''there are no 'cheap' mines & no suitable substitutes...''
oh please ---------------------- materials technology is discovering new things every year
there are substitutes for many things and there are always going to be technologies that supersede was existing technologies
copper replaced stone, bronze replaced copper, iron replaced bronze - etc etc.
that is not going to stop anytime soon. The one constant change that has been with mankind since the first hominids is technological change and development
