The application of Monte Carlo modelling to downhole total-count logging of uranium: part II – high grade mineralisation
Bruce Dickson 1 3 Geoff Beckitt 21 47 Amiens St, Gladesville, NSW 2111, Australia.
2 Global Ore Discovery, 15a Tate St, Albion, Qld 4010, Australia.
3 Corresponding author. Email: bruce.dickson@optusnet.com.au
Exploration Geophysics 44(3) 199-205 https://doi.org/10.1071/EG12068
Submitted: 29 October 2012 Accepted: 22 March 2013 Published: 3 May 2013
Abstract
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.
Key words: dead-time, gamma ray, GEANT, high grade, Kintyre, logging, modelling, uranium.
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