Jim Dowling - Mining Engineer

BACK

 

STRIPPING RATIO

 

The first planning study for a new mine, once the reserve is deemed to be adequate, is to decide whether to use surface or underground methods. If surface mining was chosen initially, there may be a subsequent planning investigation to decide whether to switch from surface to underground as the pit deepens. Surface mining is much cheaper, all else being equal. Cost per tonne of surface mining is often around 10% of the cost of mining underground, but this varies considerably and the gap narrows as surface mining goes deeper. There are other important differences between underground and surface mining:

Surface methods produce earlier cash inflows
Surface methods are safer
Surface methods have greater environmental impacts, such as dust, noise and visual intrusion
Post-mining restoration of surface mines is much more difficult and costly
Surface methods are less flexible in planning terms – mining can only proceed from the top down

Orebodies at or near the surface are usually mined, at least initially, by surface methods, because of the lower operating cost. Orebodies which occur beneath overlying waste require the waste to be removed before ore mining can start. The amount of waste to be removed to expose mineable ore, compared to the amount of ore mined by that exposure, is called the Stripping Ratio (SR). Stripping ratio can refer to the entire reserve or a particular mining stage. Units can be weight or volume, imperial or metric, even linear measurements of depth. The SG of waste usually differs from that of ore. Care must be taken to properly compare like with like.

 

 

Stripping ratio worsening as ore reserve thins

Stripping ratio worsening as ore reserve thins

 

 

Stripping ratio worsening as ore reserve deepens

Stripping ratio worsening as ore reserve deepens

 

 

Stripping ratio worsening as pit deepens

Stripping ratio worsening as pit deepens

 

 

Stripping ratio worsening as pit slope angles decrease

Stripping ratio worsening as pit slope angles decrease

 

BACK

 

Copyright © 2021 Jim Dowling