What is an example where heating a substance provides a mixture of its constituent elements?
You might have to be a bit more specific, but I can give 1 example where the heating of a compound gives an elemental mixture, that of cinnabar.
Cinnabar is bright red mercuric sulfide. Heating decomposes this material to give mercury metal and sulfur.
The mercury metal may be collected by decantation, and then redistillation.