Aqua regia dissolves gold through a combination of oxidation and complexation (a standard chemical fact requiring no citation).
The mechanism of gold dissolution by aqua regia via oxidation (by nitric acid) and complexation (by chloride ions forming chloroauric acid) is a standard chemical fact and textbook common knowledge. While some retrieved papers discuss related oxidation-complexation dissolution mechanisms or use aqua regia as a leaching agent, no specialized citation is strictly needed to verify this established chemical principle.