The thing I wonder about is this - what if there's a city on Mars that has a 10 ton block of gold.

What's the price of gold on Earth? Is it the same as now? What if I could email someone on Mars and buy 50oz of gold? Could I sell it to someone here? What if it's cost prohibitive to move all of the gold to Earth? Or any of the gold to Earth? How refined does the Martian gold have to be before someone on Mars can say the own it?

The answers to all of those are clear (or at least only marginally unclear) for materials that are intrinsically valuable but for the "store of vaule" as opposed to industrial use of something like gold it gets weird for me.

I guess the answer to all of those questions is - whatever someone will pay.