Why asteroid mining, if Asteroid Mining Venture Could Change Supply/Demand Ratio On Earth? According to an authoritative source, the gold market is rather small.
“The World Gold Council is the authoritative source for gold production, (and) states that all of the gold ever mined ‘would fit into a crate of 20 meters cubed.’ That’s 8000 cubic meters,” Lawrence H. White, Professor of Economics at George Mason University, told RedOrbit.com. “A standard Olympic swimming pool is 50 m long x 25 m wide x 2 m deep or 2500 meters cubed. So that’s 3.2 Olympic pools.”If an asteroid with significant gold deposits were to be found and successfully mined ---
a large quantity of gold were brought to Earth from an asteroid, it would indeed lower the price of gold, emphasized White. “Possibly, but not necessarily, by enough to doom the venture, supposing that it would have been profitable at the previous price of gold.”
What to do, then? If going to an asteroid is uneconomical to begin with, why make matters worse and destroy markets by flooding it with excessive supply?
In order to answer that question, let's take a look at aluminum. Aluminum used to be a precious metal. It was rare and expensive until a better way to refine it was found. It so happens that Aluminum is a useful metal in its own right, so a new market- worth more than the old market as a precious metal- was created. Such may not be the case with gold, but it could be the case with platinum. Platinum is a useful catalyst. Its economic value extends beyond its role as a precious metal.
A primary goal should be to mine platinum group metals. The profit would come from volume--- selling a lot of the stuff could recover costs sufficiently in order to make a reasonable profit. But it could use some additional help. You could leverage the venture with another substance that is not so rare on Earth, but useful in space.
A case could be made for mining water as well, as it still costs plenty to lift the precious substance to LEO. That gives two opportunities for making money. But, you still have to get there, which is still expensive.
The point of the coaster is to reduce costs of getting there. If a high ISP rocket can be developed, it can lower the costs of getting to the asteroids- and back with cargo. A plentiful source of water can provide the affordable fuel for mining expeditions. This could make the asteroid mining venture for platinum cost-effective.