Although relations between radioactive elements and both mineral deposits and petroleum accumulations are indicated by many published investigations, the exploration effectiveness of the gamma-ray survey generally remains in doubt. Increased effectiveness of gamma-ray surveys is possible through increased accuracy of collected data and improved data interpretation. Increased data accuracy is accomplished through adequate detector capacity and the correction for environmental variables. Improved data interpretation involves the use of the geologist-statistician-programmer team to reduce a vast amount of data to a manageable number of geologically significant values.

To attain geologic significance, gamma-ray spectrometer data must be integrated with other types of geologic and geophysical data. To test this premise, a set of gamma-ray data covering complex metamorphic and igneous geology of the Duchess area, Queensland, Australia, was processed as a function of mapped surface geology, and statistical methods were used to identify statistically significant anomalous records relative to the background of each rock type, rather than for the entire survey area. Design of the data-presentation format allowed quick screening of anomalous values from the large total number of records. Examination of statistical parameters indicated the possibility of using the gamma-ray data to map surface geology without the aid of photogeology or field mapping. Stacke profiles of U, Th, K, and their ratios were analyzed for obvious "breaks," and the units thus defined were correlated by computer processing. Results indicated that surface mapping by this procedure is feasible.

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