Rock movement due to blasting and its impact on ore grade control in Nevada open pit gold mines
Mining and Metallurgical Engineering
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This thesis presents the results of a research project into blast induced rock movement and its impact on ore grade control at the Rain Mine of the Newmont Gold Company and the Coeur Rochester Mine. A total of twelve blasts were monitored between the two mines using additional holes loaded with marker bags and a Quarryman laser profiler to locate the bags and survey the surface rock movement. An average of 4.5-6 .0 feet horizontal movement occurred at the Rain Mine with a powder factor of 0.3-0.4 lb ANFO/ton. An average of I 0-45 feet horizontal rock movement occurred at the Coeur Rochester Mine with a powder factor of0.57-0.76lb Heavy ANFO/ton. This rock movement resulted in a theoretical dilution from three percent up to eighty percent depending on the amount of rock movement and the size of polygon. A method to adjust the pre-blast polygon according to the rock movement is discussed in order to decrease dilution when digging. It is concluded that dilution induced by blasting can be minimized, if the position of a digging polygon is modified as a result of systematic measurements of rock movement.
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