Answer:
One example of a mixture is rock and copper ore.
These are separated by froth flotation.
Froth flotation is when the crushed copper and ore is mixed with water and a variety of different chemicals, and air is forced through the water making bubbles which carry the copper (and not the rock) to the surface. From the surface the copper can be collected and smelted.
During smelting the copper can be mixed with other substances to get rid of impurities, and these substances float on top of the molten copper as slag. The slag can be poured off or smelted again to pick up any more traces of copper still left behind.
The smelting technique is also used for other minerals like gold and tin.
I hope this answers your question.