Hard to say with 100% certainty based on your pic, but I'm pretty comfortable saying that it's PMD. Something gouged the area and exposed the zinc. Zinc is very reactive and based on the toning on the rest of the coin and some circulation wear, if it had left the mint with a missing area of copper plating, I would have expected it to be corroded by now.
Hoopster nailed it, I agree. I love naming coins this ones “ Head shot Abe “ the bullet exited out the back of his head. Looks like the start of a named coin collection.
