Cost of production to mine anything in space will be astronomical so you're wasting my time even mentioning it. You might as well claim we will mine gold inside a black hole or alternate dimension. We would probably attempt to mine metals 2 miles under the ocean long before space but that is of course no threat to anyone buying at current prices.
http://www.planetaryresources.com/http://deepspaceindustries.com/Cost to start mining will be astronomical but so will be the quantities mined. Asteroid mining is not that far away in time. Privatization of space industry is bringing down costs. You don't really know whether the costs will be so high that the market won't be flooded enough to keep the price of precious metals down.