K–Ar and (or) 40Ar/39Ar apparent ages are reported for 28 samples of biotite and muscovite from Nova Scotia's South Mountain batholith and associated northern satellite stocks. In addition, 14 mica samples from the southern satellite stocks were dated. Previous workers, using primarily K–Ar and Rb/Sr techniques, have reported a spread of apparent ages ranging from ~240–420 Ma for these intrusive rocks. The present data set is internally consistent and has been calibrated against accepted interlaboratory standards. A mean age of 367 Ma was obtained for the South Mountain batholith and the northern stocks, a value consistent with results recently obtained in an Rb/Sr study by Clarke and Halliday. No differences in apparent age among the various phases or clear geographic age distribution patterns were evident. Satellite stocks in the southern part of the province have, in general, younger apparent ages clustered in the range ~300–320 Ma. We suggest that in southern areas mica–argon systems record the effects of a Late Carboniferous intrusive and (or) thermotectonic event. This conclusion may have important metallogenic implications.

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