That much platinum (90 million tons) on the asteroid would flood the market even in its initial mining and production stages to the point that it would quickly be pennies an ounce. Probably cheaper than aluminum.

A more practical economic exploitation of the rock would be for Ian Flemming’s S.P.E.C.T.R.E. (with a white, long haired cat on its lap) to initiate a project to attach thrusters to it so as to cause a trajectory with the earth, then extort $5.4 trillion from global nations not to do so.