I am not sure if there is enough of this coin left for an attribution, but hopefully so. It is 24.6mm along it's longest edge and weighs 5.9g. As usual, any thoughts regarding authenticity, attribution, age, rarity, value, etc. would be greatly appreciated.
Looks like the real deal. The mint is unknown (could be Lima, Peru or Potosi, Bolivia - most likely the latter, but all of the mintmarks, assayer and other indicators aren't visible), date is 1745, not particularly rare given its condition but still popular as a cob coin. It's worth about $25 to $30.