Borehole logging in a bauxite mine by use of prompt gamma neutron activation analysis

A technique, called ROXANE, using prompt gamma emissions from neutron capture processes, has been successfully employed for grade logging in a bauxite deposit. On the basis of field results, the following conclusions are drawn: the standard deviations are (at a speed of 12 m/h): 1.75% for SiO2, 0.2% for TiO2 and 1% for Fe2O3. Al2O3 is determined by differences, between the two methods used, the main components of bauxite being SiO2, TiO2, Fe2O3, Al2O3 and water. Comparisons between ROXANE (speed: 12 m/h or 45 m/h) and the analysis of cores show that TiO2 content is generally in excellent agreement for both methods. This is due both to the high sensitivity of Ti and to the fact that it is relatively constant throughout the deposit, which tends to diminish sampling problems. The clay lenses are identified without ambiguity by the presence of SiO2. The starting and ending distances are sometimes in disagreement with the core analyses, owing to poor 'recuperation' at the contact between bauxite and clay minerals. With regard to Fe2O3, as for SiO2, divergences can appear owing to sampling problems. For Al2O3, agreement is, in general, good if we exclude the problems associated with sampling in transition zones (poor recuperation of cores or erratic variations in contents). It should be possible to carry out 200 m of analysis per shift. Generation of the results on the site allows the density of the grid of preproduction holes to be increased. Better knowledge of the ore bed (accurate reconnaissance of clay lenses, ferruginous zones and quality of bauxite) permits improved planning of extraction and processing. (author). 5 refs, 5 figs, 1 tab