Even if a safe is fireproof, it's not cooled. Can the silver or gold be destroyed by the intense heat?

 What if it's not in a safe. It might take awhile to find one. Perhaps I'll just hide it in the basement gravel at the bottom of the fishtank :) Will the coins get destroyed once the water in the fishtank boils (oh those poor clownfish ) and the tank explodes and the silver and gold are exposed directly to the flames?