Not the right comparison to make when comparing gold vs paper currency that can be printed at a whim. The comparison would hold if they pulled out physical fiat currency reserves.
The sum of 12 billion USD would be correct for paper gold probably. But in practice, the supply of paper gold exceeds that of physical gold.
To put in human terms, it's roughly three day's labor of every worker in the Netherlands.
Make that the cat wise.
GDP is just a number in a spreadsheet. This is a physical asset.
GDP is a proxy for economic output. This is a static collection of a certain element producing nothing.