A significant content of radioactive material was recognized in a few placer concentrates from Sweepstakes and Rube Creeks in the Koyuk district of eastern Seward Peninsula, Alaska, when old collections were scanned for radioactivity in the spring of 1945. Subsequent field investigations with a Geiger-Mueller counter were made of the creek gravels and the placer-gold paystreak on the bench ground of Sweepstakes Creek and its tributaries, the syenite stock of Granite Mountain to the north, of Sweepstakes Creek, and the creek gravels of Rube and Anzac Creeks which are tributaries of the Peace River east of the syenite stock.
The content of radioactive minerals in the gravels and in the placer-gold paystreak was found to be disappointingly low. There concentration ratios were between 45 and 169 to 1, the content of concentrates from the creek gravels is only .001 to .016 percent equivalent uranium the average content of the creek gravels in place is computed as .0001 percent equivalent uranium. The placer-gold paystreak was not accessible in place, but the content was computed as .0003 percent equivalent uranium from the sluice-box concentrates and tailings at Winder's open-cut,the only active placer mine in the area in 1945. The radioactive minerals are relatively abundant in such gravity concentrates as the sluice-box concentrates, and are particularly abundant in certain size fractions of these sluice concentrates Thus the concentrates from the aluiee-fcex, after screening through 20-mesh, showed 0.04 percent equivalent uranium. An even greater concentration of radioactive minerals is
obtained in the "blowings," which represent a further cleaning of the sluice-box concontrates, one saample showing 14.20 percent equivalent uranium.
