As stated in the previous post, most irons found in the galaxy come from type 1-A supernova, however, heavier elements like gld , silver and uranium comes from another type of supernova- a single star supernova.
A star must be much bigger than our sun to go supernova. The bigger the star, the faster it burns. When the nuclear reactions in the star speed up. Unlike the double star supernova, the single star supernova creates a lot more elements before they explode. Once they turn hydrogen into helium, helium into carbon and carbon into oxygen, they do not turn into white dwarf stars. Instead, they keep on burning and turn these elements into the heavier elements. And when it eventually explode, the atoms inside the core starts to crush together to a incredible density and it explodes. The elements transform into elements heavier than iron. From iron to cobalt , on and on to gold and uranium. The explosion blast these elements far away in the universe.
