They hoard them. Dwarves love gold/diamonds/precious elements just for themselves, and not for what it can buy them.
This obsession to mine and hoard these elements is unlike someone who sees diamonds etc. as a commodity or currency and what these things can do for them. In themselves, these things have no real value besides looking pretty. Or of course you have industrial use for them, for example. Dwarves in western myth have a natural and innate love for diamonds and/or other precious metals/stones which results in coveting them for the sake of coveting them, having possession of them alone (kind of like a drug addict and the drug they are addicted to). These dwarves are no different. They mine and hoard because they can't help themselves.
(The irony in this is the fact that dwarves seem to be attracted to elements that others find valuable (because of their high trade in or market value), which to me, seems to show a kind of tendency to hoard something that others like, and this fact may actually be the real cause of their obsession, which is something to consider as well. But that's a topic for another question.)