Airborne radioactivity surveys in geologic exploration

Abstract

The value of airborne radioactivity surveys in guiding uranium exploration has been well established. Recent improvements in circuitry and development of semiquantitative analytical techniques permit a more comprehensive evaluation of the geologic distribution of radioactive materials that may prove useful in exploration for other minerals and in regional geologic studies. It is shown that placer deposits of heavy minerals can be detected from the air, and that the geometric configuration and average grade of the surficial part of the deposit can be approximated. Uranium-bearing phosphorite deposits may be similarly evaluated. Airborne surveys over the Coastal Plain area, Texas, show that the radioactivity profiles in some instances reflect the lithologic character of the underlying rocks. The sandstones are generally low in radioactivity (≈ 10 ppm equivalent uranium), the clays and tuffaceous rocks relatively higher. The intrinsic radioactivity of some lithologic units is sufficiently uniform and distinctive in character to permit their identification and lateral correlation on the airborne survey records. The results suggest that airborne surveys may thereby provide useful guidance in delineating lithologic continuity where the geology is poorly known or obscured.