I am no scientist but since the only elements that existed after the big bang were hydrogen and helium... I would have to say that all the other elements were created in stars. Stars use the lighter elements for fuel by nuclear fusion creating heaver elements. When a star uses up its fuel of lighter elements, it dies often in a huge explosion called a super nova. The materials that were created in the star a flung out into space allowing new stars to be born that can use the heavier elements as fuel.

As I said, I am not a scientist but that is my understanding of the process. Neil DeGrasse Tyson has a great explanation of the process in his book "Death by Black Hole.
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The Big Bang jumpstarts the initial large-scale production of hydrogen, deuterium, helium and lithium.The earliest stages of heavy element formation in the Galaxy were dominated by stars with masses ten times that of the Sun or more, and lifetimes of a few million years or less. These supermassive stars produced small amounts of all the elements, but their presence can be identified most clearly by excesses of elements like strontium, yttrium and zirconium. Released by supernovae and absorbed by new star-forming clouds, these elements were incorporated into the next generation of stars.
Source(s):
http://www.spacedaily.com/news/milkyway-00b.html

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