In article , stmx3 wrote:

Find a solid gold asteroid...then you'll have the killer app. Space
transportation would leap a century into the future.

Or not. The problem with relying on "valuable minerals" is that the
market can glut; the world produces some 2500 tonnes of gold a year. A
10m diameter gold asteroid would have about four years worth of that
production; it scales up from there. IANAEconomist (I mean, I can do
sums g), but you get the idea... that'd do really weird things to the
market.

The oceans contain some $1.5 *quadrillion* worth of gold (or so my
slighlty hyperbolic-looking source says; this number seems inherently
WAG); about ten million tonnes, or four thousand years of production.
I'm not drawing an explict analogy, just making a point; "valuable"
resources are really only valuable should it be possible to make a
profit on them. No-one's made a profit evaporating seawater to get it...

If there's an economic reason, it won't (I suspect) be precious metal in
the Belt, or the discovery of diamonds on Enceladus, or the like...

--
-Andrew Gray