I know it is difficult, but please try not to be a spoiler.
To this point I have read nothing about gold and nothing about Galt’s Gulch.
Now I can guess way more than I wanted to.
See the videos at this thread; I found them very enlightening. They constitute an interview with Ayn, and what is so surprising is that the interview takes on a surreal form as if the interviewer, Mike Wallace, were a character straight from Atlas Shrugged interviewing Dagny.
http://www.freerepublic.com/focus/f-bloggers/2172674/posts
Rest assured, the twists in the plot ahead will quite eclipse any thought of a particular currency used in a particular place.