"PGM ore is mined underground and less usually in open-cast pits. It is blasted out of the ground before being crushed and milled into smaller rock particles which are mixed with water and reagents and pumped through with air to form a "froth flotation". PGM-rich particles adhere to the bubbles created by this process. They are then removed at the surface and the remaining material is put through the process a second time." (Quoted from article)