QUANTITATIVE INTERPRETATION OF GAMMA‐RAY LOGS

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Abstract
A quantitative method for determining the concentration of gamma‐ray emitting elements in layered rock penetrated by boreholes has been developed by the U. S. Atomic Energy Commission. It is based on the relationship [Formula: see text] where [Formula: see text] is the mean thickness T, k is a constant of proportionality, and I is the intensity of the gamma‐ray field along the borehole axis at a distance z from a fixed point of reference on the axis. This relationship has been confirmed theoretically and empirically. In application, the grade‐thickness product of a mineralized zone intersected in the borehole is determined by multiplying the area under the gamma‐ray log curve by a constant of proportionality. The mean grade of the zone is determined by dividing the grade‐thickness product by the zone thickness. Corrections applied for nonstandard conditions in the borehole reduce the data to equivalence with standard calibration conditions. Because the volume sampled in this logging method is significantly larger than that of core samples, the resulting data are more representative than data from chemically‐assayed core.

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