Economic analysis of drilling and blasting: a case study — Ghana Bauxite Company Limited - Awaso

Ghana Bauxite Company Limited (GBC) at Awaso in the Western Region of Ghana produces bauxite ores by open pit technology. One of the methods of loosening in-situ material for excavation and loadin9 on the mine is by drilling and blasting. Analysis of records from the mine has shown that tonnage produced by blasting constitutes about 60 % of total annual production. Drilling and blasting constitute major cost centres in the whole mining cost. There is therefore the need to reduce drilling and blasting cost as much as possible. This can only be achieved if the optimum drilling and blasting patterns are achieved. In this research work, the present drilling and blasting practices have been studied. Alternative blast design parameters have been determined, taking into consideration the prevailing conditions at the mine. These parameters have been field tested and effective blasting technique designed to improve the performance of the mine. This study established that the multiple row delay blasts produce better fragmentation than the initial single row blasting at a minimum cost. It has also been found the blast design using a 2.5 m x 3.5 m staggered drilling pattern produces the best results. Fragmentation was far better for the multiple rows blasting than the initial mine practice. The reduction of secondary blasting of boulders will reduce drilling and blasting cost to a minimum. The thesis also found out that, to achieve the desired performance from the blasting technique using the 2.5 m x 3.5 m drilling pattern, a stemming length of 1.8 m is required to provide the necessary explosives confinement. Millisecond delays of magnitude 17, 25, and 42 respectively and 1kg of emulsion in conjunction with primadet (350ms) to form the base primer for each hole are also to be used as intergral part of the blasting technique. The incorporation of the millisecond delays serves to improve fragmentation as it permits the movement of rocks at various time intervals with the result that as the rock pieces are lifted into the air, there is collision resulting in secondary crushing before the pieces reach the ground. Also a minimum of 5 rows of 50 holes to produce a tonnage of (S x B x H x Z x no. of holes mt) where S = spacing = 3.5 m, B = burden = 2.5 m, H bench height = 10.7 m and z = tonnage factor =2.4t/m3 yielding a tonnage of (3.5 x 2.5 x 10.7 x 2.4 x 50) mt 11,235 mt has to be blasted at a time as fragmentation increases with increased number of rows and holes. It has also been demonstrated that the overall cost involved in single row blasting from primary drilling to secondary blasting was $ 1 662 00 per shift compared with $ 1 390.66 for multiple row drilling and blasting, savings of $ 271.34 per shift i.e. 16.34 %. It has also been shown that the present method of preparing ANFO on the mine is not the best. Apart from being labour intensive and time consuming, there is loss of fuel oil due to leakages from the wooden fry in which the ANFQ is prepared. This leads to high cost and poor fragmentation since the required proportion of 94% Ammonium Nitrate and 6% fuel would not be maintained.

Source: KNUST