What mechanism is necessary to create elements heavier than iron, like gold or uranium?

Answer

Neutron capture processes

Because fusion beyond iron requires an energy input rather than releasing energy, elements heavier than iron are created through processes involving the capture of free neutrons, such as the s-process or r-process.

What mechanism is necessary to create elements heavier than iron, like gold or uranium?
ElementstarastrophysicsFusionnucleosynthesis