Just think one Asteroid with the diameter one kilometer. Can provide all the world iron production for a year, all the world production for gold and silver for 10 years. All platinum production for a thousand years. And this only for a small asteroid and there are more than 750k other asteriods with same size other even called dwarf planet.
So you are saying that the discovery of such an asteroid and the subsequent mining thereof would herald the End of The World As We Know It?
My $.02.
I don't know why you are thinking that world would end if we are starting mine asteriods? Lol
Most of this ores are to be used in space. Like to build cities in mars, space cities, moon base and many other things. Do you know the cost of getting 1pound of payload to space?