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Minimising dilution and ore loss is an important part of ensuring profitability of a gold mining operation.

White Foil open pit gold deposit is a low grade deposit and therefore managing ore quality is a high priority. Ground movement through blasting can displace ore and waste boundaries up to 10 m from their in-situ location and therefore requires stringent ore movement monitoring and adjustment.  There are currently only two options for monitoring blast movement – utilising visual targets (commonly lengths of polypipe) but this has widely been replaced by electronic blast movement monitors (or BMMs). Regardless of the technology used, the basic principal is to compare the pre- and post-blast locations of the targets to determine the movement of the rockmass during blasting, which is then used to determine the final location of ore and waste boundaries.

The Blast Movement Technologies (BMT) BMM system has been used at White Foil since June 2014. The system has been effective and reliable during that time however the annual cost of using the BMM system is greater than other monitoring alternatives.  As such, the open pit geology team conducted a study comparing the BMM system against the conventional polypipe technique. The objective was to quantify the profit and loss that would occur based on the ore block transformations from both methods.  Eight blasts were selected where polypipes were installed in additional holes adjacent to the BMM monitoring holes. The resulting movement vectors from the respective methods were used to create post-blast ore blocks by transforming the in situ ore blocks by using their respective methods.

• While polypipe is a cheaper alternative, the BMM system tracks ore and waste boundaries more effectively resulting in better quality control, enhanced ability to minimise dilution and ore loss and maximising profit.
• For these eight blasts, it is calculated that the BMM system resulted in $664 978 extra profit through a reduction of ore loss alone.
• The total cost of a yearly BMM package was recovered in the first two blasts of this study.
• The primary reason for the difference is that polypipe had a poor recovery rate of 32% compared with 92% for BMM at White Foil.  Therefore, the data used to transform the ore blocks was less representative, resulting in inaccurate post-blast ore block boundaries when using polypipe.

M E Watson
Senior Mine Geologist, Evolution Mining, Kalgoorlie WA 6430
Presented at the Tenth International Mining Geology Conference 2017