SPECTRAL GAMMA LOGGING IN THE COPPER MOUNTAIN URANIUM DISTRICT
A Case Study in Fractured Quartz Monzonite
Stanton H. Moll
Bendix Field Engineering Corporation
Grand Junction, Colorado 81502
ABSTRACT
Bendix Field Engineering Corporation, as prime contractor to the U.S. Department of Energy for its National Uranium Resource Evaluation (NURE) program, logged sixteen (16) drill holes with spectral gamma (KUT) sondes in an area of about 1.5 mi2 within the Canning stock of the Copper Mountain uranium district of central Wyoming. The holes were logged as part of a research project designed to test and evaluate integrated exploration systems for uranium in a granitic environment. The district consists of Precambrian quartz monzonite thrusted and faulted during the Laramide and partially overlain by Tertiary sediments. Mineralization is associated with fractured and crushed zones in the quartz monzonite and in the gneissic and mafic inclusions in the pluton.
KUT logs were used to characterize the geochemical variation of the Canning stock, and to test the allogenic versus authigenic hypotheses of uranium mineralization there. Raw log data were converted to concentrations of potassium (K), uranium (eU), and thorium (eTh), then the data were block averaged over 25-foot intervals to obtain mean concentrations. Based on the resultant values, slice maps were constructed by contouring the data at various horizons, and standard statistics were calculated.
The preliminary results from the concentration data indicate that the Canning stock contains high K, eU, and eTh concentrations in the vicinity of the North Canning deposit. Thorium and potassium contents are correlated while uranium does not correlate with either to a significant degree. A general decrease in Th/U ratios toward the deposit suggests the lack of correlation of uranium with potassium or thorium is due to its greater geochemical mobility. It appears that local remobilization of uranium within the parent stock is at least partially responsible for concentration in the prepared rock.