Plutonium 238 is neither mined nor refined, it is created by exposing the element neptunium-237 to a high neutron flux and separating out the isotope. Before you ask, you get neptunium-237 from nuclear waste, it is created in a high neutron flux environment, but it has to be separated out and exposed separately in order to get the more pure plutonium that is needed for an RSG.
Thorium-232 is used in reactors, but it itself is not fissile, it must capture a neutron and become protactinium then beta decay to uranium 233. the uranium is fissile and can be used in a standard nuclear reactor, but would not work for a RSG.