If Greece should default the euro will sell off against the US dollar. When it does, the price of gold will depreciate in the short term, as gold is denominated in US dollars.Gold will turn into an appreciating asset as people around the world will not want to hold all of their wealth in their domestic currency. People will not want to hold foreign currencies in inflationary, low interest rates, and high risk economic times, but will want another store of value other than their domestic currency.

When gold stops tracking the euro and until its value is no longer determined on the lack of European demand, or increase in European supply (where people sell their gold for money - not production through new mines), the price will appreciate.

The US dollar will only be propped up as long as people pour their euros into it. Once the US dollar eventually starts to depreciate, gold will have its time.