Last Chinese mine design I reviewed set the portal beneath a...

Last Chinese mine design I reviewed set the portal beneath a coffer dam in glacial till "designed" (I use the word loosely) to hold back a glacier in an active seismic zone. Work force was around 3,000 exploiting something like 3g/t underground at a remote location using mechanised open stoping with fill (so not a technically simple operation).

Cheap labour? Perhaps at the individual level, but you're paying, feeding and housing 3,000 of 'em and productivity is at the lower end of the range, at around 20%. So the thing's patently uneconomic.

I'm still amazed at the coffer dam. Extraordinary. I've never before or since seen a design guaranteed to kill 3,000 people in one go.