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Centerra Gold’s Mount Milligan recovered over US$600,000 of ore in one blast

Mount Milligan Blast

 

Commodity Ore Grade Geology Powder Factor Location
Gold-Copper-Porphyry 0.35 g/t Au1
0.18 % Cu
Porphyry 0.47 – 0.65 kg/m3 North America

Centerra Gold’s Mount Milligan mine is a gold-copper-porphyry deposit located in central British Columbia, Canada.

  • A large-scale open pit mined in single-pass 15 m benches using conventional truck-shovel method
  • Low grade, gradational deposit
  • Ore blending from different zones smooths delivery of copper and gold head grades

Challenges

Substantial movement of ore was not properly monitored or accounted for, resulting in varied dilution and ore loss
  • High powder factors required to achieve fragmentation for complex mill processing resulted in substantial and highly variable movement
  • Ore movement was not properly accounted for, resulting in various degrees of dilution and ore loss across the different ore grades

Solution

The BMM System accurately transposed post-blast dig lines
  • Blast movement monitors (BMMs) were installed in monitoring holes throughout the shot
  • Installation and detection as per site standard operating procedures
  • BMM Explorer software calculated new dig lines, and areas of ore loss, misclassification and dilution that would have occurred without monitoring

Results

US$600,000 additional ore recovered in one blast
Improved ore blending for mill processing

The results from this blast at Mount Milligan (shown right) demonstrate the value created from blast monitoring.

Significant movement occurs within all blasts. Variation of ±50% from the mean horizontal movement is common and occurred in this blast.

  • Measured horizontal movement2 ranged from 10 – 17m (36 – 56 ft) and vertical movement was up to 6.2 m (20 ft)

As a result of accurately accounting for blast movement, Mount Milligan:

  • Avoided 10% dilution by diverting 53,825 tonnes of waste from the mill
  • Prevented the misclassification of 73,130 tonnes of ore
  • Maximized ore yield by recovering 45,982 tonnes (9%) of additional ore, valued at over US$600,0003

1. Ore grades inferred from Centerra Gold Technical Reports
2. Movement measured by BMT’s BMM System
3. Calculated using BMM System- and Centerra Gold-supplied data.

Adjusting for blast movement saved Mount Milligan over US$600,000 by
reducing ore loss, dilution and misclassification of differing grade ore bodies.