From a guy living in S. Korea, who has found similar pieces here. The coin is authentic, dating from the late 1700s to the early 1800s.
It is a common coin, although I would have to see the other side of the coin to determine where it was minted. It seems the oriental
people connected coins together, or just put holes in them, to make them from a common coin into a religious charm of some kind. I have coins with one or two holes in them to dozens of holes in them. But, when holed, the coins go from the "coin" catagory into the "charm" catagory. There were other pieces that are coin size/shapes, but they were always charms and never coins.
A good find, and it is not surprising that it is in the same area/at the same depth of the Civil War buckle.