Print3.2.7: Impact of Pit Expansion on Stripping Ratio
Imagine a steeply pitching orebody, as shown below. We would like to extract this tabular deposit using open pit mining method. Let’s assume that two pits with different sizes are being considered for this mining operation. We would like to study the impact of pit expansion on stripping ratio by comparing the overall stripping ratios for these two pits.
This figure shows the pit areas as a block model. The smaller pit (Pit A) includes 32 blocks. 16 blocks are ore and the other 16 are waste blocks. Therefore, the stripping ratio is 16/16 = 1. The larger pit includes 437 blocks in total. Using Pit 2, 76 blocks of ore can be extracted. Therefore, the stripping ratio is: (437-76)/76 = 4.75. This example shows that as we expand the pit in a steeply pitching orebody, overall stripping ratio dramatically increases. Therefore, more waste blocks have to be mined out to uncover one block of ore. It should be noted that as we go deeper in an open pit, the unit cost of mining will increase. Because the material will be transported for a longer distance, which takes more time, and which may necessitate that we add additional trucks to the fleet.
Now, you should be able to:
- Determine ISR for given pit dimensions
- Find the pit limit when the pit dimensions, average ore grade of the strip and g-SR plot are given.