They were smuggling gold that was illegally mined (or at least a lot of it was). That's why they had to smuggle it. They are paying the crime ring of miners for it so they are essentially keeping it going and supporting it. There are huge area's where organized crime go into public land and start tearing it all up, using dangerous chemicals and destroying everything in the environment to be able to mine cheap and fast. It's pretty horrible.
Dore is a reasonably liquid asset.
It would have gone on with or without an outlet to the States.
And yes, they use a lot of mercury, in particular, some of which is recovered by distillation from the dore, but most is just lost physically.
I remember seeing something in the news, probably over a year ago, in which it was believed that there was a huge money laundering operation in which either transfers were being made to South America to pay for imaginary gold, or maybe just paying way too much for real gold.
The big picture was that payments for gold were supposedly being used to get money raised from selling drugs in the USA back to the sources of the drugs without the risk of smuggling huge amounts of physical cash, as well as possibly being able to make the money look legit.
I didn't pay a lot of attention to it, and can't say if it related to the same people/companies, etc., but it sure sounds familiar.
The whole drug/money laundering part of the story seems to have disappeared if it was the same group.