Yeah... When we excavated the Castle grounds, we brought a lot of indigenous rock strata with us. We squirreled even more away from our various "filtration" efforts to come up with enough isotopic volatiles to get this flying fantasy-land into the air and into orbit.
Since then, we've been mining every piece of space junk that comes along. Spider-bots seeded back out to the asteroid belt send us care packages every now and then. Everything from water ice to rare earth elements.
We have plenty left over to make new silverware (out of real silver), tin cans, spare shuttles, new wine stomping outfits, etc...
So — what are you saying? That we owe our continued spacefaring existence to heavy metal?