I'm assuming this is referring to the incident referred to in this article:
https://www.georgiaencyclopedia.org/arti...erate-gold
I haven't read the book linked to by Laurie, but if the thieves had any "street smarts" they probably sold the gold for a fraction of its value (in hard Union currency) to a fence/middleman who arranged for the gold to be melted down. That is if somebody who couldn't melt down the gold wasn't connected to the original group of thieves. Melting the gold down would've made it untraceable from authorities.
It doesn't make much sense for the thieves to bury the gold for a long time after they've stolen it.