To minimize ore dilution induced by blast movement in surface mines, it is
necessary to quantify such movement. This will enable more accurate locatio
n of the grade boundaries beneath the surface of a blasted rock pile before
excavation. A method has been developed and tested to accurately measure t
he direction and magnitude of subsurface blast movement. This technique use
s a cesium vapour gradiometer and a real-time, differentially corrected GPS
system to locale pre- and post-blast position of magnetically enhanced tar
get objects placed within blastholes inside a bench. The procedure develope
d does not require the blasted rock to be disturbed, and the movement infor
mation is available within a sufficient time to allow for modification of t
he selective mining boundaries for each surveyed blast. It was found that t
he maximum depth of target detection was 18 m, with the overall accuracy be
ing measured as ii m (horizontally) and +/- 1.2 m (vertically).