That mechanism occurs in large stars when fusion runs out of control. Layers of different elements are created in a spiral of increasing ferocity until a star explodes with fantastic force. This is a supernova, the most explosive event in the universe. In a few seconds, as much energy as the sun could radiate in 9 billion years is released into space, creating a furnace thick with neutrons. These highly energetic particles crash into the various elements as they pour from the star, creating a soup of even denser, heavier elements which then decay into gold, silver and other atoms.
Space is seeded with precious metals.
At least that's the theory that most astronomers accept. We need exact information about the way dense, neutron-rich atoms were created inside supernovae. Then we will be able to calculate how these atoms would have behaved and find out if supernovae were indeed the crucibles in which the elements were first manufactured. We shall do this over the next five years. Supernovae are very rare events, as British astronomer Paul Murdin points out.