The concentrations of U and Th in Paleozoic rhyolites of Nova Scotia are closely related to their contents of K. The rhyolites were affected by secondary processes including low-grade metamorphism that could lead either to enrichment or depletion of these elements. The average abundances of U (ppm), Th (ppm), and K (%) in rhyolites are: Cambrian—2.69, 9.77, and 2.58, respectively; Silurian—4.50, 17.3, and 4.09, respectively; and Devono-Carboniferous—4.64, 18.3, and 5.67, respectively. The depletion of U, Th, and K in Cambrian rocks compared with younger Paleozoic rhyolites is probably related to secondary processes. In Silurian and Devono-Carboniferous rhyolites, these elements were mainly redistributed during the secondary processes, but not removed.

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