (AF) and thermal step demagnetizations were done on two specimens from each site up to 100 mT and 650 °C, respectively. AF demagnetization led to the isolation of an A component in 33 sites, a B component in three sites, and both components in two sites. Fold tests demonstrate that both the A and B components are postfolding in origin at the >97 and >80% confidence level, respectively. It is argued that the A component (pole 154°W, 56°N, δp = 8°, δm = 10°) was acquired during the Penokean Orogeny at ~2215 ± 40 Ma, and that the B component (pole 60°W, 20°S, δp = 8°, δm = 13°) was acquired probably at ~ 1900 ± 100 Ma in response to some geographically restricted thermal or chemical event. The results indicate that the coeval Thessalon volcanics studied by Symons and O'Leary retain the Penokean A component. This leads to the retraction of their conclusion that the superadjacent uranium ores were formed at an ~35° paleolatitude and to the conclusion by analogy that the Penokean Orogeny was the only significant orogenic event in the evolution of the ore deposits.

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