At the outset, discovery does not equate availability. Huge amounts of platinum (or the material at issue) might be discovered, but that does not necessarily mean that its extraction is feasible or practicable with the currently available techniques. See here and here.
Assuming that the discovered material is economically available, then supply would increase, thereby pushing prices down. At the same time, demand for that material would increase because agents (consumers) might deem that material a convenient substitute of other [now relatively costlier] alternatives. The net effect would be a higher quantity of that material being traded, and at a lower price.