I'm pretty sure this is a lead seal. It's about 1" in diameter and .36" thick. Says" "exportation" on one side, "...DEATIX" on the other. Appears to be letters on the rim also. There is nice patina on it - can anyone ballpark its age? I have found some older items/coins at this site.
It's definitely a seal. But those go back before the civil war and are still in use today, so to date it could be difficult. You may be better served to let the other items you are digging give you an estimate of age.