Most likely one of the post WWII cents made from 1944 - 1946 with material from recycled shell and bullet casings. I've read that they had to play with the alloys quite a bit to get the mix right and even then the gunpowder residue introduced all sorts of other elements into the mix in trace amounts.
I think the leaning to gold toning is more common in S mint coins than in the D or P mint versions.