The application of Monte Carlo modelling to downhole total-count logging of uranium: part I – low 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(1) 56-62 https://doi.org/10.1071/EG12018
Submitted: 20 March 2012 Accepted: 14 October 2012 Published: 19 November 2012
Abstract
Gamma-ray logging probes are used extensively within the uranium industry to assist with in situ ore-grade estimates by relating count rates to those obtained from model pits. Correction factors are required to accommodate for the differences between field conditions and the model pits, which are often difficult or even impractical to derive empirically. Gamma-ray transport modelling provides the means to better understand how gamma rays are affected by different logging situations. Corrections for casing, water presence and borehole diameter can be calculated for the relevant probe characteristics such as crystal size and composition, low-energy threshold and probe housing (including shielding). An integral part of correcting gamma probe data is the dead-time and Z-effect correction which can be obtained from logging model pits. Modelling has identified the significance of the low-energy threshold of the detector and the effect of the U grades itself on the correction factors. The proposed method for conversion to equivalent uranium is demonstrated by application to data collected at the Angela deposit in the Northern Territory, Australia.
Key words: Angela, gamma ray, GEANT, logging, modelling, uranium.
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