I didn't understand why colliding gold atoms would create a big bang like situation.
They use Gold partially because it doesn't react with anything - they know that there will no peturbations from Gold Oxide contaminants for instance.
They don't use a whole lot of Gold, if you're worried :0)
Sorry only partially answered your question: Gold is used as a collision target somewhat the reason I gave, but as to why they would expect a BB situation - well they carry out High Energy collisions for any and every experiment in Particle Physics. The actual metals they use in targets is not that important (as long as you avoid contamination).