One of the things that is still a mystery is why Putin don't want to receive Gold as payment,
The US/UN has told Maduro he's not allowed to burn the country's gold reserves to keep himself propped up. Gold can be spectrographically analyzed to figure out where it came from even if its melted & remolded. That means that if shit ever settles down, all the countries that accepted gold since the order was put in place will be expected by the UN to return it.
Iran is willing to take the gold because they don't give any fucks about the international community, and the people they're giving the gold to are also unlikely to give two shits about the origin. So when the EU says "Hey, you better give that gold back", the Islamic peoples republic will tell them to go fuck themselves, its our gold now, we have to have some way pay the terrorists we sent to kill your people.
The EU will then pout and show Iran that they mean business by only giving Iran $999 million dollars in aid, instead of the $1 billion dollars promised.
Russia relies on a lot of trade with faggy countries that follow lame shit like "UN regulations" so there is a good chance that if they took payment in gold, they would be expected to return it. And they could get tariffed/taxed enough to actually have to return a portion of it.
(Also since Maduro's government is under sanctions and banned from the international finance network, the US can leverage cascading sanctions if anyone does business with them.
For example, if Russia's central bank accepted a deposting including Venezeulan gold, the US could lock the Russian Central Bank out of the international finance network until auditors could be assured that the bank has cut all ties with Maduro. Which means letting US auditors go through the records of Russia's Central Bank.)