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We tested the hypothesis that radioelements are either enriched or depleted over petroleum accumulations. Total count surveys are subject to signal variations due to changes in soil composition and to variations in soil moisture. Methods have been determined to lower the variations due to soil composition and to eliminate variations due to soil moisture. We conclude that, if hydrocarbon-related anomalies are present, they are overwhelmed by changes in soil composition.
Changes in soil composition can cause: (1) a fourfold change in total count and eU, (2) a twofold change in K, and (3) a thirteenfold change in eTh. Modified eU/K, eTh/K, and eU/eTh ratios reduce the variations caused by soil composition to ±50% of normal conditions. This permits detection of anomalies as low as 1.0 ppm eU, 2.0 ppm eTh, or 0.7% K. Statistical detection limit for the surveys is ±0.24 ppm eU at 2.0 ppm eU concentration.
The detected anomalies are of equal amplitude and frequency both on and off the fields. This, plus the lack of anomaly repeatability from line to line, precludes a hydrocarbon source. The majority of all anomalies are attributed to soil or lithologic sources. The others are caused by uranium mineralization.
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