Reduce dilution and increase ore recovery

Controlling ore loss and dilution is critical to every mining operation. If you get it wrong, the result can mean tens of millions of dollars in lost revenue.

As a grade control geologist, you are tasked with maintaining the grade going to your mill. Dilution can be a major contributor to poor grade results, and blast movement is a significant cause of dilution and ore loss1.

BMT works with geologists from over 105 open pit operations around the world to accurately measure 3D blast movement so that the ore is sent to the mill and waste ends up in the waste pile.

The impact of blast movement on grade control.

Grade control geologists spend many hours modelling the distribution of minerals throughout a rock mass based on data from drilling and assaying a significant investment. After all this effort, mining engineers blast the in situ rock so it can be efficiently handled in the mill. In open pit mines the required explosive displaces ore boundaries from where the geologists originally defined them.

  • Failure to accurately account for blast movement results in ore loss, dilution, or misclassification (low grade to high grade ore, sulfide to oxide, or other contaminates).
  • The financial consequence of getting this wrong is significant and diminishes the geological QA/QC done in defining the ore body.
Cowal gold mine increased mill feed grade by 7% through blast movement monitoring


The main challenge for the geologists at Cowal is to maintain grades through the mill. Dilution and ore loss are the major factors in this and the Cowal team utilize blast monitoring equipment to eliminate them. Monitoring blast movement has improved grade and end-of-month reconciliation, and being a low-grade bulk tonnage mine, this has substantially increased revenue.

Studies at Cowal show a 7% increase in their mill head grade on a yearly basis.


What is blast movement?

So that solid rock can be excavated, explosives rapidly release energy to fragment the mineral resource. The explosive exerts a force equally in all directions, and the rocks with least resistance begin to move. Typically, movement is perpendicular to the blast initiation timing contours. The moving rocks in turn act on neighbouring rocks, which results in bulk movement of the rock mass.

  1. Upon detonation, each discrete element of the explosive exerts a force equally in all directions on the adjacent rock. The rocks with least resistance, that is rocks with less unblasted rock in front of them, begin to move. These rocks in turn act on neighbouring rocks, which results in bulk movement of the rock mass.
  2. The rock moves in the direction of least resistance. The material moves into the void created by the hole before it and the new material settles into the new location, making movement approximately perpendicular to the initiation timing contours.
  3. The rock at the top of the bench is not directly impacted by the explosive but instead is indirectly moved by collisions from other rocks from the drill hole behind. The further a rock is above the explosive column, the less energy it receives and therefore the less distance it will move.
  4. Greater movement is in the mid-to-lower level of the bench and movement reduces near the floor due to friction from the unbroken floor.

 

blast movement-blast progression

Blast Movement. Each hole goes off in sequence. Blasted material moves into the void created before it, and then settles into this new location.


Why is adjusting for blast movement so important?

Because your grade control process has to account for blast movement.

Blast conditions are unique—the blast design, explosive or firing change with every blast. And the impact of changes in the rock mass or voids is unpredictable.

BMT’s research, over 13 years, shows the variability of blast movement means it is not possible to predict or model with sufficient accuracy for grade control. From measuring tens of thousands of blasts, we found that:

  • Actual blast movement varies from 0.5m (2 ft) to 30m (100 ft)
  • Horizontal movement is commonly ± 50% from the mean
  • Movement varies within the bench, i.e. surface movement is much less than mid bench movement
  • Movement varies across blast zones and edges

blast monitoring mid bench movement

Blast movement varies with depth: horizontal mid-bench displacement  (3) was twice the surface movement (2) in this blast.

What is the financial impact of blast movement?

If post-blast ore movement is not accounted for, BMT estimate’s that up to 25% of your mine’s total recoverable product could end up as waste, potentially costing your mine tens of millions of dollars in lost revenue per year.

  • Canada’s largest gold mine, Canadian Malartic estimated that they saved CA$7 Million in Q1 2018 by accounting for blast movement.
  • Teck’s Red Dog surface zinc mine adds US$6.5 million annually through blast monitoring.
  • Centerra Gold’s Mount Milligan open cast copper mine recovered over US$600,000 of ore in one blast.
  • Anaconda Mining’s Pine Cove gold mine reduced dilution from 20% to less than 5% and generated a 15% increase in recovered tonnes, valued at US$15-30k per blast.
  • Asanko Gold’s Nkran mine in Ghana improved reconciliation—from 88% to 98%— with blast monitoring.

 

“…blast movement technology is making a significant contribution to the management of ore losses and dilution, as evidenced by the positive variances we are seeing in grade and ounces.”

Peter Breese, President and CEO, Asanko Gold


Find out more

 

  • This field is for validation purposes and should be left unchanged.

Read how customers have implemented blast monitoring to reduce dilution and ore loss.

Find out how you can reduce dilution and increase ore recovery.


7 easy steps to monitoring a blast

  1. Activate the BMM sensors
  2. Install BMMs in dedicated monitoring holes prior to blasting and record their position
  3. Blast
  4. Detect BMMs by walking the muckpile with our detector to locate the position of each BMM sensor
  5. Combine drill and blast, geology and BMM system data in our software, BMM Explorer
  6. Proprietary translation defines post-blast polygons
  7. Excavate new accurate ore location to maximise ore recovery
The result: Ore boundaries are redefined to reflect the measured movement, allowing the production team to dig in the precise location of the ore and waste.

 

Note: 1 Definitions

  • 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.

The blast movement monitoring process

Learn more about blast movement monitoring

See it in action: Garry Luffman, senior geologist at Pine Cove mine

“Knowing that we’ve saved ourselves between 15 to 30 thousand dollars per blast, it’s quite a good feeling to have. By using this technology I’m assured that I’m making them more money.”
Garry Luffman, senior geologist at Anaconda Mining’s Pine Cove mine

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“The decrease in overall dilution, from 20% to less than 5%, has made a huge impact to our project.”
Gordana Slepcev,
COO,
Anaconda Mining