Gold’s atomic number of 79 makes it one of the higher atomic number elements that occur naturally in the universe. It is thought to have been produced in supernova nucleosynthesis from the collision of two neutron stars and to have been present in the dust from which the Solar System formed. Because the Earth was molten when it was just formed, almost all of the gold present in the early Earth probably sank into the planetary core. Therefore, most of the gold that is present today in the Earth’s crust and mantle is thought to have been delivered to Earth later, by asteroid impacts during the late heavy bombardment, about 4 billion years ago.
Gold resists attacks by individual acids, but it can be dissolved by aqua regia (nitro-hydrochloric acid, literally “royal water”). The acid mixture causes the formation of a soluble gold tetrachloride anion. Gold metal also dissolves in alkaline solutions of cyanide, which are used in mining and electroplating. It is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in items, giving rise to the term acid test; it dissolves in mercury, though, forming amalgam alloys, but this is not a chemical reaction.
Courtesy : Wikipedia