K-Ar dates have been determined for two biotites and one feldspar from the Precambrian of West Greenland. Biotite from granodioritic gneiss from the northeast end of Søndre Strømfjord gave 1.65 b.y. as a minimum age for the Nagssugtôqidian fold belt. A date of 2.7 b.y. was obtained on biotite from a granodioritic gneiss from Godthaab in a pre-Nagssugtôqidian fold belt. A pegmatite feldspar from Ivigtut gave a date of 560 m.y., possibly indicating a late thermal event involving 1.1–1.2-b.y. intrusives dated by Moorbath and others (1960) using the Rb-Sr and K-Ar methods. The Precambrian orogenic periods in Greenland are correlated with those of the Canadian shield.

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