[SergeyMaikov]

Because cost ramps up with both declining grade and also the remoteness or depth of the orebody. By the same token, the unit cost of carting payloads in space will decrease slowly over the coming decades. What makes you think that the two might never meet?

I'm not talking this century but to say it might never happen is a bit odd imo.

But if past trends are anything to go by, technological advancements will mean that deposits of ever decreasing grade will continue to become economically viable to extract.

Also, if we could get to the point where metal extraction from sea water is viable, we'll likely not need to go looking elsewhere.

I agree, never is a long time... but most of my posts have been limited to the 'foreseeable future'.