Hi ZogTo answer your question. Split firing can be a method used...

Hi Zog

To answer your question. Split firing can be a method used to develop ore drives with narrow orebodies. What it involves is boring holes in the waste portion of the face and firing off that waste rock. They will then remove that broken waste rock and then bore holes into the remaining "ore" that's left. They will fire off that ore and remove that to the ore pad on the surface. Essentially fire/blast each face twice to reduce the dilution sending the waste component to the waste dump and the ore to the ore pad. The size of each firing will depend on the amount of waste/ore on each face and I have seen it done with 75% to waste and the last 25% as ore.
An example is, if you have a one metre wide orebody at 4g/t in an ore drive that is 4m wide, then if you fire the heading as 1 cut then you have turned that 4g/t ore into 1g/t at the mill. Yes you still get all the ounces, but, your costs increase as you have to mill 4 times the tonnes. If you can fire off 2 - 2.5m of waste first and then the ore, you reduce the grade to the mill to 2 - 3g/t and increase the milling cost by about 50%. There will also be an increase in mining cost and that will depend on the contract with the mining contractor. Haulage costs should be reduced as you are not hauling excess waste to the mill.

Hope it helps