"In space, a single platinum-rich 500 meter wide asteroid contains about 174 times the yearly world output of platinum, and 1.5 times the known world-reserves of platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum)." -- Planetary Resources,
http://www.planetaryresources.com/asteroids/composition/ (take with as many grains of salt as you feel like)
But hey, I'm sure they can spare a mission to retrieve us some gold sooner or later. :P