There are numerous stylistic variations in portrait and also various mintmarks and other symbols around the eagle on the reverse, but it appears to be a tetradrachm from the Greek Ptolemaic Kingdom of Egypt. Looks to be Ptolemy II Philadelphos (285-254BC).
At least that’s what it’s trying to be, but it appears to be a poor fake that has been silver-washed or plated. I would say modern rather than a contemporary counterfeit.