Dickinson and Campbell reported in 1982 that geologic evidence suggests that the Lower Tertiary Kootziiahoo Formation in the southern part of the Admiralty trough in southeastern Alaska may be favorable for uranium. The area of this study includes the outcrop belt along the southwestern side of Zarembo Island, a small area east of Point Nesbit along the southwest coast of Zarembo Island, and another small area in California Bay on the north coast of Prince of Wales Island. Uranium was investigated in the Zarembo Island area by Eakins (1975) who reported only 2 ppm uranium and attributed a slight radioactive anomaly to thorium or potassium. Radioactive veins of hematitic carbonatite are present near the entrance to Salmon Bay on the northwest coast of Prince of Wales Island. The radioactivity in these veins, hosted by Silurian graywacke, seems to result mostly from thorium bearing accessory minerals (Houston and others, 1958).
Samples were collected from outcrops of the Kootznahoo Formation and the overlying volcanic rock. These samples were analyzed for uranium and thorium by the delayed-neutron method (MiHard, 1976) and for other elements by semiquantitative spectroscopy. Chemical analyses were carried out in the analytical laboratories of the U.S. Geological Survey in Denver, Colorado.
Mineralogical analyses were by whole-rock X-ray diffraction and by thin section examination. Clay minerals were determined by X-ray diffraction before and after heating, glycolation, and acidization (Dixon and Weed, 1977). Sandstone grains were identified, counted, and measured in thin sections of a few samples. Petrographic descriptions were conducted.
The authors concluded that the Kootznahoo Formation is potentially an excellent host rock for uranium. It includes permeable sandstone and conglomerate beds together with suitable reductants. Carbonaceous fragments are common in some of the sandstone and conglomerate beds and pyrite is present in a coal bed. Slight epigenetic uranium enrichment is present in some of the conglomerate and sandstone beds and possibly in the coal bed. Surface oxidation would probably have destroyed any surficial uranium deposits, but deposits could be found in subsurface reduced zones. The Kootznahoo is overlain by volcanic rock that includes dacite and rhyolite that have abnormally high uranium content in some places.
The Th/U ratio of the few samples analyzed, however, suggests that these potential source rocks have not lost uranium by leaching. A potential for uranium deposits cannot be ruled out, however, because uranium leaching may have occurred from the same rock in other areas or from other rocks and because there must have been a source of uranium for the occurrence found in the northern part of the Admiralty trough (Dickinson, 1979).
Additional source document: https://pubs.usgs.gov/tei/073/report.pdf
http://www.i2mconsultants.com/downloads/corp/Dickison1982USGS.pdf
Managed & Built by I2M Consulting, LLC | © 2010-
