Old metallic coins often have a strong odor, whereas clean metal doesn’t have any particular smell at all. That smell does not come from the metal itself, but rather from the skin oils and the compounds dissolved in them, which become concentrated and oxidized by the metal in the coins. The biggest contributor is a compound called 1-octen-3-one, which humans are very sensitive to, and which has a mushroom-like odor that many people tend to describe as “metallic” by association.
▻http://www.nature.com/news/2006/061023/full/news061023-7.html