Operation Amadjuak, a helicopter-supported project, completed the geological reconnaissance of that part of Bafin Island that lies south of latitude G6" N and southwest of Cumberland Sound, an area. of about 50,000 square miles. Southern Baffin Island is composed
primarily of a wide variety of metamorphic rocks, which on the basis of the few currently available isotopic age determinations, are all part of the Churchill Structural Province. Palaeozoic carbonate and argillaceous carbonate rocks outcrop to the south and northwest of Amadjuak Lake. Several small
outliers including Silliman's Fossil Mount occur between the main outcrop area and Frobisher Bay. A Middle Ordovician age has tentatively been assigned to the Palaeozoic rocks
Boothia Peninsula and we tern Somerset Island are dominated by the Boothia Arch, a structural and topographic high composed of Precambrian igneous and metamorphic rocks. Relatively fiat-lying unfossiliferous sedimentary strata overlie the northernmost exposures
of Boothia Arch, and they are in turn overlain by lower Palaeozoic sedimentary rocks. All pre-Palaeozoic rocks are cut by gabbro dykes and sill s. These are most abundant in western Somerset Island. Potassium-argon age determinations made on biotite indicate an Aphebian (early Proterozoic) age for
the la test metamorphism of the gneissic complex. The results of modal analyses and 82 'rap id method' chemical analyses accompany the descriptions of the gneissic and igneous rocks.
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