Using a blockchain for a settlement would mean a ledger of keys that should match 1:1 with the gold held by a company.
If I were to open up a mine and dump several tons of gold on the market, your 1:1 bitcoin value disappears entirely. I think you should check out why we moved away from a gold standard in the first place - it was too subject to supply pressures.
You're purposely ignoring basic economic principles required to understand the gist of my comment. Spend some time doing day trading in the metals market and you'll see how a blockchain isn't going to help with keeping gold inventory straight when the prices are tied up. This is gold settlement, not simple inventory tracking, so this is a much more complex issue than you're trying to make it out to be.
I love how everything eventually comes full circle.