Analysis of blasting techniques at Ghana National Manganese Corporation, Nsuta-Wassa, Ghana
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Date
1992
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Abstract
Ghana National Manganese Corporation (GNMC) at Nsuta-Wassa in Ghana produces manganese ores by open—pit technology. The deposits are Pre-Cambrian in age, and are characterised by a series of strong folding and faulting. These rocks are of medium to high strength and have high densities (2.81-3.72 kg/rn3).
One of the methods of loosening in situ material for excavation and loading on the mine is by drilling and blasting. Analysis of records from the mine has shown that tonnage produced by blasting constitutes about 38% of total annual production.
It has been observed that primary blasts produce coarse fragmentation. The cause of the poor rock fragmentation is improper blasting practice. The poor blast performance explains why unit cost of drilling and blasting constitutes as much as 65% of unit costs of mining.
In this research work, the present drilling and blasting practices have been studied. Alternative blast design paramaters have been determined, taking into consideration the geomechanica1 properties of the rocks and the prevailing operational conditions at the mine. These parameters have been field tested. Eventually, an effective blasting technique has been designed to improve the performance of the mine.
It has been established that of all the design parameters, including that of the present mine practice, which have been field tested, the technique using a 2.0m by 2.8m drilling pattern produces best results. This technique requires 50-60% less drilling and 30-40% less explosives. When drilling and blasting are considered together as one operation, an overall improvement of 40-50% was achieved over the present mine practice.
It is suggested that, to achieve the desired performance from the blasting technique using 2.0m by 2.8m drilling pattern, a stemming length of l.6m is required to provide the necessary explosives confinement. Millisecond delays are also to be used as an integral part of the blasting technique for an improved blast performance.
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A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Philosophy in Mining Engineering.