While polypipe is a cheaper alternative, the BMM system was shown to track ore and waste boundaries more effectively, resulting in better quality control that minimized dilution and ore loss and maximized profit.
The White Foil study monitored eight blasts where polypipes were installed adjacent to BMM monitoring holes. The resulting movement vectors were used to move ore blocks to post-blast locations.
Polypipe had a poor recovery rate of 32%, whereas the BMMs overall detection rate was 93%
The improved data accuracy produces significantly better results and is more representative of the bulk movement
For the eight monitored blasts, the geology team calculated that the BMM system increased recovered value by A$664,978 (US$450k) through a reduction of ore loss alone.
Waste prevented from going to the mill totalled 7610 t (as 0 grade), avoiding $179 589 in processing costs
High-grade misclassified as LG was minor; prevented 420 t @ 1.57 g/t Au
Low-grade misclassified as high grade prevention was 2030 t @ 0.82 g/t Au
Potential ore loss using BVIs vs BMMs was 9850 t @ 1.47 g/t Au
Revenue lost by using BVIs would have been $664,978
Ore loss occurs when material containing grade (ore) is incorrectly sent to a waste dump. When a cost is given for Ore Loss, it is the sale value of the metal (gold, copper) recovered from this ore (i.e. ore tonnes x grade x recovery rate x metal price).
Dilution occurs when waste is unintentionally with material containing ore and sent to the mill. When a cost is given for Dilution, it is the cost of processing the waste material through the mill.
Misclassification occurs when material containing grade (ore) is sent to an incorrect downstream location (i.e. a stockpile); for example, sending high grade material to a low grade stockpile.
Note: 1. Presented at the AusIMM Tenth International Mining Geology Conference 2017, Hobart, Tasmania, 20-22 September 2017, by Marcelle Watson, Senior Mine Geologist, Evolution Mining, Kalgoorlie, WA