Blast movement measurement to control dilution in surface mines

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).