This comparison study of high-resolution MGT and conventional HNGS gamma ray logs at Site 1179 shows that the total natural gamma ray values from both agree well, with substantially greater vertical resolution observed in the MGT log. Uncertainties in both data sets are introduced by enlarged borehole size and changes in the in situ conditions over time. Corrections for borehole size may be accurately applied with the acquisition of reliable caliper logs and calibration data.
Comparison of K and U concentration estimates from these tools agree well, measuring between 1 and 2.5 wt% for K and 2 and 5 ppm for U over this interval. The higher vertical resolution of the MGT highlights some offset of gamma values from the HNGS log in thin layers, primarily consisting of ash-bearing clays within the study interval. The HNGS measures lower U concentrations by ~1–2 ppm in these rocks, which may be explained by the processing system used or the detection threshold. The MGT measures lower Th concentrations by 70%–80% at this site, which may be explained by its small detector size, enlarged borehole size, and the low Th concentration in these sediments. Differences between the logs may be attributed to the intrinsic differences in vertical resolution as well as to the effects of borehole size on natural gamma ray measurements. Further comparisons of the MGT and HNGS logs in other environments, preferably at sites with good borehole conditions, will provide a range of different geochemical concentrations for study and improve the accuracy of these estimates.