Seems a piece of the "coating" has chipped off from under Licinius's chin, if it is the patina it is very shiny and silvery in hand.. is this what they call silvering?
It's possible that it is a fouree siliqua, that is, an anceint, plated counterfeit of a silver coin. What's the reverse look like?
I can't tell what the mint is from the photo, but it looks like a typical silvered bronze issue. These were mostly bronze coins that contained a small amount of silver, typically around 2 - 5%, in the alloy and a thin silver "wash" on the surface. Sometimes the silver wash reacts with the chemistry of the ground that the coin has lain in, forming a layer of silver nitrate and/or other compounds that build up on the surface of the coin over time. So I don't think your coin is silver plated. Rather, a chip came off of this encrustation layer, removing the silver wash with it and revealing the interior of the coin. You can see something similar in the reverse photo on the left side around 9:00, just above the letters IOVI.
