A time-traveler steals gold from a Confederacy squad of men. When it shows up in the future 100+ years later, George Spota claims that they were able to date it through carbon-dating. You can't identify the date of refined gold through carbon-dating: the process only works on items with an organic component, or that previously had an organic component. The odds of some small amount of organic material from the Civil War era clinging to the gold by the time it was brought back, and then sold, are infinitesimally small.