Sell gold for what? Dollars? They don't want dollars.
Under Sharia, Islamic banking is gold-based. They will use the gold to set themselves up as one of many banking centers for the Islamic world. It will be the first step in demanding that customers for oil pay in gold, not dollars or euros.
This is precisely what the Arab oil producers did in the waning days of World War II, before the Bretton Woods agreement set up the dollar as the world's reserve currency backed by gold for non-domestic purposes. The dollar is failing, and this is about replacing a dying currency with gold.