A reconnaissance study of the U and Th contents of plutonic rocks of the southeastern Seward Peninsula, Alaska

Large granitic Cretaceous plutons are exposed along and adjacent to an arcuate belt of igneous and high-grade metamorphic rocks in the southeastern Seward Peninsula of Alaska. Reconnaissance studies of these plutons have shown that the Darby pluton has well above average amounts of U and Th (11.2 ppm and 58.7 ppm respectively), the Kachauik pluton ranges from average to above average U and Th (5.7 ppm and 22.5 ppm respectively), and the Bendeleben pluton contains average amounts of U and Th (3.4 ppm and 16.7 ppm respectively). The three plutons show compositional and textural differences indicative of different source materials which may have controlled the distribution of U and Th.

The high U and Th contents of the Darby pluton, similar to that of the Conway Granite of New Hampshire which has been mentioned as a possible low grade Th resource, suggests that this pluton may be a favorable area for economic concentrations of U and Th.