Chemical ages and mobility of U and Th in anatectites of the Cree Lake zone, Saskatchewan

Microprobe analyses have been carried out, and chemical ages determined, on the radioactive phases in anatectites from five localities in the Cree Lake zone (Saskatchewan). In addition, bulk analyses for U, Th and Pb were completed on over 150 samples of the anatectites and their host rocks. Exclusive of zircon and monazite, the U- and Th-bearing phases range from old 'uraninite' through various unnamed U-Th silicates to young 'uranophane', 'coffinite' and 'kasolite'. Only one rare phase, a U-Fe silicate was encountered; the only known analog occurs in Styria (Austria). Chemical ages range from 1.9 to <0.1 Ga and bulk values from 23 to 413 ppm U, 10 to 285 ppm Th and 26 to 144 ppm Pb. Both the petrographic data and the inferred ages indicate that extensive mobilization of the radioactive phases has occurred, either continuously or episodically. The mobility, however, was restricted to the interior of the anatectite bodies, which behaved essentially as closed systems. The oldest chemical ages are in close agreement with geological estimates of the timing of anatectite formation