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.

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.

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

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

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

Learn more about blast movement monitoring