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The value of airborne radioactivity surveys in guiding uranium exploration has been well established. Improved circuitry and development of semiquantitative analytical techniques now permit examination of more complex geologic problems. It is shown that the airborne technique can be used in exploration for thorium‐bearing heavy mineral deposits and for uraniferous phosphorites. The observed radiation intensity and configuration of the gamma radiation field may be used to approximate the equivalent uranium content and extent of the surficial part of such deposits. The equivalent uranium content of infinite sources can probably be determined within a few thousandths of a percent and the boundaries fixed within a few hundred feet. As the areal extent of the source decreases, the accuracy of the analytical results likewise decreases.

A radiometric reconnaissance of the areas adjacent to the principal highways and secondary roads of south-central Alaska was carried out during the summer of 1947. The investigation included the examination of nine gold-placer workings, five gold lodes, a gypsum mine, and a copper prospect. Nearly all types of rock cropping out in the highway belt were tested. No significant amounts of radioactive material were found.

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