I have a small solid cast bronze bust of Johns Hopkins, the founder of the University bearing his name, and if I hold it close to my nose I can detect the unique odor of bronze metal. Why does bronze metal have a smell at all? I thought there had to be free molecules of a substance in the air for a “smell” to be detected. So far as I know the bronze metal isn’t shedding molecules.
I’d guess the oxidation hypothesis for something as old as you describe.
There is a famous brief phrase in Joyce’s Ulysses with an astounding wealth of synasthesia (it has been used as a book title, I believe) that is relevant, I think, although not with metal. The phrase is lovely to unpack.
[As Bloom walks by a church]: The cold smell of sacred stone called him.