Nine samples of granites and gneisses collected along a 125 mi traverse running south from Red Lake have been analyzed in a Rb–Sr whole-rock study. It is concluded that an isochron may meaningfully be drawn through points representing these sample on a Nicolaysen (1961) plot. A slope equivalent to an age of 2.45 ± 0.10 b.y. results. If the gneisses represent the residue of an ancient crust then the Rb–Sr data yield little evidence of this and the effect of the Kenoran orogeny is clearly the dominant feature. K–Ar and Rb–Sr dating of biotites separated from two of the gneisses indicates that the area has been more mildly affected by a later metamorphism.

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