The Implications of Blast-Induced Movement to Grade Control
Grade control is an important process for most mining operations since the sole reason for the existence of the mine is to extract the valuable mineral from the ground.
As the first step of the beneficiation process, if grade control is not optimised, then no matter how good the downstream processes are the full potential of the operation will not be realised.
The detailed implementation of grade control varies between mines but typically consists of sampling and assaying to determine the quantity and location of the mineral and then defining economic, minable ore zones. Considerable research has been done in the field of geology to improve these processes; however, there is a significant event that takes place before the mineral can be excavated and extracted – blasting.
Again, considerable research has been done in the area of blast optimisation but this has had a strong emphasis on production, such as fragmentation, diggability, vibration and damage. However, blasting also has a significant impact on grade control due to the movement of the rock, but blast movement, and blast dynamics in general, is not well understood.
This paper is the product of six years of research into quantifying and understanding blast movement and its impact on grade control.
The data set currently includes 1500 movement vectors from 28 sites around the world and covers most of the practical range of blasting conditions (eg powder factors from 0.36 kg/m3 to 1.7 kg/m3; rock densities up to 3200 kg/m3; bench heights from 5 m to 15 m and all methods of initiation).
The benefits of measuring blast movement to reduce ore loss and dilution have been recognised by many people for many years and various methods have been used with limited success. Most use ad-hoc visual targets such as pipe, chain, rope and coloured sandbags.The disadvantages of these methods include:
have to be excavated before their position is known, and
some only provide two-dimensional movement.
Electronic methods promise to alleviate some of the shortcomings of the visual methods, especially the last two items. Again, several techniques have been tested including ground penetrating radar, magnetometery, metal detection and recently, radio-frequency identification (RFID) tags. Most suffer from limited range, which means the targets must be placed close to the surface or indeed, on the surface, which is inherently inaccurate due to movement dynamics.
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