I have started a Gold mine next to a Foundry and coal mine. They are producing a lot of gold bars, but the gold bars are just piling up in the Foundry storage (350 now) and not being moved to the Vault. As a test someone suggested I allowed gold storage in a Storehouse, but it is not being moved there either. I have stopped producing gold bars there, and have adjusted workers up and down. I see workers transferring Iron from there, but never Gold. I also have ample laborers and I have wagons that have idle time. It is also impossible to set storage limits on Gold, as you can with Iron.
I have watched this for years now, nothing is ever moved out. I’m worried about Raiders.
Update: by moving all gold from my town to the trading post, stopping when the Vault was emptied, and then buying a building upgrade, some of the gold was carted from a Foundry to the build site. I think some was carted to the Trading post. I retransferred the money back to the Vault, but most of the gold is still sitting in the Foundry.