Results from the first field trial of a borehole gravity meter for mining applications

Scintrex is in the final stages of the development of a borehole gravity meter, for mining and geotechnical applications, designed to log inside NQ drill rods to 2,000 m depth, using standard 4 conductor cable, with a sensitivity of better than 5 µgal, and operable in boreholes inclined from 300 to vertical. Ecole Polytechnique of Montreal has developed forward modelling software, as part of this project. The first field test of the prototype probe was successfully conducted in December 2008 for Vale Inco in a deep borehole located in Norman township near Sudbury, Ontario. The results of this test show a large amplitude bipolar residual gravity anomaly, with the crossover at the location where the borehole intersected sulphides. Further analysis of the data is underway. A repeat log of the hole indicates that the Gravilog system has achieved operational specifications very close to its targets. Field tests for the other sponsors are planned during the first half of 2009, with production surveys to follow during the second half of the year. Gravity measurements inside boreholes provide evidence of density variations both in the immediate vicinity and at a distance from the hole. Scintrex?s development of a new borehole gravimeter will, for the first time, allow the application of gravity logging in typical mining and geotechnical boreholes. Primary applications of the Gravilog system in mining include the sensing and mass-estimates of massive sulphide bodies, either intersected by or remote from the hole; and accurate bulk density measurements of formations intersected by the hole.