The application of Monte Carlo modelling to downhole total-count logging of uranium: part II-High grade mineralisation

Calibration facilities for total-count radiation probes used to measure high-grade uranium (> 2 %) are scarce and the conventional method using correction factors to convert to equivalent uranium has severe shortcomings. In this paper gamma-ray transport modelling is utilised to directly convert logging data into in situ U grade estimates, taking into account casing, water, borehole diameter, probe size and detector shielding corrections which at high U grades are dependent on the U grade itself. The method uses interpolation between modelled results and avoids the usual calibration factors. It is demonstrated using data collected at the Angela U deposit, Northern Territory, and at the Kintyre deposit, Western Australia. At the Kintyre deposit, the uranium grades exceed 20% and both unshielded and shielded NaI(Tl) detectors were tested, with the latter showing the best performance at high grades.