Stripping ratios 1/0 = divide by zero error.Check out this Sierra Leone (SL) mine. Koidu is the official government diamond miner. The proceeds go back to the country. Note that all guns are banned in Sierra Leone now, bar for the military.
Koidu mine
These kimberlites are 0.5 hectare. Note the pictures of the K1 vertical pit. What stripping ratios!! lol.
Notice the guys standing at the bottom!!? They should be replaced by remote control machinery.
You get an idea looking at all these pictures as to what size operation a 1Ha pipe should be. The setup will not be anywhere near $700M.
Lots of pictures scattered in strange places throughout the site. Another picture shows a pit that looks like a small one with smaller Volvo and CAT gear in it. No backhoes, but no big daddy expensive gear either. Note IMO that drilling an blasting will be phased out in diamond mines in future and be replaced with much more efficient kimberlite grinding machines like you would see in a coal mine. The kimberlite is soft enough to grind in situ, rather than drill and blast.
Finding a primary source of diamonds in SL is pretty rare. They are all eroded down to the root zone and thus are small. When you find them though they are profitable.