| Summary: | A system has been developed for the continuous and stepwise scanning of rock drill cores for gamma-ray spectrometric determinations of uranium, thorium, and potassium. The apparatus accomodates 3- to 4-cm-diameter core as it passes two opposing 2-inch diameter by 3-inch- thick NaI(Tl) detectors, either continuously, at speeds ranging from one to several meters per hour, or in steps of 5 cm or more. Resulting gamma-ray spectra, as recorded with a multi channel analyzer, are computer processed, furnishing scale diagrams of individual radioelement contents and Th/U ratios in the core. Whole-rock assays of one-meter-long core sections by continuous scanning are accurate and precise to within 10 percent or better. In the step-scanning mode, the system can resolve peak concentrations of U and Th with an accuracy of about 15 percent. Continuous one-meter scans of 3500 m of core from the Ilímaussaq intrusion, South Greenland, provided an evaluation of uranium resources in the course of seven months. Examination of the continuous-scan diagrams indicated areas of geochemical interest, such as sharp and transitional contacts and mineralized zones. These were investigated more closely by step scanning, disclosing detailed variations of U and Th. Contents of U and Th determined by scanning of drill core were consistent with the gross gamma-ray counting rates measured in the boreholes. ©1972 Society of Exploration Geophysicists
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